LATTICE BOLTZMANN SIMULATION OF EFFECTIVE THERMAL CONDUCTIVITY OF POROUS MEDIA WITH MULTIPHASE

Abstract

The particle size, distribution, and orientation will decide the heat conduction behavior of porous media, and the trends of different effects can be obtained according to the various model assumptions. With or without consideration of the thermal contact resistance, the effects of the grain size on the thermal conductivity of porous materials may be adverse. The lattice Boltzmann method has microscopic and mesoscopic features that facilitate the processing of irregular boundary conditions for porous media. A corrected heat flux of the thermal lattice Boltzmann model is proposed in this paper, which naturally ensures heat flux continuity at the phase−phase interface. A new equivalent relaxation time is set at the phase−phase interface in the thermal lattice Boltzmann model, and through the use of the thermal energy transport model with series and parallel sets, the reliability of the new method in dealing with the phase−phase interface is verified. Porous media are generated by the quartet structure generation set. The effective thermal conductivity is obtained both with single-phase and multiphase fluid in the porous media. The effective thermal conductivity of porous media increases with increasing particle size. The connectivity of the particles along the heat transfer direction provides a preferential path for heat transfer, which creates higher effective thermal conductivity. When wetting fluid, with lower thermal conductivity, is absorbed on the porous matrix, the predicted effective thermal conductivity is close to the Hashin−Shtrikman lower bound.