An experimental investigation on the heat transfer characteristics of cascaded thermal storage units based on multichannel flat tubes

A latent heat storage unit made of a two-stage phase change material (PCM) can decrease the mismatch between supply and demand of energy. The cascaded phase change thermal storage stores and utilizes energy hierarchically. A two-stage cascaded thermal storage unit based on multichannel flat tubes and compact fins is developed in this study. The device uses water as the heat transfer fluid (HTF). Melting/solidification time, charging/discharging power, thermal efficiency, and exergy efficiency are evaluated for different HTF inlet temperatures and PCM volume flow rates. At the charging conditions of 70 °C and 1.5 L/min, the melting time for paraffin and lauric acid are 21and 20 min, respectively. The thermal efficiencies of the first and second stages of the thermal storage unit are 70.62 % and 70.40 %, respectively, and the exergy efficiencies are 81.25 % and 81.19 %. Given the small pressure loss of the pump and the high heat transfer performance of the heat storage system, using 70 °C and 1.5 L/min as experimental conditions for HTF is the key to obtaining short PCM melting times and high power.