Investigation on heat transfer characteristics of PCM during heat storage/release in pumped thermal electricity storage system

In this paper, a two-dimensional mathematical model and physical model of the heat storage unit are established, and the experimental device is designed and built. The effects of heat transfer fluid (HTF) inlet flow rate and temperature, phase change material (PCM) initial temperature on the heat transfer performance of the heat storage unit in the process of heat storage and heat release are studied. The results show that when the import speed is increased from 5 m/s to 6 m/s, 7 m/s, 8 m/s, 9 m/s and 10 m/s, the melting time is shortened by 8.2 %, 10.7 %, 17.8 %, 32.5 % and 38.2 %, respectively; When the inlet temperature of R245fa increased from 125 degrees C to 130 degrees C, 135 degrees C, 140 degrees C, 145 degrees C and 150 degrees C, the time required for complete melting of PCM decreased from 1777 s to 1135 s, 799 s, 607 s, 493 s and 425 s, shortening by 36.13 %, 29.6 %, 24.03 %, 18.78 % and 13.79 %, respectively; When the initial temperature of PCM is 125 degrees C, 130 degrees C, 135 degrees C, 140 degrees C, 145 degrees C and 150 degrees C, the time required for complete solidification of PCM is 1523 s, 1542 s, 1575 s, 1597 s, 1626 s and 1668 s, respectively. Compared with the initial temperature of 125 degrees C, the total solidification time of PCM increased by 1.25 %, 2.14 %, 1.4 %, 1.82 % and 2.58 % for every 5 degrees C increase in the initial temperature, respectively. The results have important guiding significance for the design and operation parameters selection of heat storage unit and heat exchanger of high temperature heat pump (HTHP) heat storage and power generation system based on Organic Rankine Cycle (ORC).