Improving the performance of a small-scale cascade latent heat storage system by using gradual melting temperature storage tank

The highest thermal energy for phase change material (PCM) is stored/discharged with unsubstantial temperature changes during the isothermal phase transition. However, the convective latent heat storage system uses temperature differences between the thermal load and working fluid. It restricts the temperature operation of the storage system since the temperature of the working fluid is limited by the melting temperature of PCM. To overcome the related issue, the present study proposes a configuration for small-scale cascade latent heat storage using three different melting points of the phase change materials. The three-stage cascade system is occupied by paraffin, RT80, and high-density polyethylene for the 1st, 2nd and 3rd storage tanks with melting temperatures of 60.9 °C, 79.6 °C and 115.4 °C, respectively. The overall system demonstrates a better performance than a single tank, with an average temperature variation of 42.9 °C and 34.5 °C during charging and discharging. The effect of partial phase change can be decreased where the power effective for discharging decreases by only 6.3% while the power effective during charging increases by 18.2%. It proves that using a multistage cascade system with gradual melting temperature PCM allows higher performance for a latent heat storage system.