Parametric Study of Rarefaction Effects on Micro- and Nanoscale Thermal Flows in Porous Structures

Abstract

Hydrodynamics and heat transfer in micro/nano channels filled with porous media for different porosities and Knudsen numbers, Kn, ranging from 0.1 to 10, are considered. The performance of standard lattice Boltzmann method (LBM) is confined to the microscale flows with a Knudsen number less than 0.1. Therefore, by considering the rarefaction effect on the viscosity and thermal conductivity, a modified thermal LBM is used, which is able to extend the ability of LBM to simulate wide range of Knudsen flow regimes. The present study reports the effects of the Knudsen number and porosity on the flow rate, permeability, and mean Nusselt number. The Knudsen's minimum effect for micro/nano channels filled with porous media was observed. In addition to the porosity and Knudsen number, the obstacle sizes have important role in the heat transfer, so that enhanced heat transfer is observed when the obstacle sizes decrease. For the same porosity and Knudsen number, the inline porous structure has the highest heat transfer performance.