WorldWideScience

Sample records for forced convective cooling

  1. Experimental StudyHigh Altitude Forced Convective Cooling of Electromechanical Actuation Systems

    Science.gov (United States)

    2016-01-01

    34 Massachusetts Institute of Technology , 1989. [3] FedBizOps.Gov, " Integrated Vehicle Energy Technology (INVENT) Development Program for the 6th...AFRL-RQ-WP-TR-2016-0043 EXPERIMENTAL STUDY—HIGH ALTITUDE FORCED CONVECTIVE COOLING OF ELECTROMECHANICAL ACTUATION SYSTEMS Evan M. Racine...TITLE AND SUBTITLE EXPERIMENTAL STUDY—HIGH ALTITUDE FORCED CONVECTIVE COOLING OF ELECTROMECHANICAL ACTUATION SYSTEMS 5a. CONTRACT NUMBER In-house

  2. Experimental and theoretical analysis of a hybrid solar thermoelectric generator with forced convection cooling

    Science.gov (United States)

    Sundarraj, Pradeepkumar; Taylor, Robert A.; Banerjee, Debosmita; Maity, Dipak; Sinha Roy, Susanta

    2017-01-01

    Hybrid solar thermoelectric generators (HSTEGs) have garnered significant research attention recently due to their potential ability to cogenerate heat and electricity. In this paper, theoretical and experimental investigations of the electrical and thermal performance of a HSTEG system are reported. In order to validate the theoretical model, a laboratory scale HSTEG system (based on forced convection cooling) is developed. The HSTEG consists of six thermoelectric generator modules, an electrical heater, and a stainless steel cooling block. Our experimental analysis shows that the HSTEG is capable of producing a maximum electrical power output of 4.7 W, an electrical efficiency of 1.2% and thermal efficiency of 61% for an average temperature difference of 92 °C across the TEG modules with a heater power input of 382 W. These experimental results of the HSTEG system are found to be in good agreement with the theoretical prediction. This experimental/theoretical analysis can also serve as a guide for evaluating the performance of the HSTEG system with forced convection cooling.

  3. A comparative design study of PB-BI cooled reactor cores with forced and natural convection cooling

    International Nuclear Information System (INIS)

    Mizuno, Tomoyasu; Enuma, Yasuhiro; Tanji, Mikio

    2003-01-01

    A comparative core design study is performed on Pb-Bi cooled reactors with forced and natural convection (FC and NC) cooling. Major interests of the study are core performance and core safety features. The designed core concepts with nitride fuel achieve reasonable breeding capability. The results of unprotected event analyses such as UTOP and ULOF show that both of concepts have possible features to withstand unprotected events due to negative reactivity feedback by Doppler effect, control rod drive line expansion, etc. These results lead to a conclusion that both of concepts have possible capability as one of future promising core concepts. A FC cooling core concept has more advantage if fuel recycle viewpoint is emphasized. (author)

  4. Experimental study of cooling BIPV modules by forced convection in the air channel

    International Nuclear Information System (INIS)

    Kaiser, A.S.; Zamora, B.; Mazón, R.; García, J.R.; Vera, F.

    2014-01-01

    Highlights: • An experimental setup for studying the effects of forced convection on cell temperature. • The induced velocity within the forced convection channel significantly affects the PV cooling. • Correlations for the Ross coefficient, module temperature, efficiency, and power output. • Prediction of the thermal behavior of the PV module in BIPV configurations. - Abstract: The efficiency of photovoltaic systems depends mainly on the cell temperature. Frequently, the PV collectors are installed on the top of the building. One cost effective method to regulate the temperature of rooftop integrated photovoltaic panels is to provide an open air channel beneath the panel. The cell temperature of these PV modules is very much influenced by the capability of ventilating this channel. The ventilation may be modified by different factors such as the wind velocity, the air gap size, and the forced convection induced by a fan or by a conventional air conditioning system. This paper describes an experimental setup to study the influence of the air gap size and the forced ventilation on the cell temperature (and consequently on the electrical efficiency of the PV module) of a BIPV configuration, for different values of the incident solar radiation, ambient temperatures, and aspect ratios, as well as for several forced ventilation conditions. Semi empirical correlations for the Ross coefficient, module temperature, electrical efficiency, and power output are proposed, showing a good agreement with respect to experimental measurements. A critical channel aspect ratio close to 0.11 can be considered to minimize overheating of PV devices. For a duct velocity V v = 6 m/s, a power output increase of 19% is observed over the natural ventilation case (V v = 0.5 m/s)

  5. Thermo-electrochemical model for forced convection air cooling of a lithium-ion battery module

    International Nuclear Information System (INIS)

    Tong, Wei; Somasundaram, Karthik; Birgersson, Erik; Mujumdar, Arun S.; Yap, Christopher

    2016-01-01

    Highlights: • Coupled thermal-electrochemical model for a Li-ion battery module resolving every functional layer in all cells. • Parametric analysis of forced convection air cooling of Li-ion battery module with a detailed multi-scale model. • Reversing/reciprocating airflow for Li-ion battery module thermal management provides uniform temperature distribution. - Abstract: Thermal management is critical for safe and reliable operation of lithium-ion battery systems. In this study, a one-dimensional thermal-electrochemical model of lithium-ion battery interactively coupled with a two-dimensional thermal-fluid conjugate model for forced convection air cooling of a lithium-ion battery module is presented and solved numerically. This coupled approach makes the model more unique and detailed as transport inside each cell in the battery module is solved for and thus covering multiple length and time scales. The effect of certain design and operating parameters of the thermal management system on the performance of the battery module is assessed using the coupled model. It is found that a lower temperature increase of the battery module can be achieved by either increasing the inlet air velocity or decreasing the distance between the cells. Higher air inlet velocity, staggered cell arrangement or a periodic reversal airflow of high reversal frequency results in a more uniform temperature distribution in the module. However, doing so increases the parasitic load as well as the volume of the battery module whence a trade-off should be taken into account between these parameters.

  6. Thermal response of core and central-cavity components of a high-temperature gas-cooled reactor in the absence of forced convection coolant flow

    International Nuclear Information System (INIS)

    Whaley, R.L.; Sanders, J.P.

    1976-09-01

    A means of determining the thermal responses of the core and the components of a high-temperature gas-cooled reactor after loss of forced coolant flow is discussed. A computer program, using a finite-difference technique, is presented together with a solution of the confined natural convection. The results obtained are reasonable and demonstrate that the computer program adequately represents the confined natural convection

  7. Determination of blade-to-coolant heat-transfer coefficients on a forced-convection, water-cooled, single-stage turbine

    Science.gov (United States)

    Freche, John C; Schum, Eugene F

    1951-01-01

    Blade-to-coolant convective heat-transfer coefficients were obtained on a forced-convection water-cooled single-stage turbine over a large laminar flow range and over a portion of the transition range between laminar and turbulent flow. The convective coefficients were correlated by the general relation for forced-convection heat transfer with laminar flow. Natural-convection heat transfer was negligible for this turbine over the Grashof number range investigated. Comparison of turbine data with stationary tube data for the laminar flow of heated liquids showed good agreement. Calculated average midspan blade temperatures using theoretical gas-to-blade coefficients and blade-to-coolant coefficients from stationary-tube data resulted in close agreement with experimental data.

  8. Analysis of coolability of the control rods of a Savannah River Site production reactor with loss of normal forced convection cooling

    International Nuclear Information System (INIS)

    Easterling, T.C.; Hightower, N.T.; Smith, D.C.; Amos, C.N.

    1992-01-01

    An analytical study of the coolability of the control rods in the Savannah River Site (SRS) K-Production Reactor under conditions of loss of normal forced convection cooling has been performed. The study was performed as part of the overall safety analysis of the reactor supporting its restart. The analysis addresses the buoyancy-driven flow over the control rods that occurs when forced cooling is lost, and the limit of critical heat flux that sets the acceptance criteria for the study. The objective of the study is to demonstrate that the control rods will remain cooled at powers representative of those anticipated for restart of the reactor. The study accomplishes this objective with a very tractable simplified analysis for the modest restart power. In addition, a best-estimate calculation is performed, and the results are compared to results from sub-scale scoping experiments. 5 refs

  9. The influence of nanoparticle migration on forced convective heat transfer of nanofluid under heating and cooling regimes.

    Science.gov (United States)

    Kozlova, Sofya V; Ryzhkov, Ilya I

    2014-09-01

    In this paper, laminar convective heat transfer of water-alumina nanofluid in a circular tube with uniform heat flux at the tube wall is investigated. The investigation is performed numerically on the basis of two-component model, which takes into account nanoparticle transport by diffusion and thermophoresis. Two thermal regimes at the tube wall, heating and cooling, are considered and the influence of nanoparticle migration on the heat transfer is analyzed comparatively. The intensity of thermophoresis is characterized by a new empirical model for thermophoretic mobility. It is shown that the nanoparticle volume fraction decreases (increases) in the boundary layer near the wall under heating (cooling) due to thermophoresis. The corresponding variations of nanofluid properties and flow characteristics are presented and discussed. The intensity of heat transfer for the model with thermophoresis in comparison to the model without thermophoresis is studied by plotting the dependence of the heat transfer coefficient on the Peclet number. The effectiveness of water-alumina nanofluid is analyzed by plotting the average heat transfer coefficient against the required pumping power. The analysis of the results reveals that the water-alumina nanofluid shows better performance in the heating regime than in the cooling regime due to thermophoretic effect.

  10. Thermal-Hydraulic Analyses of Transients in an Actinide-Burner Reactor Cooled by Forced Convection of Lead Bismuth

    Energy Technology Data Exchange (ETDEWEB)

    Davis, Cliff Bybee

    2003-09-01

    The Idaho National Engineering and Environmental Laboratory (INEEL) and the Massachusetts Institute of Technology (MIT) are investigating the suitability of lead or lead–bismuth cooled fast reactors for producing low-cost electricity as well as for actinide burning. The current analysis evaluated a pool type design that relies on forced circulation of the primary coolant, a conventional steam power conversion system, and a passive decay heat removal system. The ATHENA computer code was used to simulate various transients without reactor scram, including a primary coolant pump trip, a station blackout, and a step reactivity insertion. The reactor design successfully met identified temperature limits for each of the transients analyzed.

  11. Numerical study on turbulent forced convective heat transfer using nanofluids TiO2 in an automotive cooling system

    Directory of Open Access Journals (Sweden)

    Adnan M. Hussein

    2017-03-01

    Full Text Available The limited thermal properties of liquids have led to the addition of solid nanoparticles to liquids in many industrial applications. In this paper, the friction factor and forced convection heat transfer of TiO2 nanoparticles dispersed in water in a car radiator was numerically determined. Four different nanofluid volume concentrations (1%, 2%, 3% and 4% were used, and the resulting thermal properties were evaluated. The Reynolds number and inlet temperature ranged from 10000 to 100000 and from 60 to 90 °C, respectively. The results showed that the friction factor decreases as the Reynolds number increases and increases as the volume concentration increases. Additionally, the Nusselt number increases as the Reynolds number and volume concentration of the nanofluid increases. The TiO2 nanofluid at low concentrations can enhance the heat transfer efficiency up to 20% compared with that of pure water. There was good agreement among the CFD analysis and experimental data available in the literature.

  12. Benchmarking of thermalhydraulic loop models for lead-alloy-cooled advanced nuclear energy systems. Phase I: Isothermal forced convection case

    International Nuclear Information System (INIS)

    2012-06-01

    Under the auspices of the NEA Nuclear Science Committee (NSC), the Working Party on Scientific Issues of the Fuel Cycle (WPFC) has been established to co-ordinate scientific activities regarding various existing and advanced nuclear fuel cycles, including advanced reactor systems, associated chemistry and flowsheets, development and performance of fuel and materials and accelerators and spallation targets. The WPFC has different expert groups to cover a wide range of scientific issues in the field of nuclear fuel cycle. The Task Force on Lead-Alloy-Cooled Advanced Nuclear Energy Systems (LACANES) was created in 2006 to study thermal-hydraulic characteristics of heavy liquid metal coolant loop. The objectives of the task force are to (1) validate thermal-hydraulic loop models for application to LACANES design analysis in participating organisations, by benchmarking with a set of well-characterised lead-alloy coolant loop test data, (2) establish guidelines for quantifying thermal-hydraulic modelling parameters related to friction and heat transfer by lead-alloy coolant and (3) identify specific issues, either in modelling and/or in loop testing, which need to be addressed via possible future work. Nine participants from seven different institutes participated in the first phase of the benchmark. This report provides details of the benchmark specifications, method and code characteristics and results of the preliminary study: pressure loss coefficient and Phase-I. A comparison and analysis of the results will be performed together with Phase-II

  13. Thermal computations for electronics conductive, radiative, and convective air cooling

    CERN Document Server

    Ellison, Gordon

    2010-01-01

    IntroductionPrimary mechanisms of heat flowConductionApplication example: Silicon chip resistance calculationConvectionApplication example: Chassis panel cooled by natural convectionRadiationApplication example: Chassis panel cooled only by radiation 7Illustrative example: Simple thermal network model for a heat sinked power transistorIllustrative example: Thermal network circuit for a printed circuit boardCompact component modelsIllustrative example: Pressure and thermal circuits for a forced air cooled enclosureIllustrative example: A single chip package on a printed circuit board-the proble

  14. Numerical investigation of double diffusive buoyancy forces induced natural convection in a cavity partially heated and cooled from sidewalls

    Directory of Open Access Journals (Sweden)

    Rasoul Nikbakhti

    2016-03-01

    Full Text Available This paper deals with a numerical investigation of double-diffusive natural convective heat and mass transfer in a cavity filled with Newtonian fluid. The active parts of two vertical walls of the cavity are maintained at fixed but different temperatures and concentrations, while the other two walls, as well as inactive areas of the sidewalls, are considered to be adiabatic and impermeable to mass transfer. The length of the thermally active part equals half of the height. The non-dimensional forms of governing transport equations that describe double-diffusive natural convection for two-dimensional incompressible flow are functions of temperature or energy, concentration, vorticity, and stream-function. The coupled differential equations are discretized via FDM (Finite Difference Method. The Successive-Over-Relaxation (SOR method is used in the solution of the stream function equation. The analysis has been done for an enclosure with different aspect ratios ranging from 0.5 to 11 for three different combinations of partially active sections. The results are presented graphically in terms of streamlines, isotherms and isoconcentrations. In addition, the heat and mass transfer rate in the cavity is measured in terms of the average Nusselt and Sherwood numbers for various parameters including thermal Grashof number, Lewis number, buoyancy ratio and aspect ratio. It is revealed that the placement order of partially thermally active walls and the buoyancy ratio influence significantly the flow pattern and the corresponding heat and mass transfer performance in the cavity.

  15. On the phenomenon of the reversal of the cooling current in the hot pipes of a swimming-pool type pile cooled by forced convection; Sur un phenomene de renversement du courant de refrigeration dans les canaux chauds d'une pile piscine refroidie en convection forcee

    Energy Technology Data Exchange (ETDEWEB)

    Boure, J [Commissariat a l' Energie Atomique, Grenoble (France).Centre d' Etudes Nucleaires

    1961-07-01

    It is shown, for a swimming-pool type pile cooled by forced convection (general flow downwards), that a permanently stable regime with downward flow in all the channels is not possible when the flow is below a critical value for a given power. In the hot channels the natural convection then becomes preponderant, the direction of the flow is reversed and a permanently stable regime exists for which the flow is upwards in the hot channels. Calculations are made, with simplifying hypotheses in the case of Melusine. (author) [French] Pour une pile piscine refrigeree en convection forcee (ecoulement global descendant), on montre qu'un regime permanent stable avec ecoulement descendant dans tous les canaux est impossible lorsque le debit est inferieur a une valeur critique pour une puissance donnee. Dans les canaux chauds, la convection naturelle l'emporte alors, le sens du courant s'inverse et un regime permanent stable existe, pour lequel le courant est ascendant dans les canaux chauds. On fait les calculs, avec des hypotheses simplificatrices, dans le cas de Melusine. (auteur)

  16. Cryogenic forced convection refrigerating system

    International Nuclear Information System (INIS)

    Klee, D.J.

    1988-01-01

    This patent describes the method of refrigerating products by contact with a refrigerating gas which comprises introducing product into a refrigeration zone, contacting the product with the refrigerating gas for a sufficient time to refrigerate it to the appropriate extent and removing the refrigerated product. The improvement for producing the refrigeration gas from a liquid cryogen such that essentially all of the liquid cryogen is fully vaporized before contacting the product comprises: (a) introducing the liquid cryogen, selected from the group consisting of liquid air and liquid nitrogen, at elevated pressure into an ejector as the motive fluid to accelerate a portion of a warm refrigerating gas through the ejector while mixing the cryogen and gas to effect complete vaporization of the liquid cryogen and substantial cooling of the portion of the refrigerating gas resulting in a cold discharge gas which is above the liquefaction temperature of the cryogen; (b) introducing the cold discharge gas into a forced circulation pathway of refrigerating gas and producing a cold refrigerating gas which contacts and refrigerates product and is then at least partially recirculated; (c) sensing the temperature of the refrigerating gas in the forced circulation pathway and controlling the introduction of liquid cryogen with regard to the sensed temperature to maintain the temperature of the discharge gas above the liquefacton temperature of the cryogen utilized

  17. Numerical Simulation on Natural Convection Cooling of a FM Target

    Energy Technology Data Exchange (ETDEWEB)

    Park, Jong Pil; Park, Su Ki [KAERI, Daejeon (Korea, Republic of)

    2016-05-15

    The irradiated FM(Fission-Molly) target is unloaded from the irradiation hole during normal operation, and then cooled down in the reactor pool for a certain period of time. Therefore, it is necessary to identify the minimum decay time needed to cool down FM target sufficiently by natural convection. In the present work, numerical simulations are performed to predict cooling capability of a FM target cooled by natural convection using commercial computational fluid dynamics (CFD) code, CFX. The present study is carried out using CFD code to investigate cooling capability of a FM target cooled by natural convection. The steady state simulation as well as transient simulation is performed in the present work. Based on the transient simulation (T1), the minimum decay time that the maximum fuel temperature does not reach the design limit temperature (TONB-3 .deg. C) is around 15.60 seconds.

  18. Forced draft wet cooling systems

    International Nuclear Information System (INIS)

    Daubert, A.; Caudron, L.; Viollet, P.L.

    1975-01-01

    The disposal of the heat released from a 1000MW power plant needs a natural draft tower of about 130m of diameter at the base, and 170m height, or a cooling system with a draft forced by about forty vans, a hundred meters in diameter, and thirty meters height. The plumes from atmospheric cooling systems form, in terms of fluid mechanics, hot jets in a cross current. They consist in complex flows that must be finely investigated with experimental and computer means. The study, currently being performed at the National Hydraulics Laboratory, shows that as far as the length and height of visible plumes are concerned, the comparison is favorable to some types of forced draft cooling system, for low and medium velocities, (below 5 or 6m/s at 10m height. Beyond these velocities, the forced draft sends the plume up to smaller heights, but the plume is generally more dilute [fr

  19. Natural convection cooling of LEU cores for Pakistan research reactor-1

    International Nuclear Information System (INIS)

    Khan, L.A.; Bokhari, I.H.; Akhtar, K.M.

    1991-08-01

    The first high power and equilibrium LEU cores of PARR-1 have been analysed to assess the maximum operating power based on natural convection cooling, need for forced cooling to remove the decay heat and to estimate safety margins that commensurate with the predetermined power limit. Computer code NATCON and standard correlations have been used for the analysis. The parameters studied includes coolant velocity, temperature distribution in the core, heat fluxes at onset of nucleate boiling, pulsed boiling and burnup. (author)

  20. Forced cooling of a nuclear waste repository mine drift - a scoping analysis

    Energy Technology Data Exchange (ETDEWEB)

    Boyd, R D [Sandia National Labs., Albuquerque, NM (USA)

    1982-12-01

    Nuclear waste repositories, with decay heat generation beneath the mine drift floors, are force-cooled with air so that re-entrance is possible many years after the waste has been buried. A numerical model has been developed which uses heat transfer coefficients as input. It has been demonstrated that mixed (forced and free) convective and surface roughness effects are significant and must be included in future experiments if reliable predictions are to be made of the time required to cool the repository. For example, when repository mine drifts in volcanic tuff are force-cooled, with forced convection being the only energy transport mechanism, it takes approx.= 0.1 year to cool the mine surface to a safe temperature. However, when mixed convection is the primary transport mechanism it takes approx.= 1.0 year to cool the mine. In addition to mixed convection, other effects are delineated.

  1. Forced convection heat transfer in rectangular ducts - general case of wall resistances and peripheral conduction for ventilation cooling of nuclear waste repositories [ heat transfer and nuclear disposal

    Energy Technology Data Exchange (ETDEWEB)

    Lyczkowski, R. W.; Solbrig, C. W.; Gidaspow, D.

    1980-01-01

    A numerical solution for laminar flow heat transfer between a flowing gas and its containing rectangular duct has been obtained for many different boundary conditions which may arise in nuclear waste repository ventilation corridors. The problem has been solved for the cases of insulation on no walls, one wall, two walls, and three walls with various finite resistances on the remaining walls. Simplifications are made to decouple the convective heat transfer problem for the far field conduction problem, but peripheral conduction is retained. Results have been obtained for several duct aspect ratios in the thermal entrance and in the fully developed regions, including the constant temperature cases. When one wall is insulated and the other three are at constant temperature, the maximum temperature occurs in the fluid rather than on the insulated wall. This maximum moves toward the insulated wall with increasing axial distance. Nusselt numbers for the same constant flux on all four walls with peripheral conduction lie in a narrow band bounded by zero and infinite peripheral conduction cases. A dimensionless wall conduction group of four can be considered infinite for the purpose of estimating fully developed Nusselt numbers to within an accuracy of 3%. A decrease in wall and bulk temperatures by finite wall conduction has been demonstrated for the case of a black body radiation boundary condition. Nusselt numbers for the case of constant temperature on the top and bottom walls and constant heat flux on the side walls exhibited unexpected behavior.

  2. Forced convection heat transfer in rectangular ducts - general case of wall resistances and peripheral conduction for ventilation cooling of nuclear waste repositories

    International Nuclear Information System (INIS)

    Lyczkowski, R.W.; Solbrig, C.W.; Gidaspow, D.

    1982-01-01

    A numerical solution for laminar flow heat transfer between a flowing gas and its containing rectangular duct has been obtained for many different boundary conditions which may arise in nuclear waste repository ventilation corridors. The problem has been solved for the cases of insulation on no walls, one wall, two walls, and three walls with various finite resistances on the remaining walls. Simplifications are made to decouple the convective heat transfer problem from the far field conduction problem, but peripheral conduction is retained. Results have been obtained for several duct aspect ratios in the thermal entrance and in the fully developed regions, including the constant temperature cases. When one wall is insulated and the other three are at constant temperature, the maximum temperature occurs in the fluid rather than on the insulated wall. This maximum moves toward the insulated wall with increasing axial distance. Nusselt numbers for the same constant flux on all four walls with peripheral conduction lie in a narrow band bounded by zero and infinite peripheral conduction cases. A dimensionsless wall conduction group of four can be considered infinite for the purpose of estimating fully developed Nusselt numbers to within an accuracy of 3%. A decrease in wall and bulk temperatures by finite wall conduction has been demonstrated for the case of a black body radiation boundary condition. Nusselt numbers for the case of constant temperature on the top and bottom walls and constant heat flux on the side walls exhibited unexpected behavior. (orig.)

  3. Forced convection heat transfer in rectangular ducts - general case of wall resistances and peripheral conduction for ventilation cooling of nuclear waste repositories

    International Nuclear Information System (INIS)

    Lyczkowski, R.W.; Solbrig, C.W.; Gidaspow, D.

    1980-01-01

    A numerical solution for laminar flow heat transfer between a flowing gas and its containing rectangular duct has been obtained for many different boundary conditions which may arise in nuclear waste repository ventilation corridors. The problem has been solved for the cases of insulation on no walls, one wall, two walls, and three walls with various finite resistances on the remaining walls. Simplifications are made to decouple the convective heat transfer problem for the far field conduction problem, but peripheral conduction is retained. Results have been obtained for several duct aspect ratios in the thermal entrance and in the fully developed regions, including the constant temperature cases. When one wall is insulated and the other three are at constant temperature, the maximum temperature occurs in the fluid rather than on the insulated wall. This maximum moves toward the insulated wall with increasing axial distance. Nusselt numbers for the same constant flux on all four walls with peripheral conduction lie in a narrow band bounded by zero and infinite peripheral conduction cases. A dimensionless wall conduction group of four can be considered infinite for the purpose of estimating fully developed Nusselt numbers to within an accuracy of 3%. A decrease in wall and bulk temperatures by finite wall conduction has been demonstrated for the case of a black body radiation boundary condition. Nusselt numbers for the case of constant temperature on the top and bottom walls and constant heat flux on the side walls exhibited unexpected behavior

  4. Forced convection heat transfer in rectangular ducts - general case of wall resistances and peripheral conduction for ventilation cooling of nuclear waste repositories

    Energy Technology Data Exchange (ETDEWEB)

    Lyczkowski, R W [Institute of Gas Technology, Chicago, IL (USA); Solbrig, C W [EG and G Idaho, Inc., Idaho Falls (USA); Gidaspow, D [Illinois Inst. of Tech., Chicago (USA). Dept. of Chemical Engineering

    1982-02-01

    A numerical solution for laminar flow heat transfer between a flowing gas and its containing rectangular duct has been obtained for many different boundary conditions which may arise in nuclear waste repository ventilation corridors. The problem has been solved for the cases of insulation on no walls, one wall, two walls, and three walls with various finite resistances on the remaining walls. Simplifications are made to decouple the convective heat transfer problem from the far field conduction problem, but peripheral conduction is retained. Results have been obtained for several duct aspect ratios in the thermal entrance and in the fully developed regions, including the constant temperature cases. When one wall is insulated and the other three are at constant temperature, the maximum temperature occurs in the fluid rather than on the insulated wall. This maximum moves toward the insulated wall with increasing axial distance. Nusselt numbers for the same constant flux on all four walls with peripheral conduction lie in a narrow band bounded by zero and infinite peripheral conduction cases. A dimensionsless wall conduction group of four can be considered infinite for the purpose of estimating fully developed Nusselt numbers to within an accuracy of 3%. A decrease in wall and bulk temperatures by finite wall conduction has been demonstrated for the case of a black body radiation boundary condition. Nusselt numbers for the case of constant temperature on the top and bottom walls and constant heat flux on the side walls exhibited unexpected behavior.

  5. Use of local convective and radiant cooling at warm environment

    DEFF Research Database (Denmark)

    Melikov, Arsen Krikor; Krejcirikova, Barbora; Kaczmarczyk, Jan

    2012-01-01

    The effect of four local cooling devices (convective, radiant and combined) on SBS symptoms reported by 24 subjects at 28 ˚C and 50% RH was studied. The devices studied were: (1) desk cooling fan, (2) personalized ventilation providing clean air, (3) two radiant panels and (4) two radiant panels...... and with radiant panel with attached fans, which also helped people to feel less fatigue. The SBS symptoms increased the most when the cooling fan, generating movement of polluted room air, was used....

  6. Boiling induced mixed convection in cooling loops

    International Nuclear Information System (INIS)

    Knebel, J.U.; Janssens-Maenhout, G.; Mueller, U.

    2000-01-01

    This article describes the SUCO program performed at the Forschungszentrum Karlsruhe. The SUCO program is a three-step series of scaled model experiments investigating the possibility of a sump cooling concept for future light water reactors. In case of a core melt accident, the sump cooling concept realises a decay heat removal system that is based on passive safety features within the containment. The article gives, first, results of the experiments in the 1:20 linearly scaled SUCOS-2D test facility. The experimental results are scaled-up to the conditions in the prototype, allowing a statement with regard to the feasibility of the sump cooling concept. Second, the real height SUCOT test facility with a volume and power scale of 1:356 that is aimed at investigating the mixed single-phase and two-phase natural circulation flow in the reactor sump, together with first measurement results, are discussed. Finally, a numerical approach to model the subcooled nucleate boiling phenomena in the test facility SUCOT is presented. Physical models describing interfacial mass, momentum and-heat transfer are developed and implemented in the commercial software package CFX4.1. The models are validated for an isothermal air-water bubbly flow experiment and a subcooled boiling experiment in vertical annular water flow. (author)

  7. Dry storage systems with free convection air cooling

    International Nuclear Information System (INIS)

    Kioes, S.R.

    1980-01-01

    Several design principles to remove heat from the spent fuel by free air convection are illustrated and described. The key safety considerations were felt to be: loss of coolant is impossible as the passive system uses air as a coolant; overheating is precluded because as the temperatures of the containers rises the coolant flow rate increases; mass of the storage building provides a large heat sink and therefore a rapid temperature rise is impossible; and lack of any active external support requirements makes the cooling process less likely to equipment or operator failures. An example of this type of storage already exists. The German HTGR is operated with spherical graphite fuel elements which are stored in canister and in storage cells. The concept is a double cooling system with free convection inside the cells and heat exchange via two side walls of the cell to the ambient air in the cooling ducts. Technical description of the TN 1300 cask is also presented

  8. Human response to local convective and radiant cooling in a warm environment

    DEFF Research Database (Denmark)

    Melikov, Arsen Krikor; Krejcirikova, Barbora; Kaczmarczyk, Jan

    2013-01-01

    The response of 24 human subjects to local convective cooling, radiant cooling, and combined radiant and convective cooling was studied at 28°C and 50% relative humidity. The local cooling devices used were (1) a tabletop cooling fan, (2) personalized ventilation providing a stream of clean air, (3...

  9. Thermal Sizing of Heat Exchanger Tubes for Air Natural Convective Cooling System of Emergency Cooling Tank

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Myoung Jun; Lee, Hee Joon [Kookmin Univ., Seoul (Korea, Republic of); Moon, Joo Hyung; Bae, Youngmin; Kim, Youngin [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2014-05-15

    For the long operation of secondary passive cooling system, however, water level goes down by evaporation in succession at emergency cooling tank. At the end there would be no place to dissipate heat from condensation heat exchanger. Therefore, steam cooling heat exchanger is put on the top of emergency cooling tank to maintain appropriate water level by collecting evaporating steam. Steam cooling heat exchanger is installed inside an air chimney and evaporated steam is cooled down by air natural convection. In this study, thermal sizing of steam cooling heat exchanger under air natural convection was conducted by TSCON program for the design of experimental setup as shown in Fig. 2. Thermal sizing of steam cooling heat exchanger tube under air natural convection was conducted by TSCON program for the design of experimental setup. 25 - 1' tubes which has a length 1687 mm was determined as steam cooling heat exchanger at 2 kW heat load and 100 liter water pool in emergency cooling tank (experimental limit condition). The corresponding width of two tubes is 50 mm and has 5 by 5 tube array for heat exchanger.

  10. Thermal Sizing of Heat Exchanger Tubes for Air Natural Convective Cooling System of Emergency Cooling Tank

    International Nuclear Information System (INIS)

    Kim, Myoung Jun; Lee, Hee Joon; Moon, Joo Hyung; Bae, Youngmin; Kim, Youngin

    2014-01-01

    For the long operation of secondary passive cooling system, however, water level goes down by evaporation in succession at emergency cooling tank. At the end there would be no place to dissipate heat from condensation heat exchanger. Therefore, steam cooling heat exchanger is put on the top of emergency cooling tank to maintain appropriate water level by collecting evaporating steam. Steam cooling heat exchanger is installed inside an air chimney and evaporated steam is cooled down by air natural convection. In this study, thermal sizing of steam cooling heat exchanger under air natural convection was conducted by TSCON program for the design of experimental setup as shown in Fig. 2. Thermal sizing of steam cooling heat exchanger tube under air natural convection was conducted by TSCON program for the design of experimental setup. 25 - 1' tubes which has a length 1687 mm was determined as steam cooling heat exchanger at 2 kW heat load and 100 liter water pool in emergency cooling tank (experimental limit condition). The corresponding width of two tubes is 50 mm and has 5 by 5 tube array for heat exchanger

  11. Forced convection heat transfer in He II

    International Nuclear Information System (INIS)

    Kashani, A.

    1986-01-01

    An investigation of forced convection heat transfer in He II is conducted. The study includes both experimental and theoretical treatments of the problem. The experiment consists of a hydraulic pump and a copper flow tube, 3 mm in ID and 2m long. The system allows measurements of one-dimensional heat and mass transfer in He II. The heat transfer experiments are performed by applying heat at the midpoint along the length of the flow tube. Two modes of heat input are employed, i.e., step function heat input and square pulse heat input. The heat transfer results are discussed in terms of temperature distribution in the tube. The experimental temperature profiles are compared with numerical solutions of an analytical model developed from the He II energy equation. The bath temperature is set at three different values of 1.65, 1.80, and 1.95 K. The He II flow velocity is varied up to 90 cm/s. Pressure is monitored at each end of the flow tube, and the He II pressure drop is obtained for different flow velocities. Results indicate that He II heat transfer by forced convention is considerably higher than that by internal convection. The theoretical model is in close agreement with the experiment. He II pressure drop and friction factor are very similar to those of an ordinary fluid

  12. Mixed convection in a two-phase flow cooling loop

    International Nuclear Information System (INIS)

    Janssens-Maenhout, G.; Daubner, M.; Knebel, J.U.

    2002-03-01

    This report summarizes the numerical simulations using the CFD code CFX4.1 which has additional models for subcooled flow boiling phenomena and the interfacial forces. The improved CFX4.1 code can be applied to the design of boiling induced mixed convection cooling loops in a defined parameter range. The experimental part describes the geysering experiments and the instability effects on the two-phase natural circulation flow. An experimentally validated flow pattern map in the Phase Change Number - Subcooling Number (N PCh - N Sub ) diagram defines the operational range in which flow instabilities such as geysering can be expected. One important perspective of this combined experimental/numerical work, which is in the field of two-phase flow, is its application to the development of accelerator driven systems (ADS). The main objective on an ADS is its potential to transmute minor actinides and long-lived fission products, thus participating in closing the fuel cycle. The development of an ADS is an important issue within the Euratom Fifth FP on Partitioning and Transmutation. One concept of an ADS, which is investigated in more detail within the ''preliminary design study of an experimental ADS'' Project (PDS-XADS) of the Euratom Fifth FP, is the XADS lead-bismuth cooled Experimental ADS of ANSALDO. An essential feature of this concept is the natural circulation of the primary coolant within the reactor pool. The natural circulation, which is driven by the density differences between the blanket and the heat exchanger, is enhanced by the injection of the nitrogen cover gas through spargers located in a riser part just above the blanket. This so-called gas-lift pump system has not been investigated in more detail nor has this gas-lift pump system been numerically/experimentally confirmed. The knowledge gained within the SUCO Programe, i.e. the modelling of the interfacial forces, the experimental work on flow instabilities and the modelling of the interfacial area

  13. Mixed convection in a two-phase flow cooling loop

    Energy Technology Data Exchange (ETDEWEB)

    Janssens-Maenhout, G.; Daubner, M.; Knebel, J.U.

    2002-03-01

    This report summarizes the numerical simulations using the CFD code CFX4.1 which has additional models for subcooled flow boiling phenomena and the interfacial forces. The improved CFX4.1 code can be applied to the design of boiling induced mixed convection cooling loops in a defined parameter range. The experimental part describes the geysering experiments and the instability effects on the two-phase natural circulation flow. An experimentally validated flow pattern map in the Phase Change Number - Subcooling Number (N{sub PCh} - N{sub Sub}) diagram defines the operational range in which flow instabilities such as geysering can be expected. One important perspective of this combined experimental/numerical work, which is in the field of two-phase flow, is its application to the development of accelerator driven systems (ADS). The main objective on an ADS is its potential to transmute minor actinides and long-lived fission products, thus participating in closing the fuel cycle. The development of an ADS is an important issue within the Euratom Fifth FP on Partitioning and Transmutation. One concept of an ADS, which is investigated in more detail within the ''preliminary design study of an experimental ADS'' Project (PDS-XADS) of the Euratom Fifth FP, is the XADS lead-bismuth cooled Experimental ADS of ANSALDO. An essential feature of this concept is the natural circulation of the primary coolant within the reactor pool. The natural circulation, which is driven by the density differences between the blanket and the heat exchanger, is enhanced by the injection of the nitrogen cover gas through spargers located in a riser part just above the blanket. This so-called gas-lift pump system has not been investigated in more detail nor has this gas-lift pump system been numerically/experimentally confirmed. The knowledge gained within the SUCO Programe, i.e. the modelling of the interfacial forces, the experimental work on flow instabilities and the

  14. Numerical analysis of a natural convection cooling system for radioactive canisters storage

    Energy Technology Data Exchange (ETDEWEB)

    Tsal, R.J.; Anwar, S.; Mercada, M.G. [Fluor Daniel Inc., Irvine, CA (United States)

    1995-02-01

    This paper describes the use of numerical analysis for studying natural convection cooling systems for long term storage of heat producing radioactive materials, including special nuclear materials and nuclear waste. The paper explains the major design philosophy, and shares the experiences of numerical modeling. The strategy of storing radioactive material is to immobilize nuclear high-level waste by a vitrification process, convertion it into borosilicate glass, and cast the glass into stainless steel canisters. These canisters are seal welded, decontaminated, inspected, and temporarily stored in an underground vault until they can be sent to a geologic repository for permanent storage. These canisters generate heat by nuclear decay of radioactive isotopes. The function of the storage facility ventilation system is to ensure that the glass centerline temperature does not exceed the glass transition temperature during storage and the vault concrete temperatures remain within the specified limits. A natural convection cooling system was proposed to meet these functions. The effectiveness of a natural convection cooling system is dependent on two major factors that affect air movement through the vault for cooling the canisters: (1) thermal buoyancy forces inside the vault which create a stack effect, and (2) external wind forces, that may assist or oppose airflow through the vault. Several numerical computer models were developed to analyze the thermal and hydraulic regimes in the storage vault. The Site Model is used to simulate the airflow around the building and to analyze different air inlet/outlet devices. The Airflow Model simulates the natural convection, thermal regime, and hydraulic resistance in the vault. The Vault Model, internal vault temperature stratification; and, finally, the Hot Area Model is used for modeling concrete temperatures within the vault.

  15. Convective Performance of Nanofluids in Commercial Electronics Cooling Systems

    International Nuclear Information System (INIS)

    Roberts, N.A.; Walker, D.G.

    2010-01-01

    Nanofluids are stable engineered colloidal suspensions of a small fraction of nanoparticles in a base fluid. Nanofluids have shown great promise as heat transfer fluids over typically used base fluids and fluids with micron sized particles. Suspensions with micron sized particles are known to settle rapidly and cause clogging and damage to the surfaces of pumping and flow equipment. These problems are dramatically reduced in nanofluids. In the current work we investigate the performance of different volume loadings of water-based alumina nanofluids in a commercially available electronics cooling system. The commercially available system is a water block used for liquid cooling of a computational processing unit. The size of the nanoparticles in the study is 20-30 nm. Results show an enhancement in convective heat transfer due to the addition of nanoparticles in the commercial cooling system with volume loadings of nanoparticles up to 1.5% by volume. The enhancement in the convective performance observed is similar to what has been reported in well controlled and understood systems and is commensurate with bulk models. The current nanoparticle suspensions showed visible signs of settling which varied from hours to weeks depending on the size of the particles used.

  16. Thermally optimum spacing of vertical, natural convection cooled, parallel plates

    Science.gov (United States)

    Bar-Cohen, A.; Rohsenow, W. M.

    Vertical two-dimensional channels formed by parallel plates or fins are a frequently encountered configuration in natural convection cooling in air of electronic equipment. In connection with the complexity of heat dissipation in vertical parallel plate arrays, little theoretical effort is devoted to thermal optimization of the relevant packaging configurations. The present investigation is concerned with the establishment of an analytical structure for analyses of such arrays, giving attention to useful relations for heat distribution patterns. The limiting relations for fully-developed laminar flow, in a symmetric isothermal or isoflux channel as well as in a channel with an insulated wall, are derived by use of a straightforward integral formulation.

  17. Forced flow cooling of ISABELLE dipole magnets

    International Nuclear Information System (INIS)

    Bamberger, J.A.; Aggus, J.; Brown, D.P.; Kassner, D.A.; Sondericker, J.H.; Strobridge, T.R.

    1976-01-01

    The superconducting magnets for ISABELLE will use a forced flow supercritical helium cooling system. In order to evaluate this cooling scheme, two individual dipole magnets were first tested in conventional dewars using pool boiling helium. These magnets were then modified for forced flow cooling and retested with the identical magnet coils. The first evaluation test used a l m-long ISA model dipole magnet whose pool boiling performance had been established. The same magnet was then retested with forced flow cooling, energizing it at various operating temperatures until quench occurred. The magnet performance with forced flow cooling was consistent with data from the previous pool boiling tests. The next step in the program was a full-scale ISABELLE dipole ring magnet, 4.25 m long, whose performance was first evaluated with pool boiling. For the forced flow test the magnet was shrunk-fit into an unsplit laminated core encased in a stainless steel cylinder. The high pressure gas is cooled below 4 K by a helium bath which is pumped below atmospheric pressure with an ejector nozzle. The performance of the full-scale dipole magnet in the new configuration with forced flow cooling, showed a 10 percent increase in the attainable maximum current as compared to the pool boiling data

  18. Enhanced Natural Convection in a Metal Layer Cooled by Boiling Water

    International Nuclear Information System (INIS)

    Cho, Jae-Seon; Suh, Kune Y.; Chung, Chang-Hyun; Park, Rae-Joon; Kim, Sang-Baik

    2004-01-01

    An experimental study is performed to investigate the natural convection heat transfer characteristics and the solidification of the molten metal pool concurrently with forced convective boiling of the overlying coolant to simulate a severe accident in a nuclear power plant. The relationship between the Nusselt number (Nu) and the Rayleigh number (Ra) in the molten metal pool region is determined and compared with the correlations in the literature and experimental data with subcooled water. Given the same Ra condition, the present experimental results for Nu of the liquid metal pool with coolant boiling are found to be higher than those predicted by the existing correlations or measured from the experiment with subcooled boiling. To quantify the observed effect of the external cooling on the natural convection heat transfer rate from the molten pool, it is proposed to include an additional dimensionless group characterizing the temperature gradients in the molten pool and in the external coolant region. Starting from the Globe and Dropkin correlation, engineering correlations are developed for the enhancement of heat transfer in the molten metal pool when cooled by an overlying coolant. The new correlations for predicting natural convection heat transfer are applicable to low-Prandtl-number (Pr) materials that are heated from below and solidified by the external coolant above. Results from this study may be used to modify the current model in severe accident analysis codes

  19. Turbulence convective heat transfer for cooling the photovoltaic cells

    Science.gov (United States)

    Arianmehr, Iman

    Solar PV (photovoltaic) is a rapidly advancing renewable energy technology which converts sunlight directly into electricity. One of the outstanding challenges of the current PV technology is the reduction in its conversion efficiency with increasing PV panel temperature, which is closely associated with the increase in solar intensity and the ambient temperature surrounding the PV panels. To more effectively capture the available energy when the sun is most intense, significant efforts have been invested in active and passive cooling research over the last few years. While integrated cooling systems can lead to the highest total efficiencies, they are usually neither the most feasible nor the most cost effective solutions. This work examines some simple passive means of manipulating the prevailing wind turbulence to enhance convective heat transfer over a heated plate in a wind tunnel.

  20. Combination technique for improving natural convection cooling in electronics

    Energy Technology Data Exchange (ETDEWEB)

    Florio, L.A.; Harnoy, A. [Department of Mechanical Engineering, New Jersey Institute of Technology, University Heights, Newark, NJ 07102 (United States)

    2007-01-15

    The combination of an appropriately placed cross-flow opening and a strategically positioned transversely vibrating plate is proposed as a means of augmenting pure natural convection in a vertical channel. This method is intended to provide a more efficient, reliable, and consumer conscious alternative to conventional techniques for lower power dissipating devices where standard natural convection cooling proves insufficient. Two-dimensional numerical simulations are employed to investigate this combination method using models consisting of a vertical channel containing two rectangular heat sources which are attached to a vertical mounting board, as well as a transversely oscillating plate and a cross-flow opening in the mounting board area between the two heat sources. Varied parameters and geometric configurations are studied. The results indicate the combined effects of the vibrating plate and the opening flow have the potential to cause significant improvement in the thermal conditions over pure natural convection. As much as a 70% improvement in the local heat transfer coefficient from that for a system with a board opening but without a vibrating plate was attained. (author)

  1. Latent cooling and microphysics effects in deep convection

    Science.gov (United States)

    Fernández-González, S.; Wang, P. K.; Gascón, E.; Valero, F.; Sánchez, J. L.

    2016-11-01

    Water phase changes within a storm are responsible for the enhancement of convection and therefore the elongation of its lifespan. Specifically, latent cooling absorbed during evaporation, melting and sublimation is considered the main cause of the intensification of downdrafts. In order to know more accurately the consequences of latent cooling caused by each of these processes (together with microphysical effects that they induce), four simulations were developed with the Wisconsin Dynamical and Microphysical Model (WISCDYMM): one with all the microphysical processes; other without sublimation; melting was suppressed in the third simulation; and evaporation was disabled in the fourth. The results show that sublimation cooling is not essential to maintain the vertical currents of the storm. This is demonstrated by the fact that in the simulation without sublimation, maximum updrafts are in the same range as in the control simulation, and the storm lifespan is similar or even longer. However, melting was of vital importance. The storm in the simulation without melting dissipated prematurely, demonstrating that melting is indispensable to the enhancement of downdrafts below the freezing level and for avoiding the collapse of low level updrafts. Perhaps the most important finding is the crucial influence of evaporative cooling above the freezing level that maintains and enhances mid-level downdrafts in the storm. It is believed that this latent cooling comes from the evaporation of supercooled liquid water connected with the Bergeron-Findeisen process. Therefore, besides its influence at low levels (which was already well known), this evaporative cooling is essential to strengthen mid-level downdrafts and ultimately achieve a quasi-steady state.

  2. Impairment of Heat Transfer in the Passive Cooling System due to Mixed Convection

    Energy Technology Data Exchange (ETDEWEB)

    Chae Myeong Seon; Chung, Bum Jin [Kyunghee University, Yongin (Korea, Republic of); Kim, Jong Hwan [KAERI, Daejeon (Korea, Republic of)

    2016-05-15

    In the passive cooling devices, the buoyant flows are induced. However the local Nusselt number of natural convective flow can be partly impaired due to the development of the mixed convective flows. This paper discusses impairment of heat transfer in the passive cooling system in relation to the development of mixed convection. The present work describes the preliminary plan to explore the phenomena experimentally. This paper is to discuss and make the plan to experiment the impairment of heat transfer in the passive cooling system due to mixed convection. In the sufficiently high passive cooling devices, the natural convection flow behavior can be mixed convection. The local Nusselt number distribution exhibits the non-monotonic behavior as axial position, since the buoyancy-aided with mixed convection was appeared. This is the part of the experimental work.

  3. The effect of internal ribbing on forced convective heat transfer in circular-sectioned tubes

    International Nuclear Information System (INIS)

    Farhadi Rahmat-Abadi, K.; Morris, W. D.

    2003-01-01

    This paper presents the results of an experimental examination of the effect of internal circumferential ribs on forced convection in circular-sectioned tubes. The work is relevant to the internal cooling of gas turbine rotor blades. The influence of rib geometry is investigated for three different rib configurations and simple design-type, empirical equations are developed for estimating heat transfer at rib and mid-rib locations. It is demonstrated that heat transfer may be improved by up to three fold in relation to fully developed forced convection in smooth-walled tubes. The geometric parameters which have been used for the experiments are typical of those currently applied to gas turbine blade cooling designs

  4. Investigation of the transition from forced to natural convection in the research reactor Munich II

    International Nuclear Information System (INIS)

    Skreba, S.; Adamek, J.; Unger, H.

    1999-01-01

    The new research reactor Munich II (FRM-II), which is under construction at the Technical University Munich, Germany, makes use of a newly developed compact reactor core consisting of a single fuel element, which is assembled of two concentric pipes. Between the fuel element's inner and outer pipe 113 involutely bent fuel plates are placed rotationally symmetric, forming 113 cooling channels of a constant width of 2.2 mm. After a shut down of the reactor, battery supported cooling pumps are started by the reactor safety system in order to remove the decay heat by a downwards directed forced flow. Three hours after they have been started, the cooling pumps are shut down and so-called 'natural convection flaps' are opened by their own weight. Through a flow path, which is provided by the opening of the natural convection flaps, the decay heat is given off to the water in the reactor pool after the direction of the flow has changed and an upwards directed natural convection flow has developed. At the Department for Nuclear and New Energy Systems of the Ruhr-University Bochum, Germany, a test facility has been built in order to confirm the concept of the decay heat removal in the FRM-II, to acquire data of single and two phase natural convection flows and to detect the dry out in a narrow channel. The thermohydraulics of the FRM-II are simulated by an electrically heated test section, which represents one cooling channel of the fuel element. At first experiments have been performed, which simulated the transition from forced to natural convection in the core of the FRM-II, both at normal operation and at a complete loss of the decay heat removal pumps. In case of normal operation, the transition from forced to natural convection takes place single phased. If a complete loss of the active decay heat removal system occurs, the decay heat removal is ensured by a quasi-steady two phase flow. In a second test series minimum heat flux densities leading to pressure pulsations

  5. Evaluation of forced-convection nucleate boiling detection by acoustic emission

    International Nuclear Information System (INIS)

    Wells, R.P.; Paterson, J.A.

    1981-10-01

    Acoustic Emission techniques are being investigated for use as protection systems in neutral beam accelerators and water cooled beam dumps. For this purpose, the characteristics of the boiling curve for forced-convection surface boiling have been compared to the Acoustic Emission (AE) produced. Results indicate that AE, in the form of count-rate, is a sensitive indicator of nucleate boiling incipience and is relatively insensitive to flow velocity in the 0 to 12 m/s range

  6. The effect of cooling conditions on convective heat transfer and flow in a steam-cooled ribbed duct

    International Nuclear Information System (INIS)

    Shui, Linqi; Gao, Jianmin; Shi, Xiaojun; Liu, Jiazeng; Xu, Liang

    2014-01-01

    This work presents a numerical and experimental investigation on the heat transfer and turbulent flow of cooling steam in a rectangular duct with 90 .deg. ribs and studies the effect of cooling conditions on the heat transfer augmentation of steam. In the calculation, the variation range of Reynolds is from 10,000 to 190,000, the inlet temperature varies from 300 .deg. C to 500 .deg. C and the outlet pressure is from 0.5MPa to 6MPa. The aforementioned wide ranges of flow parameters cover the actual operating condition of coolant used in the gas turbine blades. The computations are carried with four turbulence models (the standard k-ε, the renormalized group (RNG) k-ε, the Launder-Reece-Rodi (LRR) and the Speziale-Sarkar-Gatski (SSG) turbulence models). The comparison of numerical and experimental results reveals that the SSG turbulence model is suitable for steam flow in the ribbed duct. Therefore, adopting the conjugate calculation technique, further study on the steam heat transfer and flow characteristics is performed with SSG turbulence model. The results show that the variation of cooling condition strongly impacts the forced convection heat transfer of steam in the ribbed duct. The cooling supply condition of a relative low temperature and medium pressure could bring a considerable advantage on steam thermal enhancement. In addition, comparing the heat transfer level between steam flow and air flow, the performance advantage of using steam is also influenced by the cooling supply condition. Changing Reynolds number has little effect on the performance superiority of steam cooling. Increasing pressure would strengthen the advantage, but increasing temperature gives an opposite result.

  7. The effect of cooling conditions on convective heat transfer and flow in a steam-cooled ribbed duct

    Energy Technology Data Exchange (ETDEWEB)

    Shui, Linqi; Gao, Jianmin; Shi, Xiaojun; Liu, Jiazeng; Xu, Liang [Xi' an Jiaotong University, Xi' an (China)

    2014-01-15

    This work presents a numerical and experimental investigation on the heat transfer and turbulent flow of cooling steam in a rectangular duct with 90 .deg. ribs and studies the effect of cooling conditions on the heat transfer augmentation of steam. In the calculation, the variation range of Reynolds is from 10,000 to 190,000, the inlet temperature varies from 300 .deg. C to 500 .deg. C and the outlet pressure is from 0.5MPa to 6MPa. The aforementioned wide ranges of flow parameters cover the actual operating condition of coolant used in the gas turbine blades. The computations are carried with four turbulence models (the standard k-ε, the renormalized group (RNG) k-ε, the Launder-Reece-Rodi (LRR) and the Speziale-Sarkar-Gatski (SSG) turbulence models). The comparison of numerical and experimental results reveals that the SSG turbulence model is suitable for steam flow in the ribbed duct. Therefore, adopting the conjugate calculation technique, further study on the steam heat transfer and flow characteristics is performed with SSG turbulence model. The results show that the variation of cooling condition strongly impacts the forced convection heat transfer of steam in the ribbed duct. The cooling supply condition of a relative low temperature and medium pressure could bring a considerable advantage on steam thermal enhancement. In addition, comparing the heat transfer level between steam flow and air flow, the performance advantage of using steam is also influenced by the cooling supply condition. Changing Reynolds number has little effect on the performance superiority of steam cooling. Increasing pressure would strengthen the advantage, but increasing temperature gives an opposite result.

  8. Design of force-cooled conductors for large fusion magnets

    Energy Technology Data Exchange (ETDEWEB)

    Dresner, L.; Lue, J.W.

    1977-01-01

    Conductors cooled by supercritical helium in forced convection are under active consideration for large toroidal fusion magnets. One of the central problems in designing such force cooled conductors is to maintain an adequate stability margin while keeping the pumping power tolerably low. A method has been developed for minimizing the pumping power for fixed stability by optimally choosing the matrix-to-superconductor and the metal-to-helium ratios. Such optimized conductors reduce pumping power requirements for fusion size magnets to acceptable limits. Furthermore, the mass flow and hence pumping losses can be varied through a magnet according to the local magnetic field and magnitude of desired stability margin. Force cooled conductors give flexibility in operation, permitting, for example, higher fields to be obtained than originally intended by lowering the bath temperature or increasing the pumping power or both. This flexibility is only available if the pumping power is low to begin with. Scaling laws for the pumping requirement and stability margin as functions of operating current density, number of strands and such physical parameters as stabilizer resistivity and critical current density, have been proved. Numerical examples will be given for design of conductors intended for use in large toroidal fusion magnet systems.

  9. Design of force-cooled conductors for large fusion magnets

    International Nuclear Information System (INIS)

    Dresner, L.; Lue, J.W.

    1977-01-01

    Conductors cooled by supercritical helium in forced convection are under active consideration for large toroidal fusion magnets. One of the central problems in designing such force cooled conductors is to maintain an adequate stability margin while keeping the pumping power tolerably low. A method has been developed for minimizing the pumping power for fixed stability by optimally choosing the matrix-to-superconductor and the metal-to-helium ratios. Such optimized conductors reduce pumping power requirements for fusion size magnets to acceptable limits. Furthermore, the mass flow and hence pumping losses can be varied through a magnet according to the local magnetic field and magnitude of desired stability margin. Force cooled conductors give flexibility in operation, permitting, for example, higher fields to be obtained than originally intended by lowering the bath temperature or increasing the pumping power or both. This flexibility is only available if the pumping power is low to begin with. Scaling laws for the pumping requirement and stability margin as functions of operating current density, number of strands and such physical parameters as stabilizer resistivity and critical current density, have been proved. Numerical examples will be given for design of conductors intended for use in large toroidal fusion magnet systems

  10. Suppression of saturated nucleate boiling by forced convective flow

    International Nuclear Information System (INIS)

    Bennett, D.L.; Davis, M.W.; Hertzler, B.L.

    1980-01-01

    Tube-side forced convective boiling nitrogen and oxygen and thin film shell-side forced convective boiling R-11 data demonstrate a reduction in the heat transfer coefficient associated with nucleate boiling as the two-phase friction pressure drop increases. Techniques proposed in the literature to account for nucleate boiling during forced convective boiling are discussed. The observed suppression of nucleate boiling for the tube-side data is compared against the Chen correlation. Although general agreement is exhibited, supporting the interactive heat transfer mechanism theory, better agreement is obtained by defining a bubble growth region within the thermal boundary layer. The data suggests that the size of the bubble growth region is independent of the friction drop, but is only a function of the physical properties of the boiling liquid. 15 refs

  11. Transition from boiling to two-phase forced convection

    International Nuclear Information System (INIS)

    Maroti, L.

    1985-01-01

    The paper presents a method for the prediction of the boundary points of the transition region between fully developed boiling and two-phase forced convection. It is shown that the concept for the determination of the onset of fully developed boiling can also be applied for the calculation of the point where the heat transfer is effected again by the forced convection. Similarly, the criterion for the onset of nucleate boiling can be used for the definition of the point where boiling is completely suppressed and pure two-phase forced convection starts. To calculate the heat transfer coefficient for the transition region, an equation is proposed that applies the boundary points and a relaxation function ensuring the smooth transition of the heat transfer coefficient at the boundaries

  12. Reynolds analogy for subcooled surface boiling under forced convection

    International Nuclear Information System (INIS)

    Avdeev, A.A.

    1982-01-01

    For the case of subcooled surface boiling under forced convection the analytic expression of analogy between the heat transfer and carry pulse (Reynolds analogy) is derived. It is concluded that the obtained dependence creates the basis for solution of a series of problems of surface boiling physics. On the basis of the performed analysis the method of coordinate calculation of the origin of intensive vapour generation is developed and the formula for calculation of the broken-off-bubble radius under forced convection is derived [ru

  13. Convection-type LH2 absorber R and D for muon ionization cooling

    International Nuclear Information System (INIS)

    Ishimoto, S.; Bandura, L.; Black, E.L.; Boghosian, M.; Cassel, K.W.; Cummings, M.A.; Darve, C.; Dyshkant, A.; Errede, D.; Geer, S.; Haney, M.; Hedin, D.; Johnson, R.; Johnstone, C.J.; Kaplan, D.M.; Kubik, D.; Kuno, Y.; Majewski, S.; Popovic, M.; Reep, M.; Summers, D.; Suzuki, S.; Yoshimura, K.

    2003-01-01

    A feasibility study on liquid hydrogen (LH 2 ) absorbers for muon ionization cooling is reported. In muon ionization cooling, an LH 2 absorber is required to have a high cooling power greater than 100 W to cool heat deposited by muons passing through. That heat in LH 2 can be removed at either external or internal heat exchangers, which are cooled by cold helium gas. As one of the internal heat exchanger types, a convection-type absorber is proposed. In the convection-type absorber, heat is taken away by the convection of LH 2 in the absorber. The heat exchanger efficiency for the convection-type absorber is calculated. A possible design is presented

  14. Convection-type LH{sub 2} absorber R and D for muon ionization cooling

    Energy Technology Data Exchange (ETDEWEB)

    Ishimoto, S. E-mail: shigeru.ishimoto@kek.jp; Bandura, L.; Black, E.L.; Boghosian, M.; Cassel, K.W.; Cummings, M.A.; Darve, C.; Dyshkant, A.; Errede, D.; Geer, S.; Haney, M.; Hedin, D.; Johnson, R.; Johnstone, C.J.; Kaplan, D.M.; Kubik, D.; Kuno, Y.; Majewski, S.; Popovic, M.; Reep, M.; Summers, D.; Suzuki, S.; Yoshimura, K

    2003-05-01

    A feasibility study on liquid hydrogen (LH{sub 2}) absorbers for muon ionization cooling is reported. In muon ionization cooling, an LH{sub 2} absorber is required to have a high cooling power greater than 100 W to cool heat deposited by muons passing through. That heat in LH{sub 2} can be removed at either external or internal heat exchangers, which are cooled by cold helium gas. As one of the internal heat exchanger types, a convection-type absorber is proposed. In the convection-type absorber, heat is taken away by the convection of LH{sub 2} in the absorber. The heat exchanger efficiency for the convection-type absorber is calculated. A possible design is presented.

  15. Convective cooling in a pool-type research reactor

    Energy Technology Data Exchange (ETDEWEB)

    Sipaun, Susan, E-mail: susan@nm.gov.my [Malaysian Nuclear Agency, Industrial Technology Division, Blok 29T, Bangi 43200, Selangor (Malaysia); Usman, Shoaib, E-mail: usmans@mst.edu [Missouri University of Science and Technology, Nuclear Engineering, 222 Fulton Hall 301 W.14th St., Rolla 64509 MO (United States)

    2016-01-22

    A reactor produces heat arising from fission reactions in the nuclear core. In the Missouri University of Science and Technology research reactor (MSTR), this heat is removed by natural convection where the coolant/moderator is demineralised water. Heat energy is transferred from the core into the coolant, and the heated water eventually evaporates from the open pool surface. A secondary cooling system was installed to actively remove excess heat arising from prolonged reactor operations. The nuclear core consists of uranium silicide aluminium dispersion fuel (U{sub 3}Si{sub 2}Al) in the form of rectangular plates. Gaps between the plates allow coolant to pass through and carry away heat. A study was carried out to map out heat flow as well as to predict the system’s performance via STAR-CCM+ simulation. The core was approximated as porous media with porosity of 0.7027. The reactor is rated 200kW and total heat density is approximately 1.07+E7 Wm{sup −3}. An MSTR model consisting of 20% of MSTR’s nuclear core in a third of the reactor pool was developed. At 35% pump capacity, the simulation results for the MSTR model showed that water is drawn out of the pool at a rate 1.28 kg s{sup −1} from the 4” pipe, and predicted pool surface temperature not exceeding 30°C.

  16. Convective cooling in a pool-type research reactor

    Science.gov (United States)

    Sipaun, Susan; Usman, Shoaib

    2016-01-01

    A reactor produces heat arising from fission reactions in the nuclear core. In the Missouri University of Science and Technology research reactor (MSTR), this heat is removed by natural convection where the coolant/moderator is demineralised water. Heat energy is transferred from the core into the coolant, and the heated water eventually evaporates from the open pool surface. A secondary cooling system was installed to actively remove excess heat arising from prolonged reactor operations. The nuclear core consists of uranium silicide aluminium dispersion fuel (U3Si2Al) in the form of rectangular plates. Gaps between the plates allow coolant to pass through and carry away heat. A study was carried out to map out heat flow as well as to predict the system's performance via STAR-CCM+ simulation. The core was approximated as porous media with porosity of 0.7027. The reactor is rated 200kW and total heat density is approximately 1.07+E7 Wm-3. An MSTR model consisting of 20% of MSTR's nuclear core in a third of the reactor pool was developed. At 35% pump capacity, the simulation results for the MSTR model showed that water is drawn out of the pool at a rate 1.28 kg s-1 from the 4" pipe, and predicted pool surface temperature not exceeding 30°C.

  17. Forced convection mixing transients in the MITR core tank

    International Nuclear Information System (INIS)

    Hu, Lin-Wen; Meyer, J.E.; Bernard, J.A.

    1995-01-01

    This paper reports the results of forced convection mixing transient experiments that were studied in the core tank of the 5-MW Massachusetts Institute of Technology (MIT) nuclear reactor as part of the studies being conducted to support a facility upgrade to 10 MW

  18. Cubic spline numerical solution of an ablation problem with convective backface cooling

    Science.gov (United States)

    Lin, S.; Wang, P.; Kahawita, R.

    1984-08-01

    An implicit numerical technique using cubic splines is presented for solving an ablation problem on a thin wall with convective cooling. A non-uniform computational mesh with 6 grid points has been used for the numerical integration. The method has been found to be computationally efficient, providing for the care under consideration of an overall error of about 1 percent. The results obtained indicate that the convective cooling is an important factor in reducing the ablation thickness.

  19. Boiling of subcooled water in forced convection

    International Nuclear Information System (INIS)

    Ricque, R.; Siboul, R.

    1970-01-01

    As a part of a research about water cooled high magnetic field coils, an experimental study of heat transfer and pressure drop is made with the following conditions: local boiling in tubes of small diameters (2 and 4 mm), high heat fluxes (about 1000 W/cm 2 ), high coolant velocities (up to 25 meters/s), low outlet absolute pressures (below a few atmospheres). Wall temperatures are determined with a good accuracy, because very thin tubes are used and heat losses are prevented. Two regimes of boiling are observed: the establishment regime and the established boiling regime and the inception of each regime is correlated. Important delays on boiling inception are also observed. The pressure drop is measured; provided the axial temperature distribution of the fluid and the axial distributions of the wall temperatures, in other words the axial distribution of the heat transfer coefficients under boiling and non boiling conditions, at the same heat flux or the same wall temperatures, are taken in account, then total pressure drop can be correlated, but probably under certain limits of void fraction only. Using the same parameters, it seems possible to correlate the experimental values on critical heat flux obtained previously, which show very important effect of length and hydraulic diameter of the test sections. (authors) [fr

  20. Design of force-cooled conductors for large fusion magnets

    International Nuclear Information System (INIS)

    Dresner, L.; Lue, J.W.

    1977-01-01

    One type of conductor under consideration for tokamak toroidal field (TF) magnets is a cable-in-conduit cooled by supercritical helium in forced convection. The main problem is designing such force-cooled conductors (fcc) is to maintain adequate stability while keeping the pumping power tolerably low. The transit time of the helium through a coil is many minutes. Since recovery of the conductor from a thermomechanical perturbation takes on the order of tens of milliseconds, for purposes of calculation, the inventory of helium available to promote recovery is finite. This means that a large enough perturbation will quench the conductor. We can then judge the stability of a fcc by the maximum perturbation of some specified type against which the conductor is stable, i.e., can still return to the superconducting state. The simplest type of perturbation is a sudden, uniform heat input over the entire length of the conductor. The maximum, sudden, uniform heat input per unit volume of metal ΔH is called the ''stability margin.''

  1. Forced convective post CHF heat transfer and quenching

    International Nuclear Information System (INIS)

    Nelson, R.A.

    1980-01-01

    This paper discusses mechanisms in the post-CHF region which provide understanding and qualitative prediction capability for several current forced convective heat transfer problems. In the area of nuclear reactor safety, the mechanisms are important in the prediction of fuel rod quenches for the reflood phase, blowdown phase, and possibly some operational transients with dryout. Results using the mechanisms to investigate forced convective quenching are presented. Data reduction of quenching experiments is discussed, and the way in which the quenching transient may affect the results of different types of quenching experiments is investigated. This investigation provides an explanation of how minimum wall superheats greater than the homogeneous nucleation temperature result, as well as how these may appear to be either hydrodynamically or thermodynamically controlled. Finally, the results of a parametric study of the effects of the mechanisms upon the LOFT L2-3 hotpin calculation are presented

  2. Transient heat transfer for forced convection flow of helium gas

    International Nuclear Information System (INIS)

    Liu, Qiusheng; Fukuda, Katsuya; Sasaki, Kenji; Yamamoto, Manabu

    1999-01-01

    Transient heat transfer coefficients for forced convection flow of helium gas over a horizontal cylinder were measured using a forced convection test loop. The platinum heater with a diameter of 1.0 mm was heated by electric current with an exponential increase of Q 0 exp(t/τ). It was clarified that the heat transfer coefficient approaches the steady-state one for the period τ over 1 s, and it becomes higher for the period of τ shorter than 1 s. The transient heat transfer shows less dependent on the gas flowing velocity when the period becomes very shorter. Semi-empirical correlations for steady-state and transient heat transfer were developed based on the experimental data. (author)

  3. Regimes of Axisymmetric Flow and Scaling Laws in a Rotating Annulus with Local Convective Forcing

    Directory of Open Access Journals (Sweden)

    Susie Wright

    2017-07-01

    Full Text Available We present a numerical study of axisymmetric flow in a rotating annulus in which local thermal forcing, via a heated annular ring on the outside of the base and a cooled circular disk in the centre of the top surface, drives convection. This new configuration is a variant of the classical thermally-driven annulus, where uniform heating and cooling are applied through the outer and inner sidewalls respectively. The annulus provides an analogue to a planetary circulation and the new configuration, with its more relaxed vertical thermal boundary conditions, is expected to better emulate vigorous convection in the tropics and polar regions as well as baroclinic instability in the mid-latitude baroclinic zone. Using the Met Office/Oxford Rotating Annulus Laboratory (MORALS code, we have investigated a series of equilibrated, two dimensional axisymmetric flows across a large region of parameter space. These are characterized in terms of their velocity and temperature fields. When rotation is applied several distinct flow regimes may be identified for different rotation rates and strengths of differential heating. These regimes are defined as a function of the ratio of the horizontal Ekman layer thickness to the non-rotating thermal boundary layer thickness and are found to be similar to those identified in previous annulus experiments. Convection without rotation is also considered and the scaling of the heat transport with Rayleigh number is calculated. This is then compared with existing work on the classical annulus as well as horizontal and Rayleigh-Bénard convection. As with previous studies on both rotating and non-rotating convection the system’s behaviour is found to be aspect ratio dependent. This dependence is seen in the scaling of the non-rotating Nusselt number and in transitions between regimes in the rotating case although further investigation is required to fully explain these observations.

  4. Convectively Driven Tropopause-Level Cooling and Its Influences on Stratospheric Moisture

    Science.gov (United States)

    Kim, Joowan; Randel, William J.; Birner, Thomas

    2018-01-01

    Characteristics of the tropopause-level cooling associated with tropical deep convection are examined using CloudSat radar and Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) GPS radio occultation measurements. Extreme deep convection is sampled based on the cloud top height (>17 km) from CloudSat, and colocated temperature profiles from COSMIC are composited around the deep convection. Response of moisture to the tropopause-level cooling is also examined in the upper troposphere and lower stratosphere using microwave limb sounder measurements. The composite temperature shows an anomalous warming in the troposphere and a significant cooling near the tropopause (at 16-19 km) when deep convection occurs over the western Pacific, particularly during periods with active Madden-Julian Oscillation (MJO). The composite of the tropopause cooling has a large horizontal scale ( 6,000 km in longitude) with minimum temperature anomaly of -2 K, and it lasts more than 2 weeks with support of mesoscale convective clusters embedded within the envelope of the MJO. The water vapor anomalies show strong correlation with the temperature anomalies (i.e., dry anomaly in the cold anomaly), showing that the convectively driven tropopause cooling actively dehydrate the lower stratosphere in the western Pacific region. The moisture is also affected by anomalous Matsuno-Gill-type circulation associated with the cold anomaly, in which dry air spreads over a wide range in the tropical tropopause layer (TTL). These results suggest that convectively driven tropopause cooling and associated transient circulation play an important role in the large-scale dehydration process in the TTL.

  5. Various aspects of magnetic field influence on forced convection

    Directory of Open Access Journals (Sweden)

    Pleskacz Lukasz

    2016-01-01

    Full Text Available Flows in the channels of various geometry can be found everywhere in industrial or daily life applications. They are used to deliver media to certain locations or they are the place where heat may be exchanged. For Authors both points of view are interesting. The enhancement methods for heat transfer during the forced convection are demanded due to a technological development and tendency to miniaturization. At the same time it is also worth to find mechanisms that would help to avoid negative effects like pressure losses or sedimentation in the channel flows. This paper shows and discuss various aspects of magnetic field influence on forced convection. A mathematical model consisted of the mass, momentum and energy conservation equations. In the momentum conservation equation magnetic force term was included. In order to calculate this magnetic force Biot-Savart’s law was utilized. Numerical analysis was performed with the usage of commonly applied software. However, userdefined functions were implemented. The results revealed that both temperature and velocity fields were influenced by the strong magnetic field.

  6. Forced and free convection hydromagnetic flow past a vertical flat plate

    International Nuclear Information System (INIS)

    Abdelkhalek, M.M.

    2004-01-01

    The effects of magnetic field and temperature heat source on the free and forced convection flow past an infinite vertical plate is studied analytically. Solutions of the reduced equation appropriate in the forced convection and free convection regime are obtained using perturbation technique. The expression for the velocity field, skin friction and Nusselt number have been obtained

  7. Sensitivity analysis of the thermal performance of radiant and convective terminals for cooling buildings

    DEFF Research Database (Denmark)

    Le Dréau, J.; Heiselberg, P.

    2014-01-01

    Heating and cooling terminals can be classified in two main categories: convective terminals (e.g. active chilled beam, air conditioning) and radiant terminals. The mode of heat transfer of the two emitters is different: the first one is mainly based on convection, whereas the second one is based...... conducted to determine the parameters influencing their thermal performance the most. The air change rate, the outdoor temperature and the air temperature stratification have the largest effect on the cooling need (maintaining a constant operative temperature). For air change rates higher than 0.5 ACH...

  8. Mechanistic modeling of CHF in forced-convection subcooled boiling

    International Nuclear Information System (INIS)

    Podowski, M.Z.; Alajbegovic, A.; Kurul, N.; Drew, D.A.; Lahey, R.T. Jr.

    1997-05-01

    Because of the complexity of phenomena governing boiling heat transfer, the approach to solve practical problems has traditionally been based on experimental correlations rather than mechanistic models. The recent progress in computational fluid dynamics (CFD), combined with improved experimental techniques in two-phase flow and heat transfer, makes the use of rigorous physically-based models a realistic alternative to the current simplistic phenomenological approach. The objective of this paper is to present a new CFD model for critical heat flux (CHF) in low quality (in particular, in subcooled boiling) forced-convection flows in heated channels

  9. FINGERING CONVECTION AND CLOUDLESS MODELS FOR COOL BROWN DWARF ATMOSPHERES

    International Nuclear Information System (INIS)

    Tremblin, P.; Amundsen, D. S.; Mourier, P.; Baraffe, I.; Chabrier, G.; Drummond, B.; Homeier, D.; Venot, O.

    2015-01-01

    This work aims to improve the current understanding of the atmospheres of brown dwarfs, especially cold ones with spectral types T and Y, whose modeling is a current challenge. Silicate and iron clouds are believed to disappear at the photosphere at the L/T transition, but cloudless models fail to reproduce correctly the spectra of T dwarfs, advocating for the addition of more physics, e.g., other types of clouds or internal energy transport mechanisms. We use a one-dimensional radiative/convective equilibrium code ATMO to investigate this issue. This code includes both equilibrium and out-of-equilibrium chemistry and solves consistently the PT structure. Included opacity sources are H 2 -H 2 , H 2 -He, H 2 O, CO, CO 2 , CH 4 , NH 3 , K, Na, and TiO, VO if they are present in the atmosphere. We show that the spectra of Y dwarfs can be accurately reproduced with a cloudless model if vertical mixing and NH 3 quenching are taken into account. T dwarf spectra still have some reddening in, e.g., J–H, compared to cloudless models. This reddening can be reproduced by slightly reducing the temperature gradient in the atmosphere. We propose that this reduction of the stabilizing temperature gradient in these layers, leading to cooler structures, is due to the onset of fingering convection, triggered by the destabilizing impact of condensation of very thin dust

  10. FINGERING CONVECTION AND CLOUDLESS MODELS FOR COOL BROWN DWARF ATMOSPHERES

    Energy Technology Data Exchange (ETDEWEB)

    Tremblin, P.; Amundsen, D. S.; Mourier, P.; Baraffe, I.; Chabrier, G.; Drummond, B. [Astrophysics Group, University of Exeter, EX4 4QL Exeter (United Kingdom); Homeier, D. [Ecole Normale Supérieure de Lyon, CRAL, UMR CNRS 5574, F-69364 Lyon Cedex 07 (France); Venot, O., E-mail: tremblin@astro.ex.ac.uk, E-mail: pascal.tremblin@cea.fr [Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven (Belgium)

    2015-05-01

    This work aims to improve the current understanding of the atmospheres of brown dwarfs, especially cold ones with spectral types T and Y, whose modeling is a current challenge. Silicate and iron clouds are believed to disappear at the photosphere at the L/T transition, but cloudless models fail to reproduce correctly the spectra of T dwarfs, advocating for the addition of more physics, e.g., other types of clouds or internal energy transport mechanisms. We use a one-dimensional radiative/convective equilibrium code ATMO to investigate this issue. This code includes both equilibrium and out-of-equilibrium chemistry and solves consistently the PT structure. Included opacity sources are H{sub 2}-H{sub 2}, H{sub 2}-He, H{sub 2}O, CO, CO{sub 2}, CH{sub 4}, NH{sub 3}, K, Na, and TiO, VO if they are present in the atmosphere. We show that the spectra of Y dwarfs can be accurately reproduced with a cloudless model if vertical mixing and NH{sub 3} quenching are taken into account. T dwarf spectra still have some reddening in, e.g., J–H, compared to cloudless models. This reddening can be reproduced by slightly reducing the temperature gradient in the atmosphere. We propose that this reduction of the stabilizing temperature gradient in these layers, leading to cooler structures, is due to the onset of fingering convection, triggered by the destabilizing impact of condensation of very thin dust.

  11. Convection in Cool Stars, as Seen Through Kepler's Eyes

    Science.gov (United States)

    Bastien, Fabienne A.

    2015-01-01

    Stellar surface processes represent a fundamental limit to the detection of extrasolar planets with the currently most heavily-used techniques. As such, considerable effort has gone into trying to mitigate the impact of these processes on planet detection, with most studies focusing on magnetic spots. Meanwhile, high-precision photometric planet surveys like CoRoT and Kepler have unveiled a wide variety of stellar variability at previously inaccessible levels. We demonstrate that these newly revealed variations are not solely magnetically driven but also trace surface convection through light curve ``flicker.'' We show that ``flicker'' not only yields a simple measurement of surface gravity with a precision of ˜0.1 dex, but it may also improve our knowledge of planet properties, enhance radial velocity planet detection and discovery, and provide new insights into stellar evolution.

  12. Calculations of combined radiation and convection heat transfer in rod bundles under emergency cooling conditions

    International Nuclear Information System (INIS)

    Sun, K.H.; Gonzalez-Santalo, J.M.; Tien, C.L.

    1976-01-01

    A model has been developed to calculate the heat transfer coefficients from the fuel rods to the steam-droplet mixture typical of Boiling Water Reactors under Emergency Core Cooling System (ECCS) operation conditions during a postulated loss-of-coolant accident. The model includes the heat transfer by convection to the vapor, the radiation from the surfaces to both the water droplets and the vapor, and the effects of droplet evaporation. The combined convection and radiation heat transfer coefficient can be evaluated with respect to the characteristic droplet size. Calculations of the heat transfer coefficient based on the droplet sizes obtained from the existing literature are consistent with those determined empirically from the Full-Length-Emergency-Cooling-Heat-Transfer (FLECHT) program. The present model can also be used to assess the effects of geometrical distortions (or deviations from nominal dimensions) on the heat transfer to the cooling medium in a rod bundle

  13. Reassessment of forced convection heat transfer correlations for refrigerant-12

    International Nuclear Information System (INIS)

    Celata, G.P.; Cuomo, M.; D'Annibale, F.; Farello, G.E.; Setaro, T.

    1986-01-01

    In the frame of a Refrigerant-12 experiment on postulated accidental transients in Pressurized Water Reactors under way at Heat Transfer Laboratory (ENEA Casaccia Research Center), an assessment of the main correlation available in scientific literature, for the different heat transfer regions encountered when a liquid is boiled in a confined heated channel, has been performed. Considering a vertical tube uniformly heated over its length with CHF at the exit, the following heat transfer regimes may be individuated: convective heat transfer to liquid, subcooled boiling, saturated nucleate boiling, forced convective heat transfer through liquid film (annular flow regime) and thermal crisis. From the comparison of computed values with an original ENEA dataset, the best correlations in predicting Refrigerant-12 data have been individuated. In a few cases, though preserving the original structure of the correlations, mainly developed for water, it was necessary to adjust some coefficients by means of best-fit procedures through our experimental data. The work has been performed in the frame of the ENEA Thermal Reactor Department Safety Research Project

  14. Forced heat convection in annular spaces; Convection forcee de la chaleur dans les espaces annulaires

    Energy Technology Data Exchange (ETDEWEB)

    Pelce, J [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1960-02-15

    This report deals with the experimental study of forced heat convection in annular spaces through which flow of air is passing when a uniform heat flux is dissipated across the inner wall. These observations took place chiefly in the region where thermal equilibrium are not yet established. Amongst other things it became apparent that, both in the region where thermal equilibrium conditions are on the way to establishment and where they are already established, the following relationship held good: the longitudinal temperature gradient, either on the wall or in the fluid stream, is proportional to the heat flux dissipated q, and inversely proportional to the average flow rate V: dT/dx = B (q/V). From this result the next step is to express the variations of the local convection coefficient {alpha} (or of the Margoulis number M) in a relationship of the form: 1/M = {psi}(V) + F(x). If this relationship is compared with the classical empirical relationship {alpha} = KV{sup n} (where n is close to 0.8), the relationship: 1/M = {xi}V{sup 1-n} + F(x) is obtained ({xi} is a constant for a given annular space); from this it was possible to coordinate the whole set of experimental results. (author) [French] Il s'agit precisement de l'etude experimentale de la convection forcee de la chaleur dans des espaces annulaires parcourus par de l'air en ecoulement turbulent, lorsqu'on dissipe a travers la paroi interieure un flux de chaleur uniforme. Ces observations ont eu lieu principalement dans la region ou le regime thermique n'est pas encore etabli. Il est apparu, entre autre, qu'il existait, tant dans la region ou le regime thermique est en voie d'etablissement qu'en regime etabli, la relation suivante: le gradient longitudinal des temperatures, que ce soit sur la paroi ou dans l'ecoulement fluide, est proportionnel au flux de la chaleur dissipee q, et inversement proportionnel a la vitesse moyenne V de l'ecoulement: dT/dx = B (q/V). Ce resultat a pour consequence de traduire

  15. Comparative analysis of heat transfer correlations for forced convection boiling

    International Nuclear Information System (INIS)

    Guglielmini, G.; Nannei, E.; Pisoni, C.

    1978-01-01

    A critical survey was conducted of the most relevant correlations of boiling heat transfer in forced convection flow. Most of the investigations carried out on partial nucleate boiling and fully developed nucleate boiling have led to the formulation of correlations that are not able to cover a wide range of operating conditions, due to the empirical approach of the problem. A comparative analysis is therefore required in order to delineate the relative accuracy of the proposed correlations, on the basis of the experimental data presently available. The survey performed allows the evaluation of the accuracy of the different calculating procedure; the results obtained, moreover, indicate the most reliable heat transfer correlations for the different operating conditions investigated. This survey was developed for five pressure range (up to 180bar) and for both saturation and subcooled boiling condition

  16. Heat transfer during forced convection condensation inside horizontal tube

    Energy Technology Data Exchange (ETDEWEB)

    Tandon, T.N. [M.M.M. Engineering College, Gorakhpur, Uttar Pradesh (India). Dept. of Mechanical Engineering; Varma, H.K.; Gupta, C.P. [Roorkee Univ., Uttar Pradesh (India). Dept. of Mechanical and Industrial Engineering

    1995-03-01

    This paper presents the results of an experimental investigation on heat transfer behaviour during forced convection condensation inside a horizontal tube for wavy, semi-annular and annular flows. A qualitative study was made of the effect of various parameters - refrigerant mass flux, vapour quality, condensate film temperature drop and average vapour mass velocity - on average condensing-heat transfer coefficient. Akers-Rosson correlations have been found to predict the heat transfer coefficients within {+-} 25% for the entire range of data. A closer examination of the data revealed that the nature of the relation for the heat transfer coefficient changes from annular and semi-annular flow to wavy flow. Akers-Rosson correlations with changed constant and power have been recommended for the two flow regimes. (author)

  17. Silk cocoon drying in forced convection type solar dryer

    International Nuclear Information System (INIS)

    Singh, Panna Lal

    2011-01-01

    The thin layer silk cocoon drying was studied in a forced convection type solar dryer. The drying chamber was provided with several trays on which the cocoons loaded in thin layer. The hot air generated in the solar air heater was forced into drying chamber to avoid the direct exposure of sunlight and UV radiation on cocoons. The drying air temperature varied from 50 to 75 o C. The cocoon was dried from the initial moisture content of about 60-12% (wb). The drying data was fitted to thin layer drying models. Drying behaviour of the silk cocoon was best fitted with the Wang and Singh drying model. Good agreement was obtained between predicted and experimental values. Quality of the cocoons dried in the solar dryer was at par with the cocoons dried in the conventional electrical oven dryer in term of the silk yield and strength of the silk. Saving of electrical energy was about 0.75 kWh/kg cocoons dried. Economic analysis indicated that the NPV of the solar dryer was higher and more stable (against escalation rate of electricity) as compare to the same for electrical oven dryer. Due to simplicity in design and construction and significant saving of operational electrical energy, solar cocoon dryer seems to be a viable option.

  18. Analysis of Forced Convection Heat Transfer for Axial Annular Flow of Giesekus Viscoelastic Fluid

    Energy Technology Data Exchange (ETDEWEB)

    Mohseni, Mehdi Moayed; Rashidi, Fariborz; Movagar, Mohammad Reza Khorsand [Amirkabir University of Technology, Tehran (Iran, Islamic Republic of)

    2015-02-15

    Analytical solutions for the forced convection heat transfer of viscoelastic fluids obeying the Giesekus model are obtained in a concentric annulus under laminar flow for both thermal and hydrodynamic fully developed conditions. Boundary conditions are assumed to be (a) constant fluxes at the walls and (b) constant temperature at the walls. Temperature profiles and Nusselt numbers are derived from dimensionless energy equation. Subsequently, effects of elasticity, mobility parameter and viscous dissipation are discussed. Results show that by increasing elasticity, Nusselt number increases. However, this trend is reversed for constant wall temperature when viscous dissipation is weak. By increasing viscous dissipation, the Nusselt number decreases for the constant flux and increases for the constant wall temperature. For the wall cooling case, when the viscous dissipation exceeds a critical value, the generated heat overcomes the heat which is removed at the walls, and fluid heats up longitudinally.

  19. Natural air convection for cooling of particle accelerator electromagnets: case studies at CERN

    CERN Document Server

    Moreira, Mariana

    Cooling by natural convection is investigated on two air-cooled corrector magnets at CERN. The heat transfer coefficient (HTC) for each magnet is estimated analytically using established empirical correlations for certain geometries. The HTC is also estimated numerically with three-dimensional steady-state finite element simulations. Air convection around the respective coils as well as heat conduction inside the coils are modelled. Different formulas for the HTC are tested in the post-processing of the simulation results. The HTC for each magnet is then determined experimentally by measuring surface temperatures on the coils through time at constant currents. A method to extract the HTC from these temperature curves is developed, in which the curves are fitted to a function that is derived from a thermodynamical analysis of the heating process. Some plausible ranges for the HTC for each magnet for different currents are obtained. The results of the different estimation methods are compared with the experimen...

  20. Forced two phase helium cooling of large superconducting magnets

    International Nuclear Information System (INIS)

    Green, M.A.; Burns, W.A.; Taylor, J.D.

    1979-08-01

    A major problem shared by all large superconducting magnets is the cryogenic cooling system. Most large magnets are cooled by some variation of the helium bath. Helium bath cooling becomes more and more troublesome as the size of the magnet grows and as geometric constraints come into play. An alternative approach to cooling large magnet systems is the forced flow, two phase helium system. The advantages of two phase cooling in many magnet systems are shown. The design of a two phase helium system, with its control dewar, is presented. The paper discusses pressure drop of a two phase system, stability of a two phase system and the method of cool down of a two phase system. The results of experimental measurements at LBL are discussed. Included are the results of cool down and operation of superconducting solenoids

  1. Improved lumped models for transient combined convective and radiative cooling of multi-layer composite slabs

    International Nuclear Information System (INIS)

    An Chen; Su Jian

    2011-01-01

    Improved lumped parameter models were developed for the transient heat conduction in multi-layer composite slabs subjected to combined convective and radiative cooling. The improved lumped models were obtained through two-point Hermite approximations for integrals. Transient combined convective and radiative cooling of three-layer composite slabs was analyzed to illustrate the applicability of the proposed lumped models, with respect to different values of the Biot numbers, the radiation-conduction parameter, the dimensionless thermal contact resistances, the dimensionless thickness, and the dimensionless thermal conductivity. It was shown by comparison with numerical solution of the original distributed parameter model that the higher order lumped model (H 1,1 /H 0,0 approximation) yielded significant improvement of average temperature prediction over the classical lumped model. In addition, the higher order (H 1,1 /H 0,0 ) model was applied to analyze the transient heat conduction problem of steel-concrete-steel sandwich plates. - Highlights: → Improved lumped models for convective-radiative cooling of multi-layer slabs were developed. → Two-point Hermite approximations for integrals were employed. → Significant improvement over classical lumped model was achieved. → The model can be applied to high Biot number and high radiation-conduction parameter. → Transient heat conduction in steel-concrete-steel sandwich pipes was analyzed as an example.

  2. Forced convective melting at an evolving ice-water interface

    Science.gov (United States)

    Ramudu, Eshwan; Hirsh, Benjamin; Olson, Peter; Gnanadesikan, Anand

    2015-11-01

    The intrusion of warm Circumpolar Deep Water into the ocean cavity between the base of ice shelves and the sea bed in Antarctica causes melting at the ice shelves' basal surface, producing a turbulent melt plume. We conduct a series of laboratory experiments to investigate how the presence of forced convection (turbulent mixing) changes the delivery of heat to the ice-water interface. We also develop a theoretical model for the heat balance of the system that can be used to predict the change in ice thickness with time. In cases of turbulent mixing, the heat balance includes a term for turbulent heat transfer that depends on the friction velocity and an empirical coefficient. We obtain a new value for this coefficient by comparing the modeled ice thickness against measurements from a set of nine experiments covering one order of magnitude of Reynolds numbers. Our results are consistent with the altimetry-inferred melting rate under Antarctic ice shelves and can be used in climate models to predict their disintegration. This work was supported by NSF grant EAR-110371.

  3. Visualization of bubble behaviors in forced convective subcooled flow boiling

    International Nuclear Information System (INIS)

    Inaba, Noriaki; Matsuzaki, Mitsuo; Kikura, Hiroshige; Aritomi, Masanori; Komeno, Toshihiro

    2007-01-01

    Condensation characteristics of vapor bubble after the departure from a heated section in forced convective subcooled flow boiling were studied visually by using a high speed camera. The purpose of the present study was to measure two-phase flow parameters in subcooled flow boiling. These two-phase flow parameters are void fraction, interfacial area concentration and Sauter mean diameter, which express bubble interface behaviors. The experimental set-up was designed to measure the two-phase flow parameters necessary for developing composite equations for the two fluid models in subcooled flow boiling. In the present experiments, the mass flux, liquid subcooling and the heater were varied within 100-1000kg/m 2 s, 2-10K and 100-300kW/m 2 respectively. Under these experimental conditions, the bubble images were obtained by a high-speed camera, and analyzed paying attention to the condensation of vapor bubbles. These two-phase parameters were obtained by the experimental data, such as the bubble parameter, the bubble volume and the bubble surface. In the calculation process of the two phase flow parameters, it was confirmed that these parameters are related to the void fraction. (author)

  4. Turbulent forced convection of nanofluids downstream an abrupt expansion

    Science.gov (United States)

    Kimouche, Abdelali; Mataoui, Amina

    2018-03-01

    Turbulent forced convection of Nanofluids through an axisymmetric abrupt expansion is investigated numerically in the present study. The governing equations are solved by ANYS 14.0 CFD code based on the finite volume method by implementing the thermo-physical properties of each nanofluid. All results are analyzed through the evolutions of skin friction coefficient and Nusselt number. For each nanofluid, the effect of both volume fraction and Reynolds number on this type of flow configuration, are examined. An increase on average Nusselt number with the volume fraction and Reynolds number, are highlighted and correlated. Two relationships are proposed. The first one, determines the average Nusselt number versus Reynolds number, volume fraction and the ratio of densities of the solid particles to that of the base fluid ( \\overline{Nu}=f(\\operatorname{Re},φ, ρ_s/ρ_f) ). The second one varies according Reynolds number, volume fraction and the conductivities ratio of solid particle to that of the base fluid ( \\overline{Nu}=f(\\operatorname{Re},φ, k_s/k_f) ).

  5. A study of forced convective subcooled flow boiling

    International Nuclear Information System (INIS)

    Serizawa, Akimi; Kenning, D.B.R.

    1979-01-01

    Based on a simple nucleation model, parameter survey technique is used to derive a predictive correlation for boiling initiation under forced convection. Results are expressed by a semi-empirical equation which considers effects of the flow turbulence on interfacial heat transfer coefficient for evaporation and condensation of vapour bubbles during their growth. This correlation agrees within +-25% with a variety of experimental water data presently available. The bubble departure diameter and the subcooling-dependence of active nucleation sites were examined, using experimental data available. Results are expressed by empirical equations. Finally, an analytical model is presented to predict conditions for the point of net vapour generation. The model is based on the formation and growth of a bubble boundary layer adjacent to the heated wall. It is shown that the point of net vapour generation is determined by the liquid subcooling at the boiling initiation and the subcooling-dependences of bubble departure diameter and bubble flux. The result implies that the bubble ejection from bubble layer is a possible mechanism for the significant void increase even at high velocities. (author)

  6. The effects of radiant cooling versus convective cooling on human eye tear film stability and blinking rate

    DEFF Research Database (Denmark)

    Nygaard, Linette; Uth, Simon C.; Bolashikov, Zhecho Dimitrov

    2014-01-01

    The effect of indoor temperature, radiant and convective cooling on tear film stability and eye blink frequency was examined. 24 human subjects were exposed to the non-uniform environment generated by localised chilled beam and a chilled ceiling combined with overhead mixing ventilation. The subj......The effect of indoor temperature, radiant and convective cooling on tear film stability and eye blink frequency was examined. 24 human subjects were exposed to the non-uniform environment generated by localised chilled beam and a chilled ceiling combined with overhead mixing ventilation....... The subjects participated in four two-hour experiments. The room air temperature was kept at 26 °C or 28 °C. Tear film samples were collected after 30 min of acclimatisation and at the end of the exposures. Eye blinking frequency was analysed for the first and last 15 min of each exposure. The tear film...... stability decreased as the temperature increased. The highest number of subjects with unchanged or improved tear film quality was observed with the localised chilled beam at 26 °C. A trend was found between subjects who reported eye irritation and had a bad tear film quality....

  7. Influence of convective cooling on a disc brake temperature distribution during repetitive braking

    International Nuclear Information System (INIS)

    Adamowicz, Adam; Grzes, Piotr

    2011-01-01

    The purpose of this study is to evaluate an impact of convective mode of heat transfer on the thermal behaviour of a disc brake system during repetitive braking process with the constant velocity using fully three-dimensional finite element model. The transient thermal analysis to determine the temperature distributions on the contact surface of a disc brake is performed. The issue of non-uniform frictional heating effects of mutual slipping of a disc over fixed pads is tested using FE models with the several possible to occur in automotive application heat transfer coefficients. To have a possibility of comparison of the temperature distributions of a disc during cyclic brake application, the energy transformed during time of every analyzed case of braking process and the subsequent release periods was equal. The time-stepping procedure is employed to develop moving heat source as the boundary heat flux acting interchangeably with the convective cooling terms. The difficulties accounted for the accurate simulation of heating during spin of the rotor is omitted by the use of the code, which enable shaping curves responsible for the thermal flux entering the disc at subsequent moments of time. The resulting evolution of temperature on the friction surface reveals a wide range of variations, distinguishing periods of heating and cooling states. It has been established, that during single braking the convective cooling has insignificant influence on the temperature distributions of a disc brake, consequently is not able to prevent overheat problem. However the brake release period after the braking operation, when the velocity of the vehicle remains on the same level, results in considerable decrease of temperature. - Highlights: → Convection does not allow to lower temperature of disc during single braking process. → Maximal temperature of disc decreases with number of brake applications. → Temperature at the end of braking increases with number of brake

  8. Forced convection and subcooled flow boiling heat transfer in asymmetrically heated ducts of T-section

    International Nuclear Information System (INIS)

    Abou-Ziyan, Hosny Z.

    2004-01-01

    This paper presents the results of an experimental investigation of heat transfer from the heated bottom side of tee cross-section ducts to an internally flowing fluid. The idea of this work is derived from the cooling of critical areas in the cylinder heads of internal combustion engines. Fully developed single phase forced convection and subcooled flow boiling heat transfer data are reported. Six T-ducts of different width and height aspect ratios are tested with distilled water at velocities of 1, 2 and 3 m/s for bulk temperatures of 60 and 80 deg. C, while the heat flux was varied from about 80 to 700 kW/m 2 . The achieved data cover Reynolds numbers in the range of 5.22 x 10 4 to 2.36 x 10 5 , Prandtl numbers in the range from 2.2 to 3.0, duct width aspect ratio between 2.19 and 3.13 and duct height aspect ratio from 0.69 to 2.0. The results revealed that the increase in either the width or height aspect ratio of the T-ducts enhances the convection heat transfer coefficients and the boiling heat fluxes considerably. The following comparisons are provided for coolant velocity of 2 m/s, bulk temperature of 60 deg. C, wall superheat of 20 K and wall to bulk temperature difference of 20 K. As the width aspect ratio increases by 43%, the convection heat transfer coefficient and the boiling heat flux increase by 27% and 39%, respectively. An increase in the height aspect ratio by 290% enhances the convection heat transfer coefficient and the boiling heat fluxes by 82% and 103%, respectively. When the coolant velocity changes from 1 to 2 m/s, the heat transfer coefficient increases by 60% and the boiling heat flux rises by 62-98% for the various tested ducts. The convection heat transfer coefficient increases by 12% and the boiling heat flux decreases by 31% as the bulk fluid temperature rises from 60 to 80 deg. C. A correlation was developed for Nusselt number as a function of Reynolds number, Prandtl number, viscosity ratio and some aspect ratios of the T-duct

  9. Effect of Forced Convection Heat Transfer on Weld Pools.

    Science.gov (United States)

    1986-01-01

    Cooling Curves for GTAW Welds Superimposed on CCT Diagram ............. 26 11 - Photomacrographs Showing Weld Macrostructure (TS Plane...decomposition kinetics. Superposition of the weld metal cooling rates measured in this study on the CCT diagram shows that the time for nucleation and growth...m - TABLE 2 - TRANSFORMATION AND COOLING TIMES FROM CCT DIAGRAM *II I I. I I I Cooling Rate I Transformation I Time to Cool tL-I- I Heat Input I

  10. Studies of decay heat removal by natural convection using the SONACO sodium-cooled 37-pin bundle

    International Nuclear Information System (INIS)

    Wydler, P.; Dury, T.V.; Hudina, M.; Weissenfluh, T. von; Sigg, B.; Dutton, P.

    1986-01-01

    Natural convection measurements in an electrically heated sodium-cooled rod bundle are being performed with the aim of contributing to a better understanding of natural convection effects in subassemblies with stagnant sodium and providing data for code validation. Measurements include temperature distributions in the bundle for different cooling configurations which simulate heat transfer to the intersubassembly gap and neighbouring subassemblies and possible thermosyphonic interaction between a subassembly and the reactor plenum above. Conditions for which stable natural convection patterns exist are identified, and results are compared with predictions of different computer codes of the porous-medium type. (author)

  11. Feasibility of maintaining natural convection mode core cooling in research reactor power upgrades

    International Nuclear Information System (INIS)

    Ha, J.J.; Belhadj, M.; Aldemir, T.; Christensen, R.N.

    1987-01-01

    Two operational concerns for natural convection coooled research reactors using plate type fuels are: 1) pool top 16 N activity (PTNA), and 2) nucleate boiling in core channels. The feasibility assessment of a power upgrade while maintaining natural convection mode core cooling requires addressing these operational concerns. Previous studies have shown that: a) The conventional technique for reducing PTNA by plume dispersion may not be effective in a large power upgrade of research reactors with small pools. b) Currently used correlations to predict onset of nucleate boiling (ONB) in thin, rectangular core channels are not valid for low-velocity, upward flows such as encountered in natural convection cooling. The PTNA depends on the velocity distribution in the reactor pool. COMMIX-1A code is used to determine the three-dimensional velocity fields in The Ohio State University Research Reactor (OSURR) pool as a function of varying design conditions, following a power upgrade to 500 kW with LEU fuel. It is shown that a sufficiently deep stagnant water layer can be created below the pool top by properly choosing the disperser flow rate. The ONB heat flux is experimentally determined for channel gaps and upward flow velocities in the range 2mm-4mm and 3-16 cm/sec., respectively. Two alternatives to plume dispersion for reducing PTNA and a new correlation to determine the ONB heat flux in thin, rectangular channels under low-velocity, upward flow conditions are proposed. (Author)

  12. Delay in convection in nocturnal boundary layer due to aerosol-induced cooling

    Science.gov (United States)

    Singh, Dhiraj Kumar; Ponnulakshmi, V. K.; Subramanian, G.; Sreenivas, K. R.

    2012-11-01

    Heat transfer processes in the nocturnal boundary layer (NBL) influence the surface energy budget, and play an important role in many micro-meteorological processes including the formation of inversion layers, radiation fog, and in the control of air-quality near the ground. Under calm clear-sky conditions, radiation dominates over other transport processes, and as a result, the air layers just above ground cool the fastest after sunset. This leads to an anomalous post-sunset temperature profile characterized by a minimum a few decimeters above ground (Lifted temperature minimum). We have designed a laboratory experimental setup to simulate LTM, involving an enclosed layer of ambient air, and wherein the boundary condition for radiation is decoupled from those for conduction and convection. The results from experiments involving both ambient and filtered air indicate that the high cooling rates observed are due to the presence of aerosols. Calculated Rayleigh number of LTM-type profiles is of the order 105-107 in the field and of order 103-105 in the laboratory. In the LTM region, there is convective motion when the Rayleigh number is greater than 104 rather than the critical Rayleigh number (Rac = 1709). The diameter of convection rolls is a function of height of minimum of LTM-type profiles. The results obtained should help in the parameterization of transport process in the nocturnal boundary layer, and highlight the need to accounting the effects of aerosols and ground emissivity in climate models.

  13. Effects of Convective Aggregation on Radiative Cooling and Precipitation in a CRM

    Science.gov (United States)

    Naegele, A. C.; Randall, D. A.

    2017-12-01

    In the global energy budget, the atmospheric radiative cooling (ARC) is approximately balanced by latent heating, but on regional scales, the ARC and precipitation rates are inversely related. We use a cloud-resolving model to explore how the relationship between precipitation and the ARC is affected by convective aggregation, in which the convective activity is confined to a small portion of the domain that is surrounded by a much larger region of dry, subsiding air. Sensitivity tests show that the precipitation rate and ARC are highly sensitive to both SST and microphysics; a higher SST and 1-moment microphysics both act to increase the domain-averaged ARC and precipitation rates. In all simulations, both the domain-averaged ARC and precipitation rates increased due to convective aggregation, resulting in a positive temporal correlation. Furthermore, the radiative effect of clouds in these simulations is to decrease the ARC. This finding is consistent with our observational results of the cloud effect on the ARC, and has implications for convective aggregation and the geographic extent in which it can occur.

  14. Development and performance evaluation of forced convection potato solar dryer

    International Nuclear Information System (INIS)

    Khan, M.A.; Sabir, M.S.; Iqbal, M.

    2011-01-01

    This research paper deals with the design development and testing of a forced convection solar dryer, for drying and converting to flour of high moisture content vegetables like potatoes. The angle of solar collector was made adjustable for the absorption of maximum solar radiation by the absorber plate. The air flow rate was controlled by adjustable gate valve to find the optimum flow rate for dehydration of the product. The penetration of solar radiation raised the temperature of the absorber plate of the dryer to 110 deg. C during the operation under stagnation or no load conditions. The maximum air temperature attained in the solar air heater, under this condition was 80 deg. C. The dryer was loaded with 12 Kg of blanched potato chips having an initial moisture content of 89.75%, and the final desired moisture content of 6.95% was achieved within five hours without losing the color of potato chips, while the moisture contents reduction was from 89.75% to 33.75% for five hours in open sun drying under shade. The drying cost for 1 Kg of potatoes was calculated as Rs. 245 and it was Rs. 329 in the case of an electric dryer. The life span of the solar dryer was assumed to be 20 years. The cumulative present worth of annual savings over the life of the solar dryer was calculated for blanched potato chips drying, and it turned out be Rs.163177.67/- which was much higher than the capital cost of the dryer (Rs. 25000). The payback period was calculated as 0.89 years, which was also very small considering the life of the system (20 years). (author)

  15. Validation of CFD modeling for VGM loss-of-forced-cooling accidents

    International Nuclear Information System (INIS)

    Wysocki, Aaron; Ahmed, Bobby; Charmeau, Anne; Anghaie, Samim

    2009-01-01

    Heat transfer and fluid flow in the VGM reactor cavity cooling system (RCCS) was modeled using Computational Fluid Dynamics (CFD). The VGM is a Russian modular-type high temperature helium-cooled reactor. In the reactor cavity, heat is removed from the pressure vessel wall through natural convection and radiative heat transfer to water-cooled vertical pipes lining the outer cavity concrete. The RCCS heat removal capability under normal operation and accident scenarios needs to be assessed. The purpose of the present study is to validate the use of CFD to model heat transfer in the VGM RCCS. Calculations were based on a benchmark problem which defines a two-dimensional temperature distribution on the pressure vessel outer wall for both Depressurized and Pressurized Loss-of-Forced Cooling events. A two-dimensional axisymmetric model was developed to determine the best numerical modeling approach. A grid sensitivity study for the air region showed that a 20 mm mesh size with a boundary layer giving a maximum y+ of 2.0 was optimal. Sensitivity analyses determined that the discrete ordinates radiative model, the k-omega turbulence model, and the ideal gas law gave the best combination for capturing radiation and natural circulation in the air cavity. A maximum RCCS pipe wall temperature of 62degC located 6 m from the top of the cavity was predicted. The model showed good agreement with previous results for both Pressurized and Depressurized Loss-of-Forced-Cooling accidents based on RCCS coolant outlet temperature, relative contributions of radiative and convective heat transfer, and RCCS heat load profiles. (author)

  16. Numerical study on film cooling and convective heat transfer characteristics in the cutback region of turbine blade trailing edge

    Directory of Open Access Journals (Sweden)

    Xie Yong-Hui

    2016-01-01

    Full Text Available Gas turbine blade trailing edge is easy to burn out under the exposure of high-temperature gas due to its thin shape. The cooling of this area is an important task in gas turbine blade design. The structure design and analysis of trailing edge is critical because of the complexity of geometry, arrangement of cooling channels, design requirement of strength, and the working condition of high heat flux. In the present paper, a 3-D model of the trailing edge cooling channel is constructed and both structures with and without land are numerically investigated at different blowing ratio. The distributions of film cooling effectiveness and convective heat transfer coefficient on cutback and land surface are analyzed, respectively. According to the results, it is obtained that the distributions of film cooling effectiveness and convective heat transfer coefficient both show the symmetrical characteristics as a result of the periodic structure of the trailing edge. The increase of blowing ratio significantly improves the film cooling effectiveness and convective heat transfer coefficient on the cutback surface, which is beneficial to the cooling of trailing edge. It is also found that the land structure is advantageous for enhancing the streamwise film cooling effectiveness of the trailing edge surface while the film cooling effectiveness on the land surface remains at a low level. Convective heat transfer coefficient exhibits a strong dependency with the blowing ratio, which suggests that film cooling effectiveness and convective heat transfer coefficient must be both considered and analyzed in the design of trailing edge cooling structure.

  17. Analysis of dynamic enhancement of natural convection cooling by a discrete vibrating plate

    Energy Technology Data Exchange (ETDEWEB)

    Florio, L.A.; Harnoy, A. [New Jersey Institute of Technology, Department of Mechanical Engineering, Newark, NJ (United States)

    2006-12-15

    A dynamic means of locally enhancing laminar natural convection cooling in a vertical channel through the localized application of fluid oscillations is numerically investigated. The two-dimensional system considered for these purposes is a vertical channel with a small transversely oscillating plate placed near a constant heat flux channel wall. The flow and heat transfer in the system resulting from the combined effects of the natural convection and the oscillating plate were determined. The results indicate that for displacement amplitudes of at least one-third of the mean spacing and with dimensionless frequencies (Re/{radical}(Gr)) of at least 2{pi}, the local heat transfer coefficient can be enhanced by as much as 41%. (orig.)

  18. Cooling and trapping neutral atoms with radiative forces

    International Nuclear Information System (INIS)

    Bagnato, V.S.; Castro, J.C.; Li, M.S.; Zilio, S.C.

    1988-01-01

    Techniques to slow and trap neutral atoms at high densities with radiative forces are discussed in this review articles. Among several methods of laser cooling, it is emphasized Zeeman Tuning of the electronic levels and frequency-sweeping techniques. Trapping of neutral atoms and recent results obtained in light and magnetic traps are discussed. Techniques to further cool atoms inside traps are presented and the future of laser cooling of neutral atoms by means of radiation pressure is discussed. (A.C.A.S.) [pt

  19. Effect of Buoyancy on Forced Convection Heat Transfer in Vertical Channels - a Literature Survey

    Energy Technology Data Exchange (ETDEWEB)

    Bhattacharyya, A

    1965-03-15

    This report contains a short resume of the available information from various sources on the effect of free convection flow on forced convection heat transfer in vertical channels. Both theoretical and experimental investigations are included. Nearly all of the theoretical investigations are concerned with laminar flow with or without internal heat generation. More consistent data are available for upward flow than for downward flow. Curves are presented to determine whether free convection or forced convection mode of heat transfer is predominant for a particular Reynolds number and Rayleigh number. At Re{sub b} > 10{sup 5} free convection effects are negligible. Downward flow through a heated channel at low Reynolds number is unstable. Under similar conditions the overall heat transfer coefficient for downward flow tends to be higher than that for upward flow.

  20. Forced-convection boiling tests performed in parallel simulated LMR fuel assemblies

    International Nuclear Information System (INIS)

    Rose, S.D.; Carbajo, J.J.; Levin, A.E.; Lloyd, D.B.; Montgomery, B.H.; Wantland, J.L.

    1985-01-01

    Forced-convection tests have been carried out using parallel simulated Liquid Metal Reactor fuel assemblies in an engineering-scale sodium loop, the Thermal-Hydraulic Out-of-Reactor Safety facility. The tests, performed under single- and two-phase conditions, have shown that for low forced-convection flow there is significant flow augmentation by thermal convection, an important phenomenon under degraded shutdown heat removal conditions in an LMR. The power and flows required for boiling and dryout to occur are much higher than decay heat levels. The experimental evidence supports analytical results that heat removal from an LMR is possible with a degraded shutdown heat removal system

  1. Thermal resistance of a convectively cooled plate with applied heat flux and variable internal heat generation

    International Nuclear Information System (INIS)

    Venkataraman, N.S.; Cardoso, H.P.; Oliveira Filho, O.B. de

    1981-01-01

    The conductive heat transfer in a rectangular plate with nonuniform internal heat generation, with one end convectively cooled and a part of the opposite end subjected to external heat flux is considered. The remaining part of this end as well as the other two sides are thermally insulated. The governing differential equation is solved by a finite difference scheme. The variation of the thermal resistance with Biot modulus, the plate geometry, the internal heat generation parameter and the type of profile of internal heat generation is discussed. (author) [pt

  2. Convective Heat Transfer Coefficients of the Human Body under Forced Convection from Ceiling

    DEFF Research Database (Denmark)

    Kurazumi, Yoshihito; Rezgals, Lauris; Melikov, Arsen Krikor

    2014-01-01

    The average convective heat transfer coefficient for a seated human body exposed to downward flow from above was determined. Thermal manikin with complex body shape and size of an average Scandinavian female was used. The surface temperature distribution of the manikin’s body was as the skin...... of the convective heat transfer coefficient of the whole body (hc [W/(m2•K)]) was proposed: hc=4.088+6.592V1.715 for a seated naked body at 20ºC and hc=2.874+7.427V1.345 for a seated naked body at 26ºC. Differences in the convective heat transfer coefficient of the whole body in low air velocity range, V

  3. Experimental characterization of self-sensing SMA actuators under controlled convective cooling

    International Nuclear Information System (INIS)

    Lewis, N; York, A; Seelecke, S

    2013-01-01

    Shape memory alloy (SMA) wires are attractive for actuation systems due to their high energy density, light weight and silent operation. In addition, they feature self-sensing capabilities by relating electrical resistance measurements to strain changes. In real world applications SMAs typically operate in non-ambient air and it is imperative to understand an actuator’s behavior under varying convective cooling conditions, especially for smaller diameter wires, where convective effects are amplified. This paper shows that the multi-functionality of SMA actuators can be further extended by related heating power to convective air speed. It investigates the relationship between the normalized excess power needed and corresponding airspeed under controlled, laminar airflow patterns in a small-scale wind tunnel. For each experiment, airflow through the wind tunnel, strain in the SMA wire, and power supplied to the SMA wire were controlled, while the stress and resistance of the wire were measured. The ability to understand and predict an SMA wire’s behavior under various external airflows will aid in the design and understanding of future SMA actuated structures, such as micro-air vehicles, and shows that SMAs can function as self-sensing actuators and airspeed sensors. (paper)

  4. Natural convection in closed vertical cylinders with particular reference to gas cooled reactor standpipes

    International Nuclear Information System (INIS)

    Spence, I.D.

    1975-09-01

    The access to the core for fuel assemblies and control rods of the Advanced Gas Cooled Reactor is through the top cap by means of standpipes. The standpipe is essentially a cylindrical, vertical tube with cooled side wall, closed upper end and an orifice at the lower end which is exposed to the hot core fluid. This creates confined natural convection flow in the empty standpipe and this is the subject of this thesis. The investigation is carried out using analytical and experimental methods. For the analytical work, solution of laminar and turbulent flow is attempted using finite-difference computer techniques. The laminar flow performance is evaluated using two different finite-difference procedures, and the results are compared to each other and to existing analytical and experimental results for the open thermosyphon with cool inflow and hot sidewall, i.e. the complementary problem to the present one. For turbulent flow a two equation turbulence model is employed which provides transport equations for the kinetic energy of turbulence and its dissipation rate. The experimental rig is a full scale replica of the Advanced Gas Cooled Reactor control rod mechanism standpipe. Carbon dioxide and helium are used as the working fluids for the series of tests. (author)

  5. Use of local convective and radiant cooling at warm environment: effect on thermal comfort and perceived air quality

    DEFF Research Database (Denmark)

    Melikov, Arsen Krikor; Duszyk, Marcin; Krejcirikova, Barbora

    2012-01-01

    The effect of four local cooling devices (convective, radiant and combined) on thermal comfort and perceived air quality reported by 24 subjects at 28 ˚C and 50% RH was studied. The devices studied were: (1) desk cooling fan, (2) personalized ventilation providing clean air, (3) two radiant panels...... and (4) two radiant panels with one panel equipped with small fans. A reference condition without cooling was tested as well. The response of the subjects to the exposed conditions was collected by computerized questionnaires. The cooling devices significantly (pthermal comfort...... compared to without cooling. The acceptability of the thermal environment was similar for all cooling devices. The acceptability of air movement and PAQ increased when the local cooling methods were used. The best results were achieved with personalized ventilation and cooling fan. The improvement in PAQ...

  6. Thermal and hydrodynamic characteristics of forced and mixed convection flow through vertical rectangular channels

    Directory of Open Access Journals (Sweden)

    Hanafi Abdalla S.

    2008-01-01

    Full Text Available This paper presents experimental and numerical studies for the case of turbulent forced and mixed convection flow of water through narrow vertical rectangular channel. The channel is composed of two parallel plates which are heated at a uniform heat flux, whereas, the other two sides of the channel are thermally insulated. The plates are of 64 mm in width, 800 mm in height, and separated from each other at a narrow gap of 2.7 mm. The Nusselt number distribution along the flow direction normalized by the Nusselt number for the case of turbulent forced convection flow is obtained experimentally with a comparison with the numerical results obtained from a commercial computer code. The quantitative determination of the nor- malized Nusselt number with respect to the dimension-less number Z = (Gr/Re21/8Pr0.5 is presented with a comparison with previous experimental results. Qualitative results are presented for the normalized temperature and velocity profiles in the transverse direction with a comparison between the forced and mixed convection flow for both the cases of upward and downward flow directions. The effect of the axial locations and the parameter Gr/Re on the variation of the normalized temperature profiles in the transverse direction for both the regions of forced and mixed convection and for both of the upward and downward flow directions are obtained. The normalized velocity profiles in the transverse directions are also determined at different inlet velocity and heat fluxes for the previous cases. It is found that the normalized Nusselt number is greater than one in the mixed convection region for both the cases of upward and downward flow and correlated well with the dimension-less parameter Z for both of the forced and mixed convection regions. The temperature profiles increase with increasing the axial location along the flow direction or the parameter Gr/Re for both of the forced and mixed convection regions, but this increase is

  7. Modeling a forced to natural convection boiling test with the program LOOP-W

    International Nuclear Information System (INIS)

    Carbajo, J.J.

    1984-01-01

    Extensive testing has been conducted in the Simulant Boiling Flow Visualization (SBFV) loop in which water is boiled in a vertical transparent tube by circulating hot glycerine in an annulus surrounding the tube. Tests ranged from nonboiling forced convection to oscillatory boiling natural convection. The program LOOP-W has been developed to analyze these tests. This program is a multi-leg, one-dimensional, two-phase equilibrium model with slip between the phases. In this study, a specific test, performed at low power where non-boiling forced convection was changed to boiling natural convection and then to non-boiling again, has been modeled with the program LOOP-W

  8. Modeling and analysis of a robust thermal control system based on forced convection thermal switches

    Science.gov (United States)

    Williams, Andrew D.; Palo, Scott E.

    2006-05-01

    There is a critical need, not just in the Department of Defense (DOD) but the entire space industry, to reduce the development time and overall cost of satellite missions. To that end, the DOD is actively pursuing the capability to reduce the deployment time of a new system from years to weeks or even days. The goal is to provide the advantages space affords not just to the strategic planner but also to the battlefield commanders. One of the most challenging aspects of this problem is the satellite's thermal control system (TCS). Traditionally the TCS must be vigorously designed, analyzed, tested, and optimized from the ground up for every satellite mission. This "reinvention of the wheel" is costly and time intensive. The next generation satellite TCS must be modular and scalable in order to cover a wide range of applications, orbits, and mission requirements. To meet these requirements a robust thermal control system utilizing forced convection thermal switches was investigated. The problem was investigated in two separate stages. The first focused on the overall design of the bus. The second stage focused on the overarching bus architecture and the design impacts of employing a thermal switch based TCS design. For the hot case, the fan provided additional cooling to increase the heat transfer rate of the subsystem. During the cold case, the result was a significant reduction in survival heater power.

  9. Assessment of RANS and LES Turbulence Modeling for Buoyancy-Aided/Opposed Forced and Mixed Convection

    Science.gov (United States)

    Clifford, Corey; Kimber, Mark

    2017-11-01

    Over the last 30 years, an industry-wide shift within the nuclear community has led to increased utilization of computational fluid dynamics (CFD) to supplement nuclear reactor safety analyses. One such area that is of particular interest to the nuclear community, specifically to those performing loss-of-flow accident (LOFA) analyses for next-generation very-high temperature reactors (VHTR), is the capacity of current computational models to predict heat transfer across a wide range of buoyancy conditions. In the present investigation, a critical evaluation of Reynolds-averaged Navier-Stokes (RANS) and large-eddy simulation (LES) turbulence modeling techniques is conducted based on CFD validation data collected from the Rotatable Buoyancy Tunnel (RoBuT) at Utah State University. Four different experimental flow conditions are investigated: (1) buoyancy-aided forced convection; (2) buoyancy-opposed forced convection; (3) buoyancy-aided mixed convection; (4) buoyancy-opposed mixed convection. Overall, good agreement is found for both forced convection-dominated scenarios, but an overly-diffusive prediction of the normal Reynolds stress is observed for the RANS-based turbulence models. Low-Reynolds number RANS models perform adequately for mixed convection, while higher-order RANS approaches underestimate the influence of buoyancy on the production of turbulence.

  10. Application of a bistable convection loop to LMFBR [liquid metal fast breeder reactor] emergency core cooling

    International Nuclear Information System (INIS)

    Anand, G.; Christensen, R.N.

    1990-01-01

    The concept of passive safety features for nuclear reactors has been developed in recent years and has gained wide acceptance. A literature survey of current reactors with passive features indicates that these reactors have some passive features but still do not fully meet the design objectives. Consider a current liquid-metal reactor design like PRISM. During normal operation, liquid sodium enters the reactor at ∼395 degree C and exits at ∼550 degree C. In the event of loss of secondary cooling with or without scram, the primary coolant (liquid sodium) initially acts as a heat sink and its temperature increases. For events without scram, the negative reactivity induced by the increase in temperature shuts the reactor down. When the average temperature of the sodium reaches ∼600 to 650 degree C, it overflows from the reactor vessel, activating the auxiliary cooling system. The auxiliary cooling system uses natural circulation of air around the reactor guard vessel. An alternative to the current design incorporates a bistable convection loop (BCL). The incorporation of the BCL concept remarkably improves the safety of the nuclear reactors. Application of the BCL concept to liquid-metal fast breeder reactors is described in this paper

  11. Predictions of the effect of stratification on superimposed forced and free convection between vertical parallel plates for various boundary conditions

    International Nuclear Information System (INIS)

    Cowan, G.H.; Irvine, T.J. Jr.; Quarini, G.L.

    1983-01-01

    The velocity and temperature equations for laminar buoyancy and forced convection flows between vertical flat parallel plates are presented. The thermal boundary conditions on the plate define the buoyancy driven field, while the channel Reynolds number defines the forced flow field. Specific examples relating to tall narrow channels with laminar convention and to closed high ratio cavities (as may be found in the proposed active and passive insulation systems for sodium cooled fast reactors) are presented. The analysis is limited to the laminar flow regimes, whilst some reactor situations are likely to be turbulent, hence a proposal for a simple extension of this analysis to the turbulent regime is made. It is shown how the analysis can be made to apply to fluids of various Prandtl numbers. (author)

  12. Combined Lorentz force and ultrasound Doppler velocimetry in a vertical convection liquid metal flow

    Science.gov (United States)

    Zürner, Till; Vogt, Tobias; Resagk, Christian; Eckert, Sven; Schumacher, Jörg

    2017-11-01

    We report experimental studies on turbulent vertical convection flow in the liquid metal alloy gallium-indium-tin. Flow measurements were conducted by a combined use of local Lorentz force velocimetry (LLFV) and ultrasound Doppler velocimetry (UDV). It is known that the forced convection flow in a duct generates a force on the LLFV magnet system, that grows proportional to the flow velocity. We show that for the slower flow of natural convection LLFV retains this linear dependence in the range of micronewtons. Furthermore experimental results on the scaling of heat and momentum transport with the thermal driving are presented. The results cover a range of Rayleigh numbers 3 ×105 Deutsche Forschungsgemeinschaft under Grant No. GRK 1567.

  13. Step-by-step approach to convective cooling of laser disc amplifiers

    International Nuclear Information System (INIS)

    Bourque, R.F.

    1979-04-01

    A step by step approach is presented to the problem of gas cooling of laser glass amplifiers. The basic equations are given for glass conduction, thermal stress, gas convection, and heat exchanger and blower design. An example calculation is then carried out for helium gas at one atmosphere with the gas flow in the direction orthogonal to the optical path. It is found that pumping powers and temperatures are acceptable for this case. Results are also presented for helium in the slant direction and for nitrogen in both directions. Included also are the effects on pumping power of gas temperature rise, gas pressure, flashtube rep rate, and flow channel width. It is found that, based on temperature rise and pumping power, nitrogen is as viable a coolant as helium

  14. Experimental investigation of the influence of the air jet trajectory on convective heat transfer in buildings equipped with air-based and radiant cooling systems

    DEFF Research Database (Denmark)

    Le Dreau, Jerome; Heiselberg, Per; Jensen, Rasmus Lund

    2015-01-01

    -state and dynamic conditions. With the air-based cooling system, a dependency of the convective heat transfer on the air jet trajectory has been observed. New correlations have been developed, introducing a modified Archimedes number to account for the air flow pattern. The accuracy of the new correlations has been...... evaluated to±15%. Besides the study with an air-based cooling system, the convective heat transfer with a radiant cooling system has also been investigated. The convective flow at the activated surface is mainly driven by natural convection. For other surfaces, the complexity of the flow and the large......The complexity and diversity of airflow in buildings make the accurate definition of convective heat transfer coefficients (CHTCs) difficult. In a full-scale test facility, the convective heat transfer of two cooling systems (active chilled beam and radiant wall) has been investigated under steady...

  15. Numerical analysis of experiments modeling LWR sump cooling by natural convection

    International Nuclear Information System (INIS)

    2002-01-01

    An optional sump cooling concept for the European pressurized water reactor EPR was investigated at the Research Center Karlsruhe. This concept foresees to utilize single phase natural convection in water to remove the decay heat from the core melt. The natural convection was investigated by the SUCOS-2D and -3D scaled experiments. A numerical investigation and interpretation of these experiments was performed by means of the computer code FLUTAN. In this paper, the numerical investigation of SUCOS-3D is summarized. Following the results of the former 2d experiments and the numerical analysis of both experiments, an unexpected temperature distribution is found in this 3d experiment. Basing on the experimental data it had to be postulated that one of the horizontal coolers was slightly tilled against the main flow direction. Additional numerical investigations show that a slope of only one percent would explain the experimental flow field. Conclusions are also drawn on the limits of scalability and transferability of the experimental results to a reactor sump. A detailed transformation will only be possible by applying well validated CFD-codes and experienced code users. As the flow in the reactor sump will be turbulent and this flow is strongly three-dimensional and time-dependent, only the method of Large Eddy Simulation is considered of being an adequate tool for reliable trans formation of the gained experience to analyses for the reactor sump at 1:1 scales. (author)

  16. Device for recirculation cooling of cooling water by natural or forced chaft

    Energy Technology Data Exchange (ETDEWEB)

    Ruehl, H; Honekamp, H; Katzmann, A

    1975-10-23

    The invention is concerned with a device for recirculation cooling of cooling water by natural or forced draft. Through a cascading system mounted on supporting columns at a vertical distance to ground level, cooling air is flowing in cross- or counterflow to the cooling water freely falling from the cascading system. The cooling water collecting zone below the cascading system has an absorption floor arranged nearly horizontal and/or inclined, with a cam-type profile on its upperside, which is bounded on its circumference by at least one cooling water release channel provided below its level and/or which is divided in the sense of a surface subdivision. By these means, a reduction of the amount of material required for the supporting columns and an increase of the stability of the columns is to be achieved. Furthermore, the deposition of mud is to be avoided as for as possible, and noise generation during operation is to be reduced considerably. For this purpose, the absorption floor may be made of material sound insulating and/or may be coated with such a material.

  17. [Constitutive correlations for wire-wrapped subchannel analysis under forced and mixed convection conditions]. Part II

    International Nuclear Information System (INIS)

    Cheng, S.K.; Todreas, N.E.

    1984-08-01

    A new version of the ENERGY series code, ENERGY-IV, was written for predicting coolant temperature distributions in wire-wrapped rod assemblies used in the Liquid Metal Fast Breeder Reactor. The ENERGY-IV Code is applicable to both steady-state forced and mixed convection operation for a single isolated assembly. (The SUPERENERGY Code, [Basehore (1980)] is applicable to core wide forced convection analysis.) ENERGY-IV is an empirical code designed to be fast running. Hence the core designer can use it as an inexpensive thermal hydraulic design or diagnosis tool

  18. Effect of Airflow Velocity on Pre-cooling Process of Pomegranate by Forced Cooling Air under Unsteady State Heat Transfer Condition

    Directory of Open Access Journals (Sweden)

    M. A Behaeen

    2018-03-01

    Full Text Available Introduction Pomegranate (Punica grantum L. is classified into the family of Punicaceae. One of the most influential factors in postharvest life and quality of horticultural products is temperature. In precooling, heat is reduced in fruit and vegetable after harvesting to prepare it quickly for transport and storage. Fikiin (1983, Dennis (1984 and Hass (1976 reported that cold air velocity is one of the effective factors in cooling vegetables and fruits. Determining the time-temperature profiles is an important step in cooling process of agricultural products. The objective of this study was the analysis of cooling rate in the center (arils and outer layer (peel of pomegranate and comparison of the two sections at different cold air velocities. These results are useful for designing and optimizing the precooling systems. Materials and Methods The pomegranate variety was Rabab (thick peel and the experiments were performed on arils (center and peel (outer layer of a pomegranate. The velocities of 0.5, 1 and 1.3 m s-1 were selected for testing. To perform the research, the cooling instrument was designed and built at Department of Biosystems Engineering of Tabriz University, Tabriz, Iran. In each experiment six pt100 temperature sensors was used in a single pomegranate. The cooling of pomegranate was continued until the central temperature reached to 10°C and then the instrument turned off. The average of air and product temperatures was 7.2 and 22.2°C, respectively. The following parameters were measured to analyze the process of precooling: a Dimensionless temperature (θ, b Cooling coefficient (C, c Lag factor (J, d Half-cooling time (H, e Seven-eighths cooling time (S, f Cooling heterogeneity, g Fruit mass loss, h Instantaneous cooling rate, and i convective heat transfer coefficient. Results and Discussion At any air velocity, with increasing the radius from center to outer layer, the lag factor decreased and cooling coefficient increased

  19. Variability of radiatively forced diurnal cycle of intense convection in the tropical west pacific

    Energy Technology Data Exchange (ETDEWEB)

    Gray, W.M.; Sheaffer, J.D.; Thorson, W.B. [Colorado State Univ., Fort Collins, CO (United States)

    1996-04-01

    Strong differences occur in daytime versus nighttime (DVN) net radiative cooling in clear versus cloudy areas of the tropical atmosphere. Daytime average cooling is approximately -0.7{degrees}C/day, whereas nighttime net tropospheric cooling rates are about -1.5{degrees}C/day, an approximately two-to-one difference. The comparatively strong nocturnal cooling in clear areas gives rise to a diurnally varying vertical circulation and horizontal convergence cycle. Various manifestations of this cyclic process include the observed early morning heavy rainfall maxima over the tropical oceans. The radiatively driven DVN circulation appears to strongly modulate the resulting diurnal cycle of intense convection which creates the highest, coldest cloudiness over maritime tropical areas and is likely a fundamental mechanism governing both small and large scale dynamics over much of the tropical environment.

  20. Modelling of subcooled boiling and DNB-type boiling crisis in forced convection

    International Nuclear Information System (INIS)

    Bricard, Patrick

    1995-01-01

    This research thesis aims at being a contribution to the modelling of two phenomena occurring during a forced convection: the axial evolution of the vacuum rate, and the boiling crisis. Thus, the first part of this thesis addresses the prediction of the vacuum rate, and reports the development of a modelling of under-saturated convection in forced convection. The author reports the development and assessment of two-fluid one-dimensional model, the development of a finer analysis based on an averaging of local equations of right cross-sections in different areas. The second part of this thesis addresses the prediction of initiation of a boiling crisis. The author presents generalities and motivations for this study, reports a bibliographical study and a detailed analysis of mechanistic models present in this literature. A mechanism of boiling crisis is retained, and then further developed in a numerical modelling which is used to assess some underlying hypotheses [fr

  1. Rotating turbulent Rayleigh-Bénard convection subject to harmonically forced flow reversals

    NARCIS (Netherlands)

    Geurts, B.J.; Kunnen, R.P.J.

    2014-01-01

    The characteristics of turbulent flow in a cylindrical Rayleigh–B´enard convection cell which can be modified considerably in case rotation is included in the dynamics. By incorporating the additional effects of an Euler force, i.e., effects induced by nonconstant rotation rates, a remarkably strong

  2. Rotating turbulent Rayleigh–Bénard convection subject to harmonically forced flow reversals

    NARCIS (Netherlands)

    Geurts, Bernardus J.; Kunnen, Rudie P.J.

    2014-01-01

    The characteristics of turbulent flow in a cylindrical Rayleigh–Bénard convection cell which can be modified considerably in case rotation is included in the dynamics. By incorporating the additional effects of an Euler force, i.e., effects induced by non-constant rotation rates, a remarkably strong

  3. Combined free and forced convection flow in a rotating channel with ...

    African Journals Online (AJOL)

    user

    free and forced convection flow of a viscous incompressible electrically conducting fluid in a .... The boundary conditions (10) and (11), in dimensionless form, become ...... On hydromagnetic Flow and heat transfer in a rotating fluid past an infinite porous ... Electrically Conducting Fluid in Non-Rotating and Rotating Media”.

  4. Onset of nuclear boiling in forced convection (Method of detection)

    International Nuclear Information System (INIS)

    Rachedi, M.

    1986-01-01

    Local onset of boiling in any pressure water cooling systems, as a PWR for instance, can mean a possible dangerous mismatch between the produced heat and the cooling capabilities. Its consequences can lead to serious accidental conditions and a reliable technique to detect such a phenomenon is therefore of particular need. Most techniques used up to now rely basically on local measurements and assume therefore usually the previous knowledge of the actual hot or boiling spot. The method proposed here based on externally located accelerometers appears to be sensitive to the global behaviour of the mechanical structure and is therefore not particularly bound to any exact localization of the sensors. The vibrations produced in the mechanical structure of the heated assembly are measured by accelerometers placed on the external surfaces that are easily accessible. The onset of the boiling, the growth and condensation of the bubbles on the heated wall, induces a resonance in the structure and an excitation at its particular eigen frequencies. Distinctive peaks are clearly observed in the spectral density function calculated from the accelerometer signal as soon as bubbles are produced. The technique is shown to be very sensitive even at the earliest phase of boiling and quite independent on sensor position. A complete hydrodynamic analysis of the experimental channels have been performed in order to assess the validity of the method both in steady conditions and during rapid power transients

  5. Emergency Cooling of Nuclear Power Plant Reactors With Heat Removal By a Forced-Draft Cooling Tower

    Energy Technology Data Exchange (ETDEWEB)

    Murav’ev, V. P., E-mail: murval1@mail.ru

    2016-07-15

    The feasibility of heat removal during emergency cooling of a reactor by a forced-draft cooling tower with accumulation of the peak heat release in a volume of precooled water is evaluated. The advantages of a cooling tower over a spray cooling pond are demonstrated: it requires less space, consumes less material, employs shorter lines in the heat removal system, and provides considerably better protection of the environment from wetting by entrained moisture.

  6. Body-force-driven multiplicity and stability of combined free and forced convection in rotating curved ducts: Coriolis force

    Science.gov (United States)

    Yang, T.; Wang, L.

    A numerical study is made on the fully developed bifurcation structure and stability of forced convection in a rotating curved duct of square cross-section. Solution structure is determined as variation of a parameter that indicates the effect of rotation (Coriolis-force-driven multiplicity). Three solutions for the flows in a stationary curved duct obtained in the work of Yang and Wang [1] are used as initial solutions of continuation calculations to unfold the solution branches. Twenty-one solution branches are found comparing with five obtained by Selmi and Nandakumar [2]. Dynamic responses of the multiple solutions to finite random disturbances are examined by the direct transient computation. Results show that characteristics of physically realizable fully developed flows changes significantly with variation of effect of rotation. Fourteen sub-ranges are identified according to characteristics of physically realizable solutions. As rotation effect changes, possible physically realizable fully-developed flows can be stable steady 2-cell state, stable multi-cell state, temporal periodic oscillation between symmetric/asymmetric 2-cell/4-cell flows, temporal oscillation with intermittency, temporal chaotic oscillation and temporal oscillation with pseudo intermittency. Among these possible physically realizable fully developed flows, stable multi-cell state and stable steady 2-cell state exist as dual stable. And oscillation with pseudo intermittency is a new phenomenon. In addition to the temporal oscillation with intermittency, sudden shift from stationary stable solution to temporal chaotic oscillation is identified to be another way of onset of chaos.

  7. Sensitivity of tropical convection in cloud-resolving WRF simulations to model physics and forcing procedures

    Science.gov (United States)

    Endo, S.; Lin, W.; Jackson, R. C.; Collis, S. M.; Vogelmann, A. M.; Wang, D.; Oue, M.; Kollias, P.

    2017-12-01

    Tropical convection is one of the main drivers of the climate system and recognized as a major source of uncertainty in climate models. High-resolution modeling is performed with a focus on the deep convection cases during the active monsoon period of the TWP-ICE field campaign to explore ways to improve the fidelity of convection permitting tropical simulations. Cloud resolving model (CRM) simulations are performed with WRF modified to apply flexible configurations for LES/CRM simulations. We have enhanced the capability of the forcing module to test different implementations of large-scale vertical advective forcing, including a function for optional use of large-scale thermodynamic profiles and a function for the condensate advection. The baseline 3D CRM configurations are, following Fridlind et al. (2012), driven by observationally-constrained ARM forcing and tested with diagnosed surface fluxes and fixed sea-surface temperature and prescribed aerosol size distributions. After the spin-up period, the simulations follow the observed precipitation peaks associated with the passages of precipitation systems. Preliminary analysis shows that the simulation is generally not sensitive to the treatment of the large-scale vertical advection of heat and moisture, while more noticeable changes in the peak precipitation rate are produced when thermodynamic profiles above the boundary layer were nudged to the reference profiles from the forcing dataset. The presentation will explore comparisons with observationally-based metrics associated with convective characteristics and examine the model performance with a focus on model physics, doubly-periodic vs. nested configurations, and different forcing procedures/sources. A radar simulator will be used to understand possible uncertainties in radar-based retrievals of convection properties. Fridlind, A. M., et al. (2012), A comparison of TWP-ICE observational data with cloud-resolving model results, J. Geophys. Res., 117, D05204

  8. Experimental determination of heat transfer critical conditions in water forced convection at low pressure in a circular channel

    International Nuclear Information System (INIS)

    Fernandes, M.P.

    1973-02-01

    An experimental determination was made of heat transfer critical conditions in a circular channel, uniformly heated, and internally cooled by water in ascending forced convection, under a pressure slightly above atmospheric pressure. Measurements were made of water flow, pressure, electric power temperature and heating, and a systematic analysis was made of the system's parameters. The values obtained for the heat critical flux are circa 50% lower than those predicted by Becker and Biasi and this is accounted to flowing instabilities of thermo-hydrodynamic nature. It is suggested that the flowing channels of circuits aiming at the study of the boiling crisis phenomenon be expanded in its upper extremity, and that the coolant circulation be kept through a pump with a pressure X flow characteristic as vertical as possible

  9. Experimental study of convective heat transfer during cooling with low air velocity in a stack of objects

    Energy Technology Data Exchange (ETDEWEB)

    Ben Amara, Sami; Laguerre, Onrawee [Cemagref - Refrigeration Processes Engineering Research Unit, parc de Tourvoie, BP 44, 92163 cedex, Antony (France); Flick, Denis [National Agronomic Institute - INAPG, 16 rue Claude Bernard, 75231 cedex 05, Paris (France)

    2004-12-01

    During cooling with low air velocity (u{<=}0.2 m.s{sup -1}) of a stack of foodstuffs (a few centimeters dimension), the radiation and conduction between products can be of the same order of magnitude as convection. A method was developed to quantify these various transfer modes. The experiment was carried out using an in-line spherical arrangement; however, the same methodology can be applied to other product shapes. The results confirm that the heat transfers by radiation and conduction cannot be neglected. In addition, the convective heat transfer coefficient varies not only with air velocity but also with the product position in the stack. (authors)

  10. Improved lumped models for transient combined convective and radiative cooling of a two-layer spherical fuel element

    International Nuclear Information System (INIS)

    Silva, Alice Cunha da; Su, Jian

    2013-01-01

    The High Temperature Gas cooled Reactor (HTGR) is a fourth generation thermal nuclear reactor, graphite-moderated and helium cooled. The HTGRs have important characteristics making essential the study of these reactors, as well as its fuel element. Examples of these are: high thermal efficiency,low operating costs and construction, passive safety attributes that allow implication of the respective plants. The Pebble Bed Modular Reactor (PBMR) is a HTGR with spherical fuel elements that named the reactor. This fuel element is composed by a particulate region with spherical inclusions, the fuel UO2 particles, dispersed in a graphite matrix and a convective heat transfer by Helium happens on the outer surface of the fuel element. In this work, the transient heat conduction in a spherical fuel element of a pebble-bed high temperature reactor was studied in a transient situation of combined convective and radiative cooling. Improved lumped parameter model was developed for the transient heat conduction in the two-layer composite sphere subjected to combined convective and radiative cooling. The improved lumped model was obtained through two-point Hermite approximations for integrals. Transient combined convective and radiative cooling of the two-layer spherical fuel element was analyzed to illustrate the applicability of the proposed lumped model, with respect to die rent values of the Biot number, the radiation-conduction parameter, the dimensionless thermal contact resistance, the dimensionless inner diameter and coating thickness, and the dimensionless thermal conductivity. It was shown by comparison with numerical solution of the original distributed parameter model that the improved lumped model, with H2,1/H1,1/H0,0 approximation yielded significant improvement of average temperature prediction over the classical lumped model. (author)

  11. Free convection flow and heat transfer in pipe exposed to cooling

    Energy Technology Data Exchange (ETDEWEB)

    Mme, Uduak Akpan

    2010-10-15

    One of the challenges with thermal insulation design in subsea equipment is to minimize the heat loss through cold spots during production shut down. Cold spots are system components where insulation is difficult to implement, resulting in an insulation discontinuity which creates by nature a thermal bridge. It is difficult to avoid cold spots or thermal bridges in items like sensors, valves, connectors and supporting structures. These areas of reduced or no insulation are referred to as cold spots. Heat is drained faster through these spots, resulting in an increased local fluid density resulting in an internal fluid flow due to gravity and accelerated cool- down. This natural convection flow is important for both heat loss and internal distribution of the temperature. This thesis is presenting both experimental work and modelling work. A series of cool down tests and Computational Fluid Dynamics (CFD) simulations of these tests are presented. These tests and simulations were carried out in order to understand the flow physics involved in heat exchange processes caused by free convection flow in pipe exposed to cooling. Inclination of the pipe relative to the direction of gravity and temperature difference between cooling water and internal pipe water are the two main parameters investigated in this study. The experimental heat removal and temperature field is discussed and further interpreted by means of computational fluid dynamics. For prediction of the evolvement of the local temperature and heat flow, selection of an appropriate turbulence model is critical. Hence, different models and wall functions are investigated. The predicted temperature profiles and heat extraction rates are compered to the experiments for the selected turbulence models. Our main conclusions, supported by our experimental and CFD results, include: (i) Heat transfer from a localized cold spot in an inclined pipe is most efficient when the pipe orientation is close to horizontal. As the

  12. Thermal-hydraulic analysis of the OSURR pool for power upgrade with natural convection core cooling

    International Nuclear Information System (INIS)

    Ha, J.J.; Aldemir, T.

    1988-01-01

    Natural convection mode core cooling will be maintained in the LEU conversion/power upgrade of The Ohio State University Research Reactor (OSURR) to 250-500 kW. The pool water will be cooled by a water-glycol-air and a water-water heat exchanger. A plume disperser will be installed in the pool to minimize evaporation from the pool top and to maintain the dose rate due to N-16 activity within allowable levels. The minimization of the pool heat removal system operation costs necessitates maximizing the inlet temperature to the water-glycol-air heat exchanger. For the maximization process, the change in the pool temperature and velocity fields have to be investigated as a function of: location and orientation of the heat removal system components and the plume disperser in the pool; mass flow rate through the plume disperser. The velocity and temperature fields in the pool are determined using COMMIX-1A. The computational system model accounts for the presence of all the pool components (i.e. core, thermal column, beam ports, ion chamber, guide tubes, rabbit, neutron source etc.). The results show that: (1) Both the heat removal system inlet point and the plume disperser have to be located close to the top of the core. (2) Using a disperser system consisting of several pipes may be more feasible than a single unit. (3) For high disperser flow, the disperser jet has to be almost parallel to the top of the core to prevent flow reversal in coolant channels. (4) More than one disperser system may be necessary to create an inversion layer in the pool

  13. Core debris cooling with flooded vessel or core-catcher. Heat exchange coefficients under natural convection

    International Nuclear Information System (INIS)

    Rouge, S.; Seiler, J.M.

    1994-09-01

    External cooling by natural water circulation is necessary for molten core retention in LWR lower head or in a core-catcher. Considering the expected heat flux levels (between 0.2 to 1.5 MW/m 2 ) film boiling should be avoided. This rises the question of the knowledge of the level of the critical heat flux for the considered geometries and flow paths. The document proposes a state of the art of the research in this field. Mainly small scale experiments have been performed in a very recent past. These experiments are not sufficient to extrapolate to large scale reactor structures. Limited large scale experimental results exist. These results together with some theoretical investigations show that external cooling by natural water circulation may be considered as a reasonable objective of severe accident R and D. Recently (in fact since the beginning of 1994) new results are available from large scale experiments (CYBL, ULPU 2000, SULTAN). These results indicate that CHF larger than 1 MW/m 2 can be obtained under natural water circulation conditions. In this report, emphasis is given to the pursuit of finding predictive models for the critical heat flux in large, naturally convective channels with thick walls. This theoretical understanding is important for the capability to extrapolate to different situations (various geometries, flow paths....). The outcome of this research should be the ability to calculate Boundary Layer Boiling situations (2D), channelling boiling situations (1D) and related CHF conditions. However, a more straightforward approach can be used for the analysis of specific designs. Today there are already some CHF data available for hemispherical geometry and these data can be used before a mechanistic understanding is achieved

  14. Simulation of transient heat transfer during cooling and heating of whole sweet potato (Ipomoea batatas (L.) Lam.) roots under forced-air conditions

    International Nuclear Information System (INIS)

    Korese, Joseph Kudadam; Sturm, Barbara; Román, Franz; Hensel, Oliver

    2017-01-01

    Highlights: • Heat transfer of whole sweet potato roots under forced-air cooling and heating is investigated. • Experiments were carried out in a cooling and heating chamber. • The cooling and heating rate and time was clearly depended on air velocity and roots size. • Simulated and experimental data on cooling and heating times were compared for validation. • Simulation results quantitatively agreed with experimental results. - Abstract: In this work, we investigated how different air velocity and temperature affect the cooling and heating rate and time of individual sweet potato roots. Additionally, we modified and applied a simulation model which is based on the fundamental solution of the transient equations for estimating the cooling and heating time at the centre of sweet potato roots. The model was adapted to receive input parameters such as thermo-physical properties of whole sweet potato roots as well as the surrounding air properties, and was verified with experimental transient temperature data. The experimental results showed that the temperature at the centre and the under skin of sweet potato roots is almost homogeneous during forced convection cooling and heating. The cooling and heating time was significantly (P < 0.05) affected by high air velocity and sweet potato root size. The simulation results quantitatively agreed with the experimental transient data. This research, thus provides a reliable experimental and theoretical basis for understanding the temperature variations as well as estimating the cooling and heating times in individual sweet potato roots under forced convection cooling and heating. The result from this study could be applied to design and optimize forced-air treatment equipments with improved energy efficiency as well as ensuring safety and the maintenance of sweet potato roots quality.

  15. Characteristic of The RSG-Gas Oxide Fuel Element Temperature Under Forced Convection And Natural Convection Mode

    International Nuclear Information System (INIS)

    Sudarmono

    2000-01-01

    One of the methods used for fuel element plate temperature measurement in RSG-Gas is a direct measurement. Evaluation on the measurement results were done by using HEATHYDE and NATCON code, which was then compared to the safety margin criteria. Results of thermalhydraulic measurement on transitional core both under forced and natural convection were compared with the results of calculations using the two codes. Measurement result for maximum fuel element plate temperature at typical working core of 30 MW, was 121 o C. The deviation between calculation and measurement result was under 9.75 %. Under normal operation, safety margin on DNB and OFI are 3.56 and 2.60, respectively. Natcon calculation result showed that the typical working core under the natural circulation mode, an onset of nucleate boiling (ONB)occurred at a core power level of 826 kW (2.8% of the nominal power)

  16. Thermohydraulic characteristics analysis of natural convective cooling mode on the steady state condition of upgraded JRR-3 core, using COOLOD-N code

    International Nuclear Information System (INIS)

    Kaminaga, Masanori; Watanabe, Shukichi; Ando, Hiroei; Sudo, Yukio; Ikawa, Hiromasa.

    1987-03-01

    This report describes the results of the steady state thermohydraulic analysis of upgraded JRR-3 core under natural convective cooling mode, using COOLOD-N code. In the code, function to calculate flow-rate under natural convective cooling mode, and a heat transfer package have been newly added to the COOLOD code which has been developed in JAERI. And this report describes outline of the COOLOD-N code. The results of analysis show that the thermohydraulics of upgraded JRR-3 core, under natural convective cooling mode have enough margine to ONB temperature, DNB heat flux and occurance of blisters in fuel meats, which are design criterion of upgraded JRR-3. (author)

  17. The deformation of Zircaloy PWR cladding with low internal pressures, under mainly convective cooling by steam

    International Nuclear Information System (INIS)

    Hindle, E.D.; Mann, C.A.; Reynolds, A.E.

    1981-08-01

    Simulated PWR fuel rods clad with Zircaloy-4 were tested under convective steam cooling conditions, by pressurising to 0.69-2.07MPa (100-300lb/in 2 ), then ramping at 10 0 C/s to various temperatures in the region 800-955 0 C and holding until either 600 s elapsed or rupture occurred. The length of cladding strained 33% or more was greatest (about 20 times the original diameter) when the initial internal pressure was 1.38+-0.17 PMa (200+-25lb/in 2 ), and the temperature 885 0 C. It is thought that this results from oxidation strengthening of the surface layers acting as an additional mechanism for stabilising the deformation and/or partial superplastic deformation. To avoid adjacent rods in a fuel assembly touching at any temperature, the pressure would have to be less than about 1MPa (145 1b/in 2 ). If the pressure was 1.38MPa (200lb/in 2 ) then the rods would not swell sufficiently to touch if the temperature did not exceed about 840 0 C. (author)

  18. Numerical analysis of laminar forced convection in a spherical annulus

    International Nuclear Information System (INIS)

    Tuft, D.B.

    1980-01-01

    Calculations of steady laminar incompressible fluid-flow and heat transfer in a spherical annulus are presented. Steady pressures, temperatures, velocities, and heat transfer coefficients are calculated for an insulated outer sphere and a 0 0 C isothermal inner sphere with 50 0 C heated water flowing in the annulus. The inner sphere radius is 13.97 cm, the outer sphere radius is 16.83 cm and the radius ratio is 1.2. The transient axisymmetric equations of heat, mass, and momentum conservation are solved numerically in spherical coordinates. The transient solution is carried out in time until steady state is achieved. A variable mesh is used to improve resolution near the inner sphere where temperature and velocity gradients are steep. It is believed that this is the first fully two-dimensional analysis of forced flow in a spherical annulus. Local and bulk Nusselt numbers are presented for Reynolds numbers from 4.4 to 440. Computed bulk Nusselt numbers ranged from 2 to 50 and are compared to experimental results from the literature. Inlet flow jetting off the inner sphere and flow separation are predicted by the analysis. The location of wall jet separation was found to be a function of Reynolds number, indicating the location of separation depends upon the ratio of inertia to viscous forces. Wall jet separation has a pronounced effect on the distribution of local heat flux. The area between inlet and separation was found to be the most significant area for heat transfer. Radial distributions of azimuthal velocity and temperature are presented for various angles beginning at the inlet. Inner sphere pressure distribution is presented and the effect on flow separation is discussed

  19. Observations of Convectively Coupled Kelvin Waves forced by Extratropical Wave Activity

    Science.gov (United States)

    Kiladis, G. N.; Biello, J. A.; Straub, K. H.

    2012-12-01

    It is well established by observations that deep tropical convection can in certain situations be forced by extratropical Rossby wave activity. Such interactions are a well-known feature of regions of upper level westerly flow, and in particular where westerlies and equatorward wave guiding by the basic state occur at low enough latitudes to interact with tropical and subtropical moisture sources. In these regions convection is commonly initiated ahead of upper level troughs, characteristic of forcing by quasi-geostrophic dynamics. However, recent observational evidence indicates that extratropical wave activity is also associated with equatorial convection even in regions where there is a "critical line" to Rossby wave propagation at upper levels, that is, where the zonal phase speed of the wave is equal to the zonal flow speed. A common manifestation of this type of interaction involves the initiation of convectively coupled Kelvin waves, as well as mixed Rossby-gravity (MRG) waves. These waves are responsible for a large portion of the convective variability within the ITCZ over the Indian, Pacific, and Atlantic sectors, as well as within the Amazon Basin of South America. For example, Kelvin waves originating within the western Pacific ITCZ are often triggered by Rossby wave activity propagating into the Australasian region from the South Indian Ocean extratropics. At other times, Kelvin waves are seen to originate along the eastern slope of the Andes. In the latter case the initial forcing is sometimes linked to a low-level "pressure surge," initiated by wave activity propagating equatorward from the South Pacific storm track. In yet other cases, such as over Africa, the forcing appears to be related to wave activity in the extratropics which is not necessarily propagating into low latitudes, but appears to "project" onto the Kelvin structure, in line with past theoretical and modeling studies. Observational evidence for extratropical forcing of Kelvin and MRG

  20. Experiment of IEA-R1 reactor core cooling by air convection after pool water loss accident

    International Nuclear Information System (INIS)

    Torres, Walmir Maximo; Baptista Filho, Benedito Dias

    2000-01-01

    This paper presents a study of a Emergency Core Cooling to be applied to the IEA-R1 reactor. This system must have the characteristics of passive action, with water spraying over the core, and feeding by gravity from elevated reservoirs. In the evaluation, this system must demonstrate that when the reservoirs are emptied, the core cooling must assure to be fulfilled by air natural convection. This work presents the results of temperature distribution in a test section with plates electrically heated simulation the heat generation conditions on the most heated reactor element

  1. Average Natural Convective Heat Transfer of Air-cooled Condensing Heat Exchanger of Emergency Cooldown Tank - Effect of Tube Banks

    Energy Technology Data Exchange (ETDEWEB)

    Huh, Seon Jeong; Lee, Hee Joon [Kookmin University, Seoul (Korea, Republic of); Kim, Myoung Jun; Moon, Joo Hyung; Bae, Youngmin; Kim, Young-In [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2016-10-15

    Recently emergency cooldown tank(ECT) is a great concern of passive cooling system for the safety of nuclear reactor. After the operation of a conventional passive cooling system for an extended period, however, the water level falls as a result of the evaporation from the ECT, as steam is emitted from the open top of the tank. In this study, the effect of heat transfer area at the air cooled condensing heat exchanger was investigated by changing 5×5 tube banks into 4×4 and 3×3. Moreover, each of air-side natural convective heat transfer coefficient of tube banks was compared to existing correlations. This study presents the effect of heat transfer area at air-cooled condensing heat exchanger. As heat transfer area decreased, the temperature of outlet increased. In other words, the cooling performance got lower with the decrease of heat transfer area. In addition, the average natural convective heat transfer coefficient was 15.3 W/m{sup 2}/K from the 4×4 tube banks, and 4.92 W/m{sup 2}/K from the 3×3 tube banks, which had quite a large error more than 46% especially with the value of 4×4 tube banks compared to the value from correlation equation. Therefore, according to this result, it is needed to measure the local heat transfer coefficient of vertical cylinder more elaborately in further study.

  2. Average Natural Convective Heat Transfer of Air-cooled Condensing Heat Exchanger of Emergency Cooldown Tank - Effect of Tube Banks

    International Nuclear Information System (INIS)

    Huh, Seon Jeong; Lee, Hee Joon; Kim, Myoung Jun; Moon, Joo Hyung; Bae, Youngmin; Kim, Young-In

    2016-01-01

    Recently emergency cooldown tank(ECT) is a great concern of passive cooling system for the safety of nuclear reactor. After the operation of a conventional passive cooling system for an extended period, however, the water level falls as a result of the evaporation from the ECT, as steam is emitted from the open top of the tank. In this study, the effect of heat transfer area at the air cooled condensing heat exchanger was investigated by changing 5×5 tube banks into 4×4 and 3×3. Moreover, each of air-side natural convective heat transfer coefficient of tube banks was compared to existing correlations. This study presents the effect of heat transfer area at air-cooled condensing heat exchanger. As heat transfer area decreased, the temperature of outlet increased. In other words, the cooling performance got lower with the decrease of heat transfer area. In addition, the average natural convective heat transfer coefficient was 15.3 W/m"2/K from the 4×4 tube banks, and 4.92 W/m"2/K from the 3×3 tube banks, which had quite a large error more than 46% especially with the value of 4×4 tube banks compared to the value from correlation equation. Therefore, according to this result, it is needed to measure the local heat transfer coefficient of vertical cylinder more elaborately in further study

  3. Blade-to-coolant heat-transfer results and operating data from a natural-convection water-cooled single-stage turbine

    Science.gov (United States)

    Diaguila, Anthony J; Freche, John C

    1951-01-01

    Blade-to-coolant heat-transfer data and operating data were obtained with a natural-convection water-cooled turbine over range of turbine speeds and inlet-gas temperatures. The convective coefficients were correlated by the general relation for natural-convection heat transfer. The turbine data were displaced from a theoretical equation for natural convection heat transfer in the turbulent region and from natural-convection data obtained with vertical cylinders and plates; possible disruption of natural convection circulation within the blade coolant passages was thus indicated. Comparison of non dimensional temperature-ratio parameters for the blade leading edge, midchord, and trailing edge indicated that the blade cooling effectiveness is greatest at the midchord and least at the trailing edge.

  4. Use of a vibrating plate to enhance natural convection cooling of a discrete heat source in a vertical channel

    Energy Technology Data Exchange (ETDEWEB)

    Florio, L.A.; Harnoy, A. [Department of Mechanical Engineering, New Jersey Institute of Technology, University Heights, Newark, NJ 07102 (United States)

    2007-09-15

    A numerical investigation was conducted into an alternative method of natural convection enhancement by the transverse oscillations of a thin short plate, strategically positioned in close proximity to a rectangular heat source. The heat source is attached to a mounting board in a vertical channel. Two-dimensional laminar flow finite element studies were carried out with the oscillation parameters, the oscillating plate-heat source mean clearance spacing, and the oscillating plate position varied. Significant cooling was found for displacement amplitudes of at least one-third of the mean clearance together with frequencies (Re/{radical}(Gr)) of over 2{pi} with the displacement being more critical to the cooling level. For the parameters investigated, up to a 52% increase in the local heat transfer coefficient relative to standard natural convection was obtained. The results indicate that this method can serve as a feasible, simpler, more energy and space efficient alternative to common methods of cooling for low power dissipating devices operating at conditions just beyond the reach of pure natural convection. (author)

  5. Laminar forced convective heat transfer to near-critical water in a tube

    International Nuclear Information System (INIS)

    Lee, Sang Ho

    2003-01-01

    Numerical modeling is carried out to investigate forced convective heat transfer to near-critical water in developing laminar flow through a circular tube. Due to large variations of thermo-physical properties such as density, specific heat, viscosity, and thermal conductivity near thermodynamic critical point, heat transfer characteristics show quite different behavior compared with pure forced convection. With flow acceleration along the tube unusual behavior of heat transfer coefficient and friction factor occurs when the fluid enthalpy passes through pseudocritical point of pressure in the tube. There is also a transition behavior from liquid-like phase to gas-like phase in the developing region. Numerical results with constant heat flux boundary conditions are obtained for reduced pressures from 1.09 to 1.99. Graphical results for velocity, temperature, and heat transfer coefficient with Stanton number are presented and analyzed

  6. Forced convection heat transfer correlation for finned plates in a duct

    International Nuclear Information System (INIS)

    Chae, Myeong-Seon; Moon, Je-Young; Chung, Bum-Jin

    2014-01-01

    Forced convection heat transfer experiments were conducted for plate-fin in a duct using various fin spacing, fin height, duct width, Reynolds number for Prandtl numbers 2,014. Based upon analogy concept, mass transfer rate were measured instead of heat transfer rates. The heat transfer rates were enhanced with the increase of fin height and decrease of fin spacing as they increase the heat transfer area. Meanwhile, heat transfer rates were impaired with the increase of the duct width as the bypass flows increased to tip clearance region. Forced convection heat transfer correlations were developed for laminar and turbulent flow conditions and for narrow and wide ducts. The work draws attention to the tip clearance on the heat transfer of the finned plate in a duct. (author)

  7. Experimental and theoretical study on forced convection film boiling heat transfer

    International Nuclear Information System (INIS)

    Liu, Qiusheng

    2001-01-01

    Theoretical solutions of forced convection film boiling heat transfer from horizontal cylinders in saturated liquids were obtained based on a two-phase laminar boundary layer film boiling model. It was clarified that author's experimental data for the cylinders with the nondimensional diameters, D, of around 1.3 in water and in Freon-113 agreed with the values of theoretical numerical solutions based on the two-phase laminar boundary layer model with the smooth vapor-liquid interface except those for low flow velocities. A forced convection film boiling heat transfer correlation including the radiation contribution from the cylinders with various diameters in saturated and subcooled liquids was developed based on the two-phase laminar boundary layer film boiling model and the experimental data for water and Freon-113 at wide ranges of flow velocities, surface superheats, system pressures and cylinder diameters. (author)

  8. Analysis of forced convective transient boiling by homogeneous model of two-phase flow

    International Nuclear Information System (INIS)

    Kataoka, Isao

    1985-01-01

    Transient forced convective boiling is of practical importance in relation to the accident analysis of nuclear reactor etc. For large length-to-diameter ratio, the transient boiling characteristics are predicted by transient two-phase flow calculations. Based on homogeneous model of two-phase flow, the transient forced convective boiling for power and flow transients are analysed. Analytical expressions of various parameters of transient two-phase flow have been obtained for several simple cases of power and flow transients. Based on these results, heat flux, velocity and time at transient CHF condition are predicted analytically for step and exponential power increases, and step, exponential and linear velocity decreases. The effects of various parameters on heat flux, velocity and time at transient CHF condition have been clarified. Numerical approach combined with analytical method is proposed for more complicated cases. Solution method for pressure transient are also described. (author)

  9. Theoretical and experimental studies on transient forced convection heat transfer of helium gas

    International Nuclear Information System (INIS)

    Liu, Qiusheng; Fukuda, Katsuya; Shibahara, Makoto

    2008-01-01

    Forced convection transient heat transfer for helium gas at various periods of exponential increase of heat input to a horizontal cylinder and a plate (ribbon) one was experimentally and theoretically studied. In the experimental studies, the authors measured heat flux, surface temperature, and transient heat transfer coefficients for forced convection flow of helium gas over a horizontal cylinder and a plate (ribbon) one under wide experimental conditions. Empirical correlations for quasi-steady-state heat transfer and transient heat transfer were obtained based on the experimental data. In the theoretical study, transient heat transfer was numerically solved based on a turbulent flow model. The values of numerical solution for surface temperature and heat flux were compared and discussed with authors' experimental data. (author)

  10. Burnout in boiling heat transfer. Part II: subcooled and low quality forced-convection systems

    International Nuclear Information System (INIS)

    Bergles, A.E.

    1977-01-01

    Recent experimental and analytical developments regrading burnout in subcooled and low quality forced-convection systems are reviewed. Much data have been accumulated which clarify the parametric trends and lead to new design correlations for water and a variety of other coolants in both simple and complex geometries. A number of critical experiments and models have been developed to attempt to clarify the burnout mechanism(s) in simpler geometries and power transients

  11. Burnout in boiling heat transfer. Part III. High-quality forced-convection systems

    International Nuclear Information System (INIS)

    Bergles, A.E.

    1979-01-01

    This is the final part of a review of burnout during boiling heat transfer. The status of burnout in high-quality forced-convection systems is reviewed, and recent developments are summarized in detail. A general guide to the considerable literature is given. Parametric effects and correlations for water in circular and noncircular ducts are presented. Other topics discussed include transients, steam-generator applications, correlations for other fluids, fouling, and augmentation

  12. Experiment of forced convection heat transfer using microencapsulated phase-change-material slurries

    International Nuclear Information System (INIS)

    Kubo, Shinji; Akino, Norio; Tanaka, Amane; Nagashima, Akira.

    1997-01-01

    The present study describes an experiment on forced convective heat transfer using a water slurry of Microencapsulated Phase-change-material. A normal paraffin hydrocarbon is microencapsulated by melamine resin, melting point of 28.1degC. The heat transfer coefficient and pressure drop in a circular tube were evaluated. The heat transfer coefficient using the slurry in case with and without phase change were compared to in case of using pure water. (author)

  13. Cryogenic recovery analysis of forced flow supercritical helium cooled superconductors

    International Nuclear Information System (INIS)

    Lee, A.Y.

    1977-08-01

    A coupled heat conduction and fluid flow method of solution was presented for cryogenic stability analysis of cabled composite superconductors of large scale magnetic coils. The coils are cooled by forced flow supercritical helium in parallel flow channels. The coolant flow reduction in one of the channels during the spontaneous recovery transient, after the conductor undergoes a transition from superconducting to resistive, necessitates a parallel channel analysis. A way to simulate the parallel channel analysis is described to calculate the initial channel inlet flow rate required for recovery after a given amount of heat is deposited. The recovery capability of a NbTi plus copper composite superconductor design is analyzed and the results presented. If the hydraulics of the coolant flow is neglected in the recovery analysis, the recovery capability of the superconductor will be over-predicted

  14. The influence of terrain forcing on the initiation of deep convection over Mediterranean islands

    Science.gov (United States)

    Barthlott, Christian; Kirshbaum, Daniel

    2013-04-01

    The influence of mountainous islands on the initiation of deep convection is investigated using the Consortium for Small-scale Modeling (COSMO) model. The study day is 26 August 2009 on which moist convection occurred over both the Corsica and Sardinia island in the Mediterranean Sea. Sensitivity runs with systematically modified topography are explored to evaluate the relative importance of the land-sea contrast and the terrain height for convection initiation. Whereas no island precipitation is simulated when the islands are completely removed, all simulations that represent these land surfaces develop convective precipitation. Although convection initiates progressively earlier in the day over taller islands, the precipitation rates and accumulations do not show a fixed relationship with terrain height. This is due to the competing effects of different physical processes. First, whereas the forcing for low-level ascent increases over taller islands, the boundary-layer moisture supply decreases, which diminishes the conditional instability and precipitable water. Second, whereas taller islands enhance the inland propagation speeds of sea-breeze fronts, they also mechanically block these fronts and prevent them from reaching the island interior. As a result, the island precipitation is rather insensitive to island terrain height except for one particular case in which the island precipitation increases considerably due to an optimal superposition of the sea breeze and upslope flow. These results demonstrate the complexity of interactions between sea breezes and orography and reinforce that an adequate representation of detailed topographic features is necessary to account for thermally induced wind systems that initiate deep convection.

  15. Hydrogen transfer in Pb–Li forced convection flow with permeable wall

    Energy Technology Data Exchange (ETDEWEB)

    Fukada, Satoshi, E-mail: sfukada@nucl.kyushu-u.ac.jp; Muneoka, Taiki; Kinjyo, Mao; Yoshimura, Rhosuke; Katayama, Kazunari

    2015-10-15

    Highlights: • The paper presents experimental and analytical results of Pb–Li eutectic alloy forced convection flow. • Analytical results are in good agreement with ones of hydrogen permeation in Pb–Li forced convection flow. • The results are useful for the design of liquid blanket of fusion reactors. - Abstract: Transient- or steady-state hydrogen permeation from a primary fluid of Li{sub 17}Pb{sub 83} (Pb–Li) through a permeable tube of Inconel-625 alloy to a secondary Ar purge is investigated experimentally under a forced convection flow in a dual cylindrical tube system. Results of the overall hydrogen permeation flux are correlated in terms of diffusivity, solubility and an average axial velocity of Pb–Li and diffusivity and solubility of the solid wall. Analytical solutions under proper assumptions are derived to simulate the transient- and steady-state rates of the overall hydrogen permeation, and close agreement is obtained between experiment and analysis. Two things are clarified from the comparison: (i) how the steady-state permeation rate is affected by the mass-transfer properties and the average velocity of Pb–Li and the properties of Inconel-625, and (ii) how its transient behavior is done by the diffusivity of the two materials. The results obtained here will give important information to estimate or to analyze the tritium transfer rate in fluidized Pb–Li blankets of DEMO or the future commercial fusion reactors.

  16. Forced convective and subcooled flow boiling heat transfer to pure water and n-heptane in an annular heat exchanger

    International Nuclear Information System (INIS)

    Peyghambarzadeh, S.M.; Sarafraz, M.M.; Vaeli, N.; Ameri, E.; Vatani, A.; Jamialahmadi, M.

    2013-01-01

    Highlights: ► The cooling performance of water and n-heptane is compared during subcooled flow boiling. ► Although n-heptane leaves the heat exchanger warmer it has a lower heat transfer coefficient. ► Flow rate, heat flux and degree of subcooling have direct effect on heat transfer coefficient. ► The predictions of some correlations are evaluated against experimental data. - Abstract: In this research, subcooled flow boiling heat transfer coefficients of pure n-heptane and distilled water at different operating conditions have been experimentally measured and compared. The heat exchanger consisted of vertical annulus which is heated from the inner cylindrical heater with variable heat flux (less than 140 kW/m 2 ). Heat flux is varied so that two different flow regimes from single phase forced convection to nucleate boiling condition are created. Meanwhile, liquid flow rate is changed in the range of 2.5 × 10 −5 –5.8 × 10 −5 m 3 /s to create laminar up to transition flow regimes. Three subcooling levels including 10, 20 and 30 °C are also considered. Experimental results demonstrated that subcooled flow boiling heat transfer coefficient increases when higher heat flux, higher liquid flow rate and greater subcooling level are applied. Furthermore, influence of the operating conditions on the bubbles generation on the heat transfer surface is also discussed. It is also shown that water is better cooling fluid in comparison with n-heptane

  17. Forced and thermocapillary convection in silicon Czochralski crystal growth in semispherical crucible

    Energy Technology Data Exchange (ETDEWEB)

    Mokhtari, F [Physics Department, Faculty of Science, University of Mouloud Mammeri, Tizi Ouzou (Algeria); Bouabdallah, A; Zizi, M [LTSE Laboratory, University of Science and Technology USTHB. BP 32 Elalia, Babezzouar, Algiers (Algeria); Hanchi, S [UER Mecanique/ E.M.P B.P 17, Bordj El Bahri, Algiers (Algeria); Alemany, A, E-mail: abouab2002@yahoo.f [Laboratoire EPM, CNRS, Grenoble (France)

    2010-03-01

    In order to understand the influence of a semispherical crucible geometry combined with different convection modes as a thermocapillary convection, natural convection and forced convection, induced by crystal rotation, on melt flow pattern in silicon Czochralski crystal growth process, a set of numerical simulations are conducted using Fluent Software. We solve the system of equations of heat and momentum transfer in classical geometry as cylindrical and modified crystal growth process geometry as cylindro-spherical. In addition, we adopt hypothesis adapted to boundary conditions near the interface and calculations are executed to determine temperature, pressure and velocity fields versus Grashof and Reynolds numbers. The analysis of the obtained results led to conclude that there is advantage to modify geometry in comparison with the traditional one. The absence of the stagnation regions of fluid in the hemispherical crucible corner and the possibility to control the melt flow using the crystal rotation enhances the quality of the process comparatively to the cylindrical one. The pressure field is strongly related to the swirl velocity.

  18. Forced and thermocapillary convection in silicon Czochralski crystal growth in semispherical crucible

    International Nuclear Information System (INIS)

    Mokhtari, F; Bouabdallah, A; Zizi, M; Hanchi, S; Alemany, A

    2010-01-01

    In order to understand the influence of a semispherical crucible geometry combined with different convection modes as a thermocapillary convection, natural convection and forced convection, induced by crystal rotation, on melt flow pattern in silicon Czochralski crystal growth process, a set of numerical simulations are conducted using Fluent Software. We solve the system of equations of heat and momentum transfer in classical geometry as cylindrical and modified crystal growth process geometry as cylindro-spherical. In addition, we adopt hypothesis adapted to boundary conditions near the interface and calculations are executed to determine temperature, pressure and velocity fields versus Grashof and Reynolds numbers. The analysis of the obtained results led to conclude that there is advantage to modify geometry in comparison with the traditional one. The absence of the stagnation regions of fluid in the hemispherical crucible corner and the possibility to control the melt flow using the crystal rotation enhances the quality of the process comparatively to the cylindrical one. The pressure field is strongly related to the swirl velocity.

  19. Experimental convective heat transfer characterization of pulsating jet in cross flow: influence of Strouhal number excitation on film cooling effectiveness

    International Nuclear Information System (INIS)

    Lalizel, Gildas; Sultan, Qaiser; Fénot, Matthieu; Dorignac, Eva

    2012-01-01

    In actual gas turbine system, unsteadiness of the mainstream flow influences heat transfer and surface pressure distribution on the blade. In order to simulate these conditions, an experimental film cooling study with externally imposed pulsation is performed with purpose of characterizing both effects of turbine unsteadiness on film cooling (with frequency ranges typical to actual turbine), and also to figure out the range of Strouhal number pulsation under various blowing conditions, which could possibly deliver a performance improvement in film cooling. Influence of injection flow pulsation on adiabatic effectiveness and convective heat transfer coefficient are determined from IR-thermography of the wall for distances to the hole exit between 0 and 30 D.

  20. Development of a system code with CFD capability for analyzing turbulent mixed convection in gas-cooled reactors

    International Nuclear Information System (INIS)

    Kim, Hyeon Il

    2010-02-01

    In order to demonstrate the accuracy of predictions in a turbulent mixed convection regime in which both inertia and buoyancy force compete with each other, we found out that assessments done using a single-dimensional system code with a recently updated heat transfer package have shown that this approach cannot give a reasonable prediction of the wall temperature in a case involving strong heating, where the regime falls into turbulent mixed convection regime. It has been known that the main reason of this deficiency comes from the degraded heat transfer in turbulent mixed convection regime, which is below that of convective heat transfer during turbulent forced convection. We investigated two mechanisms that cause this deterioration in convective heat transfer influenced by buoyancy: (1) modification of turbulence, also known as the direct (structural) effect, through the buoyancy-induced production of turbulent kinetic energy: and (2) an indirect (external) effect that occurs through modification of the mean flow. We investigated the Launder-Sharma model of turbulence whether it can appropriately represent the mechanisms causing the degraded heat transfer in Computational Fluid Dynamics (CFD). We found out that this model can capture low Re effects such that a non-equilibrium turbulent boundary layer in turbulent mixed convection regime can be resolved. The model was verified and validated extensively initially with the commercial CFD code, Fluent with a user application package known as the User Defined Function (UDF). The results from this implementation were compared to a set of data that included (1) an experimental data commonly accepted as a standardized problem to verify a turbulent flow, (2) the results from a Direct Numerical Simulation (DNS) in a turbulent forced and mixed convection regime, (3) empirical correlations regarding the friction coefficient and the non-dimensional heat transfer coefficient, the Nusselt number for a turbulent forced

  1. Evaluation of T-111 forced-convection loop tested with lithium at 13700C

    International Nuclear Information System (INIS)

    DeVan, J.H.; Long, E.L. Jr.

    1975-04-01

    A T-111 alloy (Ta--8 percent W--2 percent Hf) forced-convection loop containing molten lithium was operated 3000 h at a maximum temperature of 1370 0 C. Flow velocities up to 6.3 m/s were used. The results obtained in this forced-convection loop are very similar to those observed in lower velocity thermal-convection loops of T-111 containing lithium. Weight changes were determined at 93 positions around the loop. The maximum dissolution rate occurred at the maximum wall temperature of the loop and was less than 1.3 μ m/year. Mass transfer of hafnium, nitrogen, and, to a lesser extent, carbon occurred from the hotter to cooler regions. Exposed surfaces in the highest temperature region were found to be depleted in hafnium to a depth of 60 μ m with no detectable change in tungsten content. There was some loss in room-temperature tensile strength for specimens exposed to lithium at 1370 0 C, attributable to depletion of hafnium and nitrogen and to attendant grain growth. (U.S.)

  2. Experimental Investigation of Convective Heat Transfer during Night Cooling with Different Ventilation Systems and Surface Emissivities

    DEFF Research Database (Denmark)

    Le Dreau, Jerome; Heiselberg, Per; Jensen, Rasmus Lund

    2013-01-01

    models for convection. In a full-scale test room, the heat transfer was investigated during 12 h of discharge by night-time ventilation. A total of 34 experiments have been performed, with different ventilation types (mixing and displacement), air change rates, temperature differences between the inlet...... air and the room, and floor emissivities. This extensive experimental study enabled a detailed analysis of the convective and radiative flow at the different surfaces of the room. The experimentally derived convective heat transfer coefficients (CHTC) have been compared to existing correlations....... For mixing ventilation, existing correlations did not predict accurately the convective heat transfer at the ceiling due to differences in the experimental conditions. But the use of local parameters of the air flow showed interesting results to obtain more adaptive CHTC correlations. For displacement...

  3. Forced and free convection flow with viscous dissipation effects: The method of parametric differentiation

    International Nuclear Information System (INIS)

    Hossain, M.A.; Arbad, O.

    1988-07-01

    Effect of buoyancy force in a laminar uniform forced convection flow past a semi-infinite vertical plate has been analyzed near the leading edge, taking into account the viscous dissipation. The coupled non-linear locally similar equations, which govern the flow, are solved by the method of parametric differentiation. Effects of the buoyancy force and the heat due to viscous dissipation on the flow and the temperature fields as well as on the wall shear-stress and the heat transfer at the surface of the plate are shown graphically for the values of the Prandtl number σ ranging from 10 -1 to 1.0. (author). 20 refs, 3 figs, 2 tabs

  4. Numerical simulation of forced convection in a duct subjected to microwave heating

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, J.; Kuznetsov, A.V. [North Carolina State University, Department of Mechanical and Aerospace Engineering, Campus Box 7910, Raleigh, NC (United States); Sandeep, K.P. [North Carolina State University, Department of Food Science, Raleigh, NC (United States)

    2007-01-15

    In this paper, forced convection in a rectangular duct subjected to microwave heating is investigated. Three types of non-Newtonian liquids flowing through the duct are considered, specifically, apple sauce, skim milk, and tomato sauce. A finite difference time domain method is used to solve Maxwell's equations simulating the electromagnetic field. The three-dimensional temperature field is determined by solving the coupled momentum, energy, and Maxwell's equations. Numerical results show that the heating pattern strongly depends on the dielectric properties of the fluid in the duct and the geometry of the microwave heating system. (orig.)

  5. Experimental study of drying kinetics by forced convection of aromatic plants

    Energy Technology Data Exchange (ETDEWEB)

    Belghit, A; Boutaleb, B C [Laboratoire de Mecanique des Fluides et Energetique, Marrakech (Morocco). Faculte des Sciences Semlalia; Kouhila, M [Laboratoire d' Energie Solaire, Marrakech (Morocco). Ecole Normale Superieure

    2000-08-01

    This paper has the objectives to determine the isotherms of sorption and the drying kinetics of verbena, which is the most consumed aromatic plant in Morocco. The experiments undertaken consist of examining the effects of drying air velocity, temperature of drying air and air moisture content on the drying kinetics of verbena in a laboratory drying tunnel working by forced convection. The results verified, with good reproducibility, that temperature is the main factor in controlling the rate of drying. The expression of the drying rate is determined empirically from the characteristic curve of drying. (author)

  6. Forced convective transition boiling: review of literature and comparison of prediction methods

    International Nuclear Information System (INIS)

    Groeneveld, D.C.; Fung, K.K.

    1976-06-01

    This report reviews the published information on transition boiling heat transfer under forced convective conditions. It was found that transition boiling data have been obtained only within a limited range of conditions and many data are considered unreliable. The data do not permit the derivation of a correlation; however the parametric trends can be isolated from the data. Several authors have proposed correlations valid in the transition boiling region. Most of the correlations are valid only within a narrow range of conditions. A comparison with the data shows that in general agreement is poor. Hsu's correlation is tentatively recommended for low flows and pressures. (author)

  7. Bifurcation and stability of forced convection in tightly coiled ducts: multiplicity

    International Nuclear Information System (INIS)

    Wang Liqiu; Pang, Ophelia; Cheng Lin

    2005-01-01

    A numerical study is made on the fully developed bifurcation structure of the forced convection in tightly coiled ducts of square cross-section. In addition to the examination of structural changes of three known solution branches found in loosely coiled ducts, three new solution branches are found. These new branches are isolated from the three known branches. The flows on these new branches are in a symmetric 4-cell state, a symmetric 8-cell state, an asymmetric 2-cell state, an asymmetric 5-cell state, an asymmetric 7-cell state, or an asymmetric 8-cell structure

  8. Heat transfer with water in forced convection without boiling in small diameter tubes

    International Nuclear Information System (INIS)

    Ricque, Roger; Siboul, Roger

    1969-01-01

    This note presents the measurements performed for the establishment of an empirical heat transfer law for water in forced convection without boiling in small diameter tubes (2 and 4 mm), with high flow velocity and strong heat flux, and for relatively low fluid temperatures. A correlation of experimental points is obtained with a very small maximum dispersion: Nu fl = 0,0092 Re fl 0,88 Pr 0,5 (μ fl /μ p ) 0,14 . A correlation for the fiction coefficient is also presented [fr

  9. Burnout in boiling heat transfer. II. Subcooled and low-quality forced-convection systems

    International Nuclear Information System (INIS)

    Bergles, A.E.

    1977-01-01

    Recent experimental and analytical developments regarding burnout in subcooled and low-quality forced-convection systems are reviewed. Many data have been accumulated which clarify the parametric trends and lead to new design correlations for water and a variety of other coolants in both simple and complex geometries. A number of critical experiments and models have been developed to attempt to clarify the burnout mechanism(s) in simpler geometries. Other topics discussed include burnout with power transients and techniques to augment burnout. 86 references

  10. A Correlation for Forced Convective Boiling Heat Transfer of Refrigerants in a Microfin Tube

    Science.gov (United States)

    Momoki, Satoru; Yu, Jian; Koyama, Shigeru; Fujii, Tetsu; Honda, Hiroshi

    The experimental study is reported on the forced convective boiling of pure refrigerants HCFC22, HFC134a and HCFC123 flowing in a horizontal microfin tube. The local heat transfer coefficient defined based on the actual inside surface area is measured in the ranges of mass velocity of 200 to 400 kg/m2s, heat flux of 5 to 64 kW/m2 and reduced pressure of 0.07 to 0.24. Using the Chen-type model, a new correlation for microfin tubes is proposed considering the enhancement effect of microfins on both the convective heat transfer and the nucleate boiling components. In the convective heat transfer component, the correlation to predict the heat transfer coefficient of liquid-only flow is determined from preliminary experiments on single-phase flow in microfin tubes, and the two-phase flow enhancement factor is determined from the present experimental data. For the nucleate boiling component, the correlation of Takamatsu et al. for smooth tube is modified. The prediction of the present correlation agrees well with present experimental data, and is available for several microfin tubes which were tested by other researchers.

  11. In-situ detection of convection and rotation striations by growth interface electromotive force spectrum

    Science.gov (United States)

    Zhu, Yunzhong; Tang, Feng; Yang, Xin; Yang, Mingming; Ma, Decai; Zhang, Xiaoyue; Liu, Yang; Lin, Shaopeng; Wang, Biao

    2018-04-01

    Nanoscale growth striations, induced by the crystal rotation and melt convection, are in-situ detected by the growth interface electromotive force (GEMF) spectrum during Czochralski (CZ) crystal growth. Specifically, the intensity and period of rotation and convection striations could be precisely revealed under different rotation rates. This is because the GEMF spectrum is affected by the combination effort of temperature difference in crystal rotation path and the melt flow in growth interface. Furthermore, the spectrum analysis (Fourier transform) reveals remarkable characteristics of periodic flow oscillation. More interestingly, in different rotation rates, the corresponding convection period and intensity show particular regularity that could barely be observed in semitransparent and high-temperature melt. Therefore, the GEMF spectrum reflects the subtle changes of a growing crystal that is far beyond the detecting precision of sensors in current CZ equipment. On the basis of this paper and our previous work, the real-time feedback of multiscale striations is established. GEMF spectrum could be a promising approach to reveal striation formation mechanism and optimize crystal quality.

  12. Analysis of Heat Transfer in Berman Flow of Nanofluids with Navier Slip, Viscous Dissipation, and Convective Cooling

    Directory of Open Access Journals (Sweden)

    O. D. Makinde

    2014-01-01

    Full Text Available Heat transfer characteristics of a Berman flow of water based nanofluids containing copper (Cu and alumina (Al2O3 as nanoparticles in a porous channel with Navier slip, viscous dissipation, and convective cooling are investigated. It is assumed that the exchange of heat with the ambient surrounding takes place at the channel walls following Newton’s law of cooling. The governing partial differential equations and boundary conditions are converted into a set of nonlinear ordinary differential equations using appropriate similarity transformations. These equations are solved analytically by regular perturbation methods with series improvement technique and numerically using an efficient Runge-Kutta Fehlberg integration technique coupled with shooting scheme. The effects of the governing parameters on the dimensionless velocity, temperature, skin friction, pressure drop, and Nusselt numbers are presented graphically and discussed quantitatively.

  13. Three dimensional modeling on airflow, heat and mass transfer in partially impermeable enclosure containing agricultural produce during natural convective cooling

    International Nuclear Information System (INIS)

    Chourasia, M.K.; Goswami, T.K.

    2007-01-01

    A three dimensional model was developed to simulate the transport phenomena in heat and mass generating porous medium cooled under natural convective environment. Unlike the previous works on this aspect, the present model was aimed for bulk stored agricultural produce contained in a permeable package placed on a hard surface. This situation made the bottom of the package impermeable to fluid flow as well as moisture transfer and adiabatic to heat transfer. The velocity vectors, isotherms and contours of rate of moisture loss were presented during transient cooling as well as at steady state using the commercially available computational fluid dynamics (CFD) code based on the finite volume technique. The CFD model was validated using the experimental data on the time-temperature history as well as weight loss obtained from a bag of potatoes kept in a cold store. The simulated and experimental values on temperature and moisture loss of the product were found to be in good agreement

  14. Single-jet gas cooling of in-beam foils or specimens: Prediction of the convective heat-transfer coefficient

    Science.gov (United States)

    Steyn, Gideon; Vermeulen, Christiaan

    2018-05-01

    An experiment was designed to study the effect of the jet direction on convective heat-transfer coefficients in single-jet gas cooling of a small heated surface, such as typically induced by an accelerated ion beam on a thin foil or specimen. The hot spot was provided using a small electrically heated plate. Heat-transfer calculations were performed using simple empirical methods based on dimensional analysis as well as by means of an advanced computational fluid dynamics (CFD) code. The results provide an explanation for the observed turbulent cooling of a double-foil, Havar beam window with fast-flowing helium, located on a target station for radionuclide production with a 66 MeV proton beam at a cyclotron facility.

  15. Experimental Investigation of Temperature Distribution along the Length of Uniform Area Fin for Forced and Free Convection

    Science.gov (United States)

    Kannojiya, Vikas; Sharma, Riya; Gaur, Rahul; Jangra, Anil; Yadav, Pushpender; Prajapati, Pooja

    2018-03-01

    The overheating of an industrial component sometimes may leads to system failure. The convection heat transfer from a heated surface can be effectively enhanced by employing fins on that surface. This Paper emphasizes on the experimental investigation of temperature distribution along the length of pin shaped fin. The analysis is performed on a 100 mm long fin made up of brass with 19.6 mm diameter having thermal conductivity as 111 W/m.K. Temperature at different section of the fin along its length is evaluated experimentally and theoretically. The influence of convection mode viz natural & forced convection and variable heat input on the temperature distribution is evaluated. The result outcomes are then compared with the widely accepted analytical relations. A comparison of convective heat transfer coefficient for uniform and non-uniform area fin is also presented. The results by experimental and analytical method are found to be in good agreement for free convection phenomenon.

  16. HANARO cooling features: design and experience

    International Nuclear Information System (INIS)

    Park, Cheol; Chae, Hee-Taek; Han, Gee-Yang; Jun, Byung-Jin; Ahn, Guk-Hoon

    1999-01-01

    In order to achieve the safe core cooling during normal operation and upset conditions, HANARO adopted an upward forced convection cooling system with dual containment arrangements instead of the forced downward flow system popularly used in the majority of forced convection cooling research reactors. This kind of upward flow system was selected by comparing the relative merits of upward and downward flow systems from various points of view such as safety, performance, maintenance. However, several operational matters which were not regarded as serious at design come out during operation. In this paper are presented the design and operational experiences on the unique cooling features of HANARO. (author)

  17. Numerical simulation for aspects of homogeneous and heterogeneous reactions in forced convection flow of nanofluid

    Science.gov (United States)

    Hayat, Tasawar; Shah, Faisal; Khan, Muhammad Ijaz; Alsaedi, Ahmed

    2018-03-01

    Mixed convection stagnation point flow of nanofluid by a vertical permeable circular cylinder has been addressed. Water is treated as ordinary liquid while nanoparticles include aluminium oxide, copper and titanium dioxide. Homogeneous-heterogeneous reactions are considered. The nonlinear higher order expressions are changed into first ordinary differential equations and then solved by built-in-Shooting method in mathematica. The results of velocity, temperature, concentration, skin friction and local Nusselt number are discussed. Our results demonstrate that surface drag force and heat transfer rate are enhanced linearly for higher estimation of curvature parameter. Further surface drag force decays for aluminium oxide and it enhances for copper nanoparticle. Heat transfer rate enhances with increasing all three types of nanoparticles. In addition, the lowest heat transfer rate is obtained in case of titanium dioxide when compared with copper and aluminium oxide.

  18. MHD forced and free convection boundary layer flow near the leading edge

    International Nuclear Information System (INIS)

    Hossain, M.A.; Ahmed, M.

    1988-07-01

    Magnetohydrodynamic forced and free convection flow of an electrically conducting viscous incompressible fluid past a vertical flat plate with uniform heat flux in the presence of a magnetic field acting normal to the plate that moves with the fluid has been studied near the leading edge of the plate. The coupled non-linear equations are solved by the method of superposition for the values of the Prandtl number ranges from 0.01 to 10.0. The velocity and the temperature profiles are presented graphically and the values of the wall shear-stress as well as the heat transfer rate are presented in tabular form showing the effect of the buoyancy force and the applied magnetic field. To show the accuracy of the present method some typical values are compared with the available one. (author). 17 refs, 3 figs, 2 tabs

  19. Study of nitrogen injection to enhance forced convection for gas fast reactors

    International Nuclear Information System (INIS)

    Tauveron, N.; Dor, I.; Bentivoglio, F.

    2011-01-01

    Highlights: → The present study concerns the use of blowers in case of nitrogen injection. It is a well-known fact that heavier gases (than helium) enhance natural circulation. The use of such heavier gases (nitrogen is considered here) can also enhance forced convection. → A specific work on the impact of the use of alternative gas on blower behaviour is presented. → These developments are used in a simplified system analysis and in a complete transient behaviour analysis in depressurised situations computed with the CATHARE2 code. - Abstract: In the frame of the international forum GenIV, the gas fast reactor is considered as a promising concept, combining the benefits of fast spectrum and high temperature, using helium as coolant. In the current preliminary viability GFR studies safety system relies on blowers in case of depressurised conditions. The present study concerns the use of blowers in case of nitrogen injection. It is a well-known fact that heavier gases (than helium) enhance natural circulation. The use of such gases (nitrogen is considered) can also enhance forced convection. A specific work on the impact of the use of alternative gas on blower behaviour is presented. Transient behaviours in depressurised situations are computed with the CATHARE2 code and analyzed.

  20. Performance of a forced convection solar drier integrated with gravel as heat storage material

    Energy Technology Data Exchange (ETDEWEB)

    Mohanraj, M. [Dr Mahalingam College of Engineering and Technology, Pollachi (India). Dept. of Mechanical Engineering; Chandrasekar, P. [Swinburne Univ. of Technology, Sarawak (Malaysia). School of Engineering Sciences

    2009-07-01

    Sun drying is the most common method used in India to dry agricultural products such as grains, fruits and vegetables. The rate of drying depends on solar radiation, ambient temperature, wind velocity, relative humidity, initial moisture content, type of crops, crop absorptivity and mass product per unit exposed area. However, this method of spreading the crop in a thin layer on the ground has several disadvantages. This paper reported on a study that focused on developing a forced convection solar drier integrated with heat storage materials for drying various agricultural crops. The indirect forced convection solar drier, integrated with gravel as a sensible heat material, was used to dry pineapple slices under conditions similar to those found in Pollachi, India. The performance of the system was discussed along with the drying characteristics, drying rate, and specific moisture extraction rate. The results showed that the moisture content (wet basis) of pineapple was reduced from about 87.5 to 14.5 per cent (equilibrium moisture content) in about 29 hours in the bottom tray and 32 hours in the top tray. The thermal efficiency of the solar air heater was also reviewed. 9 refs., 5 figs.

  1. Evaluating a tobacco-curing oven using a forced-convection heat exchanger USCO — MADR

    Directory of Open Access Journals (Sweden)

    Néstor Enrique Cerquera Peña

    2010-01-01

    Full Text Available A traditional oven for curing tobacco leaves was redesigned (based on existing infrastructure; a forced-convection heat exchan- ger system was implemented in it which worked with coffee hulls as fuel. This oven (called a forced-convection tobacco leaf curing oven was evaluated during the harvesting season. It was found that temperature and relative humidity inside the furnace could be controlled with this assembly during the three stages involved in curing tobacco leaves. The equipment used performed excellently when using coffee hulls as fuel, having the following approximate consumption during curing: 8.92 kilograms per hour during the yellowing stage, 17.75 kilograms per hour during the leaf drying and color fixation phase and 19.29 kilograms per hour during the stem drying stage. Comparative analysis of the oven’s operating costs along with the proposed adjustments to be made to it would allow its implementation as a promising alternative in the existing tobacco chain.

  2. The Impact of Convective Fluid Inertia Forces on Operation of Tilting-Pad Journal Bearings

    Directory of Open Access Journals (Sweden)

    Thomas Hagemann

    2017-01-01

    Full Text Available This paper presents a combination of experimental data, CFD analyses, and bearing code predictions on emergence of convective inertia fluid forces within the lube oil flow of tilting-pad journal bearings. Concordantly, experimental data and CFD analyses show a significant rise of local pressure at the transition between inlet and leading edge of tilting-pad, especially for high-speed applications with surface speeds up to 100 m/s. This effect can be related to convective inertia forces within fluid flow as cross-sections and flow character rapidly change at the pad entrance. An energy-based approach is implemented in the bearing code in order to provide enhanced boundary conditions for Reynolds equation considering this effect. As a result, predictions of bearing code achieved significant improved correlation with measured pressure distributions and CFD-data. Further, beside the local influence, a nonnegligible impact on characteristic parameters of bearing operation such as maximum temperature and stiffness and damping coefficients is observed. Finally, the results are critically analyzed and requirements to gain more distinct and reliable data are specified.

  3. An experimental study of forced convective flow boiling CHF in nanofluid

    International Nuclear Information System (INIS)

    Ahn, Hoseon; Kim, Seontae; Jo, Hangjin; Kim, Dongeok; Kang, Soonho; Kim, Moohwan

    2008-01-01

    Recently the enhancement of CHF (critical heat flux) in nanofluids under the pool boiling condition is known as a result of nanoparticle deposition on the heating surface. The deposition phenomenon of nanoparticles on the heating surface is induced dominantly by the vigorous boiling on the heating surface. Considering the importance of flow boiling conditions in various practical heat transfer applications, an experimental study was performed to verify whether or not the enhancement of CHF in nanofluids exists in a forced convective flow boiling condition. The nanofluid used in this research was Al 2 O 3 -water dispersed by the ultra-sonic vibration method in very low concentration (0.01% Vol). A heater specimen was made of a copper block easily detachable to look into the surface condition after the experiment. The heating method was a thermal-heating made with a conductive material. The flow channel took a rectangular type (10mm x 10mm) and had a length of 1.2 m to assure a hydrodynamically fully-developed region. In result, CHF in the nanofluid under the forced convective flow boiling condition has been enhanced distinctively along with the effect of flow rates. To reason the CHF increase in the nanofluids, the boiling surface was investigated thoroughly with the SEM image. (author)

  4. An investigation of transition boiling mechanisms of subcooled water under forced convective conditions

    Energy Technology Data Exchange (ETDEWEB)

    Kwang-Won, Lee; Sang-Yong, Lee

    1995-09-01

    A mechanistic model for forced convective transition boiling has been developed to investigate transition boiling mechanisms and to predict transition boiling heat flux realistically. This model is based on a postulated multi-stage boiling process occurring during the passage time of the elongated vapor blanket specified at a critical heat flux (CHF) condition. Between the departure from nucleate boiling (DNB) and the departure from film boiling (DFB) points, the boiling heat transfer is established through three boiling stages, namely, the macrolayer evaporation and dryout governed by nucleate boiling in a thin liquid film and the unstable film boiling characterized by the frequent touches of the interface and the heated wall. The total heat transfer rates after the DNB is weighted by the time fractions of each stage, which are defined as the ratio of each stage duration to the vapor blanket passage time. The model predictions are compared with some available experimental transition boiling data. The parametric effects of pressure, mass flux, inlet subcooling on the transition boiling heat transfer are also investigated. From these comparisons, it can be seen that this model can identify the crucial mechanisms of forced convective transition boiling, and that the transition boiling heat fluxes including the maximum heat flux and the minimum film boiling heat flux are well predicted at low qualities/high pressures near 10 bar. In future, this model will be improved in the unstable film boiling stage and generalized for high quality and low pressure situations.

  5. Characterization of Radial Curved Fin Heat Sink under Natural and Forced Convection

    Science.gov (United States)

    Khadke, Rishikesh; Bhole, Kiran

    2018-02-01

    Heat exchangers are important structures widely used in power plants, food industries, refrigeration, and air conditioners and now widely used in computing systems. Finned type of heat sink is widely used in computing systems. The main aim of the design of the heat sink is to maintain the optimum temperature level. To achieve this goal so many geometrical configurations are implemented. This paper presents a characterization of radially curved fin heat sink under natural and forced convection. Forced convection is studied for the optimization of temperature for better efficiency. The different alternatives in geometry are considered in characterization are heat intensity, the height of the fin and speed of the fan. By recognizing these alternatives the heat sink is characterized by the heat flux usually generated in high-end PCs. The temperature drop characteristics across height and radial direction are presented for the constant heat input and air flow in the heat sink. The effect of dimensionless elevation height (0 ≤ Z* ≤ 1) and Elenbaas Number (0.4 ≤ El ≤ 2.8) of the heat sink were investigated for study of the Nusselt number. Based on experimental characterization, process plan has been developed for the selection of the similar heat sinks for desired output (heat dissipation and temperature distribution).

  6. Visualization study for forced convection heat transfer of supercritical carbon dioxide near pseudo-boiling point

    International Nuclear Information System (INIS)

    Sakurai, K.; Ko, H.S.; Okamoto, K.; Madarame, H.

    2001-01-01

    For development of new reactor, supercritical water is expected to be used as coolant to improve thermal efficiency. However, the thermal characteristics of supercritical fluid is not revealed completely because its difficulty for experiment. Specific phenomena tend to occur near the pseudo-boiling point which is characterised by temperature corresponding to the saturation point in ordinary fluid. Around this point, the physic properties such as density, specific heat and thermal conductivity are drastically varying. Although there is no difference between gas and liquid phases in supercritical fluids, phenomena similar to boiling (with heat transfer deterioration) can be observed round the pseudo-boiling point. Experiments of heat transfer have been done for supercritical fluid in forced convective condition. However, these experiments were mainly realised inside stainless steel cylinder pipes, for which flow visualisation is difficult. Consequently, this work has been devoted to the development of method allowing the visualisation of supercritical flows. The experiment setup is composed of main loop and test section for the visualisation. Carbon dioxide is used as test fluid. Supercritical carbon dioxide flows upward in rectangular channel and heated by one-side wall to generate forced convection heat transfer. Through window at mid-height of the test section, shadowgraphy was applied to visualize density gradient distribution. The behavior of the density wave in the channel is visualized and examined through the variation of the heat transfer coefficient. (author)

  7. Experimental study on forced convection boiling heat transfer on molten alloy

    International Nuclear Information System (INIS)

    Nishimura, Satoshi; Ueda, Nobuyuki; Nishi, Yoshihisa; Furuya, Masahiro; Kinoshita, Izumi

    1999-01-01

    In order to clarify the characteristics of forced convection boiling heat transfer on molten metal, basic experiments have been carried out with subcooled water flowing on molten Wood's alloy pool surface. In these experiments, water flows horizontally in a rectangular duct. A cavity filled with Wood's alloy is present in a portion of the bottom of the duct. Wood's alloy is heated by a copper conductor at the bottom of the cavity. The experiments have been carried out with various velocities and subcoolings of water, and temperature of Wood's alloy. Boiling curves on the molten alloy surface were obtained and compared with that on a solid heat transfer surface. It is observed that the boiling curve on molten alloy is in a lower superheat region than the boiling curve on a solid surface. This indicates that the heat transfer performance of forced convection boiling on molten alloy is enhanced by increase of the heat transfer area, due to oscillation of the surface and fragmentation of molten alloy

  8. Study on hydrogen isotope behavior in Pb-Li forced convection flow with permeable wall

    Energy Technology Data Exchange (ETDEWEB)

    Yoshimura, Ryosuke; Fukada, Satoshi, E-mail: sfukada@nucl.kyushu-u.ac.jp; Muneoka, Taiki; Kinjo, Mao; Katayama, Kazunari

    2016-12-15

    Highlights: • Transient- and steady-state hydrogen permeation from Li-Pb forced convection flow through permeable tube to outside Ar purge gas was investigated at 600 °C. • It was found that the overall permeation rates were limited by diffusion in the Li-Pb boundary layer developed from the flow inlet. • The effect of the boundary layer was correlated in terms of mass transfer coefficient. The values of mass transfer coefficients at 600 °C were compared with those of 400 °C and 500 °C obtained beforehand. - Abstract: Transient- and steady-state hydrogen permeation from Li-Pb forced convection flow in a permeable tube to outside Ar purge gas was investigated between 400–600 °C. The values of the steady-state permeation rate increased with the increase of the Li-Pb flow rate. It was found that the overall permeation rates were limited by diffusion in a Li-Pb boundary layer developed from flow inlet. The effect of the boundary layer was correlated in terms of the mass-transfer coefficient. The values of the mass-transfer coefficient at 600 °C were compared with those of 400 °C and 500 °C obtained beforehand. Judged from these data of mass-transfer coefficients, it can be predicted that the effect of boundary layer varies with the increase of Li-Pb flow rate at different temperature conditions.

  9. Investigation of combined free and forced convection in a 2 x 6 rod bundle during controlled flow transients

    International Nuclear Information System (INIS)

    Bates, J.M.; Khan, E.U.

    1980-10-01

    An experimental study was performed to obtain local fluid velocity and temperature measurements in the mixed (combined free and forced) convection regime for specific flow coastdown transients. A brief investigation of steady-state flows for the purely free-convection regime was also completed. The study was performed using an electrically heated 2 x 6 rod bundle contained in a flow housing. In addition a transient data base was obtained for evaluating the COBRA-WC thermal-hydraulic computer program

  10. Phenomenological and statistical analyses of turbulence in forced convection with temperature-dependent viscosity under non-Boussinesq condition.

    Science.gov (United States)

    Yahya, S M; Anwer, S F; Sanghi, S

    2013-10-01

    In this work, Thermal Large Eddy Simulation (TLES) is performed to study the behavior of weakly compressible Newtonian fluids with anisotropic temperature-dependent viscosity in forced convection turbulent flow. A systematic analysis of variable-viscosity effects, isolated from gravity, with relevance to industrial cooling/heating applications is being carried out. A LES of a planar channel flow with significant heat transfer at a low Mach number was performed to study effects of fluid property variation on the near-wall turbulence structure. In this flow configuration the top wall is maintained at a higher temperature (T hot ) than the bottom wall (T cold ). The temperature ratio (R θ = T hot /T cold ) is fixed at 1.01, 2 and 3 to study the effects of property variations at low Mach number. Results indicate that average and turbulent fields undergo significant changes. Compared with isothermal flow with constant viscosity, we observe that turbulence is enhanced in the cold side of the channel, characterized by locally lower viscosity whereas a decrease of turbulent kinetic energy is found at the hot wall. The turbulent structures near the cold wall are very short and densely populated vortices but near the hot wall there seems to be a long streaky structure or large elongated vortices. Spectral study reveals that turbulence is completely suppressed at the hot side of the channel at a large temperature ratio because no inertial zone is obtained (i.e. index of Kolmogorov scaling law is zero) from the spectra in these region.

  11. Heat and mass transfer during cooling and storage of agricultural products as influenced by natural convection

    NARCIS (Netherlands)

    Beukema, K.J.

    1980-01-01

    Three different models of bulk-stored agricultural products with air flow through the bulk, predicting the temperature profiles or the velocity of natural convection, are developed. The temperature distribution in a cylindrical container with insulated walls and open top and bottom, filled

  12. Thermal environment in simulated offices with convective and radiant cooling systems under cooling (summer) mode of operation

    DEFF Research Database (Denmark)

    Mustakallio, Panu; Bolashikov, Zhecho Dimitrov; Kostov, Kalin

    2016-01-01

    The thermal environment in a double office room and in a six-person meeting room obtained with chilled beam (CB), chilled beam with radiant panel (CBR), chilled ceiling with ceiling installed mixing ventilation (CCMV) and four desk partition-mounted local radiant cooling panels with mixing...... calculated. Manikin-based equivalent temperature (MBET) was determined by using two thermal manikins to identify the impact of the local thermal conditions generated by the studied systems on occupants' thermal perception. The results revealed that the differences in the thermal conditions achieved...

  13. Study and Application of Forced Convection in Road Bus Heating System

    Directory of Open Access Journals (Sweden)

    Scheila Sandi Biazus

    2015-03-01

    Full Text Available This work deals with a replacing the heating system of intercity buses, made by long heat exchangers distributed on the sides of the passenger saloon by small and compact ones that use forced convection to heat dissipation. At the beginning the calculation was made of the heat capacity of a heat exchanger with the parameters defined by the supplier, and then conducted an analysis of change in these parameters in order to improve its efficiency. The method for examining the heat exchanger is based on the correlations available in the convection flow inside and outside to determine the respective convective coefficients, and therefore the overall coefficient of heat transfer. Following, the heat exchanger in its original form, was tested on bench. Thus, from the thermal load of the bus model studied, the amount of exchangers required has been defined to satisfy the thermal comfort of passengers. Field tests of the heating systems with new heat exchangers were performed to obtain actual data of the proposed system. The original factory system showed to be efficient in meeting the needs thermal load and economically viable, such that the critical thermal load can be met with ten heaters installed along the body. Furthermore, this system offers the possibility of varying the parameters to best fit to the project, where the flow variation of the fans or the spacing between the fins of the heat exchanger decreases the amount of heaters required. At the same time, the system showed the need for further study to assess its distribution along the passenger saloon in order to meet a best uniformity temperature distribution.

  14. Operation of a forced two phase cooling system on a large superconducting magnet

    International Nuclear Information System (INIS)

    Green, M.A.; Burns, W.A.; Eberhard, P.H.; Gibson, G.H.; Pripstein, M.; Ross, R.R.; Smits, R.G.; Taylor, J.D.; Van Slyke, H.

    1980-05-01

    This paper describes the operation of a forced two phase cooling system on a two meter diameter superconducting solenoid. The magnet is a thin high current density superconducting solenoid which is cooled by forced two phase helium in tubes around the coil. The magnet, which is 2.18 meters in diameter and 3.4 meters long, has a cold mass of 1700 kg. The two phase cooling system contains less than 300 liters of liquid helium, most of which is contained in a control dewar. This paper describes the operating characteristics of the LBL two phase forced cooling system during cooldown and warm up. The paper presents experimental data on operations of the magnet using either a helium pump or the refrigerator compressor to circulate two phase helium through the superconducting coil cooling tubes

  15. The onset of nonpenetrative convection in a suddenly cooled layer of fluid

    Energy Technology Data Exchange (ETDEWEB)

    Ihle, Christian F. [Program in Fluid Dynamics, Facultad de Ciencias Fisicas y Matematicas, Universidad de Chile, Blanco Encalada 2002 Of. 327, Santiago (Chile); Nino, Yarko [Departamento de Ingenieria Civil, Division de Recursos Hidricos y Medio Ambiente, Universidad de Chile, Av. Blanco Encalada 2002, Santiago (Chile)

    2006-04-15

    Conditions for the onset of nonpenetrative convection in a horizontal Boussinesq fluid layer subject to a step change in temperature are studied using propagation theory. A wide range of Prandtl numbers and two different kinematic boundary conditions are considered. It is shown that for high Rayleigh numbers, critical conditions for the onset of convective motion reproduce exactly those for the unsteady Rayleigh-Benard instability. Present results extend those of previous research and show a tendency of the rigid-rigid and free-rigid critical curves to converge for low Prandtl numbers. Comparison between present and previously reported results on critical conditions for the onset of instabilities and onset time using different methods yields good agreement on a middle to high Prandtl number range. A ratio of 10 between experimentally measured and theoretically predicted onset times is suggested for stress-free bounded systems. (author)

  16. A Thermal Physiological Comparison of Two HazMat Protective Ensembles With and Without Active Convective Cooling

    Science.gov (United States)

    Williamson, Rebecca; Carbo, Jorge; Luna, Bernadette; Webbon, Bruce W.

    1998-01-01

    Wearing impermeable garments for hazardous materials clean up can often present a health and safety problem for the wearer. Even short duration clean up activities can produce heat stress injuries in hazardous materials workers. It was hypothesized that an internal cooling system might increase worker productivity and decrease likelihood of heat stress injuries in typical HazMat operations. Two HazMat protective ensembles were compared during treadmill exercise. The different ensembles were created using two different suits: a Trelleborg VPS suit representative of current HazMat suits and a prototype suit developed by NASA engineers. The two life support systems used were a current technology Interspiro Spirolite breathing apparatus and a liquid air breathing system that also provided convective cooling. Twelve local members of a HazMat team served as test subjects. They were fully instrumented to allow a complete physiological comparison of their thermal responses to the different ensembles. Results showed that cooling from the liquid air system significantly decreased thermal stress. The results of the subjective evaluations of new design features in the prototype suit were also highly favorable. Incorporation of these new design features could lead to significant operational advantages in the future.

  17. A block-iterative nodal integral method for forced convection problems

    International Nuclear Information System (INIS)

    Decker, W.J.; Dorning, J.J.

    1992-01-01

    A new efficient iterative nodal integral method for the time-dependent two- and three-dimensional incompressible Navier-Stokes equations has been developed. Using the approach introduced by Azmy and Droning to develop nodal mehtods with high accuracy on coarse spatial grids for two-dimensional steady-state problems and extended to coarse two-dimensional space-time grids by Wilson et al. for thermal convection problems, we have developed a new iterative nodal integral method for the time-dependent Navier-Stokes equations for mechanically forced convection. A new, extremely efficient block iterative scheme is employed to invert the Jacobian within each of the Newton-Raphson iterations used to solve the final nonlinear discrete-variable equations. By taking advantage of the special structure of the Jacobian, this scheme greatly reduces memory requirements. The accuracy of the overall method is illustrated by appliying it to the time-dependent version of the classic two-dimensional driven cavity problem of computational fluid dynamics

  18. Control of cooling processes with forced-air aimed at efficiency energetic and the cooling time of horticultural products

    Energy Technology Data Exchange (ETDEWEB)

    Silva, Joao Carlos Teles Ribeiro da; Mederos, Barbara Janet Teruel [Universidade Estadual de Campinas (FEAGRI/UNICAMP), SP (Brazil). Fac. de Engenharia Agricola

    2008-07-01

    The application of cooling technologies for the conservation of horticultural products is one of the stages the Cold Chain. In Brazil particularly, as a country with tropical climate with average high temperature almost all year, the application of these technologies is very important because the shelf-life of fresh horticultural products, with quality that the market demands, is directly related to temperature. In particular, the systems of forced air cooling operate according to the flow of air predetermined in the project according to the quantity of product to cool. When actual conditions differ from considerations of the project, as to the quantity of product, a situation very common in agricultural properties and packing houses, the fan will continue providing the nominal flow rate, causing alteration of the cost-benefit relation of process. This project aims at the development of a micro-processing equipment (output current of 4 to 20 mA) to control the rotational speed of the motor of the fan systems, air forced through an inverter of frequency. The objective is development of a Man-Machine Interface, based on an algorithm, which, through the introduction of mass product data and the automatic acquisition of data from temperature of the product and the camera, is calculated the cooling time. The rotation of the engine fan will be amended automatically, to maintain air flow with a proper cost-benefit, in connection with the reduction of cooling time, energy consumption, for the increasing the shelf life of products. (author)

  19. Experimental-theoretical analysis of laminar internal forced convection with nanofluids

    Energy Technology Data Exchange (ETDEWEB)

    Cerqueira, Ivana G.; Cotta, Renato M. [Lab. of Transmission and Technology of Heat-LTTC. Mechanical Eng. Dept. - POLI and COPPE/UFRJ, Rio de Janeiro, RJ (Brazil)], E-mail: cotta@mecanica.coppe.ufrj.br; Mota, Carlos Alberto A. [Conselho Nacional de Pesquisas - CNPq, Brasilia, DF (Brazil)], e-mail: carlosal@cnpq.br; Nunes, Jeziel S. [INPI, Rio de Janeiro, RJ (Brazil)], e-mail: jeziel@inpi.gov.br

    2010-07-01

    This work reports fundamental experimental-theoretical research related to heat transfer enhancement in laminar channel flow with nanofluids, which are essentially modifications of the base fluid with the dispersion of metal oxide nanoparticles. The theoretical work was performed by making use of mixed symbolic-numerical computation (Mathematica 7.0 platform) and a hybrid numerical-analytical methodology (Generalized Integral Transform Technique - GITT) in accurately handling the governing partial differential equations for the heat and fluid flow problem formulation with temperature dependency in all the thermophysical properties. Experimental work was also undertaken based on a thermohydraulic circuit built for this purpose, and sample results are presented to verify the proposed model. The aim is to illustrate detailed modeling and robust simulation attempting to reach an explanation of the controversial heat transfer enhancement observed in laminar forced convection with nanofluids. (author)

  20. Simulation of forced convection in non-Newtonian fluid through sandstones

    Science.gov (United States)

    Gokhale, M. Y.; Fernandes, Ignatius

    2017-11-01

    Numerical simulation is carried out to study forced convection in non-Newtonian fluids flowing through sandstones. Simulation is carried out using lattice Boltzmann method (LBM) for both shear-thinning and shear-thickening, by varying the power law index from 0.5 to 1.5 in Carreau-Yasuda model. Parameters involved in LBM and Carreau model are identified to achieve numerical convergence. Permeability and porosity are varied in the range of 10-10-10-6 and 0.1-0.7, respectively, to match actual geometrical properties of sandstone. Numerical technology is validated by establishing Darcy's law by plotting the graph between velocity and pressure gradient. Consequently, investigation is carried out to study the influence of material properties of porous media on flow properties such as velocity profiles, temperature profiles, and Nusselt number.

  1. Electrochemical characterization of tenoxicam using a bare carbon paste electrode under stagnant and forced convection conditions

    International Nuclear Information System (INIS)

    Guzmán-Hernández, D.S.; Ramírez-Silva, M.T.; Palomar-Pardavé, M.; Corona-Avendaño, S.; Galano, Annia; Rojas-Hernández, A.; Romero-Romo, M.

    2012-01-01

    Highlights: ► Tenoxicam electrochemical oxidation was studied from aqueous solution with a CPE. ► Both stagnant and forced convection conditions were considered. ► We found tenoxicam electrochemical oxidation is a mass transfer-controlled process. ► An EC mechanism was found where the electrodic and chemical kinetics are fast. ► It was found that in this case n = 2 and E 1/2 = 0.770 V. ► Calculated D was 4.09 × 10 −6 cm 2 s −1 which compares with theoretically estimated. - Abstract: From potentiostatic current transients and voltammetry studies, carried out under both stagnant and forced convection conditions, the tenoxicam electrochemical behavior on a bare carbon paste rotating disk electrode was assessed in an aqueous solution (pH = 0.403). It was found that tenoxicam's electrochemical oxidation is a mass transfer-controlled process where a current peak is clearly formed at around 0.74 V when the potential scan was varied in the positive direction. However, when the potential was switched to the negative direction, up to the initial potential value, no reduction peak was formed. Tenoxicam's electrochemical oxidation follows an EC mechanism where the electrodic and chemical kinetics are fast. From sample-current voltammetry both the number of electrons, n, that tenoxicam losses during its electro-oxidation and its half-wave potential, E 1/2 , were determined to be 2 and 0.770 V vs. Ag/AgCl, respectively. Moreover, from differential pulse voltammetry plots it was confirmed that effectively in this case n = 2. Considering 2 electrons and both the Randles-Sevcik and Cotrell equations, the tenoxicam's diffusion coefficient, D, was determined to be (3.745 ± 0.077) × 10 −6 and (4.116 ± 0.086) × 10 −6 cm 2 s −1 , respectively. From linear sweep voltammetry plots recorded under forced convection conditions, it was found that Levich's equation describes adequately the limiting current recorded as a function of the electrode rotation rate, from

  2. A numerical investigation of laminar forced convection in a solar collector with non-circular duct

    Directory of Open Access Journals (Sweden)

    Teleszewski Tomasz Janusz

    2017-01-01

    Full Text Available This paper presents a two-dimensional numerical study to investigate laminar flow in a flat plate solar collector with non-circular duct (regular polygonal, elliptical, and Cassini oval shape featuring forced convection with constant axial wall heat flux and constant peripheral wall temperature (H1 condition. Applying the velocity profile obtained for the duct laminar flow, the energy equation was solved exactly for the constant wall heat flux using the Boundary Element Method (BEM. Poiseuille and Nusselt numbers were obtained for flows having a different number of geometrical factors. The results are presented and discussed in the form of tables and graphs. The area goodness factor and volume goodness factor are calculated. The predicted correlations for Poiseuille and Nusselt numbers may be a very useful resource for the design and optimization of solar collectors with non-circular ducts.

  3. Experiments on forced convection form a horizontal heated plate in a packed bed of glass spheres

    Energy Technology Data Exchange (ETDEWEB)

    Renken, K.J. (Univ. of Wisconsin, Milwaukee (USA)); Poulikakos, D. (Univ. of Illinois, Chicago (USA))

    1989-02-01

    This paper presents an experimental investigation of boundary-layer forced convective heat transfer from a flat isothermal plate in a packed bed of spheres. Extensive experimental results are reported for the thermal boundary-layer thickness, the temperature field, and the local wall heat flux (represented by the local Nusselt number). Theoretical findings of previous investigations using the Darcy flow model as well as a general model for themomentum equation accouting for flow inertia and macroscopic shear wtih and without variable porosity are used to evaluate the theoretical models. Several trends are revealed regarding the conditions of validity of these flow models. Overall the general flow model including variable porosity appears to perform better, even through the need for serious improvements in modeling becomes apparent.

  4. Eulerian-Eulerian two-phase numerical simulation of nanofluid laminar forced convection in a microchannel

    International Nuclear Information System (INIS)

    Kalteh, Mohammad; Abbassi, Abbas; Saffar-Avval, Majid; Harting, Jens

    2011-01-01

    In this paper, laminar forced convection heat transfer of a copper-water nanofluid inside an isothermally heated microchannel is studied numerically. An Eulerian two-fluid model is considered to simulate the nanofluid flow inside the microchannel and the governing mass, momentum and energy equations for both phases are solved using the finite volume method. For the first time, the detailed study of the relative velocity and temperature of the phases are presented and it has been observed that the relative velocity and temperature between the phases is very small and negligible and the nanoparticle concentration distribution is uniform. However, the two-phase modeling results show higher heat transfer enhancement in comparison to the homogeneous single-phase model. Also, the heat transfer enhancement increases with increase in Reynolds number and nanoparticle volume concentration as well as with decrease in the nanoparticle diameter, while the pressure drop increases only slightly.

  5. A theoretical study of the spheroidal droplet evaporation in forced convection

    Energy Technology Data Exchange (ETDEWEB)

    Li, Jie, E-mail: leejay1986@163.com; Zhang, Jian

    2014-11-07

    In many applications, the shape of a droplet may be assumed to be an oblate spheroid. A theoretical study is conducted on the evaporation of an oblate spheroidal droplet under forced convection conditions. Closed-form analytical expressions of the mass evaporation rate for an oblate spheroid are derived, in the regime of controlled mass-transfer and heat-transfer, respectively. The variation of droplet size during the evaporation process is presented in the regime of shrinking dynamic model. Comparing with the droplets having the same surface area, an increase in the aspect ratio enhances the mass evaporation rate and prolongs the burnout time. - Highlights: • Fully algebraic solutions for the spheroidal droplet evaporation rate is obtained. • We examine the effect of aspect ratio on the droplet evaporation. • We propose a calculation method of Nusselt number for spheroidal droplet.

  6. Study of turbulent natural-circulation flow and low-Prandtl-number forced-convection flow

    International Nuclear Information System (INIS)

    Chung, K.S.; Thompson, D.H.

    1980-01-01

    Calculational methods and results are discussed for the coupled energy and momentum equations of turbulent natural circulation flow and low Prandtl number forced convection flow. The objective of this paper is to develop a calculational method for the study of the thermal-hydraulic behavior of coolant flowing in a liquid metal fast breeder reactor channel under natural circulation conditions. The two-equation turbulence model is used to evaluate the turbulent momentum transport property. Because the analogy between momentum transfer and heat transfer does not generally hold for low Prandtl number fluid and natural circulation flow conditions, the turbulent thermal conductivity is calculated independently using equations similar to the two-equation turbulence model. The numerical technique used in the calculation is the finite element method

  7. Thermally developing forced convection and the corresponding thermal stresses in a porous plate channel

    Institute of Scientific and Technical Information of China (English)

    YANG Xiao; LIU Xuemei

    2007-01-01

    Based on the Darcy fluid model, by considering the effects of viscous dissipation due to the interaction between solid skeleton and pore fluid flow and thermal conduction in the direction of the fluid flow, the thermally developing forced convection of the local thermal equili- brium and the corresponding thermal stresses in a semi- infmite saturated porous plate channel are investigated in this paper. The expressions of temperature, local Nusselt number and corresponding thermal stresses are obtained by means of the Fourier series, and the distributions of the same are also shown. Furthermore, influences of the Péclet number (Pe) and Brinkman number (Br) on temperature, Nusselt number (Nu) and thermal stress are revealed numerically.

  8. A theoretical study of the spheroidal droplet evaporation in forced convection

    International Nuclear Information System (INIS)

    Li, Jie; Zhang, Jian

    2014-01-01

    In many applications, the shape of a droplet may be assumed to be an oblate spheroid. A theoretical study is conducted on the evaporation of an oblate spheroidal droplet under forced convection conditions. Closed-form analytical expressions of the mass evaporation rate for an oblate spheroid are derived, in the regime of controlled mass-transfer and heat-transfer, respectively. The variation of droplet size during the evaporation process is presented in the regime of shrinking dynamic model. Comparing with the droplets having the same surface area, an increase in the aspect ratio enhances the mass evaporation rate and prolongs the burnout time. - Highlights: • Fully algebraic solutions for the spheroidal droplet evaporation rate is obtained. • We examine the effect of aspect ratio on the droplet evaporation. • We propose a calculation method of Nusselt number for spheroidal droplet

  9. A numerical investigation of laminar forced convection in a solar collector with non-circular duct

    Science.gov (United States)

    Janusz Teleszewski, Tomasz

    2017-11-01

    This paper presents a two-dimensional numerical study to investigate laminar flow in a flat plate solar collector with non-circular duct (regular polygonal, elliptical, and Cassini oval shape) featuring forced convection with constant axial wall heat flux and constant peripheral wall temperature (H1 condition). Applying the velocity profile obtained for the duct laminar flow, the energy equation was solved exactly for the constant wall heat flux using the Boundary Element Method (BEM). Poiseuille and Nusselt numbers were obtained for flows having a different number of geometrical factors. The results are presented and discussed in the form of tables and graphs. The area goodness factor and volume goodness factor are calculated. The predicted correlations for Poiseuille and Nusselt numbers may be a very useful resource for the design and optimization of solar collectors with non-circular ducts.

  10. Performance of a Forced-Convection Greenhouse Dryer for Fish Drying

    Directory of Open Access Journals (Sweden)

    Martunis Martunis

    2013-04-01

    Full Text Available ABSTRACT. This research present experimental performance of a forced convection greenhouse dryer for drying of fish. The greenhouse dryer was installed at Aceh province, Indonesia. It has a concrete floor with the area of 6×4 m2. The roof of dryer is built in semi-cylindrical shape and covered with transparent polycarbonate sheets. Two axial flow fans powered by a 50-watt solar cell module was used to generate forced convection for ventilating the dryer.To investigate its performance, the dryer was used to dry two batches of fish. The Results showed that to dry 50 kg fish with initial moisture 68 % required 11 hours. Incontrast, to dry the same amount of fish using sun drying take a time about 2 days. The air temperature inside greenhouse dryer at noon in the clear day was 45-55°C. Kinerja Pengering Rumah Kaca Dengan Metode Konveksi Paksa Untuk Pengeringan Ikan ABSTRAK. Penelitian ini memperlihatkan hasil percobaan terhadap kinerja pengering rumah kaca dengan metode konveksi udara secara paksa pada pengeringan ikan. Penelitian pengering rumah kaca ini dilakukan di Propinsi Aceh, Indonesia. Pengering ini berlantaikan beton dengan luas sebesar 6x4 m2. .Atapnya dibuat berbentuk semi-selinder dan ditutup dengan lembaran plastik transparan berbahan polikarbonat. Dua buah kipas dengan aliran udara secara aksial dipasang dengan sumber daya berasal dari panel surya sebesar 50 Watt dan dipakai untuk menghasilkan konveksi udara paksa pada ventilasi pengering. Untuk menginvestigasi kinerja rumah kaca ini, pengering ini digunakan untuk mengeringkan dua tumpukan ikan. Hasilnya menunjukkan bahwa untuk mengeringkan sebanyak 50 kg ikan dengan kadar air awalnya sebesar 68% membutuhkan waktu selama 11 jam. Sebaliknya, dengan menggunakan sinar matahari secara langsung, untuk mengeringkan ikan dengan jumlah yang sama, maka waktu yang dibutuhkan lebih lama yaitu sekitar 2 hari. Suhu udara di dalam rumah pengering tepat pada siang hari yang cerah berkisar antara 45

  11. Computational modelling of internally cooled wet (ICW) electrodes for radiofrequency ablation: impact of rehydration, thermal convection and electrical conductivity.

    Science.gov (United States)

    Trujillo, Macarena; Bon, Jose; Berjano, Enrique

    2017-09-01

    (1) To analyse rehydration, thermal convection and increased electrical conductivity as the three phenomena which distinguish the performance of internally cooled electrodes (IC) and internally cooled wet (ICW) electrodes during radiofrequency ablation (RFA), (2) Implement a RFA computer model with an ICW which includes these phenomena and (3) Assess their relative influence on the thermal and electrical tissue response and on the coagulation zone size. A 12-min RFA in liver was modelled using an ICW electrode (17 G, 3 cm tip) by an impedance-control pulsing protocol with a constant current of 1.5 A. A model of an IC electrode was used to compare the ICW electrode performance and the computational results with the experimental results. Rehydration and increased electrical conductivity were responsible for an increase in coagulation zone size and a delay (or absence) in the occurrence of abrupt increases in electrical impedance (roll-off). While the increased electrical conductivity had a remarkable effect on enlarging the coagulation zone (an increase of 0.74 cm for differences in electrical conductivity of 0.31 S/m), rehydration considerably affected the delay in roll-off, which, in fact, was absent with a sufficiently high rehydration level. In contrast, thermal convection had an insignificant effect for the flow rates considered (0.05 and 1 mL/min). Computer results suggest that rehydration and increased electrical conductivity were mainly responsible for the absence of roll-off and increased size of the coagulation zone, respectively, and in combination allow the thermal and electrical performance of ICW electrodes to be modelled during RFA.

  12. NUMERICAL STUDY OF DEVELOPING LAMINAR FORCED CONVECTION OF A NANOFLUID HEAT TRANSFER IN AN ANNULAR HORIZONTAL PIPE

    Directory of Open Access Journals (Sweden)

    M BENKHEDDA

    2014-12-01

    Full Text Available This study reports numerical simulation for 3D laminar forced convection of a nanofluid flow in horizontal annulus with constant heat flux at the outer cylinder will the inner cylinder is considered adiabatic. The numerical model is carried out by solving the governing equation of continuity, momentum and energy using take account for thee finite volume method, with the assistance of SIMPLER algorithm. The results shows that for the Reynolds numbers and Prandtl fixed, the dimensionless velocity profile for the laminar forced convection of a nanofluid consisting of water does not vary with the volume concentration of nanoparticles while the effect of the concentration of nanoparticles on the temperature of the mass is significant nanofluid. These results are consistent with those found in the literature. In general the use of nanofluid with a volume concentration of nanoparticles causes a increase in the coefficient of heat transfer by convection.

  13. A numerical investigation of the effect of ambient conditions on natural convection cooling of electronics

    DEFF Research Database (Denmark)

    Shojaee Nasirabadi, Parizad; Hattel, Jesper Henri

    2017-01-01

    Thermal management is a serious concern in electronic industry. It is important to understand the effects of ambient conditions on cooling of electronics. In this work, the effect of ambient conditions on the thermophysical properties of humid air is estimated in five cities (Copenhagen, Mashhad...

  14. Safety aspects of forced flow cooldown transients in modular high temperature gas-cooled reactors

    International Nuclear Information System (INIS)

    Kroeger, P.G.

    1992-01-01

    During some of the design basis accidents in Modular High Temperature Gas Cooled Reactors (MHTGRs) the main Heat Transport System (HTS) and the Shutdown Cooling System (SCS), are assumed to have failed. Decay heat is then removed by the passive Reactor Cavity Cooling System (RCCS) only. If either forced flow cooling system becomes available during such a transient, its restart could significantly reduce the down-time. This paper uses the THATCH code to examine whether such restart, during a period of elevated core temperatures, can be accomplished within safe limits for fuel and metal component temperatures. If the reactor is scrammed, either system can apparently be restarted at any time, without exceeding any safe limits. However, under unscrammed conditions a restart of forced cooling can lead to recriticality, with fuel and metal temperatures significantly exceeding the safety limits

  15. Experimental investigation of forced-convection in a finned rhombic tube of the flat-plate solar collectors

    DEFF Research Database (Denmark)

    Taherian, Hessam; Yazdanshenas, Eshagh

    2006-01-01

    Due to scarcity of literature on forced-convection heat transfer in a solar collector with rhombic cross-section absorbing tubes, a series of experiments was arranged and conducted to determine heat transfer coefficient. In this study, a typical rhombic cross-section finned tube of flat...

  16. Assessment of thermal conductivity, viscosity and specific heat of nanofluids in single phase laminar indernal forced convection

    NARCIS (Netherlands)

    Vanapalli, Srinivas; ter Brake, Hermanus J.M.

    2013-01-01

    Nanofluids are considered for improving the heat exchange in forced convective flow. In literature, the benefit of nanofluids compared to the corresponding base fluid is represented by several figures-of-merit in which the heat transfer benefit and the cost of pumping the fluid are considered. These

  17. Dynamical and statistical phenomena of circulation and heat transfer in periodically forced rotating turbulent Rayleigh-Bénard convection

    NARCIS (Netherlands)

    Sterl, S.H.; Li, H.M.; Zhong, J.Q.

    2016-01-01

    In this paper, we present results from an experimental study into turbulent Rayleigh-Bénard convection forced externally by periodically modulated unidirectional rotation rates. We find that the azimuthal rotation velocity θ(t) and thermal amplitude δ(t) of the large-scale circulation (LSC) are

  18. Fastbus non-forced air-cooling tests

    International Nuclear Information System (INIS)

    Downing, R.W.

    1981-07-01

    Tests were conducted on a closed box with all walls at room temperature with heat test units positioned between the plates with small cardboard spacers. The rear of the test unit was taped closed, and no external air was allowed to flow through the box. Outside wall temperature was monitored for all tests. Tests were performed to test a possible method of conducting heat away from high powered I.C.'s in a closed chamber. The effect of a brass strip attached to the top of the I.C. and making mechanical contact with the wall of the box is tested. Tests show that some heatsinking technique is needed for I.C.'s of more than 3/4 watt dissipation. It is concluded that conventional air-cooled printed circuit boards can be effectively cooled by simply installing them in a cool-walled box. The chassis construction could also consist of card slots divided by water filled plates similar to refrigeration walls. Problems relating to wire-wrap modules are addressed

  19. Forcings and feedbacks on convection in the 2010 Pakistan flood: Modeling extreme precipitation with interactive large-scale ascent

    Science.gov (United States)

    Nie, Ji; Shaevitz, Daniel A.; Sobel, Adam H.

    2016-09-01

    Extratropical extreme precipitation events are usually associated with large-scale flow disturbances, strong ascent, and large latent heat release. The causal relationships between these factors are often not obvious, however, the roles of different physical processes in producing the extreme precipitation event can be difficult to disentangle. Here we examine the large-scale forcings and convective heating feedback in the precipitation events, which caused the 2010 Pakistan flood within the Column Quasi-Geostrophic framework. A cloud-revolving model (CRM) is forced with large-scale forcings (other than large-scale vertical motion) computed from the quasi-geostrophic omega equation using input data from a reanalysis data set, and the large-scale vertical motion is diagnosed interactively with the simulated convection. Numerical results show that the positive feedback of convective heating to large-scale dynamics is essential in amplifying the precipitation intensity to the observed values. Orographic lifting is the most important dynamic forcing in both events, while differential potential vorticity advection also contributes to the triggering of the first event. Horizontal moisture advection modulates the extreme events mainly by setting the environmental humidity, which modulates the amplitude of the convection's response to the dynamic forcings. When the CRM is replaced by either a single-column model (SCM) with parameterized convection or a dry model with a reduced effective static stability, the model results show substantial discrepancies compared with reanalysis data. The reasons for these discrepancies are examined, and the implications for global models and theoretical models are discussed.

  20. Convective Heat Transfer with and without Film Cooling in High Temperature, Fuel Rich and Lean Environments

    Science.gov (United States)

    2014-09-01

    Figure 3.2: Control panel used in experimental facility the controller throttles a solenoid valve until the desired flow rate is achieved. Finally...test objectives. Namely, quartz windows enabled visual spectrum images or laser diagnostics of reacting film cooling layers. Additionally, a sapphire...rate by a solenoid which throttled a valve restrict the flow appropriately. To measure the flow, the controllers pass the bulk flow through a

  1. Preliminary experimentally-validated forced and mixed convection computational simulations of the Rotatable Buoyancy Tunnel

    International Nuclear Information System (INIS)

    Clifford, Corey E.; Kimber, Mark L.

    2015-01-01

    Although computational fluid dynamics (CFD) has not been directly utilized to perform safety analyses of nuclear reactors in the United States, several vendors are considering adopting commercial numerical packages for current and future projects. To ensure the accuracy of these computational models, it is imperative to validate the assumptions and approximations built into commercial CFD codes against physical data from flows analogous to those in modern nuclear reactors. To this end, researchers at Utah State University (USU) have constructed the Rotatable Buoyancy Tunnel (RoBuT) test facility, which is designed to provide flow and thermal validation data for CFD simulations of forced and mixed convection scenarios. In order to evaluate the ability of current CFD codes to capture the complex physics associated with these types of flows, a computational model of the RoBuT test facility is created using the ANSYS Fluent commercial CFD code. The numerical RoBuT model is analyzed at identical conditions to several experimental trials undertaken at USU. Each experiment is reconstructed numerically and evaluated with the second-order Reynolds stress model (RSM). Two different thermal boundary conditions at the heated surface of the RoBuT test section are investigated: constant temperature (isothermal) and constant surface heat flux (isoflux). Additionally, the fluid velocity at the inlet of the test section is varied in an effort to modify the relative importance of natural convection heat transfer from the heated wall of the RoBuT. Mean velocity, both in the streamwise and transverse directions, as well as components of the Reynolds stress tensor at three points downstream of the RoBuT test section inlet are compared to results obtained from experimental trials. Early computational results obtained from this research initiative are in good agreement with experimental data obtained from the RoBuT facility and both the experimental data and numerical method can be used

  2. A numerical model of the shortbread baking process in a forced convection oven

    International Nuclear Information System (INIS)

    Kokolj, Uroš; Škerget, Leopold; Ravnik, Jure

    2017-01-01

    Highlights: • The evaporation of water had a significant effect on the temperature field. • The numerical model associated the grade of browning with the temperature field. • The results of the numerical and experimental grade of browning are comparable. • The difference between the measured and simulated temperature at the oven was 2.8 K. - Abstract: The objective of all manufacturers and users of ovens is to achieve uniform browning of various baked foods. In recent years, manufacturers have found it difficult to achieve this, due to the rapid appearance of new trends and due to progressively shorter development times. In this paper, we present the development and validation of a time-dependent 3D computational fluid dynamics model, which enables the numerical prediction of the baking performance and grade of browning of a forced convection oven. Flow and heat transfer of hot air in an oven, where a round heating element and a fan are both operating, are simulated. Radiative and convective heat transfer is taken into account. We found, that it is necessary to include water evaporation in the model. The numerical model was validated by performing experimental measurements of temperature and by performing baking tests of shortbread. After baking, the grade of browning was measured for the shortbread. To determine the grade of browning, the method of identification of colour contrasts was used, based on the colour space CIE L"∗a"∗b. Based on the results, we proposed a linear model, which enabled the prediction of the grade of browning based on the results of the fluid dynamics simulation.

  3. The diurnal interaction between convection and peninsular-scale forcing over South Florida

    Science.gov (United States)

    Cooper, H. J.; Simpson, J.; Garstang, M.

    1982-01-01

    One of the outstanding problems in modern meterology is that of describing in detail the manner in which larger scales of motion interact with, influence and are influenced by successively smaller scales of motion. The present investigation is concerned with a study of the diurnal evolution of convection, the interaction between the peninsular-scale convergence and convection, and the role of the feedback produced by the cloud-scale downdrafts in the maintenance of the convection. Attention is given to the analysis, the diurnal cycle of the network area-averaged divergence, convective-scale divergence, convective mass transports, and the peninsular scale divergence. The links established in the investigation between the large scale (peninsular), the mesoscale (network), and the convective scale (cloud) are found to be of fundamental importance to the understanding of the initiation, maintenance, and decay of deep precipitating convection and to its theoretical parameterization.

  4. The effect of ultrasound irradiation on the convective heat transfer rate during immersion cooling of a stationary sphere.

    Science.gov (United States)

    Kiani, Hossein; Sun, Da-Wen; Zhang, Zhihang

    2012-11-01

    were the main cause of heating effect. The results showed that closer distances to the transducer surface showed higher cooling rates. On the other hand, despite having a bigger distance from the transducer, when the sphere was located close to the gas-liquid interface the enhancement factor of heat transfer was higher. Ultrasound irradiation showed promising effect for the enhancement of convective heat transfer rate during immersion cooling. More investigations are required to demonstrate the behavior of ultrasound assisted heat transfer and resolve the proper way of the application of ultrasound to assist the cooling and/or freezing processes. Copyright © 2012 Elsevier B.V. All rights reserved.

  5. Comparison of radiant and convective cooling of office room: effect of workstation layout

    DEFF Research Database (Denmark)

    Bolashikov, Zhecho Dimitrov; Melikov, Arsen Krikor; Rezgals, Lauris

    2014-01-01

    and compared. The room was furnished with two workstations, two laptops and two thermal manikins resembling occupants. Two heat load levels, design (65 W/m2) and usual (39 W/m2), were generated by adding heat from warm panels simulating solar radiation. Two set-ups were studied: occupants sitting......The impact of heat source location (room layout) on the thermal environment generated in a double office room with four cooling ventilation systems - overhead ventilation, chilled ceiling with overhead ventilation, active chilled beam and active chilled beam with radiant panels was measured...

  6. Thermal Conditions in a Simulated Office Environment with Convective and Radiant Cooling Systems

    DEFF Research Database (Denmark)

    Mustakallio, Panu; Bolashikov, Zhecho Dimitrov; Kostov, Kalin

    2013-01-01

    velocity and turbulent intensity were measured and draft rate levels calculated in the room. Manikin-based equivalent temperature (MBET) was determined by two thermal manikins to identify the impact of the local thermal conditions generated by the studied systems on occupants’ thermal comfort. The results......The thermal conditions in a two person office room were measured with four air conditioning systems: chilled beam (CB), chilled beam with radiant panel (CBR), chilled ceiling with ceiling installed mixing ventilation (CCMV) and four desk partition mounted local radiant cooling panels with mixing...

  7. Large scale three-dimensional topology optimisation of heat sinks cooled by natural convection

    DEFF Research Database (Denmark)

    Alexandersen, Joe; Sigmund, Ole; Aage, Niels

    2016-01-01

    the Bousinessq approximation. The fully coupled non-linear multiphysics system is solved using stabilised trilinear equal-order finite elements in a parallel framework allowing for the optimisation of large scale problems with order of 20-330 million state degrees of freedom. The flow is assumed to be laminar...... topologies verify prior conclusions regarding fin length/thickness ratios and Biot numbers, but also indicate that carefully tailored and complex geometries may improve cooling behaviour considerably compared to simple heat fin geometries. (C) 2016 Elsevier Ltd. All rights reserved....

  8. Conceptual Design of Forced Convection Molten Salt Heat Transfer Testing Loop

    Energy Technology Data Exchange (ETDEWEB)

    Manohar S. Sohal; Piyush Sabharwall; Pattrick Calderoni; Alan K. Wertsching; S. Brandon Grover

    2010-09-01

    This report develops a proposal to design and construct a forced convection test loop. A detailed test plan will then be conducted to obtain data on heat transfer, thermodynamic, and corrosion characteristics of the molten salts and fluid-solid interaction. In particular, this report outlines an experimental research and development test plan. The most important initial requirement for heat transfer test of molten salt systems is the establishment of reference coolant materials to use in the experiments. An earlier report produced within the same project highlighted how thermophysical properties of the materials that directly impact the heat transfer behavior are strongly correlated to the composition and impurities concentration of the melt. It is therefore essential to establish laboratory techniques that can measure the melt composition, and to develop purification methods that would allow the production of large quantities of coolant with the desired purity. A companion report describes the options available to reach such objectives. In particular, that report outlines an experimental research and development test plan that would include following steps: •Molten Salts: The candidate molten salts for investigation will be selected. •Materials of Construction: Materials of construction for the test loop, heat exchangers, and fluid-solid corrosion tests in the test loop will also be selected. •Scaling Analysis: Scaling analysis to design the test loop will be performed. •Test Plan: A comprehensive test plan to include all the tests that are being planned in the short and long term time frame will be developed. •Design the Test Loop: The forced convection test loop will be designed including extensive mechanical design, instrument selection, data acquisition system, safety requirements, and related precautionary measures. •Fabricate the Test Loop. •Perform the Tests. •Uncertainty Analysis: As a part of the data collection, uncertainty analysis will

  9. The sensitivity of tropical convective precipitation to the direct radiative forcings of black carbon aerosols emitted from major regions

    Directory of Open Access Journals (Sweden)

    C. Wang

    2009-10-01

    Full Text Available Previous works have suggested that the direct radiative forcing (DRF of black carbon (BC aerosols are able to force a significant change in tropical convective precipitation ranging from the Pacific and Indian Ocean to the Atlantic Ocean. In this in-depth analysis, the sensitivity of this modeled effect of BC on tropical convective precipitation to the emissions of BC from 5 major regions of the world has been examined. In a zonal mean base, the effect of BC on tropical convective precipitation is a result of a displacement of ITCZ toward the forcing (warming hemisphere. However, a substantial difference exists in this effect associated with BC over different continents. The BC effect on convective precipitation over the tropical Pacific Ocean is found to be most sensitive to the emissions from Central and North America due to a persistent presence of BC aerosols from these two regions in the lowermost troposphere over the Eastern Pacific. The BC effect over the tropical Indian and Atlantic Ocean is most sensitive to the emissions from South as well as East Asia and Africa, respectively. Interestingly, the summation of these individual effects associated with emissions from various regions mostly exceeds their actual combined effect as shown in the model run driven by the global BC emissions, so that they must offset each other in certain locations and a nonlinearity of this type of effect is thus defined. It is known that anthropogenic aerosols contain many scattering-dominant constituents that might exert an effect opposite to that of absorbing BC. The combined aerosol forcing is thus likely differing from the BC-only one. Nevertheless, this study along with others of its kind that isolates the DRF of BC from other forcings provides an insight of the potentially important climate response to anthropogenic forcings particularly related to the unique particulate solar absorption.

  10. Thermo-fluid analysis of water cooled research reactors in natural convection

    International Nuclear Information System (INIS)

    Veloso, Maria Auxiliadora Fortini

    2004-01-01

    The STHIRP-1 computer program, which fundamentals are described in this work, uses the principles of the subchannels analysis and has the capacity to simulate, under steady state and transient conditions, the thermal and hydraulic phenomena which occur inside the core of a water-refrigerated research reactor under a natural convection regime. The models and empirical correlations necessary to describe the flow phenomena which can not be described by theoretical relations were selected according to the characteristics of the reactor operation. Although the primary objective is the calculation of research reactors, the formulation used to describe the fluid flow and the thermal conduction in the heater elements is sufficiently generalized to extend the use of the program for applications in power reactors and other thermal systems with the same features represented by the program formulations. To demonstrate the analytical capacity of STHIRP-l, there were made comparisons between the results calculated and measured in the research reactor TRIGA IPR-R1 of CDTN/CNEN. The comparisons indicate that the program reproduces the experimental data with good precision. Nevertheless, in the future there must be used more consistent experimental data to corroborate the validation of the program. (author)

  11. Effect of Thermophysical Properties on Coupled Heat and Mass Transfer in Porous Material during Forced Convective Drying

    Directory of Open Access Journals (Sweden)

    Wei Cai

    2014-06-01

    Full Text Available The convective drying kinetics of porous medium was investigated numerically. A mathematical model for forced convective drying was established to estimate the evolution of moisture content and temperature inside multilayered porous medium. The set of coupled partial differential equations with the specified boundary and initial conditions were solved numerically using a MATLAB code. An experimental setup of convective drying had been constructed and validated the theoretical model. The temperature and moisture content of the potato samples were dynamically measured and recorded during the drying process. Results indicate that thermal diffusion coefficient has significant positive impact on temperature distribution and mass diffusion coefficient might directly affect the moisture content distribution. Soret effect has a significant impact on heat flux and temperature distribution in the presence of large temperature gradient.

  12. Thermal convection in a closed cavity in zero-gravity space conditions with stationary magnetic forces

    International Nuclear Information System (INIS)

    Lyubimova, T; Mailfert, A

    2013-01-01

    The paper deals with the investigation of thermo-magnetic convection in a paramagnetic liquid subjected to a non-uniform magnetic field in weightlessness conditions. Indeed, in zero-g space conditions such as realized in International Space Station (ISS), or in artificial satellite, or in free-flight space vessels, the classical thermo-gravitational convection in fluid disappears. In any cases, it may be useful to restore the convective thermal exchange inside fluids such as liquid oxygen. In this paper, the restoration of heat exchange by the way of creation of magnetic convection is numerically studied.

  13. Simulation of natural convection cooling phenomena for research reactors using the code PARET

    International Nuclear Information System (INIS)

    Hainoun, A.; Al-Habit, E.

    2006-01-01

    This study deals with testing the capacity of the code PARET to simulate natural circulation phenomena under different boundary conditions in addition to assessment of some new options related to simulation of control rod movement and the reactivity effect of thermal expansion fuel elements. the experiments of the simple thermal hydraulic loop of Missouri University about natural circulation phenomena in narrow parallel channel were used to validate the code. The results indicate good agreements regarding the evolution of coolant velocity and clad temperature. In particular the heat transfer coefficient of natural convection has been calculated in good agreement with the experiment. On the other hand, the core of MNSR reactor has been modelled to stimulate the reactor dynamic behaviour under natural circulation condition for different initial power level. The observed oscillations during the initial phase vanish gradually with passing time. In this context three experiment of step reactivity insertion were calculated using two different options of boundary conditions, either using initial velocity or pressure drop along the core. The results indicate good agreement with the experiments regarding the evolution of relative power. The validations included also sensitivity analysis against some important parameters like initial velocity and radial distance of fuel rod. The new option for simulation of control rod movement was also tested. For this purpose the MNSR experiment of all control rod withdraw was selected. This means control rod velocity was estimated using experimental measurement. The simulation result of relative power evolution shows good agreement with the experiment during the first phase of the transient. However, an increased deviation is observed in the following phase due to the effect of closed hydrodynamics loop, which can be modelled with the code PARET. (Authors)

  14. Zircaloy PWR fuel cladding deformation tests under mainly convective cooling conditions

    International Nuclear Information System (INIS)

    Hindle, E.D.; Mann, C.A.

    1980-01-01

    In a loss-of-coolant accident the temperature of the cladding of the fuel rods may rise to levels (650-810 0 C) where the ductility of Zircaloy is high (approximately 80%). The net outward pressure which will obtain if the coolant pressure falls to a small fraction of its normal working value produces stresses in the cladding which can result in large strain through secondary creep. An earlier study of the deformation of specimens of PWR Zircaloy cladding tubing 450 mm long under internal pressure had shown that strains of over 50% could be produced over considerable lengths (greater than twenty tube diameters). Extended deformation of this sort might be unacceptable if it occurred in a fuel element. The previous tests had been carried out under conditions of uniform radiative heat loss, and the work reported here extends the study to conditions of mainly convective heat loss believed to be more representative of a fuel element following a loss of coolant. Zircaloy-4 cladding specimens 450 mm long were filled with alumina pellets and tested at temperatures between 630 and 845 0 C in flowing steam at atmospheric pressure. Internal test pressures were in the range 2.9-11.0 MPa (400-1600 1b/in 2 ). Maximum strains were observed of the same magnitude as those seen in the previous tests, but the shape of the deformation differed; in these tests the deformation progressively increased in the direction of the steam flow. These results are compared with those from multi-rod tests elsewhere, and it is suggested that heat transfer has a dominant effect in determining deformation. The implications for the behaviour of fuel elements in a loss-of-coolant accident are outlined. (author)

  15. Forced Convection Heat Transfer of a sphere in Packed Bed Arrangement

    International Nuclear Information System (INIS)

    Lee, Dong-Young; Chung, Bum-Jin

    2016-01-01

    This paper analysis and discuss the forced convective heat transfer from heated single sphere, which is buried in unheated packed bed, depending on Re d with porosity. The present work determines the test matrix for the packed bed experiment. And this study discuss difference of heat transfer according to the location of heated sphere and compared heated bed with heated sphere in packed bed and compared FCC (Face Centered Cubic), HCP (Hexagonal Closed Packed) structured packed bed with random packed. This paper is to discuss and make the plan to experiment the heat transfer for depending on location of heated single sphere in unheated packed bed, to compare single sphere in packed bed with heated packed bed and to compare the structured packed bed with random packed bed. The Nu d increase as heated single sphere is close to the wall and bottom because of increasing porosity and enhancing eddy motion respectively. The existing experiment of heated sphere in packed bed do not consider the preheating effect which decrease heat transfer on downstream. The heat transfer rate of structured packed bed is different from random packed bed because of unsteady flow in random packed bed. In this study, mass transfer experiments will replace heat transfer experiments based on analogy concept. An electroplating system is adopted using limiting current technique

  16. Forced convective heat transfer in boundary layer flow of Sisko fluid over a nonlinear stretching sheet.

    Science.gov (United States)

    Munir, Asif; Shahzad, Azeem; Khan, Masood

    2014-01-01

    The major focus of this article is to analyze the forced convective heat transfer in a steady boundary layer flow of Sisko fluid over a nonlinear stretching sheet. Two cases are studied, namely (i) the sheet with variable temperature (PST case) and (ii) the sheet with variable heat flux (PHF case). The heat transfer aspects are investigated for both integer and non-integer values of the power-law index. The governing partial differential equations are reduced to a system of nonlinear ordinary differential equations using appropriate similarity variables and solved numerically. The numerical results are obtained by the shooting method using adaptive Runge Kutta method with Broyden's method in the domain[Formula: see text]. The numerical results for the temperature field are found to be strongly dependent upon the power-law index, stretching parameter, wall temperature parameter, material parameter of the Sisko fluid and Prandtl number. In addition, the local Nusselt number versus wall temperature parameter is also graphed and tabulated for different values of pertaining parameters. Further, numerical results are validated by comparison with exact solutions as well as previously published results in the literature.

  17. Desorption isotherms, drying characteristics and qualities of glace tropical fruits undergoing forced convection solar drying

    Energy Technology Data Exchange (ETDEWEB)

    Jamradloedluk, Jindaporn; Wiriyaumpaiwong, Songchai [Mahasarakham Univ. Khamriang, Kantarawichai, Mahasarakham (Thailand)

    2008-07-01

    Solar energy, a form of sustainable energy, has a great potential for a wide variety of applications because it is abundant and accessible, especially for countries located in the tropical region. Drying process is one of the prominent techniques for utilization of solar energy. This research work proposes a forced convection solar drying of osmotically pretreated fruits viz. mango, guava, and pineapple. The fruit cubes with a dimension of 1cm x 1cm x 1cm were immersed in 35% w./w. sucrose solution prior to the drying process. Drying kinetics, color and hardness of the final products obtained from solar drying were investigated and compared with those obtained from open air-sun drying. Desorption isotherms of the osmosed fruits were also examined and five mathematical models were used to fit the desorption curves. Experimental results revealed that solar drying provided higher drying rate than natural sun drying. Color of glace fruit processed by solar drying was more intense, indicated by lower value of lightness and higher value of yellowness, than that processed by sun drying. Hardness of the products dehydrated by both drying methods, however, was not significantly different (p>0.05). Validation of the mathematical models developed showed that the GAB model was most effective for describing desorption isotherms of osmotically pretreated mango and pineapple whereas Peleg's model was most effective for describing desorption isotherms of osmotically pretreated guava. (orig.)

  18. Experimental and numerical studies on the treatment of wet astronaut trash by forced-convection drying

    Science.gov (United States)

    Arquiza, J. M. R. Apollo; Morrow, Robert; Remiker, Ross; Hunter, Jean B.

    2017-09-01

    During long-term space missions, astronauts generate wet trash, including food containers with uneaten portions, moist hygiene wipes and wet paper towels. This waste produces two problems: the loss of water and the generation of odors and health hazards by microbial growth. These problems are solved by a closed-loop, forced-convection, heat-pump drying system which stops microbial activity by both pasteurization and desiccation, and recovers water in a gravity-independent porous media condensing heat exchanger. A transient, pseudo-homogeneous continuum model for the drying of wet ersatz trash was formulated for this system. The model is based on the conservation equations for energy and moisture applied to the air and solid phases and includes the unique trash characteristic of having both dry and wet solids. Experimentally determined heat and mass transfer coefficients, together with the moisture sorption equilibrium relationship for the wet material are used in the model. The resulting system of differential equations is solved by the finite-volume method as implemented by the commercial software COMSOL. Model simulations agreed well with experimental data under certain conditions. The validated model will be used in the optimization of the entire closed-loop system consisting of fan, air heater, dryer vessel, heat-pump condenser, and heat-recovery modules.

  19. Constitutive correlations for wire-wrapped subchannel analysis under forced and mixed convection conditions. Part 1

    International Nuclear Information System (INIS)

    Cheng, S.K.; Todreas, N.E.

    1984-08-01

    A simple subchannel analysis method based on the ENERGY series of codes, ENERGY-IV, has been established for predicting the temperature field in a single isolated wire-wrapped Liquid Metal Fast Breeder Reactor (LMFBR) subassembly under steady state forced and mixed convection conditions. The ENERGY-IV is a totally empirical code employed for fast running purposes and requires well calibrated lead length averaged input parameters to achieve satisfactory predictions. These input parameters were identified to be the inlet flow split parameters, the subchannel friction factors, the interchannel mixing parameters, the conduction shape factor, and the transverse velocity at the edge gap. Experiments were performed in a 37-pin wire-wrapped rod bundle with a geometry between that of a typical LMFBR fuel subassembly and blanket subassembly for filling the gap in the available data base for the input parameters. The isokinetic extraction method for measuring subchannel velocity, the pitot-static probe for measuring pressure drop, and the salt tracer injection method for estimating the interchannel mixing, were used in these experiments

  20. Numerical investigation of forced convection heat transfer in unsteady flow past a row of square cylinders

    International Nuclear Information System (INIS)

    Chatterjee, Dipankar; Biswas, Gautam; Amiroudine, Sakir

    2009-01-01

    This paper presents the unsteady laminar forced convection heat transfer from a row of five isothermal square cylinders placed in a side-by-side arrangement at a Reynolds number of 150. The numerical simulations are performed using a finite volume code based on the PISO algorithm in a collocated grid system. Special attention is paid to investigate the effect of the spacing between the cylinders on the overall transport processes for the separation ratios (spacing to size ratio) between 0.2 and 10. No significant interaction between the wakes is observed for spacing greater than four times the diameter at this Reynolds number. However, at smaller spacing, the wakes interact in a complicated manner resulting different thermo-hydrodynamic regimes. The vortex structures and isotherm patterns obtained are systematically presented and discussed for different separation ratios. In addition, the mean and instantaneous drag and lift coefficients, mean and local Nusselt number and Strouhal number are determined and discussed for various separation ratios. A new correlation is derived for mean Nusselt number as a function of separation ratio for such flows.

  1. Forced Convection Heat Transfer of a sphere in Packed Bed Arrangement

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Dong-Young; Chung, Bum-Jin [Kyung Hee University, Yongin (Korea, Republic of)

    2016-10-15

    This paper analysis and discuss the forced convective heat transfer from heated single sphere, which is buried in unheated packed bed, depending on Re{sub d} with porosity. The present work determines the test matrix for the packed bed experiment. And this study discuss difference of heat transfer according to the location of heated sphere and compared heated bed with heated sphere in packed bed and compared FCC (Face Centered Cubic), HCP (Hexagonal Closed Packed) structured packed bed with random packed. This paper is to discuss and make the plan to experiment the heat transfer for depending on location of heated single sphere in unheated packed bed, to compare single sphere in packed bed with heated packed bed and to compare the structured packed bed with random packed bed. The Nu{sub d} increase as heated single sphere is close to the wall and bottom because of increasing porosity and enhancing eddy motion respectively. The existing experiment of heated sphere in packed bed do not consider the preheating effect which decrease heat transfer on downstream. The heat transfer rate of structured packed bed is different from random packed bed because of unsteady flow in random packed bed. In this study, mass transfer experiments will replace heat transfer experiments based on analogy concept. An electroplating system is adopted using limiting current technique.

  2. A forced convective heat transfer model for two-phase hydrogen systems

    International Nuclear Information System (INIS)

    Pasch, J.; Anghaie, S.

    2007-01-01

    A consistent event in the use of hydrogen in nuclear thermal propulsion is film boiling, in which the wall heat is so large that liquid can not exist at the wall. Instead, vapor interfaces with the wall and liquid flows in the core of the duct. To better understand heat transfer under these conditions, a select set of hydrogen test data from these conditions are analyzed. This paper presents the results of an extensive literature search for film boiling heat transfer models. A representative cross-section of these models is then applied to the data. The heat transfer coefficient data were found difficult to predict and highly dependent upon the flow regime. Pre-critical heat flux correlations completely fail to predict the heat transfer of inverted film boiling conditions. Pool boiling models for inverted film boiling also are inappropriate. Current force convection models for inverted film boiling, while far better than the previous two classes of models, still generate large predictive errors. It is recommended that for the inverted annular film boiling flow regime the modified equilibrium bulk Dittus-Boelter model be used. For agitated inverted annular film boiling and dispersed film boiling regimes associated with positive equilibrium qualities, the Hendricks model should be used. (A.C.)

  3. Regressed relations for forced convection heat transfer in a direct injection stratified charge rotary engine

    Science.gov (United States)

    Lee, Chi M.; Schock, Harold J.

    1988-01-01

    Currently, the heat transfer equation used in the rotary combustion engine (RCE) simulation model is taken from piston engine studies. These relations have been empirically developed by the experimental input coming from piston engines whose geometry differs considerably from that of the RCE. The objective of this work was to derive equations to estimate heat transfer coefficients in the combustion chamber of an RCE. This was accomplished by making detailed temperature and pressure measurements in a direct injection stratified charge (DISC) RCE under a range of conditions. For each specific measurement point, the local gas velocity was assumed equal to the local rotor tip speed. Local physical properties of the fluids were then calculated. Two types of correlation equations were derived and are described in this paper. The first correlation expresses the Nusselt number as a function of the Prandtl number, Reynolds number, and characteristic temperature ratio; the second correlation expresses the forced convection heat transfer coefficient as a function of fluid temperature, pressure and velocity.

  4. Model Based Analysis of Forced and Natural Convection Effects in an Electrochemical Cell

    Directory of Open Access Journals (Sweden)

    D Brunner

    2017-03-01

    Full Text Available High purity copper, suitable for electrical applications, can only be obtained by electro-winning. The hallmark of this process is its self-induced natural convection through density variations of the electrolyte at both anode and cathode. In order to do this, first the full dynamic complexity of the process needs to be understood. Thus an OpenFoam®-based 2D model of the process has been created. This finite-volume multiphysics approach solves the laminar momentum and copper-ion species conservation equations, as well as local copper-ion conversion kinetics. It uses a Boussinesq approximation to simulate the species-momentum coupling, namely natural draft forces induced by variations of the spatial copper concentration within the fluid. The model shows good agreement with benchmark-cases of real-life electrochemical cells found in literature. An additional flow was imposed at the bottom of a small scale electrochemical cell in order to increase the ionic transport and thereby increase the overall performance of the cell. In a small scale electrochemical cell in strictly laminar flow, the overall performance could be increased and stratification decreased.

  5. Forced convective boiling of water inside helically coiled tube. Characteristics of oscillation of dryout point

    International Nuclear Information System (INIS)

    Nagai, Niro; Sugiyama, Kenta; Takeuchi, Masanori; Yoshikawa, Shinji; Yamamoto, Fujio

    2006-01-01

    The helically coiled tube of heat exchanger is used for the evaporator of prototype fast breeder reactor 'Monju'. This paper aims at the grasp of two-phase flow phenomena of forced convective boiling of water inside helical coiled tube, especially focusing on oscillation phenomena of dryout point. A glass-made helically coiled tube was used to observe the inside water boiling behavior flowing upward, which was heated by high temperature oil outside the tube. This oil was also circulated through a glass made tank to provide the heat source for water evaporation. The criterion for oscillation of dryout point was found to be a function of inlet liquid velocity and hot oil temperature. The observation results suggest the mechanism of dryout point oscillation mainly consists of intensive nucleate boiling near the dryout point and evaporation of thin liquid film flowing along the helical tube. In addition, the oscillation characteristics were experimentally confirmed. As inlet liquid velocity increases, oscillation amplitude also increases but oscillation cycle does not change so much. As hot oil temperature increases, oscillation amplitude and cycle gradually decreases. (author)

  6. Kinetics modeling of the drying of sunflower stem (Helianthus annuus L.) in a forced convection tunnel

    Science.gov (United States)

    López, R.; Vaca, M.; Terres, H.; Lizardi, A.; Morales, J.; Flores, J.; Chávez, S.

    2015-01-01

    The sunflower is an annual plant native to the Americas. It possesses a large inflorescence (flowering head), and its name is derived from the flower's shape and image, which is often used to capture the sun. The plant has a rough, broad, hairy stem, coarsely toothed, with rough leaves, and circular flower heads. The sunflower seeds are appreciated for their oil, which has become a widespread cooking ingredient. Leaves of the sunflower can be used as cattle feed, while the stems contain a fiber that may be used in paper production. Recently this flower has been used in phytoremediation of soils, contaminated with heavy metals. Sunflower has been probed as an efficient phytoextractor of chromium, lead, aluminum, zinc, cadmium from soil. In this work we present the experimental results of the drying of the sunflower stem, cut in 100 mm longitudinal sections, with diameters in the range of 11-18 mm. The aim was to obtain a dry and easy-to-handle final product, since these plants were originally cultivated in order to extract heavy metals from a polluted soil. The dried stems could then be easily confined or sent to recycle premises to concentrate the metals. The drying process was done in forced convection within a hot air tunnel. The used temperature was 60 °C, the velocity of air was 3 m/s and the required times were 8 hours. The initial average wet mass was 28 g and the final value was 5 g, resulting in the aimed product.

  7. Controlling the structure of forced convective flow by means of rotating magnetic-field inductors

    International Nuclear Information System (INIS)

    Sorkin, M.Z.; Mozgirs, O.Kh.

    1993-01-01

    The forced convective flow generated by a rotating magnetic-field inductor is used in a melt as a means of controlling the transfer of mass and heat in the case of directed crystallization. An obvious advantage in using a rotating field is the generation of azimuthal twisting of the fluid, this providing for an evening out of the crystallization conditions in the azimuthal direction under nonsymmetrical boundary conditions in an actual technological process. From the standpoint of affecting the crystallization processes it would be preferable to use an inductor which would allow alteration of the intensity and of the direction of the meridional flow. Mixing in the form of velocity pulsations generated by the inductor within the melt would be if interest from the standpoint of affecting the crystallization processes, in particular to intensify the crystallization purification. The authors propose the use of a double magnetohydrodynmic rotator which consists of two rotating magnetic-field inductors, separated in altitude, with separate power supplies. The supply of power to the inductors with various current loads allows the generation of a controllable nonuniformity in field distribution and in the azimuthal velocity through the altitude and thus allows control of both the intensity and configuration of the meridional flows. The dual rotator makes it possible to purposefully control the structure of the meridional flows and the pulsation component of velocity and can be recommended for use in processes of directed crystallization as well as in crystallization purification. 4 refs., 3 figs

  8. Control of dynamical self-assembly of strongly Brownian nanoparticles through convective forces induced by ultrafast laser

    Science.gov (United States)

    Ilday, Serim; Akguc, Gursoy B.; Tokel, Onur; Makey, Ghaith; Yavuz, Ozgun; Yavuz, Koray; Pavlov, Ihor; Ilday, F. Omer; Gulseren, Oguz

    We report a new dynamical self-assembly mechanism, where judicious use of convective and strong Brownian forces enables effective patterning of colloidal nanoparticles that are almost two orders of magnitude smaller than the laser beam. Optical trapping or tweezing effects are not involved, but the laser is used to create steep thermal gradients through multi-photon absorption, and thereby guide the colloids through convective forces. Convective forces can be thought as a positive feedback mechanism that helps to form and reinforce pattern, while Brownian motion act as a competing negative feedback mechanism to limit the growth of the pattern, as well as to increase the possibilities of bifurcation into different patterns, analogous to the competition observed in reaction-diffusion systems. By steering stochastic processes through these forces, we are able to gain control over the emergent pattern such as to form-deform-reform of a pattern, to change its shape and transport it spatially within seconds. This enables us to dynamically initiate and control large patterns comprised of hundreds of colloids. Further, by not relying on any specific chemical, optical or magnetic interaction, this new method is, in principle, completely independent of the material type being assembled.

  9. Simulation-based prediction of hot-rolled coil forced cooling

    Energy Technology Data Exchange (ETDEWEB)

    Saboonchi, Ahmad [Department of Mechanical Engineering, Isfahan University of Technology, Isfahan 84154 (Iran); Hassanpour, Saeid [Rayan Tahlil Sepahan Co., Isfahan Science and Technology Town, Isfahan 84155 (Iran)

    2008-09-15

    Hot-rolled coils take a long time to cool under normal storehouse conditions due to their high mass. Hotter seasons will lead to even longer storage times and, thus, to shortage of space. Forced cooling methods such as water-immersion and water-spray can be employed to reduce hot-rolled coil cooling time. In this paper, a mathematical model of the thermal behavior of coils is developed to predict and to evaluate the results expected from employing these methods before any real changes can be made on the ground. The results obtained from the model were compared with those from various experiments to verify the model's accuracy. The cooling time was then computed based on changes effected in the boundary conditions appropriate to each of the forced cooling methods employed. Moreover, the savings in storage times were compared to identify the best cooling method. Predictions showed that water immersion at the beginning of cooling cycle was more effective and that the cycle should not exceed 1 h for cost efficiency considerations. When using nozzles to spray it was found that spraying water on end surfaces of coils would be the optimum option resulting in savings in time, water and energy, and with restricted temperature gradient. (author)

  10. Heat transfer in a sodium-to-sodium heat exchanger under conditions of combined force and free convection

    International Nuclear Information System (INIS)

    Jackson, J.D.; Axcell, B.P.; Johnston, S.E.

    1987-01-01

    A combined experimental and theoretical investigation of heat transfer in a vertical tube and annulus, countercurrent flow heat exchanger is reported. The working fluid was liquid sodium. Included in the range of conditions covered were those which are of interest in connection with the low flow rate operation of fast reactor intermediate heat exchanger systems. The heat transfer process ranged from that of pure forced convection to combined forced and free convection. By changing the direction of fluid flow or the direction of heat flow four different configurations were studied. In two cases the convection process was buoyancy aided and in the other two it was buoyancy opposed. Results are presented showing the influence of flow rate and temperature difference on overall heat transfer coefficient for each case. A theoretical model of turbulent flow and heat transfer incorporating influences of buoyancy was used to produce results for the range of conditions covered in the experiments. The predictions of overall heat transfer coefficient were found to be in reasonable general agreement with the measurements. It was clear from these calculations that the influence of buoyancy on heat transfer stemmed largely, under the conditions of the present experiment, from the modification of the convection process due to the distortion of the velocity field. This led to an enhancement of the heat transfer for the buoyancy-aided process and an impairment for the buoyancy-opposed process. The contribution of the turbulent diffusion of heat was relatively small. (author)

  11. PERFORMANCE OF A FORCED CONVECTION SOLAR DRIER INTEGRATED WITH GRAVEL AS HEAT STORAGE MATERIAL FOR CHILI DRYING

    Directory of Open Access Journals (Sweden)

    M. MOHANRAJ

    2009-09-01

    Full Text Available An indirect forced convection solar drier integrated with different sensible heat storage maternal has been developed and tested its performance for drying chili under the metrological conditions of Pollachi, India. The system consists of a flat plate solar air heater with heat storage unit, a drying chamber and a centrifugal blower. Drying experiments have been performed at an air flow rate of 0.25 kg/s. Drying of chili in a forced convection solar drier reduces the moisture content from around 72.8% (wet basis to the final moisture content about 9.1% in 24 h. Average drier efficiency was estimated to be about 21%. The specific moisture extraction rate was estimated to be about 0.87 kg/kWh.

  12. Investigations on cooling with forced flow of He II

    International Nuclear Information System (INIS)

    Srinivasan, R.; Hofmann, A.

    1985-01-01

    Investigations on heat transfer to flowing subcooled He II at a pressure of 7 bar have been carried out. The value of the conductivity function, f(T), at a temperature greater than Tsub(max), drops rapidly with increasing pressure. Below Tsub(max) the change in f(T) with pressure is less drastic. The Gorter-Mellink constant Asub(GM), increases linearly with pressure in the range 1.5-2 K and its pressure coefficient at 1 bar is 0.038+-0.01 per bar, independent of temperature. The temperature distribution in the test section with and without flow is adequately described by the one-dimensional model discussed in Part 1. It is concluded that for heat transfer to He II in forced flow there is no advantage in working at pressures > 1 bar. (author)

  13. Forced, combined and natural convections of water in a vertical nine-rod bundle with a square lattice and P/C = 1.5

    International Nuclear Information System (INIS)

    El-Genk, M.S.; Su, Bingjing; Guo, Zhanxiong

    1992-01-01

    Heat transfer correlations are developed for forced turbulent and laminar, combined, and natural convections of water in a uniformly heated, square arranged, nine-rod bundle having a P/D ratio of 1.5. In all correlations, the heated equivalent diameter is used in all the dimensionless quantities, and the water physical properties are evaluated at the water bulk temperature. In the experiments, Re is varied from 300 to 2.5 X 10 4 , Pr from 4 to 9, Ra q from 3 x 10 6 to 3 x 10 8 for natural convection and from 5 x 10 7 to 7 , 10 8 for combined convection, and Ri from 0.04 to 100. In both upflow and downflow experiments, the transition from forced turbulent to forced laminar convection occurs at Re T = 6,700; while the transition from forced laminar to buoyancy assisted combined convection occurs at Ri = 2.0. Results show that the rod arrangement in the bundle has little effect on the values of Nu in the forced and natural convection regimes. In general, Nu values for the square arranged rod bundle are less than 8% higher and less than 10% lower than those for a triangularly arranged rod bundle in the forced and natural convection regimes, respectively. 16 refs., 7 figs

  14. Turbulent Convection Insights from Small-Scale Thermal Forcing with Zero Net Heat Flux at a Horizontal Boundary.

    Science.gov (United States)

    Griffiths, Ross W; Gayen, Bishakhdatta

    2015-11-13

    A large-scale circulation, a turbulent boundary layer, and a turbulent plume are noted features of convection at large Rayleigh numbers under differential heating on a single horizontal boundary. These might be attributed to the forcing, which in all studies has been limited to a unidirectional gradient over the domain scale. We instead apply forcing on a length scale smaller than the domain, and with variation in both horizontal directions. Direct numerical simulations show turbulence throughout the domain, a regime transition to a dominant domain-scale circulation, and a region of logarithmic velocity in the boundary layer, despite zero net heat flux. The results show significant similarities to Rayleigh-Bénard convection, demonstrate the significance of plume merging, support the hypothesis that the key driver of convection is the production of available potential energy without necessarily supplying total potential energy, and imply that contributions to domain-scale circulation in the oceans need not be solely from the large-scale gradients of forcing.

  15. Temperature-controlled radiofrequency ablation of cardiac tissue: an in vitro study of the impact of electrode orientation, electrode tissue contact pressure and external convective cooling

    DEFF Research Database (Denmark)

    Petersen, H H; Chen, X; Pietersen, A

    1999-01-01

    A variety of basic factors such as electrode tip pressure, flow around the electrode and electrode orientation influence lesion size during radiofrequency ablation, but importantly is dependent on the chosen mode of ablation. However, only little information is available for the frequently used...... temperature-controlled mode. The purpose of the present experimental study was to evaluate the impact during temperature-controlled radiofrequency ablation of three basic factors regarding electrode-tissue contact and convective cooling on lesion size....

  16. Simulation and transient analyses of a complete passive heat removal system in a downward cooling pool-type material testing reactor against a complete station blackout and long-term natural convection mode using the RELAP5/3.2 code

    Directory of Open Access Journals (Sweden)

    Afshin Hedayat

    2017-08-01

    Full Text Available In this paper, a complete station blackout (SBO or complete loss of electrical power supplies is simulated and analyzed in a downward cooling 5-MW pool-type Material Testing Reactor (MTR. The scenario is traced in the absence of active cooling systems and operators. The code nodalization is successfully benchmarked against experimental data of the reactor's operating parameters. The passive heat removal system includes downward water cooling after pump breakdown by the force of gravity (where the coolant streams down to the unfilled portion of the holdup tank, safety flapper opening, flow reversal from a downward to an upward cooling direction, and then the upward free convection heat removal throughout the flapper safety valve, lower plenum, and fuel assemblies. Both short-term and long-term natural core cooling conditions are simulated and investigated using the RELAP5 code. Short-term analyses focus on the safety flapper valve operation and flow reversal mode. Long-term analyses include simulation of both complete SBO and long-term operation of the free convection mode. Results are promising for pool-type MTRs because this allows operators to investigate RELAP code abilities for MTR thermal–hydraulic simulations without any oscillation; moreover, the Tehran Research Reactor is conservatively safe against the complete SBO and long-term free convection operation.

  17. Simulation and transient analyses of a complete passive heat removal system in a downward cooling pool-type material testing reactor against a complete station blackout and long-term natural convection mode using the RELAP5/3.2 code

    Energy Technology Data Exchange (ETDEWEB)

    Hedayat, Afshin [Reactor and Nuclear Safety School, Nuclear Science and Technology Research Institute (NSTRI), Tehran (Iran, Islamic Republic of)

    2017-08-15

    In this paper, a complete station blackout (SBO) or complete loss of electrical power supplies is simulated and analyzed in a downward cooling 5-MW pool-type Material Testing Reactor (MTR). The scenario is traced in the absence of active cooling systems and operators. The code nodalization is successfully benchmarked against experimental data of the reactor's operating parameters. The passive heat removal system includes downward water cooling after pump breakdown by the force of gravity (where the coolant streams down to the unfilled portion of the holdup tank), safety flapper opening, flow reversal from a downward to an upward cooling direction, and then the upward free convection heat removal throughout the flapper safety valve, lower plenum, and fuel assemblies. Both short-term and long-term natural core cooling conditions are simulated and investigated using the RELAP5 code. Short-term analyses focus on the safety flapper valve operation and flow reversal mode. Long-term analyses include simulation of both complete SBO and long-term operation of the free convection mode. Results are promising for pool-type MTRs because this allows operators to investigate RELAP code abilities for MTR thermal–hydraulic simulations without any oscillation; moreover, the Tehran Research Reactor is conservatively safe against the complete SBO and long-term free convection operation.

  18. Forced convection flow boiling and two-phase flow phenomena in a microchannel

    Science.gov (United States)

    Na, Yun Whan

    2008-07-01

    The present study was performed to numerically analyze the evaporation phenomena through the liquid-vapor interface and to investigate bubble dynamics and heat transfer behavior during forced convective flow boiling in a microchannel. Flow instabilities of two-phase flow boiling in a microchannel were studied as well. The main objective of this research is to investigate the fundamental mechanisms of two-phase flow boiling in a microchannel and provide predictive tools to design thermal management systems, for example, microchannel heat sinks. The numerical results obtained from this study were qualitatively and quantitatively compared with experimental results in the open literature. Physical and mathematical models, accounting for evaporating phenomena through the liquid-vapor interface in a microchannel at constant heat flux and constant wall temperature, have been developed, respectively. The heat transfer mechanism is affected by the dominant heat conduction through the thin liquid film and vaporization at the liquid-vapor interface. The thickness of the liquid film and the pressure of the liquid and vapor phases were simultaneously solved by the governing differential equations. The developed semi-analytical evaporation model that takes into account of the interfacial phenomena and surface tension effects was used to obtain solutions numerically using the fourth-order Runge-Kutta method. The effects of heat flux 19 and wall temperature on the liquid film were evaluated. The obtained pressure drops in a microchannel were qualitatively consistent with the experimental results of Qu and Mudawar (2004). Forced convective flow boiling in a single microchannel with different channel heights was studied through a numerical simulation to investigate bubble dynamics, flow patterns, and heat transfer. The momentum and energy equations were solved using the finite volume method while the liquid-vapor interface of a bubble is captured using the VOF (Volume of Fluid

  19. Similarity Solution for Combined Free-Forced Convection Past a Vertical Porous Plate in a Porous Medium with a Convective Surface Boundary Condition

    Directory of Open Access Journals (Sweden)

    Garg P.

    2016-12-01

    Full Text Available This paper studies the mathematical implications of the two dimensional viscous steady laminar combined free-forced convective flow of an incompressible fluid over a semi infinite fixed vertical porous plate embedded in a porous medium. It is assumed that the left surface of the plate is heated by convection from a hot fluid which is at a temperature higher than the temperature of the fluid on the right surface of the vertical plate. To achieve numerical consistency for the problem under consideration, the governing non linear partial differential equations are first transformed into a system of ordinary differential equations using a similarity variable and then solved numerically under conditions admitting similarity solutions. The effects of the physical parameters of both the incompressible fluid and the vertical plate on the dimensionless velocity and temperature profiles are studied and analysed and the results are depicted both graphically and in a tabular form. Finally, algebraic expressions and the numerical values are obtained for the local skin-friction coefficient and the local Nusselt number.

  20. Kinetics modeling of the drying of sunflower stem (Helianthus annuus L.) in a forced convection tunnel

    International Nuclear Information System (INIS)

    López, R; Vaca, M; Terres, H; Lizardi, A; Morales, J; Flores, J; Chávez, S

    2015-01-01

    The sunflower is an annual plant native to the Americas. It possesses a large inflorescence (flowering head), and its name is derived from the flower's shape and image, which is often used to capture the sun. The plant has a rough, broad, hairy stem, coarsely toothed, with rough leaves, and circular flower heads. The sunflower seeds are appreciated for their oil, which has become a widespread cooking ingredient. Leaves of the sunflower can be used as cattle feed, while the stems contain a fiber that may be used in paper production. Recently this flower has been used in phytoremediation of soils, contaminated with heavy metals. Sunflower has been probed as an efficient phytoextractor of chromium, lead, aluminum, zinc, cadmium from soil. In this work we present the experimental results of the drying of the sunflower stem, cut in 100 mm longitudinal sections, with diameters in the range of 11-18 mm. The aim was to obtain a dry and easy-to-handle final product, since these plants were originally cultivated in order to extract heavy metals from a polluted soil. The dried stems could then be easily confined or sent to recycle premises to concentrate the metals. The drying process was done in forced convection within a hot air tunnel. The used temperature was 60 °C, the velocity of air was 3 m/s and the required times were 8 hours. The initial average wet mass was 28 g and the final value was 5 g, resulting in the aimed product

  1. Liquid Hydrogen Recirculation System for Forced Flow Cooling Test of Superconducting Conductors

    Science.gov (United States)

    Shirai, Y.; Kainuma, T.; Shigeta, H.; Shiotsu, M.; Tatsumoto, H.; Naruo, Y.; Kobayashi, H.; Nonaka, S.; Inatani, Y.; Yoshinaga, S.

    2017-12-01

    The knowledge of forced flow heat transfer characteristics of liquid hydrogen (LH2) is important and necessary for design and cooling analysis of high critical temperature superconducting devices. However, there are few test facilities available for LH2 forced flow cooling for superconductors. A test system to provide a LH2 forced flow (∼10 m/s) of a short period (less than 100 s) has been developed. The test system was composed of two LH2 tanks connected by a transfer line with a controllable valve, in which the forced flow rate and its period were limited by the storage capacity of tanks. In this paper, a liquid hydrogen recirculation system, which was designed and fabricated in order to study characteristics of superconducting cables in a stable forced flow of liquid hydrogen for longer period, was described. This LH2 loop system consists of a centrifugal pump with dynamic gas bearings, a heat exchanger which is immersed in a liquid hydrogen tank, and a buffer tank where a test section (superconducting wires or cables) is set. The buffer tank has LHe cooled superconducting magnet which can produce an external magnetic field (up to 7T) at the test section. A performance test was conducted. The maximum flow rate was 43.7 g/s. The lowest temperature was 22.5 K. It was confirmed that the liquid hydrogen can stably circulate for 7 hours.

  2. Reduction of vibration forces transmitted from a radiator cooling fan to a vehicle body

    Science.gov (United States)

    Lim, Jonghyuk; Sim, Woojeong; Yun, Seen; Lee, Dongkon; Chung, Jintai

    2018-04-01

    This article presents methods for reducing transmitted vibration forces caused by mass unbalance of the radiator cooling fan during vehicle idling. To identify the effects of mass unbalance upon the vibration characteristics, vibration signals of the fan blades were experimentally measured both with and without an added mass. For analyzing the vibration forces transmitted to the vehicle body, a dynamic simulation model was established that reflected the vibration characteristics of the actual system. This process included a method described herein for calculating the equivalent stiffness and the equivalent damping of the shroud stators and rubber mountings. The dynamic simulation model was verified by comparing its results with experimental results of the radiator cooling fan. The dynamic simulation model was used to analyze the transmitted vibration forces at the rubber mountings. Also, a measure was established to evaluate the effects of varying the design parameters upon the transmitted vibration forces. We present design guidelines based on these analyses to reduce the transmitted vibration forces of the radiator cooling fan.

  3. The GeoFlow experiment-spherical Rayleigh-Benard convection under the influence of an artificial central force field

    International Nuclear Information System (INIS)

    Gellert, M; Beltrame, P; Egbers, C

    2005-01-01

    Spherical Rayleigh-Benard convection under the influence of an artificial central force field produced by the so-called dielectrophoretic effect is studied as a simplified model of the flow in the outer earth core. The fluid motion there is most probably driving the earth's dynamo and the energy source for the earth's magnetic field. Studying convective flows in earth-like geometry could lead to a deeper understanding of the basics of these processes. This research is a preparatory study for the experiments on the International Space Station (ISS). A bifurcation-theoretical approach shows the existence of heteroclinic cycles between spherical modes (l, l + 1) for the non-rotating system. This behavior depends strong on the radius ratio of the spheres and will be hard to detect in the experiment. For slow rotations interactions of the azimuthal modes (m, m + 1) found in numerical simulations for supercritical states are supposed to be experimentally observable

  4. Low cryogen inventory, forced flow Ne cooling system with room temperature compression stage and heat recuperation

    CERN Document Server

    Shornikov, A; Wolf, A

    2014-01-01

    We present design and commissioning results of a forced flow cooling system utilizing neon at 30 K. The cryogen is pumped through the system by a room-temperature compression stage. To decouple the cold zone from the compression stage a recuperating counterflow tube-in-tube heat exchanger is used. Commissioning demonstrated successful condensation of neon and transfer of up to 30 W cooling power to the load at 30 K using only 30 g of the cryogen circulating in the system at pressures below 170 kPa.

  5. The influence of local effects on thermal sensation under non-uniform environmental conditions — Gender differences in thermophysiology, thermal comfort and productivity during convective and radiant cooling

    DEFF Research Database (Denmark)

    Schellen, L.; Loomans, M.G.L.C.; de Wit, M.H.

    2012-01-01

    , thermal comfort and productivity in response to thermal non-uniform environmental conditions. Twenty healthy subjects (10 males and 10 females, age 20–29years) were exposed to two different experimental conditions: a convective cooling situation (CC) and a radiant cooling situation (RC). During...... the experiments physiological responses, thermal comfort and productivity were measured. The results show that under both experimental conditions the actual mean thermal sensation votes significantly differ from the PMV-index; the subjects are feeling colder than predicted. Furthermore, the females are more...... of the occupants. Non-uniform thermal conditions, which may occur due to application of high temperature cooling systems, can be responsible for discomfort. Contradictions in literature exist regarding the validity of the often used predicted mean vote (PMV) index for both genders, and the index is not intended...

  6. HEXEREI: a multi-channel heat conduction convection code for use in transient thermal hydraulic analysis of high-temperature, gas-cooled reactors. Interim report

    International Nuclear Information System (INIS)

    Giles, G.E.; DeVault, R.M.; Turner, W.D.; Becker, B.R.

    1976-05-01

    A description is given of the development and verification of a generalized coupled conduction-convection, multichannel heat transfer computer program to analyze specific safety questions involving high temperature gas-cooled reactors (HTGR). The HEXEREI code was designed to provide steady-state and transient heat transfer analysis of the HTGR active core using a basic hexagonal mesh and multichannel coolant flow. In addition, the core auxiliary cooling systems were included in the code to provide more complete analysis of the reactor system during accidents involving reactor trip and cooling down on the auxiliary systems. Included are brief descriptions of the components of the HEXEREI code and sample HEXEREI analyses compared with analytical solutions and other heat transfer codes

  7. On the prediction of single-phase forced convection heat transfer in narrow rectangular channels

    International Nuclear Information System (INIS)

    Ghione, Alberto; Noel, Brigitte; Vinai, Paolo; Demazière, Christophe

    2014-01-01

    In this paper, selected heat transfer correlations for single-phase forced convection are assessed for the case of narrow rectangular channels. The work is of interest in the thermal-hydraulic analysis of the Jules Horowitz Reactor (JHR), which is a research reactor under construction at CEA-Cadarache (France). In order to evaluate the validity of the correlations, about 300 tests from the SULTAN-JHR database were used. The SULTAN-JHR program was carried out at CEA-Grenoble and it includes different kinds of tests for two different vertical rectangular channels with height of 600 mm and gap of 1.51 and 2.16 mm. The experimental conditions range between 2 - 9 bar for the pressure; 0.5 - 18 m/s for the coolant velocity and 0.5 - 7.5 MW/m 2 for the heat flux (whose axial distribution is uniform). Forty-two thermocouples and eight pressure taps were placed at several axial locations, measuring wall temperature and pressure respectively. The analysis focused on turbulent flow with Reynolds numbers between 5.5 x 10 3 - 2.4 x 10 5 and Prandtl numbers between 1.5 - 6. It was shown that standard correlations as the Dittus-Boelter and Seider-Tate significantly under-estimate the heat transfer coefficient, especially at high Reynolds number. Other correlations specifically designed for narrow rectangular channels were also taken into account and compared. The correlation of Popov-Petukhov in the form suggested by Siman-Tov still under-estimates the heat transfer coefficient, even if slight improvements could be seen. A better agreement for the tests with gap equal to 2.16 mm could be found with the correlation of Ma and the one of Liang. However the heat transfer coefficient when the gap is equal to 1.51 mm could not be predicted accurately. Furthermore these correlations were based on data at low Reynolds numbers (up to 13000) and low heat flux, so the use of them for SULTAN-JHR may be questionable. According to the authors’ knowledge, existing models of heat transfer

  8. Thermodynamic investigation and optimization of laminar forced convection in a rotating helical tube heat exchanger

    International Nuclear Information System (INIS)

    Shi, Zhongyuan; Dong, Tao

    2014-01-01

    Highlights: • Variation of total entropy generation is investigated parametrically. • Pareto solution sets for heat transfer and flow friction components are obtained. • Dominant irreversibility component and impact of key variables are discussed. - Abstract: Based on the second law of thermodynamics, an entropy generation investigation is carried out under given dimensionless parameters, i.e. heat exchanger duty, heat flux, with respect to heat transfer and frictional pressure drop in a rotating helical tube heat exchanger with laminar convective flow. The entropy generation from heat transfer across a finite temperature difference – Ψ h decreases with increasing Dean number which represents the impact of centrifugal force induced secondary flow in enhancing heat transfer. Another aspect of increasing Dean number is that intensified momentum transfer in the radial direction also raises the entropy generation from frictional pressure drop – Ψ f , the superposed effect of which yields a decreasing–increasing trend of the total entropy generation-Ψ, a local minimum located in between. The rotation of the helical tube in streamwise (co-rotation) or counter streamwise (counter-rotation) direction leads to a decrease in Ψ h and a increase in Ψ f which complicates the situation that whether or where the minimum of total entropy generation exists is dependent on whether Ψ is dominated by Ψ h or Ψ f or somewhere in between. No difference is discerned between pairs of cases with constant wall temperature and uniform wall heat flux but the same set of variables and parameters. A multi-objective optimization targeting Ψ h and Ψ f simultaneously is implemented using the non-dominated sorting genetic algorithm II (NSGA II). Five solution sets are selected and compared with the conventional optimization in regard of Ψ distinguishing the Ψ h -dominated region from the Ψ f -dominated region, the dimensionless variable η 1 is found to be the most suitable

  9. Investigation of a double oscillating-fan cooling device using electromagnetic force

    International Nuclear Information System (INIS)

    Su, Hsien-Chin; Xu, Han Yang

    2016-01-01

    Highlights: • The characteristics of a double oscillating-fan cooling device using electromagnetic force was investigated. • The driving current can be either DC PWM or AC within 3–12 V. • The comparison between a double blower pair, the model and a synjet were examined. • A 50 mm ∗ 50 mm ∗ 15 mm model can provide the flow rate of 154.89 l/min while consuming 0.65 W. • The flow rate, sound pressure, power consumption and two thermal tests have been done. - Abstract: This study proposes a double oscillating-fan cooling device using electromagnetic force. The device consists of two oscillating-fans. It requires only one electromagnet and two fan sheets with one magnet on each of them. The electromagnet and fan sheets are situated on a base and arranged accordingly. The electromagnetic force generated by the electromagnet can actuate the fan sheets. The main advantage of the device is its simple structure because there is no bearing and motor in the device. The driving current can be either DC PWM (Pulse width modulation) or AC (Alternating current) within 3–12 V so it is compatible with most electronic devices. The dimensions of the proposed model are 50 mm ∗ 50 mm ∗ 15 mm during operation. Concerning flow rate, sound pressure, power consumption and resonant frequency tests, a comparison between the proposed model and different type of cooling devices has been completed. The result shows that the model can provide cooling ability similar to a rotary fan while consuming 40% of the power of the rotary fan. It shows not only a good cooling ability but also a great potential for structural reliability and design flexibility.

  10. Laminar forced convective/conductive heat transfer by finite element method

    International Nuclear Information System (INIS)

    Kushwaha, H.S.; Kakodkar, A.

    1982-01-01

    The present study is directed at developing a finite element computer program for solution of decoupled convective/conductive heat transfer problems. Penalty function formulation has been used to solve momentum equations and subsequently transient energy equation is solved using modified Crank-Nicolson method. The optimal upwinding scheme has been employed in energy equation to remove oscillations at high Peclet number. (author)

  11. The effect of Coriolis force on nonlinear convection in a porous medium

    Directory of Open Access Journals (Sweden)

    D. H. Riahi

    1994-01-01

    Full Text Available Nonlinear convection in a porous medium and rotating about vertical axis is studied in this paper. An upper bound to the heat flux is calculated by the method initiated first by Howard [6] for the case of infinite Prandtl number.

  12. A critical review of predictive models for the onset of significant void in forced-convection subcooled boiling

    International Nuclear Information System (INIS)

    Dorra, H.; Lee, S.C.; Bankoff, S.G.

    1993-06-01

    This predictive models for the onset of significant void (OSV) in forced-convection subcooled boiling are reviewed and compared with extensive data. Three analytical models and seven empirical correlations are considered in this review. These models and correlations are put onto a common basis and are compared, again on a common basis, with a variety of data. The evaluation of their range of validity and applicability under various operating conditions are discussed. The results show that the correlations of Saha-Zuber seems to be the best model to predict OSV in vertical subcooled boiling flow

  13. The Impact of the Aerosol Direct Radiative Forcing on Deep Convection and Air Quality in the Pearl River Delta Region

    Science.gov (United States)

    Liu, Z.; Yim, Steve H. L.; Wang, C.; Lau, N. C.

    2018-05-01

    Literature has reported the remarkable aerosol impact on low-level cloud by direct radiative forcing (DRF). Impacts on middle-upper troposphere cloud are not yet fully understood, even though this knowledge is important for regions with a large spatial heterogeneity of emissions and aerosol concentration. We assess the aerosol DRF and its cloud response in June (with strong convection) in Pearl River Delta region for 2008-2012 at cloud-resolving scale using an air quality-climate coupled model. Aerosols suppress deep convection by increasing atmospheric stability leading to less evaporation from the ground. The relative humidity is reduced in middle-upper troposphere due to induced reduction in both evaporation from the ground and upward motion. The cloud reduction offsets 20% of the aerosol DRF. The weaker vertical mixing further increases surface aerosol concentration by up to 2.90 μg/m3. These findings indicate the aerosol DRF impact on deep convection and in turn regional air quality.

  14. R-HPDC Process with Forced Convection Mixing Device for Automotive Part of A380 Aluminum Alloy

    Directory of Open Access Journals (Sweden)

    Bing Zhou

    2014-04-01

    Full Text Available The continuing quest for cost-effective and complex shaped aluminum castings with fewer defects for applications in the automotive industries has aroused the interest in rheological high pressure die casting (R-HPDC. A new machine, forced convection mixing (FCM device, based on the mechanical stirring and convection mixing theory for the preparation of semisolid slurry in convenience and functionality was proposed to produce the automotive shock absorber part by R-HPDC process. The effect of barrel temperature and rotational speed of the device on the grain size and morphology of semi-solid slurry were extensively studied. In addition, flow behavior and temperature field of the melt in the FCM process was investigated combining computational fluid dynamics simulation. The results indicate that the microstructure and pore defects at different locations of R-HPDC casting have been greatly improved. The vigorous fluid convection in FCM process has changed the temperature field and composition distribution of conventional solidification. Appropriately increasing the rotational speed can lead to a uniform temperature filed sooner. The lower barrel temperature leads to a larger uniform degree of supercooling of the melt that benefits the promotion of nucleation rate. Both of them contribute to the decrease of the grain size and the roundness of grain morphology.

  15. Simulation of Thermomagnetic Convection in a Cavity Using the Lattice Boltzmann Model

    Directory of Open Access Journals (Sweden)

    Mahshid Hadavand

    2011-01-01

    Full Text Available Thermomagnetic convection in a differentially heated square cavity with an infinitely long third dimension is numerically simulated using the single relaxation time lattice Boltzmann method (LBM. This problem is of considerable interest when dealing with cooling of microelectronic devices, in situations where natural convection does not meet the cooling requirements, and forced convection is not viable due to the difficulties associated with pumping a ferrofluid. Therefore, circulation is achieved by imposing a magnetic field, which is created and controlled by placing a dipole at the bottom of the enclosure. The magnitude of the magnetic force is controlled by changing the electrical current through the dipole. In this study, the effects of combined natural convection and magnetic convection, which is commonly known as “thermomagnetic convection,” are analysed in terms of the flow modes and heat transfer characteristics of a magnetic fluid.

  16. Properties of forced convection experimental with silicon carbide based nano-fluids

    Science.gov (United States)

    Soanker, Abhinay

    -fluids. The nano-fluid properties were tested at three different volume concentrations; 0.55%, 1% and 1.6%. Thermal conductivity was measured for the three-volume concentration as function of temperature. Thermal conductivity enhancement increased with the temperature and may be attributed to increased Brownian motion of colloidal particles at higher temperatures. Measured thermal conductivity values are compared with results obtained by theoretical model derived in this work. Effect of temperature and volume concentration on viscosity was also measured and reported. Viscosity increase and related consequences are important issues for the use of nano-fluids. Extensive measurements of heat transfer and pressure drop for forced convection in circular pipes with nano-fluids was also conducted. Parameters such as heat transfer coefficient, Nusselt number, pressure drop and a thermal hydraulic performance factor that takes into account the gains made by increase in thermal conductivity as well as penalties related to increase in pressure drop are evaluated for laminar and transition flow regimes. No significant improvement in heat transfer (Nusselt number) compared to its based fluid was observed. It is also observed that the values evaluated for the thermal-hydraulic performance factor (change in heat transfer/change in pressure drop) was under unity for many flow conditions indicating poor overall applicability of SiC based nano-fluids.

  17. Design of Test Loops for Forced Convection Heat Transfer Studies at Supercritical State

    Science.gov (United States)

    Balouch, Masih N.

    Worldwide research is being conducted to improve the efficiency of nuclear power plants by using supercritical water (SCW) as the working fluid. One such SCW reactor considered for future development is the CANDU-Supercritical Water Reactor (CANDU-SCWR). For safe and accurate design of the CANDU-SCWR, a detailed knowledge of forced-convection heat transfer in SCW is required. For this purpose, two supercritical fluid loops, i.e. a SCW loop and an R-134a loop are developed at Carleton University. The SCW loop is designed to operate at pressures as high as 28 MPa, temperatures up to 600 °C and mass fluxes of up to 3000 kg/m2s. The R-134a loop is designed to operate at pressures as high as 6 MPa, temperatures up to 140 °C and mass fluxes in the range of 500-6000 kg/m2s. The test loops designs allow for up to 300 kW of heating power to be imparted to the fluid. Both test loops are of the closed-loop design, where flow circulation is achieved by a centrifugal pump in the SCW loop and three parallel-connected gear pumps in the R-134a loop, respectively. The test loops are pressurized using a high-pressure nitrogen cylinder and accumulator assembly, which allows independent control of the pressure, while simultaneously dampening pump induced pressure fluctuations. Heat exchangers located upstream of the pumps control the fluid temperature in the test loops. Strategically located measuring instrumentation provides information on the flow rate, pressure and temperature in the test loops. The test loops have been designed to accommodate a variety of test-section geometries, ranging from a straight circular tube to a seven-rod bundle, achieving heat fluxes up to 2.5 MW/m2 depending on the test-section geometry. The design of both test loops allows for easy reconfiguration of the test-section orientation relative to the gravitational direction. All the test sections are of the directly-heated design, where electric current passing through the pressure retaining walls of the

  18. Dual reciprocity boundary element analysis for the laminar forced heat convection problem in concentric annulus

    International Nuclear Information System (INIS)

    Choi, Chang Yong

    1999-01-01

    This paper presents a study of the Dual Reciprocity Boundary Element Method (DRBEM) for the laminar heat convection problem in a concentric annulus with constant heat flux boundary condition. DRBEM is one of the most successful technique used to transform the domain integrals arising from the nonhomogeneous term of the poisson equation into equivalent boundary only integrals. This recently developed and highly efficient numerical method is tested for the solution accuracy of the fluid flow and heat transfer study in a concentric annulus. Since their exact solutions are available, DRBEM solutions are verified with different number of boundary element discretization and internal points. The results obtained in this study are discussed with the relative error percentage of velocity and temperature solutions, and potential applicability of the method for the more complicated heat convection problems with arbitrary duct geometries

  19. Single-phase liquid flow forced convection under a nearly uniform heat flux boundary condition in microchannels

    KAUST Repository

    Lee, Man; Lee, Yi-Kuen; Zohar, Yitshak

    2012-01-01

    A microchannel heat sink, integrated with pressure and temperature microsensors, is utilized to study single-phase liquid flow forced convection under a uniform heat flux boundary condition. Utilizing a waferbond-and-etch- back technology, the heat source, temperature and pressure sensors are encapsulated in a thin composite membrane capping the microchannels, thus allowing experimentally good control of the thermal boundary conditions. A three-dimensional physical model has been constructed to facilitate numerical simulations of the heat flux distribution. The results indicate that upstream the cold working fluid absorbs heat, while, within the current operating conditions, downstream the warmer working fluid releases heat. The Nusselt number is computed numerically and compared with experimental and analytical results. The wall Nusselt number in a microchannel can be estimated using classical analytical solutions only over a limited range of the Reynolds number, Re: both the top and bottom Nusselt numbers approach 4 for Re < 1, while the top and bottom Nusselt numbers approach 0 and 5.3, respectively, for Re > 100. The experimentally estimated Nusselt number for forced convection is highly sensitive to the location of the temperature measurements used in calculating the Nusselt number. © 2012 IOP Publishing Ltd.

  20. Analysis of optimal Reynolds number for developing laminar forced convection in double sine ducts based on entropy generation minimization principle

    International Nuclear Information System (INIS)

    Ko, T.H.

    2006-01-01

    In the present paper, the entropy generation and optimal Reynolds number for developing forced convection in a double sine duct with various wall heat fluxes, which frequently occurs in plate heat exchangers, are studied based on the entropy generation minimization principle by analytical thermodynamic analysis as well as numerical investigation. According to the thermodynamic analysis, a very simple expression for the optimal Reynolds number for the double sine duct as a function of mass flow rate, wall heat flux, working fluid and geometric dimensions is proposed. In the numerical simulations, the investigated Reynolds number (Re) covers the range from 86 to 2000 and the wall heat flux (q'') varies as 160, 320 and 640 W/m 2 . From the numerical simulation of the developing laminar forced convection in the double sine duct, the effect of Reynolds number on entropy generation in the duct has been examined, through which the optimal Reynolds number with minimal entropy generation is detected. The optimal Reynolds number obtained from the analytical thermodynamic analysis is compared with the one from the numerical solutions and is verified to have a similar magnitude of entropy generation as the minimal entropy generation predicted by the numerical simulations. The optimal analysis provided in the present paper gives worthy information for heat exchanger design, since the thermal system could have the least irreversibility and best exergy utilization if the optimal Re can be used according to practical design conditions

  1. Single-phase liquid flow forced convection under a nearly uniform heat flux boundary condition in microchannels

    KAUST Repository

    Lee, Man

    2012-02-22

    A microchannel heat sink, integrated with pressure and temperature microsensors, is utilized to study single-phase liquid flow forced convection under a uniform heat flux boundary condition. Utilizing a waferbond-and-etch- back technology, the heat source, temperature and pressure sensors are encapsulated in a thin composite membrane capping the microchannels, thus allowing experimentally good control of the thermal boundary conditions. A three-dimensional physical model has been constructed to facilitate numerical simulations of the heat flux distribution. The results indicate that upstream the cold working fluid absorbs heat, while, within the current operating conditions, downstream the warmer working fluid releases heat. The Nusselt number is computed numerically and compared with experimental and analytical results. The wall Nusselt number in a microchannel can be estimated using classical analytical solutions only over a limited range of the Reynolds number, Re: both the top and bottom Nusselt numbers approach 4 for Re < 1, while the top and bottom Nusselt numbers approach 0 and 5.3, respectively, for Re > 100. The experimentally estimated Nusselt number for forced convection is highly sensitive to the location of the temperature measurements used in calculating the Nusselt number. © 2012 IOP Publishing Ltd.

  2. Vertical microphysical profiles of convective clouds as a tool for obtaining aerosol cloud-mediated climate forcings

    Energy Technology Data Exchange (ETDEWEB)

    Rosenfeld, Daniel [Hebrew Univ. of Jerusalem (Israel)

    2015-12-23

    Quantifying the aerosol/cloud-mediated radiative effect at a global scale requires simultaneous satellite retrievals of cloud condensation nuclei (CCN) concentrations and cloud base updraft velocities (Wb). Hitherto, the inability to do so has been a major cause of high uncertainty regarding anthropogenic aerosol/cloud-mediated radiative forcing. This can be addressed by the emerging capability of estimating CCN and Wb of boundary layer convective clouds from an operational polar orbiting weather satellite. Our methodology uses such clouds as an effective analog for CCN chambers. The cloud base supersaturation (S) is determined by Wb and the satellite-retrieved cloud base drop concentrations (Ndb), which is the same as CCN(S). Developing and validating this methodology was possible thanks to the ASR/ARM measurements of CCN and vertical updraft profiles. Validation against ground-based CCN instruments at the ARM sites in Oklahoma, Manaus, and onboard a ship in the northeast Pacific showed a retrieval accuracy of ±25% to ±30% for individual satellite overpasses. The methodology is presently limited to boundary layer not raining convective clouds of at least 1 km depth that are not obscured by upper layer clouds, including semitransparent cirrus. The limitation for small solar backscattering angles of <25º restricts the satellite coverage to ~25% of the world area in a single day. This methodology will likely allow overcoming the challenge of quantifying the aerosol indirect effect and facilitate a substantial reduction of the uncertainty in anthropogenic climate forcing.

  3. Analytical prediction of friction factors and Nusselt numbers of turbulent forced convection in rod bundles with smooth and rough surfaces

    International Nuclear Information System (INIS)

    Su Jian; Silva Freire, Atila P.

    2002-01-01

    A simple analytical method was developed for the prediction of the friction factor, f, of fully developed turbulent flow and the Nusselt number, Nu, of fully developed turbulent forced convection in rod bundles arranged in square or hexagonal arrays. The friction factor equation for smooth rod bundles was presented in a form similar to the friction factor equation for turbulent flow in a circular pipe. An explicit equation for the Nusselt number of turbulent forced convection in rod bundles with smooth surface was developed. In addition, we extended the analysis to rod bundles with rough surface and provided a method for the prediction of the friction factor and the Nusselt number. The method was based on the law of the wall for velocity and the law of the wall for the temperature, which were integrated over the entire flow area to yield algebraic equations for the prediction of f and Nu. The present method is applicable to infinite rod bundles in square and hexagonal arrays with low pitch to rod diameter ratio, P/D<1.2

  4. Dynamic electro-thermal modeling of all-vanadium redox flow battery with forced cooling strategies

    International Nuclear Information System (INIS)

    Wei, Zhongbao; Zhao, Jiyun; Xiong, Binyu

    2014-01-01

    Highlights: • A dynamic electro-thermal model is proposed for VRB with forced cooling. • The Foster network is adopted to model the battery cooling process. • Both the electrolyte temperature and terminal voltage can be accurately predicted. • The flow rate of electrolyte and coolant significantly impact battery performance. - Abstract: The present study focuses on the dynamic electro-thermal modeling for the all-vanadium redox flow battery (VRB) with forced cooling strategies. The Foster network is adopted to dynamically model the heat dissipation of VRB with heat exchangers. The parameters of Foster network are extracted by fitting the step response of it to the results of linearized CFD model. Then a complete electro-thermal model is proposed by coupling the heat generation model, Foster network and electrical model. Results show that the established model has nearly the same accuracy with the nonlinear CFD model in electrolyte temperature prediction but drastically improves the computational efficiency. The modeled terminal voltage is also benchmarked with the experimental data under different current densities. The electrolyte temperature is found to be significantly influenced by the flow rate of coolant. As compared, although the electrolyte flow rate has unremarkable impact on electrolyte temperature, its effect on system pressure drop and battery efficiency is significant. Increasing the electrolyte flow rate improves the coulombic efficiency, voltage efficiency and energy efficiency simultaneously but at the expense of higher pump power demanded. An optimal flow rate exists for each operating condition to maximize the system efficiency

  5. Convective heat transfer the molten metal pool heated from below and cooled by two-phase flow

    International Nuclear Information System (INIS)

    Cho, J. S.; Suh, K. Y.; Chung, C. H.; Park, R. J.; Kim, S. B.

    1998-01-01

    During a hypothetical servere accident in the nuclear power plant, a molten core material may form stratified fluid layers. These layers may be composed of high temperature molten debris pool and water coolant in the lower plenum of the reactor vessel or in the reactor cavity. This study is concerned with the experimental test and numerical analysis on the heat transfer and solidification of the molten metal pool with overlying coolant with boiling. This work examines the crust formation and the heat transfer characteristics of the molten metal pool immersed in the boiling coolant. The metal pool is heated from the bottom surface and coolant is injected onto the molten metal pool. The simulant molten pool material is tin (Sn) with the melting temperature of 232 .deg. C. Demineralized water is used as the working coolant. Tests were performed under the condition of the bottom surface heating in the test section and the forced convection of the coolant being injected onto the molten metal pool. The constant temperature and constant heat flux conditions are adopted for the bottom heating. The test parameters included the heated bottom surface temperature of the molten metal pool, the input power to the heated bottom surface of the test section, and the coolant injection rate. Numerical analyses were simultaneously performed in a two-dimensional rectangular domain of the molten metal pool to check on the measured data. The numerical program has been developed using the enthalpy method, the finite volume method and the SIMPLER algorithm. The experimental results of the heat transfer show general agreement with the calculated values. In this study, the relationship between the Nusselt number and Rayleigh number in the molten metal pool region was estimated and compared with the dry experiment without coolant nor solidification of the molten metal pool, and with the crust formation experiment with subcooled coolant, and against other correlations. In the experiments, the

  6. On the determination of the overall heat transmission coefficient and soil heat flux for a fog cooled, naturally ventilated greenhouse: Analysis of radiation and convection heat transfer

    International Nuclear Information System (INIS)

    Abdel-Ghany, Ahmed M.; Kozai, Toyoki

    2006-01-01

    A physical model for analyzing the radiative and convective heat transfer in a fog cooled, naturally ventilated greenhouse was developed for estimating the overall heat transmission coefficient based on the conduction, convection and thermal radiation heat transfer coefficients and for predicting the soil heat flux. The contribution of the water vapor of the inside air to the emission and absorption of thermal radiation was determined. Measurements of the outside and inside greenhouse environments to be used in the analysis were conducted around solar noon (12:19-13:00) on a hot sunny day to provide the maximum solar radiation transmission into the greenhouse. The net solar radiation flux measured at the greenhouse floor showed a reasonable agreement with the predicted value. The net fluxes were estimated around noon. The average net radiation (solar and thermal) at the soil surface was 220.0 W m -2 , the average soil heat flux was 155.0 W m -2 and the average contribution of the water vapor of the inside air to the thermal radiation was 22.0 W m -2 . The average overall heat transmission coefficient was 4.0 W m -2 C -1 and was in the range between 3.0 W m -2 C -1 and 6.0 W m -2 C -1 under the different hot summer conditions between the inside and outside of the naturally ventilated, fog cooled greenhouse

  7. Design Report for the ½ Scale Air-Cooled RCCS Tests in the Natural convection Shutdown heat removal Test Facility (NSTF)

    Energy Technology Data Exchange (ETDEWEB)

    Lisowski, D. D. [Argonne National Lab. (ANL), Argonne, IL (United States); Farmer, M. T. [Argonne National Lab. (ANL), Argonne, IL (United States); Lomperski, S. [Argonne National Lab. (ANL), Argonne, IL (United States); Kilsdonk, D. J. [Argonne National Lab. (ANL), Argonne, IL (United States); Bremer, N. [Argonne National Lab. (ANL), Argonne, IL (United States); Aeschlimann, R. W. [Argonne National Lab. (ANL), Argonne, IL (United States)

    2014-06-01

    The Natural convection Shutdown heat removal Test Facility (NSTF) is a large scale thermal hydraulics test facility that has been built at Argonne National Laboratory (ANL). The facility was constructed in order to carry out highly instrumented experiments that can be used to validate the performance of passive safety systems for advanced reactor designs. The facility has principally been designed for testing of Reactor Cavity Cooling System (RCCS) concepts that rely on natural convection cooling for either air or water-based systems. Standing 25-m in height, the facility is able to supply up to 220 kW at 21 kW/m2 to accurately simulate the heat fluxes at the walls of a reactor pressure vessel. A suite of nearly 400 data acquisition channels, including a sophisticated fiber optic system for high density temperature measurements, guides test operations and provides data to support scaling analysis and modeling efforts. Measurements of system mass flow rate, air and surface temperatures, heat flux, humidity, and pressure differentials, among others; are part of this total generated data set. The following report provides an introduction to the top level-objectives of the program related to passively safe decay heat removal, a detailed description of the engineering specifications, design features, and dimensions of the test facility at Argonne. Specifications of the sensors and their placement on the test facility will be provided, along with a complete channel listing of the data acquisition system.

  8. A homogeneous cooling scheme investigation for high power slab laser

    Science.gov (United States)

    He, Jianguo; Lin, Weiran; Fan, Zhongwei; Chen, Yanzhong; Ge, Wenqi; Yu, Jin; Liu, Hao; Mo, Zeqiang; Fan, Lianwen; Jia, Dan

    2017-10-01

    The forced convective heat transfer with the advantages of reliability and durability is widely used in cooling the laser gain medium. However, a flow direction induced temperature gradient always appears. In this paper, a novel cooling configuration based on longitudinal forced convective heat transfer is presented. In comparison with two different types of configurations, it shows a more efficient heat transfer and more homogeneous temperature distribution. The investigation of the flow rate reveals that the higher flow rate the better cooling performance. Furthermore, the simulation results with 20 L/min flow rate shows an adequate temperature level and temperature homogeneity which keeps a lower hydrostatic pressure in the flow path.

  9. Fuel Cooling in Absence of Forced Flow at Shutdown Condition with PHTS Partially Drained

    Energy Technology Data Exchange (ETDEWEB)

    Parasca, L.; Pecheanu, D.L., E-mail: laurentiu.parasca@cne.ro, E-mail: doru.pecheanu@cne.ro [Cernavoda Nuclear Power Plant, Cernavoda (Romania)

    2014-09-15

    During the plant outage for maintenance on primary side (e.g. for the main Heat Transport System pumps maintenance, the Steam Generators inspection), there are situations which require the primary heat transport system (HTS) drainage to a certain level for opening the circuit. The primary fuel heat sink for this configuration is provided by the shutdown cooling system (SDCS). In case of losing the forced cooling (e.g. due to the loss of SDCS, design basis earthquake-DBE), flow conditions in the reactor core may become stagnant. Inside the fuel channels, natural circulation phenomena known as Intermittent Buoyancy Induced Flow (IBIF) will initiate, providing an alternate heat sink mechanism for the fuel. However, this heat sink is effective only for a limited period of time (recall time). The recall time is defined as the elapsed time until the water temperature in the HTS headers exceeds a certain limit. Until then, compensatory measures need to be taken (e.g. by re-establishing the forced flow or initiate Emergency Core Cooling system injection) to preclude fuel failures. The present paper briefly presents the results of an analysis performed to demonstrate that fuel temperature remains within acceptable limits during IBIF transient. One of the objectives of this analysis was to determine the earliest moment since the reactor shut down when maintenance activities on the HTS can be started such that IBIF is effective in case of losing the forced circulation. The resulting peak fuel sheath and pressure tube temperatures due to fuel heat up shall be within the acceptable limits to preclude fuel defect or fuel channel defects.Thermalhydraulic circuit conditions were obtained using a CATHENA model for the primary side of HTS (drained to a certain level), an ECC system model and a system model for SDCS. A single channel model was developed in GOTHIC code for the fuel assessment analysis. (author)

  10. Numerical simulation of forced convection over a periodic series of rectangular cavities at low Prandtl number

    International Nuclear Information System (INIS)

    Stalio, E.; Angeli, D.; Barozzi, G.S.

    2011-01-01

    Highlights: → We investigate laminar convective heat transfer in channels with periodic cavities. → Heat transfer rates are lower than for the flat channel. → This is ascribed to the steady circulating motion within the cavities. → Diffusion in a low Prandtl number fluid can locally overcome the heat transfer decrease due to advection only for isothermal boundary conditions. - Abstract: Convective heat transfer in laminar conditions is studied numerically for a Prandtl number Pr = 0.025, representative of liquid lead-bismuth eutectic (LBE). The geometry investigated is a channel with a periodic series of shallow cavities. Finite-volume simulations are carried out on structured orthogonal curvilinear grids, for ten values of the Reynolds number based on the hydraulic diameter between Re m = 24.9 and Re m = 2260. Flow separation and reattachment are observed also at very low Reynolds numbers and wall friction is found to be remarkably unequal at the two walls. In almost all cases investigated, heat transfer rates are smaller than the corresponding flat channel values. Low-Prandtl number heat transfer rates, investigated by comparison with Pr = 0.71 results, are large only for uniform wall temperature and very low Re. Influence of flow separation on local heat transfer rates is discussed, together with the effect of different thermal boundary conditions. Dependency of heat transfer performance on the cavity geometry is also considered.

  11. Thermal modeling of the forced convection Sandwich Greenhouse drying system for rubber sheets

    International Nuclear Information System (INIS)

    Tanwanichkul, B.; Thepa, S.; Rordprapat, W.

    2013-01-01

    Highlights: • Sandwich Greenhouse is designed for better quality and efficiency of rubber sheet drying. • Thermal models are developed to predict the convection heat transfer coefficient. • The models are validated and show good agreement with the actual experimental data. • The proposed greenhouse can maintain 40–60 °C, suitable for rubber sheet drying. • This greenhouse can bring down the moisture content to 2.8% in fewer than 2 days. - Abstract: In this paper, a novel “Sandwich Greenhouse” for rubber sheet drying is proposed. Using solar energy as the only heat source instead of traditional smoke house that requires firewood, it eliminates shortcomings such as skilled labor monitoring requirement, possible fire hazard, and darken-color rubber sheets due to soot particle contamination. Our greenhouse is specially designed to retain solar energy within, while minimizing the heat loss to the outside environment. The mathematical models are developed to predict the convection mass transfer coefficient and to study the thermal behavior during the drying of rubber sheets under our proposed greenhouse design. Validated with experimental observations, the models show good agreement with the actual experimental data. The experiment demonstrates an effectiveness of our proposed Sandwich Greenhouse, as the temperature of the rubber sheet is 15 °C and 5 °C higher than the ambient temperature during the daytime and nighttime, respectively. As a result, the moisture content of the rubber sheets can decrease from 36.4% to 2.8% in fewer than 2 days

  12. Entropy Generation Analysis and Performance Evaluation of Turbulent Forced Convective Heat Transfer to Nanofluids

    Directory of Open Access Journals (Sweden)

    Yu Ji

    2017-03-01

    Full Text Available The entropy generation analysis of fully turbulent convective heat transfer to nanofluids in a circular tube is investigated numerically using the Reynolds Averaged Navier–Stokes (RANS model. The nanofluids with particle concentration of 0%, 1%, 2%, 4% and 6% are treated as single phases of effective properties. The uniform heat flux is enforced at the tube wall. To confirm the validity of the numerical approach, the results have been compared with empirical correlations and analytical formula. The self-similarity profiles of local entropy generation are also studied, in which the peak values of entropy generation by direct dissipation, turbulent dissipation, mean temperature gradients and fluctuating temperature gradients for different Reynolds number as well as different particle concentration are observed. In addition, the effects of Reynolds number, volume fraction of nanoparticles and heat flux on total entropy generation and Bejan number are discussed. In the results, the intersection points of total entropy generation for water and four nanofluids are observed, when the entropy generation decrease before the intersection and increase after the intersection as the particle concentration increases. Finally, by definition of Ep, which combines the first law and second law of thermodynamics and attributed to evaluate the real performance of heat transfer processes, the optimal Reynolds number Reop corresponding to the best performance and the advisable Reynolds number Read providing the appropriate Reynolds number range for nanofluids in convective heat transfer can be determined.

  13. Heat transfer in pool boiling liquid neon, deuterium and hydrogen, and critical heat flux in forced convection of liquid neon

    International Nuclear Information System (INIS)

    Astruc, J.M.

    1967-12-01

    In the first part, free-convection and nucleate pool boiling heat transfer (up to burn-out heat flux) between a platinum wire of 0.15 mm in diameter in neon, deuterium and hydrogen has been studied at atmospheric pressure. These measurements were continued in liquid neon up to 23 bars (Pc ≅ 26.8 b). Film boiling heat transfer coefficients have been measured in pool boiling liquid neon at atmospheric pressure with three heating wires (diameters 0.2, 0.5, 2 mm). All the results have been compared with existing correlations. The second part is devoted to measurements of the critical heat flux limiting heat transfer with small temperature differences between the wall and the liquid neon flowing inside a tube (diameters 3 x 3.5 mm) heated by joule effect on 30 cm of length. Influences of flow stability, nature of electrical current, pressure, mass flow rate and subcooling are shown. In conclusion, the similarity of the heat transfer characteristics in pool boiling as well as in forced convection of liquid neon and hydrogen is emphasized. (author) [fr

  14. Non-Equilibrium Thermodynamic Analysis of Double Diffusive, Nanofluid Forced Convection in Catalytic Microreactors with Radiation Effects

    Directory of Open Access Journals (Sweden)

    Lilian Govone

    2017-12-01

    Full Text Available This paper presents a theoretical investigation of the second law performance of double diffusive forced convection in microreactors with the inclusion of nanofluid and radiation effects. The investigated microreactors consist of a single microchannel, fully filled by a porous medium. The transport of heat and mass are analysed by including the thick walls and a first order, catalytic chemical reaction on the internal surfaces of the microchannel. Two sets of thermal boundary conditions are considered on the external surfaces of the microchannel; (1 constant temperature and (2 constant heat flux boundary condition on the lower wall and convective boundary condition on the upper wall. The local thermal non-equilibrium approach is taken to thermally analyse the porous section of the system. The mass dispersion equation is coupled with the transport of heat in the nanofluid flow through consideration of Soret effect. The problem is analytically solved and illustrations of the temperature fields, Nusselt number, total entropy generation rate and performance evaluation criterion (PEC are provided. It is shown that the radiation effect tends to modify the thermal behaviour within the porous section of the system. The radiation parameter also reduces the overall temperature of the system. It is further demonstrated that, expectedly, the nanoparticles reduce the temperature of the system and increase the Nusselt number. The total entropy generation rate and consequently PEC shows a strong relation with radiation parameter and volumetric concentration of nanoparticles.

  15. Experimental study of pistachio drying behavior in a mixed-mode PV operated forced convection solar dryer

    Energy Technology Data Exchange (ETDEWEB)

    Zangiabadi, B [Univ. of Stavanger, Stavanger (Norway); Ameri, M; Mahmoudabadi, M M [Shahid Bahonar Univ., Kerman (Iran, Islamic Republic of)

    2008-07-01

    According to FAO statistics, Iran is the largest exporter of pistachios. Kerman province -south east of Iran- has approximately 200000 hectares of pistachio orchards, which provides practically 80% of whole country production of pistachios. After harvesting the pistachio, nuts must be washed to prevent staining. Therefore the nuts have almost 40% moisture content and it must be decreased to storage moisture of 6% or below. Simply decreasing in the moisture content of the products is called drying. In some areas where the environment conditions meet the minimum standard, solar drying can be an alternative approach for drying agricultural products. This work deals with the design, construction and testing a mixed-mode forced convection PV operated solar dryer. (orig.)

  16. Forced convection on a heated horizontal flat plate with finite thermal conductivity in a non-Darcian porous medium

    Energy Technology Data Exchange (ETDEWEB)

    Luna, N. [Direccion de Operacion Petrolera, Direccion General de Exploracion y Explotacion de Hidrocarburos, Secretaria de Energia, 03100 Mexico DF (Mexico); Mendez, F. [Facultad de Ingenieria, UNAM, 04510 Mexico DF (Mexico)

    2005-07-01

    The steady-state analysis of conjugated heat transfer process for the hydrodynamically developed forced convection flow on a heated flat plate embedded in a porous medium is studied. The governing equations for the fluid-saturated porous medium are solved analytically using the integral boundary layer approximation. This integral solution is coupled to the energy equation for the flat plate, where the longitudinal heat conduction effects are taken into account. The resulting equations are then reduced to an integro-differential equation which is solved by regular perturbation techniques and numerical methods. The analytical and numerical predictions for the temperature profile of the plate and appropriate local and average Nusselt numbers are plotted for finite values of the conduction parameter, {alpha}, which represents the presence of the longitudinal heat conduction effects. (authors)

  17. A dry-spot model of critical heat flux and transition boiling in pool and subcooled forced convection boiling

    International Nuclear Information System (INIS)

    Ha, Sang Jun

    1998-02-01

    A new dry-spot model for critical heat flux (CHF) is proposed. The new concept for dry area formation based on Poisson distribution of active nucleation sites and the critical active site number is introduced. The model is based on the boiling phenomena observed in nucleate boiling such as Poisson distribution of active nucleation sites and formation of dry spots on the heating surface. It is hypothesized that when the number of bubbles surrounding one bubble exceeds a critical number, the surrounding bubbles restrict the feed of liquid to the microlayer under the bubble. Then a dry spot of vapor will form on the heated surface. As the surface temperature is raised, more and more bubbles will have a population of surrounding active sites over the critical number. Consequently, the number of the spots will increase and the size of dry areas will increase due to merger of several dry spots. If this trend continues, the number of effective sites for heat transport through the wall will diminish, and CHF and transition boiling occur. The model is applicable to pool and subcooled forced convection boiling conditions, based on the common mechanism that CHF and transition boiling are caused by the accumulation and coalescences of dry spots. It is shown that CHF and heat flux in transition boiling can be determined without any empirical parameter based on information on the boiling parameters such as active site density and bubble diameter, etc., in nucleate boiling. It is also shown that the present model well represents actual phenomena on CHF and transition boiling and explains the mechanism on how parameters such as flow modes (pool or flow) and surface wettability influence CHF and transition boiling. Validation of the present model for CHF and transition boiling is achieved without any tuning parameter always present in earlier models. It is achieved by comparing the predictions of CHF and heat flux in transition boiling using measured boiling parameters in nucleate

  18. Forced convective boiling heat transfer of water in vertical rectangular narrow channel

    International Nuclear Information System (INIS)

    Chen, Chong; Gao, Pu-zhen; Tan, Si-chao; Chen, Han-ying; Chen, Xian-bing

    2015-01-01

    Highlights: • Chen correlation cannot well predict the coefficient of rectangular channel. • Kim and Mudawar correlation is the best one among the Chen type correlations. • Lazarek and Black correlation predicted 7.0% of data within the ±30% error band. • The new correlation can well predict the coefficient with a small MAE of 14.4%. - Abstract: In order to research the characteristics of boiling flows in a vertical rectangular narrow channel, a series of convective boiling heat transfer experiments are performed. The test section is made of stainless steel with an inner diameter of 2 × 40 mm and heated length of 1100 mm. The 3194 experimental data points are obtained for a heat flux range of 10–700 kW/m 2 , a mass flux range of 200–2400 kg/m 2 s, a system pressure range of 0.1–2.5 MPa, and a quality range of 0–0.8. Eighteen prediction models are used to predict the flow boiling heat transfer coefficient of the rectangular narrow channel and the predicted value is compared against the database including 3194 data points, the results show that Chen type correlations and Lazarek and Black type correlations are not suitable for the rectangular channel very much. The Kim and Mudawar correlation is the best one among the 18 models. A new correlation is developed based on the superposition concept of nucleate boiling and convective boiling. the new correlation is shown to provide a good prediction against the database, evidenced by an overall MAE of 14.4%, with 95.2% and 98.6% of the data falling within ±30% and ±35% error bands, respectively

  19. A methodology to determine boundary conditions from forced convection experiments using liquid crystal thermography

    Science.gov (United States)

    Jakkareddy, Pradeep S.; Balaji, C.

    2017-02-01

    This paper reports the results of an experimental study to estimate the heat flux and convective heat transfer coefficient using liquid crystal thermography and Bayesian inference in a heat generating sphere, enclosed in a cubical Teflon block. The geometry considered for the experiments comprises a heater inserted in a hollow hemispherical aluminium ball, resulting in a volumetric heat generation source that is placed at the center of the Teflon block. Calibrated thermochromic liquid crystal sheets are used to capture the temperature distribution at the front face of the Teflon block. The forward model is the three dimensional conduction equation which is solved within the Teflon block to obtain steady state temperatures, using COMSOL. Match up experiments are carried out for various velocities by minimizing the residual between TLC and simulated temperatures for every assumed loss coefficient, to obtain a correlation of average Nusselt number against Reynolds number. This is used for prescribing the boundary condition for the solution to the forward model. A surrogate model obtained by artificial neural network built upon the data from COMSOL simulations is used to drive a Markov Chain Monte Carlo based Metropolis Hastings algorithm to generate the samples. Bayesian inference is adopted to solve the inverse problem for determination of heat flux and heat transfer coefficient from the measured temperature field. Point estimates of the posterior like the mean, maximum a posteriori and standard deviation of the retrieved heat flux and convective heat transfer coefficient are reported. Additionally the effect of number of samples on the performance of the estimation process has been investigated.

  20. Dynamical and statistical phenomena of circulation and heat transfer in periodically forced rotating turbulent Rayleigh-Bénard convection

    Science.gov (United States)

    Sterl, Sebastian; Li, Hui-Min; Zhong, Jin-Qiang

    2016-12-01

    In this paper, we present results from an experimental study into turbulent Rayleigh-Bénard convection forced externally by periodically modulated unidirectional rotation rates. We find that the azimuthal rotation velocity θ ˙(t ) and thermal amplitude δ (t ) of the large-scale circulation (LSC) are modulated by the forcing, exhibiting a variety of dynamics including increasing phase delays and a resonant peak in the amplitude of θ ˙(t ) . We also focus on the influence of modulated rotation rates on the frequency of occurrence η of stochastic cessation or reorientation events, and on the interplay between such events and the periodically modulated response of θ ˙(t ) . Here we identify a mechanism by which η can be amplified by the modulated response, and these normally stochastic events can occur with high regularity. We provide a modeling framework that explains the observed amplitude and phase responses, and we extend this approach to make predictions for the occurrence of cessation events and the probability distributions of θ ˙(t ) and δ (t ) during different phases of a modulation cycle, based on an adiabatic approach that treats each phase separately. Last, we show that such periodic forcing has consequences beyond influencing LSC dynamics, by investigating how it can modify the heat transport even under conditions where the Ekman pumping effect is predominant and strong enhancement of heat transport occurs. We identify phase and amplitude responses of the heat transport, and we show how increased modulations influence the average Nusselt number.

  1. A heat exchanger between forced flow helium gas at 14 to 18 K and liquid hydrogen at 20 K circulated by natural convection

    International Nuclear Information System (INIS)

    Green, M.A.; Ishimoto, S.; Lau, W.; Yang, S.

    2003-01-01

    The Muon Ionization Cooling Experiment (MICE) has three 350-mm long liquid hydrogen absorbers to reduce the momentum of 200 MeV muons in all directions. The muons are then re-accelerated in the longitudinal direction by 200 MHz RF cavities. The result is cooled muons with a reduced emittance. The energy from the muons is taken up by the liquid hydrogen in the absorber. The hydrogen in the MICE absorbers is cooled by natural convection to the walls of the absorber that are in turn cooled by helium gas that enters at 14 K. This report describes the MICE liquid hydrogen absorber and the heat exchanger between the liquid hydrogen and the helium gas that flows through passages in the absorber wall

  2. RCCS Experiments and Validation for High Temperature Gas-Cooled Reactor

    International Nuclear Information System (INIS)

    Chang Oh; Cliff Davis; Goon C. Park

    2007-01-01

    A reactor cavity cooling system (RCCS), an air-cooled helical coil RCCS unit immersed in the water pool, was proposed to overcome the disadvantages of the weak cooling ability of air-cooled RCCS and the complex structure of water-cooled RCCS for the high temperature gas-cooled reactor (HTGR). An experimental apparatus was constructed to investigate the various heat transfer phenomena in the water pool type RCCS, such as the natural convection of air inside the cavity, radiation in the cavity, the natural convection of water in the water pool and the forced convection of air in the cooling pipe. The RCCS experimental results were compared with published correlations. The CFX code was validated using data from the air-cooled portion of the RCCS. The RELAP5 code was validated using measured temperatures from the reactor vessel and cavity walls

  3. A zonally symmetric model for the monsoon-Hadley circulation with stochastic convective forcing

    Science.gov (United States)

    De La Chevrotière, Michèle; Khouider, Boualem

    2017-02-01

    Idealized models of reduced complexity are important tools to understand key processes underlying a complex system. In climate science in particular, they are important for helping the community improve our ability to predict the effect of climate change on the earth system. Climate models are large computer codes based on the discretization of the fluid dynamics equations on grids of horizontal resolution in the order of 100 km, whereas unresolved processes are handled by subgrid models. For instance, simple models are routinely used to help understand the interactions between small-scale processes due to atmospheric moist convection and large-scale circulation patterns. Here, a zonally symmetric model for the monsoon circulation is presented and solved numerically. The model is based on the Galerkin projection of the primitive equations of atmospheric synoptic dynamics onto the first modes of vertical structure to represent free tropospheric circulation and is coupled to a bulk atmospheric boundary layer (ABL) model. The model carries bulk equations for water vapor in both the free troposphere and the ABL, while the processes of convection and precipitation are represented through a stochastic model for clouds. The model equations are coupled through advective nonlinearities, and the resulting system is not conservative and not necessarily hyperbolic. This makes the design of a numerical method for the solution of this system particularly difficult. Here, we develop a numerical scheme based on the operator time-splitting strategy, which decomposes the system into three pieces: a conservative part and two purely advective parts, each of which is solved iteratively using an appropriate method. The conservative system is solved via a central scheme, which does not require hyperbolicity since it avoids the Riemann problem by design. One of the advective parts is a hyperbolic diagonal matrix, which is easily handled by classical methods for hyperbolic equations, while

  4. Double Diffusive Natural Convection in a Nuclear Waste Repository

    International Nuclear Information System (INIS)

    Y. Hao; J. Nitao; T.A. Buscheck; Y. Sun

    2006-01-01

    In this study, we conduct a two-dimensional numerical analysis of double diffusive natural convection in an emplacement drift for a nuclear waste repository. In-drift heat and moisture transport is driven by combined thermal- and compositional-induced buoyancy forces. Numerical results demonstrate buoyancy-driven convective flow patterns and configurations during both repository heat-up and cool-down phases. It is also shown that boundary conditions, particularly on the drip-shield surface, have strong impacts on the in-drift convective flow and transport

  5. Forced convection heat transfer of steam in a square ribbed channel

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Jiazeng; Gao, Jianmin; Gao, Tieyu [Xi' an Jiaotong University, Shaanxi (China)

    2012-04-15

    An experimental study of heat transfer characteristics of steam in a square channel (simulating a gas turbine blade cooling passage) with two opposite surfaces roughened by 60 deg parallel ribs was performed. The ranges of key governing parameters were: Reynolds numbers (Re) based on the channel hydraulic diameter (30000-140000), entry gauge pressure (0.2Mpa-0.5Mpa), heat flux of heat transfer surface area (5kWm{sup -2}-20kWm{sup -2}), and steam superheat (13 .deg. C-51 .deg. C). The test channel length was 1000mm, while the rib spacing (p/e) was 10, and the ratio of rib height (e) to hydraulic diameter (D) was 0.048. The test channel was heated by passing current through stainless steel walls instrumented with thermocouples. The local heat transfer coefficients on the ribbed wall from the channel entrance to the fully developed regions were measured. The semi-empirical correlation was fitted out by using the average Nusselt numbers in the fully developed region to cover the range of Reynolds number. The correlation can be used in the design of new generation of gas turbine blade cooled by steam.

  6. Experimental Investigation of Solar Drying for Orange Peels by Forced convection

    International Nuclear Information System (INIS)

    Ben Slama, Romdhane; Mechlouch, Fethi; Ben Daoud, Houcine

    2009-01-01

    Solar drier does not degrade any more the dried products with the manner of the products dried at the natural sun. The drying unit is composed mainly of a solar air collector and an enclosure of drying. The transformation of the solar radiation into heat is done thanks to the solar collector whose effectiveness is increased by the addition of suitable baffles in the mobile air vein. The efficiency of the collector reaches then 80. The hot air on the outlet side of the collector arrives in the enclosure of drying where the heat transfer with the product to be dried is done by convection. The kinetics drying study shows that in addition to the dependence of the temperature and air velocity of drying, the speed of drying also depends on fragmentation on the product to dry, and mainly, of the product surface in contact with the drying air. Thus, the hygrometry is reduced from 76 to 13 pour cent in one day.. The total efficiency of the drier reached 28 pour cent

  7. Primary Issues of Mixed Convection Heat Transfer Phenomena

    Energy Technology Data Exchange (ETDEWEB)

    Chae, Myeong-Seon; Chung, Bum-Jin [Kyung Hee University, Yongin (Korea, Republic of)

    2015-10-15

    The computer code analyzing the system operating and transient behavior must distinguish flow conditions involved with convective heat transfer flow regimes. And the proper correlations must be supplied to those flow regimes. However the existing safety analysis codes are focused on the Light Water Reactor and they are skeptical to be applied to the GCRs (Gas Cooled Reactors). One of the technical issues raise by the development of the VHTR is the mixed convection, which occur when the driving forces of both forced and natural convection are of comparable magnitudes. It can be encountered as in channel of the stacked with fuel elements and a decay heat removal system and in VHTR. The mixed convection is not intermediate phenomena with natural convection and forced convection but independent complicated phenomena. Therefore, many researchers have been studied and some primary issues were propounded for phenomena mixed convection. This paper is to discuss some problems identified through reviewing the papers for mixed convection phenomena. And primary issues of mixed convection heat transfer were proposed respect to thermal hydraulic problems for VHTR. The VHTR thermal hydraulic study requires an indepth study of the mixed convection phenomena. In this study we reviewed the classical flow regime map of Metais and Eckert and derived further issues to be considered. The following issues were raised: (1) Buoyancy aided an opposed flows were not differentiated and plotted in a map. (2) Experimental results for UWT and UHF condition were also plotted in the same map without differentiation. (3) The buoyancy coefficient was not generalized for correlating with buoyancy coefficient. (4) The phenomenon analysis for laminarization and returbulization as buoyancy effects in turbulent mixed convection was not established. (5) The defining to transition in mixed convection regime was difficult.

  8. Air-cooled volcanoes ? New insights on convective airflow process within Miyakejima and Piton de la Fournaise volcanoes

    Science.gov (United States)

    Antoine, R.; Geshi, N.; Kurita, K.; Aoki, Y.; Ichihara, M.; Staudacher, T.; Bachelery, P.

    2012-04-01

    Subsurface airflow in the unsaturated zone of the soil has been extensively investigated in a variety of disciplines such as mining, nuclear waste or agriculture science. In volcanology, the recent discovery of subsurface airflow close to the terminal cone of Piton de La Fournaise volcano (La Réunion Island, France) provides for the first time insights into the convective behavior of air within the unsaturated layer [1]. The characteristics of the aerothermal system, its occurrence in other volcanoes, its ability to transport heat during quiescent periods and the perturbation of this system before eruptions are the key questions we want to address following this discovery. In this study, we present observations of subsurface convective airflow within opened fractures located at the summit of Miyakejima and Piton de la Fournaise volcanoes from anemometric and temperature data. Two anemometers and thermocouples were placed at the surface and at the center of the fracture at two-meter depth during a diurnal cycle. Six thermocouples also measured the temperature at 1 meter-depth, on a profile set perpendicularly to the fracture. Finally, a thermal camera was used to make punctual measurements of the surface temperature of the fracture. At Miyakejima, two surveys were realized in winter 2010 and summer 2011. During the winter, mild air exit was detected from the fracture with a central vertical velocity of 20 to 50 cm/s. The temperature of the site was constant during the diurnal cycle (~ 22°C), leading to a maximum temperature contrast of 15°C between the fracture and the atmosphere just before sunrise. During summer, a different hydrodynamic behavior was observed: Air inflow was detected during the whole diurnal cycle with a mean velocity of 20 cm/s. The temperature of the fracture followed the temperature of the atmosphere at 2 meters-depth. In the case of Piton de la Fournaise volcano, the same convective behavior was observed at two different fractures during

  9. Lorentz force effect on mixed convection micropolar flow in a vertical conduit

    Science.gov (United States)

    Abdel-wahed, Mohamed S.

    2017-05-01

    The present work provides a simulation of control and filtration process of hydromagnetic blood flow with Hall current under the effect of heat source or sink through a vertical conduit (pipe). This work meets other engineering applications, such as nuclear reactors cooled during emergency shutdown, geophysical transport in electrically conducting and heat exchangers at low velocity conditions. The problem is modeled by a system of partial differential equations taking the effect of viscous dissipation, and these equations are simplified and solved analytically as a series solution using the Differential Transformation Method (DTM). The velocities and temperature profiles of the flow are plotted and discussed. Moreover, the conduit wall shear stress and heat flux are deduced and explained.

  10. Combined free and forced convection flow of a second order liquid through porous parallel walls

    International Nuclear Information System (INIS)

    Mishra, S.P.

    1977-01-01

    An analysis of the flow of a second order fluid through porous parallel walls with heat transfer under the influence of buoyancy forces is carried out. Solutions for the velocity and temperature fields have been obtained by an iterative procedure. The flow phenomena have been characterized by parameters like: R (cross flow Reynolds number), Λ (elastic parameter), G (Grashof number), σ (Prandtl number) and the effects of these numbers on the flow characteristics have been presented in several graphs and tables. (author)

  11. Thermal investigation of lithium-ion battery module with different cell arrangement structures and forced air-cooling strategies

    International Nuclear Information System (INIS)

    Wang, Tao; Tseng, K.J.; Zhao, Jiyun; Wei, Zhongbao

    2014-01-01

    Highlights: • Three-dimensional CFD model with forced air cooling are developed for battery modules. • Impact of different air cooling strategies on module thermal characteristics are investigated. • Impact of different model structures on module thermal responses are investigated. • Effect of inter-cell spacing on cell thermal characteristics are also studied. • The optimal battery module structure and air cooling strategy is recommended. - Abstract: Thermal management needs to be carefully considered in the lithium-ion battery module design to guarantee the temperature of batteries in operation within a narrow optimal range. This article firstly explores the thermal performance of battery module under different cell arrangement structures, which includes: 1 × 24, 3 × 8 and 5 × 5 arrays rectangular arrangement, 19 cells hexagonal arrangement and 28 cells circular arrangement. In addition, air-cooling strategies are also investigated by installing the fans in the different locations of the battery module to improve the temperature uniformity. Factors that influence the cooling capability of forced air cooling are discussed based on the simulations. The three-dimensional computational fluid dynamics (CFD) method and lumped model of single cell have been applied in the simulation. The temperature distributions of batteries are quantitatively described based on different module patterns, fan locations as well as inter-cell distance, and the conclusions are arrived as follows: when the fan locates on top of the module, the best cooling performance is achieved; the most desired structure with forced air cooling is cubic arrangement concerning the cooling effect and cost, while hexagonal structure is optimal when focus on the space utilization of battery module. Besides, the optimized inter-cell distance in battery module structure has been recommended

  12. Tests of the heat transfer characteristic of air cooler during cooling by natural convection of the Fast Breeder Reactor plants

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2013-08-15

    The purpose of this study is to confirm the heat transfer characteristics of the air cooler (AC) of the Fast Breeder Reactor(FBR) which has a function to remove the residual heat of the reactor by heat exchange between sodium and air in natural convection region if electric power would be lost. In order to confirm the characteristics of the AC installed in the FBR plant, the heat transfer test by using the AC which is installed in the sodium test loop owned by Toshiba Corporation has been planned. In this study, the heat transfer characteristic tests were performed by using the AC in sodium test loop, and the CFD analyses were conducted to evaluate the test results and the heat transfer characteristics of the plant scale AC at the condition of natural convection. In addition, the elemental tests to confirm the influence of the heat transfer tube placement by using the heat transfer tube of the same specification as the AC of Monju were performed. (author)

  13. Analysis of turbulent natural convection heat transfer in a lower plenum during external cooling using the COSMO code

    International Nuclear Information System (INIS)

    Noguchi, H.; Sawatari, Y.; Imada, T.

    2000-01-01

    The behavior of a large volumetrically heated melt pool is important to evaluate the feasibility of in-vessel retention by external flooding as an accident management. The COSMO (Coolability Simulation of Molten corium during severe accident) code has been developed at NUPEC to simulate turbulent natural convection heat transfer with internal heat source. The COSMO code solves thermal hydraulic conservation equations with turbulent model and can simulate melting and solidification process. The standard k-ε model has a limitation to describe the turbulent natural convection in the very high Rayleigh number condition (10 16 -10 17 ) assumed to occur in a lower plenum of RPV during a severe accident. This limitation results from the assumption of an analogy of momentum and energy transfer phenomena in the standard model. In this paper the modified turbulent model in which the turbulent number is treated, as a function of the flux Richardson number derived from the experiment, has been incorporated and verified by using the BALI experiments. It was found that the prediction of averaged Nusselt number became better than that of the standard model. In order to extend the COSMO code to the actual scale analysis under the external flooding conditions, more realistic boundary condition derived from the experiments should be treated. In this work the CHF correlation from ULPU experiment or the heat transfer coefficient correlation from CYBL experiment have been applied. The preliminary analysis of an actual scale analysis has been carried out under the condition of the TMI-2 accident. (author)

  14. Cryogenic analysis of forced-cooled, superconducting TF magnets for compact tokamak reactors

    International Nuclear Information System (INIS)

    Kerns, J.A.; Slack, D.S.; Miller, J.R.

    1988-01-01

    Current designs for compact tokamak reactors require the toroidal- field (TF) superconducting magnets to produce fields from 10 to 15 T at the winding pack, using high-current densities to high nuclear heat loads (greater than 1 kW/coil in some instances), which are significantly greater than the conduction and radiation heat loads for which cryogenic systems are usually designed. A cryogenic system for the TF winding pack for two such tokamak designs has been verified by performing a detailed, steady-state heat-removal analysis. Helium properties along the forced-cooled conductor flow path for a range of nuclear heat loads have been calculated. The results and implications of this analysis are presented. 12 refs., 6 figs

  15. Theoretical and experimental studies on transient heat transfer for forced convection flow of helium gas over a horizontal cylinder

    International Nuclear Information System (INIS)

    Liu Qiusheng; Katsuya Fukuda; Zhang Zheng

    2005-01-01

    Forced convection transient heat transfer for helium gas at various periods of exponential increase of heat input to a horizontal cylinder (heater) was theoretically and experimentally studied. In the theoretical study, transient heat transfer was numerically solved based on a turbulent flow model. It was clarified that the surface superheat and heat flux increase exponentially as the heat generation rate increases with the exponential function. The temperature distribution near the cylinder becomes larger as the surface temperature increases. The values of numerical solution for surface temperature and heat flux agree well with the experimental data for the cylinder diameter of 1 mm. However, the heat flux shows difference from the experimental values for the cylinder diameters of 0.7 mm and 2.0 mm. In the experimental studies, the authors measured heat flux, surface temperature, and transient heat transfer coefficients for forced convection flow of helium gas over horizontal cylinders under wide experimental conditions. The platinum cylinders with diameters of 1.0 mm, 0.7 mm, and 2.0 mm were used as test heaters and heated by electric current with an exponential increase of Q 0exp (t/τ) . The gas flow velocities ranged from 2 to 10 m/s, the gas temperatures ranged from 303 to 353 K, and the periods ranged from 50 ms to 20 s. It was clarified that the heat transfer coefficient approaches the quasi-steady-state one for the period τ longer than about 1 s, and it becomes higher for the period shorter than around 1 s. The transient heat transfer shows less dependence on the gas flowing velocity when the period becomes very shorter. The heat transfer shifts to the quasi-steady-state heat transfer for longer periods and shifts to the transient heat transfer for shorter periods at the same flow velocity. It also approaches the quasi-steady-state one for higher flow velocity at the same period. The transient heat transfer coefficients show significant dependence on

  16. A one-dimensional model of the semiannual oscillation driven by convectively forced gravity waves

    Science.gov (United States)

    Sassi, Fabrizio; Garcia, Rolando R.

    1994-01-01

    A one-dimensional model that solves the time-dependent equations for the zonal mean wind and a wave of specified zonal wavenumber has been used to illustrate the ability of gravity waves forced by time-dependent tropospheric heating to produce a semiannual oscillation (SAO) in the middle atmosphere. When the heating has a strong diurnal cycle, as observed over tropical landmasses, gravity waves with zonal wavelengths of a few thousand kilometers and phase velocities in the range +/- 40-50 m/sec are excited efficiently by the maximum vertical projection criterion (vertical wavelength approximately equals 2 x forcing depth). Calculations show that these waves can account for large zonal mean wind accelerations in the middle atmosphere, resulting in realistic stratopause and mesopause oscillations. Calculations of the temporal evolution of a quasi-conserved tracer indicate strong down-welling in the upper stratosphere near the equinoxes, which is associated with the descent of the SAO westerlies. In the upper mesosphere, there is a semiannual oscillation in tracer mixing ratio driven by seasonal variability in eddy mixing, which increases at the solstices and decreases at the equinoxes.

  17. Numerical study of magnetic field effect on nano-fluid forced convection in a channel

    Energy Technology Data Exchange (ETDEWEB)

    Heidary, H., E-mail: Heidary_ha@aut.ac.ir [Department of Mechanical Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran (Iran, Islamic Republic of); Hosseini, R. [Department of Mechanical Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran (Iran, Islamic Republic of); Pirmohammadi, M., E-mail: Pirmohamadi@pardisiau.ac.ir [Department of Mechanical Engineering, Pardis Branch, Islamic Azad University, Pardis New City, Tehran (Iran, Islamic Republic of); Kermani, M.J. [Department of Mechanical Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran (Iran, Islamic Republic of)

    2015-01-15

    In this study heat transfer and fluid flow analysis in a straight channel utilizing nano-fluid is numerically studied, while flow field is under magnetic field. Usage of nano-particles in base fluid and also applying magnetic field transverse to fluid velocity are two ways recommended in this paper to enhance heat exchange in straight duct. The fluid temperature at the channel inlet (T{sub in}) is taken less than that of the walls (T{sub w}). With assuming thermal equilibrium state of both the fluid phase and nano-particles and ignoring the slip velocity between the phases, single phase approach is used for modeling of nano-fluid. The governing equations are numerically solved in the domain by the control volume approach based on the SIMPLE technique. Numerical studies are performed over a range of Reynolds number, nano-fluid volume fraction and Hartmann number. The influence of these parameters is investigated on the local and average Nusselt numbers. Computations show excellent agreement with the literature. From this study, it is concluded that heat transfer in channels can enhance up to 75% due to the presence of nano-particles and magnetic field in channels. In industrial applications for cooling or heating purposes, the recommended ways in this paper, can provide helpful guidelines to the manufacturers to enhance efficiencies without heat exchanger area increase. - Highlights: • Addition of 10% nano-particles (copper here) can enhance the heat exchange by 26%. • Presence of magnetic field with Ha=30 in pure fluid can enhance the heat exchange by 50%. • Presence of magnetic field and nanofluid with Ha=30 and ϕ=0.1, can enhance the heat exchange by 76%. • Increasing Re{sub H} from 50 to 1000, the average Nu number can increase by a factor of ≈3.

  18. Analysis of turbulent natural convection heat transfer in a lower plenum during external cooling using the COSMO code

    Energy Technology Data Exchange (ETDEWEB)

    Noguchi, H. [Nuclear Power Engineering Corp., Tokyo (Japan); Sawatari, Y.; Imada, T. [Fuji Research Institute Corporation, Tokyo (Japan)

    2000-11-01

    The behavior of a large volumetrically heated melt pool is important to evaluate the feasibility of in-vessel retention by external flooding as an accident management. The COSMO (Coolability Simulation of Molten corium during severe accident) code has been developed at NUPEC to simulate turbulent natural convection heat transfer with internal heat source. The COSMO code solves thermal hydraulic conservation equations with turbulent model and can simulate melting and solidification process. The standard k-{epsilon} model has a limitation to describe the turbulent natural convection in the very high Rayleigh number condition (10{sup 16}-10{sup 17}) assumed to occur in a lower plenum of RPV during a severe accident. This limitation results from the assumption of an analogy of momentum and energy transfer phenomena in the standard model. In this paper the modified turbulent model in which the turbulent number is treated, as a function of the flux Richardson number derived from the experiment, has been incorporated and verified by using the BALI experiments. It was found that the prediction of averaged Nusselt number became better than that of the standard model. In order to extend the COSMO code to the actual scale analysis under the external flooding conditions, more realistic boundary condition derived from the experiments should be treated. In this work the CHF correlation from ULPU experiment or the heat transfer coefficient correlation from CYBL experiment have been applied. The preliminary analysis of an actual scale analysis has been carried out under the condition of the TMI-2 accident. (author)

  19. A visual study of forced convection boiling. Part I: Results for a flat vertical heater

    International Nuclear Information System (INIS)

    Kirby, G.J.; Staniforth, R.; Kinneir, J.H.

    1965-03-01

    This report presents the first results of a visual study of the hydrodynamics of boiling in channels and of burnout. It was found that the bubbles formed did not diffuse into the main stream at high heat fluxes, but remained close to the heater. Consequently severe coalescence took place, resulting in the formation of large regularly shaped bubbles. An analysis of the forces acting on these bubbles is given; this accounts qualitatively for the observed behaviour. The above bubble formations result from the addition of heat at a wall so that clearly isothermal models, such as those using air-water mixtures, cannot give a true representation of the flow pattern. Attempts to view the heater surface at burnout were frustrated by poor visibility through the boiling mixture. (author)

  20. Effects of rolling on single-phase water forced convective heat transfer characteristics

    International Nuclear Information System (INIS)

    Guo Yanming; Gao Puzhen; Huang Zhen

    2010-01-01

    A series of single-phase forced circulation tests in a vertical tube with rolling motion were performed in order to investigate effects of rolling motion on thermal-hydraulic characteristics. The amplitudes of the rolling motion in the tests were 10 degree, 15 degree and 20 degree. The rolling periods were 7.5 s, 10 s, 15 s and 20 s. The Reynolds number was from 6000 to 15000. Heat transfer in the test tube is bated by the rolling motion. As the test-bed rolling more acutely, the heat transfer coefficient of the test tube becomes smaller when the mass flow rate in the test tube is a constant. The heat transfer coefficient calculated by the formula which is for stable state doesn't fit very well with that from experiments. At last a formula for calculating heat transfer in rolling motion was introduced. (authors)

  1. Experimental investigation on TBAB clathrate hydrate slurry flows in a horizontal tube: Forced convective heat transfer behaviors

    Energy Technology Data Exchange (ETDEWEB)

    Wenji, Song [Guangzhou Institute of Energy Conversion, CAS, No. 2 Nengyuan Road, Tianhe District, Guangzhou 510640 (China); Key Laboratory of Renewable Energy and Gas Hydrate, CAS, No. 2 Nengyuan Road, Tianhe District, Guangzhou 510640 (China); Graduate School of Chinese Academy of Sciences, Beijing 100039 (China); Rui, Xiao; Chong, Huang; Shihui, He; Kaijun, Dong; Ziping, Feng [Guangzhou Institute of Energy Conversion, CAS, No. 2 Nengyuan Road, Tianhe District, Guangzhou 510640 (China); Key Laboratory of Renewable Energy and Gas Hydrate, CAS, No. 2 Nengyuan Road, Tianhe District, Guangzhou 510640 (China)

    2009-11-15

    Tetra-n-butyl-ammonium bromide (TBAB) clathrate hydrate slurry (CHS) is one kind of secondary refrigerants, which is promising to be applied into air-conditioning or latent-heat transportation systems as a thermal storage or cold carrying medium for energy saving. It is a solid-liquid two phase mixture which is easy to produce and has high latent heat and good fluidity. In this paper, the heat transfer characteristics of TBAB slurry were investigated in a horizontal stainless steel tube under different solid mass fractions and flow velocities with constant heat flux. One velocity region of weakened heat transfer was found. Moreover, TBAB CHS was treated as a kind of Bingham fluids, and the influences of the solid particles, flow velocity and types of flow on the forced convective heat transfer coefficients of TBAB CHS were investigated. At last, criterial correlations of Nusselt number for laminar and turbulent flows in the form of power function were summarized, and the error with experimental results was within {+-}20%. (author)

  2. Augmentation of forced-convection heat transfer by applying electric fields to disturb flow near a wall

    International Nuclear Information System (INIS)

    Nariai, H.; Ishiguro, H.; Nagata, S.; Yabe, A.

    1991-01-01

    This paper reports on the augmentation effect of electrohydrodynamically (EHD) induced flow disturbance on forced-convection heat transfer in a channel that was experimentally investigated in order to determine the applicability of the enhanced heat transfer into a low- pressure drop heat exchanger, such as a high-performance oil cooler. The investigation is mainly based on the study carried out on the unique point where the flow is disturbed actively and controllably by applying electric fields between the wall and array of wire electrodes installed near the wall along the main stream. The liquid mixture of refrigerant R113 (96 wt %) and ethanol (4 wt %), called Fronsorubu AE, was selected as a working fluid. Heat transfer was found to be promoted intensely in the turbulent flow as well as in the laminar flow, up to a factor of about twenty-three in the case of laminar flow. It is noteworthy that the rate of increase in heat transfer coefficient is larger compared to that in the pressure drop. From a measurement of velocities by a laser Doppler velocimeter, it was made clear that the electrohydrodynamically induced flow disturbance brings about large heat transfer coefficients

  3. Numerical investigation of laminar forced convection heat transfer in rectangular channels with different block geometries using nano-fluids

    Directory of Open Access Journals (Sweden)

    Foroutani Saeed

    2017-01-01

    Full Text Available This research investigates the laminar steady-forced convection heat transfer of a Cu-water nanofluid in a 2-D horizontal channel with different block geometries attached to the bottom wall. The block geometries assumed in this research are triangular and curve blocks. The governing equations associated with the required boundary conditions are solved using finite volume method based on the SIMPLE technique and the effects of Reynolds number, nanofluid volume fraction, block geometry, and the numbers of blocks on the local and average Nusselt numbers are explored. The obtained results show that nanoparticles can effectively enhance the heat transfer in a channel. Furthermore, the local and average Nusselt number distribution is strongly dependent on the block geometry. As observed, the heat transfer augments with the increase in the Reynolds number and nanofluid volume fraction for both block geometries. It is also concluded that the average Nusselt number of the curve block is higher than that of the triangular block for different Reynolds numbers which declares the importance of the block geometry in the heat transfer enhancement.

  4. Effect of Magnetic Field on Entropy Generation Due to Laminar Forced Convection Past a Horizontal Flat Plate

    Directory of Open Access Journals (Sweden)

    Moh'd A. Al-Nimr

    2004-06-01

    Full Text Available Magnetic field effect on local entropy generation due to steady two-dimensional laminar forced convection flow past a horizontal plate was numerically investigated. This study was focused on the entropy generation characteristics and its dependency on various dimensionless parameters. The effect of various dimensionless parameters, such as Hartmann number (Ha, Eckert number (Ec, Prandtl number (Pr, Joule heating parameter (R and the free stream temperature parameter (θ∞ on the entropy generation characteristics is analyzed. The dimensionless governing equations in Cartesian coordinate were solved by an implicit finite difference technique. The solutions were carried out for Ha2=0.5-3, Ec=0.01-0.05, Pr=1-5 and θ∞=1.1-2.5. It was found that, the entropy generation increased with increasing Ha, Ec and R. While, increasing the free stream temperature parameter, and Prandtl number tend to decrease the local entropy generation.

  5. Impact of forced convective radiative heat and mass transfer mechanisms on 3D Carreau nanofluid: A numerical study

    Science.gov (United States)

    Khan, M.; Irfan, M.; Khan, W. A.

    2017-12-01

    Nanoliquids retain remarkable features that have fascinated various researchers owing to their utilization in nanoscience and nanotechnology. We will present a mathematical relation for 3D forced convective heat and mass transfer mechanism of a Carreau nanoliquid over a bidirectional stretched surface. Additionally, the features of heat source/sink and nonlinear thermal radiation are considered for the 3D Carreau nanoliquid. The governing nonlinear PDEs are established and altered into a set of nonlinear ODEs by utilizing a suitable conversion. A numerical approach, namely the bvp4c is adopted to resolve the resultant equations. The achieved outcomes are schemed and conferred in detail for somatic parameters. It is realized that amassed values of Brownian motion parameter Nb lead to enhance the temperature of the Carreau nanoliquid while quite conflicting behavior is being noticed for the concentration of the Carreau nanoliquid. Moreover, it is also noted that the influence of heat source δ > 0 is relatively antithetic to heat sink δ communication with these results.

  6. Burnout experiment in subcooled forced-convection boiling of water for beam dumps of a high power neutral beam injector

    International Nuclear Information System (INIS)

    Horiike, Hiroshi; Kuriyama, Masaaki; Morita, Hiroaki

    1982-01-01

    Experimental studies were made on burnout heat flux in highly subcooled forced-convection boiling of water for the design of beam dumps of a high power neutral beam injector for Japan Atomic Energy Research Institute Tokamak-60. These dumps are composed of many circular tubes with two longitudinal fins. The tube was irradiated with nonuniformly distributed hydrogen ion beams of 120 to 200 kW for as long as 10 s. The coolant water was circulated at flow velocities of 3 to 7.5 m/s at exit pressures of 0.4 to 0.9 MPa. The burnout and film-boiling data were obtained at local heat fluxes of 8 to 15 MW/m 2 . These values were as high as 2.5 times larger than those for the circumferentially uniform heat flux case with the same parameters. These data showed insensitivity to local subcooling as well as to pressure, and simple burnout correlations were derived. From these results, the beam dumps have been designed to receive energetic beam fluxes of as high as 5 MW/m 2 with a margin of a factor of 2 for burnout

  7. Theoretical models to predict the transient heat transfer performance of HIFAR fuel elements under non-forced convective conditions

    International Nuclear Information System (INIS)

    Green, W.J.

    1987-04-01

    Simple theoretical models have been developed which are suitable for predicting the thermal responses of irradiated research fuel elements of markedly different geometries when they are subjected to loss-of-coolant accident conditions. These models have been used to calculate temperature responses corresponding to various non-forced convective conditions. Comparisons between experimentally observed temperatures and calculated values have shown that a suitable value for surface thermal emissivity is 0.35; modelling of the fuel element beyond the region of the fuel plate needs to be included since these areas account for approximately 25 per cent of the thermal power dissipated; general agreement between calculated and experimental temperatures for both transient and steady-state conditions is good - the maximum discrepancy between calculated and experimental temperatures for a HIFAR Mark IV/V fuel element is ∼ 70 deg C, and for an Oak Ridge Reactor (ORR) box-type fuel element ∼ 30 deg C; and axial power distribution does not significantly affect thermal responses for the conditions investigated. Overall, the comparisons have shown that the models evolved can reproduce experimental data to a level of accuracy that provides confidence in the modelling technique and the postulated heat dissipation mechanisms, and that these models can be used to predict thermal responses of fuel elements in accident conditions that are not easily investigated experimentally

  8. Drying of prickly pear cactus cladodes (Opuntia ficus indica) in a forced convection tunnel

    Energy Technology Data Exchange (ETDEWEB)

    Lopez, R.; de Ita, A.; Vaca, M. [Universidad Autonoma Metropolitana-Azcapotzalco, DePt. de Energia, Area de Termofluidos, Av. San Pablo 180, Col. Reynosa Tamaulipas, Del. Azcapotzalco, C.P. 02200, Mexico D.F. (Mexico)

    2009-09-15

    In this work we evaluated the kinetics of drying of Opuntia's cladodes observing two conditions: complete cladode with the protective cuticle of the intact product and with reduced cuticle (partially removed), using a drying tunnel with forced flow. The temperature of the air was set at 35, 45, and 60 C with velocities of 1.5 and 3.0 m/s. The conditions of the environment were controlled and maintained at 22 C and 30% of relative humidity. The results show that the drying time was considerably reduced when approximately 30% of the cuticle that protects the product was removed. Additionally, the temperature had greater influence than the velocity of the air. The numerical model that best describes the behavior of the drying process is the double logarithmic one, with the imposed restrictions of r close to the unit, the lowest possible {chi}{sup 2} and the RSEM tending to zero. The characteristic drying function of the product resulted in a third-grade exponential curve, where r and SD were the corresponding selection criteria. (author)

  9. Drying of prickly pear cactus cladodes (Opuntia ficus indica) in a forced convection tunnel

    International Nuclear Information System (INIS)

    Lopez, R.; Ita, A. de; Vaca, M.

    2009-01-01

    In this work we evaluated the kinetics of drying of Opuntia's cladodes observing two conditions: complete cladode with the protective cuticle of the intact product and with reduced cuticle (partially removed), using a drying tunnel with forced flow. The temperature of the air was set at 35, 45, and 60 deg. C with velocities of 1.5 and 3.0 m/s. The conditions of the environment were controlled and maintained at 22 deg. C and 30% of relative humidity. The results show that the drying time was considerably reduced when approximately 30% of the cuticle that protects the product was removed. Additionally, the temperature had greater influence than the velocity of the air. The numerical model that best describes the behavior of the drying process is the double logarithmic one, with the imposed restrictions of r close to the unit, the lowest possible χ 2 and the RSEM tending to zero. The characteristic drying function of the product resulted in a third-grade exponential curve, where r and SD were the corresponding selection criteria.

  10. Correlation of Normal Gravity Mixed Convection Blowoff Limits with Microgravity Forced Flow Blowoff Limits

    Science.gov (United States)

    Marcum, Jeremy W.; Olson, Sandra L.; Ferkul, Paul V.

    2016-01-01

    The axisymmetric rod geometry in upward axial stagnation flow provides a simple way to measure normal gravity blowoff limits to compare with microgravity Burning and Suppression of Solids - II (BASS-II) results recently obtained aboard the International Space Station. This testing utilized the same BASS-II concurrent rod geometry, but with the addition of normal gravity buoyant flow. Cast polymethylmethacrylate (PMMA) rods of diameters ranging from 0.635 cm to 3.81 cm were burned at oxygen concentrations ranging from 14 to 18% by volume. The forced flow velocity where blowoff occurred was determined for each rod size and oxygen concentration. These blowoff limits compare favorably with the BASS-II results when the buoyant stretch is included and the flow is corrected by considering the blockage factor of the fuel. From these results, the normal gravity blowoff boundary for this axisymmetric rod geometry is determined to be linear, with oxygen concentration directly proportional to flow speed. We describe a new normal gravity 'upward flame spread test' method which extrapolates the linear blowoff boundary to the zero stretch limit in order to resolve microgravity flammability limits-something current methods cannot do. This new test method can improve spacecraft fire safety for future exploration missions by providing a tractable way to obtain good estimates of material flammability in low gravity.

  11. Investigation of forced convection heat transfer of supercritical pressure water in a vertically upward internally ribbed tube

    International Nuclear Information System (INIS)

    Wang Jianguo; Li Huixiong; Guo Bin; Yu Shuiqing; Zhang Yuqian; Chen Tingkuan

    2009-01-01

    In the present paper, the forced convection heat transfer characteristics of water in a vertically upward internally ribbed tube at supercritical pressures were investigated experimentally. The six-head internally ribbed tube is made of SA-213T12 steel with an outer diameter of 31.8 mm and a wall thickness of 6 mm and the mean inside diameter of the tube is measured to be 17.6 mm. The experimental parameters were as follows. The pressure at the inlet of the test section varied from 25.0 to 29.0 MPa, and the mass flux was from 800 to 1200 kg/(m 2 s), and the inside wall heat flux ranged from 260 to 660 kW/m 2 . According to experimental data, the effects of heat flux and pressure on heat transfer of supercritical pressure water in the vertically upward internally ribbed tube were analyzed, and the characteristics and mechanisms of heat transfer enhancement, and also that of heat transfer deterioration, were also discussed in the so-called large specific heat region. The drastic changes in thermophysical properties near the pseudocritical points, especially the sudden rise in the specific heat of water at supercritical pressures, may result in the occurrence of the heat transfer enhancement, while the covering of the heat transfer surface by fluids lighter and hotter than the bulk fluid makes the heat transfer deteriorated eventually and explains how this lighter fluid layer forms. It was found that the heat transfer characteristics of water at supercritical pressures were greatly different from the single-phase convection heat transfer at subcritical pressures. There are three heat transfer modes of water at supercritical pressures: (1) normal heat transfer, (2) deteriorated heat transfer with low HTC but high wall temperatures in comparison to the normal heat transfer, and (3) enhanced heat transfer with high HTC and low wall temperatures in comparison to the normal heat transfer. It was also found that the heat transfer deterioration at supercritical pressures was

  12. Forecasting Cool Season Daily Peak Winds at Kennedy Space Center and Cape Canaveral Air Force Station

    Science.gov (United States)

    Barrett, Joe, III; Short, David; Roeder, William

    2008-01-01

    The expected peak wind speed for the day is an important element in the daily 24-Hour and Weekly Planning Forecasts issued by the 45th Weather Squadron (45 WS) for planning operations at Kennedy Space Center (KSC) and Cape Canaveral Air Force Station (CCAFS). The morning outlook for peak speeds also begins the warning decision process for gusts ^ 35 kt, ^ 50 kt, and ^ 60 kt from the surface to 300 ft. The 45 WS forecasters have indicated that peak wind speeds are a challenging parameter to forecast during the cool season (October-April). The 45 WS requested that the Applied Meteorology Unit (AMU) develop a tool to help them forecast the speed and timing of the daily peak and average wind, from the surface to 300 ft on KSC/CCAFS during the cool season. The tool must only use data available by 1200 UTC to support the issue time of the Planning Forecasts. Based on observations from the KSC/CCAFS wind tower network, surface observations from the Shuttle Landing Facility (SLF), and CCAFS upper-air soundings from the cool season months of October 2002 to February 2007, the AMU created multiple linear regression equations to predict the timing and speed of the daily peak wind speed, as well as the background average wind speed. Several possible predictors were evaluated, including persistence, the temperature inversion depth, strength, and wind speed at the top of the inversion, wind gust factor (ratio of peak wind speed to average wind speed), synoptic weather pattern, occurrence of precipitation at the SLF, and strongest wind in the lowest 3000 ft, 4000 ft, or 5000 ft. Six synoptic patterns were identified: 1) surface high near or over FL, 2) surface high north or east of FL, 3) surface high south or west of FL, 4) surface front approaching FL, 5) surface front across central FL, and 6) surface front across south FL. The following six predictors were selected: 1) inversion depth, 2) inversion strength, 3) wind gust factor, 4) synoptic weather pattern, 5) occurrence of

  13. Coupled calculation of external heat transfer and material temperatures of convection-cooled turbine blades. Final report; Gekoppelte Berechnung des aeusseren Waermeuebergangs und der Materialtemperaturen konvektionsgekuehlter Turbinenschaufeln. Abschlussbericht

    Energy Technology Data Exchange (ETDEWEB)

    Heselhaus, A.

    1997-05-01

    In this work a hybrid program system consisting of a 3D finite-volume Navier-Stokes flow solver and a 3D finite-element heat conduction solver has been developed. It enables the coupled calculation of structure temperatures in diabatic solid/fluid configurations. The grids of both the finite element and the finite volume computational domain may be completely independent. The coupled program fully resolves the thermal interaction between heat transfer and the resulting material temperatures. The developed coupling algorithm is numerically stable, conservative and works without the need to define ambient temperatures in the flowfield. This allows for the simulation of any solid/fluid configuration. When simulating combined blade/endwall cooling or filmcooling, only a coupled procedure is capable to completely account for the interaction between all relevant thermal parameters. It is found that the coupled calculation of convective cooling in a realistic guide vane leads locally to 45 K higher and 107 K lower blade temperatures than the uncoupled calculation. This shows that accounting for the thermal interaction between the flow and the structure offers both potential to save cooling air and a lower margin of safety when designing cooling systems close to the thermal limits of the blade material. (orig.) [Deutsch] Im Rahmen der vorliegenden Arbeit wurde ein Verfahren zur Berechnung der Temperaturverteilung in diabat umstroemten Koerpern entwickelt, bei dem ein 3D-Finite Volumen Navier-Stokes Stroemungsloeser und ein 3D-Finite Elemente Waermeleitungsloeser zu einem hybriden Programmsystem gekoppelt werden. Dabei besteht die Moeglichkeit, voellig unabhaengige Rechennetze fuer Stroemung und Struktur zu verwenden. Mit dem gekoppelten Verfahren kann die Wechselwirkung zwischen resultierenden Materialtemperaturen und dem davon rueck-beeinflussten Waermeuebergang beruecksichtigt werden. Weiterhin ist der hier entwickelte, stabile und konservative Kopplungsalgorithmus nicht

  14. Heat Transfer and Cooling Techniques at Low Temperature

    CERN Document Server

    Baudouy, B

    2014-07-17

    The first part of this chapter gives an introduction to heat transfer and cooling techniques at low temperature. We review the fundamental laws of heat transfer (conduction, convection and radiation) and give useful data specific to cryogenic conditions (thermal contact resistance, total emissivity of materials and heat transfer correlation in forced or boiling flow for example) used in the design of cooling systems. In the second part, we review the main cooling techniques at low temperature, with or without cryogen, from the simplest ones (bath cooling) to the ones involving the use of cryocoolers without forgetting the cooling flow techniques.

  15. Heat Transfer and Cooling Techniques at Low Temperature

    Energy Technology Data Exchange (ETDEWEB)

    Baudouy, B [Saclay (France)

    2014-07-01

    The first part of this chapter gives an introduction to heat transfer and cooling techniques at low temperature. We review the fundamental laws of heat transfer (conduction, convection and radiation) and give useful data specific to cryogenic conditions (thermal contact resistance, total emissivity of materials and heat transfer correlation in forced or boiling flow for example) used in the design of cooling systems. In the second part, we review the main cooling techniques at low temperature, with or without cryogen, from the simplest ones (bath cooling) to the ones involving the use of cryocoolers without forgetting the cooling flow techniques.

  16. Wall-cooling-induced mixed-convection flow recirculation in a vertical square-array multi-rod channel

    International Nuclear Information System (INIS)

    Luangdilok, W.; Todreas, N.E.

    1989-01-01

    This work investigated the structure of penetrative flow recirculation and associated flow conditions in a multi-rod channel induced by interassembly heat transfer that causes cooling through channel walls. Three investigation approaches, experimental, numerical, and analytical were employed in a complimentary fashion. Physical experiments involved water flow visualization and temperature measurement in a 4x4 rod square channel. Numerical experiments involved 3-dimensional simulations of water and sodium flow in a 2x2-rod channels. An approximate reverse flow model including Prandtl number effect was developed. A correlating equation based on the model and experiments was verified for water to correctly predict the trend of the 4x4-rod experimental penetration depth data. (orig.)

  17. The Physical Connection and Magnetic Coupling of the MICE Cooling Channel Magnets and the Magnet Forces for Various MICE Operating Modes

    International Nuclear Information System (INIS)

    Yang, Stephanie Q.; Baynham, D.E.; Fabricatore, Pasquale; Farinon, Stefania; Green, Michael A.; Ivanyushenkov, Yury; Lau, Wing W.; Maldavi, S.M.; Virostek, Steve P.; Witte, Holger

    2006-01-01

    A key issue in the construction of the MICE cooling channel is the magnetic forces between various elements in the cooling channel and the detector magnets. This report describes how the MICE cooling channel magnets are hooked to together so that the longitudinal magnetic forces within the cooling channel can be effectively connected to the base of the experiment. This report presents a magnetic force and stress analysis for the MICE cooling channel magnets, even when longitudinal magnetic forces as large as 700 kN (70 tons) are applied to the vacuum vessel of various magnets within the MICE channel. This report also shows that the detector magnets can be effectively separated from the central MICE cooling channel magnets without damage to either type of magnet component

  18. Estimation of radiative forcing and chore length of shallow convective clouds (SCC) based on broadband pyranometer measurement network

    Science.gov (United States)

    Shi, H.

    2017-12-01

    We presented a method to identify and calculate cloud radiative forcing (CRF) and horizontal chore length (L) of shallow convective clouds (SCC) using a network of 9 broadband pyranometers. The analyzing data was collected from the SCC campaign during two years summers (2015 2016) at Baiqi site over Inner Mongolia grassland. The network of pyranometers was operated across a spatial domain covering 42.16-42.30° N and 114.83-114.98° E. The SCC detection method was verified by observer reports and cameras, which showed that the detection method and human observations were in agreement about 75 %. The differences between the SCC detection method and human observations can be responsible for following factors: 1) small or dissipating clouds can be neglected for the value of 1 min of temporal resolution of pyranometer; 2) human observation recorded weather conditions four times every day; 3) SCC was indistinguishable from coexistence of SCC and Cirrus (Ci); 4) the SCC detection method is weighted toward clouds crossing the sun's path, while the human observer can view clouds over the entire sky. The deviation of L can be attributed to two factors: 1) the accuracy of wind speed at height of SCC and the ratio of horizontal and vertical length play a key role in determine values of L; 2) the effect of variance of solar zenith angle can be negligible. The downwelling shortwave CRF of SCC was -134.1 Wm-2. The average value of L of SCC was 1129 m. Besides, the distribution of normalized cloud chore length agreed well with power-law fit.

  19. Using C-Band Dual-Polarization Radar Signatures to Improve Convective Wind Forecasting at Cape Canaveral Air Force Station and NASA Kennedy Space Center

    Science.gov (United States)

    Amiot, Corey G.; Carey, Lawrence D.; Roeder, William P.; McNamara, Todd M.; Blakeslee, Richard J.

    2017-01-01

    The United States Air Force's 45th Weather Squadron (45WS) is the organization responsible for monitoring atmospheric conditions at Cape Canaveral Air Force Station and NASA Kennedy Space Center (CCAFS/KSC) and issuing warnings for hazardous weather conditions when the need arises. One such warning is issued for convective wind events, for which lead times of 30 and 60 minutes are desired for events with peak wind gusts of 35 knots or greater (i.e., Threshold-1) and 50 knots or greater (i.e., Threshold-2), respectively (Roeder et al. 2014).

  20. Investigation of the loss of forced cooling test by using the high temperature engineering test reactor (HTTR) (Contract research)

    International Nuclear Information System (INIS)

    Nakagawa, Shigeaki; Takamatsu, Kuniyoshi; Inaba, Yoshitomo; Goto, Minoru; Tochio, Daisuke

    2007-09-01

    The three gas circulators trip test and the vessel cooling system stop test as the safety demonstration test by using the High Temperature engineering Test Reactor (HTTR) are under planning to demonstrate inherent safety features of High Temperature Gas-cooled Reactor. All three gas circulators to circulate the helium gas as the coolant are stopped to simulate the loss of forced cooling in the three gas circulators trip test. The stop of the vessel cooling system located outside the reactor pressure vessel to remove the residual heat of the reactor core follows the stop of all three gas circulators in the vessel cooling system stop test. The analysis of the reactor transient for such tests and abnormal events postulated during the test was performed. From the result of analysis, it was confirmed that the three gas circulators trip test and the vessel cooling system stop test can be performed within the region of the normal operation in the HTTR and the safety of the reactor facility is ensured even if the abnormal events would occur. (author)

  1. An experimental investigation into the deployment of 3-D, finned wing and shape memory alloy vortex generators in a forced air convection heat pipe fin stack

    International Nuclear Information System (INIS)

    Aris, M.S.; McGlen, R.; Owen, I.; Sutcliffe, C.J.

    2011-01-01

    Forced air convection heat pipe cooling systems play an essential role in the thermal management of electronic and power electronic devices such as microprocessors and IGBT's (Integrated Gate Bipolar Transistors). With increasing heat dissipation from these devices, novel methods of improving the thermal performance of fin stacks attached to the heat pipe condenser section are required. The current work investigates the use of a wing type surface protrusions in the form of 3-D delta wing tabs adhered to the fin surface, thin wings punched-out of the fin material and TiNi shape memory alloy delta wings which changed their angles of attack based on the fin surface temperature. The longitudinal vortices generated from the wing designs induce secondary mixing of the cooler free stream air entering the fin stack with the warmer fluid close to the fin surfaces. The change in angle of the attack of the active delta wings provide heat transfer enhancement while managing flow pressure losses across the fin stack. A heat transfer enhancement of 37% compared to a plain fin stack was obtained from the 3-D tabs in a staggered arrangement. The punched-out delta wings in the staggered and inline arrangements provided enhancements of 30% and 26% respectively. Enhancements from the active delta wings were lower at 16%. However, as these devices reduce the pressure drop through the fin stack by approximately 19% in the de-activate position, over the activated position, a reduction in fan operating cost may be achieved for systems operating with inlet air temperatures below the maximum inlet temperature specification for the device. CFD analysis was also carried out to provide additional detail of the local heat transfer enhancement effects. The CFD results corresponded well with previously published reports and were consistent with the experimental findings. - Highlights: → Heat transfer enhancements of heat pipe fin stacks was successfully achieved using fixed and active delta

  2. Experimental and numerical thermohydraulic study of a supercritical helium loop in forced convection under pulsed heat loads

    International Nuclear Information System (INIS)

    Lagier, Benjamin

    2014-01-01

    Future fusion reactor devices such as ITER or JT-60SA will produce thermonuclear fusion reaction in plasmas at several millions of degrees. The confinement in the center of the chamber is achieved by very intense magnetic fields generated by superconducting magnets. These coils have to be cooled down to 4.4 K through a forced flow of supercritical helium. The cyclic behavior of the machines leads to pulsed thermal heat loads which will have to be handled by the refrigerator. The HELIOS experiment built in CEA Grenoble is a scaled down model of the helium distribution system of the tokamak JT-60SA composed of a saturated helium bath and a supercritical helium loop. The thesis work explores HELIOS capabilities for experimental and numerical investigations on three heat load smoothing strategies: the use of the saturated helium bath as an open thermal buffer, the rotation speed variation of the cold circulator and the bypassing of the heated section. The developed model describes well the physical evolutions of the helium loop (pressure, temperature, mass flow) submitted to heat loads observed during experiments. Advanced controls have been tested and validated to improve the stability of the refrigerator and to optimize the refrigeration power. (author) [fr

  3. An experimental and multi-objective optimization study of a forced draft cooling tower with different fills

    International Nuclear Information System (INIS)

    Singh, Kuljeet; Das, Ranjan

    2016-01-01

    Highlights: • Experimental and optimization study on forced draft cooling tower is done. • New correlations for splash, trickle and film type fills are proposed. • Multi-objective performance optimization study has been done using NSGA-II. • Weighted decision making criterion is proposed depending upon user priority. • Proposed generalized methodology can be implemented in industrial cooling towers. - Abstract: In the present study, a forced draft mechanical cooling tower has been experimentally investigated using trickle, film and splash fills. Various performance parameters such as range, tower characteristic ratio, effectiveness and water evaporation rate are first analyzed for each fill. Thereafter, based upon the experimental data, pertinent correlations have been developed for performance parameters by considering mass flow rates of water and air as design variables. Each of the performance parameters is considered to be an individual objective function and all objectives are then simultaneously optimized for maximizing the performance of the cooling tower using elitist Non-Dominated Sorting Genetic Algorithm (NSGA-II). The multi-objective optimization algorithm gives a set of possible combinations of design variables, which is referred as the optimal Pareto-front, out of which a unique combination is selected based upon a decision making criterion. The proposed decision making procedure evaluates a Decision Making Score (DMS) based on assigned performance priorities for each point of the Pareto-front. Depending on DMS a unique combination of design variables is then selected for each type of fill that maximizes the tower’s performance. These optimal points and the corresponding objective function are finally compared and based upon the highest DMS value, the wire-mesh (trickle) fill is found to be the most efficient fill under the present experimental conditions. The methodology presented in this work has been made more generalized, so that it

  4. Prediction of hottest spot temperature in power transformer windings with non-directed and directed oil-forced cooling

    Energy Technology Data Exchange (ETDEWEB)

    Taghikhani, M.A.; Gholami, A. [Electrical Engineering Department, Iran University of Science and Technology (IUST), Narmak, 16846 Tehran (Iran)

    2009-09-15

    Power transformer outages have a considerable economic impact on the operation of an electrical network. One of the most important parameters governing transformer's life expectancy is the hottest spot temperature (HST) value. The classical approach has been to consider the hottest spot temperature as the sum of the ambient temperature, the top-oil temperature rise, and the hottest spot to top-oil temperature gradient. The authors proposed a numerical method based on heat transfer theory using the finite element method and they only needed to solve heat conduction equation. The transformer selected for simulation was a 32 MVA transformer with non-directed oil-forced (NDOF) cooling and directed oil-forced (DOF) cooling. A comparison of the authors results with those obtained from finite integral transform and experimental test confirms the validity and accuracy of the proposed method. (author)

  5. The influence of cooling techniques on cutting forces and surface roughness during cryogenic machining of titanium alloys

    Directory of Open Access Journals (Sweden)

    Wstawska Iwona

    2016-12-01

    Full Text Available Titanium alloys are one of the materials extensively used in the aerospace industry due to its excellent properties of high specific strength and corrosion resistance. On the other hand, they also present problems wherein titanium alloys are extremely difficult materials to machine. In addition, the cost associated with titanium machining is also high due to lower cutting velocities and shorter tool life. The main objective of this work is a comparison of different cooling techniques during cryogenic machining of titanium alloys. The analysis revealed that applied cooling technique has a significant influence on cutting force and surface roughness (Ra parameter values. Furthermore, in all cases observed a positive influence of cryogenic machining on selected aspects after turning and milling of titanium alloys. This work can be also the starting point to the further research, related to the analysis of cutting forces and surface roughness during cryogenic machining of titanium alloys.

  6. Modeling of the Cutting Forces in Turning Process Using Various Methods of Cooling and Lubricating: An Artificial Intelligence Approach

    Directory of Open Access Journals (Sweden)

    Djordje Cica

    2013-01-01

    Full Text Available Cutting forces are one of the inherent phenomena and a very significant indicator of the metal cutting process. The work presented in this paper is an investigation of the prediction of these parameters in turning using soft computing techniques. During the experimental research focus is placed on the application of various methods of cooling and lubricating of the cutting zone. On this occasion were used the conventional method of cooling and lubricating, high pressure jet assisted machining, and minimal quantity lubrication technique. The data obtained by experiment are used to create two different models, namely, artificial neural network and adaptive networks based fuzzy inference systems for prediction of cutting forces. Furthermore, both models are compared with the experimental data and results are indicated.

  7. Convective behaviour in vapour-gas-aerosol mixtures

    International Nuclear Information System (INIS)

    Clement, C.F.

    1986-01-01

    Unusual convective behaviour can occur in mixtures of gases and heavy vapour, including stabilization of mixtures hot at the base and 'upside-down' convection in mixtures hot at the top. Previous work produced a criterion for this behaviour which ignored the necessary presence of an aerosol. Modification arising from aerosol condensation is derived and is shown to involve the Lewis and condensation numbers of the mixture, as well as a quantity involving the temperature drop across a boundary layer. It becomes negligible at high temperatures, but can crucially affect the temperature for the onset of unusual behaviour. Aerosol formation produces an asymmetry between the convective forces in boundary layers in which the mixture is being heated and cooled, respectively, for example at the base and roof of a cavity. The convective behaviour discussed could occur in situations relevant to nuclear safety. (author)

  8. A system for the discharge of gas bubbles from the coolant flow of a nuclear reactor cooled by forced circulation

    International Nuclear Information System (INIS)

    Markfort, D.; Kaiser, A.; Dohmen, A.

    1975-01-01

    In a reactor cooled by forced circulation the gas bubbles carried along with the coolant flow are separated before entering the reactor core or forced away into the external zones. For this purpose the coolant is radially guided into a plenum below the core and deflected to a tangential direction by means of flow guide elements. The flow runs spirally downwards. On the bubbles, during their dwell time in this channel, the buoyant force and a force towards the axis of symmetry of the tank are exerted. The major part of the coolant is directed into a radial direction by means of a guiding apparatus in the lower section of the channel and guided through a chimney in the plenum to the center of the reactor core. This inner chimney is enclosed by an outer chimney for the core edge zones through which coolant with a small share of bubbles is taken away. (RW) [de

  9. Alternatives for metal hydride storage bed heating and cooling

    International Nuclear Information System (INIS)

    Fisher, I.A.; Ramirez, F.B.; Koonce, J.E.; Ward, D.E.; Heung, L.K.; Weimer, M.; Berkebile, W.; French, S.T.

    1991-01-01

    The reaction of hydrogen isotopes with the storage bed hydride material is exothermic during absorption and endothermic during desorption. Therefore, storage bed operation requires a cooling system to remove heat during absorption, and a heating system to add the heat needed for desorption. Three storage bed designs and their associated methods of heating and cooling and accountability are presented within. The first design is the current RTF (Replacement Tritium Facility) nitrogen heating and cooling system. The second design uses natural convection cooling with ambient glove box nitrogen and electrical resistance for heating. This design is referred to as the Naturally Cooled/Electrically Heated (NCEH) design. The third design uses forced convection cooling with ambient glove box nitrogen and electrical resistance for heating. The design is referred to as the Forced Convection Cooled/Electrically Heated (FCCEH) design. In this report the operation, storage bed design, and equipment required for heating, cooling, and accountability of each design are described. The advantages and disadvantages of each design are listed and discussed. Based on the information presented within, it is recommended that the NCEH design be selected for further development

  10. Experimental and Numerical Investigation of Forced Convection Heat Transfer in Heat Sink with Rectangular Plates at Varying Inclinations on Vertical Base

    Science.gov (United States)

    Patil, Harshal Bhauso; Dingare, Sunil Vishnu

    2018-03-01

    Heat exchange upgrade is a vital territory of research area. Utilization of reasonable systems can bring about noteworthy specialized points of interest coming about reserve funds of cost. Rectangular plates are viewed as best balance arrangement utilized for heat exchange improvement. This gives an enlargement strategy to heat exchange with beginning of limit layer and vortex development. To assess and look at the rate of heat exchange enhancement by rectangular plate fins with differing inclinations (0°-30°-60°), shifting Re and heat supply under forced convection are the principle destinations of this study. The study is done by fluctuating introductions of fins with various inclinations, input heat supply and Re under forced convection. The coefficient of heat transfer increments observed with the expansion in air speed for all the examined designs. The coefficient of the heat transfer is discovered higher at the edge of introduction of fins at 30° for inline arrangement and 0° for staggered arrangement. Looking at both the arrangements, it is discovered that the heat transfer coefficient in 0° fin staggered arrangement is about 17% higher than 30° inline arrangement and 76% higher than the vertical plate fin. For plate fin heat sink, boundary layer formation and growth results in decrease of the coefficient of heat transfer in forced convection. This issue is overcome by accommodating some rectangular fins on the plate fin. It brings about increment of heat transfer coefficient of the RPFHS under the states of trial factors. As indicated by past research, it is discovered that examination of the plate fin heat sink with various sorts of fins for horizontal orientation is done yet but this investigation expects to discover the upgrade of transfer coefficient of plate fin heat sink for its vertical position with rectangular plates at different inclinations under the shifting scopes of heat input supply, fin arrangements and Reynolds number (Re).

  11. On the optimum performance of forced draft counter flow cooling towers

    International Nuclear Information System (INIS)

    Soeylemez, M.S.

    2004-01-01

    A thermo-hydraulic performance optimization analysis is presented, yielding simple algebraic formula for estimating the optimum performance point of counter current mechanical draft wet cooling towers. The effectiveness-Ntu method is used in the present study, together with the derivation of psychometric properties of moist air based on a numerical approximation method, for thermal performance analysis of wet cooling towers of the counter flow type

  12. Long-term unsteadiness and large-scale structures in Rayleigh-Bénard convection with and without electromagnetic forcing

    NARCIS (Netherlands)

    Verdoold, J.

    2010-01-01

    This dissertation focuses on turbulent thermal convection, which occurs in a wide range of (geo)physical situations, like in the atmosphere, the oceans, the interior of stars or planets, and engineering applications, like metal casting or crystal growth processes. In this work, a special type of

  13. Tool for Forecasting Cool-Season Peak Winds Across Kennedy Space Center and Cape Canaveral Air Force Station

    Science.gov (United States)

    Barrett, Joe H., III; Roeder, William P.

    2010-01-01

    The expected peak wind speed for the day is an important element in the daily morning forecast for ground and space launch operations at Kennedy Space Center (KSC) and Cape Canaveral Air Force Station (CCAFS). The 45th Weather Squadron (45 WS) must issue forecast advisories for KSC/CCAFS when they expect peak gusts for >= 25, >= 35, and >= 50 kt thresholds at any level from the surface to 300 ft. In Phase I of this task, the 45 WS tasked the Applied Meteorology Unit (AMU) to develop a cool-season (October - April) tool to help forecast the non-convective peak wind from the surface to 300 ft at KSC/CCAFS. During the warm season, these wind speeds are rarely exceeded except during convective winds or under the influence of tropical cyclones, for which other techniques are already in use. The tool used single and multiple linear regression equations to predict the peak wind from the morning sounding. The forecaster manually entered several observed sounding parameters into a Microsoft Excel graphical user interface (GUI), and then the tool displayed the forecast peak wind speed, average wind speed at the time of the peak wind, the timing of the peak wind and the probability the peak wind will meet or exceed 35, 50 and 60 kt. The 45 WS customers later dropped the requirement for >= 60 kt wind warnings. During Phase II of this task, the AMU expanded the period of record (POR) by six years to increase the number of observations used to create the forecast equations. A large number of possible predictors were evaluated from archived soundings, including inversion depth and strength, low-level wind shear, mixing height, temperature lapse rate and winds from the surface to 3000 ft. Each day in the POR was stratified in a number of ways, such as by low-level wind direction, synoptic weather pattern, precipitation and Bulk Richardson number. The most accurate Phase II equations were then selected for an independent verification. The Phase I and II forecast methods were

  14. Natural-circulation-cooling characteristics during PWR accident simulations

    International Nuclear Information System (INIS)

    Adams, J.P.; McCreery, G.E.; Berta, V.T.

    1983-01-01

    A description of natural circulation cooling characteristics is presented. Data were obtained from several pressurized water reactor accident simulations in the Loss-of-Fluid Test (LOFT) pressurized water reactor (PWR). The reliability of natural circulation cooling, its cooling effectiveness, and the effect of changing system conditions are described. Quantitative comparison of flow rates and time constants with theory for both single- and two-phase fluid conditions were made. It is concluded that natural circulation cooling can be relied on in plant recovery procedures in the absence of forced convection whenever the steam generator heat sink is available

  15. Experimental investigation of the effect of an electric field on heat transfers at boiling point for a high-resistivity water in forced convection

    International Nuclear Information System (INIS)

    Morin, Henri; Verdier, Jacques

    1964-10-01

    The enhancement of heat exchanges with boiling water in forced convection in an annular duct is studied when applying an electric field between the two walls of the duct. At the local boiling and at saturation temperature, for a water resistivity comprised between 0.5 and 1 M Ω cm, with fields on the cylindrical interior surface of the canal comprised between 4 and 8 kV/cm, significant enhancements of the exchanged heat fluxes are noticed, 2.5 to 10 time superior to exchanges without electric field. When heating, heat fluxes may be increased from two to three times [fr

  16. Research on water hammer forces caused by rapid growth of bubbles at severe accidents of water cooled reactors

    International Nuclear Information System (INIS)

    Inasaka, Fujio; Adachi, Masaki; Aya, Izuo

    2004-01-01

    At severe accidents of Water Cooled Reactors a great deal of gas is expected to be produced in a short time within the water of lower part of nuclear pressure vessel and containment vessel caused by hydrogen production with a metal water reaction and steam explosions with direct contact of melting core and water. Water hammer forces caused by rapid growth of bubbles shall work on the wall of containment vessel and affect its integrity. Coherency of water block movement is not clear, whether simultaneous or in the same direction. Water block behavior and water hammer forces caused by rapid growth of bubbles have been tested using a modified scale model and analyzed to obtain experimental correlated equation to estimate water block's rising distance and velocity from water hammer data. Numerical analysis using RELAP5-3D (Reactor Excursion and Leak Analysis Program) has been conducted to evaluate water hammer forces and makes clear its modifications needed. (T. Tanaka)

  17. Conceptual design of a 20-kA current lead using forced-flow cooling and Ag-alloy-sheathed Bi-2223 high-temperature superconductors

    International Nuclear Information System (INIS)

    Heller, R.; Hull, J.R.

    1994-01-01

    High-temperature superconductors (HTSs), consisting of Bi-2223 HTS tapes sheathed with Ag alloys are proposed for a 20-kA current lead for the planned stellarator WENDELSTEIN 7-X. Forced-flow He cooling is used, and 4-K He cooling of the whole lead as well as 60-K He cooling of the copper part of the lead, is discussed. Power consumption and behavior in case of loss of He flow are given

  18. Theoretical study to determine the heat transfer by forced convection coefficient in an empirical correlation in single phase, for annular channels

    International Nuclear Information System (INIS)

    Herrera A, E.

    1994-01-01

    In the heat transfer studies by forced convection, we have few data about behavior of the fluids in an annular channel heated by a concentric pipe, such date is necessary to know the heat transfer coefficient that establish the interchange of energy and the thermic properties of the fluid with the geometry of the flow. In this work the objective, was to compare some empirical correlations that we needed for determinate the heat transfer coefficient for annular channels, where we obtained similar at the theoretical results of an experiment made by Miller and Benforado. It is important to know such coefficients because we can determinate the heat quantity transmitted to a probe zone, in which we simulate a nuclear fuel element that developed huge heat quantity that must be dispersed in short time. We give theoretical data of the heat forced transfer convection and we analyzed the phenomena in annular channels given some empirical correlations employed by some investigators and we analyzed each one. (Author)

  19. Effects of Cooling Fluid Flow Rate on the Critical Heat Flux and Flow Stability in the Plate Fuel Type 2 MW TRIGA Reactor

    OpenAIRE

    H. P. Rahardjo; V. I. Sri Wardhani

    2017-01-01

    The conversion program of the 2 MW TRIGA reactor in Bandung consisted of the replacement of cylindrical fuel (produced by General Atomic) with plate fuel (produced by BATAN). The replacement led into the change of core cooling process from upward natural convection type to downward forced convection type, and resulted in different thermohydraulic safety criteria, such as critical heat flux (CHF) limit, boiling limit, and cooling fluid flow stability. In this paper, a thermohydraulic safety an...

  20. 2D study of wind forces around multiple cooling towers using ...

    African Journals Online (AJOL)

    A comprehensive numerical study for the determination of wind pressure coefficients on multiple cooling towers by simulating turbulence using Reynolds Averaged Navier-Stokes Equations (RANS) models of Computational Fluid Dynamics techniques (CFD) such as, Standard k −ε , RNG k −ε , Realizable k −ε and Reynolds ...

  1. 2D study of wind forces around multiple cooling towers using ...

    African Journals Online (AJOL)

    user

    above, a pure numerical study were done on three and five cooling towers (in ... Invent of high speed digital computer technology had enabled the solution of flow ... The purpose of this work was to present a new design method, which ...

  2. On the Reconstruction of the Convection Pattern Below an Active Region of Solar Corona

    International Nuclear Information System (INIS)

    Pirot, Dorian; Gaudet, Jonathan; Vincent, Alain

    2012-01-01

    In order to better understand magneto-convective patterns and flux emergence, we use the Nudging Back and Forth, a data assimilation method with an anelastic convection model to reconstruct the convection zone below a solar active region from observed solar surface magnetograms. To mimic photosphere, vector magnetograms are computed using force free hypothesis. We find that the observed arcade system of AR9077-20000714 ( t he slinky ) of magnetic lines is actually formed by Ω and U loops generated in the convection zone. We generate temperature maps at top of the convective zone and find that high magnetic fields on either sides of the neutral line produce a local cooling by impeding the overturning motions.

  3. State of Art Report for the OECD-NEA Loss-of-Forced Cooling (LOFC) Test Project using HTTR Reactor

    International Nuclear Information System (INIS)

    Jun, Ji Su

    2011-05-01

    The OECD/NEA Project is planned to perform the LOFC (Loss Of Forced Cooling) test using the HTTR (High Temperature engineering Test Reactor) in Japan from 31 March 2011 to 31 March 2013 in order to obtain the data for the code validation of the VHTR safety analysis. Based on the Project Agreement Document, this report gives a description of the HTTR-LOFC test, HTTR test facility, project schedule and deliverable items as the technical state art of the project, and appends the full translation of the project agreement articles on the project management

  4. Forced convection of ammonia. 2. part.: gaseous ammonia - very high wall temperatures (1000 to 3000 K); Convection forcee de l'ammoniac. 2. partie: ammoniac gazeux - cas de tres hautes temperatures de paroi (1000 a 3000{sup 0} K)

    Energy Technology Data Exchange (ETDEWEB)

    Perroud, P.; Rebiere, J.; Strittmatter, R. [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires

    1969-07-01

    Heat transfer coefficients and pressure drop of gaseous ammonia in forced convection are experimentally determined. The fluid flows (mass flow rate 0.6 to 2.4 g/s) in a long tungsten tube (d{sub i} = 2.8 mm, d{sub e} = 5.1 mm, L = 700 mm) electrically heated. The temperature of the wall reaches 3000 deg. K and the fluid 2500 deg. K; maximum heat flux 530 w/cm{sup 2}. Ammonia is completely dissociated and the power necessary for dissociation reaches 30 per cent of the total power exchanged. Inlet pressure varies between 6 and 16 bars and the maximum pressure drop in the tube reaches 15 bars. Two regimes of dissociation have been shown: catalytic and homogeneous and the variation of dissociation along the length of the tube is studied. The measured heat transfer coefficients may be about 10 times these calculated by the means of classical formulae. A correlation of experimental results using enthalpy as a driving force for heat transmission is presented. Pressure drops may be calculated by the means of a classical friction factor. (authors) [French] On determine experimentalement les coefficients d'echange thermique et les pertes de charge de l'ammoniac gazeux en convection forcee. Le fluide circule avec un debit en masse compris entre 0.6 et 2.4 g/s (G = 10 a 40 g/cm{sup 2}.s) dans un tube long en tungstene (d{sub i} = 2.8 mm, d{sub e} = 5.1 mm, L = 700 mm), chauffe electriquement. La temperature de paroi atteint 3000 deg. K, celle du fluide 2500 deg. K et le flux de chaleur maximal est de 530 W/cm{sup 2}. L'ammoniac se dissocie completement, la puissance correspondant a la dissociation atteint 30 pour cent de la puissance totale echangee. La pression d'entree varie entre 6 et 16 bars et la chute de pression maximale dans le canal est de 15 bars. On distingue deux regimes de dissociation, catalytique et homogene, et on etudie la variation du taux de dissociation en fonction de la longueur du tube. Les coefficients d'echange thermique mesures

  5. Forced convection of ammonia. 2. part.: gaseous ammonia - very high wall temperatures (1000 to 3000 K); Convection forcee de l'ammoniac. 2. partie: ammoniac gazeux - cas de tres hautes temperatures de paroi (1000 a 3000{sup 0} K)

    Energy Technology Data Exchange (ETDEWEB)

    Perroud, P; Rebiere, J; Strittmatter, R [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires

    1969-07-01

    Heat transfer coefficients and pressure drop of gaseous ammonia in forced convection are experimentally determined. The fluid flows (mass flow rate 0.6 to 2.4 g/s) in a long tungsten tube (d{sub i} = 2.8 mm, d{sub e} = 5.1 mm, L = 700 mm) electrically heated. The temperature of the wall reaches 3000 deg. K and the fluid 2500 deg. K; maximum heat flux 530 w/cm{sup 2}. Ammonia is completely dissociated and the power necessary for dissociation reaches 30 per cent of the total power exchanged. Inlet pressure varies between 6 and 16 bars and the maximum pressure drop in the tube reaches 15 bars. Two regimes of dissociation have been shown: catalytic and homogeneous and the variation of dissociation along the length of the tube is studied. The measured heat transfer coefficients may be about 10 times these calculated by the means of classical formulae. A correlation of experimental results using enthalpy as a driving force for heat transmission is presented. Pressure drops may be calculated by the means of a classical friction factor. (authors) [French] On determine experimentalement les coefficients d'echange thermique et les pertes de charge de l'ammoniac gazeux en convection forcee. Le fluide circule avec un debit en masse compris entre 0.6 et 2.4 g/s (G = 10 a 40 g/cm{sup 2}.s) dans un tube long en tungstene (d{sub i} = 2.8 mm, d{sub e} = 5.1 mm, L = 700 mm), chauffe electriquement. La temperature de paroi atteint 3000 deg. K, celle du fluide 2500 deg. K et le flux de chaleur maximal est de 530 W/cm{sup 2}. L'ammoniac se dissocie completement, la puissance correspondant a la dissociation atteint 30 pour cent de la puissance totale echangee. La pression d'entree varie entre 6 et 16 bars et la chute de pression maximale dans le canal est de 15 bars. On distingue deux regimes de dissociation, catalytique et homogene, et on etudie la variation du taux de dissociation en fonction de la longueur du tube. Les coefficients d'echange thermique mesures peuvent etre environ 10

  6. Non-uniform current distribution in a force-cooled superconductor under changing magnetic field

    International Nuclear Information System (INIS)

    Koizumi, Norikiyo

    2000-02-01

    Strands in a large current force-cooled superconductor, referred to a CICC (cable-in-conduit conductor) hereafter, are coated with formvar (insulated layer) or chrome plating (high resistive layer) to reduce coupling current loss due to magnetic field variation. The author first carried out an experiment of the large superconducting coil consisting of such CICCs for demonstration of their applicability to a large superconducting coil. These CICCs exhibited instability, i.e. the normal zone propagation with thermal runaway (quench), at 1/20 and 1/5 of the expected conductor critical currents, respectively. The author constructed the database of this instability and studies its reason through experimental and theoretical investigations and then finds such instability is caused as a result of non-uniform current distribution in the conductor. Joule heating loss at electrical connections at the ends of the conductor should be small. Therefore, the strands in the CICC are electrically connected from each other with low resistance there. Circulation current is induced in the loop composed of the strands electrically connected at the ends of the conductor if its leakage magnetic flux is not completely vanished. The non-uniform current distribution is caused as a result of superimposition of the circulation and transport currents. The strand carrying large current becomes the normal state when it reaches or approaches to its critical current. Thus, the strands are twisted in order to vanish the leakage magnetic flux. The instability due to the current imbalance was not observed in the middle-scale coil (an element coil, such as a single double-pancake, of a large superconducting coil) consisting of the conductor in which the formvar-coated strands were twisted as above-mentioned. Consequently, it was believed that the leakage magnetic flux could be vanished by the normal twisting. However, the magnetic field increases in a large coil as a result of piling element coils

  7. Convective environment in pre-monsoon and monsoon conditions over the Indian subcontinent: the impact of surface forcing

    Directory of Open Access Journals (Sweden)

    L. Thomas

    2018-05-01

    Full Text Available Thermodynamic soundings for pre-monsoon and monsoon seasons from the Indian subcontinent are analysed to document differences between convective environments. The pre-monsoon environment features more variability for both near-surface moisture and free-tropospheric temperature and moisture profiles. As a result, the level of neutral buoyancy (LNB and pseudo-adiabatic convective available potential energy (CAPE vary more for the pre-monsoon environment. Pre-monsoon soundings also feature higher lifting condensation levels (LCLs. LCL heights are shown to depend on the availability of surface moisture, with low LCLs corresponding to high surface humidity, arguably because of the availability of soil moisture. A simple theoretical argument is developed and showed to mimic the observed relationship between LCLs and surface moisture. We argue that the key element is the partitioning of surface energy flux into its sensible and latent components, that is, the surface Bowen ratio, and the way the Bowen ratio affects surface buoyancy flux. We support our argument with observations of changes in the Bowen ratio and LCL height around the monsoon onset, and with idealized simulations of cloud fields driven by surface heat fluxes with different Bowen ratios.

  8. Improvement of thermal comfort by cooling clothing in warm climate

    DEFF Research Database (Denmark)

    Sakoi, Tomonori; Melikov, Arsen Krikor; Kolencíková, Sona

    2014-01-01

    on the inner surface. We conducted experiments with human subjects in climate chambers maintained at 30 °C and RH 50% to compare the effectiveness of the cooling clothing with that of other convective cooling devices. The use of cooling clothing with a convective cooling device improved the subjects’ thermal...... comfort compared to convective cooling alone. The supply of a small amount of water allowed the cooling clothing to provide a continuous cooling effect, whereas the effect of convective cooling alone decreased as sweat dried. However, the controllability of the cooling clothing needs to be improved....

  9. A three-dimensional mathematical model to predict air-cooling flow and temperature distribution of wire loops in the Stelmor air-cooling system

    International Nuclear Information System (INIS)

    Hong, Lingxiang; Wang, Bo; Feng, Shuai; Yang, Zhiliang; Yu, Yaowei; Peng, Wangjun; Zhang, Jieyu

    2017-01-01

    Highlights: • A 3-dimentioanl mathematical models for complex wire loops was set up in Stelmor. • The air flow field in the cooling process was simulated. • The convective heat transfer coefficient was simulated coupled with air flow field. • The temperature distribution with distances was predicted. - Abstract: Controlling the forced air cooling conditions in the Stelmor conveyor line is important for improving the microstructure and mechanical properties of steel wire rods. A three-dimensional mathematical model incorporating the turbulent flow of the cooling air and heat transfer of the wire rods was developed to predict the cooling process in the Stelmor air-cooling line of wire rolling mills. The distribution of cooling air from the plenum chamber and the forced convective heat transfer coefficient for the wire loops were simulated at the different locations over the conveyor. The temperature profiles and cooling curves of the wire loops in Stelmor conveyor lines were also calculated by considering the convective heat transfer, radiative heat transfer as well as the latent heat during transformation. The calculated temperature results using this model agreed well with the available measured results in the industrial tests. Thus, it was demonstrated that this model can be useful for studying the air-cooling process and predicting the temperature profile and microstructure evolution of the wire rods.

  10. Optimal selection of annulus radius ratio to enhance heat transfer with minimum entropy generation in developing laminar forced convection of water-Al2O3 nanofluid flow

    Institute of Scientific and Technical Information of China (English)

    Siavashi Majid; Jamali Mohammad

    2017-01-01

    Heat transfer and entropy generation of developing laminar forced convection flow of water-Al2O3 nanofluid in a concentric annulus with constant heat flux on the walls is investigated numerically. In order to determine entropy generation of fully developed flow, two approaches are employed and it is shown that only one of these methods can provide appropriate results for flow inside annuli. The effects of concentration of nanoparticles, Reynolds number and thermal boundaries on heat transfer enhancement and entropy generation of developing laminar flow inside annuli with different radius ratios and same cross sectional areas are studied. The results show that radius ratio is a very important decision parameter of an annular heat exchanger such that in each Re, there is an optimum radius ratio to maximize Nu and minimize entropy generation. Moreover, the effect of nanoparticles concentration on heat transfer enhancement and minimizing entropy generation is stronger at higher Reynolds.

  11. An experimental comparison between forced convection burn-out in freon 12 flowing vertically upwards through uniformly and non-uniformly heated round tubes

    International Nuclear Information System (INIS)

    Stevens, G.F.; Elliott, D.F.; Wood, R.W.

    1965-05-01

    Some correlations of forced convection burn-out data are based on the approximate linearity of the relationship between burn-out heat flux and the channel-averaged quality at the burn-out point. These correlations perform satisfactorily on data obtained from uniformly heated configurations. Therefore the further inference is sometimes made that the burn-out heat flux is uniquely related to the quality, and that the burn-out in non-uniformly heated configurations can be calculated from measurements made with uniform heating. This report presents burn-out data for Freon 12 flowing vertically upwards through both uniformly and non-uniformly heated round tubes. This data shows that the quality at burn-out does depend on the heat flux profile, and that the inference mentioned above is not justified. (author)

  12. Mixed convection around calandria tubes in a ¼ scale CANDU-6 moderator circulation tank

    Energy Technology Data Exchange (ETDEWEB)

    Atkins, M.D.; Rossouw, D.J.; Boer, M. [Nuclear Science Division, School of Mechanical and Aeronautical Engineering, University of the Witwatersrand, Johannesburg (South Africa); Kim, T., E-mail: tong.kim@wits.ac.za [Nuclear Science Division, School of Mechanical and Aeronautical Engineering, University of the Witwatersrand, Johannesburg (South Africa); Rhee, B.W.; Kim, H.T. [Severe Accident and PHWR Safety Research Division, Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2017-05-15

    Highlights: • A secondary jet is formed at a stagnation region and is directed towards the center of the MCT. • The secondary jet undergoes the significant dissipation and mixing due to calandria tubes (CTs). • Its cooling effectiveness is reduced on the CTs in the bottom of the MCT. • With forced convection dominance, peak heat transfer is on the upper CT surface. • With natural convection dominance, peak heat transfer is on the lower CT surface. - Abstract: This study experimentally characterizes mixed convection around calandria tubes (CTs) in a ¼ scale CANDU-6 moderator circulation tank (MCT) that uses air as the working fluid. In a full scale CANDU-6 reactor that undergoes a postulated dual failure with a loss-of-coolant accident without the emergency core cooling system available, mixed convection heat transfer occurs around the CTs. The cooling effectiveness of the moderator is diminished as an emergency heat sink if overheating eventually leads to film boiling. To prevent the onset of film boiling, local sub-cooling margins of the moderator needs to be maintained or else the critical heat flux should be increased. Circulating the moderator which interacts with the overheated CTs increases the heat transfer into the moderator which may suppress film boiling. The present experimental results demonstrate that the cooling effectiveness of the circulating moderator, in particular the secondary jet, is attenuated substantially as it is convected away from the inner wall towards the center of the MCT. The momentum of the secondary jet is diffused through the CTs. At a low jet Reynolds number, the secondary jet becomes ineffective so that some overheated CTs positioned in the other half of the MCT are cooled only by natural convection.

  13. Conceptual design of a superconducting coil system cooled by forced flow HE II for the central column of net

    International Nuclear Information System (INIS)

    Ciazynski, D.; Duchateau, J.L.; Turck, B.

    1987-01-01

    In order to increase the maximum flux sweep, a present trend is to design ohmic coils producing fields as high as II teslas. In Niobium-Titanium, critical current densities of 10 9 A/m 2 at 1.8 K under a field of 11 teslas are now claimed by several manufacturers. This in addition enables to make use of the outstanding cooling properties of He II. The forced flow technics can again be envisaged for He II to remove the heat load. Two solutions are investigated. The first one uses a 40 kA cable wound in double pancakes. The second one makes use of several conductors layer wound and current supplied in parallel

  14. Actively convected liquid metal divertor

    International Nuclear Information System (INIS)

    Shimada, Michiya; Hirooka, Yoshi

    2014-01-01

    The use of actively convected liquid metals with j × B force is proposed to facilitate heat handling by the divertor, a challenging issue associated with magnetic fusion experiments such as ITER. This issue will be aggravated even more for DEMO and power reactors because the divertor heat load will be significantly higher and yet the use of copper would not be allowed as the heat sink material. Instead, reduced activation ferritic/martensitic steel alloys with heat conductivities substantially lower than that of copper, will be used as the structural materials. The present proposal is to fill the lower part of the vacuum vessel with liquid metals with relatively low melting points and low chemical activities including Ga and Sn. The divertor modules, equipped with electrodes and cooling tubes, are immersed in the liquid metal. The electrode, placed in the middle of the liquid metal, can be biased positively or negatively with respect to the module. The j × B force due to the current between the electrode and the module provides a rotating motion for the liquid metal around the electrodes. The rise in liquid temperature at the separatrix hit point can be maintained at acceptable levels from the operation point of view. As the rotation speed increases, the current in the liquid metal is expected to decrease due to the v × B electromotive force. This rotating motion in the poloidal plane will reduce the divertor heat load significantly. Another important benefit of the convected liquid metal divertor is the fast recovery from unmitigated disruptions. Also, the liquid metal divertor concept eliminates the erosion problem. (letter)

  15. Observing Convective Aggregation

    Science.gov (United States)

    Holloway, Christopher E.; Wing, Allison A.; Bony, Sandrine; Muller, Caroline; Masunaga, Hirohiko; L'Ecuyer, Tristan S.; Turner, David D.; Zuidema, Paquita

    2017-11-01

    Convective self-aggregation, the spontaneous organization of initially scattered convection into isolated convective clusters despite spatially homogeneous boundary conditions and forcing, was first recognized and studied in idealized numerical simulations. While there is a rich history of observational work on convective clustering and organization, there have been only a few studies that have analyzed observations to look specifically for processes related to self-aggregation in models. Here we review observational work in both of these categories and motivate the need for more of this work. We acknowledge that self-aggregation may appear to be far-removed from observed convective organization in terms of time scales, initial conditions, initiation processes, and mean state extremes, but we argue that these differences vary greatly across the diverse range of model simulations in the literature and that these comparisons are already offering important insights into real tropical phenomena. Some preliminary new findings are presented, including results showing that a self-aggregation simulation with square geometry has too broad distribution of humidity and is too dry in the driest regions when compared with radiosonde records from Nauru, while an elongated channel simulation has realistic representations of atmospheric humidity and its variability. We discuss recent work increasing our understanding of how organized convection and climate change may interact, and how model discrepancies related to this question are prompting interest in observational comparisons. We also propose possible future directions for observational work related to convective aggregation, including novel satellite approaches and a ground-based observational network.

  16. Assessment of the forced air-cooling performance for cylindrical lithium-ion battery packs: A comparative analysis between aligned and staggered cell arrangements

    International Nuclear Information System (INIS)

    Yang, Naixing; Zhang, Xiongwen; Li, Guojun; Hua, Dong

    2015-01-01

    An appropriate cell arrangement plays significant role to design a highly efficient cooling system for the lithium-ion battery pack. This paper performs a comparative analysis of thermal performances on different arrangements of cylindrical cells for a LiFePO 4 battery pack. A thermal model for the battery pack is developed and is solved in couple with the governing equations of fluid flow in the numerical simulations. The experiments for model validation are conducted on a single cell of the battery pack with forced-air cooling system. The effects of longitudinal and transverse spacing on the cooling performances are analyzed for the battery pack with the aligned and the staggered arrays. Under a specified flow rate of cooling air, the maximum temperature rise is proportional to the longitudinal interval for the staggered arrays, while it is in inverse for the aligned arrangement. Increasing the transverse interval leads to the increase of the battery temperature rise for both aligned and staggered arrangements. By trade-off the design requirements (maximum temperature rise, temperature uniformity, power requirement and cooling index), an appropriate solution in term of the optimal combination of the longitudinal interval, transverse interval, and air inlet width is obtained for the aligned arrangement. - Highlights: • Forced air-cooling performance for cylindrical lithium-ion battery is evaluated. • Thermal performances for aligned and staggered cell arrangements are compared. • Geometric optimization is investigated for the battery air-cooling system

  17. Dynamics and developing of natural circulation cooling from vertical upflow and downflow conditions

    International Nuclear Information System (INIS)

    Yang, B.W.; Ouyang, W.

    2004-01-01

    Several research programs have been conducted to evaluate the capability of natural circulation cooling of reactors following a loss of cooling accident. Both experimental and RELAP5 simulation results were obtained for these studies in a facility with vertical heated tube(s) and a unheated bypass channel. The analytical results showed that, under a certain power level, a natural circulation pattern can be developed from both initial upflow and downflow conditions, and maintained for a significant cooling period. This power level, for the discussion of this paper, is defined as the natural circulation cooling (NCC) power limit. Two import factors, namely the pump coastdown rate and the initial flow direction, are examined in this paper. In the benchmark case, as compared to the experimental results, the RELAP5 simulation program accurately predicted the transient phenomena from forced convection through flow reversal, then, into natural circulation cooling. Generally, the two-phase NCC power limit is higher and also more stable for the cases with initial upflow forced convection than for the cases with initial downflow. The transient phenomena (dynamics) of the natural circulation cooling was examined by varying the pump coast down rate in approaching the flow reversal natural circulation. A significant pump coastdown effect on the NCC power limit was observed for the analytical tests with initial downflow forced convection. For the tests with initial downflow condition, the higher the coastdown rate (or the shorter the coastdown period), the higher the NCC power limit. For the case with initial upflow forced convection, there may be an optimal coastdown rate for a given subcooled condition. However, for the subcooled condition used in this study, the effect of pump coast down rate is not as significant as in the downward forced convection. (author)

  18. How We Got to the Northern Hemisphere Ice Ages: Late Miocene Global Cooling and Plate Tectonic CO2 Forcing

    Science.gov (United States)

    Herbert, T.; Dalton, C. A.; Carchedi, C.

    2017-12-01

    The evolution of Earth's climate between "refrigeration" of East Antarctica and the onset of cyclic Northern Hemisphere glaciation spanned more than 11 Myr. In the latest Miocene (Messinian) time, approximately half way on this journey, changes on land, ranging from the expansion of arid zones to major floral and faunal ecosystem shifts, accelerated. Recent compilations of marine surface temperatures reveal that global cooling from the Miocene Optimum (14-16Ma) also accelerated in late Miocene (7-5.35 Ma) time to reach temperatures not much above Holocene conditions. Both hemispheres cooled in parallel, with the changes amplified at higher latitudes in comparison to the tropics. Despite the strong circumstantial case for CO2 decline as the dominant cause of late Miocene climatic and evolutionary change, proxy indicators of CO2concentrations paint an equivocal picture of greenhouse forcing. Here we provide evidence that global sea floor spreading (SFS) rates decelerated at exactly the times of major climatic cooling, linking a decline in tectonic degassing (at both subduction zones and mid-ocean ridges) to fundamental shifts in the global carbon cycle. Our work utilizes newly available global compilations of seafloor fabric and marine magnetic anomalies provided by the NSF-funded Global Seafloor Fabric and Magnetic Lineation Data Base Project. Previous global compilations of SFS typically binned estimates over 10 Myr increments, losing critical resolution on the timescale of late Neogene climate changes. We further improve the signal:noise of SFS estimates by incorporating recent advances in the astronomical calibration of the Miocene geomagnetic polarity timescale. We use two approaches to compile spreading rate estimates over the past 20 Myr at each spreading system: optimized finite rotation calculations, and averages of sea floor-spreading derived from the distances of magnetic lineations along flow lines on the sea floor. Weighted by ridge length, we find an 25

  19. Effect of microscale protrusions on local fluid flow and mass transport in the presence of forced convection

    Energy Technology Data Exchange (ETDEWEB)

    Matzen, Gehard W. [Univ. of California, Berkeley, CA (United States)

    1997-01-01

    Three-dimensional creeping flow around single, axisymmetric protrusions is studied numerically using the boundary-integral technique. Emphasis is placed upon cylindrical protrusions on plane walls for various height-to-radius (h-to-a) aspect ratios, but cones and sections of spheres protruding from plane walls are also briefly examined. The presented items include shear-stress distributions, shear-stress contours, extents of the fluid-flow disturbance, total forces and torques on the cylinders, streamlines, and skin-friction lines. Also included is a discussion of flow topology around axisymmetric geometries. No flow reversal is observed for cylindrical protrusions with aspect ratios greater than 2.4 to 2.6. At higher aspect ratios, the fluid tends to be swept around cylindrical protrusions with little vertical motion. At lower aspect ratios, the strength of the recirculation increases, and the recirculation region becomes wider in the transverse direction and narrower in the flow direction. Also, the recirculation pattern begins to resemble the closed streamline patterns in two-dimensional flow over square ridges. However, unlike two-dimensional flow, closed streamline patterns are not observed. For arbitrary axisymmetric geometries, the extent of the fluid-flow disturbance can be estimated with the total force that is exerted on the protrusion. When the same force is exerted on protrusions with different aspect ratios, the protrusion with the higher aspect ratio tends to have a greater disturbance in the flow direction and a smaller disturbance in the transverse direction. The total force exerted on cylindrical protrusions with rounded corners is only slightly lower than the total force exerted on cylindrical protrusions with sharp corners.

  20. Time evolution simulation of heat removal in a small water tank by natural convection

    Energy Technology Data Exchange (ETDEWEB)

    Freitas, Carlos Alberto de, E-mail: carlos.freitas1950@hotmail.com [Instituto Federal do Rio de Janeiro (IFRJ), Nilopolis, RJ (Brazil); Jachic, Joao; Moreira, Maria de Lourdes, E-mail: jjachic@ien.gov.br, E-mail: malu@ien.gov.br [Instituto de Engenharia Nuclear (IEN/CNEN-RJ), Rio de Janeiro, RJ (Brazil)

    2013-07-01

    One of the cooling modes for any source of heat such as in a shutdown nuclear core is the natural convection. The design specifications of any cooling pool can only be done when the removal heat rate and the corresponding mass flow rate is reasonably established. In our simulation scheme, we assumed that the body forces acting in the cubic water cell are: the weight, the drag force and the integrated pressure forces on the horizontal surfaces, the viscosity shear forces on the vertical surfaces and also a special viscosity drag force due to the mass dislocation along a Bernoulli type current tube outside the motive region. For a suitable time step, the uprising convection velocity is determined by an implicit and also by an explicit solution algorithm. The resulting differential equation depends on updating specific mass, dynamic viscosity and constant pressure heat coefficient with the last known temperature in the cell that absorbed heat. Numerical calculation software was performed using MATLAB’s technical computing language and then applied for a heat generation plate simulating a spent fuel assembler from a shutdown nuclear core. The results show time evolution of convection, terminal velocity and water temperature distribution. Pool dimension as well as pool level decrement are also determined for various air exhausting system conditions and heat rate of the spent fuel plate being cooled. (author)

  1. Time evolution simulation of heat removal in a small water tank by natural convection

    International Nuclear Information System (INIS)

    Freitas, Carlos Alberto de; Jachic, Joao; Moreira, Maria de Lourdes

    2013-01-01

    One of the cooling modes for any source of heat such as in a shutdown nuclear core is the natural convection. The design specifications of any cooling pool can only be done when the removal heat rate and the corresponding mass flow rate is reasonably established. In our simulation scheme, we assumed that the body forces acting in the cubic water cell are: the weight, the drag force and the integrated pressure forces on the horizontal surfaces, the viscosity shear forces on the vertical surfaces and also a special viscosity drag force due to the mass dislocation along a Bernoulli type current tube outside the motive region. For a suitable time step, the uprising convection velocity is determined by an implicit and also by an explicit solution algorithm. The resulting differential equation depends on updating specific mass, dynamic viscosity and constant pressure heat coefficient with the last known temperature in the cell that absorbed heat. Numerical calculation software was performed using MATLAB’s technical computing language and then applied for a heat generation plate simulating a spent fuel assembler from a shutdown nuclear core. The results show time evolution of convection, terminal velocity and water temperature distribution. Pool dimension as well as pool level decrement are also determined for various air exhausting system conditions and heat rate of the spent fuel plate being cooled. (author)

  2. Noninvasive estimation of transmitral pressure drop across the normal mitral valve in humans: importance of convective and inertial forces during left ventricular filling

    Science.gov (United States)

    Firstenberg, M. S.; Vandervoort, P. M.; Greenberg, N. L.; Smedira, N. G.; McCarthy, P. M.; Garcia, M. J.; Thomas, J. D.

    2000-01-01

    OBJECTIVES: We hypothesized that color M-mode (CMM) images could be used to solve the Euler equation, yielding regional pressure gradients along the scanline, which could then be integrated to yield the unsteady Bernoulli equation and estimate noninvasively both the convective and inertial components of the transmitral pressure difference. BACKGROUND: Pulsed and continuous wave Doppler velocity measurements are routinely used clinically to assess severity of stenotic and regurgitant valves. However, only the convective component of the pressure gradient is measured, thereby neglecting the contribution of inertial forces, which may be significant, particularly for nonstenotic valves. Color M-mode provides a spatiotemporal representation of flow across the mitral valve. METHODS: In eight patients undergoing coronary artery bypass grafting, high-fidelity left atrial and ventricular pressure measurements were obtained synchronously with transmitral CMM digital recordings. The instantaneous diastolic transmitral pressure difference was computed from the M-mode spatiotemporal velocity distribution using the unsteady flow form of the Bernoulli equation and was compared to the catheter measurements. RESULTS: From 56 beats in 16 hemodynamic stages, inclusion of the inertial term ([deltapI]max = 1.78+/-1.30 mm Hg) in the noninvasive pressure difference calculation significantly increased the temporal correlation with catheter-based measurement (r = 0.35+/-0.24 vs. 0.81+/-0.15, pforces are significant components of the maximal pressure drop across the normal mitral valve. These can be accurately estimated noninvasively using CMM recordings of transmitral flow, which should improve the understanding of diastolic filling and function of the heart.

  3. Turbulent mixed convection in asymmetrically heated vertical channel

    Directory of Open Access Journals (Sweden)

    Mokni Ameni

    2012-01-01

    Full Text Available In this paper an investigation of mixed convection from vertical heated channel is undertaken. The aim is to explore the heat transfer obtained by adding a forced flow, issued from a flat nozzle located in the entry section of a channel, to the up-going fluid along its walls. Forced and free convection are combined studied in order to increase the cooling requirements. The study deals with both symmetrically and asymmetrically heated channel. The Reynolds number based on the nozzle width and the jet velocity is assumed to be 3 103 and 2.104; whereas, the Rayleigh number based on the channel length and the wall temperature difference varies from 2.57 1010 to 5.15 1012. The heating asymmetry effect on the flow development including the mean velocity and temperature the local Nusselt number, the mass flow rate and heat transfer are examined.

  4. Liquid Salts as Media for Process Heat Transfer from VHTR's: Forced Convective Channel Flow Thermal Hydraulics, Materials, and Coating

    Energy Technology Data Exchange (ETDEWEB)

    Sridharan, Kumar; Anderson, Mark; Allen, Todd; Corradini, Michael

    2012-01-30

    on Cr-carbide on the graphite surface. Ni-electroplating dramatically reduced corrosion of alloys, although some diffusion of Fe and Cr were observed occur through the Ni plating. A pyrolytic carbon and SiC (PyC/SiC) CVD coating was also investigated and found to be effective in mitigating corrosion. The KCl-MgCl2 molten salt was less corrosive than FLiNaK fluoride salts for corrosion tests performed at 850oC. Cr dissolution in the molten chloride salt was still observed and consequently Ni-201 and Hastelloy N exhibited the least depth of attack. Grain-boundary engineering (GBE) of Incoloy 800H improved the corrosion resistance (as measured by weight loss and maximum depth of attack) by nearly 50% as compared to the as-received Incoloy 800H sample. Because Cr dissolution is an important mechanism of corrosion, molten salt electrochemistry experiments were initiated. These experiments were performed using anodic stripping voltammetry (ASV). Using this technique, the reduction potential of Cr was determined against a Pt quasi-reference electrode as well as against a Ni(II)-Ni reference electrode in molten FLiNaK at 650 oC. The integrated current increased linearly with Cr-content in the salt, providing for a direct assessment of the Cr concentration in a given salt of unknown Cr concentration. To study heat transfer mechanisms in these molten salts over the forced and mixed convection regimes, a forced convective loop was constructed to measure heat transfer coefficients, friction factors and corrosion rates in different diameter tubes in a vertical up flow configuration in the laminar flow regime. Equipment and instrumentation for the forced convective loop was designed, constructed, and tested. These include a high temperature centrifugal pump, mass flow meter, and differential pressure sensing capabilities to an uncertainty of < 2 Pa. The heat transfer coefficient for the KCl-MgCl2 salt was measured in two different diameter channels (0.083 and 0.370Ã). In the 0

  5. A numerical modeling study of the interaction between the tides and the circulation forced by high-latitude plasma convection

    International Nuclear Information System (INIS)

    Mikkelsen, I.S.; Larsen, M.F.

    1991-01-01

    A spectral, time-varying thermospheric general circulation model has been used to study the nonlinear interaction at high latitudes between the tides propagating into the thermosphere from below and the circulation induced by magnetospheric forcing and in situ solar heating. The model is discrete in the vertical with 27 layers spaced by half a scale height. In the horizontal, the fields are expanded in a series of spherical harmonics using a triangular truncation at wave number 31, equivalent to a homogeneous global resolution with a minimum wavelength of 1,270 km. A hypothetical uniform grid point model would require a horizontal spacing of 417 km to describe the same minimum wavelength. In the high-latitude F region the tides affect the dusk vortex of the neutral flow very little, but the dawn vortex is either suppressed or amplified dependent upon the universal time and tidal phase. In the E region neutral flow, both the dusk and dawn vortices are shifted in local time by the tides, again as a function of universal time and tidal phase. At dusk a nonlinear amplification of the sunward winds occurs for certain combination of parameters, and at dawn the winds may be completely suppressed. Below 120 km altitude the magnetospheric forcing creates a single cyclonic vortex which is also sensitive to the high-latitude tidal structure

  6. Impacts of raindrop evaporative cooling on tropical cyclone secondary eyewall formation

    Science.gov (United States)

    Ge, Xuyang; Guan, Liang; Yan, Ziyu

    2018-06-01

    The impacts of raindrop evaporative cooling on secondary eyewall formation (SEF) of simulated tropical cyclones are investigated using idealized numerical experiments. The results suggest that the raindrop evaporative cooling effect is beneficial to the development of secondary eyewall through the planetary boundary layer (PBL) cold pool process. The evaporative cooling-driven downdrafts bring about the surface cold pool beneath a precipitation cloud. This cold pool dynamics act as a lifting mechanism to trigger the outer convection. The radially outward propagation of spiral rainbands broadens the TC size, by which modifies the surface heat fluxes and thus outer convection. Furthermore, the unbalanced PBL process contributes to the SEF. The radially outward surface outflows forces convection at outer region and thus favors a larger TC size. A larger TC implies an enhanced inertial stability at the outer region, which favors a higher conversion efficiency of diabatic heating to kinetic energy.

  7. Extended Subadiabatic Layer in Simulations of Overshooting Convection

    Energy Technology Data Exchange (ETDEWEB)

    Käpylä, Petri J.; Arlt, Rainer [Leibniz-Institut für Astrophysik, An der Sternwarte 16, D-14482 Potsdam (Germany); Rheinhardt, Matthias; Käpylä, Maarit J.; Olspert, Nigul [ReSoLVE Centre of Excellence, Department of Computer Science, P.O. Box 15400, FI-00076 Aalto (Finland); Brandenburg, Axel [NORDITA, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, SE-10691 Stockholm (Sweden); Lagg, Andreas; Warnecke, Jörn [Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen (Germany)

    2017-08-20

    We present numerical simulations of hydrodynamic overshooting convection in local Cartesian domains. We find that a substantial fraction of the lower part of the convection zone (CZ) is stably stratified according to the Schwarzschild criterion while the enthalpy flux is outward directed. This occurs when the heat conduction profile at the bottom of the CZ is smoothly varying, based either on a Kramers-like opacity prescription as a function of temperature and density or a static profile of a similar shape. We show that the subadiabatic layer arises due to nonlocal energy transport by buoyantly driven downflows in the upper parts of the CZ. Analysis of the force balance of the upflows and downflows confirms that convection is driven by cooling at the surface. We find that the commonly used prescription for the convective enthalpy flux being proportional to the negative entropy gradient does not hold in the stably stratified layers where the flux is positive. We demonstrate the existence of a non-gradient contribution to the enthalpy flux, which is estimated to be important throughout the convective layer. A quantitative analysis of downflows indicates a transition from a tree-like structure where smaller downdrafts merge into larger ones in the upper parts to a structure in the deeper parts where a height-independent number of strong downdrafts persist. This change of flow topology occurs when a substantial subadiabatic layer is present in the lower part of the CZ.

  8. Storage of HLW in engineered structures: air-cooled and water-cooled concepts

    International Nuclear Information System (INIS)

    Ahner, S.; Dekais, J.J.; Puttke, B.; Staner, P.

    1981-01-01

    A comparative study on an air-cooled and a water-cooled intermediate storage of vitrified, highly radioactive waste (HLW) in overground installations has been performed by Nukem and Belgonucleaire respectively. In the air-cooled storage concept the decay heat from the storage area will be removed using natural convection. In the water-cooled storage concept the decay heat is carried off by a primary and secondary forced-cooling system with redundant and diverse devices. The safety study carried out by Nukem used a fault tree method. It shows that the reliability of the designed water-cooled system is very high and comparable to the inherent, safe, air-cooled system. The impact for both concepts on the environment is determined by the release route, but even during accident conditions the release is far below permissible limits. The economic analysis carried out by Belgonucleaire shows that the construction costs for both systems do not differ very much, but the operation and maintenance costs for the water-cooled facility are higher than for the air cooled facility. The result of the safety and economic analysis and the discussions with the members of the working group have shown some possible significant modifications for both systems, which are included in this report. The whole study has been carried out using certain national criteria which, in certain Member States at least, would lead to a higher standard of safety than can be justified on any social, political or economic grounds

  9. Developing the laminar MHD forced convection flow of water/FMWNT carbon nanotubes in a microchannel imposed the uniform heat flux

    Energy Technology Data Exchange (ETDEWEB)

    Karimipour, Arash; Taghipour, Abdolmajid [Department of Mechanical Engineering, Najafabad Branch, Islamic Azad University, Najafabad (Iran, Islamic Republic of); Malvandi, Amir, E-mail: amirmalvandi@aut.ac.ir [Department of Mechanical Engineering, Neyshabur Branch, Islamic Azad University, Neyshabur (Iran, Islamic Republic of)

    2016-12-01

    This paper aims to investigate magnetic field and slip effects on developing laminar forced convection of nanofluids in the microchannels. A novel mixture of water and FMWNT carbon nanotubes is used as the working fluid. To do this, fluid flow and heat transfer through a microchannel is simulated by a computer code in FORTRAN language. The mixture of FMWNT carbon nanotubes suspended in water is considered as the nanofluid. Slip velocity is supposed as the hydrodynamic boundary condition while the microchannel's lower wall is insulated and the top wall is under the effect of a constant heat flux. Moreover, the flow field is subjected to a magnetic field with a constant strength. The results are presented as the velocity, temperature and Nusselt number profiles. It is observed that nanofluid composed of water and carbon nanotubes (FMWNT) can work well to increase the heat transfer rate along the microchannel walls. Furthermore, it is indicated that imposing the magnetic field is very effective at the thermally developing region. In contrast, the magnetic field effect at fully developed region is insignificant, especially at low values of Reynolds number. - Highlights: • Simulation of water/FMWNT carbon nanotubes flow in a microchannel. • The effects of magnetic field strength on nanofluid's slip velocity. • The effects of Ha, Re, ϕ and slip coefficient on averaged Nusselt number. • Magnetic field effect at developing flow region is significant.

  10. Influence of Lorentz force, Cattaneo-Christov heat flux and viscous dissipation on the flow of micropolar fluid past a nonlinear convective stretching vertical surface

    Science.gov (United States)

    Gnaneswara Reddy, Machireddy

    2017-12-01

    The problem of micropolar fluid flow over a nonlinear stretching convective vertical surface in the presence of Lorentz force and viscous dissipation is investigated. Due to the nature of heat transfer in the flow past vertical surface, Cattaneo-Christov heat flux model effect is properly accommodated in the energy equation. The governing partial differential equations for the flow and heat transfer are converted into a set of ordinary differential equations by employing the acceptable similarity transformations. Runge-Kutta and Newton's methods are utilized to resolve the altered governing nonlinear equations. Obtained numerical results are compared with the available literature and found to be an excellent agreement. The impacts of dimensionless governing flow pertinent parameters on velocity, micropolar velocity and temperature profiles are presented graphically for two cases (linear and nonlinear) and analyzed in detail. Further, the variations of skin friction coefficient and local Nusselt number are reported with the aid of plots for the sundry flow parameters. The temperature and the related boundary enhances enhances with the boosting values of M. It is found that fluid temperature declines for larger thermal relaxation parameter. Also, it is revealed that the Nusselt number declines for the hike values of Bi.

  11. Analysis of SONACO axial cooling experiments

    International Nuclear Information System (INIS)

    Sigg, B.; Dury, T.V.; Hudina, M.

    1994-01-01

    The SONACO test rig contained a sodium-cooled, electrically heated 37-pin bundle. On this rig, a series of forced, mixed and natural convection experiments have been performed with the aim of contributing to the understanding of thermal-hydraulic phenomena and providing data for code validation for a subassembly at decay heat power level with low flow or stagnant coolant. The test section and especially the heater pins were equipped with an extensive number of chromel-alumel thermocouples. In addition, special permanent-magnet probes were used for measuring local velocities. In this paper we give a survey of results from axial cooling experiments, where heat was removed by natural convection to a cooling coil situated in the coolant channel (plenum) above the bundle. The experimental conditions led to turbulent convection with a slowly varying, large scale flow pattern. It is shown that a power tilt in the bundle reduces these fluctuations but does not eliminate them. For the uniformly heated bundle, aglebraic expressions for the average turbulent heat flux as well as for temperature and velocity fluctuations are derived from a second-moments model and compared with experimental data. Furthermore, heat transfer in the plenum and the consequences of the SONACO experiments for the coolability of reactor fuel elements under loss-of-flow conditions are discussed. ((orig.))

  12. Hydrogen and helium recycling from a JxB-force convected liquid metal Ga{sub 67}In{sub 20.5}Sn{sub 12.5} under steady state plasma bombardment

    Energy Technology Data Exchange (ETDEWEB)

    Hirooka, Yoshi, E-mail: hirooka.yoshihiko@nifs.ac.jp [National institute for Fusion Science, Oroshi, Toki, Gifu 509-5292 (Japan); Graduate University for Advanced Studies, Oroshi, Toki, Gifu 509-5292 (Japan); Bi, Hailin [Graduate University for Advanced Studies, Oroshi, Toki, Gifu 509-5292 (Japan); Shimada, Michiya [Japan Atomic Energy Agency, Rokkasho, Kamikita, Aomori 039-3212 (Japan); Ono, Masa [Princeton Plasma Physics Laboratory, Princeton, NJ 08543 (United States)

    2017-04-15

    A series of first-of-a-kind laboratory-scale experiments on the JxB-force convected liquid metal divertor concept have been carried out in the temperature range from room temperature to ∼200 °C, employing a eutectic alloy: Ga{sub 67}In{sub 20.5}Sn{sub 12.5}, the melting point of which is 10.5 °C. The electrical current conducted through the alloy is set at about 70A and the magnetic field is set at about 700 G. It has reproducibly been observed that hydrogen as well as helium particle recycling is noticeably reduced under steady state plasma bombardment when the liquid is convected by the JxB force.

  13. Subcritical thermal convection of liquid metals in a rapidly rotating sphere

    Science.gov (United States)

    Cardin, P.; Schaeffer, N.; Guervilly, C.; Kaplan, E.

    2017-12-01

    Planetary cores consist of liquid metals (low Prandtl number Pr) that convect as the core cools. Here we study nonlinear convection in a rotating (low Ekman number Ek) planetary core using a fully 3D direct (down to Ek=10-7) and a quasi geostrophic (down to Ek=10-10) numerical simulations. Near the critical thermal forcing (Rayleigh number Ra), convection onsets as thermal Rossby waves, but as Ra increases, this state is superceded by one dominated by advection. At moderate rotation, these states (here called the weak branch and strong branch, respectively) are continuously connected. As the planetary core rotates faster, the continuous transition is replaced by hysteresis cycles and subcriticality until the weak branch disappears entirely and the strong branch onsets in a turbulent state at Ekforcing decreases well below the linear onset of convection (Ra 0.4Racrit in this study for Ek=10-10 and Pr=0.01). We highlight the importance of the Reynolds stress, which is required for convection to persist below the linear onset. We further note the presence of a strong zonal flow that is nonetheless unimportant to the convective subcritical state. Our study suggests that, in the asymptotic regime of rapid rotation relevant for planetary interiors, thermal convection of liquid metals in a sphere onsets and shuts down through a subcritical bifurcation. This scenario may be relevant to explain the lunar and martian dynamo extinctions.

  14. Convective mixing and accretion in white dwarfs

    International Nuclear Information System (INIS)

    Koester, D.

    1976-01-01

    The evolution of convection zones in cooling white dwarfs with helium envelopes and outer hydrogen layers is calculated with a complete stellar evolution code. It is shown that white dwarfs of spectral type DB cannot be formed from DA stars by convective mixing. However, for cooler temperatures (Tsub(e) [de

  15. Consequences of high effective Prandtl number on solar differential rotation and convective velocity

    Science.gov (United States)

    Karak, Bidya Binay; Miesch, Mark; Bekki, Yuto

    2018-04-01

    Observations suggest that the large-scale convective velocities obtained by solar convection simulations might be over-estimated (convective conundrum). One plausible solution to this could be the small-scale dynamo which cannot be fully resolved by global simulations. The small-scale Lorentz force suppresses the convective motions and also the turbulent mixing of entropy between upflows and downflows, leading to a large effective Prandtl number (Pr). We explore this idea in three-dimensional global rotating convection simulations at different thermal conductivity (κ), i.e., at different Pr. In agreement with previous non-rotating simulations, the convective velocity is reduced with the increase of Pr as long as the thermal conductive flux is negligible. A subadiabatic layer is formed near the base of the convection zone due to continuous deposition of low entropy plumes in low-κ simulations. The most interesting result of our low-κ simulations is that the convective motions are accompanied by a change in the convection structure that is increasingly influenced by small-scale plumes. These plumes tend to transport angular momentum radially inward and thus establish an anti-solar differential rotation, in striking contrast to the solar rotation profile. If such low diffusive plumes, driven by the radiative-surface cooling, are present in the Sun, then our results cast doubt on the idea that a high effective Pr may be a viable solution to the solar convective conundrum. Our study also emphasizes that any resolution of the conundrum that relies on the downward plumes must take into account the angular momentum transport and heat transport.

  16. A passive cooling system proposal for multifunction and high-power displays

    Science.gov (United States)

    Tari, Ilker

    2013-03-01

    Flat panel displays are conventionally cooled by internal natural convection, which constrains the possible rate of heat transfer from the panel. On one hand, during the last few years, the power consumption and the related cooling requirement for 1080p displays have decreased mostly due to energy savings by the switch to LED backlighting and more efficient electronics. However, on the other hand, the required cooling rate recently started to increase with new directions in the industry such as 3D displays, and ultra-high-resolution displays (recent 4K announcements and planned introduction of 8K). In addition to these trends in display technology itself, there is also a trend to integrate consumer entertainment products into displays with the ultimate goal of designing a multifunction device replacing the TV, the media player, the PC, the game console and the sound system. Considering the increasing power requirement for higher fidelity in video processing, these multifunction devices tend to generate very high heat fluxes, which are impossible to dissipate with internal natural convection. In order to overcome this obstacle, instead of active cooling with forced convection that comes with drawbacks of noise, additional power consumption, and reduced reliability, a passive cooling system relying on external natural convection and radiation is proposed here. The proposed cooling system consists of a heat spreader flat heat pipe and aluminum plate-finned heat sink with anodized surfaces. For this system, the possible maximum heat dissipation rates from the standard size panels (in 26-70 inch range) are estimated by using our recently obtained heat transfer correlations for the natural convection from aluminum plate-finned heat sinks together with the surface-to-surface radiation. With the use of the proposed passive cooling system, the possibility of dissipating very high heat rates is demonstrated, hinting a promising green alternative to active cooling.

  17. Thermo-fluid analysis of water cooled research reactors in natural convection; Analise termofluidodinamica de reatores nucleares de pesquisa refrigerados a agua em regime de conveccao natural

    Energy Technology Data Exchange (ETDEWEB)

    Veloso, Maria Auxiliadora Fortini

    2004-07-01

    The STHIRP-1 computer program, which fundamentals are described in this work, uses the principles of the subchannels analysis and has the capacity to simulate, under steady state and transient conditions, the thermal and hydraulic phenomena which occur inside the core of a water-refrigerated research reactor under a natural convection regime. The models and empirical correlations necessary to describe the flow phenomena which can not be described by theoretical relations were selected according to the characteristics of the reactor operation. Although the primary objective is the calculation of research reactors, the formulation used to describe the fluid flow and the thermal conduction in the heater elements is sufficiently generalized to extend the use of the program for applications in power reactors and other thermal systems with the same features represented by the program formulations. To demonstrate the analytical capacity of STHIRP-l, there were made comparisons between the results calculated and measured in the research reactor TRIGA IPR-R1 of CDTN/CNEN. The comparisons indicate that the program reproduces the experimental data with good precision. Nevertheless, in the future there must be used more consistent experimental data to corroborate the validation of the program. (author)

  18. AN EXPERIMENTAL STUDY FOR HEAT TRANSFER ENHANCEMENT BY LAMINAR FORCED CONVECTION FROM HORIZONTAL AND INCLINED TUBE HEATED WITH CONSTANT HEAT FLUX, USING TWO TYPES OF POROUS MEDIA

    Directory of Open Access Journals (Sweden)

    Thamir K. Jassem

    2015-02-01

    Full Text Available An experimental forced laminar study was presented in this research for an air flowing through a circular channel for different angles ( ,30o,45o,60o, the channel was heated at constant heat flux , the channel also was packed with steel and glass spheres respectively . The tests were done for three values of Peclets number (2111.71,3945.42,4575.47 with changing the heat flux for each case and five times for each number.The results showed that the dimensionless temperature distribution  will decrease with increasing the dimensionless channel length for all cases with changing Peclet number, heat flux and inclination angles, and its lowest value will be for glass spheres at highest flux, while at lower flux for , and the decreasing in dimensionless temperature was closed for both types of packed at other inclination angles.The study declared that the local Nusselt number decreases with increasing the dimensionless length of the channel for both packeds and for different applied heat flux, also through this study it was declared that the average Nusselt increases as Peclet number increases for both packed. Its value for the glass spheres is greater than the steel spheres with percentage (98.3% at small Peclet, and percentage (97.2% at large Peclet number for the horizontal tube, and (98.3% at small Peclet number and (97.8% at large Peclet number at  .Through this study its was found that average Nusselt number increases along the channel as the heat flux increases, because the bulk temperature will increase as the flow proceeds toward the end of the channel , so the heat transfer coefficient will increase.  It was declared from this study that in the case of the steel packed the heat transfer will occur mainly by conduction, while in the case of glass packed the heat transfer will occur mainly by laminar forced convection, where the lowest Nusselt number (Nu=3.8 was found when the pipe is horizontal and lowest heat flux and lowest Peclet number.  

  19. Numerical Study of Developing Laminar Forced Convection Flow of Water/CuO Nanofluid in a Circular Tube with a 180 Degrees Curve

    OpenAIRE

    Hamed K. Arzani; Hamid K. Arzani; S.N. Kazi; A. Badarudin

    2016-01-01

    Numerical investigation into convective heat transfer of CuO-Water based nanofluid in a pipe with return bend under laminar flow conditions has been done. The impacts of Reynolds number and the volume concentration of nanoparticles on the flow and the convective heat transfer behaviour are investigated. The results indicate that the increase in Reynolds number leads to the enhancement of average Nusselt number, and the increase in specific heat in the presence of the nanofluid results in impr...

  20. Experimental study of a thermoelectrically-driven liquid chiller in terms of COP and cooling down period

    International Nuclear Information System (INIS)

    Faraji, Amir Yadollah; Goldsmid, H.J.; Akbarzadeh, Aliakbar

    2014-01-01

    Highlights: • A COP of 0.8 is achievable for a thermoelectrically-driven water chiller. • With two market available TEC modules with ZT around 0.7 sub-zero temperatures became applicable. • Forced air convection heat exchangers have better COP and CDP compared with natural convection. • A PID controller has several advantages against on–off controller for controlling TEC module. - Abstract: To study COP and other cooling parameters of a thermoelectically-driven liquid chiller, a 430 ml capacity liquid chiller incorporating two commercially available thermoelectric modules as its active components, has been designed, built and assessed. The system can use natural or forced air convection in heat exchangers attached to the thermoelectric module surfaces. The coefficient of performance (COP) and cooling down period (CDP) of the system for different thermoelectric input voltages have been measured. The COP of the thermoelectric chiller was found to be in the range 0.2–1.4 for forced convection and 0.2–1 for natural convection at a cooled liquid temperature of 10 °C and an ambient temperature of 18 °C. For the chiller, heat pumping capacity, minimum achievable water temperature, and temperature difference across the thermoelectric surfaces were investigated for input voltages of 3 V, 5 V, 7 V, 10 V and 12 V. Furthermore, as a basis for reliable and convenient control of the chiller, a proportional integral derivative (PID) controller has been proposed

  1. Ceramics and healthy heating and cooling systems: thermal ceramic panels in buildings. Conditions of comfort and energy demand versus convective systems

    Directory of Open Access Journals (Sweden)

    V. Echarri Iribarren

    2016-12-01

    Full Text Available Porcelain stoneware is a widely used building material. In recent years, its range of uses has expanded to encompass a new spectrum of innovative and inventive applications in architecture. In this research, we analysed the patented Thermal Ceramic Panel. This consists of a thin porcelain stoneware panel that incorporates a capillary system of polypropylene tubes measuring 3.5 mm in diameter embedded in a conductive ceramic interface. The system works with hot or cold water, producing healthy heating and cooling by means of radiant surfaces. Following an initial prototype test in which panels were placed on the walls of an office, we conducted simulations at the University of Alicante Museum using wall, ceiling and baffle panels, having previously monitored the state of the building. Thermal behaviour parameters were analysed and compared with those of other standard finishing materials, obtaining results for thermal comfort and energy savings in comparison with all-air systems.

  2. Force convective solar drying system

    International Nuclear Information System (INIS)

    Ruslan, M.H.; Othman, M.Y.; Baharuddin Yatim; Kamaruzzaman Sopian; Ibarahim, Z.

    2006-01-01

    This paper presents design and performance of V-groove back-pass solar collector for solar drying system. In this study three V-groove back-pass solar collector each with dimension of 4.6 m x 1.0 m x 0.15 m have been fabricated for solar drying system. An outdoor test at mean solar intensity for 600-800 Wm -2 by using 0.15m 3 s -1 of air flow rate which also been suggested by (Zeroul et al. 1994) was carried out at Solar Research Energy Park. Universiti Kebangsaan Malaysia. Analysis on the collector performance based on daily data was reported that the value of FR ) e and FRUL was 0.709 ± 0.001 and 5.89 ± 0.31 Wm -2o C -1 respectively with 60-70 o C of output temperature (Ruslan et al. 2001). The three V-groove collectors each with dimension 4.6 m x 0.15 m were connected in series array mounted on the roof of a solar assisted drying system. By using two electric fans of 85W and 2700 rpm each, the speed of air was regulated at 0.11 kgs -1 to 0.31 kgs -1 using a voltage regulator. Performance of the collector based on the thermal analysis showed that at mean daily solar radiation 700 Wm -2 , the output temperature of 52 o C to 73 o C could be achieved using 0.11-0.31 kgs -1 of flow rate. Thermal analysis also showed that the efficiencies of 45% to 61% could be obtains using the same flow rate and solar radiation. Analysis of daily data showed that for radiation from 300 Wm -2 to 1000 Wm -2 the power generated from the collector was within 1.5 kW to 8.9 kW. The study concluded that the levels of the levels of the solar radiation and flow rate used influenced the performance of the collector

  3. Transitions in rapidly rotating convection dynamos

    Science.gov (United States)

    Tilgner, A.

    2013-12-01

    It is commonly assumed that buoyancy in the fluid core powers the geodynamo. We study here the minimal model of a convection driven dynamo, which is a horizontal plane layer in a gravity field, filled with electrically conducting fluid, heated from below and cooled from above, and rotating about a vertical axis. Such a plane layer may be viewed as a local approximation to the geophysically more relevant spherical geometry. The numerical simulations have been run on graphics processing units with at least 960 cores. If the convection is driven stronger and stronger at fixed rotation rate, the flow behaves at some point as if it was not rotating. This transition shows in the scaling of the heat transport which can be used to distinguish slow from rapid rotation. One expects dynamos to behave differently in these two flow regimes. But even within the convection flows which are rapidly rotating according to this criterion, it will be shown that different types of dynamos exist. In one state, the magnetic field strength obeys a scaling indicative of a magnetostrophic balance, in which the Lorentz force is in equilibrium with the Coriolis force. The flow in this case is helical. A different state exists at higher magnetic Reynolds numbers, in which the magnetic energy obeys a different scaling law and the helicity of the flow is much reduced. As one increases the Rayleigh number, all other parameters kept constant, one may find both types of dynamos separated by an interval of Rayleigh numbers in which there are no dynamos at all. The effect of these transitions on energy dissipation and mean field generation have also been studied.

  4. Cooling Characteristic Analysis of Transformer's Radiator

    International Nuclear Information System (INIS)

    Kim, Hyun Jae; Yang, Si Won; Kim, Won Seok; Kweon, Ki Yeoung; Lee, Min Jea

    2007-01-01

    A transformer is a device that changes the current and voltage by electricity induced between coil and core steel, and it is composed of metals and insulating materials. In the core of the transformer, the thermal load is generated by electric loss and the high temperature can make the break of insulating. So we must cool down the temperature of transformer by external radiators. According to cooling fan's usage, there are two cooling types, OA(Oil Natural Air Natural) and FA(Oil Natural Air Forced). For this study , we used Fluent 6.2 and analyzed the cooling characteristic of radiator. we calculated 1-fin of detail modeling that is similar to honeycomb structure and multi-fin(18-fin) calculation for OA and FA types. For the sensitivity study, we have different positions(side, under) of cooling fans for forced convection of FA type. The calculation results were compared with the measurement data which obtained from 135.45/69kV ultra transformer flowrate and temperature test. The aim of the study is to assess the Fluent code prediction on the radiator calculation and to use the data for optimizing transformer radiator design

  5. Optimization of force-cooled power transmission cables by means of 3D FEM simulations; Optimierung zwangsgekuehlter Energiekabel durch dreidimensionale FEM-Simulationen

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Dongping

    2009-10-26

    Lateral forced cooling can significantly increase the temporary overload capacity of a cable system, but the design of such systems requires a time-dependent 3D analysis of the nonlinear thermal behavior as the cooling water along the cable is heated up, resulting in position-dependent and time-dependent heat uptake. For this, a new calculation method was developed on the basis of an available 3D FEM software. The new method enables 3D simulation of force-cooled cables in consideration of the potential partial dryout of soil and of thermal stabilizations. The new method was first applied to a 110 kV wind power transmission cable for different configurations and grid conditions. It was found that with lateral forced cooling, the 110 kV will have a temporal 50 percent overload capacity. Further, the thermal characteristics and limiting capacity of a force-cooled 380 kV cable system were investigated. According to the results so far, laterally cooled cable systems open up new operating options, with advantages in terms of availability, economic efficiency, and flexibility. (orig.) [German] Eine laterale Zwangskuehlung kann die temporaere Ueberlastbarkeit einer Kabelanlage signifikant erhoehen. Der Entwurf solcher zwangsgekuehlter Kabelanlagen erfordert jedoch eine zeitabhaengige, dreidimensionale Analyse des nichtlinearen thermischen Verhaltens, da sich das Kuehlwasser entlang der Trasse erwaermt und sich so eine orts- und zeitabhaengige Waermeaufnahme ergibt. Zu diesem Zweck wurde auf der Basis eines vorhandenen zweidimensionalen FEM-Programms ein neues Berechnungsverfahren entwickelt, das die dreidimensionale Simulation zwangsgekuehlter Kabelanlagen unter Beruecksichtigung einer moeglicherweise auftretenden partiellen Bodenaustrocknung und von thermischen Stabilisierungen erlaubt. Mit Hilfe dieses Berechnungsverfahrens wurde zuerst eine 110-kV-Kabelanlage zur Windenergieuebertragung bei unterschiedlichen Anordnungen und unterschiedlichen Netzsituationen untersucht

  6. Heat Convection

    Science.gov (United States)

    Jiji, Latif M.

    Professor Jiji's broad teaching experience lead him to select the topics for this book to provide a firm foundation for convection heat transfer with emphasis on fundamentals, physical phenomena, and mathematical modelling of a wide range of engineering applications. Reflecting recent developments, this textbook is the first to include an introduction to the challenging topic of microchannels. The strong pedagogic potential of Heat Convection is enhanced by the follow ing ancillary materials: (1) Power Point lectures, (2) Problem Solutions, (3) Homework Facilitator, and, (4) Summary of Sections and Chapters.

  7. A Numerical Study of Nonlinear Nonhydrostatic Conditional Symmetric Instability in a Convectively Unstable Atmosphere.

    Science.gov (United States)

    Seman, Charles J.

    1994-06-01

    gradient and Coriolis forces accelerated the meridional outflow toward the baroclinically cool side, transporting zonal momentum horizontally. The vertical (horizontal) momentum transport occurred on a convective (inertial) time scale. Taken together, the sloping convective updraft/cool side outflow represents the release of the CSI in the convectively unstable atmosphere. Further diagnostics showed that mass transports in the horizontal outflow branch ventilated the upper levels of the system, with enhanced mesoscale lifting in the core and on the leading edge of the MCS, which assisted in convective redevelopments on mesoscale time scales. Geostrophic adjustment acted to balance the convectively generated zonal momentum anomalies, thereby limiting the strength of the meridional outflow predicted by CSI theory. Circulation tendency diagnostics showed that the mesoscale circulation developed in response to thermal wind imbalances generated by the deep convection.Comparison of the BCF and BTNF simulations showed that baroclinicity enhanced mesoscale circulation growth. The BTNF circulation was more transient on mesoscale time and space scales. Overall, the BCF system produced more rainfall than the BTNF.Based on the present and past work in CSI theory, a new definition for the term `slantwise convection' is proposed.

  8. Rotating thermal convection at very large Rayleigh numbers

    Science.gov (United States)

    Weiss, Stephan; van Gils, Dennis; Ahlers, Guenter; Bodenschatz, Eberhard

    2016-11-01

    The large scale thermal convection systems in geo- and astrophysics are usually influenced by Coriolis forces caused by the rotation of their celestial bodies. To better understand the influence of rotation on the convective flow field and the heat transport at these conditions, we study Rayleigh-Bénard convection, using pressurized sulfur hexaflouride (SF6) at up to 19 bars in a cylinder of diameter D=1.12 m and a height of L=2.24 m. The gas is heated from below and cooled from above and the convection cell sits on a rotating table inside a large pressure vessel (the "Uboot of Göttingen"). With this setup Rayleigh numbers of up to Ra =1015 can be reached, while Ekman numbers as low as Ek =10-8 are possible. The Prandtl number in these experiment is kept constant at Pr = 0 . 8 . We report on heat flux measurements (expressed by the Nusselt number Nu) as well as measurements from more than 150 temperature probes inside the flow. We thank the Deutsche Forschungsgemeinschaft (DFG) for financial support through SFB963: "Astrophysical Flow Instabilities and Turbulence". The work of GA was supported in part by the US National Science Foundation through Grant DMR11-58514.

  9. Atmospheric forcing of cool subsurface water events in Bahía Culebra, Gulf of Papagayo, Costa Rica

    Directory of Open Access Journals (Sweden)

    Eric J. Alfaro

    2012-04-01

    Full Text Available Bahía Culebra, at Gulf of Papagayo on the north Pacific coast of Costa Rica, is an area of seasonal upwelling where more intense cooling events may occur during some boreal winter weeks mainly. To study these extreme cool events, records of nine sea subsurface temperature stations from 1998 to 2010 were analyzed. Five events associated with extremely cool temperatures in this region were identified from these records and taken as study cases. Sea temperatures decreased about 8-9ºC during these events and occurred while cold fronts were present in the Caribbean, with strong trade wind conditions over Central America. These strong wind conditions may have favored the offshore displacement of the sea surface water. The axis of Bahía Culebra runs northeastsouthwest, a condition that favors and triggers cool water events, mainly because the displaced water is replaced by water from deeper levels.

  10. Convection in complex shaped vessel; Convection dans des enceintes de forme complexe

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2000-07-01

    The 8 november 2000, the SFT (Societe Francaise de Thermique) organized a technical day on the convection in complex shaped vessels. Nine papers have been presented in the domains of the heat transfers, the natural convection, the fluid distribution, the thermosyphon effect, the steam flow in a sterilization cycle and the transformers cooling. Eight papers are analyzed in ETDE and one paper dealing with the natural convection in spent fuels depository is analyzed in INIS. (A.L.B.)

  11. Numerical calculation and analysis of natural convection removal of the spent fuel residual heat of 10 MW high temperature gas cooled reactor

    International Nuclear Information System (INIS)

    Wang Jinhua; Huang Yifan; Wu Bin

    2013-01-01

    The spent fuel of 10 MW High Temperature Gas Cooled Reactor (HTR-10) could be stored in the shielded tank, and the tank is stored in the concrete shielded canister in spent fuel storage room, the residual heat of the spent fuel could be removed by the air. The ability of residual heat removal is analyzed in the paper, and the temperature field is numerically calculated through FEA program ANSYS, the analysis and the calculation are used to validate the safety of the spent fuel and the tank, the ultimate temperature of the spent fuel and the tank should below the safety limit. The calculation shows that the maximum temperature locates in the middle of the fuel pebble bed in the spent fuel tank, and the temperature decreases gradually with radial distance, the temperature in the tank body is evenly distributed, and the temperature in the concrete shielded canister decreases gradually with radial distance. It is feasible to remove the residual heat of the spent fuel storage tank by natural ventilation, in natural ventilation condition, the temperature of the spent fuel and the tank is lower than the temperature limit, which provides theoretical evidence for the choice of the residual heat removal method. (authors)

  12. A Multi-Response Optimization of Thrust Forces, Torques, and the Power of Tapping Operations by Cooling Air in Reinforced and Unreinforced Polyamide PA66

    Directory of Open Access Journals (Sweden)

    Rosario Domingo

    2018-03-01

    Full Text Available The use of cooling air during machining is an environmentally conscious procedure, and its applicability to different processes is a research priority. We studied tapping operations, an important operation in the assembly process, using cooling air with unreinforced polyamide (PA66 and polyamide reinforced with glass fiber (PA66-GF30. These materials are widely used in industry, but their behavior with respect to tapping has not been studied. We analyze the outcomes regarding the thrust force, torque, and power at cutting speeds between 15 and 60 m/min. The experimental tests were executed using cooling air at 22 °C, 2 °C, and −18 °C in dry conditions. The M12 × 1.75 mm taps were high-speed steel, with cobalt as the base material and coatings of TiN and AlCrN. To identify the more influential factors, an analysis of variance was performed, along with multi-response optimization to identify the desirability values. This optimization shows that the optimum for PA66can be found in environments close to 3 °C, while the optimum for PA66-GF30 is found at the minimal temperature studied (−18 °C. Thus, cooling air can be considered an adequate procedure for tapping operations, to increase the sustainability of the manufacturing processes.

  13. Effect of field cooling heights on the levitation force of pure and starch/polystyrene/MWCNT added bulk MgB{sub 2} superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Tripathi, D.; Dey, T.K., E-mail: tapasdey@hijli.iitkgp.ernet.in

    2014-12-15

    Highlights: • Levitation force between PM and starch/PS/MWCNT added MgB{sub 2} are studied in FC mode. • MgB{sub 2} added with 1 wt.% PS gives best result. • Levitation forces do not display hysteresis during ascending and descending mode. • Exponential variation in Max. Levitation (F{sub MLF}) and attractive forces (F{sub MAF}). • The gap between PM and SC for F{sub MAF} and F{sub 0AF} varies linearly with FC height. - Abstract: A series of MgB{sub 2} pellets with and without addition of carbon from different sources (viz. starch, polystyrene and carbon nanotubes) have been synthesized by solid state reaction under argon atmosphere. XRD analysis indicates a decrease in lattice parameters of MgB{sub 2} with addition of starch, polystyrene (PS) and MWCNT and confirms substitution of carbon in boron sites. The presence of nanosized carbon inclusions between the grain boundaries in the present set of samples is evident in TEM photographs. Resistivity data confirms a decrease in superconducting transition temperature (T{sub c0}) for MgB{sub 2} doped with starch/PS/MWCNT. The effect of different field cooling heights (H{sub IFC}) at 20 K on maximum levitation force (F{sub MLF}) and maximum attractive force (F{sub MAF}) of pure MgB{sub 2} and MgB{sub 2} doped with starch/PS/MWCNT have been investigated. Except for MWCNT, doping of starch and PS in MgB{sub 2} is found to improve F{sub MLF} and F{sub MAF} and the best result is obtained for MgB{sub 2} doped with 1 wt.% PS. Levitation force measured as a function of decreasing initial field cooling height indicates exponential dependence of both maximum levitation force (F{sub MLF}) and maximum attractive force (F{sub MAF}). However, the gap distance between PM and the sample (H{sub 0AF} and H{sub MAF}) corresponding to maximum attractive force (F{sub MAF}) and zero attractive force (F{sub 0AF}) varies linearly and their difference remains constant. This constancy in (H{sub MAF} − H{sub 0AF}) is understood in

  14. Potential of enhancing a natural convection loop with a thermomagnetically pumped ferrofluid

    Energy Technology Data Exchange (ETDEWEB)

    Aursand, Eskil; Gjennestad, Magnus Aa.; Lervåg, Karl Yngve, E-mail: karl.lervag@sintef.no; Lund, Halvor

    2016-11-01

    The feasibility of using a thermomagnetically pumped ferrofluid to enhance the performance of a natural convection cooling loop is investigated. First, a simplified analytical estimate for the thermomagnetic pumping action is derived, and then design rules for optimal solenoid and ferrofluid are presented. The design rules are used to set up a medium-scale (1 m, 10–1000 W) case study, which is modeled using a previously published and validated model (Aursand et al. [1]). The results show that the thermomagnetic driving force is significant compared to the natural convection driving force, and may in some cases greatly surpass it. The results also indicate that cooling performance can be increased by factors up to 4 and 2 in the single-phase and two-phase regimes, respectively, even when taking into the account the added heat from the solenoid. The performance increases can alternatively be used to obtain a reduction in heat-sink size by up to 75%. - Highlights: • We consider a thermomagnetically pumped ferrofluid for heat transfer. • The performance of the thermomagnetic pump is compared to natural convection. • The flow is simulated using a two-phase flow model. • The thermomagnetic driving force improves heat transfer significantly.

  15. A Self-Contained Cold Plate Utilizing Force-fed Evaporation for Cooling of High flux Electronics

    Science.gov (United States)

    2007-01-01

    additional improvement. The second advanced heat sink to be covered was developed and studied by Sung and Mudawar [27]. They created a hybrid jet...cooling by using manifold microchannel heat sinks.” Advanced Electronic Packaging. 2 (1997) 1837-1842. [27] Sung, M. K. & Mudawar , I

  16. Thermal Hydraulic Analysis of RPV Support Cooling System for HTGR

    International Nuclear Information System (INIS)

    Min Qi; Wu Xinxin; Li Xiaowei; Zhang Li; He Shuyan

    2014-01-01

    Passive safety is now of great interest for future generation reactors because of its reduction of human interaction and avoidance of failures of active components. reactor pressure vessel (RPV) support cooling system (SCS) for high temperature gas-cooled reactor (HTGR) is a passive safety system and is used to cool the concrete seats for the four RPV supports at its bottom. The SCS should have enough cooling capacity to ensure the temperature of the concrete seats for the supports not exceeding the limit temperature. The SCS system is composed of a natural circulation water loop and an air cooling tower. In the water loop, there is a heat exchanger embedded in the concrete seat, heat is transferred by thermal conduction and convection to the cooling water. Then the water is cooled by the air cooler mounted in the air cooling tower. The driving forces for water and air are offered by the density differences caused by the temperature differences. In this paper, the thermal hydraulic analysis for this system was presented. Methods for decoupling the natural circulation and heat transfer between the water loop and air flow were introduced. The operating parameters for different working conditions and environment temperatures were calculated. (author)

  17. Hydrodynamical simulation of the core helium flash with two-dimensional convection

    International Nuclear Information System (INIS)

    Cole, P.W.

    1981-01-01

    The thermonuclear runaway of helium reactions under the condition of electron degeneracy in the hot, dense central regions of a low mass Population II red giant is investigated. A two-dimensional finite difference approach to time dependent convection has been applied to a peak energy production model of this phenomenon called the core helium flash. The dynamical conservation equations are integrated in two spatial dimensions and time which allow the horizontal variations of the dynamical variables to be followed explicitly. The unbalanced bouyancy forces in convectively unstable regions lead to mass flow (i.e., convective energy transport) by calculation of the velocity flow patterns produced by the conservation laws of mass, momentum, and energy without recourse to any phenomenological theory of convection. The initial phase of this hydrodynamical simulation is characterized by a thermal readjustment via downward convective energy transport into the neutrino cooled core in a series of convection modulated thermal pulses. Each of these pulses is driven by the thermal runaway and quenched by the convective energy transport when the actual temperature gradient in the flash region becomes sufficiently superadiabatic. These convection modulated thermal pulses are observed throughout 95% of the calculation, the duration of which is approximately 570,000 cycles or nearly 96,000 seconds of evolution. After this initial thermal restructuring, there ensues in the simulation a dynamic phase in which the thermonuclear runaway becomes violent. The degree of violence, the final composition, and the peak temperature depend sensitively on the nuclear energy generation rates of those reactions involving alpha particle captures

  18. Conceptual design of a forced-flow-cooled 20-kA current lead using Ag-alloy-sheathed Bi-2223 high-temperature superconductors

    International Nuclear Information System (INIS)

    Heller, R.

    1994-11-01

    The use of high-temperature superconductors in current leads to reduce refrigeration power has been investigated by many groups in the past. Most used YBCO and Bi-2212 bulk superconductors, although their critical current density is not very high. In this paper, BI-2223 HTSC tapes sheathed with Ag alloys are used in the design of a 20-kA current lead because of their higher critical current in medium magnetic fields. The lead current of 20 kA is related to the coil current of the planned stellarator WENDELSTEIN 7-X. Forced-now helium cooling has been used in the design, allowing position-independent and well-controlled operation. The design characteristics of the lead are presented and 4-K helium cooling of the whole lead, as well as 60-K helium cooling of the copper part of the lead, is discussed. The power consumption at zero current, and the lead's behaviour in case of loss of coolant flow, are given, The results of the design allow extrapolation to current leads of the 50-kA range

  19. What favors convective aggregation and why?

    Science.gov (United States)

    Muller, Caroline; Bony, Sandrine

    2015-07-01

    The organization of convection is ubiquitous, but its physical understanding remains limited. One particular type of organization is the spatial self-aggregation of convection, taking the form of cloud clusters, or tropical cyclones in the presence of rotation. We show that several physical processes can give rise to self-aggregation and highlight the key features responsible for it, using idealized simulations. Longwave radiative feedbacks yield a "radiative aggregation." In that case, sufficient spatial variability of radiative cooling rates yields a low-level circulation, which induces the upgradient energy transport and radiative-convective instability. Not only do vertically integrated radiative budgets matter but the vertical profile of cooling is also crucial. Convective aggregation is facilitated when downdrafts below clouds are weak ("moisture-memory aggregation"), and this is sufficient to trigger aggregation in the absence of longwave radiative feedbacks. These results shed some light on the sensitivity of self-aggregation to various parameters, including resolution or domain size.

  20. Relationships between radiation, clouds, and convection during DYNAMO

    Science.gov (United States)

    Ciesielski, Paul E.; Johnson, Richard H.; Jiang, Xianan; Zhang, Yunyan; Xie, Shaocheng

    2017-03-01

    The relationships between radiation, clouds, and convection on an intraseasonal time scale are examined with data taken during the Dynamics of the Madden-Julian Oscillation (MJO) field campaign. Specifically, column-net, as well as vertical profiles of radiative heating rates, computed over Gan Island in the central Indian Ocean (IO) are used along with an objective analysis of large-scale fields to examine three MJO events that occurred during the 3 month period (October to December 2011) over this region. Longwave (LW) and shortwave radiative heating rates exhibit tilted structures, reflecting radiative effects associated with the prevalence of shallow cumulus during the dry, suppressed MJO phase followed by increasing deep convection leading into the active phase. As the convection builds going into the MJO active phase, there are increasingly top-heavy anomalous radiative heating rates while the column-net radiative cooling rate progressively decreases. Temporal fluctuations in the cloud radiative forcing, being quite sensitive to changes in high cloudiness, are dominated by LW effects with an intraseasonal variation of 0.4-0.6 K/d. While both the water vapor and cloud fields are inextricably linked, it appears that the tilted radiative structures are more related to water vapor effects. The intraseasonal variation of column-net radiative heating enhances the convective signal in the mean by 20% with a minimum in this enhancement 10 days prior to peak MJO rainfall and maximum 7 days after. This suggests that as MJO convective envelope weakens over the central IO, cloud-radiative feedbacks help maintain the mature MJO as it moves eastward.

  1. Tropical teleconnections via the ocean and atmosphere induced by Southern Ocean deep convective events

    Science.gov (United States)

    Marinov, I.; Cabre, A.; Gunn, A.; Gnanadesikan, A.

    2016-12-01

    The current generation (CMIP5) of Earth System Models (ESMs) shows a huge variability in their ability to represent Southern Ocean (SO) deep-ocean convection and Antarctic Bottom Water, with a preference for open-sea convection in the Weddell and Ross gyres. A long control simulation in a coarse 3o resolution ESM (the GFDL CM2Mc model) shows a highly regular multi-decadal oscillation between periods of SO open sea convection and non-convective periods. This process also happens naturally, with different frequencies and durations of convection across most CMIP5 models under preindustrial forcing (deLavergne et al, 2014). Here we assess the impact of SO deep convection and resulting sea surface temperature (SST) anomalies on the tropical atmosphere and ocean via teleconnections, with a focus on interannual to multi-decadal timescales. We combine analysis of our low-resolution coupled model with inter-model analysis across historical CMIP5 simulations. SST cooling south of 60S during non-convective decades triggers a stronger, northward shifted SH Hadley cell, which results in intensified northward cross-equatorial moist heat transport and a poleward shift in the ITCZ. Resulting correlations between the cross-equatorial atmospheric heat transport and ITCZ location are in good agreement with recent theories (e.g. Frierson et al. 2013; Donohoe et al. 2014). Lagged correlations between a SO convective index and cross-equatorial heat transports (in the atmosphere and ocean), as well as various tropical (and ENSO) climate indices are analyzed. In the ocean realm, we find that non-convective decades result in weaker AABW formation and weaker ACC but stronger Antarctic Intermediate Water (AAIW) formation, likely as a result of stronger SO westerlies (more positive SAM). The signals of AABW and AAIW are seen in the tropics on short timescales of years to decades in the temperature, heat storage and heat transport anomalies and also in deep and intermediate ocean oxygen. Most

  2. Secagem de fatias de abóboras (Cucurbita moschata, L. por convecção natural e forçada Drying of pumpkin (Cucurbita moschata, L. slices by natural and forced convection

    Directory of Open Access Journals (Sweden)

    Soraia Vilela Borges

    2008-12-01

    Full Text Available A abóbora (Cucurbita moschata, L. é uma importante fonte de provitamina A, de baixo custo, e sob a forma desidratada oferece diferentes opções de utilização e consumo. Secagens por convecção natural e forçada foram comparadas quanto ao grau de secagem atingido e encolhimento, em função da temperatura, velocidade de ar e dimensões do produto. Os resultados obtidos mostraram que o uso de fatias com volume de 6,25 cm³ em secador por convecção forçada a 50 °C e à velocidade de 5,5 x 10-4 ms-1 resultaram em produtos de menor encolhimento, sendo recomendadas estas condições.Besides its low price, Pumpkin (Cucurbita moschata, L. is an important source of provitamin-A, and when dehydrated it offers different options of utilizations and consumption. Natural and forced convection drying were compared according to the drying degree shrinkage as a function of temperature, and air velocity and product dimensions. The obtained results showed that slices with the volume of 6.25 cm³ in forced convection oven at 50 °C and at the velocity of 5.5 x 10-4 ms-1 resulted in a lower shrinkage products, so these conditions were recommended.

  3. ESTUDO TEÓRICO DO RESFRIAMENTO COM AR FORÇADO DE FRUTAS DE GEOMETRIAS DIFERENTES THEORETICAL STUDY OF FRUITS COOLING WITH DIFFERENT FORMS GEOMETRICAL IN THE FORCED-AIR SYSTEM

    Directory of Open Access Journals (Sweden)

    Bárbara TERUEL

    2001-08-01

    positions along the bed and conditioned in package with 40% of effective opening area. The fruits were pre-cooled in a forced-air system (1.933m³/h, at 1°C and 7°C, RH= 88,4 ± 2,0% and air velocity around 1m/s. A two-dimensional mathematical model was applied, assuming prolate spheroid coordinate, to characterize the transient heat transfer process inside the fruits considering convective profile conditions at the surface of the body. The generated equations were numerically solved by finite-volume method. The convective heat transfer coefficients were obtained using the least square method by comparison between experimental and numerical data. The comparative analysis of the theoretical and experimental curves presented a satisfactory agreement, with error between 5% and 7%. It was noted that the convective heat transfer coefficient changes with the fruits position in the bed and cooling time present a variation of approximately 38% among the different points. The spatial distributions of temperature inside the fruits, for three times, demonstrate the existence of a temperature differential between the center and the surface of 30%, approximately. The model predicts that the cooling rate is in the extremes of the banana. The Bi and Fo numbers obtained represent very well the heat transfer process in the fruits under different relationships of volume/area.

  4. Topology Optimisation for Coupled Convection Problems

    DEFF Research Database (Denmark)

    Alexandersen, Joe

    This thesis deals with topology optimisation for coupled convection problems. The aim is to extend and apply topology optimisation to steady-state conjugate heat transfer problems, where the heat conduction equation governs the heat transfer in a solid and is coupled to thermal transport...... in a surrounding uid, governed by a convection-diffusion equation, where the convective velocity field is found from solving the isothermal incompressible steady-state Navier-Stokes equations. Topology optimisation is also applied to steady-state natural convection problems. The modelling is done using stabilised...... finite elements, the formulation and implementation of which was done partly during a special course as prepatory work for this thesis. The formulation is extended with a Brinkman friction term in order to facilitate the topology optimisation of fluid flow and convective cooling problems. The derived...

  5. International symposium on transient convective heat transfer: book of abstracts

    International Nuclear Information System (INIS)

    1996-01-01

    The international symposium on convective heat transfer was held on 19-23 August 1996, in Cesme, Izmir, Turkey. The spesialists discussed forced convection, heat exchangers, free convection and multiphase media and phase change at the meeting. Almost 53 papers were presented in the meeting

  6. Atmospheric forcing of cool subsurface water events in Bahía Culebra, Gulf of Papagayo, Costa Rica

    Directory of Open Access Journals (Sweden)

    Eric J. Alfaro

    2012-04-01

    Full Text Available Bahía Culebra, at Gulf of Papagayo on the north Pacific coast of Costa Rica, is an area of seasonal upwelling where more intense cooling events may occur during some boreal winter weeks mainly. To study these extreme cool events, records of nine sea subsurface temperature stations from 1998 to 2010 were analyzed. Five events associated with extremely cool temperatures in this region were identified from these records and taken as study cases. Sea temperatures decreased about 8-9ºC during these events and occurred while cold fronts were present in the Caribbean, with strong trade wind conditions over Central America. These strong wind conditions may have favored the offshore displacement of the sea surface water. The axis of Bahía Culebra runs northeastsouthwest, a condition that favors and triggers cool water events, mainly because the displaced water is replaced by water from deeper levels.Bahía Culebra, localizada en el Golfo de Papagayo, al norte de la costa del Pacífico de Costa Rica, es un área de afloramiento estacional, en donde pueden ocurrir eventos de enfriamiento más intensos, principalmente durante algunas semanas del invierno boreal. Para estudiar estos eventos de enfriamiento extremo, se analizaron datos de nueve estaciones con registros de la temperatura subsuperficial del mar, desde 1998 hasta el 2010. A partir de estos registros, se identificaron cinco casos de estudio asociados a enfriamientos del mar en la región. Los descensos de la temperatura de estos eventos fueron de aproximadamente 8-9ºC y se asociaron al paso de empujes fríos en la región del Caribe y una fuerte magnitud del viento alisio sobre América Central. Este reforzamiento del flujo alisio favorece el desplazamiento del agua superficial hacia afuera de Bahía Culebra, cuyo eje principal se ubica en la dirección noreste-suroeste. Lo anterior favorece y provoca un enfriamiento de la temperatura del mar en la bahía, ya que el agua desplazada es

  7. SAFE AND FAST QUENCH RECOVERY OF LARGE SUPERCONDUCTING SOLENOIDS COOLED BY FORCED TWO-PHASE HELIUM FLOW

    International Nuclear Information System (INIS)

    Jia, L.X.

    1999-01-01

    The cryogenic characteristics in energy extraction of the four fifteen-meter-diameter superconducting solenoids of the g-2 magnet are reported in this paper. The energy extraction tests at full-current and half-current of its operating value were deliberately carried out for the quench analyses and evaluation of the cryogenic system. The temperature profiles of each coil mandrel and pressure profiles in its helium cooling tube during the energy extraction are discussed. The low peak temperature and pressure as well as the short recovery time indicated the desirable characteristics of the cryogenic system

  8. National Convective Weather Diagnostic

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Current convective hazards identified by the National Convective Weather Detection algorithm. The National Convective Weather Diagnostic (NCWD) is an automatically...

  9. Convective Heat Transfer Scaling of Ignition Delay and Burning Rate with Heat Flux and Stretch Rate in the Equivalent Low Stretch Apparatus

    Science.gov (United States)

    Olson, Sandra

    2011-01-01

    To better evaluate the buoyant contributions to the convective cooling (or heating) inherent in normal-gravity material flammability test methods, we derive a convective heat transfer correlation that can be used to account for the forced convective stretch effects on the net radiant heat flux for both ignition delay time and burning rate. The Equivalent Low Stretch Apparatus (ELSA) uses an inverted cone heater to minimize buoyant effects while at the same time providing a forced stagnation flow on the sample, which ignites and burns as a ceiling fire. Ignition delay and burning rate data is correlated with incident heat flux and convective heat transfer and compared to results from other test methods and fuel geometries using similarity to determine the equivalent stretch rates and thus convective cooling (or heating) rates for those geometries. With this correlation methodology, buoyant effects inherent in normal gravity material flammability test methods can be estimated, to better apply the test results to low stretch environments relevant to spacecraft material selection.

  10. Study of liquid metal mixed convection in cavities

    International Nuclear Information System (INIS)

    Abadie, Philippe.

    1979-10-01

    This study has enabled some results to be obtained on the flow of liquid metals in cavities. The effects of different adimensional parameters characteristic of mixed convection flows were experimentally demonstrated. In the case of a roof heated cavity, three zones were distinguished: the mixing zone at the channel exit, a quasi constant temperature recirculation zone and a stratified zone at the top of the cavity. The thickness of this last region depends on natural convection effects: it disappears completely in a pure forced convection regime. A simple model using a critical Richardson number concept was developed in order to be able to predict the thickness of this region. Heat transfer correlation formulas were established both for the heated roof and forward direction heated wall cases. Some data was also obtained on temperature fluctuations for both cases. The different topics investigated are useful for defining heat transfers in certain regions of fast neutron sodium cooled reactors. A more extensive program is currently being developed in order to be able to investigate a wider range of variations in the above mentioned parameters and to more closely approximate reactor vessels [fr

  11. Meltdown reactor core cooling facility

    International Nuclear Information System (INIS)

    Matsuoka, Tsuyoshi.

    1992-01-01

    The meltdown reactor core cooling facility comprises a meltdown reactor core cooling tank, a cooling water storage tank situates at a position higher than the meltdown reactor core cooling tank, an upper pipeline connecting the upper portions of the both of the tanks and a lower pipeline connecting the lower portions of them. Upon occurrence of reactor core meltdown, a high temperature meltdown reactor core is dropped on the cooling tank to partially melt the tank and form a hole, from which cooling water is flown out. Since the water source of the cooling water is the cooling water storage tank, a great amount of cooling water is further dropped and supplied and the reactor core is submerged and cooled by natural convection for a long period of time. Further, when the lump of the meltdown reactor core is small and the perforated hole of the meltdown reactor cooling tank is small, cooling water is boiled by the high temperature lump intruding into the meltdown reactor core cooling tank and blown out from the upper pipeline to the cooling water storage tank to supply cooling water from the lower pipeline to the meltdown reactor core cooling tank. Since it is constituted only with simple static facilities, the facility can be simplified to attain improvement of reliability. (N.H.)

  12. Temperature-Driven Convection

    Science.gov (United States)

    Bohan, Richard J.; Vandegrift, Guy

    2003-02-01

    Warm air aloft is stable. This explains the lack of strong winds in a warm front and how nighttime radiative cooling can lead to motionless air that can trap smog. The stability of stratospheric air can be attributed to the fact that it is heated from above as ultraviolet radiation strikes the ozone layer. On the other hand, fluid heated from below is unstable and can lead to Bernard convection cells. This explains the generally turbulent nature of the troposphere, which receives a significant fraction of its heat directly from the Earth's warmer surface. The instability of cold fluid aloft explains the violent nature of a cold front, as well as the motion of Earth's magma, which is driven by radioactive heating deep within the Earth's mantle. This paper describes how both effects can be demonstrated using four standard beakers, ice, and a bit of food coloring.

  13. Turbulent natural convection in an enclosure formed by an array of vertical cylinders

    International Nuclear Information System (INIS)

    McEligot, D.M.; Stoots, C.M.; Christenson, W.A.; O'Brien, J.E.; Larson, T.K.; Mecham, D.C.; Lussie, W.G.

    1992-04-01

    A number of situations can be hypothesized to occur in an advanced or special purpose nuclear reactor such that the core is filled with a gas but there is no forced flow to remove the thermal energy evolved. Typically, the dimensions are so large that the magnitudes of the governing parameters indicate that the flow regime is probably turbulent. The generic situation considered in the present work is natural convection between heated, slender, vertical, circular cylinders and a surrounding array of cooler vertical cylinders in a triangular pattern. Experiments were conducted by resistively heating a vertical circular cylinder of length-to-diameter ratio of about 160 centered inside a concentric perforated tube which was, in turn, surrounded by three larger diameter tubes cooled internally with water flow. The medium was air. In order to deduce the contribution due to thermal radiation, thermal emissivities of the tubes were determined in-situ during the experiment and the emissivities of samples of the surfaces involved were measured separately. The ratio of the test section temperature to the cooling tube temperature was varied up to 2.6 by adjusting the electrical power. The Rayleigh number, based on tube diameter and properties evaluated at the cooling tube temperature, ranged from 2.9 x 10 4 to 9.2 x 10 5 . Results indicate that the convective heat transfer parameters for the perforated tube are about fifteen per cent higher than for the smooth bare tube centered in the same position relative to the array. The Nusselt number for convective heat transfer across the annulus-between the heated test section and the perforated tube corresponded to parallel laminar flow. Data with water films flowing down the outside surfaces of the cooling tubes demonstrated no significant change in the convective heat transfer parameters deduced

  14. Transient Mixed Convection Validation for NGNP

    Energy Technology Data Exchange (ETDEWEB)

    Smith, Barton [Utah State Univ., Logan, UT (United States); Schultz, Richard [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2015-10-19

    The results of this project are best described by the papers and dissertations that resulted from the work. They are included in their entirety in this document. They are: (1) Jeff Harris PhD dissertation (focused mainly on forced convection); (2) Blake Lance PhD dissertation (focused mainly on mixed and transient convection). This dissertation is in multi-paper format and includes the article currently submitted and one to be submitted shortly; and, (3) JFE paper on CFD Validation Benchmark for Forced Convection.

  15. Transient Mixed Convection Validation for NGNP

    International Nuclear Information System (INIS)

    Smith, Barton; Schultz, Richard

    2015-01-01

    The results of this project are best described by the papers and dissertations that resulted from the work. They are included in their entirety in this document. They are: (1) Jeff Harris PhD dissertation (focused mainly on forced convection); (2) Blake Lance PhD dissertation (focused mainly on mixed and transient convection). This dissertation is in multi-paper format and includes the article currently submitted and one to be submitted shortly; and, (3) JFE paper on CFD Validation Benchmark for Forced Convection.

  16. The status of thermal-hydraulic studies on the decay heat removal by natural convection using RAMONA and NEPTUN models

    International Nuclear Information System (INIS)

    Hoffmann, H.; Hain, K.; Marten, K.; Rust, K.; Weinberg, D.; Ohira, H.

    2004-01-01

    Thermal-hydraulic experiments were performed with water in order to simulate the decay heat removal by natural convection in a pool-type sodium-cooled reactor. Two test rigs of different scales were used, namely RAMONA (1:20) and NEPTUN (1:5). RAMONA served to study the transition from nominal operation by forced convection to decay heat removal operation by natural convection. Steady-state similarity tests were carried out in both facilities. The investigations cover nominal and non-nominal operation conditions. These data provide a broad basis for the verification of computer programs. Numerical analyses performed with the three-dimensional FLUTAN code indicated that the thermal-hydraulic processes can be quantitatively simulated even for the very complex geometry of the NEPTUN test rig. (author)

  17. Prediction of heat transfer coefficients for forced convective boiling of N2-hydrocarbon mixtures at cryogenic conditions using artificial neural networks

    Science.gov (United States)

    Barroso-Maldonado, J. M.; Belman-Flores, J. M.; Ledesma, S.; Aceves, S. M.

    2018-06-01

    A key problem faced in the design of heat exchangers, especially for cryogenic applications, is the determination of convective heat transfer coefficients in two-phase flow such as condensation and boiling of non-azeotropic refrigerant mixtures. This paper proposes and evaluates three models for estimating the convective coefficient during boiling. These models are developed using computational intelligence techniques. The performance of the proposed models is evaluated using the mean relative error (mre), and compared to two existing models: the modified Granryd's correlation and the Silver-Bell-Ghaly method. The three proposed models are distinguished by their architecture. The first is based on directly measured parameters (DMP-ANN), the second is based on equivalent Reynolds and Prandtl numbers (eq-ANN), and the third on effective Reynolds and Prandtl numbers (eff-ANN). The results demonstrate that the proposed artificial neural network (ANN)-based approaches greatly outperform available methodologies. While Granryd's correlation predicts experimental data within a mean relative error mre = 44% and the S-B-G method produces mre = 42%, DMP-ANN has mre = 7.4% and eff-ANN has mre = 3.9%. Considering that eff-ANN has the lowest mean relative error (one tenth of previously available methodologies) and the broadest range of applicability, it is recommended for future calculations. Implementation is straightforward within a variety of platforms and the matrices with the ANN weights are given in the appendix for efficient programming.

  18. A powerful way of cooling computer chip using liquid metal with low melting point as the cooling fluid

    Energy Technology Data Exchange (ETDEWEB)

    Li Teng; Lv Yong-Gang [Chinese Academy of Sciences, Beijing (China). Cryogenic Lab.; Chinese Academy of Sciences, Beijing (China). Graduate School; Liu Jing; Zhou Yi-Xin [Chinese Academy of Sciences, Beijing (China). Cryogenic Lab.

    2006-12-15

    With the improvement of computational speed, thermal management becomes a serious concern in computer system. CPU chips are squeezing into tighter and tighter spaces with no more room for heat to escape. Total power-dissipation levels now reside about 110 W, and peak power densities are reaching 400-500 W/mm{sup 2} and are still steadily climbing. As a result, higher performance and greater reliability are extremely tough to attain. But since the standard conduction and forced-air convection techniques no longer be able to provide adequate cooling for sophisticated electronic systems, new solutions are being looked into liquid cooling, thermoelectric cooling, heat pipes, and vapor chambers. In this paper, we investigated a novel method to significantly lower the chip temperature using liquid metal with low melting point as the cooling fluid. The liquid gallium was particularly adopted to test the feasibility of this cooling approach, due to its low melting point at 29.7 C, high thermal conductivity and heat capacity. A series of experiments with different flow rates and heat dissipation rates were performed. The cooling capacity and reliability of the liquid metal were compared with that of the water-cooling and very attractive results were obtained. Finally, a general criterion was introduced to evaluate the cooling performance difference between the liquid metal cooling and the water-cooling. The results indicate that the temperature of the computer chip can be significantly reduced with the increasing flow rate of liquid gallium, which suggests that an even higher power dissipation density can be achieved with a large flow of liquid gallium and large area of heat dissipation. The concept discussed in this paper is expected to provide a powerful cooling strategy for the notebook PC, desktop PC and large computer. It can also be extended to more wide area involved with thermal management on high heat generation rate. (orig.)

  19. EXPERIMENTAL VERIFICATION OF COMPUTER MODEL OF COOLING SYSTEM FOR POWERFUL SEMI- CONDUCTOR DEVICE

    Directory of Open Access Journals (Sweden)

    I. A. Khorunzhii

    2007-01-01

    Full Text Available A cooling system for powerful semi-conductor device (power -1 kW consisting of a pin-type radiator and a body is considered in the paper. Cooling is carried out by forced convection of a coolant. Calculated values of temperatures on the radiator surface and experimentally measured values of temperatures in the same surface points have been compared in the paper. It has been shown that the difference between calculated and experimentally measured temperatures does not exceed 0,1-0,2 °C and it is comparable with experimental error value. The given results confirm correctness of a computer model.

  20. Influence of different means of turbine blade cooling on the thermodynamic performance of combined cycle

    International Nuclear Information System (INIS)

    Sanjay; Singh, Onkar; Prasad, B.N.

    2008-01-01

    A comparative study of the influence of different means of turbine blade cooling on the thermodynamic performance of combined cycle power plant is presented. Seven schemes involving air and steam as coolants under open and closed loop cooling techniques have been studied. The open loop incorporates the internal convection, film and transpiration cooling techniques. Closed loop cooling includes only internal convection cooling. It has been found that closed loop steam cooling offers more specific work and consequently gives higher value of plant efficiency of about 60%, whereas open loop transpiration steam cooling, open loop steam internal convection cooling, transpiration air cooling, film steam cooling, film air, and internal convection air cooling have been found to yield lower values of plant efficiency in decreasing order as compared to closed loop steam cooling

  1. Thermo-electro-hydrodynamic convection under microgravity: a review

    Energy Technology Data Exchange (ETDEWEB)

    Mutabazi, Innocent; Yoshikawa, Harunori N; Fogaing, Mireille Tadie; Travnikov, Vadim; Crumeyrolle, Olivier [Laboratoire Ondes et Milieux Complexes, UMR 6294, CNRS-Université du Havre, CS 80450, F-76058 Le Havre Cedex (France); Futterer, Birgit; Egbers, Christoph, E-mail: Innocent.Mutabazi@univ-lehavre.fr [Department of Aerodynamics and Fluid Mechanics, Brandenburg University of Technology Cottbus-Senftenberg, Cottbus (Germany)

    2016-12-15

    Recent studies on thermo-electro-hydrodynamic (TEHD) convection are reviewed with focus on investigations motivated by the analogy with natural convection. TEHD convection originates in the action of the dielectrophoretic force generated by an alternating electric voltage applied to a dielectric fluid with a temperature gradient. This electrohydrodynamic force is analogous to Archimedean thermal buoyancy and can be regarded as a thermal buoyancy force in electric effective gravity. The review is concerned with TEHD convection in plane, cylindrical, and spherical capacitors under microgravity conditions, where the electric gravity can induce convection without any complexities arising from geometry or the buoyancy force due to the Earth’s gravity. We will highlight the convection in spherical geometry, comparing developed theories and numerical simulations with the GEOFLOW experiments performed on board the International Space Station (ISS). (paper)

  2. Analysis of Turbine Blade Relative Cooling Flow Factor Used in the Subroutine Coolit Based on Film Cooling Correlations

    Science.gov (United States)

    Schneider, Steven J.

    2015-01-01

    Heat transfer correlations of data on flat plates are used to explore the parameters in the Coolit program used for calculating the quantity of cooling air for controlling turbine blade temperature. Correlations for both convection and film cooling are explored for their relevance to predicting blade temperature as a function of a total cooling flow which is split between external film and internal convection flows. Similar trends to those in Coolit are predicted as a function of the percent of the total cooling flow that is in the film. The exceptions are that no film or 100 percent convection is predicted to not be able to control blade temperature, while leaving less than 25 percent of the cooling flow in the convection path results in nearing a limit on convection cooling as predicted by a thermal effectiveness parameter not presently used in Coolit.

  3. Measurements of convective and radiative heating in wildland fires

    Science.gov (United States)

    David Frankman; Brent W. Webb; Bret W. Butler; Daniel Jimenez; Jason M. Forthofer; Paul Sopko; Kyle S. Shannon; J. Kevin Hiers; Roger D. Ottmar

    2012-01-01

    Time-resolved irradiance and convective heating and cooling of fast-response thermopile sensors were measured in 13 natural and prescribed wildland fires under a variety of fuel and ambient conditions. It was shown that a sensor exposed to the fire environment was subject to rapid fluctuations of convective transfer whereas irradiance measured by a windowed sensor was...

  4. Tool for Forecasting Cool-Season Peak Winds Across Kennedy Space Center and Cape Canaveral Air Force Station (CCAFS)

    Science.gov (United States)

    Barrett, Joe H., III; Roeder, William P.

    2010-01-01

    Peak wind speed is important element in 24-Hour and Weekly Planning Forecasts issued by 45th Weather Squadron (45 WS). Forecasts issued for planning operations at KSC/CCAFS. 45 WS wind advisories issued for wind gusts greater than or equal to 25 kt. 35 kt and 50 kt from surface to 300 ft. AMU developed cool-season (Oct - Apr) tool to help 45 WS forecast: daily peak wind speed, 5-minute average speed at time of peak wind, and probability peak speed greater than or equal to 25 kt, 35 kt, 50 kt. AMU tool also forecasts daily average wind speed from 30 ft to 60 ft. Phase I and II tools delivered as a Microsoft Excel graphical user interface (GUI). Phase II tool also delivered as Meteorological Interactive Data Display System (MIDDS) GUI. Phase I and II forecast methods were compared to climatology, 45 WS wind advisories and North American Mesoscale model (MesoNAM) forecasts in a verification data set.

  5. Numerical Investigation of Thermal Radiation and Viscous Effects on Entropy Generation in Forced Convection Blood Flow over an Axisymmetric Stretching Sheet

    Directory of Open Access Journals (Sweden)

    Mohammad Yaghoub Abdollahzadeh Jamalabadi

    2016-05-01

    Full Text Available Numerical and analytical investigation of the effects of thermal radiation and viscous heating on a convective flow of a non-Newtonian, incompressible fluid in an axisymmetric stretching sheet with constant temperature wall is performed. The power law model of the blood is used for the non-Newtonian model of the fluid and the Rosseland model for the thermal radiative heat transfer in an absorbing medium and viscous heating are considered as the heat sources. The non-dimensional governing equations are transformed to similarity form and solved numerically. A parameter study on entropy generation in medium is presented based on the Second Law of Thermodynamics by considering various parameters such as the thermal radiation parameter, the Brinkman number, Prandtl number, Eckert number.

  6. Thermal boundary condition effects on forced convection heat transfer. Application of a numerical solution of an adjoint problem; Kyosei tairyu netsudentatsu mondai ni okeru netsuteki kyokai joken no eikyo. Zuihan mondai no suchi kai wo mochiita kosatsu

    Energy Technology Data Exchange (ETDEWEB)

    Momose, K.; Saso, K.; Kimoto, H. [Osaka University, Osaka (Japan). Faculty of Engineering Science

    1997-11-25

    We propose a numerical solution for the adjoint operator of a forced convection heat transfer problem to evaluate mean heat transfer characteristics under arbitrary thermal conditions. Using the numerical solutions of the adjoint problems under Dirichlet and Neumann conditions, both of which can be computed using a conventional CFD code, the influence function of the local surface temperature on the total heat transfer and that of the local surface heat flux on the mean surface temperature are obtained. As a result, the total heat fluxes for arbitrary surface temperature distributions and the mean surface temperatures for arbitrary surface heat flux distributions can be calculated using these influence functions. The influence functions for a circular cylinder and for an in-line square rod array are presented. 14 refs., 9 figs., 1 tab.

  7. Clausius-Clapeyron Scaling of Convective Available Potential Energy (CAPE) in Cloud-Resolving Simulations

    Science.gov (United States)

    Seeley, J.; Romps, D. M.

    2015-12-01

    Recent work by Singh and O'Gorman has produced a theory for convective available potential energy (CAPE) in radiative-convective equilibrium. In this model, the atmosphere deviates from a moist adiabat—and, therefore, has positive CAPE—because entrainment causes evaporative cooling in cloud updrafts, thereby steepening their lapse rate. This has led to the proposal that CAPE increases with global warming because the strength of evaporative cooling scales according to the Clausius-Clapeyron (CC) relation. However, CAPE could also change due to changes in cloud buoyancy and changes in the entrainment rate, both of which could vary with global warming. To test the relative importance of changes in CAPE due to CC scaling of evaporative cooling, changes in cloud buoyancy, and changes in the entrainment rate, we subject a cloud-resolving model to a suite of natural (and unnatural) forcings. We find that CAPE changes are primarily driven by changes in the strength of evaporative cooling; the effect of changes in the entrainment rate and cloud buoyancy are comparatively small. This builds support for CC scaling of CAPE.

  8. Experimental study of the effect of an electric field on thermal exchanges under forced convection with gaseous carbon anhydride in presence of the radiation of the Melusine pile; Etude experimentale de l'effet d'un champ electrique sur les echanges thermiques en convection forcee avec l'anhydride carbonique gazeux en presence du rayonnement de la pile Melusine

    Energy Technology Data Exchange (ETDEWEB)

    Perroud, P.; Rebiere, J.; Verdier, J.

    1961-01-21

    Previous studies showed that, under free or forced convection, the application of a non-uniform electric field with a sufficient intensity at the neighbourhood of the heating elements resulted in a significant improvement of the thermal exchange coefficient under some flow rate and pressure conditions. But these improvements first required the creation of ions in the gas (shock ionization and existence of a corona effect above a sufficient voltage). This document therefore report further studies performed at the neighbourhood of the Melusine atomic pile which would provide ionizing radiations of much greater intensity. The objectives were, on the one hand, a global verification of work hypotheses imagined for the exchange improvement mechanism, and, on the other hand, to obtain data on the conditions under which this exchange improvement mechanism could be used in channels of a reactor. The authors present the instrumentation (measurement cells, gas circuit, heating circuit, high voltage circuit), describe how physical values are measured (pressure, gas flow rate, temperature of the heating element, gas temperature, high voltage). They describe how they compare powers exchanged under forced convection between dioxide carbon and a heated wire with or without external ionizing radiations, and report the various performed calculations (power supplied to the gas, temperature shift, Nusselt and Reynolds numbers). They report and discuss experimental results obtained outside the pile without ionizing radiations, and within the pile in presence of a ionizing radiation [French] Les essais ont ete effectues dans les conditions suivantes: nombres de Reynolds variant de 20.000 a 80.000, pression de 11 a 21 kg/cm{sup 2}, temperatures moyennes de l'element chauffant de 200 a 600 deg. C, tension electrique de 0 a 30 kV eff et intensite maximum du rayonnement γ, 3x10{sup 7} roentgen/h. On a confirme, hors pile, que l'augmentation de la puissance echangee, au dessus du seuil d

  9. WRF nested large-eddy simulations of deep convection during SEAC4RS

    Science.gov (United States)

    Heath, Nicholas K.; Fuelberg, Henry E.; Tanelli, Simone; Turk, F. Joseph; Lawson, R. Paul; Woods, Sarah; Freeman, Sean

    2017-04-01

    Large-eddy simulations (LES) and observations are often combined to increase our understanding and improve the simulation of deep convection. This study evaluates a nested LES method that uses the Weather Research and Forecasting (WRF) model and, specifically, tests whether the nested LES approach is useful for studying deep convection during a real-world case. The method was applied on 2 September 2013, a day of continental convection that occurred during the Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) campaign. Mesoscale WRF output (1.35 km grid length) was used to drive a nested LES with 450 m grid spacing, which then drove a 150 m domain. Results reveal that the 450 m nested LES reasonably simulates observed reflectivity distributions and aircraft-observed in-cloud vertical velocities during the study period. However, when examining convective updrafts, reducing the grid spacing to 150 m worsened results. We find that the simulated updrafts in the 150 m run become too diluted by entrainment, thereby generating updrafts that are weaker than observed. Lastly, the 450 m simulation is combined with observations to study the processes forcing strong midlevel cloud/updraft edge downdrafts that were observed on 2 September. Results suggest that these strong downdrafts are forced by evaporative cooling due to mixing and by perturbation pressure forces acting to restore mass continuity around neighboring updrafts. We conclude that the WRF nested LES approach, with further development and evaluation, could potentially provide an effective method for studying deep convection in real-world cases.

  10. Boundary Layer Control of Rotating Convection Systems

    Science.gov (United States)

    King, E. M.; Stellmach, S.; Noir, J.; Hansen, U.; Aurnou, J. M.

    2008-12-01

    Rotating convection is ubiquitous in the natural universe, and is likely responsible for planetary processes such magnetic field generation. Rapidly rotating convection is typically organized by the Coriolis force into tall, thin, coherent convection columns which are aligned with the axis of rotation. This organizational effect of rotation is thought to be responsible for the strength and structure of magnetic fields generated by convecting planetary interiors. As thermal forcing is increased, the relative influence of rotation weakens, and fully three-dimensional convection can exist. It has long been assumed that rotational effects will dominate convection dynamics when the ratio of buoyancy to the Coriolis force, the convective Rossby number, Roc, is less than unity. We investigate the influence of rotation on turbulent Rayleigh-Benard convection via a suite of coupled laboratory and numerical experiments over a broad parameter range: Rayleigh number, 10310; Ekman number, 10-6≤ E ≤ ∞; and Prandtl number, 1≤ Pr ≤ 100. In particular, we measure heat transfer (as characterized by the Nusselt number, Nu) as a function of the Rayleigh number for several different Ekman and Prandtl numbers. Two distinct heat transfer scaling regimes are identified: non-rotating style heat transfer, Nu ~ Ra2/7, and quasigeostrophic style heat transfer, Nu~ Ra6/5. The transition between the non-rotating regime and the rotationally dominant regime is described as a function of the Ekman number, E. We show that the regime transition depends not on the global force balance Roc, but on the relative thicknesses of the thermal and Ekman boundary layers. The transition scaling provides a predictive criterion for the applicability of convection models to natural systems such as Earth's core.

  11. Gas cooled reactors

    International Nuclear Information System (INIS)

    Kojima, Masayuki.

    1985-01-01

    Purpose: To enable direct cooling of reactor cores thereby improving the cooling efficiency upon accidents. Constitution: A plurality sets of heat exchange pipe groups are disposed around the reactor core, which are connected by way of communication pipes with a feedwater recycling device comprising gas/liquid separation device, recycling pump, feedwater pump and emergency water tank. Upon occurrence of loss of primary coolants accidents, the heat exchange pipe groups directly absorb the heat from the reactor core through radiation and convection. Although the water in the heat exchange pipe groups are boiled to evaporate if the forcive circulation is interrupted by the loss of electric power source, water in the emergency tank is supplied due to the head to the heat exchange pipe groups to continue the cooling. Furthermore, since the heat exchange pipe groups surround the entire circumference of the reactor core, cooling is carried out uniformly without resulting deformation or stresses due to the thermal imbalance. (Sekiya, K.)

  12. A 'backward' free-convective boundary layer

    NARCIS (Netherlands)

    Kuiken, H.K.

    1981-01-01

    In this paper the cooling of a low-heat-resistance sheet that moves downwards is considered. The free-convective velocities are assumed to be much larger than the velocity of the sheet. As a result the motion of the fluid is mainly towards the point where the sheet enters the system and a ‘backward’

  13. Investigations on passive containment cooling

    International Nuclear Information System (INIS)

    Knebel, J.U.; Cheng, X.; Neitzel, H.J.; Erbacher, F.J.; Hofmann, F.

    1997-01-01

    The composite containment design for advanced LWRs that has been examined under the PASCO project is a promising design concept for purely passive decay heat removal after a severe accident. The passive cooling processes applied are natural convection and radiative heat transfer. Heat transfer through the latter process removes at an emission coefficient of 0.9 about 50% of the total heat removed via the steel containment, and thus is an essential factor. The heat transferring surfaces must have a high emission coefficient. The sump cooling concept examined under the SUCO project achieves a steady, natural convection-driven flow from the heat source to the heat sink. (orig./CB) [de

  14. Economizer Based Data Center Liquid Cooling with Advanced Metal Interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Timothy Chainer

    2012-11-30

    A new chiller-less data center liquid cooling system utilizing the outside air environment has been shown to achieve up to 90% reduction in cooling energy compared to traditional chiller based data center cooling systems. The system removes heat from Volume servers inside a Sealed Rack and transports the heat using a liquid loop to an Outdoor Heat Exchanger which rejects the heat to the outdoor ambient environment. The servers in the rack are cooled using a hybrid cooling system by removing the majority of the heat generated by the processors and memory by direct thermal conduction using coldplates and the heat generated by the remaining components using forced air convection to an air- to- liquid heat exchanger inside the Sealed Rack. The anticipated benefits of such energy-centric configurations are significant energy savings at the data center level. When compared to a traditional 10 MW data center, which typically uses 25% of its total data center energy consumption for cooling this technology could potentially enable a cost savings of up to $800,000-$2,200,000/year (assuming electricity costs of 4 to 11 cents per kilowatt-hour) through the reduction in electrical energy usage.

  15. An alternative cooling system to enhance the safety of Li-ion battery packs

    Science.gov (United States)

    Kizilel, Riza; Sabbah, Rami; Selman, J. Robert; Al-Hallaj, Said

    A passive thermal management system is evaluated for high-power Li-ion packs under stressful or abusive conditions, and compared with a purely air-cooling mode under normal and abuse conditions. A compact and properly designed passive thermal management system utilizing phase change material (PCM) provides faster heat dissipation than active cooling during high pulse power discharges while preserving sufficiently uniform cell temperature to ensure the desirable cycle life for the pack. This study investigates how passive cooling with PCM contributes to preventing the propagation of thermal runaway in a single cell or adjacent cells due to a cell catastrophic failure. Its effectiveness is compared with that of active cooling by forced air flow or natural convection using the same compact module and pack configuration corresponding to the PCM matrix technology. The effects of nickel tabs and spacing between the cells were also studied.

  16. Thermal performance of cooling system for a laptop computer using a boiling enhancement microstructure

    International Nuclear Information System (INIS)

    Cho, N. H.; Jeong, W. Y.; Park, S. H.

    2008-01-01

    The increasing heat generation rates in CPU of notebook computers motivate a research on cooling technologies with low thermal resistance. This paper develops a closed-loop two-phase cooling system using a micropump to circulate a dielectric liquid(PF5060). The cooling system consists of an evaporator containing a boiling enhancement microstructure connected to a condenser with mini fans providing external forced convection. The cooling system is characterized by a parametric study which determines the effects of volume fill ratio of coolant, existence of a boiling enhancement microstructure and pump flow rates on thermal performance of the closed loop. Experimental data shows the optimal parametric values which can dissipate 33.9W with a film heater maintained at 95 .deg. C

  17. Thermal performance of cooling system for a laptop computer using a boiling enhancement microstructure

    Energy Technology Data Exchange (ETDEWEB)

    Cho, N. H.; Jeong, W. Y.; Park, S. H. [Kumoh National Institute of Technology, Gumi (Korea, Republic of)

    2008-07-01

    The increasing heat generation rates in CPU of notebook computers motivate a research on cooling technologies with low thermal resistance. This paper develops a closed-loop two-phase cooling system using a micropump to circulate a dielectric liquid(PF5060). The cooling system consists of an evaporator containing a boiling enhancement microstructure connected to a condenser with mini fans providing external forced convection. The cooling system is characterized by a parametric study which determines the effects of volume fill ratio of coolant, existence of a boiling enhancement microstructure and pump flow rates on thermal performance of the closed loop. Experimental data shows the optimal parametric values which can dissipate 33.9W with a film heater maintained at 95 .deg. C.

  18. An alternative cooling system to enhance the safety of Li-ion battery packs

    Energy Technology Data Exchange (ETDEWEB)

    Kizilel, Riza; Sabbah, Rami [Department of Chemical and Biological Engineering, Illinois Institute of Technology, 10 W. 33rd Street, Chicago, IL 60616 (United States); Selman, J. Robert [Department of Chemical and Biological Engineering, Illinois Institute of Technology, 10 W. 33rd Street, Chicago, IL 60616 (United States); All Cell Technologies, LLC, IIT University Technology Park, 3440 S. Dearborn Street, Suite 117N, Chicago, IL 60616 (United States); Al-Hallaj, Said [All Cell Technologies, LLC, IIT University Technology Park, 3440 S. Dearborn Street, Suite 117N, Chicago, IL 60616 (United States)

    2009-12-01

    A passive thermal management system is evaluated for high-power Li-ion packs under stressful or abusive conditions, and compared with a purely air-cooling mode under normal and abuse conditions. A compact and properly designed passive thermal management system utilizing phase change material (PCM) provides faster heat dissipation than active cooling during high pulse power discharges while preserving sufficiently uniform cell temperature to ensure the desirable cycle life for the pack. This study investigates how passive cooling with PCM contributes to preventing the propagation of thermal runaway in a single cell or adjacent cells due to a cell catastrophic failure. Its effectiveness is compared with that of active cooling by forced air flow or natural convection using the same compact module and pack configuration corresponding to the PCM matrix technology. The effects of nickel tabs and spacing between the cells were also studied. (author)

  19. Modeling the overall heat conductive and convective properties of open-cell graphite foam

    International Nuclear Information System (INIS)

    Tee, C C; Yu, N; Li, H

    2008-01-01

    This work develops analytic models on the overall thermal conductivity, pressure drop and overall convective heat transfer coefficient of graphite foam. The models study the relationship between the overall heat conductive and convective properties, and foam microstructure, temperature, foam surface friction characteristics and cooling fluid properties. The predicted thermal conductivity, convective heat transfer coefficient and pressure drop agree well with experimental data

  20. Numerical simulations of convectively excited gravity waves

    International Nuclear Information System (INIS)

    Glatzmaier, G.A.

    1983-01-01

    Magneto-convection and gravity waves are numerically simulated with a nonlinear, three-dimensional, time-dependent model of a stratified, rotating, spherical fluid shell heated from below. A Solar-like reference state is specified while global velocity, magnetic field, and thermodynamic perturbations are computed from the anelastic magnetohydrodynamic equations. Convective overshooting from the upper (superadiabatic) part of the shell excites gravity waves in the lower (subadiabatic) part. Due to differential rotation and Coriolis forces, convective cell patterns propagate eastward with a latitudinally dependent phase velocity. The structure of the excited wave motions in the stable region is more time-dependent than that of the convective motions above. The magnetic field tends to be concentrated over giant-cell downdrafts in the convective zone but is affected very little by the wave motion in the stable region

  1. Cooling techniques

    International Nuclear Information System (INIS)

    Moeller, S.P.

    1994-01-01

    After an introduction to the general concepts of cooling of charged particle beams, some specific cooling methods are discussed, namely stochastic, electron and laser cooling. The treatment concentrates on the physical ideas of the cooling methods and only very crude derivations of cooling times are given. At the end three other proposed cooling schemes are briefly discussed. (orig.)

  2. Laminar Mixed Convection Heat Transfer Correlation for Horizontal Pipes

    International Nuclear Information System (INIS)

    Chae, Myeong Seon; Chung, Bum Jin

    2013-01-01

    This study aimed at producing experimental results and developing a new heat transfer correlation based upon a semi-empirical buoyancy coefficient. Mixed convection mass transfers inside horizontal pipe were investigated for the pipe of various length-to-diameters with varying Re. Forced convection correlation was developed using a very short cathode. With the length of cathode increase and Re decrease, the heat transfer rates were enhanced and becomes higher than that of forced convection. An empirical buoyancy coefficient was derived from correlation of natural convection and forced convection with the addition of L/D. And the heat transfer correlation for laminar mixed convection was developed using the buoyancy coefficient, it describes not only current results, but also results of other studies. Mixed convection occurs when the driving forces of both forced and natural convections are of comparable magnitude (Gr/Re 2 ∼1). It is classical problem but is still an active area of research for various thermal applications such as flat plate solar collectors, nuclear reactors and heat exchangers. The effect of buoyancy on heat transfer in a forced flow is varied by the direction of the buoyancy force. In a horizontal pipe the direction of the forced and buoyancy forces are perpendicular. The studies on the mixed convections of the horizontal pipes were not investigated very much due to the lack of practical uses compared to those of vertical pipes. Even the definitions on the buoyancy coefficient that presents the relative influence of the forced and the natural convections, are different by scholars. And the proposed heat transfer correlations do not agree

  3. Correlation development of natural convection heat transfer in consideration of aspect ratio change and coolant boiling

    International Nuclear Information System (INIS)

    Park, L. J.; Cho, Y. L.; Kang, K. H.; Kim, S. B.; Kim, H. D.; Cho, J. S.; Jung, C. H.

    1999-01-01

    A new correlation on natural convection heat transfer with crust formation in the molten metal pool has been developed in consideration of coolant boiling effect and of aspect ratio change by an increase in crust thickness. Two test results of the convection cooling case, natural and forced convection cooling cases, and of the boiling case were used in the present study. The experimental results have shown that the Nusselt number of the case with boiling condition in the molten metal pool is greater than that of the case with non-boiling condition at the same Rayleigh number. Even though the Rayleigh number rapidly decreases due to an increase of the crust thickness, the Nusselt number does not rapidly decrease because of the aspect ratio effect. From the experimental results, the new correlation between the Nusselt number and Rayleigh number in the molten metal pool with the crust formation has been developed as Nu 0.051(Ra) 1/3 (AR) . 0 .2441 (Φ) 0.025 using Globe and Dropkin correlation

  4. Natural convection in superposed fluid-porous layers

    CERN Document Server

    Bagchi, Aniruddha

    2013-01-01

    Natural Convection in Composite Fluid-Porous Domains provides a timely overview of the current state of understanding on the phenomenon of convection in composite fluid-porous layers. Natural convection in horizontal fluid-porous layers has received renewed attention because of engineering problems such as post-accident cooling of nuclear reactors, contaminant transport in groundwater, and convection in fibrous insulation systems. Because applications of the problem span many scientific domains, the book serves as a valuable resource for a wide audience.

  5. Forced convection of liquid hydrogen - Part 2 (continued) - case of large temperature differences between the fluid and the wall (rectangular channel)

    International Nuclear Information System (INIS)

    Perroud, P.; Rebiere, J.

    1965-01-01

    Liquid hydrogen flows in a canal of rectangular cross section of 1 x 6 mm ; only one of the larger side is heated (length 190 mm) in order to simulate the cooling of a missile nozzle. The liquid is admitted subcooled at 25 deg. K in average and under a pressure of 8 bars. Mass velocity from 8.9 to 102 g/cm 2 .s, heat flux from 18 to 296.6 W/cm 2 and wall temperature reaching 800 deg. K. Two correlations of local heat transfer coefficients are presented, one for the region in two-phase flow and the other for the region in homogeneous gas-phase which are compared with the formula previously established for a cylindrical canal. An analysis of pressure drop is also given. Gross experimental results are separately published. (authors) [fr

  6. Southern Ocean Convection and tropical telleconnections

    Science.gov (United States)

    Marinov, I.; Cabre, A.; Gnanadesikan, A.

    2014-12-01

    We show that Southern Ocean (SO) temperatures in the latest generation of Earth System Models exhibit two major modes of variation, one driven by deep convection, the other by tropical variability. We perform a CMIP5 model intercomparison to understand why different climate models represent SO variability so differently in long, control simulations. We show that multiyear variability in Southern Ocean sea surface temperatures (SSTs) can in turn influence oceanic and atmospheric conditions in the tropics on short (atmospheric) time-scales. We argue that the strength and pattern of SO-tropical teleconnections depends on the intensity of SO deep convection. Periodic convection in the SO is a feature of most CMIP5 models under preindustrial forcing (deLavergne et al., 2014). Models show a wide distribution in the spatial extent, periodicity and intensity of their SO convection, with some models convecting most of the time, and some showing very little convection. In a highly convective coupled model, we find that multidecadal variability in SO and global SSTs, as well as SO heat storage are driven by Weddell Sea convective variability, with convective decades relatively warm due to the heat released from the deep southern ocean and non-convective decades cold due to the subsurface storage of heat. Furthermore, pulses of SO convection drive SST and sea ice variations, influencing absorbed shortwave and emitted longwave radiation, wind, cloud and precipitation patterns, with climatic implications for the low latitudes via fast atmospheric teleconnections. We suggest that these high-low latitude teleconnection mechanisms are relevant for understanding hiatus decades. Additionally, Southern Ocean deep convection varied significantly during past, natural climate changes such as during the last deglaciation. Weddell Sea open convection was recently weakened, likely as a consequence of anthropogenic forcing and the resulting surface freshening. Our study opens up the

  7. Mixed convection flow of nanofluid in a square enclosure with an intruded rectangular fin

    International Nuclear Information System (INIS)

    Cong, Ran; Zhou, Xuanyu; De Souza Machado, Bruno; Das, Prodip K.

    2016-01-01

    Mixed convection flow in enclosures has been a subject of interest for many years due to their ever increasing applications in solar collectors, electronic cooling, lubrication technologies, food processing, and nuclear reactors. In comparison, little effort has been given to the problem of mixed convection in enclosures filled with nanofluids, while the addition of nanoparticles in a fluid base to alter specific material properties is considered a feasible solution for many heat transfer problems. Mixed convection of nanofluids is a challenging problem as the addition of nanoparticles changes the fluid’s thermo-physical properties as well as due to the complex interactions among inertia, viscous, and buoyancy forces. In this study, a two-dimensional steady-state numerical model has been developed to investigate mixed convection flow of nanofluids in a square enclosure with an intruded rectangular fin and to optimize the fin geometry for maximizing the heat transfer using the Constructal design. The model has been developed using ANSYS-FLUENT for various fin geometries. Flow fields, temperature fields, and heat transfer rates are examined for different values of Rayleigh and Reynolds numbers for several geometries of the fin with the aim of maximizing the heat transfer from the fin to the surrounding flow. Outcome of this study provides important insight into the heat transfer behavior of nanofluids, which will help in developing novel geometries with enhanced and controlled heat transfer for solar collectors and electronic devices.

  8. Mixed convection flow of nanofluid in a square enclosure with an intruded rectangular fin

    Energy Technology Data Exchange (ETDEWEB)

    Cong, Ran; Zhou, Xuanyu; De Souza Machado, Bruno; Das, Prodip K., E-mail: prodip.das@ncl.ac.uk [School of Mechanical and Systems Engineering Newcastle University Newcastle upon Tyne, NE1 7RU United Kingdom (United Kingdom)

    2016-07-12

    Mixed convection flow in enclosures has been a subject of interest for many years due to their ever increasing applications in solar collectors, electronic cooling, lubrication technologies, food processing, and nuclear reactors. In comparison, little effort has been given to the problem of mixed convection in enclosures filled with nanofluids, while the addition of nanoparticles in a fluid base to alter specific material properties is considered a feasible solution for many heat transfer problems. Mixed convection of nanofluids is a challenging problem as the addition of nanoparticles changes the fluid’s thermo-physical properties as well as due to the complex interactions among inertia, viscous, and buoyancy forces. In this study, a two-dimensional steady-state numerical model has been developed to investigate mixed convection flow of nanofluids in a square enclosure with an intruded rectangular fin and to optimize the fin geometry for maximizing the heat transfer using the Constructal design. The model has been developed using ANSYS-FLUENT for various fin geometries. Flow fields, temperature fields, and heat transfer rates are examined for different values of Rayleigh and Reynolds numbers for several geometries of the fin with the aim of maximizing the heat transfer from the fin to the surrounding flow. Outcome of this study provides important insight into the heat transfer behavior of nanofluids, which will help in developing novel geometries with enhanced and controlled heat transfer for solar collectors and electronic devices.

  9. Mixed convection flow of nanofluid in a square enclosure with an intruded rectangular fin

    Science.gov (United States)

    Cong, Ran; Zhou, Xuanyu; De Souza Machado, Bruno; Das, Prodip K.

    2016-07-01

    Mixed convection flow in enclosures has been a subject of interest for many years due to their ever increasing applications in solar collectors, electronic cooling, lubrication technologies, food processing, and nuclear reactors. In comparison, little effort has been given to the problem of mixed convection in enclosures filled with nanofluids, while the addition of nanoparticles in a fluid base to alter specific material properties is considered a feasible solution for many heat transfer problems. Mixed convection of nanofluids is a challenging problem as the addition of nanoparticles changes the fluid's thermo-physical properties as well as due to the complex interactions among inertia, viscous, and buoyancy forces. In this study, a two-dimensional steady-state numerical model has been developed to investigate mixed convection flow of nanofluids in a square enclosure with an intruded rectangular fin and to optimize the fin geometry for maximizing the heat transfer using the Constructal design. The model has been developed using ANSYS-FLUENT for various fin geometries. Flow fields, temperature fields, and heat transfer rates are examined for different values of Rayleigh and Reynolds numbers for several geometries of the fin with the aim of maximizing the heat transfer from the fin to the surrounding flow. Outcome of this study provides important insight into the heat transfer behavior of nanofluids, which will help in developing novel geometries with enhanced and controlled heat transfer for solar collectors and electronic devices.

  10. Numerical modelling of convective heat transport by air flow in permafrost talus slopes

    Directory of Open Access Journals (Sweden)

    J. Wicky

    2017-06-01

    Full Text Available Talus slopes are a widespread geomorphic feature in the Alps. Due to their high porosity a gravity-driven internal air circulation can be established which is forced by the gradient between external (air and internal (talus temperature. The thermal regime is different from the surrounding environment, leading to the occurrence of permafrost below the typical permafrost zone. This phenomenon has mainly been analysed by field studies and only few explicit numerical modelling studies exist. Numerical simulations of permafrost sometimes use parameterisations for the effects of convection but mostly neglect the influence of convective heat transfer in air on the thermal regime. In contrast, in civil engineering many studies have been carried out to investigate the thermal behaviour of blocky layers and to improve their passive cooling effect. The present study further develops and applies these concepts to model heat transfer in air flows in a natural-scale talus slope. Modelling results show that convective heat transfer has the potential to develop a significant temperature difference between the lower and the upper parts of the talus slope. A seasonally alternating chimney-effect type of circulation develops. Modelling results also show that this convective heat transfer leads to the formation of a cold reservoir in the lower part of the talus slope, which can be crucial for maintaining the frozen ground conditions despite increasing air temperatures caused by climate change.

  11. Measurement of the Convective Heat-Transfer Coefficient

    Science.gov (United States)

    Conti, Rosaria; Gallitto, Aurelio Agliolo; Fiordilino, Emilio

    2014-01-01

    We propose an experiment for investigating how objects cool down toward the thermal equilibrium with their surroundings. We describe the time dependence of the temperature difference of the cooling objects and the environment with an exponential decay function. By measuring the thermal constant t, we determine the convective heat-transfer…

  12. National Convective Weather Forecast

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The NCWF is an automatically generated depiction of: (1) current convection and (2) extrapolated signficant current convection. It is a supplement to, but does NOT...

  13. Control system for forced-air cooling of horticultural products Sistema de controle para o resfriamento com ar forçado de produtos hortícolas

    Directory of Open Access Journals (Sweden)

    João C. T. R. da Silva

    2011-01-01

    Full Text Available This work is a study of the implementation of a classical controller using a tuning method referred to as IMC (Internal Model Control and aimed at the reduction of electrical energy consumption by the appropriate relation between energy consumption and the cooling time with forced air. The supervisory system installed was able to manipulate the variable of frequency of the signal power of the exhaust fan engine (forced air module, to accelerate or decelerate the loss of heat from the product to be cooled by airflow variation that passes through the mass of the produce. The results demonstrated a reduction in energy consumption from 64% and an increase of only 8% in the cooling time to the system using PI/IMC (Proportional - Integral with IMC tuning method compared with the system in its operating nominal condition. This PI/IMC control may be implemented directly in a frequency converter, without the need to purchase a computer or PLC (programmable logic controller to run the dedicated application, increasing its economical viability.Este trabalho consiste no estudo da implementação de um controlador clássico utilizando o método de sintonia denominado por Controle de Modelo Interno, visando à redução do consumo de energia elétrica que decorra na adequada relação entre este consumo e o tempo de resfriamento do processo de resfriamento com ar forçado de produtos hortícolas. Para isto, o sistema supervisório instalado manipulou a variável de frequência do sinal de alimentação do motor de indução trifásico do exaustor (módulo de ar forçado, para acelerar ou desacelerar a perda de calor do produto a ser resfriado por intermédio da variação da vazão de ar que perpassava a massa deste produto. Obteve-se como resultado uma redução no consumo de energia elétrica de 64% e um acréscimo de apenas 8% no tempo de resfriamento para o sistema utilizando um controle proporcional e integral associado ao método de sintonia promovido

  14. Cooling tower calculations

    International Nuclear Information System (INIS)

    Simonkova, J.

    1988-01-01

    The problems are summed up of the dynamic calculation of cooling towers with forced and natural air draft. The quantities and relations are given characterizing the simultaneous exchange of momentum, heat and mass in evaporative water cooling by atmospheric air in the packings of cooling towers. The method of solution is clarified in the calculation of evaporation criteria and thermal characteristics of countercurrent and cross current cooling systems. The procedure is demonstrated of the calculation of cooling towers, and correction curves and the effect assessed of the operating mode at constant air number or constant outlet air volume flow on their course in ventilator cooling towers. In cooling towers with the natural air draft the flow unevenness is assessed of water and air relative to its effect on the resulting cooling efficiency of the towers. The calculation is demonstrated of thermal and resistance response curves and cooling curves of hydraulically unevenly loaded towers owing to the water flow rate parameter graded radially by 20% along the cross-section of the packing. Flow rate unevenness of air due to wind impact on the outlet air flow from the tower significantly affects the temperatures of cooled water in natural air draft cooling towers of a design with lower demands on aerodynamics, as early as at wind velocity of 2 m.s -1 as was demonstrated on a concrete example. (author). 11 figs., 10 refs

  15. Thermal performance of a closed advanced two-phase thermosyphon loop for cooling of radio base stations at different operating conditions

    International Nuclear Information System (INIS)

    Khodabandeh, Rahmatollah

    2004-01-01

    In this investigation an advanced thermosyphon loop with extended evaporator and condenser surfaces has been tested at high heat fluxes. The thermosyphon investigated is designed for the cooling of three parallel high heat flux electronic components. The tested evaporators were made from small blocks of copper in which five vertical channels with a diameter of 1.5 mm and length of 14.6 mm were drilled. The riser and downcomer connected the evaporators to the condenser, which is an air-cooled roll-bond type with a total surface area of 1.5 m 2 on the airside. Tests were done with Isobutane (R600a) at heat loads in the range of 10-90 W/cm 2 to each of the components with forced convection condenser cooling and with natural convection with heat loads of 10-70 W

  16. Turbulent natural convection between a perforated vertical cylinder and a surrounding array

    International Nuclear Information System (INIS)

    McEligot, D.M.; Stoots, C.M.; Christenson, W.A.; O'Brien, J.E.; Mecham, D.C.; Lussie, W.G.

    1992-01-01

    A number of situations can be hypothesized to occur in an advanced or special purpose nuclear reactor such that the core is filled with a gas but there is no forced flow to remove the thermal energy evolved. Experiments were conducted by resistively hearing a vertical circular cylinder of length-to-diameter ratio of about 160 centered inside a concentric perforated tube which was, in turn, surrounded by three larger diameter tubes cooled internally with water flow. The ratio of the test section temperature to the cooling tube temperature was varied up to 2.6; and the Rayleigh number, based on tube diameter and properties evaluated at the cooling tube temperature, ranged from 2.9 x 10 4 to 9.2 x 10 5 . Results indicate that the convective heat transfer parameters for the perforated tube are about fifteen per cent higher than for the smooth bare tube centered in the same position relative to the array. The Nusselt number for convective heat transfer across the annulus between the heated test section and the perforated tube corresponded to parallel laminar flow

  17. Prediction of flow recirculation in a blanket assembly under worst-case natural-convection conditions

    International Nuclear Information System (INIS)

    Khan, E.U.; Rector, D.R.

    1982-01-01

    Reactor fuel and blanket assemblies within a Liquid Metal Fast Breeder Reactor (LMFBR) can be subjected to severe radial heat flux gradients. At low-flow conditions, with power-to-flow ratios of nearly the same magnitude as design conditions, buoyancy forces cause flow redistribution to the side of a bundle with the higher heat generation rate. Recirculation of fluid within a rod bundle can occur during a natural convection transient because of the combined effect of flow coastdown and buoyancy-induced redistribution. An important concern is whether recirculation leads to high coolant temperatures. For this reason, the COBRA-WC code was developed with the capability of modeling recirculating flows. Experiments have been conducted in a 2 x 6 rod bundle for flow and power transients to study recirculation in the mixed-convection (forced cooled) and natural-convection regimes. The data base developed was used to validate the recirculation module in the COBRA-WC code. COBRA-WC code calculations were made to predict flow and temperature distributions in a typical LMFBR blanket assembly for the worst-case, natural-circulation transient

  18. Behaviors and transitions along the path to magnetostrophic convection

    Science.gov (United States)

    Grannan, A. M.; Vogt, T.; Horn, S.; Hawkins, E. K.; Aggarwal, A.; Aurnou, J. M.

    2017-12-01

    The generation of magnetic fields in planetary and stellar interiors are believed to be controlled primarily by turbulent convection constrained by Coriolis and Lorentz forces in their electrically conducting fluid layers. Yet relatively few laboratory experiments are capable of investigating the different regimes of turbulent magnetohydrodynamic convection. In this work, we perform one laboratory experiment in a cylinder at a fixed heat flux using the liquid metal gallium in order to investigate, sequentially: Rayleigh-Bènard convection without any imposed constraints, magnetoconvection with a Lorentz constraint imposed by vertical magnetic field, rotating convection with a Coriolis constraint imposed by rotation, and finally the magnetostrophic convective regime where both Coriolis and Lorentz are imposed and equal. Using an array of internal and external temperature probes, we show that each regime along the path to magnetostrophic convection is unique. The behaviors and transitions in the dominant modes of convection as well as their fundamental frequencies and wavenumbers are investigated.

  19. Heat transfer measurements in a forced convection loop with two molten-fluoride salts: LiF--BeF2--ThF2--UF4 and eutectic NaBF4--NaF

    International Nuclear Information System (INIS)

    Silverman, M.D.; Huntley, W.R.; Robertson, H.E.

    1976-10-01

    Heat transfer coefficients were determined experimentally for two molten-fluoride salts [LiF-BeF 2 -ThF 2 -UF 4 (72-16-12-0.3 mole %) and NaBF 4 -NaF (92-8 mole %] proposed as the fuel salt and coolant salt, respectively, for molten-salt breeder reactors. Information was obtained over a wide range of variables, with salt flowing through 12.7-mm-OD (0.5-in.) Hastelloy N tubing in a forced convection loop (FCL-2b). Satisfactory agreement with the empirical Sieder-Tate correlation was obtained in the fully developed turbulent region at Reynolds moduli above 15,000 and with a modified Hausen equation in the extended transition region (Re approx.2100-15,000). Insufficient data were obtained in the laminar region to allow any conclusions to be drawn. These results indicate that the proposed salts behave as normal heat transfer fluids with an extended transition region

  20. Cool snacks

    DEFF Research Database (Denmark)

    Grunert, Klaus G; Brock, Steen; Brunsø, Karen

    2016-01-01

    Young people snack and their snacking habits are not always healthy. We address the questions whether it is possible to develop a new snack product that adolescents will find attractive, even though it is based on ingredients as healthy as fruits and vegetables, and we argue that developing...... such a product requires an interdisciplinary effort where researchers with backgrounds in psychology, anthropology, media science, philosophy, sensory science and food science join forces. We present the COOL SNACKS project, where such a blend of competences was used first to obtain thorough insight into young...... people's snacking behaviour and then to develop and test new, healthier snacking solutions. These new snacking solutions were tested and found to be favourably accepted by young people. The paper therefore provides a proof of principle that the development of snacks that are both healthy and attractive...

  1. Steady, three-dimensional, internally heated convection

    International Nuclear Information System (INIS)

    Schubert, G.; Glatzmaier, G.A.; Travis, B.

    1993-01-01

    Numerical calculations have been carried out of steady, symmetric, three-dimensional modes of convection in internally heated, infinite Prandtl number, Boussinesq fluids at a Rayleigh number of 1.4x10 4 in a spherical shell with inner/outer radius of 0.55 and in a 3x3x1 rectangular box. Multiple patterns of convection occur in both geometries. In the Cartesian geometry the patterns are dominated by cylindrical cold downflows and a broad hot upwelling. In the spherical geometry the patterns consist of cylindrical cold downwellings centered either at the vertices of a tetrahedron or the centers of the faces of a cube. The cold downflow cylinders are immersed in a background of upwelling within which there are cylindrical hot concentrations (plumes) and hot halos around the downflows. The forced hot upflow return plumes of internally heated spherical convection are fundamentally different from the buoyancy-driven plumes of heated from below convection

  2. Turbine airfoil with an internal cooling system having vortex forming turbulators

    Science.gov (United States)

    Lee, Ching-Pang

    2014-12-30

    A turbine airfoil usable in a turbine engine and having at least one cooling system is disclosed. At least a portion of the cooling system may include one or more cooling channels having a plurality of turbulators protruding from an inner surface and positioned generally nonorthogonal and nonparallel to a longitudinal axis of the airfoil cooling channel. The configuration of turbulators may create a higher internal convective cooling potential for the blade cooling passage, thereby generating a high rate of internal convective heat transfer and attendant improvement in overall cooling performance. This translates into a reduction in cooling fluid demand and better turbine performance.

  3. Comparison between predicted duct effectiveness from proposed ASHRAE Standard 152P and measured field data for residential forced air cooling systems; TOPICAL

    International Nuclear Information System (INIS)

    Siegel, Jeffrey A.; McWilliams, Jennifer A.; Walker, Iain S.

    2002-01-01

    The proposed ASHRAE Standard 152P ''Method of Test for Determining the Design and Seasonal Efficiencies of Residential Thermal Distribution Systems'' (ASHRAE 2002) has recently completed its second public review. As part of the standard development process, this study compares the forced air distribution system ratings provided by the public review draft of Standard 152P to measured field results. 58 field tests were performed on cooling systems in 11 homes in the summers of 1998 and 1999. Seven of these houses had standard attics with insulation on the attic floor and a well-vented attic space. The other four houses had unvented attics where the insulation is placed directly under the roof deck and the attic space is not deliberately vented. Each house was tested under a range of summer weather conditions at each particular site, and in some cases the amount of duct leakage was intentionally varied. The comparison between 152P predicted efficiencies and the measured results includes evaluation of the effects of weather, duct location, thermal conditions, duct leakage, and system capacity. The results showed that the difference between measured delivery effectiveness and that calculated using proposed Standard 152P is about 5 percentage points if weather data, duct leakage and air handler flow are well known. However, the accuracy of the standard is strongly dependent on having good measurements of duct leakage and system airflow. Given that the uncertainty in the measured delivery effectiveness is typically also about 5 percentage points, the Standard 152P results are acceptably close to the measured data

  4. Mixed convection of nanofluids in a lid-driven rough cavity

    Science.gov (United States)

    Guo, Zhimeng; Wang, Jinyu; Mozumder, Aloke K.; Das, Prodip K.

    2017-06-01

    Mixed convection heat transfer and fluid flow of air, water or oil in enclosures have been studied extensively using experimental and numerical means for many years due to their ever-increasing applications in many engineering fields. In comparison, little effort has been given to the problem of mixed convection of nanofluids in spite of several applications in solar collectors, electronic cooling, lubrication technologies, food processing, and nuclear reactors. Mixed convection of nanofluids is a challenging problem due to the complex interactions among inertia, viscous, and buoyancy forces. In this study, mixed convection of nanofluids in a lid-driven square cavity with sinusoidal roughness elements at the bottom is studied numerically using the Navier-Stokes equations with the Boussinesq approximation. The numerical model is developed using commercial finite volume software ANSYS-FLUENT for Al2O3-water and CuO-water nanofluids inside a square cavity with various roughness elements. The effects of number and amplitude of roughness elements on the heat transfer and fluid flow are analysed for various volume concentrations of Al2O3 and CuO nanoparticles. The flow fields, temperature fields, and heat transfer rates are examined for different values of Rayleigh and Reynolds numbers. The outcome of this study provides some important insight into the heat transfer behaviour of Al2O3-water and CuO-water nanofluids inside a lid-driven rough cavity. This knowledge can be further used in developing novel geometries with enhanced and controlled heat transfer for solar collectors, electronic cooling, and food processing industries.

  5. A continuous and prognostic convection scheme based on buoyancy, PCMT

    Science.gov (United States)

    Guérémy, Jean-François; Piriou, Jean-Marcel

    2016-04-01

    A new and consistent convection scheme (PCMT: Prognostic Condensates Microphysics and Transport), providing a continuous and prognostic treatment of this atmospheric process, is described. The main concept ensuring the consistency of the whole system is the buoyancy, key element of any vertical motion. The buoyancy constitutes the forcing term of the convective vertical velocity, which is then used to define the triggering condition, the mass flux, and the rates of entrainment-detrainment. The buoyancy is also used in its vertically integrated form (CAPE) to determine the closure condition. The continuous treatment of convection, from dry thermals to deep precipitating convection, is achieved with the help of a continuous formulation of the entrainment-detrainment rates (depending on the convective vertical velocity) and of the CAPE relaxation time (depending on the convective over-turning time). The convective tendencies are directly expressed in terms of condensation and transport. Finally, the convective vertical velocity and condensates are fully prognostic, the latter being treated using the same microphysics scheme as for the resolved condensates but considering the convective environment. A Single Column Model (SCM) validation of this scheme is shown, allowing detailed comparisons with observed and explicitly simulated data. Four cases covering the convective spectrum are considered: over ocean, sensitivity to environmental moisture (S. Derbyshire) non precipitating shallow convection to deep precipitating convection, trade wind shallow convection (BOMEX) and strato-cumulus (FIRE), together with an entire continental diurnal cycle of convection (ARM). The emphasis is put on the characteristics of the scheme which enable a continuous treatment of convection. Then, a 3D LAM validation is presented considering an AMMA case with both observations and a CRM simulation using the same initial and lateral conditions as for the parameterized one. Finally, global

  6. Experimental Studies of NGNP Reactor Cavity Cooling System With Water

    Energy Technology Data Exchange (ETDEWEB)

    Corradini, Michael; Anderson, Mark; Hassan, Yassin; Tokuhiro, Akira

    2013-01-16

    This project will investigate the flow behavior that can occur in the reactor cavity cooling system (RCCS) with water coolant under the passive cooling-mode of operation. The team will conduct separate-effects tests and develop associated scaling analyses, and provide system-level phenomenological and computational models that describe key flow phenomena during RCCS operation, from forced to natural circulation, single-phase flow and two-phase flow and flashing. The project consists of the following tasks: Task 1. Conduct separate-effects, single-phase flow experiments and develop scaling analyses for comparison to system-level computational modeling for the RCCS standpipe design. A transition from forced to natural convection cooling occurs in the standpipe under accident conditions. These tests will measure global flow behavior and local flow velocities, as well as develop instrumentation for use in larger scale tests, thereby providing proper flow distribution among standpipes for decay heat removal. Task 2. Conduct separate-effects experiments for the RCCS standpipe design as two-phase flashing occurs and flow develops. As natural circulation cooling continues without an ultimate heat sink, water within the system will heat to temperatures approaching saturation , at which point two-phase flashing and flow will begin. The focus is to develop a phenomenological model from these tests that will describe the flashing and flow stability phenomena. In addition, one could determine the efficiency of phase separation in the RCCS storage tank as the two-phase flashing phenomena ensues and the storage tank vents the steam produced. Task 3. Develop a system-level computational model that will describe the overall RCCS behavior as it transitions from forced flow to natural circulation and eventual two-phase flow in the passive cooling-mode of operation. This modeling can then be used to test the phenomenological models developed as a function of scale.

  7. Interaction of externally-driven acoustic waves with compressible convection

    International Nuclear Information System (INIS)

    Jones, P.; Merryfield, W.

    1992-01-01

    Two-dimensional numerical simulations are used to examine the interaction of acoustic waves with a compressible convecting fluid. Acoustic waves are forced at the lower boundary of the computational domain and propagate through a three-layer system undergoing vigorous penetrative convection. Energy exchange between the wave and the fluid is analyzed using a work integral formulation

  8. Experimental and numerical study of flow deflection effects on electronic air-cooling

    International Nuclear Information System (INIS)

    Arfaoui, Ahlem; Ben Maad, Rejeb; Hammami, Mahmoud; Rebay, Mourad; Padet, Jacques

    2009-01-01

    This work present a numerical and experimental investigation of the influence of transversal flow deflector on the cooling of a heated block mounted on a flat plate. The deflector is inclined and therefore it guides the air flow to the upper surface of the block. This situation is simulating the air-cooling of a rectangular integrated circuit or a current converter mounted on an electronic board. The electronic component are assumed dissipating a low or medium heat flux (with a density lower than 5000 W/m 2 ), as such the forced convection air cooling without fan or heat sink is still sufficient. The study details the effects of the angle of deflector on the temperature and the heat transfer coefficient along the surface of the block and around it. The results of the numerical simulations and the InfraRed camera measurements show that the deviation caused by deflector may significantly enhance the heat transfer on the top face of block

  9. The ultra low mass cooling system of the Belle II DEPFET detector

    International Nuclear Information System (INIS)

    Ruiz-Valls, P.; Marinas, C.

    2013-01-01

    The new Japanese Super Flavor Factory Belle II is designed with high precision in mind, making a good vertex resolution a necessity. In order to achieve the required resolution in the vertex reconstruction, besides highly segmented pixel detectors, the material budget has to be kept at very low levels, since more material results in multiple scattering and degrades the resolution. As a consequence, there is a direct impact on the cooling system, that has to be carefully designed, not allowing active cooling pipes inside the acceptance region. In this asymmetric e + e − experiment the angular acceptance ranges from 17° to 150°, leaving room for support structures outside this range. The Belle II vertex detector includes DEPFET technology in its vertex detector the front end electronics (FEE) of which, placed outside the acceptance, can be cooled by 2-phase CO 2 through massive support structures while the sensitive area relies on forced convection with cold nitrogen gas

  10. Comparison of immersed liquid and air cooling of NASA's Airborne Information Management System

    Science.gov (United States)

    Hoadley, A. W.; Porter, A. J.

    1992-01-01

    The Airborne Information Management System (AIMS) is currently under development at NASA Dryden Flight Research Facility. The AIMS is designed as a modular system utilizing surface mounted integrated circuits in a high-density configuration. To maintain the temperature of the integrated circuits within manufacturer's specifications, the modules are to be filled with Fluorinert FC-72. Unlike ground based liquid cooled computers, the extreme range of the ambient pressures experienced by the AIMS requires the FC-72 be contained in a closed system. This forces the latent heat absorbed during the boiling to be released during the condensation that must take within the closed module system. Natural convection and/or pumping carries the heat to the outer surface of the AIMS module where the heat transfers to the ambient air. This paper will present an evaluation of the relative effectiveness of immersed liquid cooling and air cooling of the Airborne Information Management System.

  11. Convective model of a microwave discharge in a gas at atmospheric pressure in the form of a spatially localized plasma

    International Nuclear Information System (INIS)

    Skovoroda, A.A.

    1997-01-01

    Experiments and a theoretical model consistent with them are presented which show that a stationary microwave discharge in a gas at atmospheric pressure under the action of free convection due to the action of the buoyant force on the heated air can be spatially localized, taking a spheroidal shape. Vortex motion inside the spheroid gives this localized plasma formation some of the properties of a material body which are manifested in a distinct material isolation from the surrounding space, in the formation of a narrow thermal boundary layer and flow separation, and in the formation of secondary vortices in the wake region. The characteristic radius of the stationary localized plasma is governed mainly by the wavelength of the microwave radiation a∼0.137λ. Energy balance is established to a significant degree by convective cooling of the microwave-heated structure

  12. Application of Sub-cooled Boiling Model to Thermal-hydraulic Analysis Inside a CANDU-6 Fuel Channel

    International Nuclear Information System (INIS)

    Kim, Man Woong; Lee, Sang Kyu; Kim, Hyun Koon; Yoo, Kun Joong; Kang, Hyoung Chul; Yoo, Seong Yeon

    2007-01-01

    Forced convection nucleate boiling is encountered in heat exchangers during normal and non-nominal modes of operation in pressurized water or boiling water reactors (PWRs or BWRs). If the wall temperature of the piping is higher than the saturation temperature of the nearby liquid, nucleate boiling occurs. In this regime, bubbles are formed at the wall. Their growth is promoted by the wall superheat (the difference between the wall and saturation temperatures), and they depart from the wall as a result of gravitational and liquid inertia forces. If the bulk liquid is subcooled, condensation at the bubble-liquid interface takes place and the bubble may collapse. This convection nucleate boiling is called as a sub-cooled nucleate boiling. As for the fuel channel of a CANDU 6 reactor, forced convection nucleate boiling models for flows along fuel elements enclosed inside typical CANDU-6 fuel channel has encountered difficulties due to the modeling of local effects along the horizontal channel. Therefore, the subcooled nucleate boiling has been modeled through temperature driven boiling heat and mass transfer, using a model developed at Rensselaer Polytechnic Institute. The objectives of this study are: (i) to investigate a proposed sub-cooled boiling model developed at Rensselaer Polytechnic Institute and (ii) to apply against a experiment and (iii) to predict local distributions of flow fields for the actual fuel channel geometries of CANDU-6 reactors. The numerical implementation is conducted using by the FLUENT 6.2 CFD computer code

  13. Experimental study of laminar mixed convection in a rod bundle with mixing vane spacer grids

    Energy Technology Data Exchange (ETDEWEB)

    Mohanta, Lokanath, E-mail: lxm971@psu.edu [Department of Mechanical and Nuclear Engineering, Pennsylvania State University, University Park, PA 16802 (United States); Cheung, Fan-Bill [Department of Mechanical and Nuclear Engineering, Pennsylvania State University, University Park, PA 16802 (United States); Bajorek, Stephen M.; Tien, Kirk; Hoxie, Chris L. [Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001 (United States)

    2017-02-15

    Highlights: • Investigated the heat transfer during mixed laminar convection in a rod bundle with linearly varying heat flux. • The Nusselt number increases downstream of the inlet with increasing Richardson number. • Developed an enhancement factor to account for the effects of mixed convection over the forced laminar heat transfer. - Abstract: Heat transfer by mixed convection in a rod bundle occurs when convection is affected by both the buoyancy and inertial forces. Mixed convection can be assumed when the Richardson number (Ri = Gr/Re{sup 2}) is on the order of unity, indicating that both forced and natural convection are important contributors to heat transfer. In the present study, data obtained from the Rod Bundle Heat Transfer (RBHT) facility was used to determine the heat transfer coefficient in the mixed convection regime, which was found to be significantly larger than those expected assuming purely forced convection based on the inlet flow rate. The inlet Reynolds (Re) number for the tests ranged from 500 to 1300, while the Grashof (Gr) number varied from 1.5 × 10{sup 5} to 3.8 × 10{sup 6} yielding 0.25 < Ri < 4.3. Using results from RBHT test along with the correlation from the FLECHT-SEASET test program for laminar forced convection, a new correlation ​is proposed for mixed convection in a rod bundle. The new correlation accounts for the enhancement of heat transfer relative to laminar forced convection.

  14. Natural convective heat transfer from square cylinder

    Energy Technology Data Exchange (ETDEWEB)

    Novomestský, Marcel, E-mail: marcel.novomestsky@fstroj.uniza.sk; Smatanová, Helena, E-mail: helena.smatanova@fstroj.uniza.sk; Kapjor, Andrej, E-mail: andrej.kapjor@fstroj.uniza.sk [University of Žilina, Faculty of Mechanical Engineering, Department of Power Engineering, Univerzitná 1, 010 26 Žilina (Slovakia)

    2016-06-30

    This article is concerned with natural convective heat transfer from square cylinder mounted on a plane adiabatic base, the cylinders having an exposed cylinder surface according to different horizontal angle. The cylinder receives heat from a radiating heater which results in a buoyant flow. There are many industrial applications, including refrigeration, ventilation and the cooling of electrical components, for which the present study may be applicable.

  15. Emergency reactor cooling circuit

    International Nuclear Information System (INIS)

    Araki, Hidefumi; Matsumoto, Tomoyuki; Kataoka, Yoshiyuki.

    1994-01-01

    Cooling water in a gravitationally dropping water reservoir is injected into a reactor pressure vessel passing through a pipeline upon occurrence of emergency. The pipeline is inclined downwardly having one end thereof being in communication with the pressure vessel. During normal operation, the cooling water in the upper portion of the inclined pipeline is heated by convection heat transfer from the communication portion with the pressure vessel. On the other hand, cooling water present at a position lower than the communication portion forms cooling water lumps. Accordingly, temperature stratification layers are formed in the inclined pipeline. Therefore, temperature rise of water in a vertical pipeline connected to the inclined pipeline is small. With such a constitution, the amount of heat lost from the pressure vessel by way of the water injection pipeline is reduced. Further, there is no worry that cooling water to be injected upon occurrence of emergency is boiled under reduced pressure in the injection pipeline to delay the depressurization of the pressure vessel. (I.N.)

  16. Superconducting magnet cooling system

    Science.gov (United States)

    Vander Arend, Peter C.; Fowler, William B.

    1977-01-01

    A device is provided for cooling a conductor to the superconducting state. The conductor is positioned within an inner conduit through which is flowing a supercooled liquid coolant in physical contact with the conductor. The inner conduit is positioned within an outer conduit so that an annular open space is formed therebetween. Through the annular space is flowing coolant in the boiling liquid state. Heat generated by the conductor is transferred by convection within the supercooled liquid coolant to the inner wall of the inner conduit and then is removed by the boiling liquid coolant, making the heat removal from the conductor relatively independent of conductor length.

  17. Evaluation of thermal hydraulics characteristics of natural cooling low level radioactive waste storage system

    International Nuclear Information System (INIS)

    Yoshii, Toshihiro; Iwaki, Chikako; Ikeda, Tatsumi; Ikeda, Hiroshi; Koyama, Tomonori; Usui, Nobuhiko; Watanabe, Hisao; Masaki, Yoshikazu

    2012-01-01

    It is necessary to design a low level radioactive waste storage system so that the decay heat of radioactive waste does not breach the structural safety limit. Currently, this waste storage system is designed as a natural cooling system, which continuously cools the radioactive waste without an active device. It consists simply of a storage pit for radioactive waste and air inlet and outlet ducts. The radioactive waste is cooled by natural convective air flow, which is generated by the buoyancy of heated air due to the decay heat of radioactive waste. It is important to clarify the flow characteristics in the systems in order to evaluate the cooling performance. The air mass flow rate through the system is determined by the balance between the natural convective flow force and pressure loss within the system. Therefore, the pressure drop and flow pattern in the waste storage pit are important flow characteristics. In this study, the pressure drop and air temperature distribution, greatly influenced by the flow pattern in the pit, were measured using a 1/5 scale model and compared with the results obtained from CFD. Flow network analysis, which is a simple model that simulates the flow by nodes and junctions, was conducted and its validity was confirmed by experimental results and CFD. (author)

  18. A hybrid convection scheme for use in non-hydrostatic numerical weather prediction models

    Directory of Open Access Journals (Sweden)

    Volker Kuell</