Performance of a thermal energy storage tank based on latent heat with different capsule allocations. Experimental study in a pilot facility

In this study, the effect of internal structuring in a thermal energy storage tank filled with phase change material (PCM) capsules on its performance was investigated. A laboratory-scale tank with a total capacity of 60 litres, connected to a pilot facility providing cold heat transfer fluid or a heat load, has been used. The system is intended to model space cooling, so the PCM was selected with a freezing point of -3 ° C , and encapsulated with different geometries, which can be oriented vertically or horizontally and parallel or perpendicular to the flow. The amount of energy stored in the tank was calculated for all configurations. The highest energy storage and most effective energy recovery were observed with vertically oriented, disk-shaped capsules. The results also indicate that energy recovery from sensible heat is more efficient than from latent heat, although latent heat storage allows for greater overall energy accumulation and recovery. An important subcooling is also reported, as the inlet fluid must be cooled below -8 ° C to freeze all the PCM in the storage tank, and reach the maximum load capacity (more than 500 kJ per kilogramme of PCM). Finally, the continuous operation of charging and discharging cycles was studied, showing that the energy in the tank varies between 80% and 30% of its total capacity in every cycle. The analysis also highlighted the significant impact of thermal gains and losses to or from the surrounding environment. • A pilot facility of thermal energy storage for space cooling applications is used. • Effect of internal structure in a PCM-based storage tank on its performance is studied. • Optimal behaviour occurs with vertically oriented, disk-shaped capsules at − 8 ° C. • Continuous cycling shows that the tank energy varies between 80%–30%. • Storage efficiency decreases by up to 40% due to thermal losses.