Effectiveness–NTU correlation for low temperature PCM encapsulated in spheres

The applicability of the effectiveness–NTU method for characterising a PCM thermal energy storage system was experimentally investigated. The system consisted of PCM encapsulated in spheres with a liquid heat transfer fluid. Freezing and melting tests have been carried out for a variety of conditions on a tank filled with 60 spheres. The investigation demonstrated that a correlation existed between the effectiveness of heat transfer and the mass flow rate in accordance with the effectiveness–NTU relationship for condensers and boilers. It has been proven experimentally that the effectiveness–NTU method is applicable for PCM encapsulated in spheres in a tank.

► PCM encapsulated in spheres was experimentally investigated.
► Freezing and melting tests carried out on 60 spheres.
► Correlation exists between effectiveness of heat transfer and mass flow rate.
► Amount of PCM needed to achieve certain useful storage capacity can be estimated from correlation.