A Lattice Boltzmann Model for Phase Change Material (PCM) Melting with Porous Media in Heat Exchanger

Phase change material (PCM) is widely used in thermal energy storage systems as it can absorb and release a large amount of heat by the phase change process. Both experimental and numerical studies of PCM have increased sub­ stantially in the past two decades. Among them, the phase change in porous media is one of the significant topics. The simulation of PCMmelting in porous media is required to characterize the fluid flow and heat transfer behavior, and to provide guidance for the further design and optimization of PCM heat exchangers and thermal energy storage systems. In this paper, a model is developed based on the Lattice Boltzmann method (LBM) to simulate transient phase change in porous media. Double distribution functions coupled with a multi­relaxation­time (MRT) scheme are utilized in LBM for the simulation of the fluid flow and temperature field, respectively. An enthalpy updating scheme is also applied to determine the liquid fraction of PCM, which is used to track the solid­liquid interface. The basic model in Cartesian coordinate is verified with the simulation of PCM phase change in a porous rectangular container. The model is further adapted for use in cylindrical coordinates for simulating the phase change process within porous media in a cylindrical heat exchanger. The developed model is verified by two vertical annulus cases and the results indicate that the developed model can successfully simulate the effects of natural convection and porous media on the thermal flow. More validation cases are expected to be conducted for the developed model to test its ability to simulate the phase change process. And the fully developed model is expected to be applied in a wider field of PCM phase change, which can benefit the design and improvement of PCM heat exchangers in thermal energy storage systems.