Lattice Boltzmann mixture model for liquid-vapor flow with phase change in porous media

In this article, we develop a lattice Boltzmann (LB) mixture model to describe liquid-vapor flow and heat transfer in porous media. The key feature of this model is that it can characterize both single and two-phase convective heat transfer at the representative elementary volume (REV) scale with or without phase change between liquid and vapor. Importantly, although simple, this model also considers the effects of gravity, buoyancy and capillary pressure, which enable it to be a preferable means for simulating complex thermal system, e.g., heat pipes. We validated the LB model developed in this article by simulating natural convection in a porous cavity. The numerical results are well agreed with those previous numerical results in the literature. We then applied the model to simulate conjugate heat transfer with liquid-vapor phase change across the void core, porous wick and solid walls in a heat pipe. Again, our model recovered the previous results under a simple assumption that only liquid occupies the wick and external-force effects are totally ignored. Significantly, our model was extended to simulating more complex transport processes in heat pipes with two-phase flow coupled with phase change in the porous wick. The effects of gravity and buoyancy were also introduced in its framework. These numerical results reveal distinct heat and mass transfer characteristics from those under the simple assumptions. Our study demonstrates the LB model proposed in this article is a viable and powerful numerical tool for studying complex heat transfer phenomena in porous media.