Dynamic Modeling of Phase Change Materials for Thermal Energy Storage Applications
This paper assesses the capability and sensitivity of COMSOL Multiphysics® to evaluate phase-changing material suitability for Thermal Energy Storage. The simulated system is a packed bed of encapsulated spheres, containing phase changing materials (PCM), placed inside a single cylindrical aluminum tank at an initial temperature of 20 °C. The PCMs and tank are heated up by the heat transfer fluid, water, entering the system at 90 °C. The velocity boundary condition is defined at the inlet, with a tangential velocity of zero and no slip wall conditions. The flow is laminar and weakly compressible. The outlet is modeled as a pressure boundary with suppressed backflow. The Heat Transfer in Fluids interface is used with linear temperature discretization. The Laminar Flow and the Heat Transfer in Fluids interfaces are coupled using the Nonisothermal Flow multiphysics coupling. The mesh is physics-controlled with approximately 140,000 mesh elements, mostly triangular prisms. The study is time dependent and the simulation time is 10 minutes with 5 second intervals. Relevant transport and thermal properties of the standard materials used, water and aluminum, were extracted from the COMSOL Multiphysics® material library. PCM properties are user defined, including phase change temperature and transition interval between phases, latent heat, thermal conductivity, density and specific heat capacity for liquid and solid phases. The range of values originally tested for each parameter was selected based on material properties reported in literature. Initial results indicate that thermal properties of phase change materials can be engineered to provide optimum heat absorption, i.e. the “perfect” phase change material. However, there is hardly any correlation between these properties, the observed dynamics of heating and the total heat stored by the system. Expected results include possible correlation between thermal parameters and their joint effect on the overall performance of the storage system.
