Enthalpy determination of phase change material objects by mixing calorimeter

Phase change materials (PCMs) store heat or cold by changing phase in a narrow temperature range and with high storage density. They are therefore used in many applications for heat or cold storage, also called thermal energy storage (TES). Many applications use the PCMs encapsulated in pouches made of polymeric film or in solid containers made of plastic or metals. Regarding characterisation, encapsulated PCM in for example a pouch is a PCM object that has a storage capacity. The heat stored by a PCM object could be calculated from the amount of PCM contained in it, but more reliable is a direct measurement as the PCM could change with time by phase separation, or show less supercooling due to larger mass. The heat stored in different types of PCM objects was determined directly using the mixing calorimeter method. For comparison, the heat stored by the PCMs only was also determined using a 3-layer calorimeter (3LC). In addition, the thermal conductivity was determined by the hot-wire method to see if it affected the results. The different methods, setups, measurement and evaluation procedures are described in the paper. The effects of different PCM and encapsulation types were studied. Commercial PCMs and PCM objects, products of Pluss Advanced Technologies Pvt. Ltd., were used in the study. The PCMs were water (to test the setups), organic PCMs of 46°C and 65°C temperatures, and inorganic PCMs of 48°C and 72°C, and the encapsulations were stainless steel balls and HDPE tabs. The heat stored, as measured on the PCM objects, was in good agreement with the cumulative value expected from measurements of PCM alone and literature data of the encapsulation material. The results showed that the mixing calorimeter method reliably presented the heat stored by a PCM object in the desired temperature range. The different thermal conductivities of PCMs did not significantly affect the experiment time of PCM object testing.