Phase change materials (PCMs) are mainly used to provide high storage densities. The spherical geometry is one of the most interesting cases for heat storage applications. The present study used the lattice Boltzmann method (LBM) to investigate constrained melting process of PCMs in a spherical capsule

which can be useful for the study on phase change phenomenon of microencapsulated PCM slurry in the future. The phase interface is traced by updating the total enthalpy

while the moving interface is treated by the immersed moving boundary scheme. The computational results of the melting process of PCMs are analyzed at different scales. The numerical simulations at macro-scale are compared with the published experimental data

and the results clearly show that the thermal stratification is in the upper of the sphere capsule while the waviness phase front is at the bottom of the solid PCM. Quantitative analysis of the temperatures at nine points

eight points along the vertical axis and the other one near the inner shell

further indicates the existence of chaotic convective motion at the bottom of the sphere capsule. In addition

the effect of the natural convection on the melting process is reduced as the decrease of capsule sizes. When the diameter of capsule is less than 3 mm

the natural convection can be ignored.