Parametric studies on packed bed storage unit filled with PCM encapsulated spherical containers for low temperature solar air heating applications

Highlights: • The performance of PCM packed bed storage system for various conditions is studied. • The ΔT between the HTF inlet and phase change temperature has significant effect. • The increase in 'k' value beyond 1 W m−1 K−1 has negligible effect. • Low mass flow rate of the HTF provides a uniform heat flux. - Abstract: The focus of the present work is to perform parametric studies on the performance of a packed bed storage unit filled with phase change material (PCM) encapsulated spherical containers, suitable for low temperature solar air heating applications. A parametric analysis was carried out using the validated enthalpy based numerical model that considers the thermal gradient inside the PCM container. The results of simulation analysis showed that the size of the PCM ball, fluid inlet temperature and the mass flow rate of the heat transfer fluid (HTF) influenced respectively the heat transfer area in the packed bed, temperature difference between the HTF and PCM and the surface convective heat transfer coefficient between the HTF and PCM balls. The poor thermal conductivity of the PCM has only negligible effect on heat transfer due to high surface convective resistance provided by the air. The influence of various parameters for the selected range of values were analyzed using the charging time, instantaneous heat stored and cumulative heat stored during the charging process