Performance analysis of Thermal Energy Storage systems using Phase Change Material

Abstract Thermal energy storage (TES) systems with phase change materials (PCM) are mainly analysed using conductive numerical models and compared doing an energy balance with the inlet and outlet heat transfer fluid (HTF) temperatures. In this paper, an alternative experimental performance analysis method is proposed and is based on the energy calculation thanks to a thorough instrumentation on the PCM side. Each PCM temperature is assigned to a PCM volume in the manner of an experimental mesh and multiplied by the PCM specific enthalpy to calculate the temporal energy evolution in the whole system. This method not only enables the calculation of the storage density, but also the heat exchange power by defining a dimensionless characteristic time as the time necessary to store 90% of the maximal storable energy in the system. The dimensionless analysis takes into account several parameters, as the metal mass or the initial and final temperatures. Experiments have been carried out on a single stainless steel tube, a steel tube with longitudinal fins and a copper tube with helical fins to validate the technique. The implementation of the method for the charging process demonstrated the interest of increasing the heat exchange surface to enhance the heat exchange power. The importance of natural convection in the liquid PCM and its impact on the heat transfer improvement has also been highlighted.

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