Studies On The Supercooling And The Thermal Cycling Stability Of Sodium Acetate Trihydrate

The hydrated salt is an important kind of low temperature heat storage materials with high latent heat and low cost,and has high application potential in thermal energy storage and thermal management.There are many kinds of the hydrated salt,but their main disadvantages of phase separation and subcooling limit the development and utilization.This study takes sodium acetate trihydrate as the object to study the problems of subcooling and thermal cycle stability.In order to study the thermal cycle characteristics of sodium acetate trihydrate,a thermal cycle device using a semiconductor thermoelectric module was designed,which could greatly shorten the thermal cycle experiment period.In the investigation of the stability of subcooling,by adding disodium hydrogen phosphate dodecahydrate and nano alumina as nucleating agents,the composite material can maintain a relatively stable subcooling after high cycles.In the investigation of latent heat stability,it was found that the low solubility of anhydrous sodium acetate in water is the main reason for the phase separation through the analysis of the phase diagram of sodium acetate trihydrate.In order to reduce the latent heat loss of the composite phase change material,the content of the disodium hydrogen phosphate dodecahydrate is increased to appropriately reduce the ratio of anhydrous sodium acetate to the bound water.The result shows that the average subcooling of the composite phase change material is about 5～8℃after 500 cycles,and the latent heat is approximately equal to the initial phase and remains stable.This study can be helpful for the application of sodium acetate trihydrate,and the thermal cycling setup using the thermoelectric module can be useful for the studies of other phase change materials.In order to further reduce the subcooling of the sodium acetate trihydrate composite phase change material,and to solve the problem of high subcooling generally existing in hydrated salts,a small semiconductor thermoelectric module was designed as the cold source of the new cold finger method.Four common hydrated salts,Na₂SO₄·10H₂O,Na₂HPO₄·12H₂O,Na₂S₂O₃·5H₂O,Na CH₃COO·3H₂O,were taken as examples and the subcooling was maintained at 2.5～4℃through the water bath.After the current was applied for a short time,the cold-end probe of the small thermoelectric module successfully triggered the nucleation of the hydrated salt due to the temperature drop.The device has a simple structure that only needs a battery to work,which can reduce energy consumption.This method provides a new way for solving the problem of the subcooling of hydrated salts.In order to further improve the cold finger method based on thermoelectric cooling,the transient cooling capacity of the micro device based on thermoelectric arm is analyzed through simulation.The results show that the micro-device has a good transient cooling effect,and can meet the requirement of cold finger method for local low temperature to nucleate hydrated salts.The pyramid structure of the PN semiconductor can effectively enhance its transient cooling effect.In addition,the lowest temperature of the cold end under transient cooling gradually decreases as the thickness of the heat sink increases.However,there is a limit value for the heat sink function,so the appropriate heat sink size should be selected according to the actual working conditions.