Begell House Inc.
Heat Transfer Research
HTR
1064-2285
44
6
2013
MELTING EFFECTS ON THE STAGNATION POINT FLOW OF A JEFFREY FLUID IN THE PRESENCE OF MAGNETIC FIELD
493-506
Kalidas
Das
Department of Mathematics, Kalyani Government Engineering College, Kalyani, W.B., Pin-741235, India
Liancun
Zheng
School of Mathematics and Physics, University of Science and Technology Beĳing, Beĳing 100083,
China
This paper is devoted to investigation of the influence of magnetic field and melting heat transfer on the stagnation point flow of an incompressible, electrically conducting Jeffrey fluid past a semi-infinite stretching sheet in the presence of viscous dissipation and Joule heating. The governing boundary-layer equations are written in a dimensionless form by similarity transformations. The transformed nonlinear ordinary differential equations are solved numerically using the symbolic software MATHEMATICA. A favorable comparison with the previously published work is performed. Numerical results for dimensionless velocity, temperature, the skin friction coefficient, and Nusselt number are presented in the form of graphs and tables for pertinent parameters to show interesting aspects of the solution.
MIXED CONVECTION AND ITS INTERACTION WITH SURFACE RADIATION IN A DIFFERENTLY HEATED ENCLOSURE: A CRITICAL APRAISAL
507-534
Swarup Kumar
Mahapatra
Indian Institute of Technology Bhubaneswar
Sikata
Samantaray
Siksha 'O' Anusandhan University
Amitava
Sarkar
Department of Mechanical Engineering, Jadavpur University, Kolkata, India-700032
The present study is based on numerical investigation of mixed convection coupled with surface radiation within a differentially heated square cavity. The effect of surface radiation on the flow regimes, because of the combined effect of shear induced flow and buoyancy, was investigated. We analyzed the flow which is steady, two-dimensional, and laminar within a differentlially heated cavity. The fluid is considered to be incompressible and the source term is evaluated using the Boussinesq approximation. The finite difference method was employed as a numerical scheme to solve the momentum and energy equations. The net radiation method is used to evaluate radiosity from diffuse and gray surfaces. A parametric study was conducted with the following controlling parameters: Rayleigh number (Ra), Richardson number (Ri), emissivity (e), and wall motion. It is found that for opposing mixed convection regimes (i.e., at Ri = 1 or more) in the presence of surface radiation, the heat transfer rate is higher for the horizontal wall movement than that for the vertical wall movement. In the presence of pure opposing mixed convection, the minimum heat transfer rate occurs at the Richardson number Ri =1 for the vertical wall movement, but at the Richardson number Ri = 1.8 for the horizontal wall movement. In contrast to the convective heat transfer, radiative heat transfer is found to be independent of Ri and wall movement.
NUMERICAL MODELING OF A PULSATING HEAT PIPE WITH HEATING FROM THE TOP
535-559
Radha Kanta
Sarangi
Mechanical Engineering Department, Don Bosco Institute of Technology, Mumbai-400070, India
M. V.
Rane
Mechanical Engineering Department, Indian Institute of Technology, Bombay, Mumbai-400076, India
A mathematical model of the hydrodynamics and heat transfer in a U-shaped PHP involving one liquid plug and two vapor bubbles is presented. The vapor bubble governing equations and liquid plug energy equation are solved numerically by the explicit finite difference method and explicit IOCV method based on the Lagrangian approach, respectively. Unlike other models, the vapor bubble state is checked, if superheated, the pressure is calculated from the ideal gas equation, otherwise saturation pressure is found from the curve fitted equation. Film thickness is calculated using correlation. The metastable state of a vapor bubble is incorporated by the modified latent heat term. The heat transfer coefficient is calculated by film thickness and spatial film thickness variation which is found by considering evaporation from a liquid film and vapor interface. The model studies different parameters like the plug velocity, bubble temperature and pressure, driving pressure, thermal conductance, and heat transfer. It is observed that film thickness variations are very small in the range from 1 to 3% of the initial thickness due to the higher oscillation frequency in the range from 11 to 13 Hz. The latent heat transfer is 7% of the total heat transfer, in the case of 2-mm ID, water as a working fluid with 80 and 20°C for the evaporator and condenser temperatures, respectively. The heat transfer rate and thermal conductance increase with the temperature difference between the evaporator and condenser, but decrease with decrease in the operating temperature for a given temperature difference between the evaporator and condenser. The vapor sensible heat has significant effects on the vapor bubble temperature.
NUMERICAL STUDY OF THREE-DIMENSIONAL CONJUGATE HEAT TRANSFER IN LIQUID MINI-SCALE HEAT SINK
561-588
Mohamed Khamis
Mansour
Department of Mechanical Engineering, Faculty of Engineering, Alexandria University
This paper presents a numerical study of the effect of the substrate material and liquid cooling medium on the heat transfer characteristics for three-dimensional conjugate heat transfer problem of laminar flow through a circular minichannel. A uniform heat flux of 100 kW/m2 is applied at the bottom-side of the substrate while the topside surface is considered adiabatic. Three different materials of the substrate have been adopted: copper (ks = 398 W/m·K), silicon (ks = 189 W/m·K), and stainless steel (ks = 15.9 W/m·K). Two different coolant liquids have also been proposed − water and mercury. The thermal characteristics of the conjugate heat transfer problem are represented by the local Nusselt (Nu) number, local bottom-side surface temperature of the channel, local heat flux, and local temperature difference between the solid and fluid domains. The effect of inlet coolant velocity is investigated with two different inlet velocities of 0.1 m/s and 0.05 m/s. The study shows that the thermal characteristics of the minichannel using water as a coolant medium with the three different substrate materials are in contradiction with those of the minichannel using mercury. The contradiction is generated as a result of the competitive effects of axial fluid conduction, and axial wall conduction as well as the competitive effects of the radial and circumferential heat diffusion in the fluid domain. The theoretical model has been verified by comparing the predicated results with those obtained from the available analytical and experimental data with maximum deviation of 6.7%. The study is considered as the benchmark and helpful guidelines in the design of small-scale circular channels which are used for electronic cooling systems.