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....
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.
Convective Heat Transfer for Ship Propulsion.
1982-04-01
RD-A124 Wi CONVECTIVE HEAT TRANSFER FOR SHIP PROPULSION (U) ARIZONA 112 UNIV TUCSON ENGINEERING EXPERIMENT STATION PARK ET AL. 01 APR 82 1248-9 N814...395 CONVECTIVE HEAT TRANSFER FOR SHIP PROPULSION Prepared for Office of Naval Research Code 431 Arlington, Virginia Prepared by J. S. Park, M. F...FOR SHIP PROPULSION By J. S. Park, M. F. Taylor and D. M. McEligot Aerospace and Mechanical Engineering Department University of Arizona Tucson
Convective heat transfer during dendritic growth
Glicksman, M. E.; Huang, S. C.
1979-01-01
Axial growth rate measurements were carried out at 17 levels of supercooling between 0.043 C and 2 C, a temperature range in which convection, instead of diffusion, becomes the controlling mechanism of heat transfer in the dentritic growth process. The growth velocity, normalized to that expected for pure diffusive heat transfer, displays a dependence on orientation. The ratio of the observed growth velocity to that for convection-free growth and the coefficients of supercooling are formulated. The dependence of normalized growth rate in supercooling is described for downward growing dendrites. These experimental correlations can be justified theoretically only to a limited extent.
Determination of the convective heat transfer coefficient
Spierings, D.; Bosman, F.; Peters, T.; Plasschaert, F.
1987-01-01
The value of the convective heat transfer coefficient (htc) is determined under different loading conditions by using a computer aided method. The thermal load has been applied mathematically as well as experimentally to the coronal surface of an axisymmetric tooth model. To verify the assumptions m
Free convection film flows and heat transfer
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.
Determination of the convective heat transfer coefficient
Spierings, D.; Bosman, F.; Peters, T.; Plasschaert, F.
1987-01-01
The value of the convective heat transfer coefficient (htc) is determined under different loading conditions by using a computer aided method. The thermal load has been applied mathematically as well as experimentally to the coronal surface of an axisymmetric tooth model. To verify the assumptions m
Forced Convection Heat Transfer in Circular Pipes
Tosun, Ismail
2007-01-01
One of the pitfalls of engineering education is to lose the physical insight of the problem while tackling the mathematical part. Forced convection heat transfer (the Graetz-Nusselt problem) certainly falls into this category. The equation of energy together with the equation of motion leads to a partial differential equation subject to various…
Natural convective heat transfer from square cylinder
Novomestský, Marcel; Smatanová, Helena; Kapjor, Andrej
2016-06-01
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
Convective heat transfer of nanofluids with correlations
Institute of Scientific and Technical Information of China (English)
Lazarus Godson Asirvatham; Balakrishnan Raja; Dhasan Mohan Lal; Somchai Wongwises
2011-01-01
To investigate the convective heat transfer of nanofluids,experiments were performed using silver-water nanofluids under laminar,transition and turbulent flow regimes in a horizontal 4.3 mm inner-diameter tube-in-tube counter-current heat transfer test section.The volume concentration of the nanoparticles varied from 0.3％ to 0.9％ in steps of 0.3％,and the effects of thermo-physical properties,inlet temperature,volume concentration,and mass flow rate on heat transfer coefficient were investigated.Experiments showed that the suspended nanoparticles remarkably increased the convective heat transfer coefficient,by as much as 28.7％ and 69.3％ for 0.3％ and 0.9％ of silver content,respectively.Based on the experimental results a correlation was developed to predict the Nusselt number of the silver-water nanofluid,with ±10％ agreement between experiments and prediction.
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.
Convective heat transfer and infrared thermography.
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.
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.
Heat flux sensors for infrared thermography in convective heat transfer.
Carlomagno, Giovanni Maria; de Luca, Luigi; Cardone, Gennaro; Astarita, Tommaso
2014-11-07
This paper reviews the most dependable heat flux sensors, which can be used with InfraRed (IR) thermography to measure convective heat transfer coefficient distributions, and some of their applications performed by the authors' research group at the University of Naples Federico II. After recalling the basic principles that make IR thermography work, the various heat flux sensors to be used with it are presented and discussed, describing their capability to investigate complex thermo-fluid-dynamic flows. Several applications to streams, which range from natural convection to hypersonic flows, are also described.
Heat Flux Sensors for Infrared Thermography in Convective Heat Transfer
Giovanni Maria Carlomagno; Luigi de Luca; Gennaro Cardone; Tommaso Astarita
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-dy...
Convective heat transfer measurement involving flow past stationary circular disks
Energy Technology Data Exchange (ETDEWEB)
Wedekind, G.L. (Oakland Univ., Rochester, MI (United States))
1989-11-01
Considerable empirical data exist in the literature for forced convection heat transfer involving external flow over a variety of geometries, and for various ranges of Reynolds number. This author is not aware of any published empirical data for forced convection heat transfer involving flow past a simple stationary circular disk, whose axis is perpendicular to the flow. Such is the purpose of this paper.
Measurement of the convective heat-transfer coefficient
Conti, Rosaria; Fiordilino, Emilio
2014-01-01
We propose an experiment for investigating how objects cool down toward the thermal equilibrium with its surrounding through convection. We describe the time dependence of the temperature difference of the cooling object and the environment with an exponential decay function. By measuring the thermal constant tau, we determine the convective heat-transfer coefficient, which is a characteristic constant of the convection system.
Laser Measurement Of Convective-Heat-Transfer Coefficient
Porro, A. Robert; Hingst, Warren R.; Chriss, Randall M.; Seablom, Kirk D.; Keith, Theo G., Jr.
1994-01-01
Coefficient of convective transfer of heat at spot on surface of wind-tunnel model computed from measurements acquired by developmental laser-induced-heat-flux technique. Enables non-intrusive measurements of convective-heat-transfer coefficients at many points across surfaces of models in complicated, three-dimensional, high-speed flows. Measurement spot scanned across surface of model. Apparatus includes argon-ion laser, attenuator/beam splitter electronic shutter infrared camera, and subsystem.
Forced convective heat transfer in curved diffusers
Rojas, J.; Whitelaw, J. H.; Yianneskis, M.
1987-01-01
Measurements of the velocity characteristics of the flows in two curved diffusers of rectangular cross section with C and S-shaped centerlines are presented and related to measurements of wall heat transfer coefficients along the heated flat walls of the ducts. The velocity results were obtained by laser-Doppler anemometry in a water tunnel and the heat transfer results by liquid crystal thermography in a wind tunnel. The thermographic technique allowed the rapid and inexpensive measurement of wall heat transfer coefficients along flat walls of arbitrary boundary shapes with an accuracy of about 5 percent. The results show that an increase in secondary flow velocities near the heated wall causes an increase in the local wall heat transfer coefficient, and quantify the variation for maximum secondary-flow velocities in a range from 1.5 to 17 percent of the bulk flow velocity.
Enhancement of laminar convective heat transfer using microparticle suspensions
Zhu, Jiu Yang; Tang, Shiyang; Yi, Pyshar; Baum, Thomas; Khoshmanesh, Khashayar; Ghorbani, Kamran
2016-04-01
This paper investigates the enhancement of convective heat transfer within a sub-millimetre diameter copper tube using Al2O3, Co3O4 and CuO microparticle suspensions. Experiments are conducted at different particle concentrations of 1.0, 2.0 and 5.0 wt% and at various flow rates ranging from 250 to 1000 µl/min. Both experimental measurements and numerical analyses are employed to obtain the convective heat transfer coefficient. The results indicate a significant enhancement in convective heat transfer coefficient due to the implementation of microparticle suspensions. For the case of Al2O3 microparticle suspension with 5.0 wt% concentration, a 20.3 % enhancement in convective heat transfer coefficient is obtained over deionised water. This is comparable to the case of Al2O3 nanofluid at the same concentration. Hence, there is a potential for the microparticle suspensions to be used for cooling of compact integrated systems.
Enhancement of laminar convective heat transfer using microparticle suspensions
Zhu, Jiu Yang; Tang, Shiyang; Yi, Pyshar; Baum, Thomas; Khoshmanesh, Khashayar; Ghorbani, Kamran
2017-01-01
This paper investigates the enhancement of convective heat transfer within a sub-millimetre diameter copper tube using Al2O3, Co3O4 and CuO microparticle suspensions. Experiments are conducted at different particle concentrations of 1.0, 2.0 and 5.0 wt% and at various flow rates ranging from 250 to 1000 µl/min. Both experimental measurements and numerical analyses are employed to obtain the convective heat transfer coefficient. The results indicate a significant enhancement in convective heat transfer coefficient due to the implementation of microparticle suspensions. For the case of Al2O3 microparticle suspension with 5.0 wt% concentration, a 20.3 % enhancement in convective heat transfer coefficient is obtained over deionised water. This is comparable to the case of Al2O3 nanofluid at the same concentration. Hence, there is a potential for the microparticle suspensions to be used for cooling of compact integrated systems.
Convective heat and mass transfer in rotating disk systems
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.
Directory of Open Access Journals (Sweden)
Nadia Potoceanu
2007-10-01
Full Text Available The paper presented the most aspects of convective circulate mode of heat transfer : heat transfer through the boundary layer formed at the surface of the heat generator; heat transfer in the heat carrier and heat transfer through the boundary layer formed at the heated surface
NANOFLUID PROPERTIES FOR FORCED CONVECTION HEAT TRANSFER: AN OVERVIEW
Directory of Open Access Journals (Sweden)
W.H.Azmi
2013-06-01
Full Text Available Nanoﬂuids offer a significant advantage over conventional heat transfer ﬂuids and consequently, they have attracted much attention in recent years. The engineered suspension of nano-sized particles in a base liquid alters the properties of these nanofluids. Many researchers have measured and modeled the thermal conductivity and viscosity of nanofluids. The estimation of forced convective heat transfer coefficients is done through experiments with either metal or nonmetal solid particles dispersed in water. Regression equations are developed for the determination of the thermal conductivity and viscosity of nanofluids. The parameters influencing the decrease in convection heat transfer, observed by certain investigators, is explained.
Endwall convective heat transfer for bluff bodies
DEFF Research Database (Denmark)
Wang, Lei; Salewski, Mirko; Sundén, Bengt
2012-01-01
The endwall heat transfer characteristics of forced flow past bluff bodies have been investigated using liquid crystal thermography (LCT). The bluff body is placed in a rectangular channel with both its ends attached to the endwalls. The Reynolds number varies from 50,000 to 100,000. In this study...
Conjugate problems in convective heat transfer
Dorfman, Abram S
2009-01-01
The conjugate heat transfer (CHT) problem takes into account the thermal interaction between a body and fluid flowing over or through it, a key consideration in both mechanical and aerospace engineering. Presenting more than 100 solutions of non-isothermal and CHT problems, this title considers the approximate solutions of CHT problems.
Heat transfer of laminar mixed convection of liquid
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...
Mechanism and control of convective heat transfer-- Coordination of velocity and heat flow fields
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
A second look has been given at the mechanism of convective heat transfer based on the analogy between convection and conduction with heat sources. The strength of convective heat transfer depends not only on the fluid velocity and fluid properties, but also on the coordination of fluid velocity and heat flow fields. Hence, based on the included angle of velocity and temperature gradient vectors, the presence of fluid motion may enhance or reduce heat transfer. With this concept, the known heat transfer phenomena may be understood in a deeper way. More important is that some novel approaches of heat transfer control can be developed.
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.
Convective heat transfer area of the human body.
Kurazumi, Yoshihito; Tsuchikawa, Tadahiro; Matsubara, Naoki; Horikoshi, Tetsumi
2004-12-01
In order to clarify the heat transfer area involved in convective heat exchange for the human body, the total body surface area of six healthy subjects was measured, and the non-convective heat transfer area and floor and chair contact areas for the following nine common body positions were measured: standing, sitting on a chair, sitting in the seiza position, sitting cross-legged, sitting sideways, sitting with both knees erect, sitting with a leg out, and the lateral and supine positions. The main non-convective heat transfer areas were: the armpits (contact between the upper arm and trunk regions), contact between the two legs, contacts between the fingers and toes, and contact between the hands and the body surface. Also, when sitting on the floor with some degree of leg contact (sitting in the seiza position, cross-legged, or sideways), there was a large non-convective heat transfer area on the thighs and legs. Even when standing or sitting in a chair, about 6-8% of the body surface did not transfer heat by convection. The results showed that the effective thermal convective area factor for the naked whole body in the standing position was 0.942. While sitting in a chair this factor was 0.860, while sitting in a chair but excluding the chair contact area it was 0.918, when sitting in the seiza position 0.818, when sitting cross-legged 0.843, in the sideways sitting position 0.855, when sitting with both knees erect 0.887, in the leg-out sitting position 0.906, while in the lateral position it was 0.877 and the supine position 0.844. For all body positions, the effective thermal convective area factor was greater than the effective thermal radiation area factor, but smaller than the total body surface area.
Convective heat transfer around vertical jet fires: an experimental study.
Kozanoglu, Bulent; Zárate, Luis; Gómez-Mares, Mercedes; Casal, Joaquim
2011-12-15
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.
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.
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.
Evidence of convective heat transfer enhancement induced by spinodal decomposition.
Poesio, P; Lezzi, A M; Beretta, G P
2007-06-01
Spinodal decomposition can be driven by either diffusion or self-induced convection; the importance of convection relative to diffusion depends on the Péclet number, defined as the ratio between convective and diffusive mass fluxes. Diffusion is the dominating mechanism of phase segregation when the Péclet number is small - i.e., when viscosity and diffusivity are large - or when the domain characteristic size is small. For low-viscosity mixtures, convection is the dominating process and the segregation is very rapid as it takes a few seconds compared to the hours needed in the case of pure diffusion. In such cases, strong convective motion of the phase segregating domains is generated even in small-size systems and is almost independent of the temperature difference as long as it is below the transition value. We study experimentally the enhancement of heat transfer in a 1-mm -thick cell. A water-acetonitrile-toulene mixture is quenched into a two-phase region so as to induce convection-driven spinodal decomposition. The heat transfer rate is measured and compared to that obtained in the absence of convective motion. A substantial reduction in the cooling time obtains in the case of spinodal decomposition. The heat transfer enhancement induced by this self-induced, disordered but effectively convective effect may be exploited in the cooling or heating of small-scale systems whereby forced convection cannot be achieved because of the small sizes involved. A scaling analysis of the data based on the diffuse interface H model for a symmetric mixture near the equilibrium point yields very encouraging agreement and insights.
Convective condensation heat transfer in a horizontal condenser tube
Energy Technology Data Exchange (ETDEWEB)
Sarma, P.K. [College of Engineering, GITAM, Visakhapatnam (India); Sastry, C.V.N.; Rao, V.D. [Andhra Univ., College of Engineering, Visakhapatnam (India); Kakac, S.; Liu, H. [Miami Univ., College of Engineering, FL (United States)
2002-03-01
The purpose of this article is to solve analytically the problem of convective condensation of vapors inside a horizontal condenser tube. Homogeneous model approach is employed in the estimation of shear velocity, which is subsequently, made use of in predicting local convective condensation heat transfer coefficients. The resulting analysis of the present study is compared with some of the available equations in the literature. It is observed that the agreement is reasonably satisfactory validating the assumptions and the theory presented. (authors)
Experimental free convection heat transfer from inclined square cylinders
Ali, Mohamed
2016-10-01
Natural convection from axisymmetric objects such as vertical or horizontal cylinders and spheres are two dimensional. However, for inclined circular or noncircular cylinders the flow and heat transfer is three dimensional and hence more complex and needs more attention. This study investigates the steady state mechanism of natural convection from inclined square cylinders in air. Five different cylinders of 1 m length, 8 × 8, 7 × 7, 6 × 6, 4 × 4 and 2.5 × 2.5 cm2 cross sections are used. The cylinders are heated using inserted heating element of 6 mm in diameter. Self-adhesive thermocouples are used at the upper, bottom and at one side of the cylinders for temperature measurement. Three inclination angles to the horizontal 30, 45 and 60o are used for each cylinder with uniform heat flux boundary conditions. For each cylinder, about ten heat fluxes are used to generate the heat transfer data. Local and average heat transfer coefficient is determined for each cylinder at each inclination angle for each uniform heat flux. Laminar and transition to turbulent regimes are obtained and characterized. Local critical axial distance where heat transfer coefficient changes the mode is obtained for each heat flux. Local and averaged Nusselt numbers are correlated with the modified Rayleigh numbers for all angles.
Heat transfer mechanisms in bubbly Rayleigh-Bénard convection
Oresta, Paolo; Verzicco, Roberto; Lohse, Detlef; Presperetti, Andrea
2009-01-01
The heat transfer mechanism in Rayleigh-Bénard convection in a liquid with a mean temperature close to its boiling point is studied through numerical simulations with pointlike vapor bubbles, which are allowed to grow or shrink through evaporation and condensation and which act back on the flow both
A critical review of convective heat transfer of nanofluids
Energy Technology Data Exchange (ETDEWEB)
Daungthongsuk, Weerapun; Wongwises, Somchai [Fluid Mechanics, Thermal Engineering and Multiphase Flow Research Laboratory (FUTURE), Department of Mechanical Engineering, King Mongkut' s University of Technology Thonburi, Bangmod, Bangkok 10140 (Thailand)
2007-06-15
A nanofluid is a suspension of ultrafine particles in a conventional base fluid which tremendously enhances the heat transfer characteristics of the original fluid. Furthermore, nanofluids are expected to be ideally suited in practical applications as their use incurs little or no penalty in pressure drop because the nanoparticles are ultrafine, therefore, appearing to behave more like a single-phase fluid than a solid-liquid mixture. About a decade ago, several published articles focused on measuring and determining the effective thermal conductivity of nanofluids, some also evaluated the effective viscosity. There are only a few published articles on deriving the forced convective heat transfer of nanofluids. The purpose of this article is to summarize the published subjects respect to the forced convective heat transfer of the nanofluids both of experimental and numerical investigation. (author)
Fundamental Research on Convective Heat Transfer in Electronic Cooling Technology
Institute of Scientific and Technical Information of China (English)
C.F.Ma; Y.P.Gan; 等
1992-01-01
During the past six years comprehensive research programs have been conducted at the Beijing Polytechnic University to provide a better understanding of heat transfer characteristics of existing and condidate cooling techniques for electronic and microelestanding of heat transfer characteristics of existing and condidate cooling techniques for electronic and microleectronic devices.This paper provides a review and summary of the programs with emphasis on direct liquid cooling.Included in this review are the heat transfer investigations related to the following cooling modes:liquid free,mixed and forced convection.liquid jet impingement,flowing liquid film cooling,pool boiling,spray cooling,foreign gas jet impingement in liquid pool,and forced convection air-cooling.
Convective heat transfer during dendritic solidification
Glicksman, M. E.; Huang, S. C.
1978-01-01
Experiments on succinonitrile are described in which the dependence of dendritic growth velocity is studied as a function of orientation with respect to gravity. Growth rate measurements were carried out at a relatively small supercooling, requiring high specimen purity as well as extreme thermal stability and precision temperature measurement. The normalized growth velocity showed a dependence on orientation described by the ratio of observed growth velocity to that expected for convection-free growth being equal to 3.52 times the n-th power of Cos half the orientation angle, where n lies between 0.5 and 0.75.
Energy Technology Data Exchange (ETDEWEB)
Tafreshi, H. Vahedi; Ercan, E.; Pourdeyhimi, B. [North Carolina State University, Nonwovens Cooperative Research Center, Raleigh, NC (United States)
2006-07-15
In this note, the evaporation rate from a vertical wet fabric sheet is calculated using a free convection heat transfer correlation. Chilton-Colburn analogy is used to derive a mass transfer correlation from a heat transfer correlation proposed by Churchill and Chu for free convection from a vertical isothermal plate. The mass transfer rate obtained from this expression has shown excellent agreement with experimental data. (orig.)
Natural convection heat transfer within horizontal spent nuclear fuel assemblies
Energy Technology Data Exchange (ETDEWEB)
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.
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.
Generalized thermal resistance for convective heat transfer and its relation to entransy dissipation
Institute of Scientific and Technical Information of China (English)
CHEN Qun; REN JianXun
2008-01-01
In order to further analyze and optimize convective heat transfer process further, the concepts of heat flux weighted average heat temperature and heat flux weighted average heat temperature difference in multi-dimensional heat transfer system were introduced in this paper. The ratio of temperature difference to heat flux is defined as the generalized thermal resistance of convective heat transfer processes,and then the minimum thermal resistance theory for convective heat transfer optimization was developed. By analyzing the relationship between generalized thermal resistance and entansy dissipation in convective heat transfer processes, it can be concluded that the minimum thermal resistance theory equals the entransy dissipation extremum theory. Finally, a two-dimensional convective heat transfer process with constant wall temperature is taken as an example to illustrate the applicability of generalized thermal resistance to convective heat transfer process analysis and optimization.
Natural convection heat transfer along vertical rectangular ducts
Ali, M.
2009-12-01
Experimental investigations have been reported on steady state natural convection from the outer surface of vertical rectangular and square ducts in air. Seven ducts have been used; three of them have a rectangular cross section and the rest have square cross section. The ducts are heated using internal constant heat flux heating elements. The temperatures along the vertical surface and the peripheral directions of the duct wall are measured. Axial (perimeter averaged) heat transfer coefficients along the side of each duct are obtained for laminar and transition to turbulent regimes of natural convection heat transfer. Axial (perimeter averaged) Nusselt numbers are evaluated and correlated using the modified Rayleigh numbers for laminar and transition regime using the vertical axial distance as a characteristic length. Critical values of the modified Rayleigh numbers are obtained for transition to turbulent. Furthermore, total overall averaged Nusselt numbers are correlated with the modified Rayleigh numbers and the area ratio for the laminar regimes. The local axial (perimeter averaged) heat transfer coefficients are observed to decrease in the laminar region and increase in the transition region. Laminar regimes are obtained at the lower half of the ducts and its chance to appear decreases as the heat flux increases.
Comparative study of convective heat transfer characteristics of nanofluids
Muryam, Hina; Ramzan, Naveed; Umer, Asim; Awan, Gul Hameed; Hassan, Ali
2017-02-01
The present research is about to draw a comparison between heat transfer characteristics of gold/deionized water (DIW) and silver/DIW based nanofluid under same heat flux for laminar flow. Experiments are performed on both nanofluid by using different concentrations (0.015, 0.045, 0.0667%) of nano-particles (NPs) in DIW as a base fluid. The experimental study concludes that an appreciable intensification in heat transfer coefficient (HTC) of both nanofluid has been attained as compare to base fluid. However, gold/DIW based nanofluid exhibit better convective heat transfer intensification compared with silver/DIW based nanofluid but Shah correlation cannot predict as much augmentation as in experimental work for both nanofluid. It is also noticed that the anomalous enhancement in Nusselt number and HTC is not only due to the accession in thermal properties but also by the formation of thinner thermal boundary layer at the entrance of the tube due to NPs.
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
Convective heat transfer in engine coolers influenced by electromagnetic fields
Karcher, C.; Kühndel, J.
2017-08-01
In engine coolers of off-highway vehicles, convective heat transfer at the coolant side limits both efficiency and performance density of the apparatus. Here, due to restrictions in construction and design, backwater areas and stagnation regions cannot be avoided. Those unwanted changes in flow characteristics are mainly triggered by flow deflections and sudden cross-sectional expansions. In application, mixtures of water and glysantine are used as appropriate coolants. Such coolants typically show an electrical conductivity of a few S/m. Coolant flow and convective heat transfer can then be controlled using Lorentz forces. These body forces are generated within the conducting fluid by the interactions of an electrical current density and a localized magnetic field, both of which are externally superimposed. In future application, this could be achieved by inserting electrodes in the cooler wall and a corresponding arrangement of permanent magnets. In this paper we perform numerical simulations of such magnetohydrodynamic flow in three model geometries that frequently appear in engine cooling applications: Carnot-Borda diffusor, 90° bend, and 180° bend. The simulations are carried out using the software package ANSYS Fluent. The present study demonstrates that, depending on the electromagnetic interaction parameter and the specific geometric arrangement of electrodes and magnetic field, Lorentz forces are suitable to break up eddy waters and separation zones and thus significantly increase convective heat transfer in these areas. Furthermore, the results show that hydraulic pressure losses can be reduced due to the pumping action of the Lorentz forces.
Single-phase convective heat transfer in microchannels
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
A comprehensive review is conducted on the investigations of the forced single-phase convective heat transfer in non-circular microchannels. The observations and results available in the open literature are inspected and compared for better understanding of the physical nature of the heat transfer performance and providing some lines of future research. There seems to be no unequivocal agreement in the understanding on the relative phenomena and the determination of the heat transfer coefficients in microchannels. The study on the interfacial phenomena and interaction at the interface will be the frontier in this area. Appropriate data reduction and the correlating parameters will be the cornerstone of comparability and evaluation for comprehensive investigations. The selection of correlating parameters will actually be the basis for the better understanding and description of new phenomena.
Lattice Boltzmann simulations of convection heat transfer in porous media
Liu, Qing; He, Ya-Ling
2017-01-01
A non-orthogonal multiple-relaxation-time (MRT) lattice Boltzmann (LB) method is developed to study convection heat transfer in porous media at the representative elementary volume scale based on the generalized non-Darcy model. In the method, two different LB models are constructed: one is constructed in the framework of the double-distribution-function approach, and the other is constructed in the framework of the hybrid approach. In particular, the transformation matrices used in the MRT-LB models are non-orthogonal matrices. The present method is applied to study mixed convection flow in a porous channel and natural convection flow in a porous cavity. It is found that the numerical results are in good agreement with the analytical solutions and/or other results reported in previous studies. Furthermore, the non-orthogonal MRT-LB method shows better numerical stability in comparison with the BGK-LB method.
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.
Finite volume simulation for convective heat transfer in wavy channels
Aslan, Erman; Taymaz, Imdat; Islamoglu, Yasar
2016-03-01
The convective heat transfer characteristics for a periodic wavy channel have been investigated experimentally and numerically. Finite volume method was used in numerical study. Experiment results are used for validation the numerical results. Studies were conducted for air flow conditions where contact angle is 30°, and uniform heat flux 616 W/m2 is applied as the thermal boundary conditions. Reynolds number ( Re) is varied from 2000 to 11,000 and Prandtl number ( Pr) is taken 0.7. Nusselt number ( Nu), Colburn factor ( j), friction factor ( f) and goodness factor ( j/ f) against Reynolds number have been studied. The effects of the wave geometry and minimum channel height have been discussed. Thus, the best performance of flow and heat transfer characterization was determined through wavy channels. Additionally, it was determined that the computed values of convective heat transfer coefficients are in good correlation with experimental results for the converging diverging channel. Therefore, numerical results can be used for these channel geometries instead of experimental results.
Energy Technology Data Exchange (ETDEWEB)
Bories, S.; Mojtabi, A.; Prat, M.; Quintard, M. [Institut de Mecanique des Fluides de Toulouse, 31 (France)
2008-10-15
Multiple physico-chemical and transport phenomena take place in porous media. The study of these phenomena requires the knowledge of fluid storage, transfer and mechanical properties of these media. Like all polyphasic heterogenous systems, these properties depend on the morphology of the matrix and of the phenomena interacting in the different phases. This makes the heat transfers in porous media a particularly huge field of researches. This article makes a synthesis of these researches. Content: 1 - classification and characterization of porous media; 2 - modeling of transfer phenomena; 3 - heat transfer by conduction: concept of equivalent thermal conductivity (ETC), modeling of conduction heat transfer, ETC determination; 4 - heat transfer by convection: modeling of convection heat transfer, natural convection (in confined media, along surfaces or impermeable bodies immersed in a saturated porous medium), forced and mixed convection; 5 - radiant heat transfer: energy status equation, approximate solutions of the radiant transfer equation, use of the approximate solutions: case of fibrous insulating materials; 6 - conclusion. (J.S.)
Mechanistic Multidimensional Modeling of Forced Convection Boiling Heat Transfer
Directory of Open Access Journals (Sweden)
Michael Z. Podowski
2009-01-01
Full Text Available Due to the importance of boiling heat transfer in general, and boiling crisis in particular, for the analysis of operation and safety of both nuclear reactors and conventional thermal power systems, extensive efforts have been made in the past to develop a variety of methods and tools to evaluate the boiling heat transfer coefficient and to assess the onset of temperature excursion and critical heat flux (CHF at various operating conditions of boiling channels. The objective of this paper is to present mathematical modeling concepts behind the development of mechanistic multidimensional models of low-quality forced convection boiling, including the mechanisms leading to temperature excursion and the onset of CHF.
Convective heat transfer for viscoelastic fluid in a curved pipe
Energy Technology Data Exchange (ETDEWEB)
Norouzi, M.; Kayhani, M.H. [Shahrood University of Technology, Mechanical Engineering Department, Shahrood (Iran); Nobari, M.R.H. [Amirkabir University of Technology, Mechanical Engineering Department, Tehran (Iran); Joneidi, A.A. [Eindhoven University of Technology, Mechanical-Polymer Technology Group, Eindhoven (Netherlands)
2010-10-15
In this paper, fully developed convective heat transfer of viscoelastic flow in a curved pipe under the constant heat flux at the wall is investigated analytically using a perturbation method. Here, the curvature ratio is used as the perturbation parameter and the Oldroyd-B model is applied as the constitutive equation. In the previous studies, the Dirichlet boundary condition for the temperature at the wall has been used to simplify the solution, but here exactly the non-homogenous Neumann boundary condition is considered to solve the problem. Based on this solution, the non-axisymmetric temperature distribution of Dean flow is obtained analytically and the effect of flow parameters on the flow field is investigated in detail. The current analytical results indicate that increasing the Weissenberg number, viscosity ratio, curvature ratio, and Prandtl number lead to the increase of the heat transfer in the Oldroyd-B fluid flow. (orig.)
Forced Convective Heat Transfer in a Porous Plate Channel
Institute of Scientific and Technical Information of China (English)
PeixueJiang; ZhanWang; 等
1997-01-01
Fored convective heat transfer in a plate channel filled with metallic spherical particales was investigated experimentally and numerically.The test section ,58mm×80mm×50mm in size,was heated by a 0.4mm thick plate electrical heater,The coolant water flow rate ranged from 0.015 to 0.833 kg/s.The local wall temperature distribution was measured along with the inlet and outlet fliud temperatures and pressures.The results illustrate the heat transfer augmentation and increased pressure drop caused by the porous medium.The heat transfer coefficient was increased 5-12 times by the porous media although the hydraulic resistance was increased even more.The Nusselt number and the heat transfer coefficient increased with decreasing particle diameter,while the pressure drop decreased as the particle diameter increased.It was found that,for the conditions studied(metallic packed bed),the effect of thermal dispersion did not need to be considered in the physical model,as opposed to a non-metallic packed bed,where thermal dispersion is important.
Modeling natural convection heat transfer from perforated plates
Institute of Scientific and Technical Information of China (English)
Zan WU; Wei LI; Zhi-jian SUN; Rong-hua HONG
2012-01-01
Staggered pattern perforations are introduced to isolated isothermal plates,vertical parallel isothermal plates,and vertical rectangular isothermal fins under natural convection conditions.The performance of perforations was evaluated theoretically based on existing correlations by considering effects of ratios of open area,inclined angles,and other geometric parameters.It was found that staggered pattern perforations can increase the total heat transfer rate for isolated isothermal plates and vertical parallel plates,with low ratios of plate height to wall-to-wall spacing (H/s),by a factor of 1.07 to 1.21,while only by a factor of 1.03 to 1.07 for vertical rectangular isothermal fins,and the magnitude of enhancement is proportional to the ratio of open area.However,staggered pattern perforations are detrimental to heat transfer enhancement of vertical parallel plates with large H/s ratios.
Characterizations and Convective Heat Transfer Performance of Nanofluids
Yang, Yijun
heat transfer enhancement to the pumping power increase (termed as merit parameter) as a function of Reynolds numbers indicates that the increase in pumping power is much greater than the corresponding heat transfer enhancement. This study additionally showed that concentrations of ND50-Syltherm800, TiO2-water and Al2O3-water nanofluids did not enhance convection heat transfer. Hence, the effect of nanoparticles on the heat transfer properties of a nanofluid appears dependent on the particular type of nanoparticle employed.
In vivo measurement of swine endocardial convective heat transfer coefficient.
Tangwongsan, Chanchana; Will, James A; Webster, John G; Meredith, Kenneth L; Mahvi, David M
2004-08-01
We measured the endocardial convective heat transfer coefficient h at 22 locations in the cardiac chambers of 15 pigs in vivo. A thin-film Pt catheter tip sensor in a Wheatstone-bridge circuit, similar to a hot wire/film anemometer, measured h. Using fluoroscopy, we could precisely locate the steerable catheter sensor tip and sensor orientation in pigs' cardiac chambers. With flows, h varies from 2500 to 9500 W/m2 x K. With zero flow, h is approximately 2400 W/m2 x K. These values of h can be used for the finite element method modeling of radiofrequency cardiac catheter ablation.
Single phase channel flow forced convection heat transfer
Energy Technology Data Exchange (ETDEWEB)
Hartnett, J.P.
1999-04-01
A review of the current knowledge of single phase forced convection channel flow of liquids (Pr > 5) is presented. Two basic channel geometries are considered, the circular tube and the rectangular duct. Both laminar flow and turbulent flow are covered. The review begins with a brief overview of the heat transfer behavior of Newtonian fluids followed by a more detailed presentation of the behavior of purely viscous and viscoelastic Non-Newtonian fluids. Recent developments dealing with aqueous solutions of high molecular weight polymers and aqueous solutions of surfactants are discussed. The review concludes by citing a number of challenging research opportunities.
Directory of Open Access Journals (Sweden)
N. Nesenchuk
2013-01-01
Full Text Available Directions pertaining to intensification of convective heat transfer in a soft heating device have been experimentally investigated in the paper and the most efficient one has been selected that is creation of artificial roughness on the device surface. The considered heating device for a heat supply system of a mobile object has been made of soft polymer material (polyvinyl chloride. Following evaluation results of heat exchange intensification a criteria equation has been obtained for calculation of external heat transfer with due account of heat transfer intensification.
Institute of Scientific and Technical Information of China (English)
LU; YuanWei; LI; XiaoLi; LI; Qiang; WU; YuTing; MA; ChongFang
2013-01-01
In order to get the natural convection heat transfer mechanism of molten salt, the experimental investigation of natural convective heat transfer of LiNO3was studied after it was simulated by numerical calculation. Experiment was carried out on the nat-ural convection heat transfer of air and water around the fine wire using the method of Joule heating. The results showed that the natural convection heat transfer of air and water around the fine wire agreed well with Fand’s correlation. Based on the aforementioned experiment, the natural convection heat transfer of molten salt LiNO3was studied by experiment and the same results were got. Therefore, the natural convection heat transfer of molten salt can be calculated by Fand’s correlation, which takes into consideration the effect of viscosity dissipation.
A laser-induced heat flux technique for convective heat transfer measurements in high speed flows
Porro, A. R.; Keith, T. G., Jr.; Hingst, W. R.
1991-01-01
A technique is developed to measure the local convective heat transfer coefficient on a model surface in a supersonic flow field. The technique uses a laser to apply a discrete local heat flux at the model test surface, and an infrared camera system determines the local temperature distribution due to the heating. From this temperature distribution and an analysis of the heating process, a local convective heat transfer coefficient is determined. The technique was used to measure the local surface convective heat transfer coefficient distribution on a flat plate at nominal Mach numbers of 2.5, 3.0, 3.5, and 4.0. The flat plate boundary layer initially was laminar and became transitional in the measurement region. The experimentally determined convective heat transfer coefficients were generally higher than the theoretical predictions for flat plate laminar boundary layers. However, the results indicate that this nonintrusive optical measurement technique has the potential to measure surface convective heat transfer coefficients in high-speed flowfields.
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...
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
Modelling of convective heat and mass transfer in rotating flows
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...
Numerical study of forced convective heat transfer around airships
Dai, Qiumin; Fang, Xiande
2016-02-01
Forced convective heat transfer is an important factor that affects the thermal characteristics of airships. In this paper, the steady state forced convective heat transfer around an ellipsoid is numerically investigated. The numerical simulation is carried out by commercial computational fluid dynamic (CFD) software over the extended Re range from 20 to 108 and the aspect ratio from 2 to 4. Based on the regression and optimization with software, a new piecewise correlation of the Nusselt number at constant wall temperature for ellipsoid is proposed, which is suitable for applications to airships and other ellipse shaped bodies such as elliptical balloons. The thermal characteristics of a stratospheric airship in midsummer located in the north hemisphere are numerical studied. The helium temperature predicated using the new correlation is compared to those predicted by correlations applicable for spheres and flat plates. The results show that the helium temperature obtained using the new correlation at noon is about 5.4 K lower than that using the correlation of spheres and about 2.1 K higher than that of flat plates.
Dag, Yusuf
Forced convection over traditional surfaces such as flat plate, cylinder and sphere have been well researched and documented. Data on forced convection over airfoil surfaces, however, remain very scanty in literature. High altitude vehicles that employ airfoils as lifting surfaces often suffer leading edge ice accretions which have tremendous negative consequences on the lifting capabilities and stability of the vehicle. One of the ways of mitigating the effect of ice accretion involves judicious leading edge convective cooling technique which in turn depends on the accuracy of convective heat transfer coefficient used in the analysis. In this study empirical investigation of convective heat transfer measurements on asymmetric airfoil is presented at different angle of attacks ranging from 0° to 20° under subsonic flow regime. The top and bottom surface temperatures are measured at given points using Senflex hot film sensors (Tao System Inc.) and used to determine heat transfer characteristics of the airfoils. The model surfaces are subjected to constant heat fluxes using KP Kapton flexible heating pads. The monitored temperature data are then utilized to determine the heat convection coefficients modelled empirically as the Nusselt Number on the surface of the airfoil. The experimental work is conducted in an open circuit-Eiffel type wind tunnel, powered by a 37 kW electrical motor that is able to generate subsonic air velocities up to around 41 m/s in the 24 square-inch test section. The heat transfer experiments have been carried out under constant heat flux supply to the asymmetric airfoil. The convective heat transfer coefficients are determined from measured surface temperature and free stream temperature and investigated in the form of Nusselt number. The variation of Nusselt number is shown with Reynolds number at various angles of attacks. It is concluded that Nusselt number increases with increasing Reynolds number and increase in angle of attack from 0
Turbulence convective heat transfer for cooling the photovoltaic cells
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.
Convective heat transfer enhancement inside tubes using inserted helical coils
Ali, R. K.; Sharafeldeen, M. A.; Berbish, N. S.; Moawed, M. A.
2016-01-01
Convective heat transfer was experimentally investigated in tubes with helical coils inserts in turbulent flow regime within Reynolds number range of 14400 ≤ Re ≤ 42900. The present work aims to extend the experimental data available on wire coil inserts to cover wire diameter ratio from 0.044 to 0.133 and coil pitch ratio from 1 to 5. Uniform heat flux was applied to the external surface of the tube and air was selected as fluid. The effects of Reynolds number and wire diameter and coil pitch ratios on the Nusselt number and friction factor were studied. The enhancement efficiency and performance criteria ranges are of (46.9-82.6%) and (100.1-128%) within the investigated range of the different parameters, respectively. Correlations are obtained for the average Nusselt number and friction factor utilizing the present measurements within the investigated range of geometrical parameters and Re.
Mixed convection flow and heat transfer in a vertical wavy channel ...
African Journals Online (AJOL)
user
Keywords: convective flow; wavy channel; porous medium; traveling thermal waves. ... the problems of forced convection in composite fluids and porous layers. ... Processes involving heat and mass transfer are often encountered in the ...
Heat transfer in forced convection boiling of oil-non-azeotropic binary refrigerant mixtures
Energy Technology Data Exchange (ETDEWEB)
Sami, S.M.; Tulej, P.; Fang, L. (Moncton Univ., NB (Canada))
1993-12-01
In this paper, the results of the heat transfer, forced convection, boiling characteristics of non-azeotropic refrigerant mixtures and oil are presented. This includes heat transfer coefficients for pure and binary mixtures under boiling conditions outside enhanced surface tubing. Local convective heat transfer coefficients have been determined using a modified Wilson-plot technique. Heat transfer correlations were established as a function of the binary mixture mass flow rate, and oil concentration, as well as key flow parameters. (author)
Thermal Performance of Laser Diode Array under Constant Convective Heat Transfer Boundary Condition
Institute of Scientific and Technical Information of China (English)
YIN Cong; HUANG Lei; HE Fa-Hong; GONG Ma-Li
2007-01-01
Three-dimensional heat transfer model of laser diode array under constant convective heat transfer coefficient boundary condition is established and analytical temperature profiles within its heat sink are obtained by separation of variables. The influences on thermal resistance and maximum temperature variation among emitters from heat sink structure parameters and convective heat transfer coefficient are brought forward. The derived formula enables the thermal optimization of laser diode array.
Convective Heat Transfer Analysis in Fluid Flow with Turbulence Promoters with Heat Pipes
Directory of Open Access Journals (Sweden)
Theodor Mateescu
2007-01-01
Full Text Available The present paper proposes the analysis and the simulation of the convection heat transfer into the fluid flow with turbulence promoters utilizing heat pipes. The study is based on the necesity of the unconventional energy forms capitalization, increasing of the energy efficiency and leads to the energy consumtion decrease in concordance with the sustainable development concept.
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
Taha, T.J.; Lefferts, L.; Meer, van der T.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
SIMULATION OF MIXED CONVECTIVE HEAT TRANSFER USING LATTICE BOLTZMANN METHOD
Directory of Open Access Journals (Sweden)
A. R. M. Rosdzimin
2010-12-01
Full Text Available In this paper, mixed (forced–natural convective heat transfer around a heated square cylinder located inside a lid driven cavity has been studied numerically using the lattice Boltzmann method in the range of 100≤ Re ≤ 1000 with the corresponding Richardson number 0.01≤Ri≤10. The double-population lattice Boltzmann formulation is used as the governing equation. Two dimensional nine-velocity models are used for the computation of the velocity field while a four-velocity model is used for the computation of the temperature field. We found that the combination of nine- and four-velocity models can be applied to the calculation without losing its accuracy. The results are presented in the form of streamline and isotherm plots as well as the variation of local Nusselt number at the top surface of the heated square. The computational results demonstrate that the flow pattern, formation of vortex and also the Nusselt number are influence by the Reynolds number and Richardson number.
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…
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…
Forced Convection Heat Transfer in Plate Channels Filled with Packed Beds or Sintered Porous Media
Institute of Scientific and Technical Information of China (English)
姜培学; 李勐; 任泽霈
2002-01-01
In the present work, forced convection heat transfer in plate channels filled with metallic or non-metallic particles (packed beds) or sintered porous media is simulated numerically using a thermal non-equilibrium model. The numerical simulation results are compared with experimental data. The difference between convection heat transfer in packed beds and in sintered porous media and the effects of the boundary condition assumptions are investigated. The results show that the numerical simulation of convection heat transfer of air or water in packed beds using the local thermal non-equilibrium model and the variable porosity model agrees well with the experimental data. The convection heat transfer coefficient in sintered porous media is much higher than that in packed beds. In the numerical simulation of convection heat transfer in sintered porous media, the boundary conditions on the wall should be that the particle temperatures are equal to the fluid temperature.
Experimental study of natural convective heat transfer in a vertical hexagonal sub channel
Tandian, Nathanael P.; Umar, Efrizon; Hardianto, Toto; Febriyanto, Catur
2012-06-01
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.
Neshat, E.; Hossainpour, S.; Bahiraee, F.
2014-06-01
Both of experimental and numerical investigations were performed to understand unsteady natural convection from outer surface of helical coils. Four helical coils with two different curvature ratios were used. Each coil was mounted in the shell both vertically and horizontally. The cold water was entered the coil and the hot water in the shell was cooling by unsteady natural convection. A CFD code was developed to simulate natural convection heat transfer. Equations of tube and shell are solved simultaneously. Statistical analyses have been done on data points of temperature and natural convection Nusselt number. It was revealed that shell-side fluid temperature and the Nusselt number of the outer surface of coils are functions of in-tube fluid mass flow rate, specific heat of fluids and geometrical parameters including length, inner diameter of the tube and the volume of the shell, and time.
Institute of Scientific and Technical Information of China (English)
LIU Wei; LIU ZhiChun; GUO ZengYuan
2009-01-01
Based on the principle of field synergy for heat transfer enhancement, the concept of physical quantity synergy in the laminar flow field is proposed in the present study according to the physical mechanism of convective heat transfer between fluid and tube wall. The synergy regulation among physical quantities of fluid particle is revealed by establishing formulas reflecting the relation between synergy angles and heat transfer enhancement. The physical nature of enhancing heat transfer and reducing flow resistance, which is directly associated with synergy angles α,βγ,φ, θ and ψ, is also explained. Be-sides, the principle of synergy among physical quantities is numerically verified by the calculation of heat transfer and flow in a thin cylinder-interpolated tube, which may guide the optimum design for better heat transfer unit and high-efficiency heat exchanger.
NUMERICAL STUDY OF THE MIXED CONVECTION HEAT TRANSFER IN ANNULUS HEATED BY JOULEAN EFFECT
Directory of Open Access Journals (Sweden)
S Touahri
2015-12-01
Full Text Available In the present work, we numerically study the three-dimensional mixed convection heat transfer in the annular space between tow concentric horizontal pipes, the external pipe is heated by an electrical intensity passing through its small thickness while the inner cylinder is insulated. The convection in the fluid domain is conjugated to thermal conduction in the pipes solid thickness. The physical properties of the fluid are thermal dependant. The heat losses from the external outside pipe surface to the surrounding ambient are considered. The model equations of continuity, momenta and energy are numerically solved by a finite volume method with a second order spatiotemporal discretization. The obtained results show the three dimensional aspect of the thermal and dynamical fields with considerable variations of the viscosity and moderate variations of the fluid thermal conductivity. As expected, the mixed convection Nusselt number becomes more superior to that of the forced convection when the Grashof number is increased. At the solid-fluid interface, the results show clearly the azimuthal and axial variations of the local heat flux and the local Nusselt numbers. Following these results, we have tried modelling the average Nusselt numberNuA as a function of Richardson numberRi. With the parameters used, the heat transfer is quantified by the correlation:NuA= 9.9130 Ri0.0816.
Measurement of the Convective Heat-Transfer Coefficient
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…
Natural convection heat transfer on surfaces of copper micro-wires
Guan, Ning; Liu, Zhigang; Zhang, Chengwu; Jiang, Guilin
2014-02-01
The natural convection heat transfer characteristics and mechanism for copper micro-wires in water and air were investigated experimentally and numerically. The wires with diameters of 39.9, 65.8 and 119.1 μm were placed horizontally in water inside of a sealed tube and in air of a large room, respectively. Using Joule heating, the heat transfer coefficients and Nusselt numbers of natural convection for micro-wires in ultra pure water and air were obtained. A three dimensional incompressible numerical model was used to investigate the natural convection, and the prediction with this model was in reasonable accordance with the experimental results. With the decrease of micro-wire diameter, the heat transfer coefficient of natural convection on the surface of micro-wire becomes larger, while the Nu number of natural convection decreases in water and air. Besides, the change rate of Nu number in water decreases apparently with the increase of heat flux and the decrease of wire diameter, which is larger than that in air. The thickness of boundary layer on the wall of micro-wire becomes thinner with the decrease of diameter in both water and air, but the ratio of boundary layer thickness in water to the diameter increases. However, there is almost no change of this ratio for natural convection in air. As a result, the proportion of conduction in total heat transfer of natural convection in water increases, while the convective heat transfer decreases. The velocity distribution, temperature field and the boundary layer in the natural convection were compared with those of tube with conventional dimension. It was found that the boundary layer around the micro-wire is an oval-shaped film on the surface, which was different from that around the conventional tube. This apparently reduces the convection strength in the natural convection, thus the heat transfer presents a conduction characteristic.
Cebeci, Tuncer
1989-01-01
This book is designed to accompany Physical and Computational Aspects of Convective Heat Transfer by T Cebeci and P Bradshaw and contains solutions to the exercises and computer programs for the numerical methods contained in that book Physical and Computational Aspects of Convective Heat Transfer begins with a thorough discussion of the physical aspects of convective heat transfer and presents in some detail the partial differential equations governing the transport of thermal energy in various types of flows The book is intended for senior undergraduate and graduate students of aeronautical, chemical, civil and mechanical engineering It can also serve as a reference for the practitioner
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.
Talebi, Maryam; Setareh, Milad; Saffar-Avval, Majid; Hosseini Abardeh, Reza
2017-04-01
Application of ultrasonic waves for heat transfer augmentation has been proposed in the last few decades. Due to limited researches on acoustic streaming induced by ultrasonic oscillation, the effect of ultrasonic waves on natural convection heat transfer is the main purpose of this paper. At first, natural convection on up-ward-facing heating surface in a cylindrical enclosure filled with air is investigated numerically by the finite difference method, then the effect of upper surface oscillation on convection heat transfer is considered. The conservation equations in Lagrangian approach and compressible fluid are assumed for the numerical simulation. Results show that acoustic pressure will become steady after some milliseconds also pressure oscillation amplitude and acoustic velocity components will be constant therefore steady state velocity is used for solving energy equation. Results show that Enhancement of heat transfer coefficient can be up to 175% by induced ultrasonic waves. In addition, the effect of different parameters on acoustic streaming and heat transfer has been studied.
Convective heat transfer and flow characteristics of Cu-water nanofluid
Institute of Scientific and Technical Information of China (English)
LI; Qiang(李强); XUAN; Yimin(宣益民)
2002-01-01
An experimental system is built to investigate convective heat transfer and flow characteristics of the nanofluid in a tube. Both the convective heat transfer coefficient and friction factor of Cu-water nanofluid for the laminar and turbulent flow are measured. The effects of such factors as the volume fraction of suspended nanoparticles and the Reynolds number on the heat transfer and flow characteristics are discussed in detail. The experimental results show that the suspended nanoparticles remarkably increase the convective heat transfer coefficient of the base fluid and show that the friction factor of the sample nanofluid with the low volume fraction of nanoparticles is almost not changed. Compared with the base fluid, for example, the convective heat transfer coefficient is increased about 60% for the nanofluid with 2.0 vol% Cu nanoparticles at the same Reynolds number. Considering the factors affecting the convective heat transfer coefficient of the nano- fluid, a new convective heat transfer correlation for nanofluid under single-phase flows in tubes is established. Comparison between the experimental data and the calculated results indicate that the correlation describes correctly the energy transport of the nanofluid.
Makinde, O. D.; Chinyoka, T.
2010-12-01
This present study consists of a numerical investigation of transient heat transfer in channel flow of an electrically conducting variable viscosity Boussinesq fluid in the presence of a magnetic field and thermal radiation. The temperature dependent nature of viscosity is assumed to follow an exponentially model and the system exchanges heat with the ambient following Newton's law of cooling. The governing nonlinear equations of momentum and energy transport are solved numerically using a semi-implicit finite difference method. Solutions are presented in graphical form and given in terms of fluid velocity, fluid temperature, skin friction and heat transfer rate for various parametric values. Our results reveal that combined effect of thermal radiation, magnetic field, viscosity variation and convective cooling have significant impact in controlling the rate of heat transfer in the boundary layer region.
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
Numerical investigation using SIMPLE algorithm with QUICK scheme for natural convection and heat transfer in the enclosure bounded by a solid wall and with heat transfer and radiation coupled in natural convection has been conducted.The various parameters are:Rayleigh number(from 103 to 105),dimensionless conductivity of bounding wall(from 0 to 100),dimensionless wall thickness(from 0 to 0.6) and radiation emissivity of all surfaces(from 0 to 1).The results suggest that flow and heat transfer are influenced by radiation.Radiation is a dominant action on flow and heat transfer.With increase of the thermal conductivity of wall,flow and heat transfer turn stronger.The temperature distribution changes obviously.When the thermal conductivity of wall is over a certain critical number,the increasing trend of flow and heat transfer may disappear.With increase of enclosure wall thickness,flow and heat transfer turn slighter.When the enclosure wall thickness is over a certain critical number,the flow and heat transfer will turn slow.
Experimental study on convective boiling heat transfer in narrow-gap annulus tubes
Institute of Scientific and Technical Information of China (English)
LI Bin; ZHAO Jian-Fu; ZHOU Fang-De; TANG Ze-Mei; HU Wen-Rui
2004-01-01
Since convective boiling or highly subcooled single-phase forced convection in micro-channels is an effective cooling mechanism with a wide range of applications, more experimental and theoretical studies are required to explain and verify the forced convection heat transfer phenomenon in narrow channels. In this experimental study, we model the convective boiling behavior of water with low latent heat substance Freon 113 (R-113), with the purpose of saving power consumption and visualizing experiments. Both heat transfer and pressure drop characteristics were measured in subcooled and saturated concentric narrow gap forced convection boiling. Data were obtained to qualitatively identify the effects of gap size, pressure, flow rate and wall superheat on boiling regimes and the transition between various regimes. Some significant differences from unconfined forced convection boiling were found,and also, the flow patterns in narrow vertical annulus tubes have been studied quantitatively.
Directory of Open Access Journals (Sweden)
Mohammad Jafari
2015-09-01
Full Text Available The effects of Single Walled Carbon Nanotube and Copper nanoparticles on natural convection heat transfer in an open cavity are investigated numerically. The problem is studied for different volume fractions of nanoparticles (0–1% and aspect ratio of the cavity (1–4 when Rayleigh number varies from 103 to 105. The volume fraction of added nanoparticles to Water is lower than 1% to make a dilute suspension. Although, results show that adding nanoparticles to the base fluid enhances the heat transfer, make a comparison between SWCNT and Cu-nanoparticles shows that the SWCNT-nanoparticle has better performance to enhance the convection rate. It is found that the aspect ratio of the cavity plays an important role on natural convection. An increase of this parameter leads to heat transfer reduction in the target problem. It is concluded that the Carbon Nanotubes can be applied as a passive way to enhance heat transfer in convection problems.
Study on Forced Convective Heat Transfer of Non-Newtonian Nanofluids
Institute of Scientific and Technical Information of China (English)
Yurong He; Yubin Men; Xing Liu; Huilin Lu; Haisheng Chen; Yulong Ding
2009-01-01
This paper is concerned with the forced convective heat transfer of dilute liquid suspensions of nanoparticles (nanofluids) flowing through a straight pipe under laminar conditions. Stable nanofluids are formulated by using the high shear mixing and ultrasonication methods. They are then characterised for their size, surface charge, thermal and rheological properties and tested for their convective heat transfer behaviour. Mathematical model-ling is performed to simulate the convective heat transfer of nanofluids using a single phase flow model and con-sidering nanofluids as both Newtonian and non-Newtonian fluid. Both experiments and mathematical modelling show that nanofluids can substantially enhance the convective heat transfer. Analyses of the results suggest that the non-Newtonian character of nanofluids influences the overall enhancement, especially for nanofluids with an obvious non-Newtonian character.
Convection heat transfer from discrete heat sources in a liquid cooled rectangular channel
Energy Technology Data Exchange (ETDEWEB)
Bhowmik, H. [Department of Mechanical Engineering, Dhaka University of Engineering and Technology, Gazipur 1700 (Bangladesh); Tso, C.P. [Faculty of Engineering and Technology, Multimedia University, Jalan Ayer Keroh Lama, 75450 Melaka (Malaysia); Tou, K.W.; Tan, F.L. [School of Mechanical and Production Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore)
2005-11-01
Steady-state experiments are performed to study general convective heat transfer from an in-line four simulated electronic chips in a vertical rectangular channel using water as the working fluid. The experimental data covers a wide range for laminar flow under natural, mixed and forced convection conditions with Reynolds number based on channel hydraulic diameter ranging from 40 to 2220 and Reynolds number based on heat source length ranging from 50 to 2775, respectively. The heat flux ranges from 0.1W/cm{sup 2} to 0.6W/cm{sup 2}. The inlet water temperature is at 24{sup o}C. The effect of heat fluxes, flow rates and geometrical parameters such as chip number are investigated. The experimental results indicate that the heat transfer coefficient is strongly affected by Reynolds number and fully-developed values of heat transfer coefficient are reached before the first chip. Empirical correlations are developed for relations using Nusselt number, Reynolds number and Grashof number, based on channel hydraulic diameter. (author)
Jiao, Anjun; Zhang, Yuwen; Ma, Hongbin; Critser, John
2009-03-01
Heat and mass transfer in a circular tube subject to the boundary condition of the third kind is investigated. The closed form of temperature and concentration distributions, the local Nusselt number based on the total external heat transfer and convective heat transfer inside the tube, as well as the Sherwood number were obtained. The effects of Lewis number and Biot number on heat and mass transfer were investigated.
Optimization of natural convection heat transfer of Newtonian nanofluids in a cylindrical enclosure
Institute of Scientific and Technical Information of China (English)
Hamid Moradi; Bahamin Bazooyar; Ahmad Moheb; Seyed Gholamreza Etemad
2015-01-01
This study characterizes and optimizes natural convection heat transfer of two Newtonian Al2O3 and TiO2/water nanofluids in a cylindrical enclosure. Nusselt number (Nu) of nanofluids in relation to Rayleigh number (Ra) for different concentrations of nanofluids is investigated at different configurations and orientations of the enclosure. Results show that adding nanoparticles to water has a negligible or even adverse influence upon natural convec-tion heat transfer of water:only a slight increase in natural convection heat transfer of Al2O3/water is observed, while natural convection heat transfer for TiO2/water nanofluid is inferior to that for the base fluid. Results also reveal that at low Ra, the likelihood of enhancement in natural convection heat transfer is more than at high Ra:at low Ra, inclination angle, aspect ratio of the enclosure and nanoparticle concentration influence natural convec-tion heat transfer more pronouncedly than that in high Ra.
Institute of Scientific and Technical Information of China (English)
Ahmad Azari; Mansour Kalbasi; Masoud Derakhshandeh; Masoud Rahimi
2013-01-01
In this work, the laminar convective heat transfer performance and the pressure drop of water-based nanofluids containing Al2O3, TiO2 and SiO2 nanoparticles flowing through a straight circular tube were experimen-tally investigated. The experimental results showed that addition of small amounts of nano-sized Al2O3 and TiO2 particles to de-ionized water increased heat transfer coefficients considerably, while the SiO2 nanofluids showed the opposite behavior attracting the authors’ interests. An average of 16%and 8.2%increase in heat transfer coefficient were observed with the average of 28%and 15%penalty in pressure drop for Al2O3 and TiO2 nanofluids.
Natural convection heat transfer in vertical triangular subchannel in Zirconia-water nanofluid
Tandian, N. P.; Alkharboushi, A. A. K.; Kamajaya, K.
2015-09-01
Natural convection heat transfer in vertical triangular sub-channel has important role in cooling mechanism of the APWR and the PHWR nuclear reactors. Unfortunately, natural convection correlation equations for such geometry are scarcely available. Recent studies showed that ZrO2-water nanofluid has a good prospect to be used in the nuclear reactor technology due to its low neutron absorption cross section. Although several papers have reported transport properties of ZrO2-water nanofluids, practically there is no correlation equation for predicting natural convection heat transfer in a vertical triangular sub-channel in ZrO2-water nanofluid. Therefore, a study for finding such heat transfer correlation equation has been done by utilizing Computational Fluid Dynamics software and reported in this paper. In the study, natural convection heat transfer in a vertical triangular sub-channel has been simulated at several values of heat transfer flux within 9.1 to 30.9 kW/m2 range and ZrO2 concentrations of 0 (pure water), 0.27, and 3 volume-% of ZrO2. The study shows that the ZrO2 concentration has no significant influence to the natural convection heat transfer at those concentration levels. The obtained theoretical heat transfer correlation equations were verified through experiment, and they showed very similar results. The correlation equations are reported in this paper.
Determining convective heat transfer coefficient using phoenics software package
Energy Technology Data Exchange (ETDEWEB)
Kostikov, A.; Matsevity, Y. [Institute of Mechanical Engineering Problems of National Academy of Sciences of Ukraine, Kharkov (Ukraine)
1997-12-31
The two methods of determination of such important quantity of heat exchange on a body surface using PHOENICS are suggested in the presentation. The first method consists in a post-processing of results of conjugate heat transfer problem solved by PHOENICS. The second one is solving an inverse heat conduction problem for solid body using PHOENICS. Comparative characteristic of these two methods is represented. (author) 4 refs.
Effect of Heated Perimeter on Forced Convection Heat Transfer of he i at a Supercritical Pressure
Doi, D.; Shiotsu, M.; Shirai, Y.; Hama, K.
2008-03-01
The forced convection heat transfer coefficients were measured on two pairs of test plates all 6.0 mm in width and located face to face on inner walls of a rectangular duct. Each pair having length of 20 mm and 80 mm, respectively, was connected in series electrically. The rectangular duct was 420 mm in length and 5 mm×6 mm in inner cross section. The experiments were performed for inlet temperatures from 2.2 to 6.5 K, flow velocities from 0.1 to 5.6 m/s, and at a supercritical pressure of 2.8 atm. Comparison of the obtained Nusselt numbers with the former results with a single test plate showed the clear effect of a heated perimeter. Non-dimensional heat transfer equation including the effect of heated perimeter is presented.
Bibliography on augmentation of convective heat and mass transfer
Energy Technology Data Exchange (ETDEWEB)
Bergles, A.E.; Webb, R.L.; Junkhan, G.H.; Jensen, M.K.
1979-05-01
Heat transfer augmentation has developed into a major specialty area in heat transfer research and development. A bibliography of world literature on augmentation is presented. The literature is classified into passive augmentation techniques, which require no external power, and active techniques, which do require external power. The fourteen techniques are grouped in terms of their application to the various modes of heat transfer. Mass transfer is included for completeness. Key words are included with each citation for technique/mode identification. The total number of publications cited is 1,967, including 75 surveys of various techniques and 42 papers on performance evaluation of passive techniques. Patents are not included as they will be the subject of a future topical report.
The effect of blowing or suction on laminar free convective heat transfer on flat horizontal plates
Brouwers, Jos
1993-01-01
In the present paper laminar free convective heat transfer on flat permeable horizontal plates is investigated. To assess the effect of surface suction or injection on heat transfer a correction factor, provided by the film model (or ldquofilm theoryrdquo), is applied. Comparing the film model predi
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.
Taha, T.J.; Lefferts, L.; Meer, van der T.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
Optimal Prandtl number for heat transfer in rotating Rayleigh-Bénard convection
Stevens, Richard Johannes Antonius Maria; Clercx, H.J.H.; Lohse, Detlef
2010-01-01
Numerical data for the heat transfer as a function of the Prandtl (Pr)and Rossby (Ro) numbers in turbulent rotating Rayleigh–Bénard convection are presented for Rayleigh number Ra = 10 8 When Ro is xed, the heat transfer enhancement with respect to the non-rotating value shows a maximum as a functi
Zeinali Heris, Saeed; Noie, Seyyed Hossein; Talaii, Elham; Sargolzaei, Javad
2011-01-01
In this article, laminar flow-forced convective heat transfer of Al2O3/water nanofluid in a triangular duct under constant wall temperature condition is investigated numerically. In this investigation, the effects of parameters, such as nanoparticles diameter, concentration, and Reynolds number on the enhancement of nanofluids heat transfer is studied. Besides, the comparison between nanofluid and pure fluid heat transfer is achieved in this article. Sometimes, because of pressure drop limita...
Slip Flow and Radiative Heat Transfer on a Convectively Heated Vertical Cylinder
Das, S.; Jana, R. N.; Makinde, O. D.
2017-05-01
An axisymmetric laminar boundary-layer slip flow of a viscous incompressible rarefied gas in a convectively heated vertical cylinder in the presence of thermal radiation is analyzed. The governing equations in cylindrical coordinates are transformed into ordinary differential equations by similarity transformation. These transformed equations are then solved numerically, using the fourth order Runge-Kutta method with shooting technique. The effects of the pertinent parameters on the gas velocity, temperature, as well as on the shear stress and heat transfer rate at the cylinder surface, are estimated.
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.
Chabi, A. R.; Zarrinabadi, S.; Peyghambarzadeh, S. M.; Hashemabadi, S. H.; Salimi, M.
2017-02-01
Forced convective heat transfer in a microchannel heat sink (MCHS) using CuO/water nanofluids with 0.1 and 0.2 vol% as coolant was investigated. The experiments were focused on the heat transfer enhancement in the channel entrance region at Re Hydraulic performance of the MCHS was also estimated by measuring friction factor and pressure drop. Results showed that higher convective heat transfer coefficient was obtained at the microchannel entrance. Maximum enhancement of the average heat transfer coefficient compared with deionized water was about 40 % for 0.2 vol% nanofluid at Re = 1150. Enhancement of the convective heat transfer coefficient of nanofluid decreased with further increasing of Reynolds number.
DEFF Research Database (Denmark)
Le Dreau, Jerome; Heiselberg, Per; Jensen, Rasmus Lund
2013-01-01
Night-time ventilation is a promising approach to reduce the energy needed for cooling buildings without reducing thermal comfort. Nevertheless actual building simulation tools have showed their limits in predicting accurately the efficiency of night-time ventilation, mainly due to inappropriate...... 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...... ventilation, the convective heat transfer was well predicted by existing correlations. Nevertheless the change of floor emissivity influenced the CHTC at the surface of interest....
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
Two-phase numerical model for thermal conductivity and convective heat transfer in nanofluids.
Kondaraju, Sasidhar; Lee, Joon Sang
2011-03-21
Due to the numerous applications of nanofluids, investigating and understanding of thermophysical properties of nanofluids has currently become one of the core issues. Although numerous theoretical and numerical models have been developed by previous researchers to understand the mechanism of enhanced heat transfer in nanofluids; to the best of our knowledge these models were limited to the study of either thermal conductivity or convective heat transfer of nanofluids. We have developed a numerical model which can estimate the enhancement in both the thermal conductivity and convective heat transfer in nanofluids. It also aids in understanding the mechanism of heat transfer enhancement. The study reveals that the nanoparticle dispersion in fluid medium and nanoparticle heat transport phenomenon are equally important in enhancement of thermal conductivity. However, the enhancement in convective heat transfer was caused mainly due to the nanoparticle heat transport mechanism. Ability of this model to be able to understand the mechanism of convective heat transfer enhancement distinguishes the model from rest of the available numerical models.
Conjugated laminar forced convective heat transfer from internally finned tubes
Energy Technology Data Exchange (ETDEWEB)
Wen-Quan Tao (Xi' an Jiaotong Univ., Shaanxi (China))
1987-08-01
The use of internal fins is a very effective means of augmenting heat transfer in a tubular heat exchanger, especially for the laminar flow case. Several theoretical investigations have been undertaken to determine heat transfer performance under fully developed conditions. Results reported in the literature are derived for prescribed thermal boundary conditions, wither with axially uniform heat flux with peripherally uniform temperature, or with constant temperature axially as well as circumferentially. However, for double pipe heat exchangers, the thermal boundary condition of the separating wall can not be prescribed a priori; it is determined by the thermal interaction between the fluid inside the tube and that in the annular space. Mikhailov and Shishedjiev (1981), and Tao (1986) have shown that Nusselt number of the tube and that of the annular are strongly dependent upon the heat capacity ratio of the two fluids. In this investigation, a performance analysis is conducted numerically for an internally finned tube which serves as the inner tube of a double pipe heat exchanger.
Transient natural convection heat and mass transfer in crystal growth
Han, Samuel S.
1990-01-01
A numerical analysis of transient combined heat and mass transfer across a rectangular cavity is performed. The physical parameters are selected to represent a range of possible crystal growth in solutions. Good agreements with measurement data are observed. It is found that the thermal and solute fields become highly oscillatory when the thermal and solute Grashof numbers are large.
Experimental study on convection heat transfer and air drag in sinter layer
Institute of Scientific and Technical Information of China (English)
潘利生; 魏小林; 彭岩; 时小宝; 刘怀亮
2015-01-01
Convection heat transfer coefficient and air pressure drop in sinter layer are important factors for the design of sinter cooling craft. Due to the lack of necessary data, the two parameters are studied by experimental method. The experimental results show that heat conduction of sinter impacts the measurement of convection heat transfer coefficient. Convection heat transfer increases with the increase of air volumetric flow rate. Sinter layer without small particles (sample I) gives higher convection heat transfer coefficient than that with small particles (sample II). Under the considered conditions, volumetric convection heat transfer coefficient is in the range of 400−1800 W/(m3·°C). Air pressure drop in sinter layer increases with the increase of normal superficial velocity, as well as with the rise of air temperature. Additionally, air pressure drop also depends on sinter particle size distribution. In considered experimental conditions, pressure drop in sinter sample II is 2−3 times that in sinter sample I, which resulted from 17% small scale particles in sinter sample II.
Simultaneous Heat and Mass Transfer Model for Convective Drying of Building Material
Upadhyay, Ashwani; Chandramohan, V. P.
2016-06-01
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.
Numerical studies of convective heat transfer in an inclined semi-annular enclosure
Wang, L.-W.; Chai, A.-T.; Yung, C.-N.; Rashidnia, N.
1989-01-01
Natural convection heat transfer in a two-dimensional differentially heated semiannular enclosure is studied. The enclosure is isothermally heated and cooled at the inner and outer walls, respectively. A commercial software based on the SIMPLER algorithm was used to simulate the velocity and temperature profiles. Various parameters that affect the momentum and heat transfer processes were examined. These parameters include the Rayleigh number, Prandtl number, radius ratio, and the angle of inclination. A flow regime extending from conduction-dominated to convection-dominated flow was examined. The computed results of heat transfer are presented as a function of flow parameter and geometric factors. It is found that the heat transfer rate attains a minimum when the enclosure is tilted about +50 deg with respect to the gravitational direction.
Numerical studies of convective heat transfer in an inclined semiannular enclosure
Wang, Lin-Wen; Yung, Chain-Nan; Chai, An-Ti; Rashidnia, Nasser
1989-01-01
Natural convection heat transfer in a two-dimensional differentially heated semiannular enclosure is studied. The enclosure is isothermally heated and cooled at the inner and outer walls, respectively. A commercial software based on the SIMPLER algorithm was used to simulate the velocity and temperature profiles. Various parameters that affect the momentum and heat transfer processes were examined. These parameters include the Rayleigh number, Prandtl number, radius ratio, and the angle of inclination. A flow regime extending from conduction-dominated to convection-dominated flow was examined. The computed results of heat transfer are presented as a function of flow parameter and geometric factors. It is found that the heat transfer rate attains a minimum when the enclosure is tilted about +50 deg with respect to the gravitational direction.
Dimensionless formulation of convective heat transfer in fry-drying of sewage sludge
Energy Technology Data Exchange (ETDEWEB)
Romdhana, M.H.; Lecomte, D.; Ladevie, B. [Ecole des Mines d' Albi-Carmaux, Centre RAPSODEE, Albi (France)
2011-11-15
Fry-drying is an alternative for heat and mass transfer intensification. The process reuses waste oil as a heating medium for drying by contact with the wet sludge. At the end of the process, a stable derived fuel is obtained, a granular solid composed of the dried indigenous sewage solid and the impregnated oil. The fry-dried sludge is storable and transportable without any pathogen elements. Knowledge about heat and mass transfer rates during the frying process is essential in order to assess the quality of the final product such as calorific value, oil uptake, porosity changes, etc. The heat transfer properties including transfer by free convection between the solid and the frying oil are fundamental for the process design and manufacturing of the fry-dried product. The convective heat coefficient by temperature measurement and overall energy balance calculation is determined. The heat flux is calculated from the fry-drying kinetics including moisture loss and oil intake kinetics. Various hydrodynamic regimes for convective heat transfer during the frying process are discussed (non-boiling, boiling, and low-boiling regime). A dimensionless formulation for estimating the convective transfer is proposed. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Radiative and free convective heat transfer from a containerless sphere
Johnson, K.
1979-01-01
A mathematical model is derived for heat loss due to radiation and free convection for a small copper sphere (approximately 0.3 to 0.4 cm diameter) cooled by a helium-argon gas mixture. A FORTRAN program written to simplify calculations and extend the range of applicability to experimentation is presented. Pressures used were less than 400 torr, and resulting temperatures ranged from 500 to 4600 K. Comparison of results for initial cooling by the gas mixture with experimental data showed a 5 percent error for temperature values and a 2.7 percent error for the temperature difference caused by the cooling. Results indicate that the accuracy could be increased significantly by using better estimates for thermal conductivities.
Institute of Scientific and Technical Information of China (English)
Pei－XueJiang; Ze－PeiRen; 等
1995-01-01
Forced and mixed convection heat and mass transfer are studied numerically for water containing metallic corrosion products in a heated or cooled vertical tube with variable thermophysical properties at super-citical pressures.the fouling mechanisms and fouling models are presented.The influence of variable properties at super-critical pressures on forced or mixed convection has been analyzed.The differences between heat and mass transfer under heating and cooling conditions are discussed.It is found that variable properties,especially buoyancy,greatly influence the fluid flow and heat mass fransfer.
Convective Heat Transfer Augmentation by Flexible fins in Laminar Channel Pulsating flow
Joshi, Rakshitha U; Bhardwaj, Rajneesh
2015-01-01
Fluid-structure interaction (FSI) of thin flexible fins coupled with convective heat transfer has applications in energy harvesting and in understanding functioning of several biological systems. We numerically investigate FSI of the thin flexible fins involving large-scale flow-induced deformation as a potential heat transfer enhancement technique. An in-house, strongly-coupled fluid-structure interaction (FSI) solver is employed in which flow and structure solvers are based on sharp-interface immersed boundary and finite element method, respectively. We consider twin flexible fins in a heated channel with laminar pulsating cross flow. The vortex ring past the fin sweep higher sources of vorticity generated on the channel walls out into the downstream - promoting the mixing of the fluid. The moving fin assists in convective mixing, augmenting convection in bulk and at the walls; and thereby reducing thermal boundary layer thickness and improving heat transfer at the channel walls. The thermal augmentation is...
Hassan, Ali; Ramzan, Naveed; Umer, Asim; Ahmad, Ayyaz; Muryam, Hina
2017-08-01
The enhancement in the convective heat transfer coefficient of the ethylene glycol (EG) base cuprous oxide (Cu2O) nanofluids were investigated. The nanofluids of different volume concentrations i-e 1%, 2.5% and 4.5% were prepared by the two step method. Cuprous oxide (Cu2O) nanoparticles were ultrasonically stirred for four hours in the ethylene glycol (EG). The experimental study has been performed through circular tube geometry in laminar flow regime at average Reynolds numbers 36, 71 and 116. The constant heat flux Q = 4000 (W/m2) was maintained during this work. Substantial enhancement was observed in the convective heat transfer coefficient of ethylene glycol (EG) base cuprous oxide (Cu2O) nanofluids than the base fluid. The maximum 74% enhancement was observed in convective heat transfer coefficient at 4.5 vol% concentration and Re = 116.
Carbon-nanotube nanofluid thermophysical properties and heat transfer by natural convection
Li, Y.; Suzuki, S.; Inagaki, T.; Yamauchi, N.
2014-11-01
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.
Energy Technology Data Exchange (ETDEWEB)
Nickell, T.W.
1988-01-01
This study numerically analyzes combined radiative and natural or forced convective heat transfer between vertical parallel plates with two-dimensional discrete heat sources. The numerical method was verified by comparing its results with other published experimental data and the agreement was excellent. It is shown that radiative heat transfer is a significant and useful mode of heat transfer in combination with both natural and forced convection in this situation and cannot be neglected. Radiative heat transfer accounted for 50-60% or more of the total heat transfer in some cases, and usually approximately 30-35% on the top of a discrete heat source. This fact can be used to advantage in the thermal design of electronic circuit boards.
A general theoretical principle for single-phase convection heat transfer enhancement
Institute of Scientific and Technical Information of China (English)
WANG SongPing; CHEN QingLin; ZHANG BingJian; HUA Ben
2009-01-01
The main methods of single-phase convection heat transfer enhancement are analyzed in this paper,and the unity of contradiction between heat transfer enhancement and energy consumption(or exergy destruction)is expounded.The thermodynamic relationship between heat(or exergy)transfer efficiency and energy consumption(or exergy destruction)as well as driving forces is established,and a general theoretical principle for single-phase convection heat transfer enhancement is further obtained.The principle shows that temperature gradient field distribution and velocity field distribution constrain each other,and that the optimum heat transfer efficiency can be obtained when they are synergetic.If the level of the synergy of temperature gradient field distribution with velocity field distribution is determined,the relative uniform temperature gradient is required,and vice versa.The principle also shows the relationship of relative temperature gradient with specific heat and coefficient of heat conductivity.The deduced results can be used as a theoretical guidance for single-phase convection heat transfer enhancement and optimum design of heat exchangers.
A general theoretical principle for single-phase convection heat transfer enhancement
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
The main methods of single-phase convection heat transfer enhancement are analyzed in this paper, and the unity of contradiction between heat transfer enhancement and energy consumption(or exergy destruction)is expounded.The thermodynamic relationship between heat(or exergy)transfer efficiency and energy consumption(or exergy destruction)as well as driving forces is established,and a general theoretical principle for single-phase convection heat transfer enhancement is further obtained. The principle shows that temperature gradient field distribution and velocity field distribution constrain each other,and that the optimum heat transfer efficiency can be obtained when they are synergetic.If the level of the synergy of temperature gradient field distribution with velocity field distribution is determined,the relative uniform temperature gradient is required,and vice versa.The principle also shows the relationship of relative temperature gradient with specific heat and coefficient of heat conductivity.The deduced results can be used as a theoretical guidance for single-phase convection heat transfer enhancement and optimum design of heat exchangers.
Convective heat transfer to Sisko fluid over a rotating disk
Munir, Asif
2016-01-01
This article deals with study of the steady flow and heat transfer characteristics of Sisko fluid over a rotating infinite disk. The flow and heat transfer aspects are thoroughly investigated encompassing highly shear thinning/thickening Sisko fluids. The modeled boundary layer equations are reduced to a system of nonlinear ordinary differential equations using the appropriate transformation. The resulting equations are then solved numerically by shooting method in the domain . The numerical data for the velocity and temperature fields are graphically sketched and effects of the relevant parameters are discussed in detail. In addition, the velocity gradients at the disk surface and the local Nusselt number for different values of the pertaining parameters are given in tabulated form. Further, the flow and temperature fields of power-law and Newtonian fluids are also compared with those Sisko fluid. Moreover, a comparison with previously published work, as a special case of the problem, has been provided and t...
Effects of very high turbulence on convective heat transfer
Moffat, R. J.; Maciejewski, P. K.
1984-01-01
The effects of high-intensity, large-scale turbulence on turbulent boundary-layer heat transfer are studied. Flow fields were produced with turbulence intensities up to 40% and length scales up to several times the boundary layer thickness. In addition, three different types of turbulence will be compared to see whether they have the same effect on the boundary layer. The three are: the far field of a free jet, flow downstream of a grid, and flow downstream of a simulated gas turbine combustor. Each turbulence field will be characterized by several measures: intensity (by component), scale, and spectrum. Heat transfer will be measured on a 2.5 m long, 0.5 m wide flat plate using the energy-balance technique. The same plate will be used in each of the four flow fields; a low-turbulence tunnel for baseline data, and the three flow situations mentioned.
Campbell, A N
2015-07-14
When any exothermic reaction proceeds in an unstirred vessel, natural convection may develop. This flow can significantly alter the heat transfer from the reacting fluid to the environment and hence alter the balance between heat generation and heat loss, which determines whether or not the system will explode. Previous studies of the effects of natural convection on thermal explosion have considered reactors where the temperature of the wall of the reactor is held constant. This implies that there is infinitely fast heat transfer between the wall of the vessel and the surrounding environment. In reality, there will be heat transfer resistances associated with conduction through the wall of the reactor and from the wall to the environment. The existence of these additional heat transfer resistances may alter the rate of heat transfer from the hot region of the reactor to the environment and hence the stability of the reaction. This work presents an initial numerical study of thermal explosion in a spherical reactor under the influence of natural convection and external heat transfer, which neglects the effects of consumption of reactant. Simulations were performed to examine the changing behaviour of the system as the intensity of convection and the importance of external heat transfer were varied. It was shown that the temporal development of the maximum temperature in the reactor was qualitatively similar as the Rayleigh and Biot numbers were varied. Importantly, the maximum temperature in a stable system was shown to vary with Biot number. This has important consequences for the definitions used for thermal explosion in systems with significant reactant consumption. Additionally, regions of parameter space where explosions occurred were identified. It was shown that reducing the Biot number increases the likelihood of explosion and reduces the stabilising effect of natural convection. Finally, the results of the simulations were shown to compare favourably with
Porro, A. Robert; Keith, Theo G., Jr.; Hingst, Warren R.; Chriss, Randall M.; Seablom, Kirk D.
1991-01-01
A technique is developed to measure the local convective heat transfer coefficient on a model surface in a supersonic flow field. The technique uses a laser to apply a discrete local heat flux at the model test surface, and an infrared camera system determines the local temperature distribution due to heating. From this temperature distribution and an analysis of the heating process, a local convective heat transfer coefficient is determined. The technique was used to measure the load surface convective heat transfer coefficient distribution on a flat plate at nominal Mach numbers of 2.5, 3.0, 3.5, and 4.0. The flat plate boundary layer initially was laminar and became transitional in the measurement region. The experimental results agreed reasonably well with theoretical predictions of convective heat transfer of flat plate laminar boundary layers. The results indicate that this non-intrusive optical measurement technique has the potential to obtain high quality surface convective heat transfer measurements in high speed flowfields.
Effects of Nonequilibrium at Edge of Boundary Layer on Convective Heat Transfer to a Blunt Body
Goekcen, Tahir; Edwards, Thomas A. (Technical Monitor)
1996-01-01
This investigation is a continuation of a previous study on nonequilibrium convective heat transfer to a blunt body. In the previous study, for relatively high Reynolds number flows, it was found that: nonequilibrium convective heat transfer to a blunt body is not strongly dependent on freestream parameters, provided that the thermochemical equilibrium is reached at the edge of boundary layer; and successful testing of convective heat transfer in an arc-jet environment is possible by duplicating the surface pressure and total enthalpy. The nonequilibrium convective heat transfer computations are validated against the results of Fay and Riddell/Goulard theory. Present work investigates low Reynolds number conditions which are typical in an actual arc-jet flow environment. One expects that there will be departures from the Fay and Riddell/Goulard result since certain assumptions of the classical theory are not satisfied. These departures are of interest because the Fay and Riddell/Goulard formulas are extensively used in arc-jet testing (e.g., to determine the enthalpy of the flow and the catalytic efficiency of heat shield materials). For practical sizes of test materials, density of the test flow (and Reynolds number) in an arc-jet is such that thermochemical equilibrium may not be reached at the edge of boundary layer. For blunt body flows of nitrogen and air, computations will be presented to show the effects of thermochemical nonequilibrium at the boundary layer edge on nonequilibrium heat transfer.
Convective Heat Transfer in the Reusable Solid Rocket Motor of the Space Transportation System
Ahmad, Rashid A.; Cash, Stephen F. (Technical Monitor)
2002-01-01
This simulation involved a two-dimensional axisymmetric model of a full motor initial grain of the Reusable Solid Rocket Motor (RSRM) of the Space Transportation System (STS). It was conducted with CFD (computational fluid dynamics) commercial code FLUENT. This analysis was performed to: a) maintain continuity with most related previous analyses, b) serve as a non-vectored baseline for any three-dimensional vectored nozzles, c) provide a relatively simple application and checkout for various CFD solution schemes, grid sensitivity studies, turbulence modeling and heat transfer, and d) calculate nozzle convective heat transfer coefficients. The accuracy of the present results and the selection of the numerical schemes and turbulence models were based on matching the rocket ballistic predictions of mass flow rate, head end pressure, vacuum thrust and specific impulse, and measured chamber pressure drop. Matching these ballistic predictions was found to be good. This study was limited to convective heat transfer and the results compared favorably with existing theory. On the other hand, qualitative comparison with backed-out data of the ratio of the convective heat transfer coefficient to the specific heat at constant pressure was made in a relative manner. This backed-out data was devised to match nozzle erosion that was a result of heat transfer (convective, radiative and conductive), chemical (transpirating), and mechanical (shear and particle impingement forces) effects combined.
Effects of Nonequilibrium at Edge of Boundary Layer on Convective Heat Transfer to a Blunt Body
Goekcen, Tahir; Edwards, Thomas A. (Technical Monitor)
1996-01-01
This investigation is a continuation of a previous study on nonequilibrium convective heat transfer to a blunt body. In the previous study, for relatively high Reynolds number flows, it was found that: nonequilibrium convective heat transfer to a blunt body is not strongly dependent on freestream parameters, provided that the thermochemical equilibrium is reached at the edge of boundary layer; and successful testing of convective heat transfer in an arc-jet environment is possible by duplicating the surface pressure and total enthalpy. The nonequilibrium convective heat transfer computations are validated against the results of Fay and Riddell/Goulard theory. Present work investigates low Reynolds number conditions which are typical in an actual arc-jet flow environment. One expects that there will be departures from the Fay and Riddell/Goulard result since certain assumptions of the classical theory are not satisfied. These departures are of interest because the Fay and Riddell/Goulard formulas are extensively used in arc-jet testing (e.g., to determine the enthalpy of the flow and the catalytic efficiency of heat shield materials). For practical sizes of test materials, density of the test flow (and Reynolds number) in an arc-jet is such that thermochemical equilibrium may not be reached at the edge of boundary layer. For blunt body flows of nitrogen and air, computations will be presented to show the effects of thermochemical nonequilibrium at the boundary layer edge on nonequilibrium heat transfer.
Predicting Turbulent Convective Heat Transfer in Fully Developed Duct Flows
Rokni, Masoud; Gatski, Thomas B.
2001-01-01
The performance of an explicit algebraic stress model (EASM) is assessed in predicting the turbulent flow and forced heat transfer in both straight and wavy ducts, with rectangular, trapezoidal and triangular cross-sections, under fully developed conditions. A comparison of secondary flow patterns. including velocity vectors and velocity and temperature contours, are shown in order to study the effect of waviness on flow dynamics, and comparisons between the hydraulic parameters. Fanning friction factor and Nusselt number, are also presented. In all cases. isothermal conditions are imposed on the duct walls, and the turbulent heat fluxes are modeled using gradient-diffusion type models. The formulation is valid for Reynolds numbers up to 10(exp 5) and this minimizes the need for wall functions that have been used with mixed success in previous studies of complex duct flows. In addition, the present formulation imposes minimal demand on the number of grid points without any convergence or stability problems. Criteria in terms of heat transfer and friction factor needed to choose the optimal wavy duct cross-section for industrial applications among the ones considered are discussed.
Directory of Open Access Journals (Sweden)
HAROON IMTIAZ
2017-04-01
Full Text Available In this paper, we investigate numerically the effect of thermal boundary conditions on conjugated conduction-free convection heat transfer in an annulus between two concentric cylinders using Fourier Spectral method. The inner wall of the annulus is heated and maintained at either CWT (Constant Wall Temperature or CHF (Constant Heat Flux, while the outer wall is maintained at constant temperature. CHF case is relatively more significant for high pressure industrial applications, but it has not received much attention. This study particularly focuses the latter case (CHF. The main influencing parameters on flow and thermal fields within the annulus are: Rayleigh number Ra; thickness of inner wall Rs; radius ratio Rr and inner wall-fluid thermal conductivity ratio Kr. The study has shown that the increase in Kr increases the heat transfer rate through the annulus for heating at CWT and decreases the inner wall dimensionless temperature for heating at CHF and vice versa. It has also been proved that as the Rs increases at fixed Ra and Rr, the heat transfer rate decreases for heating at CWT and the inner wall dimensionless temperature increases for heating at CHF at Kr 1 depends on Rr. It has been shown that for certain combinations of controlling parameters there will be a value of Rr at which heat transfer rate will be minimum in the annulus in case of heating at CWT, while
DEFF Research Database (Denmark)
Steskens, Paul Wilhelmus Maria Hermanus; Janssen, Hans; Rode, Carsten
2009-01-01
HAM conditions. The paper focuses on the influence of the interior surface heat and moisture transfer coefficients, and investigates its effect on the hygrothermal performance. The parameter study showed that the magnitude of the convective surface transfer coefficients have a relatively large......Current models to predict heat, air and moisture (HAM) conditions in buildings assume constant boundary conditions for the temperature and relative humidity of the neighbouring air and for the surface heat and moisture transfer coefficients. These assumptions may introduce errors in the predicted...... influence on the predicted hygrothermal conditions at the surface of a building component and on the heat and vapour exchange with the indoor environment....
Nanofluid flow and forced convection heat transfer over a stretching surface considering heat source
Mohammadpour, M.; Valipour, P.; Shambooli, M.; Ayani, M.; Mirparizi, M.
2015-07-01
In this paper, magnetic field effects on the forced convection flow of a nanofluid over a stretching surface in the presence of heat generation/absorption are studied. The equations of continuity, momentum and energy are transformed into ordinary differential equations and solved numerically using the fourth-order Runge-Kutta integration scheme featuring the shooting technique. Different types of nanoparticles as copper (Cu), silver (Ag), alumina (Al2O3) and titania (TiO2) with water as their base fluid has been considered. The influence of significant parameters, such as magnetic parameter, volume fraction of the nanoparticles, heat generation/absorption parameter, velocity ratio parameter and temperature index parameter on the flow and heat transfer characteristics are discussed. The results show that the values of temperature profiles increase with increasing heat generation/absorption and volume fraction of the nanoparticles but they decrease with increasing velocity ratio parameter and temperature index parameter. Also, it can be found that selecting silver as nanoparticle leads to the highest heat transfer enhancement.
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.
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.
Convective Heat Transfer Between the Wall Surface of a Cavity and the External Main Stream
Yoshiwara, Masahiro; Katto, Yoshiro; Yokoyama, Masanori
An experimental study has been made under the following conditions for convective heat transfer between the wall surface of a cavity of which both width and depth are 25 mm and the external main stream; the range of Reynolds numbers is from 104 to 105, and the ratio of tripping wire diameter to cavity width is 0.08. The oncoming boundary layer to a cavity is turbulent by the tripping wire with the existing study. Convective heat transfer between a cavity wall surface and the external main stream is treated by the following two phenomena; one is the heat transfer which is related to the temperature difference between the wall surface and the fluid in the cavity, and the other the heat transfer which is related to the temperature difference between the fluid in a cavity and the external mainstream. Experimental data obtained for the foregoing conditions is almost coincide with the existing dimensionless correlations of two of the authors.
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...
Experimental Study on Convective Boiling Heat Transfer in Vertical Narrow Gap Annular Tube
Institute of Scientific and Technical Information of China (English)
Li Bin; He Anding; Wang Yueshe; Zhou Fangde
2001-01-01
Experiments are conducted to investigate the characteristics of single-phase forced-flow convection and boiling heat transfer of R113 flowing through annular tube with gap of 1, 1.5 and 2.5 mm, and also the visualization test are carried out to get two-phase flow regime. The data show that the Nusselt numbers for the narrow-gap are higher than those predicted by traditional large channel correlation and boiling heat transfer is enhanced. Based on the data obtained in this investigation, correlations for single-phase, forced convection and flow boiling in annular tube of different gap size has been developed.
Mixed convection heat transfer from a vertical plate to non-Newtonian fluids
Wang, T.-Y.
1995-02-01
The nonsimilar boundary-layer analysis of steady laminar mixed-convection heat transfer between a vertical plate and non-Newtonian fluids is extended and unified. A mixed-convection parameter zeta is proposed to replace the conventional Richardson number, Gr/Re(exp 2/(2 - n)) and to serve as a controlling parameter that determines the relative importance of the forced and the free convection. The value of mixed-convection parameter lies between 0 and 1. In addition, the power-law model is used for non-Newtonian fluids with exponent n less than 1 for pseudoplastics; n = 1 for Newtonian fluids; and n greater than 1 for dilatant fluids. Furthermore, the coordinates and dependent variables are transformed to yield computationally efficient numerical solutions that are valid over the entire range of mixed convection, from the pure forced-convection limit to the pure free-convection limit, and the whole domain of non-Newtonian fluids, from pseudoplastics to dilatant fluids. The effects of the mixed-convection parameter, the power-law viscosity index, and the generalized Prandtl number on the velocity profiles, the temperature profiles, as well as on the wall skin friction and heat transfer rate are clearly illustrated for both cases of buoyancy assisting and opposing flow conditions.
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.
Hayat, T.; Farooq, S.; Ahmad, B.; Alsaedi, A.
2016-04-01
This article addresses the characteristics of convective heat transfer and radially imposed magnetic field on peristaltic flow of an incompressible Carreau fluid in a curved channel. Joule heating is also present. Mathematical analysis has been carried out under long wavelength and low Reynolds number considerations. Solutions of the resulting non-linear system for small values of Weissenberg number are constructed. The salient features of flow quantities are pointed out with particular focus to pumping, velocity, temperature and trapping. It is observed pressure gradient enhances for larger values of power law index parameter. The velocity and temperature are decreasing functions of radial magnetic field parameter. Further the impact of Weissenberg and Biot numbers on the temperature are opposite.
Institute of Scientific and Technical Information of China (English)
安刚; 李俊明; 王补宣
2001-01-01
Theoretical investigations have been performed on the convective heat transfer for incompressible laminar flow of gases through microtube and parallel-plates micropassages with constant wall temperature. Considering the change in thermal conductivity and viscosity of gas in wall adjacent region from the kinetic theory, mathematical models are built for both of the micropassages. The dimensionless temperature distribution and the corresponding heat transfer characteristics are simulated numerically, and the results discussed briefly.
Measurement of convective heat transfer to solid cylinders inside ventilated shrouds
Daryabeigi, K.; Germain, E. F.; Ash, R. L.
1984-01-01
The influence of ventilated cylindrical shrouds on the convective heat transfer to circular cylinders has been studied experimentally. Geometries studied were similar to those used in commercially available platinum resistance thermometers. Experiments showed that thermal response (convection) was enhanced when the shroud ventilation factor was approximately 20 percent (80 percent solid), and that maximum enhancement occurred when the ventilation holes were located symmetrically on either side of the stagnation lines.
Convection Heat Transfer and Flow Calculations Suitable for Electric Machines Thermal Models
Cavagnino, Andrea
2008-01-01
This paper deals with the formulations used to predict convection cooling and flow in electric machines. Empirical dimensionless analysis formulations are used to calculate convection heat transfer. The particular formulation used is selected to match the geometry of the surface under consideration and the cooling type used. Flow network analysis, which is used to study the ventilation inside the machine, is also presented. In order to focus the discussion using examples, a commercial softwar...
Brandon, S.; Derby, J. J.
1992-01-01
In the present investigation of crystalline phase internal radiation and heat conduction during the vertical Bridgman growth of a YAG-like oxide crystal, where transport through the melt is dominated by convection and conduction, heat is also noted to be conducted through ampoule walls via natural convection and enclosure radiation. The results of a quasi-steady-state axisymmetric Galerkin FEM indicate that heat transfer through the system is powerfully affected by the optical absorption coefficient of the crystal. The coupling of internal radiation through the crystal with conduction through the ampoule walls promotes melt/crystal interface shapes that are highly reflected near the ampoule wall.
Kumar, Varun; Kumar, Manoj; Shakher, Chandra
2014-09-20
In this paper, the local convective heat transfer coefficient (h) is measured along the surface of an electrically heated vertical wire using digital holographic interferometry (DHI). Experiments are conducted on wires of different diameters. The experimentally measured values are within the range as given in the literature. DHI is expected to provide a more accurate local convective heat transfer coefficient (h) as the value of the temperature gradient required for the calculation of "h" can be obtained more accurately than by other existing optical interferometric techniques without the use of a phase shifting technique. This is because in digital holography phase measurement accuracy is expected to be higher.
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.
CFD Analysis of Convective Heat Transfer Coefficient on External Surfaces of Buildings
Directory of Open Access Journals (Sweden)
Andrea de Lieto Vollaro
2015-07-01
Full Text Available Convective heat transfer coefficients for external building surfaces are essential in building energy simulation (BES to calculate convective heat gains and losses from building facades and roofs to the environment. These coefficients are complex functions of: building geometry, building surroundings, local air flow patterns and temperature differences. A microclimatic analysis in a typical urban configuration, has been carried out using Ansys Fluent Version 14.0, an urban street canyon, with a given H/W ratio, has been considered to simulate a three-dimensional flow field and to calculate the thermal fluid dynamics parameters that characterize the street canyon. In this paper, the convective heat transfer coefficient values on the windward external façade of the canyon and on the windward and leeward inner walls are analyzed and a comparison with values from experimental and numerical correlations is carried out.
Convective Heat Transfer over a Wall Mounted Cube Using Large Eddy Simulation
Directory of Open Access Journals (Sweden)
Habibollah Heidarzadeh
2012-06-01
Full Text Available Fluid flow and convective heat transfer over wall mounted cube have been studied numerically using Large Eddy Simulation. Surface of wall mounted cube and plane floor has a constant heat flux. Two subgrid scale models were used in this study; Wall-Adapting Eddy viscosity (WALE and Dynamic Smagorinsky (DS. The numerical results were compared with the experimental data of Nakamura et al [2] that showed DS model has better results toward WALE model. Results contain the plots of time averaged normalized streamwise velocity and Reynolds stress in different positions, Temperature contours, local Nusselt number over the surfaces of cube and some characteristics of flow field and heat transfer. The local convective heat transfer from the surfaces of the cube and plate are directly related to the complexity of flow field.
Sabin, C. M.; Poppendiek, H. F.
1971-01-01
A number of heat transfer and fluid flow mechanisms that control once-through, forced convection potassium boiling are studied analytically. The topics discussed are: (1) flow through tubes containing helical wire inserts, (2) motion of droplets entrained in vapor flow, (3) liquid phase distribution in boilers, (4) temperature distributions in boiler tube walls, (5) mechanisms of heat transfer regime change, and (6) heat transfer in boiler tubes. Whenever possible, comparisons of predicted and actual performances are made. The model work presented aids in the prediction of operating characteristics of actual boilers.
Convective heat transfer of nanofluid flow through conduits with different cross-sectional shapes
Energy Technology Data Exchange (ETDEWEB)
Salimpour, Mohammad Reza; Dehshiri-Parizi, Amir [Isfahan University of Technology, Isfahan (Iran, Islamic Republic of)
2015-02-15
This study investigates the laminar forced convective heat transfer of TiO{sub 2}/water nanofluids through conduits with different cross sections, experimentally. The effects of different parameters, such as cross-sectional shape, Reynolds number, and concentration of nanoparticles, on the enhanced heat transfer are examined by designing and assembling an experimental apparatus. Results show that adding a small amount of nanoparticles to the base fluid improves heat transfer behavior in conduits. A conduit with a circular cross section performs better than conduits with square and triangular cross sections. However, conduits with square and triangular cross sections exhibit more relative enhancements than a conduit with a circular cross section.
Influence of humidity on the convective heat transfer from small cylinders
Still, M.; Venzke, H.; Durst, F.; Melling, A.
The convective heat transfer from a cylinder to a humid air stream flowing normal to the cylinder was investigated experimentally at atmospheric pressure over a range of variables which is relevant to the use of hot-wire anemometry: air temperatures between 30°C and 70°C and velocities between 12 and 37 m/s. For molar fractions of water vapour up to 0.27, the heat transfer increased with increasing humidity. The ratio of heat transfer rates in humid air and dry air is a unique function of the molar fraction of water vapour, independent of the air temperature and flow velocity.
A numerical study of momentum and forced convection heat transfer ...
African Journals Online (AJOL)
temperature fields, axial velocity profiles, local and average Nusselt numbers, and skin frictions were ... Key words: Finite volume method - Turbulent flow - Forced convection - Waved baffles. .... numerical simulations are conducted in a two-.
Kim, K.; Wiedner, B.; Camci, C.
1993-01-01
A combined convective heat transfer and fluid dynamics investigation in a turbulent round jet impinging on a flat surface is presented. The experimental study uses a high resolution liquid crystal technique for the determination of the convective heat transfer coefficients on the impingement plate. The heat transfer experiments are performed using a transient heat transfer method. The mean flow and the character of turbulent flow in the free jet is presented through five hole probe and hot wire measurements, respectively. The flow field character of the region near the impingement plate plays an important role in the amount of convective heat transfer. Detailed surveys obtained from five hole probe and hot wire measurements are provided. An extensive validation of the liquid crystal based heat transfer method against a conventional technique is also presented. After a complete documentation of the mean and turbulent flow field, the convective heat transfer coefficient distributions on the impingement plate are presented. The near wall of the impingement plate and the free jet region is treated separately. The current heat transfer distributions are compared to other studies available from the literature. The present paper contains complete sets of information on the three dimensional mean flow, turbulent velocity fluctuations, and convective heat transfer to the plate. The experiments also prove that the present nonintrusive heat transfer method is highly effective in obtaining high resolution heat transfer maps with a heat transfer coefficient uncertainty of 5.7 percent.
An analytical comparison of convective heat transfer correlations in supercritical hydrogen
Dziedzic, William M.; Jones, Stuart C.; Gould, Dana C.; Petley, Dennis H.
1991-01-01
Four correlations that cover the ranges of liquid to gas for turbulent flow convection of hydrogen are compared with CFD analysis over a range of expected design conditions for active cooling of hypersonic aircraft. Analysis of hydrogen cooling in a typical cooling panel shows how predicted design performance varies with the correlation utilized. The CFD heat transfer coefficient results for a heat spike differed significantly from all four correlations. An acceptable heat transfer coefficient can be calculated at the heat spike location by overlooking the coefficient at the spike and averaging the coefficient before and after the spike.
Wang, J. X.; Jia, P. Y.; Wang, Y. S.; Jiang, L.
2010-03-01
In this article, using Gibson-Ashby constitutive model, we suggest a new method for numerical investigation of forced convection heat transfer in porous foam metal, and try to consolidate the study for mechanical property and that for thermal characteristic. By available experimental data, we simulated to two cases, namely as the transfer in porous media for diameter is 0.6 mm and porosity is 0.402, and for diameter is 1.6 mm and porosity is 0.462. The result, from our constitutive model for single forced convection heat transfer, corresponds well with the experimental data. As for pressure drop prediction in porous is in good agreement with experiment, and the error is only 5% to 10%, but for transfer is less accurate, the error is about 20%, which is acceptable in practice. So it is done that constitutive model is used to simulate the transfer property.
Maldonado, Jaime J.
1994-01-01
Hypersonic vehicles are exposed to extreme thermal conditions compared to subsonic aircraft; therefore, some level of thermal management is required to protect the materials used. Normally, hypersonic vehicles experience the highest temperatures in the nozzle throat, and aircraft and propulsion system leading edges. Convective heat transfer augmentation techniques can be used in the thermal management system to increase heat transfer of the cooling channels in those areas. The techniques studied in this report are pin-fin, offset-fin, ribbed and straight roughened channel. A smooth straight channel is used as the baseline for comparing the techniques. SINDA '85, a lumped parameter finite difference thermal analyzer, is used to model the channels. Subroutines are added to model the fluid flow assuming steady one dimensional compressible flow with heat addition and friction. Correlations for convective heat transfer and friction are used in conjunction with the fluid flow analysis mentioned. As expected, the pin-fin arrangement has the highest heat transfer coefficient and the largest pressure drop. All the other devices fall in between the pin-fin and smooth straight channel. The selection of the best heat augmentation method depends on the design requirements. A good approach may be a channel using a combination of the techniques. For instance, several rows of pin-fins may be located at the region of highest heat flux, surrounded by some of the other techniques. Thus, the heat transfer coefficient is maximized at the region of highest heat flux while the pressure drop is not excessive.
Directory of Open Access Journals (Sweden)
Qiming Men
2014-01-01
Full Text Available Aiming at the heat transfer calculation of the Passive Residual Heat Removal Heat Exchanger (PRHR HX, experiments on the heat transfer of C-shaped tube immerged in a water tank were performed. Comparisons of different correlation in literatures with the experimental data were carried out. It can be concluded that the Dittus-Boelter correlation provides a best-estimate fit with the experimental results. The average error is about 0.35%. For the tube outside, the McAdams correlations for both horizontal and vertical regions are best-estimated. The average errors are about 0.55% for horizontal region and about 3.28% for vertical region. The tank mixing characteristics were also investigated in present work. It can be concluded that the tank fluid rose gradually which leads to a thermal stratification phenomenon.
Heat transfer in a gray tube with forced convection, internal radiation and axial wall conduction
Chung, B. T. F.; Thompson, J. E.
1983-01-01
A method of successive approximations is employed to solve the problem of heat transfer to a transparent gas flowing through a radiating-conducting tube with turbulent forced convection between the tube wall and the gas, and with energy generation in the wall. Emphasis is given to the effect of emissivity of the wall to the tube and gas temperature profiles.
Forced Convective Heat Transfer in a Plate Channel Filled with Solid Particles
Institute of Scientific and Technical Information of China (English)
Pei－XueJiang; Ze－PeiRen; 等
1996-01-01
A numerical study of fluid flow and convective heat transfer in a plate channel filled with solid(metallic)perticles is presented in this paper,The study uses the thermal equilibrium model and a newly developed numerical model which does not assume idealized local thermal equilibrium between the solid particles and the fluid.The numerical simulation results are compared with the experimental data in reference[2].The paper investigates the effects of the assumption of local thermal equilibrium versus non-thermal equilibrium,the thermal conductivity of the solid particles and the particle diameter on convective heat transfer.For the conditions studied.the convective heat transfer and the temperature filed assuming local thermal equilibrium are much different from that for the non-thermal equilibrium assumption when the difference between the solid and fluid thermal conductivities is large,The relative values of the thermal conductivities of the solid particles and the fluid also have a profound effect on the temperature distribution in the channel.The pressure drop decreases as the particle diameter increases and the convective heat transfer coefficient may decrease of increase as the particle diameter increasws depending on the values of ε，λs，λf,λd,αu，ρu.
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...
Institute of Scientific and Technical Information of China (English)
张寅平; 胡先旭; 郝磬; 王馨
2003-01-01
This paper analyzes the convective heat transfer enhancement mechanism of latent heat functionally thermal fluid. By using the proposed internal heat source model, the influence of each factor affecting the heat transfer enhancement of laminar flow in a circular tube with constant heat flux is analyzed. The main influencing factors and the mechanisms of heat transfer enhancement are clarified, and the influences of the main factors on the heat transfer enhancement are quantitatively analyzed. A modified Nusselt number for internal flow is introduced to describe more effectively the degree of heat transfer enhancement for latent functionally thermal fluid.
Determination of drying kinetics and convective heat transfer coefficients of ginger slices
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.
Methods for characterizing convective cryoprobe heat transfer in ultrasound gel phantoms.
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
Guo, Ning; Finnerman, Oskar; Ström, Henrik
2016-06-01
The effect of turbulent velocity fluctuations on the convective heat transfer to single droplets in a turbulent channel flow are investigated numerically. It is found that for properties relevant to typical liquid spray applications, the convective heat transfer is enhanced with increasing droplet size and bulk Reynolds number. The combined effect of convective heat transfer enhancement and increased driving forces for heat and mass transfer due to droplet dispersion is thereafter investigated for a commercial spray application. The probability distribution functions of droplet properties in the spray are found to be significantly affected by the presence of turbulent velocity fluctuations in the carrier phase.
Theoretical Convective Heat Transfer Model Developement of Cold Storage Using Taguchi Analysis.
Directory of Open Access Journals (Sweden)
Dr.N.Mukhopadhyay
2015-01-01
Full Text Available Energy crisis is one of the most important problems the world is facing now-a-days. With the increase of cost of electrical energy operating cost of cold storage storing is increasing which forces the increased cost price of the commodities that are kept. In this situation if the maximum heat energy(Q is absorbed by the evaporator inside the cold room through convective heat transfer process in terms of –heat transfer due to convection and heat transfer due to condensation, more energy has to be wasted to maintain the evaporator space at the desired temperature range of 2- 8 degree centigrade. In this paper we have proposed a theoretical heat transfermodel of convective heat transfer incold storage using Taguchi L9 orthogonal array. Velocity of air(V, Temperature difference(dT, RelativeHumidity(RHare the basic variable and three ranges are taken each of them in the model development. Graphical interpretations from the model justifies the reality
Enhanced convective heat transfer using graphene dispersed nanofluids.
Baby, Tessy Theres; Ramaprabhu, Sundara
2011-04-04
Nanofluids are having wide area of application in electronic and cooling industry. In the present work, hydrogen exfoliated graphene (HEG) dispersed deionized (DI) water, and ethylene glycol (EG) based nanofluids were developed. Further, thermal conductivity and heat transfer properties of these nanofluids were systematically investigated. HEG was synthesized by exfoliating graphite oxide in H2 atmosphere at 200°C. The nanofluids were prepared by dispersing functionalized HEG (f-HEG) in DI water and EG without the use of any surfactant. HEG and f-HEG were characterized by powder X-ray diffractometry, electron microscopy, Raman and FTIR spectroscopy. Thermal and electrical conductivities of f-HEG dispersed DI water and EG based nanofluids were measured for different volume fractions and at different temperatures. A 0.05% volume fraction of f-HEG dispersed DI water based nanofluid shows an enhancement in thermal conductivity of about 16% at 25°C and 75% at 50°C. The enhancement in Nusselts number for these nanofluids is more than that of thermal conductivity.
Enhanced convective heat transfer using graphene dispersed nanofluids
Directory of Open Access Journals (Sweden)
Baby Tessy
2011-01-01
Full Text Available Abstract Nanofluids are having wide area of application in electronic and cooling industry. In the present work, hydrogen exfoliated graphene (HEG dispersed deionized (DI water, and ethylene glycol (EG based nanofluids were developed. Further, thermal conductivity and heat transfer properties of these nanofluids were systematically investigated. HEG was synthesized by exfoliating graphite oxide in H2 atmosphere at 200°C. The nanofluids were prepared by dispersing functionalized HEG (f-HEG in DI water and EG without the use of any surfactant. HEG and f-HEG were characterized by powder X-ray diffractometry, electron microscopy, Raman and FTIR spectroscopy. Thermal and electrical conductivities of f-HEG dispersed DI water and EG based nanofluids were measured for different volume fractions and at different temperatures. A 0.05% volume fraction of f-HEG dispersed DI water based nanofluid shows an enhancement in thermal conductivity of about 16% at 25°C and 75% at 50°C. The enhancement in Nusselts number for these nanofluids is more than that of thermal conductivity.
Investigating Convective Heat Transfer with an Iron and a Hairdryer
Gonzalez, Manuel I.; Lucio, Jesus H.
2008-01-01
A simple experimental set-up to study free and forced convection in undergraduate physics laboratories is presented. The flat plate of a domestic iron has been chosen as the hot surface, and a hairdryer is used to generate an air stream around the plate. Several experiments are proposed and typical numerical results are reported. An analysis and…
Influence of ventilated shrouds on the convective heat transfer to a circular cylinder
Daryabeigi, Kamran; Ash, Robert L.; Dillon-Townes, Lawrence A.
1987-01-01
Convective heat transfer to shrouded cylinders in transverse flow has been studied over the Reynolds number range 2000-20,000. The influence of shroud ventilation, relative shroud diameters, and orientation of the ventilation holes was studied. In some cases, average inner-cylinder Nusselt numbers were found to exceed the comparable bare-cylinder values by as much as 50 percent. Cylinder heat convection was influenced more by the degree of ventilation and shroud diameter than by hole orientation. An equivalent inner bare cylinder diameter, based on degree of shroud ventilation and shroud diameter, was developed which can be useful in shroud design studies.
Alam, Muntasir; Kamruzzaman, Ahsan, Faraz; Hasan, Mohammad Nasim
2016-07-01
A numerical study of mixed convection heat transfer phenomena in a square cavity containing a heat conducting rotating cylinder has been investigated. A discrete isoflux heater is placed at the bottom wall of the enclosure while the top wall is kept adiabatic. Left and right sidewalls of the enclosure are assumed to be maintained at constant low temperature. A two-dimensional solution for steady laminar mixed convection flow is obtained by using the finite element scheme based on the Galerkin method of weighted residuals for different rotating speeds of the cylinder varying over the range of 0-1000 keeping the Rayleigh number fixed at 5×104 and the Prandtl number at 0.7. The effects of rotating speeds of the cylinder, its radius and conductivity ratio of the rotating cylinder and working fluid on the streamlines, isotherms, local Nusselt number, average Nusselt number and other heat transfer and fluid flow phenomena are investigated. The results indicate that the flow field, temperature distribution and heat transfer rate are dependent on rotating speeds and cylinder size. However, it has been observed that the effect of conductivity ratio is not so prominent.
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.
The Impact of Reduced Gravity on Free Convective Heat Transfer from a Finite, Flat, Vertical Plate
Lotto, Michael A.; Johnson, Kirstyn M.; Nie, Christopher W.; Klaus, David M.
2017-09-01
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 1g 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 1g, 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.
Directory of Open Access Journals (Sweden)
DONG-GYU LEE
2013-12-01
The predicted temperature field has indicated that the peak temperature is located in the second basket from the top along the vertical center line by effects of the natural convection. As the Rayleigh number increases, the convective heat transfer is dominant and the heat transfer due to the local circulation becomes stronger. The heat transfer characteristics show that the Nusselt numbers corresponding to 1.5×106 1.0×107.
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.
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.
Feedback control and heat transfer measurements in a Rayleigh-Bénard convection cell
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 convection pattern formed by 6 transverse rolls throughout the range of Rayleigh numbers.
Directory of Open Access Journals (Sweden)
Zeinali Heris Saeed
2011-01-01
Full Text Available Abstract In this article, laminar flow-forced convective heat transfer of Al2O3/water nanofluid in a triangular duct under constant wall temperature condition is investigated numerically. In this investigation, the effects of parameters, such as nanoparticles diameter, concentration, and Reynolds number on the enhancement of nanofluids heat transfer is studied. Besides, the comparison between nanofluid and pure fluid heat transfer is achieved in this article. Sometimes, because of pressure drop limitations, the need for non-circular ducts arises in many heat transfer applications. The low heat transfer rate of non-circular ducts is one the limitations of these systems, and utilization of nanofluid instead of pure fluid because of its potential to increase heat transfer of system can compensate this problem. In this article, for considering the presence of nanoparticl: es, the dispersion model is used. Numerical results represent an enhancement of heat transfer of fluid associated with changing to the suspension of nanometer-sized particles in the triangular duct. The results of the present model indicate that the nanofluid Nusselt number increases with increasing concentration of nanoparticles and decreasing diameter. Also, the enhancement of the fluid heat transfer becomes better at high Re in laminar flow with the addition of nanoparticles.
Zeinali Heris, Saeed; Noie, Seyyed Hossein; Talaii, Elham; Sargolzaei, Javad
2011-02-28
In this article, laminar flow-forced convective heat transfer of Al2O3/water nanofluid in a triangular duct under constant wall temperature condition is investigated numerically. In this investigation, the effects of parameters, such as nanoparticles diameter, concentration, and Reynolds number on the enhancement of nanofluids heat transfer is studied. Besides, the comparison between nanofluid and pure fluid heat transfer is achieved in this article. Sometimes, because of pressure drop limitations, the need for non-circular ducts arises in many heat transfer applications. The low heat transfer rate of non-circular ducts is one the limitations of these systems, and utilization of nanofluid instead of pure fluid because of its potential to increase heat transfer of system can compensate this problem. In this article, for considering the presence of nanoparticl: es, the dispersion model is used. Numerical results represent an enhancement of heat transfer of fluid associated with changing to the suspension of nanometer-sized particles in the triangular duct. The results of the present model indicate that the nanofluid Nusselt number increases with increasing concentration of nanoparticles and decreasing diameter. Also, the enhancement of the fluid heat transfer becomes better at high Re in laminar flow with the addition of nanoparticles.
Directory of Open Access Journals (Sweden)
Missoum Abdelkrim
2016-01-01
Full Text Available This study focuses on the numerical simulation of heat transfer by natural convection in a rectangular enclosure, filled with a liquid metal (low Prandtl number partially heated from below with a sinusoidal temperature. The value of the study lies in its involvement in the crystal growth for the manufacture of semiconductors and electronics cooling. Indeed, the occurrence of convection during crystal growth can lead to in homogeneities that lead to striations and defects that affect the quality of the crystals obtained by the Bridgman techniques or Chochrawlski. Temperature of the oscillations, due to the instabilities of the convective flow in the liquid metal, also induces non-uniform cooling in the solidification front. Convection is then studied in order to reduce it. A modelling of the problem in two dimensions was conducted using Comsol computer code that is based on the finite element method, by varying the configuration of the control parameters, namely, the Rayleigh number, the nature of fluid (Prandtl number and amplitude of temperature on heat transfer rate (Nusselt number on convective structures that appear.
A convective and radiative heat transfer analysis for the FIRE II forebody
Greendyke, Robert B.; Hartung, Lin C.
1993-01-01
A Navier-Stokes flowfield solution method (LAURA code) using finite-rate chemistry and two-temperature thermal nonequilibrium was used in combination with two nonequilibrium radiative heat transfer codes to calculate heating for the FIRE II vehicle. An axisymmetric model of the actual body shape was used. One radiative heating code (NEQAIR) was used in uncoupled fashion with the flowfield solver's energy equations, while the other code (LORAN) was used in both coupled and uncoupled variations. Several trajectory points ranging from highly nonequilibrium flow to near-equilibrium flow were used for a study of both convective and radiative heating over the vehicle. Considerable variation in radiative heating was seen at the extremes, while agreement was good in the intermediate trajectory points. Total heat transfer calculations gave good comparison until the peak heating trajectory points were encountered, and returned to good agreement for the last two equilibrium points.
Two phase convective heat transfer augmentation in swirl flow with non-boiling
Energy Technology Data Exchange (ETDEWEB)
Cha, K.O. [Myong Ji University, Kyonggi-do (Korea, Republic of); Kim, J.G. [Myongji University Graduate School, Kyonggi-do (Korea, Republic of)
1995-10-01
Two phase flow phenomena are observed in many industrial facilities and make much importance of optimum design for nuclear power plant and various heat exchangers. This experimental study has been investigated the classification of the flow pattern, the local void distribution and convective heat transfer in swirl and non-swirl two phase flow under the isothermal and nonisothermal conditions. The convective heat transfer coefficients in the single phase water flow were measured and compared with the calculated results from the Sieder-Tate correlation. These coefficients were used for comparisons with the two-phase heat transfer coefficients in the flow orientations. The experimental results indicate, that the void probe signal and probability density function of void distribution can used into classify the flow patterns, no significant difference in voidage distribution was observed between isothermal and non-isothermal condition in non-swirl flow, the values of two phase heat transfer coefficients increase when superficial air velocities increase, and the enhancement of the values is observed to be most pronounced at the highest superficial water velocity in non-swirl flow. Also two phase heat transfer coefficients in swirl flow are increased when the twist ratios are decreased. (author). 13 refs., 15 figs.
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)
Heat transfers in a double-skin roof ventilated by natural convection in summer time
Biwole, Pascal; Pompeo, C
2013-01-01
The double-skin roofs investigated in this paper are formed by adding a metallic screen on an existing sheet metal roof. The system enhances passive cooling of dwellings and can help diminishing power costs for air conditioning in summer or in tropical and arid countries. In this work, radiation, convection and conduction heat transfers are investigated. Depending on its surface properties, the screen reflects a large amount of oncoming solar radiation. Natural convection in the channel underneath drives off the residual heat. The bi-dimensional numerical simulation of the heat transfers through the double skin reveals the most important parameters for the system's efficiency. They are, by order of importance, the sheet metal surface emissivity, the screen internal and external surface emissivity, the insulation thickness and the inclination angle for a channel width over 6 cm. The influence of those parameters on Rayleigh and Nusselt numbers is also investigated. Temperature and air velocity profiles on seve...
Measurements of local convective heat transfer coefficients on ice accretion shapes
Arimilli, R. V.; Keshock, E. G.; Smith, M. E.
1984-01-01
The thin-skin heat rate technique was used to determine local convective heat transfer coefficients for four representative ice accretion shapes. The shapes represented three stages of glaze ice formation and one rime ice formation; the ice models had varying degrees of surface roughness. In general, convective heat transfer was higher in regions where the model's surfaces were convex and lower in regions where the surfaces were concave. The effect of roughness was different for the glaze and rime ice shapes. On the glaze ice shapes, roughness increased the maximum Nu by 80 percent, but the other Nu values were virtually unchanged. On the rime ice shape, the Nu numbers near the stagnation point were unchanged. The maximum Nu value increased by 45 percent, and the Nu number downstream of the peak increased by approximately 150 percent.
Institute of Scientific and Technical Information of China (English)
无
1996-01-01
A numerical study of natural convection beat transfer in an inclined cylindrical annulus has been conducted.The inner cylinder of the annulus is maintained at uniform heat flux and the outer cylinder at constant temperature.the two end walls are assumed to be insulated.A numerical code has been developed to calculate the steady state three-dimensional natural convection in an inclined cylindrical annulus,and the research emphasis is placed on the influences of inclination angle α and modified Rayleigh number Ra on the natural convection heat transfer in the annulus.Computations were carried out in the ranges of 0°≤α≤90*,2.5×105≤Ra*≤7and Pr=0.7 with fixed aspect ratio of H=28.97 and radius ratio of K=3.33,The numerical results are compared with the experimental correlations from the literature and the inclination angle effect on heat transfer is found to be insignificant.Detailed results of heat transfer rate,temperature,and velocity fields are presented for the case of α=45° and discussion is also made concerning the comparison between the numerical and experimental results for the specific case of α=90°。
Mixed convection heat transfer from confined tandem square cylinders in a horizontal channel
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.
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
Energy Technology Data Exchange (ETDEWEB)
Castell, Albert; Sole, Cristian; Medrano, Marc; Roca, Joan; Cabeza, Luisa F. [Departament d' Informatica i Enginyeria Industrial, Universitat de Lleida, Pere de Cabrera s/n, 25001 Lleida (Spain); Garcia, Daniel [Departament Projectes d' Enginyeria, Universitat Politecnica de Catalunya, Colom 11, 08222 Terrassa (Spain)
2008-09-15
To determine the heat transfer coefficient by natural convection for specific geometries, experimental correlations are used. No correlations were found in the literature for the geometries studied in this work. These geometries consisted of a cylindrical module of 88 mm of diameter and 315 mm height with external vertical fins of 310 mm height and 20 and 40 mm length. To determine the heat transfer coefficient by natural convection, experimental work was done. This module, containing PCM (sodium acetate trihydrate), was situated in the middle upper part of a cylindrical water tank of 440 mm of diameter and 450 mm height. The calculated heat transfer coefficient changed by using external fins, as the heat transfer surface was increased. The temperature variation of the PCM and the water are presented as a function of time, and the heat transfer coefficient for different fins is presented as a function of the temperature difference. Experimental correlations were obtained, presenting the Nusselt number as a function of different dimensionless numbers. Different correlations were analysed to find which one fit better to the experimental data. (author)
Khan, Mohammed; Khan, Arham Amin; Hasan, Mohammad Nasim
2016-07-01
This article reports a numerical investigation of mixed convection heat transfer phenomena around an active rotating heated cylinder placed inside a trapezoidal enclosure. The cavity is configured such that top and bottom walls remain thermally insulated while the remaining two sidewalls experience a constant cold temperature. The heated cylinder is located at the centre of the trapezoidal enclosure and undergoes counter clockwise rotation. The numerical solution of various governing equations (i.e. continuity, momentum and energy equations) for the present problem is obtained by using Galerkin finite element method. The present study focused on the influence of the variation of inertia effect of the rotating cylinder as manifested by the parameter, Reynolds number (Re) for various Grashof number (Gr) ranging from 103 to 105 while keeping the Richardson number constant as 1, which essentially represents the case of pure mixed convection. An envision of flow field and thermal field has been made by studying the streamlines, isotherms respectively while for the study of heat transfer characteristics, local and average Nusselt number over the heated cylinder has been considered. The result indicates that both the side wall inclination angle as well as the inertia effect of the rotating cylinder has greater impact on heat transfer characteristics compared to the case of motionless heated cylinder placed in a square cavity.
Convective heat transfer from rotating disks subjected to streams of air
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.
Optimal Prandtl number for heat transfer in rotating Rayleigh-Benard convection
Stevens, Richard J A M; Lohse, Detlef
2009-01-01
Numerical data for the heat transfer as a function of the Prandtl (Pr) and Rossby (Ro) numbers in turbulent rotating Rayleigh-Benard convection are presented for Rayleigh number Ra = 10^8. When Ro is fixed the heat transfer enhancement with respect to the non-rotating value shows a maximum as function of Pr. This maximum is due to the reduced efficiency of Ekman pumping when Pr becomes too small or too large. When Pr becomes small, i.e. for large thermal diffusivity, the heat that is carried by the vertical vortices spreads out in the middle of the cell, and Ekman pumping thus becomes less efficient. For higher Pr the thermal boundary layers (BLs) are thinner than the kinetic BLs and therefore the Ekman vortices do not reach the thermal BL. This means that the fluid that is sucked into the vertical vortices is colder than for lower Pr which limits the efficiency of the upwards heat transfer.
Convection Heat Transfer in Three-Dimensional Turbulent Separated/Reattached Flow
Energy Technology Data Exchange (ETDEWEB)
Bassem F. Armaly
2007-10-31
The measurements and the simulation of convective heat transfer in separated flow have been a challenge to researchers for many years. Measurements have been limited to two-dimensional flow and simulations failed to predict accurately turbulent heat transfer in the separated and reattached flow region (prediction are higher than measurements by more than 50%). A coordinated experimental and numerical effort has been initiated under this grant for examining the momentum and thermal transport in three-dimensional separated and reattached flow in an effort to provide new measurements that can be used for benchmarking and for improving the simulation capabilities of 3-D convection in separated/reattached flow regime. High-resolution and non-invasive measurements techniques are developed and employed in this study to quantify the magnitude and the behavior of the three velocity components and the resulting convective heat transfer. In addition, simulation capabilities are developed and employed for improving the simulation of 3-D convective separated/reattached flow. Such basic measurements and simulation capabilities are needed for improving the design and performance evaluation of complex (3-D) heat exchanging equipment. Three-dimensional (3-D) convective air flow adjacent to backward-facing step in rectangular channel is selected for the experimental component of this study. This geometry is simple but it exhibits all the complexities that appear in any other separated/reattached flow, thus making the results generated in this study applicable to any other separated and reattached flow. Boundary conditions, inflow, outflow, and wall thermal treatment in this geometry can be well measured and controlled. The geometry can be constructed with optical access for non-intrusive measurements of the flow and thermal fields. A three-component laser Doppler velocimeter (LDV) is employed to measure simultaneously the three-velocity components and their turbulent fluctuations
Directory of Open Access Journals (Sweden)
Mohammed Hussein A.
2008-01-01
Full Text Available The problem of the laminar upward mixed convection heat transfer for thermally developing air flow in the entrance region of a vertical circular cylinder under buoyancy effect and wall heat flux boundary condition has been numerically investigated. An implicit finite difference method and the Gauss elimination technique have been used to solve the governing partial differential equations of motion (Navier Stocks equations for two-dimensional model. This investigation covers Reynolds number range from 400 to 1600, heat flux is varied from 70 W/m2 to 400 W/m2. The results present the dimensionless temperature profile, dimensionless velocity profile, dimensionless surface temperature along the cylinder, and the local Nusselt number variation with the dimensionless axial distance Z+. The dimensionless velocity and temperature profile results have revealed that the secondary flow created by natural convection have a significant effect on the heat transfer process. The results have also shown an increase in the Nusselt number values as the heat flux increases. The results have been compared with the available experimental study and with the available analytical solution for pure forced convection in terms of the local Nusselt number. The comparison has shown satisfactory agreement. .
A note on convective heat transfer of an MHD Jeffrey fluid over a stretching sheet
Ahmed, Jawad; Shahzad, Azeem; Khan, Masood; Ali, Ramzan
2015-11-01
This article focuses on the exact solution regarding convective heat transfer of a magnetohydrodynamic (MHD) Jeffrey fluid over a stretching sheet. The effects of joule and viscous dissipation, internal heat source/sink and thermal radiation on the heat transfer characteristics are taken in account in the presence of a transverse magnetic field for two types of boundary heating process namely prescribed power law surface temperature (PST) and prescribed heat flux (PHF). Similarity transformations are used to reduce the governing non-linear momentum and thermal boundary layer equations into a set of ordinary differential equations. The exact solutions of the reduced ordinary differential equations are developed in the form of confluent hypergeometric function. The influence of the pertinent parameters on the temperature profile is examined. In addition the results for the wall temperature gradient are also discussed in detail.
A note on convective heat transfer of an MHD Jeffrey fluid over a stretching sheet
Energy Technology Data Exchange (ETDEWEB)
Ahmed, Jawad; Shahzad, Azeem [Department of Basic Sciences, University of Engineering and Technology, Taxila 47050 (Pakistan); Khan, Masood [Department of Mathematics, Quaid-i-Azam University, Islamabad 44000 (Pakistan); Ali, Ramzan, E-mail: alian.qau@gmail.com [Department of Applied Mathematics, TU-Dortmund (Germany); University of Central Asia, 720001 Bishkek (Kyrgyzstan)
2015-11-15
This article focuses on the exact solution regarding convective heat transfer of a magnetohydrodynamic (MHD) Jeffrey fluid over a stretching sheet. The effects of joule and viscous dissipation, internal heat source/sink and thermal radiation on the heat transfer characteristics are taken in account in the presence of a transverse magnetic field for two types of boundary heating process namely prescribed power law surface temperature (PST) and prescribed heat flux (PHF). Similarity transformations are used to reduce the governing non-linear momentum and thermal boundary layer equations into a set of ordinary differential equations. The exact solutions of the reduced ordinary differential equations are developed in the form of confluent hypergeometric function. The influence of the pertinent parameters on the temperature profile is examined. In addition the results for the wall temperature gradient are also discussed in detail.
A note on convective heat transfer of an MHD Jeffrey fluid over a stretching sheet
Directory of Open Access Journals (Sweden)
Jawad Ahmed
2015-11-01
Full Text Available This article focuses on the exact solution regarding convective heat transfer of a magnetohydrodynamic (MHD Jeffrey fluid over a stretching sheet. The effects of joule and viscous dissipation, internal heat source/sink and thermal radiation on the heat transfer characteristics are taken in account in the presence of a transverse magnetic field for two types of boundary heating process namely prescribed power law surface temperature (PST and prescribed heat flux (PHF. Similarity transformations are used to reduce the governing non-linear momentum and thermal boundary layer equations into a set of ordinary differential equations. The exact solutions of the reduced ordinary differential equations are developed in the form of confluent hypergeometric function. The influence of the pertinent parameters on the temperature profile is examined. In addition the results for the wall temperature gradient are also discussed in detail.
Bilal Ashraf, M.; Alsaedi, A.; Hayat, T.; Shehzad, S. A.
2017-06-01
Heat and mass transfer effects in the three-dimensional mixed convection flow of a viscoelastic fluid with internal heat source/sink and chemical reaction have been investigated in the present work. The flow generation is because of an exponentially stretching surface. Magnetic field normal to the direction of flow is considered. Convective conditions at the surface are also encountered. Appropriate similarity transformations are utilized to reduce the boundary layer partial differential equations into the ordinary differential equations. The homotopy analysis method is used to develop the solution expressions. Impacts of different controlling parameters such as ratio parameter, Hartman number, internal heat source/sink, chemical reaction, mixed convection, concentration buoyancy parameter and Biot numbers on the velocity, temperature and concentration profiles are analyzed. The local Nusselt and Sherwood numbers are sketched and examined.
Mixed Convection Heat Transfer Enhancement in a Vented Cavity Filled with a Nanofluid
Directory of Open Access Journals (Sweden)
Ahmed BAHLAOUI
2016-01-01
Full Text Available In this paper, a numerical investigation is carried out on mixed convection in a vertical vented rectangular enclosure filled with Al2O3-water nanofluid. The mixed convection effect is attained by heating the right wall by a constant hot temperature and cooling the cavity by an injected or sucked imposed flow. The effects of some pertinent parameters such as the Reynolds number, 100 Re 5000, the solid volume fraction of the nanoparticles, 0 0.1, and the aspect ratio of the cavity, 1 A 4, on flow and temperature patterns as well as on the heat transfer rate within the enclosure are presented for the two ventilation modes. For a value of the aspect ratio A = 2, the obtained results demonstrate that the increase of volume fraction of nanoparticles contributes to an enhancement of the heat transfer and to an increase of the mean temperature within the cavity. Also, it was revealed that the fluid suction mode yields the best heat transfer performance. In the case when A is varied from 1 to 4, it was obtained that the heat transfer enhancement, using nanofluids, is more pronounced at shallow enclosures than at tall ones.
CFD Study on Wall/Nanoparticle Interaction in Nanofluids Convective Heat Transfer
Directory of Open Access Journals (Sweden)
Mohammad Reza Tarybakhsh
2013-01-01
Full Text Available The Brownian motion of the nanoparticles in nanofluid is one of the potential contributors to enhance effective thermal conductivity and the mechanisms that might contribute to this enhancement are the subject of considerable discussion and debate. In this paper, the mixing effect of the base fluid in the immediate vicinity of the nanoparticles caused by the Brownian motion was analyzed, modeled, and compared with existing experimental data available in the literature. CFD was developed to study the effect of wall/nanoparticle interaction on forced convective heat transfer in a tube under constant wall temperature condition. The results showed that the motion of the particle near the wall which can decrease boundary layer and the hydrodynamics effects associated with the Brownian motion have a significant effect on the convection heat transfer of nanofluid.
Review of fluid flow and convective heat transfer within rotating disk cavities with impinging jet
Harmand, Souad; Poncet, Sébastien; Shevchuk, Igor V; 10.1016/j.ijthermalsci.2012.11.009
2013-01-01
Fluid flow and convective heat transfer in rotor-stator configurations, which are of great importance in different engineering applications, are treated in details in this review. The review focuses on convective heat transfer in predominantly outward air flow in the rotor-stator geometries with and without impinging jets and incorporates two main parts, namely, experimental/theoretical methodologies and geometries/results. Experimental methodologies include naphthalene sublimation techniques, steady state (thin layer) and transient (thermochromic liquid crystals) thermal measurements, thermocouples and infra-red cameras, hot-wire anemometry, laser Doppler and particle image velocimetry, laser plane and smoke generator. Theoretical approaches incorporate modern CFD computational tools (DNS, LES, RANS etc). Geometries and results part being mentioned starting from simple to complex elucidates cases of a free rotating disk, a single disk in the crossflow, single jets impinging onto stationary and rotating disk,...
Novak, Milos H.; Nowak, Edwin S.
1993-12-01
To analyze the laminar natural convection heat transfer and fluid flow distribution in vertical rectangular cavities with or without inner partitions, the personal computer finite difference program entitled CAV is used. The CAV program was tested successfully for slender cavities with aspect ratios as high as R = H/ L = 90 and for the Grashof numbers, based on the cavity height, up to GrH = 3 x10 9. To make the CAV program useful for a number of applications, various types of boundary conditions can also be imposed on the program calculations. Presented are program applications dealing with the 2-D numerical analysis of natural convection heat transfer in very slender window cavities with and without small inner partitions and recommendations are made for window design.
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.
Enhanced heat transfer of forced convective fin flow with transverse ribs
Energy Technology Data Exchange (ETDEWEB)
Chang, Shyy Woei; Chiou, Shyr Fuu [Thermal Fluids Laboratory, National Kaohsiung Institute of Marine Technology, No. 142, Hai-Chuan Road, Nan-Tzu District, Post code 811, Kaohsiung, Taiwan (China); Su, Lo May [Department of Electrical Engineering, Tung Fang Institute of Technology, Taiwan (China); Yang, Tsun Lirng [Department of Electrical Engineering, Fortune Institute of Technology, Taiwan (China)
2004-02-01
This experimental study investigates the heat transfers in three side-opened and bottom-sealed rectangular channels with two opposite walls roughened by 90 staggered ribs, which simulate the enhanced cooling passages in the fin-type heat sinks of electronic chip-sets. The various degrees of interactive effects due to the surface ribs, side-profile leakage flows and stream-wise weakened coolant flow are functionally related with Reynolds number (Re) and channel length-to-gap ratio (L/B), which unravel the considerable impacts on local and spatially averaged heat transfers over the rib-roughened fin surfaces. A selection of detailed heat transfer measurements over the rib-roughened fin surfaces illustrates the manner by which the isolated and interactive influences of Re and L/B-ratio affect the local and spatially averaged heat transfers. Relative to the heat transfer results acquired from the smooth-walled test channels, the augmentations of spatially averaged heat transfers generated by the present surface ribs are in the range of 140-200% of the flat fin reference levels. In conformity with the experimentally revealed heat transfer physics, a regression-type analysis is performed to develop the correlation of spatially-averaged Nusselt number over rib-roughened fin surface, which permits the individual and interactive effect of Re and L/B on heat transfer to be evaluated. A criterion for selecting the optimal length-to-gap ratio of a fin channel, which provides the maximum convective heat flux from the rib-roughened fin surface, is formulated as an engineering tool to assist the design activity for the cooling device of electronic chip-sets. (authors)
A p-version finite element method for steady incompressible fluid flow and convective heat transfer
Winterscheidt, Daniel L.
1993-01-01
A new p-version finite element formulation for steady, incompressible fluid flow and convective heat transfer problems is presented. The steady-state residual equations are obtained by considering a limiting case of the least-squares formulation for the transient problem. The method circumvents the Babuska-Brezzi condition, permitting the use of equal-order interpolation for velocity and pressure, without requiring the use of arbitrary parameters. Numerical results are presented to demonstrate the accuracy and generality of the method.
Institute of Scientific and Technical Information of China (English)
F M Abbasi; A Alsaedi; T Hayat
2014-01-01
The present investigation addresses the simultaneous effects of heat and mass transfer in the mixed convection peristaltic flow of viscous fluid in an asymmetric channel. The channel walls exhibit the convective boundary conditions. In addition, the effects due to Soret and Dufour are taken into consideration. Resulting problems are solved for the series solutions. Numerical values of heat and mass transfer rates are displayed and studied. Results indicate that the concentration and temperature of the fluid increase whereas the mass transfer rate at the wall decreases with increase of the mass transfer Biot number. Furthermore, it is observed that the temperature decreases with the increase of the heat transfer Biot number.
Natural convection heat transfer of nanofluids along a vertical plate embedded in porous medium.
Uddin, Ziya; Harmand, Souad
2013-02-07
The unsteady natural convection heat transfer of nanofluid along a vertical plate embedded in porous medium is investigated. The Darcy-Forchheimer model is used to formulate the problem. Thermal conductivity and viscosity models based on a wide range of experimental data of nanofluids and incorporating the velocity-slip effect of the nanoparticle with respect to the base fluid, i.e., Brownian diffusion is used. The effective thermal conductivity of nanofluid in porous media is calculated using copper powder as porous media. The nonlinear governing equations are solved using an unconditionally stable implicit finite difference scheme. In this study, six different types of nanofluids have been compared with respect to the heat transfer enhancement, and the effects of particle concentration, particle size, temperature of the plate, and porosity of the medium on the heat transfer enhancement and skin friction coefficient have been studied in detail. It is found that heat transfer rate increases with the increase in particle concentration up to an optimal level, but on the further increase in particle concentration, the heat transfer rate decreases. For a particular value of particle concentration, small-sized particles enhance the heat transfer rates. On the other hand, skin friction coefficients always increase with the increase in particle concentration and decrease in nanoparticle size.
Kwon, Younghwan; Lee, Kwangho; Park, Minchan; Koo, Kyoungmin; Lee, Jaekeun; Doh, Youngjin; Lee, Soowon; Kim, Doohyun; Jung, Yoongho
2013-12-01
An experimental investigation on the characteristics of the convective heat transfer in the fully developing region of a circular straight tube with a constant heat flux was carried out with Al2O3 nanofluids. Stable nanofluids, which were water-based suspensions of Al2O3 nanoparticles, were prepared by two-step method. The effects of the thermal conductivity, viscosity, and heat capacity of the nanofluids on convective heat transfer were investigated. The result showed that the coefficient enhancement of the convective heat transfer in the Al2O3 nanofluids was increased with increasing fluid temperature compared to that of water at a volume fraction of 3.0% in the turbulent flow region. Thermal conductivity was increased from 8% to 20%, and the increment of convective heat transfer coefficient was enhanced from 14% to 30% with fluid temperature from 22 degrees C to 75 degrees C, respectively. We observed that the increment of convective heat transfer coefficient in nanofluids was much higher than that of the thermal conductivity at a given temperature condition. The enhancement of Brownian motion due to the decreasing kinematic viscosity led to a higher convective heat transfer coefficient at a higher temperature condition.
Institute of Scientific and Technical Information of China (English)
LU Wenqiang; BAI Fengwu
2004-01-01
In this paper, a new model to analyze laminar forced convective enhanced heat transfer in latent functionally thermal fluid is developed. The main characteristics of the model are: I) a new formula of the specific heat at constant pressure is used; ii) a real heat transfer process is considered; that is, heat transfer processes occur not only between working fluid and microcapsules, but also between the mixture and tube wall; iii) the new method, which combines the newly developed axisymmetrical dual reciprocity boundary element method (DRBEM) with finite difference method (FDM), is used to solve the control equations of this problem. The new model is validated by experimental data.Some new physical results on the variational characteristics of the specific heat at constant pressure with space and time during phase-change process, the time-marching history of the phase-change interfaces and so on are obtained. Several main physical factors that affect enhanced heat transfer in latent functionally thermal fluid are numerically analyzed.Some new understandings for the mechanism of enhanced heat transfer in the functionally fluid are obtained.
Evaluation of heat transfer in acupuncture needles: convection and conduction approaches.
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.
Thermal Performance of Convective-Radiative Heat Transfer in Porous Fins
Directory of Open Access Journals (Sweden)
Majid SHAHBABAEI
2014-01-01
Full Text Available Forced and natural convection in porous fins with convective coefficient at the tips under radiation and convection effects are investigated in this paper. Aluminum and copper as fin materials are investigated. In forced and natural convection, air and water are applied as working fluids, respectively. In order to solve this nonlinear equation, Homotopy Perturbation Method (HPM and Variational Iteration Method (VIM are used. To verify the accuracy of the methods, a comparison is made to the exact solution (BVP. In this work, the effects of porosity parameter (, Radiation parameter (α and Temperature-Ratio parameter (µ on non-dimensional temperature distribution for both of the flows are shown. The results show that the effects of (α and (µ on temperature distribution in natural convection are based on porosity and in forced convection are uniform, approximately. Also, it is shown that both VIM and HPM are capable of being used to solve this nonlinear heat transfer equation.doi:10.14456/WJST.2014.64
An instrument to measure the convective heat transfer coefficient on large vessels.
Miguel, Alaor Faria; de O Nascimento, Francisco Assis; da Rocha, Adson Ferreira; dos Santos, Icaro
2008-01-01
Hepatocellular carcinoma is one of the most common malignancies worldwide. During radiofrequency hepatic ablation, the tumor is heated by means of radiofrequency energy. The heating causes necrosis of the malignant tumor. Thus, if the procedure is successful it can cure the patient. Studies have shown that recurrences occur after the treatment and these recurrences frequently take place next to the hepatic artery and portal vein. The recurrences occur due to the high convective loss on these vessels. This work proposed, developed and tested an instrument for the measurement of the convective heat transfer coefficient (h) in large vessels. Moreover, this work developed a mechanical simulator and validated an equation developed by Consiglieri et al, which analytically determines the value of h. The instrument was tested using a mechanical simulator that reproduces the flow conditions and the geometry of large vessels in the liver. A flow velocity of 0.2 m/s was simulated in order to mock the typical flow at the portal vein. The average value of h using the experimental apparatus was 2130+/-40 W.m(-2).K(-1) (mean+/-SD). The results showed that the error of the proposed method is approximately 22%. This work showed that the instrument can be used for measuring h in vitro and that the Consiglieri's equation can be used to determine the convective heat transfer coefficient on large vessels.
Progress towards understanding and predicting convection heat transfer in the turbine gas path
Simoneau, Robert J.; Simon, Frederick F.
1992-01-01
A new era is drawing in the ability to predict convection heat transfer in the turbine gas path. We feel that the technical community now has the capability to mount a major assault on this problem, which has eluded significant progress for a long time. We hope to make a case for this bold statement by reviewing the state of the art in three major heat transfer, configuration-specific experiments, whose data have provided the big picture and guided both the fundamental modeling research and the code development. Following that, we review progress and directions in the development of computer codes to predict turbine gas path heat transfer. Finally, we cite examples and make observations on the more recent efforts to do all this work in a simultaneous, interactive, and more synergistic manner. We conclude with an assessment of progress, suggestions for how to use the current state of the art, and recommendations for the future.
Convective heat transfer from circular cylinders located within perforated cylindrical shrouds
Daryabeigi, K.; Ash, R. L.
1986-01-01
The influence of perforated cylindrical shrouds on the convective heat transfer to circular cylinders in transverse flow has been studied experimentally. Geometries studied were similar to those used in industrial platinum resistance thermometers. The influence of Reynolds number, ventilation factor (ratio of the open area to the total surface area of shroud), radius ratio (ratio of shroud's inside radius to bare cylinder's radius), and shroud orientation with respect to flow were studied. The experiments showed that perforated shrouds with ventilation factors in the range 0.1 to 0.4 and radius ratios in the range 1.1 to 2.1 could enhance the convective heat transfer to bare cylinders up to 50%. The maximum enhancement occurred for a radius ratio of 1.4 and ventilation factors between 0.2 and 0.3. It was found that shroud orientation influenced the heat transfer, with maximum heat transfer generally occurring when the shroud's holes were centered on either side of the stagnation line. However, the hole orientation effect is of second order compared to the influence of ventilation factor and radius ratio.
Terzis, Alexandros
2016-09-01
The correspondence between local fluid flow structures and convective heat transfer is a fundamental aspect that is not yet fully understood for multiple jet impingement. Therefore, flow field and heat transfer experiments are separately performed investigating mutual-jet interactions exposed in a self-gained crossflow. The measurements are taken in two narrow impingement channels with different cross-sectional areas and a single exit design. Hence, a gradually increased crossflow momentum is developed from the spent air of the upstream jets. Particle image velocimetry (PIV) and liquid crystal thermography (LCT) are used in order to investigate the aerothermal characteristics of the channel with high spatial resolution. The PIV measurements are taken at planes normal to the target wall and along the centreline of the jets, providing quantitative flow visualisation of jet and crossflow interactions. Spatially resolved heat transfer coefficient distributions on the target plate are evaluated with transient techniques and a multi-layer of thermochromic liquid crystals. The results are analysed aiming to provide a better understanding about the impact of near-wall flow structures on the convective heat transfer augmentation for these complex flow phenomena.
Directory of Open Access Journals (Sweden)
Hsien-Hung Ting
2016-07-01
Full Text Available This study numerically investigates heat transfer augmentation using water-based Al2O3 and CuO nanofluids flowing in a triangular cross-sectional duct under constant heat flux in laminar flow conditions. The Al2O3/water nanofluids with different volume fractions (0.1%, 0.5%, 1%, 1.5%, and 2% and CuO/water nanofluids with various volume fractions (0.05%, 0.16%, 0.36%, 0.5%, and 0.8% are employed, and Reynolds numbers in the range of 700 to 1900 in a laminar flow are considered. The heat transfer rate becomes more remarkable when employing nanofluids. As compared with pure water, at a Peclet number of 7000, a 35% enhancement in the convective heat transfer coefficient, is obtained for an Al2O3/water nanofluid with 2% particle volume fraction; at the same Peclet number, a 41% enhancement in the convective heat transfer coefficient is achieved for a CuO/water nanofluid with 0.8% particle volume concentration. Heat transfer enhancement increases with increases in particle volume concentration and Peclet number. Moreover, the numerical results are found to be in good agreement with published experimental data.
Directory of Open Access Journals (Sweden)
M Safaei
2016-09-01
Full Text Available In the present study, first the turbulent natural convection and then laminar mixed convection of air flow was solved in a room and the calculated outcomes are compared with results of other scientists and after showing validation of calculations, aforementioned flow is solved as a turbulent mixed convection flow, using the valid turbulence models Standard k-ε, RNG k-ε and RSM. To solve governing differential equations for this flow, finite volume method was used. This method is a specific case of residual weighting method. The results show that at high Richardson Numbers, the flow is rather stationary at the center of the enclosure. Moreover, it is distinguished that when Richardson Number increases the maximum of local Nusselt decreases. Therefore, it can be said that less number of Richardson Number, more rate of heat transfer.
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...... condition and six eccentricities from 0.1 to 0.92 at five different heat fluxes. The surface temperature of the heated rod is measured at different heights, and the Nusselt number is calculated at the temperature measurement locations. A correlation is suggested to determine the Nusselt number based...
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.
Institute of Scientific and Technical Information of China (English)
Pei－XueJiang; Ze－PeiRen; 等
1993-01-01
A numerical study is reported of laminar natural convective heat and mass transfer on a vertical cooled plate for water containing metal corrosion products at super-critical pressures.The influence of variable properties at super-critical pressures on natural convertion has been analyzed.The difference between heat and mass transfer under cooling or heating conditions is also discussed and some correlations for heat and mass transfer under cooling conditions are recommended.
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.
Laminar convective heat transfer characteristic of Al2O3/water nanofluid in a circular microchannel
Trinavee, K.; Gogoi, T. K.; Pandey, M.
2016-10-01
In this study, laminar convective heat transfer characteristics Al2O3/water nanofluid in a circular microchannel is investigated using a two-phase (discrete phase) model. The computational fluid dynamic code FLUENT (ANSYS) is employed to solve the coupled momentum and energy equations with the boundary conditions of uniform wall heat flux and velocity at channel inlet. Detail analysis is done showing variation of wall temperature, fluid bulk mean temperature, heat transfer coefficient, Nusselt number, shear stress, friction, pressure drop, entropy generation etc. along the microchannel at two particle volume concentrations (1% and 4%) of the nanofluid. Comparison of results is provided between base and nanofluid and also for two cases, one with constant property and the other with variable temperature thermal conductivity and viscosity. Results show that heat transfer is enhanced in case of the nanofluid with low entropy generation and the heat transfer parameters increase with increase in nanoparticle volume concentration and Reynolds number. However, use of nanofluid also causes increase in pressure drop and shear stress. A comparison of the constant and variable property model showed that heat transfer is further enhanced; entropy, shear stress and pressure drop further decrease when temperature dependent properties of the nanofluid are considered instead of constant properties.
Institute of Scientific and Technical Information of China (English)
LI Guang-zheng; HUANG Jian-chun
2005-01-01
Numerical simulations are performed for laminar natural convection heat transfer from a centered conducting body enclosed in a square cavity. A high accuracy unsteady numerical method is used, combining the unique condition of the pressure, the convergent solutions and the stream-function value of the inside heat-conducting body are given simultaneously. Two examples are simulated with this numerical method and compared with the experimental results. The results of the numerical solutions are consistent with the experimental results. It shows that the numerical method is valid and feasible.
High Prandtl number effect on Rayleigh-Bénard convection heat transfer at high Rayleigh number
Ma, Li; Li, Jing; Ji, Shui; Chang, Huajian
2017-02-01
This paper represents results of the Rayleigh-Bénard convection heat transfer in silicon oil confined by two horizontal plates, heated from below, and cooled from above. The Prandtl numbers considered as 100-10,000 corresponding to three types of silicon oil. The experiments covered a range of Rayleigh numbers from 2.14·109 to 2.27·1013. The data points that the Nusselt number dependents on the Rayleigh number, which is asymptotic to a 0.248 power. Furthermore, the experiment results can fit the data in low Rayleigh number well.
Institute of Scientific and Technical Information of China (English)
ZhangHeng－Yun; GeXin－Shi
1997-01-01
Heat transfer in the evacuated collector tube is a three-dimensional laminar natural convection problem driven by buoyancy.Because of its complexity,no effective theoretical model is available despite of limited experimental work which is confined to one aspect.The present work aims to depict the convective heat transfer inside a two-ended inclined tube with East-West symmetric heat input using numerical methods,Based on reasonable assumptions,governing equations of the inside fluid are established.The corresponding discretizated equations are solved by emplogying numerical metholds.The calculated results are displayed for velocity and temperature profiles on different cross-sectional plasnes.which present the flow pattern characterized by upflow and downflow along the axial direction and adherent flow along the peripheral direction,and the heat transfer rpocess from the wall to the center,Furthermore,the transient Nusselt number and average temperature level are shown and discussed.Finally,the parametric effects of the tube radius and the heat input on the flow and heat transfer are also given.
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.
Experimental and numerical investigation on natural convection heat transfer in nanofluids
Energy Technology Data Exchange (ETDEWEB)
Nayak, A.K.; Kulkarni, P.P.; Chinchole, A.S. [Bhabha Atomic Research Centre, Mumbai (India). Reactor Engineering Div.; Mulye, S.M. [Walchand College of Engineering, Sangli (India)
2016-03-15
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 cylindrical heater having 7.1 mm O. D. and 0.5 mm thickness with 100 mm heated length was used as heater surface. The heat flux was varied from 0 to 50 000 W/m{sup 2} and the corresponding Rayleigh number range is varied from 3 x 10{sup 4} to 1.65 x 10{sup 5}. Different Nanofluids were used i. e. Aluminium oxide, Titanium dioxide, Silicon dioxide and Copper oxide with concentration varying from 0.0005 % to 0.05 % by weight. 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 as it does not take into account the effect of particle concentration. A new empirical model was developed based on the experimental data including the effect of nanoparticles concentration which predicts the experimental data satisfactorily.
3D modelling of coupled mass and heat transfer of a convection-oven roasting process.
Feyissa, Aberham Hailu; Gernaey, Krist V; Adler-Nissen, Jens
2013-04-01
A 3D mathematical model of coupled heat and mass transfer describing oven roasting of meat has been developed from first principles. The proposed mechanism for the mass transfer of water is modified and based on a critical literature review of the effect of heat on meat. The model equations are based on a conservation of mass and energy, coupled through Darcy's equations of porous media - the water flow is mainly pressure-driven. The developed model together with theoretical and experimental assessments were used to explain the heat and water transport and the effect of the change in microstructure (permeability, water binding capacity and elastic modulus) that occur during the meat roasting process. The developed coupled partial differential equations were solved by using COMSOL Multiphysics®3.5 and state variables are predicted as functions of both position and time. The proposed mechanism was partially validated by experiments in a convection oven where temperatures were measured online.
Heat transfer enhancement induced by wall inclination in turbulent thermal convection.
Kenjereš, Saša
2015-11-01
We present a series of numerical simulations of turbulent thermal convection of air in an intermediate range or Rayleigh numbers (10(6)≤Ra≤10(9)) with different configurations of a thermally active lower surface. The geometry of the lower surface is designed in such a way that it represents a simplified version of a mountain slope with different inclinations (i.e., "Λ"- and "V"-shaped geometry). We find that different wall inclinations significantly affect the local heat transfer by imposing local clustering of instantaneous thermal plumes along the inclination peaks. The present results reveal that significant enhancement of the integral heat transfer can be obtained (up to 32%) when compared to a standard Rayleigh-Bénard configuration with flat horizontal walls. This is achieved through combined effects of the enlargement of the heated surface and reorganization of the large-scale flow structures.
Convective Heat Transfer from Castings of Ice Roughened Surfaces in Horizontal Flight
Dukhan, Nihad; Vanfossen, G. James, Jr.; Masiulaniec, K. Cyril; Dewitt, Kenneth J.
1995-01-01
A technique was developed to cast frozen ice shapes that had been grown on a metal surface. This technique was applied to a series of ice shapes that were grown in the NASA Lewis Icing Research Tunnel on flat plates. Eight different types of ice growths, characterizing different types of roughness, were obtained from these plates, from which aluminum castings were made. Test strips taken from these castings were outfitted with heat flux gages, such that when placed in a dry wind tunnel, they could be used to experimentally map out the convective heat transfer coefficient in the direction of flow from the roughened surfaces. The effects on the heat transfer coefficient for parallel flow, which simulates horizontal flight, were studied. The results of this investigation can be used to help size heaters for wings, helicopter rotor blades, jet engine intakes, etc., or de-icing for anti-icing applications where the flow is parallel to the iced surface.
Masiulaniec, K. Cyril; Vanfossen, G. James, Jr.; Dewitt, Kenneth J.; Dukhan, Nihad
1995-01-01
A technique was developed to cast frozen ice shapes that had been grown on a metal surface. This technique was applied to a series of ice shapes that were grown in the NASA Lewis Icing Research Tunnel on flat plates. Nine flat plates, 18 inches square, were obtained from which aluminum castings were made that gave good ice shape characterizations. Test strips taken from these plates were outfitted with heat flux gages, such that when placed in a dry wind tunnel, can be used to experimentally map out the convective heat transfer coefficient in the direction of flow from the roughened surfaces. The effects on the heat transfer coefficient for both parallel and accelerating flow will be studied. The smooth plate model verification baseline data as well as one ice roughened test case are presented.
Parametric Study of Mixed Convective RadiativeHeat Transfer in an Inclined Annulus
Directory of Open Access Journals (Sweden)
Raed G. Saihood
2008-01-01
Full Text Available The steady state laminar mixed convection and radiation through inclined rectangular duct with an interior circular tube is investigated numerically for a thermally and hydrodynamicaly fully developed flow. The two heat transfer mechanisms of convection and radiation are treated independently and simultaneously. The governing equations which used are continuity, momentum and energy equations. These equations are normalized and solved using the Vorticity-Stream function and the Body Fitted Coordinates (B.F.C methods. The finite difference approach with the Line Successive Over-Relaxation (LSOR method is used to obtain all the computational results. The (B.F.C method is used to generate the grid of the problem. A computer program (Fortran 90 is built to calculate the steady state Nusselt number (Nu for Aspect Ratio AR (0.55-1 and Geometry Ratio GR (0.1-0.9. The fluid Prandtl number is 0.7, Rayleigh number Ra = 400, Reynolds number Re = 100, Optical Thickness (0 ≤ t ≤ 10, Conduction- Radiation parameter (0 ≤ N ≤ 100 and Inclination angle λ = 45. For the range of parameters considered, results show that radiation enhance heat transfer. It is also indicated in the results that heat transfer from the surface of the circle exceeds that of the rectangular duct. Generally, Nu is increased with increasing GR, t and N but it decreased with AR increase. When the radiation effect added to the heat transfer mechanism, the heat transfer rate increased. This effect increased with increasing in GR and decreasing with AR. The increasing in radiation properties lead to increase the radiation effect. Tecplot 7 program was used to plot the curves which cleared these relations and isotherms and streamlines which illustrate the behavior of air through the channel and its variation with other parameters. A correlation equation is concluded to describe the radiation effect. Comparison of the results with the previous work shows a good agreement.
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)
Institute of Scientific and Technical Information of China (English)
An; Gang; (
2001-01-01
［1］Tuckermann, D. B., Pease, R. F., Optimized convective cooling using micromachined structure, J. Electro-Chemical Society, 1982, 129(3): 98c.［2］Wu Peiyi, Little, W. A., Measurement of friction factor for the flow of gases in very fine channel used for microminiature Joule-Thomson refrigerators, Cryogenics, 1983, 23(5): 273.［3］Wu Peiyi, Little, W. A., Measurement of the heat transfer characteristics of gas flow in fine channel heat exchangers used for microminiature refrigerators, Cryogenics, 1984, 24(8): 415.［4］Choi, B., Barron, R. F., Warrington, R. O., Fluid flow and heat transfer in microtubes, ASME DSC, 1991, 32: 123.［5］Pfahler, J., Harley, J., Bua, H. et al., Gas and liquid flow in small channel, ASME DSC, 1991, 32: 49.［6］Beskok, A., Karniadakis, G. E., Simulation of slip-flow in complex micro-geometries, ASME DSC, 1992, 40: 355.［7］Mohiuddin, M. G., Li Dongqing, Dale, J. D., Heat transfer and fluid flow in microchannels, Int. J. Heat and Mass Transfer, 1997, 40(13): 3079.［8］Li, J. M., Wang, B. X., Peng, X. F., The wall effect for laminar flow through microtube, in Int. Center for Heat and Mass Transfer (ICHMT) Symposium on Molecular and Microscale Heat Transfer in Material Processing and Other Application Yokohama, Japan, (eds. Tanasawa, I., Nishio, S.), New York: Begell House,1996, 55-65.［9］Li, J. M., Wang, B. X., Peng, X. F., Laminar flow of gas through extremely narrow parallel plates, in Heat Transfer and Technology 1996, Proc. Fourth ISHT (ed. Wang, B. X.), Beijing: Higher Education Press, 1996, 318-322.［10］Li, J. M., Wang, B. X., Peng, X. F., Wall effect of gas laminar heat transfer in microtubes, Journal of Engineering Thermophysics (in Chinese), 1998, 19(5): 596.［11］Li, J. M., Wang, B. X., Peng, X. F., Laminar heat transfer of gas in microchannels between two paralled plates, Journal of Engineering Thermophysics (in Chinese), 1999, 20(2): 194.［12］Tao, W. Q., Numerical Heat Transfer (in Chinese), Xi
Convective heat transfer in a measurement cell for scanning electrochemical microscopy.
Novev, Javor K; Compton, Richard G
2016-11-21
Electrochemical experiments, especially those performed with scanning electrochemical microscopy (SECM), are often carried out without taking special care to thermostat the solution; it is usually assumed that its temperature is homogeneous and equal to the ambient. The present study aims to test this assumption via numerical simulations of the heat transfer in a particular system - the typical measurement cell for SECM. It is assumed that the temperature of the solution is initially homogeneous but different from that of its surroundings; convective heat transfer in the solution and the surrounding air is taken into account within the framework of the Boussinesq approximation. The hereby presented theoretical treatment indicates that an initial temperature difference of the order of 1 K dissipates with a characteristic time scale of ∼1000 s; the thermal equilibration is accompanied by convective flows with a maximum velocity of ∼10(-4) m s(-1); furthermore, the temporal evolution of the temperature profile is influenced by the sign of the initial difference. These results suggest that, unless the temperature of the solution is rigorously controlled, convection may significantly compromise the interpretation of data from SECM and other electrochemical techniques, which is usually done on the basis of diffusion-only models.
Mixed convection laminar flow and heat transfer of liquids in horizontal internally finned tubes
Energy Technology Data Exchange (ETDEWEB)
Shome, B. [Univ. of Delaware, Newark, DE (United States). Dept. of Mechanical Engineering
1998-01-01
Energy and material savings, as well as economic incentives, have led to concentrated efforts over the past several decades in the field of heat transfer enhancement to produce more efficient and compact heat exchangers. Internally finned tubes are widely used for heat transfer enhancement, particularly in chemical process and petroleum industries. A finned tube heat exchanger with optimum geometry could offer 35--40% increase in heat duty for equal pumping power and size over a smooth tube heat exchanger or a comparable decrease in the heat exchanger size for a given heat duty. Developing mixed convection flow in internally finned tubes with variable viscosity was numerically investigated for a fin geometry range of 8 {le} N {le} 24, 0.1 {le} H {le} 0.3 and an operating condition range of 50 {le} Pr{sub in} {le} 1,250, 0 {le} Ra{sub in} {le} 10{sup 7}, and 0 {le} q{sub w}d/k{sub in} {le} 2,000. The numerical model was validated by comparison with existing numerical and experimental data. Internal finning was found to produce a complex two-cell, buoyancy-induced vortex structure. The results show that coring (retarded velocity in the interfin region) leads to poor heat transfer performance of tubes with large numbers of fins or with tall fins. The overall results indicated that large enhancement in the heat transfer can be obtained in the entrance region. Furthermore, variable viscosity effects are seen to have a pronounced effect on the friction factor and Nusselt number predictions.
Convective heat transfer in foams under laminar flow in pipes and tube bundles
Attia, Joseph A.; McKinley, Ian M.; Moreno-Magana, David; Pilon, Laurent
2014-01-01
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. PMID:25552745
Convective heat transfer in foams under laminar flow in pipes and tube bundles.
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.
Sato, Norikazu; Takeuchi, Shintaro; Kajishima, Takeo; Inagaki, Masahide; Horinouchi, Nariaki
2016-09-01
A new discretization scheme on Cartesian grids, namely, a "consistent direct discretization scheme", is proposed for solving incompressible flows with convective and conjugate heat transfer around a solid object. The Navier-Stokes and the pressure Poisson equations are discretized directly even in the immediate vicinity of a solid boundary with the aid of the consistency between the face-velocity and the pressure gradient. From verifications in fundamental flow problems, the present method is found to significantly improve the accuracy of the velocity and the wall shear stress. It is also confirmed that the numerical results are less sensitive to the Courant number owing to the consistency between the velocity and pressure fields. The concept of the consistent direct discretization scheme is also explored for the thermal field; the energy equations for the fluid and solid phases are discretized directly while satisfying the thermal relations that should be valid at their interface. It takes different forms depending on the thermal boundary conditions: Dirichlet (isothermal) and Neumann (adiabatic/iso-heat-flux) boundary conditions for convective heat transfer and a fluid-solid thermal interaction for conjugate heat transfer. The validity of these discretizations is assessed by comparing the simulated results with analytical solutions for the respective thermal boundary conditions, and it is confirmed that the present schemes also show high accuracy for the thermal field. A significant improvement for the conjugate heat transfer problems is that the second-order spatial accuracy and numerical stability are maintained even under severe conditions of near-practical physical properties for the fluid and solid phases.
Conjugate Heat Transfer in Rayleigh-Bénard Convection in a Square Enclosure
Directory of Open Access Journals (Sweden)
Habibis Saleh
2014-01-01
Full Text Available Conjugate natural convection-conduction heat transfer in a square enclosure with a finite wall thickness is studied numerically in the present paper. The governing parameters considered are the Rayleigh number 5×103≤Ra≤106, the wall-to-fluid thermal conductivity ratio 0.5≤Kr≤10, and the ratio of wall thickness to its height 0.2≤D≤0.4. The staggered grid arrangement together with MAC method was employed to solve the governing equations. It is found that the fluid flow and the heat transfer can be controlled by the thickness of the bottom wall, the thermal conductivity ratio, and the Rayleigh number.
Conjugate heat transfer in Rayleigh-Bénard convection in a square enclosure.
Saleh, Habibis; Hashim, Ishak
2014-01-01
Conjugate natural convection-conduction heat transfer in a square enclosure with a finite wall thickness is studied numerically in the present paper. The governing parameters considered are the Rayleigh number (5 × 10(3) ≤ Ra ≤ 10(6)), the wall-to-fluid thermal conductivity ratio (0.5 ≤ Kr ≤ 10), and the ratio of wall thickness to its height (0.2 ≤ D ≤ 0.4). The staggered grid arrangement together with MAC method was employed to solve the governing equations. It is found that the fluid flow and the heat transfer can be controlled by the thickness of the bottom wall, the thermal conductivity ratio, and the Rayleigh number.
Transient natural convection and heat transfer during the storage of granular media
Energy Technology Data Exchange (ETDEWEB)
Avila-Acevedo, J.G.; Tsotsas, E. [Institute of Process Engineering, Otto-von-Guericke-University, P.O. Box 4120, 39106 Magdeburg (Germany)
2008-07-01
Transient heat transfer in an originally isothermal cylinder filled with a porous medium after sudden change of wall temperature is studied experimentally and computationally. Lab-scale experiments with water as the interstitial fluid are used in order to imitate the conditions prevailing in large, air-filled industrial silos. The proposed model assumes isotropy of the porous medium, local thermal equilibrium between the phases, Darcy flow and applicability of the Boussinesq approximation. Its predictions are in satisfactory agreement with the experimental results. Simulations reveal the role of dimensionless parameters like the modified porous media Rayleigh number and the cylinder aspect ratio. A criterion for neglecting the influence of natural convection on heat transfer is established. (author)
Tamma, Kumar K.; Railkar, Sudhir B.
1988-01-01
This paper describes new and recent advances in the development of a hybrid transfinite element computational methodology for applicability to conduction/convection/radiation heat transfer problems. The transfinite element methodology, while retaining the modeling versatility of contemporary finite element formulations, is based on application of transform techniques in conjunction with classical Galerkin schemes and is a hybrid approach. The purpose of this paper is to provide a viable hybrid computational methodology for applicability to general transient thermal analysis. Highlights and features of the methodology are described and developed via generalized formulations and applications to several test problems. The proposed transfinite element methodology successfully provides a viable computational approach and numerical test problems validate the proposed developments for conduction/convection/radiation thermal analysis.
Tamma, Kumar K.; Railkar, Sudhir B.
1988-01-01
This paper describes new and recent advances in the development of a hybrid transfinite element computational methodology for applicability to conduction/convection/radiation heat transfer problems. The transfinite element methodology, while retaining the modeling versatility of contemporary finite element formulations, is based on application of transform techniques in conjunction with classical Galerkin schemes and is a hybrid approach. The purpose of this paper is to provide a viable hybrid computational methodology for applicability to general transient thermal analysis. Highlights and features of the methodology are described and developed via generalized formulations and applications to several test problems. The proposed transfinite element methodology successfully provides a viable computational approach and numerical test problems validate the proposed developments for conduction/convection/radiation thermal analysis.
Energy Technology Data Exchange (ETDEWEB)
Lee, Sin Pyo [Kyonggi Univ., Suwon (Korea, Republic of)
2016-02-15
Fine wires made from platinum have been used as sensors to evaluate the convection performance of nanofluids. However, the wire sensor is difficult to handle due to its fragility. Additionally, an unrealistic convective heat transfer coefficient (h) is obtained if a rigorous calibration process combined with precision equipment is not used for measurement. This paper proposes a new evaluation apparatus for h of nanofluids that uses a thermistor sensor instead of the platinum wire. The working principles are also explained in detail. Validation experiments for pure engine oil comparing h from the two sensors confirmed numerous practical benefits of the thermistor. The proposed system can be used as a useful tool to justify the adoption of developed nanofluids.
Directory of Open Access Journals (Sweden)
Sourtiji Ehsan
2012-01-01
Full Text Available A numerical study of natural convection heat transfer through an alumina-water nanofluid inside L-shaped cavities in the presence of an external magnetic field is performed. The study has been carried out for a wide range of important parameters such as Rayleigh number, Hartmann number, aspect ratio of the cavity and solid volume fraction of the nanofluid. The influence of the nanoparticle, buoyancy force and the magnetic field on the flow and temperature fields have been plotted and discussed. The results show that after a critical Rayleigh number depending on the aspect ratio, the heat transfer in the cavity rises abruptly due to some significant changes in flow field. It is also found that the heat transfer enhances in the presence of the nanoparticles and increases with solid volume fraction of the nanofluid. In addition, the performance of the nanofluid utilization is more effective at high Rayleigh numbers. The influence of the magnetic field has been also studied and deduced that it has a remarkable effect on the heat transfer and flow field in the cavity that as the Hartmann number increases the overall Nusselt number is significantly decreased specially at high Rayleigh numbers.
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.
Studying regimes of convective heat transfer in the production of high-temperature silicate melts
Volokitin, O. G.; Sheremet, M. A.; Shekhovtsov, V. V.; Bondareva, N. S.; Kuzmin, V. I.
2016-09-01
The article presents the results of theoretical and experimental studies of the production of high-temperature silicate melts using the energy of low-temperature plasma in a conceptually new setup. A mathematical model of unsteady regimes of convective heat and mass transfer is developed and numerically implemented under the assumption of non-Newtonian nature of flow in the melting furnace with plasma-chemical synthesis of high-temperature silicate melts. Experiments on melting silicate containing materials were carried out using the energy of low-temperature plasma. The dependence of dynamic viscosity of various silicate materials (basalt, ash, waste of oil shale) was found experimentally.
Energy Technology Data Exchange (ETDEWEB)
Fox, E.; Visser, A.; Bridges, N.
2011-07-18
This paper presents an experimental study of natural convection heat transfer for an Ionic Liquid. The experiments were performed for 1-butyl-2, 3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide, ([C{sub 4}mmim][NTf{sub 2}]) at a Raleigh number range of 1.26 x 10{sup 7} to 8.3 x 10{sup 7}. In addition to determining the convective heat transfer coefficients, this study also included experimental determination of thermophysical properties of [C{sub 4}mmim][NTf{sub 2}] such as, density, viscosity, heat capacity, and thermal conductivity. The results show that the density of [C{sub 4}mmim][NTf{sub 2}] varies from 1.437-1.396 g/cm{sup 3} within the temperature range of 10-50 C, the thermal conductivity varies from 0.105-0.116 W/m.K between a temperature of 10 to 60 C, the heat capacity varies from 1.015 J/g.K - 1.760 J/g.K within temperature range of 25-340 C and the viscosity varies from 18cp-243cp within temperature range 10-75 C. The results for density, thermal conductivity, heat capacity, and viscosity were in close agreement with the values in the literature. Measured dimensionless Nusselt number was observed to be higher for the ionic liquid than that of DI water. This is expected as Nusselt number is the ratio of heat transfer by convection to conduction and the ionic liquid has lower thermal conductivity (approximately 18%) than DI water.
Nanofluid heat transfer under mixed convection flow in a tube for solar thermal energy applications.
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.
Institute of Scientific and Technical Information of China (English)
Pei－xueJiang; Ze－peiRen; 等
1992-01-01
Corrosion products of structural materials when contained in water usually are in two states:soluble state and colloidal particles with dimeter about 10-3-10-1um,Deposits of such corrosion products on tube surfaces under high pressure will jeopardize the operating economy of power plant equipment and even esult in accidents.A numerical study is reported in this paper of the natural convective heat and mass transfer on a vertical heated plate subject to the flrst or mixed kind of boundary conditions for high-pressure water(P=17MPa) containing metal corrosion products with consideration of varialbe thermophysical properties.
Coaxial radiative and convective heat transfer in gray and nongray gases
Mattick, A. T.
1980-01-01
Coupled radiative and convective heat transfer is investigated for an absorbing gas flowing in a finite length channel and heated by blackbody radiation directed along the flow axis. The problem is formulated in one dimension and numerical solutions are obtained for the temperature profile of the gas and for the radiation escaping the channel entrance, assuming both gray and nongray absorption spectra. Due to radiation trapping, the flowing gas is found to have substantially smaller radiation losses for a given peak gas temperature than a solid surface that is radiatively heated to this temperature. A greenhouse effect is also evident whereby radiation losses are minimized for a gas having stronger absorption at long wavelengths.
Effect of natural convection heat transfer during polymer optical fiber drawing
Reeve, Hayden Matane
The quality of polymer optical fiber is dependent on the diametral uniformity of the fiber and the applied drawing force. In this study, the force required to draw a polymer preform into optical fiber is predicted and measured as it is heated in an enclosed cylindrical furnace. The draw force is a function of the highly temperature dependent polymer viscosity. Therefore accurate prediction of the drawing force requires a detailed investigation of the heat transfer within the furnace. In this investigation, the full axi-symmetric conjugate problem (including both natural convection and thermal radiation) was solved. In addition, the location of the polymer/air interface was solved for as part of the problem and was not prescribed beforehand. Numerical results compared well with the experimentally measured draw tension and neck-down profiles for several preform diameters, draw speeds, and furnace temperatures. The experimental investigation also found that as the buoyant potential of the air within the furnace was increased the natural convection transitioned from time-invariant to oscillatory, and finally, to chaotic flow. The time-varying heating caused by the oscillatory and chaotic regimes alters the rheology of the elongating polymer preform, causing detrimental variations in the fiber diameter. When subjected to oscillatory and chaotic natural convection the standard deviation of the fiber diameter variations was up to 2.5 to 10 times greater, respectively, than that measured under time-invariant heating conditions. Experimental visualization of the unsteady natural convection flow indicates that the instability occurs at the interface between two counter-rotating cells. Numerical simulations of natural convection within a tall non-isothermal axi-symmetric annular cavity with an aspect ratio of 10 and a radius ratio of 0.6 predicted unsteady phenomena. At low Rayleigh numbers a steady bi-cellular flow was predicted. As the Rayleigh number was increased the
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.
Qiu, Yan; Tian, Maocheng; Guo, Zhixiong
2013-03-01
A three-dimensional numerical study was made to investigate effects of fin angle, fin surface emissivity, and tube wall temperature on heat transfer enhancement for a longitudinal externally-finned tube placed vertically in a small chamber. The numerical model was first validated through comparison with experimental measurements and the appropriateness of general boundary conditions was examined. The numerical results show that the mean Nusselt number increases with Rayleigh number for all the fin angles investigated. The maximum heat transfer rate per mass occurs when the fin angle is about 60° for fin surface emissivity between 0.7 and 0.8 and 55° when the surface emissivity increases to 0.9. With increasing tube wall temperature, both the natural convection and radiation heat transfer are enhanced, but the fraction of radiation heat transfer decreases in the temperature range studied. Radiation fraction increases with increasing fin surface emissivity. Both convection and radiation heat transfer modes are important.
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.
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.
Aspect ratio dependence of heat transfer and large-scale flow in turbulent convection
Bailon-Cuba, Jorge; Schumacher, Joerg
2010-01-01
The heat transport and corresponding changes in the large-scale circulation (LSC) in turbulent Rayleigh-B\\'{e}nard convection are studied by means of three-dimensional direct numerical simulations as a function of the aspect ratio $\\Gamma$ of a closed cylindrical cell and the Rayleigh number $Ra$. For small and moderate aspect ratios, the global heat transfer law $Nu=A\\times Ra^{\\beta}$ shows a power law dependence of both fit coefficients $A$ and $\\beta$ on the aspect ratio. A minimum Nusselt number coincides with the point where the LSC undergoes a transition from a single-roll to a double-roll pattern. With increasing aspect ratio, we detect complex multi-roll LSC configurations. The aspect ratio dependence of the turbulent heat transfer for small and moderate $\\Gamma$ is in line with a varying amount of energy contained in the LSC, as quantified by the Proper Orthogonal Decomposition analysis. For $\\Gamma\\gtrsim 8$ the heat transfer becomes independent of the aspect ratio.
In-space experiment on thermoacoustic convection heat transfer phenomenon-experiment definition
Parang, M.; Crocker, D. S.
1991-01-01
The definition phase of an in-space experiment in thermoacoustic convection (TAC) heat transfer phenomenon is completed and the results are presented and discussed in some detail. Background information, application and potential importance of TAC in heat transfer processes are discussed with particular focus on application in cryogenic fluid handling and storage in microgravity space environment. Also included are the discussion on TAC space experiment objectives, results of ground support experiments, hardware information, and technical specifications and drawings. The future plans and a schedule for the development of experiment hardware (Phase 1) and flight tests and post-flight analysis (Phase 3/4) are also presented. The specific experimental objectives are rapid heating of a compressible fluid and the measurement of the fluid temperature and pressure and the recording and analysis of the experimental data for the establishment of the importance of TAC heat transfer process. The ground experiments that were completed in support of the experiment definition included fluid temperature measurement by a modified shadowgraph method, surface temperature measurements by thermocouples, and fluid pressure measurements by strain-gage pressure transducers. These experiments verified the feasibility of the TAC in-space experiment, established the relevance and accuracy of the experimental results, and specified the nature of the analysis which will be carried out in the post-flight phase of the report.
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)
Shateyi, Stanford
2017-07-01
The spectral relaxation method is employed to examine natural convective heat and mass transfer, MHD flow over a permeable moving vertical plate with convective boundary condition in the presence of viscous dissipation, thermal radiation and chemical reaction. The governing partial differential equations were transformed into a system of nonlinear ordinary differential equations by using a similarity approach. The pertinent results are then displayed in tabular form and graphically.
Natrajan, V. K.; Christensen, K. T.
2009-11-01
The convective heat-transfer behavior of laminar flow through smooth- and rough-wall microchannels is investigated by performing non-intrusive measurements of fluid temperature using a microscale adaptation of two-color laser-induced fluorescent thermometry for flow through a heated copper microchannel testbed of hydraulic diameter Dh=600,μm. These measurements, in concert with pressure-drop measurements, are performed for a smooth-wall case and two different rough-wall cases with roughness that is reminiscent of the surface irregularities one might encounter due to imperfect fabrication methods. Pressure-drop measurements reveal the onset of transition above Recr=1800 for the smooth-wall case and deviation from laminar behavior at progressively lower Re with increasing surface roughness. The local Nusselt number (Nu) for smooth-wall flow over the range 200flow.
Convective Heat Transfer at the Martian Boundary Layer, Measurement and Model
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.
Avallone, F.; Greco, C. S.; Schrijer, F. F. J.; Cardone, G.
2015-04-01
The measurement of the convective wall heat flux in hypersonic flows may be particularly challenging in the presence of high-temperature gradients and when using high-thermal-conductivity materials. In this case, the solution of multidimensional problems is necessary, but it considerably increases the computational cost. In this paper, a low-computational-cost inverse data reduction technique is presented. It uses a recursive least-squares approach in combination with the trust-region-reflective algorithm as optimization procedure. The computational cost is reduced by performing the discrete Fourier transform on the discrete convective heat flux function and by identifying the most relevant coefficients as objects of the optimization algorithm. In the paper, the technique is validated by means of both synthetic data, built in order to reproduce physical conditions, and experimental data, carried out in the Hypersonic Test Facility Delft at Mach 7.5 on two wind tunnel models having different thermal properties.
Solution of mixed convection heat transfer from isothermal in-line fins
Khalilollahi, Amir
1993-11-01
Transient and steady state combined natural and forced convective flows over two in-line finite thickness fins (louvers) in a vertical channel are numerically solved using two methods. The first method of solution is based on the 'Simple Arbitrary Lagrangian Eulerian' (SALE) technique which incorporates mainly two computational phases: (1) a Lagrangian phase in which the velocity field is updated by the effects of all forces, and (2) an Eulerian phase that executes all advective fluxes of mass, momentum and energy. The second method of solution uses the finite element code entitled FIDAP. In the first part, comparison of the results by FIDAP, SALE, and available experimental work were done and discussed for steady state forced convection over louvered fins. Good agreements were deduced between the three sets of results especially for the flow over a single fin. In the second part and in the absence of experimental literature, the numerical predictions were extended to the transient transports and to the opposing flow where pressure drop is reversed. Results are presented and discussed for heat transfer and pressure drop in assisting and opposing mixed convection flows.
Heat transfer in a porous saturated wavy channel with asymmetric convective boundary conditions
Institute of Scientific and Technical Information of China (English)
Q Hussain; S Asghar; T Hayat; A Alsaedi
2015-01-01
The viscous flow in a wavy channel with convective boundary conditions is investigated. The channel is filled with a porous viscous fluid. Two cases of equal and different external convection coefficients on the walls are taken into account. Effect of viscous dissipation is also considered. The governing equations are derived employing long wavelength and low Reynolds number approximations. Exact closed form solutions are obtained for the simplified equations. Important physical features for peristaltic flow caused by the wavy wave are pumping, trapping and heat transfer rate at the channel walls. These are discussed one by one in depth and detail through graphical illustrations. Special attention has been given to the effects of convective boundary conditions. The results show that for Bi1≠Bi2, there exists a critical value of Brinkman number Brc at which the temperatures of both the walls become equal. And, for Bi1>Bi2 and Br>Brc, the temperature of the cold wall exceeds the temperature of hot wall.
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.
Directory of Open Access Journals (Sweden)
Heidarzadeh Habibollah
2014-01-01
Full Text Available Turbulent fluid flow and convective heat transfer over the wall mounted cube in different flow angle of attack have been studied numerically using Large Eddy Simulation. Cube faces and plate have a constant heat flux. Dynamic Smagorinsky (DS subgrid scale model were used in this study. Angles were in the range 0≤θ≤45 and Reynolds number based on the cube height and free stream velocity was 4200. The numerical simulation results were compared with the experimental data of Nakamura et al [6, 7]. Characteristics of fluid flow field and heat transfer compared for four angles of attack. Flow around the cube was classified to four regimes. Results was represented in the form of time averaged normalized streamwise velocity and Reynolds stress in different positions, temperature contours, local and average Nusselt number over the faces of cube. Local convective heat transfer on cube faces was affected by flow pattern around the cube. The local convective heat transfer from the faces of the cube and plate are directly related to the complex phenomena such as horse shoe vortex, arch vortexes in behind the cube, separation and reattachment. Results show that overall convective heat transfer of cube and mean drag coefficient have maximum and minimum value at θ=0 deg and θ=25 deg respectively.
Taha, T.J.; Thakur, D.B.; van der Meer, Theodorus H.
2012-01-01
In this work, heat transfer surface modification and heat transfer measurement technique is developed. Heat transfer investigation was aimed to study the effect of carbon nano fibers (extremely high thermal conductive material) on the enhancement level in heat transfer. Synthesis of these carbon nan
Taha, T.J.; Thakur, D.B.; Meer, van der T.H.
2012-01-01
In this work, heat transfer surface modification and heat transfer measurement technique is developed. Heat transfer investigation was aimed to study the effect of carbon nano fibers (extremely high thermal conductive material) on the enhancement level in heat transfer. Synthesis of these carbon nan
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
Manson, Steven James
The Pantex facility near Amarillo, Texas, is the only U.S. site charged with the disassembly of nuclear weapons. Concerns over the safety of weapons handling procedures are now being revisited, due to the enhanced safety requirements of the peace time disassembly effort. This research is a detailed examination of one possible nuclear weapons-related accident. In this hypothetical accident, a chemical explosion equivalent to over 50 kilos of TNT destroys unassembled nuclear weapons components, and may potentially result in some amount of plutonium reaching the environment. Previous attempts to simulate this accident have centered around the one-dimensional node and branch approach of the MELCOR code. This approach may be adequate in calculating pressure driven flow through narrow rampways and leak sites, however, its one-dimensionality does not allow it to accurately calculate the multi-dimensional aspects of heat transfer. This research effort uses an axi-symmetric stream function---vorticity formulation of the Navier-Stokes equations to model a Pantex cell building following a successfully contained chemical explosion. This allows direct calculation of the heat transfer within the cell room during the transient. The tool that was developed to perform this analysis is called PET (Post-Explosion Transient), and it simulates natural convection thermal hydraulics taking into account temperature-related fluid density differences, variable fluid transport properties, and a non-linear equation of state. Results obtained using the PET code indicate that previous analyses by other researchers using the MELCOR code have been overly conservative in estimating the effects of cell room heat transfer. An increase in the calculated heat transfer coefficient of approximately 20% is indicated. This has been demonstrated to significantly decrease the projected consequences of the hypothetical accident.
Deng, Bi-Li; Kanda, Yuki; Chen, Lin; Okajima, Junnosuke; Komiya, Atsuki; Maruyama, Shigenao
2017-08-01
Supercritical fluids have become a hot topic in recent years, due to their wide applications in chemical and energy systems. With its sensitive thermal-transport properties in the near-critical region, supercritical/near-critical fluids behaviors, under both microgravity and terrestrial conditions, have become very interesting and challenging topic. This brief review is focused on the visualization experiments of fluid convection and heat transfer related critical phenomena by interferometer. Due to the sensitive property changes of critical fluids, it is very difficult to control and measure the supercritical fluid behaviors. In this review, non-intrusive visualization systems by interferometry are introduced and analyzed for experimental studies of fluids in the near-critical region. For near-critical and supercritical experiments, the temperature/density control and parameter analysis are of critical importance. The analysis of boundary conditions, convection behaviors and energy transfer modes of critical fluids, mainly under weightlessness, are also reviewed with recent opinions toward future development. It is hoped that this review could be helpful for related studies.
Directory of Open Access Journals (Sweden)
Sarvari Seyed
2011-01-01
Full Text Available Abstract Laminar mixed convection of a nanofluid consisting of water and Al2O3 in an inclined tube with heating at the top half surface of a copper tube has been studied numerically. The bottom half of the tube wall is assumed to be adiabatic (presenting a tube of a solar collector. Heat conduction mechanism through the tube wall is considered. Three-dimensional governing equations with using two-phase mixture model have been solved to investigate hydrodynamic and thermal behaviours of the nanofluid over wide range of nanoparticle volume fractions. For a given nanoparticle mean diameter the effects of nanoparticle volume fractions on the hydrodynamics and thermal parameters are presented and discussed at different Richardson numbers and different tube inclinations. Significant augmentation on the heat transfer coefficient as well as on the wall shear stress is seen.
Allahyari, Shahriar; Behzadmehr, Amin; Sarvari, Seyed Masoud Hosseini
2011-04-26
Laminar mixed convection of a nanofluid consisting of water and Al2O3 in an inclined tube with heating at the top half surface of a copper tube has been studied numerically. The bottom half of the tube wall is assumed to be adiabatic (presenting a tube of a solar collector). Heat conduction mechanism through the tube wall is considered. Three-dimensional governing equations with using two-phase mixture model have been solved to investigate hydrodynamic and thermal behaviours of the nanofluid over wide range of nanoparticle volume fractions. For a given nanoparticle mean diameter the effects of nanoparticle volume fractions on the hydrodynamics and thermal parameters are presented and discussed at different Richardson numbers and different tube inclinations. Significant augmentation on the heat transfer coefficient as well as on the wall shear stress is seen.
Energy Technology Data Exchange (ETDEWEB)
Kim, Donghyun; Son, Gihun [Sogang University, Seoul (Korea, Republic of); Kim, Sungil [Korea Institute of Energy Research, Daejeon (Korea, Republic of)
2016-02-15
A numerical approach is developed for computing convective drying of a moist object. The conservation equations of mass, momentum, energy and moisture in the internal and external regions of an object are solved with the coupled heat and mass transfer conditions on the object surface, including the effect of evaporation. A numerical approach is applied to predict the internal and external temperature and moisture distributions during the convective drying with variations in the initial moisture content and the water activity. The numerical results show that the water activity is an important parameter for determining the drying rate pattern and the analogy between the heat and mass transfer on the object surface.
Munir, Asif; Shahzad, Azeem; Khan, Masood
2014-01-01
The major focus of this article is to analyze the forced convective heat transfer in a steady boundary layer flow of Sisko fluid over a nonlinear stretching sheet. Two cases are studied, namely (i) the sheet with variable temperature (PST case) and (ii) the sheet with variable heat flux (PHF case). The heat transfer aspects are investigated for both integer and non-integer values of the power-law index. The governing partial differential equations are reduced to a system of nonlinear ordinary differential equations using appropriate similarity variables and solved numerically. The numerical results are obtained by the shooting method using adaptive Runge Kutta method with Broyden's method in the domain[Formula: see text]. The numerical results for the temperature field are found to be strongly dependent upon the power-law index, stretching parameter, wall temperature parameter, material parameter of the Sisko fluid and Prandtl number. In addition, the local Nusselt number versus wall temperature parameter is also graphed and tabulated for different values of pertaining parameters. Further, numerical results are validated by comparison with exact solutions as well as previously published results in the literature.
Munir, Asif; Shahzad, Azeem; Khan, Masood
2014-01-01
The major focus of this article is to analyze the forced convective heat transfer in a steady boundary layer flow of Sisko fluid over a nonlinear stretching sheet. Two cases are studied, namely (i) the sheet with variable temperature (PST case) and (ii) the sheet with variable heat flux (PHF case). The heat transfer aspects are investigated for both integer and non-integer values of the power-law index. The governing partial differential equations are reduced to a system of nonlinear ordinary differential equations using appropriate similarity variables and solved numerically. The numerical results are obtained by the shooting method using adaptive Runge Kutta method with Broyden’s method in the domain. The numerical results for the temperature field are found to be strongly dependent upon the power-law index, stretching parameter, wall temperature parameter, material parameter of the Sisko fluid and Prandtl number. In addition, the local Nusselt number versus wall temperature parameter is also graphed and tabulated for different values of pertaining parameters. Further, numerical results are validated by comparison with exact solutions as well as previously published results in the literature. PMID:24949738
Stalmach, C. J., Jr.
1975-01-01
Several model/instrument concepts employing electroless metallic skin were considered for improvement of surface condition, accuracy, and cost of contoured-geometry convective heat transfer models. A plated semi-infinite slab approach was chosen for development and evaluation in a hypersonic wind tunnel. The plated slab model consists of an epoxy casting containing fine constantan wires accurately placed at specified surface locations. An electroless alloy was deposited on the plastic surface that provides a hard, uniformly thick, seamless skin. The chosen alloy forms a high-output thermocouple junction with each exposed constantan wire, providing means of determining heat transfer during tunnel testing of the model. A selective electroless plating procedure was used to deposit scaled heatshield tiles on the lower surface of a 0.0175-scale shuttle orbiter model. Twenty-five percent of the tiles were randomly selected and plated to a height of 0.001-inch. The purpose was to assess the heating effects of surface roughness simulating misalignment of tiles that may occur during manufacture of the spacecraft.
Henselowsky, C.; Kuhlmann, H. C.; Rath, H. J.
2001-03-01
The heat transfer from an electrically heated cylinder (wire) of finite length to the surrounding fluid can be divided into heat radiation, conduction and convection. A technical application of these cylinders with typical dimensions of 1-2 mm length and a few micrometers diameter is the Hot-Wire-Anemometry. This systematic study should clarify the influence of free convection to three dimensional heat transfer of cylinders. For this aim it is planned to investigate Reynolds numbers below Re=1 (creeping flow). For this reason measurements should be done under 1g in the earth laboratory and also under microgravity (µg) conditions. Comparisons of these measurements under otherwise same conditions allows to distinguish between the pure convection heat transfer and the contributions due to conduction and other effects. For measurements under µg the Drop Tower Bremen can be used as research facility. Due to the fast response of convection to changes in the gravity conditions the Drop Tower is an ideal and cost efficient experimental tool. The experimental setup is build to operate at velocity range of 0-1 m/s which includes the whole range of convection from pure free convection at 0 m/s over mixed convection up to pure forced convection at velocities above about 0.15 m/s. This velocity region corresponds to a range of the Reynolds number of Re=0-0.18 for a cylinder of 5 µ m diameter at Tf=140°C in air at an ambient temperature of about 21°C.
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.
Heat Transfer in MHD Mixed Convection Flow of a Ferrofluid along a Vertical Channel.
Gul, Aaiza; Khan, Ilyas; Shafie, Sharidan; Khalid, Asma; Khan, Arshad
2015-01-01
This study investigated heat transfer in magnetohydrodynamic (MHD) mixed convection flow of ferrofluid along a vertical channel. The channel with non-uniform wall temperatures was taken in a vertical direction with transverse magnetic field. Water with nanoparticles of magnetite (Fe3O4) was selected as a conventional base fluid. In addition, non-magnetic (Al2O3) aluminium oxide nanoparticles were also used. Comparison between magnetic and magnetite nanoparticles were also conducted. Fluid motion was originated due to buoyancy force together with applied pressure gradient. The problem was modelled in terms of partial differential equations with physical boundary conditions. Analytical solutions were obtained for velocity and temperature. Graphical results were plotted and discussed. It was found that temperature and velocity of ferrofluids depend strongly on viscosity and thermal conductivity together with magnetic field. The results of the present study when compared concurred with published work.
Heat Transfer in MHD Mixed Convection Flow of a Ferrofluid along a Vertical Channel.
Directory of Open Access Journals (Sweden)
Aaiza Gul
Full Text Available This study investigated heat transfer in magnetohydrodynamic (MHD mixed convection flow of ferrofluid along a vertical channel. The channel with non-uniform wall temperatures was taken in a vertical direction with transverse magnetic field. Water with nanoparticles of magnetite (Fe3O4 was selected as a conventional base fluid. In addition, non-magnetic (Al2O3 aluminium oxide nanoparticles were also used. Comparison between magnetic and magnetite nanoparticles were also conducted. Fluid motion was originated due to buoyancy force together with applied pressure gradient. The problem was modelled in terms of partial differential equations with physical boundary conditions. Analytical solutions were obtained for velocity and temperature. Graphical results were plotted and discussed. It was found that temperature and velocity of ferrofluids depend strongly on viscosity and thermal conductivity together with magnetic field. The results of the present study when compared concurred with published work.
A modified lattice Bhatnagar-Gross-Krook model for convection heat transfer in porous media
Wang, Liang; Guo, Zhaoli
2015-01-01
The lattice Bhatnagar-Gross-Krook (LBGK) model has become the most popular one in the lattice Boltzmann method for simulating the convection heat transfer in porous media. However, the LBGK model generally suffers from numerical instability at low fluid viscosities and effective thermal diffusivities. In this paper, a modified LBGK model is developed for incompressible thermal flows in porous media at the representative elementary volume scale, in which the shear rate and temperature gradient are incorporated into the equilibrium distribution functions. With two additional parameters, the relaxation times in the collision process can be fixed at a proper value invariable to the viscosity and the effective thermal diffusivity. In addition, by constructing a modified equilibrium distribution function and a source term in the evolution equation of temperature field, the present model can recover the macroscopic equations correctly through the Chapman-Enskog analysis, which is another key point different from pre...
Energy Technology Data Exchange (ETDEWEB)
Mondal, Rabindra Nath, E-mail: rnmondal71@yahoo.com; Shaha, Poly Rani [Department of Mathematics, Jagannath University, Dhaka-1100 (Bangladesh); Roy, Titob [Department of Mathematics, Vikarunnesa Nun School and College, Boshundhara, Dhaka (Bangladesh); Yanase, Shinichiro, E-mail: yanase@okayama-u.ac.jp [Department of Mechanical and Systems Engineering, Okayama University, Okayama 700-8530 (Japan)
2016-07-12
Unsteady laminar flow with convective heat transfer through a curved square duct rotating at a constant angular velocity about the center of curvature is investigated numerically by using a spectral method, and covering a wide range of the Taylor number −300≤Tr≤1000 for the Dean number Dn = 1000. A temperature difference is applied across the vertical sidewalls for the Grashof number Gr = 100, where the outer wall is heated and the inner wall cooled, the top and bottom walls being adiabatic. Flow characteristics are investigated with the effects of rotational parameter, Tr, and the pressure-driven parameter, Dn, for the constant curvature 0.001. Time evolution calculations as well as their phase spaces show that the unsteady flow undergoes through various flow instabilities in the scenario ‘multi-periodic → chaotic → steady-state → periodic → multi-periodic → chaotic’, if Tr is increased in the positive direction. For negative rotation, however, time evolution calculations show that the flow undergoes in the scenario ‘multi-periodic → periodic → steady-state’, if Tr is increased in the negative direction. Typical contours of secondary flow patterns and temperature profiles are obtained at several values of Tr, and it is found that the unsteady flow consists of two- to six-vortex solutions if the duct rotation is involved. External heating is shown to generate a significant temperature gradient at the outer wall of the duct. This study also shows that there is a strong interaction between the heating-induced buoyancy force and the centrifugal-Coriolis instability in the curved channel that stimulates fluid mixing and consequently enhances heat transfer in the fluid.
Mondal, Rabindra Nath; Roy, Titob; Shaha, Poly Rani; Yanase, Shinichiro
2016-07-01
Unsteady laminar flow with convective heat transfer through a curved square duct rotating at a constant angular velocity about the center of curvature is investigated numerically by using a spectral method, and covering a wide range of the Taylor number -300≤Tr≤1000 for the Dean number Dn = 1000. A temperature difference is applied across the vertical sidewalls for the Grashof number Gr = 100, where the outer wall is heated and the inner wall cooled, the top and bottom walls being adiabatic. Flow characteristics are investigated with the effects of rotational parameter, Tr, and the pressure-driven parameter, Dn, for the constant curvature 0.001. Time evolution calculations as well as their phase spaces show that the unsteady flow undergoes through various flow instabilities in the scenario `multi-periodic → chaotic → steady-state → periodic → multi-periodic → chaotic', if Tr is increased in the positive direction. For negative rotation, however, time evolution calculations show that the flow undergoes in the scenario `multi-periodic → periodic → steady-state', if Tr is increased in the negative direction. Typical contours of secondary flow patterns and temperature profiles are obtained at several values of Tr, and it is found that the unsteady flow consists of two- to six-vortex solutions if the duct rotation is involved. External heating is shown to generate a significant temperature gradient at the outer wall of the duct. This study also shows that there is a strong interaction between the heating-induced buoyancy force and the centrifugal-Coriolis instability in the curved channel that stimulates fluid mixing and consequently enhances heat transfer in the fluid.
Joule-Thomson effect and internal convection heat transfer in turbulent He II flow
Walstrom, P. L.
1988-01-01
The temperature rise in highly turbulent He II flowing in tubing was measured in the temperature range 1.6-2.1 K. The effect of internal convection heat transport on the predicted temperature profiles is calculated from the two-fluid model with mutual friction. The model predictions are in good agreement with the measurements, provided that the pressure gradient term is retained in the expression for internal convection heat flow.
Joule-Thomson effect and internal convection heat transfer in turbulent He II flow
Walstrom, P. L.
1988-03-01
The temperature rise in highly turbulent He II flowing in tubing was measured in the temperature range 1.6-2.1 K. The effect of internal convection heat transport on the predicted temperature profiles is calculated from the two-fluid model with mutual friction. The model predictions are in good agreement with the measurements, provided that the pressure gradient term is retained in the expression for internal convection heat flow.
Heat Transfer by Thermo-capillary Convection -Sounding Rocket COMPERE Experiment SOURCE
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
Zebib, A.; Schubert, G.; Dein, J. L.; Paliwal, R. C.
1983-01-01
The influence of shell size and mode of heating on the behavior and stability of axisymmetric, infinite Prandtl number convection in a spherical geometry is studied. Heating from within and below features convection onset governed by a self-adjoint system of equations and boundary conditions. For heating only from within or from below, linearized equations and boundary conditions are non-self-adjoint. Identification of the parameter which initiates the departure from self-adjointness, together with the properties of the self-adjoint solution, provide a basis for calculating the heat transfer characteristics of the non-self-adjoint situations. The investigations are an effort to develop a model for heat transfer in planetary interiors. Further development of the technique by modifying the Galerkin method by the introduction of diagonal mode truncation is suggested to permit the consideration of higher values of the Rayleigh numbers, i.e., those more commensurate with terrestrial planet mantles.
Experimental study on convective heat transfer coefficient around a vertical hexagonal rod bundle
Makhmalbaf, M. H. M.
2012-06-01
Research on convective heat transfer coefficient around a rod bundle has many diverse applications in industry. So far, many studies have been conducted in correlations related to internal and turbulent fully-developed flow. Comparison shows that Dittus-Boelter, Sieder-Tate and Petukhov have so far been the most practical correlations in fully-developed turbulent fluid flow heat transfer. The present study conducts an experimental examination of the validity of these frequently-applied correlations and introduces a manufactured test facility as well. Due to its generalizibility, the unique geometry of this test facility (hexagonal arranged, 7 vertical rods in a hexagonal tube) can fulfil extensive applications. The paper also studies the major deviation sources in data measurements, calibrations and turbulence of fluid flow in this. Finally, regarding to sufficient number of experiments in a vast fluid mean velocity range (3,800 < Re < 40,000), a new curve and correlation are presented and the results are compared with the above mentioned commonly-applied correlations.
Institute of Scientific and Technical Information of China (English)
C. Henselowsky; H.C. Kuhlmann; H.J. Rath
2001-01-01
The heat transfer from an electrically heated cylinder (wire) of finite length to the surrounding fluid can be divided into heat radiation, conduction and convection. A technical application of these cylinders with typical di mensions of 1-2 mm length and a few micrometers diameter is the Hot-Wire-Anemometry. This systematic study should clarify the influence of free convection to three dimensional heat transfer of cylinders. For this aim it is planned to investigate Reynolds numbers below Re = 1 (creeping flow). For this reason measurements should be done under lg in the earth laboratory and also under microgravity (μg) conditions. Comparisons of these meas urements under otherwise same conditions allows to distinguish between the pure convection heat transfer and the contributions due to conduction and other effects.For measurements underμg the Drop Tower Bremen can be used as research facility. Due to the fast response of convection to changes in the gravity conditions the Drop Tower is an ideal and cost efficient experimental tool.The experimental setup is build to operate at velocity range of 0-1 m/s which includes the whole range of con vection from pure free convection at 0 m/s over mixed convection up to pure forced convection at velocities abo ve about 0.15 m/s. This velocity region corresponds to a range of the Reynolds number of Re = 0 - 0.18 for a cylinder of 5 μ m diameter at Tf= 140℃ in air at an ambient temperature of about 21℃.
Numerical simulation of convective heat transfer of nonhomogeneous nanofluid using Buongiorno model
Sayyar, Ramin Onsor; Saghafian, Mohsen
2017-03-01
The aim is to study the assessment of the flow and convective heat transfer of laminar developing flow of Al2O3-water nanofluid inside a vertical tube. A finite volume method procedure on a structured grid was used to solve the governing partial differential equations. The adopted model (Buongiorno model) assumes that the nanofluid is a mixture of a base fluid and nanoparticles, with the relative motion caused by Brownian motion and thermophoretic diffusion. The results showed the distribution of nanoparticles remained almost uniform except in a region near the hot wall where nanoparticles volume fraction were reduced as a result of thermophoresis. The simulation results also indicated there is an optimal volume fraction about 1-2% of the nanoparticles at each Reynolds number for which the maximum performance evaluation criteria can be obtained. The difference between Nusselt number and nondimensional pressure drop calculated based on two phase model and the one calculated based on single phase model was less than 5% at all nanoparticles volume fractions and can be neglected. In natural convection, for 4% of nanoparticles volume fraction, in Gr = 10 more than 15% enhancement of Nusselt number was achieved but in Gr = 300 it was less than 1%.
Numerical simulation of convective heat transfer of nonhomogeneous nanofluid using Buongiorno model
Sayyar, Ramin Onsor; Saghafian, Mohsen
2017-08-01
The aim is to study the assessment of the flow and convective heat transfer of laminar developing flow of Al2O3-water nanofluid inside a vertical tube. A finite volume method procedure on a structured grid was used to solve the governing partial differential equations. The adopted model (Buongiorno model) assumes that the nanofluid is a mixture of a base fluid and nanoparticles, with the relative motion caused by Brownian motion and thermophoretic diffusion. The results showed the distribution of nanoparticles remained almost uniform except in a region near the hot wall where nanoparticles volume fraction were reduced as a result of thermophoresis. The simulation results also indicated there is an optimal volume fraction about 1-2% of the nanoparticles at each Reynolds number for which the maximum performance evaluation criteria can be obtained. The difference between Nusselt number and nondimensional pressure drop calculated based on two phase model and the one calculated based on single phase model was less than 5% at all nanoparticles volume fractions and can be neglected. In natural convection, for 4% of nanoparticles volume fraction, in Gr = 10 more than 15% enhancement of Nusselt number was achieved but in Gr = 300 it was less than 1%.
Directory of Open Access Journals (Sweden)
Prasad Kerehalli
2015-01-01
Full Text Available An analysis is carried out to study the effects of temperature-dependent transport properties on the fully developed free and forced MHD convection flow in a vertical channel. In this model, viscous and Ohmic dissipation terms are also included. The governing nonlinear equations (in non-dimensional form are solved numerically by a second order finite difference scheme. A parametric study is performed in order to illustrate the interactive influences of the model parameters; namely, the magnetic parameter, the variable viscosity parameter, the mixed convection parameter, the variable thermal conductivity parameter, the Brinkmann number and the Eckert number. The velocity field, the temperature field, the skin friction and the Nusselt number are evaluated for several sets of values of these parameters. For some special cases, the obtained numerical results are compared with the available results in the literature: Good agreement is found. Of all the parameters, the variable thermo-physical transport property has the strongest effect on the drag, heat transfer characteristics, the stream-wise velocity, and the temperature field.
Institute of Scientific and Technical Information of China (English)
Abdullah H. AlEssa; Mohamad I. Al-Widyan
2008-01-01
This study examines the heat transfer enhancement from a horizontal rect- angular fin embedded with triangular perforations (their bases parallel and toward the fin tip) under natural convection. The fin's heat dissipation rate is compared to that of an equivalent solid one. The parameters considered axe geometrical dimensions and thermal properties of the fin and the perforations. The gain in the heat transfer enhancement and the fin weight reduction due to the perforations are considered. The study shows that the heat dissipation from the perforated fin for a certain range of triangular perforation di- mensions and spaces between perforations result in improvement in the heat transfer over the equivalent solid fin. The heat transfer enhancement of the perforated fin increases as the fin thermal conductivity and its thickness are increased.
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.
Delcov, A.; Hodenkov, A.; Zhuikov, D.
2015-10-01
This paper covered the problem of assessing the effectiveness of the section of the fin-tube radiator of space thermal control system. The task of calculating the conjugate radiation-convective heat transfer is presented. The results of numerical simulation are described.
Directory of Open Access Journals (Sweden)
Chi-Thanh Tran
2013-01-01
Full Text Available This paper is concerned with the development of approaches for assessment of core debris heat transfer and Control Rod Guide Tube (CRGT cooling effectiveness in case of a Boiling Water Reactor (BWR severe accident. We consider a hypothetical scenario with stratified (metal layer atop melt pool in the lower plenum. Effective Convectivity Model (ECM and Phase-Change ECM (PECM are developed for the modeling of molten metal layer heat transfer. The PECM model takes into account reduced convection heat transfer in mushy zone and compositional convection that enables simulations of noneutectic binary mixture solidification and melting. The ECM and PECM are (i validated against relevant experiments for both eutectic and noneutectic mixtures and (ii benchmarked against CFD-generated data including the local heat transfer characteristics. The PECM is then applied to the analysis of heat transfer in a stratified heterogeneous debris pool taking into account CRGT cooling. The PECM simulation results show apparent efficacy of the CRGT cooling which can be utilized as Severe Accident Management (SAM measure to protect the vessel wall from focusing effect caused by metallic layer.
Kahani, M.; Zeinali Heris, S.; Mousavi, S. M.
2014-05-01
Coiled tubes and nanofludics are two significant techniques to enhance the heat transfer ability of thermal equipments. The forced convective heat transfer and the pressure drop of nanofluid inside straight tube and helical coiled one with a constant wall heat flux were studied experimentally. Distilled water was used as a host fluid and Nanofluids of aqueous TiO2 nanoparticles (50 nm) suspensions were prepared in various volume concentrations of 0.25-2 %. The heat transfer coefficient of nanofluids is obtained for different nanoparticle concentrations as well as various Reynolds numbers. The experiments covered a range of Reynolds number of 500-4,500. The results show the considerable enhancement of heat transfer rate, which is due to the nanoparticles present in the fluid. Heat transfer coefficient increases by increasing the volume concentration of nanoparticles as well as Reynolds number. Moreover, due to the curvature of the tube when fluid flows inside helical coiled tube instead of straight one, both convective heat transfer coefficient and the pressure drop of fluid grow considerably. Also, the thermal performance factors for tested nanofluids are greater than unity and the maximum thermal performance factor of 3.72 is found with the use of 2.0 % volume concentration of nanofluid at Reynolds number of 1,750.
Energy Technology Data Exchange (ETDEWEB)
Francisco Valentin; Narbeh Artoun; Masahiro Kawaji; Donald M. McEligot
2015-08-01
Fundamental high pressure/high temperature forced convection experiments have been conducted in support of the development of a Very High Temperature Reactor (VHTR) with a prismatic core. The experiments utilize a high temperature/high pressure gas flow test facility constructed for forced convection and natural circulation experiments. The test section has a single 16.8 mm ID flow channel in a 2.7 m long, 108 mm OD graphite column with four 2.3kW electric heater rods placed symmetrically around the flow channel. This experimental study presents the role of buoyancy forces in enhancing or reducing convection heat transfer for helium at high pressures up to 70 bar and high temperatures up to 873 degrees K. Wall temperatures have been compared among 10 cases covering the inlet Re numbers ranging from 500 to 3,000. Downward flows display higher and lower wall temperatures in the upstream and downstream regions, respectively, than the upward flow cases due to the influence of buoyancy forces. In the entrance region, convection heat transfer is reduced due to buoyancy leading to higher wall temperatures, while in the downstream region, buoyancyinduced mixing causes higher convection heat transfer and lower wall temperatures. However, their influences are reduced as the Reynolds number increases. This experimental study is of specific interest to VHTR design and validation of safety analysis codes.
Taha, T.J.; Mojet, Barbara; Lefferts, Leonardus; van der Meer, Theodorus H.
2016-01-01
In this work, heat transfer surface modification is made by layers of carbon nanofiber (CNF) on a 50 μm nickel wire using Thermal chemical vapor deposition process (TCVD). Three different CNF layer morphologies are made, at 500 °C, 600 °C and 700 °C, to investigate the influence of morphology on hea
Parvin, Salma; Ahmed, Sajid; Chowdhury, Raju
2017-06-01
The present work investigates numerically the convective and radiative heat transfer performance and entropy generation of forced convection through a direct absorption solar collector (DASC). Four different fluids; Cu-water nanofluid, Al2O3-waternanofluid, TiO2-water nanofluid and pure water are used as the working fluid. Entropy production has been taken into account in addition to the collector efficiency and heat transfer enhancement. Penalty finite element method with Galerkin's weighted residual technique is used to solve the governing non-linear partial differential equations. Numerical simulations are performed for the variation of solar irradiation (I). The outcomes are presented in the form of isotherms, average output temperature, the average Nusselt number, collector efficiency, average entropy generation and Bejan number. The results present that the rate of heat transfer and collector efficiency enhance significantly for raising the values of I upto a certain range.
Kamajaya, Ketut; Umar, Efrizon; Sudjatmi, K. S.
2012-06-01
This study focused on natural convection heat transfer using a vertical rectangular sub-channel and water as the coolant fluid. To conduct this study has been made pipe heaters are equipped with thermocouples. Each heater is equipped with five thermocouples along the heating pipes. The diameter of each heater is 2.54 cm and 45 cm in length. The distance between the central heating and the pitch is 29.5 cm. Test equipment is equipped with a primary cooling system, a secondary cooling system and a heat exchanger. The purpose of this study is to obtain new empirical correlations equations of the vertical rectangular sub-channel, especially for the natural convection heat transfer within a bundle of vertical cylinders rectangular arrangement sub-channels. The empirical correlation equation can support the thermo-hydraulic analysis of research nuclear reactors that utilize cylindrical fuel rods, and also can be used in designing of baffle-free vertical shell and tube heat exchangers. The results of this study that the empirical correlation equations of natural convection heat transfer coefficients with rectangular arrangement is Nu = 6.3357 (Ra.Dh/x)0.0740.
DEFF Research Database (Denmark)
Le Dreau, Jerome; Heiselberg, Per; Jensen, Rasmus Lund
2015-01-01
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......-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...
Convective heat transfer and experimental icing aerodynamics of wind turbine blades
Wang, Xin
The total worldwide base of installed wind energy peak capacity reached 94 GW by the end of 2007, including 1846 MW in Canada. Wind turbine systems are being installed throughout Canada and often in mountains and cold weather regions, due to their high wind energy potential. Harsh cold weather climates, involving turbulence, gusts, icing and lightning strikes in these regions, affect wind turbine performance. Ice accretion and irregular shedding during turbine operation lead to load imbalances, often causing the turbine to shut off. They create excessive turbine vibration and may change the natural frequency of blades as well as promote higher fatigue loads and increase the bending moment of blades. Icing also affects the tower structure by increasing stresses, due to increased loads from ice accretion. This can lead to structural failures, especially when coupled to strong wind loads. Icing also affects the reliability of anemometers, thereby leading to inaccurate wind speed measurements and resulting in resource estimation errors. Icing issues can directly impact personnel safety, due to falling and projected ice. It is therefore important to expand research on wind turbines operating in cold climate areas. This study presents an experimental investigation including three important fundamental aspects: (1) heat transfer characteristics of the airfoil with and without liquid water content (LWC) at varying angles of attack; (2) energy losses of wind energy while a wind turbine is operating under icing conditions; and (3) aerodynamic characteristics of an airfoil during a simulated icing event. A turbine scale model with curved 3-D blades and a DC generator is tested in a large refrigerated wind tunnel, where ice formation is simulated by spraying water droplets. A NACA 63421 airfoil is used to study the characteristics of aerodynamics and convective heat transfer. The current, voltage, rotation of the DC generator and temperature distribution along the airfoil
Film Boiling Heat Transfer Properties of Liquid Hydrogen in Natural Convection
Horie, Y.; Shirai, Y.; Shiotsu, M.; Matsuzawa, T.; Yoneda, K.; Shigeta, H.; Tatsumoto, H.; Hata, K.; Naruo, Y.; Kobayashi, H.; Inatani, Y.
Film boiling heat transfer properties of LH2 for various pressures and subcooling conditions were measured by applying electric current to give an exponential heat input to a PtCo wire with a diameter of 1.2 mm submerged in LH2. The heated wire was set to be horizontal to the ground. The heat transfer coefficient in the film boiling region was higher for higher pressure and higher subcooling. The experimental results are compared with the equation of pool film boiling heat transfer. It is confirmed that the pool film boiling heat transfer coefficients in LH2 can be expressed by this equation.
Beukema, K.J.
1980-01-01
Three different models of bulk-stored agricultural products with air flow through the bulk, predicting the temperature profiles or the velocity of natural convection, are developed. The temperature distribution in a cylindrical container with insulated walls and open top and bottom, filled with heat-generating model material is studied experimentally, used to calculate the velocity of natural convection and compared with model predictions. A two-dimensional two-phase model of temper...
Energy Technology Data Exchange (ETDEWEB)
Hayat, Tasawar [Quaid-i-Azam Univ., Islamabad (Pakistan). Dept. of Mathematics; King Saud Univ., Riyadh (Saudi Arabia). Dept. of Physics; Iqbal, Zahid [Quaid-i-Azam Univ., Islamabad (Pakistan). Dept. of Mathematics; Qasim, Muhammad [COMSATS Institute of Information Technology (CIIT), Islamabad (Pakistan). Dept. of Mathematics; Aldossary, Omar M. [King Saud Univ., Riyadh (Saudi Arabia). Dept. of Physics
2012-05-15
This investigation reports the boundary layer flow and heat transfer characteristics in a couple stress fluid flow over a continuos moving surface with a parallel free stream. The effects of heat generation in the presence of convective boundary conditions are also investigated. Series solutions for the velocity and temperature distributions are obtained by the homotopy analysis method (HAM). Convergence of obtained series solutions are analyzed. The results are obtained and discussed through graphs for physical parameters of interest. (orig.)
Experimental and numerical studies on convective heat transfer in a neonatal incubator.
Kim, Y H; Kwon, C H; Yoo, S C
2002-01-01
Thermo-neutrality is one of the major environmental factors affecting a premature or low-birth-weight neonate inside an incubator. Severe temperature differences inside an incubator lead to neonate heat loss, hypothermia and apnoea, which are closely related to air flow and air velocity. In the study, flow visualisations, hot-wire velocity measurements and computational fluid dynamics simulate the airflow inside a neonatal incubator. An anatomically correct neonate model is designed using a three-dimensional laser scanner system and a rapid prototyping machine. Flow visualisations demonstrate that large-scale rotating airflow is produced inside the chamber, and a number of small, stationary eddies are found in regions between the air inlet and the neonate. Hot-wire measurements show that air velocities along the long inlets are not uniform. Computational fluid dynamics show relatively uniform temperatures of about 34 degrees C on the neonate's anterior aspect and the highest temperature of 36.1 degrees C at the right armpit and the crotch. Flow fields from airflow visualisations, hot-wire measurements and computational fluid dynamics are very similar, both qualitatively and quantitatively. The small eddies produced between the neonate and the mattress could interfere with convective and evaporative heat transfers from the neonate. Therefore it is important to eliminate eddies around the neonate in future designs of neonatal incubators.
Defraeye, Thijs; Blocken, Bert; Koninckx, Erwin; Hespel, Peter; Carmeliet, Jan
2011-06-03
This study aims at investigating drag and convective heat transfer for cyclists at a high spatial resolution. Such an increased spatial resolution, when combined with flow-field data, can increase insight in drag reduction mechanisms and in the thermo-physiological response of cyclists related to heat stress and hygrothermal performance of clothing. Computational fluid dynamics (steady Reynolds-averaged Navier-Stokes) is used to evaluate the drag and convective heat transfer of 19 body segments of a cyclist for three different cyclist positions. The influence of wind speed on the drag is analysed, indicating a pronounced Reynolds number dependency on the drag, where more streamlined positions show a dependency up to higher Reynolds numbers. The drag and convective heat transfer coefficient (CHTC) of the body segments and the entire cyclist are compared for all positions at racing speeds, showing high drag values for the head, legs and arms and high CHTCs for the legs, arms, hands and feet. The drag areas of individual body segments differ markedly for different cyclist positions whereas the convective heat losses of the body segments are found to be less sensitive to the position. CHTC-wind speed correlations are derived, in which the power-law exponent does not differ significantly for the individual body segments for all positions, where an average value of 0.84 is found. Similar CFD studies can be performed to assess drag and CHTCs at a higher spatial resolution for applications in other sport disciplines, bicycle equipment design or to assess convective moisture transfer.
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)
Enhanced convective and film boiling heat transfer by surface gas injection
Energy Technology Data Exchange (ETDEWEB)
Duignan, M.R.; Greene, G.A. (Brookhaven National Lab., Upton, NY (United States)); Irvine, T.F., Jr. (State Univ. of New York, Stony Brook, NY (United States). Dept. of Mechanical Engineering)
1992-04-01
Heat transfer measurements were made for stable film boiling of water over a horizontal, flat stainless steel plate from the minimum film boiling point temperature, T{sub SURFACE} {approximately}500K, to T{sub SURFACE} {approximately}950K. The pressure at the plate was approximately 1 atmosphere and the temperature of the water pool was maintained at saturation. The data were compared to the Berenson film-boiling model, which was developed for minimum film-boiling-point conditions. The model accurately represented the data near the minimum film-boiling point and at the highest temperatures measured, as long it was corrected for the heat transferred by radiation. On the average, the experimental data lay within {plus minus}7% of the model. Measurements of heat transfer were made without film boiling for nitrogen jetting into an overlying pool of water from nine 1-mm- diameter holes, drilled in the heat transfer plate. The heat flux was maintained constant at approximately 26.4 kW/m{sup 2}. For water-pool heights of less than 6cm the heat transfer coefficient deceased linearly with a decrease in heights. Above 6cm the heat transfer coefficient was unaffected. For the entire range of gas velocities measured (0 to 8.5 cm/s), the magnitude of the magnitude of the heat transfer coefficient only changed by approximately 20%. The heat transfer data bound the Konsetov model for turbulent pool heat transfer which was developed for vertical heat transfer surfaces. This agreement suggests that surface orientation may not be important when the gas jets do not locally affect the surface heat transfer. Finally, a database was developed for heat transfer from the plate with both film boiling and gas jetting occurring simultaneously, in a pool of water maintained at its saturation temperature. The effect of passing nitrogen through established film boiling is to increase the heat transfer from that surface. 60 refs.
Enhanced convective and film boiling heat transfer by surface gas injection
Energy Technology Data Exchange (ETDEWEB)
Duignan, M.R.; Greene, G.A. [Brookhaven National Lab., Upton, NY (United States); Irvine, T.F., Jr. [State Univ. of New York, Stony Brook, NY (United States). Dept. of Mechanical Engineering
1992-04-01
Heat transfer measurements were made for stable film boiling of water over a horizontal, flat stainless steel plate from the minimum film boiling point temperature, T{sub SURFACE} {approximately}500K, to T{sub SURFACE} {approximately}950K. The pressure at the plate was approximately 1 atmosphere and the temperature of the water pool was maintained at saturation. The data were compared to the Berenson film-boiling model, which was developed for minimum film-boiling-point conditions. The model accurately represented the data near the minimum film-boiling point and at the highest temperatures measured, as long it was corrected for the heat transferred by radiation. On the average, the experimental data lay within {plus_minus}7% of the model. Measurements of heat transfer were made without film boiling for nitrogen jetting into an overlying pool of water from nine 1-mm- diameter holes, drilled in the heat transfer plate. The heat flux was maintained constant at approximately 26.4 kW/m{sup 2}. For water-pool heights of less than 6cm the heat transfer coefficient deceased linearly with a decrease in heights. Above 6cm the heat transfer coefficient was unaffected. For the entire range of gas velocities measured [0 to 8.5 cm/s], the magnitude of the magnitude of the heat transfer coefficient only changed by approximately 20%. The heat transfer data bound the Konsetov model for turbulent pool heat transfer which was developed for vertical heat transfer surfaces. This agreement suggests that surface orientation may not be important when the gas jets do not locally affect the surface heat transfer. Finally, a database was developed for heat transfer from the plate with both film boiling and gas jetting occurring simultaneously, in a pool of water maintained at its saturation temperature. The effect of passing nitrogen through established film boiling is to increase the heat transfer from that surface. 60 refs.
Umer, Asim; Naveed, Shahid; Ramzan, Naveed
2016-10-01
Nanofluids, having 1-100 nm size particles in any base fluid are promising fluid for heat transfer intensification due to their enhanced thermal conductivity as compared with the base fluid. The forced convection of nanofluids is the major practical application in heat transfer equipments. In this study, heat transfer enhancements at constant wall heat flux under laminar flow conditions were investigated. Nanofluids of different volume fractions (1, 2 and 4 %) of copper (I) oxide nanoparticles in deionized water were prepared using two step technique under mechanical mixing and ultrasonication. The results were investigated by increasing the Reynolds number of the nanofluids at constant heat flux. The trends of Nusselt number variation with dimensionless length (X/D) and Reynolds numbers were studied. It was observed that heat transfer coefficient increases with increases particles volume concentration and Reynolds number. The maximum enhancement in heat transfer coefficient of 61 % was observed with 4 % particle volume concentration at Reynolds number (Re ~ 605).
Taha, T. J.; Thakur, D. B.; Van der Meer, T. H.
2012-11-01
In this work, heat transfer surface modification and heat transfer measurement technique is developed. Heat transfer investigation was aimed to study the effect of carbon nano fibers (extremely high thermal conductive material) on the enhancement level in heat transfer. Synthesis of these carbon nano structures is achieved using thermal catalytic chemical vapor deposition process (TCCVD) on a 50 μm pure nickel (Ni270) wire. The micro wire samples covered with CNF layers were subjected to a uniform flow from a nozzle. Heat transfer measurement was achieved by a controlled heat dissipation through the micro wire to attain a constant temperature during the flow. This measurement technique is adopted from hot wire anemometry calibration method. Synthesis of carbon nano structures, heat transfer surface characterization and measurement technique are evaluated. Preliminary results indicate that an average enhancement in Nusselt Number of 17% is achieved.
Effect of the fins configuration on natural convection heat transfer experimentally and numerically
Directory of Open Access Journals (Sweden)
Ahmed F. Khudheyer, Zaid Hameed Hasan
2015-01-01
Full Text Available The cooling of the electronic systems, electrical systems, and CPU of the computer is very important; therefore this study is prepared to improve this aims. In this study, natural convection heat transfer from rectangular fins with five different figures (continuous fins, 1-interrupted fins, 4-interrupted fins, inclined fins and V-fins are investigated at different heat flux values (175, 350, 525, 700 and 875 Watt per square meter.The effect of base to ambient temperature difference for continuous fins, 1-interrupted fins, 4-interrupted fins, inclined fins and V-fins were determined. All types of the fins are made with different geometries by using CNC machine and wire cut machine, but it have some dimensions in common such as fins thickness (5mm, fins height (18mm, space between the fins (10mm, and the volume of the base plat of heat sink (300*95*2mm. The heat sink base plate was heated by an attached maximum electric heater 2225 W/m2 with an identical size with the base plate of the heat sink, which could supply a specific heat flux. The steady-state temperature of the base plate was measured by eleven copper-constantan (K-type thermocouples inserted into different grooves in the base plate and glued with thermal tape and epoxy to ensure good thermal contact. The mathematical model of the base plate and fins are solved numerically using COMSOL (5.0 after describing the mesh model using the COMSOL (5.0 and assuming the properties of air variation with film temperature. After finding the numerical result, the validation between experimental and numerical results has been verified. Good agreement has been found between the experimental and CFD results. Empirical correlations for the overall Nusselt number versus average Rayleigh number for these configurations are obtained and compared to other correlations sited in the literature. The range of Rayleigh number, Nusselt number and base plate temperature are, (1.7e7 - 12.5e7, (37 – 83 and (25.6
Directory of Open Access Journals (Sweden)
Khairy Zaimi
2015-01-01
Full Text Available This paper concerns with the boundary layer flow and heat transfer over a permeable stretching/shrinking sheet in a viscous fluid, with the bottom surface of the plate is heated by convection from a hot fluid. The partial differential equations governing the flow and heat transfer are converted into ordinary differential equations using a similarity transformation, before being solved numerically. The effects of the suction, convection and stretching/shrinking parameters on the skin friction coefficient and the local Nusselt number are examined and graphically illustrated. Dual solutions are found to exist for a certain range of the suction and stretching/shrinking parameters. The numerical results also show that suction widens the range of the stretching/shrinking parameter for which the solution exists.
Shang, De-Yi; Zhong, Liang-Cai
2016-04-01
Our novel models for fluid's variable physical properties are improved and reported systematically in this work for enhancement of theoretical and practical value on study of convection heat and mass transfer. It consists of three models, namely (1) temperature parameter model, (2) polynomial model, and (3) weighted-sum model, respectively for treatment of temperature-dependent physical properties of gases, temperature-dependent physical properties of liquids, and concentration- and temperature-dependent physical properties of vapour-gas mixture. Two related components are proposed, and involved in each model for fluid's variable physical properties. They are basic physic property equations and theoretical similarity equations on physical property factors. The former, as the foundation of the latter, is based on the typical experimental data and physical analysis. The latter is built up by similarity analysis and mathematical derivation based on the former basic physical properties equations. These models are available for smooth simulation and treatment of fluid's variable physical properties for assurance of theoretical and practical value of study on convection of heat and mass transfer. Especially, so far, there has been lack of available study on heat and mass transfer of film condensation convection of vapour-gas mixture, and the wrong heat transfer results existed in widespread studies on the related research topics, due to ignorance of proper consideration of the concentration- and temperature-dependent physical properties of vapour-gas mixture. For resolving such difficult issues, the present novel physical property models have their special advantages.
Shang, De-Yi; Zhong, Liang-Cai
2017-01-01
Our novel models for fluid's variable physical properties are improved and reported systematically in this work for enhancement of theoretical and practical value on study of convection heat and mass transfer. It consists of three models, namely (1) temperature parameter model, (2) polynomial model, and (3) weighted-sum model, respectively for treatment of temperature-dependent physical properties of gases, temperature-dependent physical properties of liquids, and concentration- and temperature-dependent physical properties of vapour-gas mixture. Two related components are proposed, and involved in each model for fluid's variable physical properties. They are basic physic property equations and theoretical similarity equations on physical property factors. The former, as the foundation of the latter, is based on the typical experimental data and physical analysis. The latter is built up by similarity analysis and mathematical derivation based on the former basic physical properties equations. These models are available for smooth simulation and treatment of fluid's variable physical properties for assurance of theoretical and practical value of study on convection of heat and mass transfer. Especially, so far, there has been lack of available study on heat and mass transfer of film condensation convection of vapour-gas mixture, and the wrong heat transfer results existed in widespread studies on the related research topics, due to ignorance of proper consideration of the concentration- and temperature-dependent physical properties of vapour-gas mixture. For resolving such difficult issues, the present novel physical property models have their special advantages.
Convective Heat Transfer Characteristics of the Elliptic Cylinder with Axis Ratio 4 : 1 in Crossflow
Institute of Scientific and Technical Information of China (English)
QI Shou-liang; LI Qing-ling; WANG Ru-zhu
2005-01-01
The heat transfer features around the elliptic cylinder of axis ratio 4: 1 in crossflow were investigated experimentally within a wide range of Reynolds number. By means of heat-mass transfer analogy and the naphthalene sublimation technique, the local heat transfer distribution and the mean heat transfer coefficient are clarified.The result shows that the mean heat transfer coefficient is higher than that of a circular cylinder in most Reynolds number range regarded, and this superiority turns to be more significant with the increase of flow speed. Moreover, the effect of axis ratio on mean heat transfer coefficient was investigated tentatively. The oil-lampblack technique was employed to enable visualization of the flow pattern around the cylinder and on the cylinder wall.
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.
Unsteady convection flow and heat transfer over a vertical stretching surface.
Cai, Wenli; Su, Ning; Liu, Xiangdong
2014-01-01
This paper investigates the effect of thermal radiation on unsteady convection flow and heat transfer over a vertical permeable stretching surface in porous medium, where the effects of temperature dependent viscosity and thermal conductivity are also considered. By using a similarity transformation, the governing time-dependent boundary layer equations for momentum and thermal energy are first transformed into coupled, non-linear ordinary differential equations with variable coefficients. Numerical solutions to these equations subject to appropriate boundary conditions are obtained by the numerical shooting technique with fourth-fifth order Runge-Kutta scheme. Numerical results show that as viscosity variation parameter increases both the absolute value of the surface friction coefficient and the absolute value of the surface temperature gradient increase whereas the temperature decreases slightly. With the increase of viscosity variation parameter, the velocity decreases near the sheet surface but increases far away from the surface of the sheet in the boundary layer. The increase in permeability parameter leads to the decrease in both the temperature and the absolute value of the surface friction coefficient, and the increase in both the velocity and the absolute value of the surface temperature gradient.
Unsteady convection flow and heat transfer over a vertical stretching surface.
Directory of Open Access Journals (Sweden)
Wenli Cai
Full Text Available This paper investigates the effect of thermal radiation on unsteady convection flow and heat transfer over a vertical permeable stretching surface in porous medium, where the effects of temperature dependent viscosity and thermal conductivity are also considered. By using a similarity transformation, the governing time-dependent boundary layer equations for momentum and thermal energy are first transformed into coupled, non-linear ordinary differential equations with variable coefficients. Numerical solutions to these equations subject to appropriate boundary conditions are obtained by the numerical shooting technique with fourth-fifth order Runge-Kutta scheme. Numerical results show that as viscosity variation parameter increases both the absolute value of the surface friction coefficient and the absolute value of the surface temperature gradient increase whereas the temperature decreases slightly. With the increase of viscosity variation parameter, the velocity decreases near the sheet surface but increases far away from the surface of the sheet in the boundary layer. The increase in permeability parameter leads to the decrease in both the temperature and the absolute value of the surface friction coefficient, and the increase in both the velocity and the absolute value of the surface temperature gradient.
Flow and heat transfer in Sisko fluid with convective boundary condition.
Malik, Rabia; Khan, Masood; Munir, Asif; Khan, Waqar Azeem
2014-01-01
In this article, we have studied the flow and heat transfer in Sisko fluid with convective boundary condition over a nonisothermal stretching sheet. The flow is influenced by non-linearly stretching sheet in the presence of a uniform transverse magnetic field. The partial differential equations governing the problem have been reduced by similarity transformations into the ordinary differential equations. The transformed coupled ordinary differential equations are then solved analytically by using the homotopy analysis method (HAM) and numerically by the shooting method. Effects of different parameters like power-law index n, magnetic parameter M, stretching parameter s, generalized Prandtl number Pr and generalized Biot number γ are presented graphically. It is found that temperature profile increases with the increasing value of M and γ whereas it decreases for Pr. Numerical values of the skin-friction coefficient and local Nusselt number are tabulated at various physical situations. In addition, a comparison between the HAM and exact solutions is also made as a special case and excellent agreement between results enhance a confidence in the HAM results.
Loh, Byoung-Gook; Hyun, Sinjae; Ro, Paul I; Kleinstreuer, Clement
2002-02-01
Acoustic streaming induced by ultrasonic flexural vibrations and the associated convection enhancement are investigated. Acoustic streaming pattern, streaming velocity, and associated heat transfer characteristics are experimentally observed. Moreover, analytical analysis based on Nyborg's formulation is performed along with computational fluid dynamics (CFD) simulation using a numerical solver CFX 4.3. Two distinctive acoustic streaming patterns in half-wavelength of the flexural vibrations are observed, which agree well with the theory. However, acoustic streaming velocities obtained from CFD simulation, based on the incompressible flow assumption, exceed the theoretically estimated velocity by a factor ranging from 10 to 100, depending upon the location along the beam. Both CFD simulation and analytical analysis reveal that the acoustic streaming velocity is proportional to the square of the vibration amplitude and the wavelength of the vibrating beam that decreases with the excitation frequency. It is observed that the streaming velocity decreases with the excitation frequency. Also, with an open-ended channel, a substantial increase in streaming velocity is observed from CFD simulations. Using acoustic streaming, a temperature drop of 40 degrees C with a vibration amplitude of 25 microm at 28.4 kHz is experimentally achieved.
Directory of Open Access Journals (Sweden)
M. Dieng
2013-02-01
Full Text Available The aim of this study is to characterize thermal insulating local material, kapok, from a study in 3 dimensions in Cartesian coordinate and in dynamic frequency regime. From a study a 3 dimensional the heat transfer through a material made of wool kapok (thermal conductivity: &lambda = 0,035 W/m/K; density: &rho = 12, 35 kg/m3; thermal diffusivity: &alpha = 17, 1.10-7 m2 /s is presented. The evolution curves of temperature versus convective heat transfer coefficient have helped highlight the importance of pulse excitation and the depth in the material. The thermal impedance is studied from representations of Nyquist and Bode diagrams allowing characterizing the thermal behavior from thermistors. The evolution of the thermal impedance with the thermal capacity of the material is presented.
Zaib, A.; Bhattacharyya, K.; Khalid, M.; Shafie, S.
2017-05-01
The thermal radiation effect on a steady mixed convective flow with heat transfer of a nonlinear (non-Newtonian) Williamson fluid past an exponentially shrinking porous sheet with a convective boundary condition is investigated numerically. In this study, both an assisting flow and an opposing flow are considered. The governing equations are converted into nonlinear ordinary differential equations by using a suitable transformation. A numerical solution of the problem is obtained by using the Matlab software package for different values of the governing parameters. The results show that dual nonsimilar solutions exist for the opposing flow, whereas the solution for the assisting flow is unique. It is also observed that the dual nonsimilar solutions exist only if a certain amount of mass suction is applied through the porous sheet, which depends on the Williamson parameter, convective parameter, and radiation parameter.
Kandasamy, R.; Jeyabalan, C.; Sivagnana Prabhu, K. K.
2016-02-01
This article examines the influence of thermophoresis, Brownian motion of the nanoparticles with variable stream conditions in the presence of magnetic field on mixed convection heat and mass transfer in the boundary layer region of a semi-infinite porous vertical plate in a nanofluid under the convective boundary conditions. The transformed boundary layer ordinary differential equations are solved numerically using Maple 18 software with fourth-fifth order Runge-Kutta-Fehlberg method. Numerical results are presented both in tabular and graphical forms illustrating the effects of these parameters with magnetic field on momentum, thermal, nanoparticle volume fraction and solutal concentration boundary layers. The numerical results obtained for the velocity, temperature, volume fraction, and concentration profiles reveal interesting phenomenon, some of these qualitative results are presented through plots. It is interesting to note that the magnetic field plays a dominant role on nanofluid flow under the convective boundary conditions.
SUNDÉN, B
2012-01-01
Presenting the basic mechanisms for transfer of heat, Introduction to Heat Transfer gives a deeper and more comprehensive view than existing titles on the subject. Derivation and presentation of analytical and empirical methods are provided for calculation of heat transfer rates and temperature fields as well as pressure drop. The book covers thermal conduction, forced and natural laminar and turbulent convective heat transfer, thermal radiation including participating media, condensation, evaporation and heat exchangers.
Directory of Open Access Journals (Sweden)
Webster John G
2006-10-01
Full Text Available Abstract Background We need a sensor to measure the convective heat transfer coefficient during ablation of the heart or liver. Methods We built a minimally invasive instrument to measure the in vivo convective heat transfer coefficient, h in animals, using a Wheatstone-bridge circuit, similar to a hot-wire anemometer circuit. One arm is connected to a steerable catheter sensor whose tip is a 1.9 mm × 3.2 mm thin film resistive temperature detector (RTD sensor. We used a circulation system to simulate different flow rates at 39°C for in vitro experiments using distilled water, tap water and saline. We heated the sensor approximately 5°C above the fluid temperature. We measured the power consumed by the sensor and the resistance of the sensor during the experiments and analyzed these data to determine the value of the convective heat transfer coefficient at various flow rates. Results From 0 to 5 L/min, experimental values of h in W/(m2·K were for distilled water 5100 to 13000, for tap water 5500 to 12300, and for saline 5400 to 13600. Theoretical values were 1900 to 10700. Conclusion We believe this system is the smallest, most accurate method of minimally invasive measurement of in vivo h in animals and provides the least disturbance of flow.
Whitesides, R. Harold; Majumdar, Alok K.; Jenkins, Susan L.; Bacchus, David L.
1990-01-01
A series of cold flow heat transfer tests was conducted with a 7.5-percent scale model of the Space Shuttle Rocket Motor (SRM) to measure the heat transfer coefficients in the separated flow region around the nose of the submerged nozzle. Modifications were made to an existing 7.5 percent scale model of the internal geometry of the aft end of the SRM, including the gimballed nozzle in order to accomplish the measurements. The model nozzle nose was fitted with a stainless steel shell with numerous thermocouples welded to the backside of the thin wall. A transient 'thin skin' experimental technique was used to measure the local heat transfer coefficients. The effects of Reynolds number, nozzle gimbal angle, and model location were correlated with a Stanton number versus Reynolds number correlation which may be used to determine the convective heating rates for the full scale Space Shuttle Solid Rocket Motor nozzle.
Natural convective heat transfer and nanofluid flow in a cavity with top wavy wall and corner heater
Institute of Scientific and Technical Information of China (English)
Mikhail A SHEREMET; Ioan POP; Hakan F ZTOP; Nidal ABU-HAMDEH
2016-01-01
A numerical analysis of natural convection of nanofluid in a wavy-walled enclosure with an isothermal corner heater has been carried out. The cavity is heated from the left bottom corner and cooled from the top wavy wall while the rest walls are adiaba- tic. Mathematical model has been formulated using the single-phase nanofluid approach. Main efforts have been focused on the effects of the dimensionless time, Rayleigh number, undulation number, nanoparticle volume fraction and length of corner heaters on the fluid flow and heat transfer inside the cavity. Numerical results have been presented in the form of streamlines, isotherms, velocity and temperature profiles, local and average Nusselt numbers. It has been found that nanoparticle volume fraction essentially affects both fluid flow and heat transfer while undulation number changes significantly only the heat transfer rate.
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.
Park, Hae-Kyun; Chung, Bum-Jin
2016-12-01
The turbulent forced convection heat transfer of rectangular fins in a duct was investigated by varying the tip clearance and Pr. Mass transfer experiments using a H2SO4-CuSO4 electroplating system were performed based on the analogy between heat and mass transfers. FLUENT 6.3 was used for calculations. Turbulent models were tested and the Reynolds Stress Model was chosen, which showed a 1.15 % discrepancy with the existing correlation for a simple tube flow when Pr = 2, but 13 % when Pr = 2014. For a more complex fin channel, the discrepancy increased up to 30 %. The optimal tip clearances, corresponding to maximum heat transfer rates, did not vary with Pr, which is explained using the temperature contours. The results were also compared with the laminar case where Pr influenced the optimal tip clearance.
Directory of Open Access Journals (Sweden)
Liping Wei
2013-01-01
Full Text Available Mixed convection heat transfer between supercritical water and particles is a major basic problem in supercritical water fluidized bed reactor, but little work focused on this new area in the past. In this paper, a numerical model fully accounting for thermophysical property variation has been established to investigate heat transfer between supercritical water and a single spherical particle under gravity. Flow field, temperature field and Nusselt number are analyzed based on the simulation results. Results show that buoyancy force has a remarkable effect on flow and heat transfer process. When the direction of gravity and flow are opposite, the gravity enhances the heat transfer before the separation point and inhibits the heat transfer after the separation point. When gravity is incorporated in calculation, a higher temperature gradient and a thinner boundary layer in the vicinity of the particle surface are observed before separation point, and the situations are just the reverse after separation point. Variation of specific heat and conductivity plays a main role in determination of heat transfer coefficient.
Directory of Open Access Journals (Sweden)
A. R. Rahmati
2017-02-01
0.02 and 0.03. In order to consider the effect of porous media, Darcy-Forchheimer model is used. The results show that the presence of the porous media decreases the velocity of nanofluid and consequently decreases the strength of the flow. With decreasing Darcy number and porosity coefficient, natural convection heat transfer weakens and the mechanism of natural convection of nano-fluids tends to that of thermal conduction. With increasing Rayleigh number, the strength of flow in cavity and average Nusselt number increases. In all cases studied, increase in volume fraction improves heat transfer. In constant properties model, by increasing solid volume fraction, average Nusselt number increases more than that of variable properties model. The results show that Lattice Boltzmann method has the ability to simulate flow in porous media.
Kumar, Rakesh
2015-01-01
This investigation deals with the analysis of stagnation point heat transfer and corresponding flow features of hydromagnetic viscous incompressible fluid over a vertical shrinking sheet. The considered sheet is assumed to be permeable and subject to addition of stagnation point to control the generated vorticity in the boundary layer. The sheet is placed on the right side of the fluid saturated porous medium which is having permeability of specified form. Nonlinear convection waves in the flow field are realized due to the envisaged nonlinear relation between density and temperature. The equations governing the nonlinear convection boundary layer flow are modeled and simplified using similarity transformations. The economized equations are solved for numerical solutions by employing the implicit finite difference scheme also known as Keller-box method. The influence of the associated parameters of the problem on velocity and temperature distributions, skin friction and rate of heat transfer are presented thr...
Bibliography of US patents on augmentation of convective heat and mass transfer
Energy Technology Data Exchange (ETDEWEB)
Webb, R.L.; Junkhan, G.H.; Bergles, A.E.
1980-09-01
Granted patents are an important source of information on the potential commercialization of augmented heat transfer technology. This report presents a bibliography of US patents pertinent to that technology. The total number of patents cited is 321. They are presented in three separate lists: by patent number, alphabetically by first inventor, and by augmentation techniques (with secondary arrangement according to mode of heat transfer).
Bibliography of US patents on augmentation of convective heat and mass transfer-II
Energy Technology Data Exchange (ETDEWEB)
Webb, R.L.; Bergles, A.E.; Junkhan, G.H.
1983-12-01
Patents are an important source of information on the potential commercialization of augmented heat transfer technology. This report presents a bibliography of US patents pertinent to that technology. The total number of patents cited is 454. They are presented in three separate lists: by patent number, alphabetically by first inventor, and by augmentation technique (with secondary arrangement according to mode of heat transfer).
3D modelling of coupled mass and heat transfer of a convection-oven roasting process
DEFF Research Database (Denmark)
Feyissa, Aberham Hailu; Adler-Nissen, Jens; Gernaey, Krist
2013-01-01
A 3D mathematical model of coupled heat and mass transfer describing oven roasting of meat has been developed from first principles. The proposed mechanism for the mass transfer of water is modified and based on a critical literature review of the effect of heat on meat. The model equations are b...
Convective Heat Transfer in Internal Gas Flows with Temperature-Dependent Properties.
1982-06-30
effects of variable properties have been provided by Petukhov [1970],specifically for turbulent flow in circular tubes.and by Leontiev o for the...243-249. Leontiev , A. I., 1966. Heat and mass transfer in turbulent boundary layers, Adv. Heat Transfer, 3, pp. 33-100. Leung, E. Y., V. M. Kays and W
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.
Convection heat transfer and pressure drop in cross flow over finned tubes
Energy Technology Data Exchange (ETDEWEB)
Baran, M.; Pronobis, M.
1984-05-15
This paper reports the results of an experimental study on the heat transfer and pressure drop in finned tube banks. The measurements were carried out for the tubes with fins arranged parallel and a certain angle to the flow direction. The performance of such a heat exchanger with that of the conventional one i.e. plain tube heat exchanger, is compared.
Design of Test Loops for Forced Convection Heat Transfer Studies at Supercritical State
Balouch, Masih N.
Worldwide research is being conducted to improve the efficiency of nuclear power plants by using supercritical water (SCW) as the working fluid. One such SCW reactor considered for future development is the CANDU-Supercritical Water Reactor (CANDU-SCWR). For safe and accurate design of the CANDU-SCWR, a detailed knowledge of forced-convection heat transfer in SCW is required. For this purpose, two supercritical fluid loops, i.e. a SCW loop and an R-134a loop are developed at Carleton University. The SCW loop is designed to operate at pressures as high as 28 MPa, temperatures up to 600 °C and mass fluxes of up to 3000 kg/m2s. The R-134a loop is designed to operate at pressures as high as 6 MPa, temperatures up to 140 °C and mass fluxes in the range of 500-6000 kg/m2s. The test loops designs allow for up to 300 kW of heating power to be imparted to the fluid. Both test loops are of the closed-loop design, where flow circulation is achieved by a centrifugal pump in the SCW loop and three parallel-connected gear pumps in the R-134a loop, respectively. The test loops are pressurized using a high-pressure nitrogen cylinder and accumulator assembly, which allows independent control of the pressure, while simultaneously dampening pump induced pressure fluctuations. Heat exchangers located upstream of the pumps control the fluid temperature in the test loops. Strategically located measuring instrumentation provides information on the flow rate, pressure and temperature in the test loops. The test loops have been designed to accommodate a variety of test-section geometries, ranging from a straight circular tube to a seven-rod bundle, achieving heat fluxes up to 2.5 MW/m2 depending on the test-section geometry. The design of both test loops allows for easy reconfiguration of the test-section orientation relative to the gravitational direction. All the test sections are of the directly-heated design, where electric current passing through the pressure retaining walls of the
Heat and mass transfer in a vertical channel under heat-gravitational convection conditions
Directory of Open Access Journals (Sweden)
Petrichenko Michail
2016-01-01
Full Text Available Heat-gravitational motion of an air flow in a vertical channel with one-sided heating in an area with low Reynolds number is stated in Boussinesq approximation. Hydraulic variables field in a heat-gravitational motion is modeled with the application of ANSYS-FLUENT. It is converted to average velocity and temperature values in a cross section of the channel. The value of an average velocity is determined by rate of heat supply in a barotropic flow with a polytropic coefficient n
Jiang, Shaohui; Liu, Changhong; Fan, Shoushan
2014-03-12
In this work, we report our studies related to the natural-convective heat transfer properties of carbon nanotube (CNT) sheets. We theoretically derived the formulas and experimentally measured the natural-convective heat transfer coefficients (H) via electrical heating method. The H values of the CNT sheets containing different layers (1, 2, 3, and 1000) were measured. We found that the single-layer CNT sheet had a unique ability on heat dissipation because of its great H. The H value of the single-layer CNT sheet was 69 W/(m(2) K) which was about twice of aluminum foil in the same environment. As the layers increased, the H values dropped quickly to the same with that of aluminum foil. We also discussed its roles on thermal dissipation, and the results indicated that the convection was a significant way of dissipation when the CNT sheets were applied on macroscales. These results may give us a new guideline to design devices based on the CNT sheets.
Henselowsky, C.; Kuhlmann, H. C.; Rath, H. J.
2002-09-01
Electrically heated cylindrical wires are used in research and industry for fluid velocity and turbulence measurements. At very low free-stream velocities (u≤0.1 m/s), hot-wire measurements are significantly influenced by buoyant convection. Below a certain Reynolds number Re* this effect degrades the accuracy of the measurements. To assess the contribution of free-convection heat transfer to the heat balance of hot-wires in cross flow, measurements under normal gravity and microgravity (µg) conditions are compared keeping all other parameters constant. Under gravity conditions, the acceleration of gravity, the hot-wire axis and the direction of the free stream are all perpendicular to each other. The microgravity experiments were carried out in the Drop-Tower Bremen in which the residual acceleration is less than 10-5 g during a period of 4.7 s. The present investigation is concerned with a velocity range of 0≤u≤0.35 m/s corresponding to a Reynolds number range Reconvection for Re→0 and forced-convection-dominated heat transfer for Re=0.1. At intermediate Reynolds numbers both transport mechanisms must be considered.
Directory of Open Access Journals (Sweden)
P H Veena
2017-04-01
Full Text Available In this paper two dimensional flow of a viscoelastic fluid due to stretching surface is considered. Flow analysis is carried out by using closed form solution of fourth order differential equation of motion of viscoelastic fluid. Further (Walters’ liquid B’ model heat transfer analysis is carried out using convective surface condition. The governing equations of flow and heat transfer are non-linear partial differential equations which are unable to solve analytically hence are solved using Runge-Kutta Numerical Method with efficient shooting technique. The flow and heat transfer characteristics are studied through plots drawn. Numerical values of Wall temperature are calculated and presented in the table and compared with earlier published results which are in good agreement
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.
Directory of Open Access Journals (Sweden)
Ding Liu
2017-07-01
Full Text Available 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.
Radiative and free-convective heat transfer from a finite horizontal plate inside an enclosure
Hrycak, Peter; Sandman, D. J.
1986-01-01
An experimental and analytical investigation of heat transfer from a horizontal, thin, square plate inside of an enclosure was carried out. Experimental results were obtained from both the upward-facing and the downward-facing sides of the heated plate. Starting with the integrated momentum and energy equations, approximate solutions were obtained for heat transfer in the laminar and the turbulent regime that correlate well with experimental data. Radiative heat transfer correction was given special attention. Effects of the enclosure-related recirculation of the test fluid, as well as effects of simultaneous heat transfer on both sides of the plate, caused an early transition, and indicated a high level of internal turbulence.
Throckmorton, D. A.
1982-01-01
Temperatures measured at the aerodynamic surface of the Orbiter's thermal protection system (TPS), and calorimeter measurements, are used to determine heating rates to the TPS surface during atmospheric entry. On the Orbiter leeside, where convective heating rates are low, it is possible that a significant portion of the total energy input may result from solar radiation, and for the wing, cross radiation from the hot (relatively) Orbiter fuselage. In order to account for the potential impact of these sources, values of solar- and cross-radiation heat transfer are computed, based upon vehicle trajectory and attitude information and measured surface temperatures. Leeside heat-transfer data from the STS-2 mission are presented, and the significance of solar radiation and fuselage-to-wing cross-radiation contributions to total energy input to Orbiter leeside surfaces is assessed.
Tatsumoto, H.; Shirai, Y.; Shiotsu, M.; Naruo, Y.; Kobayashi, H.; Inatani, Y.
2014-12-01
Forced convection heat transfer from a PtCo wire with a length of 120 mm and a diameter of 1.2 mm that was inserted into a vertically-mounted pipe with a diameter of 8.0 mm to liquid hydrogen flowing upward was measured with a quasi-steady increase of a heat generation rate for wide ranges of flow rate under saturated conditions. The pressures were varied from 0.4 MPa to 1.1 MPa. The non-boiling heat transfer characteristic agrees with that predicted by Dittus-Boelter correlation. The critical heat fluxes are higher for higher flow rates and lower pressures. Effect of Weber number on the CHF was clarified and a CHF correlation that can describe the experimental data is derived based on our correlation for a pipe.
Directory of Open Access Journals (Sweden)
Yacine Khelili
2017-03-01
Full Text Available Numerical investigation of heat transfer phenomena of low Reynolds number nano-fluid flow over an isothermal cylinder is presented in this paper. Steady state governing equations (continuity, N–S and energy equations have been solved using finite volume method. Stationary heat transfer, and flow characteristics over the cylinder have been studied for water based copper nanofluid with different solid fraction values. The effect of volume fraction of nano- particles on the fluid flow and heat transfer were investigated numerically. It was found that at a given Nusselt number, drag coefficient, re-circulation length, and pressure coefficient increase by increasing the volume fraction of nano-particles.
Convective heat transfer under unsteady impinging jets: the effect of the shape of the unsteadiness
Middelberg, G.; Herwig, H.
2009-10-01
Unsteady impinging jets are systematically controlled with respect to their time dependence in order to investigate the influence of unsteadiness on the heat transfer performance. This is achieved by a special mass flow control device, which allows almost arbitrary shapes of unsteadiness to be imposed onto the impinging jet. Three different standard signals (sinusoidal, triangular, rectangular) and two specially designed signals are applied and their influence on heat transfer is determined in terms of an enhancement factor. Heat transfer augmentation up to 30% was found and could be physically explained with the help of PIV and hot-wire measurements of the flow field.
REA, The Editors of
1988-01-01
REA's Essentials provide quick and easy access to critical information in a variety of different fields, ranging from the most basic to the most advanced. As its name implies, these concise, comprehensive study guides summarize the essentials of the field covered. Essentials are helpful when preparing for exams, doing homework and will remain a lasting reference source for students, teachers, and professionals. Heat Transfer II reviews correlations for forced convection, free convection, heat exchangers, radiation heat transfer, and boiling and condensation.
Directory of Open Access Journals (Sweden)
S. S. Das, S. Parija, R. K. Padhy, M. Sahu
2012-01-01
Full Text Available This paper investigates the natural convection unsteady magnetohydrodynamic mass transfer flow of a viscous incompressible electrically conducting fluid past an infinite vertical porous flat plate in presence of constant suction and heat sink. Using multi parameter perturbation technique, the governing equations of the flow field are solved and approximate solutions are obtained. The effects of the flow parameters on the velocity, temperature, concentration distribution and also on the skin friction and rate of heat transfer are discussed with the help of figures and table. It is observed that a growing magnetic parameter or Schmidt number or heat sink parameter leads to retard the transient velocity of the flow field at all points, while the Grashof numbers for heat and mass transfer show the reverse effect. It is further found that a growing Prandtl number or heat sink parameter decreases the transient temperature of the flow field at all points while the heat source parameter reverses the effect. The concentration distribution of the flow field suffers a decrease in boundary layer thickness in presence of heavier diffusive species (growing Sc at all points of the flow field. The effect of increasing Prandtl number Pr is to decrease the magnitude of skin-friction and to increase the rate of heat transfer at the wall for MHD flow, while the effect of increasing magnetic parameter M is to decrease their values at all points.
Directory of Open Access Journals (Sweden)
Marijn Billiet
2015-10-01
Full Text Available Two differently-produced open-cell aluminum foams were compared to a commercially available finned heat sink. Further, an aluminum plate and block were tested as a reference. All heat sinks have the same base plate dimensions of four by six inches. The first foam was made by investment casting of a polyurethane preform and has a porosity of 0.946 and a pore density of 10 pores per linear inch. The second foam is manufactured by casting over a solvable core and has a porosity of 0.85 and a pore density of 2.5 pores per linear inch. The effects of orientation and radiative heat transfer are experimentally investigated. The heat sinks are tested in a vertical and horizontal orientation. The effect of radiative heat transfer is investigated by comparing a painted/anodized heat sink with an untreated one. The heat flux through the heat sink for a certain temperature difference between the environment and the heat sink’s base plate is used as the performance indicator. For temperature differences larger than 30 °C, the finned heat sink outperforms the in-house-made aluminum foam heat sink on average by 17%. Furthermore, the in-house-made aluminum foam dissipates on average 12% less heat than the other aluminum foam for a temperature difference larger than 40 °C. By painting/anodizing the heat sinks, the heat transfer rate increased on average by 10% to 50%. Finally, the thermal performance of the horizontal in-house-made aluminum foam heat sink is up to 18% larger than the one of the vertical aluminum foam heat sink.
Directory of Open Access Journals (Sweden)
Hussein Ahmed Mohammed
2005-01-01
Full Text Available Natural convection heat transfer is experimentally investigated for laminar air flow in a vertical circular tube by using the boundary condition of constant wall heat flux in the ranges of (RaL from (1.1*109 to (4.7*109. The experimental set-up was designed for determining the effect of different types of restrictions placed at entry of heated tube in bottom position, on the surface temperature distribution and on the local and average heat transfer coefficients. The apparatus was made with an electrically heated cylinder of a length (900mm and diameter (30mm. The entry restrictions were included a circular tube of same diameter as the heated cylinder but with lengths of (60cm, 120cm, sharp-edge and bell-mouth. The surface temperature along the cylinder surface for same heat flux would be higher values for circular restriction with length of (120cm and would be smaller values for bell-mouth restriction. The results show that the local Nusselt number (Nux and average Nusselt number are higher for bell-mouth restriction and smaller values for (120cm restriction. For all entry shape restrictions, the results show that the Nusselt number values increases as the heat flux increases. From the present work an empirical correlations were obtained in a form of (Log versus (Log for each case investigated and obtained a general correlation for all cases which reveals the effect of restriction existence on the natural convection heat transfer process in a vertical circular tube.
Convective Heat Transfer Enhancement of a Rectangular Flat Plate by an Impinging Jet in Cross Flow
Institute of Scientific and Technical Information of China (English)
李国能; 郑友取; 胡桂林; 张治国
2014-01-01
Experiments were carried out to study the heat transfer performance of an impinging jet in a cross flow. Several parameters including the jet-to-cross-flow mass ratio (X=2%-8%), the Reynolds number (Red=1434-5735) and the jet diameter (d=2-4 mm) were explored. The heat transfer enhancement factor was found to increase with the jet-to-cross-flow mass ratio and the Reynolds number, but decrease with the jet diameter when other parameters maintain fixed. The presence of a cross flow was observed to degrade the heat transfer performance in respect to the effect of impinging jet to the target surface only. In addition, an impinging jet was confirmed to be capable of en-hancing the heat transfer process in considerable amplitude even though the jet was not designed to impinge on the target surface.
Electroless-plating technique for fabricating thin-wall convective heat-transfer models
Avery, D. E.; Ballard, G. K.; Wilson, M. L.
1984-01-01
A technique for fabricating uniform thin-wall metallic heat-transfer models and which simulates a Shuttle thermal protection system tile is described. Two 6- by 6- by 2.5-in. tiles were fabricated to obtain local heat transfer rates. The fabrication process is not limited to any particular geometry and results in a seamless thin-wall heat-transfer model which uses a one-wire thermocouple to obtain local cold-wall heat-transfer rates. The tile is relatively fragile because of the brittle nature of the material and the structural weakness of the flat-sided configuration; however, a method was developed and used for repairing a cracked tile.
Measurements of mixed convective heat transfer to low temperature helium in a horizontal channel
Yeroshenko, V. M.; Kuznetsov, Y. V.; Shevchenko, O. A.; Hendricks, R. C.; Daney, D. E.
1979-01-01
A horizontal 2.85 m long, 19 mm i.d. stainless steel heated circular channel was employed to measure coefficients of heat transfer to low temperature helium flow. Experimental parameters range from 6.5 to 15 K, from 0.12 to 0.3 MPa at heat fluxes up to 1000 W/m square and Reynolds numbers from 9,000 to 20,000. A significantly nonuniform distribution of heat transfer coefficients over the tube periphery is observed. Difference between temperatures on the upper and lower surfaces of the stainless steel channel wall was found to reach 9 K. It was noted that the highest temperature on the wall outer surface is displaced from its uppermost point. Measurements of local flow temperatures revealed vortical structure of the flow. The displacement of the point with the highest temperature is attributable to the effect of vortices. The relationships for calculating local and averaged coefficients of heat transfer are proposed.
Energy analysis of the engineering-economic optimization of convective heat-transfer surfaces
Stoyanov, N. M.
1991-07-01
The influence of the specific costs of the heat transfer surface, 1 kW of installed power of the blower and motor, 1 kW·h of electrical energy consumption by it, operating time of the surface, and other factors on the optimum specific power expenditure to force heat-transfer fluids through the ducts of heattransfer surfaces is investigated. The minimum engineering-economically justified operating time of the surface is determined.
2010-05-11
oil based suspension in the miniaturized tests. 45 5. Endnotes 1 Incropera ...Microchannels,” Proceedings of ASME Thermal Engineering Summer Heat Transfer Conference. 10 Incropera , F.P., DeWitt, D.P., Bergman, T.L., and Lavine, A.S...Pogrebnyak,, 2002, “Effect of coarse particles on the heat transfer in a particle-laden turbulent boundary layer,” Int. J. Multiph. Flow, 28,12. Incropera
Camci, C.; Kim, K.; Hippensteele, S. A.
1992-01-01
A new image processing based color capturing technique for the quantitative interpretation of liquid crystal images used in convective heat transfer studies is presented. This method is highly applicable to the surfaces exposed to convective heating in gas turbine engines. It is shown that, in the single-crystal mode, many of the colors appearing on the heat transfer surface correlate strongly with the local temperature. A very accurate quantitative approach using an experimentally determined linear hue vs temperature relation is found to be possible. The new hue-capturing process is discussed in terms of the strength of the light source illuminating the heat transfer surface, the effect of the orientation of the illuminating source with respect to the surface, crystal layer uniformity, and the repeatability of the process. The present method is more advantageous than the multiple filter method because of its ability to generate many isotherms simultaneously from a single-crystal image at a high resolution in a very time-efficient manner.
DEFF Research Database (Denmark)
Sigurdsson, Eythor; Ingvorsen, Kristian Mark; Jensen, Michael Vincent
2014-01-01
A novel computational fluid dynamics (CFD) model is presented for the study of the scavenging processand convective heat transfer in a large two-stroke low-speed uniflow-scavenged marine diesel engine.The engine is modeled using a fully resolved 12 sector, corresponding to one scavenge port...... an effective scavenging and a low convective heat loss in agreement with experimental data forlarge marine diesel engines.© 2014 Elsevier Ltd. All rights reserved......., with cyclicboundaries in the tangential direction. The CFD model is strongly coupled to experiments and effectivelyprovides a high order ‘‘interpolation’’ of the engine processes through the solution of the Reynolds-AveragedNavier–Stokes (RANS) equations subject to boundary conditions obtained through experiments...
Natural Convection Heat and Mass Transfer from Falling Films in Vertical Channels
Buck, Gregory Allen
1990-01-01
In the design of solar collector/regenerators for use in open cycle absorption refrigeration (OCAR) units, the problem of predicting evaporation rates and solution temperatures is of paramount importance in determining overall cycle performance. This transport of heat and mass is dominated by natural convection with buoyant forces primarily generated as a result of film heating by the solar flux, but aided by the evaporation of water (the lighter species) into the rising moist air stream. In order to better understand the mechanism of these combined buoyant interactions, the governing equations for natural convection flow in a vertical channel bounded by a heated falling film (simulating a glazed collector/regenerator) were solved using several different finite difference techniques. The numerical results were validated against existing experimental and numerical results for simplified boundary conditions. The appropriate nondimensionalization for the falling film boundary condition was established, ostensibly for the first time, and a parametric study for an air-water vapor mixture has been presented. Curve fits to the numerical results were determined for engineering design applications. To further confirm the validity of the numerical solutions, an experimental apparatus was constructed using electric resistance heat to simulate the constant heat flux of the solar source. Water was introduced at the top of this heated vertical surface at various flow rates and under various supplied heat fluxes, and a natural convection channel flow generated between the heated falling film and a parallel, plexiglass surface. Film temperatures and moist air velocity profiles were measured at various streamwise (vertical) locations for comparison with the numerical results. In general, measured film temperatures were 15 to 20 percent lower than the predicted values, but came to within 3 percent of the predictions when experimental uncertainty was incorporated into the numerical
Directory of Open Access Journals (Sweden)
V. Ramachandra Prasad
2016-01-01
Full Text Available This article presents the nonlinear free convection boundary layer flow and heat transfer of an incompressible Tangent Hyperbolic non-Newtonian fluid from a vertical porous plate with velocity slip and thermal jump effects. The transformed conservation equations are solved numerically subject to physically appropriate boundary conditions using a second-order accurate implicit finite-difference Keller Box technique. The numerical code is validated with previous studies. The influence of a number of emerging non-dimensional parameters, namely the Weissenberg number (We, the power law index (n, Velocity slip (Sf, Thermal jump (ST, Prandtl number (Pr and dimensionless tangential coordinate ( on velocity and temperature evolution in the boundary layer regime are examined in detail. Furthermore, the effects of these parameters on surface heat transfer rate and local skin friction are also investigated. Validation with earlier Newtonian studies is presented and excellent correlation achieved. It is found that velocity, skin friction and heat transfer rate (Nusselt number is increased with increasing Weissenberg number (We, whereas the temperature is decreased. Increasing power law index (n enhances velocity and heat transfer rate but decreases temperature and skin friction. An increase in Thermal jump (ST is observed to decrease velocity, temperature, local skin friction and Nusselt number. Increasing Velocity slip (Sf is observed to increase velocity and heat transfer rate but decreases temperature and local skin friction. An increasing Prandtl number, (Pr, is found to decrease both velocity and temperature. The study is relevant to chemical materials processing applications.
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.
Directory of Open Access Journals (Sweden)
R. M. Kasmani
2016-01-01
Full Text Available The aim of the present study is to examine the convective heat transfer of nanofluid past a wedge subject to first-order chemical reaction, heat generation/absorption and suction effects. The influence of wedge angle parameter, thermophoresis, Dufour and Soret type diffusivity are included. The local similarity transformation is applied to convert the governing nonlinear partial differential equations into ordinary differential equations. Shooting method integrated with fourth-order Runge-Kutta method is used to solve the ordinary differential equations. The skin friction, heat and mass transfer rates as well as the effects of various parameters on velocity, temperature and solutal concentration profiles are analyzed. The results indicate that when the chemical reaction parameter increases, the heat transfer coefficient increases while the mass transfer coefficient decreases. The effect of chemical reaction parameter is very important in solutal concentration field compared to velocity and temperature profiles since it decreases the solutal concentration of the nanoparticle.
Directory of Open Access Journals (Sweden)
M.M. Rahman
2012-12-01
Full Text Available This paper presents the numerical study on two-dimensional forced convection heat transfer across three in-line flat tubes confined in a channel under incompressible, steady-state conditions. This system is solved in body-fitted coordinates (BFC using the finite volume method (FVM. The constant heat flux is imposed on the surface of the tubes as the thermal boundary conditions. The range of the longitudinal pitch-to-diameter ratio (SL/Ds of 2.0–4.0 is considered, the Reynolds number varies within the range 25–300, and the Prandtl number is taken as 0.7. The temperature contours, local Nusselt number distributions at the tube surface and mean Nusselt number were analyzed. The strength of the heat transfer between the surface of the tubes and the air flow increases with an increase in Reynolds number and pitch-to-diameter ratio.
El-Amin, Mohamed
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 is employed in the flow equation to express the non-Darcy model. The fluid viscosity varies as an inverse linear function of temperature. The coefficient of thermal diffusivity has been assumed to be the sum of the molecular diffusivity and the dynamic diffusivity due to mechanical dispersion. Similarity solutions of the governing equations, for an isothermally heated plate, are obtained. Effects of the physical parameters, which govern the problem, on the rate of heat transfer in terms of Nusselt number, the slip velocity, and the boundary layer thickness, for the two cases Darcy and non-Darcy, are shown on graphs or entered in tables. © 2013 by Begell House, Inc.
Chung, S.
1973-01-01
Heat transfer phenomena of rarefied gas flows is discussed based on a literature survey of analytical and experimental rarefied gas dynamics. Subsonic flows are emphasized for the purposes of meteorological thermometry in the high atmosphere. The heat transfer coefficients for three basic geometries are given in the regimes of free molecular flow, transition flow, slip flow, and continuum flow. Different types of heat phenomena, and the analysis of theoretical and experimental data are presented. The uncertainties calculated from the interpolation rule compared with the available experimental data are discussed. The recovery factor for each geometry in subsonic rarefied flows is also given.
Raheimpour Angeneh, Saeid; Aktas, Murat K.
This study mainly focuses on the thermal convection in a rectangular enclosure in the presence of streaming motion while temperature profile of bottom wall is sinusoidal. The effect of wall displacement amplitude and the bottom wall temperature profile on convective heat transfer in the enclosure are determined with the help of a parametric study. By vibrating side wall of the enclosure, oscillating flow is actuated. The top wall of the enclosure is kept at initial temperature and isothermal while the side walls are adiabatic. In order to predict the oscillatory and time averaged mean flow fields, fully compressible form of the Navier - Stokes equations are considered. Simulation of the convective transport in the enclosure is obtained by a control-volume method based, explicit computational scheme is used. The aim of this study is to provide interpretation of the flow and thermal transport physics. The influence of nonzero mean vibrational flow on the thermal convection from a surface with sinusoidal temperature distribution has never been investigated before. Conclusions may lead up to design of new heat removal applications.
Directory of Open Access Journals (Sweden)
Ferdows M.
2017-02-01
Full Text Available The aim of this work is to study the mixed convection boundary layer flow from a horizontal surface embedded in a porous medium with exponential decaying internal heat generation (IHG. Boundary layer equations are reduced to two ordinary differential equations for the dimensionless stream function and temperature with two parameters: ε, the mixed convection parameter, and λ, the exponent of x. This problem is numerically solved with a system of parameters using built-in codes in Maple. The influences of these parameters on velocity and temperature profiles, and the Nusselt number, are thoroughly compared and discussed.
Energy Technology Data Exchange (ETDEWEB)
Hashemabadi, S.H. [Iran Univ. of Science and Technology, Dept. of Chemical Engineering, Tehran (Iran); Etemad, S.Gh. [Isfahan Univ. of Technology, Dept. of Chemical Engineering, Isfahan (Israel); Thibault, J. [Ottawa Univ., Dept. of Chemical Engineering, Ottawa, ON (Canada)
2004-08-01
Heat transfer to viscoelastic fluids is frequently encountered in various industrial processing. In this investigation an analytical solution was obtained to predict the fully developed, steady and laminar heat transfer of viscoelastic fluids between parallel plates. One of the plates was stationary and was subjected to a constant heat flux. The other plate moved with constant velocity and was insulated. The simplified Phan-Thien-Tanner (SPTT) model, believed to be a more realistic model for viscoelastic fluids, was used to represent the rheological behavior of the fluid. The energy equation was solved for a wide range of Brinkman number, dimensionless viscoelastic group, and dimensionless pressure drop. Results highlight the strong effects of these parameters on the heat transfer rate. (Author)
Convective heat transfer characters of nanoparticle enhanced latent functionally thermal fluid
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
The latent heat of the microencapsulated phase change material(MPCM)increases the effective ther-mal capacity of latent functionally thermal fluid.However,researchers found that the heat transfer performance of such fluids was diminished due to the reduction of the low thermal conductivity of MPCM.For this reason,the nanoparticle enhanced latent functionally thermal fluids were formulated and the heat transfer behaviors of these fluids in a vertical circular tube at the laminar regime were conducted.The result showed that slurries containing 0.5% TiO2 nanoparticles by mass and 5%―20% MPCM by mass exhibited improved heat transfer rates in comparison with the conventional latent functionally thermal fluid and that the enhancement increased with the increasing MPCM concentration and up to 18.9% of the dimensionless wall temperature was reduced.
Convective heat transfer characters of nanoparticle enhanced latent functionally thermal fluid
Institute of Scientific and Technical Information of China (English)
WANG Liang; LIN GuiPing; CHEN HaiSheng; DING YuLong
2009-01-01
The latent heat of the microencapsulated phase change material (MPCM) increases the effective ther-mal capacity of latent functionally thermal fluid. However, researchers found that the heat transfer performance of such fluids was diminished due to the reduction of the low thermal conductivity of MPCM. For this reason, the nanoparticle enhanced latent functionally thermal fluids were formulated and the heat transfer behaviors of these fluids in a vertical circular tube at the laminar regime were conducted. The result showed that slurries containing 0.5% TiO2 nanoparticles by mass and 5%-20% MPCM by mass exhibited improved heat transfer rates in comparison with the conventional latent functionally thermal fluid and that the enhancement increased with the increasing MPCM concentration and up to 18.9% of the dimensionless wall temperature was reduced.
Bibliography on augmentation of convective heat and mass transfer-II
Energy Technology Data Exchange (ETDEWEB)
Bergles, A.E.; Nirmalan, V.; Junkhan, G.H.; Webb, R.L.
1983-12-01
Heat transfer augmentation has developed into a major specialty area in heat transfer research and development. This report presents and updated bibliography of world literature on augmentation. The literature is classified into passive augmentation techniques, which require no external power, and active techniques, which do require external power. The fifteen techniques are grouped in terms of their applications to the various modes of heat transfer. Mass transfer is included for completeness. Key words are included with each citation for technique/mode identification. The total number of publications cited is 3045, including 135 surveys of various techniques and 86 papers on performance evaluation of passive techniques. Patents are not included, as they are the subject of a separate bibliographic report.
Rosas, A. S.; Ali, R. K.; Abdel-Aziz, A. A.; Elshazly, K. M.
2017-03-01
This work investigated experimentally the heat transfer and pressure drop in electronic module using a curved deflector to direct the flow towards the recirculation zone enclosed between the two heat sources. The experiments were carried out to investigate the effect of deflector dimensionless radius ( R r ) and both horizontal and vertical distances ( R x , R y ) within a range of Reynolds number from 5223 to 11,380. The results show that larger deflector at small vertical distance enhances the heat transfer for upstream and downstream heat sources while the horizontal distance has a contrast effect. Correlations are obtained for the average Nusselt number of both upstream and downstream heat sources utilizing the present measurements within 5223 ≤ Re L ≤ 11,380, 0.02 ≤ R x ≤ 0.4, 0.3 ≤ R y ≤ 0.5 and 0.15 ≤ R r ≤ 0.35.
Rosas, A. S.; Ali, R. K.; Abdel-Aziz, A. A.; Elshazly, K. M.
2016-07-01
This work investigated experimentally the heat transfer and pressure drop in electronic module using a curved deflector to direct the flow towards the recirculation zone enclosed between the two heat sources. The experiments were carried out to investigate the effect of deflector dimensionless radius (R r ) and both horizontal and vertical distances (R x , R y ) within a range of Reynolds number from 5223 to 11,380. The results show that larger deflector at small vertical distance enhances the heat transfer for upstream and downstream heat sources while the horizontal distance has a contrast effect. Correlations are obtained for the average Nusselt number of both upstream and downstream heat sources utilizing the present measurements within 5223 ≤ Re L ≤ 11,380, 0.02 ≤ R x ≤ 0.4, 0.3 ≤ R y ≤ 0.5 and 0.15 ≤ R r ≤ 0.35.
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.
Yadav, Rakesh K; Christensen, Ulrich R; Duarte, Lucia; Reiners, Ansgar
2015-01-01
We study rotating thermal convection in spherical shells as prototype for flow in the cores of terrestrial planets, gas planets or in stars. We base our analysis on a set of about 450 direct numerical simulations of the (magneto)hydrodynamic equations under the Boussinesq approximation. The Ekman number ranges from $10^{-3}$ to $10^{-6}$. Four sets of simulations are considered: non-magnetic simulations and dynamo simulations with either free-slip or no-slip flow boundary conditions. The non-magnetic setup with free-slip boundaries generates the strongest zonal flows. Both non-magnetic simulations with no-slip flow boundary conditions and self-consistent dynamos with free-slip boundaries have drastically reduced zonal-flows. Suppression of shear leads to a substantial gain in heat-transfer efficiency, increasing by a factor of 3 in some cases. Such efficiency enhancement occurs as long as the convection is significantly influenced by rotation. At higher convective driving the heat-transfer efficiency trends t...
Rose, J. W.
The paper gives a brief description of some of the better understood aspects of condensation heat transfer and includes discussion of the liquid-vapour interface, natural and forced convection laminar film condensation and dropwise condensation.
Shitzer, Avraham
2006-03-01
The wind-chill index (WCI), developed in Antarctica in the 1940s and recently updated by the weather services in the USA and Canada, expresses the enhancement of heat loss in cold climates from exposed body parts, e.g., face, due to wind. The index provides a simple and practical means for assessing the thermal effects of wind on humans outdoors. It is also used for indicating weather conditions that may pose adverse risks of freezing at subfreezing environmental temperatures. Values of the WCI depend on a number of parameters, i.e, temperatures, physical properties of the air, wind speed, etc., and on insolation and evaporation. This paper focuses on the effects of various empirical correlations used in the literature for calculating the convective heat transfer coefficients between humans and their environment. Insolation and evaporation are not included in the presentation. Large differences in calculated values among these correlations are demonstrated and quantified. Steady-state wind-chill-equivalent temperatures (WCETs) are estimated by a simple, one-dimensional heat-conducting hollow-cylindrical model using these empirical correlations. Partial comparison of these values with the published "new" WCETs is presented. The variability of the estimated WCETs, due to different correlations employed to calculate them, is clearly demonstrated. The results of this study clearly suggest the need for establishing a "gold standard" for estimating convective heat exchange between exposed body elements and the cold and windy environment. This should be done prior to the introduction and adoption of further modifications to WCETs and indices. Correlations to estimate the convective heat transfer coefficients between exposed body parts of humans in windy and cold environments influence the WCETs and need to be standardized.
Simulation of MHD CuO–water nanofluid flow and convective heat transfer considering Lorentz forces
Energy Technology Data Exchange (ETDEWEB)
Sheikholeslami, Mohsen; Bandpy, Mofid Gorji [Department of Mechanical Engineering, Babol University of Technology, Babol (Iran, Islamic Republic of); Ellahi, R., E-mail: rellahi@engr.ucr.edu [Department of Mechanical Engineering, University of California Riverside (United States); Department of Mathematics and Statistics, FBAS, IIUI, H-10 Sector, Islamabad (Pakistan); Zeeshan, A. [Department of Mathematics and Statistics, FBAS, IIUI, H-10 Sector, Islamabad (Pakistan)
2014-11-15
Magnetic field effect on CuO–water nanofluid flow and heat transfer in an enclosure which is heated from below is investigated. Lattice Boltzmann method is applied to solve the governing equations. The effective thermal conductivity and viscosity of nanofluid are calculated by KKL (Koo–Kleinstreuer–Li) correlation. In this model effect of Brownian motion on the effective thermal conductivity is considered. Effect of active parameter such as: Hartmann number, heat source length, nanoparticle volume fraction and Rayleigh numbers on the flow and heat transfer characteristics have been examined. The results reveal that the enhancement in heat transfer increases as Hartmann number and heat source length increase but it decreases with increase of Rayleigh number. Also it can be found that effect of Hartmann number and heat source length is more pronounced at high Rayleigh number. - Highlights: • This paper analyses the magnetic effect on CuO–water nanofluid. • Koo–Kleinstreuer–Li correlation and Lattice Boltzmann method are used. • Effects of pertinent parameters are presented through tables and graphs.
Energy Technology Data Exchange (ETDEWEB)
Wenji, Song [Guangzhou Institute of Energy Conversion, CAS, No. 2 Nengyuan Road, Tianhe District, Guangzhou 510640 (China); Key Laboratory of Renewable Energy and Gas Hydrate, CAS, No. 2 Nengyuan Road, Tianhe District, Guangzhou 510640 (China); Graduate School of Chinese Academy of Sciences, Beijing 100039 (China); Rui, Xiao; Chong, Huang; Shihui, He; Kaijun, Dong; Ziping, Feng [Guangzhou Institute of Energy Conversion, CAS, No. 2 Nengyuan Road, Tianhe District, Guangzhou 510640 (China); Key Laboratory of Renewable Energy and Gas Hydrate, CAS, No. 2 Nengyuan Road, Tianhe District, Guangzhou 510640 (China)
2009-11-15
Tetra-n-butyl-ammonium bromide (TBAB) clathrate hydrate slurry (CHS) is one kind of secondary refrigerants, which is promising to be applied into air-conditioning or latent-heat transportation systems as a thermal storage or cold carrying medium for energy saving. It is a solid-liquid two phase mixture which is easy to produce and has high latent heat and good fluidity. In this paper, the heat transfer characteristics of TBAB slurry were investigated in a horizontal stainless steel tube under different solid mass fractions and flow velocities with constant heat flux. One velocity region of weakened heat transfer was found. Moreover, TBAB CHS was treated as a kind of Bingham fluids, and the influences of the solid particles, flow velocity and types of flow on the forced convective heat transfer coefficients of TBAB CHS were investigated. At last, criterial correlations of Nusselt number for laminar and turbulent flows in the form of power function were summarized, and the error with experimental results was within {+-}20%. (author)
Impact of Chemical Reaction on MHD Mixed Convection Heat and Mass Transfer Flow with Thermophoresis
Directory of Open Access Journals (Sweden)
Prabir Kumar KUNDU
2014-02-01
Full Text Available A mathematical model is analyzed in order to study the effects of chemical reaction and thermophoresis on MHD mixed convection boundary layer flow of an incompressible, electrically conducting fluid past a heated vertical permeable flat plate embedded in a uniform porous medium, by taking into account the radiative heat flux and variable suction. The governing partial differential equations are transformed into a set of coupled ordinary differential equations which are solved analytically using the regular perturbation technique. Numerical results for dimensionless velocity, temperature, concentration as well as the skin friction coefficient, Nusselt number and Sherwood number are presented through graphs and a table for pertinent parameters to show interesting aspects of the solution.doi:10.14456/WJST.2014.35
Sensitivity studies of heat transfer: forced convection across a cylindrical pipe and duct flow
Ferrantelli, Andrea; Viljanen, Martti
2013-01-01
We consider two common heat transfer processes and perform a through sensitivity study of the variables involved. We derive and discuss analytical formulas for the heat transfer coefficient in function of film velocity, air temperature and pipe diameter. The according plots relate to a qualitative analysis of the multi-variable function $h$, according to functional optimization. For each process, we provide with graphs and tables of the parameters of interest, such as the Reynolds number. This method of study and the specific values can constitute a useful reference for didactic purposes.
A review of high-speed, convective, heat-transfer computation methods
Tauber, Michael E.
1989-01-01
The objective of this report is to provide useful engineering formulations and to instill a modest degree of physical understanding of the phenomena governing convective aerodynamic heating at high flight speeds. Some physical insight is not only essential to the application of the information presented here, but also to the effective use of computer codes which may be available to the reader. A discussion is given of cold-wall, laminar boundary layer heating. A brief presentation of the complex boundary layer transition phenomenon follows. Next, cold-wall turbulent boundary layer heating is discussed. This topic is followed by a brief coverage of separated flow-region and shock-interaction heating. A review of heat protection methods follows, including the influence of mass addition on laminar and turbulent boundary layers. Also discussed are a discussion of finite-difference computer codes and a comparison of some results from these codes. An extensive list of references is also provided from sources such as the various AIAA journals and NASA reports which are available in the open literature.
Institute of Scientific and Technical Information of China (English)
Tao Zhi; Cheng Zeyuan; Zhu Jianqin; Li Haiwang
2016-01-01
A variety of turbulence models were used to perform numerical simulations of heat transfer for hydrocarbon fuel flowing upward and downward through uniformly heated vertical pipes at supercritical pressure. Inlet temperatures varied from 373 K to 663 K, with heat flux rang-ing from 300 kW/m2 to 550 kW/m2. Comparative analyses between predicted and experimental results were used to evaluate the ability of turbulence models to respond to variable thermophys-ical properties of hydrocarbon fuel at supercritical pressure. It was found that the prediction per-formance of turbulence models is mainly determined by the damping function, which enables them to respond differently to local flow conditions. Although prediction accuracy for experimental results varied from condition to condition, the shear stress transport (SST) and launder and sharma models performed better than all other models used in the study. For very small buoyancy-influenced runs, the thermal-induced acceleration due to variations in density lead to the impairment of heat transfer occurring in the vicinity of pseudo-critical points, and heat transfer was enhanced at higher temperatures through the combined action of four thermophysical properties: density, viscosity, thermal conductivity and specific heat. For very large buoyancy-influenced runs, the thermal-induced acceleration effect was over predicted by the LS and AB models.
Directory of Open Access Journals (Sweden)
Tao Zhi
2016-10-01
Full Text Available A variety of turbulence models were used to perform numerical simulations of heat transfer for hydrocarbon fuel flowing upward and downward through uniformly heated vertical pipes at supercritical pressure. Inlet temperatures varied from 373 K to 663 K, with heat flux ranging from 300 kW/m2 to 550 kW/m2. Comparative analyses between predicted and experimental results were used to evaluate the ability of turbulence models to respond to variable thermophysical properties of hydrocarbon fuel at supercritical pressure. It was found that the prediction performance of turbulence models is mainly determined by the damping function, which enables them to respond differently to local flow conditions. Although prediction accuracy for experimental results varied from condition to condition, the shear stress transport (SST and launder and sharma models performed better than all other models used in the study. For very small buoyancy-influenced runs, the thermal-induced acceleration due to variations in density lead to the impairment of heat transfer occurring in the vicinity of pseudo-critical points, and heat transfer was enhanced at higher temperatures through the combined action of four thermophysical properties: density, viscosity, thermal conductivity and specific heat. For very large buoyancy-influenced runs, the thermal-induced acceleration effect was over predicted by the LS and AB models.
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)
Chandramohan, V. P.
2016-01-01
Convective drying of rectangular-shaped moist object has been analyzed both experimentally and numerically. Transient mass of the potato sample is measured experimentally. Moisture content, diffusivity, and density of the object are calculated at different drying air temperatures from 40°C to 70°C with an air velocity of 2 m/s. A three-dimensional (3D) finite volume method (FVM) based numerical model is developed to predict the temperature and moisture distribution. A computational fluid dynamics (CFD) code is used for predicting heat and mass transfer coefficients required in the boundary conditions of the heat and mass transfer model. The experimental and numerical data are compared and good agreement is observed.
Institute of Scientific and Technical Information of China (English)
M.A.R.Akhanda
2000-01-01
Experimental study of natural convection heat transfer across air layers bounded by a lower hot rectangular and a square corrugated plates to an upper cold flat plate has been carried out.The surroundings of this space are adiabatic.The effect of the angle of inclination,the aspect ratio,the temperature potential and the Rayleigh number on average heat transfer coefficients are investigated within a range of 0°≤θ≤75°,2.33≤A≤6.33,10°≤ΔT≤35°，and 3.29×104≤RaL≤2.29×106,The developed correlation predicts well the experimental data within an error of ±15%.
Indian Academy of Sciences (India)
ASHOK K BARIK; PRASANTA K SATAPATHY; SUDHANSU S SAHOO
2016-07-01
In this paper, the forced convective heat transfer enhancement with nanofluids in a 90° pipe bend has been presented. Numerical investigation is carried out for the turbulent flow through the pipe employing finite volume method. The governing differential equations are discretized using hexahedral cells, and theresulting algebraic equations are solved using Commercial solver Fluent 6.3. In order to close the time averaged Navier–Stokes equations, the two-equation k–e turbulence model with a standard wall function have been used.The duct Reynolds number is varied in the range of 2,500–6,000. It is observed that the heat transfer is enhanced significantly by varying the volume fraction of the nanofluid. It is also found that the heat transfer is increased with Reynolds number. A strong secondary flow is observed due to the presence of the wall. Turbulent kinetic energy near outer wall is found to be higher than the inner wall of the bend. A comparative assessment for the heat transfer enhancement with different types of nanofluids is also presented. The computed results of areaweighted average Nusselt numbers are validated with some of the existing literature
Van Fossen, G. James; De Witt, Kenneth J.; Newton, James E.; Poinsatte, Phillip E.
1988-01-01
Wind tunnels typically have higher free stream turbulence levels than are found in flight. Turbulence intensity was measured to be 0.5 percent in the NASA Lewis Icing Research Tunnel (IRT) with the cloud making sprays off and around 2 percent with cloud making equipment on. Turbulence intensity for flight conditions was found to be too low to make meaningful measurements for smooth air. This difference between free stream and wind tunnel conditions has raised questions as to the validity of results obtained in the IRT. One objective of these tests was to determine the effect of free stream turbulence on convective heat transfer for the NASA Lewis LEWICE ice growth prediction code. These tests provide in-flight heat transfer data for a NASA-0012 airfoil with a 533 cm chord. Future tests will measure heat transfer data from the same airfoil in the Lewis Icing Research Tunnel. Roughness was obtained by the attachment of small, 2 mm diameter hemispheres of uniform size to the airfoil in three different patterns. Heat transfer measurements were recorded in flight on the NASA Lewis Twin Otter Icing Research Aircraft. Measurements were taken for the smooth and roughened surfaces at various aircraft speeds and angles of attack up to four degrees. Results are presented as Frossling number versus position on the airfoil for various roughnesses and angles of attack.
Newton, James E.; Vanfossen, G. James; Poinsatte, Phillip E.; Dewitt, Kenneth J.
1988-01-01
Wind tunnels typically have higher free stream turbulence levels than are found in flight. Turbulence intensity was measured to be 0.5 percent in the NASA Lewis Icing Research Tunnel (IRT) with the cloud making sprays off and around 2 percent with cloud making equipment on. Turbulence intensity for flight conditions was found to be too low to make meaningful measurements for smooth air. This difference between free stream and wing tunnel conditions has raised questions as to the validity of results obtained in the IRT. One objective of these tests was to determine the effect of free stream turbulence on convective heat transfer for the NASA Lewis LEWICE ice growth prediction code. These tests provide in-flight heat transfer data for a NASA-0012 airfoil with a 533 cm chord. Future tests will measure heat transfer data from the same airfoil in the Lewis Icing Research Tunnel. Roughness was obtained by the attachment of small, 2 mm diameter hemispheres of uniform size to the airfoil in three different patterns. Heat transfer measurements were recorded in flight on the NASA Lewis Twin Otter Icing Research Aircraft. Measurements were taken for the smooth and roughened surfaces at various aircraft speeds and angles of attack up to four degrees. Results are presented as Frossling number versus position on the airfoil for various roughnesses and angles of attack.
Ullmer, Dirk; Peschke, Philip; Terzis, Alexandros; Ott, Peter; Weigand, Bernhard
2015-09-01
This paper demonstrates that the impact of nanosecond pulsed dielectric barrier discharge (ns-DBD) actuators on the structure of the boundary layer can be investigated using quantitative convective heat transfer measurements. For the experiments, the flow over a flat plate with a C4 leading edge thickness distribution was examined at low speed incompressible flow (6.6-11.5 m s-1). An ns-DBD plasma actuator was mounted 5 mm downstream of the leading edge and several experiments were conducted giving particular emphasis on the effect of actuation frequency and the freestream velocity. Local heat transfer distributions were measured using the transient liquid crystal technique with and without plasma activated. As a result, any effect of plasma on the structure of the boundary layer is interpreted by local heat transfer coefficient distributions which are compared with laminar and turbulent boundary layer correlations. The heat transfer results, which are also confirmed by hot-wire measurements, show the considerable effect of the actuation frequency on the location of the transition point elucidating that liquid crystal thermography is a promising method for investigating plasma-flow interactions very close to the wall. Additionally, the hot-wire measurements indicate possible velocity oscillations in the near wall flow due to plasma activation.
Institute of Scientific and Technical Information of China (English)
无
2011-01-01
This paper studies mixed convection,double dispersion and chemical reaction effects on heat and mass transfer in a non-Darcy non-Newtonian fluid over a vertical surface in a porous medium under the constant temperature and concentration.The governing boundary layer equations,namely,momentum,energy and concentration,are converted to ordinary differential equations by introducing similarity variables and then are solved numerically by means of fourth-order Runge-Kutta method coupled with double-shooting techn...
Hayat, T; Saeed, Yusra; Alsaedi, A; Asad, Sadia
2015-01-01
The aim here is to investigate the effects of convective heat and mass transfer in the flow of Eyring-Powell fluid past an inclined exponential stretching surface. Mathematical formulation and analysis have been performed in the presence of Soret, Dufour and thermal radiation effects. The governing partial differential equations corresponding to the momentum, energy and concentration are reduced to a set of non-linear ordinary differential equations. Resulting nonlinear system is computed for the series solutions. Interval of convergence is determined. Physical interpretation is seen for the embedded parameters of interest. Skin friction coefficient, local Nusselt number and local Sherwood number are numerically computed and examined.
Raju, C. S. K.; Sandeep, N.; Malvandi, A.
2016-12-01
Nanofluids are potential heat transfer fluids with enhanced thermal and physical properties can be applied in many areas. External magnetic field have tendency to set the thermal and physical properties of nanofluids. With this motivation, we investigated the effects of temperature dependent viscosity, heat source/sink and viscous dissipation on natural convective heat transfer of radiative magnetohydrodynamic (MHD) non-Newtonian nanofluid caused by a cone. For this study, a simulation is performed by mixing of copper nanoparticles in the kerosene. The self similar transformed governing equations are solved by enforcing Runge-Kutta based shooting technique. We acquire the significant accuracy of the recent results by comparing with the published results. In addition, it is indicated that the dual solutions exist for both the base fluid and nanofluid cases. The effects of dimensionless parameters including Eckert number, Weissenberg number, Power-law index, viscous variation parameter, heat source/sink, thermal radiation parameter, and magnetic field parameter on velocity and temperature fields along with the friction factor coefficient and the local Nusselt number are discussed with the help of graphs and tables. It is shown that nanoparticles inclusion into the non-Newtonian fluids has a positive effect on thermal performance. In addition, the viscous variation parameter has a tendency to encourage the friction factor coefficient as well as the heat transfer rate. Moreover, Cu-kerosene nanofluid signifies a better thermal performance than the Ag-kerosene nanofluid.
Directory of Open Access Journals (Sweden)
A. Malvandi
2015-01-01
Full Text Available The objective of this paper is to consider both effects of slip and convective heat boundary conditions on steady two-dimensional boundary layer flow of a nanofluid over a stretching sheet in the presence of blowing/suction simultaneously. Flow meets the Navier's slip condition at the surface and Biot number is also used to consider the effects of convective heat transfer. The employed model for nanofluid includes two-component four-equation nonhomogeneous equilibrium model that incorporates the effects of nanoparticle migration owing to Brownian motion and thermophoresis. The basic partial boundary layer equations have been transformed into a two-point boundary value problem via similarity variables. Results for impermeable isothermal surface and also no-slip boundary condition were in best agreements with those existing in literatures. Effects of governing parameters such as Biot number (Bi, slip parameter (λ, thermophoresis (Nt, Prandtl number (Pr, Lewis number (Le, Brownian motion (Nb and blowing/suction (S on reduced Nusselt and Sherwood numbers are analyzed and discussed in details. The obtained results indicate that unlike heat transfer rate, concentration rate is very sensitive to all parameters among which Le, S and Pr are the most effective ones.
Raheimpour Angeneh, Saeid; Aktas, Murat Kadri
2016-11-01
Effects of the acoustic streaming motion on convective heat transfer in a rectangular shallow enclosure with sinusoidal spatial bottom wall temperature distribution are investigated numerically. Acoustic excitation is generated by the periodic vibration of left wall. The top wall of the enclosure is isothermal while the side walls are adiabatic. A FORTRAN code is developed to predict the oscillatory and mean flow fields by considering the compressible form of the Navier -Stokes equation and solved by flux-corrected transport algorithm. In order to validate the results of the simulations, a case with an unheated bottom wall is considered and compared with the existing literature. Applying the sinusoidal temperature profile to the bottom wall provides axial and transverse temperature gradients. In return these gradients strongly affect the flow pattern in the enclosure. Heat transfer depends on the flow structure considerably. This is the first time that the effect of nonzero mean vibrational flow on thermal convection from a surface with sinusoidal temperature profile investigated. Results of this study may lead up to design of new heat removal applications.
Bacon, D H
2013-01-01
Basic Heat Transfer aims to help readers use a computer to solve heat transfer problems and to promote greater understanding by changing data values and observing the effects, which are necessary in design and optimization calculations.The book is concerned with applications including insulation and heating in buildings and pipes, temperature distributions in solids for steady state and transient conditions, the determination of surface heat transfer coefficients for convection in various situations, radiation heat transfer in grey body problems, the use of finned surfaces, and simple heat exc
Core flows and heat transfer induced by inhomogeneous cooling with sub- and supercritical convection
Dietrich, Wieland; Wicht, Johannes
2016-01-01
The amount and spatial pattern of heat extracted from cores of terrestrial planets is ultimately controlled by the thermal structure of the lower rocky mantle. Using the most common model to tackle this problem, a rapidly rotating and differentially cooled spherical shell containing an incompressible and viscous liquid is numerically investigated. To gain the physical basics, we consider a simple, equatorial symmetric perturbation of the CMB heat flux shaped as a spherical harmonic $Y_{11}$. The thermodynamic properties of the induced flows mainly depend on the degree of nonlinearity parametrised by a horizontal Rayleigh number $Ra_h=q^\\ast Ra$, where $q^\\ast$ is the relative CMB heat flux anomaly amplitude and $Ra$ is the Rayleigh number which controls radial buoyancy-driven convection. Depending on $Ra_h$ we characterise three flow regimes through their spatial patterns, heat transport and flow speed scalings: in the linear conductive regime the radial inward flow is found to be phase shifted $90^\\circ$ eas...
Effects of radiation on convection heat transfer of Cu-water nanofluid past a moving wedge
Directory of Open Access Journals (Sweden)
Salama Faiza A.
2016-01-01
Full Text Available Heat transfer characteristics of a two-dimensional steady hydrodynamic flow of water-based copper(Cu nanofluid over a moving wedge, taking into account the effects of thermal radiation, have been investigated numerically. The Rosseland approximation is used to describe the radiative heat flux in the energy equation. The governing fundamental equations are first transformed into a system of ordinary differential equations and solved numerically by using the fourth-order Runge-kutta method with shooting technique. A comparison with previously published work has been carried out and the results are found to be in good agreement. The existence of unique and dual solutions for self-similar equations of the flow and heat transfer are analyzed numerically. The results indicate that there is strong dependence of the thermal gradient at the surface of the wedge on both velocity ratio parameter and thermal radiation.
Moshizi, S. A.; Pop, I.
2016-07-01
In the current study, the conjugated effect of Joule heating and magnetohydrodynamics (MHD) on the forced convective heat transfer of fully developed laminar nanofluid flows inside annular pipes, under the influence of MHD field, has been investigated. The temperature and nanoparticle distributions at both the inner and outer walls are assumed to vary in the direction of the fluid. Furthermore, owing to the nanoparticle migrations in the fluid, a slip condition becomes far more important than the no-slip condition of the fluid-solid interface, which appropriately represents the non-equilibrium region near the interface. The governing equations—obtained by employing the Buongiorno's model for nanofluid in cylindrical coordinates—are converted into two-point ordinary boundary value differential equations and solved numerically. The effects of various controlling parameters on the flow characteristics, the average Nusselt number and the average Sherwood number have been assessed in detail. Additionally, the effect of the inner to outer diameter ratio on the heat and mass transfer rate has been studied. The results obtained indicate that, in the presence of a magnetic field when the fluid is electrically conductive, heat transfer will be reduced significantly due to the influences of Joule heating, while the average mass transfer rate experiences an opposite trend. Moreover, the increase in the slip velocity on both the walls causes the average heat transfer to rise and the average mass transfer to decrease.
Directory of Open Access Journals (Sweden)
Thamir K. Jassem
2013-05-01
Full Text Available An experimental forced laminar study was presented in this research for an air flowing through a circular channel for different angles ( ,30o,45o,60o, the channel was heated at constant heat flux , the channel also was packed with steel and glass spheres respectively . The tests were done for three values of Peclets number (2111.71,3945.42,4575.47 with changing the heat flux for each case and five times for each number.The results showed that the dimensionless temperature distribution will decrease with increasing the dimensionless channel length for all cases with changing Peclet number, heat flux and inclination angles, and its lowest value will be for glass spheres at highest flux, while at lower flux for , and the decreasing in dimensionless temperature was closed for both types of packed at other inclination angles.The study declared that the local Nusselt number decreases with increasing the dimensionless length of the channel for both packeds and for different applied heat flux, also through this study it was declared that the average Nusselt increases as Peclet number increases for both packed. Its value for the glass spheres is greater than the steel spheres with percentage (98.3% at small Peclet, and percentage (97.2% at large Peclet number for the horizontal tube, and (98.3% at small Peclet number and (97.8% at large Peclet number at .Through this study its was found that average Nusselt number increases along the channel as the heat flux increases, because the bulk temperature will increase as the flow proceeds toward the end of the channel , so the heat transfer coefficient will increase. It was declared from this study that in the case of the steel packed the heat transfer will occur mainly by conduction, while in the case of glass packed the heat transfer will occur mainly by laminar forced convection, where the lowest Nusselt number (Nu=3.8 was found when the pipe is horizontal and lowest heat flux and lowest Peclet number.
Shibahara, M.; Fukuda, K.; Liu, Q. S.; Hata, K.
2017-03-01
Steady and transient heat transfer coefficients for water flowing in small tubes with exponentially increasing heat inputs were measured. Platinum tubes with inner diameters of 1.0 and 2.0 mm were used as test tubes, which were mounted vertically in the experimental water loop. In the experiment, the upward flow velocity ranged from 2 to 16 m/s, and the corresponding Reynolds numbers ranged from 4.77 × 103 to 9.16 × 104 at the inlet liquid temperatures ranged from 298 to 343 K. The heat generation rate exponentially increased with the function. The period of the heat generation rate ranged from 24 ms to 17.5 s. Experimental results indicate that steady heat transfer coefficients decreased with the increase in the inner diameter of the small tube. Moreover, the ratio of bulk viscosity to near-wall viscosity of water increased with the rise in surface temperature of the vertical tube. From the experimental data, correlations of steady-state heat transfer for inner diameters of 1.0 and 2.0 mm were obtained. The heat transfer coefficient increased with decreasing the period of the heat generation rate as the flow velocity decreased. Moreover, the Nusselt number under the transient condition was affected by the Fourier number and the Reynolds number.
Shibahara, M.; Fukuda, K.; Liu, Q. S.; Hata, K.
2016-06-01
Steady and transient heat transfer coefficients for water flowing in small tubes with exponentially increasing heat inputs were measured. Platinum tubes with inner diameters of 1.0 and 2.0 mm were used as test tubes, which were mounted vertically in the experimental water loop. In the experiment, the upward flow velocity ranged from 2 to 16 m/s, and the corresponding Reynolds numbers ranged from 4.77 × 103 to 9.16 × 104 at the inlet liquid temperatures ranged from 298 to 343 K. The heat generation rate exponentially increased with the function. The period of the heat generation rate ranged from 24 ms to 17.5 s. Experimental results indicate that steady heat transfer coefficients decreased with the increase in the inner diameter of the small tube. Moreover, the ratio of bulk viscosity to near-wall viscosity of water increased with the rise in surface temperature of the vertical tube. From the experimental data, correlations of steady-state heat transfer for inner diameters of 1.0 and 2.0 mm were obtained. The heat transfer coefficient increased with decreasing the period of the heat generation rate as the flow velocity decreased. Moreover, the Nusselt number under the transient condition was affected by the Fourier number and the Reynolds number.
Sivakumar, A.; Alagumurthi, N.; Senthilvelan, T.
2016-07-01
The microchannels are device used to remove high heat fluxes from smaller area. In this experimental research work the heat transfer performance of nanofluids of Al2O3/water and CuO/water were compared. The important character of such fluids is the enhanced thermal conductivity, in comparison with base fluid without considerable alteration in physical and chemical properties. The effect of forced convective heat transfer coefficient was calculated using serpentine shaped microchannel heat exchanger. Furthermore we calculated the forced convective heat transfer coefficient of the nanofluids using theoretical correlations in order to compare the results with the experimental data. The heat transfer coefficient for different particle concentration and temperature were analysed using forced convection heat transfer using nanofluids. The findings indicate considerable enhancement in convective heat transfer coefficient of the nanofluids as compared to the basefluid. The results also shows that CuO/water nanofluid has increased heat transfer coefficient compared with Al2O3/water and base fluids. Moreover the experimental results indicate there is increased forced convective heat transfer coefficient with the increase in nano particle concentration.
Simulation of brush insert for leading-edge-passage convective heat transfer
Hendricks, R. C.; Braun, M. J.; Canacci, V.; Mullen, R. L.
1991-01-01
Current and proposed high speed aircraft have high leading edge heat transfer (to 160 MW/sq m, 100 Btu/sq in/sec) and surface temperatures to 1370 K (2000 F). Without cooling, these surfaces could not survive. In one proposal the coolant hydrogen is circulated to the leading edge through a passage and returned to be consumed by the propulsion system. Simulated flow studies and visualizations have shown flow separation within the passage with a stagnation locus that isolates a zone of recirculation at the most critical portion of the passage, namely the leading edge itself. A novel method is described for mitigating the flow separation and the isolated recirculation zones by using a brush insert in the flow passage near the leading edge zone, thus providing a significant increase in heat transfer.
Theoretical and Computational Study of Forced-Convection Heat Transfer at Supercritical Pressures
Zhong, Jianguo
In the simulation of turbulent fluid flow and heat transfer at supercritical pressures, substantial difficulties have been encountered in the modeling of turbulence and bounda-ry layer. This is due to significant fluid property variations with respect to the local temperature and pressure, especially in the near-wall region of a heated wall, where large temperature differences occur. The classical turbulence models available in literature were typically developed for constant-property fluids, where an empirical wall function in the high-Re k-epsilon model, and a damping function in the low-Re k-epsilon model were derived based on the constant-property data to solve the boundary layer. As it can be found in the existing literature, large differences have been observed between the experimental and numerical simulation results of the heat transfer coefficient predictions in the en-hanced and deteriorated heat transfer situations for supercritical fluids. In this thesis, a novel near-wall treatment method is proposed to treat large property variations in the thermal and velocity sub-layers. In the near-wall region, the supercritical fluids can be considered thermal-conductive and viscous forces dominated. The thick-ness of the viscous sub-layer (VSL) and the conduction sub-layer (CSL) can be related to the wall shear stress and local Prandtl number information by using computational CFD models, such as that implemented in the NPHASE-CMFD code. The fluids' bulk and wall temperature information has been obtained from the literature review of experi-mental measurements. The wall temperature and heat transfer coefficient calculated from the k-epsilon model with the proposed wall treatment method have been found to be in good agreement with experimental data for both heat transfer enhancement and deterioration cases for two most widely used fluids: CO2 and water. The proposed model has been applied in the reactor-scale thermal-hydraulic analysis of different flow path
Effect of Magnetic Field on Mixed Convection Heat Transfer in a Lid-Driven Square Cavity
Directory of Open Access Journals (Sweden)
N. A. Bakar
2016-01-01
Full Text Available The effect of magnetic field on fluid flow and heat transfer in two-dimensional square cavity is analyzed numerically. The vertical walls are insulated; the top wall is maintained at cold temperature, Tc while the bottom wall is maintained at hot temperature, Th where Th>Tc. The dimensionless governing equations are solved using finite volume method and SIMPLE algorithm. The streamlines and isotherm plots and the variation of Nusselt numbers on hot and cold walls are presented.
Institute of Scientific and Technical Information of China (English)
李成; 李俊明
2011-01-01
Condensation of humid air along a vertical plate was numerically investigated, with the mathematical model built on the full boundary layer equations and the film-wise condensation assumption. The velocity, heat and mass transfer characteristics at the gas-liquid interface were numerical analyzed and the results indicated that it was not reasonable to neglect the condensate film from the point of its thickness only. The condensate film thickness, interface temperature drop and the interface tangential velocity affect the physical fields weakly. However, the subcooling and the interface normal velocity were important factors to be considered before the simplification was made. For higher wall temperature, the advective mass transfer contributed much to the total mass transfer. Therefore, the boundary conditions were the key to judge the rationality of neglecting the condensate film for numerical solutions. The numerical results were checked by comparing with experiments and correlations.
Directory of Open Access Journals (Sweden)
O. D. Makinde
2014-01-01
Full Text Available Heat transfer characteristics of a Berman flow of water based nanofluids containing copper (Cu and alumina (Al2O3 as nanoparticles in a porous channel with Navier slip, viscous dissipation, and convective cooling are investigated. It is assumed that the exchange of heat with the ambient surrounding takes place at the channel walls following Newton’s law of cooling. The governing partial differential equations and boundary conditions are converted into a set of nonlinear ordinary differential equations using appropriate similarity transformations. These equations are solved analytically by regular perturbation methods with series improvement technique and numerically using an efficient Runge-Kutta Fehlberg integration technique coupled with shooting scheme. The effects of the governing parameters on the dimensionless velocity, temperature, skin friction, pressure drop, and Nusselt numbers are presented graphically and discussed quantitatively.
Directory of Open Access Journals (Sweden)
Gauri Shanker Seth
2015-01-01
Full Text Available An investigation of unsteady hydromagnetic natural convection heat and mass trans fer flow with Hall current of a viscous, incompressible, electrically conducting, heat absorbing and optically thin radiating fluid past an accelerated moving vertical plate through fluid saturated porous medium in a rotating environment is carried out when temperature of the plate has a temporarily ramped profile. The exact solutions of momentum, energy and concentration equations are obtained in closed form by Laplace transform technique. The expressions of skin friction, Nusselt number and Sherwood number are also derived. For both ramped temperature and isothermal plates, Hall current tends to accelerate primary and secondary fluid velocities whereas heat absorption and radiation have reverse effect on it. Rotation tends to retard primary fluid velocity whereas it has a reverse effect on secondary fluid velocity. Heat absorption and radiation have tendency to enhance rate of heat transfer at the plate.
Hussain, S. M.; Jain, J.; Seth, G. S.; Rashidi, M. M.
2017-01-01
The unsteady MHD free convective heat and mass transfer flow of an electrically conducting, viscous and incompressible fluid over an accelerated moving vertical plate in the presence of heat absorption and chemical reaction with ramped temperature and ramped surface concentration through a porous medium in a rotating system is studied, taking Hall effects into account. The governing equations are solved analytically with the help of Laplace transform technique. The unified closed-form expressions are obtained for fluid velocity, fluid temperature, species concentration, skin friction, Nusselt number and Sherwood numbers. The effects of various parameters on fluid velocity, fluid temperature and species concentration are discussed by graphs whereas numerical values of skin friction, Nusselt and Sherwood numbers are presented in tabular form for different values of pertinent flow parameters. The numerical results are also compared with free convective flow near ramped temperature plate with ramped surface concentration with the corresponding flow near isothermal plate with uniform surface concentration.
Energy Technology Data Exchange (ETDEWEB)
Salimpour, Mohammad Reza; Golmohammadi, Kia; Sedaghat, Ahmad [Isfahan University of Technology, Isfahan (Iran, Islamic Republic of); Campo, Antonio [The University of Texas at San Antonio, San Antonio (United States)
2015-09-15
The convective heat transfer for the turbulent flow of water/TiO{sub 2} nanofluid inside helically horizontal corrugated tubes is investigated in this paper using experimental techniques. The tube boundary condition is a uniform wall temperature. The test apparatus was designed and assembled with a test section containing 93 cm copper tubes with internal and external diameters of 7.71 mm and 9.52 mm, respectively. First, the heat transfer characteristics of the distilled water turbulent flow in a plain copper tube were measured preliminarily. Second, various test runs were performed for nanofluids with two nanoparticle concentrations (0.1% and 0.5%), two corrugation depth to diameter ratios (0.0648 and 0.103), two corrugation pitch to diameter ratios (0.917 and 1.297), and two corrugation width to diameter ratios (0.363 and 0.492) that were all within the range of turbulent Reynolds numbers (3000 < Re < 15000). The experimental results reveal that the Nusselt number augments the dual increments in corrugation depth and width and with the decrements in corrugation pitch, particularly for high Reynolds numbers. The nanoparticles have a stronger effect on the heat transfer in helically corrugated tubes with higher corrugation depths and widths as well as lower corrugation pitches. A correlation for the Nusselt number in terms of the helically corrugated tubes is introduced based on the linear regression analysis of the experimental data.
Predicting Turbulent Convective Heat Transfer in Three-Dimensional Duct Flows
Rokni, M.; Gatski, T. B.
1999-01-01
The performance of an explicit algebraic stress model is assessed in predicting the turbulent flow and forced heat transfer in straight ducts, with square, rectangular, trapezoidal and triangular cross-sections, under fully developed conditions over a range of Reynolds numbers. Iso-thermal conditions are imposed on the duct walls and the turbulent heat fluxes are modeled by gradient-diffusion type models. At high Reynolds numbers (>/= 10(exp 5)), wall functions are used for the velocity and temperature fields; while at low Reynolds numbers damping functions are introduced into the models. Hydraulic parameters such as friction factor and Nusselt number are well predicted even when damping functions are used, and the present formulation imposes minimal demand on the number of grid points without any convergence or stability problems. Comparison between the models is presented in terms of the hydraulic parameters, friction factor and Nusselt number, as well as in terms of the secondary flow patterns occurring within the ducts.
Hartnett, James P; Cho, Young I; Greene, George A
2001-01-01
Heat transfer is the exchange of heat energy between a system and its surrounding environment, which results from a temperature difference and takes place by means of a process of thermal conduction, mechanical convection, or electromagnetic radiation. Advances in Heat Transfer is designed to fill the information gap between regularly scheduled journals and university-level textbooks by providing in-depth review articles over a broader scope than is allowable in either journals or texts.
Natural convective magneto-nanofluid flow and radiative heat transfer past a moving vertical plate
Directory of Open Access Journals (Sweden)
S. Das
2015-03-01
Full Text Available An investigation of the hydromagnetic boundary layer flow past a moving vertical plate in nanofluids in the presence of a uniform transverse magnetic field and thermal radiation has been carried out. Three different types of water-based nanofluids containing copper, aluminum oxide and titanium dioxide are taken into consideration. The governing equations are solved using Laplace transform technique and the solutions are presented in closed form. The numerical values of nanofluid temperature, velocity, the rate of heat transfer and the shear stress at the plate are presented graphically for several values of the pertinent parameters. The present study finds applications in engineering devices.
Energy Technology Data Exchange (ETDEWEB)
Mundra, K.; DebRoy, T.; Babu, S.S. [Pennsylvania State Univ., University Park, PA (United States). Dept. of Materials Science and Engineering; David, S.A. [Oak Ridge National Lab., TN (United States)
1995-12-31
Heat transfer and fluid flow during manual metal arc welding of low alloy steels were investigated by solving the equations of conservation of mass, momentum, and energy in three dimensions. Cooling rates were calculated at various locations in the weldment. Calculated cooling rates were coupled with an existing phase transformation model to predict percentages of acicular, allotriomorphic, and Widmanstaetten ferrites in various low alloy steel welds containing different concentration of V and Mn. Computed microstructures were in good agreement with experiment, indicating promise for predicting weld metal microstructure from the fundamentals of transport phenomena.
Martyushev, S. G.; Miroshnichenko, I. V.; Sheremet, M. A.
2014-01-01
Unsteady regimes of convective-radiative heat transfer in a cubic enclosure with finitely thick heat-conducting walls in the presence of a constant-temperature energy source have been modeled mathematically under the conditions of convective heat exchange with the environment. A mathematical model has been formulated in dimensionless variables "vector potential-vorticity vector-temperature;" the model was realized numerically by the finite-difference method. An analysis of radiative heat transfer has been made on the basis of the surface-radiation approximation with the balance method in Polyak's version. Three-dimensional temperature and velocity fields and dependences for the average Nusselt number have been obtained; they reflect the influence of the reduced emissivity factor of interior surfaces of enclosing walls, of the relative thermal conductivity, and of the unsteadiness factor on the flow regimes and heat transfer.
Natrajan, V. K.; Christensen, K. T.
2010-11-01
The convective heat transfer behavior of laminar flow through a smooth- and two rough-wall microchannels is investigated by performing non-intrusive and spatially resolved measurements of fluid temperature via two-color fluorescent thermometry under constant heat flux conditions at three of the four microchannel walls. Pressure-drop measurements reveal that the apparent friction factors for all surfaces agree well with established macroscale predictions for laminar flow through rectangular ducts with the onset of transition at Re > Recr = 1,800 for smooth-wall flow and deviation from laminar behavior at progressively lower Re with increasing surface roughness. The local Nu for smooth-wall flow agrees well with macroscale predictions in both the thermally developing and developed regimes. With increasing roughness, while an enhancement in local Nu is noted for flow in the thermally developing regime, no measurable influence is noted upon attainment of a thermally developed state. These observations are supported by the examination of temperature profiles across the microchannel at various axial positions and Re, which suggest that the thermal boundary layer may be regenerated locally by roughness in the thermal entrance region of the flow resulting in an increased axial distance (compared to smooth-wall behavior) at which thermally developed flow is attained in the presence of roughness. Finally, estimates of the bulk Nu indicate enhancement in convective heat transfer over the smooth-wall case for laminar flow at higher Re while the smooth-wall bulk Nu data are found to agree well with macroscale predictions.
El-Aziz, Mohamed Abd; Yahya, Aishah S.
2017-09-01
Simultaneous effects of thermal and concentration diffusions in unsteady magnetohydrodynamic free convection flow past a moving plate maintained at constant heat flux and embedded in a viscous fluid saturated porous medium is presented. The transport model employed includes the effects of thermal radiation, heat sink, Soret and chemical reaction. The fluid is considered as a gray absorbing-emitting but non-scattering medium and the Rosseland approximation in the energy equations is used to describe the radiative heat flux for optically thick fluid. The dimensionless coupled linear partial differential equations are solved by using Laplace transform technique. Numerical results for the velocity, temperature, concentration as well as the skin friction coefficient and the rates of heat and mass transfer are shown graphically for different values of physical parameters involved.
Kasmani, Ruhaila Md; Sivasankaran, S.; Bhuvaneswari, M.; Siri, Zailan
2015-10-01
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.
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.
Ito, Takehiro; Nishikawa, Kaneyasu; Shigechi, Tooru
1981-01-01
Forced convection film boiling heat transfer from a horizontal cylinder to saturated liquid cross-flowing upward is analyzed based on the two-phase boundary-layer theory. Numerical solution of the conservation equations is determined by means of the integral method of boundary-layer for water, ethanol and hexane under the atmospheric pressure. The velocity profile, separation point of the boundary-layer, thickness of the boundary-layer, distribution of the heat transfer coefficients and avera...
Directory of Open Access Journals (Sweden)
B. R. Rout
2013-01-01
Full Text Available This paper aims to investigate the influence of chemical reaction and the combined effects of internal heat generation and a convective boundary condition on the laminar boundary layer MHD heat and mass transfer flow over a moving vertical flat plate. The lower surface of the plate is in contact with a hot fluid while the stream of cold fluid flows over the upper surface with heat source and chemical reaction. The basic equations governing the flow, heat transfer, and concentration are reduced to a set of ordinary differential equations by using appropriate transformation for variables and solved numerically by Runge-Kutta fourth-order integration scheme in association with shooting method. The effects of physical parameters on the velocity, temperature, and concentration profiles are illustrated graphically. A table recording the values of skin friction, heat transfer, and mass transfer at the plate is also presented. The discussion focuses on the physical interpretation of the results as well as their comparison with previous studies which shows good agreement as a special case of the problem.
Davarnejad, Reza; Barati, Sara; Kooshki, Maryam
2013-12-01
The CFD simulation of heat transfer characteristics of a nanofluid in a circular tube under constant heat flux was considered using Fluent software (version 6.3.26) in the laminar flow. Al2O3 nanoparticles in water with concentrations of 0.5%, 1.0%, 1.5%, 2% and 2.5% were used in this simulation. All of the thermo-physical properties of nanofluids were assumed to be temperature independent. Two particle sizes with average size of 20 and 50 nm were used in this research. It was concluded that heat transfer coefficient increased by increasing the Reynolds number and the concentration of nanoparticles. The maximum convective heat transfer coefficient was observed at the highest concentration of nano-particles in water (2.5%). Furthermore, the two nanofluids showed higher heat transfer than the base fluid (water) although the nanofluid with particles size of 20 nm had the highest heat transfer coefficient.
Natrajan, V. K.; Christensen, K. T.
2011-08-01
The thermal-transport characteristics of transitional and turbulent flow through smooth- and rough-wall rectangular microchannels (Dh = 600 μm) under constant-heat-flux conditions at three of the four walls were investigated by performing non-intrusive and spatially resolved measurements of fluid temperature via two-color fluorescent thermometry. These measurements, along with bulk pressure-drop measurements, were performed over the Reynolds-number range 1300\\le {\\emph {Re}} \\le 5200. The pressure-drop results revealed the onset of transition above {\\emph {Re}_{cr}}\\cong 1800 for the smooth-wall case, consistent with the onset of transition at the macroscale. However, with increasing surface roughness, deviation from laminar behavior was noted at progressively lower Re which indicates that {\\emph {Re}_{cr}} is a function of roughness. Mean temperature profiles calculated from data sets acquired in the transitional regime for the smooth- and rough-wall cases illustrated deviation from fully developed laminar behavior for {\\emph {Re} \\gt \\emph {Re}_{cr}}. Nevertheless, these profiles still suggest similarities in the transitional pathway of the thermal-transport behavior for the smooth and rough cases save for a relative shift due to the onset of transition at lower Re with increasing surface roughness. Estimates of the bulk Nusselt number indicated enhancement in thermal transport over the smooth-wall case with increasing surface roughness in both the transitional and turbulent regimes, though the smooth-wall data agreed well with macroscale predictions over the range of turbulent Re considered. While the shift in the transitional pathway of the thermal transport behavior toward lower Re accounts for a portion of this enhancement, an increase in turbulent convection with increasing surface roughness might also contribute in this regard.
Directory of Open Access Journals (Sweden)
G.S. Seth
2014-06-01
Full Text Available An investigation of the effects of Hall current and rotation on unsteady hydromagnetic natural convection flow with heat and mass transfer of an electrically conducting, viscous, incompressible and optically thick radiating fluid past an impulsively moving vertical plate embedded in a fluid saturated porous medium, when temperature of the plate has a temporarily ramped profile, is carried out. Exact solution of the governing equations is obtained in closed form by Laplace transform technique. Exact solution is also obtained in case of unit Schmidt number. Expressions for skin friction due to primary and secondary flows and Nusselt number are derived for both ramped temperature and isothermal plates. Expression for Sherwood number is also derived. The numerical values of primary and secondary fluid velocities, fluid temperature and species concentration are displayed graphically whereas those of skin friction are presented in tabular form for various values of pertinent flow parameters.
Kiani, Hossein; Sun, Da-Wen; Zhang, Zhihang
2012-11-01
were the main cause of heating effect. The results showed that closer distances to the transducer surface showed higher cooling rates. On the other hand, despite having a bigger distance from the transducer, when the sphere was located close to the gas-liquid interface the enhancement factor of heat transfer was higher. Ultrasound irradiation showed promising effect for the enhancement of convective heat transfer rate during immersion cooling. More investigations are required to demonstrate the behavior of ultrasound assisted heat transfer and resolve the proper way of the application of ultrasound to assist the cooling and/or freezing processes. Copyright © 2012 Elsevier B.V. All rights reserved.
Numerical Simulation of Transient Free Convection Flow and Heat Transfer in a Porous Medium
Directory of Open Access Journals (Sweden)
Rajesh Sharma
2013-01-01
Full Text Available The coupled momentum and heat transfer in unsteady, incompressible flow along a semi-infinite vertical porous moving plate adjacent to an isotropic porous medium with viscous dissipation effect are investigated. The Darcy-Forchheimer nonlinear drag force model which includes the effects of inertia drag forces is employed. The governing differential equations of the problem are transformed into a system of nondimensional differential equations which are solved numerically by the finite element method (FEM. The non-dimensional velocity and temperature profiles are presented for the influence of Darcy number, Forchheimer number, Grashof number, Eckert number, Prandtl number, plate velocity, and time. The Nusselt number is also evaluated and compared with finite difference method (FDM, which shows excellent agreement.
Zhang, Yiqiang; Alexander, J. I. D.; Ouazzani, J.
1994-01-01
Free and moving boundary problems require the simultaneous solution of unknown field variables and the boundaries of the domains on which these variables are defined. There are many technologically important processes that lead to moving boundary problems associated with fluid surfaces and solid-fluid boundaries. These include crystal growth, metal alloy and glass solidification, melting and name propagation. The directional solidification of semi-conductor crystals by the Bridgman-Stockbarger method is a typical example of such a complex process. A numerical model of this growth method must solve the appropriate heat, mass and momentum transfer equations and determine the location of the melt-solid interface. In this work, a Chebyshev pseudospectra collocation method is adapted to the problem of directional solidification. Implementation involves a solution algorithm that combines domain decomposition, finite-difference preconditioned conjugate minimum residual method and a Picard type iterative scheme.
Bai, Bing; He, Yuanyuan; Hu, Shaobin; Li, Xiaochun
2017-07-01
The convective heat transfer coefficient (HTC) is a useful indicator that characterizes the convective heat transfer properties between flowing fluid and hot dry rock. An analytical method is developed to explore a more realistic formula for the HTC. First, a heat transfer model is described that can be used to determine the general expression of the HTC. As one of the novel elements, the new model can consider an arbitrary function of temperature distribution on the fracture wall along the direction of the rock radius. The resulting Dirichlet problem of the Laplace equation on a semi-disk is successfully solved with the Green's function method. Four specific formulas for the HTC are derived and compared by assuming the temperature distributions along the radius of the fracture wall to be zeroth-, first-, second-, and third-order polynomials. Comparative verification of the four specific formulas based on the test data shows that the formula A corresponding to the zeroth-order polynomial always predicts stable HTC values. At low flow rates, the four formulas predict similar values of HTC, but at higher flow rates, formulas B and D, respectively, corresponding to the first- and third-order polynomials, predict either too large or too small values of the HTC, while formula C, corresponding to the second-order polynomial, predicts relatively acceptable HTC values. However, we cannot tell which one is the more rational formula between formulas A and C due to the limited information measured. One of the clear advantages of formula C is that it can avoid the drawbacks of the discontinuity of temperature and the singular integral of HTC at the points (± R, 0). Further experimental work to measure the actual temperature distribution of water in the fracture will be of great value. It is also found that the absorbed heat of the fluid, Q, has a significant impact on the prediction results of the HTC. The temperatures at the inlet and the outlet used for Q should be
Li, Xin-Jun; Zhang, Jing-zhou; Tan, Xiao-ming
2017-09-01
Experimental tests are carried out to investigate the convective heat transfer performances on a flat surface around the vibration envelope of a vertically-oriented piezoelectric fan in the presence of cross flow. Distinct behaviors of convective heat transfer are illustrated under the present conditions of piezoelectric-fan excitation voltage ( U = 50, 150, 250 V) or characteristic velocity ( u PF = 0.83, 1.67, 2.34 m/s) fan tip-to-heated surface gap ( G = 3, 5, 7 mm) and cross flow velocity ( u CH = 0.94, 1.56 m/s). In addition, three-dimensional flow field simulations are conducted to illustrate the instantaneous flow fields around the vibrating fan. By comparing with the pure piezoelectric fan, the vortex induced by the vibrating fan is pushed downward by the cross flow and a series of vortices are displayed down the vibrating fan. It is confirmed that the presence of cross flow is contributive to the improvement of convective heat transfer in the rear zone downstream fan vibration envelope. The impingement role of streaming flow induced by piezoelectric fan is reduced by the presence of cross flow in the fan vibration envelope. On the other hand, the oscillating movement of the piezoelectric fan promotes the disturbance intensity of cross flow passing through the fan vibration envelope. These two aspects make the conjugated convective heat transfer in the vicinity of fan vibration envelope complicated. In general, the convective heat transfer in the vicinity of fan vibration envelope is mostly improved by the combined action of fan-excited steaming flow and cross flow in the situation where the piezoelectric fan is placed very close to the heated surface.
Cianfrini, C.; Corcione, M.; Habib, E.; Quintino, A.
2017-06-01
Natural convection in air-filled rectangular cavities inclined with respect to gravity, so that the heated wall is facing upwards, is studied numerically under the assumption of two-dimensional laminar flow. A computational code based on the SIMPLE-C algorithm is used for the solution of the system of the mass, momentum and energy transfer governing equations. Simulations are performed for height-to-width aspect ratios of the enclosure from 0.25 to 8, Rayleigh numbers based on the length of the heated and cooled walls from 102 to 107, and tilting angles of the enclosure from 0° to 75°. The existence of an optimal tilting angle is confirmed for any investigated configuration, at a location that increases as the Rayleigh number is decreased, and the height-to-width aspect ratio of the cavity are increased, unless the value of the Rayleigh number is that corresponding to the onset of convection or just higher. Dimensionless correlating equations are developed to predict the optimal tilting angle and the heat transfer performance of the enclosure.
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.
Heat transfer equipment design
Shah, R. K.; Subbarao, Eleswarapu Chinna; Mashelkar, R. A.
A comprehensive presentation is made of state-of-the-art configurations and design methodologies for heat transfer devices applicable to industrial processes, automotive systems, air conditioning/refrigeration, cryogenics, and petrochemicals refining. Attention is given to topics in heat exchanger mechanical design, single-phase convection processes, thermal design, two-phase exchanger thermal design, heat-transfer augmentation, and rheological effects. Computerized analysis and design methodologies are presented for the range of heat transfer systems, as well as advanced methods for optimization and performance projection.
Narahari, Marneni; Raju, S. Suresh Kumar; Nagarani, P.
2016-11-01
The unsteady MHD free convective boundary-layer flow along an impulsively started semi-infinite vertical plate with variable heat flux and mass transfer have been investigated numerically. The effects of chemical reaction, thermal radiation and Joule heating are incorporated in the governing equations. Crank-Nicolson finite-difference method is used to solve the governing coupled non-linear partial differential equations. The influence of thermal radiation, chemical reaction and Joule heating on flow characteristics are presented graphically and discussed in detailed. To validate the present numerical results, a comparison study has been performed with the previously published results and found that the results are in excellent agreement. It is found that the local Nusselt and Sherwood numbers decreases with the intensification of magnetic field and the local Sherwood number slightly decreases with the increase of radiation parameter.
Khurana, Deepak; Choudhary, Rajesh; Subudhi, Sudhakar
2017-01-01
Nanofluid is the colloidal suspension of nanosized solid particles like metals or metal oxides in some conventional fluids like water and ethylene glycol. Due to its unique characteristics of enhanced heat transfer compared to conventional fluid, it has attracted the attention of research community. The forced convection heat transfer of nanofluid is investigated by numerous researchers. This paper critically reviews the papers published on experimental studies of forced convection heat transfer and pressure drop of Al2O3, TiO2 and CuO based nanofluids dispersed in water, ethylene glycol and water-ethylene glycol mixture. Most of the researchers have shown a little rise in pressure drop with the use of nanofluids in plain tube. Literature has reported that the pumping power is appreciably high, only at very high particle concentration i.e. more than 5 %. As nanofluids are able to enhance the heat transfer at low particle concentrations so most of the researchers have used less than 3 % volume concentration in their studies. Almost no disagreement is observed on pressure drop results of different researchers. But there is not a common agreement in magnitude and mechanism of heat transfer enhancement. Few studies have shown an anomalous enhancement in heat transfer even at low particle concentration. On the contrary, some researchers have shown little heat transfer enhancement at the same particle concentration. A large variation (2-3 times) in Nusselt number was observed for few studies under similar conditions.
Variable viscosity effects on mixed convection heat and mass ...
African Journals Online (AJOL)
Variable viscosity effects on mixed convection heat and mass transfer along a ... PROMOTING ACCESS TO AFRICAN RESEARCH ... Keywords: Variable viscosity, Chemical Reaction, Viscous Dissipation, Finite difference method, Suction.
Directory of Open Access Journals (Sweden)
Nemat Dalir
2014-12-01
Full Text Available Entropy generation for the steady two-dimensional laminar forced convection flow and heat transfer of an incompressible Jeffrey non-Newtonian fluid over a linearly stretching, impermeable and isothermal sheet is numerically investigated. The governing differential equations of continuity, momentum and energy are transformed using suitable similarity transformations to two nonlinear coupled ordinary differential equations (ODEs. Then the ODEs are solved by applying the numerical implicit Keller’s box method. The effects of various parameters of the flow and heat transfer including Deborah number, ratio of relaxation to retardation times, Prandtl number, Eckert number, Reynolds number and Brinkman number on dimensionless velocity, temperature and entropy generation number profiles are analyzed. The results reveal that the entropy generation number increases with the increase of Deborah number while the increase of ratio of relaxation to retardation times causes the entropy generation number to reduce. A comparative study of the numerical results with the results from an exact solution for the dimensionless velocity gradient at the sheet surface is also performed. The comparison shows excellent agreement within 0.05% error.
Directory of Open Access Journals (Sweden)
Ahmad Reza Rahmati
2016-12-01
Full Text Available In this study, mixed convection heat transfer of water-Cu nanofluid in a double lid-driven cavity has been analyzed by lattice Boltzmann method. The double lid-driven are insulated and the side walls have sinusoidal temperature distribution. Simulations have been carried out at constant Grashof number 100, the Richardson numbers of 0.01, 0.1,1,10 and 100, temperature phase deviation of 0, π/4, π/2, 3π/4 and π, the solid volume fraction from zero to 0.06 and the Prandtl number of 6.57. The thermal modeling of passive scalar is applied and two separate distribution functions for the flow and temperature fields are considered. In order to calculate the thermal conductivity coefficient of nanofluid, constant and variable properties models are used. The results showed that in high Richardson numbers, the effect of the thermal phase deviation changes on the flow pattern is evident and in low Richardson numbers, the phase deviation changes do not affect the flow pattern. In all thermal phase deviations by reducing the Richardson number, the Nusselt number increases and thus the heat transfer increases. Also the average Nusselt number obtained for the constant properties model is higher compared with that of variable properties model.
Chen, Qing; Zhang, Xiaobing; Zhang, Junfeng
2013-09-01
In spite of the increasing applications of the lattice Boltzmann method (LBM) in simulating various flow and transport systems in recent years, complex boundary conditions for the convection-diffusion and heat transfer processes in LBM have not been well addressed. In this paper, we propose an improved bounce-back method by using the midpoint concentration value to modify the bounced-back density distribution for LBM simulations of the concentration field. An accurate finite-difference scheme in the normal boundary direction has also been introduced for gradient boundary conditions. Compared with existing boundary methods, our method has a simple algorithm and can easily deal with boundaries with general geometries, motions, and surface conditions (the Dirichlet, Neumann, and mixed conditions). Carefully designed simulations are performed to examine the capacity and accuracy of this proposed boundary method. Simulation results are compared with those from theory and a representative boundary method, and an improved performance is observed. We have also simulated the effect of reference velocity on global accuracy to examine the performance of our model in preserving the fundamental Galilean invariance. These boundary treatments for concentration boundary conditions can be readily applied to other processes such as heat transfer systems.
Chen, Qing; Zhang, Xiaobing; Zhang, Junfeng
2013-09-01
In spite of the increasing applications of the lattice Boltzmann method (LBM) in simulating various flow and transport systems in recent years, complex boundary conditions for the convection-diffusion and heat transfer processes in LBM have not been well addressed. In this paper, we propose an improved bounce-back method by using the midpoint concentration value to modify the bounced-back density distribution for LBM simulations of the concentration field. An accurate finite-difference scheme in the normal boundary direction has also been introduced for gradient boundary conditions. Compared with existing boundary methods, our method has a simple algorithm and can easily deal with boundaries with general geometries, motions, and surface conditions (the Dirichlet, Neumann, and mixed conditions). Carefully designed simulations are performed to examine the capacity and accuracy of this proposed boundary method. Simulation results are compared with those from theory and a representative boundary method, and an improved performance is observed. We have also simulated the effect of reference velocity on global accuracy to examine the performance of our model in preserving the fundamental Galilean invariance. These boundary treatments for concentration boundary conditions can be readily applied to other processes such as heat transfer systems.
Moufekkir, F.; Moussaoui, M. A.; Mezrhab, A.; Naji, H.; Lemonnier, D.
2012-09-01
This paper deals with the numerical solution for natural convection and volumetric radiation in an isotropic scattering medium within a heated square cavity using a hybrid thermal lattice Boltzmann method (HTLBM). The multiple relaxation time lattice Boltzmann method (MRT-LBM) has been coupled to the finite difference method (FDM) to solve momentum and energy equations, while the discrete ordinates method (DOM) has been adopted to solve the radiative transfer equation (RTE) using the S8 quadrature. Based on these approaches, the effects of various influencing parameters such as the Rayleigh number (Ra), the wall emissivity (ει), the Planck number (Pl), and the scattering albedo (ω), have been considered. The results presented in terms of isotherms, streamlines and averaged Nusselt number, show that in absence of radiation, the temperature and the flow fields are centro-symmetrics and the cavity core is thermally stratified. However, radiation causes an overall increase in the temperature and velocity gradients along both thermally active walls. The maximum heat transfer rate is obtained when the surfaces of the enclosure walls are regarded as blackbodies. It is also seen that the scattering medium can generate a multicellular flow.
Khan, Ilyas; Shah, Nehad Ali; Dennis, L. C. C.
2017-03-01
This scientific report investigates the heat transfer analysis in mixed convection flow of Maxwell fluid over an oscillating vertical plate with constant wall temperature. The problem is modelled in terms of coupled partial differential equations with initial and boundary conditions. Some suitable non-dimensional variables are introduced in order to transform the governing problem into dimensionless form. The resulting problem is solved via Laplace transform method and exact solutions for velocity, shear stress and temperature are obtained. These solutions are greatly influenced with the variation of embedded parameters which include the Prandtl number and Grashof number for various times. In the absence of free convection, the corresponding solutions representing the mechanical part of velocity reduced to the well known solutions in the literature. The total velocity is presented as a sum of both cosine and sine velocities. The unsteady velocity in each case is arranged in the form of transient and post transient parts. It is found that the post transient parts are independent of time. The solutions corresponding to Newtonian fluids are recovered as a special case and comparison between Newtonian fluid and Maxwell fluid is shown graphically.
Khan, Ilyas; Shah, Nehad Ali; Dennis, L. C. C.
2017-01-01
This scientific report investigates the heat transfer analysis in mixed convection flow of Maxwell fluid over an oscillating vertical plate with constant wall temperature. The problem is modelled in terms of coupled partial differential equations with initial and boundary conditions. Some suitable non-dimensional variables are introduced in order to transform the governing problem into dimensionless form. The resulting problem is solved via Laplace transform method and exact solutions for velocity, shear stress and temperature are obtained. These solutions are greatly influenced with the variation of embedded parameters which include the Prandtl number and Grashof number for various times. In the absence of free convection, the corresponding solutions representing the mechanical part of velocity reduced to the well known solutions in the literature. The total velocity is presented as a sum of both cosine and sine velocities. The unsteady velocity in each case is arranged in the form of transient and post transient parts. It is found that the post transient parts are independent of time. The solutions corresponding to Newtonian fluids are recovered as a special case and comparison between Newtonian fluid and Maxwell fluid is shown graphically. PMID:28294186
Oliveira, A Virgílio M; Gaspar, Adélio R; Francisco, Sara C; Quintela, Divo A
2012-03-01
The present experimental work is dedicated to the analysis of the effect of walking on the thermal insulation of the air layer (I (a)) and on the convective heat transfer coefficients (h (conv)) of the human body. Beyond the standing static posture, three step rates were considered: 20, 30 and 45 steps/min. This corresponds to walking speeds of approximately 0.23, 0.34 and 0.51 m/s, respectively. The experiments took place in a climate chamber with an articulated thermal manikin with 16 independent parts. The indoor environment was controlled through the inner wall temperatures since the objective of the tests was restricted to the influence of the walking movements under calm conditions. Five set points were selected: 10, 15, 20, 25 and 30°C, and the operative temperature within the test chamber varied between 11.9 and 29.6°C. The highest and lowest I ( a ) values obtained were equal to 0.87 and 0.71 clo, respectively, and the reduction in insulation due to walking ranged between 9.8 and 11.5%. The convective coefficients (h (conv)) for the whole body and for the different body segments were also determined for each step rate. In the case of the whole body, for the standing static reference posture, the mean value of h (conv) was equal to 3.3 W/m(2)°C and a correlation [Nu = Nu(Gr)] for natural convection is also presented in good agreement with previous results. For the other postures, the values of h (conv) were equal to 3.7, 3.9 and 4.2 W/m(2)°C, respectively for 20, 30 and 45 steps/min.
Directory of Open Access Journals (Sweden)
Sivaraja Subramania Pillai
2013-01-01
Full Text Available This study investigates the effect of flow velocity and building surface temperature effects on Convective Heat Transfer Coefficient (CHTC from urban building surfaces by numerical simulation. The thermal effects produced by geometrical and physical properties of urban areas generate a relatively differential heating and uncomfortable environment compared to rural regions called as Urban Heat Island (UHI phenomena. The urban thermal comfort is directly related to the CHTC from the urban canopy surfaces. This CHTC from urban canopy surfaces expected to depend upon the wind velocity flowing over the urban canopy surfaces, urban canopy configurations, building surface temperature etc. But the most influential parameter on CHTC has not been clarified yet. Urban canopy type experiments in thermally stratified wind tunnel have normally been used to study the heat transfer issues. But, it is not an easy task in wind tunnel experiments to evaluate local CHTC, which vary on individual canyon surfaces such as building roof, walls and ground. Numerical simulation validated by wind tunnel experiments can be an alternative for the prediction of CHTC from building surfaces in an urban area. In our study, wind tunnel experiments were conducted to validate the low-Reynolds-number k- ε model which was used for the evaluation of CHTC from surfaces. The calculated CFD results showed good agreement with experimental results. After this validation, the effects of flow velocity and building surface temperature effects on CHTC from urban building surfaces were investigated. It has been found that the change in velocity remarkably affects the CHTC from urban canopy surfaces and change in surface temperature has almost no effect over the CHTC from urban canopy surfaces.
Directory of Open Access Journals (Sweden)
Sivaraja Subramania Pillai
2013-06-01
Full Text Available This study investigates the effect of flow velocity and building surface temperature effects on Convective Heat Transfer Coefficient (CHTC from urban building surfaces by numerical simulation. The thermal effects produced by geometrical and physical properties of urban areas generate a relatively differential heating and uncomfortable environment compared to rural regions called as Urban Heat Island (UHI phenomena. The urban thermal comfort is directly related to the CHTC from the urban canopy surfaces. This CHTC from urban canopy surfaces expected to depend upon the wind velocity flowing over the urban canopy surfaces, urban canopy configurations, building surface temperature etc. But the most influential parameter on CHTC has not been clarified yet. Urban canopy type experiments in thermally stratified wind tunnel have normally been used to study the heat transfer issues. But, it is not an easy task in wind tunnel experiments to evaluate local CHTC, which vary on individual canyon surfaces such as building roof, walls and ground. Numerical simulation validated by wind tunnel experiments can be an alternative for the prediction of CHTC from building surfaces in an urban area. In our study, wind tunnel experiments were conducted to validate the low-Reynolds-number k-ε model which was used for the evaluation of CHTC from surfaces. The calculated CFD results showed good agreement with experimental results. After this validation, the effects of flow velocity and building surface temperature effects on CHTC from urban building surfaces were investigated. It has been found that the change in velocity remarkably affects the CHTC from urban canopy surfaces and change in surface temperature has almost no effect over the CHTC from urban canopy surfaces.
Institute of Scientific and Technical Information of China (English)
Zhang Ning; Li Guang-zheng; Huang Jian-chun
2003-01-01
The influence of buoyancy on vortex shedding from a heated square cylinder and its effects on the heat transfer of mixed convection were simulated.The flow equations, based on the velocity and the pressure, were solved along with the energy equation by a modified SIMPLER algorithm-the Quick Scheme and small Control Volume (QSCV) algorithm developed by the authors of the present paper.A set of optimized computational domain and artificial lateral boundary conditions were used along with the QSCV algorithm.Several cases were simulated for the Grashof numbers up to 1.8×105, the Reynolds numbers up to 500, and a range of angles between free stream velocity and gravity from 0 to 1.5π.In opposing flow, the results distinguish two different flow patterns: periodic flow for Gr＜Grc and steady flow with attached twin vortices for Gr＞Grc, and a precise correlation between Grc and Re expressed as Grc=0.00166(Re)2.97795 for Re up to 500 was firstly obtained.In cross flow, it could be seen that the Ri=Gr/Re2 plays a great role in the wake vortex patterns and the temperature fields.In aiding flow, it is found that the main flow currents cause a large expansion of the streamlines and isotherms in the direction normal to the free stream velocity.These changes in the wake vortex patterns and the temperature fields greatly modify the heat flux along the surface of the square cylinder and consequently, the heat transfer rate is strongly dependent upon the Reynolds numbers, the Grashof numbers, and the gravity direction.
Siroux, Monica; Harmand, Souad; Desmet, Bernard
2002-07-01
We present an experimental identification of the local and mean Nusselt number from a rotating TGV brake disk model in the actual environment and exposed to an air flow parallel to the disk surface. This method is based on the use of a heated thermally thick disk combined with the technique of temperature measurement by infrared thermography. The local and mean convective heat transfer coefficient from the disk surface is identified by solving the steady state heat equation by a finite difference method using the experimental temperature distribution as boundary conditions. The experimental setup is constituted of a model disk with all the representative parts of the actual TGV brake system. The disk and its actual environment are inside a wind tunnel test section, so that the rotational disk speed and the air flow velocity can be varied. Tests were carried out for rotational speeds w between 325 and 2000 rpm (rotational Reynolds number Re between 88,500 and 545,000), and for an air flow velocity U ranging between 0 and 12 m(DOT)s-1 (air flow Reynolds number Re0 between 0 and 153,000).
Energy Technology Data Exchange (ETDEWEB)
Arenas, A.; Madrid, C.N.; Herranz, A. (Universidad Politecnica de Madrid (Spain). Escuela de Ingenieria Tecnica Industrial)
1989-01-01
We solve by Dimensional Analysis the problem of heat transfer by free convection in vertical and horizontal cylinders using the amplified dimensional base proposed by us for this class of phenomena. We obtain more precise solutions than those given by the classical Dimensional Analysis and are in accord with the empirical results obtained by various authors. (Author)
Heat Transfer and Flows of Thermal Convection in a Fluid-Saturated Rotating Porous Medium
Directory of Open Access Journals (Sweden)
Jianhong Kang
2015-01-01
Full Text Available Thermal convection at the steady state for high Rayleigh number in a rotating porous half space is investigated. Taking into account the effect of rotation, Darcy equation is extended to incorporate the Coriolis force term in a rotating reference frame. The velocity and temperature fields of thermal convection are obtained by using the homotopy analysis method. The influences of Taylor number and Rayleigh number on the Nusselt number, velocity profile, and temperature distribution are discussed in detail. It is found that the Nusselt number decreases rapidly with the increase of Taylor number but tends to have an asymptotic value. Besides, the rotation can give rise to downward flow in contrast with the upward thermal convection.
V, Sudarev A.; V, Sudarev B.; A, Suryaninov A.
2012-05-01
The introduction of new structural materials and technologies contributes to the efficiency increase for the compact IPMs used in various branches of engineering. Use of a driving high-temperature (TIT600K), regenerative (the regeneration ratio is E>85%) micro gas turbine engine μGTE, major components which are made of structural ceramics, allows not only to maintain the effective efficiency at ηe=26-30%, but, also, sharply reduce the material consumption rate for the micro source as a whole. Application of the laser prototyping technique to manufacture the air heater, which is a part of μGTE, increases the IPM compactness. Miniaturization of the air heater, manufactured by the structural ceramics laser fusion, can significantly reduce the hydraulic diameter (dh<=1.0 mm) of the channels, designed to transport the working media inside it. Reducing dh leads to a significant increase in the hydraulic resistance of the micro channels. The associated increase in the energy consumption for μGTE's own needs is compensated by increasing the TIT, E, and heat transfer coefficients in micro channels, and by eliminating the need in cooling for high temperature IPM components.
Adiabatic partition effect on natural convection heat transfer inside a square cavity
DEFF Research Database (Denmark)
Mahmoudinezhad, S.; Rezania, A.; Yousefi, T.
2017-01-01
. 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...
Beukema, K.J.
1980-01-01
Three different models of bulk-stored agricultural products with air flow through the bulk, predicting the temperature profiles or the velocity of natural convection, are developed. The temperature distribution in a cylindrical container with insulated walls and open top and bottom, filled
Heat transfer and large scale dynamics in turbulent Rayleigh-Bénard convection
Ahlers, Guenter; Grossmann, Siegfried; Lohse, Detlef
2009-01-01
The progress in our understanding of several aspects of turbulent Rayleigh-Bénard convection is reviewed. The focus is on the question of how the Nusselt number and the Reynolds number depend on the Rayleigh number Ra and the Prandtl number Pr, and on how the thicknesses of the thermal and the kinet
Yano, T.; Nishino, K.; Ueno, I.; Matsumoto, S.; Kamotani, Y.
2017-04-01
This paper reports the sensitivity of hydrothermal wave (HTW) instability of Marangoni convection to the interfacial heat transfer in liquid bridges (LBs) of high Prandtl number fluids (Pr = 67, 112, and 207) formed under the microgravity environment on the International Space Station. The data for instability are collected for a wide range of AR and for TC = 15 and 20 °C, where AR is the aspect ratio (=height/diameter) of the LB and TC is the cooled disk temperature. A significant decrease in critical oscillation frequency as well as an appreciable decrease in the critical Marangoni number is observed for AR > 1.25. This drastic change of instability mechanisms is associated with the reversal of axial traveling direction of HTWs and roll-structures as reported previously. It is found that this reversal is closely related to the interfacial heat transfer, which is evaluated numerically through accounting for both convective and radiative components. A heat transfer ratio, QI/QH, is introduced as a dimensionless parameter for interfacial heat transfer, where QI and QH are the heat transfer rates at the LB-gas and LB-heated disk interfaces, respectively. It is found that HTWs travel in the same direction as the surface flow for QI/QH > 0 (heat-loss condition) while in the opposite direction for QI/QH alters slightly but appreciably the basic temperature and flow field, the alteration that is not accounted for in the previous linear stability analyses for an infinite LB.
Zannouni, K.; El Abrach, H.; Dhahri, H.; Mhimid, A.
2016-12-01
The present paper reports a numerical study to investigate the drying of rectangular gypsum sample based on a diffusive model. Both vertical and low sides of the porous media are treated as adiabatic and impermeable surfaces plate. The upper face of the plate represents the permeable interface. The energy equation model is based on the local thermal equilibrium assumption between the fluid and the solid phases. The lattice Boltzmann method (LBM) is used for solving the governing differential equations system. The obtained numerical results concerning the moisture content and the temperature within a gypsum sample were discussed. A comprehensive analysis of the influence of the mass transfer coefficient, the convective heat transfer coefficient, the external temperature, the relative humidity and the diffusion coefficient on macroscopic fields are also investigated. They all presented results in this paper and obtained in the stable regime correspond to time superior than 4000 s. Therefore the numerical error is inferior to 2%. The experimental data and the descriptive information of the approach indicate an excellent agreement between the results of our developed numerical code based on the LBM and the published ones.
Zannouni, K.; El Abrach, H.; Dhahri, H.; Mhimid, A.
2017-06-01
The present paper reports a numerical study to investigate the drying of rectangular gypsum sample based on a diffusive model. Both vertical and low sides of the porous media are treated as adiabatic and impermeable surfaces plate. The upper face of the plate represents the permeable interface. The energy equation model is based on the local thermal equilibrium assumption between the fluid and the solid phases. The lattice Boltzmann method (LBM) is used for solving the governing differential equations system. The obtained numerical results concerning the moisture content and the temperature within a gypsum sample were discussed. A comprehensive analysis of the influence of the mass transfer coefficient, the convective heat transfer coefficient, the external temperature, the relative humidity and the diffusion coefficient on macroscopic fields are also investigated. They all presented results in this paper and obtained in the stable regime correspond to time superior than 4000 s. Therefore the numerical error is inferior to 2%. The experimental data and the descriptive information of the approach indicate an excellent agreement between the results of our developed numerical code based on the LBM and the published ones.
Arabi, Pouria; Jafarpur, Khosrow
2016-08-01
In the present study, effect of different flow regimes on free convection heat transfer has been examined. In the light of this, a novel analytical method is developed to calculate free convection heat transfer from isothermal convex bodies with arbitrary shape over all range of Rayleigh number in fluids with any Prandtl number. The crux of this method is based on the concept of dynamic behaviors existing in natural convection flow. In the previous models the Body Gravity Function (BGF) and Turbulent Function (TF) have been taken as constant values. In this study, BGF accounts for the effect of body shape and orientation with respect to gravity vector in laminar free convection. Besides, TF accounts for the impact of Prandtl number, body shape and orientation with regard to gravity vector in turbulent free convection. By contrast, it is shown that these two parameters undergo a change through the variation of Rayleigh number and cannot be considered as a constant. These two parameters are modeled based upon the thermal resistance concept. Moreover, two transition criteria happening in free convection heat transfer will be obtained according to this new analytical method (conduction-laminar and laminar-turbulent transitions). Finally, three models (models 1, 2 and 3) are proposed for calculation free convection heat transfer and present results for ten isothermal convex bodies with various aspect ratios (0.298 ≤ √ A /P ≤ 2.470) have been compared with the available experimental and numerical data. Here, the results of model 2 are almost equal to those of model 3. Also, the results of model 1 are more precise than those of model 3 while the parameters computation of model 1 is more intricate in comparison with model 3. On the one hand, the model 1 has an average difference <6 % vis-à-vis numerical data in entire range of Rayleigh number (laminar and turbulent). On the other hand, the average difference of model 1 is not more than 8 % versus experimental data
Heat and mass transfer analysis of convective drying of chickpea (Cicer arietinum)
López, R.; Vaca, M.; Terres, H.; Lizardi, A.; Morales, J.; Flores, J.; Chávez, S.
2015-01-01
The objective of this article is to describe the modelling and simulation of the dehydration of chickpea in a complex drying system process, using COMSOL Multiphysics Program. A model, based on mass and energy balances, was developed for the simulation of unsteady convective drying with air (3.0 m/s and 60 °C). The program predicted an 8 hours-dehydration time, with an effective moisture diffusivity of 3.1 *10- 10 which was experimentally obtained. The empirical model that best represented the process was the exponential one.
Free Convection in Heat Transfer Flow over a Moving Sheet in Alumina Water Nanofluid
Directory of Open Access Journals (Sweden)
Padam Singh
2014-01-01
Full Text Available The present paper deals with study of free convection in two-dimensional magnetohydrodynamic (MHD boundary layer flow of an incompressible, viscous, electrically conducting, and steady nanofluid. The governing equations representing fluid flow are transformed into a set of simultaneous ordinary differential equations by using appropriate similarity transformation. The equations thus obtained have been solved numerically using adaptive Runge-Kutta method with shooting technique. The effects of physical parameters like magnetic parameter, temperature buoyancy parameter on relative velocity and temperature distribution profile, shear stress profile, and temperature gradient profile were depicted graphically and analyzed. Significant changes were observed due to these parameters in velocity and temperature profiles.
Energy Technology Data Exchange (ETDEWEB)
Noghrehabadi, Aminreza; Pourrajab, Rashid [Shahid Chamran University of Ahvaz, Ahvaz (Iran, Islamic Republic of)
2016-02-15
The effect of nanofluids on heat transfer inside circular tubes under uniform constant heat flux boundary condition was investigated. The working nanofluid was a suspension of γ-Al{sub 2}O{sub 3} nanoparticles of average diameter 20 nm. The heat transfer coefficients were calculated experimentally in the range of 1057 < Re < 2070 with different particle volume concentrations of 0.1%, 0.3% and 0.9%. Increasing the particle volume fraction led to enhancement of the convective heat transfer coefficient. The results show that the average heat transfer coefficient increased 16.8% at 0.9% volume concentration and Reynolds number of 2070 compared with distilled water. In addition, the enhancement of the convective heat transfer was particularly significant in the entrance region and decreased with axial distance. Finally, an empirical correlation for Nusselt number has been proposed for the present range of nanofluids. The mean deviation between the predicted Nusselt number and experimental values for the new correlation is 3.57%.
Institute of Scientific and Technical Information of China (English)
H.Sun; C.F.Ma; 等
1997-01-01
Using seven working fluids,a systematic experimental study was performed to investigate the local convective heat transfer from vertical heaters to impinging circular submerged jets in the range of Reynolds number between 1.17×102 and 3.69×104 with the emphasis placed on the examination of Prandtl number dependence.Heat transfer coefficients at the stagnation point were collected and correlated with the plate held within and beyond the potential core.Radial distribution of the local heat transfer coefficient was measured with five test liquids.Based on the measured profiles of the local heat transfer,a correlation was developed to cover the entire range of the adial distance.Basides the present data,the correlations developed in this work were also compared with a large quantity of available data of circular air jets.General agreement was observed between the air data and the correlations.
Hal E. Anderson
1969-01-01
Experimental testing of a mathematical model showed that radiant heat transfer accounted for no more than 40% of total heat flux required to maintain rate of spread. A reasonable prediction of spread was possible by assuming a horizontal convective heat transfer coefficient when certain fuel and flame characteristics were known. Fuel particle size had a linear relation...
Institute of Scientific and Technical Information of China (English)
赵振兴; 杨震; 刘宏; 常勇强; 曹子栋
2011-01-01
对煤粉加压气化炉对流段的不同换热结构进行了换热特性的实验研究,其中换热结构包括膜式螺旋管环形通道换热器和膜式蛇形管平行通道换热器,实验气体为单质气体N、He及其混合气,实验压力为0.5～3.5 MPa.为此,针对不同冲刷形式、不同气体和压力提出了换热器换热系数及其扩展的计算方法,同时给出了典型冲刷形式的对流换热的关联式和适用条件.实验研究表明:冲刷形式对换热系数有很大影响,单通道和多通道换热系数与换热面积之间呈加权平均的关系;在相同换热条件下,膜式螺旋管环形通道换热器的换热系数高于膜式蛇形管平行通道换热器.%An experiment was conducted to study the heat transfer characteristics for a convection cooling section with the different heat transfer structures at high temperature and pressure in a coal pressurized gasifier. The heat transfer structures included an annular channel heat exchanger with membrane spiral tubes and a parallel channel heat exchanger with membrane serpentine tubes. In this study, the high pressure single gas (He or N2) and mixture gas (He+N2) were used to replace the high pressure syngas, and the test pressure for each gas was from 0.5 MPa to 3MPa. The heat transfer coefficients and extension method under different working pressure, gas composition and flow forms were presented. The correlations of the typical flow forms and their applicable condition were obtained. The results show that flow form greatly influenced the heat transfer coefficient of the high pressure gas convection. The heat transfer coefficients of the single annular channel heat exchanger and multi-annular channel heat exchanger displayed the areaweighted average relation. In addition, the heat transfer capacity of the annular channel heat exchanger with membrane spiral tubes was higher than that of the parallel channel under the same heat transfer conditions.
Kuhn, S.; Kenjeres, S.; Von Rohr, P.R.
2009-01-01
In this numerical study the mixed convective flow of water over a heated wavy surface over a range of Reynolds and Richardson numbers, including transitional and turbulent flow regimes (20 ≤ Re ≤ 2000 and 0.5 ≤ Ri ≤ 5000) is investigated. A dynamic Large Eddy Simulation (LES) approach is applied whe
da Silva, Wilton Pereira; E Silva, Cleide M D P S
2014-09-01
Cooling of fruits and vegetables, immediately after the harvest, has been a widely used method for maximizing post-harvest life. In this paper, an optimization algorithm and a numerical solution are used to determine simultaneously the convective heat transfer coefficient, hH, and the thermal diffusivity, α, for an individual solid with cylindrical shape, using experimental data obtained during its cooling. To this end, the one-dimensional diffusion equation in cylindrical coordinates is discretized and numerically solved through the finite volume method, with a fully implicit formulation. This solution is coupled to an optimizer based on the inverse method, in which the chi-square referring to the fit of the numerical simulation to the experimental data is used as objective function. The optimizer coupled to the numerical solution was applied to experimental data relative to the cooling of a cucumber. The obtained results for α and hH were coherent with the values available in the literature. With the results obtained in the optimization process, the cooling kinetics of cucumbers was described in details.
Lienhard, John H
2011-01-01
This introduction to heat transfer offers advanced undergraduate and graduate engineering students a solid foundation in the subjects of conduction, convection, radiation, and phase-change, in addition to the related topic of mass transfer. A staple of engineering courses around the world for more than three decades, it has been revised and updated regularly by the authors, a pair of recognized experts in the field. The text addresses the implications, limitations, and meanings of many aspects of heat transfer, connecting the subject to its real-world applications and developing students' ins
Institute of Scientific and Technical Information of China (English)
Xiaoyan Sheng; Liancun Zheng; Xinxin Zhang
2008-01-01
A similarity analysis for Marangoni convection induced flow over a vapor-liquid interface due to an imposed temperature gradient was carried out. The analysis assumes that the surface tension varies linearly with temperature but the temperature variation is a power law function of the location. The similarity solutions are presented numerically and the associated transfer characteristics are discussed.
Dhanai, Ruchika; Rana, Puneet; Kumar, Lokendra
2016-05-01
The motivation behind the present analysis is to focus on magneto-hydrodynamic flow and heat transfer characteristics of non-Newtonian fluid (Sisko fluid) past a permeable nonlinear shrinking sheet utilizing nanoparticles involving convective boundary condition. The non-homogenous nanofluid transport model considering the effect of Brownian motion, thermophoresis, suction/injection and no nanoparticle flux at the sheet with convective boundary condition has been solved numerically by the RKF45 method with shooting technique. Critical points for various pertinent parameters are evaluated in this study. The dual solutions (both first and second solutions) are captured in certain range of material constant (ncthermophoresis parameter.
Preliminary Evaluation of Convective Heat Transfer in a Water Shield for a Surface Power Reactor
Pearson J. Boise; Reid, Robert S.
2007-01-01
As part of the Vision for Space Exploration, the end of the next decade will bring man back to the surface of the moon. A crucial issue for the establishment of human presence on the moon will be the availability of compact power sources. This presence could require greater than 10's of kWt's in follow on years. Nuclear reactors are well suited to meet the needs for power generation on the lunar or Martian surface. Radiation shielding is a key component of any surface power reactor system. Several competing concepts exist for lightweight, safe, robust shielding systems such as a water shield, lithium hydride (LiH), and boron carbide. Water offers several potential advantages, including reduced cost, reduced technical risk, and reduced mass. Water has not typically been considered for space reactor applications because of the need for gravity to fix the location of any vapor that could form radiation streaming paths. The water shield concept relies on the predictions of passive circulation of the shield water by natural convection to adequately cool the shield. This prediction needs to be experimentally evaluated, especially for shields with complex geometries. NASA Marshall Space Flight Center has developed the experience and facilities necessary to do this evaluation in its Early Flight Fission - Test Facility (EFF-TF).
Holman, J P
2010-01-01
As one of the most popular heat transfer texts, Jack Holman's "Heat Transfer" is noted for its clarity, accessible approach, and inclusion of many examples and problem sets. The new tenth edition retains the straight-forward, to-the-point writing style while covering both analytical and empirical approaches to the subject. Throughout the book, emphasis is placed on physical understanding while, at the same time, relying on meaningful experimental data in those situations that do not permit a simple analytical solution. New examples and templates provide students with updated resources for computer-numerical solutions.
Energy Technology Data Exchange (ETDEWEB)
Eter, Ahmad, E-mail: eng.eter@yahoo.com; Groeneveld, Dé, E-mail: degroeneveld@gmail.com; Tavoularis, Stavros, E-mail: stavros.tavoularis@uottawa.ca
2017-03-15
Highlights: • Measurements of supercritical heat transfer in tubes equipped with obstacles were obtained and compared with results in base tubes. • In general, flow obstacles improve supercritical heat transfer, but under certain conditions have a negative effect on it. • New correlations describing obstacle-enhanced supercritical heat transfer in the liquid-like and gas-like regimes are fitted to the data. - Abstract: Heat transfer measurements to CO{sub 2}-cooled tubes with and without flow obstacles at supercritical pressures were obtained at the University of Ottawa’s supercritical pressure test facility. The effects of obstacle geometry (obstacle pitch, obstacle shape, flow blockage) on the wall temperature and heat transfer coefficient were investigated. Tests were performed for vertical upward flow in a directly heated 8 mm ID tube for a pressure range from 7.69 to 8.36 MPa, a mass flux range from 200 to 1184 kg/m{sup 2} s, and a heat flux range from 1 to 175 kW/m{sup 2}. The results are presented graphically in plots of wall temperature and heat transfer coefficient vs. bulk specific enthalpy of the fluid. The effects of flow parameters and flow obstacle geometry on supercritical heat transfer for both normal and deteriorated heat transfer are discussed. A comparison of the measurements with leading prediction methods for supercritical heat transfer in bare tubes and for spacer effects is also presented. The optimum increase in heat transfer coefficient was found to be for blunt obstacles, having a large flow blockage, and a short obstacle pitch.
Directory of Open Access Journals (Sweden)
Sundus Hussein Abd
2012-01-01
Full Text Available In this research, an experimental study was conducted to high light the impact of the exterior shape of a cylindrical body on the forced and free convection heat transfer coefficients when the body is hold in the entrance of an air duct. The impact of changing the body location within the air duct and the air speed are also demonstrated. The cylinders were manufactured with circular, triangular and square sections of copper for its high thermal conductivity with appropriate dimensions, while maintaining the surface area of all shapes to be the same. Each cylinder was heated to a certain temperature and put inside the duct at certain locations. The temperature of the cylinder was then monitored. The heat transfer coefficient were then calculated for forced convection for several Reynolds number (4555-18222.The study covered free convection impact for values of Rayleigh number ranging between (1069-3321. Imperical relationships were obtained for all cases of forced and free convection and compared with equations of circular cylindrical shapes found in literature. These imperical equations were found to be in good comparison with that of other sources.
Scaling for Mixed Convection Heat Transfer in Passive Containments and Experiment Design
Energy Technology Data Exchange (ETDEWEB)
Wang, Shengfei; Yu, Yu; Lv, Xuefeng; Niu, Fenglei [State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources/North China Electric Power Univ., Beijing (China); Yan, Xiuping [Nuclear and Radiation Safety Center, Beijing (China)
2012-03-15
Most of the advanced nuclear reactor design utilizes passive systems to remove heat from the core by natural circulation. The passive systems will be widely used in generation III pressurized water reactor. One of the typical passive systems is passive containment cooling system (PCCS), which is a passive condenser system designed to remove heat from the containment for long term cooling after a postulated reactor accident. In order to establish empirical correlations and develop simulation models, a scaling analysis is performed in designing an experiment for the prototype PCCS. This paper presents a scaling method and the design of the experimental facility. The key dimensionless parameters governing the dominant processes are given at last.
Han, Samuel S.; Schafer, Charles F.
1988-01-01
A numerical analysis of transient heat and solute transport across a rectangular cavity with combined horizontal temperature and concentration gradients is performed by a numerical method based on the SIMPLE. Numerical results show that the average Nusselt and Sherwood numbers both decrease markedly when the solutal and thermal buoyancy forces act in the opposite directions. When the solutal and thermal buoyancy forces act in the same directions, however, the average Sherwood number increases significantly and yet the average Nusselt number decreases slightly.
2014-09-01
the test section, a metal sleeve was placed around the entire ceramic transition as seen at the bottom left of Fig. 3.4. Despite the structural...Wade, W. R. Measurements of Total Hemispherical Emissivity of Several Stably Oxidized Metals and Some Refractory Oxide Coatings. Technical report...materials. Ceramics are capable of withstanding the high Taw condition but crack after repeated heating and cooling cycles. Thus, ceramics not viable in
Nero-fuzzy modeling of the convection heat transfer coefficient for the nanofluid
Salehi, H.; Zeinali-Heris, S.; Esfandyari, M.; Koolivand, M.
2013-04-01
In this study, experiments were performed by six different volume fractions of Al2O3 nanoparticles in distilled water. Then, actual nanofluid Nusslet number compared by Adaptive neuro fuzzy inference system (ANFIS) predicted number in square cross-section duct in laminar flow under uniform heat flux condition. Statistical values, which quantify the degree of agreement between experimental observations and numerically calculated values, were found greater than 0.99 for all cases.
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.
Brouwers, Jos
1994-01-01
The present paper addresses heat and mass transfer between a permeable wall and a fluid-saturated porous medium. To assess the effect of wall suction or injection on sensible heat transfer, a stagnant film model is developed. The model yields a thermal correction factor accounting for the effect of
Mohseni, Kamran; Young, Patrick
2007-11-01
This presentation presents theoretical and numerical results describing digitized heat transfer (DHT), an active thermal management technique for high-power electronics and integrated micro systems. In digitized heat transfer discrete droplets are employed. The internal flow inside a discrete droplet is dominated by internal circulation imposed by the boundaries. This internal circulation imposes a new timescale for recirculating cold liquid from the middle of the droplet to the boundary. This internal circulation produces periodic oscillation in the overall convective heat transfer rate. Numerical simulations are presented for heat transfer in the droplet for both constant temperature and flux boundary conditions. The effectiveness of DHT for managing both localized temperature spikes and steady state cooling is demonstrated, identifying key parameters for optimization of the DHT method.
Calculation of convective heat transfer on highly blunt bodies at flow incidence
Li, C. P.
1989-01-01
An implicit finite-difference code is used to study three-dimensional viscous heat-conducting flows over the forebody of hypersonic vehicles. In the method, adaptive grids are generated to the shock and body contour, and local flow gradients and total enthalpy are used to control numerical dissipation. Typical axisymmetric configurations of a sphere, ellipsoid, and flat-face disk are considered, along with the cases of a blunt 70-deg cone at 0 and 20 deg flow incidences and an asymmetric 60-deg cone raked off at a 73-deg angle.
Shigechi, Tooru; Ito, Takehiro; Nishikawa, Kaneyasu
1983-01-01
Forced convection film boiling heat transfer from a horizontal cylinder to a subcooled liquid cross-flowing upward is analysed based on the two-phase boundary-layer theory. Numerical solution of the conservation equations is determined for subcooled water, ethanol and hexane under the atmospheric pressure by the method similar to that of the first report for saturated liquid. The velocity profile, the separation point in the vapor film, the thickness of the boundary-layer and the average Nuss...
Calonne, N.; Geindreau, C.; Flin, F.
2015-12-01
At the microscopic scale, i.e., pore scale, dry snow metamorphism is mainly driven by the heat and water vapor transfer and the sublimation-deposition process at the ice-air interface. Up to now, the description of these phenomena at the macroscopic scale, i.e., snow layer scale, in the snowpack models has been proposed in a phenomenological way. Here we used an upscaling method, namely, the homogenization of multiple-scale expansions, to derive theoretically the macroscopic equivalent modeling of heat and vapor transfer through a snow layer from the physics at the pore scale. The physical phenomena under consideration are steady state air flow, heat transfer by conduction and convection, water vapor transfer by diffusion and convection, and phase change (sublimation and deposition). We derived three different macroscopic models depending on the intensity of the air flow considered at the pore scale, i.e., on the order of magnitude of the pore Reynolds number and the Péclet numbers: (A) pure diffusion, (B) diffusion and moderate convection (Darcy's law), and (C) strong convection (nonlinear flow). The formulation of the models includes the exact expression of the macroscopic properties (effective thermal conductivity, effective vapor diffusion coefficient, and intrinsic permeability) and of the macroscopic source terms of heat and vapor arising from the phase change at the pore scale. Such definitions can be used to compute macroscopic snow properties from 3-D descriptions of snow microstructures. Finally, we illustrated the precision and the robustness of the proposed macroscopic models through 2-D numerical simulations.