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ISSN 打印: 2151-4798
ISSN 在线: 2151-562X

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DOI: 10.1615/SpecialTopicsRevPorousMedia.2015012003
pages 121-131

EFFECT OF VARIABLE POROSITY ON COMPOSITE HEAT TRANSFER IN A BOUNDARY LAYER FLOW

Puttabsavasetty Nagaraju
Department of Physics, Vijaya College, Bangalore 560004, India

ABSTRACT

The effects of variable porosity and thermal conductivity of a medium, and also the emission, absorption, and scattering of radiation, are studied in this paper. A comparative study has been made for three different situations, namely, (1) variable porosity; (2) constant porosity; and (3) absence of porous medium. In carrying out the solution, as a first step the temperature profile within the radiation layer is determined and hence the heat transfer in the presence as well as in the absence of radiation parameter is obtained. The momentum and energy equations are coupled and they are solved simultaneously by the Runge-Kutta-Gill method in conjunction with the Newton-Raphson iterative scheme. The results of the analyses show that in the cases of variable porosity and absence of porous medium the velocity profiles possess very small curvature at the wall, whereas in the case of the constant porosity situation the velocity profile is almost zero up to a certain distance and then increases. Nevertheless, it reaches unity asymptotically in all three cases. The temperature profile becomes linear as the value of the ratio of the thermal conductivity of a solid to a fluid, λsf , increases. Another important result of the analyses is that the rise in temperature in a variable porosity medium is about 25% more in comparison with the absence of porous medium. Furthermore, the results show that the total heat flux in a variable porosity medium is about 79% more compared to a constant porosity medium, and the variable conductivity enhances the total heat flux by about 33% compared to the constant conductivity of the medium. The results also show that as the radiation parameter increases the total heat flux decreases in all three cases.


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