多孔介质孔隙率对池沸腾传热性能影响机理的模拟研究OA北大核心CSTPCD

The mesoscopic phase change lattice Boltzmann method was used to study the effect of the medium porosity on pool boiling heat transfer at the pore scale.The motion processes of bubbles were mainly consid-ered for different porosities,and the force balance was analyzed in typical states of bubbles in porous media,to explore the mechanism of the influence of medium porosity on boiling heat transfer.The results show that,compared with the flat surface without a porous medium,porous materials can effectively reduce the wall su-perheat of initial nucleation,enhance the disturbance of fluid,and significantly improve the critical heat flux(CHF).In the simulation case,the CHF value grows the greatest with porosity ε = 73.2%,which is about 3.6 times that of the flat plate case.In the cases of other porosity values,the presence of porous media can in-crease the CHF value for at least 2.3 times that of the flat plate case.The numerical simulation further demon-strates that,as the porosity gradually decreases from 97.7%,the CHF value will gradually increases,and the boiling heat transfer curve will shift to the upper left.This is because a decrease in the porosity can increase the effective heat transfer area,reduce the wall superheat of bubble nucleation,and strengthen boiling heat trans-fer.When the porosity decreases to ε = 73.2%,the heat flux density will suddenly drop and the boiling heat transfer performance will significantly decrease with the reduction of the porosity.The analysis of force balance of the bubbles during the boiling process indicates that,for a low porosity,too small pore diameters would sig-nificantly increase the escape resistance of bubbles,reduce their rising speed,and lengthen the time of bubbles leaving the porous medium;at the same time,bubbles will gather on the surface of the heater under the com-bined actions of the evaporation momentum,the contact pressure,and the friction,thus deteriorating the boil-ing heat transfer performance.