Experimental Study On Latent Heat Storage Of Sodium Acetate Trihydrate In Phase Change Units

Latent heat can provide a reservoir of energy to adjust the mismatch between energy demand and availability. Inorganic hydrates salt is a kind of low-to-medium phase-change materials with a large of latent heat and widespread use. Indeed, these materials have been utilized in household thermal insulation and industry because of their phase change temperature. Sodium acetate trihydrate (CH3COONa·3H2O, SAT) is a kind of representative inorganic salt phase-change material with a great value in application. However, SAT displays a relatively large degree of supercooling, at the same time, phase separation in SAT limits the possible number of heating-cooling cycles. These two defects greatly affect its recycling opportunity, as a result, getting a poor ability to store heat. Meanwhile, SAT get a poor property of heat conducting, but latent heat is required to be stored and released at short notice. It is very important to solve these problems so that the thermal storage performances of inorganic hydrates salt can be improved. Some methods were applied to restrain the supercooling and phase separation. Enhancing the capacity of heat conduction by some ways Major work is as following.(1) Some phase change units were designed as accumulators. It have shown that molten state SAT does not crystalize at room temperature even after 3 hours and in the units with a good performance of thermal conduction, which illustrates that SAT can’t released the heat stored at the period of phase change, and its degree of supercooling is too high. Some inorganic salt phase-change materials can be used as nucleating agents, and Sodium phosphate dibasic dodecahydrate (Na2HPO4·12H2O) is the best one. It is because that Na2HPO4·12H2O promoted the nucleation of SAT. To be more stable, Na2HPO4·12H2O is need to be used in conjunction with thickener to improve the stability of mixed system. There are a lot of organic matter used as thickener, such as polyacrylamide, carboxymethylcellulose (CMC), arabic gum, gelatin and sucrose. Gelatin and carboxymethylcellulose are more reliable.(2) Methods of enhancing the heat transfer aim at increasing the rate of storing and releasing heat by preparing mixed phase change materials and fins inside the units. The mixed phase change materials made up of SAT, Nano-Cu or Nano-SiO2, dispersing agent and thickener is 20% higher than the pure materials for the rate of storing and releasing heat. As an additive, Nano-Cu can improve the supercooling properties and enhance thermal conductivity, either. When appling fins inside the units, the rate would be increased by 2 times. So this method was confirmed to have a big advantage and application value in the real-world usage. Nanomaterials (Nano-Cu and Nano-SiO2) with thickener (i.e, CMC) has been applied to improve the supercooling characteristics of phase-change materials, which also held a low degree of supercooling and a high stability. But the precondition is that nanomaterials should be scattered to the molten state SAT evenly.(3) Some external disturbance may affect the phase change property of SAT. At present, there are three ways used, i.e., ultrasonic irradiation, mechanical stirring and mechanical vibration. The main goal is to provide a stable crystal core in the units.1) The ultrasonic can be introduced to SAT molten as power. Besides, the solubilities of the salts would be improved, and subcooling and phase separation can be controlled.2) The way mechanical stirring can provide a stable crystal core from the axes, at the same time, improving the dissolubility of salt, so the heat release rate would be increased.3) The way vibration can provide a stable resource of power for crystallization. The crystal nucleus would come off from the vessel wall when vibrating starts. As a result, it will prevent phase separating.(4) Analysising the merits or defects of the way for nucleating by usage occasion, economical efficiency, and the characteristic and sizes of the accumulators. It is also necessary to choose any of them according to the usage occasion, economical efficiency, and feasibility.