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Sample records for vivo convective heat

  1. Convective heat transfer

    CERN Document Server

    Kakac, Sadik; Pramuanjaroenkij, Anchasa

    2014-01-01

    Intended for readers who have taken a basic heat transfer course and have a basic knowledge of thermodynamics, heat transfer, fluid mechanics, and differential equations, Convective Heat Transfer, Third Edition provides an overview of phenomenological convective heat transfer. This book combines applications of engineering with the basic concepts of convection. It offers a clear and balanced presentation of essential topics using both traditional and numerical methods. The text addresses emerging science and technology matters, and highlights biomedical applications and energy technologies. What’s New in the Third Edition: Includes updated chapters and two new chapters on heat transfer in microchannels and heat transfer with nanofluids Expands problem sets and introduces new correlations and solved examples Provides more coverage of numerical/computer methods The third edition details the new research areas of heat transfer in microchannels and the enhancement of convective heat transfer with nanofluids....

  2. Heat Convection

    Science.gov (United States)

    Jiji, Latif M.

    Professor Jiji's broad teaching experience lead him to select the topics for this book to provide a firm foundation for convection heat transfer with emphasis on fundamentals, physical phenomena, and mathematical modelling of a wide range of engineering applications. Reflecting recent developments, this textbook is the first to include an introduction to the challenging topic of microchannels. The strong pedagogic potential of Heat Convection is enhanced by the follow ing ancillary materials: (1) Power Point lectures, (2) Problem Solutions, (3) Homework Facilitator, and, (4) Summary of Sections and Chapters.

  3. Natural convection in heat-generating fluids

    International Nuclear Information System (INIS)

    Bol'shov, Leonid A; Kondratenko, Petr S; Strizhov, Valerii F

    2001-01-01

    Experimental and theoretical studies of convective heat transfer from a heat-generating fluid confined to a closed volume are reviewed. Theoretical results are inferred from analytical estimates based on the relevant conservation laws and the current understanding of the convective heat-transfer processes. Four basic and one asymptotic regime of heat transfer are identified depending on the heat generation rate. Limiting heat-transfer distribution patterns are found for the lower boundary. Heat transfer in a quasi-two-dimensional geometry is analyzed. Quasi-steady-state heat transfer from a cooling-down fluid without internal heat sources is studied separately. Experimental results and theoretical predictions are compared. (reviews of topical problems)

  4. Convection heat transfer

    CERN Document Server

    Bejan, Adrian

    2013-01-01

    Written by an internationally recognized authority on heat transfer and thermodynamics, this second edition of Convection Heat Transfer contains new and updated problems and examples reflecting real-world research and applications, including heat exchanger design. Teaching not only structure but also technique, the book begins with the simplest problem solving method (scale analysis), and moves on to progressively more advanced and exact methods (integral method, self similarity, asymptotic behavior). A solutions manual is available for all problems and exercises.

  5. Steady, three-dimensional, internally heated convection

    International Nuclear Information System (INIS)

    Schubert, G.; Glatzmaier, G.A.; Travis, B.

    1993-01-01

    Numerical calculations have been carried out of steady, symmetric, three-dimensional modes of convection in internally heated, infinite Prandtl number, Boussinesq fluids at a Rayleigh number of 1.4x10 4 in a spherical shell with inner/outer radius of 0.55 and in a 3x3x1 rectangular box. Multiple patterns of convection occur in both geometries. In the Cartesian geometry the patterns are dominated by cylindrical cold downflows and a broad hot upwelling. In the spherical geometry the patterns consist of cylindrical cold downwellings centered either at the vertices of a tetrahedron or the centers of the faces of a cube. The cold downflow cylinders are immersed in a background of upwelling within which there are cylindrical hot concentrations (plumes) and hot halos around the downflows. The forced hot upflow return plumes of internally heated spherical convection are fundamentally different from the buoyancy-driven plumes of heated from below convection

  6. Comparing convective heat fluxes derived from thermodynamics to a radiative-convective model and GCMs

    Science.gov (United States)

    Dhara, Chirag; Renner, Maik; Kleidon, Axel

    2015-04-01

    The convective transport of heat and moisture plays a key role in the climate system, but the transport is typically parameterized in models. Here, we aim at the simplest possible physical representation and treat convective heat fluxes as the result of a heat engine. We combine the well-known Carnot limit of this heat engine with the energy balances of the surface-atmosphere system that describe how the temperature difference is affected by convective heat transport, yielding a maximum power limit of convection. This results in a simple analytic expression for convective strength that depends primarily on surface solar absorption. We compare this expression with an idealized grey atmosphere radiative-convective (RC) model as well as Global Circulation Model (GCM) simulations at the grid scale. We find that our simple expression as well as the RC model can explain much of the geographic variation of the GCM output, resulting in strong linear correlations among the three approaches. The RC model, however, shows a lower bias than our simple expression. We identify the use of the prescribed convective adjustment in RC-like models as the reason for the lower bias. The strength of our model lies in its ability to capture the geographic variation of convective strength with a parameter-free expression. On the other hand, the comparison with the RC model indicates a method for improving the formulation of radiative transfer in our simple approach. We also find that the latent heat fluxes compare very well among the approaches, as well as their sensitivity to surface warming. What our comparison suggests is that the strength of convection and their sensitivity in the climatic mean can be estimated relatively robustly by rather simple approaches.

  7. Laminar Mixed Convection Heat Transfer Correlation for Horizontal Pipes

    International Nuclear Information System (INIS)

    Chae, Myeong Seon; Chung, Bum Jin

    2013-01-01

    This study aimed at producing experimental results and developing a new heat transfer correlation based upon a semi-empirical buoyancy coefficient. Mixed convection mass transfers inside horizontal pipe were investigated for the pipe of various length-to-diameters with varying Re. Forced convection correlation was developed using a very short cathode. With the length of cathode increase and Re decrease, the heat transfer rates were enhanced and becomes higher than that of forced convection. An empirical buoyancy coefficient was derived from correlation of natural convection and forced convection with the addition of L/D. And the heat transfer correlation for laminar mixed convection was developed using the buoyancy coefficient, it describes not only current results, but also results of other studies. Mixed convection occurs when the driving forces of both forced and natural convections are of comparable magnitude (Gr/Re 2 ∼1). It is classical problem but is still an active area of research for various thermal applications such as flat plate solar collectors, nuclear reactors and heat exchangers. The effect of buoyancy on heat transfer in a forced flow is varied by the direction of the buoyancy force. In a horizontal pipe the direction of the forced and buoyancy forces are perpendicular. The studies on the mixed convections of the horizontal pipes were not investigated very much due to the lack of practical uses compared to those of vertical pipes. Even the definitions on the buoyancy coefficient that presents the relative influence of the forced and the natural convections, are different by scholars. And the proposed heat transfer correlations do not agree

  8. 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

  9. 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.

  10. Unravelling convective heat transfer in the Rotated Arc Mixer

    NARCIS (Netherlands)

    Speetjens, M.F.M.; Baskan, O.; Metcalfe, G.; Clercx, H.J.H.

    2014-01-01

    Thermal homogenization is essentially a transient problem and convective heat transfer by (chaotic) advection is known to accelerate this process. Convective heat transfer traditionally is examined in terms of heat-transfer coefficients at domain walls and characterised by Nusselt relations.

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

    DEFF Research Database (Denmark)

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

    2014-01-01

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

  12. Conjugated heat transfer of natural convection in pool with internal heat sources and convection in the tube

    International Nuclear Information System (INIS)

    Li Longjian; Liu Hongtao; Cui Wenzhi

    2007-01-01

    The conjugated heat transfer of natural convection in pool with internal heat source and the forced convection in the tube was analyzed, and the corresponding three-dimensional physical and mathematical model was proposed. A control volume based finite element method was employed to solve numerically the problem. The computations were performed for different internal heat source intensity of the pool and the different flow velocity in the tube. The computed heat transfer coefficients on the inner and outer wall showed well consistency of those calculated with the empirical correlations. Compared with the measured total heat transfer coefficients between the fluids in and out of the tube, the computed ones showed also the well consistency, which implied that the numerical model proposed in this paper was reliable. The research results revealed that the total heat transfer coefficients between the fluids were strongly affected by the internal heat source intensity of the pool liquid and the flow velocity in the tube. (authors)

  13. Novel Natural Convection Heat Sink Design Concepts From First Principles

    Science.gov (United States)

    2016-06-01

    CONVECTION HEAT SINK DESIGN CONCEPTS FROM FIRST PRINCIPLES by Derek E. Fletcher June 2016 Thesis Advisor: Garth Hobson Second Reader...COVERED Master’s Thesis 4. TITLE AND SUBTITLE NOVEL NATURAL CONVECTION HEAT SINK DESIGN CONCEPTS FROM FIRST PRINCIPLES 5. FUNDING NUMBERS 6...CONVECTION HEAT SINK DESIGN CONCEPTS FROM FIRST PRINCIPLES Derek E. Fletcher Lieutenant Commander, United States Navy B.S., Southwestern

  14. Mixing in heterogeneous internally-heated convection

    Science.gov (United States)

    Limare, A.; Kaminski, E. C.; Jaupart, C. P.; Farnetani, C. G.; Fourel, L.; Froment, M.

    2017-12-01

    Past laboratory experiments of thermo chemical convection have dealt with systems involving fluids with different intrinsic densities and viscosities in a Rayleigh-Bénard setup. Although these experiments have greatly improved our understanding of the Earth's mantle dynamics, they neglect a fundamental component of planetary convection: internal heat sources. We have developed a microwave-based method in order to study convection and mixing in systems involving two layers of fluid with different densities, viscosities, and internal heat production rates. Our innovative laboratory experiments are appropriate for the early Earth, when the lowermost mantle was likely enriched in incompatible and heat producing elements and when the heat flux from the core probably accounted for a small fraction of the mantle heat budget. They are also relevant to the present-day mantle if one considers that radioactive decay and secular cooling contribute both to internal heating. Our goal is to quantify how two fluid layers mix, which is still very difficult to resolve accurately in 3-D numerical calculations. Viscosities and microwave absorptions are tuned to achieve high values of the Rayleigh-Roberts and Prandtl numbers relevant for planetary convection. We start from a stably stratified system where the lower layer has higher internal heat production and density than the upper layer. Due to mixing, the amount of enriched material gradually decreases to zero over a finite time called the lifetime. Based on more than 30 experiments, we have derived a scaling law that relates the lifetime of an enriched reservoir to the layer thickness ratio, a, to the density and viscosity contrasts between the two layers, and to their two different internal heating rates in the form of an enrichment factor beta=1+2*a*H1/H, where H1 is the heating rate of the lower fluid and H is the average heating rate. We find that the lifetime of the lower enriched reservoir varies as beta**(-7/3) in the low

  15. Primary Issues of Mixed Convection Heat Transfer Phenomena

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-10-15

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

  16. International symposium on transient convective heat transfer: book of abstracts

    International Nuclear Information System (INIS)

    1996-01-01

    The international symposium on convective heat transfer was held on 19-23 August 1996, in Cesme, Izmir, Turkey. The spesialists discussed forced convection, heat exchangers, free convection and multiphase media and phase change at the meeting. Almost 53 papers were presented in the meeting

  17. Natural convection of nanofluids over a convectively heated vertical plate embedded in a porous medium

    Energy Technology Data Exchange (ETDEWEB)

    Ghalambaz, M.; Noghrehabadi, A.; Ghanbarzadeh, A., E-mail: m.ghalambaz@gmail.com, E-mail: ghanbarzadeh.a@scu.ac.ir [Department of Mechanical Engineering, Shahid Chamran University of Ahvaz, Ahvaz (Iran, Islamic Republic of)

    2014-04-15

    In this paper, the natural convective flow of nanofluids over a convectively heated vertical plate in a saturated Darcy porous medium is studied numerically. The governing equations are transformed into a set of ordinary differential equations by using appropriate similarity variables, and they are numerically solved using the fourth-order Runge-Kutta method associated with the Gauss-Newton method. The effects of parametric variation of the Brownian motion parameter (Nb), thermophoresis parameter (Nt) and the convective heating parameter (Nc) on the boundary layer profiles are investigated. Furthermore, the variation of the reduced Nusselt number and reduced Sherwood number, as important parameters of heat and mass transfer, as a function of the Brownian motion, thermophoresis and convective heating parameters is discussed in detail. The results show that the thickness of the concentration profiles is much lower than the temperature and velocity profiles. For low values of the convective heating parameter (Nc), as the Brownian motion parameter increases, the non-dimensional wall temperature increases. However, for high values of Nc, the effect of the Brownian motion parameter on the non-dimensional wall temperature is not significant. As the Brownian motion parameter increases, the reduced Sherwood number increases and the reduced Nusselt number decreases. (author)

  18. Mixed convection heat transfer experiments using analogy concept

    International Nuclear Information System (INIS)

    Ko, Bong Jin; Chung, Bum Jin; Lee, Won Jea

    2009-01-01

    A Series of the turbulent mixed convective heat transfer experiments in a vertical cylinder was carried out. In order to achieve high Gr and/or Ra with small scale test rigs, the analogy concept was adopted. Using the concept, heat transfer systems were simulated by mass transfer systems, and large Grashof numbers could be achieved with reasonable facility heights. The tests were performed with buoyancy-aided flow and opposed flow for Reynolds numbers from 4,000 to 10,000 with a constant Grashof number, Gr H of 6.2 x 10 9 and Prandtl number of about 2,000. The test results reproduced the typical of the mixed convection heat transfer phenomena in a turbulent situation and agree well with the experimental study performed by Y. Palratan et al. The analogy experimental method simulated the mixed convection heat transfer phenomena successfully and seems to be a useful tool for heat transfer studies for VHTR as well as the systems with high buoyancy condition and high Prandtl number

  19. Experimental study of natural convective heat transfer in a vertical hexagonal sub channel

    International Nuclear Information System (INIS)

    Tandian, Nathanael P.; Umar, Efrizon; Hardianto, Toto; Febriyanto, Catur

    2012-01-01

    The development of new practices in nuclear reactor safety aspects and optimization of recent nuclear reactors, including the APWR and the PHWR reactors, needs a knowledge on natural convective heat transfer within sub-channels formed among several nuclear fuel rods or heat exchanger tubes. Unfortunately, the currently available empirical correlation equations for such heat transfer modes are limited and researches on convective heat transfer within a bundle of vertical cylinders (especially within the natural convection modes) are scarcely done. Although boundary layers around the heat exchanger cylinders or fuel rods may be dominated by their entry regions, most of available convection correlation equations are for fully developed boundary layers. Recently, an experimental study on natural convective heat transfer in a subchannel formed by several heated parallel cylinders that arranged in a hexagonal configuration has been being done. The study seeks for a new convection correlation for the natural convective heat transfer in the sub-channel formed among the hexagonal vertical cylinders. A new convective heat transfer correlation equation has been obtained from the study and compared to several similar equations in literatures.

  20. Terminal project heat convection in thin cylinders

    International Nuclear Information System (INIS)

    Morales Corona, J.

    1992-01-01

    Heat convection in thin cylinders and analysis about natural convection for straight vertical plates, and straight vertical cylinders submersed in a fluid are presented some works carry out by different authors in the field of heat transfer. In the part of conduction, deduction of the equation of heat conduction in cylindrical coordinates by means of energy balance in a control volume is presented. Enthalpy and internal energy are used for the outlining of the equation and finally the equation in its vectorial form is obtained. In the convection part development to calculate the Nusselt number for a straight vertical plate by a forces analysis, an energy balance and mass conservation over a control volume is outlined. Several empiric correlations to calculate the Nusselt number and its relations with other dimensionless numbers are presented. In the experimental part the way in which a prototype rode is assembled is presented measurements of temperatures attained in steady state and in free convection for working fluids as air and water are showed in tables. Also graphs of Nusselt numbers obtained in the experimental way through some empiric correlations are showed (Author)

  1. Combined convective heat transfer of liquid sodium flowing across tube banks

    International Nuclear Information System (INIS)

    Ma, Ying; Sugiyama, Ken-ichiro; Ishiguro, Ryoji

    1989-01-01

    In order to clarify the heat transfer characteristics of combined convection of liquid sodium, a numerical analysis is performed for liquid sodium which flows through a single horizontal row of tubes in the direction of gravity. The correlation of heat transfer characteristics between liquid sodium and ordinary fluids is also discussed. The heat transfer characteristics at large Reynolds numbers are improved when the Richardson number is increased, and the improvement rate is enlarged with increase in p/d value, since convection effect is relatively large. However heat transfer coefficients do not differ from those of forced convection at small Reynolds numbers even when the Richardson number reaches a high value because of conduction effect. A good consistence of heat transfer characteristics of combined convection between liquid sodium and air is obtained at the same Peclet number and Richardson number. This means that the fundamental heat transfer characteristics of combined convection of liquid sodium can be investigated with ordinary fluids. (author)

  2. Heat transfer of laminar mixed convection of liquid

    CERN Document Server

    Shang, De-Yi

    2016-01-01

    This book presents a new algorithm to calculate fluid flow and heat transfer of laminar mixed convection. It provides step-by-step tutorial help to learn quickly how to set up the theoretical and numerical models of laminar mixed convection, to consider the variable physical properties of fluids, to obtain the system of numerical solutions, to create a series of formalization equations for the convection heat transfer by using a curve-fitting approach combined with theoretical analysis and derivation. It presents the governing ordinary differential equations of laminar mixed convection, equivalently transformed by an innovative similarity transformation with the description of the related transformation process. A system of numerical calculations of the governing ordinary differential equations is presented for the water laminar mixed convection. A polynomial model is induced for convenient and reliable treatment of variable physical properties of liquids. The developed formalization equations of mixed convec...

  3. Natural convection heat transfer in SIGMA experiment

    International Nuclear Information System (INIS)

    Lee, Seung Dong; Lee, Gang Hee; Suh, Kune Yull

    2004-01-01

    A loss-of-coolant accident (LOCA) results in core melt formation and relocation at various locations within the reactor core over a considerable period of time. If there is no effective cooling mechanism, the core debris may heat up and commence natural circulation. The high temperature pool of molten core material will threaten the structural integrity of the reactor vessel. The extent and urgency of this threat depend primarily upon the intensity of the internal heat sources and upon the consequent distribution of the heat fluxes on the vessel walls in contact with the molten core material pools. In such a steady molten pool convection state, the thermal loads against the vessel would be determined by the in-vessel heat transfer distribution involving convective and conductive heat transfer from the decay-heated core material pool to the lower head wall in contact with the core material. In this study, upward and downward heat transfer fraction ratio is focused on

  4. Natural convection heat transfer coefficient for newborn baby - Thermal manikin assessed convective heat loses

    Science.gov (United States)

    Ostrowski, Ziemowit; Rojczyk, Marek

    2017-11-01

    The energy balance and heat exchange for newborn baby in radiant warmer environment are considered. The present study was performed to assess the body dry heat loss from an infant in radiant warmer, using copper cast anthropomorphic thermal manikin and controlled climate chamber laboratory setup. The total body dry heat losses were measured for varying manikin surface temperatures (nine levels between 32.5 °C and 40.1 °C) and ambient air temperatures (five levels between 23.5 °C and 29.7 °C). Radiant heat losses were estimated based on measured climate chamber wall temperatures. After subtracting radiant part, resulting convective heat loses were compared with computed ones (based on Nu correlations for common geometries). Simplified geometry of newborn baby was represented as: (a) single cylinder and (b) weighted sum of 5 cylinders and sphere. The predicted values are significantly overestimated relative to measured ones by: 28.8% (SD 23.5%) for (a) and 40.9% (SD 25.2%) for (b). This showed that use of adopted general purpose correlations for approximation of convective heat losses of newborn baby can lead to substantial errors. Hence, new Nu number correlating equation is proposed. The mean error introduced by proposed correlation was reduced to 1.4% (SD 11.97%), i.e. no significant overestimation. The thermal manikin appears to provide a precise method for the noninvasive assessment of thermal conditions in neonatal care.

  5. Natural convection heat transfer from a horizontal cylinder in liquid sodium. Pt. 2. Generalized correlation for laminar natural convection heat transfer

    International Nuclear Information System (INIS)

    Hata, K.; Takeuchi, Y.

    1999-01-01

    For pt.I see ibid., vol.193, p.105-18, 1999. Rigorous numerical solution of natural convection heat transfer, from a horizontal cylinder with uniform surface heat flux or with uniform surface temperature, to liquid sodium was derived by solving the fundamental equations for laminar natural convection heat transfer without the boundary layer approximation. It was made clear that the local and average Nusselt numbers experimentally obtained and reported in part 1 of this paper were described well by the numerical solutions for uniform surface heat fluxes, but that those for uniform surface temperatures could not describe the angular distribution of the local Nusselt numbers and about 10% underpredicted the average Nusselt numbers. Generalized correlation for natural convection heat transfer from a horizontal cylinder with a uniform surface heat flux in liquid metals was presented based on the rigorous theoretical values for a wide range of Rayleigh numbers. It was confirmed that the correlation can describe the authors' and other workers' experimental data on horizontal cylinders in various kinds of liquid metals for a wide range of Rayleigh numbers. Another correlation for a horizontal cylinder with a uniform surface temperature in liquid metals, which may be applicable for special cases such as natural convection heat transfer in a sodium-to-sodium heat exchanger etc. was also presented based on the rigorous theoretical values for a wide range of Rayleigh numbers. These correlations can also describe the rigorous numerical solutions for non-metallic liquids and gases for the Prandtl numbers up to 10. (orig.)

  6. Magnetically Modulated Heat Transport in a Global Simulation of Solar Magneto-convection

    Energy Technology Data Exchange (ETDEWEB)

    Cossette, Jean-Francois [Laboratory for Atmospheric and Space Physics, Campus Box 600, University of Colorado, Boulder, CO 80303 (United States); Charbonneau, Paul [Département de Physique, Université de Montréal, C.P. 6128, Succ. Centre-Ville, Montréal, QC H3C 3J7 (Canada); Smolarkiewicz, Piotr K. [European Centre for Medium-Range Weather Forecasts, Reading, RG2 9AX (United Kingdom); Rast, Mark P., E-mail: Jean-Francois.Cossette@lasp.colorado.edu, E-mail: paulchar@astro.umontreal.ca, E-mail: smolar@ecmwf.int, E-mail: Mark.Rast@lasp.colorado.edu [Department of Astrophysical and Planetary Sciences, Laboratory for Atmospheric and Space Physics, Campus Box 391, University of Colorado, Boulder, CO 80303 (United States)

    2017-05-20

    We present results from a global MHD simulation of solar convection in which the heat transported by convective flows varies in-phase with the total magnetic energy. The purely random initial magnetic field specified in this experiment develops into a well-organized large-scale antisymmetric component undergoing hemispherically synchronized polarity reversals on a 40 year period. A key feature of the simulation is the use of a Newtonian cooling term in the entropy equation to maintain a convectively unstable stratification and drive convection, as opposed to the specification of heating and cooling terms at the bottom and top boundaries. When taken together, the solar-like magnetic cycle and the convective heat flux signature suggest that a cyclic modulation of the large-scale heat-carrying convective flows could be operating inside the real Sun. We carry out an analysis of the entropy and momentum equations to uncover the physical mechanism responsible for the enhanced heat transport. The analysis suggests that the modulation is caused by a magnetic tension imbalance inside upflows and downflows, which perturbs their respective contributions to heat transport in such a way as to enhance the total convective heat flux at cycle maximum. Potential consequences of the heat transport modulation for solar irradiance variability are briefly discussed.

  7. Analysis of natural convection in volumetrically-heated melt pools

    International Nuclear Information System (INIS)

    Sehgal, B.R.; Dinh, T.N.; Nourgaliev, R.R.

    1996-12-01

    Results of series of studies on natural convection heat transfer in decay-heated core melt pools which form in a reactor lower plenum during the progression of a core meltdown accident are described. The emphasis is on modelling and prediction of turbulent heat transfer characteristics of natural convection in a liquid pool with an internal energy source. Methods of computational fluid dynamics, including direct numerical simulation, were applied for investigation

  8. Experimental transient natural convection heat transfer from a vertical cylindrical tank

    International Nuclear Information System (INIS)

    Fernandez-Seara, Jose; Uhia, Francisco J.; Alberto Dopazo, J.

    2011-01-01

    In this paper heat transfer experimental data is presented and compared to general correlations proposed in the literature for transient laminar free convection from a vertical cylindrical tank. The experimental data has been obtained from heating and cooling experiments carried out with a cylindrical full-scale hot water storage tank working under real operating conditions. The experimental device and the data acquisition system are described. The calculation procedures established to obtain the experimental values of the heat transfer coefficients, as well as the data reduction process, are detailed. The local convection and radiation heat transfer coefficients are obtained from different heating power conditions for local Rayleigh numbers within the range of 1x10 5 -3x10 8 . The great quantity of available experimental data allows a detailed analysis with a reliable empirical base. The experimental local convection heat transfer coefficients are correlated and compared to correlations proposed in open literature for engineering calculations. - Highlights: → Experimental data of transient local convection heat transfer coefficients from a cylindrical tank for heating and cooling processes is obtained. → The transient behaviour of the convection coefficients is dependent on temperature difference evolutions between the surface and the air. → The Nu.Ra -1/4 ratio decreases proportionally in (T s -T ∞ ) -0.9 . → A new correlation based on the semi-infinite region theory for laminar transient free convection is proposed.

  9. Convective heat transfer around vertical jet fires: An experimental study

    Energy Technology Data Exchange (ETDEWEB)

    Kozanoglu, Bulent, E-mail: bulentu.kozanoglu@udlap.mx [Universidad de las Americas, Puebla (Mexico); Zarate, Luis [Universidad Popular Autonoma del Estado de Puebla (Mexico); Gomez-Mares, Mercedes [Universita di Bologna (Italy); Casal, Joaquim [Universitat Politecnica de Catalunya (Spain)

    2011-12-15

    Highlights: Black-Right-Pointing-Pointer Experiments were carried out to analyze convection around a vertical jet fire. Black-Right-Pointing-Pointer Convection heat transfer is enhanced increasing the flame length. Black-Right-Pointing-Pointer Nusselt number grows with higher values of Rayleigh and Reynolds numbers. Black-Right-Pointing-Pointer In subsonic flames, Nusselt number increases with Froude number. Black-Right-Pointing-Pointer Convection and radiation are equally important in causing a domino effect. - Abstract: The convection heat transfer phenomenon in vertical jet fires was experimentally analyzed. In these experiments, turbulent propane flames were generated in subsonic as well as sonic regimes. The experimental data demonstrated that the rate of convection heat transfer increases by increasing the length of the flame. Assuming the solid flame model, the convection heat transfer coefficient was calculated. Two equations in terms of adimensional numbers were developed. It was found out that the Nusselt number attains greater values for higher values of the Rayleigh and Reynolds numbers. On the other hand, the Froude number was analyzed only for the subsonic flames where the Nusselt number grows by this number and the diameter of the orifice.

  10. Heat transfer by natural convection into an horizontal cavity

    International Nuclear Information System (INIS)

    Arevalo J, P.

    1998-01-01

    At this thesis it is studied the heat transfer by natural convection in an horizontal cavity, it is involved a boiling's part that is described the regimes and correlations differences for boiling's curve. It is designed a horizontal cavity for realize the experimental part and it's mention from equipment or instrumentation to succeed in a experimentation that permits to realize the analysis of heat transfer, handling as water fluid at atmospheric pressure and where it's present process from natural convection involving part boiling's subcooled. The system consists of heater zone submerged in a horizontal cavity with water. Once part finished experimental with information to obtained it's proceeded to obtain a correlation, realized starting from analysis dimensionless such as: Jakob, Bond and Grasoft (Boiling) besides of knows in natural convection: Prandtl and Nusselt. The mathematical model explains the behavior for natural convection continued part boiling's subcooled. It is realize analysis graphics too where it's show comparing with Globe Dropkin and Catton equations by natural convection with bottom heating. (Author)

  11. Analysis of natural convection in volumetrically-heated melt pools

    Energy Technology Data Exchange (ETDEWEB)

    Sehgal, B.R.; Dinh, T.N.; Nourgaliev, R.R. [Royal Inst. of Tech., Stockholm (Sweden). Div. of Nuclear Power Safety

    1996-12-01

    Results of series of studies on natural convection heat transfer in decay-heated core melt pools which form in a reactor lower plenum during the progression of a core meltdown accident are described. The emphasis is on modelling and prediction of turbulent heat transfer characteristics of natural convection in a liquid pool with an internal energy source. Methods of computational fluid dynamics, including direct numerical simulation, were applied for investigation. Refs, figs, tabs.

  12. Heating-insensitive scale increase caused by convective precipitation

    Science.gov (United States)

    Haerter, Jan; Moseley, Christopher; Berg, Peter

    2017-04-01

    The origin of intense convective extremes and their unusual temperature dependence has recently challenged traditional thermodynamic arguments, based on the Clausius-Clapeyron relation. In a sequence of studies (Lenderink and v. Mejgaard, Nat Geosc, 2008; Berg, Haerter, Moseley, Nat Geosc, 2013; and Moseley, Hohenegger, Berg, Haerter, Nat Geosc, 2016) the argument of convective-type precipitation overcoming the 7%/K increase in extremes by dynamical, rather than thermodynamic, processes has been promoted. How can the role of dynamical processes be approached for precipitating convective cloud? One-phase, non-precipitating Rayleigh-Bénard convection is a classical problem in complex systems science. When a fluid between two horizontal plates is sufficiently heated from below, convective rolls spontaneously form. In shallow, non-precipitating atmospheric convection, rolls are also known to form under specific conditions, with horizontal scales roughly proportional to the boundary layer height. Here we explore within idealized large-eddy simulations, how the scale of convection is modified, when precipitation sets in and intensifies in the course of diurnal solar heating. Before onset of precipitation, Bénard cells with relatively constant diameter form, roughly on the scale of the atmospheric boundary layer. We find that the onset of precipitation then signals an approximately linear (in time) increase in horizontal scale. This scale increase progresses at a speed which is rather insensitive to changes in surface temperature or changes in the rate at which boundary conditions change, hinting at spatial characteristics, rather than temperature, as a possible control on spatial scales of convection. When exploring the depth of spatial correlations, we find that precipitation onset causes a sudden disruption of order and a subsequent complete disintegration of organization —until precipitation eventually ceases. Returning to the initial question of convective

  13. Analysis of natural convection heat transfer and flows in internally heated stratified liquid pools

    International Nuclear Information System (INIS)

    Gubaidullin, A.A. Jr.; Dinh, T.N.; Sehgal, B.R.

    1999-01-01

    In this paper, natural convection flows and heat transfer in a liquid pool, with two superposed immiscible fluid layers, are analyzed. The objective of the study is to examine the effect of interfacial hydrodynamics and to develop a method which enables energy splitting to be evaluated in a stratified liquid pool. The thermal convection, with and without an internal heat source, in a rectangular cavity with different pairs of fluids was numerically simulated by a CFD code FLOW-3D. It was found that the code performs very well for prediction of heat transfer coefficients for different conditions. The hydrodynamic coupling between immiscible layers was found to have minor, if any, impact on the natural convection heat transfer for the conditions examined. Calculated results were used to develop, and validate, a new correlation for energy splitting and for heat transfer in stratified liquid pools

  14. Predictions of laminar natural convection in heated cavities

    International Nuclear Information System (INIS)

    Winters, K.H.

    1982-06-01

    Several examples of laminar, natural convection in heated cavities are discussed with illustrative calculations. These include convection in a square cavity at high Rayleigh number; in a narrow cavity at moderate aspect ratio; in a rectangular cavity heated from below; in a trapezoidal cavity, and in a rectangular cavity containing a conducting obstruction. The steady equations for the velocity, pressure and temperature are solved in the Boussinesq approximation, using a standard Galerkin formulation of the finite-element method. (author)

  15. Natural Convective Heat Transfer from Narrow Plates

    CERN Document Server

    Oosthuizen, Patrick H

    2013-01-01

    Natural Convective Heat Transfer from Narrow Plates deals with a heat transfer situation that is of significant practical importance but which is not adequately dealt with in any existing textbooks or in any widely available review papers. The aim of the book is to introduce the reader to recent studies of natural convection from narrow plates including the effects of plate edge conditions, plate inclination, thermal conditions at the plate surface and interaction of the flows over adjacent plates. Both numerical and experimental studies are discussed and correlation equations based on the results of these studies are reviewed.

  16. Experimental investigation of natural convection heat transfer in volumetrically heated spherical segments. Final report

    International Nuclear Information System (INIS)

    Asfia, F.; Dhir, V.

    1998-03-01

    One strategy for preventing the failure of lower head of a nuclear reactor vessel is to flood the concrete cavity with subcooled water in accidents in which relocation of core material into the vessel lower head occurs. After the core material relocates into the vessel, a crust of solid material forms on the inner wall of the vessel, however, most of the pool remains molten and natural convection exists in the pool. At present, uncertainty exists with respect to natural convection heat transfer coefficients between the pool of molten core material and the reactor vessel wall. In the present work, experiments were conducted to examine natural convection heat transfer in internally heated partially filled spherical pools with external cooling. In the experiments, Freon-113 contained in a Pyrex bell jar was used as a test liquid. The pool was bounded with a spherical segment at the bottom, and was heated with magnetrons taken from a conventional microwave oven. The vessel was cooled from the outside with natural convection of water or with nucleate boiling of liquid nitrogen

  17. The role of the velocity gradient in laminar convective heat transfer through a tube with a uniform wall heat flux

    International Nuclear Information System (INIS)

    Wang Liangbi; Zhang Qiang; Li Xiaoxia

    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 conservation equation of convective heat transfer is used to explain convective heat transfer there are two points that are difficult for teachers to explain and for undergraduates to understand: thermal diffusivity is placed before the Laplacian operator of temperature; on the wall surface (the fluid side) the velocity is zero, a diffusion equation of temperature is gained from energy conservation equation, however, temperature cannot be transported. Consequently, the real physical meaning of thermal diffusivity is not clearly reflected in the energy conservation equation, and whether heat transfer occurs through a diffusion process or a convection process on the wall surface is not clear. Through a simple convective heat transfer case: laminar convective heat transfer in a tube with a uniform wall heat flux on the tube wall, this paper explains these points more clearly. The results declare that it is easier for teachers to explain and for undergraduates to understand these points when a description of heat transfer in terms of the heat flux is used. In this description, thermal diffusivity is placed before the Laplacian operator of the heat flux; the role of the velocity gradient in convective heat transfer appears, on the wall surface, the fact whether heat transfer occurs through a diffusion process or a convection process can be explained and understood easily. The results are not only essential for teachers to improve the efficiency of university-level physics education regarding heat transfer, but they also enrich the theories for understanding heat transfer

  18. Heat transfer in melt ponds with convection and radiative heating: observationally-inspired modelling

    Science.gov (United States)

    Wells, A.; Langton, T.; Rees Jones, D. W.; Moon, W.; Kim, J. H.; Wilkinson, J.

    2016-12-01

    Melt ponds have key impacts on the evolution of Arctic sea ice and summer ice melt. Small changes to the energy budget can have significant consequences, with a net heat-flux perturbation of only a few Watts per square metre sufficient to explain the thinning of sea ice over recent decades. Whilst parameterisations of melt-pond thermodynamics often assume that pond temperatures remain close to the freezing point, recent in-situ observations show more complex thermal structure with significant diurnal and synoptic variability. We here consider the energy budget of melt ponds and explore the role of internal convective heat transfer in determining the thermal structure within the pond in relatively calm conditions with low winds. We quantify the energy fluxes and temperature variability using two-dimensional direct numerical simulations of convective turbulence within a melt pond, driven by internal radiative heating and surface fluxes. Our results show that the convective flow dynamics are modulated by changes to the incoming radiative flux and sensible heat flux at the pond surface. The evolving pond surface temperature controls the outgoing longwave emissions from the pond. Hence the convective flow modifies the net energy balance of a melt pond, modulating the relative fractions of the incoming heat flux that is re-emitted to the atmosphere or transferred downward into the sea ice to drive melt.

  19. Heat convection in a set of three vertical cylinders

    International Nuclear Information System (INIS)

    Serrano Ramirez, M.L. de.

    1993-01-01

    Experimental results on temperature and heat flow in a set of three vertical cylinders with internal generation of heat, water submerged and in free convection are presented in this work . Temperature distribution, Nusselt number and convective coefficient (h) for each rod, developed for the distance between the axis of cylinders in vertical position, as a consequence of the application of power in its outside, are analyzed. Experimental information about heat transfer by free convection in vertical cylinders and surfaces is analyzed. Information of the several author who have carried out studies about the heat transfer on vertical cylinders was compiled, and the proposed equations with the experimental data obtained in the thermo fluids laboratory of National Institute of Nuclear Research (ININ) were tested. The way in which separation distance, s, distribution temperature array, Nusselt number, and convective coefficient calculated for the proposed channel with the Keyhani, Dutton and experimental equations are tabulated and they are plotted for each power value and for each separation between rods. The scheme of the used equipment and the experimentation description as well as the observations of tests and graphical results are included. (Author)

  20. Heat Transfer Correlations for Free Convection from Suspended Microheaters

    Directory of Open Access Journals (Sweden)

    David GOSSELIN

    2016-08-01

    Full Text Available Portability and autonomy for biomedical diagnostic devices are two rising requirements. It is recognized that low-energy heating of such portable devices is of utmost importance for molecular recognition. This work focuses on screen-printed microheaters based on on Joule effect, which constitute an interesting solution for low-energy heating. An experimental study of the natural convection phenomena occurring with such microheaters is conducted. When they are suspended in the air, and because of the thinness of the supporting film, it is shown that the contributions of both the upward and downward faces have to be taken into account. A total Nusselt number and a total convective heat transfer coefficient have been used to describe the natural convection around these microheaters. In addition a relation between the Nusselt number and the Rayleigh number is derived, leading to an accurate prediction of the heating temperature (MRE< 2 %.

  1. Heat transfer measurements of internally heated liquids in cylindrical convection cells

    International Nuclear Information System (INIS)

    Fieg, G.

    1978-10-01

    In hypothetical reactor accidents, the thermohydraulic behaviour of core melts heated by the after-heat must be analyzed. For this purpose model experiments have been performed to study the stationary, natural convective heat transfer of internally heated fluids in cylindrical convertion cells investigating also the influence of geometry (aspect ratio) as well as of difference thermal wall conditions on to the heat transport characteristics. Axial temperature profiles, local heat flux densities at the vertical walls and their dependence, on the external Rayleigh number ar in detail reported, besides the Nusselt vs Rayleigh correlations for the aspect ratios HID=1 and 0,25. The results of these experiments are compared, as for ar possible, with existing thermohydraulic codes and simpler model asoumptions like the zone-model of Baker et. al. and after experimental verification, be used to study realistic PAHR situations. Velocity measurements by means of Laser-Doppler-Method yield information about the flow characteristics near the vertical walls and within the central part of the convecting fluid. (GL) [de

  2. Open Channel Natural Convection Heat Transfer on a Vertical Finned Plate

    International Nuclear Information System (INIS)

    Park, Joo Hyun; Heo, Jeong Hwan; Chung, Bum Jin

    2013-01-01

    The natural convection heat transfer of vertical plate fin was investigated experimentally. Heat transfer systems were replaced by mass-transfer systems, based on the analogy concept. The experimental results lie within the predictions of the existing heat transfer correlations of plate-fin for the natural convections. An overlapped thermal boundary layers caused increasing heat transfer, and an overlapped momentum boundary layers caused decreasing heat transfer. As the fin height increases, heat transfer was enhanced due to increased inflow from the open side of the fin spacing. When fin spacing and fin height are large, heat transfer was unaffected by the fin spacing and fin height. Passive cooling by natural convection becomes more and more important for the nuclear systems as the station black out really happened at the Fukushima NPPs. In the RCCS (Reactor Cavity Cooling System) of a VHTR (Very High Temperature Reactor), natural convection cooling through duct system is adopted. In response to the stack failure event, extra cooling capacity adopting the fin array has to be investigated. The finned plate increases the surface area and the heat transfer increases. However, the plate of fin arrays may increase the pressure drop and the heat transfer decreases. Therefore, in order to enhance the passive cooling with fin arrays, the parameters for the fin arrays should be optimized. According to Welling and Wooldridge, a natural convection on vertical plate fin is function of Gr, Pr, L, t, S, and H. The present work investigated the natural convection heat transfer of a vertical finned plate with varying the fin height and the fin spacing. In order achieve high Rayleigh numbers, an electroplating system was employed and the mass transfer rates were measured using a copper sulfate electroplating system based on the analogy concept

  3. Experimental evaluation on natural convection heat transfer of microencapsulated phase change materials slurry in a rectangular heat storage tank

    International Nuclear Information System (INIS)

    Zhang Yanlai; Rao Zhonghao; Wang Shuangfeng; Zhang Zhao; Li Xiuping

    2012-01-01

    Highlights: ► It gives heat transfer characteristics in a rectangular heat storage tank as the basic unit for reservoir of thermal storage. ► Onset of natural convection gets easier for the MPCMS with a higher mass concentration. ► It enhances the heat transfer ability of natural convection for the MPCMS. ► Obtained the relationship between Ra and Nu of the MPCMS. - Abstract: The main purpose of this experiment is to evaluate natural convection heat transfer characteristics of microencapsulated PCM (phase change material) slurry (MPCMS) during phase change process in a rectangular heat storage tank heated from the bottom and cooled at the top. The microencapsulated PCM is several material compositions of n-paraffin waxes (mainly nonadecane) as the core materials, outside a layer of a melamine resin wrapped. In the present study, its slurry is used mixing with water. And the specific heat capacity with latent heat shows a peak value at the temperature of about T = 31 °C. We investigate the influences of the phase change process of the MPCMS on natural convection heat transfer. The experimental results indicate that phase change process of the MPCMS promote natural convection heat transfer. The local maximum heat transfer enhancement occurs at approximately T H = 34 °C corresponding to the heated plate temperature. With high mass concentration C m , the onset of natural convection gets easier for the MPCMS. The temperature gradient is larger near top plate and bottom plate of a rectangular heat storage tank. Heat transfer coefficient increases with the phase change of the PCM. And it summarizes that the phase change process of the PCM promote the occurrence of natural convection.

  4. Natural convection heat transfer in a rectangular pool with volumetric heat sources

    International Nuclear Information System (INIS)

    Lee, Seung Dong; Lee, Kang Hee; Suh, Kune Y.

    2003-01-01

    Natural convection plays an important role in determining the thermal load from debris accumulated in the reactor vessel lower head during a severe accident. The heat transfer within the molten core material can be characterized by buoyancy-induced flows resulting from internal heating due to decay of fission products. The thermo-fluid dynamic characteristics of the molten pool depend strongly on the thermal boundary conditions. The spatial and temporal variation of heat flux on the pool wall boundaries and the pool superheat are mainly characterized by the natural convection flow inside the molten pool. In general, natural convection involving internal heat generation is delineated in terms of the modified Rayleigh number, Ra', which quantifies the internal heat source and hence the strength of buoyancy. The test section is of rectangular cavity whose length, width, and height are 500 mm, 80 mm, and 250 mm, respectively. A total of twenty-four T-type thermocouples were installed in the test loop to measure temperature distribution. Four T-type thermocouples were utilized to measure temperatures on the boundary. A direct heating method was adopted in this test to simulate the uniform heat generation. The experiments covered a range of Rayleigh number, Ra, between 4.87x10 7 and 2.32x10 14 and Prandtl number, Pr, between 0.7 and 3.98. Tests were conducted with water and air as simulant. The upper and lower boundary conditions were maintained at a uniform temperature of 10degC. (author)

  5. Natural convection heat transfer in the molten metal pool

    International Nuclear Information System (INIS)

    Park, R.J.; Kim, S.B.; Kim, H.D.; Choi, S.M.

    1997-01-01

    Analytical studies using the FLOW-3D computer program have been performed on natural convection heat transfer of a high density molten metal pool, in order to evaluate the coolability of the corium pool. The FLOW-3D results on the temperature distribution and the heat transfer rate in the molten metal pool region have been compared and evaluated with the experimental data. The FLOW-3D results have shown that the developed natural convection flow contributes to the solidified crust formation of the high density molten metal pool. The present FLOW-3D results, on the relationship between the Nusselt number and the Rayleigh number in the molten metal pool region, are more similar to the calculated results of Globe and Dropkin's correlation than any others. The natural convection heat transfer in the low aspect ratio case is more substantial than that in the high aspect ratio case. The FLOW-3D results, on the temperature profile and on the heat transfer rate in the molten metal pool region, are very similar to the experimental data. The heat transfer rate of the internal heat generation case is higher than that of the bottom heating case at the same heat supply condition. (author)

  6. Tests for removal of decay heat by natural convection

    International Nuclear Information System (INIS)

    Kashiwagi, E.; Wataru, M.; Gomi, Y.; Hattori, Y.; Ozaki, S.

    1993-01-01

    Interim storage technology for spent fuel by dry storage casks have been investigated. The casks are vertically placed in a storage building. The decay heat is removed from the outer cask surface by natural convection of air entering from the building wall to the roof. The air flow pattern in the storage building was governed by the natural driving pressure difference and circulating flow. The purpose of this study is to understand the mechanism of the removal of decay heat from casks by natural convection. The simulated flow conditions in the building were assumed as a natural and forced combined convection and were investigated by the turbulent quantities near wall. (author)

  7. Turbulent mixed convection in asymmetrically heated vertical channel

    Directory of Open Access Journals (Sweden)

    Mokni Ameni

    2012-01-01

    Full Text Available In this paper an investigation of mixed convection from vertical heated channel is undertaken. The aim is to explore the heat transfer obtained by adding a forced flow, issued from a flat nozzle located in the entry section of a channel, to the up-going fluid along its walls. Forced and free convection are combined studied in order to increase the cooling requirements. The study deals with both symmetrically and asymmetrically heated channel. The Reynolds number based on the nozzle width and the jet velocity is assumed to be 3 103 and 2.104; whereas, the Rayleigh number based on the channel length and the wall temperature difference varies from 2.57 1010 to 5.15 1012. The heating asymmetry effect on the flow development including the mean velocity and temperature the local Nusselt number, the mass flow rate and heat transfer are examined.

  8. Characterizing convective heat transfer using infrared thermography and the heated-thin-foil technique

    International Nuclear Information System (INIS)

    Stafford, Jason; Walsh, Ed; Egan, Vanessa

    2009-01-01

    Convective heat transfer, due to axial flow fans impinging air onto a heated flat plate, is investigated with infrared thermography to assess the heated-thin-foil technique commonly used to quantify two-dimensional heat transfer performance. Flow conditions generating complex thermal profiles have been considered in the analysis to account for dominant sources of error in the technique. Uncertainties were obtained in the measured variables and the influences on the resultant heat transfer data are outlined. Correction methods to accurately account for secondary heat transfer mechanisms were developed and results show that as convective heat transfer coefficients and length scales decrease, the importance of accounting for errors increases. Combined with flow patterns that produce large temperature gradients, the influence of heat flow within the foil on the resultant heat transfer becomes significant. Substantial errors in the heat transfer coefficient are apparent by neglecting corrections to the measured data for the cases examined. Methods to account for these errors are presented here, and demonstrated to result in an accurate measurement of the local heat transfer map on the surface

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

    International Nuclear Information System (INIS)

    Abou-Ziyan, Hosny Z.

    2004-01-01

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

  10. Forced convection heat transfer in He II

    International Nuclear Information System (INIS)

    Kashani, A.

    1986-01-01

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

  11. Modeling the overall heat conductive and convective properties of open-cell graphite foam

    International Nuclear Information System (INIS)

    Tee, C C; Yu, N; Li, H

    2008-01-01

    This work develops analytic models on the overall thermal conductivity, pressure drop and overall convective heat transfer coefficient of graphite foam. The models study the relationship between the overall heat conductive and convective properties, and foam microstructure, temperature, foam surface friction characteristics and cooling fluid properties. The predicted thermal conductivity, convective heat transfer coefficient and pressure drop agree well with experimental data

  12. 10,000 - A reason to study granular heat convection

    Energy Technology Data Exchange (ETDEWEB)

    Einav, I.; Rognon, P.; Gan, Y.; Miller, T.; Griffani, D. [Particles and Grains Laboratory, School of Civil Engineering, University of Sydney, Sydney, NSW 2006 (Australia)

    2013-06-18

    In sheared granular media, particle motion is characterized by vortex-like structures; here this is demonstrated experimentally for disks system undergoing indefinite deformation during simple shear, as often imposed by the rock masses hosting earthquake fault gouges. In traditional fluids it has been known for years that vortices represent a major factor of heat transfer enhancement via convective internal mixing, but in analyses of heat transfer through earthquake faults and base planes of landslides this has been continuously neglected. Can research proceed by neglecting heat convection by internal mixing? Our answer is astonishingly far from being yes.

  13. Sunspots and the physics of magnetic flux tubes. VI - Convective propulsion. VII - Heat flow in a convective downdraft

    Science.gov (United States)

    Parker, E. N.

    1979-01-01

    The effect of negative aerodynamic drag in an ideal fluid subject to convective instability is considered. It is shown that a cylinder moving in such a fluid is propelled forward in its motion by the convective forces and that the characteristic acceleration time is comparable to the onset time of convective motions in the fluid. It is suggested that convective propulsion plays an important role in the dynamics of flux tubes extending through the surface of the sun. The suppression of the upward heat flow in a Boussinesq convective cell with free upper and lower boundaries by a downdraft is then analyzed. Application to the solar convection zone indicates that downdrafts of 1 to 2 km/s at depths of 1000 to 4000 km beneath the visible surface of the sun are sufficient to reduce the upward heat flux to a small fraction of the ambient value.

  14. Single-phase convective heat transfer in rod bundles

    International Nuclear Information System (INIS)

    Holloway, Mary V.; Beasley, Donald E.; Conner, Michael E.

    2008-01-01

    The convective heat transfer for turbulent flow through rod bundles representative of nuclear fuel rods used in pressurized water reactors is examined. The rod bundles consist of a square array of parallel rods that are held on a constant pitch by support grids spaced axially along the rod bundle. Split-vane pair support grids, which create swirling flow in the rod bundle, as well as disc and standard support grids are investigated. Single-phase convective heat transfer coefficients are measured for flow downstream of support grids in a rod bundle. The rods are heated using direct resistance heating, and a bulk axial flow of air is used to cool the rods in the rod bundle. Air is used as the working fluid instead of water to reduce the power required to heat the rod bundle. Results indicate heat transfer enhancement for up to 10 hydraulic diameters downstream of the support grids. A general correlation is developed to predict the heat transfer development downstream of support grids. In addition, circumferential variations in heat transfer coefficients result in hot streaks that develop on the rods downstream of split-vane pair support grids

  15. Single-phase convective heat transfer in rod bundles

    Energy Technology Data Exchange (ETDEWEB)

    Holloway, Mary V. [Mechanical Engineering Department, United States Naval Academy, 590 Holloway Rd., Annapolis, MD 21402 (United States)], E-mail: holloway@usna.edu; Beasley, Donald E. [Mechanical Engineering Department, Clemson University, Clemson, SC 29634 (United States); Conner, Michael E. [Westinghouse Nuclear Fuel, 5801 Bluff Road, Columbia, SC 29250 (United States)

    2008-04-15

    The convective heat transfer for turbulent flow through rod bundles representative of nuclear fuel rods used in pressurized water reactors is examined. The rod bundles consist of a square array of parallel rods that are held on a constant pitch by support grids spaced axially along the rod bundle. Split-vane pair support grids, which create swirling flow in the rod bundle, as well as disc and standard support grids are investigated. Single-phase convective heat transfer coefficients are measured for flow downstream of support grids in a rod bundle. The rods are heated using direct resistance heating, and a bulk axial flow of air is used to cool the rods in the rod bundle. Air is used as the working fluid instead of water to reduce the power required to heat the rod bundle. Results indicate heat transfer enhancement for up to 10 hydraulic diameters downstream of the support grids. A general correlation is developed to predict the heat transfer development downstream of support grids. In addition, circumferential variations in heat transfer coefficients result in hot streaks that develop on the rods downstream of split-vane pair support grids.

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

    Energy Technology Data Exchange (ETDEWEB)

    Bhattacharyya, A

    1965-03-15

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

  17. Analysis of a convection loop for GFR post-LOCA decay heat removal

    International Nuclear Information System (INIS)

    Williams, W.C.; Hejzlar, P.; Saha, P.

    2004-01-01

    A computer code (LOCA-COLA) has been developed at MIT for steady state analysis of convective heat transfer loops. In this work, it is used to investigate an external convection loop for decay heat removal of a post-LOCA gas-cooled fast reactor (GFR). The major finding is that natural circulation cooling of the GFR is feasible under certain circumstances. Both helium and CO 2 cooled system components are found to operate in the mixed convection regime, the effects of which are noticeable as heat transfer enhancement or degradation. It is found that CO 2 outdoes helium under identical natural circulation conditions. Decay heat removal is found to have a quadratic dependence on pressure in the laminar flow regime and linear dependence in the turbulent flow regime. Other parametric studies have been performed as well. In conclusion, convection cooling loops are a credible means for GFR decay heat removal and LOCA-COLA is an effective tool for steady state analysis of cooling loops. (authors)

  18. Mechanisms of convective and boiling heat transfer enhancement via ultrasonic vibration

    International Nuclear Information System (INIS)

    Kim, Yi Gu; Kim, Ho Young; Kang, Seoung Min; Kang, Byung Ha; Lee, Jin Ho

    2003-01-01

    This work experimentally studies the fundamental mechanisms by which the ultrasonic vibration enhances convection and pool boiling heat transfer. A thin platinum wire is used as both a heat source and a temperature sensor. A high speed video imaging system is employed to observe the behavior of cavitation and thermal bubbles. It is found that when the liquid temperature is below its boiling point, cavitation takes place due to ultrasonic vibration while cavitation disappears when the liquid reaches the boiling point. Moreover, when the gas dissolved in liquid is removed by pre-degassing, the cavitation arises only locally. Depending on the liquid temperature, heat transfer rates in convection, subcooled boiling and saturated boiling regimes are examined. In convection heat transfer regime, fully agitated cavitation is the most efficient heat transfer enhancement mechanism. Subcooled boiling is most enhanced when the local cavitation is induced after degassing. In saturated boiling regime, acoustic pressure is shown to be a dominant heat transfer enhancement mechanism

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

    International Nuclear Information System (INIS)

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

    1999-01-01

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

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

    International Nuclear Information System (INIS)

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

    1987-01-01

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

  1. Solution of heat removal from nuclear reactors by natural convection

    Directory of Open Access Journals (Sweden)

    Zitek Pavel

    2014-03-01

    Full Text Available This paper summarizes the basis for the solution of heat removal by natural convection from both conventional nuclear reactors and reactors with fuel flowing coolant (such as reactors with molten fluoride salts MSR.The possibility of intensification of heat removal through gas lift is focused on. It might be used in an MSR (Molten Salt Reactor for cleaning the salt mixture of degassed fission products and therefore eliminating problems with iodine pitting. Heat removal by natural convection and its intensification increases significantly the safety of nuclear reactors. Simultaneously the heat removal also solves problems with lifetime of pumps in the primary circuit of high-temperature reactors.

  2. Numerical Investigation of Turbulent Natural Convection Heat Transfer in an Internally-Heated Melt Pool and Metallic Layer

    International Nuclear Information System (INIS)

    Nourgaliev, R.R.; Dinh, A.T.; Dinh, T.N.; Sehgal, B.R.

    1999-01-01

    This paper presents results of numerical investigation of turbulent natural convection in an internally-heated oxidic pool, and in a metallic layer heated from below and cooled from top and sidewalls. Emphasis is placed upon applicability of the existing heat transfer correlations (obtained from simulant-material experiments) in assessments of a prototypic severe reactor accident. The objectives of this study are (i) to improve the current understanding of the physics of unstably stratified flows, and (ii) to reduce uncertainties associated with modeling and assessment of natural convection heat transfer in the above configuration. Prediction capabilities of different turbulence modeling approaches are first examined and discussed, based on extensive results of numerical investigations performed by present authors. Findings from numerical modeling of turbulent natural convection flow and heat transfer in melt pools and metallic layers are then described. (authors)

  3. Heat and momentum transport scalings in vertical convection

    Science.gov (United States)

    Shishkina, Olga

    2016-11-01

    For vertical convection, where a fluid is confined between two differently heated isothermal vertical walls, we investigate the heat and momentum transport, which are measured, respectively, by the Nusselt number Nu and the Reynolds number Re . For laminar vertical convection we derive analytically the dependence of Re and Nu on the Rayleigh number Ra and the Prandtl number Pr from our boundary layer equations and find two different scaling regimes: Nu Pr 1 / 4 Ra 1 / 4 , Re Pr - 1 / 2 Ra 1 / 2 for Pr > 1 . Direct numerical simulations for Ra from 105 to 1010 and Pr from 0.01 to 30 are in excellent ageement with our theoretical findings and show that the transition between the regimes takes place for Pr around 0.1. We summarize the results from and present new theoretical and numerical results for transitional and turbulent vertical convection. The work is supported by the Deutsche Forschungsgemeinschaft (DFG) under the Grant Sh 405/4 - Heisenberg fellowship.

  4. Natural convection heat transfer of fluid with temperature-dependent specific heat

    International Nuclear Information System (INIS)

    Tanaka, Amane; Kubo, Shinji; Akino, Norio

    1998-01-01

    The present study investigates natural convection from a heated vertical plate of fluid with temperature-dependent specific heat, which is introduced as a model of microencapsulated phase change material slurries (MCPCM slurries). The temperature dependence of specific heat is represented by Gauss function with three physical parameters (peak temperature, width of phase change temperature and latent heat). Boundary layer equations are solved numerically, and the velocity and temperature fields of the flow are obtained. The relation between the heat transfer coefficients and the physical parameters of specific heat is discussed. The results show that the velocities and temperatures are smaller, and the heat transfer coefficients are larger comparing with those of the fluid with constant specific heat. (author)

  5. Methods for characterizing convective cryoprobe heat transfer in ultrasound gel phantoms.

    Science.gov (United States)

    Etheridge, Michael L; Choi, Jeunghwan; Ramadhyani, Satish; Bischof, John C

    2013-02-01

    While cryosurgery has proven capable in treating of a variety of conditions, it has met with some resistance among physicians, in part due to shortcomings in the ability to predict treatment outcomes. Here we attempt to address several key issues related to predictive modeling by demonstrating methods for accurately characterizing heat transfer from cryoprobes, report temperature dependent thermal properties for ultrasound gel (a convenient tissue phantom) down to cryogenic temperatures, and demonstrate the ability of convective exchange heat transfer boundary conditions to accurately describe freezing in the case of single and multiple interacting cryoprobe(s). Temperature dependent changes in the specific heat and thermal conductivity for ultrasound gel are reported down to -150 °C for the first time here and these data were used to accurately describe freezing in ultrasound gel in subsequent modeling. Freezing around a single and two interacting cryoprobe(s) was characterized in the ultrasound gel phantom by mapping the temperature in and around the "iceball" with carefully placed thermocouple arrays. These experimental data were fit with finite-element modeling in COMSOL Multiphysics, which was used to investigate the sensitivity and effectiveness of convective boundary conditions in describing heat transfer from the cryoprobes. Heat transfer at the probe tip was described in terms of a convective coefficient and the cryogen temperature. While model accuracy depended strongly on spatial (i.e., along the exchange surface) variation in the convective coefficient, it was much less sensitive to spatial and transient variations in the cryogen temperature parameter. The optimized fit, convective exchange conditions for the single-probe case also provided close agreement with the experimental data for the case of two interacting cryoprobes, suggesting that this basic characterization and modeling approach can be extended to accurately describe more complicated

  6. Natural convective heat transfer from square cylinder

    Energy Technology Data Exchange (ETDEWEB)

    Novomestský, Marcel, E-mail: marcel.novomestsky@fstroj.uniza.sk; Smatanová, Helena, E-mail: helena.smatanova@fstroj.uniza.sk; Kapjor, Andrej, E-mail: andrej.kapjor@fstroj.uniza.sk [University of Žilina, Faculty of Mechanical Engineering, Department of Power Engineering, Univerzitná 1, 010 26 Žilina (Slovakia)

    2016-06-30

    This article is concerned with natural convective heat transfer from square cylinder mounted on a plane adiabatic base, the cylinders having an exposed cylinder surface according to different horizontal angle. The cylinder receives heat from a radiating heater which results in a buoyant flow. There are many industrial applications, including refrigeration, ventilation and the cooling of electrical components, for which the present study may be applicable.

  7. New external convective heat transfer coefficient correlations for isolated low-rise buildings

    Energy Technology Data Exchange (ETDEWEB)

    Emmel, M. G.; Mendes, N. [Pontifical Catholic University of Parana, PUCPR/CCET, Thermal Systems Laboratory, LST, Curitiba (Brazil); Abadie, M. O. [Pontifical Catholic University of Parana, PUCPR/CCET, Thermal Systems Laboratory, LST, Curitiba (Brazil); Laboratoire d' Etude des Phenomenes de Transfert Appliques au batiment (LEPTAB), University of La Rochelle, La Rochelle (France)

    2007-07-01

    Building energy analyses are very sensitive to external convective heat transfer coefficients so that some researchers have conducted sensitivity calculations and proved that depending on the choice of those coefficients, energy demands estimation values can vary from 20% to 40%. In this context, computational fluid dynamics calculations have been performed to predict convective heat transfer coefficients at the external surfaces of a simple shape low-rise building. Effects of wind velocity and orientation have been analyzed considering four surface-to-air temperature differences. Results show that the convective heat transfer coefficient value strongly depends on the wind velocity, that the wind direction has a notable effect for vertical walls and for roofs and that the surface-to-air temperature difference has a negligible effect for wind velocity higher than 2 m/s. External convective heat transfer coefficient correlations are provided as a function of the wind free stream velocity and wind-to-surface angle. (author)

  8. Optimization of fin geometry in heat convection with entransy theory

    International Nuclear Information System (INIS)

    Cheng Xue-Tao; Xu Xiang-Hua; Liang Xin-Gang; Zhang Qin-Zhao

    2013-01-01

    The entransy theory developed in recent years is used to optimize the aspect ratio of a plate fin in heat convection. Based on a two-dimensional model, the theoretical analysis shows that the minimum thermal resistance defined with the concept of entransy dissipation corresponds to the maximum heat transfer rate when the temperature of the heating surface is fixed. On the other hand, when the heat flux of the heating surface is fixed, the minimum thermal resistance corresponds to the minimum average temperature of the heating surface. The entropy optimization is also given for the heat transfer processes. It is observed that the minimum entropy generation, the minimum entropy generation number, and the minimum revised entropy generation number do not always correspond to the best heat transfer performance. In addition, the influence factors on the optimized aspect ratio of the plate fin are also discussed. The optimized ratio decreases with the enhancement of heat convection, while it increases with fin thermal conductivity increasing. (general)

  9. Heat transfer in a one-dimensional mixed convection loop

    International Nuclear Information System (INIS)

    Kim, Min Joon; Lee, Yong Bum; Kim, Yong Kyun; Kim, Jong Man; Nam, Ho Yun

    1999-01-01

    Effects of non-uniform heating in the core and additional forced circulation during decay heat removal operation are studied with a simplified mixed convection loop. The heat transfer coefficient is calculated analytically and measured experimentally. The analytic solution obtained from a one-dimensional heat equation is found to agree well with the experimental results. The effects of the non-uniform heating and the forced circulation are discussed

  10. Conjugate Problems in Convective Heat Transfer: Review

    Directory of Open Access Journals (Sweden)

    Abram Dorfman

    2009-01-01

    Full Text Available A review of conjugate convective heat transfer problems solved during the early and current time of development of this modern approach is presented. The discussion is based on analytical solutions of selected typical relatively simple conjugate problems including steady-state and transient processes, thermal material treatment, and heat and mass transfer in drying. This brief survey is accompanied by the list of almost two hundred publications considering application of different more and less complex analytical and numerical conjugate models for simulating technology processes and industrial devices from aerospace systems to food production. The references are combined in the groups of works studying similar problems so that each of the groups corresponds to one of selected analytical solutions considered in detail. Such structure of review gives the reader the understanding of early and current situation in conjugate convective heat transfer modeling and makes possible to use the information presented as an introduction to this area on the one hand, and to find more complicated publications of interest on the other hand.

  11. Heat-transfer correlations for natural convection boiling

    International Nuclear Information System (INIS)

    Stephan, K.; Abdelsalam, M.

    1980-01-01

    To-date there exists no comprehensive theory allowing the prediction of heat-transfer coefficients in natural convection boiling, in spite of the many efforts made in this field. In order to establish correlations with wide application, the methods of regression analysis were applied to the nearly 500 existing experimental data points for natural convection boiling heat transfer. As demonstrated by the analysis, these data can best be represented by subdividing the substances into four groups (water, hydrocarbons, cryogenic fluids and refrigerants) and employing a different set of dimensionless numbers for each group of substances, because certain dimensionless numbers important for one group of substances are unimportant to another. One equation valid for all substances could be built up, but its accuracy would be less than that obtained for the individual correlations without adding undesirable complexity. (author)

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

    International Nuclear Information System (INIS)

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

    2014-01-01

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

  13. Free surface deformation and heat transfer by thermocapillary convection

    Science.gov (United States)

    Fuhrmann, Eckart; Dreyer, Michael; Basting, Steffen; Bänsch, Eberhard

    2016-04-01

    Knowing the location of the free liquid/gas surface and the heat transfer from the wall towards the fluid is of paramount importance in the design and the optimization of cryogenic upper stage tanks for launchers with ballistic phases, where residual accelerations are smaller by up to four orders of magnitude compared to the gravity acceleration on earth. This changes the driving forces drastically: free surfaces become capillary dominated and natural or free convection is replaced by thermocapillary convection if a non-condensable gas is present. In this paper we report on a sounding rocket experiment that provided data of a liquid free surface with a nonisothermal boundary condition, i.e. a preheated test cell was filled with a cold but storable liquid in low gravity. The corresponding thermocapillary convection (driven by the temperature dependence of the surface tension) created a velocity field directed away from the hot wall towards the colder liquid and then in turn back at the bottom towards the wall. A deformation of the free surface resulting in an apparent contact angle rather different from the microscopic one could be observed. The thermocapillary flow convected the heat from the wall to the liquid and increased the heat transfer compared to pure conduction significantly. The paper presents results of the apparent contact angle as a function of the dimensionless numbers (Weber-Marangoni and Reynolds-Marangoni number) as well as heat transfer data in the form of a Nusselt number. Experimental results are complemented by corresponding numerical simulations with the commercial software Flow3D and the inhouse code Navier.

  14. Developing mixed convection in a coiled heat exchanger

    NARCIS (Netherlands)

    Sillekens, J.J.M.; Rindt, C.C.M.; Steenhoven, van A.A.

    1998-01-01

    In this paper the development of mixed convection in a helically coiled heat exchanger for Re = 500, Pr = 5 and d = 1/14 is studied. The influence of buoyancy forces (Gr = ¢O (105)) on heat transfer and secondary flow is analyzed. In the method used the parabolized equations are solved using a

  15. Modified Laser Flash Method for Thermal Properties Measurements and the Influence of Heat Convection

    Science.gov (United States)

    Lin, Bochuan; Zhu, Shen; Ban, Heng; Li, Chao; Scripa, Rosalia N.; Su, Ching-Hua; Lehoczky, Sandor L.

    2003-01-01

    The study examined the effect of natural convection in applying the modified laser flash method to measure thermal properties of semiconductor melts. Common laser flash method uses a laser pulse to heat one side of a thin circular sample and measures the temperature response of the other side. Thermal diffusivity can be calculations based on a heat conduction analysis. For semiconductor melt, the sample is contained in a specially designed quartz cell with optical windows on both sides. When laser heats the vertical melt surface, the resulting natural convection can introduce errors in calculation based on heat conduction model alone. The effect of natural convection was studied by CFD simulations with experimental verification by temperature measurement. The CFD results indicated that natural convection would decrease the time needed for the rear side to reach its peak temperature, and also decrease the peak temperature slightly in our experimental configuration. Using the experimental data, the calculation using only heat conduction model resulted in a thermal diffusivity value is about 7.7% lower than that from the model with natural convection. Specific heat capacity was about the same, and the difference is within 1.6%, regardless of heat transfer models.

  16. Measurements of convective and radiative heating in wildland fires

    Science.gov (United States)

    David Frankman; Brent W. Webb; Bret W. Butler; Daniel Jimenez; Jason M. Forthofer; Paul Sopko; Kyle S. Shannon; J. Kevin Hiers; Roger D. Ottmar

    2012-01-01

    Time-resolved irradiance and convective heating and cooling of fast-response thermopile sensors were measured in 13 natural and prescribed wildland fires under a variety of fuel and ambient conditions. It was shown that a sensor exposed to the fire environment was subject to rapid fluctuations of convective transfer whereas irradiance measured by a windowed sensor was...

  17. Analysis of the convective heat transfer of a fluid flow over an ...

    African Journals Online (AJOL)

    Convective heat transfer in a homogeneous fluid flow Reynolds number of order less than 2000 over an immersed axi-symmetrical body with curved surfaces has been investigated. The fluid flow in consideration was unsteady and of constant density .This study analysed the extent to which convective heat transfer has on ...

  18. Specialists' meeting on evaluation of decay heat removal by natural convection

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1993-02-01

    Decay heat removal by natural convection (DHRNC) is essential to enhancing the safety of liquid metal fast reactors (LMFRs). Various design concepts related to DHRNC have been proposed and experimental and analytical studies have been carried out in a number of countries. The purpose of this Specialists' Meeting on 'Decay Heat Removal by Natural Convection' organized by the International Working Group on Fast Reactors IAEA, is to exchange information about the state of the art related to methodologies on evaluation of DHRNC features (experimental studies and code developments) and to discuss problems which need to be solved in order to evaluate DHRNC properly and reasonably. The following main topical areas were discussed by delegates: Overview; Experimental studies and code validation; Design study. Two main DHR systems for LMFR are under consideration: (i) direct reactor auxiliary cooling system (DRACS) with immersed DFIX in main vessel, intermediate sodium loop and sodium-air heat exchanger; and (ii) auxiliary cooling system which removes heat from the outside surface of the reactor vessel by natural convection of air (RVACS). The practicality and economic viability of the use of RVACS is possible up to a modular type reactor or a middle size reactor based on current technology. For the large monolithic plant concepts DRACS is preferable. The existing experimental results and the codes show encouraging results so that the decay heat removal by pure natural convection is feasible. Concerning the objective, 'passive safety', the DHR by pure natural convection is essential feature to enhance the reliability of DHR.

  19. Specialists' meeting on evaluation of decay heat removal by natural convection

    International Nuclear Information System (INIS)

    1993-02-01

    Decay heat removal by natural convection (DHRNC) is essential to enhancing the safety of liquid metal fast reactors (LMFRs). Various design concepts related to DHRNC have been proposed and experimental and analytical studies have been carried out in a number of countries. The purpose of this Specialists' Meeting on 'Decay Heat Removal by Natural Convection' organized by the International Working Group on Fast Reactors IAEA, is to exchange information about the state of the art related to methodologies on evaluation of DHRNC features (experimental studies and code developments) and to discuss problems which need to be solved in order to evaluate DHRNC properly and reasonably. The following main topical areas were discussed by delegates: Overview; Experimental studies and code validation; Design study. Two main DHR systems for LMFR are under consideration: (i) direct reactor auxiliary cooling system (DRACS) with immersed DFIX in main vessel, intermediate sodium loop and sodium-air heat exchanger; and (ii) auxiliary cooling system which removes heat from the outside surface of the reactor vessel by natural convection of air (RVACS). The practicality and economic viability of the use of RVACS is possible up to a modular type reactor or a middle size reactor based on current technology. For the large monolithic plant concepts DRACS is preferable. The existing experimental results and the codes show encouraging results so that the decay heat removal by pure natural convection is feasible. Concerning the objective, 'passive safety', the DHR by pure natural convection is essential feature to enhance the reliability of DHR

  20. Heat transfer in Rockwool modelling and method of measurement. The effect of natural convection on heat transfer in fibrous materials

    Energy Technology Data Exchange (ETDEWEB)

    Dyrboel, Susanne

    1998-05-01

    Fibrous materials are some of the most widely used materials for thermal insulation. In this project the focus of interest has been on fibrous materials for building application. Interest in improving the thermal properties of insulation materials is increasing as legislation is being tightened to reduce the overall energy consumption. A knowledge of the individual heat transfer mechanisms - whereby heat is transferred within a particular material is an essential tool to improve continuously the thermal properties of the material. Heat is transferred in fibrous materials by four different transfer mechanisms: conduction through air, conduction through fibres, thermal radiation and convection. In a particular temperature range the conduction through air can be regarded as a constant, and conduction through fibres is an insignificant part of the total heat transfer. Radiation, however, constitutes 25-40% of the total heat transfer in light fibrous materials. In Denmark and a number of other countries convection in fibrous materials is considered as non-existent when calculating heat transmission as well as when designing building structures. Two heat transfer mechanisms have been the focus of the current project: radiation heat transfer and convection. The radiation analysis serves to develop a model that can be used in further work to gain a wider knowledge of the way in which the morphology of the fibrous material, i.e. fibre diameter distribution, fibre orientation distribution etc., influences the radiation heat transfer under different conditions. The convection investigation serves to examine whether considering convection as non-existent is a fair assumption to use in present and future building structures. The assumption applied in practically is that convection makes a notable difference only in very thick insulation, at external temperatures below -20 deg. C, and at very low densities. For large thickness dimensions the resulting heat transfer through the

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-05-15

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

  2. Convective heat flow probe

    Science.gov (United States)

    Dunn, James C.; Hardee, Harry C.; Striker, Richard P.

    1985-01-01

    A convective heat flow probe device is provided which measures heat flow and fluid flow magnitude in the formation surrounding a borehole. The probe comprises an elongate housing adapted to be lowered down into the borehole; a plurality of heaters extending along the probe for heating the formation surrounding the borehole; a plurality of temperature sensors arranged around the periphery of the probe for measuring the temperature of the surrounding formation after heating thereof by the heater elements. The temperature sensors and heater elements are mounted in a plurality of separate heater pads which are supported by the housing and which are adapted to be radially expanded into firm engagement with the walls of the borehole. The heat supplied by the heater elements and the temperatures measured by the temperature sensors are monitored and used in providing the desired measurements. The outer peripheral surfaces of the heater pads are configured as segments of a cylinder and form a full cylinder when taken together. A plurality of temperature sensors are located on each pad so as to extend along the length and across the width thereof, with a heating element being located in each pad beneath the temperature sensors. An expansion mechanism driven by a clamping motor provides expansion and retraction of the heater pads and expandable packer-type seals are provided along the probe above and below the heater pads.

  3. Developing mixed convection in a coiled heat exchanger

    NARCIS (Netherlands)

    Sillekens, J.J.M.; Rindt, C.C.M.; Steenhoven, van A.A.

    1998-01-01

    In this paper the development of mixed convection in a helically coiled heat exchanger for Re = 500, Pr = 5 and
    δ =114
    is studied. The influence of buoyancy forces ¢
    (Gr = ¢O (105))
    on heat transfer and secondary flow is analyzed. In the method used the parabolized equations are

  4. Evaluation of convective heat transfer coefficient of various crops in cyclone type dryer

    International Nuclear Information System (INIS)

    Akpinar, E. Kavak

    2005-01-01

    In this paper, an attempt was made to evaluate the convective heat transfer coefficient during drying of various crops and to investigate the influences of drying air velocity and temperature on the convective heat transfer coefficient. Drying was conducted in a convective cyclone type dryer at drying air temperatures of 60, 70 and 80 deg. C and velocities of 1 and 1.5 m/s using rectangle shaped potato and apple slices (12.5 x 12.5 x 25 mm) and cylindrical shaped pumpkin slices (35 x 5 mm). The temperature changes of the dried crops and the temperature of the drying air were measured during the drying process. It was found that the values of convective heat transfer coefficient varied from crop to crop with a range 30.21406 and 20.65470 W/m 2 C for the crops studied, and it was observed that the convective heat transfer coefficient increased in large amounts with the increase of the drying air velocity but increased in small amounts with the rise of the drying air temperature

  5. Evaluation of convective heat transfer coefficient of various crops in cyclone type dryer

    Energy Technology Data Exchange (ETDEWEB)

    Akpinar, E. Kavak [Mechanical Engineering Department, Firat University, 23279 Elazig (Turkey)]. E-mail: eakpinar@firat.edu.tr

    2005-09-15

    In this paper, an attempt was made to evaluate the convective heat transfer coefficient during drying of various crops and to investigate the influences of drying air velocity and temperature on the convective heat transfer coefficient. Drying was conducted in a convective cyclone type dryer at drying air temperatures of 60, 70 and 80 deg. C and velocities of 1 and 1.5 m/s using rectangle shaped potato and apple slices (12.5 x 12.5 x 25 mm) and cylindrical shaped pumpkin slices (35 x 5 mm). The temperature changes of the dried crops and the temperature of the drying air were measured during the drying process. It was found that the values of convective heat transfer coefficient varied from crop to crop with a range 30.21406 and 20.65470 W/m{sup 2} C for the crops studied, and it was observed that the convective heat transfer coefficient increased in large amounts with the increase of the drying air velocity but increased in small amounts with the rise of the drying air temperature.

  6. Heat transport in bubbling turbulent convection.

    Science.gov (United States)

    Lakkaraju, Rajaram; Stevens, Richard J A M; Oresta, Paolo; Verzicco, Roberto; Lohse, Detlef; Prosperetti, Andrea

    2013-06-04

    Boiling is an extremely effective way to promote heat transfer from a hot surface to a liquid due to numerous mechanisms, many of which are not understood in quantitative detail. An important component of the overall process is that the buoyancy of the bubble compounds with that of the liquid to give rise to a much-enhanced natural convection. In this article, we focus specifically on this enhancement and present a numerical study of the resulting two-phase Rayleigh-Bénard convection process in a cylindrical cell with a diameter equal to its height. We make no attempt to model other aspects of the boiling process such as bubble nucleation and detachment. The cell base and top are held at temperatures above and below the boiling point of the liquid, respectively. By keeping this difference constant, we study the effect of the liquid superheat in a Rayleigh number range that, in the absence of boiling, would be between 2 × 10(6) and 5 × 10(9). We find a considerable enhancement of the heat transfer and study its dependence on the number of bubbles, the degree of superheat of the hot cell bottom, and the Rayleigh number. The increased buoyancy provided by the bubbles leads to more energetic hot plumes detaching from the cell bottom, and the strength of the circulation in the cell is significantly increased. Our results are in general agreement with recent experiments on boiling Rayleigh-Bénard convection.

  7. Natural convection heat transfer within horizontal spent nuclear fuel assemblies

    International Nuclear Information System (INIS)

    Canaan, R.E.

    1995-12-01

    Natural convection heat transfer is experimentally investigated in an enclosed horizontal rod bundle, which characterizes a spent nuclear fuel assembly during dry storage and/or transport conditions. The basic test section consists of a square array of sixty-four stainless steel tubular heaters enclosed within a water-cooled rectangular copper heat exchanger. The heaters are supplied with a uniform power generation per unit length while the surrounding enclosure is maintained at a uniform temperature. The test section resides within a vacuum/pressure chamber in order to subject the assembly to a range of pressure statepoints and various backfill gases. The objective of this experimental study is to obtain convection correlations which can be used in order to easily incorporate convective effects into analytical models of horizontal spent fuel systems, and also to investigate the physical nature of natural convection in enclosed horizontal rod bundles in general. The resulting data consist of: (1) measured temperatures within the assembly as a function of power, pressure, and backfill gas; (2) the relative radiative contribution for the range of observed temperatures; (3) correlations of convective Nusselt number and Rayleigh number for the rod bundle as a whole; and (4) correlations of convective Nusselt number as a function of Rayleigh number for individual rods within the array

  8. Convective Heat Transfer Scaling of Ignition Delay and Burning Rate with Heat Flux and Stretch Rate in the Equivalent Low Stretch Apparatus

    Science.gov (United States)

    Olson, Sandra

    2011-01-01

    To better evaluate the buoyant contributions to the convective cooling (or heating) inherent in normal-gravity material flammability test methods, we derive a convective heat transfer correlation that can be used to account for the forced convective stretch effects on the net radiant heat flux for both ignition delay time and burning rate. The Equivalent Low Stretch Apparatus (ELSA) uses an inverted cone heater to minimize buoyant effects while at the same time providing a forced stagnation flow on the sample, which ignites and burns as a ceiling fire. Ignition delay and burning rate data is correlated with incident heat flux and convective heat transfer and compared to results from other test methods and fuel geometries using similarity to determine the equivalent stretch rates and thus convective cooling (or heating) rates for those geometries. With this correlation methodology, buoyant effects inherent in normal gravity material flammability test methods can be estimated, to better apply the test results to low stretch environments relevant to spacecraft material selection.

  9. About the possible options for models of convective heat transfer in closed volumes with local heating source

    Directory of Open Access Journals (Sweden)

    Maksimov Vyacheslav I.

    2015-01-01

    Full Text Available Results of mathematical modeling of convective heat transfer in air area surrounded on all sides enclosing structures, in the presence of heat source at the lower boundary of the media are presented. Solved the system of differential equations of unsteady Navier-Stokes equations with the appropriate initial and boundary conditions. The process of convective heat transfer is calculated using the models of turbulence Prandtl and Prandtl-Reichard. Takes into account the processes of heat exchange region considered with the environment. Is carried out the analysis of the dimensionless heat transfer coefficient at interfaces “air – enclosures”. The distributions average along the gas temperature range are obtained.

  10. Heat removal by natural convection in a RPR reactor

    International Nuclear Information System (INIS)

    Sampaio, P.A.B. de

    1987-01-01

    In this paper natural convection in RPR reactor is analysed. The effect of natural convection valves size on cladding temperature is studied. The reactor channel heat transfer problem is solved using finite elements in a two-dimensional analysis. Results show that two valves with Φ = 0.16 m are suited to keep coolant and cladding temperatures below 73 0 C. (author) [pt

  11. Natural convection heat transfer between vertical channel with flow resistance at the lower end

    International Nuclear Information System (INIS)

    Iwamoto, S.; Nishimura, S.; Ishihara, I.

    2003-01-01

    For natural convection in the geometrically complicated channel, the convection flow is suppressed by flow resistance due to such channel itself and the lopsided flow may take place. This could result in serious influences on the heat transfer in the channel. In order to investigate fundamentally the natural convection flow and heat transfer in such the channel, the vertical channel in which wall was heated with uniform heat flux and the flow resistance was given by small clearance between the lower end of channel and a wide horizontal floor. Flow pattern was observed by illuminating smoke filled in the channel and heat transfer rate was measured. (author)

  12. Natural convection heat transfer for a staggered array of heated, horizontal cylinders within a rectangular enclosure

    Energy Technology Data Exchange (ETDEWEB)

    Triplett, C.E.

    1996-12-01

    This thesis presents the results of an experimental investigation of natural convection heat transfer in a staggered array of heated cylinders, oriented horizontally within a rectangular enclosure. The main purpose of this research was to extend the knowledge of heat transfer within enclosed bundles of spent nuclear fuel rods sealed within a shipping or storage container. This research extends Canaan`s investigation of an aligned array of heated cylinders that thermally simulated a boiling water reactor (BWR) spent fuel assembly sealed within a shipping or storage cask. The results are presented in terms of piecewise Nusselt-Rayleigh number correlations of the form Nu = C(Ra){sup n}, where C and n are constants. Correlations are presented both for individual rods within the array and for the array as a whole. The correlations are based only on the convective component of the heat transfer. The radiative component was calculated with a finite-element code that used measured surface temperatures, rod array geometry, and measured surface emissivities as inputs. The correlation results are compared to Canaan`s aligned array results and to other studies of natural convection in horizontal tube arrays.

  13. Natural convection heat transfer for a staggered array of heated, horizontal cylinders within a rectangular enclosure

    International Nuclear Information System (INIS)

    Triplett, C.E.

    1996-12-01

    This thesis presents the results of an experimental investigation of natural convection heat transfer in a staggered array of heated cylinders, oriented horizontally within a rectangular enclosure. The main purpose of this research was to extend the knowledge of heat transfer within enclosed bundles of spent nuclear fuel rods sealed within a shipping or storage container. This research extends Canaan's investigation of an aligned array of heated cylinders that thermally simulated a boiling water reactor (BWR) spent fuel assembly sealed within a shipping or storage cask. The results are presented in terms of piecewise Nusselt-Rayleigh number correlations of the form Nu = C(Ra) n , where C and n are constants. Correlations are presented both for individual rods within the array and for the array as a whole. The correlations are based only on the convective component of the heat transfer. The radiative component was calculated with a finite-element code that used measured surface temperatures, rod array geometry, and measured surface emissivities as inputs. The correlation results are compared to Canaan's aligned array results and to other studies of natural convection in horizontal tube arrays

  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 analysis in aggregates rotary drum reactor

    International Nuclear Information System (INIS)

    Le Guen, Laurédan; Huchet, Florian; Dumoulin, Jean; Baudru, Yvan; Tamagny, Philippe

    2013-01-01

    Heat transport characterisation inside rotary drum dryer has a considerable importance linked to many industrial applications. The present paper deals with the heat transfer analysis from experimental apparatus installed in a large-scale rotary drum reactor applied to the asphalt materials production. The equipment including in-situ thermal probes and external visualization by mean of infrared thermography gives rise to the longitudinal evaluation of inner and external temperatures. The assessment of the heat transfer coefficients by an inverse methodology is resolved in order to accomplish a fin analysis of the convective mechanism inside baffled (or flights) rotary drum. The results are discussed and compared with major results of the literature. -- Highlights: ► A thermal and flow experimentation is performed on a large-scale rotary drum. ► Four working points is chosen in the frame of asphalt materials production. ► Evaluation of the convective transfer mechanisms is calculated by inverse method. ► The drying stage is performed in the combustion area. ► Wall/aggregates heat exchanges have a major contribution in the heating stage

  16. A meshless method for modeling convective heat transfer

    Energy Technology Data Exchange (ETDEWEB)

    Carrington, David B [Los Alamos National Laboratory

    2010-01-01

    A meshless method is used in a projection-based approach to solve the primitive equations for fluid flow with heat transfer. The method is easy to implement in a MATLAB format. Radial basis functions are used to solve two benchmark test cases: natural convection in a square enclosure and flow with forced convection over a backward facing step. The results are compared with two popular and widely used commercial codes: COMSOL, a finite element model, and FLUENT, a finite volume-based model.

  17. Microwave heating device for internal heating convection experiments, applied to Earth's mantle dynamics.

    Science.gov (United States)

    Surducan, E; Surducan, V; Limare, A; Neamtu, C; Di Giuseppe, E

    2014-12-01

    We report the design, construction, and performances of a microwave (MW) heating device for laboratory experiments with non-contact, homogeneous internal heating. The device generates MW radiation at 2.47 GHz from a commercial magnetron supplied by a pulsed current inverter using proprietary, feedback based command and control hardware and software. Specially designed MW launchers direct the MW radiation into the sample through a MW homogenizer, devised to even the MW power distribution into the sample's volume. An adjustable MW circuit adapts the MW generator to the load (i.e., the sample) placed in the experiment chamber. Dedicated heatsinks maintain the MW circuits at constant temperature throughout the experiment. Openings for laser scanning for image acquisition with a CCD camera and for the cooling circuits are protected by special MW filters. The performances of the device are analyzed in terms of heating uniformity, long term output power stability, and load matching. The device is used for small scale experiments simulating Earth's mantle convection. The 30 × 30 × 5 cm(3) convection tank is filled with a water‑based viscous fluid. A uniform and constant temperature is maintained at the upper boundary by an aluminum heat exchanger and adiabatic conditions apply at the tank base. We characterize the geometry of the convective regime as well as its bulk thermal evolution by measuring the velocity field by Particle Image Velocimetry and the temperature field by using Thermochromic Liquid Crystals.

  18. Planform structure and heat transfer in turbulent free convection over horizontal surfaces

    Science.gov (United States)

    Theerthan, S. Ananda; Arakeri, Jaywant H.

    2000-04-01

    This paper deals with turbulent free convection in a horizontal fluid layer above a heated surface. Experiments have been carried out on a heated surface to obtain and analyze the planform structure and the heat transfer under different conditions. Water is the working fluid and the range of flux Rayleigh numbers (Ra) covered is 3×107-2×1010. The different conditions correspond to Rayleigh-Bénard convection, convection with either the top water surface open to atmosphere or covered with an insulating plate, and with an imposed external flow on the heated boundary. Without the external flow the planform is one of randomly oriented line plumes. At large Rayleigh number Ra and small aspect ratio (AR), these line plumes seem to align along the diagonal, presumably due to a large scale flow. The side views show inclined dyelines, again indicating a large scale flow. When the external flow is imposed, the line plumes clearly align in the direction of external flow. The nondimensional average plume spacing, Raλ1/3, varies between 40 and 90. The heat transfer rate, for all the experiments conducted, represented as RaδT-1/3, where δT is the conduction layer thickness, varies only between 0.1-0.2, showing that in turbulent convection the heat transfer rates are similar under the different conditions.

  19. Strategy of experimental studies in PNC on natural convection decay heat removal

    International Nuclear Information System (INIS)

    Ieda, Y.; Kamide, H.; Ohshima, H.; Sugawara, S.; Ninokata, H.

    1993-01-01

    Experimental studies have been and are being carried out in PNC to establish the design and safety evaluation methods and the design and safety evaluation guide lines for decay heat removal by natural convection. A strategy of the experimental studies in PNC is described in this paper. The sphere of studies in PNC is to develop the evaluation methods to be available to DRACS as well as PRACS and IRACS for the plant where decay heat is removed by natural convection in some cases of loss of station service power. Similarity parameters related to natural convection are derived from the governing equations. The roles of both sodium and water experiments are defined in consideration of the importance of the similarity parameters and characteristics of scale model experiments. The experimental studies in PNC are reviewed. On the basis of the experimental results, recommended evaluation methods are shown for decay heat removal feature by natural convection. Future experimental works are also proposed. (author)

  20. Natural convection in enclosures. Proceedings of the nineteenth national heat transfer conference, Orlando, FL, July 27-30, 1980

    International Nuclear Information System (INIS)

    Torrance, K.E.; Catton, I.

    1980-01-01

    Natural convection in low aspect ratio rectangular enclosures is considered along with three-dimensional convection within rectangular boxes, natural convection flow visualization in irradiated water cooled by air flow over the surface, free convection in vertical slots, the stratification in natural convection in vertical enclosures, the flow structure with natural convection in inclined air-filled enclosures, and natural convection across tilted, rectangular enclosures of small aspect ratio. Attention is given to the effect of wall conduction and radiation on natural convection in a vertical slot with uniform heat generation of the heated wall, a numerical study of thermal insulation enclosure, free convection in a piston-cylinder enclosure with sinusoidal piston motion, natural convection heat transfer between bodies and their spherical enclosure, an experimental study of the steady natural convection in a horizontal annulus with irregular boundaries, three-dimensional natural convection in a porous medium between concentric inclined cylinders, a numerical solution for natural convection in concentric spherical annuli, and heat transfer by natural convection in porous media between two concentric spheres

  1. A computational procedure for finding multiple solutions of convective heat transfer equations

    International Nuclear Information System (INIS)

    Mishra, S; DebRoy, T

    2005-01-01

    In recent years numerical solutions of the convective heat transfer equations have provided significant insight into the complex materials processing operations. However, these computational methods suffer from two major shortcomings. First, these procedures are designed to calculate temperature fields and cooling rates as output and the unidirectional structure of these solutions preclude specification of these variables as input even when their desired values are known. Second, and more important, these procedures cannot determine multiple pathways or multiple sets of input variables to achieve a particular output from the convective heat transfer equations. Here we propose a new method that overcomes the aforementioned shortcomings of the commonly used solutions of the convective heat transfer equations. The procedure combines the conventional numerical solution methods with a real number based genetic algorithm (GA) to achieve bi-directionality, i.e. the ability to calculate the required input variables to achieve a specific output such as temperature field or cooling rate. More important, the ability of the GA to find a population of solutions enables this procedure to search for and find multiple sets of input variables, all of which can lead to the desired specific output. The proposed computational procedure has been applied to convective heat transfer in a liquid layer locally heated on its free surface by an electric arc, where various sets of input variables are computed to achieve a specific fusion zone geometry defined by an equilibrium temperature. Good agreement is achieved between the model predictions and the independent experimental results, indicating significant promise for the application of this procedure in finding multiple solutions of convective heat transfer equations

  2. Free convection film flows and heat transfer

    CERN Document Server

    Shang, Deyi

    2010-01-01

    Presents development of systematic studies for hydrodynamics and heat and mass transfer in laminar free convection, accelerating film boiling and condensation of Newtonian fluids, and accelerating film flow of non-Newtonian power-law fluids. This book provides a system of analysis models with a developed velocity component method.

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

    International Nuclear Information System (INIS)

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

    1986-01-01

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

  4. Heat transfer within hydrodissection fluids: An analysis of thermal conduction and convection using liquid and gel materials.

    Science.gov (United States)

    Johnson, Alexander; Brace, Christopher

    2015-01-01

    Interventional oncology procedures such as thermal ablation are becoming widely used for many tumours in the liver, kidney and lung. Thermal ablation refers to the focal destruction of tissue by generating cytotoxic temperatures in the treatment zone. Hydrodissection - separating tissues with fluids - protects healthy tissues adjacent to the ablation treatment zone to improve procedural safety, and facilitate more aggressive power application or applicator placement. However, fluids such as normal saline and 5% dextrose in water (D5W) can migrate into the peritoneum, reducing their protective efficacy. As an alternative, a thermo-gelable poloxamer 407 (P407) solution has been recently developed to facilitate hydrodissection procedures. We hypothesise that the P407 gel material does not provide convective heat dissipation from the ablation site, and therefore may alter the heat transfer dynamics compared to liquid materials during hydrodissection-assisted thermal ablation. The purpose of this study was to investigate the heat dissipation mechanics within D5W, liquid P407 and gel P407 hydrodissection barriers. Overall it was shown that the gel P407 dissipated heat primarily through conduction, whereas the liquid P407 and D5W dissipated heat through convection. Furthermore, the rate of temperature change within the gel P407 was greater than liquid P407 and D5W. Testing to evaluate the in vivo efficacy of the fluids with different modes of heat dissipation seems warranted for further study.

  5. Heat Transfer Convection in The Cooking of Apple Using a Solar Cooker Box-Type

    International Nuclear Information System (INIS)

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

    2015-01-01

    In this work, experimental results to determine the convection heat transfer coefficient in the cooking process of apple using a solar cooker box-type are presented. Experimental data of temperatures for water, surface and central point of the apple were used. To determine the convection coefficient, the apple was modelled as a sphere. The temperatures evolution was defined using thermocouples located at water, surface and central point in the vegetables. Using heat transfer convection equations in transitory state and the temperatures measured, the Biot number and the convection coefficient were determined

  6. Heat Transfer Convection in The Cooking of Apple Using a Solar Cooker Box-Type

    Science.gov (United States)

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

    2015-01-01

    In this work, experimental results to determine the convection heat transfer coefficient in the cooking process of apple using a solar cooker box-type are presented. Experimental data of temperatures for water, surface and central point of the apple were used. To determine the convection coefficient, the apple was modelled as a sphere. The temperatures evolution was defined using thermocouples located at water, surface and central point in the vegetables. Using heat transfer convection equations in transitory state and the temperatures measured, the Biot number and the convection coefficient were determined.

  7. Measurement of the Convective Heat-Transfer Coefficient

    Science.gov (United States)

    Conti, Rosaria; Gallitto, Aurelio Agliolo; Fiordilino, Emilio

    2014-01-01

    We propose an experiment for investigating how objects cool down toward the thermal equilibrium with their surroundings. We describe the time dependence of the temperature difference of the cooling objects and the environment with an exponential decay function. By measuring the thermal constant t, we determine the convective heat-transfer…

  8. Solar Hot Water Heating by Natural Convection.

    Science.gov (United States)

    Noble, Richard D.

    1983-01-01

    Presents an undergraduate laboratory experiment in which a solar collector is used to heat water for domestic use. The working fluid is moved by natural convection so no pumps are required. Experimental apparatus is simple in design and operation so that data can be collected quickly and easily. (Author/JN)

  9. Natural convection in porous media with heat generation

    International Nuclear Information System (INIS)

    Hardee, H.C. Jr.; Nilson, R.H.

    1976-12-01

    Heat transfer characteristics of a fluid saturated porous media are investigated for the case of uniform internal heat generation with cooling from above. Analytical models of conduction and single phase cellular convection show good agreement with previous Rayleigh number correlations and with experimental data obtained by Joule heating of salt water in a sand bed. An approximate dryout criterion is also derived for two phase boiling heat transfer in a fixed bed which is neither channeled nor fluidized. Correlation of dryout data using this criterion is encouraging, especially considering the analytical rather than correlational basis of the criterion

  10. Carbon-nanotube nanofluid thermophysical properties and heat transfer by natural convection

    International Nuclear Information System (INIS)

    Li, Y; Inagaki, T; Suzuki, S; Yamauchi, N

    2014-01-01

    We measured the thermophysical properties of suspensions of carbon nanotubes in water as a type of nanofluid, and experimentally investigated their heat transfer characteristics in a horizontal, closed rectangular vessel. Using a previously constructed system for high- reliability measurement, we quantitatively determined their thermophysical properties and the temperature dependence of these properties. We also investigated the as yet unexplained mechanism of heat transport in carbon-nanotube nanofluids and their flow properties from a thermal perspective. The results indicated that these nanofluids are non-Newtonian fluids, whose high viscosity impedes convection and leads to a low heat transfer coefficient under natural convection, despite their high thermal conductivity

  11. Wind effects on convective heat loss from a cavity receiver for a parabolic concentrating solar collector

    Energy Technology Data Exchange (ETDEWEB)

    Ma, R.Y. [California State Polytechnic Univ., Pomoma, CA (United States). Dept. of Mechanical Engineering

    1993-09-01

    Tests were performed to determine the convective heat loss characteristics of a cavity receiver for a parabolid dish concentrating solar collector for various tilt angles and wind speeds of 0-24 mph. Natural (no wind) convective heat loss from the receiver is the highest for a horizontal receiver orientation and negligible with the reveler facing straight down. Convection from the receiver is substantially increased by the presence of side-on wind for all receiver tilt angles. For head-on wind, convective heat loss with the receiver facing straight down is approximately the same as that for side-on wind. Overall it was found that for wind speeds of 20--24 mph, convective heat loss from the receiver can be as much as three times that occurring without wind.

  12. Performance of a convective, infrared and combined infrared- convective heated conveyor-belt dryer.

    Science.gov (United States)

    El-Mesery, Hany S; Mwithiga, Gikuru

    2015-05-01

    A conveyor-belt dryer was developed using a combined infrared and hot air heating system that can be used in the drying of fruits and vegetables. The drying system having two chambers was fitted with infrared radiation heaters and through-flow hot air was provided from a convective heating system. The system was designed to operate under either infrared radiation and cold air (IR-CA) settings of 2000 W/m(2) with forced ambient air at 30 °C and air flow of 0.6 m/s or combined infrared and hot air convection (IR-HA) dryer setting with infrared intensity set at 2000 W/m(2) and hot at 60 °C being blown through the dryer at a velocity of 0.6 m/s or hot air convection (HA) at an air temperature of 60 °C and air flow velocity 0.6 m/s but without infrared heating. Apple slices dried under the different dryer settings were evaluated for quality and energy requirements. It was found that drying of apple (Golden Delicious) slices took place in the falling rate drying period and no constant rate period of drying was observed under any of the test conditions. The IR-HA setting was 57.5 and 39.1 % faster than IR-CA and HA setting, respectively. Specific energy consumption was lower and thermal efficiency was higher for the IR-HA setting when compared to both IR-CA and HA settings. The rehydration ratio, shrinkage and colour properties of apples dried under IR-HA conditions were better than for either IR-CA or HA.

  13. Non intrusive measurement of the convective heat transfer coefficient

    Energy Technology Data Exchange (ETDEWEB)

    Rebay, M.; Mebarki, G.; Padet, J. [Reims Univ., Reims (France). Faculty of Science, GRESPI Thermomechanical Lab; Arfaoui, A. [Reims Univ., Reims (France). Faculty of Science, GRESPI Thermomechanical Lab; Tunis Univ., Tunis (Tunisia). Faculty of Science, EL MANAR, LETTM; Maad, B.R. [Tunis Univ., Tunis (Tunisia). Faculty of Science, EL MANAR, LETTM

    2010-07-01

    The efficiency of cooling methods in thermal systems such as radiators and heat exchangers must be improved in order to enhance performance. The evaluation of the heat transfer coefficients between a solid and a fluid is necessary for the control and the dimensioning of thermal systems. In this study, the pulsed photothermal method was used to measure the convective heat transfer coefficient on a solid-fluid interface, notably between an air flow and a heated slab mounted on a PVC flat plate. This configuration simulated the electronic air-cooling inside enclosures and racks. The influence of the deflector's inclination angle on the enhancement of heat transfer was investigated using 2 newly developed identification models. The first model was based on a constant heat transfer coefficient during the pulsed experiment, while the second, improved model was based on a variable heat transfer coefficient. The heat transfer coefficient was deduced from the evolution of the transient temperature induced by a sudden deposit of a luminous energy on the front face of the slab. Temperature evolutions were derived by infrared thermography, a camera for cartography and a detector for precise measurement in specific locations. The results show the improvement of measurement accuracies when using a model that considers the temporal evolution of the convective heat transfer coefficient. The deflection of air flow on the upper surface of the heated slab demonstrated better cooling of the slab by the deflection of air flow. 11 refs., 1 tab., 8 figs.

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

    Directory of Open Access Journals (Sweden)

    Scheila Sandi Biazus

    2015-03-01

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

  15. Magnetic flux tubes and transport of heat in the convection zone of the sun

    International Nuclear Information System (INIS)

    Spruit, H.C.

    1977-01-01

    This thesis consists of five papers dealing with transport of heat in the solar convection zone on the one hand, and with the structure of magnetic flux tubes in the top of the convection zone on the other hand. These subjects are interrelated. For example, the heat flow in the convection zone is disturbed by the presence of magnetic flux tubes, while exchange of heat between a flux tube and the convection zone is important for the energy balance of such a tube. A major part of this thesis deals with the structure of small magnetic flux tubes. Such small tubes (diameters less than about 2'') carry most of the flux appearing at the solar surface. An attempt is made to construct models of the surface layers of such small tubes in sufficient detail to make a comparison with observations possible. Underlying these model calculations is the assumption that the magnetic elements at the solar surface are flux tubes in a roughly static equilibrium. The structure of such tubes is governed by their pressure equilibrium, exchange of heat with the surroundings, and transport of heat by some modified form of convection along the tube. The tube models calculated are compared with observations

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

    Science.gov (United States)

    Freche, John C; Schum, Eugene F

    1951-01-01

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

  17. Experimental study on convective heat transfer with thin porous bodies

    International Nuclear Information System (INIS)

    Nishi, Yoshihisa; Kinoshita, Izumi; Furuya, Masahiro

    2001-01-01

    Experimental studies are made on the convective heat transfer of three types of thin porous bodies. Heat transfer performances, flow patterns and temperature profiles near the porous bodies are compared with each other. The heat transfer performance of porous bodies with the largest pore diameter is large. It became clear that the high heat transfer performance depends on an excellent heat transportation ability inside the pore and near the surface of the porous bodies. (author)

  18. Visualization of Natural Convection Heat Transfer on a Single Sphere using the Electroplating System

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-05-15

    The natural convective flows on outer sphere rise along surface. At top of sphere, the flows are lifted-up plume shape. For laminar flows, the local heat transfer shows maximum at the bottom of sphere and a monotonic decreases as flows approached to the top. The laminar natural convection heat transfer on a single sphere has been studied experimentally and numerically by several researchers. However, relatively less study has been performed for turbulent flows as it requires large facilities to achieve high Rayleigh numbers. The flows, which occur transition, is hard to experiment because of unstable. This study tried measurement of heat transfer and visualization external natural convection on a single sphere. The basic idea is that the plating patterns of copper on the sphere in mass transfer system will reveal the amount of heat transfer according to angular distance from the bottom. This study simulated natural convection on a single sphere and performed a mass transfer experiment using heat and mass transfer analogy concept. For visualization experiment, streak form plating pattern was observed. In this case, it seems that turbulence sets on the top of sphere and increases local heat transfer.

  19. Performance and optimum design of convective-radiative rectangular fin with convective base heating, wall conduction resistance, and contact resistance between the wall and the fin base

    International Nuclear Information System (INIS)

    Aziz, Abdul; Beers-Green, Arlen B.

    2009-01-01

    This paper investigates the performance and optimum design of a longitudinal rectangular fin attached to a convectively heated wall of finite thickness. The exposed surfaces of the fin lose heat to the environmental sink by simultaneous convection and radiation. The tip of the fin is assumed to lose heat by convection and radiation to the same sink. The analysis and optimization of the fin is conducted numerically using the symbolic algebra package Maple. The temperature distribution, the heat transfer rates, and the fin efficiency data is presented illustrating how the thermal performance of the fin is affected by the convection-conduction number, the radiation-conduction number, the base convection Biot number, the convection and radiation Biot numbers at the tip, and the dimensionless sink temperature. Charts are presented showing the relationship between the optimum convection-conduction number and the optimum radiation-conduction number for different values of the base convection Biot number and dimensionless sink temperature and fixed values of the convection and radiation Biot numbers at the tip. Unlike the few other papers which have applied the Adomian's decomposition and the differential quadrature element method to this problem but give illustrative results for specific fin geometry and thermal variables, the present graphical data are generally applicable and can be used by fin designers without delving into the mathematical details of the computational techniques.

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

    International Nuclear Information System (INIS)

    Liu, Qiusheng; Fukuda, Katsuya; Shibahara, Makoto

    2008-01-01

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

  1. Effective thermal conductivity of a heat generating rod bundle dissipating heat by natural convection and radiation

    International Nuclear Information System (INIS)

    Senve, Vinay; Narasimham, G.S.V.L.

    2011-01-01

    Highlights: → Transport processes in isothermal hexagonal sheath with 19 heat generating rods is studied. → Correlation is given to predict the maximum temperature considering all transport processes. → Effective thermal conductivity of rod bundle can be obtained using max temperature. → Data on the critical Rayleigh numbers for p/d ratios of 1.1-2.0 is presented. → Radiative heat transfer contributes to heat dissipation of 38-65% of total heat. - Abstract: A numerical study of conjugate natural convection and surface radiation in a horizontal hexagonal sheath housing 19 solid heat generating rods with cladding and argon as the fill gas, is performed. The natural convection in the sheath is driven by the volumetric heat generation in the solid rods. The problem is solved using the FLUENT CFD code. A correlation is obtained to predict the maximum temperature in the rod bundle for different pitch-to-diameter ratios and heat generating rates. The effective thermal conductivity is related to the heat generation rate, maximum temperature and the sheath temperature. Results are presented for the dimensionless maximum temperature, Rayleigh number and the contribution of radiation with changing emissivity, total wattage and the pitch-to-diameter ratio. In the simulation of a larger system that contains a rod bundle, the effective thermal conductivity facilitates simplified modelling of the rod bundle by treating it as a solid of effective thermal conductivity. The parametric studies revealed that the contribution of radiation can be 38-65% of the total heat generation, for the parameter ranges chosen. Data for critical Rayleigh number above which natural convection comes into effect is also presented.

  2. Experimental and numerical analysis of convective heat losses from spherical cavity receiver of solar concentrator

    Directory of Open Access Journals (Sweden)

    Shewale Vinod C.

    2017-01-01

    Full Text Available Spherical cavity receiver of solar concentrator is made up of Cu tubing material having cavity diameter 385 mm to analyze the different heat losses such as conduction, convection and radiation. As the convection loss plays major role in heat loss analysis of cavity receiver, the experimental analysis is carried out to study convective heat loss for the temperature range of 55-75°C at 0°, 15°, 30°, 45°, 60°, and 90° inclination angle of downward facing cavity receiver. The numerical analysis is carried out to study convective heat loss for the low temperature range (55-75°C as well as high temperature range (150-300 °C for no wind condition only. The experimental set-up mainly consists of spherical cavity receiver which is insulated with glass wool insulation to reduce the heat losses from outside surface. The numerical analysis is carried out by using CFD software and the results are compared with the experimental results and found good agreement. The result shows that the convective loss increases with decrease in cavity inclination angle and decreases with decrease in mean cavity receiver temperature. The maximum losses are obtained at 0° inclination angle and the minimum losses are obtained at 90° inclination angle of cavity due to increase in stagnation zone in to the cavity from 0° to 90° inclination. The Nusselt number correlation is developed for the low temperature range 55-75°C based on the experimental data. The analysis is also carried out to study the effect of wind speed and wind direction on convective heat losses. The convective heat losses are studied for two wind speeds (3 m/s and 5 m/s and four wind directions [α is 0° (Side-on wind, 30°, 60°, and 90° (head-on wind]. It is found that the convective heat losses for both wind speed are higher than the losses obtained by no wind test. The highest heat losses are found for wind direction α is 60° with respect to receiver stand and lowest heat losses are found

  3. Combined natural convection and radiation in a volumetrically heated fluid layer

    International Nuclear Information System (INIS)

    Chawla, T.C.; Chan, S.H.; Cheung, F.B.; Cho, D.H.

    1980-01-01

    The effect of radiation in combination with turbulent natural convection on the rates of heat transfer in volumetrically heated fluid layers characterized by high temperatures has been considered in this study. It is demonstrated that even at high Rayleigh numbers the radiation mode is as effective as the turbulent natural convection mode in removing the heat from the upper surface of the molten pools with adiabatic lower boundary. As a result of this improved heat transfer, it is shown that considerably thicker molten pools with internal heat generation can be supported without boiling inception. The total Nusselt number at a moderate but fixed value of conduction-radiation parameter, can be represented as a function of Rayleigh number in a simple power-law form. As a consequence of this relationship it is shown that maximum nonboiling pool thicknesses vary approximately inversely as the 0.9% power of internal heat generation rate. A comparison between exact analysis using the integral formulation of radiation flux and Rosseland approximation shows that the latter approximation bears out very adequately for optically thick pools with conduction-radiation parameters greater than or equal to 0.4 inspite of the fact that individual components of Nusselt number due to radiation and convection, respectively, are grossly in error. These errors in component heat fluxes are compensating due to the total heat balance constraint. However, the comparison between Rosseland approximation and exact formulation gets poorer as the value of conduction-radiation parameters decreases. This increase in error is principally incurred due to the error in estimating wall temperature differences

  4. Combined natural convection and radiation in a volumetrically heated fluid layer

    International Nuclear Information System (INIS)

    Chawla, T.C.; Chan, S.H.; Cheung, F.B.; Cho, D.H.

    1980-01-01

    The effect of radiation in combining with turbulent natural convection on the rates of heat transfer in volumetrically heated fluid layers characterized by high temperatures has been considered in this study. It is demonstrated that even at high Rayleigh numbers the radiation mode is as effective as the turbulent natural convection mode in removing the heat from the upper surface of molten pools with adiabatic lower boundary. As a result of this improved heat transfer, it is shown that considerably thicker molten pools with internal heat generation can be supported without boiling inception. The total Nusselt number at a moderate but fixed value of conduction-radiation parameter, can be represented as a function of Rayleigh number in a simple power-law form. As a consequence of this relationship it is shown that maximum nonboiling pool thicknesses vary approximately inversely as the 0.9 power of internal heat generation rate. A comparison between exact analysis using the integral formulation of radiation flux and Rosseland approximateion shows that the latter approximation bears out very adequately for optically thick pools with conduction-radiation parameter > or approx. =0.4 inspite of the fact that individual components of Nusselt number due to radiation and convection, respectively, are grossly in error. These errors in component heat fluxes are compensating due to the total heat balance constraint. However, the comparison between Rosseland approximation and exact formulation gets poorer as the value of conduction-radiation parameter decreases. This increase in error is principally incurred due to the error in estimating wall temperature differences

  5. Experimental and numerical investigation on natural convection heat transfer in nanofluids

    International Nuclear Information System (INIS)

    Kulkarni, P.P.; Nayak, A.K.; Vijayan, P.K.

    2014-01-01

    Currently, a lot of research is being carried out on the potential application of nanofluids as a coolant in nuclear reactors owing to their enhanced heat transfer characteristics as compared to base fluid. In this regards, an experimental study has been undertaken concerning natural convection heat transfer of nanofluids over a cylindrical heater with a constant wall heat flux condition. The heat flux was varied from 0-50000 W/m 2 and Rayleigh number range is 30000 to 1.65 X 10 5 . Results show that there was a reduction in natural convection heat transfer coefficient of nanofluids as compared to water. Experimental results were compared with existing models for similar geometry. However, the available correlation was found to be unable to predict experimental data. A new empirical model was developed based on the experimental data including the effect of nanoparticles concentration which predicts the experimental data satisfactorily. (author)

  6. Convective heat transfer from a heated elliptic cylinder at uniform wall temperature

    Energy Technology Data Exchange (ETDEWEB)

    Kaprawi, S.; Santoso, Dyos [Mechanical Department of Sriwijaya University, Jl. Raya Palembang-Prabumulih Km. 32 Inderalaya 50062 Ogan Ilir (Indonesia)

    2013-07-01

    This study is carried out to analyse the convective heat transfer from a circular and an elliptic cylinders to air. Both circular and elliptic cylinders have the same cross section. The aspect ratio of cylinders range 0-1 are studied. The implicit scheme of the finite difference is applied to obtain the discretized equations of hydrodynamic and thermal problem. The Choleski method is used to solve the discretized hydrodynamic equation and the iteration method is applied to solve the discretized thermal equation. The circular cylinder has the aspect ratio equal to unity while the elliptical cylinder has the aspect ratio less than unity by reducing the minor axis and increasing the major axis to obtain the same cross section as circular cylinder. The results of the calculations show that the skin friction change significantly, but in contrast with the elliptical cylinders have greater convection heat transfer than that of circular cylinder. Some results of calculations are compared to the analytical solutions given by the previous authors.

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

    International Nuclear Information System (INIS)

    Lee, Sang Ho

    2003-01-01

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

  8. Determination of drying kinetics and convective heat transfer coefficients of ginger slices

    Science.gov (United States)

    Akpinar, Ebru Kavak; Toraman, Seda

    2016-10-01

    In the present work, the effects of some parametric values on convective heat transfer coefficients and the thin layer drying process of ginger slices were investigated. Drying was done in the laboratory by using cyclone type convective dryer. The drying air temperature was varied as 40, 50, 60 and 70 °C and the air velocity is 0.8, 1.5 and 3 m/s. All drying experiments had only falling rate period. The drying data were fitted to the twelve mathematical models and performance of these models was investigated by comparing the determination of coefficient ( R 2), reduced Chi-square ( χ 2) and root mean square error between the observed and predicted moisture ratios. The effective moisture diffusivity and activation energy were calculated using an infinite series solution of Fick's diffusion equation. The average effective moisture diffusivity values and activation energy values varied from 2.807 × 10-10 to 6.977 × 10-10 m2/s and 19.313-22.722 kJ/mol over the drying air temperature and velocity range, respectively. Experimental data was used to evaluate the values of constants in Nusselt number expression by using linear regression analysis and consequently, convective heat transfer coefficients were determined in forced convection mode. Convective heat transfer coefficient of ginger slices showed changes in ranges 0.33-2.11 W/m2 °C.

  9. The role of a convective surface in models of the radiative heat transfer in nanofluids

    Energy Technology Data Exchange (ETDEWEB)

    Rahman, M.M., E-mail: mansurdu@yahoo.com; Al-Mazroui, W.A.; Al-Hatmi, F.S.; Al-Lawatia, M.A.; Eltayeb, I.A.

    2014-08-15

    Highlights: • The role of a convective surface in modelling with nanofluids is investigated over a wedge. • Surface convection significantly controls the rate of heat transfer in nanofluid. • Increased volume fraction of nanoparticles to the base-fluid may not always increase the rate of heat transfer. • Effect of nanoparticles solid volume fraction depends on the types of constitutive materials. • Higher heat transfer in nanofluids is found in a moving wedge rather than in a static wedge. - Abstract: Nanotechnology becomes the core of the 21st century. Nanofluids are important class of fluids which help advancing nanotechnology in various ways. Convection in nanofluids plays a key role in enhancing the rate of heat transfer either for heating or cooling nanodevices. In this paper, we investigate theoretically the role of a convective surface on the heat transfer characteristics of water-based nanofluids over a static or moving wedge in the presence of thermal radiation. Three different types of nanoparticles, namely copper Cu, alumina Al{sub 2}O{sub 3} and titanium dioxide TiO{sub 2} are considered in preparation of nanofluids. The governing nonlinear partial differential equations are made dimensionless with the similarity transformations. Numerical simulations are carried out through the very robust computer algebra software MAPLE 13 to investigate the effects of various pertinent parameters on the flow field. The obtained results presented graphically as well as in tabular form and discussed from physical and engineering points of view. The results show that the rate of heat transfer in a nanofluid in the presence of thermal radiation significantly depends on the surface convection parameter. If the hot fluid side surface convection resistance is lower than the cold fluid side surface convection resistance, then increased volume fraction of the nanoparticles to the base fluid may reduces the heat transfer rate rather than increases from the surface of

  10. Convective heat and mass transfer in rotating disk systems

    CERN Document Server

    Shevchuk, Igor V

    2009-01-01

    The book describes results of investigations of a series of convective heat and mass transfer problems in rotating-disk systems. Methodology used included integral methods, self-similar and approximate analytical solutions, as well as CFD.

  11. Experimental study on convective heat transfer of water flow in a heated tube under natural circulation

    International Nuclear Information System (INIS)

    Yang Ruichang; Liu Ruolei; Zhong Yong; Liu Tao

    2006-01-01

    This paper reports on an experimental study on transitional heat transfer of water flow in a heated vertical tube under natural circulation conditions. In the experiments the local and average heat transfer coefficients were obtained. The experimental data were compared with the predictions by a forced flow correlation available in the literature. The comparisons show that the Nusselt number value in the fully developed region is about 30% lower than the predictions by the forced flow correlation due to flow laminarization in the layer induced by co-current bulk natural circulation and free convection. By using the Rayleigh number Ra to represent the influence of free convection on heat transfer, the empirical correlations for the calculation of local and average heat transfer behavior in the tube at natural circulation have been developed. The empirical correlations are in good agreement with the experimental data. Based on the experimental results, the effect of the thermal entry-length behavior on heat transfer design in the tube under natural circulation was evaluated

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

    International Nuclear Information System (INIS)

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

    1999-01-01

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

  13. Time-Dependent Natural Convection Couette Flow of Heat ...

    African Journals Online (AJOL)

    Time-Dependent Natural Convection Couette Flow of Heat Generating/Absorbing Fluid between Vertical Parallel Plates Filled With Porous Material. ... The numerical simulation conducted for some saturated liquids reveled that at t ≥ Pr the steady and unsteady state velocities (as well as the temperature of the fluid) ...

  14. A fractal model for heat transfer of nanofluids by convection in a pool

    Energy Technology Data Exchange (ETDEWEB)

    Xiao Boqi, E-mail: xiaoboqi2006@126.co [Department of Physics and Electromechanical Engineering, Sanming University, 25 Jingdong Road, Sanming 365004 (China); Yu Boming [School of Physics, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan 430074 (China); Wang Zongchi; Chen Lingxia [Department of Physics and Electromechanical Engineering, Sanming University, 25 Jingdong Road, Sanming 365004 (China)

    2009-11-02

    Based on the fractal distribution of nanoparticles, a fractal model for heat transfer of nanofluids is presented in the Letter. Considering heat convection between nanoparticles and liquids due to the Brownian motion of nanoparticles in fluids, the formula of calculating heat flux of nanofluids by convection is given. The proposed model is expressed as a function of the average size of nanoparticle, concentration of nanoparticle, fractal dimension of nanoparticle, temperature and properties of fluids. It is shown that the fractal model is effectual according to a good agreement between the model predictions and experimental data.

  15. A fractal model for heat transfer of nanofluids by convection in a pool

    International Nuclear Information System (INIS)

    Xiao Boqi; Yu Boming; Wang Zongchi; Chen Lingxia

    2009-01-01

    Based on the fractal distribution of nanoparticles, a fractal model for heat transfer of nanofluids is presented in the Letter. Considering heat convection between nanoparticles and liquids due to the Brownian motion of nanoparticles in fluids, the formula of calculating heat flux of nanofluids by convection is given. The proposed model is expressed as a function of the average size of nanoparticle, concentration of nanoparticle, fractal dimension of nanoparticle, temperature and properties of fluids. It is shown that the fractal model is effectual according to a good agreement between the model predictions and experimental data.

  16. Microwave heating device for internal heating convection experiments, applied to Earth's mantle dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Surducan, E.; Surducan, V.; Neamtu, C., E-mail: camelia.neamtu@itim-cj.ro [National Institute for Research and Development of Isotopic and Molecular Technologies (INCDTIM), 67-103 Donat St., 400293, Cluj‑Napoca (Romania); Limare, A.; Di Giuseppe, E. [Institut de Physique du Globe de Paris (IPGP), Univ. Paris Diderot, UMR CNRS 7154, 1 rue Jussieu, 75005, Paris (France)

    2014-12-15

    We report the design, construction, and performances of a microwave (MW) heating device for laboratory experiments with non-contact, homogeneous internal heating. The device generates MW radiation at 2.47 GHz from a commercial magnetron supplied by a pulsed current inverter using proprietary, feedback based command and control hardware and software. Specially designed MW launchers direct the MW radiation into the sample through a MW homogenizer, devised to even the MW power distribution into the sample's volume. An adjustable MW circuit adapts the MW generator to the load (i.e., the sample) placed in the experiment chamber. Dedicated heatsinks maintain the MW circuits at constant temperature throughout the experiment. Openings for laser scanning for image acquisition with a CCD camera and for the cooling circuits are protected by special MW filters. The performances of the device are analyzed in terms of heating uniformity, long term output power stability, and load matching. The device is used for small scale experiments simulating Earth's mantle convection. The 30 × 30 × 5 cm{sup 3} convection tank is filled with a water‑based viscous fluid. A uniform and constant temperature is maintained at the upper boundary by an aluminum heat exchanger and adiabatic conditions apply at the tank base. We characterize the geometry of the convective regime as well as its bulk thermal evolution by measuring the velocity field by Particle Image Velocimetry and the temperature field by using Thermochromic Liquid Crystals.

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

    Science.gov (United States)

    Diaguila, Anthony J; Freche, John C

    1951-01-01

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

  18. Effect of Wind Flow on Convective Heat Losses from Scheffler Solar Concentrator Receivers

    Science.gov (United States)

    Nene, Anita Arvind; Ramachandran, S.; Suyambazhahan, S.

    2018-05-01

    Receiver is an important element of solar concentrator system. In a Scheffler concentrator, solar rays get concentrated at focus of parabolic dish. While radiation losses are more predictable and calculable since strongly related to receiver temperature, convective looses are difficult to estimate in view of additional factors such as wind flow direction, speed, receiver geometry, prior to current work. Experimental investigation was carried out on two geometries of receiver namely cylindrical and conical with 2.7 m2 Scheffler to find optimum condition of tilt to provide best efficiency. Experimental results showed that as compared to cylindrical receiver, conical receiver gave maximum efficiency at 45° tilt angle. However effect of additional factors like wind speed, wind direction on especially convective losses could not be separately seen. The current work was undertaken to investigate further the same two geometries using computation fluid dynamics using FLUENT to compute convective losses considering all variables such at tilt angle of receiver, wind velocity and wind direction. For cylindrical receiver, directional heat transfer coefficient (HTC) is remarkably high to tilt condition meaning this geometry is critical to tilt leading to higher convective heat losses. For conical receiver, directional average HTC is remarkably less to tilt condition leading to lower convective heat loss.

  19. Transient testing of the FFTF for decay-heat removal by natural convection

    International Nuclear Information System (INIS)

    Beaver, T.R.; Johnson, H.G.; Stover, R.L.

    1982-06-01

    This paper reports on the series of transient tests performed in the FFTF as a major part of the pre-operations testing program. The structure of the transient test program was designed to verify the capability of the FFTF to safely remove decay heat by natural convection. The series culminated in a scram from full power to complete natural convection in the plant, simulating a loss of all electrical power. Test results and acceptance criteria related to the verification of safe decay heat removal are presented

  20. Combined Natural Convection and Radiation Heat Transfer of Various Absorbing-Emitting-Scattering Media in a Square Cavity

    Directory of Open Access Journals (Sweden)

    Xianglong Liu

    2014-01-01

    Full Text Available A numerical model is developed to simulate combined natural convection and radiation heat transfer of various anisotropic absorbing-emitting-scattering media in a 2D square cavity based on the discrete ordinate (DO method and Boussinesq assumption. The effects of Rayleigh number, optical thickness, scattering ratio, scattering phase function, and aspect ratio of square cavity on the behaviors of heat transfer are studied. The results show that the heat transfer of absorbing-emitting-scattering media is the combined results of radiation and natural convection, which depends on the physical properties and the aspect ratio of the cavity. When the natural convection becomes significant, the convection heat transfer is enhanced, and the distributions of NuR and Nuc along the walls are obviously distorted. As the optical thickness increases, NuR along the hot wall decreases. As the scattering ratio decreases, the NuR along the walls decreases. At the higher aspect ratio, the more intensive thermal radiation and natural convection are formed, which increase the radiation and convection heat fluxes. This paper provides the theoretical research for the optimal thermal design and practical operation of the high temperature industrial equipments.

  1. Free convection effects and radiative heat transfer in MHD Stokes ...

    Indian Academy of Sciences (India)

    The present note deals with the effects of radiative heat transfer and free convection in MHD for a flow of an electrically conducting, incompressible, dusty viscous fluid past an impulsively started vertical non-conducting plate, under the influence of transversely applied magnetic field. The heat due to viscous dissipation and ...

  2. Radiation and convective heat transfer, and burnout in oxy-coal combustion

    Energy Technology Data Exchange (ETDEWEB)

    J.P. Smart; P. O' Nions; G.S. Riley [RWE npower, Swindon (United Kingdom)

    2010-09-15

    Measurements of radiative and convective heat transfer, and carbon-in-ash have been taken on the RWEn 0.5 MWth combustion test facility (CTF) firing two different coals under oxy-fuel firing conditions. The two coals fired were a Russian Coal and a South African Coal. Recycle ratios were varied within the range of 65-75% dependent on coal. Furnace exit O{sub 2} values were maintained at 3% and 6% for the majority of tests. Air firing tests were also performed to generate baseline data. The work gives a comprehensive insight into the effect of oxy-fuel combustion on both radiative and convective heat transfer, and carbon-in-ash compared to air under dry simulated recycle conditions. Results have shown peak radiative heat flux values are inversely related to the recycle ratio for the two coals studied. Conversely, the convective heat flux values increase with increasing recycle ratio. It was also observed that the axial position of the peak in radiative heat flux moves downstream away from the burner as recycle ratio is increased. A 'working range' of recycle ratios exists where both the radiative and convective heat fluxes are comparable with air. Carbon-in-ash (CIA) was measured for selected conditions. For air firing of Russian Coal, the CIA for follows and expected trend with CIA decreasing with increasing furnace exit O{sub 2}. The CIA data for the two recycle ratios of 72% and 68% for the same coal show that the CIA values are lower than for air firing for corresponding furnace exit O{sub 2} levels and vary little with the value of furnace exit O{sub 2}. CIA measurements were taken for the South African Coal for a range of recycle ratios at 3% and 6% furnace exit O{sub 2} levels. Results indicate that the CIA values are lower for higher furnace exit O{sub 2}. 32 refs., 11 figs., 1 tab.

  3. Mixed convection in inclined lid driven cavity by Lattice Boltzmann Method and heat flux boundary condition

    International Nuclear Information System (INIS)

    D'Orazio, A; Karimipour, A; Nezhad, A H; Shirani, E

    2014-01-01

    Laminar mixed convective heat transfer in two-dimensional rectangular inclined driven cavity is studied numerically by means of a double population thermal Lattice Boltzmann method. Through the top moving lid the heat flux enters the cavity whereas it leaves the system through the bottom wall; side walls are adiabatic. The counter-slip internal energy density boundary condition, able to simulate an imposed non zero heat flux at the wall, is applied, in order to demonstrate that it can be effectively used to simulate heat transfer phenomena also in case of moving walls. Results are analyzed over a range of the Richardson numbers and tilting angles of the enclosure, encompassing the dominating forced convection, mixed convection, and dominating natural convection flow regimes. As expected, heat transfer rate increases as increases the inclination angle, but this effect is significant for higher Richardson numbers, when buoyancy forces dominate the problem; for horizontal cavity, average Nusselt number decreases with the increase of Richardson number because of the stratified field configuration

  4. Control strategy on the double-diffusive convection in a nanofluid layer with internal heat generation

    Science.gov (United States)

    Mokhtar, N. F. M.; Khalid, I. K.; Siri, Z.; Ibrahim, Z. B.; Gani, S. S. A.

    2017-10-01

    The influences of feedback control and internal heat source on the onset of Rayleigh-Bénard convection in a horizontal nanofluid layer is studied analytically due to Soret and Dufour parameters. The confining boundaries of the nanofluid layer (bottom boundary-top boundary) are assumed to be free-free, rigid-free, and rigid-rigid, with a source of heat from below. Linear stability theory is applied, and the eigenvalue solution is obtained numerically using the Galerkin technique. Focusing on the stationary convection, it is shown that there is a positive thermal resistance in the presence of feedback control on the onset of double-diffusive convection, while there is a positive thermal efficiency in the existence of internal heat generation. The possibilities of suppress or augment of the Rayleigh-Bénard convection in a nanofluid layer are also discussed in detail.

  5. Feedback control and heat transfer measurements in a Rayleigh-Bénard convection cell

    Science.gov (United States)

    Vial, M.; Hernández, R. H.

    2017-07-01

    We report experimental results on the heat transfer and instability onset of a Rayleigh-Bénard convection cell of aspect ratios 6:3:1 filled with a high Prandtl aqueous solution of glycerol under feedback control. We investigate the transient and stationary response of both local temperature readings and heat transfer fluxes on the Rayleigh Bénard cell in both conductive and convective states when we perform two independent feedback control actions on both hot and cold walls. We evaluate the performance of both controllers to maintain a temperature gradient independently if the system is below or above the convection threshold. As the convection cell can be rotated at 180° about the shorter axis of the cell, it was possible to perform transitions between thermal conduction and convection regimes and vice versa under a constant temperature difference maintained by both independent controllers. The experimental setup provided an accurate measurement of the critical Rayleigh number and the evolution of the Nusselt number as a function of the Rayleigh number in the moderately supercritical regime (R a cellular convection pattern formed by 6 transverse rolls throughout the range of Rayleigh numbers.

  6. Sensory quality and energy use for scrambled eggs and beef patties heated in institutional microwave and convection ovens

    Energy Technology Data Exchange (ETDEWEB)

    Cremer, M.L.

    1982-05-01

    Scrambled eggs (96 portions) and beef patties (96 portions) were heated in institutional microwave and convection ovens to determine energy use in heating and sensory quality of food. For both products, significantly (P < 0.01) more energy (BTU) was used for heating in the convection than in the microwave oven and respective amounts (BTU) were 28658.7 and 9385.7 for eggs; 31313.3 and 9365.0 for beef patties. All scores for sensory quality were significantly (P < 0.01) higher for eggs heated in the microwave than in the convection, but for beef patties, scores were higher for all characteristics and significantly (P < 0.01) higher for appearance, flavor, and general acceptability after heating in the convection rather than the microwave oven.

  7. Heat and mass transfer of a second grade magnetohydrodynamic fluid over a convectively heated stretching sheet

    Directory of Open Access Journals (Sweden)

    Kalidas Das

    2016-10-01

    Full Text Available The present work is concerned with heat and mass transfer of an electrically conducting second grade MHD fluid past a semi-infinite stretching sheet with convective surface heat flux. The analysis accounts for thermophoresis and thermal radiation. A similarity transformations is used to reduce the governing equations into a dimensionless form. The local similarity equations are derived and solved using Nachtsheim-Swigert shooting iteration technique together with Runge–Kutta sixth order integration scheme. Results for various flow characteristics are presented through graphs and tables delineating the effect of various parameters characterizing the flow. Our analysis explores that the rate of heat transfer enhances with increasing the values of the surface convection parameter. Also the fluid velocity and temperature in the boundary layer region rise significantly for increasing the values of thermal radiation parameter.

  8. Microwave Heating of a Liquid Stably Flowing in a Circular Channel Under the Conditions of Nonstationary Radiative-Convective Heat Transfer

    Science.gov (United States)

    Salomatov, V. V.; Puzyrev, E. M.; Salomatov, A. V.

    2018-05-01

    A class of nonlinear problems of nonstationary radiative-convective heat transfer under the microwave action with a small penetration depth is considered in a stabilized coolant flow in a circular channel. The solutions to these problems are obtained, using asymptotic procedures at the stages of nonstationary and stationary convective heat transfer on the heat-radiating channel surface. The nonstationary and stationary stages of the solution are matched, using the "longitudinal coordinate-time" characteristic. The approximate solutions constructed on such principles correlate reliably with the exact ones at the limiting values of the operation parameters, as well as with numerical and experimental data of other researchers. An important advantage of these solutions is that they allow the determination of the main regularities of the microwave and thermal radiation influence on convective heat transfer in a channel even before performing cumbersome calculations. It is shown that, irrespective of the heat exchange regime (nonstationary or stationary), the Nusselt number decreases and the rate of the surface temperature change increases with increase in the intensity of thermal action.

  9. The effect of sampling rate on interpretation of the temporal characteristics of radiative and convective heating in wildland flames

    Science.gov (United States)

    David Frankman; Brent W. Webb; Bret W. Butler; Daniel Jimenez; Michael Harrington

    2012-01-01

    Time-resolved radiative and convective heating measurements were collected on a prescribed burn in coniferous fuels at a sampling frequency of 500 Hz. Evaluation of the data in the time and frequency domain indicate that this sampling rate was sufficient to capture the temporal fluctuations of radiative and convective heating. The convective heating signal contained...

  10. Mixed convection heat transfer from confined tandem square cylinders in a horizontal channel

    KAUST Repository

    Huang, Zhu

    2013-11-01

    This paper presents a numerical study on the two-dimensional laminar mixed convective flow and heat transfer around two identical isothermal square cylinders arranged in tandem and confined in a channel. The spacing between the cylinders is fixed with four widths of the cylinder and the blockage ratio and the Prandtl number are fixed at 0.1 and 0.7 respectively. The mixed convective flow and heat transfer is simulated by high accuracy multidomain pseudospectral method. The Reynolds number (Re) is studied in the range 80 ≤ Re ≤ 150, the Richardson number (Ri) demonstrating the influence of thermal buoyancy ranges from 0 to 1. Numerical results reveal that, with the thermal buoyancy effect, the mixed convective flow sheds vortex behind the cylinders and keeps periodic oscillating. The variations of characteristic quantities related to flow and heat transfer processes, such as the overall drag and lift coefficients and the Nusselt numbers, are presented and discussed. Furthermore, the influence of thermal buoyancy on the fluid flow and heat transfer are discussed and analysed. © 2013 Elsevier Ltd. All rights reserved.

  11. Conjugate transient natural convection in a cylindrical enclosure with internal volumetric heat generation

    International Nuclear Information System (INIS)

    Sharma, Anil Kumar; Velusamy, K.; Balaji, C.

    2008-01-01

    This paper reports the results of a numerical investigation of transient turbulent natural convection heat transfer from a volumetric energy generating source placed inside a cylindrical enclosure filled with low Prandtl number fluid (liquid sodium, Pr = 0.005). Two-dimensional conservation equations of mass, momentum and energy, coupled with the Boussinesq approximation, are solved using a finite volume based discretisation method employing the SIMPLE algorithm for the pressure velocity coupling. Turbulence is modeled using the k-ε model with physical boundary conditions. The study presents the transient features of confined turbulent natural convection, due to time varying generation of heat in the volumetric source. The intensity of heat source exponentially decays with time and the source is placed over circular plates with a central opening. Results obtained from the numerical model compare favorably with those reported in the literature for steady state natural convection. Numerical simulations are carried out to display the sequential evolution of flow and thermal fields and the maximum temperature reached in the source. The advantages of distributing the heat source on multi trays have been quantified

  12. Numerical modelling of convective heat transport by air flow in permafrost talus slopes

    Directory of Open Access Journals (Sweden)

    J. Wicky

    2017-06-01

    Full Text Available Talus slopes are a widespread geomorphic feature in the Alps. Due to their high porosity a gravity-driven internal air circulation can be established which is forced by the gradient between external (air and internal (talus temperature. The thermal regime is different from the surrounding environment, leading to the occurrence of permafrost below the typical permafrost zone. This phenomenon has mainly been analysed by field studies and only few explicit numerical modelling studies exist. Numerical simulations of permafrost sometimes use parameterisations for the effects of convection but mostly neglect the influence of convective heat transfer in air on the thermal regime. In contrast, in civil engineering many studies have been carried out to investigate the thermal behaviour of blocky layers and to improve their passive cooling effect. The present study further develops and applies these concepts to model heat transfer in air flows in a natural-scale talus slope. Modelling results show that convective heat transfer has the potential to develop a significant temperature difference between the lower and the upper parts of the talus slope. A seasonally alternating chimney-effect type of circulation develops. Modelling results also show that this convective heat transfer leads to the formation of a cold reservoir in the lower part of the talus slope, which can be crucial for maintaining the frozen ground conditions despite increasing air temperatures caused by climate change.

  13. Natural convection heat transfer of water in a horizontal circular gap

    Institute of Scientific and Technical Information of China (English)

    SU Guanghui; Kenichiro Sugiyama; WU Yingwei

    2007-01-01

    An experimental study on the natural convection heat transfer on a horizontal downward facing heated surface in a water gap was carried out under atmospheric pressure conditions. A total of 700 experimental data points were correlated using Rayleigh versus Nusselt number in various forms, based on different independent variables. The effects of different characteristic lengths and film temperatures were discussed. The results show that the buoyancy force acts as a resistance force for natural convecti on beat transfer ona downward facing horizontal heated surface in a confined space. For the estimation of the natural convection heat transfer under the present conditions, empirical correlations in which Nusselt number is expressed as a function of the Rayleigh number, or both Rayleigh and Prandtl numbers, may be used. When it is accurately predicted, the Nusselt number is expressed as a function of the Rayleigh and Prandtl numbers, as well as the gap width-to-heated surface diameter ratio; and uses the temperature difference between the heated surface and the ambient fluid in the definition of Rayleigh number. The characteristic length is the gap size and the film temperature is the average fluid temperature.

  14. Heat Transfer by Thermo-Capillary Convection. Sounding Rocket COMPERE Experiment SOURCE

    Science.gov (United States)

    Fuhrmann, Eckart; Dreyer, Michael

    2009-08-01

    This paper describes the results of a sounding rocket experiment which was partly dedicated to study the heat transfer from a hot wall to a cold liquid with a free surface. Natural or buoyancy-driven convection does not occur in the compensated gravity environment of a ballistic phase. Thermo-capillary convection driven by a temperature gradient along the free surface always occurs if a non-condensable gas is present. This convection increases the heat transfer compared to a pure conductive case. Heat transfer correlations are needed to predict temperature distributions in the tanks of cryogenic upper stages. Future upper stages of the European Ariane V rocket have mission scenarios with multiple ballistic phases. The aims of this paper and of the COMPERE group (French-German research group on propellant behavior in rocket tanks) in general are to provide basic knowledge, correlations and computer models to predict the thermo-fluid behavior of cryogenic propellants for future mission scenarios. Temperature and surface location data from the flight have been compared with numerical calculations to get the heat flux from the wall to the liquid. Since the heat flux measurements along the walls of the transparent test cell were not possible, the analysis of the heat transfer coefficient relies therefore on the numerical modeling which was validated with the flight data. The coincidence between experiment and simulation is fairly good and allows presenting the data in form of a Nusselt number which depends on a characteristic Reynolds number and the Prandtl number. The results are useful for further benchmarking of Computational Fluid Dynamics (CFD) codes such as FLOW-3D and FLUENT, and for the design of future upper stage propellant tanks.

  15. MHD natural convection in open inclined square cavity with a heated circular cylinder

    Science.gov (United States)

    Hosain, Sheikh Anwar; Alim, M. A.; Saha, Satrajit Kumar

    2017-06-01

    MHD natural convection in open cavity becomes very important in many scientific and engineering problems, because of it's application in the design of electronic devices, solar thermal receivers, uncovered flat plate solar collectors having rows of vertical strips, geothermal reservoirs, etc. Several experiments and numerical investigations have been presented for describing the phenomenon of natural convection in open cavity for two decades. MHD natural convection and fluid flow in a two-dimensional open inclined square cavity with a heated circular cylinder was considered. The opposite wall to the opening side of the cavity was first kept to constant heat flux q, at the same time the surrounding fluid interacting with the aperture was maintained to an ambient temperature T∞. The top and bottom wall was kept to low and high temperature respectively. The fluid with different Prandtl numbers. The properties of the fluid are assumed to be constant. As a result a buoyancy force is created inside the cavity due to temperature difference and natural convection is formed inside the cavity. The Computational Fluid Dynamics (CFD) code are used to discretize the solution domain and represent the numerical result to graphical form.. Triangular meshes are used to obtain the solution of the problem. The streamlines and isotherms are produced, heat transfer parameter Nu are obtained. The results are presented in graphical as well as tabular form. The results show that heat flux decreases for increasing inclination of the cavity and the heat flux is a increasing function of Prandtl number Pr and decreasing function of Hartmann number Ha. It is observed that fluid moves counterclockwise around the cylinder in the cavity. Various recirculations are formed around the cylinder. The almost all isotherm lines are concentrated at the right lower corner of the cavity. The object of this work is to develop a Mathematical model regarding the effect of MHD natural convection flow around

  16. The effect of location of a convective heat source on displacement ventilation: CFD study

    Energy Technology Data Exchange (ETDEWEB)

    Park, H.J.; Holland, D. [Dunham Associates, Inc., Minneapolis, MN (United States). Advanced Technologies Group

    2001-08-01

    Two-dimensional computational simulations are performed to examine the effect of vertical location of a convective heat source on thermal displacement ventilation systems. In this study, a heat source is modeled with seven different heights from the floor (0.5, 0.75, 1.0, 1.25, 1.5, 1.75, 2.0 m) in a displacement ventilation environment. The flow and temperature fields in thermal displacement ventilation systems vary depending on the location of the heat source. As the heat source rises, the convective heat gain from the heat source to an occupied zone becomes less significant. This effect changes the temperature field and results in the reduction of the cooling load in the occupied zone. The stratification level is also affected by the heat source location at a given flow rate. (author)

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

    Science.gov (United States)

    Khadke, Rishikesh; Bhole, Kiran

    2018-02-01

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

  18. Convective heat transfer enhancement using Carbon nanofibers (CNFs): influence of amorphous carbon layer on heat transfer performance

    NARCIS (Netherlands)

    Taha, T.J.; Lefferts, Leonardus; van der Meer, Theodorus H.

    2013-01-01

    In this work, an experimental heat transfer investigation was carried out to investigate the combined influence of both amorphous carbon (a-C) layer thickness and carbon nanofibers (CNFs) on the convective heat transfer behavior. Synthesis of these carbon nano structures was achieved using catalytic

  19. Industrial Application of Topology Optimization for Combined Conductive and Convective Heat Transfer Problems

    DEFF Research Database (Denmark)

    Zhou, Mingdong; Alexandersen, Joe; Sigmund, Ole

    2016-01-01

    This paper presents an industrial application of topology optimization for combined conductive and convective heat transfer problems. The solution is based on a synergy of computer aided design and engineering software tools from Dassault Systemes. The considered physical problem of steady......-state heat transfer under convection is simulated using SIMULIA-Abaqus. A corresponding topology optimization feature is provided by SIMULIA-Tosca. By following a standard workflow of design optimization, the proposed solution is able to accommodate practical design scenarios and results in efficient...

  20. Temperature and heat flux scaling laws for isoviscous, infinite Prandtl number mixed heating convection.

    Science.gov (United States)

    Vilella, Kenny; Deschamps, Frederic

    2018-04-01

    Thermal evolution of terrestrial planets is controlled by heat transfer through their silicate mantles. A suitable framework for modelling this heat transport is a system including bottom heating (from the core) and internal heating, e.g., generated by secular cooling or by the decay of radioactive isotopes. The mechanism of heat transfer depends on the physical properties of the system. In systems where convection is able to operate, two different regimes are possible depending on the relative amount of bottom and internal heating. For moderate internal heating rates, the system is composed of active hot upwellings and cold downwellings. For large internal heating rates, the bottom heat flux becomes negative and the system is only composed of active cold downwellings. Here, we build theoretical scaling laws for both convective regimes following the approach of Vilella & Kaminski (2017), which links the surface heat flux and the temperature jump across both the top and bottom thermal boundary layer (TBL) to the Rayleigh number and the dimensionless internal heating rate. Theoretical predictions are then verified against numerical simulations performed in 2D and 3D-Cartesian geometry, and covering a large range of the parameter space. Our theoretical scaling laws are more successful in predicting the thermal structure of systems with large internal heating rates than that of systems with no or moderate internal heating. The differences between moderate and large internal heating rates are interpreted as differences in the mechanisms generating thermal instabilities. We identified three mechanisms: conductive growth of the TBL, instability impacting, and TBL erosion, the last two being present only for moderate internal heating rates, in which hot plumes are generated at the bottom of the system and are able to reach the surface. Finally, we apply our scaling laws to the evolution of the early Earth, proposing a new model for the cooling of the primordial magma ocean

  1. Simultaneous Heat and Mass Transfer Model for Convective Drying of Building Material

    Science.gov (United States)

    Upadhyay, Ashwani; Chandramohan, V. P.

    2018-04-01

    A mathematical model of simultaneous heat and moisture transfer is developed for convective drying of building material. A rectangular brick is considered for sample object. Finite-difference method with semi-implicit scheme is used for solving the transient governing heat and mass transfer equation. Convective boundary condition is used, as the product is exposed in hot air. The heat and mass transfer equations are coupled through diffusion coefficient which is assumed as the function of temperature of the product. Set of algebraic equations are generated through space and time discretization. The discretized algebraic equations are solved by Gauss-Siedel method via iteration. Grid and time independent studies are performed for finding the optimum number of nodal points and time steps respectively. A MATLAB computer code is developed to solve the heat and mass transfer equations simultaneously. Transient heat and mass transfer simulations are performed to find the temperature and moisture distribution inside the brick.

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

    DEFF Research Database (Denmark)

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

    2013-01-01

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

  3. CONVECTIVE HEAT TRANSFER IN CYCLONE DEVICE WITH EXTERNAL GAS RECIRCULATION

    Directory of Open Access Journals (Sweden)

    S. V. Karpov

    2016-01-01

    Full Text Available The article considers the convective heat transfer on the surface of a hollow cylinder or several billets in a cyclone device with the new principle of external gas recirculation. According to this principle, transport of coolant from the lateral surface of the chamber, where the temperature is the highest, in the axial region is being fulfilled due to the pressure drop between the wall and axial areas of cyclonic flow. Dependency analysis of average and local heat transfer coefficients from operational and geometrical parameters has been performed; the generalized similarity equations for the calculation of the latter have been suggested. It is demonstrated that in case of download of a cyclone chamber with several billets, the use of the considered scheme of the external recirculation due to the specific characteristics of aerodynamics practically does not lead to noticeable changes in the intensity of convective heat transfer. Both experimental data and the numerical simulation results obtained with the use of OpenFOAM platform were used in the work. The investigations fulfilled will expand the area of the use of cyclone heating devices.

  4. EXPERIMENTAL INVESTIGATION OF THE CONVECTIVE HEAT TRANSFER IN A SPIRALLY COILED CORRUGATED TUBE WITH RADIANT HEATING

    Directory of Open Access Journals (Sweden)

    Milan Đorđević

    2017-12-01

    Full Text Available The Archimedean spiral coil made of a transversely corrugated tube was exposed to radiant heating in order to represent a heat absorber of the parabolic dish solar concentrator. The main advantage of the considered innovative design solution is a coupling effect of the two passive methods for heat transfer enhancement - coiling of the flow channel and changes in surface roughness. The curvature ratio of the spiral coil varies from 0.029 to 0.234, while water and a mixture of propylene glycol and water are used as heat transfer fluids. The unique focus of this study is on specific boundary conditions since the heat flux upon the tube external surfaces varies not only in the circumferential direction, but in the axial direction as well. Instrumentation of the laboratory model of the heat absorber mounted in the radiation field includes measurement of inlet fluid flow rate, pressure drop, inlet and outlet fluid temperature and 35 type K thermocouples welded to the coil surface. A thermal analysis of the experimentally obtained data implies taking into consideration the externally applied radiation field, convective and radiative heat losses, conduction through the tube wall and convection to the internal fluid. The experimental results have shown significant enhancement of the heat transfer rate compared to spirally coiled smooth tubes, up to 240% in the turbulent flow regime.

  5. Experimental study on the effects of channel gap size on mixed convection heat transfer characteristics in vertical rectangular channels heated from both sides

    International Nuclear Information System (INIS)

    Sudo, Y.; Kaminaga, M.

    1990-01-01

    The effects of channel gap size on mixed forced and free convective heat transfer characteristics were experimentally investigated for water flowing near atmospheric pressure in a 750 mm long and 50 mm wide channel heated from both sides. The channel gap sizes investigated were 2.5, 6, 18 and 50 mm. Experiments were carried out for both aiding and opposing forced convective flows with a Reynolds number Re x of 4x10 to 6x10 6 and a Grashof number Gr x of 2x10 4 to 6x10 11 , where the distance x from the inlet of the channel is adopted as the characteristic length in Re x and Gr x . As for the results, the following were revealed for the parameters ranges investigated in this study. (1) When the dimensionless parameter, Gr x /Re x 21/8 Pr 1/2 is less than 10 -4 , the flow shows the nature of forced convective heat transfer for a channel with any channel gap size in both aiding and opposing flows. (2) When Gr x /Re x 21/8 Pr 1/2 is larger than 10 -2 , the flow shows the nature of free convective heat transfer for a channel with any channel gap size in both aiding and opposing flows. (3) When Gr x /Re x 21/8 Pr 1/2 is between 10 -4 and 10 -2 for the channel with a channel gap size equal to or larger than 6 mm, the heat transfer coefficients in both aiding and opposing flows become, on the average, higher than those predicted by the previous correlations for either the pure turbulent forced convection or the pure free convection, and can be expressed in simple forms with a combination of Gr x /Re x 21/8 Pr 1/2 and the previous correlation for either the pure turbulent forced convection or the free convection along a flat plate. (4) When Gr x /Re x 21/8 Pr 1/2 is between 10 -4 and 10 -2 for the channel with a channel gap size of 2.5 mm, the heat transfer coefficients in both aiding and opposing flows also become, on the average, higher than those predicted by the previous correlations for either the pure turbulent forced convection or the pure free convection. (orig./GL)

  6. A highly stable microchannel heat sink for convective boiling

    International Nuclear Information System (INIS)

    Lu, Chun Ting; Pan Chin

    2009-01-01

    To develop a highly stable two-phase microchannel heat sink, we experimented with convective boiling in diverging, parallel microchannels with different distributions of laser-etched artificial nucleation sites. Each microchannel had a mean hydraulic diameter of 120 µm. The two-phase flow visualization and the magnitudes of pressure drop and inlet temperature oscillations under boiling conditions demonstrated clearly the merits of using artificial nucleation sites to further stabilize the flow boiling in diverging, parallel microchannels. The stability map showed the plane of subcooling number versus phase change number. It illustrated that diverging, parallel microchannels with artificial nucleation cavities have a much wider stable region than parallel microchannels with uniform cross-sections or diverging, parallel microchannels without artificial nucleation cavities. In addition, the results revealed that the design with cavities distributed uniformly along the downstream half of the channel presented the best stability performance among the three distributions of nucleation sites. This particular design can be regarded as a highly stable microchannel heat sink for convective boiling

  7. The optimization of longitudinal convective fins with internal heat generation

    International Nuclear Information System (INIS)

    Razelos, P.

    1979-01-01

    The solution of the optimization problem for longitudinal convective fins of constant thickness, triangular or parabolic profile, and uniform internal heat generation, is presented. The cases considered are those of a given heat generation density, total heat generation and heat generation per unit width of the fin, when either the heat dissipation or the width of the fin is prescribed. The results are set forth in a nondimensional form, which are presented graphically. The effect of the fin's thermal conductivity upon the optimum dimensions is discussed, and limiting values for the heat generation and the heat dissipation, which may be imposed on the fin for a feasible optimization, are also obtained. (Auth.)

  8. Second Law Analysis in Convective Heat and Mass Transfer

    Directory of Open Access Journals (Sweden)

    A. Ben Brahim

    2006-02-01

    Full Text Available This paper reports the numerical determination of the entropy generation due to heat transfer, mass transfer and fluid friction in steady state for laminar double diffusive convection, in an inclined enclosure with heat and mass diffusive walls, by solving numerically the mass, momentum, species conservation and energy balance equations, using a Control Volume Finite-Element Method. The influences of the inclination angle, the thermal Grashof number and the buoyancy ratio on total entropy generation were investigated. The irreversibilities localization due to heat transfer, mass transfer and fluid friction is discussed for three inclination angles at a fixed thermal Grashof number.

  9. Periodic mixed convection in horizontal porous layer heated from below by isoflux heater

    International Nuclear Information System (INIS)

    Saeid, Nawaf H.; Pop, I.

    2006-01-01

    Numerical study for transient mixed convection in a two-dimensional horizontal porous layer heated from below by a constant heat flux source is carried out in the present paper. The transient thermal field, flow field and average Nusselt number are presented for a wide range of the Peclet number, Pe, for the particular case of Rayleigh number Ra=10x2 and the ratio of heater length to the porous layer thickness A=1, 3 and 5. It is found that for A=3 and A=5 with small values of the Peclet number, the free convection mode is dominated, while for large values, of the Peclet number, the forced convection mode is dominated. However, for moderate values the oscillatory mixed convection is observed and a periodic variation of the average Nusselt number is obtained. When the heater length is equal to the porous layer thickness (A=1) the steady-state results are obtained for the range of Pe=0.01-10. (author)

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

    International Nuclear Information System (INIS)

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

    1981-01-01

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

  11. Heat transfer enhancement in a turbulent natural convection boundary layer along a vertical flat plate

    International Nuclear Information System (INIS)

    Tsuji, Toshihiro; Kajitani, Tsuyoshi; Nishino, Tatsuhiko

    2007-01-01

    An experimental study on heat transfer enhancement for a turbulent natural convection boundary layer in air along a vertical flat plate has been performed by inserting a long flat plate in the spanwise direction (simple heat transfer promoter) and short flat plates aligned in the spanwise direction (split heat transfer promoter) with clearances into the near-wall region of the boundary layer. For a simple heat transfer promoter, the heat transfer coefficients increase by a peak value of approximately 37% in the downstream region of the promoter compared with those in the usual turbulent natural convection boundary layer. It is found from flow visualization and simultaneous measurements of the flow and thermal fields with hot- and cold-wires that such increase of heat transfer coefficients is mainly caused by the deflection of flows toward the outer region of the boundary layer and the invasion of low-temperature fluids from the outer region to the near-wall region with large-scale vortex motions riding out the promoter. However, heat transfer coefficients for a split heat transfer promoter exhibit an increase in peak value of approximately 60% in the downstream region of the promoter. Flow visualization and PIV measurements show that such remarkable heat transfer enhancement is attributed to longitudinal vortices generated by flows passing through the clearances of the promoter in addition to large-scale vortex motions riding out the promoter. Consequently, it is concluded that heat transfer enhancement of the turbulent natural convection boundary layer can be substantially achieved in a wide area of the turbulent natural convection boundary layer by employing multiple column split heat transfer promoters. It may be expected that the heat transfer enhancement in excess of approximately 40% can be accomplished by inserting such promoters

  12. Heat transfer coefficient correlation for convective boiling inside plain and micro fin tubes using genetic algorithms

    International Nuclear Information System (INIS)

    Picanco, Marco Antonio Silva; Bandarra Filho, Enio Pedone; Passos, Julio Cesar

    2006-01-01

    Two-phase flow heat transfer has been exhaustively studied over recent years. However, in this field several questions remain unanswered. Heat transfer coefficient prediction related to nucleate and convective boiling have been studied using different approaches, numerical, analytical and experimental. In this work, an experimental analysis, data representation and heat transfer coefficient prediction on two-phase heat transfer on nucleate and convective boiling are presented. An empirical correlation is obtained based on genetic algorithms search engine over a dimensional analysis of the two-phase flow heat transfer problem. (author)

  13. Numerical research on natural convection in molten salt reactor with non-uniformly distributed volumetric heat generation

    International Nuclear Information System (INIS)

    Qian Libo; Qiu Suizheng; Zhang Dalin; Su Guanghui; Tian Wenxi

    2010-01-01

    Molten salt reactor is one of the six Generation IV systems capable of breeding and transmutation of actinides and long-lived fission products, which uses the liquid molten salt as the fuel solvent, coolant and heat generation simultaneously. The present work presents a numerical investigation on natural convection with non-uniform heat generation through which the heat generated by the fluid fuel is removed out of the core region when the reactor is under post-accident condition or zero-power condition. The two-group neutron diffusion equation is applied to calculated neutron flux distribution, which leads to non-uniform heat generation. The SIMPLER algorithm is used to calculate natural convective heat transfer rate with isothermal or adiabatic rigid walls. These two models are coupled through the temperature field and heat sources. The peculiarities of natural convection with non-uniform heat generation are investigated in a range of Ra numbers (10 3 ∼ 10 7 ) for the laminar regime of fluid motion. In addition, the numerical results are also compared with those containing uniform heat generation.

  14. Natural Convection Heat Transfer in Concentric Horizontal Annuli Containing a Saturated Porous Medi

    Directory of Open Access Journals (Sweden)

    Ahmed F. Alfahaid, R.Y. Sakr

    2012-10-01

    Full Text Available Natural convection in horizontal annular porous media has become a subject receiving increasing attention due to its practical importance in the problem of insulators, such as ducting system in high temperature gas-cooled reactors, heating systems, thermal energy storage systems, under ground cable systems, etc. This paper presents a numerical study for steady state thermal convection in a fully saturated porous media bounded by two horizontal concentric cylinders, the cylinders are impermeable to fluid motion and maintained at different, uniform temperatures.  The solution scheme is based on two-dimensional model, which is governed by Darcy-Oberbeck-Boussinesq equations. The finite element method using Galerkin technique is developed and employed to solve the present problem. A numerical simulation is carried out to examine the parametric effects of Rayleigh number and radius ratio on the role played by natural convection heat transfer in the porous annuli. The numerical results obtained from the present model were compared with the available published results and good agreement is observed. The average Nusselt number at the heating surface of the inner cylinder is correlated to Rayleigh number and radius ratio.Keywords: Natural convection, numerical investigation, saturated porous media, finite element method, concentric horizontal annuli.

  15. Geothermal Heating, Convective Flow and Ice Thickness on Mars

    Science.gov (United States)

    Rosenberg, N. D.; Travis, B. J.; Cuzzi, J.

    2001-01-01

    Our 3D calculations suggest that hydrothermal circulation may occur in the martian regolith and may significantly thin the surface ice layer on Mars at some locations due to the upwelling of warm convecting fluids driven solely by background geothermal heating. Additional information is contained in the original extended abstract.

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

    Science.gov (United States)

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

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

  17. Time-dependent mixed convection heat transfer from a sphere in a micro-gravity environment

    International Nuclear Information System (INIS)

    Hommel, M.J.

    1987-01-01

    A fundamental problem of interest for crystal growth in micro-gravity applications involves the mixed convection heat transfer from a sphere in a uniform flow of fluid at a differing temperature. Under the combined influence of the imposed free stream as well as an induced buoyancy force due to thermal expansion of the fluid, the heat transfer from the sphere will be different from that of either the pure forced convection flow or the pure free convection flow. For the present study, the method of matched asymptotic expansions is applied to the laminar flow problem of an impulsively heated, impulsively started sphere in an originally quiescent fluid. Time series expansions are developed for the dependent variables by acknowledging the existence of two district regions: one, an inner region, near the sphere, in which viscous effects are significant; and two, an outer region in which the fluid may be treated as inviscid. The time series expansions are developed in terms of the Reynolds number and Richardson number (Buoyancy Parameter), and the relevant heat transfer and drag coefficients are calculated and plotted

  18. Development of natural convection heat transfer correlation for liquid metal with overlying boiling coolant

    International Nuclear Information System (INIS)

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

    1999-01-01

    Experimental study was performed to investigate the natural convection heat transfer characteristics and the crust formation of the molten metal pool concurrent with forced convective boiling of the overlying coolant. Tests were performed under the condition of the bottom surface heating in the test section and the forced convection of the coolant being injected onto the molten metal pool. The constant temperature and constant heater input power conditions were adopted for the bottom heating. Test results showed that the temperature distribution and crust layer thickness in the metal layer are appreciably affected by the heated bottom surface temperature of the test section, but not much by the coolant injection rate. The relationship between the Nu number and Ra number in the molten metal pool region is determined and compared with the correlations in the literature, and the experiment without coolant boiling. A new correlation on the relationship between the Nu number and Ra number in the molten metal pool with crust formation is developed from the experimental data

  19. Mathematical Simulation of Convective Heat Transfer in the Low-Temperature Storage of Liquefied Natural Gas

    Directory of Open Access Journals (Sweden)

    Shestakov Igor A.

    2015-01-01

    Full Text Available The article shows the results of mathematical modeling of convective heat transfer in the low-temperature storage of liquefied natural gas. Regime of natural convection in an enclosure with different intensity of the heat flux at the external borders are investigated. Was examined two-dimensional nonstationary problem within the model of Navier-Stokes in dimensionless variables “vorticity - stream function - temperature”. Distributions of hydrodynamic parameters and temperatures that characterize the basic regularities of the processes are obtained. Circulating flows are determined and carried out the analysis of vortices formation mechanism and the temperature distribution in solution at conditions of natural convection when the Grashof number (Gr = 106. A significant influence of heat transfer rate on solutions boundary on flow structure and temperature field in LNG storage tanks.

  20. Combined natural convection heat and mass transfer from vertical fin arrays

    International Nuclear Information System (INIS)

    Giri, A.; Narasimham, G.S.V.L.; Krishna Murthy, M.V.

    2003-01-01

    Natural convection transport processes play an important role in many applications like ice-storage air-conditioning. A mathematical formulation of natural convection heat and mass transfer over a shrouded vertical fin array is developed. The base plate is maintained at a temperature below the dew point of the surrounding moist air. Hence there occurs condensation of moisture on the base plate, while the fins may be partially or fully wet. A numerical study is performed by varying the parameters of the problem. The local and average Nusselt numbers decrease in streamwise direction and tend to approach fully developed values for sufficiently large values of the fin length. The results show that beyond a certain streamwise distance, further fin length does not improve the sensible and latent heat transfer performance, and that if dry fin analysis is used under moisture condensation conditions, the overall heat transfer will be underestimated by about 50% even at low buoyancy ratios

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-05-15

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

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

    International Nuclear Information System (INIS)

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

    2014-01-01

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

  3. Use of Artificial Neural Networks for Prediction of Convective Heat Transfer in Evaporative Units

    Directory of Open Access Journals (Sweden)

    Romero-Méndez Ricardo

    2014-01-01

    Full Text Available Convective heat transfer prediction of evaporative processes is more complicated than the heat transfer prediction of single-phase convective processes. This is due to the fact that physical phenomena involved in evaporative processes are very complex and vary with the vapor quality that increases gradually as more fluid is evaporated. Power-law correlations used for prediction of evaporative convection have proved little accuracy when used in practical cases. In this investigation, neural-network-based models have been used as a tool for prediction of the thermal performance of evaporative units. For this purpose, experimental data were obtained in a facility that includes a counter-flow concentric pipes heat exchanger with R134a refrigerant flowing inside the circular section and temperature controlled warm water moving through the annular section. This work also included the construction of an inverse Rankine refrigeration cycle that was equipped with measurement devices, sensors and a data acquisition system to collect the experimental measurements under different operating conditions. Part of the data were used to train several neural-network configurations. The best neural-network model was then used for prediction purposes and the results obtained were compared with experimental data not used for training purposes. The results obtained in this investigation reveal the convenience of using artificial neural networks as accurate predictive tools for determining convective heat transfer rates of evaporative processes.

  4. Convective heat transfer and infrared thermography.

    Science.gov (United States)

    Carlomagno, Giovanni M; Astarita, Tommaso; Cardone, Gennaro

    2002-10-01

    Infrared (IR) thermography, because of its two-dimensional and non-intrusive nature, can be exploited in industrial applications as well as in research. This paper deals with measurement of convective heat transfer coefficients (h) in three complex fluid flow configurations that concern the main aspects of both internal and external cooling of turbine engine components: (1) flow in ribbed, or smooth, channels connected by a 180 degrees sharp turn, (2) a jet in cross-flow, and (3) a jet impinging on a wall. The aim of this study was to acquire detailed measurements of h distribution in complex flow configurations related to both internal and external cooling of turbine components. The heated thin foil technique, which involves the detection of surface temperature by means of an IR scanning radiometer, was exploited to measure h. Particle image velocimetry was also used in one of the configurations to precisely determine the velocity field.

  5. Convective and conduction heat transfer study on a mig-type electron gun

    International Nuclear Information System (INIS)

    Patire Junior, H.; Barroso, J.J.

    1996-01-01

    A convective and conducting heat transfer study of a magnetron injection electron gun has been made to minimize the temperature distribution in the gun elements while keeping the required operating temperature at 1000 0 C of the emitter. Appropriate materials were selected to reduce thermal losses and to improve the gun design from a constructional point of view aiming at extending the capabilities of the electron gun. A thermal probe to determine the air velocity and the convective heat transfer coefficient has been constructed to determine the external boundary condition of the ceramic shell and external flanges. A study the contact resistance for all the gun elements has been made to minimize the conduction thermal losses. A software has been used to simulate a thermal model considering the three processes of thermal transfer, namely, conduction, convection and radiation and the influence of the physical properties of the materials used. (author). 7 refs., 5 figs., 1 tab

  6. Heat transfer during forced convection condensation inside horizontal tube

    Energy Technology Data Exchange (ETDEWEB)

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

    1995-03-01

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

  7. Numerical Modeling of Conjugate Thermogravitational Convection in a Closed System with a Radiant Energy Source in Conditions of Convective-Radiative Heat Exchange at the External Boundary

    Directory of Open Access Journals (Sweden)

    Nee Alexander

    2016-01-01

    Full Text Available Mathematical modeling of conjugate natural convection in a closed rectangular cavity with a radiant energy source in conditions of convective-radiative heat exchange at the external boundary was conducted. The radiant energy distribution was set by the Lambert’s law. Conduction and convection processes analysis showed that the air masses flow pattern is modified slightly over the time. The temperature increases in the gas cavity, despite the heat removal from the one of the external boundary. According to the results of the integral heat transfer analysis were established that the average Nusselt number (Nuav increasing occurs up to τ = 200 (dimensionless time. Further Nuav has changed insignificantly due to the temperature field equalization near the interfaces “gas – wall”.

  8. Mathematical Simulation of Convective Heat Transfer in the Low-Temperature Storage of Liquefied Natural Gas

    OpenAIRE

    Shestakov, Igor; Dolgova, Anastasia; Maksimov, Vyacheslav Ivanovich

    2015-01-01

    The article shows the results of mathematical modeling of convective heat transfer in the low-temperature storage of liquefied natural gas. Regime of natural convection in an enclosure with different intensity of the heat flux at the external borders are investigated. Was examined two-dimensional nonstationary problem within the model of Navier-Stokes in dimensionless variables “vorticity - stream function - temperature”. Distributions of hydrodynamic parameters and temperatures that characte...

  9. Thermal histories of convective earth models and constraints on radiogenic heat production in the earth

    International Nuclear Information System (INIS)

    Davies, G.F.

    1980-01-01

    Thermal histories have been calculated for simple models of the earth which assume that heat is transported by convection throughout the interior. The application of independent constraints to these solutions limits the acceptable range of the ratio of present radiogenic heat production in the earth to the present surface heat flux. The models use an empirical relation between the rate of convective heat transport and the temperature difference across a convecting fluid. This is combined with an approximate proportionality between effective mantle viscosity and T/sup -n/, where T is temperature and it is argued that n is about 30 throughout the mantle. The large value of n causes T to be strongly buffered against changes in the earth's energy budget and shortens by an order of magnitude the response time of surface heat flux to changes in energy budget as compared to less temperature-dependent heat transport mechanisms. Nevertheless, response times with n=30 are still as long as 1 or 2 b.y. Assuming that the present heat flux is entirely primordial (i.e., nonradiogenic) in a convective model leads back to unrealistically high temperatures about 1.7 b.y. ago. Inclusion of exponentially decaying (i.e., radiogenic) heat sources moves the high temperatures further into the past and leads to a transition from 'hot' to 'cool' calculated thermal histories for the case when the present rate of heat production is near 50% of the present rate of heat loss. Requiring the calculated histories to satisfy minimal geological constraints limits the present heat production/heat loss ratio to between about 0.3 and 0.85. Plausible stronger constraints narrow this range to between 0.45 and 0.65. These results are compatible with estimated radiogentic heat production rates in some meteorites and terrestrial rocks, with a whole-earth K/U ratio of 1--2 x 10 4 giving optimal agreement

  10. Network model of free convection within internally heated porous media

    International Nuclear Information System (INIS)

    Conrad, P.W.

    1977-01-01

    A hypothetical core-disruptive accident (HCDA) in a liquid metal fast breeder reactor (LMFBR) may result in the formation of an internally heated debris bed. Considerable attention has been given to postulated mechanisms by which such beds may be cooled. It is the purpose of the work described to demonstrate a method for computing the heat transfer from such a bed to the overlying sodium pool due to single-phase, free convection

  11. Natural Convection Heat Transfer of Oxide Pool During In-Vessel Retention of Core Melts

    Energy Technology Data Exchange (ETDEWEB)

    Park, Hae-Kyun; Chung, Bum-Jin [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2015-10-15

    The integrity of reactor vessel may be threatened by the heat generation at the oxide pool and to the natural convection heat transfer to the reactor vessel by those two layers. Therefore, External Reactor Vessel Cooling (ERVC) is performed in order to secure the integrity of the reactor vessel. Whether the IVR(In-Vessel Retention) Strategy can be applicable to a larger reactor is the technical concern, which nourished the research interest for the natural convection heat transfer of metal and oxide pool and ERVC performance. Especially, it is hard to simulate oxide pool by experimentally due to the high level of buoyancy. Moreover, the volumetrically exothermic working fluid should be adopted to simulate the behavior of the core melts. Therefore, the volumetric heat sources that immersed in the working fluid have been adopted to simulate oxide pool by experiment. We investigated oxide pool with two different designs of the volumetric heat sources that adopted previous experiments. The investigation was performed by mass transfer experiment using analogy between heat and mass transfers. The results were compared to previous studies. We simulated the natural convection heat transfer of the oxide pool by mass transfer experiment. The isothermally cooled condition was established by limiting current technique firstly. The results were compared to previous studies under identical design of the volumetric heat sources. The average Nu's of the curvature and the top plate were close to the previous studies.

  12. The Natural Convection Heat Transfer inside Vertical Pipe: Characteristic of Pipe Flow according to the Boundary layer

    Energy Technology Data Exchange (ETDEWEB)

    Ohk, Seung Min; Chung, Bum Jin [Kyunghee University, Yongin (Korea, Republic of)

    2016-05-15

    The Passive Cooling System (PCS) driven by natural forces drew research attention since Fukushima nuclear power plant accident. This study investigated the natural convection heat transfer inside of vertical pipe with emphasis on the phenomena regarding the boundary layer interaction. Numerical calculations were carried out using FLUENT 6.3. Experiments were performed for the parts of the cases to explore the accuracy of calculation. Based on the analogy, heat transfer experiment is replaced by mass transfer experiment using sulfuric acid copper sulfate (CuSO{sub 4}. H{sub 2}SO{sub 4}) electroplating system. The natural convection heat transfer inside a vertical pipe is studied experimentally and numerically. Experiments were carried out using sulfuric acid-copper sulfate (H{sub 2}SO{sub 4}-CuSO{sub 4}) based on the analogy concept between heat and mass transfer system. Numerical analysis was carried out using FLUENT 6.3. It is concluded that the boundary layer interaction along the flow passage influences the heat transfer, which is affected by the length, diameter, and Prandtl number. For the large diameter and high Prandtl number cases, where the thermal boundary layers do not interfered along the pipe, the heat transfer agreed with vertical flat plate for laminar and turbulent natural convection correlation within 8%. When the flow becomes steady state, the forced convective flow appears in the bottom of the vertical pipe and natural convection flow appears near the exit. It is different behavior from the flow on the parallel vertical flat plates. Nevertheless, the heat transfer was not different greatly compared with those of vertical plate.

  13. Assessment of Haar Wavelet-Quasilinearization Technique in Heat Convection-Radiation Equations

    Directory of Open Access Journals (Sweden)

    Umer Saeed

    2014-01-01

    Full Text Available We showed that solutions by the Haar wavelet-quasilinearization technique for the two problems, namely, (i temperature distribution equation in lumped system of combined convection-radiation in a slab made of materials with variable thermal conductivity and (ii cooling of a lumped system by combined convection and radiation are strongly reliable and also more accurate than the other numerical methods and are in good agreement with exact solution. According to the Haar wavelet-quasilinearization technique, we convert the nonlinear heat transfer equation to linear discretized equation with the help of quasilinearization technique and apply the Haar wavelet method at each iteration of quasilinearization technique to get the solution. The main aim of present work is to show the reliability of the Haar wavelet-quasilinearization technique for heat transfer equations.

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

    International Nuclear Information System (INIS)

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

    2010-01-01

    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. Natural convection in wavy enclosures with volumetric heat sources

    International Nuclear Information System (INIS)

    Oztop, H.F.; Varol, Y.; Abu-Nada, E.; Chamkha, A.

    2011-01-01

    In this paper, the effects of volumetric heat sources on natural convection heat transfer and flow structures in a wavy-walled enclosure are studied numerically. The governing differential equations are solved by an accurate finite-volume method. The vertical walls of enclosure are assumed to be heated differentially whereas the two wavy walls (top and bottom) are kept adiabatic. The effective governing parameters for this problem are the internal and external Rayleigh numbers and the amplitude of wavy walls. It is found that both the function of wavy wall and the ratio of internal Rayleigh number (Ra I ) to external Rayleigh number (Ra E ) affect the heat transfer and fluid flow significantly. The heat transfer is predicted to be a decreasing function of waviness of the top and bottom walls in case of (IRa/ERa)>1 and (IRa/ERa)<1. (authors)

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

    International Nuclear Information System (INIS)

    Astruc, J.M.

    1967-12-01

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

  17. Heat Convection at the Density Maximum Point of Water

    Science.gov (United States)

    Balta, Nuri; Korganci, Nuri

    2018-01-01

    Water exhibits a maximum in density at normal pressure at around 4° degree temperature. This paper demonstrates that during cooling, at around 4 °C, the temperature remains constant for a while because of heat exchange associated with convective currents inside the water. Superficial approach implies it as a new anomaly of water, but actually it…

  18. Nonlinear convective flow of Powell-Erying magneto nanofluid with Newtonian heating

    Directory of Open Access Journals (Sweden)

    Sajid Qayyum

    Full Text Available Objective of present article is to describe magnetohydrodynamic (MHD non-linear convective flow of Powell-Erying nanofluid over a stretching surface. Characteristics of Newtonian heat and mass conditions in this attempt is given attention. Heat and mass transfer analysis is examined in the frame of thermal radiation and chemical reaction. Brownian motion and thermophoresis concept is introduced due to presence of nanoparticles. Nonlinear equations of momentum, energy and concentration are transformed into dimensionless expression by invoking suitable variables. The series solutions are obtained through homotopy analysis method (HAM. Impact of embedded variables on the velocity, temperature and nanoparticles concentration is graphically presented. Numerical values of skin friction coefficient, local Nusselt and Sherwood numbers are computed and analyzed. It is concluded that velocity field enhances for fluid variable while reverse situation is noticed regarding Hartman number. Temperature and heat transfer rate behave quite reverse for Prandtl number. It is also noted that the concentration and local Sherwood number have opposite behavior in the frame of Brownian motion. Keywords: Powell-Erying nanofluid, Magnetohydrodynamic (MHD, Nonlinear convection, Thermal radiation, Chemical reaction, Newtonian heat and mass conditions

  19. Time evolution simulation of heat removal in a small water tank by natural convection

    Energy Technology Data Exchange (ETDEWEB)

    Freitas, Carlos Alberto de, E-mail: carlos.freitas1950@hotmail.com [Instituto Federal do Rio de Janeiro (IFRJ), Nilopolis, RJ (Brazil); Jachic, Joao; Moreira, Maria de Lourdes, E-mail: jjachic@ien.gov.br, E-mail: malu@ien.gov.br [Instituto de Engenharia Nuclear (IEN/CNEN-RJ), Rio de Janeiro, RJ (Brazil)

    2013-07-01

    One of the cooling modes for any source of heat such as in a shutdown nuclear core is the natural convection. The design specifications of any cooling pool can only be done when the removal heat rate and the corresponding mass flow rate is reasonably established. In our simulation scheme, we assumed that the body forces acting in the cubic water cell are: the weight, the drag force and the integrated pressure forces on the horizontal surfaces, the viscosity shear forces on the vertical surfaces and also a special viscosity drag force due to the mass dislocation along a Bernoulli type current tube outside the motive region. For a suitable time step, the uprising convection velocity is determined by an implicit and also by an explicit solution algorithm. The resulting differential equation depends on updating specific mass, dynamic viscosity and constant pressure heat coefficient with the last known temperature in the cell that absorbed heat. Numerical calculation software was performed using MATLAB’s technical computing language and then applied for a heat generation plate simulating a spent fuel assembler from a shutdown nuclear core. The results show time evolution of convection, terminal velocity and water temperature distribution. Pool dimension as well as pool level decrement are also determined for various air exhausting system conditions and heat rate of the spent fuel plate being cooled. (author)

  20. Time evolution simulation of heat removal in a small water tank by natural convection

    International Nuclear Information System (INIS)

    Freitas, Carlos Alberto de; Jachic, Joao; Moreira, Maria de Lourdes

    2013-01-01

    One of the cooling modes for any source of heat such as in a shutdown nuclear core is the natural convection. The design specifications of any cooling pool can only be done when the removal heat rate and the corresponding mass flow rate is reasonably established. In our simulation scheme, we assumed that the body forces acting in the cubic water cell are: the weight, the drag force and the integrated pressure forces on the horizontal surfaces, the viscosity shear forces on the vertical surfaces and also a special viscosity drag force due to the mass dislocation along a Bernoulli type current tube outside the motive region. For a suitable time step, the uprising convection velocity is determined by an implicit and also by an explicit solution algorithm. The resulting differential equation depends on updating specific mass, dynamic viscosity and constant pressure heat coefficient with the last known temperature in the cell that absorbed heat. Numerical calculation software was performed using MATLAB’s technical computing language and then applied for a heat generation plate simulating a spent fuel assembler from a shutdown nuclear core. The results show time evolution of convection, terminal velocity and water temperature distribution. Pool dimension as well as pool level decrement are also determined for various air exhausting system conditions and heat rate of the spent fuel plate being cooled. (author)

  1. Convective heat transfer characteristics in the turbulent region of molten salt in concentric tube

    International Nuclear Information System (INIS)

    Chen, Y.S.; Wang, Y.; Zhang, J.H.; Yuan, X.F.; Tian, J.; Tang, Z.F.; Zhu, H.H.; Fu, Y.; Wang, N.X.

    2016-01-01

    In order to better understand the heat transfer behavior and characteristics of molten salt in heat exchanger, the convective heat transfer characteristics of molten salt in salt-to-oil concentric tube are studied. Overall heat transfer coefficients of the heat exchanger are calculated using Wilson plots. Heat transfer coefficients of tube side molten salt with the range of Reynolds number from 10,000 to 50,000 and the Prandtl number from 11 to 27 are evaluated invoking the calculated overall heat transfer coefficients. The effects of velocity and temperature on the convective heat transfer in the turbulent region of molten salt are studied by comparing with the traditional correlations. The results show that the heat transfer characteristics of molten salt are in line with the empirical heat transfer correlation; however, Dittus–Boelter, Gnielinski, Sieder–Tate and Hausen correlations all give a larger deviation for the experimental data. Finally, based on the experimental data and Sieder–Tate correlation, a modified heat transfer correlation is proposed and good agreement is observed between the experimental data and the modified correlation. The results will also provide an important reference for the design of the heat exchangers in the Thorium-based Molten Salt Reactor.

  2. Effect of surface radiation on natural convection in an asymmetrically heated channel-chimney system

    Science.gov (United States)

    Nasri, Zied; Derouich, Youssef; Laatar, Ali Hatem; Balti, Jalloul

    2018-05-01

    In this paper, a more realistic numerical approach that takes into account the effect of surface radiation on the laminar air flow induced by natural convection in a channel-chimney system asymmetrically heated at uniform heat flux is used. The aim is to enrich the results given in Nasri et al. (Int J Therm Sci 90:122-134, 2015) by varying all the geometric parameters of the system and by taking into account the effect of surface radiation on the flows. The numerical results are first validated against experimental and numerical data available in the literature. The computations have allowed the determination of optimal configurations that maximize the mass flow rate and the convective heat transfer and minimize the heated wall temperatures. The analysis of the temperature fields with the streamlines and the pressure fields has helped to explain the effects of surface radiation and of the different thermo-geometrical parameters on the system performances to improve the mass flow rate and the heat transfer with respect to the simple channel. It is shown that the thermal performance of the channel-chimney system in terms of lower heated wall temperatures is little affected by the surface radiation. At the end, simple correlation equations have been proposed for quickly and easily predict the optimal configurations as well as the corresponding enhancement rates of the induced mass flow rate and the convective heat transfer.

  3. Comparison of CFD Natural Convection and Conduction-only Models for Heat Transfer in the Yucca Mountain Project Drifts

    International Nuclear Information System (INIS)

    Hadgu, T.; Webb, S.; Itamura, M.

    2004-01-01

    Yucca Mountain, Nevada has been designated as the nation's high-level radioactive waste repository and the U.S. Department of Energy has been approved to apply to the U.S. Nuclear Regulatory Commission for a license to construct a repository. Heat transfer in the Yucca Mountain Project (YMP) drift enclosures is an important aspect of repository waste emplacement. Canisters containing radioactive waste are to be emplaced in tunnels drilled 500 m below the ground surface. After repository closure, decaying heat is transferred from waste packages to the host rock by a combination of thermal radiation, natural convection and conduction heat transfer mechanism?. Current YMP mountain-scale and drift-scale numerical models often use a simplified porous medium code to model fluid and heat flow in the drift openings. To account for natural convection heat transfer, the thermal conductivity of the air was increased in the porous medium model. The equivalent thermal conductivity, defined as the ratio of total heat flow to conductive heat flow, used in the porous media models was based on horizontal concentric cylinders. Such modeling does not effectively capture turbulent natural convection in the open spaces as discussed by Webb et al. (2003) yet the approach is still widely used on the YMP project. In order to mechanistically model natural convection conditions in YMP drifts, the computational fluid dynamics (CFD) code FLUENT (Fluent, Incorporated, 2001) has been used to model natural convection heat transfer in the YMP emplacement drifts. A two-dimensional (2D) model representative of YMP geometry (e.g., includes waste package, drip shield, invert and drift wall) has been developed and numerical simulations made (Francis et al., 2003). Using CFD simulation results for both natural convection and conduction-only heat transfer in a single phase, single component fluid, equivalent thermal conductivities have been calculated for different Rayleigh numbers. Correlation

  4. Simulation of nonlinear convective thixotropic liquid with Cattaneo-Christov heat flux

    Science.gov (United States)

    Zubair, M.; Waqas, M.; Hayat, T.; Ayub, M.; Alsaedi, A.

    2018-03-01

    In this communication we utilized a modified Fourier approach featuring thermal relaxation effect in nonlinear convective flow by a vertical exponentially stretchable surface. Temperature-dependent thermal conductivity describes the heat transfer process. Thixotropic liquid is modeled. Convergent local similar solutions by homotopic approach are obtained. Graphical results for emerging parameters of interest are analyzed. Skin friction is calculated and interpreted. Consideration of larger local buoyancy and nonlinear convection parameters yields an enhancement in velocity distribution. Temperature and thermal layer thickness are reduced for larger thermal relaxation factor.

  5. Modelling of convective heat and mass transfer in rotating flows

    CERN Document Server

    Shevchuk, Igor V

    2016-01-01

     This monograph presents results of the analytical and numerical modeling of convective heat and mass transfer in different rotating flows caused by (i) system rotation, (ii) swirl flows due to swirl generators, and (iii) surface curvature in turns and bends. Volume forces (i.e. centrifugal and Coriolis forces), which influence the flow pattern, emerge in all of these rotating flows. The main part of this work deals with rotating flows caused by system rotation, which includes several rotating-disk configurations and straight pipes rotating about a parallel axis. Swirl flows are studied in some of the configurations mentioned above. Curvilinear flows are investigated in different geometries of two-pass ribbed and smooth channels with 180° bends. The author demonstrates that the complex phenomena of fluid flow and convective heat transfer in rotating flows can be successfully simulated using not only the universal CFD methodology, but in certain cases by means of the integral methods, self-similar and analyt...

  6. Influence of high range of mass transfer coefficient and convection heat transfer on direct contact membrane distillation performance

    KAUST Repository

    Lee, Jung Gil

    2017-11-03

    In order to improve water production of membrane distillation (MD), the development of high performance membrane having better mass transfer and enhancement of convection heat transfer in MD module have been continuously investigated. This paper presents the relationship between the heat and mass transfer resistance across the membrane and the performance improvement. Various ranges of mass transfer coefficient (MTC) from normal (0.3×10−6 to 2.1×10−6kg/m2sPa: currently available membranes) to high (>2.1×10−6kg/m2sPa: membranes under development) were simulated using an experimentally validated model at different ranges of convection heat transfer by varying the inlet flow rates and spacer enhancement factor. The effect of mass transfer and convection heat transfer on the MD performance parameters including temperature polarization coefficient (TPC), mean permeate flux, and specific energy consumption were investigated in a direct contact MD (DCMD) configuration. Results showed that improving the MTC at the low ranges is more important than that at the high ranges where the heat transfer resistance becomes dominant and hence the convection heat transfer coefficient must be increased. Therefore, an effort on designing MD modules using feed and permeate spacers and controlling the membrane surface roughness to increase the convection heat transfer and TPC in the channel aiming to enhance the flux is required because the currently developed mass transfer has almost reached the critical point.

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

    International Nuclear Information System (INIS)

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

    1986-01-01

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

  8. Mixed convective heat transfer from a vertical plate embedded in a ...

    Indian Academy of Sciences (India)

    Melting effect with heat and mass transfer in porous media has much ... convection boundary layer flow about a vertical surface embedded in a porous medium, ..... Salama A 2008 Combined effect of thermal dispersion and radiation on free.

  9. Convection Heat Transfer Modeling of Ag Nanofluid Using Different Viscosity Theories

    Directory of Open Access Journals (Sweden)

    Ali Bakhsh Kasaeian

    2012-04-01

    Full Text Available ABSTRACT: In this paper, the effects of adding nanoparticles (including Ag to a fluid media for improving free convection heat transfer were analysed. The free convective heat transfer was assumed to be in laminar flow regime, and the corresponding calculations and solutions were all done by the integral method. Water, as a Newtonian fluid, was considered as the base and all relevant thermo physical properties of the nanofluids were considered to be unvarying. The calculations performed and the graphs generated showed that, in general, the addition of nanoparticles to the fluid media resulted in an increment or improvement of its heat transfer coefficient. With increase in the concentration of the nanoparticles, the heat transfer rate of the fluid also increased. The increment in heat transfer is also dependent on the nanoparticles’ thermal conductivity and the viscosity theory which was utilized in the calculations. In this study, four different theories were used to calculate the viscosities of the nanofluids. The effects of viscosity on the nanofluids’ thermal conductivity were apparent from the calculations which were performed for nanoparticle concentrations of 4% or less. ABSTRAK: Kajian ini menganalisis kesan penambahan nanopartikel Ag ke dalam media bendalir bagi tujuan pembaikkan pemindahan haba perolakan bebas. Perolakan bebas diandaikan berada di zon aliran laminar, di mana penyelesaian dan pengiraan telah dilakukan mengunakan kaedah kamilan. Air yang merupakan cecair Newtonian, dianggap sebagai asas dan sifat terma fizikal nanocecair dianggapkan tidak berubah. Mengikut pengiraan yang dilakukan dan graf yang diplotkan, umumnya penambahan nanopartikel kepada media bendalir menyebabkan peningkatan dan pengembangan pekali pemindahan haba. Kadar pemindahan haba meningkat dengan nanopartikel. Peningkatan pemindahan haba juga bergantung kepada pengalir haba nanopartikel dan teori kelikatan yang digunakan. Di dalam kajian ini, empat

  10. Convective heat transfer in foams under laminar flow in pipes and tube bundles.

    Science.gov (United States)

    Attia, Joseph A; McKinley, Ian M; Moreno-Magana, David; Pilon, Laurent

    2012-12-01

    The present study reports experimental data and scaling analysis for forced convection of foams and microfoams in laminar flow in circular and rectangular tubes as well as in tube bundles. Foams and microfoams are pseudoplastic (shear thinning) two-phase fluids consisting of tightly packed bubbles with diameters ranging from tens of microns to a few millimeters. They have found applications in separation processes, soil remediation, oil recovery, water treatment, food processes, as well as in fire fighting and in heat exchangers. First, aqueous solutions of surfactant Tween 20 with different concentrations were used to generate microfoams with various porosity, bubble size distribution, and rheological behavior. These different microfoams were flowed in uniformly heated circular tubes of different diameter instrumented with thermocouples. A wide range of heat fluxes and flow rates were explored. Experimental data were compared with analytical and semi-empirical expressions derived and validated for single-phase power-law fluids. These correlations were extended to two-phase foams by defining the Reynolds number based on the effective viscosity and density of microfoams. However, the local Nusselt and Prandtl numbers were defined based on the specific heat and thermal conductivity of water. Indeed, the heated wall was continuously in contact with a film of water controlling convective heat transfer to the microfoams. Overall, good agreement between experimental results and model predictions was obtained for all experimental conditions considered. Finally, the same approach was shown to be also valid for experimental data reported in the literature for laminar forced convection of microfoams in rectangular minichannels and of macrofoams across aligned and staggered tube bundles with constant wall heat flux.

  11. Study of natural convection heat transfer characteristics. (1) Influence of ventilation duct height

    International Nuclear Information System (INIS)

    Wakamatsu, Mitsuo; Iwaki, Chikako; Ikeda, Tatsumi; Morooka, Shinichi; Ikeda, Hiroshi; Nakada, Kotaro; Masaki, Yoshikazu

    2008-01-01

    Natural cooling system has been investigated in waste storage. It is important to evaluate the flow by natural draft enough to removal the decay heat from the waste. In this study, we carried out the fundamental experiment of ventilation duct height effect for natural convection on vertical cylindrical heater in atmospheric air. The scale of test facility is about 4m height with single heater. The heating value is varied in the range of 33-110W, where Rayleigh number is over 10 10 . Natural convection flow rate were calculated by measured velocity with thermo anemometer in the inlet duct. The temperature of the cylindrical heater wall and fluid were measured with thermocouples. It was found that the heat transfer coefficient difference between long duct and short duct is small in this experiment. (author)

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

    International Nuclear Information System (INIS)

    Liu, Qiusheng

    2001-01-01

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

  13. Convection flows driven by laser heating of a liquid layer

    OpenAIRE

    Rivière , David; Selva , Bertrand; Chraibi , Hamza; Delabre , Ulysse; Delville , Jean-Pierre

    2016-01-01

    International audience; When a fluid is heated by the absorption of a continuous laser wave, the fluid density decreases in the heated area. This induces a pressure gradient that generates internal motion of the fluid. Due to mass conservation, convection eddies emerge in the sample. To investigate these laser-driven bulk flows at the microscopic scale, we built a setup to perform temperature measurements with a fluorescent-sensitive dye on the one hand, and measured the flow pattern at diffe...

  14. Computational simulation of two-dimensional transient natural convection in volumetrically heated square enclosure

    International Nuclear Information System (INIS)

    Vieira, Camila Braga; Jian Su

    2010-01-01

    Natural convection is a physical phenomenon that has been investigated in nuclear engineering so as to provide information about heat transfer in severe accident conditions involving nuclear reactors. This research reported transient natural convection of fluids with uniformly distributed volumetrically heat generation in square cavity with isothermal side walls and adiabatic top/bottom walls. Two Prandtl numbers were considered, 0:0321 and 0:71. Direct numerical simulations were applied in order to obtain results about the velocities of the fluid in directions x and y. These results were used in Fast Fourier Transform, which showed the periodic, quasi-chaotic and chaotic behavior of transient laminar flow. (author)

  15. Research of heat transfer of staggered horizontal bundles of finned tubes at free air convection

    Science.gov (United States)

    Novozhilova, A. V.; Maryna, Z. G.; Samorodov, A. V.; Lvov, E. A.

    2017-11-01

    The study of free-convective processes is important because of the cooling problem in many machines and systems, where other ways of cooling are impossible or impractical. Natural convective processes are common in the steam turbine air condensers of electric power plants located within the city limits, in dry cooling towers of circulating water systems, in condensers cooled by air and water, in radiators cooling oil of power electric transformers, in emergency cooling systems of nuclear reactors, in solar power, as well as in air-cooling of power semiconductor energy converters. All this makes actual the synthesis of the results of theoretical and experimental research of free convection for heat exchangers with finned tube bundles. The results of the study of free-convection heat transfer for two-, three- and four-row staggered horizontal bundles of industrial bimetallic finned tubes with finning factor of 16.8 and equilateral tubes arrangement are presented. Cross and diagonal steps in the bundles are the same: 58; 61; 64; 70; 76; 86; 100 mm, which corresponds to the relative steps: 1.042; 1.096; 1.152; 1.258; 1.366; 1.545; 1.797. These steps are standardized for air coolers. An equation for calculating the free-convection heat transfer, taking into account the influence of geometrical parameters in the range of Rayleigh number from 30,000 to 350,000 with an average deviation of ± 4.8%, has been obtained. The relationship presented in the article allows designing a wide range of air coolers for various applications, working in the free convection modes.

  16. A theory for natural convection turbulent boundary layers next to heated vertical surfaces

    International Nuclear Information System (INIS)

    George, W.K. Jr.; Capp, S.P.

    1979-01-01

    The turbulent natural convection boundary layer next to a heated vertical surface is analyzed by classical scaling arguments. It is shown that the fully developed turbulent boundary layer must be treated in two parts: and outer region consisting of most of the boundary layer in which viscous and conduction terms are negligible and an inner region in which the mean convection terms are negligible. The inner layer is identified as a constant heat flux layer. A similarity analysis yields universal profiles for velocity and temperature in the outer and constant heat flux layers. An asymptotic matching of these profiles in an intermediate layer (the buoyant sublayer) yields analytical expressions for the buoyant sublayer profiles. Asymptotic heat transfer and friction laws are obtained for the fully developed boundary layers. Finally, conductive and thermo-viscous sublayers characterized by a linear variation of velocity and temperature are shown to exist at the wall. All predictions are seen to be in excellent agreement with the abundant experimental data. (author)

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

    International Nuclear Information System (INIS)

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

    1997-01-01

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

  18. Integral transform solution of natural convection in a square cavity with volumetric heat generation

    Directory of Open Access Journals (Sweden)

    C. An

    2013-12-01

    Full Text Available The generalized integral transform technique (GITT is employed to obtain a hybrid numerical-analytical solution of natural convection in a cavity with volumetric heat generation. The hybrid nature of this approach allows for the establishment of benchmark results in the solution of non-linear partial differential equation systems, including the coupled set of heat and fluid flow equations that govern the steady natural convection problem under consideration. Through performing the GITT, the resulting transformed ODE system is then numerically solved by making use of the subroutine DBVPFD from the IMSL Library. Therefore, numerical results under user prescribed accuracy are obtained for different values of Rayleigh numbers, and the convergence behavior of the proposed eigenfunction expansions is illustrated. Critical comparisons against solutions produced by ANSYS CFX 12.0 are then conducted, which demonstrate excellent agreement. Several sets of reference results for natural convection with volumetric heat generation in a bi-dimensional square cavity are also provided for future verification of numerical results obtained by other researchers.

  19. The Impact of Reduced Gravity on Free Convective Heat Transfer from a Finite, Flat, Vertical Plate

    Science.gov (United States)

    Lotto, Michael A.; Johnson, Kirstyn M.; Nie, Christopher W.; Klaus, David M.

    2017-10-01

    Convective heat transfer is governed by a number of factors including various fluid properties, the presence of a thermal gradient, geometric configuration, flow condition, and gravity. Empirically-derived analytical relationships can be used to estimate convection as a function of these governing parameters. Although it is relatively straightforward to experimentally quantify the contributions of the majority of these variables, it is logistically difficult to assess the influence of reduced-gravity due to practical limitations of establishing this environment. Therefore, in order to explore this regime, a series of tests was conducted to evaluate convection under reduced-gravity conditions averaging 0.45 m/sec2 (0.05 g) achieved aboard a parabolic aircraft. The results showed a reduction in net heat transfer of approximately 61% in flight relative to a 1 g terrestrial baseline using the same setup. The average experimental Nusselt Number of 19.05 ± 1.41 statistically correlated with the predicted value of 18.90 ± 0.63 (N = 13), estimated using the Churchill-Chu correlation for free convective heat transfer from a finite, flat, vertical plate. Extrapolating this to similar performance in true microgravity (10-6 g) indicates that these conditions should yield a Nusselt Number of 1.27, which is 2.6% the magnitude of free convection at 1 g, or a reduction of 97.4%. With advection essentially eliminated, heat transfer becomes limited to diffusion and radiation, which are gravity-independent and nearly equivalent in magnitude in this case. These results offer a general guideline for integrating components that utilize natural (free) convective gas cooling in a spacecraft habitat and properly sizing the thermal control system.

  20. Study on the natural convection heat transfer characteristics in the air duct

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Y K; Lee, Y B; Choi, S K; Hwang, J S; Nam, H Y [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)

    1998-12-31

    Temperature distribution measurements in the mockup apparatus of reactor vessel were performed to determine the effective thermal conductivity of porous media with different geometry and to obtain the experimental data for the heat transfer processes by natural convection occurring in the air duct. The temperature distributions at four separated sections with different arrangements of porous media have different slopes according to the geometrical configuration. From the measured temperature distribution, effective thermal conductivity have been derived using the least square fitting method. The test at air duct was performed to the high heat removal at 3.4kW/m{sup 2} by the natural convection from the outer wall to the air. And also the temperature distributions in the sir duct agree well with the 1/7th power-law turbulent temperature distribution. The obtained heat transfer data have been compared with the Shin`s and Sieger`s correlations. 10 refs., 6 figs. (Author)

  1. Study on the natural convection heat transfer characteristics in the air duct

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Y. K.; Lee, Y. B.; Choi, S. K.; Hwang, J. S.; Nam, H. Y. [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)

    1997-12-31

    Temperature distribution measurements in the mockup apparatus of reactor vessel were performed to determine the effective thermal conductivity of porous media with different geometry and to obtain the experimental data for the heat transfer processes by natural convection occurring in the air duct. The temperature distributions at four separated sections with different arrangements of porous media have different slopes according to the geometrical configuration. From the measured temperature distribution, effective thermal conductivity have been derived using the least square fitting method. The test at air duct was performed to the high heat removal at 3.4kW/m{sup 2} by the natural convection from the outer wall to the air. And also the temperature distributions in the sir duct agree well with the 1/7th power-law turbulent temperature distribution. The obtained heat transfer data have been compared with the Shin`s and Sieger`s correlations. 10 refs., 6 figs. (Author)

  2. Forced convective post CHF heat transfer and quenching

    International Nuclear Information System (INIS)

    Nelson, R.A.

    1980-01-01

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

  3. Characteristics of convective heat transport in a packed pebble-bed reactor

    Energy Technology Data Exchange (ETDEWEB)

    Abdulmohsin, Rahman S., E-mail: rsar62@mst.edu [Department of Chemical and Biochemical Engineering, Missouri University of Science and Technology, 400 West 11th Street/231 Schrenk Hall, Rolla, MO 65409-1230 (United States); Al-Dahhan, Muthanna H., E-mail: aldahhanm@mst.edu [Department of Chemical and Biochemical Engineering, Missouri University of Science and Technology, 400 West 11th Street/231 Schrenk Hall, Rolla, MO 65409-1230 (United States); Department of Nuclear Engineering, 301 W. 14th St./222 Fulton Hall (United States)

    2015-04-01

    Highlights: • A fast-response heat transfer probe has been developed and used in this work. • Heat transport has been quantified in terms of local heat transfer coefficients. • The method of the electrically heated single sphere in packing has been applied. • The heat transfer coefficient increases from the center to the wall of packed bed. • This work advancing the knowledge of heat transport in the studied packed bed. - Abstract: Obtaining more precise results and a better understanding of the heat transport mechanism in the dynamic core of packed pebble-bed reactors is needed because this mechanism poses extreme challenges to the reliable design and efficient operation of these reactors. This mechanism can be quantified in terms of a solid-to-gas convective heat transfer coefficient. Therefore, in this work, the local convective heat transfer coefficients and their radial profiles were measured experimentally in a separate effect pilot-plant scale and cold-flow experimental setup of 0.3 m in diameter, using a sophisticated noninvasive heat transfer probe of spherical type. The effect of gas velocity on the heat transfer coefficient was investigated over a wide range of Reynolds numbers of practical importance. The experimental investigations of this work include various radial locations along the height of the bed. It was found that an increase in coolant gas flow velocity causes an increase in the heat transfer coefficient and that effect of the gas flow rate varies from laminar to turbulent flow regimes at all radial positions of the studied packed pebble-bed reactor. The results show that the local heat transfer coefficient increases from the bed center to the wall due to the change in the bed structure, and hence, in the flow pattern of the coolant gas. The findings clearly indicate that one value of an overall heat transfer coefficient cannot represent the local heat transfer coefficients within the bed; therefore, correlations are needed to

  4. CONVECTIVE HEAT EXCHANGE ON THE LATERAL SURFACE OF A RELATIVELY LONG CYCLONE CHAMBER

    Directory of Open Access Journals (Sweden)

    E. N. Saburov

    2016-01-01

    Full Text Available The high-turbulent swirling flows of heat carrier that are created by a cyclone chamber are used in industry. They make it possible to intensify processes of heat and mass exchange. The results of an experimental study of convective heat transfer on the lateral surface of the active volume of a relatively long cyclone chamber considerably exceeding the length of the chambers that were used in previously performed studies are presented and analyzed in the article. Air supply in the swirler of the chamber was performed tangentially from diametrically opposite sides of the two input channels. The gas outlet was implemented from the opposite end. The heat transfer by convection to the swirling air flow was studied by the method of changing the state of aggregation of a heating agent – condensation of slightly superheated steam. Collecting condensate from the working section was made through a water seal for maintaining a constant pressure calorimeter. The amount of heat transferred during experiment was determined by weight of the collected condensate. The specific features of influence of geometrical characteristics of cyclone chamber on intensity of heat exchange are considered. In the experiments we varied the relative diameter of the outlet port of the chamber dвых and the relative area of the input channels fвх. Segmental construction of the chamber made it possible to move a calorimeter on its length. The local heat transfer coefficient was determined for various values of the dimensionless longitudinal coordinate z coinciding with the axis of the chamber, and counted from the back end of the swirler. The estimated equations of heat transfer obtained during the research are presented and recommended for use in practice of engineering. The considered problem is of an interest from the point of view of further research of aerodynamics and of convective heat transfer in a highly swirling flow cyclone devices, in order to improve the

  5. Natural convection heat transfer from a heated horizontal cylinder with Microencapsulated Phase-Change-Material slurries

    International Nuclear Information System (INIS)

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

    1998-01-01

    The present study investigates natural convection heat transfer from a heated cylinder cooled by a water slurry of Microencapsulated Phase Change Material (MCPCM). A normal paraffin hydrocarbon with carbon number of 18 and melting point of 27.9degC, is microencapsulated by Melamine resin into particles of which average diameter is 9.5 μm and specific weight is same as water. The slurry of the MCPCM and water is put into a rectangular enclosure with a heated horizontal cylinder. The heat transfer coefficients of the cylinder were evaluated. Changing the concentrations of PCM and temperature difference between cylinder surface and working fluid. Addition of MCPCM into water, the heat transfer is enhanced significantly comparison with pure water in cases with phase change and is reduced slightly in cases without phase change. (author)

  6. Multiple zonal jets and convective heat transport barriers in a quasi-geostrophic model of planetary cores

    Science.gov (United States)

    Guervilly, C.; Cardin, P.

    2017-10-01

    We study rapidly rotating Boussinesq convection driven by internal heating in a full sphere. We use a numerical model based on the quasi-geostrophic approximation for the velocity field, whereas the temperature field is 3-D. This approximation allows us to perform simulations for Ekman numbers down to 10-8, Prandtl numbers relevant for liquid metals (˜10-1) and Reynolds numbers up to 3 × 104. Persistent zonal flows composed of multiple jets form as a result of the mixing of potential vorticity. For the largest Rayleigh numbers computed, the zonal velocity is larger than the convective velocity despite the presence of boundary friction. The convective structures and the zonal jets widen when the thermal forcing increases. Prograde and retrograde zonal jets are dynamically different: in the prograde jets (which correspond to weak potential vorticity gradients) the convection transports heat efficiently and the mean temperature tends to be homogenized; by contrast, in the cores of the retrograde jets (which correspond to steep gradients of potential vorticity) the dynamics is dominated by the propagation of Rossby waves, resulting in the formation of steep mean temperature gradients and the dominance of conduction in the heat transfer process. Consequently, in quasi-geostrophic systems, the width of the retrograde zonal jets controls the efficiency of the heat transfer.

  7. TRIP: a finite element computer program for the solution of convection heat transfer problems

    International Nuclear Information System (INIS)

    Slagter, W.; Roodbergen, H.A.

    1976-01-01

    The theory and use of the finite element code TRIP are described. The code calculates temperature distributions in three-dimensional continua subjected to convection heat transfer. A variational principle for transport phenomena is applied to solve the convection heat transfer problem with temperature and heat flux boundary conditions. The finite element discretization technique is used to reduce the continuous spatial solution into a finite number of unknowns. The method is developed in detail to determine temperature distributions in coolant passages of fuel rod bundles which are idealized by hexahedral elements. The development of the TRIP code is discussed and the listing of the program is given in FORTRAN IV. An example is given to illustrate the validity and practicality of the method

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

    International Nuclear Information System (INIS)

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

    1976-01-01

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

  9. Numerical Investigation of the Thermal Regime of Underground Channel Heat Pipelines Under Flooding Conditions with the Use of a Conductive-Convective Heat Transfer Model

    Science.gov (United States)

    Polovnikov, V. Yu.

    2018-05-01

    This paper presents the results of numerical analysis of thermal regimes and heat losses of underground channel heating systems under flooding conditions with the use of a convective-conductive heat transfer model with the example of the configuration of the heat pipeline widely used in the Russian Federation — a nonpassage ferroconcrete channel (crawlway) and pipelines insulated with mineral wool and a protective covering layer. It has been shown that convective motion of water in the channel cavity of the heat pipeline under flooding conditions has no marked effect on the intensification of heat losses. It has been established that for the case under consideration, heat losses of the heat pipeline under flooding conditions increase from 0.75 to 52.39% due to the sharp increase in the effective thermal characteristics of the covering layer and the heat insulator caused by their moistening.

  10. Peculiarities of natural convective heat removal from complex pools

    International Nuclear Information System (INIS)

    Groetzbach, Guenther

    2002-01-01

    Considerable sensitivities are investigated in using natural convection for cooling large pools. Such a flow occurred in a sump cooling concept for a water cooled reactor. The related SUCOS model experiments were analyzed by means of the FLUTAN code. The numerical interpretations show, the natural convection in large pools is strongly influenced by local thermal disturbances, either due to structures in the fluid domain, or by bounding structures interacting thermally with the fluid. These experiment specific disturbances must be recorded in the numerical model in order to achieve adequate simulations of the heat transport. Some geometric imperfections of horizontal coolers or heaters could also have tremendous influences. As a consequence, not only the numerical model has to record all relevant phenomena as realistic as possible, but also the model experiment. (author)

  11. Experimental and Numerical Investigation of Forced Convection Heat Transfer in Heat Sink with Rectangular Plates at Varying Inclinations on Vertical Base

    Science.gov (United States)

    Patil, Harshal Bhauso; Dingare, Sunil Vishnu

    2018-03-01

    Heat exchange upgrade is a vital territory of research area. Utilization of reasonable systems can bring about noteworthy specialized points of interest coming about reserve funds of cost. Rectangular plates are viewed as best balance arrangement utilized for heat exchange improvement. This gives an enlargement strategy to heat exchange with beginning of limit layer and vortex development. To assess and look at the rate of heat exchange enhancement by rectangular plate fins with differing inclinations (0°-30°-60°), shifting Re and heat supply under forced convection are the principle destinations of this study. The study is done by fluctuating introductions of fins with various inclinations, input heat supply and Re under forced convection. The coefficient of heat transfer increments observed with the expansion in air speed for all the examined designs. The coefficient of the heat transfer is discovered higher at the edge of introduction of fins at 30° for inline arrangement and 0° for staggered arrangement. Looking at both the arrangements, it is discovered that the heat transfer coefficient in 0° fin staggered arrangement is about 17% higher than 30° inline arrangement and 76% higher than the vertical plate fin. For plate fin heat sink, boundary layer formation and growth results in decrease of the coefficient of heat transfer in forced convection. This issue is overcome by accommodating some rectangular fins on the plate fin. It brings about increment of heat transfer coefficient of the RPFHS under the states of trial factors. As indicated by past research, it is discovered that examination of the plate fin heat sink with various sorts of fins for horizontal orientation is done yet but this investigation expects to discover the upgrade of transfer coefficient of plate fin heat sink for its vertical position with rectangular plates at different inclinations under the shifting scopes of heat input supply, fin arrangements and Reynolds number (Re).

  12. Conjugate Heat Transfer of Mixed Convection for Viscoelastic Fluid Past a Stretching Sheet

    Directory of Open Access Journals (Sweden)

    Kai-Long Hsiao

    2007-01-01

    Full Text Available A conjugate heat transfer problem of a second-grade viscoelastic fluid past a stretching sheet has been studied. Governing equations include heat conduction equation of a stretching sheet, continuity equation, momentum equation, and energy equation of a second-grade fluid, analyzed by a combination of a series expansion method, the similarity transformation, and a second-order accurate finite-difference method. These solutions are used to iterate with the heat conduction equation of the stretching sheet to obtain distributions of the local convective heat transfer coefficient and the stretching sheet temperature. Ranges of dimensionless parameters, the Prandtl number Pr, the elastic number E and the conduction-convection coefficient Ncc are from 0.001 to 10, 0.0001 to 0.01, and 0.5 to 2.0, respectively. A parameter G, which is used to represent the dominance of the buoyant effect, is present in governing equations. Results indicated that elastic effect in the flow could increase the local heat transfer coefficient and enhance the heat transfer of a stretching sheet. In addition, same as the results from Newtonian fluid flow and conduction analysis of a stretching sheet, a better heat transfer is obtained with a larger Ncc, G, and E.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1960-02-15

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

  14. Indirect involvement of armorphous carbon layer on convective heat transfer enhancement using carbon nanofibers

    NARCIS (Netherlands)

    Taha, T.J.; Lefferts, Leonardus; van der Meer, Theodorus H.

    2015-01-01

    In this work, an experimental heat transfer investigation was carried out to investigate the combined influence of both amorphous carbon (a-C) layer thickness and carbon nanofibers (CNFs) on the convective heat transfer behavior. Synthesis of these carbon nanostructures was achieved using catalytic

  15. Natural convection heat transfer from a long heated vertical cylinder to an adjacent air gap of concentric and eccentric conditions

    DEFF Research Database (Denmark)

    Hosseini, R.; Kolaei, Alireza Rezania; Alipour, M.

    2012-01-01

    In this work, the natural convection heat transfer from a long vertical electrically heated cylinder to an adjacent air gap is experimentally studied. The aspect and diameter ratios of the cylinder are 55.56 and 6.33, respectively. The experimental measurements were obtained for a concentric cond...

  16. Heat transfer characteristics of induced mixed convection

    International Nuclear Information System (INIS)

    Weiss, Y.; Lahav, C.; Szanto, M.; Shai, I.

    1996-01-01

    In the present work we focus our attention on the opposed Induced Mixed Convection case, i.e. the flow field structure in a vertical cylinder, closed at its bottom, opens at the top, and being heated circumferentially. The paper reports an experimental study of this complex heat transfer process. For a better understanding of the flow field and the related heat transfer process, two different experimental systems were built. The first was a flow visualization system, with water as the working fluid, while the second system enabled quantitative measurements of the temperature field in air. All the experiments were performed in the turbulent flow regime. In order to learn about all possible flow regimes, the visualization tests were conducted in three different length-to-diameter ratios (1/d=1,5,10). Quantitative measurements of the cylindrical wall temperature, as well as the radial and axial temperature profiles in the flow field, were taken in the air system. Based on the visualization observation and the measured wall temperature profile, it was found that the OIMC can be characterized by three main regimes: a mixing regime at the top, a central turbulent core and a boundary layer type of flow adjacent to the heated wall. (authors)

  17. Analytical solutions for tomato peeling with combined heat flux and convective boundary conditions

    Science.gov (United States)

    Cuccurullo, G.; Giordano, L.; Metallo, A.

    2017-11-01

    Peeling of tomatoes by radiative heating is a valid alternative to steam or lye, which are expensive and pollutant methods. Suitable energy densities are required in order to realize short time operations, thus involving only a thin layer under the tomato surface. This paper aims to predict the temperature field in rotating tomatoes exposed to the source irradiation. Therefore, a 1D unsteady analytical model is presented, which involves a semi-infinite slab subjected to time dependent heating while convective heat transfer takes place on the exposed surface. In order to account for the tomato rotation, the heat source is described as the positive half-wave of a sinusoidal function. The problem being linear, the solution is derived following the Laplace Transform Method. In addition, an easy-to-handle solution for the problem at hand is presented, which assumes a differentiable function for approximating the source while neglecting convective cooling, the latter contribution turning out to be negligible for the context at hand. A satisfying agreement between the two analytical solutions is found, therefore, an easy procedure for a proper design of the dry heating system can be set up avoiding the use of numerical simulations.

  18. Free convection film flows and heat transfer laminar free convection of phase flows and models for heat-transfer analysis

    CERN Document Server

    Shang, De-Yi

    2012-01-01

    This book presents recent developments in our systematic studies of hydrodynamics and heat and mass transfer in laminar free convection, accelerating film boiling and condensation of Newtonian fluids, as well as accelerating film flow of non-Newtonian power-law fluids (FFNF). These new developments provided in this book are (i) novel system of analysis models based on the developed New Similarity Analysis Method; (ii) a system of advanced methods for treatment of gas temperature- dependent physical properties, and liquid temperature- dependent physical properties; (iii) the organically combined models of the governing mathematical models with those on treatment model of variable physical properties; (iv) rigorous approach of overcoming a challenge on accurate solution of three-point boundary value problem related to two-phase film boiling and condensation; and (v) A pseudo-similarity method of dealing with thermal boundary layer of FFNF for greatly simplifies the heat-transfer analysis and numerical calculati...

  19. Multiregional coupled conduction--convection model for heat transfer in an HTGR core

    International Nuclear Information System (INIS)

    Giles, G.E. Jr.; Childs, K.W.; Sanders, J.P.

    1978-01-01

    HEXEREI is a three-dimensional, coupled conduction-convection heat transfer and multichannel fluid dynamic analysis computer code with both steady-state and transient capabilities. The program was developed to provide thermal-fluid dynamic analysis of a core following the general design for high-temperature gas-cooled reactors (HTGRs); its purpose was to provide licensing evaluations for the U.S. Nuclear Regulatory Commission. In order to efficiently model the HTGR core, the nodal geometry of HEXEREI was chosen as a regular hexagonal array perpendicular to the axis of and bounded by a right circular cylinder. The cylindrical nodal geometry surrounds the hexagonal center portion of the mesh; these two different types of nodal geometries must be connected by interface nodes to complete the accurate modeling of the HTGR core. HEXEREI will automatically generate a nodal geometry that will accurately model a complex assembly of hexagonal and irregular prisms. The accuracy of the model was proven by a comparison of computed values with analytical results for steady-state and transient heat transfer problems. HEXEREI incorporates convective heat transfer to the coolant in many parallel axial flow channels. Forced and natural convection (which permits different flow directions in parallel channels) is included in the heat transfer and fluid dynamic models. HEXEREI incorporates a variety of steady-state and transient solution techniques that can be matched with a particular problem to minimize the computational time. HEXEREI was compared with a code of similar capabilities that was based on a Cartesian mesh. This code modeled only one specific core design, and the mesh spacing was closer than that generated by HEXEREI. Good agreement was obtained with the detail provided by the representations

  20. Diffusive and convective transport modelling from analysis of ECRH-stimulated electron heat wave propagation. [ECRH (Electron Cyclotron Resonance Heating)

    Energy Technology Data Exchange (ETDEWEB)

    Erckmann, V; Gasparino, U; Giannone, L. (Max-Planck-Institut fuer Plasmaphysik, Garching (Germany)) (and others)

    1992-01-01

    ECRH power modulation experiments in toroidal devices offer the chance to analyze the electron heat transport more conclusively: the electron heat wave propagation can be observed by ECE (or SX) leading to radial profiles of electron temperature modulation amplitude and time delay (phase shift). Taking also the stationary power balance into account, the local electron heat transport can be modelled by a combination of diffusive and convective transport terms. This method is applied to ECRH discharges in the W7-AS stellarator (B=2.5T, R=2m, a[<=]18 cm) where the ECRH power deposition is highly localized. In W7-AS, the T[sub e] modulation profiles measured by a high resolution ECE system are the basis for the local transport analysis. As experimental errors limit the separation of diffusive and convective terms in the electron heat transport for central power deposition, also ECRH power modulation experiments with off-axis deposition and inward heat wave propagation were performed (with 70 GHz o-mode as well as with 140 GHz x-mode for increased absorption). Because collisional electron-ion coupling and radiative losses are only small, low density ECRH discharges are best candidates for estimating the electron heat flux from power balance. (author) 2 refs., 3 figs.

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

    International Nuclear Information System (INIS)

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

    2016-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-10-15

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

  3. Mixed convection heat transfer between a steam/non-condensable gas mixture and an inclined finned tube bundle

    Energy Technology Data Exchange (ETDEWEB)

    De Cachard, F.; Lompersky, S.; Monauni, G.R. [Paul Scherrer Institute, Villigen (Switzerland). Thermal Hydraulic Lab.

    1999-07-01

    An experimental and analytical program was performed at PSI (Paul Scherrer Institute) to study the performance of a finned-tube condenser in the presence of non-condensable gases at low gas mass fluxes. The model developed for this application includes mixed convection heat transfer between the vapour/non-condensable mixture and the finned tubes, heat conduction through the fins and tubes, and evaporative heat transfer inside the tubes. On the gas, heat transfer correlations are used, and the condensation rate is calculated using the heat/mass transfer analogy. A combination of various available correlations for forced convection in staggered finned tube bundles is used, together with a correction accounting for superimposed natural convection. For the condensate heat transfer resistance, the beatty and Katz model for gravity driven liquid films on the tubes is used. The fine efficiency is accounted for using classical iterative calculations. Evaporative heat transfer inside the tubes is predicted using the Chen correlation. The finned tube condenser model has been assessed against data obtained at the PSI LINX facility with two test condensers. For the 62 LINX experiments performed, the model predictions are very good, i.e., less then 10% standard deviation between experimental and predicted results.

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

    International Nuclear Information System (INIS)

    Choi, Chang Yong

    1999-01-01

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

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

    International Nuclear Information System (INIS)

    Kushwaha, H.S.; Kakodkar, A.

    1982-01-01

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

  6. Critical heat flux for free convection boiling in thin rectangular channels

    International Nuclear Information System (INIS)

    Cheng, Lap Y.; Tichler, P.R.

    1991-01-01

    A review of the experimental data on free convection boiling critical heat flux (CHF) in vertical rectangular channels reveals three mechanisms of burnout. They are the pool boiling limit, the circulation limit, and the flooding limit associated with a transition in flow regime from churn to annular flow. The dominance of a particular mechanism depends on the dimensions of the channel. Analytical models were developed for each free convection boiling limit. Limited agreement with data is observed. A CHF correlation, which is valid for a wide range of gap sizes, was constructed from the CHFs calculated according to the three mechanisms of burnout. 17 refs., 7 figs

  7. Mixed convection flow and heat transfer in a vertical wavy channel ...

    African Journals Online (AJOL)

    Mixed convection flow and heat transfer in a vertical wavy channel filled with porous and fluid layers is studied analytically. The flow in the porous medium is modeled using Darcy-Brinkman equation. The coupled non-linear partial differential equations describing the conservation of mass, momentum and energy are solved ...

  8. Heat transfer by natural convection into an horizontal cavity; Transferencia de calor por conveccion natural en una cavidad horizontal

    Energy Technology Data Exchange (ETDEWEB)

    Arevalo J, P

    1998-12-31

    At this thesis it is studied the heat transfer by natural convection in an horizontal cavity, it is involved a boiling`s part that is described the regimes and correlations differences for boiling`s curve. It is designed a horizontal cavity for realize the experimental part and it`s mention from equipment or instrumentation to succeed in a experimentation that permits to realize the analysis of heat transfer, handling as water fluid at atmospheric pressure and where it`s present process from natural convection involving part boiling`s subcooled. The system consists of heater zone submerged in a horizontal cavity with water. Once part finished experimental with information to obtained it`s proceeded to obtain a correlation, realized starting from analysis dimensionless such as: Jakob, Bond and Grasoft (Boiling) besides of knows in natural convection: Prandtl and Nusselt. The mathematical model explains the behavior for natural convection continued part boiling`s subcooled. It is realize analysis graphics too where it`s show comparing with Globe Dropkin and Catton equations by natural convection with bottom heating. (Author)

  9. Heat transfer by natural convection into an horizontal cavity; Transferencia de calor por conveccion natural en una cavidad horizontal

    Energy Technology Data Exchange (ETDEWEB)

    Arevalo J, P

    1999-12-31

    At this thesis it is studied the heat transfer by natural convection in an horizontal cavity, it is involved a boiling`s part that is described the regimes and correlations differences for boiling`s curve. It is designed a horizontal cavity for realize the experimental part and it`s mention from equipment or instrumentation to succeed in a experimentation that permits to realize the analysis of heat transfer, handling as water fluid at atmospheric pressure and where it`s present process from natural convection involving part boiling`s subcooled. The system consists of heater zone submerged in a horizontal cavity with water. Once part finished experimental with information to obtained it`s proceeded to obtain a correlation, realized starting from analysis dimensionless such as: Jakob, Bond and Grasoft (Boiling) besides of knows in natural convection: Prandtl and Nusselt. The mathematical model explains the behavior for natural convection continued part boiling`s subcooled. It is realize analysis graphics too where it`s show comparing with Globe Dropkin and Catton equations by natural convection with bottom heating. (Author)

  10. Experimental investigation of the effects of orientation angle on heat transfer performance of pin-finned surfaces in natural convection

    International Nuclear Information System (INIS)

    Sertkaya, Ahmet Ali; Bilir, Sefik; Kargici, Suna

    2011-01-01

    Natural convection heat transfer in air from a pin-finned surface is investigated experimentally by considering the effect of radiation heat transfer. The plate was oriented as the pin arrays facing either downwards or upwards from vertical axis with different angles and the experiments were performed for different values of heater power input. From the results of the experiments it is observed that the pin fins increase the heat transfer considerably when compared to the unpinned surface. The upfacing pins are more enhancing heat transfer than the downfacing pins and the enhancement is decreasing with increasing orientation angle from the vertical axis. -- Research highlights: → Effect of orientation in free convection heat transfer from a pin-finned surface. → The upfacing pins are more enhancing heat transfer than the downfacing pins. → Radiation view factor is calculated by a modular analysis. → The radiation is comparable to free convection as not to be neglected. → The radiative part is 25-40% and increases for low heat transfer rates.

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

    Directory of Open Access Journals (Sweden)

    Xie Yong-Hui

    2016-01-01

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

  12. A Coupled Model for Natural Convection and Condensation in Heated Subsurface Enclosures Embedded in Fractured Rock

    International Nuclear Information System (INIS)

    Halecky, N.; Birkholzer, J.T.; Webb, S.W.; Peterson, P.F.; Bodvarsson, G.S.

    2006-01-01

    In heated tunnels such as those designated for emplacement of radioactive waste at Yucca Mountain, axial temperature gradients may cause natural convection processes that can significantly influence the moisture conditions in the tunnels and in the surrounding fractured rock. Large-scale convection cells would provide an effective mechanism for axial vapor transport, driving moisture out of the formation away from the heated tunnel section into cool end sections (where no waste is emplaced). To study such processes, we have developed and applied an enhanced version of TOUGH2 (Pruess et al., 1999) adding a new module that solves for natural convection in open cavities. The new TOUGH2 simulator simultaneously handles (1) the flow and energy transport processes in the fractured rock; (2) the flow and energy transport processes in the cavity; and (3) the heat and mass exchange at the rock-cavity interface. The new module is applied to simulate the future thermal-hydrological (TH) conditions within and near a representative waste emplacement tunnel at Yucca Mountain. Particular focus is on the potential for condensation along the emplacement section, a possible result of heat output differences between individual waste packages

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

    International Nuclear Information System (INIS)

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

    2003-01-01

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

  14. Convection in a nematic liquid crystal with homeotropic alignment and heated from below

    Energy Technology Data Exchange (ETDEWEB)

    Ahlers, G. [Univ. of California, Santa Barbara, CA (United States)

    1995-12-31

    Experimental results for convection in a thin horizontal layer of a homeotropically aligned nematic liquid crystal heated from below and in a vertical magnetic field are presented. A subcritical Hopf bifurcation leads to the convecting state. There is quantitative agreement between the measured and the predicted bifurcation line as a function of magnetic field. The nonlinear state near the bifurcation is one of spatio-temporal chaos which seems to be the result of a zig-zag instability of the straight-roll state.

  15. Numerical investigation of supercritical LNG convective heat transfer in a horizontal serpentine tube

    Science.gov (United States)

    Han, Chang-Liang; Ren, Jing-Jie; Dong, Wen-Ping; Bi, Ming-Shu

    2016-09-01

    The submerged combustion vaporizer (SCV) is indispensable general equipment for liquefied natural gas (LNG) receiving terminals. In this paper, numerical simulation was conducted to get insight into the flow and heat transfer characteristics of supercritical LNG on the tube-side of SCV. The SST model with enhanced wall treatment method was utilized to handle the coupled wall-to-LNG heat transfer. The thermal-physical properties of LNG under supercritical pressure were used for this study. After the validation of model and method, the effects of mass flux, outer wall temperature and inlet pressure on the heat transfer behaviors were discussed in detail. Then the non-uniformity heat transfer mechanism of supercritical LNG and effect of natural convection due to buoyancy change in the tube was discussed based on the numerical results. Moreover, different flow and heat transfer characteristics inside the bend tube sections were also analyzed. The obtained numerical results showed that the local surface heat transfer coefficient attained its peak value when the bulk LNG temperature approached the so-called pseudo-critical temperature. Higher mass flux could eliminate the heat transfer deteriorations due to the increase of turbulent diffusion. An increase of outer wall temperature had a significant influence on diminishing heat transfer ability of LNG. The maximum surface heat transfer coefficient strongly depended on inlet pressure. Bend tube sections could enhance the heat transfer due to secondary flow phenomenon. Furthermore, based on the current simulation results, a new dimensionless, semi-theoretical empirical correlation was developed for supercritical LNG convective heat transfer in a horizontal serpentine tube. The paper provided the mechanism of heat transfer for the design of high-efficiency SCV.

  16. Natural convection heat transfer from a vertical circular tube sheet

    International Nuclear Information System (INIS)

    Dharne, S.P.; Gaitonde, U.N.

    1996-01-01

    Experiments were conducted to determine natural convection heat transfer coefficients (a) on a plain vertical circular plate, and (b) on a similar plate with a square array of non-conducting tubes fixed in it. The experiments were carried out using air as the heat transfer medium. The diameter of the brass plates used was 350 mm. The diameter of the bakelite tubes used was 19.2 mm. The range of Rayleigh numbers was from 1.06x10 8 to 1.66x10 8 . The results show that the heat transfer coefficients in case (a) are very close to those obtained using standard correlations for vertical flat plates, whereas for case (b) the heat transfer coefficients are at least 50 percent higher than those predicted by the Churchill-Chu correlation. It is hence concluded that the disturbance to boundary layer caused by the presence of tubes enhances the heat transfer coefficient significantly. (author). 4 refs., 3 figs

  17. Convective heat transfer from rotating disks subjected to streams of air

    CERN Document Server

    aus der Wiesche, Stefan

    2016-01-01

    This Brief describes systematically results of research studies on a series of convective heat transfer phenomena from rotating disks in air crossflow. Phenomena described in this volume were investigated experimentally using an electrically heated disk placed in the test section of a wind tunnel. The authors describe findings in which transitions between different heat transfer regimes can occur in dependency on the involved Reynolds numbers and the angle of incidence, and that these transitions could be related to phenomenological Landau and Landau-de Gennes models. The concise volume closes a substantial gap in the scientific literature with respect to flow and heat transfer in rotating disk systems and provides a comprehensive presentation of new and recent results not previously published in book form.

  18. Natural convection heat transfer enhancement using Microencapsulated Phase-Change-Material slurries

    International Nuclear Information System (INIS)

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

    1997-01-01

    The present study investigates natural convection heat transfer from a heated cylinder cooled by a water slurry of Microencapsulated Phase Change Material (MCPCM). A normal paraffin hydrocarbon with carbon number of 18 and melting point of 27.9degC, is microencapsulated by Melamine resin into particles of which average diameter is 9.5μm and specific weight is same as water. The slurry of the MCPCM and water is put into a test apparatus, which is a rectangular enclosure with a heated horizontal cylinder. As the concentrations of PCM in the slurry are changed in 1,3 and 5%, the heat transfer coefficients of the cylinder are larger than that of water as working fluid, by 3,20 and 35% enhancements respectively. (author)

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

    DEFF Research Database (Denmark)

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

    2015-01-01

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

  20. Dynamics of a secondary instability in Benard-Marangoni convection with unidimensional heating

    International Nuclear Information System (INIS)

    Burguete, J.; Mancini, H.L.; Perez-Garcia, C.

    1993-01-01

    The dynamics of Benard-Marangoni convection with unidimensional heating in a pure fluid is studied experimentally. Convection begins with rolls parallel to the heater. The characteristics of these primary rolls have been determined. When the temperature difference across the liquid layer is increased beyond a critical value a secondary instability appears. Motions transverse to the heater with a definite wavelength can be seen. Moreover, for small angles between the heater and the fluid surface, the pattern drifts along the heater with a velocity that depends almost linearly on the inclination. A phenomenological phase equation is proposed to interpret this observation. (orig.)

  1. Influence of fluid-property variation on turbulent convective heat transfer in vertical annular CHANNEL FLOWS

    International Nuclear Information System (INIS)

    Joong Hun Bae; Jung Yul Yoo; Haecheon Choi

    2005-01-01

    Full text of publication follows: The influence of variable fluid property on turbulent convective heat transfer is investigated using direct numerical simulations. We consider thermally-developing flows of air and supercritical-pressure CO 2 in a vertical annular channel where the inner wall is heated with a constant heat flux and the outer wall is insulated. Turbulence statistics show that the heat and momentum transport characteristics of variable-property flows are significantly different from those of constant-property flows. The difference is mainly caused by the spatial and temporal variations of fluid density. The non-uniform density distribution causes fluid particles to be accelerated either by expansion or buoyancy force, while the temporal density fluctuations change the heat and momentum transfer via transport of turbulent mass flux, ρ'u' i . Both effects of the spatial and temporal variations of density are shown to be important in the analysis of turbulent convective heat transfer for supercritical-pressure fluids. For variable-property heated air flows, however, the effect of temporal density fluctuations can be neglected at low Mach number, which is in good accordance with the Morkovin's hypothesis. (authors)

  2. Flow and Convective Heat Transfer of Cylinder Misaligned from Aerodynamic Axis of Cyclone Flow

    Directory of Open Access Journals (Sweden)

    I. L. Leukhin

    2008-01-01

    Full Text Available The paper provides and analyzes results of experimental investigations on physical specific features of hydrodynamics and convective heat transfer of a cyclone flow with a group of round cylinders located symmetrically relative to its aerodynamic axis, calculative equations for average and local heat transfer factors at characteristic sections of cylinder surface.

  3. Book of short papers : International symposium on convective heat and mass transfer in sustainable energy Conv - 09. Volume 1

    International Nuclear Information System (INIS)

    2009-01-01

    This book contains the short papers from the International Symposium on Convective heat and Mass Transfer in sustainable Energy ( Conv-09), organized on behalf of the International Centre for Heat and Mass Transfer, it was held on April 26- 1st May, In Hammamet, Tunisia. The objective of this conference is to bring together researchers in a forum to exchange innovative ideas, methods and results, and visions of the future related to the general theme of convective heat and mass transfer

  4. Book of short papers : International symposium on convective heat and mass transfer in sustainable energy conv - 09. Volume 2

    International Nuclear Information System (INIS)

    2009-01-01

    This book contains the short papers from the International Symposium on convective heat and Mass Transfer in sustainable Energy ( conv-09), organized on behalf of the International Centre for Heat and Mass Transfer, it was held on April 26- 1st May, In Hammamet, Tunisia. The objective of this conference is to bring together researchers in a forum to exchange innovative ideas, methods and results, and visions of the future related to the general theme of convective heat and mass transfer

  5. Convective Heating of the LIFE Engine Target During Injection

    Energy Technology Data Exchange (ETDEWEB)

    Holdener, D S; Tillack, M S; Wang, X R

    2011-10-24

    Target survival in the hostile, high temperature xenon environment of the proposed Laser Inertial Fusion Energy (LIFE) engine is critical. This work focuses on the flow properties and convective heat load imposed upon the surface of the indirect drive target while traveling through the xenon gas. While this rarefied flow is traditionally characterized as being within the continuum regime, it is approaching transition where conventional CFD codes reach their bounds of operation. Thus ANSYS, specifically the Navier-Stokes module CFX, will be used in parallel with direct simulation Monte Carlo code DS2V and analytically and empirically derived expressions for heat transfer to the hohlraum for validation. Comparison of the viscous and thermal boundary layers of ANSYS and DS2V were shown to be nearly identical, with the surface heat flux varying less than 8% on average. From the results herein, external baffles have been shown to reduce this heat transfer to the sensitive laser entrance hole (LEH) windows and optimize target survival independent of other reactor parameters.

  6. A fluid-solid coupling simulation method for convection heat transfer coefficient considering the under-vehicle condition

    Science.gov (United States)

    Tian, C.; Weng, J.; Liu, Y.

    2017-11-01

    The convection heat transfer coefficient is one of the evaluation indexes of the brake disc performance. The method used in this paper to calculate the convection heat transfer coefficient is a fluid-solid coupling simulation method, because the calculation results through the empirical formula method have great differences. The model, including a brake disc, a car body, a bogie and flow field, was built, meshed and simulated in the software FLUENT. The calculation models were K-epsilon Standard model and Energy model. The working condition of the brake disc was considered. The coefficient of various parts can be obtained through the method in this paper. The simulation result shows that, under 160 km/h speed, the radiating ribs have the maximum convection heat transfer coefficient and the value is 129.6W/(m2·K), the average coefficient of the whole disc is 100.4W/(m2·K), the windward of ribs is positive-pressure area and the leeward of ribs is negative-pressure area, the maximum pressure is 2663.53Pa.

  7. Diffusive and convective transport modelling from analysis of ECRH-stimulated electron heat wave propagation

    International Nuclear Information System (INIS)

    Erckmann, V.; Gasparino, U.; Giannone, L.

    1992-01-01

    ECRH power modulation experiments in toroidal devices offer the chance to analyze the electron heat transport more conclusively: the electron heat wave propagation can be observed by ECE (or SX) leading to radial profiles of electron temperature modulation amplitude and time delay (phase shift). Taking also the stationary power balance into account, the local electron heat transport can be modelled by a combination of diffusive and convective transport terms. This method is applied to ECRH discharges in the W7-AS stellarator (B=2.5T, R=2m, a≤18 cm) where the ECRH power deposition is highly localized. In W7-AS, the T e modulation profiles measured by a high resolution ECE system are the basis for the local transport analysis. As experimental errors limit the separation of diffusive and convective terms in the electron heat transport for central power deposition, also ECRH power modulation experiments with off-axis deposition and inward heat wave propagation were performed (with 70 GHz o-mode as well as with 140 GHz x-mode for increased absorption). Because collisional electron-ion coupling and radiative losses are only small, low density ECRH discharges are best candidates for estimating the electron heat flux from power balance. (author) 2 refs., 3 figs

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2007-01-15

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

  9. Experimental investigation of convection heat transfer of CO2 at supercritical pressures in a vertical circular tube at high Re

    International Nuclear Information System (INIS)

    Li Zhihui; Jiang Peixue

    2008-01-01

    Convection heat transfer during the upward flow of CO 2 at supercritical pressures in a vertical circular tube (d in = 2 mm) at high Reynolds numbers was investigated experimentally, and the effects of heat fluxes, mass fluxes, inlet temperatures, pressures, buoyancy and thermal acceleration on the convection heat transfer was analyzed. The results show that the tube wall temperature occurs abnormally distribution for high heat-fluxes with upward flow. The degree of deteriorated heat transfer increases with increasing heat flux. Increasing of the mass flux delays the occurrence of the deterioration of heat transfer and weakens the deterioration of heat transfer down-stream section. The inlet temperature strongly influences the heat transfer. The deterioration degree of heat transfer decreases with increasing pressure. (authors)

  10. Comparison of microwave and conduction-convection heating autohydrolysis pretreatment for bioethanol production.

    Science.gov (United States)

    Aguilar-Reynosa, Alejandra; Romaní, Aloia; Rodríguez-Jasso, Rosa M; Aguilar, Cristóbal N; Garrote, Gil; Ruiz, Héctor A

    2017-11-01

    This work describes the application of two forms of heating for autohydrolysis pretreatment on isothermal regimen: conduction-convection heating and microwave heating processing using corn stover as raw material for bioethanol production. Pretreatments were performed using different operational conditions: residence time (10-50 min) and temperature (160-200°C) for both pretreatments. Subsequently, the susceptibility of pretreated solids was studied using low enzyme loads, and high substrate loads. The highest conversion was 95.1% for microwave pretreated solids. Also solids pretreated by microwave heating processing showed better ethanol conversion in simultaneous saccharification and fermentation process (92% corresponding to 33.8g/L). Therefore, microwave heating processing is a promising technology in the pretreatment of lignocellulosic materials. Copyright © 2017 Elsevier Ltd. All rights reserved.

  11. Entropy generation in natural convection in a symmetrically and uniformly heated vertical channel

    Energy Technology Data Exchange (ETDEWEB)

    Andreozzi, Assunta [Dipartimento di Energetica, Termofluidodinamica applicata e Condizionamenti ambientali, Universita degli Studi di Napoli Federico II, Piazzale Tecchio 80, 80125 Napoli (Italy); Auletta, Antonio [CIRA - Centro Italiano Ricerche Aerospaziali, Via Maiorise 1, 81043 Capua (CE) (Italy); Manca, Oronzio [Dipartimento di Ingegneria Aerospaziale e Meccanica, Seconda Universita degli Studi di Napoli, Real Casa dell' Annunziata, Via Roma 29, 81031 Aversa (CE) (Italy)

    2006-08-15

    In this study numerical predictions of local and global entropy generation rates in natural convection in air in a vertical channel symmetrically heated at uniform heat flux are reported. Results of entropy generation analysis are obtained by solving the entropy generation equation based on the velocity and temperature data. The analyzed regime is two-dimensional, laminar and steady state. The numerical procedure expands an existing computer code on natural convection in vertical channels. Results in terms of fields and profiles of local entropy generation, for various Rayleigh number, Ra, and aspect ratio values, L/b, are given. The distributions of local values show different behaviours for the different Ra values. A correlation between global entropy generation rates, Rayleigh number and aspect ratio is proposed in the ranges 10{sup 3}=

  12. The Weight Loss Effect of Heated Inner Cylinder by Free Convection in Horizontal Cylindrical Enclosure

    Science.gov (United States)

    Sboev, I. O.; Kondrashov, A. N.; Rybkin, K. A.; Burkova, L. N.; Goncharov, M. M.

    2018-03-01

    The work presents results of numerical simulations of natural convection in cavity formed by the surfaces of two horizontal coaxial cylinders. The temperature of the outer cylinder is constant. The area between the cylinders is filled with an ideal incompressible fluid. The inner cylinder is set as the heater. The solution of the equations of thermal convection in a two-dimensional approximation performed by the software package ANSYS Fluent with finite volume method. The study compares the results of numerical simulation with several well-known theoretical and experimental results. The nature of interaction of the inner cylinder with a convection current created in the gap was observed. It was shown that the flux appeared around a heated cylinder affects the weight of the heat source and causes an additional lift force from the surrounding fluid. The various Rayleigh numbers (from 1.0 ṡ 103 to 1.5 ṡ 106) and fluid with different Prandtl number (from 0.5 to 1.0 ṡ 105) are considered.

  13. Radiative properties effects on unsteady natural convection inside a saturated porous medium. Application for porous heat exchangers

    International Nuclear Information System (INIS)

    Abdesslem, Jbara; Khalifa, Slimi; Abdelaziz, Nasr; Abdallah, Mhimid

    2013-01-01

    The present article deals with a numerical study of coupled fluid flow and heat transfer by transient natural convection and thermal radiation in a porous bed confined between two-vertical hot plates and saturated by a homogeneous and isotropic fluid phase. The main objective is to study the effects of radiative properties on fluid flow and heat transfer behavior inside the porous material. The numerical results show that the temperature, the axial velocity, the volumetric flow rate and the convective heat flux exchanged at the channel's exit are found to be increased when the particle emissivity (ε) and/or the absorption coefficient (κ) increase or when the scattering coefficient (σ s ) and/or the single scattering albedo (ω) decrease. Furthermore, the amount of heat (Q c ) transferred to fluid and the energetic efficiency E c are found to be increased when there is a raise in the particle emissivity values. In order to improve the performance of heat exchanger, we proposed the model of a porous heat exchanger which includes a porous bed of large spherical particles with high emissivity as a practical application of the current study. - Highlights: • The temperature increases with the particle emissivity ε. • The volumetric flow rate and the convective heat flux exchanged increase with the particle emissivity ε. • The amount of heat transferred to fluid and the energetic efficiency increase with the particle emissivity ε. • A heat exchanger including a porous bed of spherical particles with high emissivity is proposed like a practical application

  14. Cu-water nanofluid flow induced by a vertical stretching sheet in presence of a magnetic field with convective heat transfer

    Directory of Open Access Journals (Sweden)

    Kalidas Das

    2017-09-01

    Full Text Available The convective heat transfer performance of nanofluid over a permeable stretching sheet with thermal convective boundary condition in presence of magnetic field and slip velocity is studied in the present paper. Cu-water nanofluid is used to investigate the effect of nanoparticles on the flow and heat transfer characteristic. The numerical results are compared with published results and are found in an excellent agreement. The influences of various relevant parameters on the velocity and temperature as well as the rate of shear stress and the rate of heat transfer are elucidated through graphs and tables. It is observed that nanoparticles volume fraction and surface convection parameter both increase the thickness of thermal boundary layer.

  15. Numerical Studies on Natural Convection Heat Losses from Open Cubical Cavities

    Directory of Open Access Journals (Sweden)

    M. Prakash

    2013-01-01

    Full Text Available The natural convection heat losses occurring from cubical open cavities are analysed in this paper. Open cubical cavities of sides 0.1 m, 0.2 m, 0.25 m, 0.5 m, and 1 m with constant temperature back wall boundary conditions and opening ratio of 1 are studied. The Fluent CFD software is used to analyse the three-dimensional (3D cavity models. The studies are carried out for cavities with back wall temperatures between 35°C and 100°C. The effect of cavity inclination on the convective loss is analysed for angles of 0° (cavity facing sideways, 30°, 45°, 60°, and 90° (cavity facing vertically downwards. The Rayleigh numbers involved in this study range between 4.5 × 105 and 1.5 × 109. The natural convection loss is found to increase with an increase in back wall temperature. The natural convection loss is observed to decrease with an increase in cavity inclination; the highest convective loss being at 0° and the lowest at 90° inclination. This is observed for all cavities analysed here. Nusselt number correlations involving the effect of Rayleigh number and the cavity inclination angle have been developed from the current studies. These correlations can be used for engineering applications such as electronic cooling, low- and medium-temperature solar thermal systems, passive architecture, and also refrigeration systems.

  16. Bifurcations and chaos in convection taking non-Fourier heat-flux

    Science.gov (United States)

    Layek, G. C.; Pati, N. C.

    2017-11-01

    In this Letter, we report the influences of thermal time-lag on the onset of convection, its bifurcations and chaos of a horizontal layer of Boussinesq fluid heated underneath taking non-Fourier Cattaneo-Christov hyperbolic model for heat propagation. A five-dimensional nonlinear system is obtained for a low-order Galerkin expansion, and it reduces to Lorenz system for Cattaneo number tending to zero. The linear stability agreed with existing results that depend on Cattaneo number C. It also gives a threshold Cattaneo number, CT, above which only oscillatory solutions can persist. The oscillatory solutions branch terminates at the subcritical steady branch with a heteroclinic loop connecting a pair of saddle points for subcritical steady-state solutions. For subcritical onset of convection two stable solutions coexist, that is, hysteresis phenomenon occurs at this stage. The steady solution undergoes a Hopf bifurcation and is of subcritical type for small value of C, while it becomes supercritical for moderate Cattaneo number. The system goes through period-doubling/noisy period-doubling transition to chaos depending on the control parameters. There after the system exhibits Shil'nikov chaos via homoclinic explosion. The complexity of spiral strange attractor is analyzed using fractal dimension and return map.

  17. DETERMINATION OF CONVECTIVE HEAT TRANSFER COEFFICIENT AT THE OUTER SURFACE OF A CRYOVIAL BEING PLUNGED INTO LIQUID NITROGEN.

    Science.gov (United States)

    Wang, T; Zhao, G; Tang, H Y; Jiang, Z D

    2015-01-01

    Cell survival upon cryopreservation is affected by the cooling rate. However, it is difficult to model the heat transfer process or to predict the cooling curve of a cryoprotective agent (CPA) solution due to the uncertainty of its convective heat transfer coefficient (h). To measure the h and to better understand the heat transfer process of cryovials filled with CPA solution being plunged in liquid nitrogen. The temperatures at three locations of the CPA solution in a cryovial were measured. Different h values were selected after the cooling process was modeled as natural convection heat transfer, the film boiling and the nucleate boiling, respectively. And the temperatures of the selected points are simulated based on the selected h values. h was determined when the simulated temperature best fitted the experimental temperature. When the experimental results were best fitted, according to natural convection heat transfer model, h(1) = 120 W/(m(2)·K) while due to film boiling and nucleate boiling regimes h(f) = 5 W/(m(2)·K) followed by h(n) = 245 W/(m(2)·K). These values were verified by the differential cooling rates at the three locations of a cryovial. The heat transfer process during cooling in liquid nitrogen is better modeled as film boiling followed by nucleate boiling.

  18. Turbulence convective heat transfer for cooling the photovoltaic cells

    Science.gov (United States)

    Arianmehr, Iman

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

  19. Heat transfer enhancement induced by electrically generated convection in a plane layer of dielectric liquid

    International Nuclear Information System (INIS)

    Traoré, P; Wu, J; Romat, H; Louste, C; Perez, A; Koulova, D

    2012-01-01

    The electro-thermo-convective motion in a plane horizontal dielectric liquid layer subjected to simultaneous action of electric field and thermal gradient is numerically investigated. We consider the case of a strong unipolar charge injection C = 10 from above or below. Therefore in this context, we only take into account the Coulomb force, disregarding the dielectric one. The effect of the electric field on the heat transfer is analyzed through the characterization of the time history of the Nusselt number as well as its evolution according to the characteristic dimensionless electric parameter T. It is demonstrated that the electric effects dominate the buoyancy ones resulting in an electrically induced convection which significantly enhance the heat transfer.

  20. Mixed convection heat transfer from confined tandem square cylinders in a horizontal channel

    KAUST Repository

    Huang, Zhu; Xi, Guang; Zhang, Wei; Wen, Suping

    2013-01-01

    with four widths of the cylinder and the blockage ratio and the Prandtl number are fixed at 0.1 and 0.7 respectively. The mixed convective flow and heat transfer is simulated by high accuracy multidomain pseudospectral method. The Reynolds number (Re

  1. Preliminary Numerical Analysis of Convective Heat Transfer Loop Using MARS Code

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Yongjae; Seo, Gwang Hyeok; Jeun, Gyoodong; Kim, Sung Joong [Hanyang Univ., Seoul (Korea, Republic of)

    2014-05-15

    The MARS has been developed adopting two major modules: RELAP5/MOD3 (USA) for one-dimensional (1D) two-fluid model for two-phase flows and COBRA-TF code for a three-dimensional (3D), two-fluid, and three-field model. In addition to the MARS code, TRACE (USA) is a modernized thermal-hydraulics code designed to consolidate and extend the capabilities of NRC's 3 legacy safety code: TRAC-P, TRAC-B and RELAP. CATHARE (French) is also thermal-hydraulic system analysis code for Pressurized Water Reactor (PWR) safety. There are several researches on comparing experimental data with simulation results by the MARS code. Kang et al. conducted natural convection heat transfer experiments of liquid gallium loop, and the experimental data were compared to MARS simulations. Bang et al. examined the capability of the MARS code to predict condensation heat transfer experiments with a vertical tube containing a non-condensable gas. Moreover, Lee et al. adopted MELCOR, which is one of the severe accident analysis codes, to evaluate several strategies for the severe accident mitigation. The objective of this study is to conduct the preliminary numerical analysis for the experimental loop at HYU using the MARS code, especially in order to provide relevant information on upcoming experiments for the undergraduate students. In this study, the preliminary numerical analysis for the convective heat transfer loop was carried out using the MARS Code. The major findings from the numerical simulations can be summarized as follows. In the calculations of the outlet and surface temperatures, the several limitations were suggested for the upcoming single-phase flow experiments. The comparison work for the HTCs shows validity for the prepared input model. This input could give useful information on the experiments. Furthermore, the undergraduate students in department of nuclear engineering, who are going to be taken part in the experiments, could prepare the program with the input, and will

  2. Preliminary Numerical Analysis of Convective Heat Transfer Loop Using MARS Code

    International Nuclear Information System (INIS)

    Lee, Yongjae; Seo, Gwang Hyeok; Jeun, Gyoodong; Kim, Sung Joong

    2014-01-01

    The MARS has been developed adopting two major modules: RELAP5/MOD3 (USA) for one-dimensional (1D) two-fluid model for two-phase flows and COBRA-TF code for a three-dimensional (3D), two-fluid, and three-field model. In addition to the MARS code, TRACE (USA) is a modernized thermal-hydraulics code designed to consolidate and extend the capabilities of NRC's 3 legacy safety code: TRAC-P, TRAC-B and RELAP. CATHARE (French) is also thermal-hydraulic system analysis code for Pressurized Water Reactor (PWR) safety. There are several researches on comparing experimental data with simulation results by the MARS code. Kang et al. conducted natural convection heat transfer experiments of liquid gallium loop, and the experimental data were compared to MARS simulations. Bang et al. examined the capability of the MARS code to predict condensation heat transfer experiments with a vertical tube containing a non-condensable gas. Moreover, Lee et al. adopted MELCOR, which is one of the severe accident analysis codes, to evaluate several strategies for the severe accident mitigation. The objective of this study is to conduct the preliminary numerical analysis for the experimental loop at HYU using the MARS code, especially in order to provide relevant information on upcoming experiments for the undergraduate students. In this study, the preliminary numerical analysis for the convective heat transfer loop was carried out using the MARS Code. The major findings from the numerical simulations can be summarized as follows. In the calculations of the outlet and surface temperatures, the several limitations were suggested for the upcoming single-phase flow experiments. The comparison work for the HTCs shows validity for the prepared input model. This input could give useful information on the experiments. Furthermore, the undergraduate students in department of nuclear engineering, who are going to be taken part in the experiments, could prepare the program with the input, and will

  3. The effect of centrifugal buoyancy on the heat transport in rotating Rayleigh-Bénard convection

    Science.gov (United States)

    Horn, Susanne; Aurnou, Jonathan

    2017-11-01

    In a rapidly rotating and differentially heated fluid, the centrifugal acceleration can play a similar role to that of gravity in generating convective motion. However, in the paradigm system of rotating Rayleigh-Bénard convection, centrifugal buoyancy is typically not considered in theoretical studies and, thus, usually undesired in laboratory experiments, despite being unavoidable. How centrifugal buoyancy affects the turbulent flow, including the heat transport, is still largely unknown, in particular, when it can be considered negligible. We study this problem by means of direct numerical simulations. Unlike in experiments, we are able to systematically vary the Froude number Fr (ratio of centrifugal to gravitational acceleration) and the Rossby number Ro (dimensionless rotation rate) independently, and even set each to zero exactly. We show that the centrifugal acceleration simultaneously leads to contending phenomena, e.g. reflected by an increase and a decrease of the center temperature, or a suppression and an enhancement of the heat transfer efficiency. Which one prevails as net effect strongly depends on the combination of Fr and Ro. Furthermore, we discuss implications for experiments of rapidly rotating convection. SH acknowledges funding by the Deutsche Forschungsgemeinschaft (DFG) under Grant HO 5890/1-1, JA by the NSF Geophysics Program.

  4. Effect of radiation on the laminar convective heat transfer through a layer of highly porous medium

    International Nuclear Information System (INIS)

    Lee, K.; Howell, J.R.

    1986-01-01

    A numerical investigation is reported of the coupled forced convective and radiative transfer through a highly porous medium. The porosity range investigated is high enough that the fluid inertia terms in the momentum equation cannot be neglected; i.e., the simple form of Darcy's law is invalid. The geometry studied is a plane layer of highly porous medium resting on one impermeable boundary and exposed to a two-dimensional laminar external flow field. The objective is to determine the effective overall heat transfer coefficients for such a geometry. The results are applicable to diverse situations, including insulation batts exposed to external flow, the heat loss and drying rates of grain fields and forest areas, and the drying of beds of porous material exposed to convective and radiative heating

  5. MHD mixed convection flow and heat transfer in an open C-shaped enclosure using water-copper oxide nanofluid

    Science.gov (United States)

    Armaghani, T.; Esmaeili, H.; Mohammadpoor, Y. A.; Pop, I.

    2018-01-01

    In this paper, the steady mixed convection flow and heat transfer of water-copper oxide nanofluid in an open C-shaped enclosure is investigated numerically. The enclosure is under constant magnetic field. Effects of Richardson number, magnetic and nanofluid volume fraction parameters are studied and discussed. The nanofluid with a cold temperature of T C and a velocity of u c enters the enclosure from the top right corner and exits from the bottom right corner. The vertical wall of the left side is subjected to a hot and constant temperature T h . Also, other walls are insulated. It is found that the heat transfer is increased via increasing the Hartmann and Reynolds numbers. For low Reynolds numbers, the enhances of the Hartman number leads to a slightly increases of the average Nusselt number, but for high Reynolds numbers, the average Nusselt number gets an ascending trend and the increase in the Hartmann number shows its effect more pronounced. Also, with increase in Ri, the effect of nanofluid on the heat transfer increases. Due to practical impotence, the study of mixed convection heat transfer in enclosures and various shaped of cavities has attracted remarkable attentions in the past few decades. Significant applications of the mixed convection flow can be found in atmospheric flows, solar energy storage, heat exchangers, lubrication technology, drying technologies, cooling of the electronic devices, etc. The present results are original and new for the problem of MHD mixed convection flow and heat transfer in an open C-shaped enclosure using water-copper oxide nanofluid. Comparison of the obtained results with those from the open literature (Mahmoodi et al. [24]) is acceptable.

  6. Study of natural convection heat transfer characteristics. (2) Verification for numerical simulation

    International Nuclear Information System (INIS)

    Ikeda, Hiroshi; Nakada, Kotaro; Ikeda, Tatsumi; Wakamatsu, Mitsuo; Iwaki, Chikako; Morooka, Shinichi; Masaki, Yoshikazu

    2008-01-01

    In the natural cooling system for waste storage, it is important to evaluate the flow by natural draft enough to remove the decay heat from the waste. In this study, we carried out the fundamental study of natural convection on vertical cylindrical heater by experiment and numerical simulation. The dimension of test facility is about 4m heights with single heater. Heating power is varied in the range of 33-110W, where Rayleigh number is over 10 10 . We surveyed the velocity distribution around heater by some turbulent models, mesh sizes around heated wall and turbulent Prandtl numbers. Results of numerical simulation of the velocity distribution and averaged heat transfer coefficient agreed well with experimental data and references. (author)

  7. Dynamical System Analysis of Thermal Convection in a Horizontal Layer of Nanofluids Heated from Below

    Directory of Open Access Journals (Sweden)

    J. M. Jawdat

    2012-01-01

    Full Text Available The effect of nanofluids on chaotic convection in a fluid layer heated from below was studied in this paper for low Prandtl number based on the theory of dynamical systems. A low-dimensional, Lorenz-like model was obtained using Galerkin-truncated approximations. The fourth-order Runge-Kutta method was employed to solve the nonlinear system. The results show that inhibition of chaotic convection can be observed when using nanofluids.

  8. Thermal performance of a porus radial fin with natural convection and radiative heat losses

    Directory of Open Access Journals (Sweden)

    Darvishi M.T.

    2015-01-01

    Full Text Available An analytic (series solution is developed to describe the thermal performance of a porous radial fin with natural convection in the fluid saturating the fin and radiation heat loss from the top and bottom surfaces of the fin. The HAM results for the temperature distribution and base heat flux are compared with the direct numerical results and found to be very accurate.

  9. Upscale Impact of Mesoscale Disturbances of Tropical Convection on Convectively Coupled Kelvin Waves

    Science.gov (United States)

    Yang, Q.; Majda, A.

    2017-12-01

    Tropical convection associated with convectively coupled Kelvin waves (CCKWs) is typically organized by an eastward-moving synoptic-scale convective envelope with numerous embedded westward-moving mesoscale disturbances. It is of central importance to assess upscale impact of mesoscale disturbances on CCKWs as mesoscale disturbances propagate at various tilt angles and speeds. Here a simple multi-scale model is used to capture this multi-scale structure, where mesoscale fluctuations are directly driven by mesoscale heating and synoptic-scale circulation is forced by mean heating and eddy transfer of momentum and temperature. The two-dimensional version of the multi-scale model drives the synoptic-scale circulation, successfully reproduces key features of flow fields with a front-to-rear tilt and compares well with results from a cloud resolving model. In the scenario with an elevated upright mean heating, the tilted vertical structure of synoptic-scale circulation is still induced by the upscale impact of mesoscale disturbances. In a faster propagation scenario, the upscale impact becomes less important, while the synoptic-scale circulation response to mean heating dominates. In the unrealistic scenario with upward/westward tilted mesoscale heating, positive potential temperature anomalies are induced in the leading edge, which will suppress shallow convection in a moist environment. In its three-dimensional version, results show that upscale impact of mesoscale disturbances that propagate at tilt angles (110o 250o) induces negative lower-tropospheric potential temperature anomalies in the leading edge, providing favorable conditions for shallow convection in a moist environment, while the remaining tilt angle cases have opposite effects. Even in the presence of upright mean heating, the front-to-rear tilted synoptic-scale circulation can still be induced by eddy terms at tilt angles (120o 240o). In the case with fast propagating mesoscale heating, positive

  10. Study on Natural Convection around a vertical heated rod using PIV/LIF technique,

    International Nuclear Information System (INIS)

    Szijarto, R.; Yamaji, B.; Aszodi, A.

    2010-01-01

    The Nuclear Training Reactor of the Institute of Nuclear Techniques (Budapest University of Technology and Economics, Hungary) is a pool-type reactor with light water moderator and with a maximum thermal power of 100 kW. The fuel elements are cooled by natural convection. An experimental setup was built to analyse the nature of the natural convection around a heated rod. The flow field was investigated using an electrically heated rod, which models the geometry of a fuel pin in the training reactor. The electric power of the model rod is variable between 0-500 W. The rod was placed in a square-based glass tank. Particle Image Velocimetry and Laser Induced Fluorescence measurement techniques were used to study the velocity and temperature field in a two-dimensional area. The thermal and the hydraulic boundary layers were detected near a rod in a lower section of the aquarium. The laminar-turbulent transition of the flow regime was observed, the maximum velocity of the up-flow was 0.025-0.05 m/s. From the temperature measurements the local heat transfer coefficient was estimated. (Authors)

  11. Lattice Boltzmann analysis of effect of heating location and Rayleigh number on natural convection in partially heated open ended cavity

    Energy Technology Data Exchange (ETDEWEB)

    Gangawane, Krunal Madhukar; Bharti, Ram Prakash; Kumar, Surendra [Indian Institute of Technology Roorkee, Uttarakhand (India)

    2015-08-15

    Natural convection characteristics of a partially heated open ended square cavity have been investigated numerically by using an in-house computational flow solver based on the passive scalar thermal lattice Boltzmann method (PS-TLBM) with D2Q9 (two-dimensional and nine-velocity link) lattice model. The partial part of left wall of the cavity is heated isothermally at either of the three different (bottom, middle and top) locations for the fixed heating length as half of characteristic length (H/2) while the right wall is open to the ambient conditions. The other parts of the cavity are thermally isolated. In particular, the influences of partial heating locations and Rayleigh number (103≤ Ra≤106) in the laminar zone on the local and global natural convection characteristics (such as streamline, vorticity and isotherm contours; centerline variations of velocity and temperature; and local and average Nusselt numbers) have been presented and discussed for the fixed value of the Prandtl number (Pr=0.71). The streamline patterns show qualitatively similar nature for all the three heating cases and Rayleigh numbers, except the change in the recirculation zone which is found to be largest for middle heating case. Isotherm patterns are shifted towards a partially heated wall on increasing Rayleigh number and/or shifting of heating location from bottom to top. Both the local and average Nusselt numbers, as anticipated, shown proportional increase with Rayleigh number. The cavity with middle heating location shown higher heat transfer rate than that for the top and bottom heating cases. Finally, the functional dependence of the average Nusselt number on flow governing parameters is also presented as a closure relationship for the best possible utilization in engineering practices and design.

  12. Natural convection as the way of heat removal from fast reactor core at cooldown regimes

    International Nuclear Information System (INIS)

    Zhukov, A.V.; Kuzina, J.A.; Uhov, V.A.; Sorokin, G.A.

    2000-01-01

    The problems of thermohydraulics in fast reactors at cooldown regimes at heat removal by natural convection are considered The results of experiments and calculations obtained in various countries in this area are presented. The special attention is given to heat removal through inter-assembly space in the core and also to problems of thermohydraulics in the upper plenum. (author)

  13. Adiabatic partition effect on natural convection heat transfer inside a square cavity

    DEFF Research Database (Denmark)

    Mahmoudi Nezhad, Sajjad; Rezaniakolaei, Alireza; yousefi, Tooraj

    2018-01-01

    A steady state and two-dimensional laminar free convection heat transfer in a partitioned cavity with horizontal adiabatic and isothermal side walls is investigated using both experimental and numerical approaches. The experiments and numerical simulations are carried out using a Mach......-Zehnder interferometer and a finite volume code, respectively. A horizontal and adiabatic partition, with angle of θ is adjusted such that it separates the cavity into two identical parts. Effects of this angel as well as Rayleigh number on the heat transfer from the side-heated walls are investigated in this study...... partition angle, the results show that the average Nusselt number and consequently the heat transfer enhance as the Rayleigh number increases. However, for a given Rayleigh number the maximum and the minimum heat transfer occurs at θ = 45°and θ = 90°, respectively. Two responsible mechanisms...

  14. Convective heat transfer of supercritical CO_2 in a rock fracture for enhanced geothermal systems

    International Nuclear Information System (INIS)

    Zhang, Le; Jiang, Peixue; Wang, Zhenchuan; Xu, Ruina

    2017-01-01

    Highlights: • Contrasting experiments between a rough and a smooth fracture were performed. • A numerical model of rough fracture was reconstructed based on CT scanning data. • Heat transfer in rough fracture was affected by channeling and disturbance effects. - Abstract: Convective heat transfer characteristics of supercritical pressure fluid in a rock fracture are important for building an accurate heat transfer model of enhanced geothermal systems. This paper presents experimental investigations of laminar convection heat transfer of supercritical pressure CO_2 in an artificial smooth parallel-plate fracture and a rough and tortuous fracture that was created using the Brazilian technique. Hot rock with a relatively high initial temperature reserves more heat, which can ensure a larger heat extraction rate for a longer time when cold fluid flows through the fracture. Compared with the smooth parallel-plate fracture, CO_2 flowing through the rough and tortuous fracture with an equivalent hydraulic aperture extracted less heat from the hot rock due to the less efficient heat exchange in a rough fracture caused by channeling effect. This was illustrated by numerical simulation results of the reconstructed fracture based on micro-computed tomography scan data. The overall Nusselt number obtained from the numerical results was larger in a rough fracture with a larger Reynolds number due to disturbance effect on the boundary layer development. The heat transfer performance in a rough fracture is therefore influenced by interactions of the channeling and disturbance effects caused by the tortuous flow path.

  15. Numerical investigation on mixed convection flow in a trapezoidal cavity heated from below

    International Nuclear Information System (INIS)

    Tmartnhad, Ilham; El Alami, Mustapha; Najam, Mostafa; Oubarra, Abdelaziz

    2008-01-01

    A numerical study of mixed convection from a trapezoidal cavity is carried out. Two openings are adjusted on the plates of the cavity. The inlet opening is horizontal or vertical, while the outlet one is placed horizontally on the bottom wall. The Navier-Stokes equations are solved using a control volume method and the SIMPLEC algorithm is used for the treatment of pressure-velocity coupling. Special emphasis is given to detail the effect of the Reynolds number on the heat transfer generated by mixed convection. The results are given for the parameters of control as, Rayleigh number (Ra = 10 5 ), Prandtl number (Pr = 0.72), the inlet and outlet opening width are respectively (C 1 = 0.38 and C 2 = 0.25), the inclination of the tilted wall (θ = 22 deg. ) and Reynolds number (10 ≤ Re ≤ 1000). The results show that the flow structure and the heat transfer depends significantly on the inlet opening site. Two principal kinds of the problem solution are raised

  16. Unsteady free convection MHD flow between two heated vertical parallel conducting plates

    International Nuclear Information System (INIS)

    Sanyal, D.C.; Adhikari, A.

    2006-01-01

    Unsteady free convection flow of a viscous incompressible electrically conducting fluid between two heated conducting vertical parallel plates subjected to a uniform transverse magnetic field is considered. The approximate analytical solutions for velocity, induced field and temperature distribution are obtained for small and large values of magnetic Reynolds number. The problem is also extended to thermometric case. (author)

  17. Natural convection in asymmetric triangular enclosures heated from below

    Science.gov (United States)

    Kamiyo, O. M.; Angeli, D.; Barozzi, G. S.; Collins, M. W.

    2014-11-01

    Triangular enclosures are typical configurations of attic spaces found in residential as well as industrial pitched-roof buildings. Natural convection in triangular rooftops has received considerable attention over the years, mainly on right-angled and isosceles enclosures. In this paper, a finite volume CFD package is employed to study the laminar air flow and temperature distribution in asymmetric rooftop-shaped triangular enclosures when heated isothermally from the base wall, for aspect ratios (AR) 0.2 <= AR <= 1.0, and Rayleigh number (Ra) values 8 × 105 <= Ra <= 5 × 107. The effects of Rayleigh number and pitch angle on the flow structure and temperature distributions within the enclosure are analysed. Results indicate that, at low pitch angle, the heat transfer between the cold inclined and the hot base walls is very high, resulting in a multi-cellular flow structure. As the pitch angle increases, however, the number of cells reduces, and the total heat transfer rate progressively reduces, even if the Rayleigh number, being based on the enclosure height, rapidly increases. Physical reasons for the above effect are inspected.

  18. A new turbine model for enhancing convective heat transfer in the presence of low volume concentration of Ag-Oil Nanofluids

    Science.gov (United States)

    Jafarimoghaddam, Amin; Aberoumand, Sadegh; Jafarimoghaddam, Reza

    2018-05-01

    This study aims to experimentally investigate and introduce a new model for enhancing convective heat transfer in the presence of Ag/ oil nanofluid. An annular tube was designed with a turbine element attached to the inner tube. The inner tube was a bearing shaft which could rotate with the rotation of turbine element. As the previous works by authors, the setup was conducted with a fully developed laminar flow regime with the Reynolds numbers less than 160. The outer surface of the annular tube was heated by an element with constant heat flux of 204 W. Ag/ oil nanofluid was used in different volume concentrations of 0.011%, 0.044% and 0.171%. The new model could enhance the convective heat transfer coefficient up to 54% (compared to the simple annular tube in the case of base fluid) for the best studied case (nanofluid with the volume concentration of 0.171%) while the friction factor remained low. The new model can be applied for related applications regarding Ag/ oil nanofluid as a new step in enhancing the convective heat transfer coefficient.

  19. 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.

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

    KAUST Repository

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

    2012-01-01

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

  1. Effect of nature convection on heat transfer in the liquid LiPb blanket for FDS-II

    Energy Technology Data Exchange (ETDEWEB)

    Wang Hongyan; Chen Hongli [Huaibei Coal Industry Teachers Coll. (China). Dept. of Physics; Zhou Tao [Chinese Academy of Sciences, Hefei (China). Inst. of Plasma Physics

    2007-07-01

    The He-cooled liquid LiPb tritium breeder (SLL) blanket concept is one of options of the blanket design of the fusion power reactor (FDS-II). The SLL blanket could be developed relatively easily with lower LiPb outlet temperature and slower LiPb flow velocity that allows the utilization of relatively mature material technology. The velocity of the liquid LiPb in the blanket is very slowly only in order to extract tritium. The magnetohydrodynamic (MHD) flow and heat transfer become very complex resulting from the differential heating of walls of the channels, especially adjacent to the First Wall (FW), and internal heat sources inside of the liquid LiPb. It is necessary to analyse the effect of the buoyancy-driven LiPb MHD flow on heat transfer in the channels with electrically and thermally conducting walls adjacent to the FW. The nature convection of the liquid LiPb, due to thermal diffusion, in the poloidal channel adjacent to the FW in the presence of the strong magnetic field of the SLL blanket has been considered and studied. The specially numerical MHD code based on the computational fluid dynamic software has been developed for analysis of the buoyancy-driven MHD flow. The properties of buoyantly convective flows have been investigated for various thermal boundary conditions. The numerical analysis was performed for the effect of nature convection on heat transfer of the liquid LiPb MHD flow in the poloidal channel in the SLL blanket. For the strong temperature gradient in the blanket and internal heat flux of Liquid LiPb, the three-dimensional temperature distributions of the LiPb, the FW and other walls have been given. Finally, The effect of the ratio of MHD buoyancy on the heat transfer characteristics of the LiPb flow have been calculated and presented. (orig.)

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

    International Nuclear Information System (INIS)

    Lee, Dong-Young; Chung, Bum-Jin

    2016-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-10-15

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

  4. Parametric numerical investigaion of natural convection in a heat-generating fluid with phase transitions

    Energy Technology Data Exchange (ETDEWEB)

    Aksenova, A.E.; Chudanov, V.V.; Strizhov, V.F.; Vabishchevich, P.N. [Institute of Nuclear Safety Russian Academy Science, Moscow (Russian Federation)

    1995-09-01

    Unsteady natural convection of a heat-generating fluid with phase transitions in the enclosures of a square section with isothermal rigid walls is investigated numerically for a wide range of dimensionless parameters. The quasisteady state solutions of conjugate heat and mass transfer problem are compared with available experimental results. Correlation relations for heat flux distributions at the domain boundaries depending on Rayleigh and Ostrogradskii numbers are obtained. It is shown that generally heat transfer is governed both by natural circulation and crust formation phenomena. Results of this paper may be used for analysis of experiments with prototypic core materials.

  5. Boiling Suppression in Convective Flow

    International Nuclear Information System (INIS)

    Aounallah, Y.

    2004-01-01

    The development of convective boiling heat transfer correlations and analytical models has almost exclusively been based on measurements of the total heat flux, and therefore on the overall two-phase heat transfer coefficient, when the well-known heat transfer correlations have often assumed additive mechanisms, one for each mode of heat transfer, convection and boiling. While the global performance of such correlations can readily be assessed, the predictive capability of the individual components of the correlation has usually remained elusive. This becomes important when, for example, developing mechanistic models for subcooled void formation based on the partitioning of the wall heat flux into a boiling and a convective component, or when extending a correlation beyond its original range of applications where the preponderance of the heat transfer mechanisms involved can be significantly different. A new examination of existing experimental heat transfer data obtained under fixed hydrodynamic conditions, whereby the local flow conditions are decoupled from the local heat flux, has allowed the unequivocal isolation of the boiling contribution over a broad range of thermodynamic qualities (0 to 0.8) for water at 7 MPa. Boiling suppression, as the quality increases, has consequently been quantified, thus providing valuable new insights on the functionality and contribution of boiling in convective flows. (author)

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2007-09-15

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

  7. Condensation heat transfer on natural convection at the high pressure

    International Nuclear Information System (INIS)

    Jong-Won, Kim; Hyoung-Kyoun, Ahn; Goon-Cherl, Park

    2007-01-01

    The Regional Energy Research Institute for the Next Generation is to develop a small scale electric power system driven by an environment-friendly and stable small nuclear reactor. REX-10 has been developed to assure high system safety in order to be placed in densely populated region and island. REX-10 adopts the steam-gas pressurizer to assure the inherent safety. The thermal-hydraulic phenomena in the steam-gas pressurizer are very complex. Especially, the condensation heat transfer with noncondensable gas on the natural convection is important to evaluate the pressurizer behavior. However, there have been few investigations on the condensation in the presence of noncondensable gas at the high pressure. In this study, the theoretical model is developed to estimate the condensation heat transfer at the high pressure using heat and mass transfer analogy. The analysis results show good agreement with correlations and experimental data. It is found that the condensation heat transfer coefficient increases as the total pressure increases or the mass fraction of the non-condensable gas decreases. In addition, the heat transfer coefficient no more increases over the specific pressure

  8. A computational fluid dynamics model for designing heat exchangers based on natural convection

    NARCIS (Netherlands)

    Dirkse, M.H.; Loon, van W.K.P.; Walle, van der T.; Speetjens, S.L.; Bot, G.P.A.

    2006-01-01

    A computational fluid dynamics model was created for the design of a natural convection shell-and-tube heat exchanger with baffles. The flow regime proved to be turbulent and this was modelled using the k¿¿ turbulence model. The features of the complex geometry were simplified considerably resulting

  9. Experimental investigation of natural convection induced by internal heat generation

    International Nuclear Information System (INIS)

    Tasaka, Y; Kudoh, Y; Takeda, Y; Yanagisawa, T

    2005-01-01

    Dilatation of a convection cell with respect to its Rayleigh number, one of the problems in internally heated convection, was quantitatively investigated by analyzing temperature field in a cell. The temperature field visualized by a thermo-chromic liquid crystal (TLC) expresses the cell dilatation. A calibration system was developed to convert the visualized photographs of the temperature field to the temperature field. A calibration curve correlating color information extracted from the photograph and temperature was determined from the approximately linear temperature distribution in the horizontal fluid layer using the hue method. Photos taken at various internal Rayleigh numbers were converted to the temperature field by the obtained curve. Extracting individual cells from a temperature field achieves a quantitative expression of the cell dilatation as the variation of the wavenumber of the cell with Rayleigh number increases. The temperature profile in a cell shows that high temperature areas appear at the apexes of the cell, largely different from the profile obtained by linear theory

  10. Evaluation of heat transfer in acupuncture needles: convection and conduction approaches.

    Science.gov (United States)

    Tzou, Chieh-Han John; Yang, Tzyy-Yih; Chung, Ya-Chien

    2015-04-01

    Originating in ancient China, acupuncture using needles has been developed for thousands of years and has received attention for its reported medical remedies, such as pain relief and chronic disease treatment. Heat transfer through the needles, which might have effects on the biomechanism of acupuncture, providing a stimulus and regulating homeostasis, has never been studied. This article analyzes the significance of heat transfer through needles via convection and conduction, approached by means of computational analysis. The needle is a cylindrical body, and an axis symmetrical steady-state heat-transfer model that viscosity and static pressure was not applied. This article evaluates heat transfer via acupuncture needles by using five metal materials: silver, copper, brass, iron, and stainless steel. A silver needle of the type extensively applied in acupuncture can dissipate more than seven times as much heat as a stainless steel needle of the same type. Heat transfer through such a needle is significant, compared to natural body-energy consumption over a range of ambient temperatures. The mechanism by which heat flows in or out of the body through the needles may be crucial in the remedial efficacy of acupuncture. Copyright © 2015. Published by Elsevier B.V.

  11. Oxy-fuel combustion of coal and biomass, the effect on radiative and convective heat transfer and burnout

    Energy Technology Data Exchange (ETDEWEB)

    Smart, John P.; Patel, Rajeshriben; Riley, Gerry S. [RWEnpower, Windmill Hill Business Park, Whitehill Way, Swindon, Wiltshire SN5 6PB, England (United Kingdom)

    2010-12-15

    This paper focuses on results of co-firing coal and biomass under oxy-fuel combustion conditions on the RWEn 0.5 MWt Combustion Test Facility (CTF). Results are presented of radiative and convective heat transfer and burnout measurements. Two coals were fired: a South African coal and a Russian Coal under air and oxy-fuel firing conditions. The two coals were also co-fired with Shea Meal at a co-firing mass fraction of 20%. Shea Meal was also co-fired at a mass fraction of 40% and sawdust at 20% with the Russian Coal. An IFRF Aerodynamically Air Staged Burner (AASB) was used. The thermal input was maintained at 0.5 MWt for all conditions studied. The test matrix comprised of varying the Recycle Ratio (RR) between 65% and 75% and furnace exit O{sub 2} was maintained at 3%. Carbon-in-ash samples for burnout determination were also taken. Results show that the highest peak radiative heat flux and highest flame luminosity corresponded to the lowest recycle ratio. The effect of co-firing of biomass resulted in lower radiative heat fluxes for corresponding recycle ratios. Furthermore, the highest levels of radiative heat flux corresponded to the lowest convective heat flux. Results are compared to air firing and the air equivalent radiative and convective heat fluxes are fuel type dependent. Reasons for these differences are discussed in the main text. Burnout improves with biomass co-firing under both air and oxy-fuel firing conditions and burnout is also seen to improve under oxy-fuel firing conditions compared to air. (author)

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

    Directory of Open Access Journals (Sweden)

    M BENKHEDDA

    2014-12-01

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

  13. Heat Transfer to Supercritical Water in Gaseous State or Affected by Mixed Convection in Vertical Tubes

    International Nuclear Information System (INIS)

    Pis'menny, E.N.; Razumovskiy, V.G.; Maevskiy, E.M.; Koloskov, A.E.; Pioro, I.L.

    2006-01-01

    The results on heat transfer to supercritical water heated above the pseudo-critical temperature or affected by mixed convection flowing upward and downward in vertical tubes of 6.28-mm and 9.50-mm inside diameter are presented. Supercritical water heat-transfer data were obtained at a pressure of 23.5 MPa, mass flux within the range from 250 to 2200 kg/(m 2 s), inlet temperature from 100 to 415 deg. C and heat flux up to 3.2 MW/m 2 . Temperature regimes of the tubes cooled with supercritical water in a gaseous state (i.e., supercritical water at temperatures beyond the pseudo-critical temperature) were stable and easily reproducible within a wide range of mass and heat fluxes. An analysis of the heat-transfer data for upward and downward flows enabled to determine a range of Gr/Re 2 values corresponding to the maximum effect of free convection on the heat transfer. It was shown that: 1) the heat transfer coefficient at the downward flow of water can be higher by about 50% compared to that of the upward flow; and 2) the deteriorated heat-transfer regime is affected with the flow direction, i.e., at the same operating conditions, the deteriorated heat transfer may be delayed at the downward flow compared to that at the upward flow. These heat-transfer data are applicable as the reference dataset for future comparison with bundle data. (authors)

  14. Onset of convection in a porous medium with sidewall heat transfer

    International Nuclear Information System (INIS)

    Kassoy, D.R.; Wang, M.; Weidman, P.D.

    1985-01-01

    A linear stability analysis is developed for convection in a vertically oriented finite slab of saturated porous material. The large vertical sidewall surfaces admit heat transfer while the small endwalls are insulated. A vertical temperature difference is imposed between the upper and lower horizontal surfaces. Results are obtained from an asymptotic evaluation of the exact stability criteria for a rectangular parallelpiped in the limit of small gap width element of → 0, where element of = narrow horizontal dimension/height. The critical Rayleigh number R/sub c/ = 0(element of/sup -2/) when the heat transfer boundary condition is applied directly to the sidewall. The convection mode consists of tightly packed three-dimensional cells with a wave number α = 0(element of/sup -1/2/). Only when the effective Biot number is sufficiently small, 0(element of/sup 2/), are the classical results approached; R/sub c/ → 4π/sup 2/, α/sub c/ = 0(1). If the slab is sandwiched between two impermeable conducting blocks with horizontal extent similar to the slab height, then the small scale modes disappear and R/sub c/ = 0(element of/sup -1/). However, sufficiently thin conducting blocks are compatible with R/sub c/ = 0(element of/sup -2/) and α = 0(element of/sup -1/2/

  15. Laminar mixed convection heat transfer in a vertical circular tube under buoyancy-assisted and opposed flows

    International Nuclear Information System (INIS)

    Mohammed, Hussein A.

    2008-01-01

    Laminar mixed convection heat transfer for assisted and opposed air flows in the entrance region of a vertical circular tube with the using of a uniform wall heat flux boundary condition has been experimentally investigated. The experimental setup was designed for determining the effect of flow direction and the effect of tube inclination on the surface temperature, local and average Nusselt numbers with Reynolds number ranged from 400 to 1600 and Grashof number from 2.0 x 10 5 to 6.2 x 10 6 . It was found that the circumferential surface temperature along the dimensionless tube length for opposed flow would be higher than that both of assisted flow and horizontal tube [Mohammed HA, Salman YK. Experimental investigation of combined convection heat transfer for thermally developing flow in a horizontal circular cylinder. Appl Therm Eng 2007;27(8-9):1522-33] due to the stronger free convective currents within the cross-section. The Nusselt number values would be lower for opposed flow than that for assisted flow. It was inferred that the behaviour of Nu x for opposed flow to be strongly dependent on the combination of Re and Gr numbers. Empirical equations expressing the average Nusselt numbers in terms of Grashof and Reynolds numbers were proposed for both assisted and opposed flow cases. The average heat transfer results were compared with previous literature and showed similar trend and satisfactory agreement

  16. Natural convection in a water tank with a heated horizontal plate facing downward

    International Nuclear Information System (INIS)

    Yang, Sun Kyoo; Jung, Moon Kee; Helmut Hoffmann

    1995-01-01

    Experimental and computational studies were carried out to investigate the natural convection of the single phase flow in a tank with a heated horizontal plate facing downward. This is a simplified model for investigations of the influence of a core melt at the bottom of a reactor vessel on the thermal hydraulic behavior in a water filled cavity surrounding the vessel. In this case the vessel is simulated by a hexahedron insulated box with a heated plate horizontally mounted at the bottom of the box. The box with the heated plate is installed in a water filled hexahedron tank. Coolers are immersed in the U-type water volume between the box and the tank. Although the multicomponent flows exist more probably below the heated plate in reality, present study concentrates on the single phase flow in a first step prior to investigating the complicated multicomponent thermal hydraulic phenomena. In the present study, in order to get a better understanding for the natural convection characteristics below the heated plate, the velocity and temperature are measured by LDA(Laser Doppler Anemometry) and thermocouples, respectively. And flow fields are visualized by taking pictures of the flow region with suspended particles. The results show the occurrence of a very effective circulation of the fluid in the whole flow area as the heater and coolers are put into operation. In the remote region below the heated plate the flow is nearly stagnant, and a remarkable temperature stratification can be observed with very thin thermal boundary. Analytical predictions using the FLUTAN code show a reasonable matching of the measured velocity fields. 18 figs., 2 tabs., 18 refs. (Author)

  17. Mixed convection boundary-layer flow from a horizontal circular cylinder with a constant surface heat flux

    Energy Technology Data Exchange (ETDEWEB)

    Nazar, R.; Amin, N. [Department of Mathematics, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor (Malaysia); Pop, I. [Faculty of Mathematics, University of Cluj, R-3400 Cluj, CP 253 (Romania)

    2004-02-01

    The laminar mixed convection boundary-layer flow of a viscous and incompressible fluid past a horizontal circular cylinder, which is maintained at a constant heat flux and is placed in a stream flowing vertically upward has been theoretically studied in this paper. The solutions for the flow and heat transfer characteristics are evaluated numerically for different values of the mixed convection parameter {lambda} with the Prandtl number Pr = 1 and 7, respectively. It is found, as for the case of a heated or cooled cylinder, considered by Merkin [5], that assisting flow delays separation of the boundary-layer and can, if the assisting flow is strong enough, suppress it completely. The opposing flow, on the other side, brings the separation point nearer to the lower stagnation point and for sufficiently strong opposing flows there will not be a boundary-layer on the cylinder. (orig.)

  18. The status of thermal-hydraulic studies on the decay heat removal by natural convection using RAMONA and NEPTUN models

    International Nuclear Information System (INIS)

    Hoffmann, H.; Hain, K.; Marten, K.; Rust, K.; Weinberg, D.; Ohira, H.

    2004-01-01

    Thermal-hydraulic experiments were performed with water in order to simulate the decay heat removal by natural convection in a pool-type sodium-cooled reactor. Two test rigs of different scales were used, namely RAMONA (1:20) and NEPTUN (1:5). RAMONA served to study the transition from nominal operation by forced convection to decay heat removal operation by natural convection. Steady-state similarity tests were carried out in both facilities. The investigations cover nominal and non-nominal operation conditions. These data provide a broad basis for the verification of computer programs. Numerical analyses performed with the three-dimensional FLUTAN code indicated that the thermal-hydraulic processes can be quantitatively simulated even for the very complex geometry of the NEPTUN test rig. (author)

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

    International Nuclear Information System (INIS)

    Abdel-Ghany, Ahmed M.; Kozai, Toyoki

    2006-01-01

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

  20. Two-dimensional numerical modeling and solution of convection heat transfer in turbulent He II

    Science.gov (United States)

    Zhang, Burt X.; Karr, Gerald R.

    1991-01-01

    Numerical schemes are employed to investigate heat transfer in the turbulent flow of He II. FEM is used to solve a set of equations governing the heat transfer and hydrodynamics of He II in the turbulent regime. Numerical results are compared with available experimental data and interpreted in terms of conventional heat transfer parameters such as the Prandtl number, the Peclet number, and the Nusselt number. Within the prescribed Reynolds number domain, the Gorter-Mellink thermal counterflow mechanism becomes less significant, and He II acts like an ordinary fluid. The convection heat transfer characteristics of He II in the highly turbulent regime can be successfully described by using the conventional turbulence and heat transfer theories.

  1. Transient convective heat transfer to laminar flow from a flat plate with constant heat capacity

    International Nuclear Information System (INIS)

    Hanawa, Juichi

    1980-01-01

    Most basic transient heat transfer problem is the transient response characteristics of forced convection heat transfer in the flow along a flat plate or in a tube. In case of the laminar flow along a flat plate, the profile method using steady temperature distribution has been mostly adopted, but its propriety has not been clarified yet. About the unsteady heat transfer in the laminar flow along a flat plate, the analysis or experiment evaluating the heat capacity of the flat plate exactly was never carried out. The purpose of this study is to determine by numerical calculation the unsteady characteristics of the boundary layer in laminar flow and to confirm them by experiment concerning the unsteady heat transfer when a flat plate with a certain heat capacity is placed in parallel in uniform flow and given a certain quantity of heat generation suddenly. The basic equation and the solution are given, and the method of numerical calculation and the result are explained. The experimental setup and method, and the experimental results are shown. Both results were in good agreement, and the response of wall temperature, the response of Nusselt number and the change of temperature distribution in course of time were able to be determined by applying Laplace transformation and numerical Laplace inverse transformation to the equation. (Kako, I.)

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

    International Nuclear Information System (INIS)

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

    2001-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2004-12-01

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

  4. Simultaneous heat and mass transfer on oscillatory free convection boundary layer flow

    International Nuclear Information System (INIS)

    Hossain, M.A.

    1985-11-01

    The problem of simultaneous heat and mass transfer in two-dimensional free convection from a semi-infinite vertical flat plate is investigated. An integral method is used to find a solution for zero wall velocity and for a mass transfer velocity at the wall with small-amplitude oscillatory wall temperature. Low and high-frequency solutions are developed separately and are discussed graphically with the effects of the parameters Gr (the Grashof number for heat transfer), Gc (the Grashof number for mass transfer) and Sc (the Schmidt number) for Pr=0.71 representing aid at 20 deg. C. (author)

  5. Experimental and analytical investigations of granular materials: Shear flow and convective heat transfer

    Science.gov (United States)

    Ahn, Hojin

    1989-12-01

    Granular materials flowing down an inclined chute were studied experimentally and analytically. Characteristics of convective heat transfer to granular flows were also investigated experimentally and numerically. Experiments on continuous, steady flows of granular materials in an inclined chute were conducted with the objectives of understanding the characteristics of chute flows and of acquiring information on the rheological behavior of granular material flow. Existing constitutive equations and governing equations were used to solve for fully developed chute flows of granular materials, and thus the boundary value problem was formulated with two parameters (the coefficient of restitution between particles, and the chute inclination) and three boundary values at the chute base wall (the values of solid fraction, granular temperature, and mean velocity at the wall). The boundary value problem was numerically solved by the shooting method. These analytical results were also compared with the present experimental values and with the computer simulations by other investigators in their literature. Experiments on heat transfer to granular flows over a flat heating plate were conducted with three sizes of glass beads, polystyrene beads, and mustard seeds. A modification on the existing model for the convective heat transfer was made using the effective Nusselt number and the effective Peclet number, which include the effects of solid fraction variations. The slightly modified model could describe the heat transfer characteristics of both fast and slow flows (supercritical and subcritical). A numerical analysis of the transfer to granular flows was also performed. The results were compared with the present experimental data, and reasonable agreement was found in the comparison.

  6. Natural convection heat transfer on two horizontal cylinders in liquid sodium

    Energy Technology Data Exchange (ETDEWEB)

    Hata, K.; Shiotsu, M.; Takeuchi, Y. [Institute of Atomic Energy, Kyoto Univ. (Japan)] [and others

    1995-09-01

    Natural convection heat transfer on two horizontal 7.6 mm diameter test cylinders assembled with the ratio of the distance between each cylinder axis to the cylinder diameter, S/D, of 2 in liquid sodium was studied experimentally and theoretically. The heat transfer coefficients on the cylinder surface due to the same heat inputs ranging from 1.0 X 10{sup 7} to 1.0 x 10{sup 9} W/m{sup 3} were obtained experimentally for various setting angeles, {gamma}, between vertical direction and the plane including both of these cylinder axis over the range of zero to 90{degrees}. Theoretical equations for laminar natural convection heat transfer from the two horizontal cylinders were numerically solved for the same conditions as the experimental ones considering the temperature dependence of thermophysical properties concerned. The average Nusselt numbers, Nu, values on the Nu versus modified Rayleigh number, R{sub f}, graph. The experimental values of Nu for the upper cylinder are about 20% lower than those for the lower cylinder at {gamma} = 0{degrees} for the range of R{sub f} tested here. The value of Nu for the upper cylinder becomes higher and approaches that for the lower cylinder with the increase in {gamma} over range of 0 to 90{degrees}. The values of Nu for the lower cylinder at each {gamma} are almost in agreement with those for a single cylinder. The theoretical values of Nu on two cylinders except those for R{sub f}<4 at {gamma} = 0{degrees} are in agreement with the experimental data at each {gamma} with the deviations less than 15%. Correlations for Nu on the upper and lower cylinders were obtained as functions of S/D and {gamma} based n the theoretical solutions for the S/D ranged over 1.5 to 4.0.

  7. Topology Optimisation for Coupled Convection Problems

    DEFF Research Database (Denmark)

    Alexandersen, Joe

    This thesis deals with topology optimisation for coupled convection problems. The aim is to extend and apply topology optimisation to steady-state conjugate heat transfer problems, where the heat conduction equation governs the heat transfer in a solid and is coupled to thermal transport...... in a surrounding uid, governed by a convection-diffusion equation, where the convective velocity field is found from solving the isothermal incompressible steady-state Navier-Stokes equations. Topology optimisation is also applied to steady-state natural convection problems. The modelling is done using stabilised...... finite elements, the formulation and implementation of which was done partly during a special course as prepatory work for this thesis. The formulation is extended with a Brinkman friction term in order to facilitate the topology optimisation of fluid flow and convective cooling problems. The derived...

  8. Multi-boiling Heat Transfer Analysis of a Convective Straight Fin with Temperature-Dependent Thermal Properties and Internal Heat Generation

    Directory of Open Access Journals (Sweden)

    Gbeminiyi Sobamowo

    2017-10-01

    Full Text Available In this study, by using the finite volume method, the heat transfer in a convective straight fin with temperature-dependent thermal properties and an internal heat generation under multi-boiling heat transfer modes are analyzed. In this regard, the local heat transfer coefficient is considered to vary within a power-law function of temperature. In the present study, the coexistence of all the boiling modes is taken into consideration. The developed heat transfer models and the corresponding numerical solutions are used to investigate the effects of various thermo-geometric parameters on the thermal performance of the longitudinal rectangular fin. The results shows that the fin temperature distribution, the total heat transfer, and the fin efficiency are significantly affected by the thermo-geometric parameters of the fin and the internal heat generation within the fin. The obtained results can provide a platform for improvements in the design of the fin in the heat transfer equipment.

  9. Mixed Convection Heat Transfer on the Outside of a Vertical Cylinder

    Energy Technology Data Exchange (ETDEWEB)

    Bhattacharyya, A

    1965-10-15

    An experimental study was made of turbulent heat transfer from a vertical cylinder placed in a square channel. The flow medium was water flowing upwards. Basic differential equations governing the mixed flow heat transfer phenomena in a vertical annulus are presented. A dimensional analysis is done to find the dimensionless variables affecting the relative magnitude of the effect of buoyancy on forced convection heat transfer. Dimensionless equations correlating the experimental data ana incorporating a buoyancy parameter of the form Gr/Re{sup 2} are presented. Reynolds number range covered is 690 to 129,500 and the Rayleigh num- ber range covered is 10{sup 9} to 4.2 x 10{sup 13} . Effect of different length parameters, like hydraulic diameter and distance of the measuring point from the inlet of the test section, on dimensionless equations are studied.

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

    International Nuclear Information System (INIS)

    Ricque, Roger; Siboul, Roger

    1969-01-01

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

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

    NARCIS (Netherlands)

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

    2013-01-01

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

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

    Science.gov (United States)

    Griffiths, Ross W; Gayen, Bishakhdatta

    2015-11-13

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

  13. Convective Heat Transfer at the Martian Boundary Layer, Measurement and Model

    Science.gov (United States)

    Tomás Soria-Salinas, Álvaro; Zorzano-Mier, María Paz; Martín-Torres, Javier

    2016-04-01

    We present a measuring concept to measure the convective heat transfer coefficient h near a spacecraft operating on the surface of Mars. This coefficient can be used to derive the speed of the wind and direction, and to detect its modulations. This measuring concept will be used in the instrument HABIT (HabitAbility: Brines, Irradiance and Temperature) for the Surface Platform of ExoMars 2018 (ESA-Roscosmos). The method is based on the use of 3 Resistance Temperature Thermodetectors (RTD) that measure the temperature at 3 locations along the axial direction of a rod of length L: at the base of the rod, Tb, an intermediate point x = L/n, TLn, and the tip,Ta. This sensing fin is called the Air Temperature Sensor (ATS). HABIT shall incorporate three ATS, oriented in perpendicular directions and thus exposed to wind in a different way. Solving these equations for each ATS, provides three fluid temperatures Tf as well as three m parameters that are used to derive three heat transfer coefficients h. This magnitude is dependent on the local forced convection and therefore is sensitive to the direction, speed and modulations of the wind. The m-parameter has already proven to be useful to investigate the convective activity at the planetary boundary layer on Mars and to determine the height of the planetary boundary layer. This method shall be presented here by: 1) Introducing the mathematical concepts for the retrieval of the m-parameter; 2) performing ANSYS simulations of the fluid dynamics and the thermal environment around the ATS-rods under wind conditions in Mars; and 3) comparing the method by using data measurements from the Rover Environmental Monitoring Station (REMS) at the Curiosity rover of NASA's Mars Science Laboratory project currently operating on Mars. The results shall be compared with the wind sensor measurements of three years of REMS operation on Mars.

  14. Magnetohydrodynamics Carreau nanofluid flow over an inclined convective heated stretching cylinder with Joule heating

    Directory of Open Access Journals (Sweden)

    Imad Khan

    Full Text Available Current work highlights the computational aspects of MHD Carreau nanofluid flow over an inclined stretching cylinder with convective boundary conditions and Joule heating. The mathematical modeling of physical problem yields nonlinear set of partial differential equations. A suitable scaling group of variables is employed on modeled equations to convert them into non-dimensional form. The integration scheme Runge-Kutta-Fehlberg on the behalf of shooting technique is utilized to solve attained set of equations. The interesting aspects of physical problem (linear momentum, energy and nanoparticles concentration are elaborated under the different parametric conditions through graphical and tabular manners. Additionally, the quantities (local skin friction coefficient, local Nusselt number and local Sherwood number which are responsible to dig out the physical phenomena in the vicinity of stretched surface are computed and delineated by varying controlling flow parameters. Keywords: MHD, Carreau nanofluid, Inclined stretching cylinder, Joule heating, Shooting technique

  15. Natural convection in asymmetric triangular enclosures heated from below

    International Nuclear Information System (INIS)

    Kamiyo, O M; Angeli, D; Enzo Ferrari, Universita di Modena e Reggio Emilia, via Vignolese 905, I-41125 Modena (Italy))" data-affiliation=" (DIEF – Dipartimento di Ingegneria Enzo Ferrari, Universita di Modena e Reggio Emilia, via Vignolese 905, I-41125 Modena (Italy))" >Barozzi, G S; Collins, M W

    2014-01-01

    Triangular enclosures are typical configurations of attic spaces found in residential as well as industrial pitched-roof buildings. Natural convection in triangular rooftops has received considerable attention over the years, mainly on right-angled and isosceles enclosures. In this paper, a finite volume CFD package is employed to study the laminar air flow and temperature distribution in asymmetric rooftop-shaped triangular enclosures when heated isothermally from the base wall, for aspect ratios (AR) 0.2 ≤ AR ≤ 1.0, and Rayleigh number (Ra) values 8 × 10 5 ≤ Ra ≤ 5 × 10 7 . The effects of Rayleigh number and pitch angle on the flow structure and temperature distributions within the enclosure are analysed. Results indicate that, at low pitch angle, the heat transfer between the cold inclined and the hot base walls is very high, resulting in a multi-cellular flow structure. As the pitch angle increases, however, the number of cells reduces, and the total heat transfer rate progressively reduces, even if the Rayleigh number, being based on the enclosure height, rapidly increases. Physical reasons for the above effect are inspected

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

    Directory of Open Access Journals (Sweden)

    Yu Ji

    2017-03-01

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

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

    Science.gov (United States)

    Kozlova, Sofya V; Ryzhkov, Ilya I

    2014-09-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2013-08-15

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

  19. Nanofluid heat transfer under mixed convection flow in a tube for solar thermal energy applications.

    Science.gov (United States)

    Sekhar, Y Raja; Sharma, K V; Kamal, Subhash

    2016-05-01

    The solar flat plate collector operating under different convective modes has low efficiency for energy conversion. The energy absorbed by the working fluid in the collector system and its heat transfer characteristics vary with solar insolation and mass flow rate. The performance of the system is improved by reducing the losses from the collector. Various passive methods have been devised to aid energy absorption by the working fluid. Also, working fluids are modified using nanoparticles to improve the thermal properties of the fluid. In the present work, simulation and experimental studies are undertaken for pipe flow at constant heat flux boundary condition in the mixed convection mode. The working fluid at low Reynolds number in the mixed laminar flow range is undertaken with water in thermosyphon mode for different inclination angles of the tube. Local and average coefficients are determined experimentally and compared with theoretical values for water-based Al2O3 nanofluids. The results show an enhancement in heat transfer in the experimental range with Rayleigh number at higher inclinations of the collector tube for water and nanofluids.

  20. Turbulent flow in spiral tubes and effect of Prandtl number on a convective heat transfer

    International Nuclear Information System (INIS)

    Shistel', R.; Goss, Zh.

    1976-01-01

    Turbulent flow is analized of the fluid in the spiral tube with a pitch which is small enough as compared to the curvature radius. The effect of the curvature and the Prandtl number on the turbulent convection is studied. A description of three-dimensional model and its application for the spiral tubes is given. The example of heat convection in curved channels reveals the opportunity for employment of three-dimensional model to calculate the recirculating flows in complex-geometry channels, description of the turbulence field, and determination of the wall friction and heat transfer. The introduction of the wall functions into the numerical method affects adversely accuracy of calculations but ensures a considerable time saving and makes it possible to study the process in the first approximation. The example illustrates possible practical application of the calculation procedure

  1. Direct numerical simulation and modeling of turbulent natural convection in a vertical differentially heated slot

    International Nuclear Information System (INIS)

    Boudjemadi, R.

    1996-03-01

    The main objectives of this thesis are the direct numerical simulation of natural convection in a vertical differentially heated slot and the improvements of second-order turbulence modelling. A three-dimensional direct numerical simulation code has been developed in order to gain a better understanding of turbulence properties in natural convection flows. This code has been validated in several physical configurations: non-stratified natural convection flows (conduction solution), stratified natural convection flows (double boundary layer solution), transitional and turbulent Poiseuille flows. For the conduction solution, the turbulent regime was reached at a Rayleigh number of 1*10 5 and 5.4*10 5 . A detailed analysis of these results has revealed the principal qualities of the available models but has also pointed our their shortcomings. This data base has been used in order to improve the triple correlations transport models and to select the turbulent time scales suitable for such flows. (author). 122 refs., figs., tabs., 4 appends

  2. Experimental determination of new statistical correlations for the calculation of the heat transfer coefficient by convection for flat plates, cylinders and tube banks

    Directory of Open Access Journals (Sweden)

    Ismael Fernando Meza Castro

    2017-07-01

    Full Text Available Introduction: This project carried out an experimental research with the design, assembly, and commissioning of a convection heat transfer test bench. Objective: To determine new statistical correlations that allow knowing the heat transfer coefficients by air convection with greater accuracy in applications with different heating geometry configurations. Methodology: Three geometric configurations, such as flat plate, cylinders and tube banks were studied according to their physical properties through Reynolds and Prandtl numbers, using a data transmission interface using Arduino® controllers Measured the air temperature through the duct to obtain real-time data and to relate the heat transferred from the heating element to the fluid and to perform mathematical modeling in specialized statistical software. The study was made for the three geometries mentioned, one power per heating element and two air velocities with 10 repetitions. Results: Three mathematical correlations were obtained with regression coefficients greater than 0.972, one for each heating element, obtaining prediction errors in the heat transfer convective coefficients of 7.50% for the flat plate, 2.85% for the plate Cylindrical and 1.57% for the tube bank. Conclusions: It was observed that in geometries constituted by several individual elements, a much more accurate statistical adjustment was obtained to predict the behavior of the convection heat coefficients, since each unit reaches a stability in the surface temperature profile with Greater speed, giving the geometry in general, a more precise measurement of the parameters that govern the transfer of heat, as it is in the case of the geometry of the tube bank.

  3. Natural convection and boiling heat transfer of a liquid metal in a magnetic field

    International Nuclear Information System (INIS)

    Seki, Masahiro; Kawamura, Hiroshi

    1983-02-01

    A liquid metal is often assumed as a coolant and a breeding material of a Tokamak fusion reactor. However, many problems on the thermo-hydraulics of a liquid metal in a magnetic field are still remained to be studied. In the present report, natural convection and boiling of a liquid metal in a strong magnetic field are studied to examine a fundamental feasibility of a fusion reactor cooled by a liquid metal. In the experimental study of the natural convection, the circulation of a liquid metal was found to be surpressed even by a magnetic field parallel to the gravity. A numerical study has confirmed the conclusion drawn by the experiment. In the study of boiling heat transfer, stable boiling of a liquid metal has been found also in a strong magnetic field. The burnout heat flux hardly affected by the magnetic field. These indicate a fundamental feasibility of the liquid-metal cooling for a Tokamak fusion reactor. (author)

  4. The effect of heat generation on mixed convection flow in nano fluids over a horizontal circular cylinder

    Science.gov (United States)

    Juliyanto, Bagus; Widodo, Basuki; Imron, Chairul

    2018-04-01

    The purpose of this research is to study the effect of heat generation on mixed convection flow on Nano fluids over a horizontal circular cylinder of a heated in two dimension form. A stream of fluids are steady and incompressible, a stream flowing vertically upwards for circular cylinder and the boundary layer at the stagnation point. Three different types of nanoparticles considered are Cu, Al2O3, and TiO2. Mixed convection flow in Nano fluids on the surface of a circular cylinder will cause the boundary layer. The governing boundary layer equations are transformed into a non-dimensional form, and then the non-dimensional forms are transformed into a similar boundary equations by using stream function. Furthermore, an implicit finite-difference scheme known as the Keller-box method is applied to solve numerically the resulting similar boundary layer equations. The result of the research by varying the non-dimensional parameters are mixed convection, Prandtl number, nanoparticle volume fraction, heat generation, and radius of a cylinder are as follows. First, the velocity profile increase and temperature profile decrease when mixed convection parameter increase. Second, the velocity and temperature profiles decrease when Prandtl number parameter increase. Third, the velocity profile with the variation of nanoparticle volume fraction (χ) is increased when the value of χ is 0,1 ≤ χ ≤ 0,15 and the velocity profile decreases when the value of χ is 0,19 ≤ χ ≤ 0,5 while the temperature profile is increasing when the value of χ is 0,1 ≤ χ ≤ 0,5. Fourth, the velocity and temperature profiles increase when heat generation and the radius of the cylinder increase. The last, Cu, Al 2 O 3, and TiO 2 nanoparticles produce the same velocity and temperature profiles, but the three types of nanoparticles are different at the velocity and temperature values.

  5. Effect of Darcy, fluid Rayleigh and heat generation parameters on natural convection in a porous square enclosure: A Brinkman-extended Darcy model

    International Nuclear Information System (INIS)

    Das, S.; Sahoo, R.K.

    1999-01-01

    Analysis of flow and convective heat transfer in volumetrically heated porous layer has become a separate topic for research in the last twenty five years in view of its importance in various engineering applications, such as heat removal from nuclear fuel debris, heat transfer associated with storage of nuclear waste, exothermic reaction in packed-bed reactors, heat recovery from geothermal systems and particularly in the field of large storage systems of agricultural products. Here, a pressure-velocity solution for natural convection for fluid saturated heat generating porous medium in a square enclosure is analyzed by finite element method. The numerical solutions obtained for wide range of fluid Rayleigh number, Ra f , Darcy number, Da, and heat generating number, Q d . The justification for taking these non-dimensional parameters independently is to establish the effect of individual parameters on flow patterns. It has been observed that peak temperature occurs at the top central part and weaker velocity prevails near the vertical walls of the enclosure due to the heat generation parameter alone. On comparison, the modified Rayleigh number used by the earlier investigators, can not explain explicitly the effect of heat generation parameter on natural convection within an enclosure having differentially heated vertical walls. At higher Darcy number, the peak temperature and peak velocity are comparatively more, resulting in better enhancement of heat transfer rate

  6. Numerical simulation of convection and heat transfer in Czochralski crystal growth by multiple-relaxation-time LBM

    Science.gov (United States)

    Liu, Ding; Huang, Weichao; Zhang, Ni

    2017-07-01

    A two-dimensional axisymmetric swirling model based on the lattice Boltzmann method (LBM) in a pseudo Cartesian coordinate system is posited to simulate Czochralski (Cz) crystal growth in this paper. Specifically, the multiple-relaxation-time LBM (MRT-LBM) combined with the finite difference method (FDM) is used to analyze the melt convection and heat transfer in the process of Cz crystal growth. An incompressible axisymmetric swirling MRT-LB D2Q9 model is applied to solve for the axial and radial velocities by inserting thermal buoyancy and rotational inertial force into the two-dimensional lattice Boltzmann equation. In addition, the melt temperature and the azimuthal velocity are solved by MRT-LB D2Q5 models, and the crystal temperature is solved by FDM. The comparison results of stream functions values of different methods demonstrate that our hybrid model can be used to simulate the fluid-thermal coupling in the axisymmetric swirling model correctly and effectively. Furthermore, numerical simulations of melt convection and heat transfer are conducted under the conditions of high Grashof (Gr) numbers, within the range of 105 ˜ 107, and different high Reynolds (Re) numbers. The experimental results show our hybrid model can obtain the exact solution of complex crystal-growth models and analyze the fluid-thermal coupling effectively under the combined action of natural convection and forced convection.

  7. Hall current and Joule heating effects on peristaltic flow of viscous fluid in a rotating channel with convective boundary conditions

    Directory of Open Access Journals (Sweden)

    Tasawar Hayat

    Full Text Available The present article has been arranged to study the Hall current and Joule heating effects on peristaltic flow of viscous fluid in a channel with flexible walls. Both fluid and channel are in a state of solid body rotation. Convective conditions for heat transfer in the formulation are adopted. Viscous dissipation in energy expression is taken into account. Resulting differential systems after invoking small Reynolds number and long wavelength considerations are numerically solved. Runge-Kutta scheme of order four is implemented for the results of axial and secondary velocities, temperature and heat transfer coefficient. Comparison with previous limiting studies is shown. Outcome of new parameters of interest is analyzed. Keywords: Rotating frame, Hall current, Joule heating, Convective conditions, Wall properties

  8. CFD modelling of convective heat transfer from a window with adjacent venetian blinds

    Energy Technology Data Exchange (ETDEWEB)

    Marjanovic, L. [Belgrade Univ., Belgrade (Yugoslavia). Faculty of Mechanical Engineering]|[DeMontfort Univ. (United Kingdom). Inst. of Energy and Sustainable Development; Cook, M; Hanby, V.; Rees, S. [DeMontfort Univ. (United Kingdom). Inst. of Energy and Sustainable Development

    2005-07-01

    There is a limited amount of 3-dimensional modeling information on the performance of glazing systems with blinds. Two-dimensional flow modeling has indicated that 1-dimensional heat transfer can lead to invalid results where 2- and 3-dimensional effects are present. In this study, a 3-dimensional numerical solution was obtained on the effect of a venetian blind on the conjugate heat transfer from an indoor window glazing system. The solution was obtained for the coupled laminar free convection and radiation heat transfer problem, including conduction along the blind slats. Continuity, momentum and energy equations for buoyant flow were solved using Computational Fluid Dynamics (CFD) software. Grey diffuse radiation exchange between the window, blind and air were considered using the Monte Carlo method. All thermophysical properties of air were assumed to be constant with the exception of density, which was modeled using the Bousinesq approximation. Both winter and summer conditions were considered. In the computational domain, the window represented an isothermal type boundary condition with no slip. The height of the domain was extended beyond the blinds to allow for inflow and outflow regions. Fluid was allowed to entrain into the domain at an ambient temperature in a direction perpendicular to the window. The results indicated that heat transfer between window and indoor air is influenced both quantitatively and qualitatively by the presence of an aluminium venetian blind, and that the cellular flow between the blind slats can have a significant effect on the convective heat transfer from the window surface that is more fully recognized and analyzed in 3 dimensions. refs., 2 tabs., 13 figs.

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

    International Nuclear Information System (INIS)

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

    1978-01-01

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

  10. Free convective heat loss from cavity-type solar furnace; Solar receiver kara no shizen tairyu ni yoru netsusonshitsu

    Energy Technology Data Exchange (ETDEWEB)

    Fujii, I; Ito, N [Meiji University, Tokyo (Japan)

    1996-10-27

    Free convective heat loss from solar heat receivers was studied, using three laboratory model receivers (different in depth L and aperture diameter d) heated by electric heaters. Most of the heat produced by heaters was transmitted to the air inside. The cylindrical vessel walls were fully insulated against heat. Heat loss being supposed to result mainly from transfer by free convection, the experiment results were edited by use of Nusselt number Nu and Rayley number Ra. Relations between Nu(D/d){sup m1} and Ra(L/D){sup m2} were plotted in a chart. Here, D is the receiver inner diameter, and m1 and m2 are constants that can be determined by computation. Tests points were provided approximately lineally, irrespective of D, L, or receiver inclination. Air currents were found to produce one or more swirls inside, thanks to the current visualization technique, when the receiver inclination was not sharper than 120{degree} (except 0{degree}). The number of swirls increased as the inner wall temperature rose. This kind of behavior of air currents directly affects the degree of heat loss. 9 refs., 4 figs.

  11. Convective losses through an air-filled gap

    Energy Technology Data Exchange (ETDEWEB)

    Baum, V A; Ovezsakhatov, N

    1976-01-01

    Simplified formulas for the heat fluxes with given parameters of the air are used to calculate the specific heat losses by convection in a number of solar-energy systems (water heater, thermal generator, double-glazed window, and still). Heat losses by convection and radiation are compared.

  12. Effects of Thermal Radiation and Chemical Reaction on MHD Free Convection Flow past a Flat Plate with Heat Source and Convective Surface Boundary Condition

    OpenAIRE

    E.Hemalatha; N. Bhaskar Reddy

    2015-01-01

    This paper analyzes the radiation and chemical reaction effects on MHD steady two-dimensional laminar viscous incompressible radiating boundary layer flow over a flat plate in the presence of internal heat generation and convective boundary condition. It is assumed that lower surface of the plate is in contact with a hot fluid while a stream of cold fluid flows steadily over the upper surface with a heat source that decays exponentially. The Rosseland approximation is used to desc...

  13. Heat transfer enhancement in a convective field by applying ionic wind

    International Nuclear Information System (INIS)

    Tada, Y.; Takimoto, A.; Hayashi, Y.

    1991-01-01

    This paper reports that this study has been conducted to pursue the heat transfer enhancement in a convective field by applying electric field. Firstly, aimed at thinning boundary layer, swirl motions were caused by utilizing the ionic wind in a channel flow with parallel wire-electrode arrangement. Secondly, ionic wind was induced at right angle to the primary flow at regular intervals by using cross wire-electrode arrangement. Thirdly, to utilize the dynamical effect of adding particles under the Coulomb force, electric field was applied to gas-solid suspensions flow field. On the basis of these results, fundamental characteristics of the combined flow structure and the heat transfer in the EHD field were clarified, and the possibility of the practical application will be insighted

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

    International Nuclear Information System (INIS)

    Bergles, A.E.

    1979-01-01

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

  15. Radiation and heat generation effects in magnetohydrodynamic mixed convection flow of nanofluids

    Directory of Open Access Journals (Sweden)

    Gul Aaiza

    2018-01-01

    Full Text Available Radiation and heat generation effects in unsteady magnetohydrodynamic mixed convection flow of nanofluids along a vertical channel are investigated. Silver nanoparticles of spherical shapes and of different sizes in water as a convection-al base fluid are incorporated. The purpose of this study is to measure the effect of different sizes of nanoparticles on velocity and temperature. Keeping in mind the size, particle material, shape, clustering and Brownian motion of nanoparticles, Koo and Kleinstreuer model is used. The problem is modeled in terms of partial differential equations with physical boundary conditions. Analytical solutions are obtained for velocity and temperature, plotted and discussed. It is concluded that increasing the size of Ag nanoparticles (up to specific size, 30 nm, results in a very small velocity increment while for large particle size (30-100 nm, no change in velocity is observed. As the small size of nanoparticles has the highest thermal conductivity and viscosity. This change in velocity with size of nano-particles is found only in water-based nanofluids with low volume fraction 0.01 while at low volume concentration, no change is observed.

  16. Al/ oil nanofluids inside annular tube: an experimental study on convective heat transfer and pressure drop

    Science.gov (United States)

    Jafarimoghaddam, Amin; Aberoumand, Sadegh; Javaherdeh, Kourosh; Arani, Ali Akbar Abbasian; Jafarimoghaddam, Reza

    2018-04-01

    In this work, an experimental study on nanofluid preparation stability, thermo-physical properties, heat transfer performance and friction factor of Al/ Oil nanofluids has been carried out. Electrical Explosion Wire ( E.E.W) which is one of the most reliable one-step techniques for nanofluids preparation has been used. An annular tube has been considered as the test section in which the outer tube was subject to a uniform heat flux boundary condition of about 204 W. The utilized nanofluids were prepared in three different volume concentrations of 0.011%, 0.044% and 0.171%. A wide range of parameters such as Reynolds number Prandtl number, viscosity, thermal conductivity, density, specific heat, convective heat transfer coefficient, Nusselt number and the friction factor have been studied. The experiment was conducted in relatively low Reynolds numbers of less than 160 and within a hydrodynamically fully-developed regime. According to the results, thermal conductivity, density and viscosity increased depending on the volume concentrations and working temperatures while the specific heat declined. More importantly, it was observed that convective heat transfer coefficient and Nusselt number enhanced by 28.6% and 16.4%, respectively, for the highest volume concentration. Finally, the friction factor (which plays an important role in the pumping power) was found to be increased around 18% in the volume fraction of 0.171%.

  17. Convective heat transfer enhancement by diamond shaped micro-protruded patterns for heat sinks: Thermal fluid dynamic investigation and novel optimization methodology

    International Nuclear Information System (INIS)

    Ventola, Luigi; Dialameh, Masoud; Fasano, Matteo; Chiavazzo, Eliodoro; Asinari, Pietro

    2016-01-01

    Highlights: • A novel methodology for optimal design of patterned heat sink surfaces is proposed. • Heat transfer enhancement by patterned surfaces is measured experimentally. • Role of fluid dynamics and geometrical scales on heat transfer is clarified. - Abstract: In the present work, micro-protruded patterns on flush mounted heat sinks for convective heat transfer enhancement are investigated and a novel methodology for thermal optimization is proposed. Patterned heat sinks are experimentally characterized in fully turbulent regime, and the role played by geometrical parameters and fluid dynamic scales is discussed. A methodology specifically suited for micro-protruded pattern optimization is designed, leading to 73% enhancement in thermal performance respect to commercially available heat sinks, at fixed costs. This work is expected to introduce a new methodological approach for a more systematic and efficient development of solutions for electronics cooling.

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

    International Nuclear Information System (INIS)

    Pasch, J.; Anghaie, S.

    2007-01-01

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

  19. Fast Prediction Method for Steady-State Heat Convection

    KAUST Repository

    Wáng, Yì

    2012-03-14

    A reduced model by proper orthogonal decomposition (POD) and Galerkin projection methods for steady-state heat convection is established on a nonuniform grid. It was verified by thousands of examples that the results are in good agreement with the results obtained from the finite volume method. This model can also predict the cases where model parameters far exceed the sample scope. Moreover, the calculation time needed by the model is much shorter than that needed for the finite volume method. Thus, the nonuniform POD-Galerkin projection method exhibits high accuracy, good suitability, and fast computation. It has universal significance for accurate and fast prediction. Also, the methodology can be applied to more complex modeling in chemical engineering and technology, such as reaction and turbulence. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Mixed convection in a nanofluid filled-cavity with partial slip subjected to constant heat flux and inclined magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Ismael, Muneer A. [Mechanical Engineering Department, Engineering College, University of Basrah, Basrah (Iraq); Mansour, M.A. [Department of Mathematics, Assuit University, Faculty of Science, Assuit (Egypt); Chamkha, Ali J. [Mechanical Engineering Department, Prince Mohammad Bin Fahd University, Al-Khobar 31952 (Saudi Arabia); Prince Sultan Endowment for Energy and Environment, Prince Mohammad Bin Fahd University, Al-Khobar 31952 (Saudi Arabia); Rashad, A.M., E-mail: am_rashad@yahoo.com [Department of Mathematics, Aswan University, Faculty of Science, Aswan 81528 (Egypt)

    2016-10-15

    Mixed convection in a lid-driven square cavity filled with Cu-water nanofluid and subjected to inclined magnetic field is investigated in this paper. Partial slip effect is considered along the lid driven horizontal walls. A constant heat flux source on the left wall is considered, meanwhile the right vertical wall is cooled isothermally. The remainder cavity walls are thermally insulted. A control finite volume method is used as a numerical appliance of the governing equations. Six pertinent parameters were studied these; the orientation of the magnetic field (Φ=0–360°), Richardson number (Ri=0.001–1000), Hartman number (Ha=0–100), the size and position of the heat source (B=0.2–0.8, D=0.3–0.7, respectively), nanoparticles volume fraction (ϕ=0.0–0.1), and the lid-direction of the horizontal walls (λ=±1) where the positive sign means lid-driven to the right while the negative sign means lid-driven to the left. The results show that the orientation and the strength of the magnetic field can play a significant role in controlling the convection under the effect of partial slip. It is also found that the natural convection decreases with increasing the length of the heat source for all ranges of the studied parameters, while it is do so due to the vertical distance up to Hartman number of 50, beyond this value the natural convection decreases with lifting the heat source narrower to the top wall. - Highlights: • Partial slip along moving walls of MHD cavity filled with nanofluid is considered. • The suppression exerted by the magnetic field decreases with its orientation. • Nusselt number is enhanced slightly with nanoparticles at shortest heat source. • Nusselt number is enhanced with nanoparticles at stronger magnetic field.

  1. Mixed convection in a nanofluid filled-cavity with partial slip subjected to constant heat flux and inclined magnetic field

    International Nuclear Information System (INIS)

    Ismael, Muneer A.; Mansour, M.A.; Chamkha, Ali J.; Rashad, A.M.

    2016-01-01

    Mixed convection in a lid-driven square cavity filled with Cu-water nanofluid and subjected to inclined magnetic field is investigated in this paper. Partial slip effect is considered along the lid driven horizontal walls. A constant heat flux source on the left wall is considered, meanwhile the right vertical wall is cooled isothermally. The remainder cavity walls are thermally insulted. A control finite volume method is used as a numerical appliance of the governing equations. Six pertinent parameters were studied these; the orientation of the magnetic field (Φ=0–360°), Richardson number (Ri=0.001–1000), Hartman number (Ha=0–100), the size and position of the heat source (B=0.2–0.8, D=0.3–0.7, respectively), nanoparticles volume fraction (ϕ=0.0–0.1), and the lid-direction of the horizontal walls (λ=±1) where the positive sign means lid-driven to the right while the negative sign means lid-driven to the left. The results show that the orientation and the strength of the magnetic field can play a significant role in controlling the convection under the effect of partial slip. It is also found that the natural convection decreases with increasing the length of the heat source for all ranges of the studied parameters, while it is do so due to the vertical distance up to Hartman number of 50, beyond this value the natural convection decreases with lifting the heat source narrower to the top wall. - Highlights: • Partial slip along moving walls of MHD cavity filled with nanofluid is considered. • The suppression exerted by the magnetic field decreases with its orientation. • Nusselt number is enhanced slightly with nanoparticles at shortest heat source. • Nusselt number is enhanced with nanoparticles at stronger magnetic field.

  2. A thermodynamically general theory for convective vortices

    Science.gov (United States)

    Renno, Nilton O.

    2008-08-01

    Convective vortices are common features of atmospheres that absorb lower-entropy-energy at higher temperatures than they reject higher-entropy-energy to space. These vortices range from small to large-scale and play an important role in the vertical transport of heat, momentum, and tracer species. Thus, the development of theoretical models for convective vortices is important to our understanding of some of the basic features of planetary atmospheres. The heat engine framework is a useful tool for studying convective vortices. However, current theories assume that convective vortices are reversible heat engines. Since there are questions about how reversible real atmospheric heat engines are, their usefulness for studying real atmospheric vortices is somewhat controversial. In order to reduce this problem, a theory for convective vortices that includes irreversible processes is proposed. The paper's main result is that the proposed theory provides an expression for the pressure drop along streamlines that includes the effects of irreversible processes. It is shown that a simplified version of this expression is a generalization of Bernoulli's equation to convective circulations. It is speculated that the proposed theory not only explains the intensity, but also sheds light on other basic features of convective vortices such as their physical appearance.

  3. Natural convection in an adiabatic vertical channel due to a dissipated heat element

    International Nuclear Information System (INIS)

    Ramos, M.A.M.S.

    1986-01-01

    An experimental study was perfomed on natural convection heat transfer to air in a vertical channel due to an isothermal heated element attached in one of the walls of the channel. The heated element dissipates heat due to the Joule effect. To determine the heat transfer coefficient, it is necessary to evaluate the heat transferred to air by natural convenction alone. Hence, the heat lost by the element due to conduction and radiation is evaluated in order to correct the measured heat transfer. The natural-convenction heat transfer coefficient is a function of the following parameters: the temperature difference between the element and the ambient air, the position of the element in the channel, and the channel spacing. An optimal value of the channel spacing, when the heat transfer coefficient attains its maximum value, was observed for each of the temperature difference investigated. These maximum values may be up to 25% higher than the value for the case of infinite spacing. Comparisons are made with results available in the literature for similar configurations, and the values found in this work are higher. (author) [pt

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

    Directory of Open Access Journals (Sweden)

    M. MOHANRAJ

    2009-09-01

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

  5. GPM SLH: Convective Latent Heating Estimated with GPM Dual-frequency Precipitation Radar Data

    Science.gov (United States)

    Takayabu, Y. N.; Hamada, A.; Yokoyama, C.; Ikuta, Y.; Shige, S.; Yamaji, M.; Kubota, T.

    2017-12-01

    Three dimensional diabatic heating distribution plays essential roles to determine large-scale circulation, as well as to generate mesoscale circulation associated with tropical convection (e.g. Hartmann et al., 1984; Houze et al. 1982). For mid-latitude systems also, diabatic heating contributes to generate PVs resulting in, for example, explosive intensifications of mid-lattitude storms (Boettcher and Wernli, 2011). Previously, with TRMM PR data, we developed a Spectral Latent Heating algorithm (SLH; Shige et al. 2004, etc.) for 36N-36S region. It was based on the spectral LH tables produced from a simulation utilizing the Goddard Cloud Ensemble Model forced with the TOGA-COARE data. With GPM DPR, the observation region is extended to 65N-65S. Here, we introduce a new version of SLH algorithm which is applicable also to the mid-latitude precipitation. A new global GPM SLH ver.5 product is released as one of NASA/JAXA GPM standard products on July 11, 2017. For GPM SLH mid-latitude algorithm, we employ the Japan Meteorological Agency (JMA)'s high resolution (horizontally 2km) Local Forecast Model (LFM) to construct the LUTs. With collaborations of JMA's forecast group, forecast data for 8 extratropical cyclone cases are collected and utilized. For mid-latitude precipitation, we have to deal with large temperature gradients and complex relationship between the freezing level and cloud base levels. LUTs are constructed for LH, Q1-QR, and Q2 (Yanai et al. 1973), for six different precipitation types: Convective and shallow stratiform LUTs are made against precipitation top heights. For deep stratiform and other precipitation, LUTs are made against maximum precipitation to handle the unknown cloud-bases. Finally, three-dimensional convective latent heating is retrieved, utilizing the LUTs and precipitation profile data from GPM 2AKu. We can confirm that retrieved LH looks very similar to simulated LH, for a consistency check. We also confirm a good continuities of

  6. Convective Propagation Characteristics Using a Simple Representation of Convective Organization

    Science.gov (United States)

    Neale, R. B.; Mapes, B. E.

    2016-12-01

    Observed equatorial wave propagation is intimately linked to convective organization and it's coupling to features of the larger-scale flow. In this talk we a use simple 4 level model to accommodate vertical modes of a mass flux convection scheme (shallow, mid-level and deep). Two paradigms of convection are used to represent convective processes. One that has only both random (unorganized) diagnosed fluctuations of convective properties and one with organized fluctuations of convective properties that are amplified by previously existing convection and has an explicit moistening impact on the local convecting environment We show a series of model simulations in single-column, 2D and 3D configurations, where the role of convective organization in wave propagation is shown to be fundamental. For the optimal choice of parameters linking organization to local atmospheric state, a broad array of convective wave propagation emerges. Interestingly the key characteristics of propagating modes are the low-level moistening followed by deep convection followed by mature 'large-scale' heating. This organization structure appears to hold firm across timescales from 5-day wave disturbances to MJO-like wave propagation.

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

    International Nuclear Information System (INIS)

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

    2015-01-01

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

  8. Analogy of convective heat transfer between developing laminar secondary flows in pipes

    OpenAIRE

    Ishigaki, Hiroshi; 石垣 博

    1998-01-01

    Analogy of convective heat transfer between developing laminar flows in curved pipes and orthogonally rotating pipes is described through similarity arguments and numerical computation. Governing parameters and a dimensionless axial distance are properly used for the respective flows. When the second parameter is large in each flow, it is shown that the temperature profiles and the Nusselt numbers of the two flows are approximately similar for the same values of the governing parameter, Prand...

  9. Intriguingly high convective heat transfer enhancement of nanofluid coolants in laminar flows

    Science.gov (United States)

    Xie, Huaqing; Li, Yang; Yu, Wei

    2010-05-01

    We reported on investigation of the convective heat transfer enhancement of nanofluids as coolants in laminar flows inside a circular copper tube with constant wall temperature. Nanofluids containing Al 2O 3, ZnO, TiO 2, and MgO nanoparticles were prepared with a mixture of 55 vol.% distilled water and 45 vol.% ethylene glycol as base fluid. It was found that the heat transfer behaviors of the nanofluids were highly depended on the volume fraction, average size, species of the suspended nanoparticles and the flow conditions. MgO, Al 2O 3, and ZnO nanofluids exhibited superior enhancements of heat transfer coefficient, with the highest enhancement up to 252% at a Reynolds number of 1000 for MgO nanofluid. Our results demonstrated that these oxide nanofluids might be promising alternatives for conventional coolants.

  10. Intriguingly high convective heat transfer enhancement of nanofluid coolants in laminar flows

    International Nuclear Information System (INIS)

    Xie Huaqing; Li Yang; Yu Wei

    2010-01-01

    We reported on investigation of the convective heat transfer enhancement of nanofluids as coolants in laminar flows inside a circular copper tube with constant wall temperature. Nanofluids containing Al 2 O 3 , ZnO, TiO 2 , and MgO nanoparticles were prepared with a mixture of 55 vol.% distilled water and 45 vol.% ethylene glycol as base fluid. It was found that the heat transfer behaviors of the nanofluids were highly depended on the volume fraction, average size, species of the suspended nanoparticles and the flow conditions. MgO, Al 2 O 3 , and ZnO nanofluids exhibited superior enhancements of heat transfer coefficient, with the highest enhancement up to 252% at a Reynolds number of 1000 for MgO nanofluid. Our results demonstrated that these oxide nanofluids might be promising alternatives for conventional coolants.

  11. Intriguingly high convective heat transfer enhancement of nanofluid coolants in laminar flows

    Energy Technology Data Exchange (ETDEWEB)

    Xie Huaqing, E-mail: hqxie@eed.sspu.c [School of Urban Development and Environmental Engineering, Shanghai Second Polytechnic University, Shanghai 201209 (China); Li Yang; Yu Wei [School of Urban Development and Environmental Engineering, Shanghai Second Polytechnic University, Shanghai 201209 (China)

    2010-05-31

    We reported on investigation of the convective heat transfer enhancement of nanofluids as coolants in laminar flows inside a circular copper tube with constant wall temperature. Nanofluids containing Al{sub 2}O{sub 3}, ZnO, TiO{sub 2}, and MgO nanoparticles were prepared with a mixture of 55 vol.% distilled water and 45 vol.% ethylene glycol as base fluid. It was found that the heat transfer behaviors of the nanofluids were highly depended on the volume fraction, average size, species of the suspended nanoparticles and the flow conditions. MgO, Al{sub 2}O{sub 3}, and ZnO nanofluids exhibited superior enhancements of heat transfer coefficient, with the highest enhancement up to 252% at a Reynolds number of 1000 for MgO nanofluid. Our results demonstrated that these oxide nanofluids might be promising alternatives for conventional coolants.

  12. Laminar natural convection heat transfer from a horizontal circular cylinder to liquid metals

    International Nuclear Information System (INIS)

    Sugiyama, K.; Ma, Y.; Ishiguro, R.

    1991-01-01

    The objective of the present study is to clarify the heat transfer characteristic of natural convection around a horizontal circular cylinder immersed in liquid metals. Experimental work concerning liquid metals sometimes involves such a degree of error that is impossible to understand the observed characteristics in measurement. Numerical analysis is a powerful means to overcome this experimental disadvantage. In the present paper the authors first show that the Boussinesq approximation is more applicable heat transfer rates, even for a cylinder with a relatively large temperature difference (>100K) between the heat transfer surface and fluid. It is found from a comparison of the present results with previous work that the correlation equations that have already been proposed predict values lower than the present ones

  13. On the development of a grid-enhanced single-phase convective heat transfer correlation

    International Nuclear Information System (INIS)

    Miller, D.J.; Cheung, F.B.; Bajorek, S.M.

    2011-01-01

    A new single-phase convective heat transfer augmentation correlation has been developed using single phase steam cooling experimental data obtained from the Penn State/NRC Rod Bundle Heat Transfer (RBHT) facility. Experimental data obtained from the RBHT single phase steam cooling tests have been evaluated and new findings identified. Previous rod bundle tests showed the importance of spacer grid on the local heat transfer, and that the augmentation in heat transfer downstream of a grid decays exponentially. The RBHT data also shows that the Reynolds number affects the rate at which this augmentation decays. The new correlation includes the strong dependence of heat transfer on both the Reynolds number and the grid blockage ratio. While the effects of both parameters were clearly evident in the RBHT experimental data, existing correlations do not account for the Reynolds number effect. The developed correlation incorporates Reynolds number in the decay curve of heat transfer. The newly developed correlation adequately accounts for the dependence of the heat transfer augmentation decay rate on the local flow Reynolds number. (author)

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

    Energy Technology Data Exchange (ETDEWEB)

    Mme, Uduak Akpan

    2010-10-15

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-09-01

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

  16. Natural convection heat transfer characteristics of the molten metal pool with solidification by boiling coolant

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Jae Seon; Suh, Kune Yull; Chung, Chang Hyun [Seoul National University, Seoul (Korea, Republic of); Paark, Rae Joon; Kim, Sang Baik [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)

    1998-12-31

    This paper presents results of experimental studies on the heat transfer and solidification of the molten metal pool with overlying coolant with boiling. The metal pool is heated from the bottom surface and coolant is injected onto the molten metal pool. Ad a result, the crust, which is a solidified layer, may form at the top of the molten metal pool. Heat transfer is accomplished by a conjugate mechanism, which consists of the natural convection of the molten metal pool, the conduction in the crust layer and the convective boiling heat transfer in the coolant. This work examines the crust formation and the heat transfer rate on the molten metal pool with boiling coolant. The simulant molten pool material is tin (Sn) with the melting temperature of 232 deg C. Demineralized water is used as the working coolant. The crust layer thickness was ostensibly varied by the heated bottom surface temperature of the test section, but not much affected by the coolant injection rate. The correlation between the Nusselt number and the Rayleigh number in the molten metal pool region of this study is compared against the crust formation experiment without coolant boiling and the literature correlations. The present experimental results are higher than those from the experiment without coolant boiling, but show general agreement with the Eckert correlation, with some deviations in the high and low ends of the Rayleigh number. This discrepancy is currently attributed to concurrent rapid boiling of the coolant on top of the metal layer. 10 refs., 4 figs., 1 tab. (Author)

  17. Natural convection heat transfer characteristics of the molten metal pool with solidification by boiling coolant

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Jae Seon; Suh, Kune Yull; Chung, Chang Hyun [Seoul National University, Seoul (Korea, Republic of); Paark, Rae Joon; Kim, Sang Baik [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)

    1997-12-31

    This paper presents results of experimental studies on the heat transfer and solidification of the molten metal pool with overlying coolant with boiling. The metal pool is heated from the bottom surface and coolant is injected onto the molten metal pool. Ad a result, the crust, which is a solidified layer, may form at the top of the molten metal pool. Heat transfer is accomplished by a conjugate mechanism, which consists of the natural convection of the molten metal pool, the conduction in the crust layer and the convective boiling heat transfer in the coolant. This work examines the crust formation and the heat transfer rate on the molten metal pool with boiling coolant. The simulant molten pool material is tin (Sn) with the melting temperature of 232 deg C. Demineralized water is used as the working coolant. The crust layer thickness was ostensibly varied by the heated bottom surface temperature of the test section, but not much affected by the coolant injection rate. The correlation between the Nusselt number and the Rayleigh number in the molten metal pool region of this study is compared against the crust formation experiment without coolant boiling and the literature correlations. The present experimental results are higher than those from the experiment without coolant boiling, but show general agreement with the Eckert correlation, with some deviations in the high and low ends of the Rayleigh number. This discrepancy is currently attributed to concurrent rapid boiling of the coolant on top of the metal layer. 10 refs., 4 figs., 1 tab. (Author)

  18. Natural convection heat transfer characteristics of the molten metal pool with solidification by boiling coolant

    International Nuclear Information System (INIS)

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

    1997-01-01

    This paper presents results of experimental studies on the heat transfer and solidifcation of the molten metal pool with overlying coolant with boiling. The metal pool is heated from the bottom surface and coolant is injected onto the molten metal pool. As a result, the crust, which is a solidified layer, may form at the top of the molten metal pool. Heat transfer is accomplished by a conjugate mechanism, which consists of the natural convection of the molten metal pool, the conduction in the crust layer and the convective boiling heat transfer in the coolant. This work examines the crust formation and the heat transfer rate on the molten metal pool with boiling coolant. The simulant molten pool material is tin (Sn) with the melting temperature of 232 .deg. C. Demineralized water is used as the working coolant. The crust layer thickness was ostensibly varied by the heated bottom surface temperature of the test section, but not much affected by the coolant injection rate. The correlation between the Nusselt number and the Rayleight number in the molten metal pool region of this study is compared against the crust formation experiment without coolant boiling and the literature correlations. The present experimental results are higher than those from the experiment without coolant boiling, but show general agreement with the Eckert correlation, with some deviations in the high and low ends of the Rayleigh number. This discrepancy is currently attributed to concurrent rapid boiling of the coolant on top of the metal layer

  19. 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.

  20. Thermo capillary and buoyancy convection in a fluid locally heated on its free surface; Convection thermocapillaire et thermogravitaire dans un fluide chauffe localement sur sa surface libre

    Energy Technology Data Exchange (ETDEWEB)

    Favre, E.

    1997-09-26

    coupled buoyancy and thermo-capillary convection lead to a convective motion of the interface liquid/gas which drastically changes the heat and mass transfer across the liquid layer. Two experiments were considered, depending on the fluid: oil or mercury. The liquid is set in a cooled cylindrical vessel, and heated by a heat flux across the center of the free surface. The basic flow, in the case of oil, is a torus. When the heat parameter increases, a stationary flow appears as petals or rays when the aspect ratio. The lateral confinement selects the azimuthal wavelength. In the case of petals-like flow, a sub-critical Hopf bifurcation is underlined. The turbulence is found to be `weak`, even for the largest values of the Marangoni number (Ma = 1.3 10{sup 5}). In the case of mercury, the thermo-capillary effect is reduced to zero to impurities at the surface which have special trajectories we describe and compare to a simpler experiment. Only the buoyancy forces induce a unstationary, weakly turbulent flow as soon as the heating power exceeds 4W (Ra = 4.5 10{sup 3}, calculated with h = 1 mm). The past part concerns the analysis of the effect on the flow of the boundary conditions, the geometry, the Prandtl number and the buoyancy force with the help of the literature. Results concerning heat transfer, in particular the exponent of the law Nusselt number vs. heating power, were compared with available data. (author) 115 refs.

  1. Theoretical study to determine the heat transfer by forced convection coefficient in an empirical correlation in single phase, for annular channels

    International Nuclear Information System (INIS)

    Herrera A, E.

    1994-01-01

    In the heat transfer studies by forced convection, we have few data about behavior of the fluids in an annular channel heated by a concentric pipe, such date is necessary to know the heat transfer coefficient that establish the interchange of energy and the thermic properties of the fluid with the geometry of the flow. In this work the objective, was to compare some empirical correlations that we needed for determinate the heat transfer coefficient for annular channels, where we obtained similar at the theoretical results of an experiment made by Miller and Benforado. It is important to know such coefficients because we can determinate the heat quantity transmitted to a probe zone, in which we simulate a nuclear fuel element that developed huge heat quantity that must be dispersed in short time. We give theoretical data of the heat forced transfer convection and we analyzed the phenomena in annular channels given some empirical correlations employed by some investigators and we analyzed each one. (Author)

  2. A note on the heat transfer in convective fins

    International Nuclear Information System (INIS)

    Razelos, P.

    1979-01-01

    In this paper a generalized approach to the problem of heat transfer through convective fins is given. The proper dimensionless variables, which specify the general problem are identified, and upper bounds of the values of the dimensionless number Nsub(r) defined as 'the ratio of the heat transferred by the fin to that of the corresponding bare surface' are derived. It was shown that these limiting values of the Nsub(r) are 1/√B 1 and √2/B 1 for longitudinal fins and spines respectively, where B 1 is the Biot number hb/k, while for annular fins of constant thickness and hyperbolic profile, Nsub(r) 1 , where K(β) is a number determined by the profile of the fin and the ratio β = x 2 /x 1 of the outside to the inside radii. It was also shown that for longitudinal fins and spinces the possible adverse insulating effect by the use of the fin is avoided, if one selects the value of √hA/kC [de

  3. Light-powered micromotor driven by geometry-assisted, asymmetric photon-heating and subsequent gas convection

    Science.gov (United States)

    Han, Li-Hsin; Wu, Shaomin; Condit, J. Christopher; Kemp, Nate J.; Milner, Thomas E.; Feldman, Marc D.; Chen, Shaochen

    2010-05-01

    We report on the design, fabrication, and analysis of a light-driven micromotor. The micromotor was created from a nanoporous polymer with close-packed gold nanoparticles which generate heat by absorbing light. The blades of the micromotor were curved, forming convex and concave sides. Upon lateral irradiation, by geometric effect the convex side transfers more photon-generated heat to the surrounding gas molecules, causing a convective motion of gas and leading to the rotation of the micromotor. The light-driven motions of gas molecules were analyzed using molecular dynamics modeling.

  4. Entropy Generation Analysis of Natural Convection in Square Enclosures with Two Isoflux Heat Sources

    Directory of Open Access Journals (Sweden)

    S. Z. Nejad

    2017-04-01

    Full Text Available This study investigates entropy generation resulting from natural convective heat transfer in square enclosures with local heating of the bottom and symmetrical cooling of the sidewalls. This analysis tends to optimize heat transfer of two pieces of semiconductor in a square electronic package. In this simulation, heaters are modeled as isoflux heat sources and sidewalls of the enclosure are isothermal heat sinks. The top wall and the non-heated portions of the bottom wall are adiabatic. Flow and temperature fields are obtained by numerical simulation of conservation equations of mass, momentum and energy in laminar, steady and two dimensional flows. With constant heat energy into the cavity, effect of Rayleigh number, heater length, heater strength ratios and heater position is evaluated on flow and temperature fields and local entropy generation. The results show that a minimum entropy generation rate is obtained under the same condition in which a minimum peak heater temperature is obtained.

  5. Experimental investigations on the transient behaviour of nuclear heat plants with natural convection

    International Nuclear Information System (INIS)

    Adam, E.; Sydow, J.; Wolff, J.

    1988-01-01

    Apart from the theoretical approach, practical experiments concerning the transient behaviour of the primary loop of reactors with natural coolant convection are necessary in order to evaluate the safety systems of reactors providing heat for industrial and communal consumers. The article presents experiments concerning the transient behaviour of the experimental plant DANTON, which models the reactor AST-500, and gives a preview of further research. (orig.) [de

  6. Radiant and convective heat transfer for flow of a transparent gas in a short tube with prescribed sinusoidal wall heat flux

    International Nuclear Information System (INIS)

    de Lemos, M.J.S.

    1982-01-01

    The present analysis accounts for radiant and convective heat transfer for a transparent fluid flowing in a short tube with prescribed wall heat flux. The heat flux distribution used was of sine shape with maximum at the middle of the tube. Such a solution is the approximate one for axial power in a nuclear reactor. The solutions for the tube wall and gas bulk temperatures were obtained by successive substitutions for the wall and gas balance energy equations. The results show a decrease of 30% for the maximum wall temperature using black surface (e = 1). In this same case, the increasing in the gas temperature shows a decrease of 58%

  7. Nonlinear thermal convection in a layer of nanofluid under G-jitter and internal heating effects

    Directory of Open Access Journals (Sweden)

    Bhadauria B. S.

    2014-01-01

    Full Text Available This paper deals with a mathematical model of controlling heat transfer in nanofluids. The time-periodic vertical vibrations of the system are considered to effect an external control of heat transport along with internal heating effects. A weakly non-linear stability analysis is based on the five-mode Lorenz model using which the Nusselt number is obtained as a function of the thermal Rayleigh number, nano-particle concentration based Rayleigh number, Prandtl number, Lewis number, modified diffusivity ratio, amplitude and frequency of modulation. It is shown that modulation can be effectively used to control convection and thereby heat transport. Further, it is found that the effect of internal Rayleigh number is to enhance the heat and nano-particles transport.

  8. Inverse determination of convective heat transfer between an impinging jet and a continuously moving flat surface

    International Nuclear Information System (INIS)

    Mobtil, Mohammed; Bougeard, Daniel; Solliec, Camille

    2014-01-01

    Highlights: • A new method for convective heat flux determination on a moving wall is proposed. • An inverse technique is used for retrieving the heat flux from IR measurements. • Heat flux distribution determination in the slot jet impingement area is performed. • The accuracy of the method is examined using CFD Based simulated experiments. • The inversion quality is tested according to several parameters of the experiments. - Abstract: In this study an inverse method is developed to determine the heat flux distribution on a moving plane wall. The method uses a thin layer of material (the measurement medium) glued on the conveyor belt. The heat flux distribution on the moving wall is then determined by an inverse method based on the temperature measurement by infrared thermography on the upper surface of the measurement medium. A finite element based inverse algorithm of a steady state heat conduction advection in the Eulerian frame is performed. The algorithm entails the use of the Tikhonov regularization method, along with the L-curve method to select an optimal regularization parameter. Both the direct solution of moving boundary problem and the inverse design formulation are presented. The accuracy of the inverse method is examined by simulating the exact and noisy data with four different values of the surface-to-jet velocity ratio, and two different materials (PVC and Aluminum) for the measurement medium. The results show a greater sensitivity to the convective heat flux allowing a better estimation of heat flux distribution for the PVC layer. An alternative underdetermined inverse scheme is also studied. This configuration allows a different extend between the retrieval heat flux surface and the measurement temperature surface

  9. Combined convective heat and airborne pollutant removals in a slot vented enclosure under different flow schemes: Parametric investigations and non unique flow solutions

    International Nuclear Information System (INIS)

    Ren, Xiu-Hong; Hu, Jiang-Tao; Liu, Di; Zhao, Fu-Yun; Li, Xiao-Hong; Wang, Han-Qing

    2016-01-01

    Highlights: • Combined convective heat and airborne transports under different flow schemes. • Natural and forced convection dominated regimes were identified with transition. • Dual solution branches were sustained for the transitional mixing flow scheme. • Rest solutions evolving from motionless flows coincided with other solution branch. • Heat and species lines were presented to delineate heat and mass transport structures. - Abstract: This paper reports a numerical study of mixed convection on a heated and polluted strip within a slot ventilated enclosure in which the displacement and mixing flow schemes are considered. Contours of streamfunction, heatfunction, and massfunction are presented to clearly scrutinize the mechanism of heat and airborne pollutant transports. For the displacement flow scheme, thermal Nusselt and pollutant Sherwood numbers under different Reynolds numbers remain almost constant as the value of Gr/Re 2 decreases down to the regime of forced convection dominated. However, as Ar increases up to the regime of natural convection dominated, both Nu and Sh increase sharply with Ar (Gr/Re 2 ). Similar trends could be observed for the situation of mixing ventilated flow scheme. In the mixing scheme, non unique steady flow solutions could be observed for the range of transitional flow regime. Upward solutions, downward solutions and rest solutions have been exemplified with varying Gr/Re 2 . Dual solution branches could be sustained at the range of 39.0 ≤ Gr/Re 2  ≤ 6.0 × 10 3 , while the rest solutions obtained from rest states were completely coinciding with former continuous solutions. The present work could be significant for the natural optimization and passive control of heat and pollutant removals from the electronic boxes or building enclosures.

  10. Doubly stratified mixed convection flow of Maxwell nanofluid with heat generation/absorption

    Energy Technology Data Exchange (ETDEWEB)

    Abbasi, F.M., E-mail: abbasisarkar@gmail.com [Department of Mathematics, Comsats Institute of Information Technology, Islamabad 44000 (Pakistan); Shehzad, S.A. [Department of Mathematics, Comsats Institute of Information Technology, Sahiwal 57000 (Pakistan); Hayat, T. [Department of Mathematics, Quaid-i-Azam University, 45320, Islamabad 44000 (Pakistan); NAAM Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589 (Saudi Arabia); Ahmad, B. [NAAM Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589 (Saudi Arabia)

    2016-04-15

    Magnetohydrodynamic (MHD) doubly stratified flow of Maxwell nanofluid in presence of mixed convection is analyzed in this article. Effects of thermophoresis, Brownian motion and heat generation/absorption are present. The flow is induced due to linear stretching of sheet. Mathematical formulation is made under boundary layer approach. Expressions of velocity, temperature and nanoparticles concentration are developed. The obtained results are plotted and discussed to examine the variations in temperature and nanoparticles concentration due to different physical parameters. Numerical computations are made to obtain the values of local Nusselt and Sherwood numbers. Impact of sundry parameters on the flow quantities is analyzed graphically. - Highlights: • Double stratified flow of Maxwell nanofluid with mixed convection is modeled. • Thermophoresis and Brownian motion effects are encountered. • Computations are made to obtain the solution expressions. • Numerical values of local Nusselt and Sherwood numbers are computed and examined.

  11. Investigation on natural convection decay heat removal for the EFR status of the program

    Energy Technology Data Exchange (ETDEWEB)

    Hofmann, F [Kernforschungszentrum Karlsruhe (Germany); Essig, C [Siemens AG, Bergisch Gladbach (Germany); Georgeoura, S [AEA Reactor Service, Dounreay (United Kingdom); Tenchine, D [CEA Grenoble (France)

    1993-02-01

    The European Research and Development (R+D) Program on decay heat removal by natural convection for the European Fast Reactor (EFR) covers the calculational methods and the model experiments performed for code validation. The studies concentrate on important physical effects of the cooling modes within the primary system and the direct reactor cooling circuits and include reactor experiments. (author)

  12. Investigation on natural convection decay heat removal for the EFR status of the program

    International Nuclear Information System (INIS)

    Hofmann, F.; Essig, C; Georgeoura, S.; Tenchine, D.

    1993-01-01

    The European Research and Development (R+D) Program on decay heat removal by natural convection for the European Fast Reactor (EFR) covers the calculational methods and the model experiments performed for code validation. The studies concentrate on important physical effects of the cooling modes within the primary system and the direct reactor cooling circuits and include reactor experiments. (author)

  13. Fully developed natural convection heat and mass transfer in a vertical annular porous medium with asymmetric wall temperatures and concentrations

    International Nuclear Information System (INIS)

    Cheng, C.-Y.

    2006-01-01

    This work examines the effects of the modified Darcy number, the buoyancy ratio and the inner radius-gap ratio on the fully developed natural convection heat and mass transfer in a vertical annular non-Darcy porous medium with asymmetric wall temperatures and concentrations. The exact solutions for the important characteristics of fluid flow, heat transfer, and mass transfer are derived by using a non-Darcy flow model. The modified Darcy number is related to the flow resistance of the porous matrix. For the free convection heat and mass transfer in an annular duct filled with porous media, increasing the modified Darcy number tends to increase the volume flow rate, total heat rate added to the fluid, and the total species rate added to the fluid. Moreover, an increase in the buoyancy ratio or in the inner radius-gap ratio leads to an increase in the volume flow rate, the total heat rate added to the fluid, and the total species rate added to the fluid

  14. Results from transient transport experiments in Rijnhuizen tokamak project: Heat convection, transport barriers and 'non-local' effects

    International Nuclear Information System (INIS)

    Mantica, P.; Gorini, G.; Hogeweij, G.M.D.; Kloe, J. de; Lopez Cardozo, N.J.; Schilham, A.M.R.

    2001-01-01

    An overview of experimental transport studies performed on the Rijnhuizen Tokamak Project (RTP) using transient transport techniques in both Ohmic and ECH dominated plasmas is presented. Modulated Electron Cyclotron Heating (ECH) and oblique pellet injection (OPI) have been used to induce electron temperature (T e ) perturbations at different radial locations. These were used to probe the electron transport barriers observed near low order rational magnetic surfaces in ECH dominated steady-state RTP plasmas. Layers of inward electron heat convection in off-axis ECH plasmas were detected with modulated ECH. This suggests that RTP electron transport barriers consist of heat pinch layers rather than layers of low thermal diffusivity. In a different set of experiments, OPI triggered a transient rise of the core T e due to an increase of the T e gradient in the 1< q<2 region. These transient transport barriers were probed with modulated ECH and found to be due to a transient drop of the electron heat diffusivity, except for off-axis ECH plasmas, where a transient inward pinch is also observed. Transient transport studies in RTP could not solve this puzzling interplay between heat diffusion and convection in determining an electron transport barrier. They nevertheless provided challenging experimental evidence both for theoretical modelling and for future experiments. (author)

  15. Conduction and convection heat transfer characteristics of water-based au nanofluids in a square cavity with differentially heated side walls subjected to constant temperatures

    Directory of Open Access Journals (Sweden)

    Ternik Primož

    2014-01-01

    Full Text Available The present work deals with the natural convection in a square cavity filled with the water-based Au nanofluid. The cavity is heated on the vertical and cooled from the adjacent wall, while the other two horizontal walls are adiabatic. The governing differential equations have been solved by the standard finite volume method and the hydrodynamic and thermal fields were coupled together using the Boussinesq approximation. The main objective of this study is to investigate the influence of the nanoparticles’ volume fraction on the heat transfer characteristics of Au nanofluids at the given base fluid’s (i.e. water Rayleigh number. Accurate results are presented over a wide range of the base fluid Rayleigh number and the volume fraction of Au nanoparticles. It is shown that adding nanoparticles in a base fluid delays the onset of convection. Contrary to what is argued by many authors, we show by numerical simulations that the use of nanofluids can reduce the heat transfer rate instead of increasing it.

  16. Convective and Stratiform Precipitation Processes and their Relationship to Latent Heating

    Science.gov (United States)

    Tao, Wei-Kuo; Lang, Steve; Zeng, Xiping; Shige, Shoichi; Takayabu, Yukari

    2009-01-01

    The global hydrological cycle is central to the Earth's climate system, with rainfall and the physics of its formation acting as the key links in the cycle. Two-thirds of global rainfall occurs in the Tropics. Associated with this rainfall is a vast amount of heat, which is known as latent heat. It arises mainly due to the phase change of water vapor condensing into liquid droplets; three-fourths of the total heat energy available to the Earth's atmosphere comes from tropical rainfall. In addition, fresh water provided by tropical rainfall and its variability exerts a large impact upon the structure and motions of the upper ocean layer. An improved convective -stratiform heating (CSH) algorithm has been developed to obtain the 3D structure of cloud heating over the Tropics based on two sources of information: 1) rainfall information, namely its amount and the fraction due to light rain intensity, observed directly from the Precipitation Radar (PR) on board the TRMM satellite and 2) synthetic cloud physics information obtained from cloud-resolving model (CRM) simulations of cloud systems. The cloud simulations provide details on cloud processes, specifically latent heating, eddy heat flux convergence and radiative heating/cooling, that. are not directly observable by satellite. The new CSH algorithm-derived heating has a noticeably different heating structure over both ocean and land regions compared to the previous CSH algorithm. One of the major differences between new and old algorithms is that the level of maximum cloud heating occurs 1 to 1.5 km lower in the atmosphere in the new algorithm. This can effect the structure of the implied air currents associated with the general circulation of the atmosphere in the Tropics. The new CSH algorithm will be used provide retrieved heating data to other heating algorithms to supplement their performance.

  17. Southern Ocean Convection and tropical telleconnections

    Science.gov (United States)

    Marinov, I.; Cabre, A.; Gnanadesikan, A.

    2014-12-01

    We show that Southern Ocean (SO) temperatures in the latest generation of Earth System Models exhibit two major modes of variation, one driven by deep convection, the other by tropical variability. We perform a CMIP5 model intercomparison to understand why different climate models represent SO variability so differently in long, control simulations. We show that multiyear variability in Southern Ocean sea surface temperatures (SSTs) can in turn influence oceanic and atmospheric conditions in the tropics on short (atmospheric) time-scales. We argue that the strength and pattern of SO-tropical teleconnections depends on the intensity of SO deep convection. Periodic convection in the SO is a feature of most CMIP5 models under preindustrial forcing (deLavergne et al., 2014). Models show a wide distribution in the spatial extent, periodicity and intensity of their SO convection, with some models convecting most of the time, and some showing very little convection. In a highly convective coupled model, we find that multidecadal variability in SO and global SSTs, as well as SO heat storage are driven by Weddell Sea convective variability, with convective decades relatively warm due to the heat released from the deep southern ocean and non-convective decades cold due to the subsurface storage of heat. Furthermore, pulses of SO convection drive SST and sea ice variations, influencing absorbed shortwave and emitted longwave radiation, wind, cloud and precipitation patterns, with climatic implications for the low latitudes via fast atmospheric teleconnections. We suggest that these high-low latitude teleconnection mechanisms are relevant for understanding hiatus decades. Additionally, Southern Ocean deep convection varied significantly during past, natural climate changes such as during the last deglaciation. Weddell Sea open convection was recently weakened, likely as a consequence of anthropogenic forcing and the resulting surface freshening. Our study opens up the

  18. Fusing Multiple Satellite Datasets Toward Defining and Understanding Organized Convection

    Science.gov (United States)

    Elsaesser, G.; Del Genio, A. D.

    2017-12-01

    How do we differentiate unorganized from organized convection? We might think of organized convection as being long lasting (at least longer than the lifetime of any individual cumulus cell), clustered at larger spatial scales (>100 km), and responsible for substantial rainfall accumulation. Organized convection is sustained on such scales due to the arrangement of moist/dry and buoyant/non-buoyant mesoscale circulations. The nature of these circulations is tied to system diabatic heating profiles; in particular, the 2nd baroclinic (top-heavy), stratiform heating mode is thought to be important for organized convection maintenance/propagation. We investigate the extent to which these characteristics are jointly found in propagating convective systems. Lifecycle information comes from hi-res IR data. Diabatic heating profiles, convective fractions and rainfall are provided by GPM retrievals mapped to convective system tracks. Moisture is provided by AIRS/AMSU and passive microwave retrievals. Instead of compositing heating profile information along a system track, where information is smoothed out, we sort system heating profile structures according to their "top heaviness" and then analyze PDFs of system rainfall, system sizes, durations, convective/stratiform ratios, etc. as a function of diabatic heating structure. Perhaps contrary to expectation, we find only small differences in PDFs of rainfall rates, system sizes, and system duration for different heating profile structures. If organization is defined according to heating structures, then one possible interpretation of these results is that organization is independent of system size, duration, and many times, even lifecycle stage. Is it possible that most systems "hobble" along and exhibit varying degrees of organization, dependent on local environment moisture/buoyancy variations, unlike the archetypical MCS paradigm? This presentation will also discuss the questions posed above within the context of

  19. Boundary Layer Control of Rotating Convection Systems

    Science.gov (United States)

    King, E. M.; Stellmach, S.; Noir, J.; Hansen, U.; Aurnou, J. M.

    2008-12-01

    Rotating convection is ubiquitous in the natural universe, and is likely responsible for planetary processes such magnetic field generation. Rapidly rotating convection is typically organized by the Coriolis force into tall, thin, coherent convection columns which are aligned with the axis of rotation. This organizational effect of rotation is thought to be responsible for the strength and structure of magnetic fields generated by convecting planetary interiors. As thermal forcing is increased, the relative influence of rotation weakens, and fully three-dimensional convection can exist. It has long been assumed that rotational effects will dominate convection dynamics when the ratio of buoyancy to the Coriolis force, the convective Rossby number, Roc, is less than unity. We investigate the influence of rotation on turbulent Rayleigh-Benard convection via a suite of coupled laboratory and numerical experiments over a broad parameter range: Rayleigh number, 10310; Ekman number, 10-6≤ E ≤ ∞; and Prandtl number, 1≤ Pr ≤ 100. In particular, we measure heat transfer (as characterized by the Nusselt number, Nu) as a function of the Rayleigh number for several different Ekman and Prandtl numbers. Two distinct heat transfer scaling regimes are identified: non-rotating style heat transfer, Nu ~ Ra2/7, and quasigeostrophic style heat transfer, Nu~ Ra6/5. The transition between the non-rotating regime and the rotationally dominant regime is described as a function of the Ekman number, E. We show that the regime transition depends not on the global force balance Roc, but on the relative thicknesses of the thermal and Ekman boundary layers. The transition scaling provides a predictive criterion for the applicability of convection models to natural systems such as Earth's core.

  20. About Navier-Stokes Equation in the Theory of Convective Heat Transfer

    Science.gov (United States)

    Davidzon, M. Y.

    2017-10-01

    A system of differential equations (Navier-Stokes, continuity, heat conductivity) is used to solve convective heat transfer problems. While solving Navier-Stokes equation, it is usually assumed that tangent stress is proportional to the velocity gradient. This assumption is valid with a small velocity gradient, for example, near an axis of the channel, but velocity gradient can be very large near the channel wall. Our paper shows that if we accept power law instead of linear law for tangential stress, then the velocity profile for creeping, laminar, and turbulent flow in the channel can be calculated without using Navier-Stokes equation. Also, in this case Navier-Stokes equation itself changes: the coefficient of dynamic viscosity changes its value from normal (in case of the creeping flow) to tending to infinity (in case of the well-developed turbulent flow).

  1. Attempts of Thermal Imaging Camera Usage in Estimations of the Convective Heat Loss From a Vertical Plate

    Directory of Open Access Journals (Sweden)

    Denda Hubert

    2014-01-01

    Full Text Available In this paper a new method for determining heat transfer coefficients using a gradient method has been developed. To verify accuracy of the proposed method vertical isothermal heating plate with natural convection mechanism has been examined. This configuration was deliberately chosen, because of the fact that such case is historically the earliest and most thoroughly studied and its rich scientific documentation – the most reliable. New method is based on temperature field visualization made in perpendicular plane to the heating surface of the plate using infrared camera. Because the camera does not record temperature of air itself but the surface only, therefore plastic mesh with low thermal conductivity has been used as a detector. Temperature of each mesh cell, placed perpendicular to the vertical heating surface and rinsed with convection stream of heated air could be already recorded by infrared camera. In the same time using IR camera surface of heating plate has been measured. By numerical processing of the results matrix temperature gradient on the surface ∂T/∂x │ x=0, local heat transfer coefficients αy, and local values of Nusselt number Nuy, can be calculated. After integration the average Nusselt number for entire plate can be calculated. Obtained relation characteristic numbers Nu = 0.647 Ra 0.236 (R2 = 0.943, has a good correlation with literature reports and proves usefulness of the method.

  2. Stability Analysis and Internal Heating Effect on Oscillatory Convection in a Viscoelastic Fluid Saturated Porous Medium Under Gravity Modulation

    Science.gov (United States)

    Bhadauria, B. S.; Singh, M. K.; Singh, A.; Singh, B. K.; Kiran, P.

    2016-12-01

    In this paper, we investigate the combined effect of internal heating and time periodic gravity modulation in a viscoelastic fluid saturated porous medium by reducing the problem into a complex non-autonomous Ginzgburg-Landau equation. Weak nonlinear stability analysis has been performed by using power series expansion in terms of the amplitude of gravity modulation, which is assumed to be small. The Nusselt number is obtained in terms of the amplitude for oscillatory mode of convection. The influence of viscoelastic parameters on heat transfer has been discussed. Gravity modulation is found to have a destabilizing effect at low frequencies and a stabilizing effect at high frequencies. Finally, it is found that overstability advances the onset of convection, more with internal heating. The conditions for which the complex Ginzgburg-Landau equation undergoes Hopf bifurcation and the amplitude equation undergoes supercritical pitchfork bifurcation are studied.

  3. Natural convection in a porous medium: External flows

    International Nuclear Information System (INIS)

    Cheng, P.

    1985-01-01

    Early theoretical work on heat transfer in porous media focussed its attention on the onset of natural convection and cellular convection in rectangular enclosures with heating from below. Recently, increased attention has been directed to the study of natural convection in a porous medium external to heated surfaces and bodies. Boundary layer approximations were introduced, and similarly solutions have been obtained for steady natural convection boundary layers adjacent to a heated flat plate, a horizontal cylinder and a sphere as well as other two-dimensional and axisymmetric bodies of arbitrary shape. Higher order boundary layer theories have been carried out to assess the accuracy of the boundary layer approximation. The effects of entrainments at the edge of the boundary layer, the inclination angle of the heated inclined plate, and the upstream geometry on the heat transfer characteristics have been investigated based on the method of matched asymptotic expansions. The conditions for the onset of vortex instability in porous layers heated from below were determined based on linear stability analyses. The effects of no-slip boundary conditions, non-Darcy and thermal dispersion, which were neglected in all of the previous theoretical investigations, have recently been re-examined. Experimental investigations on natural convection about a vertical and inclined heated plate, a horizontal cylinder, as well as plume rise from a horizontal line source of heat have been conducted. All of this work is reviewed in this paper

  4. Experimental study on the convective heat transfer enhancement in single-phase steam flow by a support grid

    International Nuclear Information System (INIS)

    Kim, Byoung Jae; Kim, Kihwan; Kim, Dong-Eok; Youn, Young-Jung; Park, Jong-Kuk; Moon, Sang-Ki; Song, Chul-Hwa

    2014-01-01

    Highlights: • The convective heat transfer enhancement by support grids is investigated. • Experiments were performed in a square array 2 × 2 rod bundle. • The enhancement was affected not only by the blockage ratio also by the Reynolds number. • For low Reynolds numbers, the enhancement depends on the Reynolds number (Re). • For high Reynolds numbers, the enhancement is nearly independent of Re. - Abstract: Single-phase flow occurs in the fuel rod bundle of a pressurized water reactor, during the normal operation period or at the early stage of the reflood phase in a loss-of-coolant accident scenario. In the former period, the flow is single-phase water flow, but in the latter case, the flow is single-phase steam flow. Support grids are required to maintain a proper geometry configuration of fuel rods within nuclear fuel assemblies. This study was conducted to elucidate the effects of support grids on the convective heat transfer in single-phase steam flow. Experiments were made in a square array 2 × 2 rod bundle. The four electrically-heating rods were maintained by support grids with mixing vanes creating a swirl flow. Two types of support grids were considered in this study. The two types are geometrically similar except the blockage ratio by different mixing vane angles. For all test runs, 2 kW power was supplied to each rod. The working fluid was superheated steam with Re = 2,301–39,594. The axial profile of the rod surface temperatures was measured, and the convective heat transfer enhancement by the presence of the support grids was examined. The peak heat transfer enhancement was a function of not only the blockage ratio but also the Reynolds number. Given the same blockage ratio, the heat transfer enhancement was sensitive to the Reynolds number in laminar flow, whereas it was nearly independent of the Reynolds number in turbulent flow

  5. Natural convection heat transfer experiments of horizontal plates with fin arrays

    Energy Technology Data Exchange (ETDEWEB)

    Moon, Je Young; Chung, Bum Jin [Jeju National University 102 Jejudaehakno, Jeju (Korea, Republic of)

    2012-10-15

    Core melt in a severe accident condition, forms a molten pool in the reactor vessel lower head. The molten pool is divided by a metallic pool (top) and an oxide pool (bottom) by the density difference. The crust between the metallic layer and the oxide pool may be formed by solidification of the molten metallic materials. So the surface of the crust is formed irregularly. Experiments were performed to investigate the irregular crust as a preparatory study before an in-depth severe accident study. The natural convection heat transfer were investigated experimentally varying the height and spacing of fins, top plate of different kinds and the plate separation distance with/without the side walls. In order to simulate irregular crust surface condition, the finned plates was used. Using the analogy concept, heat transfer experiments were replaced by mass transfer experiments. A cupric acid.copper sulfate (H{sup 2S}O{sup 4-}CuSO{sup 4)} electroplating system was adopted as the mass transfer system and the electric currents were measured rather than the heat transfer rates.

  6. Investigation on natural convection decay heat removal for the EFR: Status of the program

    Energy Technology Data Exchange (ETDEWEB)

    Hoffmann, H; Weinberg, D [Kernforschungszentrum Karlsruhe GmbH, IATF, Karlsruhe (Germany); Webster, R [AEA Reactor Services, Dounreay (United Kingdom)

    1991-07-01

    The European Research and Development Program on decay heat removal by natural convection for the European Fast Reactor (EFR) covers the calculational methods and the model experiments performed for code validation. The studies concentrate on important physical effects of the cooling modes withinthe primary system and the direct reactor cooling circuits and include fundamental tests as well as reactor experiments. (author)

  7. Investigation of forced convection heat transfer of supercritical pressure water in a vertically upward internally ribbed tube

    International Nuclear Information System (INIS)

    Wang Jianguo; Li Huixiong; Guo Bin; Yu Shuiqing; Zhang Yuqian; Chen Tingkuan

    2009-01-01

    In the present paper, the forced convection heat transfer characteristics of water in a vertically upward internally ribbed tube at supercritical pressures were investigated experimentally. The six-head internally ribbed tube is made of SA-213T12 steel with an outer diameter of 31.8 mm and a wall thickness of 6 mm and the mean inside diameter of the tube is measured to be 17.6 mm. The experimental parameters were as follows. The pressure at the inlet of the test section varied from 25.0 to 29.0 MPa, and the mass flux was from 800 to 1200 kg/(m 2 s), and the inside wall heat flux ranged from 260 to 660 kW/m 2 . According to experimental data, the effects of heat flux and pressure on heat transfer of supercritical pressure water in the vertically upward internally ribbed tube were analyzed, and the characteristics and mechanisms of heat transfer enhancement, and also that of heat transfer deterioration, were also discussed in the so-called large specific heat region. The drastic changes in thermophysical properties near the pseudocritical points, especially the sudden rise in the specific heat of water at supercritical pressures, may result in the occurrence of the heat transfer enhancement, while the covering of the heat transfer surface by fluids lighter and hotter than the bulk fluid makes the heat transfer deteriorated eventually and explains how this lighter fluid layer forms. It was found that the heat transfer characteristics of water at supercritical pressures were greatly different from the single-phase convection heat transfer at subcritical pressures. There are three heat transfer modes of water at supercritical pressures: (1) normal heat transfer, (2) deteriorated heat transfer with low HTC but high wall temperatures in comparison to the normal heat transfer, and (3) enhanced heat transfer with high HTC and low wall temperatures in comparison to the normal heat transfer. It was also found that the heat transfer deterioration at supercritical pressures was

  8. 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.

  9. Post shut-down decay heat removal from nuclear reactor core by natural convection loops in sodium pool

    Energy Technology Data Exchange (ETDEWEB)

    Rajamani, A. [Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036 (India); Sundararajan, T., E-mail: tsundar@iitm.ac.in [Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036 (India); Prasad, B.V.S.S.S. [Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036 (India); Parthasarathy, U.; Velusamy, K. [Nuclear Engineering Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 (India)

    2016-05-15

    Highlights: • Transient simulations are performed for a worst case scenario of station black-out. • Inter-wrapper flow between various sub-assemblies reduces peak core temperature. • Various natural convection paths limits fuel clad temperatures below critical level. - Abstract: The 500 MWe Indian pool type Prototype Fast Breeder Reactor (PFBR) has a passive core cooling system, known as the Safety Grade Decay Heat Removal System (SGDHRS) which aids to remove decay heat after shut down phase. Immediately after reactor shut down the fission products in the core continue to generate heat due to beta decay which exponentially decreases with time. In the event of a complete station blackout, the coolant pump system may not be available and the safety grade decay heat removal system transports the decay heat from the core and dissipates it safely to the atmosphere. Apart from SGDHRS, various natural convection loops in the sodium pool carry the heat away from the core and deposit it temporarily in the sodium pool. The buoyancy driven flow through the small inter-wrapper gaps (known as inter-wrapper flow) between fuel subassemblies plays an important role in carrying the decay heat from the sub-assemblies to the hot sodium pool, immediately after reactor shut down. This paper presents the transient prediction of flow and temperature evolution in the reactor subassemblies and the sodium pool, coupled with the safety grade decay heat removal system. It is shown that with a properly sized decay heat exchanger based on liquid sodium and air chimney stacks, the post shutdown decay heat can be safely dissipated to atmospheric air passively.

  10. Mixed convective heat transfer to Sisko fluid over a radially stretching sheet in the presence of convective boundary conditions

    Energy Technology Data Exchange (ETDEWEB)

    Khan, Masood; Malik, Rabia, E-mail: rabiamalik.qau@gmail.com; Munir, Asif [Department of Mathematics, Quaid-i-Azam University, Islamabad 44000 (Pakistan)

    2015-08-15

    In this article, the mixed convective heat transfer to Sisko fluid over a radially stretching surface in the presence of convective boundary conditions is investigated. The viscous dissipation and thermal radiation effects are also taken into account. The suitable transformations are applied to convert the governing partial differential equations into a set of nonlinear coupled ordinary differential equations. The analytical solution of the governing problem is obtained by using the homotopy analysis method (HAM). Additionally, these analytical results are compared with the numerical results obtained by the shooting technique. The obtained results for the velocity and temperature are analyzed graphically for several physical parameters for the assisting and opposing flows. It is found that the effect of buoyancy parameter is more prominent in case of the assisting flow as compared to the opposing flow. Further, in tabular form the numerical values are given for the local skin friction coefficient and local Nusselt number. A remarkable agreement is noticed by comparing the present results with the results reported in the literature as a special case.

  11. Mixed convective heat transfer to Sisko fluid over a radially stretching sheet in the presence of convective boundary conditions

    International Nuclear Information System (INIS)

    Khan, Masood; Malik, Rabia; Munir, Asif

    2015-01-01

    In this article, the mixed convective heat transfer to Sisko fluid over a radially stretching surface in the presence of convective boundary conditions is investigated. The viscous dissipation and thermal radiation effects are also taken into account. The suitable transformations are applied to convert the governing partial differential equations into a set of nonlinear coupled ordinary differential equations. The analytical solution of the governing problem is obtained by using the homotopy analysis method (HAM). Additionally, these analytical results are compared with the numerical results obtained by the shooting technique. The obtained results for the velocity and temperature are analyzed graphically for several physical parameters for the assisting and opposing flows. It is found that the effect of buoyancy parameter is more prominent in case of the assisting flow as compared to the opposing flow. Further, in tabular form the numerical values are given for the local skin friction coefficient and local Nusselt number. A remarkable agreement is noticed by comparing the present results with the results reported in the literature as a special case

  12. Convection in complex shaped vessel; Convection dans des enceintes de forme complexe

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2000-07-01

    The 8 november 2000, the SFT (Societe Francaise de Thermique) organized a technical day on the convection in complex shaped vessels. Nine papers have been presented in the domains of the heat transfers, the natural convection, the fluid distribution, the thermosyphon effect, the steam flow in a sterilization cycle and the transformers cooling. Eight papers are analyzed in ETDE and one paper dealing with the natural convection in spent fuels depository is analyzed in INIS. (A.L.B.)

  13. A new predictive dynamic model describing the effect of the ambient temperature and the convective heat transfer coefficient on bacterial growth.

    Science.gov (United States)

    Ben Yaghlene, H; Leguerinel, I; Hamdi, M; Mafart, P

    2009-07-31

    In this study, predictive microbiology and food engineering were combined in order to develop a new analytical model predicting the bacterial growth under dynamic temperature conditions. The proposed model associates a simplified primary bacterial growth model without lag, the secondary Ratkowsky "square root" model and a simplified two-parameter heat transfer model regarding an infinite slab. The model takes into consideration the product thickness, its thermal properties, the ambient air temperature, the convective heat transfer coefficient and the growth parameters of the micro organism of concern. For the validation of the overall model, five different combinations of ambient air temperature (ranging from 8 degrees C to 12 degrees C), product thickness (ranging from 1 cm to 6 cm) and convective heat transfer coefficient (ranging from 8 W/(m(2) K) to 60 W/(m(2) K)) were tested during a cooling procedure. Moreover, three different ambient air temperature scenarios assuming alternated cooling and heating stages, drawn from real refrigerated food processes, were tested. General agreement between predicted and observed bacterial growth was obtained and less than 5% of the experimental data fell outside the 95% confidence bands estimated by the bootstrap percentile method, at all the tested conditions. Accordingly, the overall model was successfully validated for isothermal and dynamic refrigeration cycles allowing for temperature dynamic changes at the centre and at the surface of the product. The major impact of the convective heat transfer coefficient and the product thickness on bacterial growth during the product cooling was demonstrated. For instance, the time needed for the same level of bacterial growth to be reached at the product's half thickness was estimated to be 5 and 16.5 h at low and high convection level, respectively. Moreover, simulation results demonstrated that the predicted bacterial growth at the air ambient temperature cannot be assumed to be

  14. Experimental investigation of turbulent mixed convection in the wake of a heated sphere

    International Nuclear Information System (INIS)

    Suckow, D.

    1993-11-01

    The axisymmetric wake of a heated sphere under conditions of turbulent mixed convection is investigated in the water test section FLUTMIK. The sphere is located in a vertical channel with forced convective upward flow. The influence of buoyancy forces to the flow field is studied by comparison with the unheated wake. The theoretical fundamentals describing turbulent flows and different versions of the k-ε turbulence model extended by buoyancy terms are described in detail. The quantities to be determined experimentally are derived. The temperature and the components of the velocity vector in axial and radial directions are measured simultaneously by means of a thermocouple probe and a two component, two color laser Doppler anemometer. The flow quantities are determined at axial distances between 5 and 106 sphere diameters. The functional principle and the basis of the laser Doppler anemometer are explained. The mean velocity, the mean temperature, the intensities of their fluctuations and the turbulent exchange quantities of momentum and heat transport are calculated. The decay laws of the quantities along the axis of the channel and the radial profiles are indicated and discussed. The applicability of the experimental results of the axisymmetric buoyancy influenced turbulent wake with respect to the turbulence models presented are shown. (orig.) [de

  15. Oscillatory magneto-convection under magnetic field modulation

    Directory of Open Access Journals (Sweden)

    Palle Kiran

    2018-03-01

    Full Text Available In this paper we investigate an oscillatory mode of nonlinear magneto-convection under time dependant magnetic field. The time dependant magnetic field consists steady and oscillatory parts. The oscillatory part of the imposed magnetic field is assumed to be of third order. An externally imposed vertical magnetic field in an electrically conducting horizontal fluid layer is considered. The finite amplitude analysis is discussed while perturbing the system. The complex Ginzburg-Landau model is used to derive an amplitude of oscillatory convection for weakly nonlinear mode. Heat transfer is quantified in terms of the Nusselt number, which is governed by the Landau equation. The variation of the modulation excitation of the magnetic field alternates heat transfer in the layer. The modulation excitation of the magnetic field is used either to enhance or diminish the heat transfer in the system. Further, it is found that, oscillatory mode of convection enhances the heat transfer and than stationary convection. The results have possible technological applications in magnetic fluid based systems involving energy transmission. Keywords: Weakly nonlinear theory, Oscillatory convection, Complex Ginzburg Landau model, Magnetic modulation

  16. Numerical study of the influence of the convective heat transport on acoustic streaming in a standing wave.

    Science.gov (United States)

    Červenka, Milan; Bednařík, Michal

    2018-02-01

    Within this work, acoustic streaming in an air-filled cylindrical resonator with walls supporting a temperature gradient is studied by means of numerical simulations. A set of equations based on successive approximations is derived from the Navier-Stokes equations. The equations take into account the acoustic-streaming-driven convective heat transport; as time-averaged secondary-field quantities are directly calculated, the equations are much easier to integrate than the original fluid-dynamics equations. The model equations are implemented and integrated employing commercial software COMSOL Multiphysics. Numerical calculations are conducted for the case of a resonator with a wall-temperature gradient corresponding to the action of a thermoacoustic effect. It is shown that due to the convective heat transport, the streaming profile is considerably distorted even in the case of weak wall-temperature gradients. The numerical results are consistent with available experimental data.

  17. Effects of heater location and heater size on the natural convection heat transfer in a square cavity using finite element method

    Energy Technology Data Exchange (ETDEWEB)

    Ngo, Ich Long; Byon, Chan [Yeungnam University, Gyeongsan (Korea, Republic of)

    2015-07-15

    Finite element method was used to investigate the effects of heater location and heater size on the natural convection heat transfer in a 2D square cavity heated partially or fully from below and cooled from above. Rayleigh number (5 X 10{sup 2} ≤ Ra ≤ 5X10{sup 5}), heater size (0.1 ≤ D/L ≤ 1.0), and heater location (0.1 ≤ x{sub h}/L ≤ 0.5) were considered. Numerical results indicated that the average Nusselt number (Nu{sub m}) increases as the heater size decreases. In addition, when x{sub h}/L is less than 0.4, Nu{sub m} increases as x{sub h}/L increases, and Num decreases again for a larger value of x{sub h}/L. However, this trend changes when Ra is less than 10{sup 4}, suggesting that Nu{sub m} attains its maximum value at the region close to the bottom surface center. This study aims to gain insight into the behaviors of natural convection in order to potentially improve internal natural convection heat transfer.

  18. Convective effects in a regulatory and proposed fire model

    International Nuclear Information System (INIS)

    Wix, S.D.; Hohnstreiter, G.F.

    1995-01-01

    Radiation is the dominant mode of heat transfer in large fires. However, convection can be as much as 10 to 20 percent of the total heat transfer to an object in a large fire. The current radioactive material transportation packaging regulations include convection as a mode of heat transfer in the accident condition scenario. The current International Atomic Energy Agency Safety Series 6 packaging regulation states ''the convection coefficient shall be that value which the designer can justify if the package were exposed to the specified fire''. The current Title 10, Code of Federal Regulations, Part 71 (10CFR71) packaging regulation states ''when significant, convection heat input must be included on the basis of still, ambient air at 800 degrees C (1475 degrees F)''. Two questions that can arise in an analysts mind from an examination of the packaging regulations is whether convection is significant and whether convection should be included in the design analysis of a radioactive materials transportation container. The objective of this study is to examine the convective effects on an actual radioactive materials transportation package using a regulatory and a proposed thermal boundary condition

  19. Adiabatic partition effect on natural convection heat transfer inside a square cavity: experimental and numerical studies

    Science.gov (United States)

    Mahmoudinezhad, S.; Rezania, A.; Yousefi, T.; Shadloo, M. S.; Rosendahl, L. A.

    2018-02-01

    A steady state and two-dimensional laminar free convection heat transfer in a partitioned cavity with horizontal adiabatic and isothermal side walls is investigated using both experimental and numerical approaches. The experiments and numerical simulations are carried out using a Mach-Zehnder interferometer and a finite volume code, respectively. A horizontal and adiabatic partition, with angle of θ is adjusted such that it separates the cavity into two identical parts. Effects of this angel as well as Rayleigh number on the heat transfer from the side-heated walls are investigated in this study. The results are performed for the various Rayleigh numbers over the cavity side length, and partition angles ranging from 1.5 × 105 to 4.5 × 105, and 0° to 90°, respectively. The experimental verification of natural convective flow physics has been done by using FLUENT software. For a given adiabatic partition angle, the results show that the average Nusselt number and consequently the heat transfer enhance as the Rayleigh number increases. However, for a given Rayleigh number the maximum and the minimum heat transfer occurs at θ = 45°and θ = 90°, respectively. Two responsible mechanisms for this behavior, namely blockage ratio and partition orientation, are identified. These effects are explained by numerical velocity vectors and experimental temperatures contours. Based on the experimental data, a new correlation that fairly represents the average Nusselt number of the heated walls as functions of Rayleigh number and the angel of θ for the aforementioned ranges of data is proposed.

  20. Comparative Study of Convective Heat Transfer Performance of Steam and Air Flow in Rib Roughened Channels

    Science.gov (United States)

    Ma, Chao; Ji, Yongbin; Ge, Bing; Zang, Shusheng; Chen, Hua

    2018-04-01

    A comparative experimental study of heat transfer characteristics of steam and air flow in rectangular channels roughened with parallel ribs was conducted by using an infrared camera. Effects of Reynolds numbers and rib angles on the steam and air convective heat transfer have been obtained and compared with each other for the Reynolds number from about 4,000 to 15,000. For all the ribbed channels the rib pitch to height ratio (p/e) is 10, and the rib height to the channel hydraulic diameter ratio is 0.078, while the rib angles are varied from 90° to 45°. Based on experimental results, it can be found that, even though the heat transfer distributions of steam and air flow in the ribbed channels are similar to each other, the steam flow can obtain higher convective heat transfer enhancement capability, and the heat transfer enhancement of both the steam and air becomes greater with the rib angle deceasing from 90° to 45°. At Reynolds number of about 12,000, the area-averaged Nusselt numbers of the steam flow is about 13.9%, 14.2%, 19.9% and 23.9% higher than those of the air flow for the rib angles of 90°, 75°, 60° and 45° respectively. With the experimental results the correlations for Nusselt number in terms of Reynolds number and rib angle for the steam and air flow in the ribbed channels were developed respectively.

  1. Effect of thermal radiation and suction on convective heat transfer of nanofluid along a wedge in the presence of heat generation/absorption

    Energy Technology Data Exchange (ETDEWEB)

    Kasmani, Ruhaila Md; Bhuvaneswari, M. [Centre for Foundation Studies in Science, University of Malaya, 50603 Kuala Lumpur (Malaysia); Sivasankaran, S.; Siri, Zailan [Institute of Mathematical Science, University of Malaya, 50603 Kuala Lumpur (Malaysia)

    2015-10-22

    An analysis is presented to find the effects of thermal radiation and heat generation/absorption on convection heat transfer of nanofluid past a wedge in the presence of wall suction. The governing partial differential equations are transformed into a system of ordinary differential equations using similarity transformation. The resulting system is solved numerically using a fourth-order Runge–Kutta method with shooting technique. Numerical computations are carried out for different values of dimensionless parameters to predict the effects of wedge angle, thermophoresis, Brownian motion, heat generation/absorption, thermal radiation and suction. It is found that the temperature increases significantly when the value of the heat generation/absorption parameter increases. But the opposite observation is found for the effect of thermal radiation.

  2. Hydromagnetic slip flow of water based nano-fluids past a wedge with convective surface in the presence of heat generation (or) absorption

    International Nuclear Information System (INIS)

    Rahman, M.M.; Al-Lawatia, M.A.; Eltayeb, I.A.; Al-Salti, N.

    2012-01-01

    Heat transfer characteristics of a two-dimensional steady hydromagnetic slip flow of water based nano-fluids (TiO 2 -water, Al 2 O 3 -water, and Cu-water) over a wedge with convective surface taking into account the effects of heat generation (or absorption) has been investigated numerically. The local similarity solutions are obtained by using very robust computer algebra software MATLAB and presented graphically as well as in a tabular form. The results show that nano-fluid velocity is lower than the velocity of the base fluid and the existence of the nano-fluid leads to the thinning of the hydrodynamic boundary layer. The rate of shear stress is significantly influenced by the surface convection parameter and the slip parameter. It is higher for nano-fluids than the base fluid. The results also show that within the boundary layer the temperature of the nano-fluid is higher than the temperature of the base fluid. The rate of heat transfer is found to increase with the increase of the surface convection and the slip parameters. Addition of nano-particles to the base fluid induces the rate of heat transfer. The rate of heat transfer in the Cu-water nano-fluid is found to be higher than the rate of heat transfer in the TiO 2 -water and Al 2 O 3 -water nano-fluids. (authors)

  3. Comparisons of RELAP5-3D Analyses to Experimental Data from the Natural Convection Shutdown Heat Removal Test Facility

    Energy Technology Data Exchange (ETDEWEB)

    Bucknor, Matthew; Hu, Rui; Lisowski, Darius; Kraus, Adam

    2016-04-17

    The Reactor Cavity Cooling System (RCCS) is an important passive safety system being incorporated into the overall safety strategy for high temperature advanced reactor concepts such as the High Temperature Gas- Cooled Reactors (HTGR). The Natural Convection Shutdown Heat Removal Test Facility (NSTF) at Argonne National Laboratory (Argonne) reflects a 1/2-scale model of the primary features of one conceptual air-cooled RCCS design. The project conducts ex-vessel, passive heat removal experiments in support of Department of Energy Office of Nuclear Energy’s Advanced Reactor Technology (ART) program, while also generating data for code validation purposes. While experiments are being conducted at the NSTF to evaluate the feasibility of the passive RCCS, parallel modeling and simulation efforts are ongoing to support the design, fabrication, and operation of these natural convection systems. Both system-level and high fidelity computational fluid dynamics (CFD) analyses were performed to gain a complete understanding of the complex flow and heat transfer phenomena in natural convection systems. This paper provides a summary of the RELAP5-3D NSTF model development efforts and provides comparisons between simulation results and experimental data from the NSTF. Overall, the simulation results compared favorably to the experimental data, however, further analyses need to be conducted to investigate any identified differences.

  4. Coupled thermo-capillary and buoyancy convection in a liquid layer locally heated on its free surface

    International Nuclear Information System (INIS)

    Favre, E.

    1997-01-01

    Coupled buoyancy and thermo-capillary convection lead to a convective motion of the interface liquid/gas, which changes drastically the heat and mass transfer across the liquid layer. Two experiments are considered, depending on the fluid: oil or mercury. The liquid is set in a cooled cylindrical vessel, and heated by a heat flux across the center of the free surface. The basic flow, in the case of oil, is a torus. When the heat parameter increases, a stationary flow looking like petals or rays appears when the aspect ratio length/depth is small, and like concentric rings in the case of large values of the aspect ratio. The lateral confinement selects the azimuthal length wave. In the case of petals-like flow, a sub-critical Hopf bifurcation is underlined. The turbulence is found to be 'weak', even for the largest values of the Marangoni number (Ma ≅ 1.3 * 10 5 ). In the case of mercury, the thermo-capillary effect is reduced to zero, due to impurities at the surface, which have special trajectories we describe and compare to a simpler experiment. The only buoyancy forces induces an un-stationary, weakly turbulent flow as soon as the heating power exceeds 4 W (≅ 4.5 * 10 3 , calculated with h = 1 mm). The last part concerns the analysis of the effect on the flow of the boundary conditions, the geometry, the Prandtl number, the buoyancy force, with the help of the literature. Results concerning heat transfer, especially the exponent of the law Nusselt number vs. heating power, are compared with available data. (author) [fr

  5. Developing natural convection in a fluid layer with localized heating and large viscosity variation

    Energy Technology Data Exchange (ETDEWEB)

    Hickox, C.E.; Chu, Tze Yao.

    1991-01-01

    Numerical simulations and laboratory experiments are used to elucidate aspects of transient natural convection in a magma chamber. The magma chamber is modeled as a horizontal fluid layer confined within an enclosure of square planform and heated from below by a strip heater centered on the lower boundary of the enclosure. The width of the strip heater and the depth of the fluid layer are one-fourth of the layer width. Corn syrup is used as the working fluid in order to approximate the large viscosity variation with temperature and the large Prandtl number typical of magma. The quiescent, uniform, fluid layer is subjected to instantaneous heating from the strip heater producing a transient flow which is dominated by two counter-rotating convective cells. Experimentally determined characteristics of the developing flow are compared with numerical simulations carried out with a finite element computer program. The results of numerical simulations are in essential agreement with experimental data. Differences between the numerical simulations and experimental measurements are conjectured to result from non-ideal effects present in the experiment which are difficult to represent accurately in a numerical simulation.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2009-07-01

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

  7. The effect of heat generation in inclined slats on the natural convective heat transfer from an isothermal heated vertical plate

    International Nuclear Information System (INIS)

    Oosthuizen, P.H.; Sun, L.; Naylor, D.

    2003-01-01

    Natural convective heat transfer from a wide heated vertical isothermal plate with adiabatic surfaces above and below the heated surface has been considered. There are a series of equally spaced vertical thin, flat surfaces (termed 'slats') near the heated surface, these surfaces being, in general, inclined to the heated surface. There is, in general, a uniform heat generation in the slats. The slats are pivoted about their centre-point and thus as their angle is changed, the distance of the tip of the slat from the plate changes. The situation considered is an approximate model of a window with a vertical blind, the particular case where the window is hotter than the room air being considered. The heat generation in the slats in this situation is the result of solar radiation passing through the window and falling on and being absorbed by the slats of the blind. The flow has been assumed to be laminar and steady. Fluid properties have been assumed constant except for the density change with temperature that gives rise to the buoyancy forces. The governing equations have been written in dimensionless form and the resulting dimensionless equations have been solved using a commercial finite-element package. The solution has the following parameters: (1) the Rayleigh number (2) the Prandtl number (3) the dimensionless heat generation rate in the slats per unit frontal area (4) the dimensionless distance of the slat center point (the pivot point) from the surface (5) the dimensionless slat size (6) the dimensionless slat spacing (7) the angle of inclination of the slats. Because of the application that motivated the study, results have only been obtained for a Prandtl number of 0.7. The effect of the other dimensionless variables on the mean dimensionless heat transfer rate from the heated vertical surface has been examined. (author)

  8. Heat Transfer by Thermo-capillary Convection -Sounding Rocket COMPERE Experiment SOURCE

    Science.gov (United States)

    Dreyer, Michael; Fuhrmann, Eckart

    The sounding rocket COMPERE experiment SOURCE was successfully flown on MASER 11, launched in Kiruna (ESRANGE), May 15th, 2008. SOURCE has been intended to partly ful-fill the scientific objectives of the European Space Agency (ESA) Microgravity Applications Program (MAP) project AO-2004-111 (Convective boiling and condensation). Three parties of principle investigators have been involved to design the experiment set-up: ZARM for thermo-capillary flows, IMFT (Toulouse, France) for boiling studies, EADS Astrium (Bremen, Ger-many) for depressurization. The topic of this paper is to study the effect of wall heat flux on the contact line of the free liquid surface and to obtain a correlation for a convective heat trans-fer coefficient. The experiment has been conducted along a predefined time line. A preheating sequence at ground was the first operation to achieve a well defined temperature evolution within the test cell and its environment inside the rocket. Nearly one minute after launch, the pressurized test cell was filled with the test liquid HFE-7000 until a certain fill level was reached. Then the free surface could be observed for 120 s without distortion. Afterwards, the first depressurization was started to induce subcooled boiling, the second one to start saturated boiling. The data from the flight consists of video images and temperature measurements in the liquid, the solid, and the gaseous phase. Data analysis provides the surface shape versus time and the corresponding apparent contact angle. Computational analysis provides information for the determination of the heat transfer coefficient in a compensated gravity environment where a flow is caused by the temperature difference between the hot wall and the cold liquid. The paper will deliver correlations for the effective contact angle and the heat transfer coefficient as a function of the relevant dimensionsless parameters as well as physical explanations for the observed behavior. The data will be used

  9. Stability Analysis and Internal Heating Effect on Oscillatory Convection in a Viscoelastic Fluid Saturated Porous Medium Under Gravity Modulation

    Directory of Open Access Journals (Sweden)

    Bhadauria B.S.

    2016-12-01

    Full Text Available In this paper, we investigate the combined effect of internal heating and time periodic gravity modulation in a viscoelastic fluid saturated porous medium by reducing the problem into a complex non-autonomous Ginzgburg-Landau equation. Weak nonlinear stability analysis has been performed by using power series expansion in terms of the amplitude of gravity modulation, which is assumed to be small. The Nusselt number is obtained in terms of the amplitude for oscillatory mode of convection. The influence of viscoelastic parameters on heat transfer has been discussed. Gravity modulation is found to have a destabilizing effect at low frequencies and a stabilizing effect at high frequencies. Finally, it is found that overstability advances the onset of convection, more with internal heating. The conditions for which the complex Ginzgburg-Landau equation undergoes Hopf bifurcation and the amplitude equation undergoes supercritical pitchfork bifurcation are studied.

  10. Experimental Study on Natural Convection Heat Transfer From two Parallel Horizontal Cylinders in Horizontal Cylindrical Enclosure

    Directory of Open Access Journals (Sweden)

    Ahmed T. Ahmed

    2013-05-01

    Full Text Available  An experimental study on natural convection heat transfer from two parallel horizontal cylinders in horizontal cylindrical enclosure was carried out under condition of constant surfaces temperature for two cylinders and cylindrical enclosure. The study included the effect of Rayleigh number, rotation angle that represent the confined angle between the passing horizontal plane in cylindrical enclosure center and passing line in two cylinders centers, and the spaces between two cylinders on their heat loss ability.39An experimental set-up was used for this purpose which consist watercontainer, test section which is formed of plastic cylinder that represent the cylindrical enclosure, and two heating elements which are formed of two copper cylinders with (19 mm in diameters heated internally by electrical sources that represents transfer and heat loss elements through this set-up.      The experiments were done at the range of Rayleigh number between ( , cylinders rotation angle at ( , and spacing ratio at ( .     The study showed that the ability of heat loss from two cylinders is a function of Rayleigh number, cylinders rotation angle, and the spaces between them. This ability is increased by increasing of Rayleigh number and it was showed that this ability reaches maximum value at the first cylinder ( and minimum value at the second cylinder ( at spacing ratio (S/D=3 and rotation angle ( for the first and ( for the second cylinder respectively.      The effective variables on natural convection heat transfer from the above two cylinders are related by two correlating equations, each one explains dimensionless relation of heat transfer from each cylinder that represented by Nusselt number against Rayleigh number, rotation angle, and the spacing ratio between two cylinders. 

  11. Calculation of Post-Closure Natural Convection Heat and Mass Transfer in Yucca Mountain Drifts

    International Nuclear Information System (INIS)

    Webb, S.; Itamura, M.

    2004-01-01

    Natural convection heat and mass transfer under post-closure conditions has been calculated for Yucca Mountain drifts using the computational fluid dynamics (CFD) code FLUENT. Calculations have been performed for 300, 1000, 3000, and 10,000 years after repository closure. Effective dispersion coefficients that can be used to calculate mass transfer in the drift have been evaluated as a function of time and boundary temperature tilt

  12. Radiative heat transfer in a heat generating and turbulently convecting fluid layer

    International Nuclear Information System (INIS)

    Cheung, F.B.; Chan, S.H.; Chawla, T.C.; Cho, D.H.

    1980-01-01

    The coupled problem of radiative transport and turbulent natural convection in a volumetrically heated, horizontal gray fluid medium, bounded from above by a rigid, isothermal wall and below by a rigid, adiabatic wall, is investigated analytically. An approximate method based upon the boundary layer approach is employed to obtain the dependence of heat transfer at the upper wall on the principal parameters of the problem, which, for moderate Prandtl number, are the Rayleigh number, Ra, the optical thickness, KL, and the conduction-radiation coupling parameter, N. Also obtained in this study is the behaviour of the thermal boundary layer at the upper wall. At large kL, the contribution of thermal radiation to heat transfer in the layer is found to be negligible for N > 10, moderate for N approximately 1, and overwhelming for N < 0.1. However, at small kL, thermal radiation is found to be important only for N < 0.01. While a higher level of turbulence results in a thinner boundary layer, a larger effect of radiation is found to result in a thicker one. Thus, in the presence of strong thermal radiation, a much larger value of Ra is required for the boundary layer approach to remain valid. Under severe radiation conditions, no boundary layer flow regime is found to exist even at very high Rayleigh numbers. Accordingly, the ranges of applicability of the present results are determined and the approximate method justified. In particular, the validity of the present analysis is tested in three limiting cases, ie those of kL → infinity, N → infinity, and Ra → infinity, and is further confirmed by comparison with the numerical solution (author)

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

    Directory of Open Access Journals (Sweden)

    Wei Cai

    2014-06-01

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

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

    International Nuclear Information System (INIS)

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

    2013-01-01

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

  15. Fully determined scaling laws for volumetrically heated convective systems, a tool for assessing habitability of exoplanets

    Science.gov (United States)

    Vilella, Kenny; Kaminski, Edouard

    2017-05-01

    The long-term habitability of a planet rises from its ability to generate and maintain an atmosphere through partial melting and volcanism. This question has been mainly addressed in the framework of plate tectonics, which may be too specific to apply to the wide range of internal dynamics expected for exoplanets, and even to the thermal evolution of the early Earth. Here we propose a more general theoretical approach of convection to build a regime diagram giving the conditions for partial melting to occur, in planetary bodies, as a function of key parameters that can be estimated for exoplanets, their size and internal heating rate. To that aim, we introduce a refined view of the Thermal Boundary Layer (TBL) in a convective system heated from within, that focuses on the temperature and thickness of the TBL at the top of the hottest temperature profiles, along which partial melting shall first occur. This ;Hottest Thermal Boundary Layer; (HotTBL) is first characterized using fully theoretical scaling laws based on the dynamics of thermal boundary layers. These laws are the first ones proposed in the literature that do not rely on empirical determinations of dimensionless constants and that apply to both low Rayleigh and high Rayleigh convective regimes. We show that the scaling laws can be successfully applied to planetary bodies by comparing their predictions to full numerical simulations of the Moon. We then use the scaling laws to build a regime diagram for exoplanets. Combined with estimates of internal heating in exoplanets, the regime diagram predicts that in the habitable zone partial melting occurs in planets younger than the Earth.

  16. The Next-Generation Goddard Convective-Stratiform Heating Algorithm: New Model Simulations for Tropical and Continental Summertime Environments

    Science.gov (United States)

    Lang, S. E.; Tao, W. K.; Wu, D.

    2016-12-01

    The Goddard Convective-Stratiform Heating (or CSH) algorithm is used to retrieve estimates of cloud heating over the global Tropics using TRMM rainfall data and a set of look-up-tables (LUTs) derived from a series of multi-week cloud-resolving model (CRM) simulations using the Goddard Cumulus Ensemble model (or GCE). These simulations link satellite observables (i.e., surface rainfall and stratiform fraction) with cloud heating profiles, which are not directly observable. The strength of the algorithm relies in part on the representativeness of the simulations; more realistic simulations provide a stronger link between the observables and simulated heating profiles. The current "TRMM" version of the CSH algorithm relies on 2D GCE simulations using an improved version of the Goddard 3-class ice scheme (3ICE), a moderate-sized domain, and 1-km horizontal resolution. Updating the LUTs, which are suitable for tropical and continental summertime environments requires new, more realistic GCE simulations. New simulations are performed using a new, improved 4-class ice scheme, which has been shown to outperform the 3ICE scheme, especially for intense convection. Additional grid configurations are also tested and evaluated to find the best overall setup to for re-deriving and updating the CSH tropical/summertime LUTs.

  17. Onset of Vibrational Convection in a Binary Fluid Saturated Non-Darcy Porous Layer Heated from Above

    Directory of Open Access Journals (Sweden)

    Saravanan S.

    2012-07-01

    Full Text Available A linear stability analysis is used to investigate the influence of mechanical vibration on the onset of thermosolutal convection in a horizontal porous layer heated and salted from above. Vibrations are considered with arbitrary amplitude and frequency. The Brinkman extended Darcy model is used to describe the flow and the Oberbeck-Boussinesq approximation is employed. Continued fraction method and Floquet theory are used to determine the convective instability threshold. It is found that the solutal Rayleigh number has the stabilizing effect. The existence of a closed disconnected loop of synchronous mode is predicted in the marginal curve for moderate values of solutal Rayleigh number and vibration amplitude.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-02-15

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

  19. Thermo-diffusion effect on free convection heat and mass transfer in a thermally linearly stratified non-darcy porous media

    KAUST Repository

    Murthy, P.V.S.N.

    2011-12-26

    Thermo-diffusion effect on free convection heat and mass transfer from a vertical surface embedded in a liquid saturated thermally stratified non - Darcy porous medium has been analyzed using a local non-similar procedure. The wall temperature and concentration are constant and the medium is linearly stratified in the vertical direction with respect to the thermal conditions. The fluid flow, temperature and concentration fields are affected by the complex interactions among the diffusion ratio Le, buoyancy ratio N, thermo-diffusion parameter Sr and stratification parameter ?. Non-linear interactions of all these parameters on the convective transport has been analyzed and variation of heat and mass transfer coefficients with thermo-diffusion parameter in the thermally stratified non-Darcy porous media is presented through computer generated plots.

  20. Thermo-diffusion effect on free convection heat and mass transfer in a thermally linearly stratified non-darcy porous media

    KAUST Repository

    Murthy, P.V.S.N.; El-Amin, Mohamed

    2011-01-01

    Thermo-diffusion effect on free convection heat and mass transfer from a vertical surface embedded in a liquid saturated thermally stratified non - Darcy porous medium has been analyzed using a local non-similar procedure. The wall temperature and concentration are constant and the medium is linearly stratified in the vertical direction with respect to the thermal conditions. The fluid flow, temperature and concentration fields are affected by the complex interactions among the diffusion ratio Le, buoyancy ratio N, thermo-diffusion parameter Sr and stratification parameter ?. Non-linear interactions of all these parameters on the convective transport has been analyzed and variation of heat and mass transfer coefficients with thermo-diffusion parameter in the thermally stratified non-Darcy porous media is presented through computer generated plots.

  1. CONVECTION HEAT TRANSFER IN A CHANNEL OF DIFFERENT CROSS SECTION FILLED WITH POROUS MEDIA

    Directory of Open Access Journals (Sweden)

    Ahmed A. Mohammad Saleh

    2018-05-01

    Full Text Available A forced convection heat transfer in ducts (circular, triangular, rectangular cross sections and (1m length with hydraulic diameter (0.1m filled with porous media (glass spheres 12 mm diameter is investigated experimentally at constant heat flux from the wall (1070W/m² with Reynolds number range of (12461-2500. Comparison was made between three ducts for local temperature distribution and local Nusselt number. The experimental results showed the effect of Reynolds number and cross section on the temperature profile and local Nusselt number,also empirical correlations for average Nusselt number and Peclet number were obtained for three ducts.

  2. A Numerical Study on Laminar Free Convection between Vertical Flat Plates with Symmetric Heating

    Directory of Open Access Journals (Sweden)

    Ameer A. Jadoaa

    2012-06-01

    Full Text Available The development of free convection in a viscous fluid between heated plates is investigated. The basic governing continuity, momentum, and energy equations are solved numerically by finite difference method. Results are obtained for the variations of Nusselt number, velocity, temperature, and pressure throughout the flow field assuming the fluid to enter the channel with ambient temperature and a flat velocity profile. The flow and heat-transfer characteristics of the channel are studied and a development height established. Heating plate condition is (C.W.T and C.H.F. An correlation equation has been deduced for the average Nusselt number as a function of Rayligt number. A comparison is made between the results of this theoretical investigation and theoretical work of (Bodoia, J.R 1962[1].

  3. Nonlinear unsteady convection on micro and nanofluids with Cattaneo-Christov heat flux

    Science.gov (United States)

    Mamatha Upadhya, S.; Raju, C. S. K.; Mahesha; Saleem, S.

    2018-06-01

    This is a theoretical study of unsteady nonlinear convection on magnetohydrodynamic fluid in a suspension of dust and graphene nanoparticles. For boosting the heat transport phenomena we consider the Cattaneo-Christov heat flux and thermal radiation. Dispersal of graphene nanoparticles in dusty fluids finds applications in biocompatibility, bio-imaging, biosensors, detection and cancer treatment, in monitoring stem cells differentiation etc. Initially the simulation is performed by amalgamation of dust (micron size) and nanoparticles into base fluid. Primarily existing partial differential system (PDEs) is changed to ordinary differential system (ODEs) with the support of usual similarity transformations. Consequently, the highly nonlinear ODEs are solved numerically through Runge-Kutta and Shooting method. The computational results for Non-dimensional temperature and velocity profiles are offered through graphs (ϕ = 0 and ϕ = 0.05) cases. Additionally, the numerical values of friction factor and heat transfer rate are tabulated numerically for various physical parameters obtained. We also validated the current outcomes with previously available study and found to be extremely acceptable. From this study we conclude that in the presence of nanofluid heat transfer rate and temperature distribution is higher compared to micro fluid.

  4. Analysis of natural convection heat transfer with crust formation in the molten metal pool using CONV-2 and 3D computer codes

    International Nuclear Information System (INIS)

    Park, R. J.; Kang, K. H.; Kim, S. B.; Kim, H. D.; Choi, S. M.

    1998-01-01

    Analytical studies have been performed on natural convection heat transfer with crust formation in a molten metal pool to validate and evaluate experimental data using the CONV-2 and 3D computer codes. Two types of steady state tests, a low and high geometric aspect ratio case in the molten metal pool, were performed to investigate crust thickness as a function of boundary conditions. The CONV-2 and 3D computer codes were developed under the OECD/NEA RASPLAV project to simulate two- and three-dimensional natural convection heat transfer with crust formation, respectively. The Rayleigh-Benard flow patterns in the molten metal pool contribute to the temperature distribution, which affects non-uniform crust formation. The CONV-2D results on crust thickness are a little higher than the experimental data because of heat loss during the test. In comparison of the CONV-3D results with the CONV-2D results on crust thickness, the three-dimensional results are higher than the two-dimensional results, because of three dimensional natural convection flow and wall effect

  5. Combined natural convection and surface radiation in the annular region between a volumetrically heated inner tube and a finite conducting outer tube

    International Nuclear Information System (INIS)

    Gianoulakis, S.; Klein, D.E.

    1993-01-01

    Buoyancy-driven natural-convection heat transfer in enclosures has been the subject of considerable research with applications to electronic packaging, solar collectors, and shipping containers for spent nuclear fuel. A numerical study has been carried out to predict combined natural-convection and radiation heat transfer in the annular region between concentric tubes. The inner tube was volumetrically heated. Both tubes were of finite conductance. The surfaces of the annular region were diffuse and gray. The gas in the annulus was assumed to be nonparticipating. A newly developed hybrid finite element finite difference method was used for the study. This method combines finite element discretization of geometries with finite difference discretized solution procedures for the governing differential equations. This study examined the effects of surface radiative properties and material conductivities on the temperature and velocity fields and on local heat transfer rates. Fluid Raleigh numbers ranging from 10 3 to 10 7 , ratios of solid to fluid region thermal conductivities ranging from 10 to 10 4 , and surface total hemispherical emissivities ranging from 0.0 to 1.0 were examined in this study. It was found that the heat transfer across the annulus was dominated by conduction and radiation for the lower Raleigh number flows. As the fluid Raleigh number increased, convection became a primary mode of heat transfer. As the surface emissivity was increased in the annulus, the average Nusselt number on the inner tube surface decreased

  6. The Characteristics of natural convection heat transfer of Al_2O_3–water nano fluid flow in a vertical annulus pipe

    International Nuclear Information System (INIS)

    Reinaldy Nazar

    2016-01-01

    Results of several researches have shown that nano fluids have better thermal characteristics than conventional fluid (water). In this regard, ideas for using nano fluids as an alternative heat transfer fluid in the reactor coolant system have been well developed. Meanwhile the natural convection in a vertical annulus pipe is one of the important mechanisms of heat transfer and is found at the TRIGA research reactor, the new generation nuclear power plants and other energy conversion devices. On the other hand, the heat transfer characteristics of nano fluids in a vertical annulus pipe has not been known. Therefore, it is important to do research continuously to analyze the heat transfer nano fluids in a vertical annulus pipe. This study has carried out numerical analysis by using computer code of CFD (computational of fluids dynamic) on natural convection heat transfer characteristics of nano fluids flow of Al_2O_3-water 2 % volume in the vertical annulus pipe. The results showed an increase in heat transfer performance (Nusselt numbers - NU) by 20.5 % - 35 %. In natural convection mode with Rayleigh numbers 2.471 e"+"0"9 ≤ Ra ≤ 1.955 e"+"1"3 obtained empirical correlations for water is N_U = 1.065 (R_a(D_H/x))"0"."1"7"9 and empirical correlations for Al_2O_3-water nano fluids is N_U = 14.869 (R_a(D_H/x))"0"."1"1"5.(author)

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

    International Nuclear Information System (INIS)

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

    2003-01-01

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

  8. Numerical investigation of a spatially developing turbulent natural convection boundary layer along a vertical heated plate

    International Nuclear Information System (INIS)

    Nakao, Keisuke; Hattori, Yasuo; Suto, Hitoshi

    2017-01-01

    Highlights: • A large-eddy simulation of a spatially developing natural convection boundary layer is conducted. • First- and second-order moments of the heat and momentum showed a reasonable agreement with past experiments. • Coherent structure of turbulent vortex inherent in this boundary layer is discussed. - Abstract: Large-eddy simulation (LES) on a spatially developing natural convection boundary layer along a vertical heated plate was conducted. The heat transfer rate, friction velocity, mean velocity and temperature, and second-order turbulent properties both in the wall-normal and the stream-wise direction showed reasonable agreement with the findings of past experiments. The spectrum of velocity and temperature fluctuation showed a -2/3-power decay slope and -2-power decay slope respectively. Quadrant analysis revealed the inclination on Q1 and Q3 in the Reynolds stress and turbulent heat flux, changing their contribution along the distance from the plate surface. Following the convention, we defined the threshold region where the stream-wise mean velocity takes local maximum, the inner layer which is closer to the plate than the threshold region, the outer layer which is farther to the plate than the threshold region. The space correlation of stream-wise velocity tilted the head toward the wall in the propagating direction in the outer layer; on the other hand, the correlated motion had little inclination in the threshold region. The time history of the second invariant of gradient tensor Q revealed that the vortex strength oscillates both in the inner and the outer layers in between the laminar and the transition region. In the turbulent region, the vortex was often dominant in the outer layer. Instantaneous three-dimensional visualization of Q revealed the existence of high-speed fluid parcels associated with arch-shape vortices. These results were considered as an intrinsic structure in the outer layer, which is symmetrical to the structure of

  9. Topology Optimisation for Coupled Convection Problems

    DEFF Research Database (Denmark)

    Alexandersen, Joe; Andreasen, Casper Schousboe; Aage, Niels

    stabilised finite elements implemented in a parallel multiphysics analysis and optimisation framework DFEM [1], developed and maintained in house. Focus is put on control of the temperature field within the solid structure and the problems can therefore be seen as conjugate heat transfer problems, where heat...... conduction governs in the solid parts of the design domain and couples to convection-dominated heat transfer to a surrounding fluid. Both loosely coupled and tightly coupled problems are considered. The loosely coupled problems are convection-diffusion problems, based on an advective velocity field from...

  10. Investigation of thermo-fluid behavior of mixed convection heat transfer of different dimples-protrusions wall patterns to heat transfer enhancement

    Science.gov (United States)

    Sobhani, M.; Behzadmehr, A.

    2018-05-01

    This study is a numerical investigation of the effect of improving heat transfer namely, modified rough (dimples and protrusions) surfaces on the mixed convective heat transfer of a turbulent flow in a horizontal tube. The effects of different dimples-protrusions arrangements on the improving the thermal performance of a rough tube are investigated at various Richardson numbers. Three dimensional governing equations are discretized by the finite-volume technique. Based on the obtained results the dimples-protrusions arrangements are modified to find a suitable configuration for which heat transfer coefficient and pressure drop to be balanced. Modified dimples-protrusions arrangements that shows higher performance is presented. Its average thermal performance 18% and 11% is higher than the other arrangements. In addition, the results show that roughening a smooth tube is more effective at the higher Richardson number.

  11. Mixed convection and heat generation/absorption aspects in MHD flow of tangent-hyperbolic nanoliquid with Newtonian heat/mass transfer

    Science.gov (United States)

    Qayyum, Sajid; Hayat, Tasawar; Shehzad, Sabir Ali; Alsaedi, Ahmed

    2018-03-01

    This article concentrates on the magnetohydrodynamic (MHD) stagnation point flow of tangent hyperbolic nanofluid in the presence of buoyancy forces. Flow analysis caused due to stretching surface. Characteristics of heat transfer are examined under the influence of thermal radiation and heat generation/absorption. Newtonian conditions for heat and mass transfer are employed. Nanofluid model includes Brownian motion and thermophoresis. The governing nonlinear partial differential systems of the problem are transformed into a systems of nonlinear ordinary differential equations through appropriate variables. Impact of embedded parameters on the velocity, temperature and nanoparticle concentration fields are presented graphically. Numerical computations are made to obtain the values of skin friction coefficient, local Nusselt and Sherwood numbers. It is concluded that velocity field enhances in the frame of mixed convection parameter while reverse situation is observed due to power law index. Effect of Brownian motion parameter on the temperature and heat transfer rate is quite reverse. Moreover impact of solutal conjugate parameter on the concentration and local Sherwood number is quite similar.

  12. Passive decay heat removal by natural air convection after severe accidents

    Energy Technology Data Exchange (ETDEWEB)

    Erbacher, F.J.; Neitzel, H.J. [Forschungszentrum Karlsruhe Institut fur Angewandte Thermo- und Fluiddynamik, Karlsruhe (Germany); Cheng, X. [Technische Universitaet Karlsruhe Institut fur Stroemungslehre und Stroemungsmaschinen, Karlsruhe (Germany)

    1995-09-01

    The composite containment proposed by the Research Center Karlsruhe and the Technical University Karlsruhe is to cope with severe accidents. It pursues the goal to restrict the consequences of core meltdown accidents to the reactor plant. One essential of this new containment concept is its potential to remove the decay heat by natural air convection and thermal radiation in a passive way. To investigate the coolability of such a passive cooling system and the physical phenomena involved, experimental investigations are carried out at the PASCO test facility. Additionally, numerical calculations are performed by using different codes. A satisfying agreement between experimental data and numerical results is obtained.

  13. Heat exchangers

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt, E L; Eisenmann, G; Hahne, E [Stuttgart Univ. (TH) (F.R. Germany). Inst. fuer Thermodynamik und Waermetechnik

    1976-04-01

    A survey is presented on publications on design, heat transfer, form factors, free convection, evaporation processes, cooling towers, condensation, annular gap, cross-flowed cylinders, axial flow through a bundle of tubes, roughnesses, convective heat transfer, loss of pressure, radiative heat transfer, finned surfaces, spiral heat exchangers, curved pipes, regeneraters, heat pipes, heat carriers, scaling, heat recovery systems, materials selection, strength calculation, control, instabilities, automation of circuits, operational problems and optimization.

  14. Maxwell-Cattaneo Heat Convection and Thermal Stresses Responses of a Semi-Infinite Medium to High-Speed Laser Heating due to High Speed Laser Heating

    Directory of Open Access Journals (Sweden)

    Abdallah I. A.

    2009-07-01

    Full Text Available Based on Maxwell-Cattaneo convection equation, the thermoelasticity problem is in- vestigated in this paper. The analytic solution of a boundary value problem for a semi- infinite medium with traction free surface heated by a high-speed laser-pulses have Dirac temporal profile is solved. The temperature, the displacement and the stresses distributions are obtained analytically using the Laplace transformation, and discussed at small time duration of the laser pulses. A numerical study for Cu as a target is performed. The results are presented graphically. The obtained results indicate that the small time duration of the laser pulses has no e ect on the finite velocity of the heat con- ductivity, but the behavior of the stress and the displacement distribution are affected due to the pulsed heating process and due to the structure of the governing equations.

  15. Numerical analysis of natural convection and radiation heat transfer from various shaped thin fin-arrays placed on a horizontal plate-a conjugate analysis

    International Nuclear Information System (INIS)

    Dogan, M.; Sivrioglu, Mecit; Yılmaz, Onder

    2014-01-01

    Highlights: • Optimum fin shape is determined for natural convection and radiation heat transfer. • Fin array with the optimum shape has a much greater average heat transfer coefficient. • The most important factors affecting the heat transfer coefficient are determined. - Abstract: Steady state natural convection and radiation heat transfer from various shaped thin fin-arrays on a horizontal base plate has been numerically investigated. A conjugate analysis has been carried out in which the conservation equations of mass, momentum and energy for the fluid in the two fin enclosure are solved together with the heat conduction equation in the fin and the base plate. Heat transfer by radiation is also considered in analysis. The heat transfer coefficient has been determined for each of the fin array considered in the present study at the same base and the same total area. The results of the analysis show that there are some important geometrical factors affecting the design of fin arrays. Taking into consideration these factors, an optimum fin shape that yields the highest average heat transfer coefficient has been determined

  16. Validation of Numerical Schemes in a Thermal-Hydraulic Analysis Code for a Natural Convection Heat Transfer of a Molten Pool

    International Nuclear Information System (INIS)

    Kim, Jong Tae; Ha, Kwang Soon; Kim, Hwan Yeol; Park, Rae Joon; Song, Jin Ho

    2010-01-01

    It is postulated that a fuel of a water-cooled nuclear reactor can be melted during a hypothetical severe accident. There are two strategies for cooling the molten corium, which are in-vessel corium cooling and exvessel corium cooling. They can be chosen depending on cooling characteristics of the reactor. The coolability of the molten pool is determined by comparing the thermal load from the pool and the maximum heat flux removable by cooling mechanism such as radiative or boiling heat transfer on the pool boundaries. In order to evaluate the molten pool coolability, it is important to correctly expect the thermal load by a natural convection heat transfer of the corium pool. Many correlations have been developed by conducting experiments for the natural convection of a pool. The main parameters of the heat transfer by the natural convection are Rayleigh (Ra) number, Prandtl (Pr) number and the geometry of the pool. Sometimes, the use of the correlations for the evaluation of the thermal load from the molten pool is limited by a high Ra number of the pool and its different shape from the existing correlations. Computational fluid dynamics (CFD) has been used for the analysis of the heat transfer by a natural convection. In principle, CFD is applicable to the corium pool analysis. But unfortunately, some difficulties are encountered during the analysis, which are from numerical and physical instabilities. The physical instability is from turbulence fluctuation and inverted thermal layer near the upper surface of the volumetric-heated molten pool with a high Ra number. In order to resolve turbulent natural convection, buoyancy-modified two-equation turbulence models such as a k-e or k-w model with time-averaged Navier- Stokes equations are commonly used. Because an unsteadiness of a natural convection becomes nontrivial in a high Ra number pool, it is very difficult to get accurate heat flux on the pool surface with the time averaged turbulence model. Recently

  17. A Numerical Study of Natural Convection Heat Transfer in Fin Ribbed Radiator

    Directory of Open Access Journals (Sweden)

    Hua-Shu Dou

    2015-01-01

    Full Text Available This paper numerically investigates the thermal flow and heat transfer by natural convection in a cavity fixed with a fin array. The computational domain consists of both solid (copper and fluid (air areas. The finite volume method and the SIMPLE scheme are used to simulate the steady flow in the domain. Based on the numerical results, the energy gradient function K of the energy gradient theory is calculated. It is observed from contours of the temperature and energy gradient function that the position where thermal instability takes place correlates well with the region of large K values, which demonstrates that the energy gradient method reveals the physical mechanism of the flow instability. Furthermore, the effects of the fin height, the fin number, and the fin shape on the heat transfer rate are also investigated. It is found that the thermal performance of the fin array is determined by the combined effect of the fin space and fin height. It is also observed that the effect of fin shape on heat transfer is insignificant.

  18. Direct numerical simulation and modeling of turbulent natural convection in a vertical differentially heated slot; Simulation numerique directe et modelisation de la convection naturelle turbulente dans un canal differentiellement chauffe

    Energy Technology Data Exchange (ETDEWEB)

    Boudjemadi, R.

    1996-03-01

    The main objectives of this thesis are the direct numerical simulation of natural convection in a vertical differentially heated slot and the improvements of second-order turbulence modelling. A three-dimensional direct numerical simulation code has been developed in order to gain a better understanding of turbulence properties in natural convection flows. This code has been validated in several physical configurations: non-stratified natural convection flows (conduction solution), stratified natural convection flows (double boundary layer solution), transitional and turbulent Poiseuille flows. For the conduction solution, the turbulent regime was reached at a Rayleigh number of 1*10{sup 5} and 5.4*10{sup 5}. A detailed analysis of these results has revealed the principal qualities of the available models but has also pointed our their shortcomings. This data base has been used in order to improve the triple correlations transport models and to select the turbulent time scales suitable for such flows. (author). 122 refs., figs., tabs., 4 appends.

  19. Study of heat removal by natural convection from the internal core catcher in PFBR using water model experiments

    International Nuclear Information System (INIS)

    Jasmin Sudha, A.; Punitha, G.; Das, S.K.; Lydia, G.; Murthy, S.S.; Malarvizhi, B.; Harvey, J.; Kannan, S.E.

    2005-01-01

    Full text of publication follows: In the event of a core meltdown accident in a Fast Breeder Reactor, the molten core material settling on the bottom of the main vessel can endanger the structural integrity of the main vessel. In the design of Prototype Fast Breeder Reactor in India, the construction of which is about to commence, a core catcher is provided as the internal core retention device to collect and retain the core debris in a coolable configuration. Heat transfer by natural convection above and below the core catcher plate, in the zone beneath the core support structure is evaluated from water mockup experiments in the 1:4 geometrically scaled setup. These studies were undertaken towards comparison of experimentally measured temperatures at different locations with the numerical results. The core catcher assembly consists of a core catcher plate, a heat shield plate and a chimney. Decay heat from the core debris is simulated by electrical heating of the heat shield plate. An opening is provided in the cover plate to reproduce the situation in the actual accident where the core debris would have breached a part of the core support structure. Experiments were carried out with different heat flux levels prevailing upon the heat shield plate. Temperature monitoring was done at more than 100 locations, distributed both on the solid components and in water. The temperature data was analysed to get the temperature profile at different steady state conditions. Flow visualisation was also carried out using water soluble dye to establish the direction of the convective currents. The captured images show that water flows through the slots provided in the top portion of the chimney in the upward direction as evidenced from the diffusion of dye injected inside the chimney. Both the temperature data and flow visualisation confirm mixing of water through the opening in the core support structure which indicates that natural convection is set up in that zone

  20. Experimental study of laminar mixed convection in a rod bundle with mixing vane spacer grids

    Energy Technology Data Exchange (ETDEWEB)

    Mohanta, Lokanath, E-mail: lxm971@psu.edu [Department of Mechanical and Nuclear Engineering, Pennsylvania State University, University Park, PA 16802 (United States); Cheung, Fan-Bill [Department of Mechanical and Nuclear Engineering, Pennsylvania State University, University Park, PA 16802 (United States); Bajorek, Stephen M.; Tien, Kirk; Hoxie, Chris L. [Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001 (United States)

    2017-02-15

    Highlights: • Investigated the heat transfer during mixed laminar convection in a rod bundle with linearly varying heat flux. • The Nusselt number increases downstream of the inlet with increasing Richardson number. • Developed an enhancement factor to account for the effects of mixed convection over the forced laminar heat transfer. - Abstract: Heat transfer by mixed convection in a rod bundle occurs when convection is affected by both the buoyancy and inertial forces. Mixed convection can be assumed when the Richardson number (Ri = Gr/Re{sup 2}) is on the order of unity, indicating that both forced and natural convection are important contributors to heat transfer. In the present study, data obtained from the Rod Bundle Heat Transfer (RBHT) facility was used to determine the heat transfer coefficient in the mixed convection regime, which was found to be significantly larger than those expected assuming purely forced convection based on the inlet flow rate. The inlet Reynolds (Re) number for the tests ranged from 500 to 1300, while the Grashof (Gr) number varied from 1.5 × 10{sup 5} to 3.8 × 10{sup 6} yielding 0.25 < Ri < 4.3. Using results from RBHT test along with the correlation from the FLECHT-SEASET test program for laminar forced convection, a new correlation ​is proposed for mixed convection in a rod bundle. The new correlation accounts for the enhancement of heat transfer relative to laminar forced convection.

  1. Mixed convection flow of couple stress nanofluid over oscillatory stretching sheet with heat absorption/generation effects

    Directory of Open Access Journals (Sweden)

    Sami Ullah Khan

    2018-03-01

    Full Text Available The aim of this article is to highlight the unsteady mixed convective couple stress nanoliquid flow passed through stretching surface. The flow is generated due to periodic oscillations of sheet. An appropriate set of dimensionless variables are used to reduce the independent variables in governing equations arising from mathematical modeling. An analytical solution has been computed by employing the technique of homotopy method. The outcomes of various sundry parameters like couple stress parameter, the ratio of angular velocity to stretching rate, thermophoresis parameter, Hartmann number, Prandtl number, heat source/sink parameter, Schmidt number described graphically and in tabular form. It is observed that the velocity profile increases by increasing mixed convection parameter and concentration buoyancy parameter. The temperature enhances for larger values of Hartmann number and Brownian. The concentration profile increases by increasing thermophoresis parameter. Results show that wall shear stress increases by increasing couple stress parameter and ratio of oscillating frequency to stretching rate. Keywords: Oscillatory surface, Couple stress fluid, Nanoparticles, Heat absorption/generation

  2. Measuring Convective Mass Fluxes Over Tropical Oceans

    Science.gov (United States)

    Raymond, David

    2017-04-01

    Deep convection forms the upward branches of all large-scale circulations in the tropics. Understanding what controls the form and intensity of vertical convective mass fluxes is thus key to understanding tropical weather and climate. These mass fluxes and the corresponding conditions supporting them have been measured by recent field programs (TPARC/TCS08, PREDICT, HS3) in tropical disturbances considered to be possible tropical storm precursors. In reality, this encompasses most strong convection in the tropics. The measurements were made with arrays of dropsondes deployed from high altitude. In some cases Doppler radar provided additional measurements. The results are in some ways surprising. Three factors were found to control the mass flux profiles, the strength of total surface heat fluxes, the column-integrated relative humidity, and the low to mid-tropospheric moist convective instability. The first two act as expected, with larger heat fluxes and higher humidity producing more precipitation and stronger lower tropospheric mass fluxes. However, unexpectedly, smaller (but still positive) convective instability produces more precipitation as well as more bottom-heavy convective mass flux profiles. Furthermore, the column humidity and the convective instability are anti-correlated, at least in the presence of strong convection. On spatial scales of a few hundred kilometers, the virtual temperature structure appears to be in dynamic balance with the pattern of potential vorticity. Since potential vorticity typically evolves on longer time scales than convection, the potential vorticity pattern plus the surface heat fluxes then become the immediate controlling factors for average convective properties. All measurements so far have taken place in regions with relatively flat sea surface temperature (SST) distributions. We are currently seeking funding for a measurement program in the tropical east Pacific, a region that exhibits strong SST gradients and

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

    Science.gov (United States)

    Steyn, Gideon; Vermeulen, Christiaan

    2018-05-01

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

  4. Convective heating of the inner core of red giants prior to the peak of the core helium flash

    International Nuclear Information System (INIS)

    Cole, P.W.; Demarque, P.; Deupree, R.G.

    1985-01-01

    The effects of convective overshooting across the temperature inversion in the cores of red giants are investigated from the onset of the core convection zone to the peak of the core helium flash using a model for overshooting in stellar evolution, based on two-dimensional and three-dimensional hydrodynamic simulations of the core helium flash. A major effect of the overshooting is the substantial heating of the material interior to the temperature inversion, producing a smoother temperature profile. This interior heating is thus unimportant until approximately 1 week preceding the time of maximum temperature, but then produces temperature changes on a time scale short with respect to the evolution time scale. Interior heating (1) alters the standard relation of the maximum temperature and the density at the point of maximum temperature, (2) makes the maximum temperature occur at a smaller mass fraction, (3) causes the time of maximum temperature to occur hundreds of years earlier in the red giant evolution, and (4) redistributes the mass from the location of maximum temperature. Since the degree of degeneracy is known to affect the violence of the flash in the hydrodynamic phase, internal heating may play an important role in determining the subsequent evolution of the core

  5. Influence of high range of mass transfer coefficient and convection heat transfer on direct contact membrane distillation performance

    KAUST Repository

    Lee, Jung Gil; Jeong, Sanghyun; Alsaadi, Ahmad Salem; Ghaffour, NorEddine

    2017-01-01

    (>2.1×10−6kg/m2sPa: membranes under development) were simulated using an experimentally validated model at different ranges of convection heat transfer by varying the inlet flow rates and spacer enhancement factor. The effect of mass transfer

  6. Heat Transfer and Mass Diffusion in Nanofluids over a Moving Permeable Convective Surface

    Directory of Open Access Journals (Sweden)

    Muhammad Qasim

    2013-01-01

    Full Text Available Heat transfer and mass diffusion in nanofluid over a permeable moving surface are investigated. The surface exhibits convective boundary conditions and constant mass diffusion. Effects of Brownian motion and thermophoresis are considered. The resulting partial differential equations are reduced into coupled nonlinear ordinary differential equations using suitable transformations. Shooting technique is implemented for the numerical solution. Velocity, temperature, and concentration profiles are analyzed for different key parameters entering into the problem. Performed comparative study shows an excellent agreement with the previous analysis.

  7. Transient natural convection in an internally heated fluid layer. Topical report, June 1975--June 1976

    International Nuclear Information System (INIS)

    Kulacki, F.A.; Emara, A.A.

    1976-06-01

    An experimental study of the transient response of a horizontal fluid layer subjected to a step change in internal energy generation has been conducted to determine the time scales for the development and decay of natural convection driven solely by the internal heat release. The layer is bounded from above by a rigid, constant temperature surface and from below by a rigid, insulated surface. Two types of unsteady convection processes are considered. In the first, the layer is brought to a motionless, isothermal state, and internal energy generation is suddenly started. In the second, steady natural convection is the initial state, and internal energy generation is suddenly stopped. For both cases, the time required for the development of the final steady state is determined by measuring the temperature response of the fluid with a small thermocouple probe. The time required for the development of the maximum temperature difference in the layer with internal generation and the time required for the complete decay of the maximum temperature difference of steady convection at a given Rayleigh number when internal energy generation is suddenly stopped are correlated with the Rayleigh number in equations which will find general application in PAHR problems in nuclear power reactors and particularly in the analysis of the small-time thermal response of in-vessel and ex-vessel molten core retention devices

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2003-05-01

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

  9. Local heat transfer estimation in microchannels during convective boiling under microgravity conditions: 3D inverse heat conduction problem using BEM techniques

    Science.gov (United States)

    Luciani, S.; LeNiliot, C.

    2008-11-01

    Two-phase and boiling flow instabilities are complex, due to phase change and the existence of several interfaces. To fully understand the high heat transfer potential of boiling flows in microscale's geometry, it is vital to quantify these transfers. To perform this task, an experimental device has been designed to observe flow patterns. Analysis is made up by using an inverse method which allows us to estimate the local heat transfers while boiling occurs inside a microchannel. In our configuration, the direct measurement would impair the accuracy of the searched heat transfer coefficient because thermocouples implanted on the surface minichannels would disturb the established flow. In this communication, we are solving a 3D IHCP which consists in estimating using experimental data measurements the surface temperature and the surface heat flux in a minichannel during convective boiling under several gravity levels (g, 1g, 1.8g). The considered IHCP is formulated as a mathematical optimization problem and solved using the boundary element method (BEM).

  10. Hydromagnetic transport phenomena from a stretching or shrinking nonlinear nanomaterial sheet with Navier slip and convective heating: A model for bio-nano-materials processing

    Energy Technology Data Exchange (ETDEWEB)

    Uddin, M.J., E-mail: jashim_74@yahoo.com [Department of Mathematics, American International University-Bangladesh, Banani Dhaka 1213 (Bangladesh); Bég, O. Anwar [Gort Engovation Research (Propulsion/Biomechanics), Gabriel' s Wing House, 15 Southmere Ave., Bradford, BD7 3NU England (United Kingdom); Amin, N. [Department of Mathematical Sciences, Faculty of Science, Universiti Teknologi Malaysia, 81310 UTM Johor (Malaysia)

    2014-11-15

    Steady two-dimensional magnetohydrodynamic laminar free convective boundary layer slip flow of an electrically conducting Newtonian nanofluid from a translating stretching/shrinking sheet in a quiescent fluid is studied. A convective heating boundary condition is incorporated. The transport equations along with the boundary conditions are first converted into dimensionless form and following the implementation of a linear group of transformations, the similarity governing equations are developed. The transformed equations are solved numerically using the Runge–Kutta–Fehlberg fourth fifth order method from Maple. Validation of the Maple solutions is achieved with previous non-magnetic published results. The effects of the emerging thermophysical parameters; namely, stretching/shrinking, velocity slip, magnetic field, convective heat transfer and buoyancy ratio parameters, on the dimensionless velocity, temperature and concentration (nanoparticle fraction) are depicted graphically and interpreted at length. It is found that velocity increases whilst temperature and concentration reduce with the velocity slip. Magnetic field causes to reduce velocity and enhances temperature and concentration. Velocity, temperature as well as concentration rises with convective heating parameter. The study is relevant to the synthesis of bio-magnetic nanofluids of potential interest in wound treatments, skin repair and smart coatings for biological devices. - Highlights: • This paper analyses MHD slip flow of nofluid with convective boundary conditions. • Group method is used to transform governing equations into similarity equations. • The Runge–Kutta–Fehlberg method is used for numerical computations. • The study is relevant to synthesis of bio-magnetic nanofluids.

  11. An Experimental Study on Rayleigh-Benard Natural Convection

    International Nuclear Information System (INIS)

    Moon, Je Young; Chung, Bum Jin

    2012-01-01

    Core melt in a severe accident condition, forms a molten pool in the reactor vessel lower head. The molten pool is divided by a metallic pool (top) and an oxide pool (bottom) by the density difference. Due to the decay heat generated in oxide pool, Rayleigh- Benard natural convection heated from below and cooled from above occurs in the metallic pool. Experiments were performed to investigate Rayleigh- Benard natural convection as a preparatory study before an in-depth severe accident study. The natural convection heat transfers were measured varying the plate separation distance and the area of plate with and without the side wall. Using the analogy concept, heat transfer experiments were replaced by mass transfer experiments. A cupric acid.copper sulfate (H 2 SO 4 -CuSO 4 ) electroplating system was adopted as the mass transfer system and the electric currents were measured rather than the heat

  12. Enhancing Oxidative Stability of Sunflower Oil during Convective and Microwave Heating Using Grape Seed Extract

    Directory of Open Access Journals (Sweden)

    Mariana-Atena Poiana

    2012-07-01

    Full Text Available This study was performed to investigate the effectiveness of grape seed extract (GSE compared to butylated hydroxytoluene (BHT on retarding lipid oxidation of sunflower oil subjected to convection and microwave heating up to 240 min under simulated frying conditions. The progress of lipid oxidation was assessed in terms of peroxide value (PV, p-anisidine value (p-AV, conjugated dienes and trienes (CD, CT, inhibition of oil oxidation (IO and TOTOX value. In addition, total phenolic content (TP was evaluated in samples before and after heating in order to assess the changes in these compounds relative to the extent of lipid oxidation. The results of this study highlight that GSE showed a significantly inhibitory effect on lipid oxidation during both treatments, although to a different extent. This ability was dose-dependent; therefore, the extent of lipid oxidation was inversely related to GSE level. Convective heating, respective microwave exposure for 240 min of samples supplemented by GSE to a level of 1000 ppm, resulted in significant decreases of investigated indices relative to the control values as follows: PV (48%; 30%, p-AV (29%; 40%, CD (45%; 30%, CT (41%; 36%, TOTOX (35%; 37%. GSE to a level of 600–800 ppm inhibited the lipid oxidation in a similar manner to BHT. These results suggested that GSE can be used as a potential natural extract for improving oxidative stability of sunflower oil during thermal applications.

  13. Combined effect of thermal dispersion and variable viscosity of non-darcy convection heat transfer in a fluidsaturated porous medium

    KAUST Repository

    El-Amin, Mohamed; Salama, Amgad; El-Amin, Ammaarah A.; Gorla, Rama Subba Reddy

    2013-01-01

    In this paper, the effects of thermal dispersion and variable viscosity on the non-Darcy free, mixed, and forced convection heat transfer along a vertical flat plate embedded in a fluid-saturated porous medium are investigated. Forchheimer extension

  14. Experimental investigation of a solar dryer with natural convective heat flow

    Energy Technology Data Exchange (ETDEWEB)

    Gbaha, P.; Yobouet Andoh, H.; Kouassi Saraka, J. [Laboratoire d' Energies d' Energies Nouvelles et Renouvelables, Institut National Polytechnique Felix Houphoeuet-Boigny, B.P. 1526 Yamoussoukro (Ivory Coast); Kamenan Koua, B.; Toure, S. [Laboratoire d' Energie Solaire, Universite de Cocody, 22 B.P.: 582, Abidjan 22 (Ivory Coast)

    2007-09-15

    A direct type natural convection solar dryer is designed. It is constructed in local materials (wood, blades of glass, metals) then tested experimentally in foodstuffs drying (cassava, bananas, mango). It is about an experimental approach which consists in analyzing the behavior of the dryer. The study relates mainly kinetics and establishment of drying heat balances. The influence of significant parameters governing heat and mass transfers, such as solar incident radiation, drying air mass flow and effectiveness, is analyzed in order to evaluate its thermal performances. Experimental data can be represented by empirical correlations of the form M(t)=M{sub i}exp(-kt) for representation of drying process. The resolution of these drying equations makes-possible to predict total drying time of each product. Moreover, this drying process allows to reduce the moisture content of cassava and sweet banana approximately to 80% in 19 and 22 h, respectively to reach the safety threshold value of 13%. This value permits the conservation of these products about one year without deterioration. The determination of parameters, like ambient temperature, drying chamber temperature, drying air mass flow and incident heat fluxes, allow to predict the drying effectiveness for modeling and refining the dimensioning of the elaborate prototype. (author)

  15. Review of Mixed Convection Flow Regime Map of a Vertical pipe

    International Nuclear Information System (INIS)

    Chae, Myeong-Seon; Chung, Bum-Jin; Kang, Gyeong-Uk

    2015-01-01

    In a vertical pipe, the natural convective force due to buoyancy acts upward only, but forced convective force can be either upward or downward. This determines buoyancy-aided and buoyancy-opposed flows depending on the direction of forced flow with respect to the buoyancy forces. Furthermore, depending on the exchange mechanism, the flow condition is classified into laminar and turbulent. In laminar mixed convection, buoyancy-aided flow presents enhanced heat transfer compared to the pure forced convection and buoyancy-opposed flow shows impaired heat transfer as the flow velocity affected by the buoyancy forces. However, in turbulent mixed convection, buoyancy-aided flow shows an impairment of the heat transfer rate for small buoyancy, and a gradational enhancement for large buoyancy. In this study, the existing flow regime map on mixed convection in a vertical pipe was reviewed through an analysis of literatures. Using the investigated data and heat transfer correlations, the flow regime map was reconstructed independently, and compared with the existing one. This study reviewed the limitations of the classical mixed convection flow regime map. Using the existing data and heat transfer correlations by Martinelli and Boelter and Watzinger and Johnson, the flow regime map was reconstructed independently. The results revealed that the existing map used the data selectively among the experimental and theoretical results, and a detailed description for lines forming mixed convection and transition regime were not given. And the information about uncertainty analysis and the evidentiary data were given insufficiently. The flow regime map and investigator commonly used the diameter as the characteristic length for both Re and Gr in place of the height of the heated wall, though the buoyancy forces are proportional to the third power of the height of heated wall

  16. Radiation effects on the mixed convection flow induced by an inclined stretching cylinder with non-uniform heat source/sink.

    Science.gov (United States)

    Hayat, Tasawar; Qayyum, Sajid; Alsaedi, Ahmed; Asghar, Saleem

    2017-01-01

    This study investigates the mixed convection flow of Jeffrey liquid by an impermeable inclined stretching cylinder. Thermal radiation and non-uniform heat source/sink are considered. The convective boundary conditions at surface are imposed. Nonlinear expressions of momentum, energy and concentration are transformed into dimensionless systems. Convergent homotopic solutions of the governing systems are worked out by employing homotopic procedure. Impact of physical variables on the velocity, temperature and concentration distributions are sketched and discussed. Numerical computations for skin friction coefficient, local Nusselt and Sherwood numbers are carried out. It is concluded that velocity field enhances for Deborah number while reverse situation is observed regarding ratio of relaxation to retardation times. Temperature and heat transfer rate are enhanced via larger thermal Biot number. Effect of Schmidt number on the concentration and local Sherwood number is quite reverse.

  17. The Earth's mantle in a microwave oven: thermal convection driven by a heterogeneous distribution of heat sources

    Science.gov (United States)

    Fourel, Loïc; Limare, Angela; Jaupart, Claude; Surducan, Emanoil; Farnetani, Cinzia G.; Kaminski, Edouard C.; Neamtu, Camelia; Surducan, Vasile

    2017-08-01

    Convective motions in silicate planets are largely driven by internal heat sources and secular cooling. The exact amount and distribution of heat sources in the Earth are poorly constrained and the latter is likely to change with time due to mixing and to the deformation of boundaries that separate different reservoirs. To improve our understanding of planetary-scale convection in these conditions, we have designed a new laboratory setup allowing a large range of heat source distributions. We illustrate the potential of our new technique with a study of an initially stratified fluid involving two layers with different physical properties and internal heat production rates. A modified microwave oven is used to generate a uniform radiation propagating through the fluids. Experimental fluids are solutions of hydroxyethyl cellulose and salt in water, such that salt increases both the density and the volumetric heating rate. We determine temperature and composition fields in 3D with non-invasive techniques. Two fluorescent dyes are used to determine temperature. A Nd:YAG planar laser beam excites fluorescence, and an optical system, involving a beam splitter and a set of colour filters, captures the fluorescence intensity distribution on two separate spectral bands. The ratio between the two intensities provides an instantaneous determination of temperature with an uncertainty of 5% (typically 1K). We quantify mixing processes by precisely tracking the interfaces separating the two fluids. These novel techniques allow new insights on the generation, morphology and evolution of large-scale heterogeneities in the Earth's lower mantle.

  18. Mixed convection heat transfer between a steam / non-condensable gas mixture and an inclined finned tube bundle

    Energy Technology Data Exchange (ETDEWEB)

    Cachard, F. de; Lomperski, S.; Monauni, G.R. [Paul Scherrer Inst. (PSI), Villigen (Switzerland). Lab. for Thermal-Hydraulics

    1999-07-01

    An experimental and analytical program was performed at PSI to study the performance of a finned-tube condenser in the presence of non-condensable gases at low gas mass fluxes. The model developed for this application includes mixed convection heat transfer between the vapour/non-condensable mixture and the finned-tubes, heat conduction through the fins and tubes, and evaporative heat transfer inside the tubes. The finned-tubes condenser model has been assessed against data obtained at the PSI LINX facility with two test condensers. For the 62 LINX experiments performed, the model predictions are very good, i.e., less than 10 % standard deviation between experimental and predicted results. (authors)

  19. Natural convection along a heated vertical plate immersed in a nonlinearly stratified medium: application to liquefied gas storage

    Science.gov (United States)

    Forestier, M.; Haldenwang, P.

    We consider free convection driven by a heated vertical plate immersed in a nonlinearly stratified medium. The plate supplies a uniform horizontal heat flux to a fluid, the bulk of which has a stable stratification, characterized by a non-uniform vertical temperature gradient. This gradient is assumed to have a typical length scale of variation, denoted Z0, while 0, and the physical properties of the medium.We then apply the new theory to the natural convection affecting the vapour phase in a liquefied pure gas tank (e.g. the cryogenic storage of hydrogen). It is assumed that the cylindrical storage tank is subject to a constant uniform heat flux on its lateral and top walls. We are interested in the vapour motion above a residual layer of liquid in equilibrium with the vapour. High-precision axisymmetric numerical computations show that the flow remains steady for a large range of parameters, and that a bulk stratification characterized by a quadratic temperature profile is undoubtedly present. The application of the theory permits a comparison of the numerical and analytic results, showing that the theory satisfactorily predicts the primary dynamical and thermal properties of the storage tank.

  20. Marangoni convection radiative flow of dusty nanoliquid with exponential space dependent heat source

    Directory of Open Access Journals (Sweden)

    Basavarajappa Mahanthesh

    2017-12-01

    Full Text Available The flow of liquids submerged with nanoparticles is of significance to industrial applications, specifically in nuclear reactors and the cooling of nuclear systems to improve energy efficiency. The application of nanofluids in water-cooled nuclear systems can result in a significant improvement of their economic performance and/or safety margins. Therefore, in this paper, Marangoni thermal convective boundary layer dusty nanoliquid flow across a flat surface in the presence of solar radiation is studied. A two phase dusty liquid model is considered. Unlike classical temperature-dependent heat source effects, an exponential space-dependent heat source aspect is considered. Stretching variables are utilized to transform the prevailing partial differential system into a nonlinear ordinary differential system, which is then solved numerically via the Runge-Kutta-Fehlberg approach coupled with a shooting technique. The roles of physical parameters are focused in momentum and heat transport distributions. Graphical illustrations are also used to consider local and average Nusselt numbers. We examined the results under both linear and quadratic variation of the surface temperature. Our simulations established that the impact of Marangoni flow is useful for an enhancement of the heat transfer rate.

  1. Thermal-hydraulic posttest analysis for the ANL/MCTF 3600 model heat-exchanger water test under mixed convection

    International Nuclear Information System (INIS)

    Yang, C.I.; Sha, W.T.; Kasza, K.E.

    1982-01-01

    As a result of the uncertainties in the understanding of the influence of thermal-buoyancy effects on the flow and heat transfer in Liquid Metal Fast Breeder Reactor heat exchangers and steam generators under off-normal operating conditions, an extensive experimental program is being conducted at Argonne National Laboratory to eliminate these uncertainties. Concurrently, a parallel analytical effort is also being pursued to develop a three-dimensional transient computer code (COMMIX-IHX) to study and predict heat exchanger performance under mixed, forced, and free convection conditions. This paper presents computational results from a heat exchanger simulation and compares them with the results from a test case exhibiting strong thermal buoyancy effects. Favorable agreement between experiment and code prediction is obtained

  2. Correlation development of natural convection heat transfer in consideration of aspect ratio change and coolant boiling

    International Nuclear Information System (INIS)

    Park, L. J.; Cho, Y. L.; Kang, K. H.; Kim, S. B.; Kim, H. D.; Cho, J. S.; Jung, C. H.

    1999-01-01

    A new correlation on natural convection heat transfer with crust formation in the molten metal pool has been developed in consideration of coolant boiling effect and of aspect ratio change by an increase in crust thickness. Two test results of the convection cooling case, natural and forced convection cooling cases, and of the boiling case were used in the present study. The experimental results have shown that the Nusselt number of the case with boiling condition in the molten metal pool is greater than that of the case with non-boiling condition at the same Rayleigh number. Even though the Rayleigh number rapidly decreases due to an increase of the crust thickness, the Nusselt number does not rapidly decrease because of the aspect ratio effect. From the experimental results, the new correlation between the Nusselt number and Rayleigh number in the molten metal pool with the crust formation has been developed as Nu 0.051(Ra) 1/3 (AR) . 0 .2441 (Φ) 0.025 using Globe and Dropkin correlation

  3. CRUCIB: an axisymmetric convection code

    International Nuclear Information System (INIS)

    Bertram, L.A.

    1975-03-01

    The CRUCIB code was written in support of an experimental program aimed at measurement of thermal diffusivities of refractory liquids. Precise values of diffusivity are necessary to realistic analysis of reactor safety problems, nuclear waste disposal procedures, and fundamental metal forming processes. The code calculates the axisymmetric transient convective motions produced in a right circular cylindrical crucible, which is surface heated by an annular heat pulse. Emphasis of this report is placed on the input-output options of the CRUCIB code, which are tailored to assess the importance of the convective heat transfer in determining the surface temperature distribution. Use is limited to Prandtl numbers less than unity; larger values can be accommodated by replacement of a single block of the code, if desired. (U.S.)

  4. The effect of inclined vertical slats on natural convective heat transfer from an isothermal heated vertical plate

    International Nuclear Information System (INIS)

    Oosthuizen, P.H.; Sun, L.; Naylor, D.

    2002-01-01

    Natural convective heat transfer from a wide heated vertical isothermal plate with adiabatic surfaces above and below the heated surface has been considered. There are a series of equally spaced vertical thin, flat adiabatic surfaces (termed 'slats') near the heated surface, these surfaces being, in general, inclined to the heated surface. The slats are pivoted about their center-point and thus as their angle is changed, the distance of the tip of the slat from the plate changes. The situation considered is an approximate model of a window with a vertical blind, the particular case where the window is hotter than the room air, i.e. where air-conditioning is being used, being considered. The flow has been assumed to be laminar and steady. Fluid properties have been assumed constant except for the density change with temperature that gives rise to the buoyancy forces, this being treated by means of the Biuniqueness type approximation. Although the flow is in general three-dimensional, the flow over each slat is assumed to be the same and attention can therefore be restricted to flow over a single slat by using repeating boundary conditions. The governing equations have been written in dimensionless form and the resulting dimensionless equations have been solved using a commercial finite-element package. The solution has the following parameters: (1) the Rayleigh number (2) the Prandtl number (3) the dimensionless distance of the slat center point (the pivot point) from the surface (4) the dimensionless slat size (5) the dimensionless slat spacing (6) the angle of inclination of the slats. Because of the application that motivated the study, results have only been obtained for a Prandtl number of 0.7. The effect of the other dimensionless variables on the mean dimensionless heat transfer rate from the heated surface has been examined. (author)

  5. Network Simulation solution of free convective flow from a vertical cone with combined effect of non- uniform surface heat flux and heat generation or absorption

    Science.gov (United States)

    Immanuel, Y.; Pullepu, Bapuji; Sambath, P.

    2018-04-01

    A two dimensional mathematical model is formulated for the transitive laminar free convective, incompressible viscous fluid flow over vertical cone with variable surface heat flux combined with the effects of heat generation and absorption is considered . using a powerful computational method based on thermoelectric analogy called Network Simulation Method (NSM0, the solutions of governing nondimensionl coupled, unsteady and nonlinear partial differential conservation equations of the flow that are obtained. The numerical technique is always stable and convergent which establish high efficiency and accuracy by employing network simulator computer code Pspice. The effects of velocity and temperature profiles have been analyzed for various factors, namely Prandtl number Pr, heat flux power law exponent n and heat generation/absorption parameter Δ are analyzed graphically.