Lattice Boltzmann simulation of fluid flow and thermal analysis in a three-layered porous heat exchanger

In the present study, fluid flow simulation and thermal analysis of a three-layered porous heat exchanger (PHE) is investigated. The proposed PHE has one high temperature (HT) and two heat recovery (HR1 and HR2) sections, such that the HT section is placed between two recovery sections. The multiple-relaxation time (MRT) lattice Boltzmann method (LBM) is used to simulate fluid flow in the porous medium. Because of non-local thermal equilibrium between gas and solid phases, it is necessary to employ and solve energy equations for both phases separately. The effects of thermal conduction are considered for both phases. In addition to convection between gas and solid phases, the porous medium can absorb, emit and scatter thermal radiation whereas the effect of gas radiation is neglected. For the purpose of thermal analysis of the proposed HE, volume-averaged velocities through the porous matrix obtained by MRT-LBM are used in the gas energy equation and then the coupled energy equations for gas and porous medium of each section along with radiative transfer equation are numerically solved to obtain gas and solid temperature distribution and radiative heat flux distribution through each section of the proposed PHE. It should be noted that discrete ordinates method is used to solve the radiative transfer equation. Furthermore, the effect of optical thickness, scattering albedo on the efficiency of PHE was studied. It was found that this type of PHE has higher efficiency when porous layers with higher optical thickness and lower scattering albedo are used in the structure of the PHE.

Keywords:

Porous Medium , Lattice Boltzmann , Porous Heat Exchanger , Radiative Heat Transfer , Thermal Efficiency