Performance optimization of sodium acetate trihydrate-based phase change material

The application of phase change heat storage technology in condensing heat recovery system of air conditioning can effectively solve the non-synchronization of condensate heat discharge and hot water demand, and thus improve the energy utilization efficiency. For this purpose, a novel sodium acetate trihydrate-based phase change material was prepared and tested in our very recent work, which presented high potential to recover condensation heat. In this work, the sodium acetate trihydrate-based phase change material was further optimized for more promising heat storage and release performance. To begin with, in order to improve the heat storage density of sodium acetate trihydrate-based phase change material, deionized water was added into the mixture and their heat storage and release tests were carried out at atmospheric pressure and vacuum degree of 0.09 and 0.10 MPa. The heat storage density of such phase change material reached 8.2581 kW·h/kg with 7 wt% deionized water added, however, the cycle measurements showed that the heat storage and release performance were unstable under negative pressures. To solve this problem, expanded graphite was used to further stabilize and optimize sodium acetate trihydrate-based phase change material with extra water to improve the cycle stability. The results showed that the addition of 15 wt% expanded graphite in 50 mesh can effectively stabilize heat storage and release performance of these phase change material samples at both atmospheric and negative pressures. In addition, the optimum sodium acetate trihydrate-expanded graphite composite phase change material presents excellent form stability, thermal conductivity (4.566 W/(m·K)) and very comparable heat energy density at both atmospheric pressure (7.6301 kW·h/kg) and vacuum degree of 0.09 MPa (6.3295 kW·h/kg).