LBM modeling and analysis on microchannel slip flow and heat transfer under different heating conditions

This article aims to explore the effects of buoyancy force and thermal boundary condition on the mixed convection heat transfer performance of air in a horizontal microchannel. Three different heat flux models, including bottom wall heated, top wall heated (single wall heating–a novel heating approach compared to recent studies) and both walls heated, are analyzed at four different values of the Grashof number (Gr = 0, 100, 300, 600) using a lattice Boltzmann method (LBM). The slip velocity boundary condition is also applied to the bottom and top walls. It can be found that the buoyancy force changes the velocity distribution structure near the bottom wall and top wall, particularly at the inlet regions in all models, and a negative slip velocity is generated due to the backflow formed at a relatively large Grashof number and it strictly determines the local wall friction coefficient. Either the bottom wall or the top wall is heated. A vortex is found close to the top wall because the mixing position of the hot and cold fluids is in the vicinity of the top wall. This feature facilitates the heat transfer near the top wall and core flow zone. The thermal performance is most positive for the case when the top wall is heated due to the generation of an induced vortex and no influence of the vortex near the bottom wall.