TED-AJ03-418 NUMERICAL STUDY OF CONJUGATE HEAT TRANSFER FOR A CHANNEL FILLED WITH POROUS INSERT

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Use of porous media as an extended heat transfer surface for plate-fin heat exchangers is recently gathering attention. In such exchangers, heat conduction inside the separation plates plays an important role in the heat exchange process between hot and cold side fluids. Thus, an evaluation of effectiveness for such porous-fins requires detailed information on heat conduction inside the solid walls in addition to heat transfer in the porous media. A numerical scheme based on the finite volume method has been developed to solve conjugate heat transfer problems between porous media and solid walls. Heat transfer in the porous media was modeled with a volume-averaged form of a two-energy equation model, which treats temperatures of fluid phase and solid phase separately. The computational domain consists of a channel filled with a porous medium and an upper solid wall which bounds the medium (Fig. A-1). For conjugate heat transfer analyses, a heat transfer model at the interface between the porous media and solid walls is proposed. The heat transfer model was obtained by considering an energy balance of the heat transferred from the solid wall to fluid and solid phases of the porous medium. Therefore, the model gives an appropriate descretized form of wall heat fluxes for fluid and solid phases at the interface. In addition, the heat transfer model clarifies the physics of a known thermal boundary condition at the interface. [figure] The effectiveness of the developed scheme for conjugate heat transfer analysis was examined by quantitative comparisons of predicted physical values with available experimental data on metal forms having high porosity from 0.9 to 0.95. Predicted wall temperature distributions (Fig. A-2) and average Nusselt numbers show very good agreement with the experimental results. Therefore, the predicted wall heat flux distributions of the solid phase and fluid phase also correspond well to the numerical results directly evaluated from the measured temperature boundary conditions. It was also found that predicted ratios of superficial wall heat flux for fluid phase to that for solid phase are far from the ratios given theoretically by assuming that the true wall heat flux is equally distributed to fluid phase and solid phase at the interface. Effect of wall thickness on heat transfer to the porous media from solid walls has also been investigated. It was found that decreases of wall thickness lead to increases of average Nusselt number due to relative increases of lateral thermal resistance in the solid walls. This indicates the importance of considering heat conduction in the solid walls as well as heat transfer in the porous media to predict the heat transfer performance of porous media accurately.[figure]
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TED-AJ03-418 NUMERICAL STUDY OF CONJUGATE HEAT TRANSFER FOR A CHANNEL FILLED WITH POROUS INSERT

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