Analysis of thermo-hydraulic characteristics in the porous-wall microchannel with microencapsulated phase change slurry

Abstract

Combining porous layer paved on the side wall and microencapsulated phase change material (MPCM) slurry as working fluid is presented in microchannel heat sink (MCHS), in which more surface area of channel matrix and larger temperature difference between coolant and heating surface during phase change will enhance heat transfer. The Brinkman-Forchheimer extended Darcy model together with energy equation in local thermal equilibrium account for heat transfer and flow in the porous layer as well as the equivalent heat capacity method for phase change of microcapsules under laminar flow. The effects of the materials of porous layer and substrate, heat sink design involving the porosity, thickness and height of porous layer as well as channel number under various inlet velocities and mass fractions of MPCM slurry on the thermo-hydraulic performance, which is evaluated with performance evaluation factor (PEF), in the porous-wall MCHS of MPCM slurry as coolant are analyzed in comparison to the non-porous mode with water passing through, and the 32.3% rise of performance evaluation factor can be obtained. The simulation results are validated with the experimental data. The lower thermal resistance occurs in the porous-wall mode of MPCM slurry as coolant with higher and thicker porous layer of higher porosity and thermal conductivity material as well as proper microchannel number in heat sink under higher inlet velocity than that in the non-porous MCHS with water flowing through, which is closely related to the phase change of MPCM in slurry, and influences PEF in consideration of flowing resistance. The MPCM mass fraction in coolant needs to be properly to avoid larger convection reduction and rise of flowing resistance, so as to obtain the better thermal and hydrodynamic performance of larger PEF.