Fabrication And Property Investigation Of MgCl₂?6H₂O-CaCl₂?6H₂O Phase Change Material For Engery Storage

The hydrated salt phase change material?PCM?has the advantages of high heat storage density,large thermal conductivity,moderate phase transition tempe rature range,low cost and easy to prepare.It can be used to reconcile the imbalance of energy supply and demand,in tht aspects of time and space.However,the hydrated salt phase change material for energy storage has the problems of supercooling and phase separation,which has become the bottleneck of its large-scale engineering application.In this paper,low-cost MgCl₂?6H₂O and CaCl₂?6H₂O were used as the main components to prepare the phase change materials,and their thermal energy storage performance prpperties were optimized.The laws of supercooling and phase separation were investigated.?1?Based on the phase diagram of CaCl₂-H₂O system,the commercially available CaCl₂?2H₂O was prepared by recrystallization of CaCl₂?6H₂O with higher purity,and then used to prepare MgCl₂?6H₂O-CaCl₂?6H₂O binary phase change materials for thermal energy storage.A series of MgCl₂?6H₂O-CaCl₂?6H₂O binary phase change materials with MgCl₂?6H₂O mass fractions of 10%,15%,20%,25%,30%and 35%were prepared.The phase change temperatures of binary phase change materials,with and without nucleating agent,were determined.The temperature change curves were plotted,and the rules were revealed.It is found that,for the binary phase change material thermal energy storage systems,as the mass content of MgCl₂?6H₂O is gradually increased,10%,15%,20%,25%,30%,35%,the phase change temperature were gradually decreased,25.0?,24.7?,24.5?,22.5?,20.7?,and 20.0?,respectively.In the absence of a nucleating agent,the degree of subcooling of the phase change material is approximately 0.5?¹.5?,while when the nucleating agent is included,the degree of subcooling of the phase change material is reduced to below 0.1?.Therefore,the nucleating agent can significantly reduce the degree of subcooling of the phase change energy storage material.?2?The phase separation phenomenon of MgCl₂?6H₂O with different mass fractions was studied.The main infusible phases were MgCl ₂?4H₂O and CaMg₂Cl₆?H₂O?_x double salts.The existence of infusible phase will affect the thermal reliability of the phase change materials.?3?The addition of the thickener sodium hydroxy methylcellulose?CMC?reduces the fluidity of the phase change material at liquid state,which making it difficult for the infusible phase to sink to the bottom,thus reducing the degree of phase separation.The addition of expanded graphite significantly improves the thermal conductivity of the phase change material,which is beneficial to the phase change material to achieve faster heat exchange.For the commercial application of the material,the thermal efficiency can be better improve d and the energy storage density of the heat storage unit can be increased.