Effect of Pore Density and Porosity of Spiral Porous Metal Fins for Waste Heat Extraction From Exhaust Gases

ABSTRACT Spiral solid fins are extensively used for the removal of waste heat from exhaust gases. However, they undergo thermal degradation due to high‐temperature conditions. This setback is addressed by the use of porous media. Hence, in this study, we used spiral fins made of high‐porosity metallic foam samples. The thermal and hydrodynamic performance of these fins was evaluated in a three‐dimensional domain using computational fluid dynamics technique. The foam samples were subjected to analysis using the Darcy–Brinkman–Forchheimer and local thermal nonequilibrium models. The foam samples had variable pore densities ranging from 5 to 40 pores per inch (PPI) and differing porosities. The study focused on spiral fin pitch ( P f ) between 2.4 and 6.4 mm. Turbulent flow conditions were modeled using the realizable κ–ϵ model in ANSYS Fluent. Samples with variable pore densities were first evaluated for their thermal and flow parameters. Flow streamlines reveal a vortex formation near the fin base that intensifies with fin spacing. The overall performance study recommends the use of a 20‐PPI foam sample due to its superior performance compared to others. To study the effect of porosity, samples with porosity varying between 0.9005 and 0.978 were used. It was observed that the resistance offered by a specific foam sample is crucial in determining the pressure drop, while the heat transfer depends on the specific surface area of the porous sample. The overall performance analysis of all foam samples based on the area goodness factor and the ratio of heat transfer per unit temperature difference to the pumping power of the assembly ( Z / E) recommends the use of a 20‐PPI foam sample with a porosity of 0.9005. On the other hand, the samples with the highest flow resistance and lowest specific surface area are termed undesirable due to their higher pressure drop and lower heat transfer rate.