Quasi-equilibrium approximation of the solidification process for micro phase change materials taking into account curvature and surface tension

Phase change materials (PCMs) have superior energy storage properties, which can be used to solve the problem of energy absorption and release at various times, intensities and locations. Energy storage using PCMs is a promising way to make the rational use of energy, which could help improving our environment. Owing to their significant applications, we investigate the solidification process of microparticles, which is also known as the Stefan problem. Due to the tiny size of microparticles, quasi-equilibrium approximation of such Stefan's problem is considered, where the effect of the curvature and the surface tension are incorporated. Here, we determine a simple but yet effective iterative model for the moving boundaries of micro PCMs (MPCMs) by assuming the homogeneous temperature distribution in molten regimes in order to avoid solving more complicated diffusion equations. We purposely investigate the solidification process of spherical and ellipsoidal MPCMs and find that both the curvature and the surface tension promote the solidification process. Due to these outcomes, peanut-shaped MPCMs are proposed to demonstrate the usage of both effects for fabricating smart MPCMs. Finally, the validity of the model is confirmed by a Computational Fluid Dynamics (CFD) method.