Thermohydraulic performance analysis of graded porous media microchannel with microencapsulated phase change material suspension

Abstract

Abstract The phase change process in microcapsules is described using equivalent heat capacity method, and the Forchheimer-Brinkman-Darcy equation based on the volume-averaging method is employed to account for the fluid flow in porous ribs. The feasibility in the novel design is validated by analyzing the effects of porosity (e) arrangement, pore size (dp) arrangement as well as geometric parameters of porous-wall microchannel heat sink (MCHS) on the thermal and hydraulic characteristics under different inlet velocity, heating flux and mass fraction of microencapsulated phase change material (MPCM) suspension. The thermal resistance of the porosity gradient in porous media is less than that of linear variation, which is due to the more uneven velocity distribution in porous and fluid regions. The lower thermal resistance and more uniform temperature distribution occur in the graded porous media microchannel with higher height ratio, as well as the smaller and larger porosity in porous media respectively near the bottom and top walls. The size of microchannel limits the size of dp, making the thermo-hydraulic characteristics of gradient-dp mode worse than that of gradient-e under the same conditions, and the thermal resistance decreases as well as pressure drop increases with the augment thickness of porous media, so it is necessary to select the appropriate structural parameters and coolants according to the specific working conditions to obtain better comprehensive performance. The performance evaluation factor (PEF) is introduced to evaluate the overall thermohydraulic performance of MCHS under different heat sink designs, and the stepwise increasing porosity mode with porosity varying along the y direction has larger velocity difference between the upper and lower layers and more reasonable MPCM particle distribution under the larger mass fraction of suspension, so as to obtain the larger rise ratio of PEF, up to 61%.