Performance analysis of industrial PCM heat storage lab prototype

A 140 l lab scale shell-and-tube PCM heat storage was built and tested, and the experimental results were compared to a numerical model. Natural convection in the PCM was found to significantly influence the local temperature distribution in the storage vessel, which could not be predicted well by the model, since the model assumes only conductive heat transport in the PCM. Nevertheless, the overall thermal power output of the storage could be predicted fairly well, if a correction term was used in the model to compensate for the enhanced heat transfer in the molten PCM. Experimentally, a horizontal orientation was found to be beneficial due to increased heat exchange during charging (melting). Comparing the two PCMs used in the testing (RT70 and MgCl2·6H2O), it was found that the RT70 had stable performance while the salt hydrate showed a reduced melting enthalpy which was ascribed to phase separation. For the RT70, a thermal power of 5 kW is obtained during phase change in the charging phase, and 3.5-2 kW during phase change in the discharging phase, while for MgCl2·6H2O this was 3.5 kW and 3-2 kW respectively.