Thermal and structural characterizations of packed bed thermal energy storage with cylindrical micro-encapsulated phase change materials

Abstract

This work evaluates the circumferential thermal stress developed in the tank wall due to the restricted contraction during discharging operation, exergy efficiency, and stratification behaviour of a cylindrical micro-encapsulated packed bed latent heat thermal energy storage (PBTES) systems. A numerical model employing the enthalpy-porosity technique and the non-equilibrium energy equations for heat transfer fluid (HTF), phase change material (PCM) and wall of the storage tank is developed. The effect of PCM melting is incorporated in the energy equation by estimating the thermal resistance that arises from the radial shifting of the solid-liquid interface inside the cylindrical capsule. Hytherm 600 is HTF that flows through the pores between cylindrical particles filled with a commercial PCM, A164. A parametric investigation is conducted to examine the effects of varied charging and discharging HTF inlet temperatures, tank wall material, and arrangement of the cylindrical capsule. The higher charging HTF inlet temperature shows better thermal stratification. The thermal stress increases on decreasing the discharging HTF inlet temperature. The HTF flow over the capsules axially shows better thermal stratification and exergy efficiency. The thermal stress in the TES wall is found higher for cross-flow arrangement over the capsules than axial flow arrangement.