WorldWideScience

Sample records for wall heat flux

  1. FDNS code to predict wall heat fluxes or wall temperatures in rocket nozzles

    Science.gov (United States)

    Karr, Gerald R.

    1993-11-01

    This report summarizes the findings on the NASA contract NAG8-212, Task No. 3. The overall project consists of three tasks, all of which have been successfully completed. In addition, some supporting supplemental work, not required by the contract, has been performed and is documented herein. Task 1 involved the modification of the wall functions in the code FDNS to use a Reynolds Analogy-based method. Task 2 involved the verification of the code against experimentally available data. The data chosen for comparison was from an experiment involving the injection of helium from a wall jet. Results obtained in completing this task also show the sensitivity of the FDNS code to unknown conditions at the injection slot. Task 3 required computation of the flow of hot exhaust gases through the P&W 40K subscale nozzle. Computations were performed both with and without film coolant injection. The FDNS program tends to overpredict heat fluxes, but, with suitable modeling of backside cooling, may give reasonable wall temperature predictions. For film cooling in the P&W 40K calorimeter subscale nozzle, the average wall temperature is reduced from 1750 R to about 1050 R by the film cooling. The average wall heat flux is reduced by a factor of three.

  2. Conjugated Conduction-Free Convection Heat Transfer in an Annulus Heated at Either Constant Wall Temperature or Constant Heat Flux

    Directory of Open Access Journals (Sweden)

    HAROON IMTIAZ

    2017-04-01

    Full Text Available In this paper, we investigate numerically the effect of thermal boundary conditions on conjugated conduction-free convection heat transfer in an annulus between two concentric cylinders using Fourier Spectral method. The inner wall of the annulus is heated and maintained at either CWT (Constant Wall Temperature or CHF (Constant Heat Flux, while the outer wall is maintained at constant temperature. CHF case is relatively more significant for high pressure industrial applications, but it has not received much attention. This study particularly focuses the latter case (CHF. The main influencing parameters on flow and thermal fields within the annulus are: Rayleigh number Ra; thickness of inner wall Rs; radius ratio Rr and inner wall-fluid thermal conductivity ratio Kr. The study has shown that the increase in Kr increases the heat transfer rate through the annulus for heating at CWT and decreases the inner wall dimensionless temperature for heating at CHF and vice versa. It has also been proved that as the Rs increases at fixed Ra and Rr, the heat transfer rate decreases for heating at CWT and the inner wall dimensionless temperature increases for heating at CHF at Kr 1 depends on Rr. It has been shown that for certain combinations of controlling parameters there will be a value of Rr at which heat transfer rate will be minimum in the annulus in case of heating at CWT, while

  3. Inverse natural convection problem of estimating wall heat flux using a moving sensor

    Energy Technology Data Exchange (ETDEWEB)

    Park, H.M.; Chung, O.Y.

    1999-11-01

    Inverse heat transfer problems have many applications in various branch of science and engineering. Here, the inverse problem of determining heat flux at the bottom wall of a two-dimensional cavity from temperature measurement in the domain is considered. The Boussinesq equation is used to model the natural convection induced by the wall heat flux. The inverse natural convection problem is posed as a minimization problem of the performance function, which is the sum of square residuals between calculated and observed temperature, by means of a conjugate gradient method. Instead of employing several fixed sensors, a single sensor is used which is moving at a given frequency over the bottom wall. The present method solves the inverse natural convection problem accurately without a priori information about the unknown function to be estimated.

  4. First wall thermal stress analysis for suddenly applied heat fluxes

    Energy Technology Data Exchange (ETDEWEB)

    Dalessandro, J A

    1978-01-01

    The failure criterion for a solid first wall of an inertial confinement reactor is investigated. Analytical expressions for induced thermal stresses in a plate are given. Two materials have been chosen for this investigation: grade H-451 graphite and chemically vapor deposited (CVD) ..beta..-silicon carbide. Structural failure can be related to either the maximum compressive stress produced on the surface or the maximum tensile stress developed in the interior of the plate; however, it is shown that compressive failure would predominate. A basis for the choice of the thermal shock figure of merit, k(1 - ..nu..) sigma/E ..cap alpha.. kappa/sup 1/2/, is identified. The result is that graphite and silicon carbide rank comparably.

  5. Estimation of transient heat flux density during the heat supply of a catalytic wall steam methane reformer

    Science.gov (United States)

    Settar, Abdelhakim; Abboudi, Saïd; Madani, Brahim; Nebbali, Rachid

    2017-08-01

    Due to the endothermic nature of the steam methane reforming reaction, the process is often limited by the heat transfer behavior in the reactors. Poor thermal behavior sometimes leads to slow reaction kinetics, which is characterized by the presence of cold spots in the catalytic zones. Within this framework, the present work consists on a numerical investigation, in conjunction with an experimental one, on the one-dimensional heat transfer phenomenon during the heat supply of a catalytic-wall reactor, which is designed for hydrogen production. The studied reactor is inserted in an electric furnace where the heat requirement of the endothermic reaction is supplied by electric heating system. During the heat supply, an unknown heat flux density, received by the reactive flow, is estimated using inverse methods. In the basis of the catalytic-wall reactor model, an experimental setup is engineered in situ to measure the temperature distribution. Then after, the measurements are injected in the numerical heat flux estimation procedure, which is based on the Function Specification Method (FSM). The measured and estimated temperatures are confronted and the heat flux density which crosses the reactor wall is determined.

  6. Estimation of transient heat flux density during the heat supply of a catalytic wall steam methane reformer

    Science.gov (United States)

    Settar, Abdelhakim; Abboudi, Saïd; Madani, Brahim; Nebbali, Rachid

    2018-02-01

    Due to the endothermic nature of the steam methane reforming reaction, the process is often limited by the heat transfer behavior in the reactors. Poor thermal behavior sometimes leads to slow reaction kinetics, which is characterized by the presence of cold spots in the catalytic zones. Within this framework, the present work consists on a numerical investigation, in conjunction with an experimental one, on the one-dimensional heat transfer phenomenon during the heat supply of a catalytic-wall reactor, which is designed for hydrogen production. The studied reactor is inserted in an electric furnace where the heat requirement of the endothermic reaction is supplied by electric heating system. During the heat supply, an unknown heat flux density, received by the reactive flow, is estimated using inverse methods. In the basis of the catalytic-wall reactor model, an experimental setup is engineered in situ to measure the temperature distribution. Then after, the measurements are injected in the numerical heat flux estimation procedure, which is based on the Function Specification Method (FSM). The measured and estimated temperatures are confronted and the heat flux density which crosses the reactor wall is determined.

  7. Bayesian inferences of the thermal properties of a wall using temperature and heat flux measurements

    KAUST Repository

    Iglesias, Marco

    2017-09-20

    The assessment of the thermal properties of walls is essential for accurate building energy simulations that are needed to make effective energy-saving policies. These properties are usually investigated through in situ measurements of temperature and heat flux over extended time periods. The one-dimensional heat equation with unknown Dirichlet boundary conditions is used to model the heat transfer process through the wall. In Ruggeri et al. (2017), it was assessed the uncertainty about the thermal diffusivity parameter using different synthetic data sets. In this work, we adapt this methodology to an experimental study conducted in an environmental chamber, with measurements recorded every minute from temperature probes and heat flux sensors placed on both sides of a solid brick wall over a five-day period. The observed time series are locally averaged, according to a smoothing procedure determined by the solution of a criterion function optimization problem, to fit the required set of noise model assumptions. Therefore, after preprocessing, we can reasonably assume that the temperature and the heat flux measurements have stationary Gaussian noise and we can avoid working with full covariance matrices. The results show that our technique reduces the bias error of the estimated parameters when compared to other approaches. Finally, we compute the information gain under two experimental setups to recommend how the user can efficiently determine the duration of the measurement campaign and the range of the external temperature oscillation.

  8. Heat Flux and Wall Temperature Estimates for the NASA Langley HIFiRE Direct Connect Rig

    Science.gov (United States)

    Cuda, Vincent, Jr.; Hass, Neal E.

    2010-01-01

    An objective of the Hypersonic International Flight Research Experimentation (HIFiRE) Program Flight 2 is to provide validation data for high enthalpy scramjet prediction tools through a single flight test and accompanying ground tests of the HIFiRE Direct Connect Rig (HDCR) tested in the NASA LaRC Arc Heated Scramjet Test Facility (AHSTF). The HDCR is a full-scale, copper heat sink structure designed to simulate the isolator entrance conditions and isolator, pilot, and combustor section of the HIFiRE flight test experiment flowpath and is fully instrumented to assess combustion performance over a range of operating conditions simulating flight from Mach 5.5 to 8.5 and for various fueling schemes. As part of the instrumentation package, temperature and heat flux sensors were provided along the flowpath surface and also imbedded in the structure. The purpose of this paper is to demonstrate that the surface heat flux and wall temperature of the Zirconia coated copper wall can be obtained with a water-cooled heat flux gage and a sub-surface temperature measurement. An algorithm was developed which used these two measurements to reconstruct the surface conditions along the flowpath. Determinations of the surface conditions of the Zirconia coating were conducted for a variety of conditions.

  9. Options for a high heat flux enabled helium cooled first wall for DEMO

    Energy Technology Data Exchange (ETDEWEB)

    Arbeiter, Frederik, E-mail: f.arbe@kit.edu; Chen, Yuming; Ghidersa, Bradut-Eugen; Klein, Christine; Neuberger, Heiko; Ruck, Sebastian; Schlindwein, Georg; Schwab, Florian; Weth, Axel von der

    2017-06-15

    Highlights: • Design challenges for helium cooled first wall reviewed and otimization approaches explored. • Application of enhanced heat transfer surfaces to the First Wall cooling channels. • Demonstrated a design point for 1 MW/m{sup 2} with temperatures <550 °C and acceptable stresses. • Feasibility of several manufacturing processes for ribbed surfaces is shown. - Abstract: Helium is considered as coolant in the plasma facing first wall of several blanket concepts for DEMO fusion reactors, due to the favorable properties of flexible temperature range, chemical inertness, no activation, comparatively low effort to remove tritium from the gas and no chemical corrosion. Existing blanket designs have shown the ability to use helium cooled first walls with heat flux densities of 0.5 MW/m{sup 2}. Average steady state heat loads coming from the plasma for current EU DEMO concepts are expected in the range of 0.3 MW/m{sup 2}. The definition of peak values is still ongoing and depends on the chosen first wall shape, magnetic configuration and assumptions on the fraction of radiated power and power fall off lengths in the scrape off layer of the plasma. Peak steady state values could reach and excess 1 MW/m{sup 2}. Higher short-term transient loads are expected. Design optimization approaches including heat transfer enhancement, local heat transfer tuning and shape optimization of the channel cross section are discussed. Design points to enable a helium cooled first wall capable to sustain heat flux densities of 1 MW/m{sup 2} at an average shell temperature lower than 500 °C are developed based on experimentally validated heat transfer coefficients of structured channel surfaces. The required pumping power is in the range of 3–5% of the collected thermal power. The FEM stress analyses show code-acceptable stress intensities. Several manufacturing methods enabling the application of the suggested heat transfer enhanced first wall channels are explored. An

  10. Measurements of laminar mixed convection flow adjacent to an inclined surface with uniform wall heat flux

    Energy Technology Data Exchange (ETDEWEB)

    Abu-Mulaweh, H.I. [Mechanical Engineering Department, Purdue University at Fort Wayne, 2101 E. Coliseum Blvd., 46805, Fort Wayne, IN (United States)

    2003-01-01

    Measurements of laminar mixed convection flow adjacent to an inclined heated flat plate with uniform wall heat flux are reported. Laser-doppler velocimeter and cold wire anemometer were used to measure simultaneously the velocity and temperature distributions, respectively. Measurements of the air velocity and temperature distributions are presented for a range of buoyancy parameters 0{<=}{xi}{<=}2.91. It was found that both the mixed convection local Nusselt number and local friction coefficient increase as the buoyancy force increases (under the buoyancy assisting condition). The velocity field was found to be more sensitive to the buoyancy force than the thermal field. Predictions from both local similarity and local non-similarity models agree well with the experimental results for the thermal field, but only the predictions from the local non-similarity model agree favorably with the measured values for the flow field. (authors)

  11. Instantaneous heat flux flowing into ceramic combustion chamber wall surface of low heat rejection engine; Shanetsu engine no ceramic nenshoshitsu hekimen eno shunji netsuryusoku

    Energy Technology Data Exchange (ETDEWEB)

    Enomoto, Y.; Hagihara, Y. [Musashi Institute of Technology, Tokyo (Japan); Kimura, S. [Nissan Motor Co. Ltd., Tokyo (Japan); Adachi, K. [Daido Hoxan Inc., Sapporo (Japan); Nagano, H. [Riso Kagaku Corp., Tokyo (Japan); Ishii, A. [Mitani Sangyo Co. Ltd., Tokyo (Japan)

    1998-08-25

    To evaluate the effectiveness of low heat rejection engine under heat loss condition, instantaneous heat fluxes flowing into ceramic piston surface and aluminum alloy (Loex) piston surface using thin film thermocouple were measured, and both were compared. As a result, in the working stroke, the instantaneous heat flux flowing into ceramic piston surface was larger than the instantaneous heat flux flowing into Loex piston surface. Accordingly, it became clear that reduction of heat loss was not effected when ceramics that thermal conductivity is small was used for combustion chamber wall. 21 refs., 14 figs.

  12. Impact of structural design criteria on first wall surface heat flux limit

    Energy Technology Data Exchange (ETDEWEB)

    Majumdar, S. [Argonne National Lab., IL (United States)

    1998-09-01

    The irradiation environment experienced by the in-vessel components of fusion reactors presents structural design challenges not envisioned in the development of existing structural design criteria such as the ASME Code or RCC-MR. From the standpoint of design criteria, the most significant issues stem from the irradiation-induced changes in material properties, specifically the reduction of ductility, strain hardening capability, and fracture toughness with neutron irradiation. Recently, Draft 7 of the ITER structural design criteria (ISDC), which provide new rules for guarding against such problems, was released for trial use by the ITER designers. The new rules, which were derived from a simple model based on the concept of elastic follow up factor, provide primary and secondary stress limits as functions of uniform elongation and ductility. The implication of these rules on the allowable surface heat flux on typical first walls made of type 316 stainless steel and vanadium alloys are discussed.

  13. Effect of Heat Flux on Creep Stresses of Thick-Walled Cylindrical Pressure Vessels

    Directory of Open Access Journals (Sweden)

    Mosayeb Davoudi Kashkoli

    2014-06-01

    Full Text Available Assuming that the thermo-creep response of the material is governed by Norton’s law, an analytical solution is presented for the calculation of time-dependent creep stresses and displacements of homogeneous thick-walled cylindrical pressure vessels. For the stress analysis in a homogeneous pressure vessel, having material creep behavior, the solutions of the stresses at a time equal to zero (i.e. the initial stress state are needed. This corresponds to the solution of materials with linear elastic behavior. Therefore, using equations of equilibrium, stress-strain and strain-displacement, a differential equation for displacement is obtained and then the stresses at a time equal to zero are calculated. Using Norton’s law in the multi-axial form in conjunction with the above-mentioned equations in the rate form, the radial displacement rate is obtained and then the radial, circumferential and axial creep stress rates are calculated. When the stress rates are known, the stresses at any time are calculated iteratively. The analytical solution is obtained for the conditions of plane strain and plane stress. The thermal loading is as follows: inner surface is exposed to a uniform heat flux, and the outer surface is exposed to an airstream. The heat conduction equation for the one-dimensional problem in polar coordinates is used to obtain temperature distribution in the cylinder. The pressure, inner radius and outer radius are considered constant. Material properties are considered as constant. Following this, profiles are plotted for the radial displacements, radial stress, circumferential stress and axial stress as a function of radial direction and time.

  14. The Role of the Velocity Gradient in Laminar Convective Heat Transfer through a Tube with a Uniform Wall Heat Flux

    Science.gov (United States)

    Wang, Liang-Bi; Zhang, Qiang; Li, Xiao-Xia

    2009-01-01

    This paper aims to contribute to a better understanding of convective heat transfer. For this purpose, the reason why thermal diffusivity should be placed before the Laplacian operator of the heat flux, and the role of the velocity gradient in convective heat transfer are analysed. The background to these analyses is that, when the energy…

  15. Convective heat transfer for a gaseous slip flow in micropipe and parallel-plate microchannel with uniform wall heat flux: effect of axial heat conduction

    Science.gov (United States)

    Haddout, Y.; Essaghir, E.; Oubarra, A.; Lahjomri, J.

    2017-12-01

    Thermally developing laminar slip flow through a micropipe and a parallel plate microchannel, with axial heat conduction and uniform wall heat flux, is studied analytically by using a powerful method of self-adjoint formalism. This method results from a decomposition of the elliptic energy equation into a system of two first-order partial differential equations. The advantage of this method over other methods, resides in the fact that the decomposition procedure leads to a selfadjoint problem although the initial problem is apparently not a self-adjoint one. The solution is an extension of prior studies and considers a first order slip model boundary conditions at the fluid-wall interface. The analytical expressions for the developing temperature and local Nusselt number in the thermal entrance region are obtained in the general case. Therefore, the solution obtained could be extended easily to any hydrodynamically developed flow and arbitrary heat flux distribution. The analytical results obtained are compared for select simplified cases with available numerical calculations and they both agree. The results show that the heat transfer characteristics of flow in the thermal entrance region are strongly influenced by the axial heat conduction and rarefaction effects which are respectively characterized by Péclet and Knudsen numbers.

  16. Hydromagnetic mixed convective flow over a wall with variable thickness and Cattaneo-Christov heat flux model: OHAM analysis

    Science.gov (United States)

    Awais, Muhammad; Awan, Saeed Ehsan; Iqbal, Khalid; Khan, Zuhaib Ashfaq; Raja, Muhammad Asif Zahoor

    2018-03-01

    The effect of Cattaneo-Christov heat flux model for the hydro-magnetic mixed convective flow of a non-Newtonian fluid is presented. The flow over a wall having variable thickness is anticipated under the influence of transverse magnetic field and internal heat generation/absorption effects. Mathematical formulation has been performed by making use of the suitable transformations. Convergence analysis has been performed and the optimal values are computed by employing optimal homotopy analysis method. The effects of physical parameters are elaborated in depth via graphical and numerical illustrations.

  17. Local wall heat flux/temperature meter for convective flow and method of utilizing same

    Science.gov (United States)

    Boyd, Ronald D. (Inventor); Ekhlassi, Ali (Inventor); Cofie, Penrose (Inventor)

    2004-01-01

    According to one embodiment of the invention, a method includes providing a conduit having a fluid flowing therethrough, disposing a plurality of temperature measurement devices inside a wall of the conduit, positioning at least some of the temperature measurement devices proximate an inside surface of the wall of the conduit, positioning at least some of the temperature measurement devices at different radial positions at the same circumferential location within the wall, measuring a plurality of temperatures of the wall with respective ones of the temperature measurement devices to obtain a three-dimensional temperature topology of the wall, determining the temperature dependent thermal conductivity of the conduit, and determining a multi-dimensional thermal characteristic of the inside surface of the wall of the conduit based on extrapolation of the three-dimensional temperature topology and the temperature dependent thermal conductivities.

  18. Measurement of Heat-Flux of New Type Façade Walls

    Directory of Open Access Journals (Sweden)

    Todorka Samardzioska

    2016-10-01

    Full Text Available The building envelope makes the most significant contribution to the reduction of building energy consumption. The application of new, alternative and improved materials and systems has an important impact on the performance of buildings. This paper is focused on thermal transmittance as an indicator of thermal conduction of the construction element. It includes comparisons of the U-values calculated by software with those measured in-situ on three representative façade walls. The walls have been constructed with the new wall system Fragmat NZ-1, a new product in Macedonian buildings. This research provides basic information on the thermal transmittance of the system. The results of the analysis show that in-situ measuring is a useful tool in validating the precision of analytically calculated values, since it was difficult to obtain precise results from the analytical calculations only, especially when the layers have non-uniform thickness.

  19. Turbulent Mixed Convection of a Nanofluid in a Horizontal Circular Tube with Non-Uniform Wall Heat Flux Using a Two-Phase Approach

    Directory of Open Access Journals (Sweden)

    F. Vahidinia

    2015-06-01

    Full Text Available In this paper, Turbulent mixed convective heat transfer of water and Al2O3 nanofluid has been numerically studied in a horizontal tube under non-uniform heat flux on the upper wall and insulation in the lower wall using mixture model. For the discretization of governing equations, the second-order upstream difference scheme and finite volume method were used. The coupling of pressure and velocity was established by using SIMPLEC algorithm. The calculated results demonstrated that the convective heat transfer coefficient of nanofluid is higher than of the base fluid and by increasing the nanoparticles volume fraction, the convective heat transfer coefficient and shear stress on the wall increase. On the other hand, with increasing the Grashof number, the shear stress and convective heat transfer coefficient decrease.

  20. High heat flux testing of first wall mock-ups with and without neutron irradiation

    Directory of Open Access Journals (Sweden)

    G. Pintsuk

    2016-12-01

    For qualification, all three flat-tile mock-ups were exposed to cyclic steady state heat loads in the electron beam facility JUDITH-1 up to a maximum of 3.0MW/m2. Thereby, each tile was loaded individually as the full loading area exceeds the limits of the facility.

  1. Electron heat flux instability

    Science.gov (United States)

    Saeed, Sundas; Sarfraz, M.; Yoon, P. H.; Lazar, M.; Qureshi, M. N. S.

    2017-02-01

    The heat flux instability is an electromagnetic mode excited by a relative drift between the protons and two-component core-halo electrons. The most prominent application may be in association with the solar wind where drifting electron velocity distributions are observed. The heat flux instability is somewhat analogous to the electrostatic Buneman or ion-acoustic instability driven by the net drift between the protons and bulk electrons, except that the heat flux instability operates in magnetized plasmas and possesses transverse electromagnetic polarization. The heat flux instability is also distinct from the electrostatic counterpart in that it requires two electron species with relative drifts with each other. In the literature, the heat flux instability is often called the 'whistler' heat flux instability, but it is actually polarized in the opposite sense to the whistler wave. This paper elucidates all of these fundamental plasma physical properties associated with the heat flux instability starting from a simple model, and gradually building up more complexity towards a solar wind-like distribution functions. It is found that the essential properties of the instability are already present in the cold counter-streaming electron model, and that the instability is absent if the protons are ignored. These instability characteristics are highly reminiscent of the electron firehose instability driven by excessive parallel temperature anisotropy, propagating in parallel direction with respect to the ambient magnetic field, except that the free energy source for the heat flux instability resides in the effective parallel pressure provided by the counter-streaming electrons.

  2. INNOVATIVE HEAT FLUX SENSOR

    Directory of Open Access Journals (Sweden)

    G. N. Lukyanov

    2017-02-01

    Full Text Available Subject of Study.We present a method for heat flux measuring with the use of polarization properties of ferroelectric ceramics. Heat flux innovative sensor is developed on the basis of the proposed method. Its experimental verification is carried out. Method. The measurements are based on maintaining a balance between the processes caused by thermal energy and the energy of the electric field in the ferroelectric ceramics. Main Results. The testing of the proposed heat flux sensor has been organized in two stages. At the first stage the primary calibration has been performed by calibrated sensors ITP MG4.03/x(y “Potok”. At the second stage the testing of heat flux sensor has been carried out for calculating the quantity of heat. The comparison of the results to the readings of serial heat meters VKT-7 and STK-15 has been performed. Experiments have shown that the polarization properties of the ferroelectric ceramics can be used to measure the heat flow. Practical Relevance. The proposed sensor can be recommended as an apartment-level heat meter. The calibration of the proposed heat flux sensor with more accurate measurement tools gives the possibility to include it on the State Register of Measuring Instruments.

  3. Behavior of divertor and first wall armour materials at plasma heat fluxes relevant to ITER ELMs and disruptions

    Directory of Open Access Journals (Sweden)

    D.V. Kovalenko

    2017-08-01

    Full Text Available The paper presents the main results of numerous experiments carried out over the past 10 years at QSPA-T and QSPA-Be plasma guns in support of ITER. Special targets made of pure W, W-1%La2O3 and two types of Be (TGP-56FW and S65-C were tested under the series of repeated plasma stream and photonic flux impact. Maximum heat load on the target surface was up to 2.5MJ/m2 in the case of plasma testing and was equal to 0.5MJ/m2 in the case of photonic flux testing. Pulse waveform was rectangular with tpulse= 0.5ms. It was found that the main erosion mechanisms of W and Be under plasma stream impact are the melt layer movement, the ejection of droplets and the cracks formation. As a result of repeated photonic fluxes a regular, “corrugated” structure are eventually formed on the Be target surface. Study of erosion products of W formed under plasma stream impact on the W target has shown that the D/W atomic ratio in the deposited W films during pulsed events may be the same or even higher than that for stationary processes.

  4. Maximum Expected Wall Heat Flux and Maximum Pressure After Sudden Loss of Vacuum Insulation on the Stratospheric Observatory for Infrared Astronomy (SOFIA) Liquid Helium (LHe) Dewars

    Science.gov (United States)

    Ungar, Eugene K.

    2014-01-01

    The aircraft-based Stratospheric Observatory for Infrared Astronomy (SOFIA) is a platform for multiple infrared observation experiments. The experiments carry sensors cooled to liquid helium (LHe) temperatures. A question arose regarding the heat input and peak pressure that would result from a sudden loss of the dewar vacuum insulation. Owing to concerns about the adequacy of dewar pressure relief in the event of a sudden loss of the dewar vacuum insulation, the SOFIA Program engaged the NASA Engineering and Safety Center (NESC). This report summarizes and assesses the experiments that have been performed to measure the heat flux into LHe dewars following a sudden vacuum insulation failure, describes the physical limits of heat input to the dewar, and provides an NESC recommendation for the wall heat flux that should be used to assess the sudden loss of vacuum insulation case. This report also assesses the methodology used by the SOFIA Program to predict the maximum pressure that would occur following a loss of vacuum event.

  5. Manufacturing of small-scale mock-ups and of a semi-prototype of the ITER Normal Heat Flux First Wall

    Energy Technology Data Exchange (ETDEWEB)

    Banetta, S., E-mail: Stefano.banetta@f4e.europa.eu [Fusion for Energy, 2 Carrer Josep Pla, 08019 Barcelona (Spain); Zacchia, F.; Lorenzetto, P. [Fusion for Energy, 2 Carrer Josep Pla, 08019 Barcelona (Spain); Bobin-Vastra, I.; Boireau, B.; Cottin, A. [AREVA NP, 30 bd de l’Industrie, 71205 Le Creusot (France); Mitteau, R.; Eaton, R.; Raffray, R. [ITER Organization, Route de Vinon sur Verdon, 13115 Saint Paul Lez Durance (France)

    2014-10-15

    This paper describes the manufacturing development and fabrication of reduced scale ITER First Wall (FW) mock-ups of the Normal Heat Flux (NHF) design, including a “semi-prototype” with a dimension of 305 mm × 660 mm, corresponding to about 1/6 of a full-scale panel. The activity was carried out in the framework of the pre-qualification of the European Domestic Agency (EU-DA or F4E) for the supply of the European share of the ITER First Wall. The hardware consists of three Upgraded (2 MW/m{sup 2}) Normal Heat Flux (U-NHF) small-scale mock-ups, bearing 3 beryllium tiles each, and of one Semi-Prototype, representing six full-scale fingers and bearing a total of 84 beryllium tiles. The manufacturing process makes extensive use of Hot Isostatic Pressing, which was developed over more than a decade during ITER Engineering Design Activity phase. The main manufacturing steps for the semi-prototype are described, with special reference to the lessons learned and the implications impacting the future fabrication of the full-scale prototype and the series which consists of 218 panels plus spares. In addition, a “tile-size” mock-up was manufactured in order to assess the performance of larger tiles. The use of larger tiles would be highly beneficial since it would allow a significant reduction of the panel assembly time.

  6. Earth's surface heat flux

    Directory of Open Access Journals (Sweden)

    J. H. Davies

    2010-02-01

    Full Text Available We present a revised estimate of Earth's surface heat flux that is based upon a heat flow data-set with 38 347 measurements, which is 55% more than used in previous estimates. Our methodology, like others, accounts for hydrothermal circulation in young oceanic crust by utilising a half-space cooling approximation. For the rest of Earth's surface, we estimate the average heat flow for different geologic domains as defined by global digital geology maps; and then produce the global estimate by multiplying it by the total global area of that geologic domain. The averaging is done on a polygon set which results from an intersection of a 1 degree equal area grid with the original geology polygons; this minimises the adverse influence of clustering. These operations and estimates are derived accurately using methodologies from Geographical Information Science. We consider the virtually un-sampled Antarctica separately and also make a small correction for hot-spots in young oceanic lithosphere. A range of analyses is presented. These, combined with statistical estimates of the error, provide a measure of robustness. Our final preferred estimate is 47±2 TW, which is greater than previous estimates.

  7. Heat Flux Instrumentation Laboratory (HFIL)

    Data.gov (United States)

    Federal Laboratory Consortium — Description: The Heat Flux Instrumentation Laboratory is used to develop advanced, flexible, thin film gauge instrumentation for the Air Force Research Laboratory....

  8. High heat flux single phase heat exchanger

    Science.gov (United States)

    Valenzuela, Javier A.; Izenson, Michael G.

    1990-01-01

    This paper presents the results obtained to date in a program to develop a high heat flux, single-phase heat exchanger for spacecraft thermal management. The intended application is a net generation interface heat exchanger to couple the crew module water thermal bus to the two-phase ammonia main thermal bus in the Space Station Freedom. The large size of the interface heat exchanger is dictated by the relatively poor water-side heat transfer characteristics. The objective of this program is to develop a single-phase heat transfer approach which can achieve heat fluxes and heat transfer coefficients comparable to those of the evaporation ammonia side. A new heat exchanger concept has been developed to meet these objecties. The main feature of this heat exchanger is that it can achieve very high heat fluxes with a pressure drop one to two orders of magnitude lower than those of previous microchannel or jet impingement high heat flux heat exchangers. This paper describes proof-of-concept experiments performed in air and water and presents analytical model of the heat exchanger.

  9. Heat transfer and critical heat flux in a spiral flow in an asymmetrical heated tube; Transfert thermique et flux critique dans un ecoulement helicoidal en tube chauffe asymetriquement

    Energy Technology Data Exchange (ETDEWEB)

    Boscary, J. [CEA Centre d`Etudes de Cadarache, 13 - Saint-Paul-lez-Durance (France). Direction des Sciences de la Matiere]|[Association Euratom-CEA, Centre d`Etudes Nucleaires de Cadarache, 13 - Saint-Paul-lez-Durance (France). Dept. de Recherches sur la Fusion Controlee

    1997-03-01

    The design of plasma facing components is crucial for plasma performance in next fusion reactors. These elements will be submitted to very high heat flux. They will be actively water-cooled by swirl tubes in the subcooled boiling regime. High heat flux experiments were conducted in order to analyse the heat transfer and to evaluate the critical heat flux. Water-cooled mock-ups were one-side heated by an electron beam gun for different thermal-hydraulic conditions. The critical heat flux was detected by an original method based on the isotherm modification on the heated surface. The wall heat transfer law including forced convection and subcooled boiling regimes was established. Numerical calculations of the material heat transfer conduction allowed the non-homogeneous distribution of the wall temperature and of the wall heat flux to be evaluated. The critical heat flux value was defined as the wall maximum heat flux. A critical heat flux model based on the liquid sublayer dryout under a vapor blanket was established. A good agreement with test results was found. (author) 197 refs.

  10. Heat transfer and critical heat flux in a asymmetrically heated tube helicoidal flow; Transfert thermique et flux critique dans un ecoulement helicoidal en tube chauffe asymetriquement

    Energy Technology Data Exchange (ETDEWEB)

    Boscary, J.

    1995-10-01

    The design of plasma facing components is crucial for plasma performance in next fusion reactors. These elements will be submitted to very high heat flux. They will be actively water-cooled by swirl tubes in the subcooled boiling regime. High heat flux experiments were conducted in order to analyse the heat transfer and to evaluate the critical heat flux. Water-cooled mock-ups were one-side heated by an electron beam gun for different thermal-hydraulic conditions. The critical heat flux was detected by an original method based on the isotherm modification on the heated surface. The wall heat transfer law including forced convection and subcooled boiling regimes was established. Numerical calculations of the material heat transfer conduction allowed the non-homogeneous distribution of the wall temperature and of the wall heat flux to be evaluated. The critical heat flux value was defined as the wall maximum heat flux. A critical heat flux model based on the liquid sublayer dryout under a vapor blanket was established. A good agreement with test results was found. (author). 198 refs., 126 figs., 21 tabs.

  11. Heat flux solarimeter

    Energy Technology Data Exchange (ETDEWEB)

    Sartarelli, A.; Vera, S.; Cyrulies, E. [Instituto de Desarrollo Humano, Univ. Nac. de Gral. Sarmiento (IDH, UNGS), Los Polvorines (Argentina); Echarri, R. [Instituto de Desarrollo Humano, Univ. Nac. de Gral. Sarmiento (IDH, UNGS), Los Polvorines (Argentina); Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET) (Argentina); Samson, I. [INTEC (Instituto Tecnologico Santo Domingo), Santo Domingo (Dominican Republic)

    2010-12-15

    The solarimeter presented in this work is easy to assemble. It is calibrated and its performance is validated by means of Hottel's method. Finally, the curves obtained with this solarimeter are compared to the ones obtained with a commercial solarimeter. This device is based on the evaluation of the heat flow in a metal rod. In consequence, measurements are not affected by ambient temperature variations. On the other hand, there is a linear relationship between the temperatures measured at the rod ends and the incident radiation, as can be concluded both from the theory of its operation and the calibration lines obtained. The results obtained from the global irradiance measurements in the area of Los Polvorines (Buenos Aires Province), together with a preliminary evaluation of the solarimeter's response time, are presented in this work. (author)

  12. Pool boiling of distilled water over tube bundle with variable heat flux

    Science.gov (United States)

    Swain, Abhilas; Mohanty, Rajiva Lochan; Das, Mihir Kumar

    2017-08-01

    The experimental investigation of saturated pool boiling heat transfer of distilled water over plain tube bundle, under uniform and varying heat flux condition along the height are presented in this article. Experiments are carried out under various heat flux configurations applied to rows of tube bundles and pitch distance to diameter ratios of 1.25, 1.6 and 1.95. The wall superheats and pool boiling heat transfer coefficients over individual rows are determined. The pool boiling heat transfer coefficients for variable heat flux and uniform heat flux conditions are compared. The results indicate that the bundle effect is found to exist for uniform as well as variable heat flux under all operating conditions in the present investigation. The variable heat flux resulted in range of wall superheat being highest for decreasing heat flux from bottom to top and lowest for increasing heat flux from bottom to top.

  13. Latent heat sink in soil heat flux measurements

    Science.gov (United States)

    The surface energy balance includes a term for soil heat flux. Soil heat flux is difficult to measure because it includes conduction and convection heat transfer processes. Accurate representation of soil heat flux is an important consideration in many modeling and measurement applications. Yet, the...

  14. Calibration of soil heat flux sensors.

    NARCIS (Netherlands)

    Loon, van W.K.P.; Bastings, H.M.H.; Moors, E.J.

    1998-01-01

    Soil heat flux is difficult to measure accurately and soil heat flux plates are difficult to calibrate. In this research the reference heat flux was calculated from the temperature gradient and independent thermal conductivity measurements. Reference conductivities, as measured by the non-steady

  15. Analysis of the Pressure Rise in a Partially Filled Liquid Tank in Microgravity with Low Wall Heat Flux and Simultaneous Boiling and Condensation

    Science.gov (United States)

    Hasan, Mohammad M.; Balasubramaniam, R.

    2012-01-01

    Experiments performed with Freon 113 in the space shuttle have shown that in a pro- cess of very slow heating, high liquid superheats can be sustained for a long period in microgravity. In a closed system explosive vaporization of superheated liquid resulted in pressure spikes of varying magnitudes. In this paper, we analyze the pressure rise in a partially lled closed tank in which a large vapor bubble (i.e., ullage) is initially present, and the liquid is subjected to a low wall heat ux. The liquid layer adjacent to the wall becomes superheated until the temperature for nucleation of the bubbles (or the incipience of boiling) is achieved. In the absence of the gravity-induced convection large quantities of superheated liquid can accumulate over time near the heated surface. Once the incipience temperature is attained, explosive boiling occurs and the vapor bubbles that are produced on the heater surface tend to quickly raise the tank pressure. The liquid-vapor saturation temperature increases as well. These two e ects tend to induce condensation of the large ullage bubble that is initially present, and tends to mitigate the tank pressure rise. As a result, the tank pressure is predicted to rise sharply, attain a maximum, and subsequently decay slowly. The predicted pressure rise is compared with experimental results obtained in the microgravity environments of the space shuttle for Freon 113. The analysis is appli- cable, in general to heating of liquid in closed containers in microgravity and to cryogenic fuel tanks, in particular where small heat leaks into the tank are unavoidable.

  16. Geometrical correction factors for heat flux meters

    Science.gov (United States)

    Baumeister, K. J.; Papell, S. S.

    1974-01-01

    General formulas are derived for determining gage averaging errors of strip-type heat flux meters used in the measurement of one-dimensional heat flux distributions. The local averaging error e(x) is defined as the difference between the measured value of the heat flux and the local value which occurs at the center of the gage. In terms of e(x), a correction procedure is presented which allows a better estimate for the true value of the local heat flux. For many practical problems, it is possible to use relatively large gages to obtain acceptable heat flux measurements.

  17. Heat Flux Distribution of Antarctica Unveiled

    Science.gov (United States)

    Martos, Yasmina M.; Catalán, Manuel; Jordan, Tom A.; Golynsky, Alexander; Golynsky, Dmitry; Eagles, Graeme; Vaughan, David G.

    2017-11-01

    Antarctica is the largest reservoir of ice on Earth. Understanding its ice sheet dynamics is crucial to unraveling past global climate change and making robust climatic and sea level predictions. Of the basic parameters that shape and control ice flow, the most poorly known is geothermal heat flux. Direct observations of heat flux are difficult to obtain in Antarctica, and until now continent-wide heat flux maps have only been derived from low-resolution satellite magnetic and seismological data. We present a high-resolution heat flux map and associated uncertainty derived from spectral analysis of the most advanced continental compilation of airborne magnetic data. Small-scale spatial variability and features consistent with known geology are better reproduced than in previous models, between 36% and 50%. Our high-resolution heat flux map and its uncertainty distribution provide an important new boundary condition to be used in studies on future subglacial hydrology, ice sheet dynamics, and sea level change.

  18. Heat flux viscosity in collisional magnetized plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Liu, C., E-mail: cliu@pppl.gov [Princeton University, Princeton, New Jersey 08544 (United States); Fox, W. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States); Bhattacharjee, A. [Princeton University, Princeton, New Jersey 08544 (United States); Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)

    2015-05-15

    Momentum transport in collisional magnetized plasmas due to gradients in the heat flux, a “heat flux viscosity,” is demonstrated. Even though no net particle flux is associated with a heat flux, in a plasma there can still be momentum transport owing to the velocity dependence of the Coulomb collision frequency, analogous to the thermal force. This heat-flux viscosity may play an important role in numerous plasma environments, in particular, in strongly driven high-energy-density plasma, where strong heat flux can dominate over ordinary plasma flows. The heat flux viscosity can influence the dynamics of the magnetic field in plasmas through the generalized Ohm's law and may therefore play an important role as a dissipation mechanism allowing magnetic field line reconnection. The heat flux viscosity is calculated directly using the finite-difference method of Epperlein and Haines [Phys. Fluids 29, 1029 (1986)], which is shown to be more accurate than Braginskii's method [S. I. Braginskii, Rev. Plasma Phys. 1, 205 (1965)], and confirmed with one-dimensional collisional particle-in-cell simulations. The resulting transport coefficients are tabulated for ease of application.

  19. Heat-pipes-based first wall

    Energy Technology Data Exchange (ETDEWEB)

    Kovalenko, V. [Research and Development Institute of Power Engineering, PO Box 788, Moscow 101000 (Russian Federation); Khripunov, V. [Russian Research Center `Kurchatov Institute`, Nuclear Fusion Institute, Kurchatov Square, Moscow 123182 (Russian Federation); Antipenkov, A. [Research and Development Institute of Power Engineering, PO Box 788, Moscow 101000 (Russian Federation); Ulianov, A. [State Enterprise `Krasnaya Zvezda`, Electrolytny pr-d., 1a, Moscow 115230 (Russian Federation)

    1995-03-01

    Feasibilities of heat pipes application for the heat transfer out of plasma facing components in test and power fusion reactors are discussed. Based on the space technology and practice the ``hot`` ITER first wall with liquid metal and water heat pipes are proposed in two options: heat-pipes and vapor-chamber options. Other high heat loading in-vessel elements such as divertor target and limiter can be provided by effective and reliable heat pipe cooling systems. (orig.).

  20. An investigation of pulsed phase thermography for detection of disbonds in HIP-bonded beryllium tiles in ITER normal heat flux first wall (NHF FW) components

    Energy Technology Data Exchange (ETDEWEB)

    Bushell, J., E-mail: joe.bushell@amec.com [AMEC Foster Wheeler, Booths Hall, Chelford Road, Knutsford, Cheshire WA16 8QZ, England (United Kingdom); Sherlock, P. [AMEC Foster Wheeler, Booths Hall, Chelford Road, Knutsford, Cheshire WA16 8QZ, England (United Kingdom); Mummery, P. [School of Mechanical, Aerospace and Civil Engineering, University of Manchester, England (United Kingdom); Bellin, B.; Zacchia, F. [Fusion for Energy, Josep Pla 2, Torres Diagonal Litoral B3, Barcelona (Spain)

    2015-10-15

    Highlights: • Pulsed phase thermography was trialled on Be-tiled plasma facing components. • Two components, one with known disbonds, one intact, were inspected and compared. • Finite element analysis was used to verify experimental observations. • PPT successfully detected disbonds in the failed component. • Good agreement found with ultrasonic test, though defect geometry was uncertain. - Abstract: Pulsed phase thermography (PPT) is a non destructive examination (NDE) technique, traditionally used in the Aerospace Industry for inspection of composite structures, which combines characteristics and benefits of flash thermography and lock-in thermography into a single, rapid inspection technique. The aim of this work was to evaluate the effectiveness of PPT as a means of inspection for the bond between the beryllium (Be) tiles and the copper alloy (CuCrZr) heatsink of the ITER NHF FW components. This is a critical area dictating the functional integrity of these components, as single tile detachment in service could result in cascade failure. PPT has advantages over existing thermography techniques using heated water which stress the component, and the non-invasive, non-contact nature presents advantages over existing ultrasonic methods. The rapid and non-contact nature of PPT also gives potential for in-service inspections as well as a quality measure for as-manufactured components. The technique has been appraised via experimental trials using ITER first wall mockups with pre-existing disbonds confirmed via ultrasonic tests, partnered with finite element simulations to verify experimental observations. This paper will present the results of the investigation.

  1. Comparison of the high temperature heat flux sensor to traditional heat flux gages under high heat flux conditions.

    Energy Technology Data Exchange (ETDEWEB)

    Blanchat, Thomas K.; Hanks, Charles R.

    2013-04-01

    Four types of heat flux gages (Gardon, Schmidt-Boelter, Directional Flame Temperature, and High Temperature Heat Flux Sensor) were assessed and compared under flux conditions ranging between 100-1000 kW/m2, such as those seen in hydrocarbon fire or propellant fire conditions. Short duration step and pulse boundary conditions were imposed using a six-panel cylindrical array of high-temperature tungsten lamps. Overall, agreement between all gages was acceptable for the pulse tests and also for the step tests. However, repeated tests with the HTHFS with relatively long durations at temperatures approaching 1000ÀC showed a substantial decrease (10-25%) in heat flux subsequent to the initial test, likely due to the mounting technique. New HTHFS gages have been ordered to allow additional tests to determine the cause of the flux reduction.

  2. Heat transfer enhancement by dynamic corrugated heat exchanger wall: Numerical study

    Science.gov (United States)

    Kumar, P.; Schmidmayer, K.; Topin, F.; Miscevic, M.

    2016-09-01

    A new concept of heat exchanger at sub-millimeter scale is proposed for applications in cooling on-board electronics devices, in which the quality of the exchanges between fluid and wall is very critical. In the proposed system, the upper wall of the channel is deformed dynamically to obtain a sinusoidal wave on this surface. The lower wall is exposed to constant heat flux simulating the imprint of an electronic component. A systematic 3-D numerical study in transient regime on the different deformation parameters allowed obtaining both the pumping characteristics and the heat transfer characteristics of the system. It was observed that the dynamic deformation of the wall induces a significant pumping effect. The intensification of the heat transfer is very important even for highly degraded waveforms, although the pumping efficiency is reduced in this case.

  3. Turbulent Heat Transfer Behavior of Nanofluid in a Circular Tube Heated under Constant Heat Flux

    Directory of Open Access Journals (Sweden)

    Shuichi Torii

    2010-01-01

    Full Text Available The aim of the present study is to disclose the forced convective heat transport phenomenon of nanofluids inside a horizontal circular tube subject to a constant and uniform heat flux at the wall. Consideration is given to the effect of the inclusion of nanoparticles on heat transfer enhancement, thermal conductivity, viscosity, and pressure loss in the turbulent flow region. It is found that (i heat transfer enhancement is caused by suspending nanoparticles and becomes more pronounced with the increase of the particle volume fraction, (ii its augmentation is affected by three different nanofluids employed here, and (iii the presence of particles produces adverse effects on viscosity and pressure loss that also increases with the particle volume fraction.

  4. Universality of the ion flux to the JET outer wall

    CERN Document Server

    Walkden, N R; Militello, F; Lipschultz, B; Matthews, G; Guillemaut, C; Harrison, J; Moulton, D; Contributors, JET

    2016-01-01

    Universality in the ion flux to the JET outer-wall is observed in outerwall limiter mounted Langmuir probe (OLP) time-series across a large range of plasma current and line-averaged density during Ohmically heated horizontal target L-mode plasmas. The mean, M, and the standard deviation, sigma, of the ion-saturation current measured by the OLP show systematic variation with plasma current and density. Both increase as either plasma current decreases and/or density increases. Upon renormalization, achieved by subtraction of M and rescaling by sigma, the probability distribution functions (PDFs) of each signal collapse approximately onto a single curve. The shape of the curve deviates from a distribution in the tail of the PDF and is better described by a log-normal distribution. The collapse occurs over 4 decades of the ordinate which, given the wide parameter space over which the data spans, is a strong indication of universality.

  5. Streaming vorticity flux from oscillating walls with finite amplitude

    Science.gov (United States)

    Wu, J. Z.; Wu, X. H.; Wu, J. M.

    1993-01-01

    How to describe vorticity creation from a moving wall is a long standing problem. This paper discusses relevant issues at the fundamental level. First, it is shown that the concept of 'vorticity flux due to wall acceleration' can be best understood by following fluid particles on the wall rather than observing the flow at fixed spatial points. This is of crucial importance when the time-averaged flux is to be considered. The averaged flux has to be estimated in a wall-fixed frame of reference (in which there is no flux due to wall acceleration at all); or, if an inertial frame of reference is used, the generalized Lagrangian mean (GLM) also gives the same result. Then, for some simple but typical configurations, the time-averaged vorticity flux from a harmonically oscillating wall with finite amplitude is analyzed, without appealing to small perturbation. The main conclusion is that the wall oscillation will produce an additional mean vorticity flux (a fully nonlinear streaming effect), which is partially responsible for the mechanism of vortex flow control by waves. The results provide qualitative explanation for some experimentally and/or computationally observed phenomena.

  6. Enhanced heat sink with geometry induced wall-jet

    Energy Technology Data Exchange (ETDEWEB)

    Hossain, Md. Mahamudul, E-mail: sohel0991@gmail.com; Tikadar, Amitav; Bari, Fazlul; Morshed, A. K. M. M. [Department of Mechanical Engineering Bangladesh University of Engineering and Technology, Dhaka-1000. Bangladesh (Bangladesh)

    2016-07-12

    Mini-channels embedded in solid matrix have already proven to be a very efficient way of electronic cooling. Traditional mini-channel heat sinks consist of single layer of parallel channels. Although mini-channel heat sink can achieve very high heat flux, its pumping requirement for circulating liquid through the channel increase very sharply as the flow velocity increases. The pumping requirements of the heat sink can be reduced by increasing its performance. In this paper a novel approach to increase the thermal performance of the mini-channel heat sink is proposed through geometry induced wall jet which is a passive technique. Geometric irregularities along the channel length causes abrupt pressure change between the channels which causes cross flow through the interconnections thus one channel faces suction and other channel jet action. This suction and jet action disrupts boundary layer causing enhanced heat transfer performance. A CFD model has been developed using commercially available software package FLUENT to evaluate the technique. A parametric study of the velocities and the effect of the position of the wall-jets have been performed. Significant reduction in thermal resistance has been observed for wall-jets, it is also observed that this reduction in thermal resistance is dependent on the position and shape of the wall jet.

  7. Diameter effect on critical heat flux

    Energy Technology Data Exchange (ETDEWEB)

    Tanase, A. [University of Ottawa, Department of Mechanical Engineering, Ottawa, ON (Canada)], E-mail: atana052@uottawa.ca; Cheng, S.C. [University of Ottawa, Department of Mechanical Engineering, Ottawa, ON (Canada); Groeneveld, D.C. [University of Ottawa, Department of Mechanical Engineering, Ottawa, ON (Canada); Chalk River Laboratories, Atomic Energy of Canada Ltd., Chalk River, ON (Canada); Shan, J.Q. [Department of Nuclear Engineering, Xi' an Jiaotong University (China)

    2009-02-15

    The critical heat flux look-up table (CHF LUT) is widely used to predict CHF for various applications, including design and safety analysis of nuclear reactors. Using the CHF LUT for round tubes having inside diameters different from the reference 8 mm involves conversion of CHF to 8 mm. Different authors [Becker, K.M., 1965. An Analytical and Experimental Study of Burnout Conditions in Vertical Round Ducts, Aktiebolaget Atomenergie Report AE 177, Sweden; Boltenko, E.A., et al., 1989. Effect of tube diameter on CHF at various two phase flow regimes, Report IPE-1989; Biasi, L., Clerici, G.C., Garriba, S., Sala, R., Tozzi, A., 1967. Studies on Burnout, Part 3, Energia Nucleare, vol. 14, pp. 530-536; Groeneveld, D.C., Cheng, S.C., Doan, T., 1986. AECL-UO critical heat flux look-up table. Heat Transfer Eng., 7, 46-62; Groeneveld et al., 1996; Hall, D.D., Mudawar, I., 2000. Critical heat flux for water flow in tubes - II subcooled CHF correlations. Int. J. Heat Mass Transfer, 43, 2605-2640; Wong, W.C., 1996. Effect of tube diameter on critical heat flux, MaSC dissertation, Ottawa Carleton Institute for Mechanical and Aeronautical Engineering, University of Ottawa] have proposed several types of correlations or factors to describe the diameter effect on CHF. The present work describes the derivation of new diameter correction factor and compares it with several existing prediction methods.

  8. Heat-Flux Gage thermophosphor system

    Energy Technology Data Exchange (ETDEWEB)

    Tobin, K.W.

    1991-08-01

    This document describes the installation, hardware requirements, and application of the Heat-Flux Gage (Version 1.0) software package developed by the Oak Ridge National Laboratory, Applied Technology Division. The developed software is a single component of a thermographic phosphor-based temperature and heat-flux measurement system. The heat-flux transducer was developed by EG G Energy Measurements Systems and consists of a 1- by 1-in. polymethylpentene sheet coated on the front and back with a repeating thermographic phosphor pattern. The phosphor chosen for this application is gadolinium oxysulphide doped with terbium. This compound has a sensitive temperature response from 10 to 65.6{degree}C (50--150{degree}F) for the 415- and 490-nm spectral emission lines. 3 refs., 17 figs.

  9. Analysis of heat transfer under high heat flux nucleate boiling conditions

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Y.; Dinh, N. [3145 Burlington Laboratories, Raleigh, NC (United States)

    2016-07-15

    Analysis was performed for a heater infrared thermometric imaging temperature data obtained from high heat flux pool boiling and liquid film boiling experiments BETA. With the OpenFOAM solver, heat flux distribution towards the coolant was obtained by solving transient heat conduction of heater substrate given the heater surface temperature data as boundary condition. The so-obtained heat flux data was used to validate them against the state-of-art wall boiling model developed by D. R. Shaver (2015) with the assumption of micro-layer hydrodynamics. Good agreement was found between the model prediction and data for conditions away from the critical heat flux (CHF). However, the data indicate a different heat transfer pattern under CHF, which is not captured by the current model. Experimental data strengthen the notion of burnout caused by the irreversible hot spot due to failure of rewetting. The observation forms a basis for a detailed modeling of micro-layer hydrodynamics under high heat flux.

  10. High-flux first-wall design for a small reversed-field pinch reactor

    Science.gov (United States)

    Cort, G. E.; Graham, A. L.; Christensen, K. E.

    To achieve the goal of a commercially economical fusion power reactor, small physical size and high power density should be combined with simplicity (minimized use of high technology systems). The Reversed-Field Pinch (RFP) is a magnetic confinement device that promises to meet these requirements with power densities comparable to those in existing fission power plants. To establish feasibility of such an RFP reactor, a practical design for a first wall capable of withstanding high levels of cyclic neutron wall loadings is needed. Associated with the neutron flux in the proposed RFP reactor is a time averaged heat flux of 4.5 MW/sq m with a conservatively estimated transient peak approximately twice the average value. The design for a modular first wall made from a high-strength copper alloy that will meet these requirements of cyclic thermal loading is presented. The heat removal from the wall is by subcooled water flowing in straight tubes at high linear velocities.

  11. Heat Flux Sensors for Infrared Thermography in Convective Heat Transfer

    Science.gov (United States)

    Carlomagno, Giovanni Maria; de Luca, Luigi; Cardone, Gennaro; Astarita, Tommaso

    2014-01-01

    This paper reviews the most dependable heat flux sensors, which can be used with InfraRed (IR) thermography to measure convective heat transfer coefficient distributions, and some of their applications performed by the authors' research group at the University of Naples Federico II. After recalling the basic principles that make IR thermography work, the various heat flux sensors to be used with it are presented and discussed, describing their capability to investigate complex thermo-fluid-dynamic flows. Several applications to streams, which range from natural convection to hypersonic flows, are also described. PMID:25386758

  12. Heat flux sensors for infrared thermography in convective heat transfer.

    Science.gov (United States)

    Carlomagno, Giovanni Maria; de Luca, Luigi; Cardone, Gennaro; Astarita, Tommaso

    2014-11-07

    This paper reviews the most dependable heat flux sensors, which can be used with InfraRed (IR) thermography to measure convective heat transfer coefficient distributions, and some of their applications performed by the authors' research group at the University of Naples Federico II. After recalling the basic principles that make IR thermography work, the various heat flux sensors to be used with it are presented and discussed, describing their capability to investigate complex thermo-fluid-dynamic flows. Several applications to streams, which range from natural convection to hypersonic flows, are also described.

  13. Heat Flux Sensors for Infrared Thermography in Convective Heat Transfer

    Directory of Open Access Journals (Sweden)

    Giovanni Maria Carlomagno

    2014-11-01

    Full Text Available This paper reviews the most dependable heat flux sensors, which can be used with InfraRed (IR thermography to measure convective heat transfer coefficient distributions, and some of their applications performed by the authors’ research group at the University of Naples Federico II. After recalling the basic principles that make IR thermography work, the various heat flux sensors to be used with it are presented and discussed, describing their capability to investigate complex thermo-fluid-dynamic flows. Several applications to streams, which range from natural convection to hypersonic flows, are also described.

  14. Critical heat flux variations on CANDU calandria tube surface

    Energy Technology Data Exchange (ETDEWEB)

    Behdadi, A.; Luxat, J.C., E-mail: behdada@mcmaster.ca, E-mail: luxatj@mcmaster.ca [McMaster Univ., Engineering Physics Dept., Hamilton, Ontario (Canada)

    2012-07-01

    Heavy water moderator surrounding each fuel channel is one of the important safety features in CANDU reactors since it provides an in-situ passive heat sink for the fuel in situations where other engineered means of heat removal from fuel channels have failed. In a critical break LOCA scenario, fuel cooling becomes severely degraded due to rapid flow reduction in the affected flow pass of the heat transport system. This can result in pressure tubes experiencing significant heat-up during early stages of the accident when coolant pressure is still high, thereby causing uniform thermal creep strain (ballooning) of the pressure tube (PT) into contact with its calandria tube (CT). The contact of the hot PT with the CT causes rapid redistribution of stored heat from the PT to CT and a large heat flux spike from the CT to the moderator fluid. For conditions where subcooling of the moderator fluid is low, this heat flux spike can cause dryout of the CT. This can detrimentally affect channel integrity if the CT post-dryout temperature becomes sufficiently high to result in continued thermal creep strain deformation of both the PT and the CT. The focus of this work is to develop a mechanistic model to predict Critical Heat Flux (CHF) on the CT surface following a contact with its pressure tube. A mechanistic CHF model is applied based on a concept of wall dry patch formation, prevention of rewetting and subsequent dry patch spreading. Results have been compared to an empirical correlation and a good agreement has been obtained. The model has been used to predict the spatial variation of CHF over a cylinder with dimensions of CANDU CT. (author)

  15. A novel approach to evaluate soil heat flux calculation: An analytical review of nine methods: Soil Heat Flux Calculation

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Zhongming [Laboratory for Atmospheric Research, Department of Civil and Environmental Engineering, Washington State University, Pullman Washington USA; Russell, Eric S. [Laboratory for Atmospheric Research, Department of Civil and Environmental Engineering, Washington State University, Pullman Washington USA; Missik, Justine E. C. [Laboratory for Atmospheric Research, Department of Civil and Environmental Engineering, Washington State University, Pullman Washington USA; Huang, Maoyi [Pacific Northwest National Laboratory, Richland Washington USA; Chen, Xingyuan [Pacific Northwest National Laboratory, Richland Washington USA; Strickland, Chris E. [Pacific Northwest National Laboratory, Richland Washington USA; Clayton, Ray [Pacific Northwest National Laboratory, Richland Washington USA; Arntzen, Evan [Pacific Northwest National Laboratory, Richland Washington USA; Ma, Yulong [Laboratory for Atmospheric Research, Department of Civil and Environmental Engineering, Washington State University, Pullman Washington USA; Liu, Heping [Laboratory for Atmospheric Research, Department of Civil and Environmental Engineering, Washington State University, Pullman Washington USA

    2017-07-12

    We evaluated nine methods of soil heat flux calculation using field observations. All nine methods underestimated the soil heat flux by at least 19%. This large underestimation is mainly caused by uncertainties in soil thermal properties.

  16. Flow Boiling Heat Transfer in Two-Phase Micro Channel Heat Sink at Low Water Mass Flux

    Science.gov (United States)

    Kuznetsov, Vladimir V.; Shamirzaev, Alisher S.

    2009-08-01

    Boiling heat transfer at water flow with low mass flux in heat sink which contained rectangular microchannels was studied. The stainless steel heat sink contained ten parallel microchannels with a size of 640 × 2050 μm in cross-section with typical wall roughness of 10-15 μm. The local flow boiling heat transfer coefficients were measured at mass velocity of 17 and 51 kg/m2s, heat flux on 30 to 150 kW/m2 and vapor quality of up to 0.8 at pressure in the channels closed to atmospheric one. It was observed that Kandlikar nucleate boiling correlation is in good agreement with the experimental data at mass flow velocity of 85 kg/m2s. At smaller mass flux the Kandlikar model and Zhang, Hibiki and Mishima model demonstrate incorrect trend of heat transfer coefficients variation with vapor quality.

  17. Dynamic ignition regime of condensed system by radiate heat flux

    Science.gov (United States)

    Arkhipov, V. A.; Zolotorev, N. N.; Korotkikh, A. G.; Kuznetsov, V. T.

    2017-05-01

    The main ignition characteristics of high-energy materials are the ignition time and critical heat flux allowing evaluation of the critical conditions for ignition, fire and explosive safety for the test solid propellants. The ignition process is typically studied in stationary conditions of heat input at constant temperature of the heating surface, environment or the radiate heat flux on the sample surface. In real conditions, ignition is usually effected at variable time-dependent values of the heat flux. In this case, the heated layer is formed on the sample surface in dynamic conditions and significantly depends on the heat flux change, i.e. increasing or decreasing falling heat flux in the reaction period of the propellant sample. This paper presents a method for measuring the ignition characteristics of a high-energy material sample in initiation of the dynamic radiant heat flux, which includes the measurement of the ignition time when exposed to a sample time varying radiant heat flux given intensity. In case of pyroxyline containing 1 wt. % of soot, it is shown that the ignition times are reduced by 20-50 % depending on the initial value of the radiant flux density in initiation by increasing or decreasing radiant heat flux compared with the stationary conditions of heat supply in the same ambient conditions.

  18. Surface renewal method for estimating sensible heat flux | Mengistu ...

    African Journals Online (AJOL)

    For short canopies, latent energy flux may be estimated using a shortened surface energy balance from measurements of sensible and soil heat flux and the net irradiance at the surface. The surface renewal (SR) method for estimating sensible heat, latent energy, and other scalar fluxes has the advantage over other ...

  19. Study and Simulation of the Density of the Incident Solar Flux on the Walls of a Building in Adrar, Algeria

    Directory of Open Access Journals (Sweden)

    A. Oudrane

    2017-10-01

    Full Text Available In this work, we studied the effect of external climatic conditions on the evolution of the daily solar flux incident on the walls of a building located at Adrar region in the South of Algeria. This building is designed for heating or air conditioning applications. Numerical simulations allowed to compare the variation of the incident solar flux over a full day on the south, east, north and west walls of the building to the values of the solar flux on a horizontal wall (the outer ceiling. The horizontal global solar flux is calculated using a Gaussian sinusoidal function. The simulations were carried out in the case of a building located in a desert zone. The results of the numerical simulation showed the effect of the orientation of the building on the evolution of the incident daily solar flux.

  20. A model for the prediction of safe heat flux from a downward-facing hot patch

    Energy Technology Data Exchange (ETDEWEB)

    Reddy, C. Nowneswara; Jayanti, S., E-mail: sjayanti@iitm.ac.in

    2013-12-15

    Highlights: • Elucidation of the effect inclination on bubble size and shape. • Computational model for heat transfer under film boiling conditions. • Elucidation of heat leakage from a hot patch. • Development of a dimensionless correlation for safe heat flux. - Abstract: Pool boiling from the underside of flat, downward-facing patch is important in analyzing possible accident scenarios related to nuclear power generation. Significant deterioration in heat transfer may occur in stationary film boiling leading to high wall temperatures. In the present work, we have studied, experimentally and through computational fluid dynamics simulations, the nature of the bubbles that are formed at a hot patch. Noting that large, flattened bubbles can be formed at a heated surface, we develop a heat transfer-only model which takes into account the conduction within the plate and the convective and boiling heat transfer to the surrounding liquid medium. It is shown that the safe heat flux, beyond which significant wall temperature rise may occur, is very small compared the critical heat flux for thick plates made of poorly conducting materials. A dimensionless correlation is proposed to calculate the safe heat flux.

  1. Thin Film Heat Flux Sensors: Design and Methodology

    Science.gov (United States)

    Fralick, Gustave C.; Wrbanek, John D.

    2013-01-01

    Thin Film Heat Flux Sensors: Design and Methodology: (1) Heat flux is one of a number of parameters, together with pressure, temperature, flow, etc. of interest to engine designers and fluid dynamists, (2) The measurement of heat flux is of interest in directly determining the cooling requirements of hot section blades and vanes, and (3)In addition, if the surface and gas temperatures are known, the measurement of heat flux provides a value for the convective heat transfer coefficient that can be compared with the value provided by CFD codes.

  2. Electric probe diagnostics for measuring SOL parameters, wall and divertor fluxes in KSTAR

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Heung-Su, E-mail: kimhs@nfri.re.kr [National Fusion Research Institute, Daejeon (Korea, Republic of); Bak, Jun-Gyo [National Fusion Research Institute, Daejeon (Korea, Republic of); Bae, Min-Keun; Chung, Kyu-Sun [Hanyang University, Seoul (Korea, Republic of); Hong, Suk-Ho [National Fusion Research Institute, Daejeon (Korea, Republic of)

    2016-11-01

    Highlights: • Some components in EPDs were improved to investigate characteristics of the SOL plasmas and to measure wall and divertor fluxes in the KSTAR tokamak plasmas. From the upgrades in the EPDs, the measured error of the elapsed distance for the evaluation of the SOL profiles can be reduced up to 1%. • In the SOL parameter measurement during IWL plasma, the e-folding lengths in the main SOL region lTe and lne were evaluated as 3.5 cm and 2.1 cm, respectively. • From flux measurement at the far SOL during a diverted ELMy H-mode, peaked heat flux toward to outboard wall during ELMs might be less than 1% of the peaked divertor heat flux. • The movement of an OSP during a diverted H-mode can be detected from the divertor probe measurement, and the peaked heat flux near the OSP was estimated as few MW m-2. - Abstract: Some components in electric probe diagnostics (EPDs) are improved in order to investigate characteristics of edge plasmas in the upstream scrape-off-layer (SOL) region and to measure wall and divertor fluxes during L-mode and H-mode plasma discharges in the Korea Superconducting Tokamak Advanced Research (KSTAR). From the upgrades in the EPDs, the measured error of the elapsed distance for the evaluation of the SOL profiles can be reduced up to 1% and the ion saturation current of up to 1.0 A near an outer strike point (OSP) can be measured at the divertor region. In the SOL profile measurements during L-mode and inner wall limited plasma (B{sub T} = 2.0 T, I{sub p} = 0.4 MA), the e-folding lengths in the main SOL region λ{sub Te} and λ{sub ne} are evaluated as 3.5 cm and 2.1 cm, respectively. From particle flux measurement at the far SOL region during a diverted ELMy H-mode discharge (B{sub T} = 1.8 T, I{sub p} = 0.65 MA), peaked heat flux toward to outboard wall during ELM bursts is estimated up to ∼20 k Wm{sup −2}, which may be less than 1% of the peaked divertor heat flux expected for the neutral beam (NB) heating power P{sub NB

  3. Wall Area of Influence and Growing Wall Heat Transfer due to Sliding Bubbles in Subcooled Boiling Flow

    Energy Technology Data Exchange (ETDEWEB)

    Yoo, Junsoo; Estrada-Perez, Carlos E.; Hassan, Yassin A.

    2016-04-01

    A variety of dynamical features of sliding bubbles and their impact on wall heat transfer were observed at subcooled flow boiling conditions in a vertical square test channel. Among the wide range of parameters observed, we particularly focus in this paper on (i) the sliding bubbles’ effect on wall heat transfer (supplemantry discussion to the authors’ previous work in Yoo et al. (2016a,b)) and (ii) the wall area influenced by sliding bubbles in subcooled boiling flow. At first, this study reveals that the degree of wall heat transfer improvement due to sliding bubbles depended less on the wall superheat condition as the mass flux increased. Also, the sliding bubble trajectory was found to be one of the critical factors in order to properly describe the wall heat transfer associated with sliding bubbles. In particular, the wall area influenced by sliding bubbles depended strongly on both sliding bubble trajectory and sliding bubble size; the sliding bubble trajectory was also observed to be closely related to the sliding bubble size. Importantly, these results indicate the limitation of current approach in CFD analyses especially for the wall area of bubble influence. In addition, the analyses on the temporal fraction of bubbles’ residence (FR) along the heated wall show that the sliding bubbles typically travel through narrow path with high frequency while the opposite was observed downstream. That is, both FR and sliding bubble trajectory depended substantially on the distance from nucleation site, which is expected to be similar for the quenching heat transfer mode induced by sliding bubbles.

  4. Heat flux measurement in SSME turbine blade tester

    Science.gov (United States)

    Liebert, Curt H.

    1990-01-01

    Surface heat flux values were measured in the turbine blade thermal cycling tester located at NASA-Marshall. This is the first time heat flux has been measured in a space shuttle main engine turbopump environment. Plots of transient and quasi-steady state heat flux data over a range of about 0 to 15 MW/sq m are presented. Data were obtained with a miniature heat flux gage device developed at NASA-Lewis. The results from these tests are being incorporated into turbine design models. Also, these gages are being considered for airfoil surface heat flux measurement on turbine vanes mounted in SSME turbopump test bed engine nozzles at Marshall. Heat flux effects that might be observed on degraded vanes are discussed.

  5. Heat transfer experiments with a central receiver tube subjected to unsteady and non-uniform heat flux

    Science.gov (United States)

    Fernández-Torrijos, María; Marugán-Cruz, Carolina; Sobrino, Celia; Santana, Domingo

    2017-06-01

    In this work, a molten salt test loop to study the heat transfer process in external molten salt receivers is described. The experimental installation is formed by a cylindrical molten salt tank, a pump, a flow meter, and an induction heater to generate the heat flux, which is applied in a small rectangular region of the tube surface. In central tower plants, the external receiver pipe is considered to be under unilateral concentrated solar radiation, because only one side of the pipe receives high heat flux. The main advantage of using an induction heater is the control of heating in different areas of the tube. In order to measure the effects of a non-homogenous and unsteady heat flux on the wall temperature distribution a series of experiments have been carried out. 4 K-type thermocouples have been welded at different axial and azimuthal positions of the pipe to obtain the wall temperature distribution. Different temperature measurements have been made varying the heat flux and water velocity to study their effects on the heat transfer process.

  6. Numerical prediction of nucleate pool boiling heat transfer coefficient under high heat fluxes

    Directory of Open Access Journals (Sweden)

    Pezo Milada L.

    2016-01-01

    Full Text Available This paper presents CFD (Computational Fluid Dynamics approach to prediction of the heat transfer coefficient for nucleate pool boiling under high heat fluxes. Three-dimensional numerical simulations of the atmospheric saturated pool boiling are performed. Mathematical modelling of pool boiling requires a treatment of vapor-liquid two-phase mixture on the macro level, as well as on the micro level, such as bubble growth and departure from the heating surface. Two-phase flow is modelled by the two-fluid model, which consists of the mass, momentum and energy conservation equations for each phase. Interface transfer processes are calculated by the closure laws. Micro level phenomena on the heating surface are modelled with the bubble nucleation site density, the bubble resistance time on the heating wall and with the certain level of randomness in the location of bubble nucleation sites. The developed model was used to determine the heat transfer coefficient and results of numerical simulations are compared with available experimental results and several empirical correlations. A considerable scattering of the predictions of the pool boiling heat transfer coefficient by experimental correlations is observed, while the numerically predicted values are within the range of results calculated by well-known Kutateladze, Mostinski, Kruzhilin and Rohsenow correlations. The presented numerical modeling approach is original regarding both the application of the two-fluid two-phase model for the determination of heat transfer coefficient in pool boiling and the defined boundary conditions at the heated wall surface. [Projekat Ministarstva nauke Republike Srbije, br. 174014

  7. INVESTIGATION OF SOLAR ABSORPTANCE OF BUILDING EXTERNAL SURFACES FROM HEAT FLUX POINT OF VIEW

    Directory of Open Access Journals (Sweden)

    Meral ÖZEL

    2006-02-01

    Full Text Available In this study, solar absorptance of external surfaces of buildings has been numerically investigated from the heat gain and losses point of view. For this purpose, external surface solar absorptance was icreased from 0 to 1with an ratio of 0.1 and, for the summer and winter conditions, heat fluxs was calculated by considering orientations of the wall and its roof for brick and concrete structure materials. Besides, external surface absorptance was assumed as 0.2, 0.5 and 0.9, respectively. Than, heat gain and losses were calculated to insulation thickness increasing on the outdoor surface of wall. Results obtained were presented as graphics

  8. Solid motor aft closure insulation erosion. [heat flux correlation for rate analysis

    Science.gov (United States)

    Stampfl, E.; Landsbaum, E. M.

    1973-01-01

    The erosion rate of aft closure insulation in a number of large solid propellant motors was empirically analyzed by correlating the average ablation rate with a number of variables that had previously been demonstrated to affect heat flux. The main correlating parameter was a heat flux based on the simplified Bartz heat transfer coefficient corrected for two-dimensional effects. A multiplying group contained terms related to port-to-throat ratio, local wall angle, grain geometry and nozzle cant angle. The resulting equation gave a good correlation and is a useful design tool.

  9. Transient critical heat flux and blowdown heat-transfer studies

    Energy Technology Data Exchange (ETDEWEB)

    Leung, J.C.

    1980-05-01

    Objective of this study is to give a best-estimate prediction of transient critical heat flux (CHF) during reactor transients and hypothetical accidents. To accomplish this task, a predictional method has been developed. Basically it involves the thermal-hydraulic calculation of the heated core with boundary conditions supplied from experimental measurements. CHF predictions were based on the instantaneous ''local-conditions'' hypothesis, and eight correlations (consisting of round-tube, rod-bundle, and transient correlations) were tested against most recent blowdown heat-transfer test data obtained in major US facilities. The prediction results are summarized in a table in which both CISE and Biasi correlations are found to be capable of predicting the early CHF of approx. 1 s. The Griffith-Zuber correlation is credited for its prediction of the delay CHF that occurs in a more tranquil state with slowly decaying mass velocity. In many instances, the early CHF can be well correlated by the x = 1.0 criterion; this is certainly indicative of an annular-flow dryout-type crisis. The delay CHF occurred at near or above 80% void fraction, and the success of the modified Zuber pool-boiling correlation suggests that this CHF is caused by flooding and pool-boiling type hydrodynamic crisis.

  10. Estimating local heat transfer coefficients from thin wall temperature measurements

    Science.gov (United States)

    Gazizov, I. M.; Davletshin, I. A.; Paereliy, A. A.

    2017-09-01

    An approach to experimental estimation of local heat transfer coefficient on a plane wall has been described. The approach is based on measurements of heat-transfer fluid and wall temperatures during some certain time of wall cooling. The wall was a thin plate, a printed circuit board, made of composite epoxy material covered with a copper layer. The temperature field can be considered uniform across the plate thickness when heat transfer is moderate and thermal resistance of the plate in transversal direction is low. This significantly simplifies the heat balance written for the wall sections that is used to estimate the heat transfer coefficient. The copper layer on the plate etched to form a single strip acted as resistance thermometers that measured the local temperature of the wall.

  11. Critical heat flux, post dry-out and their augmentation

    Energy Technology Data Exchange (ETDEWEB)

    Celata, G.P.; Mariani, A. [ENEA, Centro Ricerche Casaccia, S. Maria di Galeria, RM (Italy). Dipt. Energia

    1999-07-01

    The report shows the state of art review on the critical heat flux and the post-dryout heat transfer. The work, which is a merge of original researches carried out at the Institute of Thermal Fluid Dynamic of ENEA (National Agency for New Technology, Energy and the Environment) and a thorough review of the recent literature, is divided in four chapters: critical heat flux in subcooled flow boiling; critical heat flux in saturated flow boiling; post-dryout heat transfer; enhancement of critical heat flux and post-dryout heat transfer. [Italian] Si passa in rassegna lo stato dell'arte sulla crisi termica e sullo scambio termico post-crisi, che compendia studi tradizionali condotti dall'ENEA. Il rapporto e' suddiviso in quattro parti: crisi termica in ebollizione sottoraffreddata; crisi termica in ebollizione satura; scambio termico dopo la crisi termica; incremento del flusso termico critico e dello scambio termico post-crisi.

  12. Heat flux anomalies in Antarctica revealed from satellite magnetic data

    DEFF Research Database (Denmark)

    Maule, Cathrine Fox; Purucker, Michael E.; Olsen, Nils

    2005-01-01

    The geothermal heat flux is an important factor in the dynamics of ice sheets; it affects the occurrence of subglacial lakes, the onset of ice streams, and mass losses from the ice sheet base. Because direct heat flux measurements in ice-covered regions are difficult to obtain, we developed a met...

  13. Tracking heat flux sensors for concentrating solar applications

    Science.gov (United States)

    Andraka, Charles E; Diver, Jr., Richard B

    2013-06-11

    Innovative tracking heat flux sensors located at or near the solar collector's focus for centering the concentrated image on a receiver assembly. With flux sensors mounted near a receiver's aperture, the flux gradient near the focus of a dish or trough collector can be used to precisely position the focused solar flux on the receiver. The heat flux sensors comprise two closely-coupled thermocouple junctions with opposing electrical polarity that are separated by a thermal resistor. This arrangement creates an electrical signal proportional to heat flux intensity, and largely independent of temperature. The sensors are thermally grounded to allow a temperature difference to develop across the thermal resistor, and are cooled by a heat sink to maintain an acceptable operating temperature.

  14. Prediction of critical heat flux using ANFIS

    Energy Technology Data Exchange (ETDEWEB)

    Zaferanlouei, Salman, E-mail: zaferanlouei@gmail.co [Nuclear Engineering and Physics Department, Faculty of Nuclear Engineering, Center of Excellence in Nuclear Engineering, Amirkabir University of Technology (Tehran Polytechnic), 424 Hafez Avenue, Tehran (Iran, Islamic Republic of); Rostamifard, Dariush; Setayeshi, Saeed [Nuclear Engineering and Physics Department, Faculty of Nuclear Engineering, Center of Excellence in Nuclear Engineering, Amirkabir University of Technology (Tehran Polytechnic), 424 Hafez Avenue, Tehran (Iran, Islamic Republic of)

    2010-06-15

    The prediction of Critical Heat Flux (CHF) is essential for water cooled nuclear reactors since it is an important parameter for the economic efficiency and safety of nuclear power plants. Therefore, in this study using Adaptive Neuro-Fuzzy Inference System (ANFIS), a new flexible tool is developed to predict CHF. The process of training and testing in this model is done by using a set of available published field data. The CHF values predicted by the ANFIS model are acceptable compared with the other prediction methods. We improve the ANN model that is proposed by to avoid overfitting. The obtained new ANN test errors are compared with ANFIS model test errors, subsequently. It is found that the ANFIS model with root mean square (RMS) test errors of 4.79%, 5.04% and 11.39%, in fixed inlet conditions and local conditions and fixed outlet conditions, respectively, has superior performance in predicting the CHF than the test error obtained from MLP Neural Network in fixed inlet and outlet conditions, however, ANFIS also has acceptable result to predict CHF in fixed local conditions.

  15. Performance of a counterflow heat exchanger with heat loss through the wall at the cold end

    Energy Technology Data Exchange (ETDEWEB)

    Narayanan, S.P.; Venkatarathnam, G. [Indian Institute of Technology, Chennai (India). Dept. of Mechanical Engineering

    1999-11-01

    The performance of high effectiveness heat exchangers used in cryogenic systems is strongly controlled by irreversibilities such as longitudinal heat conduction and heat leak from ambient. In all heat exchanger analyses, it is assumed that no heat is lost through the heat exchanger walls. In the case of small J-T refrigerators such as microminiature refrigerators, the heat exchanger cold end is almost directly connected to the evaporator, which may result in a large amount of heat loss through the heat exchanger wall at the cold end. The rate of heat loss through the wall at the cold end is also strongly dependent on the longitudinal thermal resistance of the wall. In this paper, we present the relationship between the effectiveness of a heat exchanger losing heat at the cold end and other resistances such as number of transfer units (NTU), longitudinal thermal resistance etc. The performance of such heat exchangers under different operating conditions is also discussed. (author)

  16. Bayesian inference of the heat transfer properties of a wall using experimental data

    KAUST Repository

    Iglesias, Marco

    2016-01-06

    A hierarchical Bayesian inference method is developed to estimate the thermal resistance and volumetric heat capacity of a wall. We apply our methodology to a real case study where measurements are recorded each minute from two temperature probes and two heat flux sensors placed on both sides of a solid brick wall along a period of almost five days. We model the heat transfer through the wall by means of the one-dimensional heat equation with Dirichlet boundary conditions. The initial/boundary conditions for the temperature are approximated by piecewise linear functions. We assume that temperature and heat flux measurements have independent Gaussian noise and derive the joint likelihood of the wall parameters and the initial/boundary conditions. Under the model assumptions, the boundary conditions are marginalized analytically from the joint likelihood. ApproximatedGaussian posterior distributions for the wall parameters and the initial condition parameter are obtained using the Laplace method, after incorporating the available prior information. The information gain is estimated under different experimental setups, to determine the best allocation of resources.

  17. Activity of the European high heat flux test facility: FE200

    Energy Technology Data Exchange (ETDEWEB)

    Bobin-Vastra, I. [AREVA Centre Technique de Framatome, FE200, Porte Magenta BP181, 71200 Le Creusot Cedex (France) and EFDA Close Support Unit, Boltzmannstr. 2, D-85748 Garching (Germany)]. E-mail: isabelle.bobinvastra@framatome-anp.com; Escourbiac, F. [Association Euratom-CEA, CEA/DSM/DRFC, CEA/Cadarache, F-13108 Saint Paul lez Durance (France)]. E-mail: escourbi@drfc.cad.cea.fr; Merola, M. [EFDA Close Support Unit, Boltzmannstr. 2, D-85748 Garching (Germany)]. E-mail: mario.merola@tech.efda.org; Lorenzetto, P. [EFDA Close Support Unit, Boltzmannstr. 2, D-85748 Garching (Germany)]. E-mail: lorenzp@tech.efda.org

    2005-11-15

    FE200 is an electron beam (EB) 200 kW test facility resulting since 1991 from partnership between Framatome Technical Centre in Le Creusot (France) and Tore Supra team in CEA Cadarache (France). It is dedicated to high heat flux testing of small and medium-sized plasma facing components. The performed tests are thermal fatigue tests (100,000 since 1992), critical heat fluxes, disruptions, glancing incidence tests on materials such as Cu-Al25 and CuCrZr alloys, carbon fibre composite (CFC) or tungsten (W). The thermal fatigue behaviour of some primary first wall (PFW), hypervapotron and divertor components is described.

  18. Radiative heat transfer with hydromagnetic flow and viscous dissipation over a stretching surface in the presence of variable heat flux

    Directory of Open Access Journals (Sweden)

    Kumar Hitesh

    2009-01-01

    Full Text Available The boundary layer steady flow and heat transfer of a viscous incompressible fluid due to a stretching plate with viscous dissipation effect in the presence of a transverse magnetic field is studied. The equations of motion and heat transfer are reduced to non-linear ordinary differential equations and the exact solutions are obtained using properties of confluent hypergeometric function. It is assumed that the prescribed heat flux at the stretching porous wall varies as the square of the distance from origin. The effects of the various parameters entering into the problem on the velocity field and temperature distribution are discussed.

  19. Effect of axial heat flux distribution on CHF

    Energy Technology Data Exchange (ETDEWEB)

    Park, Cheol

    2000-10-01

    Previous investigations for the effect of axial heat flux distributions on CHF and the prediction methods are reviewed and summarized. A total of 856 CHF data in a tube with a non-uniform axial heat flux distribution has been compiled from the articles and analyzed using the 1995 Groeneveld look-up table. The results showed that two representative correction factors, K5 of the look-up table and Tongs F factor, can be applied to describe the axial heat flux distribution effect on CHF. However, they overpredict slightly the measured CHF, depending on the quality and flux peak shape. Hence, a corrected K5 factor, which accounts for the axial heat flux distribution effect is suggested to correct these trends. It predicted the CHF power for the compiled data with an average error of 1.5% and a standard deviation of 10.3%, and also provides a reasonable prediction of CHF locations.

  20. Heat transfer characteristics of building walls using phase change material

    Science.gov (United States)

    Irsyad, M.; Pasek, A. D.; Indartono, Y. S.; Pratomo, A. W.

    2017-03-01

    Minimizing energy consumption in air conditioning system can be done with reducing the cooling load in a room. Heat from solar radiation which passes through the wall increases the cooling load. Utilization of phase change material on walls is expected to decrease the heat rate by storing energy when the phase change process takes place. The stored energy is released when the ambient temperature is low. Temperature differences at noon and evening can be utilized as discharging and charging cycles. This study examines the characteristics of heat transfer in walls using phase change material (PCM) in the form of encapsulation and using the sleeve as well. Heat transfer of bricks containing encapsulated PCM, tested the storage and released the heat on the walls of the building models were evaluated in this study. Experiments of heat transfer on brick consist of time that is needed for heat transfer and thermal conductivity test as well. Experiments were conducted on a wall coated by PCM which was exposed on a day and night cycle to analyze the heat storage and heat release. PCM used in these experiments was coconut oil. The measured parameter is the temperature at some points in the brick, walls and ambient temperature as well. The results showed that the use of encapsulation on an empty brick can increase the time for thermal heat transfer. Thermal conductivity values of a brick containing encapsulated PCM was lower than hollow bricks, where each value was 1.3 W/m.K and 1.6 W/m.K. While the process of heat absorption takes place from 7:00 am to 06:00 pm, and the release of heat runs from 10:00 pm to 7:00 am. The use of this PCM layer can reduce the surface temperature of the walls of an average of 2°C and slows the heat into the room.

  1. Tropical Gravity Wave Momentum Fluxes and Latent Heating Distributions

    Science.gov (United States)

    Geller, Marvin A.; Zhou, Tiehan; Love, Peter T.

    2015-01-01

    Recent satellite determinations of global distributions of absolute gravity wave (GW) momentum fluxes in the lower stratosphere show maxima over the summer subtropical continents and little evidence of GW momentum fluxes associated with the intertropical convergence zone (ITCZ). This seems to be at odds with parameterizations forGWmomentum fluxes, where the source is a function of latent heating rates, which are largest in the region of the ITCZ in terms of monthly averages. The authors have examined global distributions of atmospheric latent heating, cloud-top-pressure altitudes, and lower-stratosphere absolute GW momentum fluxes and have found that monthly averages of the lower-stratosphere GW momentum fluxes more closely resemble the monthly mean cloud-top altitudes rather than the monthly mean rates of latent heating. These regions of highest cloud-top altitudes occur when rates of latent heating are largest on the time scale of cloud growth. This, plus previously published studies, suggests that convective sources for stratospheric GW momentum fluxes, being a function of the rate of latent heating, will require either a climate model to correctly model this rate of latent heating or some ad hoc adjustments to account for shortcomings in a climate model's land-sea differences in convective latent heating.

  2. Baseline high heat flux and plasma facing materials for fusion

    Science.gov (United States)

    Ueda, Y.; Schmid, K.; Balden, M.; Coenen, J. W.; Loewenhoff, Th.; Ito, A.; Hasegawa, A.; Hardie, C.; Porton, M.; Gilbert, M.

    2017-09-01

    In fusion reactors, surfaces of plasma facing components (PFCs) are exposed to high heat and particle flux. Tungsten and Copper alloys are primary candidates for plasma facing materials (PFMs) and coolant tube materials, respectively, mainly due to high thermal conductivity and, in the case of tungsten, its high melting point. In this paper, recent understandings and future issues on responses of tungsten and Cu alloys to fusion environments (high particle flux (including T and He), high heat flux, and high neutron doses) are reviewed. This review paper includes; Tritium retention in tungsten (K. Schmid and M. Balden), Impact of stationary and transient heat loads on tungsten (J.W. Coenen and Th. Loewenhoff), Helium effects on surface morphology of tungsten (Y. Ueda and A. Ito), Neutron radiation effects in tungsten (A. Hasegawa), and Copper and copper alloys development for high heat flux components (C. Hardie, M. Porton, and M. Gilbert).

  3. Divertor Heat Flux Mitigation in the National Spherical Torus Experiment

    Energy Technology Data Exchange (ETDEWEB)

    Soukhanovskii, V A; Maingi, R; Gates, D A; Menard, J E; Paul, S F; Raman, R; Roquemore, A L; Bell, M G; Bell, R E; Boedo, J A; Bush, C E; Kaita, R; Kugel, H W; LeBlanc, B P; Mueller, D

    2008-08-04

    Steady-state handling of divertor heat flux is a critical issue for both ITER and spherical torus-based devices with compact high power density divertors. Significant reduction of heat flux to the divertor plate has been achieved simultaneously with favorable core and pedestal confinement and stability properties in a highly-shaped lower single null configuration in the National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40, 557 2000] using high magnetic flux expansion at the divertor strike point and the radiative divertor technique. A partial detachment of the outer strike point was achieved with divertor deuterium injection leading to peak flux reduction from 4-6 MW m{sup -2} to 0.5-2 MW m{sup -2} in small-ELM 0.8-1.0 MA, 4-6 MW neutral beam injection-heated H-mode discharges. A self-consistent picture of outer strike point partial detachment was evident from divertor heat flux profiles and recombination, particle flux and neutral pressure measurements. Analytic scrape-off layer parallel transport models were used for interpretation of NSTX detachment experiments. The modeling showed that the observed peak heat flux reduction and detachment are possible with high radiated power and momentum loss fractions, achievable with divertor gas injection, and nearly impossible to achieve with main electron density, divertor neutral density or recombination increases alone.

  4. Anthropogenic heat flux estimation from space: first results

    Science.gov (United States)

    Chrysoulakis, Nektarios; Heldens, Wieke; Gastellu-Etchegorry, Jean-Philippe; Grimmond, Sue; Feigenwinter, Christian; Lindberg, Fredrik; Del Frate, Fabio; Klostermann, Judith; Mitraka, Zina; Esch, Thomas; Albitar, Ahmad; Gabey, Andrew; Parlow, Eberhard; Olofson, Frans

    2016-04-01

    While Earth Observation (EO) has made significant advances in the study of urban areas, there are several unanswered science and policy questions to which it could contribute. To this aim the recently launched Horizon 2020 project URBANFLUXES (URBan ANthrpogenic heat FLUX from Earth observation Satellites) investigates the potential of EO to retrieve anthropogenic heat flux, as a key component in the urban energy budget. The anthropogenic heat flux is the heat flux resulting from vehicular emissions, space heating and cooling of buildings, industrial processing and the metabolic heat release by people. Optical, thermal and SAR data from existing satellite sensors are used to improve the accuracy of the radiation balance spatial distribution calculation, using also in-situ reflectance measurements of urban materials are for calibration. EO-based methods are developed for estimating turbulent sensible and latent heat fluxes, as well as urban heat storage flux and anthropogenic heat flux spatial patterns at city scale and local scale by employing an energy budget closure approach. Independent methods and models are engaged to evaluate the derived products and statistical analyses provide uncertainty measures as well. Ultimate goal of the URBANFLUXES is to develop a highly automated method for estimating urban energy budget components to use with Copernicus Sentinel data, enabling its integration into applications and operational services. Thus, URBANFLUXES prepares the ground for further innovative exploitation of European space data in scientific activities (i.e. Earth system modelling and climate change studies in cities) and future and emerging applications (i.e. sustainable urban planning) by exploiting the improved data quality, coverage and revisit times of the Copernicus data. The URBANFLUXES products will therefore have the potential to support both sustainable planning strategies to improve the quality of life in cities, as well as Earth system models to

  5. Augmentation of Critical Heat Flux of High Velocity Liquid Jet Flow utilizing Flat-Narrow Rectangular Channel

    Science.gov (United States)

    Sakurai, Hisashi; Koizumi, Yasuo; Ohtake, Hiroyasu

    Sub-cooled flow boiling heat transfer experiments were performed for narrow-flat flow passages of 2 mm wide and 0.2 mm high. A heat transfer surface of 2 mm × 2 mm was placed at the just downstream of the flow channel outlet. A fast wall plane-jet was formed on the heat transfer surface and space for vapor generated on the heat transfer surface to leave freely form the plane jet was provided The experiments covered the flow rate from 5 m⁄s through 20 m⁄s and the inlet sub-cooling from 30 K through 70 K. Critical heat fluxes were greatly augmented about twice compared with those in the previous experiments where the heat transfer surface was located at the outlet end of the same flow channel as that in the present experiments. This has indicated that the present idea of the flow system is effective to enhance the critical heat flux. When the flow velocity was slower than 10 m⁄s, a large secondary bubble that was formed as a result of coalescence of many primary bubbles on the heat transfer surface covered the heat transfer surface. The large-coalesced bubble triggered the occurrence of the critical heat flux. When the flow velocity became faster than 10 m⁄s, the heat transfer surface was covered with many tiny-primary bubbles even at the critical heat flux condition. The critical heat fluxes in the present experiments were much larger than predictions of correlations. The triggering mechanism of the critical heat flux condition was proposed based on the observation mentioned above. It has two parts; for low flow velocity and for high flow velocity. The boundary is 10 m⁄s. In both cases, disappearance of a liquid film under the bubble due to evaporation is related to the appearance of the critical heat flux condition. The predicted critical heat fluxes were larger than that measured, however, qualitatively agreed well.

  6. Study on coal char ignition by radiant heat flux.

    Science.gov (United States)

    Korotkikh, A. G.; Slyusarskiy, K. V.

    2017-11-01

    The study on coal char ignition by CO2-continuous laser was carried out. The coal char samples of T-grade bituminous coal and 2B-grade lignite were studied via CO2-laser ignition setup. Ignition delay times were determined at ambient condition in heat flux density range 90–200 W/cm2. The average ignition delay time value for lignite samples were 2 times lower while this difference is larger in high heat flux region and lower in low heat flux region. The kinetic constants for overall oxidation reaction were determined using analytic solution of simplified one-dimensional heat transfer equation with radiant heat transfer boundary condition. The activation energy for lignite char was found to be less than it is for bituminous coal char by approximately 20 %.

  7. Heat transfer in flow past a continuously moving porous flat plate with heat flux

    Digital Repository Service at National Institute of Oceanography (India)

    Murty, T.V.R.; Sarma, Y.V.B.

    The analysis of the heat transfer in flow past a continuously moving semi-infinite plate in the presence of suction/ injection with heat flux has been presented. Similarity solutions have been derived and the resulting equations are integrated...

  8. Influence of wall properties on peristaltic transport with heat transfer

    Science.gov (United States)

    Radhakrishnamacharya, G.; Srinivasulu, Ch.

    2007-07-01

    The effect of elasticity of the flexible walls on peristaltic transport of an incompressible viscous fluid, with heat transfer, in a two dimensional uniform channel has been investigated under long wave length approximation. The perturbation solution has been obtained in terms of wall slope parameter and closed form expressions have been derived for velocity, temperature and heat transfer. The effects of elastic tension, damping and mass characterizing parameters on temperature and heat transfer have been studied. It is found that heat transfer increases with elastic tension and mass characterizing parameters. To cite this article: G. Radhakrishnamacharya, Ch. Srinivasulu, C. R. Mecanique 335 (2007).

  9. Effect of Triangular Fins on Critical Heat Flux in Ethanol-cooled Combustion Chamber

    Science.gov (United States)

    Takegoshi, Masao; Suzuki, Ryosuke; Saito, Toshihito; Ono, Fumiei; Hiraiwa, Tetsuo; Tomioka, Sadatake

    A pressure-fed engine with a regeneratively-cooled combustion chamber is studied in JAXA. Operation chamber pressure is approximately 1 MPa. A proposed propellant combination is liquid oxygen and ethanol. However, it is necessary to understand the critical heat flux when ethanol is used as a coolant for regeneratively-cooled combustion chamber because the saturation pressure of it is 6.3 MPa. In general, it is known that the cooling wall with fins improves the cooling performance. In this study, the effect of triangular fins on critical heat flux of ethanol in ethanol-cooled combustion chamber was investigated. As the result, it was found that the critical heat flux of cooling wall with triangular fins was 23 % higher than that of that without fin in the same velocity condition of the coolant. The critical heat flux increases by the triangular fins on the cooling surface due to the effect of the combination cooling with film boiling and nucleate boiling.

  10. Heat and mass transfer in magnetohydrodynamic flow of micropolar fluid on a circular cylinder with uniform heat and mass flux

    CERN Document Server

    Mansour, M A; El-Kabeir, S M

    2000-01-01

    Steady laminar boundary layer analysis of heat and mass transfer characteristics in magnetohydrodynamic (MHD) flow of a micropolar fluid on a circular cylinder maintained at uniform heat and mass flux has been conducted. The solution of the energy equation inside the boundary layer is obtained as a power series of the distance measured along the surface from the front stagnation point of the cylinder. The results of dimensionless temperature, Nusselt number, wall shear stress, wall couple stress and Sherwood number have been presented graphically for various values of the material parameters. The results indicate that the micropolar fluids display a reduction in drag as well as heat transfer rate when compared with Newtonian fluids.

  11. Heat flux decay length during RF power operation in the Tore Supra tokamak

    Science.gov (United States)

    Corre, Y.; Gunn, J. P.; Firdaouss, M.; Carpentier, S.; Chantant, M.; Colas, L.; Ekedahl, A.; Gardarein, J.-L.; Lipa, M.; Loarer, T.; Courtois, X.; Guilhem, D.; Saint-Laurent, F.

    2014-01-01

    The upgrade of its ion cyclotron resonance (ICRH) and lower hybrid current drive (LHCD) heating systems makes the Tore Supra (TS) tokamak particularly well suited to address the physics and technology of high-power and steady-state plasma-surface interactions. High radio frequency (RF) heating powers have been successfully applied up to 12.2 MW coupled to the plasma, in which about 7.85 MW flows through the scrape-off layer. Thermal calculation based on thermography measurements gives the heat flux density distribution on the TS toroidal limiter located at the bottom of the machine. The target heat flux densities are divided by the incidence angle of the field lines with the surface and mapped to the magnetic flux surface to evaluate the power flowing in the scrape-off layer (SOL). The power profile shows a narrow component near the last closed flux surface and a wide component in the rest of the SOL. The narrow component is attributed to significant cross-field heat flux density around the plasma contact point, about 0.8% of the parallel heat flux density in the SOL, when incident angles are nearly tangential to the surface. The wide component is used to derive the experimental heat flux decay length (λq) and parallel heat flux in the SOL. The power widths are measured for a series of 1 MA/3.8 T discharges involving a scan of RF injected power 3.5 ⩽ Ptot ⩽ 12.2 MW. Independently of the heating power, we measured λq,OMP = 14.5 ± 1.5 mm at the outer mid-plane and parallel heat flux in the SOL in the range 130\\le Q_{\\parallel}^{LCFS}\\le 490\\,MW\\,m^{-2} . TS values obtained with L-mode limiter plasmas are broader than those derived from L-mode divertor plasmas, confirming earlier results obtained with an ohmically heated plasma leaning on the inboard wall of TS.

  12. Critical heat flux in flow boiling in microchannels

    CERN Document Server

    Saha, Sujoy Kumar

    2015-01-01

    This Brief concerns the important problem of critical heat flux in flow boiling in microchannels. A companion edition in the SpringerBrief Subseries on Thermal Engineering and Applied Science to “Heat Transfer and Pressure Drop in Flow Boiling in Microchannels,” by the same author team, this volume is idea for professionals, researchers, and graduate students concerned with electronic cooling.

  13. Charring rate of wood exposed to a constant heat flux

    Science.gov (United States)

    R. H. White; H. C. Tran

    1996-01-01

    A critical factor in the fire endurance of a wood member is its rate of charring. Most available charring rate data have been obtained using the time-temperature curves of the standard fire resistance tests (ASTM E 119 and ISO 834) to define the fire exposure. The increased use of heat release calorimeters using exposures of constant heat flux levels has broadened the...

  14. SIRHEX—A new experimental facility for high heat flux testing of plasma facing components

    Energy Technology Data Exchange (ETDEWEB)

    Kunze, André, E-mail: andre.kunze@kit.edu [Karlsruhe Institute of Technology (KIT), Institute for Neutron Physics and Reactor Technology (Germany); Ghidersa, Bradut-Eugen [Karlsruhe Institute of Technology (KIT), Institute for Neutron Physics and Reactor Technology (Germany); Bonelli, Flavia [Politecnico di Torino, Dipartimento Energia (Italy)

    2015-10-15

    Highlights: • Commercial infrared heaters have been qualified for future First Wall experiments. • In first tests surface heat flux densities up to 470 kW/m were achieved. • The homogeneity of the heat distribution stayed within ±5% of the nominal value. • With the heaters a typical ITER pulse can be reproduced. • An adequate testing strategy will be required to improve heater lifetime. - Abstract: SIRHEX (“Surface Infrared Radiation Heating Experiment”) is a small-scale experimental facility at KIT, which has been built for testing and qualifying high heat flux radiation heaters for blanket specific conditions using an instrumented water cooled target. This paper describes the SIRHEX facility and the experimental set-up for the heater tests. The results of a series of tests focused on reproducing homogeneous surface heat flux densities up to 500 kW/m{sup 2} will be presented and the impact of the heater performance on the design of the First Wall test rig will be discussed.

  15. Reconciling heat-flux and salt-flux estimates at a melting ice-ocean interface

    CERN Document Server

    Keitzl, Thomas; Notz, Dirk

    2016-01-01

    The ratio of heat and salt flux is employed in ice-ocean models to represent ice-ocean interactions. In this study, this flux ratio is determined from direct numerical simulations of free convection beneath a melting, horizontal, smooth ice-ocean interface. We find that the flux ratio at the interface is three times as large as previously assessed based on turbulent-flux measurements in the field. As a consequence, interface salinities and melt rates are overestimated by up to 40\\% if they are based on the three-equation formulation. We also find that the interface flux ratio depends only very weakly on the far-field conditions of the flow. Lastly, our simulations indicate that estimates of the interface flux ratio based on direct measurements of the turbulent fluxes will be difficult because at the interface the diffusivities alone determine the mixing and the flux ratio varies with depth. As an alternative, we present a consistent evaluation of the flux ratio based on the total heat and salt fluxes across t...

  16. Wall heat transfer in gas-fired furnaces: Effect of radiation modelling

    Directory of Open Access Journals (Sweden)

    Vondál J.

    2015-06-01

    Full Text Available The purpose of this work is to study heat transfer to cooled walls in a MW-scale laboratory furnace with a dominating thermal radiation component. Experiment is performed in a specially designed combustion chamber with segmental water-cooled walls and profile of absorbed heat flux is measured along the flame. Non-premixed natural gas flame is stabilized by a guide-vane swirler. The unsteady governing equations of turbulent flow are solved by a finite-volume code with a two-equation k-ε realizable turbulence model, a combination of first-order and second-order upwind schemes and implicit time integration. The coupling of pressure with velocity is treated by SIMPLE (semi-implicit method for pressure-linked equations algorithm. Radiative heat transfer as the main heat transfer method is modelled with special care by discrete ordinates method and gas absorption coefficient is calculated by two alternatives of WSGGM (weighted sum of grey gases model. The predicted total heat transfer rate is found to depend strongly on method chosen for the computation of mean beam length. The results of numerical simulations show that overall heat transfer in a process furnace can be successfully predicted, while heat flux profile along the flame is more difficult to predict accurately. Good engineering accuracy is nevertheless achievable with reasonable computational resources. The trend of deviations is reported, which is useful for the interpretation of practical predictions of process furnaces (fired heaters.

  17. Hybrid Heat Pipes for High Heat Flux Applications Project

    Data.gov (United States)

    National Aeronautics and Space Administration — The thermal transport requirements for future spacecraft missions continue to increase, approaching several kilowatts. At the same time the heat acquisition areas...

  18. Prediction of forced convective heat transfer and critical heat flux for subcooled water flowing in miniature tubes

    Science.gov (United States)

    Shibahara, Makoto; Fukuda, Katsuya; Liu, Qiusheng; Hata, Koichi

    2018-02-01

    The heat transfer characteristics of forced convection for subcooled water in small tubes were clarified using the commercial computational fluid dynamic (CFD) code, PHENICS ver. 2013. The analytical model consists of a platinum tube (the heated section) and a stainless tube (the non-heated section). Since the platinum tube was heated by direct current in the authors' previous experiments, a uniform heat flux with the exponential function was given as a boundary condition in the numerical simulation. Two inner diameters of the tubes were considered: 1.0 and 2.0 mm. The upward flow velocities ranged from 2 to 16 m/s and the inlet temperature ranged from 298 to 343 K. The numerical results showed that the difference between the surface temperature and the bulk temperature was in good agreement with the experimental data at each heat flux. The numerical model was extended to the liquid sublayer analysis for the CHF prediction and was evaluated by comparing its results with the experimental data. It was postulated that the CHF occurs when the fluid temperature near the heated wall exceeds the saturated temperature, based on Celata et al.'s superheated layer vapor replenishment (SLVR) model. The suggested prediction method was in good agreement with the experimental data and with other CHF data in literature within ±25%.

  19. Analytical Solution of Flow and Heat Transfer over a Permeable Stretching Wall in a Porous Medium

    Directory of Open Access Journals (Sweden)

    M. Dayyan

    2013-01-01

    Full Text Available Boundary layer flow through a porous medium over a stretching porous wall has seen solved with analytical solution. It has been considered two wall boundary conditions which are power-law distribution of either wall temperature or heat flux. These are general enough to cover the isothermal and isoflux cases. In addition to momentum, both first and second laws of thermodynamics analyses of the problem are investigated. The governing equations are transformed into a system of ordinary differential equations. The transformed ordinary equations are solved analytically using homotopy analysis method. A comprehensive parametric study is presented, and it is shown that the rate of heat transfer increases with Reynolds number, Prandtl number, and suction to the surface.

  20. Boiling Heat-Transfer Processes and Their Application in the Cooling of High Heat Flux Devices

    Science.gov (United States)

    1993-06-01

    presented previously in Eq. (8). Bjorge , et al. (Ref. 170) and Stephan and Auracher (Ref. 171) later presented variations of the superposition approach...ofHeat Transfer, Vol. 90, May 1968, pp. 239-247. 170. Bjorge , R. W., Hall, G. R., and Rohsenow, W. M. "Correlation of Forced Convection Boiling Heat... Communications on Heat Mass Transfer, Vol. 18, No.5, September-October 1991, pp. 659-667. 383. Boyd, R. D., Sr. "Critical Heat Flux and Heat Transfer

  1. Heat flux in the coastal zone

    DEFF Research Database (Denmark)

    Mahrt, L.; Vickers, D.; Edson, J.

    1998-01-01

    Various difficulties with application of Monin-Obukhov similarity theory are surveyed including the influence of growing waves, advection and internal boundary-layer development. These complications are normally important with offshore flow. The transfer coefficient for heat is computed from eddy...... the heat transfer and thermal roughness length but has no obvious influence on momentum roughness length. A new formulation of the thermal roughness length based on the internal boundary-layer depth is calibrated to the RASEX data. For the very stable case, the turbulence is mainly detached from...... the surface and existing formulations do not apply. As an alternative to adjusting the thermal roughness length, the transfer coefficient is related directly to the stability and the internal boundary-layer depth. This avoids specification of roughness lengths resulting from the usual integration of the non...

  2. Analysis of edge stability for models of heat flux width

    Directory of Open Access Journals (Sweden)

    M.A. Makowski

    2017-08-01

    Full Text Available Detailed measurements of the ne, Te, and Ti profiles in the vicinity of the separatrix of ELMing H-mode discharges have been used to examine plasma stability at the extreme edge of the plasma and assess stability dependent models of the heat flux width. The results are strongly contrary to the critical gradient model, which posits that a ballooning instability determines a gradient scale length related to the heat flux width. The results of this analysis are not sensitive to the choice of location to evaluate stability. Significantly, it is also found that the results are completely consistent with the heuristic drift model for the heat flux width. Here the edge pressure gradient scales with plasma density and is proportional to the pressure gradient inferred from the equilibrium in accordance with the predictions of that theory.

  3. Statistical analysis of the ion flux to the JET outer wall

    Science.gov (United States)

    Walkden, N. R.; Wynn, A.; Militello, F.; Lipschultz, B.; Matthews, G.; Guillemaut, C.; Harrison, J.; Moulton, D.; Contributors, JET

    2017-03-01

    Statistical analysis of the ion flux to the JET outer-wall is conducted in outer-wall limiter mounted Langmuir probe (OLP) time-series across a wide range of plasma current and line-averaged density during Ohmically heated horizontal target L-mode plasmas. The mean, μ, and the standard deviation, σ, of the ion-saturation current measured by the OLP show systematic variation with plasma current and density. Both increase as either plasma current decreases and/or density increases. Upon renormalization, achieved by subtraction of μ and rescaling by σ, the probability distribution functions (PDFs) of each signal collapse approximately onto a single curve. The shape of the curve deviates from a Γ distribution in the tail of the PDF and is better described by a log-normal distribution. The invariance in the shape of the PDF, which occurs over approximately four decades of the ordinate, is shown to be the result of a balance between the duration time of the average burst wave-form, {τd} and the waiting time between bursts, {τw} . This implies that the intermittency parameter, {τd}/{τw} , can be considered constant at the JET outer wall during horizontal target Ohmic L-mode operation. This result may be important both for model validation and prediction.

  4. Distributed Sensible Heat Flux Measurements for Wireless Sensor Networks

    Science.gov (United States)

    Huwald, H.; Brauchli, T.; Lehning, M.; Higgins, C. W.

    2015-12-01

    The sensible heat flux component of the surface energy balance is typically computed using eddy covariance or two point profile measurements while alternative approaches such as the flux variance method based on convective scaling has been much less explored and applied. Flux variance (FV) certainly has a few limitations and constraints but may be an interesting and competitive method in low-cost and power limited wireless sensor networks (WSN) with the advantage of providing spatio-temporal sensible heat flux over the domain of the network. In a first step, parameters such as sampling frequency, sensor response time, and averaging interval are investigated. Then we explore the applicability and the potential of the FV method for use in WSN in a field experiment. Low-cost sensor systems are tested and compared against reference instruments (3D sonic anemometers) to evaluate the performance and limitations of the sensors as well as the method with respect to the standard calculations. Comparison experiments were carried out at several sites to gauge the flux measurements over different surface types (gravel, grass, water) from the low-cost systems. This study should also serve as an example of spatially distributed sensible heat flux measurements.

  5. Simulation for heat flux mitigation by gas puffing in KSTAR

    Science.gov (United States)

    Shim, Seung Bo; Kotov, Vladislav; Hong, Suk-Ho; Detlev, Reiter; Kim, Jin Yong; Na, Yong Su; Lee, Hae June

    2013-10-01

    Control of heat flux is very important to achieve high performance long pulse operation in tokamaks. There are so many efforts to reduce the heat flux like change of divertor structure, snowflake divertor, and RMP, etc. Detachment by gas puffing is used for long time to reduce the heat flux. In this paper edge plasma scenarios of KSTAR are analyzed numerically by well-known B2-Eirene code package(SOLPS4.3). High performance discharges with heating power ~ 8 MW and core flux ~ 1021 s-1 is used. Gas puffed on the outer mid-plane(OMP), both divertors is likely to stay attached. So, gas puffed on the outer target, one is near the private flux region(PFR) and the other is near the scrape-off-layer(SOL). When gas puffed near the SOL is still attached, and it is worse than gas puff from OMP because it is too close to cryo-pump. The case near the PFR shows high recycling region easily compared with OMP case. When one forth gas puffed on the PFR, results are similar with OMP case. But it is still not good for detachment operation. Detachment operation window is too small for the gas puffing on the PFR. This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MEST)(No. 2012-0000579).

  6. Predicting critical heat flux in slug flow regime of uniformly heated ...

    African Journals Online (AJOL)

    Numerical computation code (PWR-DNBP) has been developed to predict Critical Heat Flux (CHF) of forced convective flow of water in a vertical heated channel. The code was based on the liquid sub-layer model, with the assumption that CHF occurred when the liquid film thickness between the heated surface and vapour ...

  7. An inverse hyperbolic heat conduction problem in estimating surface heat flux by the conjugate gradient method

    Energy Technology Data Exchange (ETDEWEB)

    Huang, C.-H.; Wu, H.-H. [Department of Systems and Naval Mechatronic Engineering National Cheng Kung University Tainan, Taiwan 701 (China)

    2006-09-21

    In the present study an inverse hyperbolic heat conduction problem is solved by the conjugate gradient method (CGM) in estimating the unknown boundary heat flux based on the boundary temperature measurements. Results obtained in this inverse problem will be justified based on the numerical experiments where three different heat flux distributions are to be determined. Results show that the inverse solutions can always be obtained with any arbitrary initial guesses of the boundary heat flux. Moreover, the drawbacks of the previous study for this similar inverse problem, such as (1) the inverse solution has phase error and (2) the inverse solution is sensitive to measurement error, can be avoided in the present algorithm. Finally, it is concluded that accurate boundary heat flux can be estimated in this study.

  8. Application of a Heat Flux Sensor in Wind Power Electronics

    Directory of Open Access Journals (Sweden)

    Elvira Baygildina

    2016-06-01

    Full Text Available This paper proposes and investigates the application of the gradient heat flux sensor (GHFS for measuring the local heat flux in power electronics. Thanks to its thinness, the sensor can be placed between the semiconductor module and the heat sink. The GHFS has high sensitivity and yields direct measurements without an interruption to the normal power device operation, which makes it attractive for power electronics applications. The development of systems for monitoring thermal loading and methods for online detection of degradation and failure of power electronic devices is a topical and crucial task. However, online condition monitoring (CM methods, which include heat flux sensors, have received little research attention so far. In the current research, an insulated-gate bipolar transistor (IGBT module-based test setup with the GHFS implemented on the base plate of one of the IGBTs is introduced. The heat flux experiments and the IGBT power losses obtained by simulations show similar results. The findings give clear evidence that the GHFS can provide an attractive condition monitoring method for the thermal loading of power devices.

  9. Cattaneo-Christov on heat and mass transfer of unsteady Eyring Powell dusty nanofluid over sheet with heat and mass flux conditions

    Directory of Open Access Journals (Sweden)

    Mamatha S. Upadhay

    2017-01-01

    Full Text Available Heat and mass flux conditions on magnetohydrodynamic unsteady Eyring-Powell dusty nanofluid over a sheet is addressed. The combined effect of Brownian motion and thermophoresis in nanofluid modeling are retained. The Cattaneo-Christov heat flux model is imposed. A set of similarity variables are utilized to form ordinary differential system from the prevailing partial differential equations. The problem of ordinary differential system (ODS is analyzed numerically through Runge-Kutta based shooting method. Graphical results of pertinent parameters on the velocity, temperature and nanoparticle concentration are studied. Skin friction coefficient, local Nusselt and Sherwood number are also addressed with help of graphs and also validated the present solutions with already existing solutions in the form of table. It is found that the thermal relaxation parameter improves the heat transfer rate and minimizes the mass transfer rate. The heat transfer rate is higher in prescribed heat flux (PHF case when compared with prescribed wall temperature (PWT case.

  10. Spatially averaged heat flux and convergence measurements at the ARM regional flux experiment

    Energy Technology Data Exchange (ETDEWEB)

    Porch, W.; Barnes, F.; Buchwald, M.; Clements, W.; Cooper, D.; Hoard, D. (Los Alamos National Lab., NM (United States)); Doran, C.; Hubbe, J.; Shaw, W. (Pacific Northwest Lab., Richland, WA (United States)); Coulter, R.; Martin, T. (Argonne National Lab., IL (United States)); Kunkel, K. (Illinois State Water Survey, Champaign, IL (United States))

    1991-01-01

    Cloud formation and its relation to climate change is the greatest weakness in current numerical climate models. Surface heat flux in some cases causes clouds to form and in other to dissipate and the differences between these cases are subtle enough to make parameterization difficult in a numerical model. One of the goals of the DOE Atmospheric Radiation Measurement program is to make long term measurements at representative sites to improve radiation and cloud formation parameterization. This paper compares spatially averaged optical measurements of heat flux and convergence with a goal of determining how point measurements of heat fluxes scale up to the larger scale used for climate modeling. It was found that the various optical techniques used in this paper compared well with each other and with independent measurements. These results add confidence that spatially averaging optical techniques can be applied to transform point measurements to the larger scales needed for mesoscale and climate modeling. 10 refs., 6 figs. (MHB)

  11. Thermotronics. Towards nanocircuits to manage radiative heat flux

    Energy Technology Data Exchange (ETDEWEB)

    Ben-Abdallah, Philippe [Univ. Paris-Sud 11, Palaiseau (France). Lab. Charles Fabry; Sherbrooke Univ., PQ (Canada). Dept. of Mechanical Engineering; Biehs, Svend-Age [Oldenburg Univ. (Germany). Inst. fuer Physik

    2017-05-01

    The control of electric currents in solids is at the origin of the modern electronics revolution that has driven our daily life since the second half of 20{sup th} century. Surprisingly, to date, there is no thermal analogue for a control of heat flux. Here, we summarise the very last developments carried out in this direction to control heat exchanges by radiation both in near and far-field in complex architecture networks.

  12. Study of heat flux deposition in the Tore Supra Tokamak; Etude des depots de chaleur dans le tokamak Tore Supra

    Energy Technology Data Exchange (ETDEWEB)

    Carpentier, S.

    2009-02-15

    Accurate measurements of heat loads on internal tokamak components is essential for protection of the device during steady state operation. The optimisation of experimental scenarios also requires an in depth understanding of the physical mechanisms governing the heat flux deposition on the walls. The objective of this study is a detailed characterisation of the heat flux to plasma facing components (PFC) of the Tore Supra tokamak. The power deposited onto Tore Supra PFCs is calculated using an inverse method, which is applied to both the temperature maps measured by infrared thermography and to the enthalpy signals from calorimetry. The derived experimental heat flux maps calculated on the toroidal pumped limiter (TPL) are then compared with theoretical heat flux density distributions from a standard SOL-model. They are two experimental observations that are not consistent with the model: significant heat flux outside the theoretical wetted area, and heat load peaking close to the tangency point between the TPL and the last closed field surface (LCFS). An experimental analysis for several discharges with variable security factors q is made. In the area consistent with the theoretical predictions, this parametric study shows a clear dependence between the heat flux length lambda{sub q} (estimated in the SOL (scrape-off layer) from the IR measurements) and the magnetic configuration. We observe that the spreading of heat fluxes on the component is compensated by a reduction of the power decay length lambda{sub q} in the SOL when q decreases. On the other hand, in the area where the derived experimental heat loads are not consistent with the theoretical predictions, we observe that the spreading of heat fluxes outside the theoretical boundary increases when q decreases, and is thus not counterbalanced. (author)

  13. Assessment of hypervapotron heat sink performance using CFD under DEMO relevant first wall conditions

    Energy Technology Data Exchange (ETDEWEB)

    Domalapally, Phani, E-mail: p_kumar.domalapally@cvrez.cz

    2016-11-01

    Highlights: • Performance of Hypervapotron heat sink was tested for First wall limiter application. • Two different materials were tested Eurofer 97 and CuCrZr at PWR conditions. • Simulations were performed to see the effect of the different inlet conditions and materials on the maximum temperature. • It was found that CuCrZr heat sink performance is far better than Eurofer heat sink at the same operating conditions. - Abstract: Among the proposed First Wall (FW) cooling concepts for European Demonstration Fusion Power Plant (DEMO), water cooled FW is one of the options. The heat flux load distribution on the FW of the DEMO reactor is not yet precisely defined. But if the heat loads on the FW are extrapolated from ITER conditions, the numbers are quite high and have to be handled none the less. The design of the FW itself is challenging as the thermal conductivity ratio of heat sink materials in ITER (CuCrZr) and in DEMO (Eurofer 97) is ∼10–12 and the operating conditions are of Pressurized Water Reactor (PWR) in DEMO instead of 70 °C and 4 MPa as in ITER. This paper analyzes the performance of Hypervapotron (HV) heat sink for FW limiter application under DEMO conditions. Where different materials, temperatures, heat fluxes and velocities are considered to predict the performance of the HV, to establish its limits in handling the heat loads before reaching the upper limits from temperature point of view. In order to assess the performance, numerical simulations are performed using commercial CFD code, which was previously validated in predicting the thermal hydraulic performance of HV geometry. Based on the results the potential usage of HV heat sink for DEMO will be assessed.

  14. Development of a real-time system for ITER first wall heat load control

    Science.gov (United States)

    Anand, Himank; de Vries, Peter; Gribov, Yuri; Pitts, Richard; Snipes, Joseph; Zabeo, Luca

    2017-10-01

    The steady state heat flux on the ITER first wall (FW) panels are limited by the heat removal capacity of the water cooling system. In case of off-normal events (e.g. plasma displacement during H-L transitions), the heat loads are predicted to exceed the design limits (2-4.7 MW/m2). Intense heat loads are predicted on the FW, even well before the burning plasma phase. Thus, a real-time (RT) FW heat load control system is mandatory from early plasma operation of the ITER tokamak. A heat load estimator based on the RT equilibrium reconstruction has been developed for the plasma control system (PCS). A scheme, estimating the energy state for prescribed gaps defined as the distance between the last closed flux surface (LCFS)/separatrix and the FW is presented. The RT energy state is determined by the product of a weighted function of gap distance and the power crossing the plasma boundary. In addition, a heat load estimator assuming a simplified FW geometry and parallel heat transport model in the scrape-off layer (SOL), benchmarked against a full 3-D magnetic field line tracer is also presented.

  15. Identification of convective heat loss on exterior cavity wall assemblies

    Science.gov (United States)

    Colantonio, Antonio

    1999-03-01

    Most present day low and medium rise buildings constructed in Canada use some form of cavity wall design for their exterior walls. These types of wall assemblies use a broad range of cladding materials such as brick, stone, wood, sheet metal, porcelain enamel or metal panels, cementitious materials and plastics. The interior assemblies of these walls include the air barrier, vapor barrier and insulation layers. The cladding is separated from the interior wall assembly by an air space of varying thickness. Dependent upon the temperature differential between the interior and exterior, the temperature between the outer surface of the interior wall assembly and the inner surface of the exterior cladding under conditions in which air movement is restricted will give rise to convective heat loss mechanisms. This paper will look at how these convective heat loss patterns manifest themselves as thermal patterns on exterior surfaces of cladding materials. Similar details will be illustrated under various pressure differential conditions through the entire building envelope assembly. Various types of exterior wall assemblies will be discussed.

  16. Selective Internal Heat Distribution in Modified Trombe Wall

    Science.gov (United States)

    Szyszka, Jerzy; Kogut, Janusz; Skrzypczak, Izabela; Kokoszka, Wanda

    2017-12-01

    At present, the requirements for thermal insulation of the external walls in buildings are being increased. There is a need to reduce energy consumption for heating rooms during the winter season. This may be achieved by increasing the thermal resistance of the outer partitions, using solutions that utilize either recuperation or solar radiation. The most popular systems include either solar collectors, or heat pump links or ground exchangers. Trombe walls (TW) are a very promising passive heating system, which requires little or no effort to operate, and may be very convenient in different climate conditions. A typical TW consists of a masonry wall painted a dark, heat absorbing paint colour and faced with a single or double layer of glass. The principle of operation is based on the photothermal conversion of solar radiation. There are various modifications of TW. They may improve the energy efficiency in relation to the climate conditions in which they operate. The hybrid solutions are also known. The efficiency of walls is related to the use of proper materials. In TW, the compromise should be sought between the thermal resistance and the ability to distribute heat from the absorbed energy of solar radiation. The paper presents an overview of the most commonly used solutions and discusses its own concept dedicated to the climate conditions of Central Europe.

  17. Longitudinal spin Seebeck coefficient: heat flux vs. temperature difference method.

    Science.gov (United States)

    Sola, A; Bougiatioti, P; Kuepferling, M; Meier, D; Reiss, G; Pasquale, M; Kuschel, T; Basso, V

    2017-04-25

    The determination of the longitudinal spin Seebeck effect (LSSE) coefficient is currently plagued by a large uncertainty due to the poor reproducibility of the experimental conditions used in its measurement. In this work we present a detailed analysis of two different methods used for the determination of the LSSE coefficient. We have performed LSSE experiments in different laboratories, by using different setups and employing both the temperature difference method and the heat flux method. We found that the lack of reproducibility can be mainly attributed to the thermal contact resistance between the sample and the thermal baths which generate the temperature gradient. Due to the variation of the thermal resistance, we found that the scaling of the LSSE voltage to the heat flux through the sample rather than to the temperature difference across the sample greatly reduces the uncertainty. The characteristics of a single YIG/Pt LSSE device obtained with two different setups was (1.143 ± 0.007) 10-7 Vm/W and (1.101 ± 0.015) 10-7 Vm/W with the heat flux method and (2.313 ± 0.017) 10-7 V/K and (4.956 ± 0.005) 10-7 V/K with the temperature difference method. This shows that systematic errors can be considerably reduced with the heat flux method.

  18. Measurement of a surface heat flux and temperature

    Science.gov (United States)

    Davis, R. M.; Antoine, G. J.; Diller, T. E.; Wicks, A. L.

    1994-01-01

    The Heat Flux Microsensor is a new sensor which was recently patented by Virginia Tech and is just starting to be marketed by Vatell Corp. The sensor is made using the thin-film microfabrication techniques directly on the material that is to be measured. It consists of several thin-film layers forming a differential thermopile across a thermal resistance layer. The measured heat flux q is proportional to the temperature difference across the resistance layer q= k(sub g)/delta(sub g) x (t(sub 1) - T(sub 2)), where k(sub g) is the thermal conductivity and delta (sub g) is the thickness of the thermal resistance layer. Because the gages are sputter coated directly onto the surface, their total thickness is less than 2 micrometers, which is two orders of magnitude thinner than previous gages. The resulting temperature difference across the thermal resistance layer (delta is less than 1 micrometer) is very small even at high heat fluxes. To generate a measurable signal many thermocouple pairs are put in series to form a differential thermopile. The combination of series thermocouple junctions and thin-film design creates a gage with very attractive characteristics. It is not only physically non-intrusive to the flow, but also causes minimal disruption of the surface temperature. Because it is so thin, the response time is less than 20 microsec. Consequently, the frequency response is flat from 0 to over 50 kHz. Moreover, the signal of the Heat Flux Microsensor is directly proportional to the heat flux. Therefore, it can easily be used in both steady and transient flows, and it measures both the steady and unsteady components of the surface heat flux. A version of the Heat Flux Microsensor has been developed to meet the harsh demands of combustion environments. These gages use platinum and platinum-10 percent rhodium as the thermoelectric materials. The thermal resistance layer is silicon monoxide and a protective coating of Al2O3 is deposited on top of the sensor. The

  19. Viscous relaxation of Ganymede's impact craters: Constraints on heat flux

    Science.gov (United States)

    Bland, Michael T.; Singer, Kelsi N.; McKinnon, William B.; Schenk, Paul M.

    2017-11-01

    Measurement of crater depths in Ganymede's dark terrain have revealed substantial numbers of unusually shallow craters indicative of viscous relaxation [see companion paper: Singer, K.N., Schenk, P. M., Bland, M.T., McKinnon, W.B., (2017). Relaxed impact craters on Ganymede: Regional variations and high heat flow. Icarus, submitted]. These viscously relaxed craters provide insight into the thermal history of the dark terrain: the rate of relaxation depends on the size of the crater and the thermal structure of the lithosphere. Here we use finite element simulations of crater relaxation to constrain the heat flux within the dark terrain when relaxation occurred. We show that the degree of viscous relaxation observed cannot be achieved through radiogenic heating alone, even if all of the relaxed craters are ancient and experienced the high radiogenic fluxes present early in the satellite's history. For craters with diameter ≥ 10 km, heat fluxes of 40-50 mW m-2 can reproduce the observed crater depths, but only if the fluxes are sustained for ∼1 Gyr. These craters can also be explained by shorter-lived ;heat pulses; with magnitudes of ∼100 mW m-2 and timescales of 10-100 Myr. At small crater diameters (4 km) the observed shallow depths are difficult to achieve even when heat fluxes as high as 150 mW m-2 are sustained for 1 Gyr. The extreme thermal conditions required to viscously relax small craters may indicate that mechanisms other than viscous relaxation, such as topographic degradation, are also in play at small crater diameters. The timing of the relaxation event(s) is poorly constrained due to the sparsity of adequate topographic information, though it likely occurred in Ganymede's middle history (neither recently, nor shortly after satellite formation). The consistency between the timing and magnitude of the heat fluxes derived here and those inferred from other tectonic features suggests that a single event caused both Ganymede's tectonic deformation and

  20. Viscous relaxation of Ganymede's impact craters: Constraints on heat flux

    Science.gov (United States)

    Bland, Michael; Singer, Kelsi N.; McKinnon, William B.; Schenk, Paul M.

    2017-01-01

    Measurement of crater depths in Ganymede’s dark terrain have revealed substantial numbers of unusually shallow craters indicative of viscous relaxation [see companion paper: Singer, K.N., Schenk, P. M., Bland, M.T., McKinnon, W.B., (2017). Relaxed impact craters on Ganymede: Regional variations and high heat flow. Icarus, submitted]. These viscously relaxed craters provide insight into the thermal history of the dark terrain: the rate of relaxation depends on the size of the crater and the thermal structure of the lithosphere. Here we use finite element simulations of crater relaxation to constrain the heat flux within the dark terrain when relaxation occurred. We show that the degree of viscous relaxation observed cannot be achieved through radiogenic heating alone, even if all of the relaxed craters are ancient and experienced the high radiogenic fluxes present early in the satellite’s history. For craters with diameter ≥ 10 km, heat fluxes of 40–50 mW m-2−2"> can reproduce the observed crater depths, but only if the fluxes are sustained for ∼1 Gyr. These craters can also be explained by shorter-lived “heat pulses” with magnitudes of ∼100 mW m-2−2"> and timescales of 10–100 Myr. At small crater diameters (4 km) the observed shallow depths are difficult to achieve even when heat fluxes as high as 150 mW m-2−2"> are sustained for 1 Gyr. The extreme thermal conditions required to viscously relax small craters may indicate that mechanisms other than viscous relaxation, such as topographic degradation, are also in play at small crater diameters. The timing of the relaxation event(s) is poorly constrained due to the sparsity of adequate topographic information, though it likely occurred in Ganymede’s middle history (neither recently, nor shortly after satellite formation). The consistency between the timing and magnitude of the heat fluxes derived here and those inferred from other tectonic features suggests that a single event

  1. Global Intercomparison of 12 Land Surface Heat Flux Estimates

    Science.gov (United States)

    Jimenez, C.; Prigent, C.; Mueller, B.; Seneviratne, S. I.; McCabe, M. F.; Wood, E. F.; Rossow, W. B.; Balsamo, G.; Betts, A. K.; Dirmeyer, P. A.; hide

    2011-01-01

    A global intercomparison of 12 monthly mean land surface heat flux products for the period 1993-1995 is presented. The intercomparison includes some of the first emerging global satellite-based products (developed at Paris Observatory, Max Planck Institute for Biogeochemistry, University of California Berkeley, University of Maryland, and Princeton University) and examples of fluxes produced by reanalyses (ERA-Interim, MERRA, NCEP-DOE) and off-line land surface models (GSWP-2, GLDAS CLM/ Mosaic/Noah). An intercomparison of the global latent heat flux (Q(sub le)) annual means shows a spread of approx 20 W/sq m (all-product global average of approx 45 W/sq m). A similar spread is observed for the sensible (Q(sub h)) and net radiative (R(sub n)) fluxes. In general, the products correlate well with each other, helped by the large seasonal variability and common forcing data for some of the products. Expected spatial distributions related to the major climatic regimes and geographical features are reproduced by all products. Nevertheless, large Q(sub le)and Q(sub h) absolute differences are also observed. The fluxes were spatially averaged for 10 vegetation classes. The larger Q(sub le) differences were observed for the rain forest but, when normalized by mean fluxes, the differences were comparable to other classes. In general, the correlations between Q(sub le) and R(sub n) were higher for the satellite-based products compared with the reanalyses and off-line models. The fluxes were also averaged for 10 selected basins. The seasonality was generally well captured by all products, but large differences in the flux partitioning were observed for some products and basins.

  2. Developing Buoyancy Driven Flow of a Nanofluid in a Vertical Channel Subject to Heat Flux

    Directory of Open Access Journals (Sweden)

    Nirmal C. Sacheti

    2014-01-01

    Full Text Available The developing natural convective flow of a nanofluid in an infinite vertical channel with impermeable bounding walls has been investigated. It is assumed that the nanofluid is dominated by two specific slip mechanisms and that the channel walls are subject to constant heat flux and isothermal temperature, respectively. The governing nonlinear partial differential equations coupling different transport processes have been solved numerically. The variations of velocity, temperature, and nanoparticles concentration have been discussed in relation to a number of physical parameters. It is seen that the approach to the steady-state profiles of velocity and temperature in the present work is different from the ones reported in a previous study corresponding to isothermal wall conditions.

  3. Heat in the Barents Sea: transport, storage, and surface fluxes

    Directory of Open Access Journals (Sweden)

    L. H. Smedsrud

    2010-02-01

    Full Text Available A column model is set up for the Barents Sea to explore sensitivity of surface fluxes and heat storage from varying ocean heat transport. Mean monthly ocean transport and atmospheric forcing are synthesised and force the simulations. Results show that by using updated ocean transports of heat and freshwater the vertical mean hydrographic seasonal cycle can be reproduced fairly well.

    Our results indicate that the ~70 TW of heat transported to the Barents Sea by ocean currents is lost in the southern Barents Sea as latent, sensible, and long wave radiation, each contributing 23–39 TW to the total heat loss. Solar radiation adds 26 TW in the south, as there is no significant ice production.

    The northern Barents Sea receives little ocean heat transport. This leads to a mixed layer at the freezing point during winter and significant ice production. There is little net surface heat loss annually in the north. The balance is achieved by a heat loss through long wave radiation all year, removing most of the summer solar heating.

    During the last decade the Barents Sea has experienced an atmospheric warming and an increased ocean heat transport. The Barents Sea responds to such large changes by adjusting temperature and heat loss. Decreasing the ocean heat transport below 50 TW starts a transition towards Arctic conditions. The heat loss in the Barents Sea depend on the effective area for cooling, and an increased heat transport leads to a spreading of warm water further north.

  4. Influence of condensation on heat flux and pressure measurements in a detonation-based short-duration facility

    Science.gov (United States)

    Haase, S.; Olivier, H.

    2017-10-01

    Detonation-based short-duration facilities provide hot gas with very high stagnation pressures and temperatures. Due to the short testing time, complex and expensive cooling techniques of the facility walls are not needed. Therefore, they are attractive for economical experimental investigations of high-enthalpy flows such as the flow in a rocket engine. However, cold walls can provoke condensation of the hot combustion gas at the walls. This has already been observed in detonation tubes close behind the detonation wave, resulting in a loss of tube performance. A potential influence of condensation at the wall on the experimental results, like wall heat fluxes and static pressures, has not been considered so far. Therefore, in this study the occurrence of condensation and its influence on local heat flux and pressure measurements has been investigated in the nozzle test section of a short-duration rocket-engine simulation facility. This facility provides hot water vapor with stagnation pressures up to 150 bar and stagnation temperatures up to 3800 K. A simple method has been developed to detect liquid water at the wall without direct optical access to the flow. It is shown experimentally and theoretically that condensation has a remarkable influence on local measurement values. The experimental results indicate that for the elimination of these influences the nozzle wall has to be heated to a certain temperature level, which exclusively depends on the local static pressure.

  5. A 2-D imaging heat-flux gauge

    Energy Technology Data Exchange (ETDEWEB)

    Noel, B.W.; Borella, H.M. (Los Alamos National Lab., NM (United States)); Beshears, D.L.; Sartory, W.K.; Tobin, K.W.; Williams, R.K. (Oak Ridge National Lab., TN (United States)); Turley, W.D. (EG and G Energy Measurements, Inc., Goleta, CA (United States). Santa Barbara Operations)

    1991-07-01

    This report describes a new leadless two-dimensional imaging optical heat-flux gauge. The gauge is made by depositing arrays of thermorgraphic-phosphor (TP) spots onto the faces of a polymethylpentene is insulator. In the first section of the report, we describe several gauge configurations and their prototype realizations. A satisfactory configuration is an array of right triangles on each face that overlay to form squares when the gauge is viewed normal to the surface. The next section of the report treats the thermal conductivity of TPs. We set up an experiment using a comparative longitudinal heat-flow apparatus to measure the previously unknown thermal conductivity of these materials. The thermal conductivity of one TP, Y{sub 2}O{sub 3}:Eu, is 0.0137 W/cm{center dot}K over the temperature range from about 300 to 360 K. The theories underlying the time response of TP gauges and the imaging characteristics are discussed in the next section. Then we discuss several laboratory experiments to (1) demonstrate that the TP heat-flux gauge can be used in imaging applications; (2) obtain a quantum yield that enumerates what typical optical output signal amplitudes can be obtained from TP heat-flux gauges; and (3) determine whether LANL-designed intensified video cameras have sufficient sensitivity to acquire images from the heat-flux gauges. We obtained positive results from all the measurements. Throughout the text, we note limitations, areas where improvements are needed, and where further research is necessary. 12 refs., 25 figs., 4 tabs.

  6. An experimental study of critical heat flux of flow boiling in minichannels at high reduced pressure

    Science.gov (United States)

    Belyaev, A. V.; Dedov, A. V.; Varava, A. N.; Komov, A. T.

    2017-10-01

    This paper presents an experimental setup and experimental data for critical heat flux. The hydraulic loop of the experimental setup allows it to maintain stable flow parameters at the inlet of the test section at pressures up to 2.7 MPa and temperatures up to 200 °C. Experiments of hydrodynamics and heat transfer were performed for R113 and RC318 in two vertical channels with diameters of 1.36 and 0.95 mm and lengths of 200 and 100 mm, respectively. The inlet pressure-to-critical pressure ratio (reduced pressure) was pr = p/pcr = 0.15 ÷ 0.9, the mass flux ranges were between 700 and 4800 kg/(m2s), and inlet temperature varied from 30 to 180 °C. The primary regimes were obtained for conditions that varied from highly subcooled flows to saturated flows. For each regime with fixed parameters, the maximum possible heating power value was applied, with the maximum limited by the maximum output of the power supply, the onset of dryout, or wall temperatures exceeding 350 °C. The influence of flow conditions (i.e., mass flow rate, pressure, inlet temperature, and the channel diameter) on the critical heat flux is presented.

  7. Heat transfer and wall temperature effects in shock wave turbulent boundary layer interactions

    CERN Document Server

    Bernardini, Matteo; Pirozzoli, Sergio; Grasso, Francesco

    2016-01-01

    Direct numerical simulations are carried out to investigate the effect of the wall temperature on the behavior of oblique shock-wave/turbulent boundary layer interactions at freestream Mach number $2.28$ and shock angle of the wedge generator $\\varphi = 8^{\\circ}$. Five values of the wall-to-recovery-temperature ratio ($T_w/T_r$) are considered, corresponding to cold, adiabatic and hot wall thermal conditions. We show that the main effect of cooling is to decrease the characteristic scales of the interaction in terms of upstream influence and extent of the separation bubble. The opposite behavior is observed in the case of heating, that produces a marked dilatation of the interaction region. The distribution of the Stanton number shows that a strong amplification of the heat transfer occurs across the interaction, and the maximum values of thermal and dynamic loads are found in the case of cold wall. The analysis reveals that the fluctuating heat flux exhibits a strong intermittent behavior, characterized by ...

  8. An assessment of CFD-based wall heat transfer models in piston engines

    Energy Technology Data Exchange (ETDEWEB)

    Sircar, Arpan [Pennsylvania State Univ., University Park, PA (United States); Paul, Chandan [Pennsylvania State Univ., University Park, PA (United States); Ferreyro-Fernandez, Sebastian [Pennsylvania State Univ., University Park, PA (United States); Imren, Abdurrahman [Pennsylvania State Univ., University Park, PA (United States); Haworth, Daniel C [Pennsylvania State Univ., University Park, PA (United States)

    2017-04-26

    The lack of accurate submodels for in-cylinder heat transfer has been identified as a key shortcoming in developing truly predictive, physics-based computational fluid dynamics (CFD) models that can be used to develop combustion systems for advanced high-efficiency, low-emissions engines. Only recently have experimental methods become available that enable accurate near-wall measurements to enhance simulation capability via advancing models. Initial results show crank-angle dependent discrepancies with respect to previously used boundary-layer models of up to 100%. However, available experimental data is quite sparse (only few data points on engine walls) and limited (available measurements are those of heat flux only). Predictive submodels are needed for medium-resolution ("engineering") LES and for unsteady Reynolds-averaged simulations (URANS). Recently, some research groups have performed DNS studies on engine-relevant conditions using simple geometries. These provide very useful data for benchmarking wall heat transfer models under such conditions. Further, a number of new and more sophisticated models have also become available in the literature which account for these engine-like conditions. Some of these have been incorporated while others of a more complex nature, which include solving additional partial differential equations (PDEs) within the thin boundary layer near the wall, are underway. These models will then be tested against the available DNS/experimental data in both SI (spark-ignition) and CI (compression-ignition) engines.

  9. Energy flux through the horizon in the black hole-domain wall systems

    Energy Technology Data Exchange (ETDEWEB)

    Stojkovic, Dejan E-mail: dejans@umich.edu

    2004-09-01

    We study various configurations in which a domain wall (or cosmic string), described by the Nambu-Goto action, is embedded in a background space-time of a black hole in (3+1) and higher dimensional models. We calculate energy fluxes through the black hole horizon. In the simplest case, when a static domain wall enters the horizon of a static black hole perpendicularly, the energy flux is zero. In more complicated situations, where parameters which describe the domain wall surface are time and position dependent, the flux is non-vanishing is principle. These results are of importance in various conventional cosmological models which accommodate the existence of domain walls and strings and also in brane world scenarios. (author)

  10. Core Fueling and Edge Particle Flux Analysis in Ohmically and Auxiliary Heated NSTX Plasmas

    Energy Technology Data Exchange (ETDEWEB)

    V.A. Soukhanovskii; R. Maingi; R. Raman; H.W. Kugel; B.P. LeBlanc; L. Roquemore; C.H. Skinner; NSTX Research Team

    2002-06-12

    The Boundary Physics program of the National Spherical Torus Experiment (NSTX) is focusing on optimization of the edge power and particle flows in b * 25% L- and H-mode plasmas of t {approx} 0.8 s duration heated by up to 6 MW of high harmonic fast wave and up to 5 MW of neutral beam injection. Particle balance and core fueling efficiencies of low and high field side gas fueling of L-mode homic and NBI heated plasmas have been compared using an analytical zero dimensional particle balance model and measured ion and neutral fluxes. Gas fueling efficiencies are in the range of 0.05-0.20 and do not depend on discharge magnetic configuration, density or poloidal location of the injector. The particle balance modeling indicates that the addition of HFS fueling results in a reversal of the wall loading rate and higher wall inventories. Initial particle source estimates obtained from neutral pressure and spectroscopic measurements indicate that ion flux into the divertor greatly exceeds midplane ion flux from the main plasma, suggesting that the scrape-off cross-field transport plays a minor role in diverted plasmas. Present analysis provides the basis for detailed fluid modeling of core and edge particle flows and particle confinement properties of NSTX plasmas. This research was supported by the U.S. Department of Energy under contracts No. DE-AC02-76CH03073, DE-AC05-00OR22725, and W-7405-ENG-36.

  11. Plasma–Surface Interactions Under High Heat and Particle Fluxes

    Directory of Open Access Journals (Sweden)

    Gregory De Temmerman

    2013-01-01

    Full Text Available The plasma-surface interactions expected in the divertor of a future fusion reactor are characterized by extreme heat and particle fluxes interacting with the plasma-facing surfaces. Powerful linear plasma generators are used to reproduce the expected plasma conditions and allow plasma-surface interactions studies under those very harsh conditions. While the ion energies on the divertor surfaces of a fusion device are comparable to those used in various plasma-assited deposition and etching techniques, the ion (and energy fluxes are up to four orders of magnitude higher. This large upscale in particle flux maintains the surface under highly non-equilibrium conditions and bring new effects to light, some of which will be described in this paper.

  12. Design of a heating system for plasma flux simulation

    OpenAIRE

    Fallas-Chinchilla, Juan Carlos; Fallas-Agüero, Manuel; Del Valle-Gamboa, Juan Ignacio; Fonseca-Flores, Luis Diego

    2013-01-01

    VASIMR® plasma rocket and its possible applications are promoting innovations in the space propulsion area. Ad Astra Rocket Company (VASIMR® designer) constantly needs instruments to evaluate the plasma engine and its components, in order to acquire critical information to warrant a safe operation. This study describes the design and construction of a heating system, to simulate a plasma flux within a ceramic tube. This part of the engine plays a critical role, transporting a gas to ionize at...

  13. An improved mechanistic critical heat flux model for subcooled flow boiling

    Energy Technology Data Exchange (ETDEWEB)

    Kwon, Young Min [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of); Chang, Soon Heung [Korea Advanced Institute of Science and Technology, Taejon (Korea, Republic of)

    1997-12-31

    Based on the bubble coalescence adjacent to the heated wall as a flow structure for CHF condition, Chang and Lee developed a mechanistic critical heat flux (CHF) model for subcooled flow boiling. In this paper, improvements of Chang-Lee model are implemented with more solid theoretical bases for subcooled and low-quality flow boiling in tubes. Nedderman-Shearer`s equations for the skin friction factor and universal velocity profile models are employed. Slip effect of movable bubbly layer is implemented to improve the predictability of low mass flow. Also, mechanistic subcooled flow boiling model is used to predict the flow quality and void fraction. The performance of the present model is verified using the KAIST CHF database of water in uniformly heated tubes. It is found that the present model can give a satisfactory agreement with experimental data within less than 9% RMS error. 9 refs., 5 figs. (Author)

  14. Mixed convective heat transfer in an inclined cavity with multiple heated elements on one wall

    Science.gov (United States)

    Oosthuizen, P. H.; de Champlain, A.

    1989-06-01

    A numerical investigation has been conducted into mixed forced and free convective heat transfer through a rectangular cavity having two or three identical rectangular elements on the walls, whose faces are heated to a uniform temperature, in the case where the forced flow enters and leaves through the same wall. The study employs the two-dimensional Navier-Stokes, energy, and continuity equations, under assumptions of steady and laminar flow characteristics. Solution parameters are Reynolds number, Grashof number, fluid Prandtl number, cavity aspect ratio, cavity inclination angle, inlet and outlet duct size, and position and aspect ratio of the heated elements.

  15. Observational & modeling analysis of surface heat and moisture fluxes

    Energy Technology Data Exchange (ETDEWEB)

    Smith, E. [Florida State Univ., Tallahassee, FL (United States)

    1995-09-01

    An observational and modeling study was conducted to help assess how well current GCMs are predicting surface fluxes under the highly variable cloudiness and flow conditions characteristic of the real atmosphere. The observational data base for the study was obtained from a network of surface flux stations operated during the First ISLSCP Field Experiment (FIFE). The study included examination of a surface-driven secondary circulation in the boundary layer resulting from a persistent cross-site gradient in soil moisture, to demonstrate the sensitivity of boundary layer dynamics to heterogeneous surface fluxes, The performance of a biosphere model in reproducing the measured surface fluxes was evaluated with and without the use of satellite retrieval of three key canopy variables with RMS uncertainties commensurate with those of the measurements themselves. Four sensible heat flux closure schemes currently being used in GCMs were then evaluated against the FIFE observations. Results indicate that the methods by which closure models are calibrated lead to exceedingly large errors when the schemes are applied to variable boundary layer conditions. 4 refs., 2 figs.

  16. Radiative heat transfer estimation in pipes with various wall emissivities

    Science.gov (United States)

    Robin, Langebach; Christoph, Haberstroh

    2017-02-01

    Radiative heat transfer is usually of substantial importance in cryogenics when systems are designed and thermal budgeting is carried out. However, the contribution of pipes is commonly assumed to be comparably low since the warm and cold ends as well as their cross section are fairly small. Nevertheless, for a first assessment of each pipe rough estimates are always appreciated. In order to estimate the radiative heat transfer with traditional “paper and pencil“ methods there is only one analytical case available in literature - the case of plane-parallel plates. This case can only be used to calculate the theoretical lower and the upper asymptotic values of the radiative heat transfer, since pipe wall radiation properties are not taken into account. For this paper we investigated the radiative heat transfer estimation in pipes with various wall emissivities with the help of numerical simulations. Out of a number of calculation series we could gain an empirical extension for the used approach of plane-parallel plates. The model equation can be used to carry out enhanced paper and pencil estimations for the radiative heat transfer through pipes without demanding numerical simulations.

  17. Soil heat flux and day time surface energy balance closure at ...

    Indian Academy of Sciences (India)

    Soil heat flux is an important input component of surface energy balance. Estimates of soil heat flux were made in the year 2008 using soil temperature data at Astronomical Observatory, Thiruvananthapuram, south Kerala. Hourly values of soil heat flux from 00 to 24 LST are presented for selected days typical of the winter ...

  18. Soil heat flux and day time surface energy balance closure at ...

    Indian Academy of Sciences (India)

    Soil heat flux is an important input component of surface energy balance. Estimates of soil heat flux were made in the year 2008 using soil temperature data at Astronomical Observatory, Thiruvananthapuram, south Kerala. Hourly values of soil heat flux from 00 to 24 LST are presented for selected days typical of the winter, ...

  19. Modern perspectives on measuring and interpreting seafloor heat flux

    Science.gov (United States)

    Harris, Reid N.; Fisher, A.; Ruppel, C.; Martinez, F.

    2008-01-01

    There has been a resurgence of interest in marine heat flow in the past 10–15 years, coinciding with fundamental achievements in understanding the Earth's thermal state and quantifying the dynamics and impacts of material and energy fluxes within and between the lithosphere and hydrosphere. At the same time, technical capabilities have dwindled to the point that no U.S. academic institution currently operates a seagoing heat flow capacity.In September 2007, a workshop was convened in Salt Lake City with sponsorship from the U.S. National Science Foundation (NSF) and participation by scientists and engineers from North America, Europe, and Asia. The primary goals of the workshop were to (1) assess high-priority scientific and technical needs and (2) to evaluate options for developing and maintaining essential capabilities in marine heat flow for the U.S. scientific community.

  20. Solar Flux Deposition And Heating Rates In Jupiter's Atmosphere

    Science.gov (United States)

    Perez-Hoyos, Santiago; Sánchez-Lavega, A.

    2009-09-01

    We discuss here the solar downward net flux in the 0.25 - 2.5 µm range in the atmosphere of Jupiter and the associated heating rates under a number of vertical cloud structure scenarios focusing in the effect of clouds and hazes. Our numerical model is based in the doubling-adding technique to solve the radiative transfer equation and it includes gas absorption by CH4, NH3 and H2, in addition to Rayleigh scattering by a mixture of H2 plus He. Four paradigmatic Jovian regions have been considered (hot-spots, belts, zones and Polar Regions). The hot-spots are the most transparent regions with downward net fluxes of 2.5±0.5 Wm-2 at the 6 bar level. The maximum solar heating is 0.04±0.01 K/day and occurs above 1 bar. Belts and zones characterization result in a maximum net downward flux of 0.5 Wm-2 at 2 bar and 0.015 Wm-2 at 6 bar. Heating is concentrated in the stratospheric and tropospheric hazes. Finally, Polar Regions are also explored and the results point to a considerable stratospheric heating of 0.04±0.02 K/day. In all, these calculations suggest that the role of the direct solar forcing in the Jovian atmospheric dynamics is limited to the upper 1 - 2 bar of the atmosphere except in the hot-spot areas. Acknowledgments: This work has been funded by Spanish MEC AYA2006-07735 with FEDER support and Grupos Gobierno Vasco IT-464-07.

  1. Gradient heat flux measurement as monitoring method for the diesel engine

    Science.gov (United States)

    Sapozhnikov, S. Z.; Mityakov, V. Yu; Mityakov, A. V.; Vintsarevich, A. V.; Pavlov, A. V.; Nalyotov, I. D.

    2017-11-01

    The usage of gradient heat flux measurement for monitoring of heat flux on combustion chamber surface and optimization of diesel work process is proposed. Heterogeneous gradient heat flux sensors can be used at various regimes for an appreciable length of time. Fuel injection timing is set by the position of the maximum point on the angular heat flux diagram however, the value itself of the heat flux may not be considered. The development of such an approach can be productive for remote monitoring of work process in the cylinders of high-power marine engines.

  2. Alongshore wind stress and heat flux divergence off Visakhapatnam, east coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Sadhuram, Y.; Rao, B.P.; Rao, D.P.

    Annual variation of heat flux divergence (Qv) was computed for the coastal waters of Visakhapatnam. The mean values of net heat exchange (Qn) and heat flux divergence (Qv) were found to be 114 and 115 W.m/2 respectively on annual scale. The net heat...

  3. Investigation of the effects of pressure gradient, temperature and wall temperature ratio on the stagnation point heat transfer for circular cylinders and gas turbine vanes

    Science.gov (United States)

    Nagamatsu, H. T.; Duffy, R. E.

    1984-01-01

    Low and high pressure shock tubes were designed and constructed for the purpose of obtaining heat transfer data over a temperature range of 390 to 2500 K, pressures of 0.3 to 42 atm, and Mach numbers of 0.15 to 1.5 with and without pressure gradient. A square test section with adjustable top and bottom walls was constructed to produce the favorable and adverse pressure gradient over the flat plate with heat gages. A water cooled gas turbine nozzle cascade which is attached to the high pressure shock tube was obtained to measuse the heat flux over pressure and suction surfaces. Thin-film platinum heat gages with a response time of a few microseconds were developed and used to measure the heat flux for laminar, transition, and turbulent boundary layers. The laminar boundary heat flux on the shock tube wall agreed with Mirel's flat plate theory. Stagnation point heat transfer for circular cylinders at low temperature compared with the theoretical prediction, but for a gas temperature of 922 K the heat fluxes were higher than the predicted values. Preliminary flat plate heat transfer data were measured for laminar, transition, and turbulent boundary layers with and without pressure gradients for free-stream temperatures of 350 to 2575 K and flow Mach numbers of 0.11 to 1.9. The experimental heat flux data were correlated with the laminar and turbulent theories and the agreement was good at low temperatures which was not the case for higher temperatures.

  4. Investigation of Body Force Effects on Flow Boiling Critical Heat Flux

    Science.gov (United States)

    Zhang, Hui; Mudawar, Issam; Hasan, Mohammad M.

    2002-11-01

    The bubble coalescence and interfacial instabilities that are important to modeling critical heat flux (CHF) in reduced-gravity systems can be sensitive to even minute body forces. Understanding these complex phenomena is vital to the design and safe implementation of two-phase thermal management loops proposed for space and planetary-based thermal systems. While reduced gravity conditions cannot be accurately simulated in 1g ground-based experiments, such experiments can help isolate the effects of the various forces (body force, surface tension force and inertia) which influence flow boiling CHF. In this project, the effects of the component of body force perpendicular to a heated wall were examined by conducting 1g flow boiling experiments at different orientations. FC-72 liquid was boiled along one wall of a transparent rectangular flow channel that permitted photographic study of the vapor-liquid interface at conditions approaching CHF. High-speed video imaging was employed to capture dominant CHF mechanisms. Six different CHF regimes were identified: Wavy Vapor Layer, Pool Boiling, Stratification, Vapor Counterflow, Vapor Stagnation, and Separated Concurrent Vapor Flow. CHF showed great sensitivity to orientation for flow velocities below 0.2 m/s, where very small CHF values where measured, especially with downflow and downward-facing heated wall orientations. High flow velocities dampened the effects of orientation considerably. Figure I shows representative images for the different CHF regimes. The Wavy Vapor Layer regime was dominant for all high velocities and most orientations, while all other regimes were encountered at low velocities, in the downflow and/or downward-facing heated wall orientations. The Interfacial Lift-off model was modified to predict the effects of orientation on CHF for the dominant Wavy Vapor Layer regime. The photographic study captured a fairly continuous wavy vapor layer travelling along the heated wall while permitting liquid

  5. High-heat-flux sensor calibration using calorimetry

    Science.gov (United States)

    Ballestrín, J.; Estrada, C. A.; Rodríguez-Alonso, M.; Pérez-Rábago, C.; Langley, L. W.; Barnes, A.

    2004-08-01

    This paper demonstrates a calorimetric procedure for calibrating high-heat-flux sensors. The results are in agreement with calibrations obtained using black-body radiation. However, the proposed method has the potential of being more accurate than traditional approaches. This new procedure calibrates sensors to measure correctly under conditions of concentrated solar radiation. At present, the thermal balance calibration technique in the laboratory is limited to solar irradiances of approximately 100 kW m-2. The next step is to demonstrate this methodology to higher irradiances under non-laboratory conditions in the CIEMAT solar furnace at Plataforma Solar de Almería.

  6. Heat Flux and Entropy Produced by Thermal Fluctuations

    DEFF Research Database (Denmark)

    Ciliberto, S.; Imparato, Alberto; Naert, A.

    2013-01-01

    We report an experimental and theoretical analysis of the energy exchanged between two conductors kept at different temperature and coupled by the electric thermal noise. Experimentally we determine, as functions of the temperature difference, the heat flux, the out-of-equilibrium variance......, and a conservation law for the fluctuating entropy, which we justify theoretically. The system is ruled by the same equations as two Brownian particles kept at different temperatures and coupled by an elastic force. Our results set strong constraints on the energy exchanged between coupled nanosystems held...

  7. Radiant heat transfer network in the simulated protective clothing ; System under high heat flux

    NARCIS (Netherlands)

    Fukazawa, T.; Hartog, E.A. den; Daanen, H.A.M.; Penders-van Elk, N.; Tochihara, Y.; Havenith, G.

    2005-01-01

    A radiant network model was developed for design of the protective clothing system against solar and infrared radiative heat flux. A one-dimensional model was employed in the present study, because the aim of this study was to obtain precise temperature distribution through the system with use of a

  8. Surface wettability effects on critical heat flux of boiling heat transfer using nanoparticle coatings

    KAUST Repository

    Hsu, Chin-Chi

    2012-06-01

    This study investigates the effects of surface wettability on pool boiling heat transfer. Nano-silica particle coatings were used to vary the wettability of the copper surface from superhydrophilic to superhydrophobic by modifying surface topography and chemistry. Experimental results show that critical heat flux (CHF) values are higher in the hydrophilic region. Conversely, CHF values are lower in the hydrophobic region. The experimental CHF data of the modified surface do not fit the classical models. Therefore, this study proposes a simple model to build the nexus between the surface wettability and the growth of bubbles on the heating surface. © 2012 Elsevier Ltd. All rights reserved.

  9. O+ and H+ ion heat fluxes at high altitudes and high latitudes

    Directory of Open Access Journals (Sweden)

    I. A. Barghouthi

    2014-08-01

    Full Text Available Higher order moments, e.g., perpendicular and parallel heat fluxes, are related to non-Maxwellian plasma distributions. Such distributions are common when the plasma environment is not collision dominated. In the polar wind and auroral regions, the ion outflow is collisionless at altitudes above about 1.2 RE geocentric. In these regions wave–particle interaction is the primary acceleration mechanism of outflowing ionospheric origin ions. We present the altitude profiles of actual and "thermalized" heat fluxes for major ion species in the collisionless region by using the Barghouthi model. By comparing the actual and "thermalized" heat fluxes, we can see whether the heat flux corresponds to a small perturbation of an approximately bi-Maxwellian distribution (actual heat flux is small compared to "thermalized" heat flux, or whether it represents a significant deviation (actual heat flux equal or larger than "thermalized" heat flux. The model takes into account ion heating due to wave–particle interactions as well as the effects of gravity, ambipolar electric field, and divergence of geomagnetic field lines. In the discussion of the ion heat fluxes, we find that (1 the role of the ions located in the energetic tail of the ion velocity distribution function is very significant and has to be taken into consideration when modeling the ion heat flux at high altitudes and high latitudes; (2 at times the parallel and perpendicular heat fluxes have different signs at the same altitude. This indicates that the parallel and perpendicular parts of the ion energy are being transported in opposite directions. This behavior is the result of many competing processes; (3 we identify altitude regions where the actual heat flux is small as compared to the "thermalized" heat flux. In such regions we expect transport equation solutions based on perturbations of bi-Maxwellian distributions to be applicable. This is true for large altitude intervals for protons

  10. Diamond thin film temperature and heat-flux sensors

    Science.gov (United States)

    Aslam, M.; Yang, G. S.; Masood, A.; Fredricks, R.

    1995-01-01

    Diamond film temperature and heat-flux sensors are developed using a technology compatible with silicon integrated circuit processing. The technology involves diamond nucleation, patterning, doping, and metallization. Multi-sensor test chips were designed and fabricated to study the thermistor behavior. The minimum feature size (device width) for 1st and 2nd generation chips are 160 and 5 micron, respectively. The p-type diamond thermistors on the 1st generation test chip show temperature and response time ranges of 80-1270 K and 0.29-25 microseconds, respectively. An array of diamond thermistors, acting as heat flux sensors, was successfully fabricated on an oxidized Si rod with a diameter of 1 cm. Some problems were encountered in the patterning of the Pt/Ti ohmic contacts on the rod, due mainly to the surface roughness of the diamond film. The use of thermistors with a minimum width of 5 micron (to improve the spatial resolution of measurement) resulted in lithographic problems related to surface roughness of diamond films. We improved the mean surface roughness from 124 nm to 30 nm by using an ultra high nucleation density of 10(exp 11)/sq cm. To deposit thermistors with such small dimensions on a curved surface, a new 3-D diamond patterning technique is currently under development. This involves writing a diamond seed pattern directly on the curved surface by a computer-controlled nozzle.

  11. Contact angle and droplet heat transfer during evaporation on structured and smooth surfaces of heated wall

    Science.gov (United States)

    Misyura, S. Y.

    2017-08-01

    Water evaporation in a wide range of droplet diameters and wall temperatures on the structured and smooth surfaces were studied experimentally. Linear dependence of evaporation rate (dV/dt) on a droplet radius varies when the volume is greater than 40-60 μl. The static contact angles on the structured surface vary with a droplet diameter for high wall superheating. Dependence of the contact angle on diameter for the corrugated surface is defined by a change in both potential energy barrier U and three-phase contact line tension τcl. This energy barrier for the structured wall changes with an increase in the initial droplet diameter and becomes constant for the large droplets. For high wall superheating, the power in the law of evaporation increases from 1 to 1.45 with an increase in the initial droplet diameter. Depending on the droplet radius, number of droplets and heater length, four different characters of evaporation are realized. Complete droplet evaporation time on structured surface is less than smooth wall. Heat transfer coefficient is greater for structured wall than smooth one. When simulating droplet evaporation and heat transfer, it is necessary to take into account free convection of air and vapor.

  12. A modified force-restore approach to modeling snow-surface heat fluxes

    Science.gov (United States)

    Charles H. Luce; David G. Tarboton

    2001-01-01

    Accurate modeling of the energy balance of a snowpack requires good estimates of the snow surface temperature. The snow surface temperature allows a balance between atmospheric heat fluxes and the conductive flux into the snowpack. While the dependency of atmospheric fluxes on surface temperature is reasonably well understood and parameterized, conduction of heat from...

  13. Magnetic flux penetration into finite length thin-walled niobium cylinders

    Science.gov (United States)

    Tsindlekht, M. I.; Genkin, V. M.; Felner, I.; Zeides, F.; Katz, N.; Gazi, Š.; Chromik, Š.; Kolăcek, J.; Maryško, M.

    2018-02-01

    The distribution of magnetic field in a finite thin-walled Nb superconducting cylinder in an axial magnetic field is analyzed. Both current density and magnetic field exhibit strong maximum in the cylinder edges. This triggers a giant flux jump in the hollow cylinder when a slowly increasing external magnetic field reaches a threshold value. Experimentally measured flux jumps were observed in a wide range of external fields, even below Hc1 of the Nb film. The field at which the jumps appear is temperature dependent. It was found that with increasing the wall thickness the singularity of the current density and magnetic field on the edges decreases, which explains the absence of giant jumps in a sample with thick walls in fields below Hc1.

  14. β-distribution for Reynolds stress and turbulent heat flux in relaxation turbulent boundary layer of compression ramp

    Science.gov (United States)

    Hu, YanChao; Bi, WeiTao; Li, ShiYao; She, ZhenSu

    2017-12-01

    A challenge in the study of turbulent boundary layers (TBLs) is to understand the non-equilibrium relaxation process after sep-aration and reattachment due to shock-wave/boundary-layer interaction. The classical boundary layer theory cannot deal with the strong adverse pressure gradient, and hence, the computational modeling of this process remains inaccurate. Here, we report the direct numerical simulation results of the relaxation TBL behind a compression ramp, which reveal the presence of intense large-scale eddies, with significantly enhanced Reynolds stress and turbulent heat flux. A crucial finding is that the wall-normal profiles of the excess Reynolds stress and turbulent heat flux obey a β-distribution, which is a product of two power laws with respect to the wall-normal distances from the wall and from the boundary layer edge. In addition, the streamwise decays of the excess Reynolds stress and turbulent heat flux also exhibit power laws with respect to the streamwise distance from the corner of the compression ramp. These results suggest that the relaxation TBL obeys the dilation symmetry, which is a specific form of self-organization in this complex non-equilibrium flow. The β-distribution yields important hints for the development of a turbulence model.

  15. Effects of ridged walls on the heat transfer in a heated square duct

    Energy Technology Data Exchange (ETDEWEB)

    Vazquez, M.S.; Rodriguez, W.V. [Ciudad Universitaria, Mexico DF (Mexico). Instituto de Ingenieria, UNAM, Coordinacion de Ingenieria de Procesos Industrails y Ambientales, Circuito Interior; Issa, R. [LEGI-MOST, INPG, Grenoble (France)

    2005-05-01

    Turbulent flows in rectangular cooling ducts of rocket engine thrust chambers are characterized by secondary motions of Prandtl's first and second kinds. These secondary currents play a prominent part in heat transfer between the thrust chamber and the cooling gas conveyed in the duct. Previous numerical and experimental works reveal that attaching ridges on the walls of the duct causes the formation of new secondary flows of Prandtl's second kind. These new structures are likely to increase the heat transfer. The present study has investigated numerically, through large eddy simulations, the effects of different forms of ridges on heat transfer in straight square duct flows. (author)

  16. Design and calibration of a novel transient radiative heat flux meter for a spacecraft thermal test.

    Science.gov (United States)

    Sheng, Chunchen; Hu, Peng; Cheng, Xiaofang

    2016-06-01

    Radiative heat flux measurement is significantly important for a spacecraft thermal test. To satisfy the requirements of both high accuracy and fast response, a novel transient radiative heat flux meter was developed. Its thermal receiver consists of a central thermal receiver and two thermal guarded annular plates, which ensure the temperature distribution of the central thermal receiver to be uniform enough for reasonably applying lumped heat capacity method in a transient radiative heat flux measurement. This novel transient radiative heat flux meter design can also take accurate measurements regardless of spacecraft surface temperature and incident radiation spectrum. The measurement principle was elaborated and the coefficients were calibrated. Experimental results from testing a blackbody furnace and an Xenon lamp show that this novel transient radiative heat flux meter can be used to measure transient radiative heat flux up to 1400 W/m(2) with high accuracy and the response time of less than 10 s.

  17. Application of the Critical Heat Flux Look-Up Table to Large Diameter Tubes

    Directory of Open Access Journals (Sweden)

    M. El Nakla

    2013-01-01

    Full Text Available The critical heat flux look-up table was applied to a large diameter tube, namely 67 mm inside diameter tube, to predict the occurrence of the phenomenon for both vertical and horizontal uniformly heated tubes. Water was considered as coolant. For the vertical tube, a diameter correction factor was directly applied to the 1995 critical heat flux look-up table. To predict the occurrence of critical heat flux in horizontal tube, an extra correction factor to account for flow stratification was applied. Both derived tables were used to predict the effect of high heat flux and tube blockage on critical heat flux occurrence in boiler tubes. Moreover, the horizontal tube look-up table was used to predict the safety limits of the operation of boiler for 50% allowable heat flux.

  18. Full velocity-scalar probability density function computation of heated channel flow with wall function approach

    Science.gov (United States)

    Pozorski, Jacek; Wacławczyk, Marta; Minier, Jean-Pierre

    2003-05-01

    A joint velocity-scalar probability density function (PDF) method is presented to model and simulate turbulent flows with passive inert scalars (here temperature). The full PDF approach is applied for wall-bounded flows. In the present work, the boundary conditions are imposed in the logarithmic region and the modeling is therefore performed in the wall-function spirit. The PDF equation is solved by a Monte Carlo method and the whole approach appears as a Lagrangian simulation using stochastic particles. The purpose of the work is to analyze the behavior of classical PDF models in the near-wall region and to develop new particle boundary conditions for the velocity and scalars attached to each particle. First of all, the logarithmic region is described as an equilibrium zone and resulting analytical formulas for second-order temperature-velocity statistics , , are derived. Boundary conditions for scalars are then developed and formulated in terms of instantaneous particle variables. These results are useful to discuss consistency issues between the formulation of scalar mixing models and the statement of boundary conditions. Finally, heated channel flow is simulated with a stand-alone PDF code for two different heat-flux conditions and results are compared with available direct numerical simulation and experimental data.

  19. Ignition and flame spread properties of wood, elaborated during a new test method based on convective heat flux

    DEFF Research Database (Denmark)

    Sørensen, Lars Schiøtt

    Ignition and flame spread properties on selected types of wood and wall papers are elaborated. Tests are established in a new test setup in which the test specimen can be fixed in different angles due to a horizontal level. The heat exposing the test objects is arranged as a convective flux......, established from a Bunsen burners pilot flame. This principal is somewhat in contrast to the more typical radiation established fluxes. For instance, the ISO 9239 (DS 2000) test method is based on a gas fired radiant panel. And in the ISO 5657 standard, the ignition properties are investigated on test...

  20. One-dimensional Simulation of Heat Structure Melting and Evaporation Under High Heat Flux Condition Using MARS

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Geon-Woo; Lee, Jeong-Hun; Cho, Hyoung-Kyu; Park, Goon-Cherl [Seoul National University, Seoul (Korea, Republic of); Im, Kihak [National Fusion Research Institute, Daejeon (Korea, Republic of)

    2016-10-15

    In order to establish the successful application for high heat flux condition, it is necessary to analyze material damage including possible phase change such as melting and evaporation due to high heat flux. In addition, in terms of coolant, water which is widely used for coolant has serious concern in that critical heat flux (CHF) occurrence can degrade the cooling capability and aggravate the integrity of cooling components. However, MARS code cannot simulate the melting and evaporation of materials under high heat flux or heat generation condition by itself due to the absence of those models. In the present study, therefore, one dimensional heat conduction calculation module for heat structure melting and evaporation was developed and coupled with MARS to overcome the limitation of material phase change simulation capability in MARS code. As clarifying the high heat flux problem, plasma facing component of Korean demonstration fusion reactor, K-DEMO, was selected. The one-dimensional simulation of melting and evaporation of high heat flux component was performed using MARS and newly developed phase change simulation module. The target component and high heat flux condition were referred to geometry of plasma facing component in Korean fusion demonstration plant and fusion reactor's plasma disruption event. In order to simulate melting and evaporation, effective heat capacity method and evaporation model were applied to phase change simulation module. The simulation results showed several phenomena such as melting, evaporation and CHF occurrence in coolant channel.

  1. Infrared thermography with non-uniform heat flux boundary conditions on the rotor endwall of an axial turbine

    Science.gov (United States)

    Lazzi Gazzini, S.; Schädler, R.; Kalfas, A. I.; Abhari, R. S.

    2017-02-01

    It is technically challenging to measure heat fluxes on the rotating components of gas turbines, yet accurate knowledge of local heat loads under engine-representative conditions is crucial for ensuring the reliability of the designs. In this work, quantitative image processing tools were developed to perform fast and accurate infrared thermography measurements on 3D-shaped film-heaters directly deposited on the turbine endwalls. The newly developed image processing method and instrumentation were used to measure the heat load on the rotor endwalls of an axial turbine. A step-transient heat flux calibration technique is applied to measure the heat flux generated locally by the film heater, thus eliminating the need for a rigorously iso-energetic boundary condition. On-board electronics installed on the rotor record the temperature readings of RTDs installed in the substrate below the heaters in order to evaluate the conductive losses in the solid. Full maps of heat transfer coefficient and adiabatic wall temperature are produced for two different operating conditions, demonstrating the sensitivity of the technique to local flow features and variations in heat transfer due to Reynolds number effect.

  2. Comprehensive Analysis of Convective Heat Transfer in Parallel Plate Microchannel with Viscous Dissipation and Constant Heat Flux Boundary Conditions

    Science.gov (United States)

    Kushwaha, Hari Mohan; Sahu, Santosh Kumar

    2017-10-01

    This paper reports the hydrodynamically and thermally fully developed, laminar, incompressible, forced convective heat transfer characteristics of gaseous flows through a parallel plate microchannel with different constant heat flux boundary conditions. The first order velocity slip and viscous dissipation effects are considered in the analysis. Here, three different thermal boundary conditions such as: both plates kept at different constant heat fluxes, both plates kept at equal constant heat fluxes and one plate kept at constant heat flux and other one insulated are considered for the analysis. The deviation in Nusselt number between the model that considers both first order velocity slip and temperature jump and the one that considers only velocity slip is reported. Also, the effect of various heat flux ratios on the Nusselt number is reported in this analysis. In addition, the deviation in Nusselt number between first and second order slip model is discussed in this study.

  3. Beam heat load due to geometrical and resistive wall impedance in COLDDIAG

    Science.gov (United States)

    Casalbuoni, S.; Migliorati, M.; Mostacci, A.; Palumbo, L.; Spataro, B.

    2012-11-01

    One of the still open issues for the development of superconductive insertion devices is the understanding of the heat intake from the electron beam. With the aim of measuring the beam heat load to a cold bore and the hope to gain a deeper understanding in the underlying mechanisms, a cold vacuum chamber for diagnostics (COLDDIAG) was built. It is equipped with the following instrumentation: retarding field analyzers to measure the electron flux, temperature sensors to measure the beam heat load, pressure gauges, and mass spectrometers to measure the gas content. Possible beam heat load sources are: synchrotron radiation, wakefield effects due to geometrical and resistive wall impedance and electron/ion bombardment. The flexibility of the engineering design will allow the installation of the cryostat in different synchrotron light sources. COLDDIAG was first installed in the Diamond Light Source (DLS) in 2011. Due to a mechanical failure of the thermal transition of the cold liner, the cryostat had to be removed after one week of operation. After having implemented design changes in the thermal liner transition, COLDDIAG has been reinstalled in the DLS at the end of August 2012. In order to understand the beam heat load mechanism it is important to compare the measured COLDDIAG parameters with theoretical expectations. In this paper we report on the analytical and numerical computation of the COLDDIAG beam heat load due to coupling impedances deriving from unavoidable step transitions, ports used for pumping and diagnostics, surface roughness, and resistive wall. The results might have an important impact on future technological solutions to be applied to cold bore devices.

  4. Scaling Flux Tower Observations of Sensible Heat Flux Using Weighted Area-to-Area Regression Kriging

    Directory of Open Access Journals (Sweden)

    Maogui Hu

    2015-07-01

    Full Text Available Sensible heat flux (H plays an important role in characterizations of land surface water and heat balance. There are various types of H measurement methods that depend on observation scale, from local-area-scale eddy covariance (EC to regional-scale large aperture scintillometer (LAS and remote sensing (RS products. However, methods of converting one H scale to another to validate RS products are still open for question. A previous area-to-area regression kriging-based scaling method performed well in converting EC-scale H to LAS-scale H. However, the method does not consider the path-weighting function in the EC- to LAS-scale kriging with the regression residue, which inevitably brought about a bias estimation. In this study, a weighted area-to-area regression kriging (WATA RK model is proposed to convert EC-scale H to LAS-scale H. It involves path-weighting functions of EC and LAS source areas in both regression and area kriging stages. Results show that WATA RK outperforms traditional methods in most cases, improving estimation accuracy. The method is considered to provide an efficient validation of RS H flux products.

  5. Regional heat flux over the NOPEX area estimated from the evolution of the mixed-layer

    DEFF Research Database (Denmark)

    Gryning, Sven-Erik; Batchvarova, E.

    1999-01-01

    of forest, agricultural fields, mires and lakes within the boreal zone, was determined for 3 days of the campaign in 1994. It was found to be lower than the heat flux over forest and higher than the heat Aux over agricultural fields. The regional heat flux estimated by the mixed-layer evolution method...

  6. Effect of wall-mounted obstacles on mixed convection heat transfer in an open channel with multiple discrete heaters

    Science.gov (United States)

    Rafi, Araf Al; Anik, Rahagir Ridwan; Sarah, Anika

    2017-12-01

    In this study a numerical investigation on two dimensional laminar steady mixed convection has been carried out in an open channel with upper wall mounted with obstacles and the lower wall is provided with different types of protruding multiple discrete heaters. The upper wall is maintained at constant low temperature. All obstacles are isotherm and have the same temperature as the walls. The heaters are also connected with adiabatic segments and the heater surfaces are assumed to release heat at constant heat flux. At inlet, a uniform velocity profile has been induced. To avoid discontinuity, the temperature of the incoming stream is supposed to change linearly. The working fluid used in this study is air and Boussinesq approximation has been applied for fluid having constant properties. Finite element method has been used to solve the non-dimensionalised governing equations of conservation of mass, momentum, and energy along with the boundary conditions. Effect of various parameters such as Reynolds number (Re), Grashof number(Gr) and Richardson number (Ri) on temperature distribution, flow patterns and heat transfer rate has been studied. The results show that increasing the Reynolds number while keeping Ri=1 gives better cooling performance. It has been observed that the wall-mounted obstacles over the channel wall, increases the Nusselt number when compared to the simple channel.

  7. Impact of melting heat transfer and nonlinear radiative heat flux mechanisms for the generalized Burgers fluids

    Directory of Open Access Journals (Sweden)

    Waqar Azeem Khan

    Full Text Available The present paper deals with the analysis of melting heat and mass transfer characteristics in the stagnation point flow of an incompressible generalized Burgers fluid over a stretching sheet in the presence of non-linear radiative heat flux. A uniform magnetic field is applied normal to the flow direction. The governing equations in dimensional form are reduced to a system of dimensionless expressions by implementation of suitable similarity transformations. The resulting dimensionless problem governing the generalized Burgers is solved analytically by using the homotopy analysis method (HAM. The effects of different flow parameters like the ratio parameter, magnetic parameter, Prandtl number, melting parameter, radiation parameter, temperature ratio parameter and Schmidt number on the velocity, heat and mass transfer characteristics are computed and presented graphically. Moreover, useful discussions in detail are carried out with the help of plotted graphs and tables. Keywords: Generalized Burgers fluid, Non-linear radiative flow, Magnetic field, Melting heat transfer

  8. Hybrid Heat Pipes for Lunar and Martian Surface and High Heat Flux Space Applications

    Science.gov (United States)

    Ababneh, Mohammed T.; Tarau, Calin; Anderson, William G.; Farmer, Jeffery T.; Alvarez-Hernandez, Angel R.

    2016-01-01

    Novel hybrid wick heat pipes are developed to operate against gravity on planetary surfaces, operate in space carrying power over long distances and act as thermosyphons on the planetary surface for Lunar and Martian landers and rovers. These hybrid heat pipes will be capable of operating at the higher heat flux requirements expected in NASA's future spacecraft and on the next generation of polar rovers and equatorial landers. In addition, the sintered evaporator wicks mitigate the start-up problems in vertical gravity aided heat pipes because of large number of nucleation sites in wicks which will allow easy boiling initiation. ACT, NASA Marshall Space Flight Center, and NASA Johnson Space Center, are working together on the Advanced Passive Thermal experiment (APTx) to test and validate the operation of a hybrid wick VCHP with warm reservoir and HiK"TM" plates in microgravity environment on the ISS.

  9. Results of high heat flux tests of tungsten divertor targets under plasma heat loads expected in ITER and tokamaks (review)

    Energy Technology Data Exchange (ETDEWEB)

    Budaev, V. P., E-mail: budaev@mail.ru [National Research Centre Kurchatov Institute (Russian Federation)

    2016-12-15

    Heat loads on the tungsten divertor targets in the ITER and the tokamak power reactors reach ~10MW m{sup −2} in the steady state of DT discharges, increasing to ~0.6–3.5 GW m{sup −2} under disruptions and ELMs. The results of high heat flux tests (HHFTs) of tungsten under such transient plasma heat loads are reviewed in the paper. The main attention is paid to description of the surface microstructure, recrystallization, and the morphology of the cracks on the target. Effects of melting, cracking of tungsten, drop erosion of the surface, and formation of corrugated and porous layers are observed. Production of submicron-sized tungsten dust and the effects of the inhomogeneous surface of tungsten on the plasma–wall interaction are discussed. In conclusion, the necessity of further HHFTs and investigations of the durability of tungsten under high pulsed plasma loads on the ITER divertor plates, including disruptions and ELMs, is stressed.

  10. Heat conduction in nanoscale materials: a statistical-mechanics derivation of the local heat flux.

    Science.gov (United States)

    Li, Xiantao

    2014-09-01

    We derive a coarse-grained model for heat conduction in nanoscale mechanical systems. Starting with an all-atom description, this approach yields a reduced model, in the form of conservation laws of momentum and energy. The model closure is accomplished by introducing a quasilocal thermodynamic equilibrium, followed by a linear response approximation. Of particular interest is the constitutive relation for the heat flux, which is expressed nonlocally in terms of the spatial and temporal variation of the temperature. Nanowires made of copper and silicon are presented as examples.

  11. Wedge Heat-Flux Indicators for Flash Thermography

    Science.gov (United States)

    Koshti, Ajay M.

    2003-01-01

    Wedge indicators have been proposed for measuring thermal radiation that impinges on specimens illuminated by flash lamps for thermographic inspection. Heat fluxes measured by use of these indicators would be used, along with known thermal, radiative, and geometric properties of the specimens, to estimate peak flash temperatures on the specimen surfaces. These indicators would be inexpensive alternatives to high-speed infrared pyrometers, which would otherwise be needed for measuring peak flash surface temperatures. The wedge is made from any suitable homogenous material such as plastic. The choice of material is governed by the equation given. One side of the wedge is covered by a temperature sensitive compound that decomposes irreversibly when its temperature exceeds a rated temperature (T-rated). The uncoated side would be positioned alongside or in place of the specimen and exposed to the flash, then the wedge thickness at the boundary between the white and blackened portions measured.

  12. Critical role of electron heat flux on Bohm criterion

    Science.gov (United States)

    Tang, Xian-Zhu; Guo, Zehua

    2016-12-01

    Bohm criterion, originally derived for an isothermal-electron and cold-ion plasma, is often used as a rule of thumb for more general plasmas. Here, we establish a more precise determination of the Bohm criterion that are quantitatively useful for understanding and modeling collisional plasmas that still have collisional mean-free-path much greater than plasma Debye length. Specifically, it is shown that electron heat flux, rather than the isothermal electron assumption, is what sets the Bohm speed to be √{ k B ( T e ∥ + 3 T i ∥ ) / m i } with T e , i ∥ the electron and ion parallel temperature at the sheath entrance and mi the ion mass.

  13. SPECTRAL data-based estimation of soil heat flux

    Science.gov (United States)

    Singh, R.K.; Irmak, A.; Walter-Shea, Elizabeth; Verma, S.B.; Suyker, A.E.

    2011-01-01

    Numerous existing spectral-based soil heat flux (G) models have shown wide variation in performance for maize and soybean cropping systems in Nebraska, indicating the need for localized calibration and model development. The objectives of this article are to develop a semi-empirical model to estimate G from a normalized difference vegetation index (NDVI) and net radiation (Rn) for maize (Zea mays L.) and soybean (Glycine max L.) fields in the Great Plains, and present the suitability of the developed model to estimate G under similar and different soil and management conditions. Soil heat fluxes measured in both irrigated and rainfed fields in eastern and south-central Nebraska were used for model development and validation. An exponential model that uses NDVI and Rn was found to be the best to estimate G based on r2 values. The effect of geographic location, crop, and water management practices were used to develop semi-empirical models under four case studies. Each case study has the same exponential model structure but a different set of coefficients and exponents to represent the crop, soil, and management practices. Results showed that the semi-empirical models can be used effectively for G estimation for nearby fields with similar soil properties for independent years, regardless of differences in crop type, crop rotation, and irrigation practices, provided that the crop residue from the previous year is more than 4000 kg ha-1. The coefficients calibrated from particular fields can be used at nearby fields in order to capture temporal variation in G. However, there is a need for further investigation of the models to account for the interaction effects of crop rotation and irrigation. Validation at an independent site having different soil and crop management practices showed the limitation of the semi-empirical model in estimating G under different soil and environment conditions.

  14. Description of heat flux measurement methods used in hydrocarbon and propellant fuel fires at Sandia.

    Energy Technology Data Exchange (ETDEWEB)

    Nakos, James Thomas

    2010-12-01

    The purpose of this report is to describe the methods commonly used to measure heat flux in fire applications at Sandia National Laboratories in both hydrocarbon (JP-8 jet fuel, diesel fuel, etc.) and propellant fires. Because these environments are very severe, many commercially available heat flux gauges do not survive the test, so alternative methods had to be developed. Specially built sensors include 'calorimeters' that use a temperature measurement to infer heat flux by use of a model (heat balance on the sensing surface) or by using an inverse heat conduction method. These specialty-built sensors are made rugged so they will survive the environment, so are not optimally designed for ease of use or accuracy. Other methods include radiometers, co-axial thermocouples, directional flame thermometers (DFTs), Sandia 'heat flux gauges', transpiration radiometers, and transverse Seebeck coefficient heat flux gauges. Typical applications are described and pros and cons of each method are listed.

  15. Accuracy of surface heat fluxes from observations of operational satellites

    Digital Repository Service at National Institute of Oceanography (India)

    Pankajakshan, T.; Sugimori, Y.

    Uncertainties in the flux estimates, resulting from the use of bulk method and remotely sensed data are worked out and are presented for individual and total fluxes. These uncertainties in satellite derived fluxes are further compared...

  16. Quantitative method for measuring heat flux emitted from a cryogenic object

    Science.gov (United States)

    Duncan, R.V.

    1993-03-16

    The present invention is a quantitative method for measuring the total heat flux, and of deriving the total power dissipation, of a heat-fluxing object which includes the steps of placing an electrical noise-emitting heat-fluxing object in a liquid helium bath and measuring the superfluid transition temperature of the bath. The temperature of the liquid helium bath is thereafter reduced until some measurable parameter, such as the electrical noise, exhibited by the heat-fluxing object or a temperature-dependent resistive thin film in intimate contact with the heat-fluxing object, becomes greatly reduced. The temperature of the liquid helum bath is measured at this point. The difference between the superfluid transition temperature of the liquid helium bath surrounding the heat-fluxing object, and the temperature of the liquid helium bath when the electrical noise emitted by the heat-fluxing object becomes greatly reduced, is determined. The total heat flux from the heat-fluxing object is determined as a function of this difference between these temperatures. In certain applications, the technique can be used to optimize thermal design parameters of cryogenic electronics, for example, Josephson junction and infrared sensing devices.

  17. Mixing rates and vertical heat fluxes north of Svalbard from Arctic winter to spring

    Science.gov (United States)

    Meyer, Amelie; Fer, Ilker; Sundfjord, Arild; Peterson, Algot K.

    2017-06-01

    Mixing and heat flux rates collected in the Eurasian Basin north of Svalbard during the N-ICE2015 drift expedition are presented. The observations cover the deep Nansen Basin, the Svalbard continental slope, and the shallow Yermak Plateau from winter to summer. Mean quiescent winter heat flux values in the Nansen Basin are 2 W m-2 at the ice-ocean interface, 3 W m-2 in the pycnocline, and 1 W m-2 below the pycnocline. Large heat fluxes exceeding 300 W m-2 are observed in the late spring close to the surface over the Yermak Plateau. The data consisting of 588 microstructure profiles and 50 days of high-resolution under-ice turbulence measurements are used to quantify the impact of several forcing factors on turbulent dissipation and heat flux rates. Wind forcing increases turbulent dissipation seven times in the upper 50 m, and doubles heat fluxes at the ice-ocean interface. The presence of warm Atlantic Water close to the surface increases the temperature gradient in the water column, leading to enhanced heat flux rates within the pycnocline. Steep topography consistently enhances dissipation rates by a factor of four and episodically increases heat flux at depth. It is, however, the combination of storms and shallow Atlantic Water that leads to the highest heat flux rates observed: ice-ocean interface heat fluxes average 100 W m-2 during peak events and are associated with rapid basal sea ice melt, reaching 25 cm/d.

  18. The effect of different aspect ratio and bottom heat flux towards contaminant removal using numerical analysis

    Science.gov (United States)

    Saadun, M. N. A.; Nor Azwadi, C. S.; Malek, Z. A. A.; Manaf, M. Z. A.; Zakaria, M. S.; Hafidzal, M. H. M.

    2013-12-01

    Cubic Interpolated Pseudo-particle (CIP) numerical simulation scheme has been anticipated to predict the interaction involving fluids and solid particles in an open channel with rectangular shaped cavity flow. The rectangular shaped cavity is looking by different aspect ratio in modelling the real pipeline joints that are in a range of sizes. Various inlet velocities are also being applied in predicting various fluid flow characteristics. In this paper, the constant heat flux is introduced at the bottom wall, showing the buoyancy effects towards the contaminant's removal rate. In order to characterize the fluid flow, the numerical scheme alone is initially tested and validated in a lid driven cavity with a single particle. The study of buoyancy effects and different aspect ratio of rectangular geometry were carried out using a MATLAB govern by Navier-Stokes equation. CIP is used as a model for a numerical scheme solver for fluid solid particles interaction. The result shows that the higher aspect ratio coupled with heated bottom wall give higher percentage of contaminant's removal rate. Comparing with the benchmark results has demonstrated the applicability of the method to reproduce fluid structure which is complex in the system. Despite a slight deviation of the formations of vortices from some of the literature results, the general pattern is considered to be in close agreement with those published in the literature.

  19. Comparison of heat flux measurement techniques during the DIII-D metal ring campaign

    Science.gov (United States)

    Barton, J. L.; Nygren, R. E.; Unterberg, E. A.; Watkins, J. G.; Makowski, M. A.; Moser, A.; Rudakov, D. L.; Buchenauer, D.

    2017-12-01

    The heat fluxes expected in the ITER divertor raise concerns about the damage tolerances of tungsten, especially due to thermal transients caused by edge localized modes (ELMs) as well as frequent temperature cycling from high to low extremes. Therefore we are motivated to understand the heat flux conditions that can cause not only enhanced erosion but also bulk thermo-mechanical damage to a tungsten divertor. For the metal ring campaign in DIII-D, tungsten-coated TZM tile inserts were installed making two toroidal arrays of metal tile inserts in the lower divertor. This study examines the deposited heat flux on these rings with embedded thermocouples (TCs) sampling at 10 kHz and compares them to Langmuir probe (LP) and infrared thermography (IRTV) heat flux measurements. We see agreement of the TC, LP, and IRTV data within 20% of the heat flux averaged over the entire discharge, and that all three diagnostics suggest parallel heat flux at the OSP location increases linearly with input heating power. The TC and LP heat flux time traces during the discharge trend together during large changes to the average heat flux. By subtracting the LP measured inter-ELM heat flux from TC data, using a rectangular ELM energy pulse shape, and taking the relative size and duration of each ELM from {{D}}α measurements, we extract the ELM heat fluxes from TC data. This over-estimates the IRTV measured ELM heat fluxes by a factor of 1.9, and could be due to the simplicity of the TC heat flux model and the assumed ELM energy pulse shape. ELM heat fluxes deposited on the inserts are used to model tungsten erosion in this campaign. These TC ELM heat flux estimates are used in addition to IRTV, especially in cases where the IRTV view to the metal ring is obstructed. We observe that some metal inserts were deformed due to exposed leading edges. The thermal conditions on these inserts are investigated with the thermal modeling code ABAQUS using our heat flux measurements when these edges

  20. Correlations of Nucleate Boiling Heat Transfer and Critical Heat Flux for External Reactor Vessel Cooling

    Energy Technology Data Exchange (ETDEWEB)

    J. Yang; F. B. Cheung; J. L. Rempe; K. Y. Suh; S. B. Kim

    2005-07-01

    Four types of steady-state boiling experiments were conducted to investigate the efficacy of two distinctly different heat transfer enhancement methods for external reactor vessel cooling under severe accident conditions. One method involved the use of a thin vessel coating and the other involved the use of an enhanced insulation structure. By comparing the results obtained in the four types of experiments, the separate and integral effect of vessel coating and insulation structure were determined. Correlation equations were obtained for the nucleate boiling heat transfer and the critical heat flux. It was found that both enhancement methods were quite effective. Depending on the angular location, the local critical heat flux could be enhanced by 1.4 to 2.5 times using vessel coating alone whereas it could be enhanced by 1.8 to 3.0 times using an enhanced insulation structure alone. When both vessel coating and insulation structure were used simultaneously, the integral effect on the enhancement was found much less than the product of the two separate effects, indicating possible competing mechanisms (i.e., interference) between the two enhancement methods.

  1. On Cattaneo-Christov heat flux model for Carreau fluid flow over a slendering sheet

    Science.gov (United States)

    Hashim; Khan, Masood

    The underlying intentions of this article are to investigate the impact of non-Fourier heat flux model on the stagnation-point flow of non-Newtonian Carreau fluid. In this study, the innovative Cattaneo-Christov constitutive model is introduced to study the characteristics of thermal relaxation time. The flow is impelled by a slendering surface which is of the variable thickness. In the model, the physical mechanism responsible for homogeneous-heterogeneous reactions are further taken into account. Also, the diffusion coefficients of the reactant and auto catalyst are considered to be equal. The governing non-linear partial differential equations consisting of the momentum, energy and concentration equations are reduced to the coupled ordinary differential equations by means of local similarity transformations. The transformed ODEs are tackled numerically by employing an effective shooting algorithm along with the Runge-Kutta Fehlberg scheme. The physical characteristics of the fluid velocity, temperature and concentration profiles are illuminated with the variation of numerous governing factors and are presented graphically. For instance, our result indicates that the temperature and thermal boundary layer thickness are lower in case of Cattaneo-Christov heat flux model when compared to classical Fourier's heat model. Meanwhile, the rate of heat transfer is significantly improved by a high wall thickness parameter and an opposite influence is found due to the thermal relaxation parameter. We further noticed that a higher value of homogeneous and heterogeneous reaction parameter corresponds to a deceleration in the concentration field and it shows an inverse relation for the Schmidt number. A correlation with accessible results for specific cases is found with fabulous consent.

  2. A study of sensing heat flow through thermal walls by using thermoelectric module

    Directory of Open Access Journals (Sweden)

    Sippawit Noppawit

    2015-01-01

    Full Text Available Demands on heat flow detection at a plane wall via a thermoelectric module have drawn researchers’ attention to quantitative understanding in order to properly implement the thermoelectric module in thermal engineering practices. Basic mathematical models of both heat transfer through a plane wall and thermoelectric effects are numerically solved to represent genuine behaviors of heat flow detection by mounting a thermoelectric module at a plane wall. The heat transfer through the plane wall is expected to be detected. It is intriguing from simulation results that the heat rejected at the plane wall is identical to the heat absorbed by the thermoelectric module when the area of the plane wall is the same as that of the thermoelectric module. Furthermore, both the area sizes of the plane walls and the convective heat transfer coefficients at the wall influence amount of the heat absorbed by the thermoelectric module. Those observational data are modeled for development of sensing heat flow through a plane wall by a thermoelectric module in practical uses.

  3. Evaluation of Heat Flux Measurement as a New Process Analytical Technology Monitoring Tool in Freeze Drying.

    Science.gov (United States)

    Vollrath, Ilona; Pauli, Victoria; Friess, Wolfgang; Freitag, Angelika; Hawe, Andrea; Winter, Gerhard

    2017-05-01

    This study investigates the suitability of heat flux measurement as a new technique for monitoring product temperature and critical end points during freeze drying. The heat flux sensor is tightly mounted on the shelf and measures non-invasively (no contact with the product) the heat transferred from shelf to vial. Heat flux data were compared to comparative pressure measurement, thermocouple readings, and Karl Fischer titration as current state of the art monitoring techniques. The whole freeze drying process including freezing (both by ramp freezing and controlled nucleation) and primary and secondary drying was considered. We found that direct measurement of the transferred heat enables more insights into thermodynamics of the freezing process. Furthermore, a vial heat transfer coefficient can be calculated from heat flux data, which ultimately provides a non-invasive method to monitor product temperature throughout primary drying. The end point of primary drying determined by heat flux measurements was in accordance with the one defined by thermocouples. During secondary drying, heat flux measurements could not indicate the progress of drying as monitoring the residual moisture content. In conclusion, heat flux measurements are a promising new non-invasive tool for lyophilization process monitoring and development using energy transfer as a control parameter. Copyright © 2017 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

  4. The Heat Transfer Coefficient of Recycled Concrete Bricks Combination with EPS Insulation Board Wall

    Directory of Open Access Journals (Sweden)

    Jianhua Li

    2015-01-01

    Full Text Available Four tectonic forms samples were conducted to test their heat transfer coefficients. By analyzing and comparing the test values and theoretical values of the heat transfer coefficient, a corrected-value calculation method for determining the heat transfer coefficient was proposed; the proposed method was proved to be reasonably correct. The results indicated that the recycled concrete brick wall heat transfer coefficient is higher than that of the clay brick wall, the heat transfer coefficient of recycled concrete brick wall could be effectively reduced when combined with the EPS insulation board, and the sandwich insulation type was better than that of external thermal insulation type.

  5. Geothermal Heat Flux Underneath Ice Sheets Estimated From Magnetic Satellite Data

    DEFF Research Database (Denmark)

    Fox Maule, Cathrine; Purucker, M.E.; Olsen, Nils

    The geothermal heat flux is an important factor in the dynamics of ice sheets, and it is one of the important parameters in the thermal budgets of subglacial lakes. We have used satellite magnetic data to estimate the geothermal heat flux underneath the ice sheets in Antarctica and Greenland...

  6. Turbulent heat and momentum fluxes in the upper ocean under Arctic sea ice

    Science.gov (United States)

    Peterson, Algot K.; Fer, Ilker; McPhee, Miles G.; Randelhoff, Achim

    2017-02-01

    We report observations of heat and momentum fluxes measured in the ice-ocean boundary layer from four drift stations between January and June 2015, covering from the typical Arctic basin conditions in the Nansen Basin to energetic spots of interaction with the warm Atlantic Water branches near the Yermak Plateau and over the North Spitsbergen slope. A wide range of oceanic turbulent heat flux values are observed, reflecting the variations in space and time over the five month duration of the experiment. Oceanic heat flux is weakly positive in winter over the Nansen Basin during quiescent conditions, increasing by an order of magnitude during storm events. An event of local upwelling and mixing in the winter-time Nansen basin highlights the importance of individual events. Spring-time drift is confined to the Yermak Plateau and its slopes, where vertical mixing is enhanced. Wind events cause an approximate doubling of oceanic heat fluxes compared to calm periods. In June, melting conditions near the ice edge lead to heat fluxes of O(100 W m-2). The combination of wind forcing with shallow Atlantic Water layer and proximity to open waters leads to maximum heat fluxes reaching 367 W m-2, concurrent with rapid melting. Observed ocean-to-ice heat fluxes agree well with those estimated from a bulk parameterization except when accumulated freshwater from sea ice melt in spring probably causes the bulk formula to overestimate the oceanic heat flux.

  7. Heat and salt fluxes in the West Spitsbergen Current area in summer

    Directory of Open Access Journals (Sweden)

    Jan Piechura

    2002-09-01

    Full Text Available Fluxes of radiation, sensible and latent heat, and fluxes of heat and salt within the upper layer of the ocean were calculated on the basis of measurements carried out in the area of the Norwegian-Atlantic and West Spitsbergen Currents during summer 2000.      The sea surface radiation balance was calculated from direct measurements of downward and upward short-wave (solar radiation, the net radiation fluxes and sea surface temperature. The daily doses of radiation energy reaching and leaving the sea surface were also estimated.      To calculate the vertical heat fluxes in the atmospheric boundary layer the bulk parameterisation method was used. In most cases, the calculated heat fluxes were rather low, the average sensible heat flux was c. 10 W m-2, and the latent heat flux about one order of magnitude higher; this is what could be expected in summer. Salt fluxes to the air in the process of aerosol production are very small and can be neglected.      In summer the highest quantities of heat and salt are exchanged during mixing with surrounding waters.      According to our measurements, Atlantic Water on its northward course from about 70oN to 79oN loses about 100 TW of heat and 900 × 103 kg of salt. We thought it could be interesting to find out what happens to them. Some preliminary results of our investigation are presented here.

  8. Aram Chaos and its constraints on the surface heat flux of Mars

    NARCIS (Netherlands)

    Schumacher, S.; Zegers, T.E.

    2011-01-01

    The surface heat flux of a planet is an important parameter to characterize its internal activity and to determine its thermal evolution. Here we report on a new method to constrain the surface heat flux of Mars during the Hesperian. For this, we explore the consequences for the martian surface

  9. Understanding of flux-limited behaviors of heat transport in nonlinear regime

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Yangyu, E-mail: yangyuhguo@gmail.com [Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Engineering Mechanics and CNMM, Tsinghua University, Beijing 100084 (China); Jou, David, E-mail: david.jou@uab.es [Departament de Física, Universitat Autònoma de Barcelona, 08193 Bellaterra, Catalonia (Spain); Wang, Moran, E-mail: mrwang@tsinghua.edu [Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Engineering Mechanics and CNMM, Tsinghua University, Beijing 100084 (China)

    2016-01-28

    The classical Fourier's law of heat transport breaks down in highly nonequilibrium situations as in nanoscale heat transport, where nonlinear effects become important. The present work is aimed at exploring the flux-limited behaviors based on a categorization of existing nonlinear heat transport models in terms of their theoretical foundations. Different saturation heat fluxes are obtained, whereas the same qualitative variation trend of heat flux versus exerted temperature gradient is got in diverse nonlinear models. The phonon hydrodynamic model is proposed to act as a standard to evaluate other heat flux limiters because of its more rigorous physical foundation. A deeper knowledge is thus achieved about the phenomenological generalized heat transport models. The present work provides deeper understanding and accurate modeling of nonlocal and nonlinear heat transport beyond the diffusive limit. - Highlights: • Exploring flux-limited behaviors based on a categorization of existing nonlinear heat transport models. • Proposing phonon hydrodynamic model as a standard to evaluate heat flux limiters. • Providing accurate modeling of nonlocal and nonlinear heat transport beyond the diffusive limit.

  10. Surface energy balance closure in an arid region: role of soil and heat flux

    NARCIS (Netherlands)

    Heusinkveld, B.G.; Jacobs, A.F.G.; Holtslag, A.A.M.; Berkowicz, S.M.

    2004-01-01

    The large soil heat fluxes in hot desert regions are very important in energy balance studies. Surface energy balance (SEB) observations, however, reveal that there is an imbalance in Surface flux measurements and that it is difficult to isolate those flux measurements causing the imbalance errors.

  11. Eddy Heat Fluxes across the Antarctic Circumpolar Current in Northern Drake Passage

    Science.gov (United States)

    Watts, D. R.; Tracey, K. L.; Donohue, K. A.; Chereskin, T. K.

    2012-12-01

    A local dynamics array of 24 current and pressure recording inverted echo sounders (CPIES) was deployed as part of the cDrake experiment for 4 years centered near 57S, 63W spanning a local maximum eddy kinetic energy region between the Subantarctic Front and Polar Front. The CPIES array provides full water-column estimates of velocity and temperature that were mapped to quantify and characterize eddy heat flux. Objective mapping was used to separate the total eddy heat fluxes into a nondivergent (rotational) part that recirculates around mean temperature-variance structures and a divergent part that accounts for the net eddy flux of heat across the Antarctic Circumpolar Current. The vertical shear, aligned along isotherms, is equivalent-barotropic and contributes only nondivergent heat flux. In contrast, the dynamically important component of eddy heat flux that transfers energy from the mean to the eddy field is driven by nearly depth-independent geostrophic currents that can cross the temperature front. Thus as in Bishop [2012], the coupling between the nearly depth-independent currents measured at the bottom and the temperatures in the baroclinic front accounts for all the divergent component of eddy heat flux. The separation reveals divergent heat fluxes that typically are oriented differently and have magnitudes a few times smaller than the total eddy heat fluxes. The mapped annual-mean eddy heat fluxes have a spatial structure that is relatively consistent from year-to-year and exhibit a region of strong poleward divergent fluxes just downstream of a prominent topographic ridge (Shackleton Fracture Zone). The fluxes peak in the upper water column at 100-200 kW m^{-2} near 200 m depth and decrease to 10-15% as large by 600 m depth, below which they are relatively constant and coherent to the sea floor. In these "hot spots" of eddy heat flux the vertically-integrated poleward divergent fluxes are 50 - 100 MW m^{-1}. The time series of daily heat flux show that

  12. Forced bulk boiling at high heat fluxes; Erzwungenes Blasensieden bei hohen Waermestromdichten

    Energy Technology Data Exchange (ETDEWEB)

    Knipping, Tobias; Humpfer, Frank; Arnemann, Michael [Hochschule Karlsruhe - Technik und Wirtschaft (HsKA) (Germany). Fakultaet fuer Maschinenbau und Mechatronik fuer Kaelte-, Klima- und Umwelttechnik (IKKU)

    2013-05-15

    The influence of very high heat flux densities (10{sup 5} to 10{sup 7} W/m{sup 2}) on the boiling behavior of R404A is investigated. By using a new evaporator design it is possible to change the evaporating effects even at these high heat flux densities to bulk boiling. This paper focuses on the experimental analysis of the new evaporator by varying the parameters geometry, mass flux, subcooling and fluid velocity. The results show that fluid velocity, mass flux and geometry have a high influence on the transferred heat-flow, while the subcooling of the liquid phase only has a small effect. (orig.)

  13. Gas-surface interactions using accommodation coefficients for a dilute and a dense gas in a micro- or nanochannel: heat flux predictions using combined molecular dynamics and Monte Carlo techniques.

    Science.gov (United States)

    Nedea, S V; van Steenhoven, A A; Markvoort, A J; Spijker, P; Giordano, D

    2014-05-01

    The influence of gas-surface interactions of a dilute gas confined between two parallel walls on the heat flux predictions is investigated using a combined Monte Carlo (MC) and molecular dynamics (MD) approach. The accommodation coefficients are computed from the temperature of incident and reflected molecules in molecular dynamics and used as effective coefficients in Maxwell-like boundary conditions in Monte Carlo simulations. Hydrophobic and hydrophilic wall interactions are studied, and the effect of the gas-surface interaction potential on the heat flux and other characteristic parameters like density and temperature is shown. The heat flux dependence on the accommodation coefficient is shown for different fluid-wall mass ratios. We find that the accommodation coefficient is increasing considerably when the mass ratio is decreased. An effective map of the heat flux depending on the accommodation coefficient is given and we show that MC heat flux predictions using Maxwell boundary conditions based on the accommodation coefficient give good results when compared to pure molecular dynamics heat predictions. The accommodation coefficients computed for a dilute gas for different gas-wall interaction parameters and mass ratios are transferred to compute the heat flux predictions for a dense gas. Comparison of the heat fluxes derived using explicit MD, MC with Maxwell-like boundary conditions based on the accommodation coefficients, and pure Maxwell boundary conditions are discussed. A map of the heat flux dependence on the accommodation coefficients for a dense gas, and the effective accommodation coefficients for different gas-wall interactions are given. In the end, this approach is applied to study the gas-surface interactions of argon and xenon molecules on a platinum surface. The derived accommodation coefficients are compared with values of experimental results.

  14. 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.

  15. Tissue responses to fractional transient heating with sinusoidal heat flux condition on skin surface.

    Science.gov (United States)

    Ezzat, Magdy A; El-Bary, Alaa A; Al-Sowayan, Noorah S

    2016-10-01

    A fractional model of Bioheat equation for describing quantitatively the thermal responses of skin tissue under sinusoidal heat flux conditions on skin surface is given. Laplace transform technique is used to obtain the solution in a closed form. The resulting formulation is applied to one-dimensional application to investigate the temperature distribution in skin with instantaneous surface heating for different cases. According to the numerical results and its graphs, conclusion about the fractional bioheat transfer equation has been constructed. Sensitivity analysis is performed to explore the thermal effects of various control parameters on tissue temperature. The comparisons are made with the results obtained in the case of the absence of time-fractional order. © 2016 Japanese Society of Animal Science. © 2016 Japanese Society of Animal Science.

  16. Development of platform to compare different wall heat transfer packages for system analysis codes

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Min-Gil; Lee, Won Woong; Lee, Jeong Ik [KAIST, Daejeon (Korea, Republic of); Shin, Sung Gil [Hanyang University, Seoul (Korea, Republic of)

    2016-10-15

    System thermal hydraulic (STH) analysis code is used for analyzing and evaluating the safety of a designed nuclear system. The system thermal hydraulic analysis code typically solves mass, momentum and energy conservation equations for multiple phases with sets of selected empirical constitutive equations to close the problem. Several STH codes are utilized in academia, industry and regulators, such as MARS-KS, SPACE, RELAP5, COBRA-TF, TRACE, and so on. Each system thermal hydraulic code consists of different sets of governing equations and correlations. However, the packages and sets of correlations of each code are not compared quantitatively yet. Wall heat transfer mode transition maps of SPACE and MARS-KS have a little difference for the transition from wall nucleate heat transfer mode to wall film heat transfer mode. Both codes have the same heat transfer packages and correlations in most region except for wall film heat transfer mode. Most of heat transfer coefficients calculated for the range of selected variables of SPACE are the same with those of MARS-KS. For the intervals between 500K and 540K of wall temperature, MARS-KS selects the wall film heat transfer mode and Bromley correlation but SPACE select the wall nucleate heat transfer mode and Chen correlation. This is because the transition from nucleate boiling to film boiling of MARS-KS is earlier than SPACE. More detailed analysis of the heat transfer package and flow regime package will be followed in the near future.

  17. An inverse method to estimate stem surface heat flux in wildland fires

    Science.gov (United States)

    Anthony S. Bova; Matthew B. Dickinson

    2009-01-01

    Models of wildland fire-induced stem heating and tissue necrosis require accurate estimates of inward heat flux at the bark surface. Thermocouple probes or heat flux sensors placed at a stem surface do not mimic the thermal response of tree bark to flames.We show that data from thin thermocouple probes inserted just below the bark can be used, by means of a one-...

  18. COMPARISON OF COOLING SCHEMES FOR HIGH HEAT FLUX COMPONENTS COOLING IN FUSION REACTORS

    Directory of Open Access Journals (Sweden)

    Phani Kumar Domalapally

    2015-04-01

    Full Text Available Some components of the fusion reactor receives high heat fluxes either during the startup and shutdown or during the operation of the machine. This paper analyzes different ways of enhancing heat transfer using helium and water for cooling of these high heat flux components and then conclusions are drawn to decide the best choice of coolant, for usage in near and long term applications.

  19. Heat transfer in flow past a continuously moving semi-infinite flat plate in transverse magnetic field with heat flux

    Digital Repository Service at National Institute of Oceanography (India)

    Murty, T.V.R.

    Thermal boundary layer on a continuously moving semi-infinite flat plate in the presence of transverse magnetic field with heat flux has been examined. Similarity solutions have been derived and the resulting equations are integrated numerically...

  20. Anthropogenic Heat Flux Estimation from Space: Results of the second phase of the URBANFLUXES Project

    Science.gov (United States)

    Chrysoulakis, Nektarios; Marconcini, Mattia; Gastellu-Etchegorry, Jean-Philippe; Grimmond, Sue; Feigenwinter, Christian; Lindberg, Fredrik; Del Frate, Fabio; Klostermann, Judith; Mitraka, Zina; Esch, Thomas; Landier, Lucas; Gabey, Andy; Parlow, Eberhard; Olofson, Frans

    2017-04-01

    The H2020-Space project URBANFLUXES (URBan ANthrpogenic heat FLUX from Earth observation Satellites) investigates the potential of Copernicus Sentinels to retrieve anthropogenic heat flux, as a key component of the Urban Energy Budget (UEB). URBANFLUXES advances the current knowledge of the impacts of UEB fluxes on urban heat island and consequently on energy consumption in cities. In URBANFLUXES, the anthropogenic heat flux is estimated as a residual of UEB. Therefore, the rest UEB components, namely, the net all-wave radiation, the net change in heat storage and the turbulent sensible and latent heat fluxes are independently estimated from Earth Observation (EO), whereas the advection term is included in the error of the anthropogenic heat flux estimation from the UEB closure. The Discrete Anisotropic Radiative Transfer (DART) model is employed to improve the estimation of the net all-wave radiation balance, whereas the Element Surface Temperature Method (ESTM), adjusted to satellite observations is used to improve the estimation the estimation of the net change in heat storage. Furthermore the estimation of the turbulent sensible and latent heat fluxes is based on the Aerodynamic Resistance Method (ARM). Based on these outcomes, QF is estimated by regressing the sum of the turbulent heat fluxes versus the available energy. In-situ flux measurements are used to evaluate URBANFLUXES outcomes, whereas uncertainties are specified and analyzed. URBANFLUXES is expected to prepare the ground for further innovative exploitation of EO in scientific activities (climate variability studies at local and regional scales) and future and emerging applications (sustainable urban planning, mitigation technologies) to benefit climate change mitigation/adaptation. This study presents the results of the second phase of the project and detailed information on URBANFLUXES is available at: http://urbanfluxes.eu

  1. Estimation of surface heat flux and surface temperature during inverse heat conduction under varying spray parameters and sample initial temperature.

    Science.gov (United States)

    Aamir, Muhammad; Liao, Qiang; Zhu, Xun; Aqeel-ur-Rehman; Wang, Hong; Zubair, Muhammad

    2014-01-01

    An experimental study was carried out to investigate the effects of inlet pressure, sample thickness, initial sample temperature, and temperature sensor location on the surface heat flux, surface temperature, and surface ultrafast cooling rate using stainless steel samples of diameter 27 mm and thickness (mm) 8.5, 13, 17.5, and 22, respectively. Inlet pressure was varied from 0.2 MPa to 1.8 MPa, while sample initial temperature varied from 600°C to 900°C. Beck's sequential function specification method was utilized to estimate surface heat flux and surface temperature. Inlet pressure has a positive effect on surface heat flux (SHF) within a critical value of pressure. Thickness of the sample affects the maximum achieved SHF negatively. Surface heat flux as high as 0.4024 MW/m(2) was estimated for a thickness of 8.5 mm. Insulation effects of vapor film become apparent in the sample initial temperature range of 900°C causing reduction in surface heat flux and cooling rate of the sample. A sensor location near to quenched surface is found to be a better choice to visualize the effects of spray parameters on surface heat flux and surface temperature. Cooling rate showed a profound increase for an inlet pressure of 0.8 MPa.

  2. Estimation of Surface Heat Flux and Surface Temperature during Inverse Heat Conduction under Varying Spray Parameters and Sample Initial Temperature

    Directory of Open Access Journals (Sweden)

    Muhammad Aamir

    2014-01-01

    Full Text Available An experimental study was carried out to investigate the effects of inlet pressure, sample thickness, initial sample temperature, and temperature sensor location on the surface heat flux, surface temperature, and surface ultrafast cooling rate using stainless steel samples of diameter 27 mm and thickness (mm 8.5, 13, 17.5, and 22, respectively. Inlet pressure was varied from 0.2 MPa to 1.8 MPa, while sample initial temperature varied from 600°C to 900°C. Beck’s sequential function specification method was utilized to estimate surface heat flux and surface temperature. Inlet pressure has a positive effect on surface heat flux (SHF within a critical value of pressure. Thickness of the sample affects the maximum achieved SHF negatively. Surface heat flux as high as 0.4024 MW/m2 was estimated for a thickness of 8.5 mm. Insulation effects of vapor film become apparent in the sample initial temperature range of 900°C causing reduction in surface heat flux and cooling rate of the sample. A sensor location near to quenched surface is found to be a better choice to visualize the effects of spray parameters on surface heat flux and surface temperature. Cooling rate showed a profound increase for an inlet pressure of 0.8 MPa.

  3. Estimation of Surface Heat Flux and Surface Temperature during Inverse Heat Conduction under Varying Spray Parameters and Sample Initial Temperature

    Science.gov (United States)

    Aamir, Muhammad; Liao, Qiang; Zhu, Xun; Aqeel-ur-Rehman; Wang, Hong

    2014-01-01

    An experimental study was carried out to investigate the effects of inlet pressure, sample thickness, initial sample temperature, and temperature sensor location on the surface heat flux, surface temperature, and surface ultrafast cooling rate using stainless steel samples of diameter 27 mm and thickness (mm) 8.5, 13, 17.5, and 22, respectively. Inlet pressure was varied from 0.2 MPa to 1.8 MPa, while sample initial temperature varied from 600°C to 900°C. Beck's sequential function specification method was utilized to estimate surface heat flux and surface temperature. Inlet pressure has a positive effect on surface heat flux (SHF) within a critical value of pressure. Thickness of the sample affects the maximum achieved SHF negatively. Surface heat flux as high as 0.4024 MW/m2 was estimated for a thickness of 8.5 mm. Insulation effects of vapor film become apparent in the sample initial temperature range of 900°C causing reduction in surface heat flux and cooling rate of the sample. A sensor location near to quenched surface is found to be a better choice to visualize the effects of spray parameters on surface heat flux and surface temperature. Cooling rate showed a profound increase for an inlet pressure of 0.8 MPa. PMID:24977219

  4. High geothermal heat flux in close proximity to the Northeast Greenland Ice Stream

    DEFF Research Database (Denmark)

    Rysgaard, Soren; Bendtsen, Jorgen; Mortensen, John

    2018-01-01

    or geothermal heat sources. Recently it was suggested that there may be a hidden heat source beneath GIS caused by a higher than expected geothermal heat flux (GHF) from the Earth's interior. Here we present the first direct measurements of GHF from beneath a deep fjord basin in Northeast Greenland. Temperature...... and salinity time series (2005-2015) in the deep stagnant basin water are used to quantify a GHF of 93 +/- 21 mW m(-2) which confirm previous indirect estimated values below GIS. A compilation of heat flux recordings from Greenland show the existence of geothermal heat sources beneath GIS and could explain...

  5. Modelling the mechanical response of an idealized ice stream to variations in geothermal heat flux

    Science.gov (United States)

    Smith-Johnsen, Silje; de Fleurian, Basile; Hestnes Nisancioglu, Kerim

    2017-04-01

    The spatial distribution of geothermal heat flux beneath the Greenland Ice Sheet is largely unknown partly due to difficulties in accessing the bed, and bore hole data providing point measurements only. Studies using tectonic, seismic and magnetic models to retrieve the geothermal heat flux show very different results indicating large uncertainties. However, modelling studies point to a geothermal heat flux anomaly that may influence the Northeast Greenland Ice Stream (NEGIS). Previous studies have investigated the impact of the uncertainty in geothermal heatflux on ice dynamics. These studies are mainly focusing on the impact on the ice rheology as the basal condition are derived from inverse modelling methods (including the geothermal heat flux variability in the variability of the friction coefficient). Another important feedback is the increase in subglacial meltwater production which may affect the sliding velocities of an ice stream, and has not been taken into account in preceding studies. In this study we investigate the impact of variations in geothermal heat flux on ice dynamics by analysing the mechanical response of a synthetic ice stream simulating NEGIS using the Ice Sheet System Model (Larour et al. 2012). We present results from model experiments using different heat flux configurations, friction laws and a hydrology model, showing the importance of geothermal heat flux on basal conditions of fast flowing ice.

  6. Investigation of thermal energy transport from an anisotropic central heating element to the adjacent channels: A multipoint flux approximation

    KAUST Repository

    Salama, Amgad

    2015-02-01

    The problem of heat transfer from a central heating element pressed between two clad plates to cooling channels adjacent and outboard of the plates is investigated numerically. The aim of this work is to highlight the role of thermal conductivity anisotropy of the heating element and/or the encompassing plates on thermal energy transport to the fluid passing through the two channels. When the medium is anisotropic with respect to thermal conductivity; energy transport to the neighboring channels is no longer symmetric. This asymmetry in energy fluxes influence heat transfer to the coolant resulting in different patterns of temperature fields. In particular, it is found that the temperature fields are skewed towards the principal direction of anisotropy. In addition, the heat flux distributions along the edges of the heating element are also different as a manifestation of thermal conductivity anisotropy. Furthermore, the peak temperature at the channel walls change location and magnitude depending on the principal direction of anisotropy. Based on scaling arguments, it is found that, the ratio of width to the height of the heating system is a key parameter which can suggest when one may ignore the effect of the cross-diagonal terms of the full conductivity tensor. To account for anisotropy in thermal conductivity, the method of multipoint flux approximation (MPFA) is employed. Using this technique, it is possible to find a finite difference stencil which can handle full thermal conductivity tensor and in the same time enjoys the simplicity of finite difference approximation. Although the finite difference stencil based on MPFA is quite complex, in this work we apply the recently introduced experimenting field approach which construct the global problem automatically.

  7. Surface Catalysis and Oxidation on Stagnation Point Heat Flux Measurements in High Enthalpy Arc Jets

    Science.gov (United States)

    Nawaz, Anuscheh; Driver, David M.; Terrazas-Salinas

    2013-01-01

    Heat flux sensors are routinely used in arc jet facilities to determine heat transfer rates from plasma plume. The goal of this study is to assess the impact of surface composition changes on these heat flux sensors. Surface compositions can change due to oxidation and material deposition from the arc jet. Systematic surface analyses of the sensors were conducted before and after exposure to plasma. Currently copper is commonly used as surface material. Other surface materials were studied including nickel, constantan gold, platinum and silicon dioxide. The surfaces were exposed to plasma between 0.3 seconds and 3 seconds. Surface changes due to oxidation as well as copper deposition from the arc jets were observed. Results from changes in measured heat flux as a function of surface catalycity is given, along with a first assessment of enthalpy for these measurements. The use of cupric oxide is recommended for future heat flux measurements, due to its consistent surface composition arc jets.

  8. E × B shear pattern formation by radial propagation of heat flux wavesa)

    Science.gov (United States)

    Kosuga, Y.; Diamond, P. H.; Dif-Pradalier, G.; Gürcan, Ã.-. D.

    2014-05-01

    A novel theory to describe the formation of E ×B flow patterns by radially propagating heat flux waves is presented. A model for heat avalanche dynamics is extended to include a finite delay time between the instantaneous heat flux and the mean flux, based on an analogy between heat avalanche dynamics and traffic flow dynamics. The response time introduced here is an analogue of the drivers' response time in traffic dynamics. The microscopic foundation for the time delay is the time for mixing of the phase space density. The inclusion of the finite response time changes the model equation for avalanche dynamics from Burgers equation to a nonlinear telegraph equation. Based on the telegraph equation, the formation of heat flux jams is predicted. The growth rate and typical interval of jams are calculated. The connection of the jam interval to the typical step size of the E ×B staircase is discussed.

  9. Methodology for estimation of time-dependent surface heat flux due to cryogen spray cooling.

    Science.gov (United States)

    Tunnell, James W; Torres, Jorge H; Anvari, Bahman

    2002-01-01

    Cryogen spray cooling (CSC) is an effective technique to protect the epidermis during cutaneous laser therapies. Spraying a cryogen onto the skin surface creates a time-varying heat flux, effectively cooling the skin during and following the cryogen spurt. In previous studies mathematical models were developed to predict the human skin temperature profiles during the cryogen spraying time. However, no studies have accounted for the additional cooling due to residual cryogen left on the skin surface following the spurt termination. We formulate and solve an inverse heat conduction (IHC) problem to predict the time-varying surface heat flux both during and following a cryogen spurt. The IHC formulation uses measured temperature profiles from within a medium to estimate the surface heat flux. We implement a one-dimensional sequential function specification method (SFSM) to estimate the surface heat flux from internal temperatures measured within an in vitro model in response to a cryogen spurt. Solution accuracy and experimental errors are examined using simulated temperature data. Heat flux following spurt termination appears substantial; however, it is less than that during the spraying time. The estimated time-varying heat flux can subsequently be used in forward heat conduction models to estimate temperature profiles in skin during and following a cryogen spurt and predict appropriate timing for onset of the laser pulse.

  10. Calculated heat-and-technical indicators of brick external walls of the historical residential buildings

    Science.gov (United States)

    Pukhkal, Viktor; Murgul, Vera

    2017-10-01

    The analysis of the external brick walls structures of the historical residential buildings (constructions of XIX century and the beginnings of the 20th century) in St. Petersburg is carried out. The heat-and-technical indicators (coefficient of heat conductivity of brick and coefficient of the heat transfer of external brick walls) are defined. That is established that the use of modern norms of design is possible. The obtained data allow to carry out some heat-and-technical and moist calculations during designing of heating systems as well during the development of measures for energy saving.

  11. Heat transfer augmentation using nanofluids in an elliptic annulus with constant heat flux boundary condition

    Directory of Open Access Journals (Sweden)

    H.K. Dawood

    2014-11-01

    Full Text Available This work reports numerical simulation for three dimensional laminar mixed convective heat transfers at different nanofluids flow in an elliptic annulus with constant heat flux. A numerical model is carried out by solving the governing equations of continuity, momentum and energy using the finite volume method (FVM with the assistance of SIMPLE algorithm. Four different types of nanofluids Al2O3, CuO, SiO2 and ZnO, with different nanoparticles size 20, 40, 60 and 80 nm, and different volume fractions ranged from 0% to 4% using water as a base fluid were used. This investigation covers a Reynolds number in the range of 200 to 1000. The results revealed that SiO2–Water nanofluid has the highest Nusselt number, followed by Al2O3–Water, ZnO–Water, CuO–Water, and lastly pure water. The Nusselt number increased as the nanoparticle volume fraction and Reynolds number increased; however, it decreased as the nanoparticle diameter increased. It is found that the glycerine–SiO2 shows the best heat transfer enhancement compared with other tested base fluids.

  12. Institute for High Heat Flux Removal (IHHFR). Phases I, II, and III

    Energy Technology Data Exchange (ETDEWEB)

    Boyd, Ronald D. [Prairie View A& M Univ., TX (United States)

    2014-08-31

    The IHHFR focused on interdisciplinary applications as it relates to high heat flux engineering issues and problems which arise due to engineering systems being miniaturized, optimized, or requiring increased high heat flux performance. The work in the IHHFR focused on water as a coolant and includes: (1) the development, design, and construction of the high heat flux flow loop and facility; (2) test section development, design, and fabrication; and, (3) single-side heat flux experiments to produce 2-D boiling curves and 3-D conjugate heat transfer measurements for single-side heated test sections. This work provides data for comparisons with previously developed and new single-side heated correlations and approaches that address the single-side heated effect on heat transfer. In addition, this work includes the addition of single-side heated circular TS and a monoblock test section with a helical wire insert. Finally, the present work includes: (1) data base expansion for the monoblock with a helical wire insert (only for the latter geometry), (2) prediction and verification using finite element, (3) monoblock model and methodology development analyses, and (4) an alternate model development for a hypervapotron and related conjugate heat transfer controlling parameters.

  13. Study of heat transfer conditions at the wall of an ingot heated by electron gun; Etude des conditions d'echange thermique a la paroi d'un lingot chauffe par un canon a electrons

    Energy Technology Data Exchange (ETDEWEB)

    Saturnin, A.; Triffart, B. [CEA Vallee du Rhone, Dept. de Technologie de l' Enrichissement (DCC/DTE/STS), 26 - Pierrelatte (France)

    2000-07-01

    A metal confined in a crucible is heated by an electron beam to produce metallic vapor. Only a small proportion of the electron beam energy is used to vaporize the metal. Another portion is lost because of backscattered electrons and thermal radiation of the ingot. The remaining energy is transmitted by convection and conduction to the water cooled crucible. The knowledge of this energy, and particularly its spatial distribution, is important. The magnitude of the heat flux can be analyzed to ensure component integrity. The spatial flux distribution provides information about the coolant system homogeneity, which is related to the position of the ingot in the crucible and the electron beam alignment. These data are useful for controlling operating conditions. In the present method, the heat flux at the crucible wall is identified by conventional measurements (thermocouples, flowmeter) and an inverse method. This approach makes it unnecessary to model complex mechanisms in the liquid metal pool, limiting the study to the heat transfers inside the crucible. Calculation of the flux at a given point of the crucible wall requires three essential data: coolant system temperature Te, crucible temperature Tmes at the measurement point Pmes and temperature sensitivity at this point to heat flux variations at the wall. This characteristic is also called the sensitivity coefficient. It is obtained by modeling heat transfers in the crucible (convective with coolant system, conductive in the crucible) with the boundary conditions Te = 0 K and {phi} 1 Wm{sup -2}. This approach is a simple application of the function specification method, which is a reference method in inverse problems. The problem is assumed to be linear and stationary because of the high thermal crucible conductivity and the measurement locations (close to the wall). If the sensitivity coefficient is known, the heat flux can be calculated by equation (1). Figure 2 shows an example of variations in Tmes and Te

  14. Critical heat flux and boiling heat transfer to water in a 3-mm-diameter horizontal tube.

    Energy Technology Data Exchange (ETDEWEB)

    Yu, W.; Wambsganss, M. W.; Hull, J. R.; France, D. M.

    2000-12-04

    Boiling of the coolant in an engine, by design or by circumstance, is limited by the critical heat flux phenomenon. As a first step in providing relevant engine design information, this study experimentally addressed both rate of boiling heat transfer and conditions at the critical point of water in a horizontal tube of 2.98 mm inside diameter and 0.9144 m heated length. Experiments were performed at system pressure of 203 kPa, mass fluxes in range of 50 to 200 kg/m{sup z}s, and inlet temperatures in range of ambient to 80 C. Experimental results and comparisons with predictive correlations are presented.

  15. A Revised Estimate of Earth's Surface Heat Flux: 47TW ± 2TW

    Science.gov (United States)

    Davies, J.; Davies, R.

    2011-12-01

    Earth's surface heat flux provides a fundamental constraint on solid Earth dynamics. However, deriving an estimate of the total surface heat flux is complex, due to the inhomogeneous distribution of heat flow measurements and difficulties in measuring heat flux in young oceanic crust, arising due to hydrothermal circulation. We derive a revised estimate of Earth's surface heat flux using a database of 38347 measurements (provided by G. Laske and G. Masters), representing a 55% increase on the number of measurements used previously, and the methods of Geographical Information Science (GIS) (Davies & Davies, 2010). To account for hydrothermal circulation in young oceanic crust, we use a model estimate of the heat flux, following the work of Jaupart et al., 2007; while for the rest of the globe, in an attempt to overcome the inhomogeneous distribution of measurements, we develop an average for different geological units. Two digital geology data sets are used to define the global geology: (i) continental geology - Hearn et al., 2003; and (ii) the global data-set of CCGM - Commission de la Carte Géologique du Monde, 2000. This leads to > 93,000 polygons defining Earth's geology. To limit the influence of clustering, we intersect the geology polygons with a 1 by 1 degree (at the equator) equal area grid. For each geology class the average heat flow in the resulting polygons is evaluated. The contribution of that geology class to the global surface heat flow is derived by multiplying the estimated surface heat flux with the area of that geology class. The total surface heat flow contributions of all the geology classes are summed. For Antarctica we use an estimate based on depth to Curie temperature and include a 1TW contribution from hot-spots in young ocean age. Geology classes with less than 50 readings are excluded. The raw data suggests that this method of correlating heat flux with geology has some power. Our revised estimate for Earth's global surface heat flux

  16. A multipoint flux approximation of the steady-state heat conduction equation in anisotropic media

    KAUST Repository

    Salama, Amgad

    2013-03-20

    In this work, we introduce multipoint flux (MF) approximation method to the problem of conduction heat transfer in anisotropic media. In such media, the heat flux vector is no longer coincident with the temperature gradient vector. In this case, thermal conductivity is described as a second order tensor that usually requires, at least, six quantities to be fully defined in general three-dimensional problems. The two-point flux finite differences approximation may not handle such anisotropy and essentially more points need to be involved to describe the heat flux vector. In the framework of mixed finite element method (MFE), the MFMFE methods are locally conservative with continuous normal fluxes. We consider the lowest order Brezzi-Douglas-Marini (BDM) mixed finite element method with a special quadrature rule that allows for nodal velocity elimination resulting in a cell-centered system for the temperature. We show comparisons with some analytical solution of the problem of conduction heat transfer in anisotropic long strip. We also consider the problem of heat conduction in a bounded, rectangular domain with different anisotropy scenarios. It is noticed that the temperature field is significantly affected by such anisotropy scenarios. Also, the technique used in this work has shown that it is possible to use the finite difference settings to handle heat transfer in anisotropic media. In this case, heat flux vectors, for the case of rectangular mesh, generally require six points to be described. Copyright © 2013 by ASME.

  17. Use of EPICS and Python technology for the development of a computational toolkit for high heat flux testing of plasma facing components

    Energy Technology Data Exchange (ETDEWEB)

    Sugandhi, Ritesh, E-mail: ritesh@ipr.res.in; Swamy, Rajamannar, E-mail: rajamannar@ipr.res.in; Khirwadkar, Samir, E-mail: sameer@ipr.res.in

    2016-11-15

    Highlights: • An integrated approach to software development for computational processing and experimental control. • Use of open source, cross platform, robust and advanced tools for computational code development. • Prediction of optimized process parameters for critical heat flux model. • Virtual experimentation for high heat flux testing of plasma facing components. - Abstract: The high heat flux testing and characterization of the divertor and first wall components are a challenging engineering problem of a tokamak. These components are subject to steady state and transient heat load of high magnitude. Therefore, the accurate prediction and control of the cooling parameters is crucial to prevent burnout. The prediction of the cooling parameters is based on the numerical solution of the critical heat flux (CHF) model. In a test facility for high heat flux testing of plasma facing components (PFC), the integration of computations and experimental control is an essential requirement. Experimental physics and industrial control system (EPICS) provides powerful tools for steering controls, data simulation, hardware interfacing and wider usability. Python provides an open source alternative for numerical computations and scripting. We have integrated these two open source technologies to develop a graphical software for a typical high heat flux experiment. The implementation uses EPICS based tools namely IOC (I/O controller) server, control system studio (CSS) and Python based tools namely Numpy, Scipy, Matplotlib and NOSE. EPICS and Python are integrated using PyEpics library. This toolkit is currently under operation at high heat flux test facility at Institute for Plasma Research (IPR) and is also useful for the experimental labs working in the similar research areas. The paper reports the software architectural design, implementation tools and rationale for their selection, test and validation.

  18. Thermal barrier coatings (TBC's) for high heat flux thrust chambers

    Science.gov (United States)

    Bradley, Christopher M.

    -section components has become critical, but at the same time the service conditions have put our best alloy systems to their limits. As a result, implementation of cooling holes and thermal barrier coatings are new advances in hot-section technologies now looked at for modifications to reach higher temperature applications. Current thermal barrier coatings used in today's turbine applications is known as 8%yttria-stabilized zirconia (YSZ) and there are no coatings for current thrust chambers. Current research is looking at the applicability of 8%yttria-stabilized hafnia (YSH) for turbine applications and the implementation of 8%YSZ onto thrust chambers. This study intends to determine if the use of thermal barrier coatings are applicable for high heat flux thrust chambers using industrial YSZ will be advantageous for improvements in efficiency, thrust and longer service life by allowing the thrust chambers to be used more than once.

  19. Hybrid space heating/cooling system with Trombe wall, underground venting, and assisted heat pump

    Energy Technology Data Exchange (ETDEWEB)

    Shirley, J.W.; James, L.C.; Stevens, S.; Autry, A.N.; Nussbaum, M.; MacQueen, S.V.

    1983-06-22

    Our goal was to design and monitor a hybrid solar system/ground loop which automatically assists the standard, thermostatically controlled home heating/cooling system. The input from the homeowner was limited to normal thermostat operations. During the course of the project it was determined that to effectively gather data and control the various component interactions, a micro-computer based control system would also allow the HVAC system to be optimized by simple changes to software. This flexibility in an untested concept helped us to achieve optimum system performance. Control ranged from direct solar heating and direct ground loop cooling modes, to assistance of the heat pump by both solar space and ground loop. Sensors were strategically placed to provide data on response of the Trombe wall (surface, 4 in. deep, 8 in. deep), and the ground loop (inlet, 3/4 length, outlet). Micro-computer hardware and computer programs were developed to make cost effective decisions between the various modes of operation. Although recent advances in micro-computer hardware make similar control systems more readily achievable utilizing standard components, attention to the decision making criteria will always be required.

  20. The Influence of Non-Uniform High Heat Flux on Thermal Stress of Thermoelectric Power Generator

    Directory of Open Access Journals (Sweden)

    Tingzhen Ming

    2015-11-01

    Full Text Available A thermoelectric generator (TEG device which uses solar energy as heat source would achieve higher efficiency if there is a higher temperature difference between the hot-cold ends. However, higher temperature or higher heat flux being imposed upon the hot end will cause strong thermal stress, which will have a negative influence on the life cycle of the thermoelectric module. Meanwhile, in order to get high heat flux, a Fresnel lens is required to concentrate solar energy, which will cause non-uniformity of heat flux on the hot end of the TEG and further influence the thermal stress of the device. This phenomenon is very common in solar TEG devices but seldom research work has been reported. In this paper, numerical analysis on the heat transfer and thermal stress performance of a TEG module has been performed considering the variation on the power of the heat flux being imposed upon the hot-end; the influence of non-uniform high heat flux on thermal stress has also been analyzed. It is found that non-uniformity of high heat flux being imposed upon the hot end has a significant effect on the thermal stress of TEG and life expectation of the device. Taking the uniformity of 100% as standard, when the heating uniformity is 70%, 50%, 30%, and 10%, respectively, the maximum thermal stress of TEG module increased by 3%, 6%, 12%, and 22% respectively. If we increase the heat flux on the hot end, the influence of non-uniformity on the thermal stress will be more remarkable.

  1. Homotopy analysis method for variable thermal conductivity heat flux gage with edge contact resistance

    Energy Technology Data Exchange (ETDEWEB)

    Aziz, Abdul [Gonzaga Univ., Spokane, WA (United States). Dept. of Mechanical Engineering; Khani, Farzad [Bakhtar Institute of Higher Education, Ilam (Iran, Islamic Republic of). Dept. of Mathematics; Darvishi, Mohammad Taghi [Razi Univ., Kermanshah (Iran, Islamic Republic of). Dept. of Mathematics

    2010-10-15

    The homotopy analysis method (HAM) has been used to develop an analytical solution for the thermal performance of a circular-thin-foil heat flux gage with temperature dependent thermal conductivity and thermal contact resistance between the edge of the foil and the heat sink. Temperature distributions in the foil are presented illustrating the effect of incident heat flux, radiation emission from the foil, variable thermal conductivity, and contact resistance between the foil and the heat sink. The HAM results agree up to four places of decimal with the numerical solutions generated using the symbolic algebra package Maple. This close comparison vouches for the high accuracy and stability of the analytic solution. (orig.)

  2. Correlation analysis of heat flux and fire behaviour and hazards of polycrystalline silicon photovoltaic panels

    Science.gov (United States)

    Ju, Xiaoyu; Zhou, Xiaodong; Peng, Fei; Wu, Zhibo; Lai, Dimeng; Hu, Yue; Yang, Lizhong

    2017-05-01

    This work aims to gain a better understanding of fire behaviour and hazards of PV panels under different radiation heat fluxes. The cone calorimeter tests were applied to simulate the situations when the front and back surfaces are exposed to heat flux in a fire, respectively. Through comparison of ignition time, mass loss rate and heat release rate, it is found that the back-up condition is more hazardous than face-up condition. Meanwhile, three key parameters: flashover propensity, total heat release and FED, were introduced to quantitatively illustrate fire hazards of a PV panel.

  3. TAO/TRITON, RAMA, and PIRATA Buoys, Monthly, Total Heat Flux

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This dataset has monthly Total Heat Flux data from the TAO/TRITON (Pacific Ocean, http://www.pmel.noaa.gov/tao/), RAMA (Indian Ocean,...

  4. TAO/TRITON, RAMA, and PIRATA Buoys, Quarterly, Total Heat Flux

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This dataset has quarterly Total Heat Flux data from the TAO/TRITON (Pacific Ocean, http://www.pmel.noaa.gov/tao/), RAMA (Indian Ocean,...

  5. Recession-Tolerant Heat Flux Sensors for Thermal Protection Systems Project

    Data.gov (United States)

    National Aeronautics and Space Administration — The Phase I project will develop a suite of diagnostic sensors using Direct Write technology to measure temperature, surface recession depth, and heat flux of an...

  6. A High Heat Flux Facility Design for Testing of Advanced Hydrocarbon Fuel Thermal Stability

    National Research Council Canada - National Science Library

    Maas, E; Irvine, S; Bates, R; Auyeung, T

    2004-01-01

    .... Of the existing thermal stability test rigs, none have the ability to accurately simulate the high heat flux conditions that will exist in the cooling channels of these new high-pressure hydrocarbon engines...

  7. Ir Thermographic Measurements of Temperatures and Heat Fluxes in Hypersonic Plasma Flow

    Science.gov (United States)

    Cardone, G.; Tortora, G.; del Vecchio, A.

    2005-02-01

    The technological development achieved in instruments and methodology concerning both flights and ground hypersonic experiment (employed in space plane planning) goes towards an updating and a standardization of the heat flux technical measurements. In fact, the possibility to simulate high enthalpy flow relative to reentry condition by hypersonic arc-jet facility needs devoted methods to measure heat fluxes. Aim of this work is to develop an experimental numerical technique for the evaluation of heat fluxes over Thermal Protection System (TPS) by means of InfraRed (IR) thermographic temperature measurements and a new heat flux sensor (IR-HFS). We tackle the numerical validation of IR-HFS, apply the same one to the Hyflex nose cap model and compare the obtained results with others ones obtained by others methodology.

  8. Latent heat flux measurements over complex terrain by airborne water vapour and wind lidars

    National Research Council Canada - National Science Library

    Kiemle, Christoph; Wirth, Martin; Fix, Andreas; Rahm, Stephan; Corsmeier, Ulrich; Di Girolamo, Paolo

    2011-01-01

    Vertical profiles of the latent heat flux in a convective boundary layer (CBL) are obtained for the first time over complex terrain with airborne water vapour differential absorption lidar and Doppler wind lidar...

  9. Active particle control experiments and critical particle flux discriminating between the wall pumping and fuelling in the compact plasma wall interaction device CPD spherical tokamak

    Science.gov (United States)

    Zushi, H.; Hirooka, Y.; Bhattacharyay, R.; Sakamoto, M.; Nakashima, Y.; Yoshinaga, T.; Higashizono, Y.; Hanada, K.; Nishino, N.; Yoshida, N.; Tokunaga, K.; Kado, S.; Shikama, T.; Kawasaki, S.; Okamoto, K.; Miyazaki, T.; Honma, H.; Sato, K. N.; Nakamura, K.; Idei, H.; Hasegawa, M.; Nakashima, H.; Higashijima, A.

    2009-05-01

    Two approaches associated with wall recycling have been performed in a small spherical tokamak device CPD (compact plasma wall interaction experimental device), that is, (1) demonstration of active particle recycling control, namely, 'active wall pumping' using a rotating poloidal limiter whose surface is continuously gettered by lithium and (2) a basic study of the key parameters which discriminates between 'wall pumping and fuelling'. For the former, active control of 'wall pumping' has been demonstrated during 50 kW RF current drive discharges whose pulse length is typically ~300 ms. Although the rotating limiter is located at the outer board, as soon as the rotating drum is gettered with lithium, hydrogen recycling measured with Hα spectroscopy decreases by about a factor of 3 not only near the limiter but also in the centre stack region. Also, the oxygen impurity level measured with O II spectroscopy is reduced by about a factor of 3. As a consequence of the reduced recycling and impurity level, RF driven current has nearly doubled at the same vertical magnetic field. For the latter, global plasma wall interaction with plasma facing components in the vessel is studied in a simple torus produced by electron cyclotron waves with Ip static gas balance (pressure measurement) without external pumping systems has been performed to investigate the role of particle flux on a transition of 'wall fuelling' to 'wall pumping'. It is found that a critical particle flux exists to discriminate between them. Beyond the critical value, a large fraction (~80%) of pressure drop ('wall pumping') is found, suggesting that almost all injected particles are retained in the wall. Below it, a significant pressure rise ('wall fuelling') is found, which indicates that particles are fuelled from the wall during/just after the discharge. Shot history effects (integrated particle recycling behaviour from the plasma facing surfaces) are seen on that the critical particle flux is reducing

  10. Convective boundary layer flow and heat transfer in a nanofluid in the presence of second order slip, constant heat flux and zero nanoparticles flux

    Energy Technology Data Exchange (ETDEWEB)

    Rahman, M.M., E-mail: mansurdu@yahoo.com [Department of Mathematics and Statistics, College of Science, Sultan Qaboos University, PO Box 36, PC 123 Al-Khod, Muscat (Oman); Al-Rashdi, Maryam H. [Department of Mathematics and Statistics, College of Science, Sultan Qaboos University, PO Box 36, PC 123 Al-Khod, Muscat (Oman); Pop, I. [Department of Mathematics, Faculty of Mathematics and Computer Science, Babeş-Bolyai University, Cluj-Napoca 400084 (Romania)

    2016-02-15

    Highlights: • Convective boundary layer flow and heat transfer in a nanofluid is investigated. • Second order slip increases the rate of shear stress and decreases the rate of heat transfer in a nanofluid. • In nanofluid flow zero normal flux of the nanoparticles at the surface is realistic to apply. • Multiple solutions are identified for certain values of the parameter space. • The upper branch solution is found to be stable, hence physically realizable. - Abstract: In this work, the effects of the second order slip, constant heat flux, and zero normal flux of the nanoparticles due to thermophoresis on the convective boundary layer flow and heat transfer characteristics in a nanofluid using Buongiorno's model over a permeable shrinking sheet is studied theoretically. The nonlinear coupled similarity equations are solved using the function bvp4c using Matlab. Similarity solutions of the flow, heat transfer and nanoparticles volume fraction are presented graphically for several values of the model parameters. The results show that the application of second order slip at the interface is found to be increased the rate of shear stress and decreased the rate of heat transfer in a nanofluid, so need to be taken into account in nanofluid modeling. The results further indicate that multiple solutions exist for certain values of the parameter space. The stability analysis provides guarantee that the lower branch solution is unstable, while the upper branch solution is stable and physically realizable.

  11. Estimation of boundary heat flux using experimental temperature data in turbulent forced convection flow

    Science.gov (United States)

    Parwani, Ajit K.; Talukdar, Prabal; Subbarao, P. M. V.

    2015-03-01

    Heat flux at the boundary of a duct is estimated using the inverse technique based on conjugate gradient method (CGM) with an adjoint equation. A two-dimensional inverse forced convection hydrodynamically fully developed turbulent flow is considered. The simulations are performed with temperature data measured in the experimental test performed on a wind tunnel. The results show that the present numerical model with CGM is robust and accurate enough to estimate the strength and position of boundary heat flux.

  12. Critical Heat Flux Phenomena at HighPressure & Low Mass Fluxes: NEUP Final Report Part I: Experiments

    Energy Technology Data Exchange (ETDEWEB)

    Corradini, Michael [Univ. of Wisconsin, Madison, WI (United States); Wu, Qiao [Oregon State Univ., Corvallis, OR (United States)

    2015-04-30

    This report is a preliminary document presenting an overview of the Critical Heat Flux (CHF) phenomenon, the High Pressure Critical Heat Flux facility (HPCHF), preliminary CHF data acquired, and the future direction of the research. The HPCHF facility has been designed and built to study CHF at high pressure and low mass flux ranges in a rod bundle prototypical of conceptual Small Modular Reactor (SMR) designs. The rod bundle is comprised of four electrically heated rods in a 2x2 square rod bundle with a prototypic chopped-cosine axial power profile and equipped with thermocouples at various axial and circumferential positions embedded in each rod for CHF detection. Experimental test parameters for CHF detection range from pressures of ~80 – 160 bar, mass fluxes of ~400 – 1500 kg/m2s, and inlet water subcooling from ~30 – 70°C. The preliminary data base established will be further extended in the future along with comparisons to existing CHF correlations, models, etc. whose application ranges may be applicable to the conditions of SMRs.

  13. Changes in fluxes of heat, H2O, CO2 caused by a large wind farm

    Science.gov (United States)

    The Crop Wind Energy Experiment (CWEX) provides a platform to investigate the effect of wind turbines and large wind farms on surface fluxes of momentum, heat, moisture and carbon dioxide (CO2). In 2010 and 2011, eddy covariance flux stations were installed between two lines of turbines at the south...

  14. A new method for simultaneous measurement of convective and radiative heat flux in car underhood applications

    Science.gov (United States)

    Khaled, M.; Garnier, B.; Harambat, F.; Peerhossaini, H.

    2010-02-01

    A new experimental technique is presented that allows simultaneous measurement of convective and radiative heat flux in the underhood. The goal is to devise an easily implemented and accurate experimental method for application in the vehicle underhood compartment. The new method is based on a technique for heat-flux measurement developed by the authors (Heat flow (flux) sensors for measurement of convection, conduction and radiation heat flow 27036-2, © Rhopoint Components Ltd, Hurst Green, Oxted, RH8 9AX, UK) that uses several thermocouples in the thickness of a thermal resistive layer (foil heat-flux sensor). The method proposed here uses a pair of these thermocouples with different radiative properties. Measurements validating this novel technique are carried out on a flat plate with a prescribed constant temperature in both natural- and forced-convection flow regimes. The test flat plate is instrumented by this new technique, and also with a different technique that is intrusive but very accurate, used as reference here (Bardon J P and Jarny Y 1994 Procédé et dispositif de mesure transitoire de température et flux surfacique Brevet n°94.011996, 22 February). Discrepancies between the measurements by the two techniques are less than 10% for both convective and radiative heat flux. Error identification and sensitivity analysis of the new method are also presented.

  15. High geothermal heat flux measured below the West Antarctic Ice Sheet.

    Science.gov (United States)

    Fisher, Andrew T; Mankoff, Kenneth D; Tulaczyk, Slawek M; Tyler, Scott W; Foley, Neil

    2015-07-01

    The geothermal heat flux is a critical thermal boundary condition that influences the melting, flow, and mass balance of ice sheets, but measurements of this parameter are difficult to make in ice-covered regions. We report the first direct measurement of geothermal heat flux into the base of the West Antarctic Ice Sheet (WAIS), below Subglacial Lake Whillans, determined from the thermal gradient and the thermal conductivity of sediment under the lake. The heat flux at this site is 285 ± 80 mW/m(2), significantly higher than the continental and regional averages estimated for this site using regional geophysical and glaciological models. Independent temperature measurements in the ice indicate an upward heat flux through the WAIS of 105 ± 13 mW/m(2). The difference between these heat flux values could contribute to basal melting and/or be advected from Subglacial Lake Whillans by flowing water. The high geothermal heat flux may help to explain why ice streams and subglacial lakes are so abundant and dynamic in this region.

  16. Heat-Flux Measurements in Laser-Produced Plasmas Using Thomson Scattering from Electron Plasma Waves

    Science.gov (United States)

    Henchen, R. J.; Goncharov, V. N.; Cao, D.; Katz, J.; Froula, D. H.; Rozmus, W.

    2017-10-01

    An experiment was designed to measure heat flux in coronal plasmas using collective Thomson scattering. Adjustments to the electron distribution function resulting from heat flux affect the shape of the collective Thomson scattering features through wave-particle resonance. The amplitude of the Spitzer-Härm electron distribution function correction term (f1) was varied to match the data and determines the value of the heat flux. Independent measurements of temperature and density obtained from Thomson scattering were used to infer the classical heat flux (q = - κ∇Te) . Time-resolved Thomson-scattering data were obtained at five locations in the corona along the target normal in a blowoff plasma formed from a planar Al target with 1.5 kJ of 351-nm laser light in a 2-ns square pulse. The flux measured through the Thomson-scattering spectra is a factor of 5 less than the κ∇Te measurements. The lack of collisions of heat-carrying electrons suggests a nonlocal model is needed to accurately describe the heat flux. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

  17. Experimental investigation and mechanism of critical heat flux enhancement in pool boiling heat transfer with nanofluids

    Science.gov (United States)

    Kamatchi, R.; Venkatachalapathy, S.; Nithya, C.

    2016-11-01

    In the present study, reduced graphene oxide (rGO) is synthesized from graphite using modified Hummer and chemical reduction methods. Various characterizations techniques are carried out to study the in-plane crystallite size, number of layers, presence of functional groups and surface morphology. Different concentrations of 0.01, 0.1, and 0.3 g/l of rGO/water nanofluids are prepared by dispersing the flakes in DI water. The colloidal stability of 0.3 g/l concentration is measured after 5 days using Zetasizer and found to be stable. The rGO/water nanofluids are then used to study the effect on the enhancement of critical heat flux (CHF) in pool boiling heat transfer. Results indicate an enhancement in CHF ranging from 145 to 245 % for the tested concentrations. The mechanisms of CHF enhancement are analyzed based on surface wettability, surface roughness, and porous layer thickness. The macrolayer dryout model sufficiently supports the mechanism of CHF enhancement of thin wire with rGO deposits, which is not reported yet.

  18. Stretched flow of Oldroyd-B fluid with Cattaneo-Christov heat flux

    Directory of Open Access Journals (Sweden)

    T. Hayat

    Full Text Available The objective of present attempt is to analyse the flow and heat transfer in the flow of an Oldroyd-B fluid over a non-linear stretching sheet having variable thickness. Characteristics of heat transfer are analyzed with temperature dependent thermal conductivity and heat source/sink. Cattaneo-Christov heat flux model is considered rather than Fourier’s law of heat conduction in the present flow analysis. Thermal conductivity varies with temperature. Resulting partial differential equations through laws of conservation of mass, linear momentum and energy are converted into ordinary differential equations by suitable transformations. Convergent series solutions for the velocity and temperature distributions are developed and discussed. Keywords: Oldroyd-B fluid, Variable sheet thickness, Cattaneo-Christov heat flux model, Heat source/sink, Temperature dependent thermal conductivity

  19. Power Efficiency of Systems Applied for Heating Building and Structure External Walls with Ventilated Air Spaces

    OpenAIRE

    I. F. Fialko; A. S. Statsenko

    2009-01-01

    The paper considers power-efficient systems applied for heating building and structure external walls with ventilated air spaces and prescribes directions and problems pertaining to power-efficiency improvement of such systems.

  20. Characteristics of combustion and heat transfer of excess enthalpy flames stabilized in a stagnation flow. 2nd Report. ; Heat flux at high flow rate and effects of Lewis number. Yodomi nagarechu ni anteika sareta choka enthalpy kaen no nensho oyobi etsudentatsu tokusei. 2. ; Koryuryo ni okeru netsuryusoku oyobi Lewis su no koka

    Energy Technology Data Exchange (ETDEWEB)

    Ito, S. (Daido Institute of Technology, Nagoya (Japan)); Asato, K.; Kawamura, T. (Gifu University, Gifu (Japan). Faculty of Engineerirng); Mazaki, T. (Daido Senior High School, Nagoya (Japan)); Umemura, H. (Mitsubishi Electric Corp., Tokyo (Japan))

    1993-08-25

    For the purpose of developing small-sized combustors of high heat transfer efficiency for household and business uses, a study has been carried out on the characteristics of an excess enthalpy flame stabilized in a stagnant flow, the maximum heat flux utilizable from flames through a heat receiver wall, the heat transfer characteristics near the extinction limits, and the effects of Lewis number (Le). Even when heat is drawn from the heat receiver wall in the downstream of flames, stable flames are kept until they extremely approach the heat receiver wall by the effect of preheating for lean methane-air flames of Le[approx equal]1.0 and lean propane-air flames of Le>1.0 and by the effect of preheating and Lewis effect for lean hydrogen-air flames of Le<1.0. In any flames, therefore, the heat flux to the heat receiver wall increases abruptly with the increase of stagnant velocity gradient and thereby the heat transfer characteristics at the heat receiver wall are improved. Heat transfer in the cases where flames exist on the outside and inside of the temperature boundary layer depend not on the thickness of the temperature boundary layer but on the position of flames. 6 refs., 9 figs.

  1. Analytical 1D models of the wall thermal resistance of rectangular minichannels applied in heat exchangers

    Directory of Open Access Journals (Sweden)

    Rybiński Witold

    2016-09-01

    Full Text Available The paper presents four 1-dimensional models of thermal resistance of walls in a heat exchanger with rectangular minichannels. The first model is the simplest one, with a single wall separating two fluids. The second model of the so called equivalent wall takes into account total volume of intermediate walls between layers of minichannels and of side walls of minichannels. The next two more complicated models take separately into account thermal resistance of these walls. In these two models side walls are treated as fins. The results of models comparison are presented. It is shown that thermal resistance may be neglected for metal walls but it should be taken into account for the walls made of plastics. For the case of non-neglected wall thermal resistance the optimum wall thickness was derived. Minichannel heat exchangers made of plastic are larger than those built of metal, but are significantly cheaper. It makes possible to use of such exchangers in inexpensive microscale ORC installations.

  2. Size effects in non-linear heat conduction with flux-limited behaviors

    Science.gov (United States)

    Li, Shu-Nan; Cao, Bing-Yang

    2017-11-01

    Size effects are discussed for several non-linear heat conduction models with flux-limited behaviors, including the phonon hydrodynamic, Lagrange multiplier, hierarchy moment, nonlinear phonon hydrodynamic, tempered diffusion, thermon gas and generalized nonlinear models. For the phonon hydrodynamic, Lagrange multiplier and tempered diffusion models, heat flux will not exist in problems with sufficiently small scale. The existence of heat flux needs the sizes of heat conduction larger than their corresponding critical sizes, which are determined by the physical properties and boundary temperatures. The critical sizes can be regarded as the theoretical limits of the applicable ranges for these non-linear heat conduction models with flux-limited behaviors. For sufficiently small scale heat conduction, the phonon hydrodynamic and Lagrange multiplier models can also predict the theoretical possibility of violating the second law and multiplicity. Comparisons are also made between these non-Fourier models and non-linear Fourier heat conduction in the type of fast diffusion, which can also predict flux-limited behaviors.

  3. Stability of narrow-gap MHD Taylor-Couette flow with radial heating and constant heat flux at the outer cylinder

    Directory of Open Access Journals (Sweden)

    Deka R.K.

    2005-01-01

    Full Text Available A linear stability analysis has been presented for hydromagnetic dissipative Couette flow, a viscous electrically conducting fluid between rotating concentric cylinders in the presence of a uniform axial magnetic field and constant heat flux at the outer cylinder. The narrow-gap equations with respect to axisymmetric disturbances are derived and solved by a direct numerical procedure. Both types of boundary conditions, conducting and non-conducting walls are considered. A parametric study covering on the basis of µ, the ratio of the angular velocity of the outer cylinder to that of inner cylinder, Q, the Hartmann number which represents the strength of the axial magnetic field, and N, the ratio of the Rayleigh number and Taylor number representing the supply of heat to the outer cylinder at constant rate is presented. The three cases of µ < 0 (counter rotating, µ > 0 (co-rotating and µ = 0 (stationary outer cylinder are considered wherein the magnetic Prandtl number is assumed to be small. Results show that the stability characteristics depend mainly on the conductivity on the cylinders and not on the heat supplied to the outer cylinder. As a departure from earlier results corresponding to isothermal as well as hydromagnetic flow, it is found that the critical wave number is strictly a monotonic decreasing function of Q for conducting walls. Also, the presence of constant heat flux leads to a fall in the critical wave number for counter rotating cylinders, which states that for large values of -µ, there occur transition from axisymmetric to non-axisymmetric disturbance whether the flow is hydrodynamic or hydromagnetic and this transition from axisymmetric to non-axisymmetric disturbance occur earlier as the strength of the magnetic field increases.

  4. The heat budgets of magmatic arcs: Discrepancies between heat flow measurements, volatile fluxes, and interpretations of the geologic record

    Science.gov (United States)

    Van Buer, N. J.

    2015-12-01

    Arc magmatic processes, from differentiation to emplacement, depend crucially on the rate at which heat and magma are supplied to the arc crust. In active arcs, the total heat flow can be estimated relatively directly by measuring and quantifying the amounts of heat lost via conduction, hydrothermal circulation, and eruption. This total heat flow can be used to calculate the implied magmatic flux at depth. Alternatively, magmatic flux in active arcs can be estimated from measured rates of volatile emissions, usually SO2. Unfortunately, heat flow and volatile flux data sufficiently detailed to make these calculations exist for only a handful of active arcs. In the geologic record, rates of arc magmatic flux have most frequently been estimated by measuring the preserved volumes of intrusive and extrusive products and dividing by the geochronologically determined duration of arc activity. This can be converted to heat flow by assuming a certain amount of heat carried per volume of magma. The ranges of magmatic flux estimated via either heat flow or SO2 are similar for modern arcs, but, on average, estimates from the geologic record are lower by about a factor of three (Fig. 1). This discrepancy may indicate that the assumption that preserved igneous rock volumes represent the total advective flux is a poor choice when interpreting the geologic record. Recycling of early solidified magma and loss of cumulates to the mantle may be important, i.e., the time-integrated advective flux might significantly exceed the net preserved intrusive volume. This is also supported by other lines of evidence, including geochemical mass-balance arguments, thermal models of basalt flux needed to allow substantial assimilation and/or crystal fractionation in the lower crust, high-temperature thermochronology in arcs, and thermal models of the conditions necessary to cause large, explosive eruptions from upper crustal magma chambers. Substantial recycling or convection within the arc crust

  5. Analytical model of particle and heat flux collection by dust immersed in dense magnetized plasmas

    Science.gov (United States)

    Vignitchouk, L.; Ratynskaia, S.; Tolias, P.

    2017-10-01

    A comprehensive analytical description is presented for the particle and heat fluxes collected by dust in dense magnetized plasmas. Compared to the widely used orbital motion limited theory, the suppression of cross-field transport leads to a strong reduction of the electron fluxes, while ion collection is inhibited by thin-sheath effects and the formation of a potential overshoot along the field lines. As a result, the incoming heat flux loses its sensitivity to the floating potential, thereby diminishing the importance of electron emission processes in dust survivability. Numerical simulations implementing the new model for ITER-like detached divertor plasmas predict a drastic enhancement of the dust lifetime.

  6. Atmospheric Forcing of the Winter Air–Sea Heat Fluxes over the Northern Red Sea

    KAUST Repository

    Papadopoulos, Vassilis P.

    2013-03-01

    The influence of the atmospheric circulation on the winter air–sea heat fluxes over the northern Red Sea is investigated during the period 1985–2011. The analysis based on daily heat flux values reveals that most of the net surface heat exchange variability depends on the behavior of the turbulent components of the surface flux (the sum of the latent and sensible heat). The large-scale composite sea level pressure (SLP) maps corresponding to turbulent flux minima and maxima show distinct atmospheric circulation patterns associated with each case. In general, extreme heat loss (with turbulent flux lower than −400 W m−2) over the northern Red Sea is observed when anticyclonic conditions prevail over an area extending from the Mediterranean Sea to eastern Asia along with a recession of the equatorial African lows system. Subcenters of high pressure associated with this pattern generate the required steep SLP gradient that enhances the wind magnitude and transfers cold and dry air masses from higher latitudes. Conversely, turbulent flux maxima (heat loss minimization with values from −100 to −50 W m−2) are associated with prevailing low pressures over the eastern Mediterranean and an extended equatorial African low that reaches the southern part of the Red Sea. In this case, a smooth SLP field over the northern Red Sea results in weak winds over the area that in turn reduce the surface heat loss. At the same time, southerlies blowing along the main axis of the Red Sea transfer warm and humid air northward, favoring heat flux maxima.

  7. Gyrokinetic projection of the divertor heat-flux width from present tokamaks to ITER

    Science.gov (United States)

    Chang, C. S.; Ku, S.; Loarte, A.; Parail, V.; Köchl, F.; Romanelli, M.; Maingi, R.; Ahn, J.-W.; Gray, T.; Hughes, J.; LaBombard, B.; Leonard, T.; Makowski, M.; Terry, J.

    2017-11-01

    The XGC1 edge gyrokinetic code is used to study the width of the heat-flux to divertor plates in attached plasma condition. The flux-driven simulation is performed until an approximate power balance is achieved between the heat-flux across the steep pedestal pressure gradient and the heat-flux on the divertor plates. The simulation results compare well against the empirical scaling λ q \\propto 1/BPγ obtained from present tokamak devices, where λ q is the divertor heat-flux width mapped to the outboard midplane, γ  =  1.19 as found by Eich et al (2013 Nucl. Fusion 53 093031), and B P is the magnitude of the poloidal magnetic field at the outboard midplane separatrix surface. This empirical scaling predicts λ q  ≲  1 mm when extrapolated to ITER, which would require operation with very high separatrix densities (n sep/n Greenwald  >  0.6) (Kukushkin et al 2013 J. Nucl. Mater. 438 S203) in the Q  =  10 scenario to achieve semi-detached plasma operation and high radiative fractions for acceptable divertor power fluxes. Using the same simulation code and technique, however, the projected λ q for ITER’s model plasma is 5.9 mm, which could be suggesting that operation in the ITER Q  =  10 scenario with acceptable divertor power loads may be obtained over a wider range of plasma separatrix densities and radiative fractions. The physics reason behind this difference is, according to the XGC1 results, that while the ion magnetic drift contribution to the divertor heat-flux width is wider in the present tokamaks, the turbulent electron contribution is wider in ITER. Study will continue to verify further this important projection. A high current C-Mod discharge is found to be in a mixed regime: While the heat-flux width by the ion neoclassical magnetic drift is still wider than the turbulent electron heat-flux width, the heat-flux magnitude is dominated by the narrower electron heat-flux.

  8. Flow boiling critical heat flux enhancement on the 2-D slice for boric acid and TSP solution

    Energy Technology Data Exchange (ETDEWEB)

    Park, H.M. [Korea Advanced Inst. of Science and Tech., Nuclear and Quantum Eng., Yuseong-gu, Daejeon (Korea, Republic of); Heo, S.; Song, C. [Korea Hydro & Nuclear Power Co., Nuclear Engineering and Technology Inst., Nuclear Engineering and Tech. Inst. (Korea, Republic of); Jeong, Y.H. [Korea Advanced Inst. of Science and Tech., Nuclear and Quantum Eng., Yuseong-gu, Daejeon (Korea, Republic of)

    2011-07-01

    The critical heat flux (CHF) on the reactor vessel external wall was measured using the small scale two-dimensional slice test section. The radius of the curvature and the channel area of the test section were 0.15 m and 0.03 mx0.03 m, respectively. The objectives are to assess the effects of additives (TSP, boric acid) and heated material (SA508) in inclination angle 90° and to investigate flow boiling CHF enhancement resulting from various working fluids of 5000 ppm tri-sodium phosphate (TSP, Na{sub 3}PO{sub 4}∙12H{sub 2}O) solution, 4000 ppm boric acid solution and mixture solution of TSP and boric acid. Boric acid solution didn't show CHF enhancement and TSP and mixture solution showed CHF enhancement (20~34%). (author)

  9. Development of advanced high heat flux and plasma-facing materials

    Science.gov (United States)

    Linsmeier, Ch.; Rieth, M.; Aktaa, J.; Chikada, T.; Hoffmann, A.; Hoffmann, J.; Houben, A.; Kurishita, H.; Jin, X.; Li, M.; Litnovsky, A.; Matsuo, S.; von Müller, A.; Nikolic, V.; Palacios, T.; Pippan, R.; Qu, D.; Reiser, J.; Riesch, J.; Shikama, T.; Stieglitz, R.; Weber, T.; Wurster, S.; You, J.-H.; Zhou, Z.

    2017-09-01

    Plasma-facing materials and components in a fusion reactor are the interface between the plasma and the material part. The operational conditions in this environment are probably the most challenging parameters for any material: high power loads and large particle and neutron fluxes are simultaneously impinging at their surfaces. To realize fusion in a tokamak or stellarator reactor, given the proven geometries and technological solutions, requires an improvement of the thermo-mechanical capabilities of currently available materials. In its first part this article describes the requirements and needs for new, advanced materials for the plasma-facing components. Starting points are capabilities and limitations of tungsten-based alloys and structurally stabilized materials. Furthermore, material requirements from the fusion-specific loading scenarios of a divertor in a water-cooled configuration are described, defining directions for the material development. Finally, safety requirements for a fusion reactor with its specific accident scenarios and their potential environmental impact lead to the definition of inherently passive materials, avoiding release of radioactive material through intrinsic material properties. The second part of this article demonstrates current material development lines answering the fusion-specific requirements for high heat flux materials. New composite materials, in particular fiber-reinforced and laminated structures, as well as mechanically alloyed tungsten materials, allow the extension of the thermo-mechanical operation space towards regions of extreme steady-state and transient loads. Self-passivating tungsten alloys, demonstrating favorable tungsten-like plasma-wall interaction behavior under normal operation conditions, are an intrinsic solution to otherwise catastrophic consequences of loss-of-coolant and air ingress events in a fusion reactor. Permeation barrier layers avoid the escape of tritium into structural and cooling

  10. Estimation of surface heat flux for ablation and charring of thermal protection material

    Science.gov (United States)

    Qian, Wei-qi; He, Kai-feng; Zhou, Yu

    2016-07-01

    Ablation of the thermal protection material of the reentry hypersonic flight vehicle is a complex physical and chemical process. To estimate the surface heat flux from internal temperature measurement is much more complex than the conventional inverse heat conduction problem case. In the paper, by utilizing a two-layer pyrogeneration-plane ablation model to model the ablation and charring of the material, modifying the finite control volume method to suit for the numerical simulation of the heat conduction equation with variable-geometry, the CGM along with the associated adjoint problem is developed to estimate the surface heat flux. This estimation method is verified with a numerical example at first, the results show that the estimation method is feasible and robust. The larger is the measurement noise, the greater is the deviation of the estimated result from the exact value, and the measurement noise of ablated surface position has a significant and more direct influence on the estimated result of surface heat flux. Furthermore, the estimation method is used to analyze the experimental data of ablation of blunt Carbon-phenolic material Narmco4028 in an arc-heater. It is shown that the estimated surface heat flux agrees with the heating power value of the arc-heater, and the estimation method is basically effective and potential to treat the engineering heat conduction problem with ablation.

  11. Effect of melter feed foaming on heat flux to the cold cap

    Czech Academy of Sciences Publication Activity Database

    Lee, S.; Hrma, P.; Pokorný, R.; Kloužek, Jaroslav; VanderVeer, B.J.; Dixon, D.R.; Luksic, S.A.; Rodriguez, C.P.; Chun, J.; Schweiger, M. J.; Kruger, A.A.

    2017-01-01

    Roč. 496, DEC 1 (2017), s. 54-65 ISSN 0022-3115 Institutional support: RVO:67985891 Keywords : cold cap * foam layer * heat flux * heat conductivity * evolved gas Subject RIV: JH - Ceramics, Fire-Resistant Materials and Glass Impact factor: 2.048, year: 2016

  12. Prediction of critical heat flux in fuel assemblies using a CHF table method

    Energy Technology Data Exchange (ETDEWEB)

    Chun, Tae Hyun; Hwang, Dae Hyun; Bang, Je Geon [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of); Baek, Won Pil; Chang, Soon Heung [Korea Advance Institute of Science and Technology, Taejon (Korea, Republic of)

    1997-12-31

    A CHF table method has been assessed in this study for rod bundle CHF predictions. At the conceptual design stage for a new reactor, a general critical heat flux (CHF) prediction method with a wide applicable range and reasonable accuracy is essential to the thermal-hydraulic design and safety analysis. In many aspects, a CHF table method (i.e., the use of a round tube CHF table with appropriate bundle correction factors) can be a promising way to fulfill this need. So the assessment of the CHF table method has been performed with the bundle CHF data relevant to pressurized water reactors (PWRs). For comparison purposes, W-3R and EPRI-1 were also applied to the same data base. Data analysis has been conducted with the subchannel code COBRA-IV-I. The CHF table method shows the best predictions based on the direct substitution method. Improvements of the bundle correction factors, especially for the spacer grid and cold wall effects, are desirable for better predictions. Though the present assessment is somewhat limited in both fuel geometries and operating conditions, the CHF table method clearly shows potential to be a general CHF predictor. 8 refs., 3 figs., 3 tabs. (Author)

  13. Dynamics of charged bulk viscous collapsing cylindrical source with heat flux

    Energy Technology Data Exchange (ETDEWEB)

    Shah, S.M.; Abbas, G. [The Islamia University of Bahawalpur, Department of Mathematics, Bahawalpur (Pakistan)

    2017-04-15

    In this paper, we have explored the effects of dissipation on the dynamics of charged bulk viscous collapsing cylindrical source which allows the out-flow of heat flux in the form of radiations. The Misner-Sharp formalism has been implemented to drive the dynamical equation in terms of proper time and radial derivatives. We have investigated the effects of charge and bulk viscosity on the dynamics of collapsing cylinder. To determine the effects of radial heat flux, we have formulated the heat transport equations in the context of Mueller-Israel-Stewart theory by assuming that thermodynamics viscous/heat coupling coefficients can be neglected within some approximations. In our discussion, we have introduced the viscosity by the standard (non-causal) thermodynamics approach. The dynamical equations have been coupled with the heat transport equation; the consequences of the resulting coupled heat equation have been analyzed in detail. (orig.)

  14. Uncertainty analysis of steady state incident heat flux measurements in hydrocarbon fuel fires.

    Energy Technology Data Exchange (ETDEWEB)

    Nakos, James Thomas

    2005-12-01

    The objective of this report is to develop uncertainty estimates for three heat flux measurement techniques used for the measurement of incident heat flux in a combined radiative and convective environment. This is related to the measurement of heat flux to objects placed inside hydrocarbon fuel (diesel, JP-8 jet fuel) fires, which is very difficult to make accurately (e.g., less than 10%). Three methods will be discussed: a Schmidt-Boelter heat flux gage; a calorimeter and inverse heat conduction method; and a thin plate and energy balance method. Steady state uncertainties were estimated for two types of fires (i.e., calm wind and high winds) at three times (early in the fire, late in the fire, and at an intermediate time). Results showed a large uncertainty for all three methods. Typical uncertainties for a Schmidt-Boelter gage ranged from {+-}23% for high wind fires to {+-}39% for low wind fires. For the calorimeter/inverse method the uncertainties were {+-}25% to {+-}40%. The thin plate/energy balance method the uncertainties ranged from {+-}21% to {+-}42%. The 23-39% uncertainties for the Schmidt-Boelter gage are much larger than the quoted uncertainty for a radiative only environment (i.e ., {+-}3%). This large difference is due to the convective contribution and because the gage sensitivities to radiative and convective environments are not equal. All these values are larger than desired, which suggests the need for improvements in heat flux measurements in fires.

  15. Diurnal Variation of Soil Heat Flux at an Antarctic Local Area during Warmer Months

    Directory of Open Access Journals (Sweden)

    Marco Alves

    2016-01-01

    Full Text Available Soil heat flux (G is one term in the energy balance equation, and it can be particularly important in regions with arid, bare, or thinly vegetated soil surfaces. However, in remote areas such as the Antarctic, this measurement is not routinely performed. The analysis of observational data collected by the ETA Project at the Brazilian Antarctic Station from December 2013 to March 2014 showed that, for the total daily energy flux, the surface soil flux heats the deeper soil layers during December and January and G acts as a heat source to the outer soil layers during February and March. With regard to daytime energy flux, G acts as a source of heat to the deeper layers. During the night-time, the soil is a heat source to the shallower soil layers and represents at least 29% of the net night-time radiation. A relatively simple method—the objective hysteresis method (OHM—was successfully applied to determine the surface soil heat flux using net radiation observations. A priori, the OHM coefficients obtained in this study may only be used for short-time parameterizations and for filling data gaps at this specific site.

  16. Impacts of soil–aquifer heat and water fluxes on simulated global climate

    Directory of Open Access Journals (Sweden)

    N. Y. Krakauer

    2013-05-01

    Full Text Available Climate models have traditionally only represented heat and water fluxes within relatively shallow soil layers, but there is increasing interest in the possible role of heat and water exchanges with the deeper subsurface. Here, we integrate an idealized 50 m deep aquifer into the land surface module of the GISS ModelE general circulation model to test the influence of aquifer–soil moisture and heat exchanges on climate variables. We evaluate the impact on the modeled climate of aquifer–soil heat and water fluxes separately, as well as in combination. The addition of the aquifer to ModelE has limited impact on annual-mean climate, with little change in global mean land temperature, precipitation, or evaporation. The seasonal amplitude of deep soil temperature is strongly damped by the soil–aquifer heat flux. This not only improves the model representation of permafrost area but propagates to the surface, resulting in an increase in the seasonal amplitude of surface air temperature of > 1 K in the Arctic. The soil–aquifer water and heat fluxes both slightly decrease interannual variability in soil moisture and in land-surface temperature, and decrease the soil moisture memory of the land surface on seasonal to annual timescales. The results of this experiment suggest that deepening the modeled land surface, compared to modeling only a shallower soil column with a no-flux bottom boundary condition, has limited impact on mean climate but does affect seasonality and interannual persistence.

  17. The CellFlux Storage Concept for Increased Flexibility in Sensible Heat Storage

    OpenAIRE

    Odenthal, Christian; Steinmann, Wolf-Dieter; Eck, Markus

    2015-01-01

    Packed beds using air at atmospheric pressure as heat transferring medium are the most cost effective systems for sensible heat storage. The basic idea of the CellFlux concept is to apply this concept also for liquid and/or pressurized primary HTFs by the introduction of an intermediate working fluid cycle. A heat exchanger is used for transferring energy between the primary HTF and the intermediate air cycle which eventually transfers the energy to a packed bed. The CellFlux concept...

  18. Remote Heat Flux Using a Self Calibration Multiwavelength Pyrometer and a Transparent Material

    Science.gov (United States)

    Ng, Daniel

    1998-01-01

    A self calibrating multiwavelength pyrometer was used to conduct remote heat flux measurements using a transparent sapphire disk by determining the sapphire disk's front and back surface temperatures. Front surface temperature (Tfs) was obtained from detection of surface emitted radiation at long wavelengths (k = 6 gm). Back surface temperature (Tbs) was obtained from short wavelength (1 to 5 gm) radiation transmitted through the sapphire disk. The thermal conductivity of the sapphire disk and the heat transfer coefficients h, and h2 of its surfaces are determined experimentally. An analysis of the heat flux measurement is presented.

  19. Remote Heat Flux Measurement Using a Self Calibration Multiwavelength Pyrometer and a Transparent Material

    Science.gov (United States)

    Ng, Daniel

    1998-01-01

    A self calibrating multiwavelength pyrometer was used to conduct remote heat flux measurements using a transparent sapphire disk by determining the sapphire disk's front and back surface temperatures. Front surface temperature (Tfs) was obtained from detection of surface emitted radiation at long wavelengths (lambda > 6 micrometers). Back surface temperature (Tbs) was obtained from short wavelength (1 to 5 micrometers) radiation transmitted through the sapphire disk. The thermal conductivity k of the sapphire disk and the heat transfer coefficients h(sub 1) and h(sub 2) of its surfaces are determined experimentally. An analysis of the heat flux measurement is presented.

  20. Effective temperature in nonequilibrium state with heat flux using discrete variable model

    Science.gov (United States)

    Sobolev, S. L.

    2017-09-01

    The effective temperature, which acts as a criterion for thermalization in systems with heat flux, has been introduced on the bases of a relatively simple discrete variable model (DVM). The DVM is inherently nonlocal and can be used to describe multi-length and -time scale heat conduction including low-dimensional and sub-continuum regimes. Under far from equilibrium conditions when the heat flux tends to its maximum possible value, the effective temperature and the corresponding nonequilibrium entropy go to zero, which points to a possible generalization of the third law in nonequilibrium situations.

  1. Numerical heat transfer in a cavity with a solar control coating deposited to a vertical semitransparent wall

    Science.gov (United States)

    Alvarez, G.; Estrada, C. A.

    2000-12-01

    A transient two-dimensional computational model of combined natural convection, conduction, and radiation in a cavity with an aspect ratio of one, containing air as a laminar and non-participating fluid, is presented. The cavity has two opaque adiabatic horizontal walls, one opaque isothermal vertical wall, and an opposite semitransparent wall, which consists of a 6-mm glass sheet with a solar control coating of SnS-CuxS facing the cavity. The semitransparent wall also exchanges heat by convection and radiation from its external surface to the surroundings and allows solar radiation pass through into the interior of the cavity. The momentum and energy equations in the transient state were solved by finite differences using the alternating direction implicit (ADI) technique. The transient conduction equation and the radiative energy flux boundary conditions are coupled to these equations. The results in this paper are limited to the following conditions: 104Gr106, an isothermal vertical cold wall of 21°C, outside air temperatures in the range 30°CT040°C and incident solar radiation of AM2 (750 W m-2) normal to the semitransparent wall. The model allows calculation of the redistribution of the absorbed component of solar radiation to the inside and outside of the cavity. The influences of the time step and mesh size were considered. Using arguments of energy balance in the cavity, it was found that the percentage difference was less than 4 per cent, showing a possible total numerical error less than this number. For Gr=106 a wave appeared in the upper side of the cavity, suggesting the influence of the boundary walls over the air flow inside the cavity. A Nusselt number correlation as a function of the Rayleigh number is presented. Copyright

  2. Satellite data based approach for the estimation of anthropogenic heat flux over urban areas

    Science.gov (United States)

    Nitis, Theodoros; Tsegas, George; Moussiopoulos, Nicolas; Gounaridis, Dimitrios; Bliziotis, Dimitrios

    2017-09-01

    Anthropogenic effects in urban areas influence the thermal conditions in the environment and cause an increase of the atmospheric temperature. The cities are sources of heat and pollution, affecting the thermal structure of the atmosphere above them which results to the urban heat island effect. In order to analyze the urban heat island mechanism, it is important to estimate the anthropogenic heat flux which has a considerable impact on the urban energy budget. The anthropogenic heat flux is the result of man-made activities (i.e. traffic, industrial processes, heating/cooling) and thermal releases from the human body. Many studies have underlined the importance of the Anthropogenic Heat Flux to the calculation of the urban energy budget and subsequently, the estimation of mesoscale meteorological fields over urban areas. Therefore, spatially disaggregated anthropogenic heat flux data, at local and city scales, are of major importance for mesoscale meteorological models. The main objectives of the present work are to improve the quality of such data used as input for mesoscale meteorological models simulations and to enhance the application potential of GIS and remote sensing in the fields of climatology and meteorology. For this reason, the Urban Energy Budget concept is proposed as the foundation for an accurate determination of the anthropogenic heat discharge as a residual term in the surface energy balance. The methodology is applied to the cities of Athens and Paris using the Landsat ETM+ remote sensing data. The results will help to improve our knowledge on Anthropogenic Heat Flux, while the potential for further improvement of the methodology is also discussed.

  3. Global anthropogenic heat flux database with high spatial resolution

    Science.gov (United States)

    Dong, Y.; Varquez, A. C. G.; Kanda, M.

    2017-02-01

    This study developed a top-down method for estimating global anthropogenic heat emission (AHE), with a high spatial resolution of 30 arc-seconds and temporal resolution of 1 h. Annual average AHE was derived from human metabolic heating and primary energy consumption, which was further divided into three components based on consumer sector. The first and second components were heat loss and heat emissions from industrial sectors equally distributed throughout the country and populated areas, respectively. The third component comprised the sum of emissions from commercial, residential, and transportation sectors (CRT). Bulk AHE from the CRT was proportionally distributed using a global population dataset, with a radiance-calibrated nighttime lights adjustment. An empirical function to estimate monthly fluctuations of AHE based on gridded monthly temperatures was derived from various Japanese and American city measurements. Finally, an AHE database with a global coverage was constructed for the year 2013. Comparisons between our proposed AHE and other existing datasets revealed that the problem of overestimation of AHE intensity in previous top-down models was mitigated by the separation of energy consumption sectors; furthermore, the problem of AHE underestimation at central urban areas was solved by the nighttime lights adjustment. A strong agreement in the monthly profiles of AHE between our database and other bottom-up datasets further proved the validity of the current methodology. Investigations of AHE for the 29 largest urban agglomerations globally highlighted that the share of heat emissions from CRT sectors to the total AHE at the city level was 40-95%; whereas that of metabolic heating varied with the city's level of development by a range of 2-60%. A negative correlation between gross domestic product (GDP) and the share of metabolic heating to a city's total AHE was found. Globally, peak AHE values were found to occur between December and February, while

  4. Estimation of peak heat flux onto the targets for CFETR with extended divertor leg

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Chuanjia; Chen, Bin [School of Nuclear Science and Technology, University of Science and Technology of China, 96 Jinzhai Road, Hefei, Anhui 230026 (China); Xing, Zhe [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, Anhui 230031 (China); Wu, Haosheng [School of Nuclear Science and Technology, University of Science and Technology of China, 96 Jinzhai Road, Hefei, Anhui 230026 (China); Mao, Shifeng, E-mail: sfmao@ustc.edu.cn [School of Nuclear Science and Technology, University of Science and Technology of China, 96 Jinzhai Road, Hefei, Anhui 230026 (China); Luo, Zhengping; Peng, Xuebing [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, Anhui 230031 (China); Ye, Minyou [School of Nuclear Science and Technology, University of Science and Technology of China, 96 Jinzhai Road, Hefei, Anhui 230026 (China); Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, Anhui 230031 (China)

    2016-11-01

    Highlights: • A hypothetical geometry is assumed to extend the outer divertor leg in CFETR. • Density scan SOLPS simulation is done to study the peak heat flux onto target. • Attached–detached regime transition in out divertor occurs at lower puffing rate. • Unexpected delay of attached–detached regime transition occurs in inner divertor. - Abstract: China Fusion Engineering Test Reactor (CFETR) is now in conceptual design phase. CFETR is proposed as a good complement to ITER for demonstrating of fusion energy. Divertor is a crucial component which faces the plasmas and handles huge heat power for CFETR and future fusion reactor. To explore an effective way for heat exhaust, various methods to reduce the heat flux to divertor target should be considered for CFETR. In this work, the effect of extended out divertor leg on the peak heat flux is studied. The magnetic configuration of the long leg divertor is obtained by EFIT and Tokamak Simulation Code (TSC), while a hypothetical geometry is assumed to extend the out divertor leg as long as possible inside vacuum vessel. A SOLPS simulation is performed to study peak heat flux of the long leg divertor for CFETR. D{sub 2} gas puffing is used and increasing of the puffing rate means increase of plasma density. Both peak heat flux onto inner and outer targets are below 10 MW/m{sup 2} is achieved. A comparison between the peak heat flux between long leg and conventional divertor shows that an attached–detached regime transition of out divertor occurs at lower gas puffing gas puffing rate for long leg divertor. While for the inner divertor, even the configuration is almost the same, the situation is opposite.

  5. The sensivity of geomagnetic reversal frequency to core-mantle boundary heat flux magnitude and heterogeneity.

    Science.gov (United States)

    Metman, Maurits; de Groot, Lennart; Thieulot, Cedric; Biggin, Andrew; Spakman, Wim

    2015-04-01

    For a number of decades the core-mantle boundary (CMB) heat flux has been thought to be a key parameter controlling the geomagnetic field. A CMB heat flow increase is assumed to destabilize the geodynamo, increasing and decreasing the reversal frequency and dipole moment, respectively. The opposite case where a CMB flux decrease induces a relatively high dipole moment, as well as a low reversal frequency, would correspond to the characteristics of a superchron (Biggin et al., 2012). So far, only the magnitude of the CMB heat flux has been subject of research. However, the temporal and spatial heat flux distribution across the CMB also appears to have an influence on the geomagnetic reversal frequency. For example, the amount of heat flux heterogeneity may also be associated with a destabilization of the dynamo, increasing the reversal frequency (Olson et al., 2010). In this work we set out to assess: - (1) How the geomagnetic field intensity and reversals are predominantly sensitive to CMB heat flux magnitude or heterogeneity; - (2) what combination of magnitude and heterogeneity best reproduces the geomagnetic record on the 10 Myr timescale. To this end we use the PARODY software and test for a number of CMB heat flow modes (spherical harmonics of increasing degree and order, with an amplitude of 10 mW/m^2) and magnitudes (ranging from 20 to 100 mW/m^2). We will show our modeling results of how CMB heat flow magnitude and heterogeneity control the paleomagnetic record in terms of reversal frequency and dipole moment. Also relevant snapshots in time of outer core convection and thermal/magnetic structure will be shown. References Biggin et al. (2012). Nature Geoscience, 5(8):526-533. Olson et al. (2010). PEPI, 180(1-2):66 - 79.

  6. CFD simulation on critical heat flux of flow boiling in IVR-ERVC of a nuclear reactor

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Xiang, E-mail: zhangxiang3@snptc.com.cn [State Nuclear Power Technology Research & Development Center, South Area, Future Science and Technology Park, Chang Ping District, Beijing 102209 (China); Hu, Teng [State Nuclear Power Technology Research & Development Center, South Area, Future Science and Technology Park, Chang Ping District, Beijing 102209 (China); Chen, Deqi, E-mail: chendeqi@cqu.edu.cn [Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Chongqing University, 400044 (China); Zhong, Yunke; Gao, Hong [Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Chongqing University, 400044 (China)

    2016-08-01

    Highlights: • CFD simulation on CHF of boiling two-phase flow in ERVC is proposed. • CFD simulation result of CHF agrees well with that of experimental result. • The characteristics of boiling two-phase flow and boiling crisis are analyzed. - Abstract: The effectiveness of in-vessel retention (IVR) by external reactor vessel cooling (ERVC) strongly depends on the critical heat flux (CHF). As long as the local CHF does not exceed the local heat flux, the lower head of the pressure vessel can be cooled sufficiently to prevent from failure. In this paper, a CFD simulation is carried out to investigate the CHF of ERVC. This simulation is performed by a CFD code fluent couple with a boiling model by UDF (User-Defined Function). The experimental CHF of ERVC obtained by State Nuclear Power Technology Research and Development Center (SNPTRD) is used to validate this CFD simulation, and it is found that the simulation result agrees well with the experimental result. Based on the CFD simulation, detailed analysis focusing on the pressure distribution, velocity distribution, void fraction distribution, heating wall temperature distribution are proposed in this paper.

  7. Heat transfer modelling of first walls subject to plasma disruption

    Energy Technology Data Exchange (ETDEWEB)

    Fillo, J.A.; Makowitz, H.

    1981-01-01

    A brief description of the plasma disruption problem and potential thermal consequences to the first wall is given. Thermal models reviewed include: a) melting of a solid with melt layer in place; b) melting of a solid with complete removal of melt (ablation); c) melting/vaporization of a solid; and d) vaporization of a solid but no phase change affecting the temperature profile.

  8. Revisiting the global surface energy budgets with maximum-entropy-production model of surface heat fluxes

    Science.gov (United States)

    Huang, Shih-Yu; Deng, Yi; Wang, Jingfeng

    2017-09-01

    The maximum-entropy-production (MEP) model of surface heat fluxes, based on contemporary non-equilibrium thermodynamics, information theory, and atmospheric turbulence theory, is used to re-estimate the global surface heat fluxes. The MEP model predicted surface fluxes automatically balance the surface energy budgets at all time and space scales without the explicit use of near-surface temperature and moisture gradient, wind speed and surface roughness data. The new MEP-based global annual mean fluxes over the land surface, using input data of surface radiation, temperature data from National Aeronautics and Space Administration-Clouds and the Earth's Radiant Energy System (NASA CERES) supplemented by surface specific humidity data from the Modern-Era Retrospective Analysis for Research and Applications (MERRA), agree closely with previous estimates. The new estimate of ocean evaporation, not using the MERRA reanalysis data as model inputs, is lower than previous estimates, while the new estimate of ocean sensible heat flux is higher than previously reported. The MEP model also produces the first global map of ocean surface heat flux that is not available from existing global reanalysis products.

  9. A Study of Heat Flux Induced Dryout in Capillary Grooves

    Science.gov (United States)

    1992-12-01

    to operate the heat pipe at or near maximum heat transfer conditions. One of the problems with maximizing the performance is the danger of living on...the characteristic dimension of the groove or pore. At this point, the pressure gradient between the condenser and evaporator is maximized , and...Note: T1|=25 - -142- RUN LETTER DESl •GATION: T9 DATE: 10-02-1992 TIME: 14:55:48 GROOVE NIB R: I THEB MRMETRIC PRESSURE IS 29.011 M OF IMER Y THE

  10. Comparison of heat flux estimations from two turbulent exchange models based on thermal UAV data.

    Science.gov (United States)

    Hoffmann, Helene; Nieto, Hector; Jensen, Rasmus; Friborg, Thomas

    2015-04-01

    Advantages of UAV (Unmanned Aerial Vehicle) data-collection, compared to more traditional data-collections are numerous and already well-discussed (Berni et al., 2009; Laliberte et al., 2011; Turner et al., 2012). However studies investigating the quality and applications of UAV-data are crucial if advantages are to be beneficial for scientific purposes. In this study, thermal data collected over an agricultural site in Denmark have been obtained using a fixed-wing UAV and investigated for the estimation of heat fluxes. Estimation of heat fluxes requires high precision data and careful data processing. Latent, sensible and soil heat fluxes are estimates through two models of the two source energy modelling scheme driven by remotely sensed observations of land surface temperature; the original TSEB (Norman et al., 1995) and the DTD (Norman et al., 2000) which builds on the TSEB. The DTD model accounts for errors arising when deriving radiometric temperatures and can to some extent compensate for the fact that thermal cameras rarely are accurate. The DTD model requires an additional set of remotely sensed data during morning hours of the day at which heat fluxes are to be determined. This makes the DTD model ideal to use when combined with UAV data, because acquisition of data is not limited by fixed time by-passing tracks like satellite images (Guzinski et al., 2013). Based on these data, heat fluxes are computed from the two models and compared with fluxes from an eddy covariance station situated within the same designated agricultural site. This over-all procedure potentially enables an assessment of both the collected thermal UAV-data and of the two turbulent exchange models. Results reveal that both TSEB and DTD models compute heat fluxes from thermal UAV data that is within a very reasonable range and also that estimates from the DTD model is in best agreement with the eddy covariance system.

  11. Spatial Disaggregation of Latent Heat Flux Using Contextual Models over India

    Directory of Open Access Journals (Sweden)

    Rajasekaran Eswar

    2017-09-01

    Full Text Available Estimation of latent heat flux at the agricultural field scale is required for proper water management. The current generation thermal sensors except Landsat-8 provide data on the order of 1000 m. The aim of this study is to test three approaches based on contextual models using only remote sensing datasets for the disaggregation of latent heat flux over India. The first two approaches are, respectively, based on the estimation of the evaporative fraction (EF and solar radiation ratio at coarser resolution and disaggregating them to yield the latent heat flux at a finer resolution. The third approach is based on disaggregation of the thermal data and estimating a finer resolution latent heat flux. The three approaches were tested using MODIS datasets and the validation was done using the Bowen Ratio energy balance observations at five sites across India. From the validation, it was observed that the first two approaches performed similarly and better than the third approach at all five sites. The third approach, based on the disaggregation of the thermal data, yielded larger errors. In addition to better performance, the second approach based on the disaggregation of solar radiation ratio was simpler and required lesser data processing than the other approaches. In addition, the first two approaches captured the spatial pattern of latent heat flux without introducing any artefacts in the final output.

  12. The Impact of Trends in the Large Scale Atmospheric Circulation on Mediterranean Surface Turbulent Heat Fluxes

    Science.gov (United States)

    Romanski, Joy; Hameed, Sultan

    2015-01-01

    Interannual variations of latent heat fluxes (LHF) and sensible heat fluxes (SHF) over the Mediterranean for the boreal winter season (DJF) show positive trends during 1958-2011. Comparison of correlations between the heat fluxes and the intensity and location of the Azores High (AH), and the NAO and East Atlantic-West Russia (EAWR) teleconnections, along with analysis of composites of surface temperature, humidity and wind fields for different teleconnection states, demonstrates that variations of the AH are found to explain the heat flux changes more successfully than the NAO and the EAWR. Trends in sea level pressure and longitude of the Azores High during DJF show a strengthening, and an eastward shift. DJF Azores High pressure and longitude are shown to co-vary such that variability of the Azores High occurs along an axis defined by lower pressure and westward location at one extreme, and higher pressure and eastward location at the other extreme. The shift of the Azores High from predominance of the low/west state to the high/east state induces trends in Mediterranean Sea surface winds, temperature and moisture. These, combined with sea surface warming trends, produce trends in wintertime Mediterranean Sea sensible and latent heat fluxes.

  13. Modelling sub-daily latent heat fluxes from a small reservoir

    Science.gov (United States)

    McGloin, Ryan; McGowan, Hamish; McJannet, David; Burn, Stewart

    2014-11-01

    Accurate methods of latent heat flux quantification are essential for water management and for use in hydrological and meteorological models. Currently the effect of small lakes in most numerical weather prediction modelling systems is either entirely ignored or crudely parameterized. In order to test methods for modelling hourly latent heat flux from small water bodies, this study compares results from several modelling approaches to values measured by the eddy covariance method at an agricultural reservoir in southeast Queensland, Australia. Mass transfer estimates of LE calculated using the theoretical mass transfer model and using the Tanny et al. (2008) and Sacks et al. (1994) bulk transfer coefficients showed the best relationship with measured values under a range of meteorological conditions. The theoretical model showed the strongest correlation with measured values, while the Tanny et al. (2008) and Sacks et al. (1994) models had regression equation slopes with the closest proximity to 1. Latent heat fluxes estimated using the Granger and Hedstrom (2011) evaporation model, that was specifically developed for use at small reservoirs, showed a poor relationship with measured values, particularly in stable atmospheric conditions. The 1-dimensional hydrodynamics model, DYRESM, was used to obtain predictions of hourly latent heat flux without the use of water surface temperature measurements. DYRESM estimates of latent heat flux showed a slightly worse relationship with measured values than those predicted using the traditional mass transfer models (which used measurements of water surface temperature). However, DYRESM performed considerably better than the Granger and Hedstrom (2011) model.

  14. Error field measurement, correction and heat flux balancing on Wendelstein 7-X

    Science.gov (United States)

    Lazerson, Samuel A.; Otte, Matthias; Jakubowski, Marcin; Israeli, Ben; Wurden, Glen A.; Wenzel, Uwe; Andreeva, Tamara; Bozhenkov, Sergey; Biedermann, Christoph; Kocsis, Gábor; Szepesi, Tamás; Geiger, Joachim; Pedersen, Thomas Sunn; Gates, David; The W7-X Team

    2017-04-01

    The measurement and correction of error fields in Wendelstein 7-X (W7-X) is critical to long pulse high beta operation, as small error fields may cause overloading of divertor plates in some configurations. Accordingly, as part of a broad collaborative effort, the detection and correction of error fields on the W7-X experiment has been performed using the trim coil system in conjunction with the flux surface mapping diagnostic and high resolution infrared camera. In the early commissioning phase of the experiment, the trim coils were used to open an n/m  =  1/2 island chain in a specially designed magnetic configuration. The flux surfacing mapping diagnostic was then able to directly image the magnetic topology of the experiment, allowing the inference of a small  ∼4 cm intrinsic island chain. The suspected main sources of the error field, slight misalignment and deformations of the superconducting coils, are then confirmed through experimental modeling using the detailed measurements of the coil positions. Observations of the limiters temperatures in module 5 shows a clear dependence of the limiter heat flux pattern as the perturbing fields are rotated. Plasma experiments without applied correcting fields show a significant asymmetry in neutral pressure (centered in module 4) and light emission (visible, H-alpha, CII, and CIII). Such pressure asymmetry is associated with plasma-wall (limiter) interaction asymmetries between the modules. Application of trim coil fields with n  =  1 waveform correct the imbalance. Confirmation of the error fields allows the assessment of magnetic fields which resonate with the n/m  =  5/5 island chain. Notice: This manuscript has been authored by Princeton University under Contract Number DE-AC02-09CH11466 with the U.S. Department of Energy. The publisher, by accepting the article for publication acknowledges, that the United States Government retains a non-exclusive, paid-up, irrevocable, world

  15. Estimation of bulk transfer coefficient for latent heat flux (Ce)

    Digital Repository Service at National Institute of Oceanography (India)

    Sadhuram, Y.

    Coefficients in Diabatic Conditions’, Bow~dary-Layer Meteo- rol. 8, 465-474. Murakami. T., Nakazowa. T., and He, T.: 1984, ‘On the 40-50 Day Oscillations During the Monsoon During the Northern Hemisphere Summer. Part II: Heat and Moisture Budget’, J. Mereoi...

  16. Round-robin test of heat flux sensors

    NARCIS (Netherlands)

    Turzo-Andras, E.; Blokland, H.; Hammerschmidt, U.; Rudtsch, S.; Stacey, C.; Krös, C.; Magyarlaki, T.; Nemeth, S.

    2011-01-01

    The first intercomparison on the density of heat flow-rate measurements has been organized by MKEH (Hungarian Trade Licensing Office, Metrology Division) within the framework of EUROMET (Project No. 426). This round-robin test gives evidence about the measurement capabilities of the local

  17. Temperature mapping, thermal diffusivity and subsoil heat flux at ...

    Indian Academy of Sciences (India)

    Thermal diffusivity () of the soil has been calculated by range and lag methods and also from amplitudes and phase angles of first and second harmonics. The two methods lead to similar results. Diurnal soil heat ux and soil temperatures at different depths are modelled and found to be comparable with observations.

  18. Temperature mapping, thermal diffusivity and subsoil heat flux at ...

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    the day by intense solar radiation than the lay- ers beneath, resulting in temperature gradient between the surface and subsoil on the one hand and surface and air layers near the ground on the other. Within the soil this causes heat flow downward as a thermal wave, the amplitude of which changes with depth. Estimation of ...

  19. On the effect of laterally varying boundary heat flux on rapidly rotating spherical shell convection

    Science.gov (United States)

    Sahoo, Swarandeep; Sreenivasan, Binod

    2017-08-01

    The onset of convection in a rotating spherical shell subject to laterally varying heat flux at the outer boundary is considered in this paper. The focus is on the geophysically relevant regime of rapid rotation (low Ekman number) where the natural length scale of convection is significantly smaller than the length scale imposed by the boundary heat flux pattern. Contrary to earlier studies at a higher Ekman number, we find a substantial reduction in the onset Rayleigh number Rac with increasing lateral variation. The decrease in Rac is shown to be closely correlated to the equatorial heat flux surplus in the steady, basic state solution. The consistency of such a correlation makes the estimation of Rac possible without solving the full stability problem. The steady baroclinic flow has a strong cyclone-anticyclone asymmetry in the kinetic helicity only for equatorially symmetric lateral variations, with possible implications for dynamo action. Equatorially antisymmetric variations, on the other hand, break the symmetry of the mean flow, in turn negating its helicity. Analysis of the perturbation solution reveals strongly localized clusters through which convection rolls drift in and out at a frequency higher than that for the reference case with homogeneous boundary heat flux. Large lateral variations produce a marked decrease in the azimuthal length scale of columns, which indicates that small-scale motions are essential to the transport of heat in rapidly rotating, localized convection. With an equatorially antisymmetric heat flux pattern, convection in individual clusters goes through an asynchronous wax-wane cycle whose frequency is much lower than the drift rate of the columns. These continual variations in convection intensity may in turn result in fluctuations in the magnetic field intensity, an effect that needs to be considered in dynamo models. Finally, there is a notable analogy between the role of a laterally varying boundary heat flux and the role of a

  20. Critical heat flux (CHF) phenomenon on a downward facing curved surface

    Energy Technology Data Exchange (ETDEWEB)

    Cheung, F.B.; Haddad, K.H.; Liu, Y.C. [Pennsylvania State Univ., University Park, PA (United States). Dept. of Mechanical Engineering

    1997-06-01

    This report describes a theoretical and experimental study of the boundary layer boiling and critical heat flux phenomena on a downward facing curved heating surface, including both hemispherical and toroidal surfaces. A subscale boundary layer boiling (SBLB) test facility was developed to measure the spatial variation of the critical heat flux and observe the underlying mechanisms. Transient quenching and steady-state boiling experiments were performed in the SBLB facility under both saturated and subcooled conditions to obtain a complete database on the critical heat flux. To complement the experimental effort, an advanced hydrodynamic CHF model was developed from the conservation laws along with sound physical arguments. The model provides a clear physical explanation for the spatial variation of the CHF observed in the SBLB experiments and for the weak dependence of the CHF data on the physical size of the vessel. Based upon the CHF model, a scaling law was established for estimating the local critical heat flux on the outer surface of a heated hemispherical vessel that is fully submerged in water. The scaling law, which compares favorably with all the available local CHF data obtained for various vessel sizes, can be used to predict the local CHF limits on large commercial-size vessels. This technical information represents one of the essential elements that is needed in assessing the efficacy of external cooling of core melt by cavity flooding as a severe accident management strategy. 83 figs., 3 tabs.

  1. Heat flux: thermohydraulic investigation of solar air heaters used in agro-industrial applications

    Science.gov (United States)

    Rahmati Aidinlou, H.; Nikbakht, A. M.

    2017-03-01

    A new design of solar air heater simulator is presented to comply with the extensive applications inagro-industry. A wise installation of increased heat transfer surface area provided uniform and efficient heat diffusion over the duct. Nusselt number and friction factor have been investigated based on the constant roughness parameters such as relative roughness height (e/D), relative roughness pitch (P/e), angle of attack (α) and aspect ratio with Reynolds numbers ranging from 5000 to 19,000 in the fully developed region. Heat fluxes of 800, 900 and 1000 Wm-2 were provided. The enhancement in friction factor is observed to be 3.1656, 3.47 and 3.0856 times, and for the Nusselt number either, augmentation is calculated to be 1.4437, 1.4963 and 1.535 times, respectively, over the smooth duct for 800, 900 and 1000 Wm-2 heat fluxes. Thermohydraulic performance is plotted versus the Reynolds number based on the aforementioned roughness parameters at varying heat fluxes. The results show up that thermohydraulic performance is found to be maximum for 1000 Wm-2 at the average Reynolds number of 5151. Based on the results, we can verify that the introduced solar simulator can help analyzing and developing solar collector installations at the simulated heat fluxes.

  2. Prototyping phase of the high heat flux scraper element of Wendelstein 7-X

    Energy Technology Data Exchange (ETDEWEB)

    Boscary, J., E-mail: jean.boscary@ipp.mpg.de [Max Planck Institute for Plasma Physics, Garching (Germany); Greuner, H. [Max Planck Institute for Plasma Physics, Garching (Germany); Ehrke, G. [Max Planck Institute for Plasma Physics, Greifswald (Germany); Böswirth, B.; Wang, Z. [Max Planck Institute for Plasma Physics, Garching (Germany); Clark, E. [University of Tennessee, Knoxville (United States); Lumsdaine, A. [Oak Ridge National Laboratory, USA National Laboratory, Oak Ridge, Tennessee (United States); Tretter, J. [Max Planck Institute for Plasma Physics, Garching (Germany); McGinnis, D.; Lore, J. [Oak Ridge National Laboratory, USA National Laboratory, Oak Ridge, Tennessee (United States); Ekici, K. [University of Tennessee, Knoxville (United States)

    2016-11-01

    Highlights: • Aim of scraper element: reduction of heat loads on high heat flux divertor ends. • Design: actively water-cooled for 20 MW/m{sup 2} local heat loads. • Technology: CFC NB31 monoblocks bonded by HIP to CuCrZr cooling tube. • Successful high heat flux testing up to 20 MW/m{sup 2}. - Abstract: The water-cooled high heat flux scraper element aims to reduce excessive heat loads on the target element ends of the actively cooled divertor of Wendelstein 7-X. Its purpose is to intercept some of the plasma fluxes both upstream and downstream before they reach the divertor surface. The scraper element has 24 identical plasma facing components (PFCs) divided into 6 modules. One module has 4 PFCs hydraulically connected in series by 2 water boxes. A PFC, 247 mm long and 28 mm wide, has 13 monoblocks made of CFC NB31 bonded by hot isostatic pressing onto a CuCrZr cooling tube equipped with a copper twisted tape. 4 full-scale prototypes of PFCs have been successfully tested in the GLADIS facility up to 20 MW/m{sup 2}. The difference observed between measured and calculated surface temperatures is probably due to the inhomogeneity of CFC properties. The design of the water box prototypes has been detailed to allow the junction between the cooling pipe of the PFCs and the water boxes by internal orbital welding. The prototypes are presently under fabrication.

  3. Dry Block Calibrator Using Heat Flux Sensors and an Adiabatic Shield

    Science.gov (United States)

    Hohmann, M.; Marin, S.; Schalles, M.; Krapf, G.; Fröhlich, T.

    2015-08-01

    The main problems of conventional dry block calibrators are axial temperature gradients and calibration results which are strongly influenced by the geometry and the thermal properties of the thermometers under test. To overcome these disadvantages, a new dry block calibrator with improved homogeneity of the inner temperature field was developed for temperatures in the range from room temperature up to . The inner part of the dry block calibrator is a cylindrical normalization block which is divided into three parts in the axial direction. Between these parts, heat flux sensors are placed to measure the heat flux in the axial direction inside the normalization block. Each part is attached to a separate tube-shaped heating zone of which the heating power can be controlled in a way that the axial heat flux measured by means of the heat flux sensors is zero. Additionally, an internal reference thermometer is used to control the absolute value of the temperature inside the normalization block. To minimize the radial heat flux, an adiabatic shield is constructed which is composed of a secondary heating zone that encloses the whole assembly. For rapid changes of the set point from high to low temperatures, the design contains an additional ventilation system to cool the normalization block. The present paper shows the operating principle as well as the results of the design process, in which numerical simulations based on the finite element method were used to evaluate and optimize the design of the dry block calibrator. The final optimized design can be used to build a prototype of the dry block calibrator.

  4. A unique high heat flux facility for testing hypersonic engine components

    Science.gov (United States)

    Melis, Matthew E.; Gladden, Herbert J.

    1990-01-01

    This paper describes the Hot Gas Facility, a unique, reliable, and cost-effective high-heat-flux facility for testing hypersonic engine components developed at the NASA Lewis Research Center. The Hot Gas Facility is capable of providing heat fluxes ranging from 200 Btu/sq ft per sec on flat surfaces up to 8000 Btu/sq ft per sec at a leading edge stagnation point. The usefulness of the Hot Gas Facility for the NASP community was demonstrated by testing hydrogen-cooled structures over a range of temperatures and pressures. Ranges of the Reynolds numbers, Prandtl numbers, enthalpy, and heat fluxes similar to those expected during hypersonic flights were achieved.

  5. On the Heat Flux Vector and Thermal Conductivity of Slags: A Brief Review

    Directory of Open Access Journals (Sweden)

    Mehrdad Massoudi

    2016-01-01

    Full Text Available The viscosity and the thermal conductivity of slag are among two of the most important material properties that need to be studied. In this paper we review the existing theoretical and experimental correlations for the thermal conductivity of slag. However, since, in general, slag behaves as a non-linear fluid, it is the heat flux vector which must be studied. Both explicit and implicit approaches are discussed and suggestions about the form of the heat flux vector and the thermal conductivity and their dependence on shear rate, porosity, deformation, etc. are provided. The discussion of the constitutive modeling of the heat flux vector for slag is from a theoretical perspective.

  6. Sensible Heat Flux Related to Variations in Atmospheric Turbulence Kinetic Energy on a Sandy Beach

    Science.gov (United States)

    2017-06-01

    FLUX RELATED TO VARIATIONS IN ATMOSPHERIC TURBULENCE KINETIC ENERGY ON A SANDY BEACH by Jessica S. Koscinski June 2017 Thesis Advisor...KINETIC ENERGY ON A SANDY BEACH 5. FUNDING NUMBERS 6. AUTHOR(S) Jessica S. Koscinski 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Naval...Sensible heat flux, turbulence kinetic energy , surf zone 15. NUMBER OF PAGES 57 16. PRICE CODE 17. SECURITY CLASSIFICATION OF REPORT

  7. Modeling Coronal Response in Decaying Active Regions with Magnetic Flux Transport and Steady Heating

    Science.gov (United States)

    Ugarte-Urra, Ignacio; Warren, Harry P.; Upton, Lisa A.; Young, Peter R.

    2017-09-01

    We present new measurements of the dependence of the extreme ultraviolet (EUV) radiance on the total magnetic flux in active regions as obtained from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. Using observations of nine active regions tracked along different stages of evolution, we extend the known radiance—magnetic flux power-law relationship (I\\propto {{{Φ }}}α ) to the AIA 335 Å passband, and the Fe xviii 93.93 Å spectral line in the 94 Å passband. We find that the total unsigned magnetic flux divided by the polarity separation ({{Φ }}/D) is a better indicator of radiance for the Fe xviii line with a slope of α =3.22+/- 0.03. We then use these results to test our current understanding of magnetic flux evolution and coronal heating. We use magnetograms from the simulated decay of these active regions produced by the Advective Flux Transport model as boundary conditions for potential extrapolations of the magnetic field in the corona. We then model the hydrodynamics of each individual field line with the Enthalpy-based Thermal Evolution of Loops model with steady heating scaled as the ratio of the average field strength and the length (\\bar{B}/L) and render the Fe xviii and 335 Å emission. We find that steady heating is able to partially reproduce the magnitudes and slopes of the EUV radiance—magnetic flux relationships and discuss how impulsive heating can help reconcile the discrepancies. This study demonstrates that combined models of magnetic flux transport, magnetic topology, and heating can yield realistic estimates for the decay of active region radiances with time.

  8. ENSO related SST anomalies and relation with surface heat fluxes over south Pacific and Atlantic

    Science.gov (United States)

    Chatterjee, S.; Nuncio, M.; Satheesan, K.

    2017-07-01

    The role of surface heat fluxes in Southern Pacific and Atlantic Ocean SST anomalies associated with El Nino Southern Oscillation (ENSO) is studied using observation and ocean reanalysis products. A prominent dipole structure in SST anomaly is found with a positive (negative) anomaly center over south Pacific (65S-45S, 120W-70W) and negative (positive) one over south Atlantic (50S-30S, 30W-0E) during austral summer (DJF) of El Nino (LaNina). During late austral spring-early summer (OND) of El Nino (LaNina), anomalous northerly (southerly) meridional moisture transport and a positive (negative) sea level pressure anomaly induces a suppressed (enhanced) latent heat flux from the ocean surface over south Pacific. This in turn results in a shallower than normal mixed layer depth which further helps in development of the SST anomaly. Mixed layer thins further due to anomalous shortwave radiation during summer and a well developed SST anomaly evolves. The south Atlantic pole exhibits exactly opposite characteristics at the same time. The contribution from the surface heat fluxes to mixed layer temperature change is found to be dominant over the advective processes over both the basins. Net surface heat fluxes anomaly is also found to be maximum during late austral spring-early summer period, with latent heat flux having a major contribution to it. The anomalous latent heat fluxes between atmosphere and ocean surface play important role in the growth of observed summertime SST anomaly. Sea-surface height also shows similar out-of-phase signatures over the two basins and are well correlated with the ENSO related SST anomalies. It is also observed that the magnitude of ENSO related anomalies over the southern ocean are weaker in LaNina years than in El Nino years, suggesting an intensified tropics-high latitude tele-connection during warm phases of ENSO.

  9. Using heat to characterize streambed water flux variability in four stream reaches.

    Science.gov (United States)

    Essaid, Hedeff I; Zamora, Celia M; McCarthy, Kathleen A; Vogel, Jason R; Wilson, John T

    2008-01-01

    Estimates of streambed water flux are needed for the interpretation of streambed chemistry and reactions. Continuous temperature and head monitoring in stream reaches within four agricultural watersheds (Leary Weber Ditch, IN; Maple Creek, NE; DR2 Drain, WA; and Merced River, CA) allowed heat to be used as a tracer to study the temporal and spatial variability of fluxes through the streambed. Synoptic methods (seepage meter and differential discharge measurements) were compared with estimates obtained by using heat as a tracer. Water flux was estimated by modeling one-dimensional vertical flow of water and heat using the model VS2DH. Flux was influenced by physical heterogeneity of the stream channel and temporal variability in stream and ground-water levels. During most of the study period (April-December 2004), flux was upward through the streambeds. At the IN, NE, and CA sites, high-stage events resulted in rapid reversal of flow direction inducing short-term surface-water flow into the streambed. During late summer at the IN site, regional ground-water levels dropped, leading to surface-water loss to ground water that resulted in drying of the ditch. Synoptic measurements of flux generally supported the model flux estimates. Water flow through the streambed was roughly an order of magnitude larger in the humid basins (IN and NE) than in the arid basins (WA and CA). Downward flux, in response to sudden high streamflows, and seasonal variability in flux was most pronounced in the humid basins and in high conductivity zones in the streambed.

  10. Free convection flow of some fractional nanofluids over a moving vertical plate with uniform heat flux and heat source

    Science.gov (United States)

    Azhar, Waqas Ali; Vieru, Dumitru; Fetecau, Constantin

    2017-08-01

    Free convection flow of some water based fractional nanofluids over a moving infinite vertical plate with uniform heat flux and heat source is analytically and graphically studied. Exact solutions for dimensionless temperature and velocity fields, Nusselt numbers, and skin friction coefficients are established in integral form in terms of modified Bessel functions of the first kind. These solutions satisfy all imposed initial and boundary conditions and reduce to the similar solutions for ordinary nanofluids when the fractional parameters tend to one. Furthermore, they reduce to the known solutions from the literature when the plate is fixed and the heat source is absent. The influence of fractional parameters on heat transfer and fluid motion is graphically underlined and discussed. The enhancement of heat transfer in such flows is higher for fractional nanofluids in comparison with ordinary nanofluids. Moreover, the use of fractional models allows us to choose the fractional parameters in order to get a very good agreement between experimental and theoretical results.

  11. Gradient heat flux measurement while researching of saturated water steam condensation

    Science.gov (United States)

    Mityakov, V. Y.; Sapozhnikov, S. Z.; Zainullina, E. R.; Babich, A. Y.; Milto, O. A.; Kalmykov, K. S.

    2017-11-01

    The heat flux measurement is used for research of heat transfer during condensation of saturated water steam at the surface of the tube made of stainless steel. A number of produced experimental setups allowed us to set different directions of movement of steam and cooling water, to change the space orientation of the tube, and also rotate the tube around its axis. In addition, the places of installation of the gradient heat flux sensors at internal and external surfaces of the tube were ranged. In the experiments we determined the local heat transfer coefficients, and their change along the length of the tube and for different values of the azimuthal angle. The obtained data allow to study in detail the formation of the film of condensate on the inside and outside surfaces of the tube and the heat transfer. The experimental results is in accordance with the classical ideas. The graphs show the pulsations of heat flux, which enable us to investigate non-stationary parameters of heat transfer during condensation. Experimental results differ from those calculated according to the Nusselt’s formula for 15% with standard uncertainty lower than 10%.

  12. 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.  

  13. Thin Film Heat Flux Sensor Development for Ceramic Matrix Composite (CMC) Systems

    Science.gov (United States)

    Wrbanek, John D.; Fralick, Gustave C.; Hunter, Gary W.; Zhu, Dongming; Laster, Kimala L.; Gonzalez, Jose M.; Gregory, Otto J.

    2010-01-01

    The NASA Glenn Research Center (GRC) has an on-going effort for developing high temperature thin film sensors for advanced turbine engine components. Stable, high temperature thin film ceramic thermocouples have been demonstrated in the lab, and novel methods of fabricating sensors have been developed. To fabricate thin film heat flux sensors for Ceramic Matrix Composite (CMC) systems, the rough and porous nature of the CMC system posed a significant challenge for patterning the fine features required. The status of the effort to develop thin film heat flux sensors specifically for use on silicon carbide (SiC) CMC systems with these new technologies is described.

  14. High speed infrared camera diagnostic for heat flux measurement in NSTX.

    Science.gov (United States)

    Ahn, J-W; Maingi, R; Mastrovito, D; Roquemore, A L

    2010-02-01

    A new high speed infrared camera has been successfully implemented and produced first set of heat flux measurements on the lower divertor tiles in the NSTX tokamak. High spatial and temporal resolutions, 6.4 mm and 1.6-6.3 kHz, respectively, enable us to investigate detailed structure of heat flux deposition pattern caused by transient events such as edge localized modes. A comparison of the data with a slow infrared camera viewing the same region of interest shows good agreement between the two independent measurements. Data analysis for various plasma conditions is in progress.

  15. Smoke Emissions from Aircraft Interior Materials at Elevated Heat Flux Levels Using Modified NBS Smoke Chamber.

    Science.gov (United States)

    1979-07-01

    sample actually grew out of the holder and extended toward the furnace, pro- ducing a dense, black , sooty smoke at the higher heat fluxes. It then...also pro- ducing vast amounts of black , sooty smoke at the higher heat fluxes. For these two plastics, smoke increased monotonically with increasing...PVF/f iberglaes-phenolic/ 0.505 89.9 Pmel Overhead Nomex Peper -phenolic Stowage honeycomb/fiberglass phenolic .26 Wool Car,e 0.250 74.0 Floering

  16. Mathematical Model of Non-stationary Heat Conduction in the Wall: Asymmetric Problem with the Boundary Conditions of Imperfect Heat Transfer

    Directory of Open Access Journals (Sweden)

    Charvátová Hana

    2016-01-01

    Full Text Available This paper deals with the study of a non-stationary heat conduction in the solid wall. It is focused on mathematical modelling of its asymmetric heating and cooling by imperfect heat transfer to both sides of the wall. It describes method used for deriving of the long time analytical solution describing temperature distribution in the heated (cooled wall by use Laplace transform and verification of its validity by numerical calculation with COMSOL Multiphysics software. In the tested example, the maximum difference between analytical and numerical solution was about 3.5 % considering the possible maximum and minimum temperatures in the wall under the given conditions.

  17. Study on critical heat flux in narrow rectangular channel with repeated-rib roughness. 1. Experimental facility and preliminary experiments

    Energy Technology Data Exchange (ETDEWEB)

    Kinoshita, Hidetaka; Terada, Atsuhiko; Kaminaga, Masanori; Hino, Ryutaro [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

    2001-10-01

    In the design of a spallation target system, the water cooling system, for example a proton beam window and a safety hull, is used with narrow channels, in order to remove high heat flux and prevent lowering of system performance by absorption of neutron. And in narrow channel, heat transfer enhancement using 2-D rib is considered for reduction the cost of cooling component and decrease inventory of water in the cooling system, that is, decrease of the amount of irradiated water. But few studies on CHF with rib have been carried out. Experimental and analytical studies with rib-roughened test section, in 10:1 ratio of pitch to height, are being carried out in order to clarify the CHF in rib-roughened channel. This paper presents the review of previous researches on heat transfer in channel with rib roughness, overview of the test facility and the preliminary experimental and analytical results. As a result, wall friction factors were about 3 times as large as that of smooth channel, and heat transfer coefficients are about 2 times as large as that of smooth channel. The obtained CHF was as same as previous mechanistic model by Sudo. (author)

  18. High Heat Flux Testing of Tungsten PFCs for the Fusion Reactor Development

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Suk-Kwon; Park, Seong Dae; Jin, Hyung Gon; Lee, Eo Hwak; Yoon, Jae-Sung; Lee, Dong Won [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2016-10-15

    Tungsten divertor plasma facing components (PFCs) were fabricated by using hot isostatic-pressing (HIP) bonding and vacuum plasma spray method (VPS) for the fusion reactor development. Tungsten mockups were designed for the high heat flux test with the Korean high heat flux test facility - electron beam (KoHLT-EB), which was constructed for the performance qualification of various PFCs. KoHLT-EB was used to qualify the PFCs performances of each fusion research. The high heat load conditions were simulated by using a thermo-hydraulic analysis tool with the ANSYS-CFX code. A high heat flux testing was performed up to the thermal life-time of each mockup with the evaluated conditions in 1 ⁓ 5 MW/m{sup 2}. HIP-bonded testing mockups consisted of 2 mm pure tungsten PFCs and ferritic-martensitic steel (FMS) as structural materials, and VPS mockups are comprised with 1 ⁓ 2 mm coated tungsten layer and FMS. These tungsten mockups are the candidate for the blanket and divertor in DEMO or a fusion power reactor. For the thermal fatigue test, two types of tungsten mock-ups were fabricated by using HIP bonding and VPS method for the fusion reactor development. The verification of the cooling performance was tested under the operation condition of ITER and fusion reactor. After the completion of the preliminary mockup test and facility qualification, the high heat flux test facility assess the performance test for two type of plasma facing components.

  19. Research of the Border Mobility Influence on the Half-Space Temperature Field Under Heat Flux

    Directory of Open Access Journals (Sweden)

    P. A. Vlasov

    2014-01-01

    Full Text Available Among the problems of unsteady heat conduction, tasks that can be solved in analytical closedform hold a special place. This species can be used both for parametric optimization of thermal protection of structures and for testing of computational algorithms.The previous paper presented an analytical solution of the problem to find the half-space temperature field with the uniformly moving boundary, which was under the external heat flux of constant power. In this paper we consider a similar problem, but the law of the moving boundary is assumed to be arbitrary nondecreasing, and the power of the heat flux can vary over time.An analytical dependence of the problem solution on the temperature of a moving boundary was obtained by using the Fourier transformation in the spatial variable. To determine the temperature of moving boundary, Volterra integral equation of the second kind was drawn. The solution of this equation was numerically conducted using a specially developed computational algorithm.The obtained representation was used to research the most characteristic features of the process to form the temperature field in studied area when implementing the various laws of boundaries motion and different operating conditions for the external heat flux influence. Using computational experiments allowed us to find that the asymptotic nature of this dependence confirms the results obtained in previous work. It has been established that the nonlinear character of both the boundary motion law and the external heat flux power variation law mainly affect the specifics of the transition process.

  20. Divertor heat flux simulations in ELMy H-mode discharges of EAST

    Science.gov (United States)

    Xia, T. Y.; Xu, X. Q.; Wu, Y. B.; Huang, Y. Q.; Wang, L.; Zheng, Z.; Liu, J. B.; Zang, Q.; Li, Y. Y.; Zhao, D.; EAST Team

    2017-11-01

    This paper presents heat flux simulations for the ELMy H-mode on the Experimental Advanced Superconducting Tokamak (EAST) using a six-field two-fluid model in BOUT++. Three EAST ELMy H-mode discharges with different plasma currents I p and geometries are studied. The trend of the scrape-off layer width λq with I p is reproduced by the simulation. The simulated width is only half of that derived from the EAST scaling law, but agrees well with the international multi-machine scaling law. Note that there is no radio-frequency (RF) heating scheme in the simulations, and RF heating can change the boundary topology and increase the flux expansion. Anomalous electron transport is found to contribute to the divertor heat fluxes. A coherent mode is found in the edge region in simulations. The frequency and poloidal wave number kθ are in the range of the edge coherent mode in EAST. The magnetic fluctuations of the mode are smaller than the electric field fluctuations. Statistical analysis of the type of turbulence shows that the turbulence transport type (blobby or turbulent) does not influence the heat flux width scaling. The two-point model differs from the simulation results but the drift-based model shows good agreement with simulations.

  1. Modeling of aerodynamic heat flux and thermoelastic behavior of nose caps of hypersonic vehicles

    Science.gov (United States)

    Persova, Marina G.; Soloveichik, Yury G.; Belov, Vasiliy K.; Kiselev, Dmitry S.; Vagin, Denis V.; Domnikov, Petr A.; Patrushev, Ilya I.; Kurskiy, Denis N.

    2017-07-01

    In this paper, the problem of numerical modeling of thermoelastic behavior of nose caps of hypersonic vehicles at different angles of attack is considered. 3D finite element modeling is performed by solving the coupled heat and elastic problems taking into account thermal and mechanical properties variations with temperature. A special method for calculating the aerodynamic heat flux entering the nose cap from its surface is proposed. This method is characterized by very low computational costs and allows calculating the aerodynamic heat flux at different values of the Mach number and angles of attack which may vary during the aerodynamic heating. The numerical results obtained by the proposed approach are compared with the numerical results and experimental data obtained by other authors. The developed approach has been used for studying the impact of the angle of attack on the thermoelastic behavior of nose caps main components.

  2. Qualification, commissioning and in situ monitoring of high heat flux plasma facing components

    Energy Technology Data Exchange (ETDEWEB)

    Escourbiac, F. [Association Euratom-CEA, CEA/DSM/DRFC, CEA/Cadarache, F-13108 Saint Paul Lez Durance (France)], E-mail: frederic.escourbiac@cea.fr; Durocher, A.; Grosman, A.; Cismondi, F.; Courtois, X.; Farjon, J.L.; Schlosser, J. [Association Euratom-CEA, CEA/DSM/DRFC, CEA/Cadarache, F-13108 Saint Paul Lez Durance (France); Merola, M.; Tivey, R. [ITER Team, CEA/Cadarache, F-13108 Saint Paul Lez Durance (France)

    2007-10-15

    Up-to-date development of actively cooled high heat flux (HHF) plasma facing components (PFC) prototypes only allows reduced margins with regards to the ITER thermal requirements. Additionally, perfect quality cannot be ensured along series manufacturing: the presence of flaws which impair the heat transfer capability of the component, in particular at the interface armour/heat sink appears to be statistically unavoidable. In order to ensure a successful series production, a qualification methodology of actively cooled high heat flux plasma facing components is proposed. Secondly, advanced non-destructive techniques developed for HHF PFC commissioning are detailed with definition of acceptance criteria. Finally, innovative diagnostics for in situ monitoring during plasma operations or tokamak shutdowns are investigated in order to prevent immediate damage (safety monitoring); or evaluate component degradation (health monitoring). This work takes into account the relevance to Tore Supra, and is applied to W7X and ITER Divertor HHF PFC.

  3. High heat flux test of tungsten brazed mock-ups developed for KSTAR divertor

    Energy Technology Data Exchange (ETDEWEB)

    Song, J.H. [National Fusion Research Institute, Daejeon (Korea, Republic of); Kim, K.M., E-mail: kyungmin@nfri.re.kr [National Fusion Research Institute, Daejeon (Korea, Republic of); Hong, S.H.; Kim, H.T.; Park, S.H.; Park, H.K.; Ahn, H.J. [National Fusion Research Institute, Daejeon (Korea, Republic of); Kim, S.K.; Lee, D.W. [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2016-11-01

    The tungsten (W) brazed flat type mock-up which consists of W, OFHC-Cu (oxygen-free high conductive copper) and CuCrZr alloy has been designed for KSTAR divertor in preparation for KSTAR upgrade with 17 MW heating power. For verification of the W brazed mock-up, the high heat flux test is performed at KoHLT-EB (Korea High Heat Load Test Facility-Electron Beam) in KAERI (Korea Atomic Energy Research Institute). Three mock-ups are tested for several thousand thermal cycles with absorbed heat flux up to 5 MW/m{sup 2} for 20 s duration. There is no evidence of the failure at the bonding joints of all mock-ups after HHF test. Finite element analysis (FEA) is performed to interpret the result of the test. As a result, it is considered that the local area in the water is in the subcooled boiling regime.

  4. Upshot of binary chemical reaction and activation energy on carbon nanotubes with Cattaneo-Christov heat flux and buoyancy effects

    Science.gov (United States)

    Lu, Dianchen; Ramzan, M.; Ahmad, Shafiq; Chung, Jae Dong; Farooq, Umer

    2017-12-01

    A mathematical model is framed to discuss the flow of carbon nanotube-suspended nanofluids with Cattaneo-Christov heat flux and binary chemical reaction. The flow analysis is performed in attendance of heat generation/absorption, energy activation, and buoyancy effects past a nonlinear stretched surface embedded in a non-Darcy permeable medium. A combination of varied nanotubes with base fluids is also taken into account. The Runge-Kutta fifth-order Fehlberg technique is engaged to find the numerical solution of a highly nonlinear problem. The impact of sundry parameters on involved distributions is illustrated graphically with requisite discussion keeping in view their physical aspects. Different tables that comprise numerically calculated values of numerous sundry parameters highlighting their physical significance are also erected. It is witnessed that velocity and temperature profiles are enhanced for mounting values of nanoparticle volume fraction parameters. Further, it is seen that for enhancing the value of the Prandtl number, the temperature profile decreases rapidly for single-walled carbon nanotubes than multi-walled carbon nanotubes.

  5. A comparison of optical and microwave scintillometers with eddy covariance derived surface heat fluxes

    KAUST Repository

    Yee, Mei Sun

    2015-11-01

    Accurate measurements of energy fluxes between land and atmosphere are important for understanding and modeling climatic patterns. Several methods are available to measure heat fluxes, and scintillometers are becoming increasingly popular because of their ability to measure sensible (. H) and latent (. LvE) heat fluxes over large spatial scales. The main motivation of this study was to test the use of different methods and technologies to derive surface heat fluxes.Measurements of H and LvE were carried out with an eddy covariance (EC) system, two different makes of optical large aperture scintillometers (LAS) and two microwave scintillometers (MWS) with different frequencies at a pasture site in a semi-arid environment of New South Wales, Australia. We used the EC measurements as a benchmark. Fluxes derived from the EC system and LAS systems agreed (R2>0.94), whereas the MWS systems measured lower H (bias ~60Wm-2) and larger LvE (bias ~65Wm-2) than EC. When the scintillometers were compared against each other, the two LASs showed good agreement of H (R2=0.98), while MWS with different frequencies and polarizations led to different results. Combination of LAS and MWS measurements (i.e., two wavelength method) resulted in performance that fell in between those estimated using either LAS or MWS alone when compared with the EC system. The cause for discrepancies between surface heat fluxes derived from the EC system and those from the MWS systems and the two-wavelength method are possibly related to inaccurate assignment of the structure parameter of temperature and humidity. Additionally, measurements from MWSs can be associated with two values of the Bowen ratio, thereby leading to uncertainties in the estimation of the fluxes. While only one solution has been considered in this study, when LvE was approximately less than 200Wm-2, the alternate solution may be more accurate. Therefore, for measurements of surface heat fluxes in a semi-arid or dry environment, the

  6. Assessment of land surface temperature and heat fluxes over Delhi using remote sensing data.

    Science.gov (United States)

    Chakraborty, Surya Deb; Kant, Yogesh; Mitra, Debashis

    2015-01-15

    Surface energy processes has an essential role in urban weather, climate and hydrosphere cycles, as well in urban heat redistribution. The research was undertaken to analyze the potential of Landsat and MODIS data in retrieving biophysical parameters in estimating land surface temperature & heat fluxes diurnally in summer and winter seasons of years 2000 and 2010 and understanding its effect on anthropogenic heat disturbance over Delhi and surrounding region. Results show that during years 2000-2010, settlement and industrial area increased from 5.66 to 11.74% and 4.92 to 11.87% respectively which in turn has direct effect on land surface temperature (LST) and heat fluxes including anthropogenic heat flux. Based on the energy balance model for land surface, a method to estimate the increase in anthropogenic heat flux (Has) has been proposed. The settlement and industrial areas has higher amounts of energy consumed and has high values of Has in all seasons. The comparison of satellite derived LST with that of field measured values show that Landsat estimated values are in close agreement within error of ±2 °C than MODIS with an error of ±3 °C. It was observed that, during 2000 and 2010, the average change in surface temperature using Landsat over settlement & industrial areas of both seasons is 1.4 °C & for MODIS data is 3.7 °C. The seasonal average change in anthropogenic heat flux (Has) estimated using Landsat & MODIS is up by around 38 W/m(2) and 62 W/m(2) respectively while higher change is observed over settlement and concrete structures. The study reveals that the dynamic range of Has values has increased in the 10 year period due to the strong anthropogenic influence over the area. The study showed that anthropogenic heat flux is an indicator of the strength of urban heat island effect, and can be used to quantify the magnitude of the urban heat island effect. Copyright © 2013 Elsevier Ltd. All rights reserved.

  7. Review of current status of high flux heat transfer techniques. Volume I. Text + Appendix A

    Energy Technology Data Exchange (ETDEWEB)

    Bauer, W.H.; Gordon, H.S.; Lackner, H.; Mettling, J.R.; Miller, J.E.

    1980-09-01

    The scope of this work comprised two tasks. The first was to review high heat flux technology with consideration given to heat transfer panel configuration, diagnostics techniques and coolant supply. The second task was to prepare a report describing the findings of the review, to recommend the technology offering the least uncertainty for scale-up for the MFTF-B requirement and to recommend any new or perceived requirements for R and D effort.

  8. Solar Coronal Heating and the Magnetic Flux Content of the Network

    Science.gov (United States)

    Moore, R. L.; Falconer, D. A.; Porter, J. G.; Hathaway, D. H.

    2003-01-01

    We investigate the heating of the quiet corona by measuring the increase of coronal luminosity with the amount of magnetic flux in the underlying network at solar minimum when there were no active regions on the face of the Sun. The coronal luminosity is measured from Fe IX/X-Fe XII pairs of coronal images from SOHO/EIT. The network magnetic flux content is measured from SOHO/MDI magnetograms. We find that the luminosity of the corona in our quiet regions increases roughly in proportion to the square root of the magnetic flux content of the network and roughly in proportion to the length of the perimeter of the network magnetic flux clumps. From (1) this result, (2) other observations of many fine-scale explosive events at the edges of network flux clumps, and (3) a demonstration that it is energetically feasible for the heating of the corona in quiet regions to be driven by explosions of granule-sized sheared-core magnetic bipoles embedded in the edges of network flux clumps, we infer that in quiet regions that are not influenced by active regions the corona is mainly heated by such magnetic activity in the edges of the network flux clumps. Our observational results together with our feasibility analysis allow us to predict that (1) at the edges of the network flux clumps there are many transient sheared-core bipoles of the size and lifetime of granules and having transverse field strengths greater than approximately - 100 G, (2) approximately 30 of these bipoles are present per supergranule, and (3) most spicules are produced by explosions of these bipoles.

  9. Momentum- and Heat-Flux Parametrization at Dome C, Antarctica: A Sensitivity Study

    Science.gov (United States)

    Vignon, Etienne; Genthon, Christophe; Barral, Hélène; Amory, Charles; Picard, Ghislain; Gallée, Hubert; Casasanta, Giampietro; Argentini, Stefania

    2017-02-01

    An extensive meteorological observational dataset at Dome C, East Antarctic Plateau, enabled estimation of the sensitivity of surface momentum and sensible heat fluxes to aerodynamic roughness length and atmospheric stability in this region. Our study reveals that (1) because of the preferential orientation of snow micro-reliefs (sastrugi), the aerodynamic roughness length z0 varies by more than two orders of magnitude depending on the wind direction; consequently, estimating the turbulent fluxes with a realistic but constant z0 of 1 mm leads to a mean friction velocity bias of 24 % in near-neutral conditions; (2) the dependence of the ratio of the roughness length for heat z_{0t} to z0 on the roughness Reynolds number is shown to be in reasonable agreement with previous models; (3) the wide range of atmospheric stability at Dome C makes the flux very sensitive to the choice of the stability functions; stability function models presumed to be suitable for stable conditions were evaluated and shown to generally underestimate the dimensionless vertical temperature gradient; as these models differ increasingly with increases in the stability parameter z / L, heat flux and friction velocity relative differences reached 100 % when z/L > 1; (4) the shallowness of the stable boundary layer is responsible for significant sensitivity to the height of the observed temperature and wind data used to estimate the fluxes. Consistent flux results were obtained with atmospheric measurements at heights up to 2 m. Our sensitivity study revealed the need to include a dynamical parametrization of roughness length over Antarctica in climate models and to develop new parametrizations of the surface fluxes in very stable conditions, accounting, for instance, for the divergence in both radiative and turbulent fluxes in the first few metres of the boundary layer.

  10. Homotopy Perturbation Method for Thin Film Flow and Heat Transfer over an Unsteady Stretching Sheet with Internal Heating and Variable Heat Flux

    Directory of Open Access Journals (Sweden)

    I-Chung Liu

    2012-01-01

    Full Text Available We have analyzed the effects of variable heat flux and internal heat generation on the flow and heat transfer in a thin film on a horizontal sheet in the presence of thermal radiation. Similarity transformations are used to transform the governing equations to a set of coupled nonlinear ordinary differential equations. The obtained differential equations are solved approximately by the homotopy perturbation method (HPM. The effects of various parameters governing the flow and heat transfer in this study are discussed and presented graphically. Comparison of numerical results is made with the earlier published results under limiting cases.

  11. Tip clearance effect on heat transfer and leakage flows on the shroud-wall surface in an axial flow turbine

    Science.gov (United States)

    Kumada, Masaya; Iwata, Satoshi; Obata, Masakazu; Watanabe, Osamu

    1992-06-01

    An axial flow turbine for a turbocharger is used as a test turbine, and the local heat transfer coefficient on the surface of the shroud is measured under uniform heat flux conditions. The nature of the tip clearance flow on the shroud surface and a flow pattern in the downstream region of the rotor blades are studied, and measurements are obtained by using a hot-wire anemometer in combination with a periodic multisampling and an ensemble averaging technique. Data are obtained under on- and off-design conditions. The effects of inlet flow angle, rotational speed and tip clearance on the local heat transfer coefficient are elucidated. The mean heat transfer coefficient is correlated with the tip clearance, and the mean velocity is calculated by the velocity triangle method for approximation. A leakage flow region exists in the downstream direction beyond the middle of the wall surface opposite the rotor blade, and a leakage vortex is recognized at the suction side near the trailing edge.

  12. Standard Test Method for Measuring Heat Flux Using Surface-Mounted One-Dimensional Flat Gages

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    2009-01-01

    1.1 This test method describes the measurement of the net heat flux normal to a surface using flat gages mounted onto the surface. Conduction heat flux is not the focus of this standard. Conduction applications related to insulation materials are covered by Test Method C 518 and Practices C 1041 and C 1046. The sensors covered by this test method all use a measurement of the temperature difference between two parallel planes normal to the surface to determine the heat that is exchanged to or from the surface in keeping with Fourier’s Law. The gages operate by the same principles for heat transfer in either direction. 1.2 This test method is quite broad in its field of application, size and construction. Different sensor types are described in detail in later sections as examples of the general method for measuring heat flux from the temperature gradient normal to a surface (1). Applications include both radiation and convection heat transfer. The gages have broad application from aerospace to biomedical en...

  13. Inverse heat conduction estimation of inner wall temperature fluctuations under turbulent penetration

    Science.gov (United States)

    Guo, Zhouchao; Lu, Tao; Liu, Bo

    2017-04-01

    Turbulent penetration can occur when hot and cold fluids mix in a horizontal T-junction pipe at nuclear plants. Caused by the unstable turbulent penetration, temperature fluctuations with large amplitude and high frequency can lead to time-varying wall thermal stress and even thermal fatigue on the inner wall. Numerous cases, however, exist where inner wall temperatures cannot be measured and only outer wall temperature measurements are feasible. Therefore, it is one of the popular research areas in nuclear science and engineering to estimate temperature fluctuations on the inner wall from measurements of outer wall temperatures without damaging the structure of the pipe. In this study, both the one-dimensional (1D) and the two-dimensional (2D) inverse heat conduction problem (IHCP) were solved to estimate the temperature fluctuations on the inner wall. First, numerical models of both the 1D and the 2D direct heat conduction problem (DHCP) were structured in MATLAB, based on the finite difference method with an implicit scheme. Second, both the 1D IHCP and the 2D IHCP were solved by the steepest descent method (SDM), and the DHCP results of temperatures on the outer wall were used to estimate the temperature fluctuations on the inner wall. Third, we compared the temperature fluctuations on the inner wall estimated by the 1D IHCP with those estimated by the 2D IHCP in four cases: (1) when the maximum disturbance of temperature of fluid inside the pipe was 3°C, (2) when the maximum disturbance of temperature of fluid inside the pipe was 30°C, (3) when the maximum disturbance of temperature of fluid inside the pipe was 160°C, and (4) when the fluid temperatures inside the pipe were random from 50°C to 210°C.

  14. Monitoring the latent and sensible heat fluxes in vineyard by applying the energy balance model METRIC

    Directory of Open Access Journals (Sweden)

    J. González-Piqueras

    2015-06-01

    Full Text Available The monitoring of the energy fluxes over vineyard applying the one source energy balance model METRIC (Allen et al., 2007b are shown in this work. This model is considered operaive because it uses an internalized calibration method derived from the selection of two extreme pixels in the scene, from the minimum ET values such as the bare soil to a maximum that corresponds to full cover active vegetation. The model provides the maps of net radiation (Rn, soil heat flux (G, sensible heat (H, latent heat (LE, evapotranspiration (ET and crop coefficient (Kc. The flux values have been validated with a flux tower installed in the plot, providing a RMSE for instantaneous fluxes of 43 W m2, 33 W m2, 55 W m2 y 40 W m2 on Rn, G, H and LE. In relative terms are 8%, 29%, 21% and 20% respectively. The RMSE at daily scale for the ET is 0.58 mm day-1, with a value in the crop coefficient for the mid stage of 0.42±0.08. These results allow considering the model adequate for crop monitoring and irrigation purposes in vineyard. The values obtained have been compared to other studies over vineyard and with alternative energy balance models showing similar results.

  15. Determination of regional heat fluxes from the growth of the mixed layer

    Energy Technology Data Exchange (ETDEWEB)

    Gryning, S.E. [Risoe National Lab., Roskilde (Denmark); Batchvarova, E. [National Inst. of Meteorology and Hydrology, Sofia (Bulgaria)

    1997-10-01

    The distribution of surface sensible heat flux is a critical factor in producing and modifying the mesoscale atmospheric flows, turbulence and evaporation. Parameterizations that assume homogeneous land characteristics are inappropriate to represent the spatial variability often found in nature. One possibility to overcome this problem is to increase the resolution of the model grid which demands unrealistic computing resources and data for model initialization. Area averaged fluxes can be obtained from aircraft measurements. It is essential that the flights are performed at a height where the individual surface features are not felt. A large number of flights and appropriate pattern to meet the task are needed in order to achieve a fair statistics. The mixed layer grows in response to the regional turbulent fluxes including the aggregation and small scale processes. The region of influence in upwind direction is typically 20 times the height of the mixed layer for convective and 100 times the height of the mixed layer for atmospheric near neutral conditions. In this study we determine the regional integrated sensible heat flux from information on the evolution of the mixed layer over the area. The required information to use the method can be derived from wind speed and temperature profiles obtained by radio-soundings when performed frequently enough to provide a reasonably detailed structure of the development of the mixed-layer. The method is applied to estimate the regional heat flux over the NOPEX experimental area for three days during the campaign in 1994. (au)

  16. Influence of spray characteristics on heat flux in dual phase spray impingement cooling of

    Directory of Open Access Journals (Sweden)

    Santosh Kumar Nayak

    2016-09-01

    Full Text Available The effects of variation of spray characteristics (mass flux, inlet pressure, flow rate, nozzle tip to target distance and plate thickness on heat flux were systematically investigated. The round spray released from a full cone internally mix atomizing nozzle was impinged with a wide range of air and water pressures on stationary hot steel surface of definite dimension. The effect of each parameter was examined while keeping others nearly fixed. Four different plate thicknesses i.e., 4 mm, 6 mm, 8 mm and 10 mm were tested and effect of plate thickness on heat transfer was determined. Surface heat flux at each experimental condition was computed from the transient temperature history measured by K-type thermocouples embedded at bottom surface of the plate. The mass impingement density was measured by the help of a simple mechanical patternator. The maximum surface heat flux of 4895.525 kW/m2 was achieved at an inlet water pressure of 4 bar, air pressure of 3 bar and nozzle height of 120 mm for an initial temperature of 850 °C of the 4 mm steel plate.

  17. Accuracy of soil heat flux plate measurements in coarse substrates - Field measurements versus a laboratory test

    NARCIS (Netherlands)

    Weber, S.; Graf, A.; Heusinkveld, B.G.

    2007-01-01

    The in-situ performance of heat flux plates within coarse porous substrates might be limited due to poor contact between plate and substrate. We tested this behaviour with a simple laboratory set-up. Two test substrates were placed above a reference material of known thermal conductivity between a

  18. Satellite evidence for no change in terrestrial latent heat flux in the ...

    Indian Academy of Sciences (India)

    Terrestrial latent heat flux (LE) in the Three-River Headwaters region (TRHR) of China plays an essential role in quantifying the amount of water evaporation and carbon sink over the high altitude. Tibetan Plateau (TP). Global warming is expected to accelerate terrestrial hydrological cycle and to increase evaporation.

  19. Study of Particle Motion in He II Counterflow Across a Wide Heat Flux Range

    Science.gov (United States)

    Mastracci, Brian; Takada, Suguru; Guo, Wei

    2017-06-01

    Some discrepancy exists in the results of He II counterflow experiments obtained using particle image velocimetry (PIV) when compared with those obtained using particle tracking velocimetry (PTV): using PIV, it was observed that tracer particles move at roughly half the expected normal fluid velocity, v_n/2, while tracer particles observed using PTV moved at approximately v_n. A suggested explanation is that two different flow regimes were examined since the range of heat flux applied in each experiment was adjacent but non-overlapping. Another PTV experiment attempted to test this model, but the applied heat flux did not overlap with any PIV experiments. We report on the beginnings of a study of solid {D}_2 particle motion in counterflow using PTV, and the heat flux range overlaps that of all previous visualization studies. The observed particle velocity distribution transitions from a two-peak structure to a single peak as the heat flux is increased. Furthermore, the mean value of one peak in the bi-modal distributions grows at approximately the same rate as v_n, while the mean value of the single-peak distributions grows at roughly 0.4v_n, in reasonable agreement with both previous experiments and with the suggested model.

  20. Estimation of surface Latent Heat Fluxes from IRS-P4/MSMR ...

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging Solutions)

    latent heat flux from satellite data. Liu and Niiler. (1984) and Liu (1986) applied the bulk formula to retrieve the surface LHF using near surface para- meters derived from satellite data. This method, hereafter referred to as the LN method, uses geo- physical parameters such as winds, sea surface tem- perature and surface ...

  1. Experimental and Numerical Investigations of RP-2 Under High Heat Fluxes

    National Research Council Canada - National Science Library

    Billingsley, M. C; Lyu, H. Y; Bates, R. W

    2007-01-01

    ... such as RP-2, an advanced grade of ultra-low sulfur rocket kerosene. This paper reports recent experiments and numerical simulations of RP-2 cooled thermal stability tests conducted in the AFRL High Heat Flux Facility located at Edwards AFB, CA...

  2. Inverse determination of heat flux into a gun barrel using temperature sensors

    Science.gov (United States)

    Jablonski, Jonathan A.; Jablonski, Melissa N.

    2017-05-01

    A mathematical model is developed to describe the thermal response of a temperature sensor located within a gun barrel, which accounts for the time-constant of the sensor and a measurement bias. The model is inversely solved to estimate the total heat flux applied to the bore surface as well as the transient history of the applied heat flux for a given thermal response of a temperature sensor. A parametric study is conducted to determine the influence of sensor time-constant, sensor location within the gun barrel, and measurement bias on the accuracy of the estimated heat flux as applied to a 155mm gun barrel. It is found that the accuracy of the estimated heat flux improves as the time-constant of the sensor decreases, the sensor is located closer to the bore surface, and the measurement bias decreases. A regression model is provided to estimate that accuracy and it is shown how a typical thermocouple would perform at various locations through the thickness of the gun barrel.

  3. Energy and water cycle over the Tibetan plateau : surface energy balance and turbulent heat fluxes

    NARCIS (Netherlands)

    Su, Zhongbo; Zhang, Ting; Ma, Yaoming; Jia, Li; Wen, Jun

    2006-01-01

    This contribution presents an overview and an outlook of studies on energy and water cycle over the Tibetan plateau with focuses on the estimation of energy balance terms and turbulent heat fluxes. On the basis of the surface energy balance calculations, we show that the phenomena of the energy

  4. Energy and water cycle over the Tibetan Plateau: surface energy balance and turbulent heat fluxes

    NARCIS (Netherlands)

    Su, Z.; Zhang, T.; Ma, Y.; Jia, L.; Wen, J.

    2006-01-01

    This contribution presents an overview and an outlook of studies on energy and water cycle over the Tibetan plateau with focuses on the estimation of energy balance terms and turbulent heat fluxes. On the basis of the surface energy balance calculations, we show that the phenomena of the energy

  5. Effect of constant heat flux at outer cylinder on stability of viscous ...

    African Journals Online (AJOL)

    DR OKE

    SCIENCE AND. TECHNOLOGY www.ijest-ng.com www.ajol.info/index.php/ijest. 2015 MultiCraft Limited. All rights reserved. Effect of constant heat flux at ... applications, there is another situation in which the outer cylinder is maintained at constant temperature while the inner cylinder ...... Bulletin of the Japan Society.

  6. Temperature regimes and turbulent heat fluxes across a heterogeneous canopy in an Alaskan boreal forest

    Science.gov (United States)

    We evaluate local differences in thermal regimes and turbulent heat fluxes across the heterogeneous canopy of a black spruce boreal forest on discontinuous permafrost in interior Alaska. The data was taken during an intensive observing period in the summer of 2013 from two micrometeorological tower...

  7. Regional fluxes of momentum and sensible heat over a sub-arctic landscape during late winter

    DEFF Research Database (Denmark)

    Batchvarova, E.; Gryning, Sven-Erik; Hasager, C.B.

    2001-01-01

    Based on measurements at Sodankyla Meteorological Observatory the regional (aggregated) momentum and sensible heat fluxes are estimated for two days over a site in Finnish Lapland during late winter. The forest covers 49% of the area. The study shows that the forest dominates and controls...

  8. Self-pressurization of a flightweight liquid hydrogen storage tank subjected to low heat flux

    Science.gov (United States)

    Hasan, M. M.; Lin, C. S.; Vandresar, N. T.

    1991-01-01

    Results are presented for an experimental investigation of self-pressurization and thermal stratification of a 4.89 cu m liquid hydrogen (LH2) storage tank subjected to low heat flux (0.35, 2.0, and 3.5 W/sq m) under normal gravity conditions. Tests were performed at fill levels of 83 to 84 percent (by volume). The LH2 tank was representative of future spacecraft tankage, having a low mass-to-volume ratio and high performance multilayer thermal insulation. Results show that the pressure rise rate and thermal stratification increase with increasing heat flux. At the lowest heat flux, the pressure rise rate is comparable to the homogenous rate, while at the highest heat flux, the rate is more than three times the homogeneous rate. It was found that initial conditions have a significant impact on the initial pressure rise rate. The quasi-steady pressure rise rates are nearly independent of the initial condition after an initial transient period has passed.

  9. High heat flux test on the thermocouple embedded ITER neutral beam duct liner mock-up

    Energy Technology Data Exchange (ETDEWEB)

    Park, C.K., E-mail: ckpark@nfri.re.kr [ITER Korea, National Fusion Research Institute, Daejeon 305-333 (Korea, Republic of); Kim, H.S., E-mail: hskim@nfri.re.kr [ITER Korea, National Fusion Research Institute, Daejeon 305-333 (Korea, Republic of); Kim, G.H.; Ahn, H.J. [ITER Korea, National Fusion Research Institute, Daejeon 305-333 (Korea, Republic of); Kim, S.K.; Lee, D.W. [Korea Atomic Energy Research Institute, Daejeon 305-353 (Korea, Republic of); Urbani, M. [ITER Organization, Route de Vinon-sur-Verdon, CS 90 046, 13067, St. Paul Lez Durance, Cedex (France)

    2016-11-01

    Highlights: • Twenty thermocouples have been installed on the NB duct liner full scale mock-up. • High heat flux test has been performed. • Four thermocouple fixation schemes had been verified by high heat flux test. • Temperature behavior of the NB duct liner has been successfully simulated. - Abstract: The ITER neutral beam duct liner is located within the tokamak VV port extension and is mounted on the VV port extension flange. The duct liner is made from CuCrZr copper alloy and is actively cooled through deep-drilled channels. A number of thermocouples should be installed on the neutral beam duct liner in order to provide the ability to detect temperature excursions on the surface of the duct liner. Twenty thermocouples have been installed on the neutral beam duct liner full scale mock-up, and a high heat flux test has been performed at the KoHLT-EB test facility, in order to simulate temperature detection in the neutral beam duct liner during ITER operation. For each thermocouple, the fixation method has been verified by high heat flux test with uniform electron beam profile, and the temperature behavior of the neutral beam duct liner has been successfully simulated by Gaussian electron beam profile.

  10. Estimation of sensible heat flux using the Surface Energy Balance System (SEBS) and ATSR measurements

    NARCIS (Netherlands)

    Jia, L.; Su, Z.; Hurk, van den B.; Menenti, M.; Moene, A.F.; Bruin, de H.A.R.; Baselga Yrisarry, J.J.; Ibanez, M.; Cuesta, A.

    2003-01-01

    This paper describes a modified version of the Surface Energy Balance System (SEBS) as regards the use of radiometric data from space and presents the results of a large area validation study on estimated sensible heat flux, extended over several months. The improvements were made possible by the

  11. Numerical investigation of fluid flow and heat transfer under high heat flux using rectangular micro-channels

    KAUST Repository

    Mansoor, Mohammad M.

    2012-02-01

    A 3D-conjugate numerical investigation was conducted to predict heat transfer characteristics in a rectangular cross-sectional micro-channel employing simultaneously developing single-phase flows. The numerical code was validated by comparison with previous experimental and numerical results for the same micro-channel dimensions and classical correlations based on conventional sized channels. High heat fluxes up to 130W/cm 2 were applied to investigate micro-channel thermal characteristics. The entire computational domain was discretized using a 120×160×100 grid for the micro-channel with an aspect ratio of (α=4.56) and examined for Reynolds numbers in the laminar range (Re 500-2000) using FLUENT. De-ionized water served as the cooling fluid while the micro-channel substrate used was made of copper. Validation results were found to be in good agreement with previous experimental and numerical data [1] with an average deviation of less than 4.2%. As the applied heat flux increased, an increase in heat transfer coefficient values was observed. Also, the Reynolds number required for transition from single-phase fluid to two-phase was found to increase. A correlation is proposed for the results of average Nusselt numbers for the heat transfer characteristics in micro-channels with simultaneously developing, single-phase flows. © 2011 Elsevier Ltd.

  12. Modelling of methanol-to-hydrogen steam reforming with a heat flux distributed along a microchannel

    Science.gov (United States)

    Kuznetsov, V. V.; Kozlov, S. P.

    2008-09-01

    The flow of reacting mixture of methanol and steam in a 2D microslot was studied numerically at activation of the reactions on the channel wall. This modelling was carried out in the framework of Navier — Stokes equations for a laminar flow of multicomponent compressible gas. Correlations between thermal, diffusion, and physical-chemical processes were studied under the conditions of intense endothermic reaction and external heat supply distributed along the channel. It is shown that not only the amount of heat supplied to the reaction zone is essential, but also the mode of heat supply along the channel length is important, which allows optimization of the compact reactor for hydrogen production.

  13. Thermoelectric conversion of heat fluxes: analytical and experimental approach

    Science.gov (United States)

    Amokrane, Mounir; Nogarede, Bertrand

    2012-08-01

    When considering electric energy harvesting from waste heat, two different solutions of direct conversion are possible: pyroelectric and thermoelectric conversions. This paper presents a study of the thermoelectric conversion by two different approaches: analytical and experimental. Furthermore, a brief historical description of the discovery and early years of development of thermoelectricity is presented. The essential objective of this work is to develop a numerical tool that can estimate the output quantities of a thermoelectric converter, without knowing all its features. For this, two analytical models were developed, based on electrical and thermal phenomena occurring within the active element. The results obtained by this model were compared successfully with experiments carried out on an industrial thermoelectric element. Considering the centimetric size of the device (16 cm2 area), the electrical power recovered by this conversion varies from 16 to 80 mW for a temperature difference between 2 and 18 °C and according to the load value. In addition, both models transcribe the behavior of the active element with an accuracy of about 10%. In agreement with this, the output voltages reached are of the same magnitude for the models and the experimental values and vary from 0.1 to 0.8 V depending on the load connected and the type of convection. Another issue which is discussed for the two cases is that an optimal recovered energy is obtained for a given electric load taking into account the physical characteristics of the considered thermoelectric element. Finally, a conversion efficiency calculation has shown that it is possible to reach 45% of the Carnot efficiency. This denotes the interest to perform load matching to optimize the output power.

  14. Optimal wall spacing for heat transport in thermal convection

    Energy Technology Data Exchange (ETDEWEB)

    Shishkina, Olga [Max Planck Institute for Dynamics and Self-Organization, Goettingen (Germany)

    2016-11-01

    The simulation of RB flow for Ra up to 1 x 10{sup 10} is computationally expensive in terms of computing power and hard disk storage. Thus, we gratefully acknowledge the computational resources supported by Leibniz-Rechenzentrum Munich. Compared to Γ=1 situation, a new physical picture of heat transport is identified here at Γ{sub opt} for any explored Ra. Therefore, a detailed comparison between Γ=1 and Γ=Γ{sub opt} is valuable for our further research, for example, their vertical temperature and velocity profiles. Additionally, we plan to compare the fluid with different Pr under geometrical confinement, which are computationally expensive for the situations of Pr<<1 and Pr>>1.

  15. Controlling Radiative Heat Transfer Across the Mold Flux Layer by the Scattering Effect of the Borosilicate Mold Flux System with Metallic Iron

    Science.gov (United States)

    Yoon, Dae-Woo; Cho, Jung-Wook; Kim, Seon-Hyo

    2017-08-01

    The present study proposes a countermeasure for regulating total heat flux through the mold flux layer by designed mold flux with additive metallic iron particles. The heat flux through the B2O3-CaO-SiO2-Na2O-CaF2-Fe system was investigated using the infrared emitter technique to evaluate total flux density across the mold flux film. Both scanning electron microscope (SEM) and X-ray diffraction analysis were employed in order to identify the morphological and compositional changes of the crystalline phase, according to increasing iron contents in the mold flux. It was confirmed that the crystalline layer of studied mold fluxes does not have a meaningful effect on the total heat flux density due to the similar structure and fraction of the crystalline phase. The extinction coefficient was measured for glassy mold fluxes using an ultraviolet/visible and a Fourier transformation-infrared ray spectrometer in the range of 0.5 to 5 μm. For analyzing the scattering behavior of iron particles on the extinction coefficient, the number density and diameter of particles were observed by an automated SEM (auto-SEM). With these data, Mie scattering theory is adopted to define the scattering behavior of dispersed iron droplets in glassy matrix. It was found that the theoretical scattering coefficient demonstrated about 1623 to 3295 m-1, which is in accordance with the experimental results. In doing so, this study successfully achieves the strong scattering behavior that would contribute greatly to the optimization of overall heat flux through the mold flux film during the casting process.

  16. Estimating land surface heat flux using radiometric surface temperature without the need for an extra resistance

    Science.gov (United States)

    Su, H.; Yang, Y.; Liu, S.

    2015-12-01

    Remotely-sensed land surface temperature (LST) is a key variable in energy balance and is widely used for estimating regional heat flux. However, the inequality between LST and aerodynamic surface temperature (Taero) poses a great challenge for regional heat flux estimation in one -source energy balance models. In this study, a one-source model for land (OSML) was proposed to estimate regional surface heat flux without a need for an empirical extra resistance. The proposed OSML employs both a conceptual VFC/LST trapezoid model and the electrical analogue formula of sensible heat flux (H) to estimate the radiometric-convective resistance (rae) by using a quartic equation. To evaluate the performance of OSML, the model was applied to the Soil Moisture-Atmosphere Coupling Experiment (SMACEX), using a remotely-sensed data set at a regional scale. Validated against tower observations, the root mean square deviation (RMSD) of H and latent heat flux (LE) from OSML was 47 W/m2 and 51 W/m2, which is comparable to other published studies. OSML and SEBS (Surface Energy Balance System) compared under the same available energy indicated that LE estimated by OSML is comparable to that derived from the SEBS model. In conducting further inter-comparisons of rae, the aerodynamic resistance derived from SEBS (ra_SEBS), and aerodynamic resistance (ra) derived from Brutsaert et al. (2005) in corn and soybean fields, we found that rae and ra_SEBS are comparable. Most importantly, our study indicates that the OSML method is applicable without having to acquire wind speed or to specify aerodynamic surface characteristics and that it is applicable to heterogeneous areas.

  17. How the Propagation of Heat-Flux Modulations Triggers E × B Flow Pattern Formation

    Science.gov (United States)

    Kosuga, Yusuke

    2013-10-01

    Recently, a new class of E × B flow pattern, called an `` E × B staircase,'' was observed in a simulation study using the full- f flux driven GYSELA code. Here, E × B staircases are quasi-regular steady patterns of localized shear layers and temperature profile corrugations. The shear layers are interspaced between regions of turbulent avalanching of the size of several correlation length (~ 10Δc). In this work, a theory to describe the formation of such E × B staircases from a bath of stochastic avalanches is presented, based on analogy of staircase formation to jam formation in traffic flow. Namely, staircase formation is viewed as a heat flux ``jam'' that causes profile corrugation, which is analogous to a traffic jam that causes corrugations in the local car density in a traffic flow. To model such an effect in plasmas, a finite response time τ is introduced, during which instantaneous heat flux relaxes to the mean heat flux, determined by symmetry constraints. The response time introduced here is an analogue of drivers' response time in traffic flow dynamics. It is shown that the extended model describes a heat flux ``jam'' and profile corrugation, which appears as an instability, in analogy to the way a clustering instability leads to a traffic jam. Such local amplification of heat and profile corrugations can lead to the formation of E × B staircases. The scale length that gives the maximum growth rate falls in the mesoscale range and is comparable to the staircase step spacing. Present address: IAS and RIAM, Kyushu University, Japan.

  18. Sabots, Obturator and Gas-In-Launch Tube Techniques for Heat Flux Models in Ballistic Ranges

    Science.gov (United States)

    Bogdanoff, David W.; Wilder, Michael C.

    2013-01-01

    For thermal protection system (heat shield) design for space vehicle entry into earth and other planetary atmospheres, it is essential to know the augmentation of the heat flux due to vehicle surface roughness. At the NASA Ames Hypervelocity Free Flight Aerodynamic Facility (HFFAF) ballistic range, a campaign of heat flux studies on rough models, using infrared camera techniques, has been initiated. Several phenomena can interfere with obtaining good heat flux data when using this measuring technique. These include leakage of the hot drive gas in the gun barrel through joints in the sabot (model carrier) to create spurious thermal imprints on the model forebody, deposition of sabot material on the model forebody, thereby changing the thermal properties of the model surface and unknown in-barrel heating of the model. This report presents developments in launch techniques to greatly reduce or eliminate these problems. The techniques include the use of obturator cups behind the launch package, enclosed versus open front sabot designs and the use of hydrogen gas in the launch tube. Attention also had to be paid to the problem of the obturator drafting behind the model and impacting the model. Of the techniques presented, the obturator cups and hydrogen in the launch tube were successful when properly implemented

  19. Distribution of the heat and current fluxes in gas tungsten arcs

    Science.gov (United States)

    Tsai, N. S.; Eagar, T. W.

    1985-12-01

    The distribution of heat flux on a water-cooled copper anode as a function of welding process parameters has been determined experimentally following an experimental technique developed previously. The results indicate that arc length is the primary variable governing heat distribution and that the distribution is closely approximated by a gaussian function. The half width of the heat flux is defined by a distribution parameter, σ, which was determined from the experimental data and is expressed as a function of arc length, current, and electrode tip angle. The distribution parameter, σ, increases from 1.5 mm to 3.6 mm as the arc length increases from 2 mm to 9 mm for a 100 A arc. The experimental data also show that arc energy transfer efficiency is greater than 80 pct on the water-cooled anode which is much higher than has been measured in the presence of a molten metal pool. For this reason, it is believed that the distribution of the heat flux and not the magnitude is the most useful information obtained in this study. The effect of helium additions to the argon on the heat distribution is also reported.

  20. Numerical Simulation of the Moving Induction Heating Process with Magnetic Flux Concentrator

    Directory of Open Access Journals (Sweden)

    Feng Li

    2013-01-01

    Full Text Available The induction heating with ferromagnetic metal powder bonded magnetic flux concentrator (MPB-MFC demonstrates more advantages in surface heating treatments of metal. However, the moving heating application is mostly applied in the industrial production. Therefore, the analytical understanding of the mechanism, efficiency, and controllability of the moving induction heating process becomes necessary for process design and optimization. This paper studies the mechanism of the moving induction heating with magnetic flux concentrator. The MPB-MFC assisted moving induction heating for Inconel 718 alloy is studied by establishing the finite element simulation model. The temperature field distribution is analyzed, and the factors influencing the temperature are studied. The conclusion demonstrates that the velocity of the workpiece should be controlled properly and the heat transfer coefficient (HTC has little impact on the temperature development, compared with other input parameters. In addition, the validity of the static numerical model is verified by comparing the finite element simulation with experimental results on AISI 1045 steel. The numerical model established in this work can provide comprehensive understanding for the process control in production.

  1. Examination of high heat flux components for the ITER divertor after thermal fatigue testing

    Energy Technology Data Exchange (ETDEWEB)

    Missirlian, M., E-mail: marc.missirlian@cea.fr [CEA, IRFM, F-13108 Saint Paul lez Durance (France); Escourbiac, F., E-mail: frederic.escourbiac@cea.fr [CEA, IRFM, F-13108 Saint Paul lez Durance (France); Schmidt, A., E-mail: a.schmidt@fz-juelich.de [Forschungszentrum Juelich, IFE-2 (Germany); Riccardi, B., E-mail: Bruno.Riccardi@f4e.europa.eu [Fusion For Energy, E-08019 Barcelona (Spain); Bobin-Vastra, I., E-mail: isabelle.bobinvastra@areva.com [AREVA-NP, 71200 Le Creusot (France)

    2011-10-01

    An extensive development programme has been carried out in the EU on high heat flux components within the ITER project. In this framework, a full-scale vertical target (VTFS) prototype was manufactured with all the main features of the corresponding ITER divertor design. The fatigue cycling campaign on CFC and W armoured regions, proved the capability of such a component to meet the ITER requirements in terms of heat flux performances for the vertical target. This paper discusses metallographic observations performed on both CFC and W part after this intensive thermal fatigue testing campaign for a better understanding of thermally induced mechanical stress within the component, especially close to the armour-heat sink interface.

  2. An inter-comparison of six latent and sensible heat flux products over the Southern Ocean

    Directory of Open Access Journals (Sweden)

    Lejiang Yu

    2011-11-01

    Full Text Available The latent heat fluxes (LHF and sensible heat fluxes (SHF over the Southern Ocean from six different data sets are inter-compared for the period 1988–2000. The six data sets include three satellite-based products, namely, the second version of the Goddard Satellite-Based Surface Turbulent Fluxes data set (GSSTF-2, the third version of the Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite Data (HOAPS-3 and the Japanese Ocean Fluxes Data Sets with Use of Remote Sensing Observations (J-OFURO; two global reanalysis products, namely, the National Centers for Environmental Prediction–Department of Energy Reanalysis 2 data set (NCEP-2 and the European Centre for Medium-Range Weather Forecasts 40 Year Re-analysis data set (ERA-40; and the Objectively Analyzed Air–Sea Fluxes for the Global Oceans data set (OAFlux. All these products reveal a similar pattern in the averaged flux fields. The zonal mean LHF fields all exhibit a continuous increase equatorward. With an exception of HOAPS-3, the zonal mean SHF fields display a minimum value near 50°S, increasing both pole- and equatorward. The differences in the standard deviation for LHF are larger among the six data products than the differences for SHF. Over the regions where the surface fluxes are significantly influenced by the Antarctic Oscillation and the Pacific–South American teleconnection, the values and distributions of both LHF and SHF are consistent among the six products. It was found that the spatial patterns of the standard deviations and trends of LHF and SHF can be explained primarily by sea–air specific humidity and temperature differences; wind speed plays a minor role.

  3. New optical method for heat flux measurements in stagnation point laminar methane/air flames and hydrogen/methane/air flames using thermographic phosphors

    Energy Technology Data Exchange (ETDEWEB)

    Elmnefi, Mohamed Salem

    2010-11-24

    In the present study, a new optical method was implemented to study the heat transfer from flat stagnation point flames which can be regarded as one-dimensional in the central part. Premixed methane-air flames and hydrogen-methane-air flames were investigated. The effects of burner-to-plate distance and the fresh gas mixture velocity on heat transfer were examined. Experiments were performed using light induced phosphorescence from thermographic phosphors to study the wall temperatures and heat fluxes of nearly one-dimensional flat premixed flames impinging upward normally on a horizontal water cooled circular flat plate. The investigated flames were stoichiometric, lean and rich laminar methane/air flames with different equivalence ratios of {phi} =1, {phi} = 0.75 and {phi} = 1.25 and stoichiometric laminar hydrogen/methane/air flames. Mixtures of air with 10, 25, 50 and 75 % hydrogen in methane (CH{sub 4}) as well as a pure hydrogen flames at ambient pressure were investigated. The central part of this plate was an alumina ceramic plate coated from both sides with chromium doped alumina (ruby) and excited with a Nd:YAG laser or a green light emitting diode (LED) array to measure the wall temperature from both sides and thus the heat flux rate from the flame. The outlet velocity of the gases was varied from 0.1 m/s to 1.2 m/s. The burner to plate distance ranged from 0.5 to 2 times the burner exit diameter (d = 30 mm).The accuracy of the method was evaluated. The measured heat flux indicate the change of the flame stabilization mechanism from a burner stabilized to a stagnation plate stabilized flame. The results were compared to modeling results of a one dimensional stagnation point flow, with a detailed reaction mechanism. In order to prove the model, also measured gas phase temperatures by OH LIF for a stoichiometric stagnation point flame were discussed. It turns out that the flame stabilization mechanism and with it the heat fluxes change from low to high

  4. Evaluation of High Temperature Composites Thermal Properties under Different Heat Flux Conditions

    Directory of Open Access Journals (Sweden)

    Ahmad Reza Bahramian

    2014-06-01

    Full Text Available The thermal protection of structures in vehicles, at instantaneous high thermal shocks, would be more effective and economically feasible among other thermal protection methods using the passive heat shields especially charring the ablative composites. The most important limitations reported are lack of compiled knowledge on designing heat shield with optimal thickness under real conditions and high surface erosion rate and low mechanical strength of char layer of a composite created by ablation process. In this paper SiAlON ceramic composites, reinforced with short carbon fiber, are identified as high performance heat shields for challenging these limitations. Ablation rate and effective thermal diffusivity at different external heat fluxes are determined and calculated using oxyacetylene flame test and modeling of temperature distributions in ablation process for evaluation of thermal protection performance and effective thermal diffusivity of this composite, as a thermal protection system. The results of this work have indicated that the carbon fiber reinforced SiAlON ceramic composite can be considered as a high ablation heat shield. Under the same condition of ablation test, SiAlON ceramic composites reinforced by carbon fiber show higher ablation performance relative to other commercial carbon fiber reinforced composite heat shields. At 8500 and 5000 kWm-2 external heat flux the ablation rates of this composite are 0.075 and 0.026 mms-1, respectively. Also, at 2500 kWm-2 external heat flux and test duration time of less than 25 s, this composite displays an adequate thermal shock protection with maximum flexural strength loss of about 23.4 %.

  5. Heat transport in cold-wall single-wafer low pressure chemical-vapor-deposition reactors

    NARCIS (Netherlands)

    Hasper, A.; Schmitz, J.E.J.; Holleman, J.; Verweij, J.F.

    1992-01-01

    A model is formulated to understand and predict wafer temperatures in a tungsten low pressure chemical‐vapor‐deposition (LPCVD) single‐wafer cold‐wall reactor equipped with hot plate heating. The temperature control is usually carried out on the hot plate temperature. Large differences can occur

  6. Heat transfer in particle-laden wall-bounded turbulent flows

    NARCIS (Netherlands)

    Jaszczur, M.; Portela, L.M.

    2006-01-01

    In present work heat transfer in particle-laden wall-bounded turbulent flows has been study with the fluid-particle one way interaction approach. Direct Numerical Simulation of the flow, combined with Lagrangian particle tracking technique has been performed to study the problem. In presented

  7. Dynamics and control of a heat pump assisted extractive dividing-wall column for bioethanol dehydration

    NARCIS (Netherlands)

    Patraşcu, Iulian; Bildea, Costin Sorin; Kiss, Anton A.

    Recently, a novel heat-pump-assisted extractive distillation process taking place in a dividing-wall column was proposed for bioethanol dehydration. This integrated design combines three distillation columns into a single unit that allows over 40% energy savings and low specific energy requirements

  8. Critical heat flux tests for a 12 finned-element assembly

    Energy Technology Data Exchange (ETDEWEB)

    Yang, J., E-mail: Jun.Yang@cnl.ca; Groeneveld, D.C.; Yuan, L.Q.

    2017-03-15

    Highlights: • CHF tests for a 12 finned-fuel-element assembly at highly subcooled conditions. • Test approach to maximize experimental information and minimize heater failures. • Three series of tests were completed in vertical upward light water flow. • Bundle simulators of two axial power profiles and three heated lengths were tested. • Results confirm that the prediction method predicts lower CHF values than measured. - Abstract: An experimental study was undertaken to provide relevant data to validate the current critical heat flux (CHF) prediction method of the NRU driver fuel for safety analysis, i.e., to confirm no CHF occurrence below the predicted values. The NRU driver fuel assembly consists of twelve finned fuel elements arranged in two rings – three in the inner ring and nine in the outer ring. To satisfy the experimental objective tests at very high heat fluxes, very high mass velocities, and high subcoolings were conducted where the CHF mechanism is the departure from nucleate boiling (DNB). Such a CHF experiment can be very difficult, costly and time consuming since failure of the heating surface due to rupture or melting (physical burnout) is expected when the DNB type of CHF is reached. A novel experimental approach has been developed to maximize the amount of relevant experimental information on safe operating conditions in the tests, and to minimize any possible heater failures that inherently accompany the CHF occurrence at these conditions. Three series of tests using electrically heated NRU driver fuel simulators with three heated lengths and two axial power profiles (or axial heat flux distribution (AFD)) were completed in vertical upward light water flow. Each series of tests covered two mass flow rates, several heat flux levels, and local subcoolings that bound the ranges of interest for the analysis of postulated slow loss-of-regulation accident (LORA) and loss-of-flow accident (LOFA) scenarios. Tests for each mass flow rate of

  9. Velocity slip effects on heat and mass fluxes of MHD viscous–Ohmic dissipative flow over a stretching sheet with thermal radiation

    Directory of Open Access Journals (Sweden)

    M. Kayalvizhi

    2016-06-01

    Full Text Available In the present article, we discussed the velocity slip effects on the heat and mass fluxes of a viscous electrically conducting fluid flow over a stretching sheet in the presence of viscous dissipation, Ohmic dissipation and thermal radiation. A system of governing nonlinear PDEs is converted into a set of nonlinear ODEs by suitable similarity transformations. The numerical and analytical solutions are presented for the governing non-dimensional ODEs using shooting method and hypergeometric function respectively. The results are discussed for skin friction coefficient, concentration field, non-dimensional wall temperature and non-dimensional wall concentration. The non-dimensional wall concentration increases with slip and magnetic parameters and decreases with Schmidt number. Furthermore, comparisons are found to be good with bench mark solutions.

  10. Heating of coronal plasma by anomalous current dissipation. [induced by solar magnetic flux

    Science.gov (United States)

    Rosner, R.; Golub, L.; Coppi, B.; Vaiana, G. S.

    1978-01-01

    It is shown that there exist heating mechanisms which connect the observed radiative properties of the inner corona in a simple way to the underlying solar magnetic field. The mechanisms considered involve the generation and consequent dissipation of coronal currents. It is argued that the spatially and temporally inhomogeneous nature of the erupting solar magnetic field is an essential element of coronal heating. Unlike heating theories conceived in the context of the 'homogeneous' corona, this class of current heating models incorporates the observed stochastic coronal structuring at the onset, and does not view it as a complication of an otherwise straightforward model. Attention is given to the generation of coronal currents, the flux-tube emergence, the gradual growth and decay of active regions, the energetics of current dissipation, current sheath geometry and heat transport, and anomalous current dissipation.

  11. Estimation of Surface Temperature and Heat Flux by Inverse Heat Transfer Methods Using Internal Temperatures Measured While Radiantly Heating a Carbon/Carbon Specimen up to 1920 F

    Science.gov (United States)

    Pizzo, Michelle; Daryabeigi, Kamran; Glass, David

    2015-01-01

    The ability to solve the heat conduction equation is needed when designing materials to be used on vehicles exposed to extremely high temperatures; e.g. vehicles used for atmospheric entry or hypersonic flight. When using test and flight data, computational methods such as finite difference schemes may be used to solve for both the direct heat conduction problem, i.e., solving between internal temperature measurements, and the inverse heat conduction problem, i.e., using the direct solution to march forward in space to the surface of the material to estimate both surface temperature and heat flux. The completed research first discusses the methods used in developing a computational code to solve both the direct and inverse heat transfer problems using one dimensional, centered, implicit finite volume schemes and one dimensional, centered, explicit space marching techniques. The developed code assumed the boundary conditions to be specified time varying temperatures and also considered temperature dependent thermal properties. The completed research then discusses the results of analyzing temperature data measured while radiantly heating a carbon/carbon specimen up to 1920 F. The temperature was measured using thermocouple (TC) plugs (small carbon/carbon material specimens) with four embedded TC plugs inserted into the larger carbon/carbon specimen. The purpose of analyzing the test data was to estimate the surface heat flux and temperature values from the internal temperature measurements using direct and inverse heat transfer methods, thus aiding in the thermal and structural design and analysis of high temperature vehicles.

  12. Advantages of analytically computing the ground heat flux in land surface models

    Science.gov (United States)

    Pauwels, Valentijn R. N.; Daly, Edoardo

    2016-11-01

    It is generally accepted that the ground heat flux accounts for a significant fraction of the surface energy balance. In land surface models, the ground heat flux is typically estimated through a numerical solution of the heat conduction equation. Recent research has shown that this approach introduces errors in the estimation of the energy balance. In this paper, we calibrate a land surface model using a numerical solution of the heat conduction equation with four different vertical spatial resolutions. It is found that the thermal conductivity is the most sensitive parameter to the spatial resolution. More importantly, the thermal conductivity values are directly related to the spatial resolution, thus rendering any physical interpretation of this value irrelevant. The numerical solution is then replaced by an analytical solution. The results of the numerical and analytical solutions are identical when fine spatial and temporal resolutions are used. However, when using resolutions that are typical of land surface models, significant differences are found. When using the analytical solution, the ground heat flux is directly calculated without calculating the soil temperature profile. The calculation of the temperature at each node in the soil profile is thus no longer required, unless the model contains parameters that depend on the soil temperature, which in this study is not the case. The calibration is repeated, and thermal conductivity values independent of the vertical spatial resolution are obtained. The main conclusion of this study is that care must be taken when interpreting land surface model results that have been obtained using numerical ground heat flux estimates. The use of exact analytical solutions, when available, is recommended.

  13. Vertical heat flux in the ocean: Estimates from observations and from a coupled general circulation model

    Science.gov (United States)

    Cummins, Patrick F.; Masson, Diane; Saenko, Oleg A.

    2016-06-01

    The net heat uptake by the ocean in a changing climate involves small imbalances between the advective and diffusive processes that transport heat vertically. Generally, it is necessary to rely on global climate models to study these processes in detail. In the present study, it is shown that a key component of the vertical heat flux, namely that associated with the large-scale mean vertical circulation, can be diagnosed over extra-tropical regions from global observational data sets. This component is estimated based on the vertical velocity obtained from the geostrophic vorticity balance, combined with estimates of absolute geostrophic flow. Results are compared with the output of a non-eddy resolving, coupled atmosphere-ocean general circulation model. Reasonable agreement is found in the latitudinal distribution of the vertical heat flux, as well as in the area-integrated flux below about 250 m depth. The correspondence with the coupled model deteriorates sharply at depths shallower than 250 m due to the omission of equatorial regions from the calculation. The vertical heat flux due to the mean circulation is found to be dominated globally by the downward contribution from the Southern Hemisphere, in particular the Southern Ocean. This is driven by the Ekman vertical velocity which induces an upward transport of seawater that is cold relative to the horizontal average at a given depth. The results indicate that the dominant characteristics of the vertical transport of heat due to the mean circulation can be inferred from simple linear vorticity dynamics over much of the ocean.

  14. CFD Study on Wall/Nanoparticle Interaction in Nanofluids Convective Heat Transfer

    Directory of Open Access Journals (Sweden)

    Mohammad Reza Tarybakhsh

    2013-01-01

    Full Text Available The Brownian motion of the nanoparticles in nanofluid is one of the potential contributors to enhance effective thermal conductivity and the mechanisms that might contribute to this enhancement are the subject of considerable discussion and debate. In this paper, the mixing effect of the base fluid in the immediate vicinity of the nanoparticles caused by the Brownian motion was analyzed, modeled, and compared with existing experimental data available in the literature. CFD was developed to study the effect of wall/nanoparticle interaction on forced convective heat transfer in a tube under constant wall temperature condition. The results showed that the motion of the particle near the wall which can decrease boundary layer and the hydrodynamics effects associated with the Brownian motion have a significant effect on the convection heat transfer of nanofluid.

  15. Inverse problem of estimating transient heat transfer rate on external wall of forced convection pipe

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Wen-Lih; Yang, Yu-Ching; Chang, Win-Jin; Lee, Haw-Long [Clean Energy Center, Department of Mechanical Engineering, Kun Shan University, Yung-Kang City, Tainan 710-03 (China)

    2008-08-15

    In this study, a conjugate gradient method based inverse algorithm is applied to estimate the unknown space and time dependent heat transfer rate on the external wall of a pipe system using temperature measurements. It is assumed that no prior information is available on the functional form of the unknown heat transfer rate; hence, the procedure is classified as function estimation in the inverse calculation. The accuracy of the inverse analysis is examined by using simulated exact and inexact temperature measurements. Results show that an excellent estimation of the space and time dependent heat transfer rate can be obtained for the test case considered in this study. (author)

  16. The signature of mesoscale eddies on the air-sea turbulent heat fluxes in the South Atlantic Ocean

    Science.gov (United States)

    Villas Bôas, A. B.; Sato, O. T.; Chaigneau, A.; Castelão, G. P.

    2015-03-01

    By collocating 10 years (1999-2009) of remotely sensed surface turbulent heat fluxes with satellite altimetry data, we investigate the impact of oceanic mesoscale eddies on the latent and sensible heat fluxes in the South Atlantic Ocean. In strongly energetic regions, such as the Brazil-Malvinas confluence and the Agulhas Current Retroflection, eddies explain up to 20% of the total variance in the surface turbulent heat fluxes with averaged anomalies of ± (10-20) W/m2. Cyclonic (anticyclonic, respectively) eddies are associated with negative (positive) heat flux anomalies that tend to cool (warm) the marine atmospheric boundary layer. A composite analysis of the turbulent heat flux anomalies inside the eddies reveals a direct relationship between eddy amplitude and the intensity of such anomalies. In addition, these anomalies are stronger near the eddy center, decaying radially to reach minimum values outside the eddies.

  17. Particle and heat flux estimates in Proto-MPEX in Helicon Mode with IR imaging

    Science.gov (United States)

    Showers, M. A.; Biewer, T. M.; Caughman, J. B. O.; Donovan, D. C.; Goulding, R. H.; Rapp, J.

    2016-10-01

    The Prototype Material Plasma Exposure eXperiment (Proto-MPEX) at Oak Ridge National Laboratory (ORNL) is a linear plasma device developing the plasma source concept for the Material Plasma Exposure eXperiment (MPEX), which will address plasma material interaction (PMI) science for future fusion reactors. To better understand how and where energy is being lost from the Proto-MPEX plasma during ``helicon mode'' operations, particle and heat fluxes are quantified at multiple locations along the machine length. Relevant diagnostics include infrared (IR) cameras, four double Langmuir probes (LPs), and in-vessel thermocouples (TCs). The IR cameras provide temperature measurements of Proto-MPEX's plasma-facing dump and target plates, located on either end of the machine. The change in surface temperature is measured over the duration of the plasma shot to determine the heat flux hitting the plates. The IR cameras additionally provide 2-D thermal load distribution images of these plates, highlighting Proto-MPEX plasma behaviors, such as hot spots. The LPs and TCs provide additional plasma measurements required to determine particle and heat fluxes. Quantifying axial variations in fluxes will help identify machine operating parameters that will improve Proto-MPEX's performance, increasing its PMI research capabilities. This work was supported by the U.S. D.O.E. contract DE-AC05-00OR22725.

  18. A Review of Boiling Heat Transfer Processes at High Heat Flux

    Science.gov (United States)

    1991-04-01

    Bjorge , et al. (Ref. 168) and Stephan and Auracher (Ref. 169) later presented variations of the superposition approach. For additional approaches... Bjorge , R. W., Hall, G. R., and Rohsenow, W. M., "Correlation of Forced Convection Boiling Heat Transfer Data," Int. J. Heat Mass Trans., Vol. 25, No

  19. Bed-To-Wall Heat Transfer in a Supercritical Circulating Fluidised Bed Boiler

    Directory of Open Access Journals (Sweden)

    Błaszczuk Artur

    2014-06-01

    Full Text Available The purpose of this work is to find a correlation for heat transfer to walls in a 1296 t/h supercritical circulating fluidised bed (CFB boiler. The effect of bed-to-wall heat transfer coefficient in a long active heat transfer surface was discussed, excluding the radiation component. Experiments for four different unit loads (i.e. 100% MCR, 80% MCR, 60% MCR and 40% MCR were conducted at a constant excess air ratio and high level of bed pressure (ca. 6 kPa in each test run. The empirical correlation of the heat transfer coefficient in a large-scale CFB boiler was mainly determined by two key operating parameters, suspension density and bed temperature. Furthermore, data processing was used in order to develop empirical correlation ranges between 3.05 to 5.35 m·s-1 for gas superficial velocity, 0.25 to 0.51 for the ratio of the secondary to the primary air, 1028 to 1137K for bed temperature inside the furnace chamber of a commercial CFB boiler, and 1.20 to 553 kg·m-3 for suspension density. The suspension density was specified on the base of pressure measurements inside the boiler’s combustion chamber using pressure sensors. Pressure measurements were collected at the measuring ports situated on the front wall of the combustion chamber. The obtained correlation of the heat transfer coefficient is in agreement with the data obtained from typical industrial CFB boilers.

  20. Convective heat transfer between a fluid-saturated porous medium and a permeable wall with fluid injection or withdrawal

    NARCIS (Netherlands)

    Brouwers, Jos

    1994-01-01

    The present paper addresses heat and mass transfer between a permeable wall and a fluid-saturated porous medium. To assess the effect of wall suction or injection on sensible heat transfer, a stagnant film model is developed. The model yields a thermal correction factor accounting for the effect of

  1. Temporal and spatial changes in mixed layer properties and atmospheric net heat flux in the Nordic Seas

    Energy Technology Data Exchange (ETDEWEB)

    Smirnov, A; Alekseev, G [SI ' Arctic and Antarctic Research Institute' , St. Petersburg (Russian Federation); Korablev, A; Esau, I, E-mail: avsmir@aari.nw.r [Nansen Environmental and Remote Sensing Centre, Bergen (Norway)

    2010-08-15

    The Nordic Seas are an important area of the World Ocean where warm Atlantic waters penetrate far north forming the mild climate of Northern Europe. These waters represent the northern rim of the global thermohaline circulation. Estimates of the relationships between the net heat flux and mixed layer properties in the Nordic Seas are examined. Oceanographic data are derived from the Oceanographic Data Base (ODB) compiled in the Arctic and Antarctic Research Institute. Ocean weather ship 'Mike' (OWS) data are used to calculate radiative and turbulent components of the net heat flux. The net shortwave flux was calculated using a satellite albedo dataset and the EPA model. The net longwave flux was estimated by Southampton Oceanography Centre (SOC) method. Turbulent fluxes at the air-sea interface were calculated using the COARE 3.0 algorithm. The net heat flux was calculated by using oceanographic and meteorological data of the OWS 'Mike'. The mixed layer depth was estimated for the period since 2002 until 2009 by the 'Mike' data as well. A good correlation between these two parameters has been found. Sensible and latent heat fluxes controlled by surface air temperature/sea surface temperature gradient are the main contributors into net heat flux. Significant correlation was found between heat fluxes variations at the OWS 'Mike' location and sea ice export from the Arctic Ocean.

  2. Roles of SST anomalies on wintertime turbulent heat fluxes over the Southern Hemisphere

    Science.gov (United States)

    Sugimoto, S.; Kasai, C.; Hanawa, K.

    2013-12-01

    Variations of turbulent heat flux (THF; sum of latent heat flux and sensible heat flux) over the Southern Hemisphere (60°-20°S) are investigated during 21 austral winters (June-August) of 1990-2010. The THF is calculated from the bulk formula using daily variables (surface wind speed, surface air specific humidity, surface air temperature, and sea surface temperature (SST)) of the Objective Analyzed air-sea Flux (OAFlux: Yu et al. 2008) dataset and bulk coefficients based on the Tropical Ocean and Global Atmosphere/Coupled Ocean-Atmosphere Response Experiment (TOGA/COARE) bulk flux algorithm 3.0. The THF have large temporal variances in five regions, where are vicinity of the strong currents: a return region of the Agulhas Current [10°-25°E, 38°-44°S], a downstream region of the Agulhas Return Current [40°-60°E, 38°-43°S], a region over the Leeuwin Current region [105°-120°E, 32°-38°S], a region over the East Australian Current [150°-160°E, 33°-39°S], and a Brazil-Malvinas Confluence region [48°-55°W, 36°-44°S]. By performing simple experiments with combinations of raw daily data and daily climatological data, we quantitatively assessed the relative contributions of SST, surface air temperature, and surface wind speed in determining the THF in the five regions. Results showed that SST is the primary control on the THF; a huge amount of heat release in the state of the positive SST anomaly.

  3. A New Paradigm for Understanding and Enhancing the Critical Heat Flux (CHF) Limit.

    Science.gov (United States)

    Fazeli, Abdolreza; Moghaddam, Saeed

    2017-07-12

    Nearly a century of research on enhancing critical heat flux (CHF) has focused on altering the boiling surface properties such as its nucleation site density, wettability, wickability and heat transfer area. But, a mechanism to manipulate dynamics of the vapor and liquid interactions above the boiling surface as a means of enhancing CHF has not been proposed. Here, a new approach is implemented to limit the vapor phase lateral expansion over the heat transfer surface and actively control the surface wetted area fraction, known to decline monotonically with increasing heat flux. This new degree of freedom has enabled reaching unprecedented CHF levels and revealed new details about the physics of CHF. The impact of wickability, effective heat transfer area, and liquid pressure on CHF is precisely quantified. Test results show that, when rewetting is facilitated, the CHF increases linearly with the effective surface heat transfer area. A maximum CHF of 1.8 kW/cm(2) was achieved on a copper structure with the highest surface area among all tested surfaces. A model developed based on the experimental data suggests that the thermal conductivity of the surface structures ultimately limits the CHF; and a maximum CHF of 7-8 kW/cm(2) may be achieved using diamond surface structures.

  4. Analysis of the Effects of Vitiates on Surface Heat Flux in Ground Tests of Hypersonic Vehicles

    Science.gov (United States)

    Cuda, Vincent; Gaffney, Richard L

    2008-01-01

    To achieve the high enthalpy conditions associated with hypersonic flight, many ground test facilities burn fuel in the air upstream of the test chamber. Unfortunately, the products of combustion contaminate the test gas and alter gas properties and the heat fluxes associated with aerodynamic heating. The difference in the heating rates between clean air and a vitiated test medium needs to be understood so that the thermal management system for hypersonic vehicles can be properly designed. This is particularly important for advanced hypersonic vehicle concepts powered by air-breathing propulsion systems that couple cooling requirements, fuel flow rates, and combustor performance by flowing fuel through sub-surface cooling passages to cool engine components and preheat the fuel prior to combustion. An analytical investigation was performed comparing clean air to a gas vitiated with methane/oxygen combustion products to determine if variations in gas properties contributed to changes in predicted heat flux. This investigation started with simple relationships, evolved into writing an engineering-level code, and ended with running a series of CFD cases. It was noted that it is not possible to simultaneously match all of the gas properties between clean and vitiated test gases. A study was then conducted selecting various combinations of freestream properties for a vitiated test gas that matched clean air values to determine which combination of parameters affected the computed heat transfer the least. The best combination of properties to match was the free-stream total sensible enthalpy, dynamic pressure, and either the velocity or Mach number. This combination yielded only a 2% difference in heating. Other combinations showed departures of up to 10% in the heat flux estimate.

  5. Progress in remote sensing of global land surface heat fluxes and evaporations with a turbulent heat exchange parameterization method

    Science.gov (United States)

    Chen, Xuelong; Su, Bob

    2017-04-01

    Remote sensing has provided us an opportunity to observe Earth land surface with a much higher resolution than any of GCM simulation. Due to scarcity of information for land surface physical parameters, up-to-date GCMs still have large uncertainties in the coupled land surface process modeling. One critical issue is a large amount of parameters used in their land surface models. Thus remote sensing of land surface spectral information can be used to provide information on these parameters or assimilated to decrease the model uncertainties. Satellite imager could observe the Earth land surface with optical, thermal and microwave bands. Some basic Earth land surface status (land surface temperature, canopy height, canopy leaf area index, soil moisture etc.) has been produced with remote sensing technique, which already help scientists understanding Earth land and atmosphere interaction more precisely. However, there are some challenges when applying remote sensing variables to calculate global land-air heat and water exchange fluxes. Firstly, a global turbulent exchange parameterization scheme needs to be developed and verified, especially for global momentum and heat roughness length calculation with remote sensing information. Secondly, a compromise needs to be innovated to overcome the spatial-temporal gaps in remote sensing variables to make the remote sensing based land surface fluxes applicable for GCM model verification or comparison. A flux network data library (more 200 flux towers) was collected to verify the designed method. Important progress in remote sensing of global land flux and evaporation will be presented and its benefits for GCM models will also be discussed. Some in-situ studies on the Tibetan Plateau and problems of land surface process simulation will also be discussed.

  6. Laminar convective heat transfer of non-Newtonian nanofluids with constant wall temperature

    Science.gov (United States)

    Hojjat, M.; Etemad, S. Gh.; Bagheri, R.; Thibault, J.

    2011-02-01

    Nanofluids are obtained by dispersing homogeneously nanoparticles into a base fluid. Nanofluids often exhibit higher heat transfer rate in comparison with the base fluid. In the present study, forced convection heat transfer under laminar flow conditions was investigated experimentally for three types of non-Newtonian nanofluids in a circular tube with constant wall temperature. CMC solution was used as the base fluid and γ-Al2O3, TiO2 and CuO nanoparticles were homogeneously dispersed to create nanodispersions of different concentrations. Nanofluids as well as the base fluid show shear thinning (pseudoplastic) rheological behavior. Results show that the presence of nanoparticles increases the convective heat transfer of the nanodispersions in comparison with the base fluid. The convective heat transfer enhancement is more significant when both the Peclet number and the nanoparticle concentration are increased. The increase in convective heat transfer is higher than the increase caused by the augmentation of the effective thermal conductivity.

  7. Experimental Realization of Extreme Heat Flux Concentration with Easy-to-Make Thermal Metamaterials

    Science.gov (United States)

    Chen, Fei; Yuan Lei, Dang

    2015-06-01

    The ability to harvest thermal energy and manipulate heat fluxes has recently attracted a great deal of research interest because this is critical to achieve efficient solar-to-thermal energy conversion in the technology of concentrated solar thermal collectors. Thermal metamaterials with engineered thermal conduction are often utilized to control the diffusive heat flow in ways otherwise not possible with naturally occurring materials. In this work, we adopt the transformation thermodynamics approach to design an annular fan-shaped thermal metamaterial which is capable of guiding heat fluxes and concentrating thermal energy to the central region of the metamaterial device without disturbing the temperature profile outside the structure - a fascinating and unique feature impossibly achieved with homogeneous materials. In experiment, this rationally-designed metamaterial structure demonstrates extreme heat flux compression from both line-shaped and point thermal sources with measured concentration efficiency up to 83.1%, providing the first experimental realization of our recent theoretical prediction (T. Han et al., Energy Environ. Sci., 2013, 6, 3537-3541). These unprecedented results may open up new possibilities for engineering thermal materials with desired properties that can be used for dramatically enhancing the efficiency of the existing solar thermal collectors.

  8. Contribution of Heat Fluxes on Cyclone Narelle as Simulated by a Mesoscale Model

    Directory of Open Access Journals (Sweden)

    Yopi Ilhamsyah

    2013-12-01

    Full Text Available Heat fluxes from oceanic evaporation particularly latent heat is important to drive the formation and intensification of Cyclone Narelle. The research was carried out by introducing a mesoscale model, namely Weather and Research Forecasting (WRF. One domain with spatial resolution at 10 km was utilized in the model. The model involved significant physical parameters, e.g., Kain-Fritsch in the cumulus scheme, Yonsei University in the Planetary Boundary Layer scheme, and WRF Single-Moment 3-class in the microphysics scheme. The analysis focused on January 8th to 14th upon all stages of Narelle. The result showed that Sea Surface Temperatures (SST higher than 26°C was a favorable environment for Cylone Narelle to form. Surface sensible and latent heat fluxes have strong positive correlation with wind speed and SST. It can be concluded that these variables were highly correlated with surface heat flux that further lead to the formation and intensification of Cyclone Narelle in early January 2013 over South Indian Ocean. The tracks and stages of the model are nearly similar to the observations, the differences are found in late phases of Narelle.

  9. Fabrication and Testing of a Thin-Film Heat Flux Sensor for a Stirling Convertor

    Science.gov (United States)

    Wilson, Scott D.; Fralick, Gustave; Wrbanek, John; Sayir, Ali

    2009-01-01

    The NASA Glenn Research Center (GRC) has been testing high efficiency free-piston Stirling convertors for potential use in radioisotope power systems since 1999. Stirling convertors are being operated for many years to demonstrate a radioisotope power system capable of providing reliable power for potential multi-year missions. Techniques used to monitor the convertors for change in performance include measurements of temperature, pressure, energy addition, and energy rejection. Micro-porous bulk insulation is used in the Stirling convertor test set up to minimize the loss of thermal energy from the electric heat source to the environment. The insulation is characterized before extended operation, enabling correlation of the net thermal energy addition to the convertor. Aging microporous bulk insulation changes insulation efficiency, introducing errors in the correlation for net thermal energy addition. A thin-mm heat flux sensor was designed and fabricated to directly measure the net thermal energy addition to the Stirling convertor. The fabrication techniques include slip casting and using Physical Vapor Deposition (PVD). One micron thick noble metal thermocouples measure temperature on the surface of an Alumina ceramic disc and heat flux is calculated. Fabrication, integration, and test results of a thin film heat flux sensor are presented.

  10. Accuracy of Zero-Heat-Flux Cutaneous Temperature in Intensive Care Adults.

    Science.gov (United States)

    Dahyot-Fizelier, Claire; Lamarche, Solène; Kerforne, Thomas; Bénard, Thierry; Giraud, Benoit; Bellier, Rémy; Carise, Elsa; Frasca, Denis; Mimoz, Olivier

    2017-07-01

    To compare accuracy of a continuous noninvasive cutaneous temperature using zero-heat-flux method to esophageal temperature and arterial temperature. Prospective study. ICU and NeuroICU, University Hospital. Fifty-two ICU patients over a 4-month period who required continuous temperature monitoring were included in the study, after informed consent. All patients had esophageal temperature probe and a noninvasive cutaneous device to monitor their core temperature continuously. In seven patients who required cardiac output monitoring, continuous iliac arterial temperature was collected. Simultaneous core temperatures were recorded from 1 to 5 days. Comparison to the esophageal temperature, considered as the reference in this study, used the Bland and Altman method with adjustment for multiple measurements per patient. The esophageal temperature ranged from 33°C to 39.7°C, 61,298 pairs of temperature using zero-heat-flux and esophageal temperature were collected and 1,850 triple of temperature using zero-heat-flux, esophageal temperature, and arterial temperature. Bias and limits of agreement for temperature using zero-heat-flux were 0.19°C ± 0.53°C compared with esophageal temperature with an absolute difference of temperature pairs equal to or lower than 0.5°C of 92.6% (95% CI, 91.9-93.4%) of cases and equal to or lower than 1°C for 99.9% (95% CI, 99.7-100.0%) of cases. Compared with arterial temperature, bias and limits of agreement were -0.00°C ± 0.36°C with an absolute difference of temperature pairs equal to or lower than 0.5°C of 99.8% (95% CI, 95.3-100%) of cases. All absolute difference of temperature pairs between temperature using zero-heat-flux and arterial temperature and between arterial temperature and esophageal temperature were equal to or lower than 1°C. No local or systemic serious complication was observed. These results suggest a comparable reliability of the cutaneous sensor using the zero-heat-flux method compared with esophageal or

  11. A preliminary assessment of the effects of heat flux distribution and penetration on the creep rupture of a reactor vessel lower head

    Energy Technology Data Exchange (ETDEWEB)

    Chu, T.Y.; Bentz, J.; Simpson, R. [Sandia National Labs., Albuquerque, NM (United States); Witt, R. [Univ. of Wisconsin, Madison, WI (United States)

    1997-02-01

    The objective of the Lower Head Failure (LHF) Experiment Program is to experimentally investigate and characterize the failure of the reactor vessel lower head due to thermal and pressure loads under severe accident conditions. The experiment is performed using 1/5-scale models of a typical PWR pressure vessel. Experiments are performed for various internal pressure and imposed heat flux distributions with and without instrumentation guide tube penetrations. The experimental program is complemented by a modest modeling program based on the application of vessel creep rupture codes developed in the TMI Vessel Investigation Project. The first three experiments under the LHF program investigated the creep rupture of simulated reactor pressure vessels without penetrations. The heat flux distributions for the three experiments are uniform (LHF-1), center-peaked (LHF-2), and side-peaked (LHF-3), respectively. For all the experiments, appreciable vessel deformation was observed to initiate at vessel wall temperatures above 900K and the vessel typically failed at approximately 1000K. The size of failure was always observed to be smaller than the heated region. For experiments with non-uniform heat flux distributions, failure typically occurs in the region of peak temperature. A brief discussion of the effect of penetration is also presented.

  12. Influence of Heat Flux and Friction Coefficient on Thermal Stresses in Risers of Drum Boilers under Dynamic Conditions of Steam Demand

    Directory of Open Access Journals (Sweden)

    M. A. Habib

    2013-01-01

    Full Text Available Boiler swing rate, which is the rate at which the boiler load is changed, has significant influence on the parameters of the boiler operating conditions such as drum water pressure and level, steam quality in the riser tubes, wall temperatures of riser tubes, and the associated thermal stresses. In this paper, the thermal stresses developed in boiler tubes due to elevated rates of heat transfer and friction are presented versus thermal stresses developed in tubes operated under normal conditions. The differential equations comprising the nonlinear model and governing the flow inside the boiler tubes were formulated to study different operational scenarios in terms of resulting dynamic response of critical variables. The experimental results and field data were obtained to validate the present nonlinear dynamic model. The calculations of the heat flux and the allowable steam quality were used to determine the maximum boiler swing rates at different conditions of riser tube of friction factor and heat flux. Diagrams for the influence of friction factor of the boiler tubes and the heat flux, that the tube is subjected to, on the maximum swing rate were examined.

  13. MHD effects and heat transfer for the UCM fluid along with Joule heating and thermal radiation using Cattaneo-Christov heat flux model

    Energy Technology Data Exchange (ETDEWEB)

    Shah, S., E-mail: sajidshah313@yahoo.com; Hussain, S.; Sagheer, M. [Department of Mathematics, Capital University of Science and Technology, Islamabad (Pakistan)

    2016-08-15

    Present study examines the numerical analysis of MHD flow of Maxwell fluid with thermal radiation and Joule heating by considering the recently developed Cattaneo-Christov heat flux model which explains the time relaxation characteristics for the heat flux. The objective is to analyze the governing parameters such as viscoelastic fluid parameter, Magnetic parameter, Eckert and Prandtl number’s impact on the velocity and temperature profiles through graphs and tables. Suitable similarity transformations have been used to reduce the formulated PDEs into a system of coupled non-linear ODEs. Shooting technique has been invoked for finding the numerical solutions of the dimensionless velocity and temperature profiles. Additionally, the MATLAB built-in routine bvp4c has also been used to verify and strengthen the results obtained by shooting method. From some special cases of the present work, a comparison with the previously published results has been presented.

  14. Direct Heat-Flux Measurement System (MDF) for Solar central Receiver Evaluation

    Energy Technology Data Exchange (ETDEWEB)

    Ballestrin, J.

    2001-07-01

    A direct flux measurement system, MDF, has been designed, constructed and mounted on top of the SSPS-CRS tower at the Plataforma Solar de Almeria (PSA) in addition to an indirect flux measurement system based on a CCD camera. It's one of the main future objectives to compare systematically both measurements of the concentrated solar power, increasing in this way the confidence in the estimate of this quantity. Today everything is prepared to perform the direct flux measurement on the aperture of solar receivers: calorimeter array, data acquisition system and software. the geometry of the receiver determines the operation and analysis procedures to obtain the indecent power onto the defined area. The study of previous experiences with direct flux measurement systems ha been useful to define a new simpler and more accurate system. A description of each component of the MDF system is included, focusing on the heat-flux sensors or calorimeters, which enables these measurements to be done in a few seconds without water-cooling. The incident solar power and the spatial flux distribution on the aperture of the volumetric receiver Hitrec II are supplied by the above-mentioned MDF system. The first results obtained during the evaluation of this solar receiver are presented including a sunrise-sunset test. All these measurements have been concentrated in one coefficient that describes the global behavior of the Solar Power Plant. (Author) 18 refs.

  15. Hybrid Heat Pipes for High Heat Flux Spacecraft Thermal Control Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Grooved aluminum/ammonia Constant Conductance Heat Pipes (CCHPs) are the standard for thermal control in zero-gravity. Unfortunately, they are limited in terms of...

  16. Prototype solar heated hot water systems and double-walled heat exchangers. Progress report

    Energy Technology Data Exchange (ETDEWEB)

    1978-10-01

    A collection of quarterly and monthly reports from Elcam, Inc., covering progress made from January 1, 1978, through September 30, 1978, is presented. Elcam, is developing two solar-heated hot water prototype systems and two heat exchangers. This effort consists of development, manufacture, installation, maintenance, problem resolution, and system evaluation.

  17. Some specific features of subcooled boiling heat transfer and crisis at extremely high heat flux densities

    Energy Technology Data Exchange (ETDEWEB)

    Gotovsky, M.A. [Polzunov Institute, Saint Petersburg (Russian Federation)

    2001-07-01

    Forced convection boiling is the process used widely in a lot of industry branches including NPP. Heat transfer intensity under forced convection boiling is considered in different way in dependence on conditions. One of main problems for the process considered is an influence of interaction between forced flow and boiling on heat transfer character. For saturated water case a transition from ''pure'' forced convection to nucleate boiling can be realized in smooth form. (author)

  18. Experimental and Computational Studies of Heat Transfer for Wall-type and Fin-type Heat Exchanger

    Science.gov (United States)

    Feng, Guochao; Xu, Peng; Gong, Linghui; Li, Laifeng; Zhang, Hengcheng; Li, Hongmei

    2017-12-01

    Wall-type heat exchangers (WTHX) and fin-type heat exchangers (FTHX) are attached to the first and second stage cold head of two G-M crycoolers respectively in the simulating experimental platform of the internal purifier (SEPEIP). WTHX and FTHX play a significant role in SEPEIP, WTHX is designed to remove heat from helium and freeze-out extremely few impurities, FTHX is for further cooling the helium. In this study, numerical simulation and experimental results for WTHX and FTHX are carried out. According to the comparison, the numerical results have a little discrepancy with the experimental results. However, the discrepancy is within the acceptable level. Finally, it is observed that the WTHX and FTHX are suitable to apply in the experimental system and are capable of guaranteeing a purifying function.

  19. Large heat and fluid fluxes driven through mid-plate outcrops on ocean crust

    Science.gov (United States)

    Hutnak, M.; Fisher, A. T.; Harris, R.; Stein, C.; Wang, K.; Spinelli, G.; Schindler, M.; Villinger, H.; Silver, E.

    2008-09-01

    Hydrothermal circulation on the sea floor at mid-ocean ridge flanks extracts ~30% of heat from the oceanic lithosphere on a global basis and affects numerous tectonic, magmatic and biogeochemical processes. However, the magnitude, mechanisms and implications of regional-scale fluid and heat flow on mid-ocean ridge flanks are poorly understood. Here we analyse swath-map, seismic and sea-floor heat-flux data to quantify the heat and fluid discharge through a few widely spaced basement outcrops on the Cocos Plate. Heat removed by conduction from a 14,500 square kilometre region of the sea floor is 60-90% lower than that predicted by lithospheric cooling models. This implies that a substantial portion of the heat is extracted by advection, which requires fluid discharge of 4-80×103 litres per second. The heat output of individual discharging outcrops is inferred to be comparable to that from black-smoker vent fields seen on mid-ocean ridges. Our analysis shows that hydrothermal circulation on mid-ocean ridge flanks through widely spaced outcrops can extract a large fraction of lithospheric heat. This circulation requires a very high crustal permeability at a regional scale. Focused flows of warm, nutrient-rich hydrothermal fluid may enhance sub-seafloor microbial habitats and enable direct sampling of these systems.

  20. The Effect of Inclination Angle on Critical Heat Flux in a Locally Heated Liquid Film Moving Under the Action of Gas Flow in a Mini-Channel

    Directory of Open Access Journals (Sweden)

    Tkachenko Egor M.

    2016-01-01

    Full Text Available Intensively evaporating liquid films moving under the action of the cocurrent gas flow in a microchannel are promising for the use in modern cooling systems of semiconductor devices with high local heat release. This work has studied the dependence of the critical heat flux on the inclination angle of the channel. It has been found that the inclination angle in the plane parallel to the flow has no significant effect on the critical heat flux. Whereas the inclination angle in the plane perpendicular to the flow, on the contrary, significantly changes the value of the critical heat flux. However, for a given flow rate of fluid there is a threshold gas velocity at which the critical heat flux does not differ from the case of zero inclination of the channel. Thus, it can be concluded that the cooling system based on shear-driven liquid films can be potentially used when direction of the gravity changes.

  1. Drag and heat flux reduction mechanism of blunted cone with aerodisks

    Science.gov (United States)

    Huang, Wei; Li, Lang-quan; Yan, Li; Zhang, Tian-tian

    2017-09-01

    The major challenge among a number of design requirements for hypersonic vehicles is the reduction of drag and aerodynamic heating. Of all these techniques of drag and heat flux reduction, application of forward facing aerospike conceived in 1950s is an effective and simpler technique to reduce the drag as well as the heat transfer rate for blunt nosed bodies at hypersonic Mach numbers. In this paper, the flow fields around a blunt cone with and without aerodisk flying at hypersonic Mach numbers are computed numerically, and the numerical simulations are conducted by specifying the freestream velocity, static pressure and static temperatures at the inlet of the computational domain with a three-dimensional, steady, Reynolds-averaged Navier-Stokes equation. An aerodisk is attached to the tip of the rod to reduce the drag and heat flux further. The influences of the length of rod and the diameter of aerodisk on the drag and heat flux reduction mechanism are analyzed comprehensively, and eight configurations are taken into consideration in the current study. The obtained results show that for all aerodisks, the reduction in drag of the blunt body is proportional to the extent of the recirculation dead air region. For long rods, the aerodisk is found not that beneficial in reducing the drag, and an aerodisk is more effective than an aerospike. The spike produces a region of recirculation separated flow that shields the blunt-nosed body from the incoming flow, and the recirculation region is formed around the root of the spike up to the reattachment point of the flow at the shoulder of the blunt body. The dynamic pressure in the recirculation area is highly reduced and thus leads to the decrease in drag and heat load on the surface of the blunt body. Because of the reattachment of the shear layer on the shoulder of the blunt body, the pressure near that point becomes large.

  2. Numerical study of heat transfer from a wall incorporating a phase change material

    Directory of Open Access Journals (Sweden)

    Bouttout A.

    2013-03-01

    Full Text Available A numerical study of the thermal behavior of walls made up of construction materials used in Algeria and walls containing a phase change materials is presented. The model, based on the enthalpy formulation, is described by an equation of heat transfer. This equation is solved by an implicit method of finite differences and algorithm of Thomas. We analyzed the influence of the wall’s thickness and its composition on the evolution during the time of the temperature of the inside face of thewall.

  3. Influence of Joule heating on current-induced domain wall depinning

    Energy Technology Data Exchange (ETDEWEB)

    Moretti, Simone, E-mail: simone.moretti@usal.es; Raposo, Victor; Martinez, Eduardo [University of Salamanca, Plaza de los Caidos, 37008 Salamanca (Spain)

    2016-06-07

    The domain wall depinning from a notch in a Permalloy nanostrip on top of a SiO{sub 2}/Si substrate is studied theoretically under application of static magnetic fields and the injection of short current pulses. The influence of Joule heating on current-induced domain wall depinning is explored self-consistently by coupling the magnetization dynamics in the ferromagnetic strip to the heat transport throughout the system. Our results indicate that Joule heating plays a remarkable role in these processes, resulting in a reduction in the critical depinning field and/or in a temporary destruction of the ferromagnetic order for typically injected current pulses. In agreement with experimental observations, similar pinning-depinning phase diagrams can be deduced for both current polarities when the Joule heating is taken into account. These observations, which are incompatible with the sole contribution of spin transfer torques, provide a deeper understanding of the physics underlying these processes and establish the real scope of the spin transfer torque. They are also relevant for technological applications based on current-induced domain-wall motion along soft strips.

  4. Partial Nucleate Pool Boiling at Low Heat Flux: Preliminary Ground Test for SOBER-SJ10

    Science.gov (United States)

    Wu, Ke; Li, Zhen-Dong; Zhao, Jian-Fu; Li, Hui-Xiong; Li, Kai

    2016-05-01

    Focusing on partial nucleate pool boiling at low heat flux, SOBER-SJ10, one of 27 experiments of the program SJ-10, has been proposed to study local convection and heat transfer around an isolated growing vapor bubble during nucleate pool boiling on a well characterized flat surface in microgravity. An integrated micro heater has been developed. By using a local pulse overheating method in the experimental mode of single bubble boiling, a bubble nucleus can be excited with accurate spatial and temporal positioning on the top-side of a quartz glass substrate with a thickness of 2 mm and an effective heating area of 4.5 mm in diameter, and then grows under an approximate constant heat input provided by the main heater on the back-side of the substrate. Ten thin film micro-RTDs are used for local temperature measurements on the heating surface underneath the growing bubble. Normal pool boiling experiments can also be carried out with step-by-step increase of heating voltage. A series of ground test of the flight module of SOBER-SJ10 have been conducted. Good agreement of the measured data of single phase natural convection with the common-used empirical correlation warrants reasonable confidence in the data. It is found that the values of the incipience superheat of pool boiling at different subcooling are consistent with each others, verifying that the influence of subcooling on boiling incipience can be neglected. Pool boiling curves are also obtained, which shows great influence of subcooling on heat transfer of partial nucleate pool boiling, particularly in lower heat flux.

  5. Two Improvements of an Operational Two-Layer Model for Terrestrial Surface Heat Flux Retrieval

    Directory of Open Access Journals (Sweden)

    Jun Xia

    2008-10-01

    Full Text Available In order to make the prediction of land surface heat fluxes more robust, two improvements were made to an operational two-layer model proposed previously by Zhang. These improvements are: 1 a surface energy balance method is used to determine the theoretical boundary lines (namely ‘true wet/cool edge’ and ‘true dry/warm edge’ in the trapezoid in the scatter plot for the surface temperature versus the fractional vegetation cover in mixed pixels; 2 a new assumption that the slope of the Tm – f curves is mainly controlled by soil water content is introduced. The variables required by the improved method include near surface vapor pressure, air temperature, surface resistance, aerodynamic resistance, fractional vegetation cover, surface temperature and net radiation. The model predictions from the improved model were assessed in this study by in situ measurements, which show that the total latent heat flux from the soil and vegetation are in close agreement with the in situ measurement with an RMSE (Root Mean Square Error ranging from 30 w/m2~50 w/m2,which is consistent with the site scale measurement of latent heat flux. Because soil evaporation and vegetation transpiration are not measured separately from the field site, in situ measured CO2 flux is used to examine the modeled λEveg. Similar trends of seasonal variations of vegetation were found for the canopy transpiration retrievals and in situ CO2 flux measurements. The above differences are mainly caused by 1 the scale disparity between the field measurement and the MODIS observation; 2 the non-closure problem of the surface energy balance from the surface fluxes observations themselves. The improved method was successfully used to predict the component surface heat fluxes from the soil and vegetation and it provides a promising approach to study the canopy transpiration and the soil evaporation quantitatively during the

  6. Design and Characterization of a High Resolution Microfluidic Heat Flux Sensor with Thermal Modulation

    Directory of Open Access Journals (Sweden)

    Sun-Kyu Lee

    2010-07-01

    Full Text Available A complementary metal-oxide semiconductor-compatible process was used in the design and fabrication of a suspended membrane microfluidic heat flux sensor with a thermopile for the purpose of measuring the heat flow rate. The combination of a thirty-junction gold and nickel thermoelectric sensor with an ultralow noise preamplifier, a low pass filter, and a lock-in amplifier can yield a resolution 20 nW with a sensitivity of 461 V/W. The thermal modulation method is used to eliminate low-frequency noise from the sensor output, and various amounts of fluidic heat were applied to the sensor to investigate its suitability for microfluidic applications. For sensor design and analysis of signal output, a method of modeling and simulating electro-thermal behavior in a microfluidic heat flux sensor with an integrated electronic circuit is presented and validated. The electro-thermal domain model was constructed by using system dynamics, particularly the bond graph. The electro-thermal domain system model in which the thermal and the electrical domains are coupled expresses the heat generation of samples and converts thermal input to electrical output. The proposed electro-thermal domain system model is in good agreement with the measured output voltage response in both the transient and the steady state.

  7. Design and characterization of a high resolution microfluidic heat flux sensor with thermal modulation.

    Science.gov (United States)

    Nam, Sung-Ki; Kim, Jung-Kyun; Cho, Sung-Cheon; Lee, Sun-Kyu

    2010-01-01

    A complementary metal-oxide semiconductor-compatible process was used in the design and fabrication of a suspended membrane microfluidic heat flux sensor with a thermopile for the purpose of measuring the heat flow rate. The combination of a thirty-junction gold and nickel thermoelectric sensor with an ultralow noise preamplifier, a low pass filter, and a lock-in amplifier can yield a resolution 20 nW with a sensitivity of 461 V/W. The thermal modulation method is used to eliminate low-frequency noise from the sensor output, and various amounts of fluidic heat were applied to the sensor to investigate its suitability for microfluidic applications. For sensor design and analysis of signal output, a method of modeling and simulating electro-thermal behavior in a microfluidic heat flux sensor with an integrated electronic circuit is presented and validated. The electro-thermal domain model was constructed by using system dynamics, particularly the bond graph. The electro-thermal domain system model in which the thermal and the electrical domains are coupled expresses the heat generation of samples and converts thermal input to electrical output. The proposed electro-thermal domain system model is in good agreement with the measured output voltage response in both the transient and the steady state.

  8. High geothermal heat flux in close proximity to the Northeast Greenland Ice Stream.

    Science.gov (United States)

    Rysgaard, Søren; Bendtsen, Jørgen; Mortensen, John; Sejr, Mikael K

    2018-01-22

    The Greenland ice sheet (GIS) is losing mass at an increasing rate due to surface melt and flow acceleration in outlet glaciers. Currently, there is a large disagreement between observed and simulated ice flow, which may arise from inaccurate parameterization of basal motion, subglacial hydrology or geothermal heat sources. Recently it was suggested that there may be a hidden heat source beneath GIS caused by a higher than expected geothermal heat flux (GHF) from the Earth's interior. Here we present the first direct measurements of GHF from beneath a deep fjord basin in Northeast Greenland. Temperature and salinity time series (2005-2015) in the deep stagnant basin water are used to quantify a GHF of 93 ± 21 mW m-2 which confirm previous indirect estimated values below GIS. A compilation of heat flux recordings from Greenland show the existence of geothermal heat sources beneath GIS and could explain high glacial ice speed areas such as the Northeast Greenland ice stream.

  9. Reliable MOSFET operation using two-phase microfluidics in the presence of high heat flux transients

    Science.gov (United States)

    Govind Singh, Shiv; Agrawal, Amit; Duttagupta, Siddhartha P.

    2011-10-01

    Randomly generated heat flux transients affect the reliability of advanced integrated circuits and can induce severe nonlinearity in the device response, resulting in the degradation of a gate dielectric in metal oxide field effect transistors (MOSFETs). The effect of high heat flux transients on MOSFET operation and mitigation, using single-phase and two-phase on-chip microfluidics, is reported in this paper. A prototype comprising monolithically integrated MOSFETs, resistance temperature detector (RTD) arrays, simulated transient source (microheaters) and microfluidic networks was developed. The application of a 10 s transient (153 W cm-2) led to the degradation of subthreshold swing (S) from 120 to 240 mV/decade. However, in the presence of water flow, effective mitigation of S (up to 75%) is observed. The rate of mitigation is higher at lower flow rates because of the higher heat-transfer efficiency for two-phase flow. Thus, an appropriate selection of flow parameters can lead to optimized cooling. Additionally, we propose a strategy to localize the transient heat sources based on the temperature profiles generated using an on-chip, distributed RTD sensor array. The proposed methodology can be applied in practical integrated circuits for localization and characterization of heat sources leading to modifications in the circuit design or process integration steps.

  10. Analytic calculation of energy transfer and heat flux in a one-dimensional system

    Science.gov (United States)

    Balakrishnan, V.; van den Broeck, C.

    2005-10-01

    In the context of the problem of heat conduction in one-dimensional systems, we present an analytical calculation of the instantaneous energy transfer across a tagged particle in a one-dimensional gas of equal-mass, hard-point particles. From this, we obtain a formula for the steady-state energy flux, and identify and separate the mechanical work and heat conduction contributions to it. The nature of the Fourier law for the model, and the nonlinear dependence of the rate of mechanical work on the stationary drift velocity of the tagged particle, are analyzed and elucidated.

  11. Design and Characterization of a High Resolution Microfluidic Heat Flux Sensor with Thermal Modulation

    OpenAIRE

    Sun-Kyu Lee; Sung-Cheon Cho; Jung-Kyun Kim; Sung-Ki Nam

    2010-01-01

    A complementary metal-oxide semiconductor-compatible process was used in the design and fabrication of a suspended membrane microfluidic heat flux sensor with a thermopile for the purpose of measuring the heat flow rate. The combination of a thirty-junction gold and nickel thermoelectric sensor with an ultralow noise preamplifier, a low pass filter, and a lock-in amplifier can yield a resolution 20 nW with a sensitivity of 461 V/W. The thermal modulation method is used to eliminate low-freque...

  12. Striation pattern of target particle and heat fluxes in three dimensional simulations for DIII-D

    Science.gov (United States)

    Frerichs, H.; Schmitz, O.; Reiter, D.; Evans, T. E.; Feng, Y.

    2014-02-01

    The application of resonant magnetic perturbations results in a non-axisymmetric striation pattern of magnetic field lines from the plasma interior which intersect the divertor targets. The impact on related particle and heat fluxes is investigated by three dimensional computer simulations for two different recycling conditions (controlled via neutral gas pumping). It is demonstrated that a mismatch between the particle and heat flux striation pattern (splitting vs. no splitting), as is repeatedly observed in ITER similar shape H-mode plasmas at DIII-D, can be reproduced by the simulations for high recycling conditions at the onset of partial detachment. These results indicate that a detailed knowledge of the particle and energy balance is at least as important for realistic simulations as the consideration of a change in the magnetic field structure by plasma response effects.

  13. Quantify the continuous dependence of SST-turbulent heat flux relationship on spatial scales

    Science.gov (United States)

    Li, Furong; Sang, Huiyan; Jing, Zhao

    2017-06-01

    Relationship among different quantities usually changes in the time, spatial, and spectral domains due to the complicated dynamics in the geosystem. In this study, we propose a general statistical modeling approach to address this problem and apply the approach to evaluating the continuous dependence of relationship between sea surface temperature (SST) and turbulent heat flux (T-Q relationship) on spatial scales. In the Kuroshio extension region, it is found that the turbulent heat flux (defined positive upward) anomalies are positively correlated to SST anomalies at scales ranging from 150 km to 4000 km. The T-Q relationship stays stable at mesoscales (<1000 km) with a regression coefficient α of 26 W/(m2K). However, its value decreases rapidly as scales further increase. In addition, α exhibits a pronounced seasonal cycle with coherent phase at all the scales. The largest and smallest values occur in winter and summer, respectively.

  14. Self-castellation of tungsten monoblock under high heat flux loading and impact of material properties

    Directory of Open Access Journals (Sweden)

    S. Panayotis

    2017-08-01

    Full Text Available In the full-tungsten divertor qualification program at ITER Organization, macro-cracks, so called self-castellation were found in a fraction of tungsten monoblocks during cyclic high heat flux loading at 20MW/m2. The number of monoblocks with macro-cracks varied with the tungsten products used as armour material. In order to understand correlation between the macro-crack appearance and W properties, an activity to characterize W monoblock materials was launched at the IO. The outcome highlighted that the higher the recrystallization resistance, the lower the number of cracks detected during high heat flux tests. Thermo-mechanical finite element modelling demonstrated that the maximum surface temperature ranges from 1800 °C to 2200 °C and in this range recrystallization of tungsten occurred. Furthermore, it indicated that loss of strength due to recrystallization is responsible for the development of macro-cracks in the tungsten monoblock.

  15. Resolving the Mantle Heat Transfer Discrepancy by Reassessing Buoyancy Flux Estimates of Upwelling Plumes

    Science.gov (United States)

    Hoggard, Mark; Parnell-Turner, Ross; White, Nicky

    2017-04-01

    The size and relative importance of mantle plumes is a controversial topic within the geodynamics community. Numerical experiments of mantle convection suggest a wide range of possible behaviours, from minor plumelets through to large scale, whole-mantle upwellings. In terms of observations, recent seismic tomographic models have identified many large, broad plume-like features within the lower mantle. In contrast, existing estimates of buoyancy flux calculated from plume swells have suggested that these upwellings transfer a relatively minor amount of material and heat into the uppermost mantle. Here, we revisit these calculations of buoyancy flux using a global map of plume swells based upon new observations of dynamic topography. Usually, plume flux is calculated from the cross-sectional area of a swell multiplied by either plate velocity or spreading rate. A key assumption is that plume head material flows laterally at or below the velocity of the overriding plate. Published results are dominated by contributions from the Pacific Ocean and suggest that a total of ˜ 2 TW of heat is carried by plumes into the uppermost mantle. An alternative approach exploits swell volume scaled by a characteristic decay time, which removes the reliance on plate velocities. The main assumption of this method is that plumes are in quasi-steady state. In this study, we have applied this volumetric approach in a new global analysis. Our results indicate that the Icelandic plume has a buoyancy flux of ˜ 27 ± 4 Mg s-1 and the Hawaiian plume is ˜ 2.9 ± 0.6 Mg s-1. These revised values are consistent with independent geophysical constraints from the North Atlantic Ocean and Hawaii. All magmatic and amagmatic swells have been included, suggesting that the total heat flux carried to the base of the plates is ˜ 10 ± 2 TW. This revised value is a five-fold increase compared with previous estimates and provides an improved match to published predictions of basal heat flux across the

  16. Stable water isotope and surface heat flux simulation using ISOLSM: Evaluation against in-situ measurements

    KAUST Repository

    Cai, Mick Y.

    2015-04-01

    The stable isotopes of water are useful tracers of water sources and hydrological processes. Stable water isotope-enabled land surface modeling is a relatively new approach for characterizing the hydrological cycle, providing spatial and temporal variability for a number of hydrological processes. At the land surface, the integration of stable water isotopes with other meteorological measurements can assist in constraining surface heat flux estimates and discriminate between evaporation (E) and transpiration (T). However, research in this area has traditionally been limited by a lack of continuous in-situ isotopic observations. Here, the National Centre for Atmospheric Research stable isotope-enabled Land Surface Model (ISOLSM) is used to simulate the water and energy fluxes and stable water isotope variations. The model was run for a period of one month with meteorological data collected from a coastal sub-tropical site near Sydney, Australia. The modeled energy fluxes (latent heat and sensible heat) agreed reasonably well with eddy covariance observations, indicating that ISOLSM has the capacity to reproduce observed flux behavior. Comparison of modeled isotopic compositions of evapotranspiration (ET) against in-situ Fourier Transform Infrared spectroscopy (FTIR) measured bulk water vapor isotopic data (10. m above the ground), however, showed differences in magnitude and temporal patterns. The disparity is due to a small contribution from local ET fluxes to atmospheric boundary layer water vapor (~1% based on calculations using ideal gas law) relative to that advected from the ocean for this particular site. Using ISOLSM simulation, the ET was partitioned into E and T with 70% being T. We also identified that soil water from different soil layers affected T and E differently based on the simulated soil isotopic patterns, which reflects the internal working of ISOLSM. These results highlighted the capacity of using the isotope-enabled models to discriminate

  17. Turbulence and heat flux observations in the Arctic north of Svalbard

    Science.gov (United States)

    Meyer, Amelie; Sundfjord, Arild; Fer, Ilker; Smedsrud, Lars Henrik

    2016-04-01

    Heat fluxes and mixing between the ocean and the sea ice in the Arctic is fundamental to understanding the new first year sea ice regime and consequences for regional and global ocean circulation. Here we present observations collected between January and June 2015 during the Norwegian Young sea Ice (N-ICE2015) campaign in the Arctic Ocean north of Svalbard. In January 2015, the Norwegian research vessel Lance was frozen into the ice at 83o.3N 21.5oE. Oceanographic, atmospheric, sea ice, snow and biological data were collected above, on, and below the ice using R/V Lance as the base for the ice camp that was drifting south towards the Fram Strait. Over the following six months, four different drifts took place in the same area, from the Nansen Basin, through the Marginal Ice Zone, to the open ocean. Throughout the drifts, the oceanography team collected turbulence measurements to estimate mixing, heat, salt, and momentum fluxes in the ice-ocean boundary layer and between the sub-surface warm Atlantic Water layer and the ice-ocean boundary layer close to freezing point. Water tracer data was collected to map water mass properties, and the distribution of the Atlantic Water inflow. Here we present 600 under-ice microstructure profiles spanning five months, from the deep Nansen Basin to the Yermak Plateau. During this period, several large atmospheric storms took place, forcing a fast drift of the ice camp. Tides were weak in the Nansen Basin and strong on the Yermak Plateau. We investigate vertical heat fluxes between the Atlantic Water layer and the surface mixed layer. Variations in mixing and heat fluxes are interpreted in terms of atmospheric forcing and regional topography.

  18. Scalings for unsteady natural convection boundary layers on an evenly heated plate with time-dependent heating flux

    Science.gov (United States)

    Lin, Wenxian; Armfield, S. W.

    2013-12-01

    It is of fundamental significance, especially with regard to application, to fully understand the flow behavior of unsteady natural convection boundary layers on a vertical plate heated by a time-dependent heat flux. Such an understanding is currently scarce. In this paper, the scaling analysis by Lin et al. [Phys. Rev. E 79, 066313 (2009), 10.1103/PhysRevE.79.066313] using a simple three-region structure for the unsteady natural convection boundary layer of a homogeneous Newtonian fluid with Pr >1 under isothermal heating was substantially extended for the case when the heating is due to a time-varying sinusoidal heat flux. A series of scalings was developed for the thermal boundary thickness, the plate temperature, the viscous boundary thicknesses, and the maximum vertical velocity within the boundary layer, which are the major parameters representing the flow behavior, in terms of the governing parameters of the flow, i.e., the Rayleigh number Ra, the Prandtl number Pr, and the dimensionless natural frequency fn of the time-varying sinusoidal heat flux, at the start-up stage, at the transition time scale which represents the ending of the start-up stage and the beginning of the transitional stage of the boundary-layer development, and at the quasi-steady stage. These scalings were validated by comparison to 10 full numerical solutions of the governing equations with Ra, Pr, and fn in the ranges 106≤Ra≤109, 3≤Pr≤100, and 0.01≤fn≤0.1 and were shown in general to provide an accurate description of the flow at different development stages, except for high-Pr runs in which a further, although weak, Pr dependence is present, which cannot be accurately predicted by the current scaling analysis using the simple three-region structure, attributed to the non-boundary-layer nature of the velocity field with high-Pr fluids. Some scalings at the transition time scale and at the quasi-steady stage also produce noticeable deviations from the numerical results when

  19. Calibration of aerodynamic roughness over the Tibetan Plateau with Ensemble Kalman Filter analysed heat flux

    Directory of Open Access Journals (Sweden)

    J. H. Lee

    2012-11-01

    Full Text Available Aerodynamic roughness height (Zom is a key parameter required in several land surface hydrological models, since errors in heat flux estimation are largely dependent on optimization of this input. Despite its significance, it remains an uncertain parameter which is not readily determined. This is mostly because of non-linear relationship in Monin-Obukhov similarity (MOS equations and uncertainty of vertical characteristic of vegetation in a large scale. Previous studies often determined aerodynamic roughness using a minimization of cost function over MOS relationship or linear regression over it, traditional wind profile method, or remotely sensed vegetation index. However, these are complicated procedures that require a high accuracy for several other related parameters embedded in serveral equations including MOS. In order to simplify this procedure and reduce the number of parameters in need, this study suggests a new approach to extract aerodynamic roughness parameter from single or two heat flux measurements analyzed via Ensemble Kalman Filter (EnKF that affords non-linearity. So far, to our knowledge, no previous study has applied EnKF to aerodynamic roughness estimation, while the majority of data assimilation study have paid attention to updates of other land surface state variables such as soil moisture or land surface temperature. The approach of this study was applied to grassland in semi-arid Tibetan Plateau and maize on moderately wet condition in Italy. It was demonstrated that aerodynamic roughness parameter can be inversely tracked from heat flux EnKF final analysis. The aerodynamic roughness height estimated in this approach was consistent with eddy covariance method and literature value. Through a calibration of this parameter, this adjusted the sensible heat previously overestimated and latent heat flux previously underestimated by the original Surface Energy Balance System (SEBS model. It was considered that

  20. Particle and heat flux measurements from XGC1 simulations: Spatial patterns and SOL width implications

    Science.gov (United States)

    Keramidas Charidakos, Ioannis; Myra, James; Parker, Scott; Ku, Seung-Hoe; Chowdhury, Jugal; Churchill, Michael; Hager, Robert; Chang, Choong-Seock

    2017-10-01

    Strong turbulence near the separatrix is believed to produce filamentary structures (blobs), whose detachment from the bulk can account for the intermittent nature of edge turbulence and impact the heat flux width. The SOL width is a parameter of paramount importance in modern tokamaks as it controls the amount of power deposited at the divertor plates, directly affecting thus the viability of fusion. Here, we analyze the results of simulations performed with the full-f, gyrokinetic code XGC1 which includes both turbulence and neoclassical effects in realistic divertor geometry. More specifically, we calculate the integrated particle and heat fluxes across the separatrix and present their spatial pattern. The flux is impacted by neoclassical effects and ExB turbulent-blobby motion. We isolate the ExB turbulent flux and estimate its contribution to the SOL width. Furthermore, we offer an interpretation of the observed patterns, tying them to the sheared perpendicular and parallel flows. We acknowledge computing resources on Titan at OLCF through the 2015 INCITE and the 2016 ALCC awards. Work supported by DOE Grant DE-FG02-97ER54392.

  1. Divertor Heat Flux Control with 3D Stochastic Magnetic Fields during ELM Suppression

    Science.gov (United States)

    Orlov, Dm; Moyer, Ra; Bykov, Io; Evans, Te; Wu, W.; Loarte, A.; Teklu, A.; Watkins, Jg; Wang, H.; Lyons, Bc; Trevisan, Gl; Makowski, Ma; Lasnier, C.; Fenstermacher, Me

    2017-10-01

    Experiments in DIII-D have been performed to modify the divertor heat and particle flux pattern during suppression of ELMs with resonant magnetic perturbation (RMP) fields. In this work, we assessed the impact of small current modulations in a subset of DIII-D I-coils on pedestal profiles, transport and stability as well as divertor conditions. Different I-coil subset ramps were performed allowing for a slow transition of the divertor footprints from n =3 to n =2 and n =1 distributions. We obtained long periods of RMP ELM suppression with slow I-coil quartet ramps. Strong divertor particle flux splitting was observed in these discharges as well as modulation of the divertor heat flux due to changes in toroidal spectrum of applied perturbation. Experimental results are compared to the TRIP3D modeling and to linear M3D-C1 simulations to understand the role of the plasma response on quantitative predictions of the divertor flux splitting. Work supported by US DOE under DE-FC02-04ER54698 and DE-FG02-05ER54809.

  2. Measurement of the Nonlinearity of Heat-Flux Sensors Employing a CO_2 laser

    Science.gov (United States)

    van der Ham, E. W. M.; Beer, C. M.; Ballico, M. J.

    2018-01-01

    Heat-flux sensors are widely used in industry to test building products and designs for resistance to bushfire, to test the flammability of textiles and in numerous applications such as concentrated solar collectors. In Australia, such detectors are currently calibrated by the National Measurement Institute Australia (NMIA) at low flux levels of 20 W \\cdot m^{-2}. Estimates of the uncertainty arising from nonlinearity at industrial levels (e.g. 50 kW \\cdot m^{-2} for bushfire testing) rely on literature information. NMIA has developed a facility to characterize the linearity response of these heat-flux sensors up to 110 kW \\cdot m^{-2} using a low-power CO_2 laser and a chopped quartz tungsten-halogen lamp. The facility was validated by comparison with the conventional flux-addition method, and used to characterize several Schmidt-Boelter-type sensors. A significant nonlinear response was found, ranging from (3.2 ± 0.9)% at 40 kW \\cdot m^{-2} to more than 8 % at 100 kW \\cdot m^{-2}. Additional measurements confirm that this is not attributable to convection effects, but due to the temperature dependence of the sensor's responsivity.

  3. Extension and application of a scaling technique for duplication of in-flight aerodynamic heat flux in ground test facilities

    NARCIS (Netherlands)

    Veraar, R.G.

    2009-01-01

    To enable direct experimental duplication of the inflight heat flux distribution on supersonic and hypersonic vehicles, an aerodynamic heating scaling technique has been developed. The scaling technique is based on the analytical equations for convective heat transfer for laminar and turbulent

  4. Additional double-wall roof in single-wall, closed, convective incubators: Impact on body heat loss from premature infants and optimal adjustment of the incubator air temperature.

    Science.gov (United States)

    Delanaud, Stéphane; Decima, Pauline; Pelletier, Amandine; Libert, Jean-Pierre; Stephan-Blanchard, Erwan; Bach, Véronique; Tourneux, Pierre

    2016-09-01

    Radiant heat loss is high in low-birth-weight (LBW) neonates. Double-wall or single-wall incubators with an additional double-wall roof panel that can be removed during phototherapy are used to reduce Radiant heat loss. There are no data on how the incubators should be used when this second roof panel is removed. The aim of the study was to assess the heat exchanges in LBW neonates in a single-wall incubator with and without an additional roof panel. To determine the optimal thermoneutral incubator air temperature. Influence of the additional double-wall roof was assessed by using a thermal mannequin simulating a LBW neonate. Then, we calculated the optimal incubator air temperature from a cohort of human LBW neonate in the absence of the additional roof panel. Twenty-three LBW neonates (birth weight: 750-1800g; gestational age: 28-32 weeks) were included. With the additional roof panel, R was lower but convective and evaporative skin heat losses were greater. This difference can be overcome by increasing the incubator air temperature by 0.15-0.20°C. The benefit of an additional roof panel was cancelled out by greater body heat losses through other routes. Understanding the heat transfers between the neonate and the environment is essential for optimizing incubators. Copyright © 2016 IPEM. Published by Elsevier Ltd. All rights reserved.

  5. Monitoring Delamination of Thermal Barrier Coatings During Interrupted High-Heat-Flux Laser Testing using Luminescence Imaging

    Science.gov (United States)

    Eldridge, Jeffrey I.; Zhu, Dongming; Wolfe, Douglas E.

    2011-01-01

    This presentation showed progress made in extending luminescence-base delamination monitoring to TBCs exposed to high heat fluxes, which is an environment that much better simulates actual turbine engine conditions. This was done by performing upconversion luminescence imaging during interruptions in laser testing, where a high-power CO2 laser was employed to create the desired heat flux. Upconverison luminescence refers to luminescence where the emission is at a higher energy (shorter wavelength) than the excitation. Since there will be negligible background emission at higher energies than the excitation, this methods produces superb contrast. Delamination contrast is produced because both the excitation and emission wavelengths are reflected at delamination cracks so that substantially higher luminescence intensity is observed in regions containing delamination cracks. Erbium was selected as the dopant for luminescence specifically because it exhibits upconversion luminescence. The high power CO2 10.6 micron wavelength laser facility at NASA GRC was used to produce the heat flux in combination with forced air backside cooling. Testing was performed at a lower (95 W/sq cm) and higher (125 W/sq cm) heat flux as well as furnace cycling at 1163C for comparison. The lower heat flux showed the same general behavior as furnace cycling, a gradual, "spotty" increase in luminescence associated with debond progression; however, a significant difference was a pronounced incubation period followed by acceleration delamination progression. These results indicate that extrapolating behavior from furnace cycling measurements will grossly overestimate remaining life under high heat flux conditions. The higher heat flux results were not only accelerated, but much different in character. Extreme bond coat rumpling occurred, and delamination propagation extended over much larger areas before precipitating macroscopic TBC failure. This indicates that under the higher heat flux (and

  6. Optimization-based design of heat flux manipulation devices with emphasis on fabricability.

    Science.gov (United States)

    Peralta, Ignacio; Fachinotti, Víctor D

    2017-07-24

    In this work, we present a new method for the design of heat flux manipulating devices, with emphasis on their fabricability. The design is obtained as solution of a nonlinear optimization problem where the objective function represents the given heat flux manipulation task, and the design variables define the material distribution in the device. In order to facilitate the fabrication of the device, the material at a given point is chosen from a set of predefined metamaterials. Each candidate material is assumed to be a laminate of materials with high conductivity contrast, so it is a metamaterial with a highly anisotropic effective conductivity. Following the discrete material optimization (DMO) approach, the fraction of each material at a given finite element of the mesh is defined as a function of continuous variables, which are ultimately the design variables. This DMO definition forces the fraction of each candidate to tend to either zero or one at the optimal solution. As an application example, we designed an easy-to-make device for heat flux concentration and cloaking.

  7. Validation of PICA Ablation and Thermal-Response Model at Low Heat Flux

    Science.gov (United States)

    Milos, Frank S.; Chen, Yih-Kanq

    2009-01-01

    Phenolic Impregnated Carbon Ablator (PICA) was the forebody heatshield material on the Stardust sample-return capsule and is also a primary candidate material for the Mars Science Lander (MSL), the Orion Crew Module, and the SpaceX Dragon vehicle. As part of the heatshield qualification for Orion, physical and thermal properties of virgin and charred PICA were measured, and an ablation and thermal response model was developed. We validated the model by comparing it with recession and temperature data from stagnation arcjet tests conducted over a wide range of stagnation heat flux of 107 to 1102 W/sq cm. The effect of orthotropic thermal conductivity was evident in the thermal response of the arcjet models. In general, model predictions compared well with the data; however, the uncertainty of the recession prediction was greatest for heat fluxes below 200 W/sq cm. More recent MSL testing focused on the low heat flux regime of 45 to 250 W/sq cm. The new results confirm the recession uncertainty, especially for pressures below 6 kPa. In this work we focus on improving the model predictions for MSL and Orion tests below 250 W/sq cm.

  8. High heat flux testing of mock-ups for a full tungsten ITER divertor

    Energy Technology Data Exchange (ETDEWEB)

    Gavila, P., E-mail: pierre.gavila@f4e.europa.eu [Fusion for Energy, 08019 Barcelona (Spain); Riccardi, B. [Fusion for Energy, 08019 Barcelona (Spain); Constans, S.; Jouvelot, J.L.; Vastra, I. Bobin [AREVA NP, Centre Technique, Fusion, 71200, Le Creusot (France); Missirlian, M.; Richou, M. [CEA, IRFM, F-13108 Saint-Paul-Lez-Durance (France)

    2011-10-15

    In order to evaluate the option to start the ITER operation with a full tungsten (W) divertor, the EU-DA launched an extensive R and D program. It consisted in its initial phase in the high heat flux (HHF) testing of W mock-ups and medium scale prototypes up to 20 MW/m{sup 2} in the AREVA FE 200 facility (F). Critical heat flux (CHF) experiments were carried out on the items which survived the above thermal fatigue testing. After 1000 cycles at 10 MW/m{sup 2}, the full W Plasma Facing Components (PFCs) mock-ups successfully sustained either 1000 cycles at 15 MW/m{sup 2} or 500 cycles at 20 MW/m{sup 2}. However, some significant surface melting, as well as the complete melting of a few monoblocks, occurred during the HHF thermal fatigue testing program representative of the present ITER requirements for the strike point region, namely 1000 cycles at 10 MW/m{sup 2} followed by 1000 cycles at 20 MW/m{sup 2}. The results of the CHF experiments were also rather encouraging, since the tested items sustained heat fluxes in the range of 30 MW/m{sup 2} in steady-state conditions.

  9. Spray Cooling Trajectory Angle Impact Upon Heat Flux Using a Straight Finned Enhanced Surface

    Science.gov (United States)

    Silk, Eric A.; Kim, Jungho; Kiger, Ken

    2005-01-01

    Experiments were conducted to study the effects of spray trajectory angles upon heat flux for flat and enhanced surface spray cooling. The surface enhancement consisted of straight fins machined on the top surface of a copper heater block. Spray cooling curves were obtained with the straight fin surface aligned both parallel (axial) and perpendicular (transverse) to the spray axis. Measurements were also obtained on a flat surface heater block for comparison purposes. Each copper block had a cross-sectional area of 2.0 sq cm. A 2x2 nozzle array was used with PF-5060 as the working fluid. Thermal performance data was obtained under nominally degassed (chamber pressure of 41.4 kPa) conditions. Results show that the maximum CHF in all cases was attained for a trajectory angle of 30' from the surface normal. Furthermore, trajectory angles applied to straight finned surfaces can have a critical heat flux (CHF) enhancement as much as 75% (heat flux value of 140 W/sq cm) relative to the vertical spray orientation for the analogous flat surface case under nominally degassed conditions.

  10. Fem Simulation of Triple Diffusive Natural Convection Along Inclined Plate in Porous Medium: Prescribed Surface Heat, Solute and Nanoparticles Flux

    Directory of Open Access Journals (Sweden)

    Goyal M.

    2017-12-01

    Full Text Available In this paper, triple diffusive natural convection under Darcy flow over an inclined plate embedded in a porous medium saturated with a binary base fluid containing nanoparticles and two salts is studied. The model used for the nanofluid is the one which incorporates the effects of Brownian motion and thermophoresis. In addition, the thermal energy equations include regular diffusion and cross-diffusion terms. The vertical surface has the heat, mass and nanoparticle fluxes each prescribed as a power law function of the distance along the wall. The boundary layer equations are transformed into a set of ordinary differential equations with the help of group theory transformations. A wide range of parameter values are chosen to bring out the effect of buoyancy ratio, regular Lewis number and modified Dufour parameters of both salts and nanofluid parameters with varying angle of inclinations. The effects of parameters on the velocity, temperature, solutal and nanoparticles volume fraction profiles, as well as on the important parameters of heat and mass transfer, i.e., the reduced Nusselt, regular and nanofluid Sherwood numbers, are discussed. Such problems find application in extrusion of metals, polymers and ceramics, production of plastic films, insulation of wires and liquid packaging.

  11. Fem Simulation of Triple Diffusive Natural Convection Along Inclined Plate in Porous Medium: Prescribed Surface Heat, Solute and Nanoparticles Flux

    Science.gov (United States)

    Goyal, M.; Goyal, R.; Bhargava, R.

    2017-12-01

    In this paper, triple diffusive natural convection under Darcy flow over an inclined plate embedded in a porous medium saturated with a binary base fluid containing nanoparticles and two salts is studied. The model used for the nanofluid is the one which incorporates the effects of Brownian motion and thermophoresis. In addition, the thermal energy equations include regular diffusion and cross-diffusion terms. The vertical surface has the heat, mass and nanoparticle fluxes each prescribed as a power law function of the distance along the wall. The boundary layer equations are transformed into a set of ordinary differential equations with the help of group theory transformations. A wide range of parameter values are chosen to bring out the effect of buoyancy ratio, regular Lewis number and modified Dufour parameters of both salts and nanofluid parameters with varying angle of inclinations. The effects of parameters on the velocity, temperature, solutal and nanoparticles volume fraction profiles, as well as on the important parameters of heat and mass transfer, i.e., the reduced Nusselt, regular and nanofluid Sherwood numbers, are discussed. Such problems find application in extrusion of metals, polymers and ceramics, production of plastic films, insulation of wires and liquid packaging.

  12. How do patchy snow covers affect turbulent sensible heat fluxes? - Numerical analysis and experimental findings

    Science.gov (United States)

    Schlögl, Sebastian; Mott, Rebecca; Lehning, Michael

    2017-04-01

    The surface energy balance of a snow cover significantly changes once the snow cover gets patchy. The substantial progress in knowledge about the surface energy balance of patchy snow covers is a mandatory requirement to reduce biases in flux parameterizations in larger scale meteorological or climatological models. The aim of this project was to numerically improve energy balance calculations late in the melting season when the spatial variability of turbulent fluxes is especially high owing to the complex feedback between bare/snow-covered areas and the atmosphere above. In order to account for the feedback between the atmosphere and the patchy snow-cover we calculated three-dimensional air temperature and wind velocity fields with the non-hydrostatic atmospheric model ARPS for an idealized flat test site initialized with different snow distributions and atmospheric conditions. The physics-based surface process model Alpine3D has been forced with these atmospheric fields close to the snow surface in order to resolve the small-scale spatial variability. We further initialized the model with atmospheric fields above the blending height as a reference case. The numerical analysis shows that for simulations initialized with fully-resolved atmospheric fields below the blending height, turbulent sensible heat fluxes are up to 50 W/m2 larger than for calculations forced without resolved atmospheric fields. This difference in turbulent sensible heat fluxes over snow increase with increasing number of snow patches and decreasing snow-cover fraction. This is mainly attributed to an increase in the mean near-surface air temperature over snow due to horizontal and vertical exchange processes induced by the heterogeneous land-surface. We used flux footprint estimations to analyse turbulence data measured during three ablation periods in the Dischma valley (Switzerland). This fundamental theory was deployed for eddy-covariance measurements revealing the origin of the measured

  13. Heat transfer in a smooth-walled reciprocating anti-gravity open thermosyphon

    Energy Technology Data Exchange (ETDEWEB)

    Chang, S.W. [Thermal Fluids Laboratory, National Kaohsiung Institute of Marine Technology, Post code: 811, ROC, Kaohsiung, Taiwan (China); Su, L.M. [Department of Electrical Engineering, Tung Fang Institute of Technology, ROC, Taiwan (China); Morris, W.D. [Department of Mechanical Engineering, University of Wales Swansea, Singleton Park, SA28PP, Swansea (United Kingdom); Liou, T.M. [Department of Power Mechanical Engineering, National Tsing Hua University, ROC, Hsinchu, Taiwan (China)

    2003-12-01

    This paper describes an experimental investigation of heat transfer in a smooth-walled reciprocating anti-gravity open thermosyphon with relevance to the 'shaker' cooling system for the pistons of marine propulsive diesel engines. A selection of experimental results illustrates the interactive effects of inertial, reciprocating and buoyancy forces on heat transfer. It is demonstrated that the gravitational and reciprocating buoyancy effects, respectively, improve heat transfer in the static and reciprocating anti-gravity open thermosyphon. The individual pulsating force effect impairs heat transfer in the axial region with 5 hydraulic diameter length measured from the entrance of thermosyphon (region I). In the vicinity of sealed end of reciprocating thermosyphon with one hydraulic diameter from the sealed surface (region II), the individual pulsating force effect improves heat transfer at low pulsating number range, over which range a subsequent heat transfer reduction in this axial region is followed. The synergistic effects of inertial force, reciprocating force and buoyancy interaction in the reciprocating anti-gravity open thermosyphon could, respectively, impede or improve the regional heat transfers in the axial regions I and II from the static references of zero-buoyancy. A set of empirical correlations, which is physically consistent, was developed that permits the individual and interactive effects of inertial, reciprocating and buoyancy forces on heat transfer to be evaluated. (authors)

  14. Application of single walled carbon nanotubes for heating agent in photothermal therapy

    CERN Document Server

    Siregar, Syahril; Nagaoka, Ryo; Saijo, Yoshifumi

    2016-01-01

    We present the theoretical investigation of the single walled carbon nanotubes (SWNTs) as the heating agent of photothermal therapy. In our model, the SWNT is modeled by rigid tube surrounded by cancer cells. In this model, we neglect the angle dependence of temperature and assume that the length of SWNT is much longer than the radius of tube. We calculated the temperature rise of the SWNT and its surrounding cancer cells during the laser heating by solving one-dimensional heat conduction equation in steady state condition. We found that the maximum temperature is located at the interface between SWNT and cancer cells. This maximum temperature is proportional to the square of SWNTs diameter and diameter of SWNTs depends on their chirality. These results extend our understanding of the temperature distribution in SWNT during the laser heating process and provide the suggested specification of SWNT for the improvement the photothermal therapy in the future.

  15. Surface thermocouples for measurement of pulsed heat flux in the divertor of the Alcator C-Mod tokamak.

    Science.gov (United States)

    Brunner, D; LaBombard, B

    2012-03-01

    A novel set of thermocouple sensors has been developed to measure heat fluxes arriving at divertor surfaces in the Alcator C-Mod tokamak, a magnetic confinement fusion experiment. These sensors operate in direct contact with the divertor plasma, which deposits heat fluxes in excess of ~10 MW/m(2) over an ~1 s pulse. Thermoelectric EMF signals are produced across a non-standard bimetallic junction: a 50 μm thick 74% tungsten-26% rhenium ribbon embedded in a 6.35 mm diameter molybdenum cylinder. The unique coaxial geometry of the sensor combined with its single-point electrical ground contact minimizes interference from the plasma/magnetic environment. Incident heat fluxes are inferred from surface temperature evolution via a 1D thermal heat transport model. For an incident heat flux of 10 MW/m(2), surface temperatures rise ~1000 °C/s, corresponding to a heat flux flowing along the local magnetic field of ~200 MW/m(2). Separate calorimeter sensors are used to independently confirm the derived heat fluxes by comparing total energies deposited during a plasma pulse. Langmuir probes in close proximity to the surface thermocouples are used to test plasma-sheath heat transmission theory and to identify potential sources of discrepancies among physical models.

  16. Numerical simulation in a subcooled water flow boiling for one-sided high heat flux in reactor divertor

    Energy Technology Data Exchange (ETDEWEB)

    Liu, P., E-mail: pinliu@aust.edu.cn [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China); University of Science and Technology of China, Hefei 230026 (China); School of Mechanical Engineering, Anhui University of Science and Technology, Huainan 232001 (China); Peng, X.B., E-mail: pengxb@ipp.ac.cn [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China); Song, Y.T. [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China); University of Science and Technology of China, Hefei 230026 (China); Fang, X.D. [Institute of Air Conditioning and Refrigeration, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Huang, S.H. [University of Science and Technology of China, Hefei 230026 (China); Mao, X. [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China)

    2016-11-15

    Highlights: • The Eulerian multiphase models coupled with Non-equilibrium Boiling model can effectively simulate the subcooled water flow boiling. • ONB and FDB appear earlier and earlier with the increase of heat fluxes. • The void fraction increases gradually along the flow direction. • The inner CuCrZr tube deteriorates earlier than the outer tungsten layer and the middle OFHC copper layer. - Abstract: In order to remove high heat fluxes for plasma facing components in International Thermonuclear Experimental Reactor (ITER) divertor, a numerical simulation of subcooled water flow boiling heat transfer in a vertically upward smooth tube was conducted in this paper on the condition of one-sided high heat fluxes. The Eulerian multiphase model coupled with Non-equilibrium Boiling model was adopted in numerical simulation of the subcooled boiling two-phase flow. The heat transfer regions, thermodynamic vapor quality (x{sub th}), void fraction and temperatures of three components on the condition of the different heat fluxes were analyzed. Numerical results indicate that the onset of nucleate boiling (ONB) and fully developed boiling (FDB) appear earlier and earlier with increasing heat flux. With the increase of heat fluxes, the inner CuCrZr tube will deteriorate earlier than the outer tungsten layer and the middle oxygen-free high-conductivity (OFHC) copper layer. These results provide a valuable reference for the thermal-hydraulic design of a water-cooled W/Cu divertor.

  17. Modeling the surface heat flux response to long-lived SST anomalies in the North Atlantic

    Energy Technology Data Exchange (ETDEWEB)

    Power, S.B.; Kleeman, R.; Colman, R.A. [Bureau of Meteorology Research Centre, Melbourne (Australia)] [and others

    1995-09-01

    An atmospheric general circulation model (AGCM), a simplified atmospheric model (SAM) of surface heat flux, and various idealized analytic models have been used to investigate the atmospheric response over the North Atlantic to SST anomalies, including a general cooling associated with a weakened thermohaline circulation. Latent heating dominates the surface heat flux response, while sensible heating plays an important secondary role. The total heat flux response is weaker than presumed in recent studies using ocean models under highly idealized surface boundary conditions. This implies that stability of the thermohaline circulation to high-latitude freshening in more sophisticated coupled systems (that incorporate either AGCMs or models like SAM) will be increased. All three kinds of atmospheric models exhibit nonrestorative behavior away from the anomaly peak that is primarily associated with the advection of cooled air eastward. This simple picture is complicated in the AGCM by the fact that the winds weaken over the SST anomaly, which helps to moderate the response. Analytic models for atmospheric temperature forced using imposed surface temperature anomalies highlight conditions under which a nonrestorative response can arise. Previous work has shown that the length scale of spatially periodic anomalies partially determines the magnitude of the response in a diffusive atmosphere. Here the authors show that this scale dependence has much wider applicability by considering more localized anomalies and by the inclusion of advective transport processes. The modification of the response by sea ice changes and the absence of any statistically significant change in the basin-averaged hydrological cycle are also discussed. 62 refs., 19 figs.

  18. Hypersonic engine component experiments in high heat flux, supersonic flow environment

    Science.gov (United States)

    Gladden, Herbert J.; Melis, Matthew E.

    1993-01-01

    A major concern in advancing the state-of-the-art technologies for hypersonic vehicles is the development of an aeropropulsion system capable of withstanding the sustained high thermal loads expected during hypersonic flight. Even though progress has been made in the computational understanding of fluid dynamics and the physics/chemistry of high speed flight, there is also a need for experimental facilities capable of providing a high heat flux environment for testing component concepts and verifying/calibrating these analyses. A hydrogen/oxygen rocket engine heat source was developed at the NASA Lewis Research Center as one element in a series of facilities at national laboratories designed to fulfill this need. This 'Hot Gas Facility' is capable of providing heat fluxes up to 450 w/sq cm on flat surfaces and up to 5,000 w/sq cm at the leading edge stagnation point of a strut in a supersonic flow stream. Gas temperatures up to 3050 K can also be attained. Two recent experimental programs conducted in this facility are discussed. The objective of the first experiment is to evaluate the erosion and oxidation characteristics of a coating on a cowl leading edge (or strut leading edge) in a supersonic, high heat flux environment. Macrophotographic data from a coated leading edge model show progressive degradation over several thermal cycles at aerothermal conditions representative of high Mach number flight. The objective of the second experiment is to assess the capability of cooling a porous surface exposed to a high temperature, high velocity flow environment and to provide a heat transfer data base for a design procedure. Experimental results from transpiration cooled surfaces in a supersonic flow environment are presented.

  19. Slug-flow dynamics with phase change heat transfer in compact heat exchangers with oblique wavy walls

    Science.gov (United States)

    Morimoto, Kenichi; Kinoshita, Hidenori; Matsushita, Ryo; Suzuki, Yuji

    2017-11-01

    With abundance of low-temperature geothermal energy source, small-scale binary-cycle power generation system has gained renewed attention. Although heat exchangers play a dominant role in thermal efficiency and the system size, the optimum design strategy has not been established due to complex flow phenomena and the lack of versatile heat transfer models. In the present study, the concept of oblique wavy walls, with which high j/f factor is achieved by strong secondary flows in single-phase system, is extended to two-phase exchangers. The present analyses are based on evaporation model coupled to a VOF technique, and a train of isolated bubbles is generated under the controlled inlet quality. R245fa is adopted as a low boiling-point working media, and two types of channels are considered with a hydraulic diameter of 4 mm: (i) a straight circular pipe and (ii) a duct with oblique wavy walls. The focus is on slug-flow dynamics with evaporation under small capillary but moderate Weber numbers, where the inertial effect as well as the surface tension is of significance. A possible direction of the change in thermo-physical properties is explored by assuming varied thermal conductivity. Effects of the vortical motions on evaporative heat transfer are highlighted. This work has been supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan.

  20. Dynamics of Soil Heat Flux in Lowland Area: Estimating the Soil Thermal Conductivy

    Science.gov (United States)

    Zimmer, T.; Silveira, M. V.; Roberti, D. R.

    2013-05-01

    In this work, it is shown soil thermal conductivity estimates in a flooded irrigated rice culture located at the Paraíso do Sul city for two distinct periods. The thermal conductivity is higher when the heat storage is higher and the soil surface temperature is lower. The soil thermal conductivity is also dependant on the soil texture, porosity and moisture. Therefore, it varies from soil to soil and in the same soil, depending on its soil moisture. For approximately 80% of its growing season, lowland flooded irrigated rice ecosystems stay under a 5 - 10 cm water layer. It affects the partitioning of the energy and water balance components. Furthermore this planting technique differs substantially from any other upland non-irrigated or irrigated crop ecosystems where the majority of observational studies have been conducted. In the present work, the dynamic of soil heat flux (G) is analyzed and the soil thermal conductivity (Ks) is estimated using experimental data form soil heat flux and soil temperature in a rice paddy farm in a subtropical location in Southern Brazil. In this region, rice grows once a year at river lowlands and wetlands while the ground is kept bare during the remaining of the year. The soil type is Planossolo Hidromórfico Distrófico, characterized as a mix between sandy and clay soil. The soil heat flux (G) was experimentally estimated with the sensor Hukseflux (HFP01SC-L) at 7 cm bellow the soil surface. The soil temperature at 5 cm and 10 cm was experimentally estimated using the sensor STP01. The experimental soil heat flux was compared with estimated soil heat flux by two forms: (1) using a know Ks from literature for this type of soil in saturated conditions (Ks=1.58); (2) using Ks estimated using the inversion of the equation Qg=-ks* ((T10-T5)/ (Z2-Z1)), where T10 and T5 are the temperature in 10 and 5 cm above the soil and Z2-Z1 is the difference between the positions in temperature measurement. The study period for estimating the Ks

  1. Prediction of critical heat flux for water in uniformly heated vertical ...

    African Journals Online (AJOL)

    Accuracy of correlations was estimated by calculating both the average and RMS error with available experimental data, and a new correlation is presented. The new correlation predicts the CHF data with average error 0.07% and RMS error 7.91 %. Keywords: CHF - Heat transfer - Water vapor - Porous coated tubes.

  2. Heat transfer in MHD unsteady stagnation point flow with variable wall temperature

    Digital Repository Service at National Institute of Oceanography (India)

    Soundalgekar, V.M.; Murty, T.V.R.; Takhar, H.S.

    ) (J~+ P, [ heated blunt-nosed cylinder whose wall temperature varies as Ax N is presented. Temparature profiles arc shown graphicaIIy for different values of N and the numerical values of the rate of heat transfer (- 0' (0», IJ...

  3. Simulations of Special Interior Ballistic Phenomena with and without Heat Transfer to Gun Tube Wall.

    Science.gov (United States)

    1986-05-01

    34Catlcurlion of Heat Trarsfer to the Gun Barrel WaLt ," J. Ballistics 6 (3), pp. 1518-1524, 1982. 7 Barlett , E.P., Anderson, L.W., Kendall, L.:!., ’Time...34Calculation of Heat Transfer to the Gun Barrel Wall," J. Ballistics 6 (3), pp. 1518-1524, 1982. 7. Barlett , E.P., Anderson, L.W., Kendall, R.M., "Time...47 HQS Santa Monica CA Only) Washington, DC 20505 90401-3297 I Foster Miller Associates General Applied Sciences Lab ATTN: A. Erickson ATTN: J. Erdos

  4. Measurement techniques for sensible and latent heat transfer coefficients during wall condensation, a feasibility study

    Energy Technology Data Exchange (ETDEWEB)

    Vonka, V.; Rij, H.M. van.

    1989-11-01

    Radioactive fission product release as the consequence of a severe accident with nuclear installations needs to be studied in considerable detail in order to predict the source term hazard with acceptable accuracy. As far as the research on the fission product behaviour in containments is concerned the international effort has been concentrated around two large experimental programmes, DEMONA and LACE. Results of the bench-mark on 'Post-test calculation of thermal-hydraulic behaviour in DEMONA experiment B3 with various computer codes used in CEC member states', show still considerable differences and uncertainties due to poor knowledge of global heat transfer coefficients for the wall condensation in containments. The objective of this study is to provide an estimate of the accuracy with which the coefficient for sensible heat transfer during wall condensation can be measured. (H.W.). 15 refs.; 7 figs.; 9 tabs.

  5. Bubble detachment and lift-off diameters at a vertical heated wall for subcooled boiling flow

    Energy Technology Data Exchange (ETDEWEB)

    Montout, Michael; Haynes, Pierre-Antoine; Peturaud, Pierre [EDF, R and D Division, Fluid Dynamics, Power Generation and Environnement Department, 6 quai Watier, 78401 Chatou Cedex (France); Colin, Catherine [Institut de Mecanique des Fluides de Toulouse, Allee du Professeur Camille Soula, 31400 Toulouse (France)

    2008-07-01

    Full text of publication follows: In the framework of the NEPTUNE project jointly carried on by EDF, CEA, AREVA NP and IRSN (Guelfi et al. (2007)), the development of the NEPTUNE-CFD code aims at (among others) improving the prediction of the Departure from Nucleate Boiling (DNB) in Pressurized Water Reactors (PWRs). In this prospect, the modeling of boiling flows up to the DNB is of prime importance, and this presentation is devoted to one major related phenomenon, the wall-to-flow heat transfer in subcooled boiling flow. Computational Fluid Dynamics (CFD) modeling of subcooled nucleate boiling has to provide the net vapor generation rate at the heated wall, as well as its related geometrical characteristic - either bubble diameter or interfacial area concentration (its velocity might also be useful). For this purpose, mechanistic models are used. Previous models (such as the widely used Kurul and Podowski model (1990)) are based on the bubble lift-off diameter, diameter from which the bubble leaves the wall to be swept along the bulk liquid flow. However, for a few years, new models (Basu et al. (2005) or Yeoh et al. (2008)) account for a finer phenomenology (bubble sliding along the heated wall) and require the knowledge of the bubble detachment diameter, diameter from which the bubble leaves its nucleation site to slide along the heated wall. Modeling these diameters is still an issue. On the one hand, several (semi-) empirical correlations are available in the open literature making it possible to provide the liftoff diameter (Uenal (1976), for instance), but they are still questionable; on the other hand, there is a great lack of information with respect to the evaluation of the detachment diameter. Therefore to progress on these concerns, an analytical work has been carried out. In a first step, a methodology providing detachment and lift-off diameters is proposed and applied. This approach is based on the resolution of a force balance model acting on a

  6. Failure analysis on unexpected wall thinning of heat-exchange tubes in ammonia evaporators

    Directory of Open Access Journals (Sweden)

    Shi-Meng Hu

    2015-04-01

    Full Text Available A failure incident of heat-exchange tubes in ammonia evaporators, which suffered from unexpected wall thinning after only one-year service with respect to their original design lifetime of fifteen years, was reported and carefully analyzed. After overall inspection, many tube walls in the evaporators were found to experience severe degradations at both sides with distinct corroded defects and general cracking of corrosion layers. Thus, comprehensive investigations including external appearance, microscopic morphology and chemical composition were carried out by using a series of characterization methods. The analysis results demonstrated that the unexpected wall thinning of tubes was primarily ascribed to multiple corrosion factors including uniform corrosion, pitting and interaction behavior between them. Relative failure mechanisms were discussed in detail and prevention measures were also proposed for ammonia evaporators under similar operating condition.

  7. A Prototype Flux-Plate Heat-Flow Sensor for Venus Surface Heat-Flow Determinations

    Science.gov (United States)

    Morgan, Paul; Reyes, Celso; Smrekar, Suzanne E.

    2005-01-01

    Venus is the most Earth-like planet in the Solar System in terms of size, and the densities of the two planets are almost identical when selfcompression of the two planets is taken into account. Venus is the closest planet to Earth, and the simplest interpretation of their similar densities is that their bulk compositions are almost identical. Models of the thermal evolution of Venus predict interior temperatures very similar to those indicated for the regions of Earth subject to solid-state convection, but even global analyses of the coarse Pioneer Venus elevation data suggest Venus does not lose heat by the same primary heat loss mechanism as Earth, i.e., seafloor spreading. The comparative paucity of impact craters on Venus has been interpreted as evidence for relatively recent resurfacing of the planet associated with widespread volcanic and tectonic activity. The difference in the gross tectonic styles of Venus and Earth, and the origins of some of the enigmatic volcano-tectonic features on Venus, such as the coronae, appear to be intrinsically related to Venus heat loss mechanism(s). An important parameter in understanding Venus geological evolution, therefore, is its present surface heat flow. Before the complications of survival in the hostile Venus surface environment were tackled, a prototype fluxplate heat-flow sensor was built and tested for use under synthetic stable terrestrial surface conditions. The design parameters for this prototype were that it should operate on a conforming (sand) surface, with a small, self-contained power and recording system, capable of operating without servicing for at least several days. The precision and accuracy of the system should be < 5 mW/sq m. Additional information is included in the original extended abstract.

  8. Using sonic anemometer temperature to measure sensible heat flux in strong winds

    Directory of Open Access Journals (Sweden)

    S. P. Burns

    2012-09-01

    Full Text Available Sonic anemometers simultaneously measure the turbulent fluctuations of vertical wind (w' and sonic temperature (Ts', and are commonly used to measure sensible heat flux (H. Our study examines 30-min heat fluxes measured with a Campbell Scientific CSAT3 sonic anemometer above a subalpine forest. We compared H calculated with Ts to H calculated with a co-located thermocouple and found that, for horizontal wind speed (U less than 8 m s−1, the agreement was around ±30 W m−2. However, for U ≈ 8 m s−1, the CSAT H had a generally positive deviation from H calculated with the thermocouple, reaching a maximum difference of ≈250 W m−2 at U ≈ 18 m s−1. With version 4 of the CSAT firmware, we found significant underestimation of the speed of sound and thus Ts in high winds (due to a delayed detection of the sonic pulse, which resulted in the large CSAT heat flux errors. Although this Ts error is qualitatively similar to the well-known fundamental correction for the crosswind component, it is quantitatively different and directly related to the firmware estimation of the pulse arrival time. For a CSAT running version 3 of the firmware, there does not appear to be a significant underestimation of Ts; however, a Ts error similar to that of version 4 may occur if the CSAT is sufficiently out of calibration. An empirical correction to the CSAT heat flux that is consistent with our conceptual understanding of the Ts error is presented. Within a broader context, the surface energy balance is used to evaluate the heat flux measurements, and the usefulness of side-by-side instrument comparisons is discussed.

  9. Estimating regional distribution of surface heat fluxes by combining satellite data and a heat budget model over the Kherlen River Basin, Mongolia

    Science.gov (United States)

    Matsushima, Dai

    2007-01-01

    SummaryThe regional distribution of surface heat fluxes and related parameters over a semi-arid region was estimated using a technique that incorporates the thermal-infrared brightness temperature from a satellite into a heat budget model of land surface including vegetation canopy. We studied the western part of the Kherlen River Basin in Mongolia, where typical steppe dominates, including forest-steppe in the northern part and dry-steppe in the southern part of the basin. Our goal was to estimate the temporal change of surface heat fluxes at a location in the typical steppe over a growing season, and to estimate the spatial distribution of surface heat fluxes over the study area. Seven parameters, including the bulk transfer coefficients, the evaporation efficiency, and the subsurface thermal inertia, which are relevant to the surface heat fluxes, were optimized employing the simplex method. To compensate for insufficient satellite data samples to reproduce the diurnal change of surface heat fluxes, the spatial distribution of the surface brightness temperature was used in the optimization rather than using diurnal change, which is referred to as spatial optimization. Diurnal changes in the surface heat fluxes estimated by spatial optimization were validated by observation. The surface heat fluxes were reasonably accurately reproduced on a daily basis, with the root-mean-squares error of the sensible and the latent heat within 15 W m -2 over the growing season. The evaporation efficiency of canopy and the subsurface thermal inertia optimized in this study correlated well with the volumetric soil water content in a shallow layer on a daily basis, which suggests that thermal inertia can be an indicator of water conditions in a shallow subsurface layer. Spatial distribution of estimated sensible and latent heat after rainfall on successive summer days is discussed.

  10. Doubling of critical heat flux using a grapheme oxide nanofluid and its repeatabiltiy

    Energy Technology Data Exchange (ETDEWEB)

    Moon, Sung Bo; Bang, In Cheol [Ulsan National Institute of Science and Technology, Ulsan (Korea, Republic of)

    2013-10-15

    CHF(Critical Heat Flux : heat flux which makes dramatic increase of temperature on heater surface) is one of the most important phenomena in the thermal hydraulic system. High CHF makes more thermal margin of heat transfer. This makes high efficiency and safety of power plant especially in nuclear power plant. Much smaller danger can be concerned to public society like radioactive material leakage in the accidents. Graphene Oxide which can be deposited on the heater surface makes nano-scale structures with enhancing thermal limit of heater. Three major models of enhancing limit of heater have been concerned in many heat transfer studies. In this study, wettability that is about ability to wet on surface and thermal activity which is about thermal property of coated layer are concerned to analyze the mechanism of CHF enhancing. Also, chemical reduction of Graphene Oxide(GO) to Reduced Graphene Oxide(RGO) on the surface will be concerned with one reason of changing wettability of nano-scale structure on the heater surface. We used GO nanofluid 0.001 volume percent. Two models are compared to explain how CHF is enhanced. Results show wettability increased with slightly reduced GO and structure. And in thermal activity model, the most powerful term, thickness of layer, is too small to affect thermal activity. It has low ability to explain how GO nanofluid can enhance CHF.

  11. Spatially Variable Geothermal Heat Flux in West Antarctica: Evidence and Implications

    Science.gov (United States)

    Begeman, Carolyn Branecky; Tulaczyk, Slawek M.; Fisher, Andrew T.

    2017-10-01

    Geothermal heat flux (GHF) is an important part of the basal heat budget of continental ice sheets. The difficulty of measuring GHF below ice sheets has directly hindered progress in the understanding of ice sheet dynamics. We present a new GHF measurement from below the West Antarctic Ice Sheet, made in subglacial sediment near the grounding zone of the Whillans Ice Stream. The measured GHF is 88 ± 7 mW m-2, a relatively high value compared to other continental settings and to other GHF measurements along the eastern Ross Sea of 55 mW m-2 and 69 ± 21 mW m-2 but within the range of regional values indicated by geophysical estimates. The new GHF measurement was made 100 km from the only other direct GHF measurement below the ice sheet, which was considerably higher at 285 ± 80 mW m-2, suggesting spatial variability that could be explained by shallow magmatic intrusions or the advection of heat by crustal fluids. Analytical calculations suggest that spatial variability in GHF exceeds spatial variability in the conductive heat flux through ice along the Siple Coast. Accurate GHF measurements and high-resolution GHF models may be necessary to reliably predict ice sheet evolution, including responses to ongoing and future climate change.

  12. Phase Change Materials-Assisted Heat Flux Reduction: Experiment and Numerical Analysis

    Directory of Open Access Journals (Sweden)

    Hussein J. Akeiber

    2016-01-01

    Full Text Available Phase change materials (PCM in the construction industry became attractive because of several interesting attributes, such as thermo-physical parameters, open air atmospheric condition usage, cost and the duty structure requirement. Thermal performance optimization of PCMs in terms of proficient storage of a large amount of heat or cold in a finite volume remains a challenging task. Implementation of PCMs in buildings to achieve thermal comfort for a specific climatic condition in Iraq is our main focus. From this standpoint, the present paper reports the experimental and numerical results on the lowering of heat flux inside a residential building using PCM, which is composed of oil (40% and wax (60%. This PCM (paraffin, being plentiful and cost-effective, is extracted locally from waste petroleum products in Iraq. Experiments are performed with two rooms of identical internal dimensions in the presence and absence of PCM. A two-dimensional numerical transient heat transfer model is developed and solved using the finite difference method. A relatively simple geometry is chosen to initially verify the numerical solution procedure by incorporating in the computer program two-dimensional elliptic flows. It is demonstrated that the heat flux inside the room containing PCM is remarkably lower than the one devoid of PCM.

  13. 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.

  14. In-pile critical heat flux and post-dryout heat transfer measurements – A historical perspective

    Energy Technology Data Exchange (ETDEWEB)

    Groeneveld, D.C., E-mail: degroeneveld@gmail.com

    2017-06-15

    In the 1960s’ and 1970s’ Canada was a world leader in performing in-reactor heat transfer experiments on fuel bundles instrumented with miniature sheath thermocouples. Several Critical Heat Flux (CHF) and Post-CHF experiments were performed in Chalk River’s NRU and NRX reactors on water-cooled 3-, 18-, 19-, 21-, and 36-element fuel bundles. Most experiments were obtained at steady-state conditions, where the power was raised gradually from single-phase conditions up to the CHF and beyond. Occasionally, post-dryout temperatures up to 600 °C were maintained for several hours. In some tests, the fuel behaviour during loss-of-flow and blowdown transients was investigated – during these transients sheath temperatures could exceed 2000 °C. Because of the increasingly more stringent licensing requirements for in-pile heat transfer tests on instrumented fuel bundles, no in-pile CHF and post-dryout tests on fuel bundles have been performed anywhere in the world for the past 40 years. This paper provides details of these unique in-pile experiments and describes some of their heat transfer results.

  15. MHD boundary layer slip flow and heat transfer of ferrofluid along a stretching cylinder with prescribed heat flux.

    Science.gov (United States)

    Qasim, Muhammad; Khan, Zafar Hayat; Khan, Waqar Ahmad; Ali Shah, Inayat

    2014-01-01

    This study investigates the magnetohydrodynamic (MHD) flow of ferrofluid along a stretching cylinder. The velocity slip and prescribed surface heat flux boundary conditions are employed on the cylinder surface. Water as conventional base fluid containing nanoparticles of magnetite (Fe3O4) is used. Comparison between magnetic (Fe3O4) and non-magnetic (Al2O3) nanoparticles is also made. The governing non-linear partial differential equations are reduced to non-linear ordinary differential equations and then solved numerically using shooting method. Present results are compared with the available data in the limiting cases. The present results are found to be in an excellent agreement. It is observed that with an increase in the magnetic field strength, the percent difference in the heat transfer rate of magnetic nanoparticles with Al2O3 decreases. Surface shear stress and the heat transfer rate at the surface increase as the curvature parameter increases, i.e curvature helps to enhance the heat transfer.

  16. Development of the heated length to diameter correction factor on critical heat flux using the artificial neural networks

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Yong Ho; Baek, Won Pil; Chang, Soon Heung [Korea Advanced Institute of Science and Technology, Taejon (Korea, Republic of); Chun, Tae Hyun [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)

    1998-12-31

    With using artificial neural networks (ANNs), an analytical study related to the heated length effect on critical heat flux (CHF) has been carried out to make an improvement of the CHF prediction accuracy based on local condition correlations or table. It has been carried out to suggest a feasible criterion of the threshold length-to-diameter (L/D) value in which heated length could affect CHF. And within the criterion, a L/D correction factor has been developed through conventional regression. In order to validate the developed L/D correction factor, CHF experiments for various heated lengths have been carried out under low and intermediate pressure conditions. The developed threshold L/D correlation provides a new feasible criterion of L/D threshold value. The developed correction factor gives a reasonable accuracy for the original database, showing the error of -2.18% for average and 27.75% for RMS, and promising results for new experimental data. 7 refs., 12 figs., 1 tab. (Author)

  17. Growth of a dry spot under a vapor bubble at high heat flux and high pressure

    CERN Document Server

    Nikolayev, Vadim; Lagier, G -L; Hegseth, J

    2016-01-01

    We report a 2D modeling of the thermal diffusion-controlled growth of a vapor bubble attached to a heating surface during saturated boiling. The heat conduction problem is solved in a liquid that surrounds a bubble with a free boundary and in a semi-infinite solid heater by the boundary element method. At high system pressure the bubble is assumed to grow slowly, its shape being defined by the surface tension and the vapor recoil force, a force coming from the liquid evaporating into the bubble. It is shown that at some typical time the dry spot under the bubble begins to grow rapidly under the action of the vapor recoil. Such a bubble can eventually spread into a vapor film that can separate the liquid from the heater thus triggering the boiling crisis (critical heat flux).

  18. Stagnation point flow over a stretching/shrinking cylinder with prescribed surface heat flux

    Science.gov (United States)

    Najib, Najwa; Bachok, Norfifah; Arifin, Norihan Md.

    2014-06-01

    The steady stagnation-point flow towards a horizontal linearly stretching/shrinking cylinder immersed in an incompressible viscous fluid with prescribed surface heat flux is investigated. The governing partial differential equations in cylindrical form are transformed into ordinary differential equations by similarity transformations. The transformed equations are solved numerically by using the shooting method. Results for the skin friction coefficient, local Nusselt number, velocity profiles and temperature profiles are presented for different values of the governing parameters. Effects of the curvature parameter, stretching/shrinking parameter and Prandtl number on the flow and heat transfer characteristics are discussed. The study indicate that the solutions for a shrinking cylinder are non-unique. It is observed that the surface shear stress and heat transfer rate at the surface increase as the curvature parameter increases.

  19. Investigation on the electron flux to the wall in the VENUS ion source

    Energy Technology Data Exchange (ETDEWEB)

    Thuillier, T., E-mail: thuillier@lpsc.in2p3.fr; Angot, J. [LPSC, Université Grenoble-Alpes, CNRS/IN2P3, 53 rue des Martyrs, 38026 Grenoble Cedex (France); Benitez, J. Y.; Hodgkinson, A.; Lyneis, C. M.; Todd, D. S.; Xie, D. Z. [Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

    2016-02-15

    The long-term operation of high charge state electron cyclotron resonance ion sources fed with high microwave power has caused damage to the plasma chamber wall in several laboratories. Porosity, or a small hole, can be progressively created in the chamber wall which can destroy the plasma chamber over a few year time scale. A burnout of the VENUS plasma chamber is investigated in which the hole formation in relation to the local hot electron power density is studied. First, the results of a simple model assuming that hot electrons are fully magnetized and strictly following magnetic field lines are presented. The model qualitatively reproduces the experimental traces left by the plasma on the wall. However, it is too crude to reproduce the localized electron power density for creating a hole in the chamber wall. Second, the results of a Monte Carlo simulation, following a population of scattering hot electrons, indicate a localized high power deposited to the chamber wall consistent with the hole formation process. Finally, a hypervapotron cooling scheme is proposed to mitigate the hole formation in electron cyclotron resonance plasma chamber wall.

  20. Investigation on the electron flux to the wall in the VENUS ion source.

    Science.gov (United States)

    Thuillier, T; Angot, J; Benitez, J Y; Hodgkinson, A; Lyneis, C M; Todd, D S; Xie, D Z

    2016-02-01

    The long-term operation of high charge state electron cyclotron resonance ion sources fed with high microwave power has caused damage to the plasma chamber wall in several laboratories. Porosity, or a small hole, can be progressively created in the chamber wall which can destroy the plasma chamber over a few year time scale. A burnout of the VENUS plasma chamber is investigated in which the hole formation in relation to the local hot electron power density is studied. First, the results of a simple model assuming that hot electrons are fully magnetized and strictly following magnetic field lines are presented. The model qualitatively reproduces the experimental traces left by the plasma on the wall. However, it is too crude to reproduce the localized electron power density for creating a hole in the chamber wall. Second, the results of a Monte Carlo simulation, following a population of scattering hot electrons, indicate a localized high power deposited to the chamber wall consistent with the hole formation process. Finally, a hypervapotron cooling scheme is proposed to mitigate the hole formation in electron cyclotron resonance plasma chamber wall.

  1. Heat fluxes from an Arctic fjord with glaciers and ice-bergs

    Science.gov (United States)

    Leikvin; Sundfjord, A.

    2013-12-01

    Glaciers on the Northern Hemisphere and on Svalbard in particular, are decreasing in volume. In Hornsund, SW Spitsbergen, the reduction of the multiple tide water glaciers has been observed for more than a century. Melt water from the glaciers represent a contribution of relatively cold fresh water to the water masses in the west, by the West -Spitsbergen current. We have used a numerical hydrodynamical model to simulate the fluxes of heat and fresh water between the Hornsund fjord and the water masses outside the fjord, with ice bergs and glacier melting included. Glacier melting and ice-berg melting are in general poorly described in hydrodynamical models of the Arctic. The Regional Ocean Modeling System (ROMS) model was set up for the Hornsund area with high resolution (160m), and fluxes through the fjord were calculated for the year 2011. The ocean current model was evaluated against current meter measurements and hydrographic data from strategic locations in the inner parts of Hornsund. An estimate of the heat flux and its seasonal signal between Hornsund and the outer water masses has been found. It is concluded that the there is a significant potential of oceanic heat contributing to facial melting of the tide water glacier fronts. Correspondingly, the glaciers contribute with a fresh water volume that mixes with the coastal northward current west of Svalbard and subsequently with the West Spitsbergen current. This flux is considered to be substantial, and indicates that glacier melting and ice-berg melting should be included in regional Arctic hydrodynamical ocean models.

  2. A One-Source Approach for Estimating Land Surface Heat Fluxes Using Remotely Sensed Land Surface Temperature

    Directory of Open Access Journals (Sweden)

    Yongmin Yang

    2017-01-01

    Full Text Available The partitioning of available energy between sensible heat and latent heat is important for precise water resources planning and management in the context of global climate change. Land surface temperature (LST is a key variable in energy balance process and remotely sensed LST is widely used for estimating surface heat fluxes at regional scale. However, the inequality between LST and aerodynamic surface temperature (Taero poses a great challenge for regional heat fluxes estimation in one-source energy balance models. To address this issue, we proposed a One-Source Model for Land (OSML to estimate regional surface heat fluxes without requirements for empirical extra resistance, roughness parameterization and wind velocity. The proposed OSML employs both conceptual VFC/LST trapezoid model and the electrical analog formula of sensible heat flux (H to analytically estimate the radiometric-convective resistance (rae via a quartic equation. To evaluate the performance of OSML, the model was applied to the Soil Moisture-Atmosphere Coupling Experiment (SMACEX in United States and the Multi-Scale Observation Experiment on Evapotranspiration (MUSOEXE in China, using remotely sensed retrievals as auxiliary data sets at regional scale. Validated against tower-based surface fluxes observations, the root mean square deviation (RMSD of H and latent heat flux (LE from OSML are 34.5 W/m2 and 46.5 W/m2 at SMACEX site and 50.1 W/m2 and 67.0 W/m2 at MUSOEXE site. The performance of OSML is very comparable to other published studies. In addition, the proposed OSML model demonstrates similar skills of predicting surface heat fluxes in comparison to SEBS (Surface Energy Balance System. Since OSML does not require specification of aerodynamic surface characteristics, roughness parameterization and meteorological conditions with high spatial variation such as wind speed, this proposed method shows high potential for routinely acquisition of latent heat flux estimation

  3. Sapflow+: a four-needle heat-pulse sap flow sensor enabling nonempirical sap flux density and water content measurements.

    Science.gov (United States)

    Vandegehuchte, Maurits W; Steppe, Kathy

    2012-10-01

    • To our knowledge, to date, no nonempirical method exists to measure reverse, low or high sap flux density. Moreover, existing sap flow methods require destructive wood core measurements to determine sapwood water content, necessary to convert heat velocity to sap flux density, not only damaging the tree, but also neglecting seasonal variability in sapwood water content. • Here, we present a nonempirical heat-pulse-based method and coupled sensor which measure temperature changes around a linear heater in both axial and tangential directions after application of a heat pulse. By fitting the correct heat conduction-convection equation to the measured temperature profiles, the heat velocity and water content of the sapwood can be determined. • An identifiability analysis and validation tests on artificial and real stem segments of European beech (Fagus sylvatica L.) confirm the applicability of the method, leading to accurate determinations of heat velocity, water content and hence sap flux density. • The proposed method enables sap flux density measurements to be made across the entire natural occurring sap flux density range of woody plants. Moreover, the water content during low flows can be determined accurately, enabling a correct conversion from heat velocity to sap flux density without destructive core measurements. © 2012 The Authors. New Phytologist © 2012 New Phytologist Trust.

  4. A three-dimensional inverse problem in estimating the internal heat flux of housing for high speed motors

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Cheng-Hung; Lo, Hung-Chi [Department of Systems and Naval Mechatronic Engineering, National Cheng Kung University, 1 Ta-Hsueh Road, Tainan 701, (Taiwan)

    2006-10-15

    The time-dependent heat flux generated in rotor and stator for the high speed electric motor is determined in this three-dimensional inverse heat conduction problem. The inverse algorithm utilizing the Steepest Descent Method (SDM) and a general purpose commercial code CFX4.4 is applied successfully in the present study in accordance with the simulated measured temperature distributions on some proper exterior surfaces. No cooling systems can be designed before the heat fluxes are estimated and identified. Two different functional forms for heat fluxes with different temperature measurement errors are used in the numerical experiments to illustrate the validity of the inverse algorithm. Results of the numerical simulation show that due to the structure of the cooling passages for motor housing, the estimated heat flux lying under the cooling passages is not accurate. However, when the concept of effective heat flux is applied, a reliable time-dependent heat flux can be obtained by using the present inverse algorithm. (author)

  5. Cu-Cr-Nb-Zr Alloy for Rocket Engines and Other High-Heat- Flux Applications

    Science.gov (United States)

    Ellis, David L.

    2013-01-01

    Rocket-engine main combustion chamber liners are used to contain the burning of fuel and oxidizer and provide a stream of high-velocity gas for propulsion. The liners in engines such as the Space Shuttle Main Engine are regeneratively cooled by flowing fuel, e.g., cryogenic hydrogen, through cooling channels in the back side of the liner. The heat gained by the liner from the flame and compression of the gas in the throat section is transferred to the fuel by the liner. As a result, the liner must either have a very high thermal conductivity or a very high operating temperature. In addition to the large heat flux (>10 MW/sq m), the liners experience a very large thermal gradient, typically more than 500 C over 1 mm. The gradient produces thermally induced stresses and strains that cause low cycle fatigue (LCF). Typically, a liner will experience a strain differential in excess of 1% between the cooling channel and the hot wall. Each time the engine is fired, the liner undergoes an LCF cycle. The number of cycles can be as few as one for an expendable booster engine, to as many as several thousand for a reusable launch vehicle or reaction control system. Finally, the liners undergo creep and a form of mechanical degradation called thermal ratcheting that results in the bowing out of the cooling channel into the combustion chamber, and eventual failure of the liner. GRCop-84, a Cu-Cr-Nb alloy, is generally recognized as the best liner material available at the time of this reporting. The alloy consists of 14% Cr2Nb precipitates in a pure copper matrix. Through experimental work, it has been established that the Zr will not participate in the formation of Laves phase precipitates with Cr and Nb, but will instead react with Cu to form the desired Cu-Zr compounds. It is believed that significant improvements in the mechanical properties of GRCop-84 will be realized by adding Zr. The innovation is a Cu-Cr-Nb-Zr alloy covering the composition range of 0.8 to 8.1 weight

  6. The Response of the Ocean Thermal Skin Layer to Air-Sea Surface Heat Fluxes

    Science.gov (United States)

    Wong, Elizabeth Wing-See

    There is much evidence that the ocean is heating as a result of an increase in concentrations of greenhouse gases (GHGs) in the atmosphere from human activities. GHGs absorb infrared radiation and re-emit infrared radiation back to the ocean's surface which is subsequently absorbed. However, the incoming infrared radiation is absorbed within the top micrometers of the ocean's surface which is where the thermal skin layer exists. Thus the incident infrared radiation does not directly heat the upper few meters of the ocean. We are therefore motivated to investigate the physical mechanism between the absorption of infrared radiation and its effect on heat transfer at the air-sea boundary. The hypothesis is that since heat lost through the air-sea interface is controlled by the thermal skin layer, which is directly influenced by the absorption and emission of infrared radiation, the heat flow through the thermal skin layer adjusts to maintain the surface heat loss, assuming the surface heat loss does not vary, and thus modulates the upper ocean heat content. This hypothesis is investigated through utilizing clouds to represent an increase in incoming longwave radiation and analyzing retrieved thermal skin layer vertical temperature profiles from a shipboard infrared spectrometer from two research cruises. The data are limited to night-time, no precipitation and low winds of less than 2 m/s to remove effects of solar radiation, wind-driven shear and possibilities of thermal skin layer disruption. The results show independence of the turbulent fluxes and emitted radiation on the incident radiative fluxes which rules out the immediate release of heat from the absorption of the cloud infrared irradiance back into the atmosphere through processes such as evaporation and increase infrared emission. Furthermore, independence was confirmed between the incoming and outgoing radiative flux which implies the heat sink for upward flowing heat at the air-sea interface is more

  7. Under-ice eddy covariance flux measurements of heat, salt, momentum, and dissolved oxygen in an artificial sea ice pool

    DEFF Research Database (Denmark)

    Else, B. G T; Rysgaard, S.; Attard, K.

    2015-01-01

    as ice grew from 5 to 25 cm thick. Heat, momentum, and dissolved oxygen fluxes were all successfully derived. Quantification of salt fluxes was unsuccessful due to noise in the conductivity sensor, a problem which appears to be resolved in a subsequent version of the instrument. Heat fluxes during...... as one possible cause of the high fluxes. Momentum fluxes showed interesting correlations with ice growth and melt but were generally higher than expected. We concluded that with the exception of the conductivity sensor, the eddy covariance system worked well, and that useful information about turbulent......Turbulent exchanges under sea ice play a controlling role in ice mass balance, ice drift, biogeochemistry, and mixed layer modification. In this study, we examined the potential to measure under-ice turbulent exchanges of heat, salt, momentum, and dissolved oxygen using eddy covariance...

  8. Seasonal effects of irrigation on land-atmosphere latent heat, sensible heat, and carbon fluxes in semiarid basin

    Science.gov (United States)

    Zeng, Yujin; Xie, Zhenghui; Liu, Shuang

    2017-02-01

    Irrigation, which constitutes ˜ 70 % of the total amount of freshwater consumed by the human population, is significantly impacting land-atmosphere fluxes. In this study, using the improved Community Land Model version 4.5 (CLM4.5) with an active crop model, two high-resolution (˜ 1 km) simulations investigating the effects of irrigation on latent heat (LH), sensible heat (SH), and carbon fluxes (or net ecosystem exchange, NEE) from land to atmosphere in the Heihe River basin in northwestern China were conducted using a high-quality irrigation dataset compiled from 1981 to 2013. The model output and measurements from remote sensing demonstrated the capacity of the developed models to reproduce ecological and hydrological processes. The results revealed that the effects of irrigation on LH and SH are strongest during summer, with a LH increase of ˜ 100 W m-2 and a SH decrease of ˜ 60 W m-2 over intensely irrigated areas. However, the reactions are much weaker during spring and autumn when there is much less irrigation. When the irrigation rate is below 5 mm day-1, the LH generally increases, whereas the SH decreases with growing irrigation rates. However, when the irrigation threshold is in excess of 5 mm day-1, there is no accrued effect of irrigation on the LH and SH. Irrigation produces opposite effects to the NEE during spring and summer. During the spring, irrigation yields more discharged carbon from the land to the atmosphere, increasing the NEE value by 0.4-0.8 gC m-2 day-1, while the summer irrigation favors crop fixing of carbon from atmospheric CO2, decreasing the NEE value by ˜ 0.8 gC m-2 day-1. The repercussions of irrigation on land-atmosphere fluxes are not solely linked to the irrigation amount, and other parameters (especially the temperature) also control the effects of irrigation on LH, SH, and NEE.

  9. Geothermal Heat Flux: Linking Deep Earth's Interior and the Dynamics of Large-Scale Ice Sheets

    Science.gov (United States)

    Rogozhina, Irina; Vaughan, Alan

    2014-05-01

    Regions covered by continental-scale ice sheets have the highest degree of uncertainty in composition and structure of the crust and lithospheric mantle, compounded by the poorest coverage on Earth of direct heat flow measurements. In addition to challenging conditions that make direct measurements and geological survey difficult Greenland and Antarctica are known to be geologically complex. Antarctica in particular is marked by two lithospherically distinct zones. In contrast to young and thin lithosphere of West Antarctica, East Antarctica is a collage of thick Precambrian fragments of Gondwana and earlier supercontinents. However, recent observations and modeling studies have detected large systems of subglacial lakes extending beneath much of the East Antarctic ice sheet base that have been linked to anomalously elevated heat flow. Outcrop samples from the rift margin with Australia (Prydz Bay) have revealed highly radiogenic Cambrian granite intrusives that are implicated in regional increase of crustal heat flux by a factor of two to three compared to the estimated continental background. Taken together, these indicate high variability of heat flow and properties of rocks across Antarctica. Similar conclusions have been made based on direct measurements and observations of the Greenland ice sheet. Airborne ice-penetrating radar and deep ice core projects show very high rates of basal melt for parts of the ice sheet in northern and central Greenland that have been explained by abnormally high heat flux. Archaean in age, the Greenland lithosphere was significantly reworked during the Early Proterozoic. In this region, the interpretation of independent geophysical data is complicated by Proterozoic and Phanerozoic collision zones, compounded by strong thermochemical effects of rifting along the western and eastern continental margins between 80 and 25 million years ago. In addition, high variability of heat flow and thermal lithosphere structure in central

  10. Diurnal variability of heat fluxes over the coastal waters off Visakhapatnam during post-monsoon and winter seasons

    Digital Repository Service at National Institute of Oceanography (India)

    Ramu, Ch V.; Bharathi, G.; Sadhuram, Y.; Prasad, K.V.S.R.

    Diurnal variability of heat fluxes in the coastal waters of Visakhapatnam has been studied during post-monsoon (Oct, 2006) and winter (Jan-Feb, 2007) seasons utilizing the surface meteorological data and radiation measurements on-board CRV Sagar...

  11. Heat flux measured acoustically at Grotto Vent, a hydrothermal vent cluster on the Endeavour Segment, Juan de Fuca Ridge

    Science.gov (United States)

    Xu, G.; Jackson, D. R.; Bemis, K. G.; Rona, P. A.

    2013-12-01

    Over the past several decades, quantifying the heat output has been a unanimous focus of studies at hydrothermal vent fields discovered around the global ocean. Despite their importance, direct measurements of hydrothermal heat flux are very limited due to the remoteness of most vent sites and the complexity of hydrothermal venting. Moreover, almost all the heat flux measurements made to date are snapshots and provide little information on the temporal variation that is expected from the dynamic nature of a hydrothermal system. The Cabled Observatory Vent Imaging Sonar (COVIS, https://sites.google.com/a/uw.edu/covis/) is currently connected to the Endeavour node of the NEPTUNE Canada observatory network (http://www.neptunecanada.ca) to monitor the hydrothermal plumes issuing from a vent cluster (Grotto) on the Endeavour Segment of the Juan de Fuca Ridge. COVIS is acquiring a long-term (20-months to date) time series of the vertical flow rate and volume flux of the hydrothermal plume above Grotto through the Doppler analysis of the acoustic backscatter data (Xu et al., 2013). We then estimate the plume heat flux from vertical flow rate and volume flux using our newly developed inverse method. In this presentation, we will briefly summarize the derivation of the inverse method and present the heat-flux time series obtained consequently with uncertainty quantification. In addition, we compare our heat-flux estimates with the one estimated from the plume in-situ temperatures measured using a Remotely Operative Vehicle (ROV) in 2012. Such comparison sheds light on the uncertainty of our heat flux estimation. Xu, G., Jackson, D., Bemis, K., and Rona, P., 2013, Observations of the volume flux of a seafloor hydrothermal plume using an acoustic imaging sonar, Geochemistry, Geophysics Geosystems, 2013 (in press).

  12. Effects of Vapor Path Structures on Critical Heat Flux and Boiling Heat Transfer in Pool Boiling

    Energy Technology Data Exchange (ETDEWEB)

    Seo, Han; Bang, In Cheol [UNIST, Ulsan (Korea, Republic of)

    2016-05-15

    Most of industry areas which have used the boiling heat transfer determine the safety margin of the power systems based on the CHF point. If the power density of the systems exceed the CHF region, the systems will be damaged because vapor films, which have much lower heat transfer capabilities, will cover the heating surface. Therefore, numerous studies related to the CHF prediction models have been extensively studied over the last 60 years, in terms of its physical mechanisms. Hydrodynamic instability, macrolayer dryout, hot/dry spot, and bubble interaction theories have been proposed as the CHF triggering and prediction models. One theory widely used to predict the CHF mechanism is hydrodynamic instability theory proposed by Zuber and modified hydrodynamic theories have been proposed and developed to analyze the CHF enhancement mechanisms. The paper concluded that the RT instability should consider the effect of heater characteristics to predict the CHF values more accurately. The CHF studies related to the hydrodynamic instabilities have been focused on finding the change of the RT instability wavelength and making a relation between the RT instability and KH instability wavelengths, but the effect of the critical height for the vapor path which can represent the KH instability wavelength has not been reported. Therefore, the effect of the critical height of the vapor path was examined using various types of intended vapor path with different heights of the structures. The effect of the vapor path with various heights of the structures was considered in the plate pool boiling facility to find the hydrodynamic instability mechanisms. The critical height of the intended vapor path was found when the height was less than 3 mm. The modified KH instability wavelength by considering numerical constant of the Zuber's prediction model predicted the critical height of the vapor path as the similar value of the experimental results. The results indicated that the

  13. Surface heat fluxes and ecosystem function in the Cretan Sea (eastern Mediterranean): a modelling study

    Science.gov (United States)

    Siddorn, J. R.; Allen, J. I.

    2003-01-01

    As a component of the Mediterranean Forecast System Pilot Project, a data buoy was deployed in the Cretan Sea. A 1-D ecosystem model of the site has been used to investigate the role of surface heat fluxes in determining modelled ecosystem behaviour. The method of calculation of these fluxes, the quality of the data used, and the temporal resolution of the data all had an impact upon the modelled ecosystem function. The effects of the changes in heat flux formulation were substantial, with both annually averaged properties of the system and the seasonal evolution of the biology being affected. It was also found that the ecosystem model was extremely sensitive to the accuracy of the meteorological forcing data used, with substantial changes in biology found when offsets in the forcing data were imposed. The frequency of forcing data was relatively unimportant in determining the biological function, although lower frequency forcing damped high frequency variability in the biology. During periods of mixing the biology showed an amplified response to changes in physical dynamics, but during periods of stratification the variations in the physics were found to be less important. Zooplankton showed more sensitivity to physical variability than either phytoplankton or bacteria. The consequences for ecosystem modelling are discussed.

  14. The button effect of CANFLEX bundle on the critical heat flux and critical channel power

    Energy Technology Data Exchange (ETDEWEB)

    Park, Joo Hwan; Jun, Jisu; Suk, Ho Chun [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of); Dimmick, G. R.; Bullock, D. E.; Inch, W. [Atomic Energy of Canada Limited, Ontario (Canada)

    1997-12-31

    A CANFLEX (CANdu FLEXible fuelling) 43-element bundle has developed for a CANDU-6 reactor as an alternative of 37-element fuel bundle. The design has two diameter elements (11.5 and 13.5 mm) to reduce maximum element power rating and buttons to enhance the critical heat flux (CHF), compared with the standard 37-element bundle. The freon CHF experiments have performed for two series of CANFLEX bundles with and without buttons with a modelling fluid as refrigerant R-134a and axial uniform heat flux condition. Evaluating the effects of buttons of CANFLEX bundle on CHF and Critical Channel Power (CCP) with the experimental results, it is shown that the buttons enhance CCP as well as CHF. All the CHF`s for both the CANFLEX bundles are occurred at the end of fuel channel with the high dryout quality conditions. The CHF enhancement ratio are increased with increase of dryout quality for all flow conditions and also with increase of mass flux only for high pressure conditions. It indicates that the button is a useful design for CANDU operating condition because most CHF flow conditions for CANDU fuel bundle are ranged to high dryout quality conditions. 5 refs., 11 figs. (Author)

  15. Roughness Length of Water Vapor over Land Surfaces and Its Influence on Latent Heat Flux

    Directory of Open Access Journals (Sweden)

    Sang-Jong Park

    2010-01-01

    Full Text Available Latent heat flux at the surface is largely dependent on the roughness length for water vapor (z0q. The determination of z0q is still uncertain because of its multifaceted characteristics of surface properties, atmospheric conditions and insufficient observations. In this study, observed values from the Fluxes Over Snow Surface II field experiment (FLOSS-II from November 2002 to March 2003 were utilized to estimate z0q over various land surfaces: bare soil, snow, and senescent grass. The present results indicate that the estimated z0q over bare soil is much smaller than the roughness length of momentum (z0m; thus, the ratio z0m/z0q is larger than those of previous studies by a factor of 20 - 150 for the available flow regime of the roughness Reynolds number, Re* > 0.1. On the snow surface, the ratio is comparable to a previous estimation for the rough flow (Re* > 1, but smaller by a factor of 10 - 50 as the flow became smooth (Re* < 1. Using the estimated ratio, an optimal regression equation of z0m/z0q is determined as a function of Re* for each surface type. The present parameterization of the ratio is found to greatly reduce biases of latent heat flux estimation compared with that estimated by the conventional method, suggesting the usefulness of current parameterization for numerical modeling.

  16. Critical heat flux on a flat plate heater located at the middle of a duct in forced flow of pressurized He II

    Science.gov (United States)

    Okamura, T.; Saeki, M.; Hata, K.; Hama, K.; Shirai, Y.; Shiotsu, M.

    2004-09-01

    Critical heat fluxes (CHFs) were measured for two types of rectangular ducts containing horizontal flat plate heaters. One has the flat plate heater of 6 mm wide and 20 mm long located on the inner lower wall at 50 mm from the inlet. The other duct has two horizontal flat plates of 6 mm wide and 20 mm long on inner upper and lower walls at 50 mm from the inlet. The equation of CHF for the forced convection containing a new nondimensional-parameter m introduced in order to calculate cross-sectionally averaged liquid temperature at the center of the duct was derived based on two fluid model, ordinary convection theorem and experimental results. It was confirmed that this correlation can describe not only the author's data on the duct but also other worker's data for channels with different shapes and sizes.

  17. Thermal performance analysis of a flat heat pipe working with carbon nanotube-water nanofluid for cooling of a high heat flux heater

    Science.gov (United States)

    Arya, A.; Sarafraz, M. M.; Shahmiri, S.; Madani, S. A. H.; Nikkhah, V.; Nakhjavani, S. M.

    2017-10-01

    Experimental investigation on the thermal performance of a flat heat pipe working with carbon nanotube nanofluid is conducted. It is used for cooling a heater working at high heat flux conditions up to 190 kW/m2. The heat pipe is fabricated from aluminium and is equipped with rectangular fin for efficient cooling of condenser section. Inside the heat pipe, a screen mesh was inserted as a wick structure to facilitate the capillary action of working fluid. Influence of different operating parameters such as heat flux, mass concentration of carbon nanotubes and filling ratio of working fluid on thermal performance of heat pipe and its thermal resistance are investigated. Results showed that with an increase in heat flux, the heat transfer coefficient in evaporator section of the heat pipe increases. For filling ratio, however, there is an optimum value, which was 0.8 for the test heat pipe. In addition, CNT/water enhanced the heat transfer coefficient up to 40% over the deionized water. Carbon nanotubes intensified the thermal performance of wick structure by creating a fouling layer on screen mesh structure, which changes the contact angle of liquid with the surface, intensifying the capillary forces.

  18. Measurements on the SOLARIX wall heating system; Messung SOLARIX-Wandheizsystem - Schlussbericht

    Energy Technology Data Exchange (ETDEWEB)

    Oesch, P.

    2009-12-15

    This illustrated final report for the Swiss Federal Office of Energy (SFOE) describes the SOLARIX wall-integrated heating system. The system features transparent heat insulation elements that are mounted on the east, south and west-facing sides of a building, as well as a photovoltaic installation on the balcony and terrace balustrades. The project's aims and the goals set for it are quoted. Also, problems encountered during the project are listed and changes made to the original project are discussed. Finally, 4 buildings were realised, three of which were built in a conventional manner to 'Minergie' low energy consumption standards. The construction of the transparent heat-insulating elements is described. Measurements made and results obtained are presented and discussed.

  19. Heating efficiency of multi-walled carbon nanotubes in the first and second biological windows

    Science.gov (United States)

    Maestro, Laura Martínez; Haro-González, Patricia; Del Rosal, Blanca; Ramiro, Julio; Caamaño, A. J.; Carrasco, Elisa; Juarranz, Angeles; Sanz-Rodríguez, Francisco; Solé, José García; Jaque, Daniel

    2013-08-01

    Quantum dot based-thermometry, in combination with double beam confocal microscopy and infrared thermal imaging, has been used to investigate the heating efficiency of multi-walled carbon nanotubes (MWCNTs) under optical excitation within the first (808 nm) and second (1090 nm) biological windows as well as in the spectral region separating them (980 nm). It has been found that for the three excitation wavelengths the heating efficiency of MWCNTs (10 nm in diameter and 1.5 μm in length) is close to 50%. Despite this ``flat'' heating efficiency, we have found that the excitation wavelength is, indeed, critical during in vivo experiments due to the spectral dependence of both tissue absorption and scattering coefficients. It has been concluded that efficiency and selectivity of in vivo photothermal treatments based on MWCNTs are simultaneously optimized when laser irradiation lies within the first or second biological window.

  20. Comparison of sensible heat flux estimates using AVHRR with scintillometer measurements over semi-arid grassland in northwest Mexico

    NARCIS (Netherlands)

    Watts, C.J.; Chehbouni, A.; Rodriguez, J.C.; Kerr, Y.H.; Hartogensis, O.K.; Bruin, de H.A.R.

    2000-01-01

    The problems associated with the validation of satellite-derived estimates of the surface fluxes are discussed and the possibility of using the large aperture scintillometer is investigated. Simple models are described to derive surface temperature and sensible heat flux from the advanced very high

  1. Patterns of water and heat flux across a biome gradient from tropical forest to savanna in Brazil

    NARCIS (Netherlands)

    Rocha, da H.R.; Manzi, A.O.; Cabral, O.M.; Miller, S.D.; Goulden, M.L.; Saleska, S.R.; Coupe, N.R.; Wofsy, S.C.; Borma, L.S.; Artaxo, P.; Vourlitis, G.; Nogueira, J.S.; Cardoso, F.L.; Nobre, A.D.; Kruijt, B.; Freitas, H.C.; Randow, von C.; Aguiar, R.G.; Maia, J.F.

    2009-01-01

    We investigated the seasonal patterns of water vapor and sensible heat flux along a tropical biome gradient from forest to savanna. We analyzed data from a network of flux towers in Brazil that were operated within the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA). These tower sites

  2. Stability of the Atlantic overturning circulation: competition between Bering Strait freshwater flux and Agulhas heat and salt sources

    NARCIS (Netherlands)

    Weijer, W.; Ruijter, W.P.M. de; Dijkstra, H.A.

    2000-01-01

    In this study we examine the role that is played by interocean fluxes of buoyancy in stabilizing the present-day overturning circulation of the Atlantic Ocean. A 2D model of the Atlantic overturning circulation is used, in which the interocean fluxes of heat and salt (via the Bering Strait, the

  3. Influence of environment factors on humidity conditions of selected external wall solutions in a heated building

    Science.gov (United States)

    Kaczmarek, Anna

    2017-10-01

    Contemporary single-family houses in Poland are often built during 3 quarters of a year (spring to autumn) are usually settled in a winter season. It is a special case when exploitation humidity coincides with technological one, causing unfavourable humidity conditions during the first years of exploitation. In consequence, thermal parameters of partitions differ from those assumed in the project. In construction stage the humidity state of a wall stabilizes as a result of water: associated with storage, entered technologically during wall construction and plastering, coming from rainfall. Thermo-insulation materials are built-in at dry state. During erection and exploitation of a building their thermal conductivity is changing depending on humidity conditions. According to building rules, construction humidity should be removed from a partition before the building transfer to usage, because it lowers the thermal partition insulation ability and increases air humidity of building interior. Walls are plastered and insulated in condition of simultaneous presence of atmospheric and technological humidity which cause special humidity condition during first years of exploitation. As a consequence, heating costs are substantially higher. In this article the results of simulation are shown performed with WUFI ®PRO 5 software, which was intended to define the time necessary for reaching the stabilised humidity in selected solutions of two-layer walls applied in a heated building. In the research performed, the partition orientation along geographic directions, short and long wave radiation, and environment humidity (air humidity, driving rain) coincidence with technological humidity in assumed wall solutions were taken into account.

  4. Heat and mass transfer analysis of unsteady MHD nanofluid flow through a channel with moving porous walls and medium

    Directory of Open Access Journals (Sweden)

    Muhammad Zubair Akbar

    2016-04-01

    Full Text Available The paper presents the numerical study of heat and mass transfer analysis in a viscous unsteady MHD nanofluid flow through a channel with porous walls and medium in the presence of metallic nanoparticles. The two cases for effective thermal conductivity are discussed in the analysis through H-C model. The impacts of the governing parameters on the flow, heat and mass transfer aspects of the issue are talked about. Under the patronage of small values of permeable Reynolds number and relaxation/contraction parameter, we locate that, when wall contraction is together with suction, flow turning is encouraged close to the wall where the boundary layer is shaped. On the other hand, when the wall relaxation is coupled with injection, the flow adjacent to the porous walls decreased. The outcome of the exploration may be beneficial for applications of biotechnology. Numerical solutions for the velocity, heat and mass transfer rate at the boundary are obtained and analyzed.

  5. Method and apparatus for active control of combustion rate through modulation of heat transfer from the combustion chamber wall

    Science.gov (United States)

    Roberts, Jr., Charles E.; Chadwell, Christopher J.

    2004-09-21

    The flame propagation rate resulting from a combustion event in the combustion chamber of an internal combustion engine is controlled by modulation of the heat transfer from the combustion flame to the combustion chamber walls. In one embodiment, heat transfer from the combustion flame to the combustion chamber walls is mechanically modulated by a movable member that is inserted into, or withdrawn from, the combustion chamber thereby changing the shape of the combustion chamber and the combustion chamber wall surface area. In another embodiment, heat transfer from the combustion flame to the combustion chamber walls is modulated by cooling the surface of a portion of the combustion chamber wall that is in close proximity to the area of the combustion chamber where flame speed control is desired.

  6. Numerical investigation of heat transfer enhancement in a rectangular heated pipe for turbulent nanofluid

    National Research Council Canada - National Science Library

    Yarmand, Hooman; Gharehkhani, Samira; Kazi, Salim Newaz; Sadeghinezhad, Emad; Safaei, Mohammad Reza

    2014-01-01

    .... The continuity, momentum, and energy equations were solved by means of a finite volume method (FVM). The symmetrical rectangular channel is heated at the top and bottom at a constant heat flux while the sides walls are insulated...

  7. Heat transfer nanofluid based on curly ultra-long multi-wall carbon nanotubes

    Science.gov (United States)

    Boncel, Sławomir; Zniszczoł, Aurelia; Pawlyta, Mirosława; Labisz, Krzysztof; Dzido, Grzegorz

    2017-08-01

    The main challenge in the use of multi-wall carbon nanotube (MWCNT) as key components of nanofluids is to transfer excellent thermal properties from individual nanotubes into the bulk systems. We present studies on the performance of heat transfer nanofluids based on ultra-long ( 2 mm), curly MWCNTs - in the background of various other nanoC-sp2, i.e. oxidized MWCNTs, commercially available Nanocyl™ MWCNTs and spherical carbon nanoparticles (SCNs). The nanofluids prepared via ultrasonication from water and propylene glycol were studied in terms of heat conductivity and heat transfer in a scaled up thermal circuit containing a copper helical heat exchanger. Ultra-long curly MWCNT (1 wt.%) nanofluids (stabilized with Gum Arabic in water) emerged as the most thermally conducting ones with a 23-30%- and 39%-enhancement as compared to the base-fluids for water and propylene glycol, respectively. For turbulent flows (Re = 8000-11,000), the increase of heat transfer coefficient for the over-months stable 1 wt.% ultra-long MWCNT nanofluid was found as high as >100%. The findings allow to confirm that longer MWCNTs are promising solid components in nanofluids and hence to predict their broader application in heat transfer media.

  8. Boundary plasma heat flux width measurements for poloidal magnetic fields above 1 Tesla in the Alcator C-Mod tokamak

    Science.gov (United States)

    Brunner, Dan; Labombard, Brian; Kuang, Adam; Terry, Jim; Alcator C-Mod Team

    2017-10-01

    The boundary heat flux width, along with the total power flowing into the boundary, sets the power exhaust challenge for tokamaks. A multi-machine boundary heat flux width database found that the heat flux width in H-modes scaled inversely with poloidal magnetic field (Bp) and was independent of machine size. The maximum Bp in the database was 0.8 T, whereas the ITER 15 MA, Q =10 scenario will be 1.2 T. New measurements of the boundary heat flux width in Alcator C-Mod extend the international database to plasmas with Bp up to 1.3 T. C-Mod was the only experiment able to operate at ITER-level Bp. These new measurements are from over 300 plasma shots in L-, I-, and EDA H-modes spanning essentially the whole operating space in C-Mod. We find that the inverse-Bp dependence of the heat flux width in H-modes continues to ITER-level Bp, further reinforcing the empirical projection of 500 μm heat flux width for ITER. We find 50% scatter around the inverse-Bp scaling and are searching for the `hidden variables' causing this scatter. Supported by USDoE award DE-FC02-99ER54512.

  9. Unsteady Heat-Flux Measurements of Second-Mode Instability Waves in a Hypersonic Boundary Layer

    Science.gov (United States)

    Kergerise, Michael A.; Rufer, Shann J.

    2016-01-01

    In this paper we report on the application of the atomic layer thermopile (ALTP) heat- flux sensor to the measurement of laminar-to-turbulent transition in a hypersonic flat plate boundary layer. The centerline of the flat-plate model was instrumented with a streamwise array of ALTP sensors and the flat-plate model was exposed to a Mach 6 freestream over a range of unit Reynolds numbers. Here, we observed an unstable band of frequencies that are associated with second-mode instability waves in the laminar boundary layer that forms on the flat-plate surface. The measured frequencies, group velocities, phase speeds, and wavelengths of these instability waves are in agreement with data previously reported in the literature. Heat flux time series, and the Morlet-wavelet transforms of them, revealed the wave-packet nature of the second-mode instability waves. In addition, a laser-based radiative heating system was developed to measure the frequency response functions (FRF) of the ALTP sensors used in the wind tunnel test. These measurements were used to assess the stability of the sensor FRFs over time and to correct spectral estimates for any attenuation caused by the finite sensor bandwidth.

  10. Assessment of the W7-X high heat flux divertor with thermo-mechanical analysis

    Energy Technology Data Exchange (ETDEWEB)

    Qian, Xinyuan [School of Nuclear Science and Technology, University of Science and Technology of China, Jinzhai Road 96, 230026 Hefei,Anhui (China); Institute of Plasma Physics, Chinese Academy of Sciences, Shushanhu Road 350, 230031 Hefei, Anhui (China); Peng, Xuebing, E-mail: pengxb@ipp.ac.cn [Institute of Plasma Physics, Chinese Academy of Sciences, Shushanhu Road 350, 230031 Hefei, Anhui (China); Fellinger, Joris [Max Planck Institute for Plasma Physics, Wendelsteinstr. 1, 17491 Greifswald (Germany); Boscary, Jean [Max Planck Institute for Plasma Physics, Boltzmannstr. 2, 85748 Garching (Germany); Bykov, Victor [Max Planck Institute for Plasma Physics, Wendelsteinstr. 1, 17491 Greifswald (Germany); Wang, Zhongwei [Institute of Plasma Physics, Chinese Academy of Sciences, Shushanhu Road 350, 230031 Hefei, Anhui (China); Ye, Minyou; Song, Yuntao [School of Nuclear Science and Technology, University of Science and Technology of China, Jinzhai Road 96, 230026 Hefei,Anhui (China); Institute of Plasma Physics, Chinese Academy of Sciences, Shushanhu Road 350, 230031 Hefei, Anhui (China)

    2016-11-01

    Highlights: • Thermo-mechanical analysis of HHF divertor module, TM2H. • Temperature of all parts is acceptable for long pulse operation. • Stress in different parts is mainly caused by different load. • Radial displacement need to be improved based on FE calculations. - Abstract: The Wendelstein 7-X is an experimental device designed with a stellarator magnetic confinement for stationary plasma operation (up to 30 min). At the first stage, it is scheduled to start with an inertially cooled test divertor unit and a shorter plasma pulse operation up to 10 s. After the completion of this stage, a water-cooled high heat flux (HHF) divertor will be installed for the steady-state operation phase. The divertor consists of individual target modules, which are sets of target elements armored with CFC tiles supported by a stainless steel structure and fed in parallel with manifolds. Detailed thermo-mechanical analysis of the target modules using the finite element method has been performed to validate and/or improve the elected design of the HHF divertor under operation. Different operating conditions have been studied and the effect of the variation of the convective heat flux pattern with localized heating loads as high as 10 MW/m{sup 2} onto the target elements has been computed. The analysis of the thermal response, stress distribution and deformation allowed a better understanding of the behavior of the divertor modules under operation and confirmed the suitability of the design.

  11. Experimental Study of Effect of Graphene Oxide Colloid on the Critical Heat Flux

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Ji Min; Kim, Moo Hwan [POSTECH, Pohang (Korea, Republic of); Ahn, Ho Seon [Incheon National Univ., Incheon (Korea, Republic of)

    2013-10-15

    We carried out the pool boiling CHF experiments in GO colloids. For analysis of surface characteristics, we conducted scanning electron microscopy (SEM) observation and contact angle (CA) measurement. The CHF enhancement of GO colloids was investigated in this study. To control the surface condition of GO deposition layer, the concentration was changed. As the concentration increased, the CHF performance was enhanced. In order to explain the CHF enhancement, we conducted morphology analysis and contact angle measurement. The deposition layer, however, showed 2D smooth surface and no wettability enhancement. Nucleate boiling is one of most efficient mode for heat transfer in real application such as power plants and chip cooling devices. In the heat flux controlled systems, its operating conditions are limited by the critical heat flux (CHF), where vapor film covers entire heating surface so that the surface temperature rapidly increases and melts down, resulting in a severe accident. In order to delay the CHF phenomena, nanofluids as working fluid are well-known as a possible method. Graphene is a new material having extraordinary thermal property and the method to synthesize the graphene as colloid was developed. Park et al. firstly reported the CHF performance of the graphene oxide (GO) and the reduced graphene oxide (RGO) colloid. The GO and RGO colloid showed about 200% and 100% enhancement of CHF, respectively. Ahn et al. reported the boiling performance of RGO colloid and unique structure formation of RGO flakes, so called self-assembled three-dimensional foam-like graphene network (SFG), on the heating surface. The important point of boiling study on the graphene based material is that their CHF enhancement could not be explained by existing theory based on wetting analysis.

  12. Modeling Studies of the Effects of Winds and Heat Flux on the Tropical Oceans

    Science.gov (United States)

    Seager, R.

    1999-01-01

    Over a decade ago, funding from this NASA grant supported the development of the Cane-Zebiak ENSO prediction model which remains in use to this day. It also supported our work developing schemes for modeling the air-sea heat flux in ocean models used for studying climate variability. We introduced a succession of simple boundary layer models that allow the fluxes to be computed internally in the model and avoid the need to specify the atmospheric thermodynamic state. These models have now reached a level of generality that allows modeling of the global, rather than just tropical, ocean, including sea ice cover. The most recent versions of these boundary layer models have been widely distributed around the world and are in use by many ocean modeling groups.

  13. Monitoring a supervolcano in repose: Heat and volatile flux at the yellostone caldera

    Science.gov (United States)

    Lowenstern, J. B.; Hurwitz, S.

    2008-01-01

    Although giant calderas ("supervolcanoes") may slumber for tens of thousands of years between eruptions, their abundant earthquakes and crustal deformation reveal the potential for future upheaval. Any eventual supereruption could devastate global human populations, so these systems must be carefully scrutinized. Insight into dormant but restless calderas can be gained by monitoring their output of heat and gas. At Yellowstone, the large thermal and CO2 fluxes require massive input of basaltic magma, which continues to invade the lower to mid-crust, sustains the overlying high-silica magma reservoir, and may result in volcanic hazard for millennia to come. The high flux of CO2 may contribute to the measured deformation of the caldera floor and can also modify the pressure, thermal, and chemical signals emitted from the magma. In order to recognize precursors to eruption, we must scrutinize the varied signals emerging from restless calderas with the goal of discriminating magmatic, hydrothermal, and hybrid phenomena.

  14. Evapotranspiration and heat fluxes over a patchy forest - studied using modelling and measurements

    DEFF Research Database (Denmark)

    Sogachev, Andrey; Dellwik, Ebba; Boegh, Eva

    , Ecological. Appl. 18, 1454-1459). In the present work, we apply the SCADIS with enhanced turbulence closure including buoyancy for investigation of the spatial distribution of latent and sensible heat vertical fluxes over patchy forested terrain in Denmark during selected days in the summer period. A closer...... look at the result shows that though the meteorological mast is located in the middle of a forest patch by size about 1x2 km2, it is not free from uncertainties regarding energy balance closure. Comparing observed and SCADIS (1D and 3D) simulated data for the mast confirms that caution is needed when...... interpreting measured flux data. The approach used in this work can be utilized in interpretation of already existed experimental data and in the planning of future experiments....

  15. Investigation of the ellipsoidal-statistical Bhatnagar-Gross-Krook kinetic model applied to gas-phase transport of heat and tangential momentum between parallel walls

    Science.gov (United States)

    Gallis, M. A.; Torczynski, J. R.

    2011-03-01

    The ellipsoidal-statistical Bhatnagar-Gross-Krook (ES-BGK) kinetic model is investigated for steady gas-phase transport of heat, tangential momentum, and mass between parallel walls (i.e., Fourier, Couette, and Fickian flows). This investigation extends the original study of Cercignani and Tironi, who first applied the ES-BGK model to heat transport (i.e., Fourier flow) shortly after this model was proposed by Holway. The ES-BGK model is implemented in a molecular-gas-dynamics code so that results from this model can be compared directly to results from the full Boltzmann collision term, as computed by the same code with the direct simulation Monte Carlo (DSMC) algorithm of Bird. A gas of monatomic molecules is considered. These molecules collide in a pairwise fashion according to either the Maxwell or the hard-sphere interaction and reflect from the walls according to the Cercignani-Lampis-Lord model with unity accommodation coefficients. Simulations are performed at pressures from near-free-molecular to near-continuum. Unlike the BGK model, the ES-BGK model produces heat-flux and shear-stress values that both agree closely with the DSMC values at all pressures. However, for both interactions, the ES-BGK model produces molecular-velocity-distribution functions that are qualitatively similar to those determined for the Maxwell interaction from Chapman-Enskog theory for small wall temperature differences and moment-hierarchy theory for large wall temperature differences. Moreover, the ES-BGK model does not produce accurate values of the mass self-diffusion coefficient for either interaction. Nevertheless, given its reasonable accuracy for heat and tangential-momentum transport, its sound theoretical foundation (it obeys the H-theorem), and its available extension to polyatomic molecules, the ES-BGK model may be a useful method for simulating certain classes of single-species noncontinuum gas flows, as Cercignani suggested.

  16. Validation experiments to determine radiation partitioning of heat flux to an object in a fully turbulent fire.

    Energy Technology Data Exchange (ETDEWEB)

    Ricks, Allen; Blanchat, Thomas K.; Jernigan, Dann A.

    2006-06-01

    It is necessary to improve understanding and develop validation data of the heat flux incident to an object located within the fire plume for the validation of SIERRA/ FUEGO/SYRINX fire and SIERRA/CALORE. One key aspect of the validation data sets is the determination of the relative contribution of the radiative and convective heat fluxes. To meet this objective, a cylindrical calorimeter with sufficient instrumentation to measure total and radiative heat flux had been designed and fabricated. This calorimeter will be tested both in the controlled radiative environment of the Penlight facility and in a fire environment in the FLAME/Radiant Heat (FRH) facility. Validation experiments are specifically designed for direct comparison with the computational predictions. Making meaningful comparisons between the computational and experimental results requires careful characterization and control of the experimental features or parameters used as inputs into the computational model. Validation experiments must be designed to capture the essential physical phenomena, including all relevant initial and boundary conditions. A significant question of interest to modeling heat flux incident to an object in or near a fire is the contribution of the radiation and convection modes of heat transfer. The series of experiments documented in this test plan is designed to provide data on the radiation partitioning, defined as the fraction of the total heat flux that is due to radiation.

  17. Influence of metal frame on heat protection properties of a polystyrene concrete wall

    Directory of Open Access Journals (Sweden)

    Tsvetkov Nikolay

    2018-01-01

    Full Text Available The use of novel thermal-efficient building materials and technologies that allow increasing the level of thermal protection of external envelope structures and reducing the time for construction are of practical interest and represent a relevant task in the conditions of rapidly changing and increasing requirements to energy efficiency of buildings. This research aims at simulating the process of spatial heat transfer in a multilayer non-uniform structure of an external cast-in-place framed wall produced from polystyrene concrete with a stay-in-place formwork. Based on the physico-mathematical model developed with the use of ANSYS and COMSOL software complexes, parametric analysis of the impact of various factors on thermal behavior of the external wall was performed with the account of heat-stressed frame elements. The nature of temperature fields distribution in a polystyrene concrete structure was defined, and its thermal protection properties were investigated. The impact of a metal frame on thermal protection properties of a wall was found to be insignificant.

  18. Dynamics of the collision of a vortex ring with a vertical heated wall

    Science.gov (United States)

    Gelderblom, G.; Palacios-Morales, C. A.; Zenit, R.; Solorio-Ordaz, F. J.

    2012-11-01

    We study the dynamics of the impact of a vortex ring with a vertical heated plate (at constant temperature). Laminar vortex rings were generated with a piston cylinder arrangement. The vertical wall is heated by a thermal bath which is held at constant temperature producing a laminar and stable thermal boundary layer. Measurements of the 2D velocity field were obtained with a PIV technique. The experimental results for the isothermal case are in agreement with previous investigations reported in the literature. To avoid azimuthal instabilities, we mainly conducted experiments for L /D0 = 1 (where L is the piston displacement and D0 is the cylinder inner diameter) with different wall temperatures and vortex translation velocities. For this case, secondary vortices were not observed. Using ink visualization we observed the evolution of the vortex shape. The initial circular shape evolves into a ``cat head'' shape after reaching the wall. The top and bottom regions of the vortex reduce and increase their vorticity, respectively. The sides are stretched and convected. An analysis of the different mechanisms leading to this shape evolution is presented and discussed.

  19. Estimation of ground heat flux from soil temperature over a bare soil

    Science.gov (United States)

    An, Kedong; Wang, Wenke; Wang, Zhoufeng; Zhao, Yaqian; Yang, Zeyuan; Chen, Li; Zhang, Zaiyong; Duan, Lei

    2017-08-01

    Ground soil heat flux, G 0, is a difficult-to-measure but important component of the surface energy budget. Over the past years, many methods were proposed to estimate G 0; however, the application of these methods was seldom validated and assessed under different weather conditions. In this study, three popular models (force-restore, conduction-convection, and harmonic) and one widely used method (plate calorimetric), which had well performance in publications, were investigated using field data to estimate daily G 0 on clear, cloudy, and rainy days, while the gradient calorimetric method was regarded as the reference for assessing the accuracy. The results showed that harmonic model was well reproducing the G 0 curve for clear days, but it yielded large errors on cloudy and rainy days. The force-restore model worked well only under rainfall condition, but it was poor to estimate G 0 under rain-free conditions. On the contrary, the conduction-convection model was acceptable to determine G 0 under rain-free conditions, but it generated large errors on rainfall days. More importantly, the plate calorimetric method was the best to estimate G 0 under different weather conditions compared with the three models, but the performance of this method is affected by the placement depth of the heat flux plate. As a result, the heat flux plate was recommended to be buried as close as possible to the surface under clear condition. But under cloudy and rainy conditions, the plate placed at depth of around 0.075 m yielded G 0 well. Overall, the findings of this paper provide guidelines to acquire more accurate estimation of G 0 under different weather conditions, which could improve the surface energy balance in field.

  20. Novel Zero-Heat-Flux Deep Body Temperature Measurement in Lower Extremity Vascular and Cardiac Surgery.

    Science.gov (United States)

    Mäkinen, Marja-Tellervo; Pesonen, Anne; Jousela, Irma; Päivärinta, Janne; Poikajärvi, Satu; Albäck, Anders; Salminen, Ulla-Stina; Pesonen, Eero

    2016-08-01

    The aim of this study was to compare deep body temperature obtained using a novel noninvasive continuous zero-heat-flux temperature measurement system with core temperatures obtained using conventional methods. A prospective, observational study. Operating room of a university hospital. The study comprised 15 patients undergoing vascular surgery of the lower extremities and 15 patients undergoing cardiac surgery with cardiopulmonary bypass. Zero-heat-flux thermometry on the forehead and standard core temperature measurements. Body temperature was measured using a new thermometry system (SpotOn; 3M, St. Paul, MN) on the forehead and with conventional methods in the esophagus during vascular surgery (n = 15), and in the nasopharynx and pulmonary artery during cardiac surgery (n = 15). The agreement between SpotOn and the conventional methods was assessed using the Bland-Altman random-effects approach for repeated measures. The mean difference between SpotOn and the esophageal temperature during vascular surgery was+0.08°C (95% limit of agreement -0.25 to+0.40°C). During cardiac surgery, during off CPB, the mean difference between SpotOn and the pulmonary arterial temperature was -0.05°C (95% limits of agreement -0.56 to+0.47°C). Throughout cardiac surgery (on and off CPB), the mean difference between SpotOn and the nasopharyngeal temperature was -0.12°C (95% limits of agreement -0.94 to+0.71°C). Poor agreement between the SpotOn and nasopharyngeal temperatures was detected in hypothermia below approximately 32°C. According to this preliminary study, the deep body temperature measured using the zero-heat-flux system was in good agreement with standard core temperatures during lower extremity vascular and cardiac surgery. However, agreement was questionable during hypothermia below 32°C. Copyright © 2016 Elsevier Inc. All rights reserved.

  1. High heat flux testing of EU tungsten monoblock mock-ups for the ITER divertor

    Energy Technology Data Exchange (ETDEWEB)

    Gavila, P., E-mail: pierre.gavila@f4e.europa.eu [Fusion for Energy, 08019 Barcelona (Spain); Riccardi, B. [Fusion for Energy, 08019 Barcelona (Spain); Pintsuk, G. [Forschungszentrum Juelich, 52425 Juelich (Germany); Ritz, G. [AREVA NP, Centre Technique France, 71205 Le Creusot (France); Kuznetsov, V. [JCS “Efremov Institute”, Doroga na Metallostroy 3, Metallostroy, Saint-Petersburg 196641 (Russian Federation); Durocher, A. [ITER Organization, Route de Vinon sur Verdon, CS 90 046, 13067 Saint Paul-lez-Durance (France)

    2015-10-15

    Highlights: • All the tested items sustained the ITER Full W divertor qualification program requirements. This confirms that the technology for the manufacturing of the first set of the ITER Divertor is available in Europe. • The surface roughening and local melting of the W surface under high heat flux was proven to be significantly reduced for an armour thickness lower or equal to 6 mm. • However, this campaign highlighted some specific areas of improvement to be implemented ideally before the upcoming ITER Divertor IVT serial production. • The issue of the self-castellation of the W monoblocks, which typically appears after a few tenths of cycles at 20 MW/m{sup 2}, is critical because it generates some uncontrolled defects at the amour to heat sink joints. Besides, they create a gap which exposure is almost perpendicular to the magnetic field lines and which might lead to local W melting in the strike point region. • This campaign also evidenced that the minimum IO requirements on the CuCrZr ductility could be revised to avoid the occurrence of rather early fatigue failures. Although the W material characterization program has been set up by the IO, the strategy on the CuCrZr still needs to be defined. - Abstract: With the aim to assess the option to start the ITER operation with a full tungsten divertor, an R&D program was launched in order to evaluate the performances of tungsten (W) armoured plasma facing components (PFCs) under high heat flux. The F4E program consisted in the manufacturing and high heat flux (HHF) testing of W monoblock mock-ups and medium scale prototypes up to 20 MW/m{sup 2}. During the test campaign, 26 W mock-ups and two medium scale prototypes manufactured by Plansee SE (Austria) and by Ansaldo Nucleare (Italy) have been tested at the FE200 (AREVA, Le Creusot, France) and ITER Divertor Test Facility (IDTF) (Efremov Institute Saint Petersburg, Russian Federation) electron beam test facilities. The high heat flux (HHF) testing

  2. Calculations of Temperature, Conductive Heat Flux, and Heat Wave Velocities Due to Radiant Heating of Opaque Materials

    Science.gov (United States)

    2011-11-01

    presentation and the help of Dr. Anthony Kotlar with the Mathcad calculations are greatly appreciated. vi INTENTIONALLY LEFT BLANK. 1 1. Introduction...Corporation. Mathcad 2001; Needham, MA, 2001. 4. Joseph, D. D.; Preziosi, L. Heat Waves. Rev. Modern Physics 1989, 61 (1), 41–73. 5. Cao, B-Y; Guo, Z-Y

  3. Development of a silicone ablator for high-heat-flux and high-shear-rate condition