Thermal performance of a solar storage packed bed using spherical capsules filled with PCM having different melting points

• Presented a new multi-type PCM packed bed for solar energy storage.
• The simulated energy and exergy performance were better than single-type one.
• The solar collector of the new packed bed showed higher thermal efficiency.

In this paper, a packed bed heat storage system using spherical capsules filled with three kinds of phase change material (PCM) was presented and numerically studied. The capsules are filled into a packed bed which is connected with a flat plate solar collector. The capsules are placed in series based on the melting temperature of PCM. Water is used as heat transfer fluid (HTF) and heated in the solar collector. Solar energy is transferred to PCM and preserved as latent thermal energy. The heat transfer processes of HTF and PCM capsules were modeled and numerically calculated by finite difference method. The effective thermal conductivity of liquid phase was used to take into account the effect of natural convection on heat transfer during melting. The energy and exergy performances of the multiple-type packed bed were studied and compared with the performances of single-type PCM packed bed. The performance of solar collector was also investigated. The comparison results indicate that this new type heat storage packed bed has higher energy and exergy transfer efficiencies than the traditional packed bed, and the average energy and exergy collection efficiency of its solar collector are higher too.