The heat capacity of low-temperature phase change materials (PCM) applied in thermal energy storage systems

Abstract

Abstract Due to dependence of energy generation from renewable sources on weather conditions, such systems require cooperation with energy storage facilities. Thermal energy storage with phase change materials (PCM) is often used in systems working with solar collectors, photovoltaic panels, heat pumps, air conditioning systems, waste heat recovery systems and other. However, the appropriate application of PCMs requires a good knowledge of the thermo-physical properties of the materials and practical knowledge of the actual stored energy which depends on the PCM heating/cooling rate. The paper presents measurements of the latent heat for PCMs that are used in low-temperature thermal energy storage. The measurement method used was differential scanning calorimetry (DSC). In the experiments, two commercially available materials – RT15 and RT22 HC – were investigated. The tests were performed at different heating/cooling rates ranging from 0.5 to 10 K/min for samples of a mass 6–11 mg. On the basis of the test results and the proposed calculation method, the total values of energy stored during the phase transition, the temperature of phase change and the heat capacity distributions were determined as a function of temperature. Attention has been paid to the effect of temperature change rate on the measured latent heat capacity that is an important issue in practical applications of PCM. The heat capacity (energy stored) versus temperature distributions for RT15 and RT22 HC materials resulting from the tests can be used in design of latent heat thermal energy storage (LHTES) systems co-working with renewable energy systems. The presented methodology can also be used for investigation of other PCMs.