Begell House Inc.
Heat Transfer Research
HTR
1064-2285
46
11
2015
NUMERICAL ANALYSIS OF HEAT EXCHANGE IN A POROUS CHANNEL WITH HEAT GENERATION AND LOCAL THERMAL NONEQUILIBRIUM
969-994
Azzedine
Abdedou
Departement du Genie Mecanique, Faculte de Genie de Construction, Universite Mouloud Mammeri De Tizi Ouzou, Algerie; USTHB, Faculty of Mechanical and Process Engineering (FGMGP), Laboratory of Multiphase Transport and Porous Media (LTPMP), Algeria
Khedidja
Bouhadef
USTHB, Faculty of Mechanical and Process Engineering (FGMGP), Laboratory of Multiphase Transport and Porous Media (LTPMP), Algeria
Frederic
Topin
Polytech Marseille, Laboratoire IUSTI, UMR CNRS 7343, Technopole de Chateau Gombert, 5 rue Enrico Fermi, 13453 Marseille Cedex 13, France
We numerically investigate forced convection heat transfer with heat generation and local thermal non-equilibrium in a porous channel bounded by parallel plates. Macroscopic continuity, momentum, and energy equations are presented and solved. Local thermal nonequilibrium is considered by means of independent equations for the solid matrix and the working fluid. The used numerical methodology is based on the control-volume approach. The effects of heat generation rate, thermal conductivity ratio, and Biot interstitial number on the local thermal equilibrium are presented. The main results obtained particularly show that lower values of the temperature difference (local thermal equilibrium) between the solid and the fluid phases are obtained at low values of conductivity ratio and high values of Biot number, while large local temperature differences (local thermal nonequilibrium) are obtained for low Biot numbers values and high thermal conductivity ratios. Moreover, increasing heat generation rate generally leads to thermal nonequilibrium accentuation, particularly and most significantly for low Biot number values.
SIMULATION STUDIES OF MULTIMODE HEAT TRANSFER FROM A DISCRETELY HEATED VERTICAL CHANNEL
995-1017
Shrikant
Londhe
Department of Mechanical Engineering, National Institute of Technology, Warangal - 506004 (A. P) India
C. Gururaja
Rao
Department of Mechanical Engineering, National Institute of Technology, Warangal - 506004 (A. P) India
Findings of certain parametric studies made on conjugate mixed convection with surface radiation from a discretely heated vertical channel are reported here. The vertical channel has three identical discrete heat sources flush-mounted in its left wall, with the right wall serving the purpose of a heat sink. The channel is considered to be of fixed height, with its width varied by altering the aspect ratio that is defined as the ratio of the height to the width of the channel. The cooling medium is air and the heat generated in the heat sources is dissipated by a combination of mixed convection and radiation after its percolation through the channel wall. The fluid flow and heat transfer equations are considered without making the conventional boundary layer approximations and are solved using the finite volume method coupled with stream function−vorticity formulation. A computer code is prepared to solve the problem. The influence of parameters like the modified Richardson number, surface emissivity, thermal conductivity, and aspect ratio on pertinent results has been analyzed. The exclusive effect of radiation has been explored and the roles taken up by mixed convection and radiation in channel heat dissipation are investigated. The studies elucidate the prominence radiation assumes in the present kind of problems in different regimes of mixed convection.
CONJUGATE HEAT TRANSFER WITH VARIABLE FLUID PROPERTIES IN A HEATED HORIZONTAL ANNULUS
1019-1038
Sofiane
Touahri
Energetic Physic Laboratory, Department of Physic, Faculty of Sciences, Mentouri University of Constantine, Algeria
Toufik
Boufendi
Energetic Physic Laboratory, Department of Physic, Faculty of Sciences, Mentouri University of Constantine, Algeria
In the present work, we numerically study the three-dimensional conjugate heat transfer in an annular space between two horizontal concentric cylinders; the outer cylinder is subjected to an internal energy generated by the Joule effect through its thickness while the inner is adiabatic. The thermal convection in the fluid domain is conjugated to the thermal conduction in the solid. The physical properties of the fluid are thermally dependent. The heat losses from the external outside pipe surface to the surrounding medium are considered. The model equations of continuity, momentum, and energy are solved numerically by a finite volume method with a second-order spatial-temporal discretization. The results obtained 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 forced convection when the Grashof number is increased. At the solid−fluid interface, the results clearly show the azimuthal and axial variations of the local heat flux and the local Nusselt numbers. Following these results, we have tried to model the average Nusselt number as a function of the Richardson number. With the parameters used, the heat transfer is quantified by the following correlation: NuA= 9.9130 Ri0.0816.
AN ASSESSMENT OF TURBULENCE MODELS FOR PREDICTING CONJUGATE HEAT TRANSFER FOR A TUBINE VANE WITH INTERNAL COOLING CHANNELS
1039-1064
Shaofei
Zheng
Institute of Thermal Engineering, TU Bergakademie Freiberg, Gustav-Zeuner-Str. 7, 09599 Freiberg,
Germany
Yidan
Song
Engineering Simulation and Aerospace Computing (ESAC), Northwestern Polytechnical University, P.O. Box 552, 710072, Xi'an, Shaanxi, China
Gongnan
Xie
Department of Mechanical and Power Engineering, Northwestern Polytechnical University, Xi'an, 710072, Shaanxi, China
Bengt
Sunden
Division of Heat Transfer, Department of Energy Sciences, Lund University, P.O. Box 118,
SE-22100, Lund, Sweden
In this study, five models, including the standard k−ε (SKE), realizable k−ε (RKE), SST k−ω, transition k−kl−ω, and the v2f model, are considered to simulate air flow and heat transfer of a turbine guide vane. The object in this paper is the well-studied NASA C3X turbine vane, for which experimental data are available. Ten internal cylindrical cooling channels are used to cool the blade. Three-dimensional temperature distributions of the turbine vane were obtained by a fluid−solid conjugated model including the external aerodynamic flow, internal convection and heat conduction region within the metal vane. In order to validate the computational results, the temperature distributions, static pressure distributions, and heat transfer coefficient distributions along the vane external mid-span surface are compared with experimental data. The 4-5-2-1 arrangement of the C3X cascade is selected, and the fluid is assumed to be an ideal gas. The results reveal that the SST k−ω turbulence model performs quite well in predicting the conjugate heat transfer. Detailed heat transfer distributions in the main passage are also shown. The representative transitional behavior of the C3X vane on both pressure and suction surfaces is further analyzed. It suggests that the transition behavior plays a significant role in predictions of the boundary-layer behavior, wall temperature distribution, and heat transfer performance.