Effects of capsule conduction and capsule outside convection on the thermal storage performance of encapsulated thermal storage tanks

The present study investigates the effects of capsule conduction and capsule outside convection of a spherical capsule on the thermal storage performance. The enthalpy-porosity method is employed to account for the phase change phenomenon. Three numerical models are examined. The first model is to apply the commonly used isothermal boundary condition on the outer surface of spherical PCM (phase change material). The second model is to apply constant temperature uniformly to the external surface of the capsule to examine the effect of capsule conduction. The last model takes into account the convection outside the spherical capsule. The results show that the effects of capsule conduction and capsule outside convection are substantial to the thermal storage performance. The effects of capsule conduction and capsule outside convection result in much lower discharging performance than the commonly used approach of the isothermal boundary model. This observation is more significant in real situation when the capsule material has low thermal conductivity.