Research And Optimization Strategy Of Phase Change Energy Storage Of Inorganic Hydrated Salt Based On Solar Thermal Utilization

Being one of the new energy storage materials for solar thermal utilization that responds to the concept of sustainable development,phase change materials have become the preferred materials for energy-saving thermal storage in the new era due to their large energy storage density,high enthalpy,non-toxic,and low price.Among them,the application range of inorganic hydrated salt phase change heat storage materials is more extensive.However,the practical application of such materials is also restricted by various defects,the most prominent of which is the supercooling degree.In short-term heat storage,it is necessary to reduce the supercooling degree of inorganic hydrated salt phase change energy storage materials as much as possible to improve its heat release efficiency;in long-term heat storage,in order to maintain the liquid state of hydrated salts stably under the interference of unfavorable external factors and to avoid the release of thermal energy by autonomous crystallization which cause the reduction of energy storage efficiency,it is necessary to explore effective strategies to optimize the supercooled stability of hydrated salt,.In order to solve the problem that supercooling degree brings to the short-term heat release efficiency of the hydrated salt,fumed silica-disodium hydrogen phosphate dodecahydrate composite phase change material(FS/DHPD)was prepared by physical blending and melting process.It is found that the addition of FS can form a three-dimensional network structure in the DHPD inorganic hydrated salt phase change heat storage material,which greatly improves the short-term heat storage effect of the hydrated salt.The hydrated salt added with 2wt% FS had better performance in reducing supercooling,enhancing thermal stability,etc.which is a potential heat storage material for further research and development.Hydrated salts at the supercooled state(liquid state)are extremely susceptible to external interference(vibration,low temperature)which would result in spontaneously crystallize and heat loss.In this paper,a microscopic visualization method for investigating the effect of inner surface materials on the supercooling stability of hydrated salts was developed for the first time.The surface free energy of four different types of common container materials were measured and the free-fall experiment of sodium thiosulfate pentahydrate droplet was carried out.An extreme low temperature supercooling experiment was done to further study the relationship between the surface free energy of the container and the supercooling stability of hydrated salt on a macro scale.The results show that a container with a lower surface free energy is beneficial to maintain the hydrated salt for a longer and more stable supercooling.In addition,Gibbs free energy theory is not only applicable to the solid-liquid interface,but also applicable to the gas-liquid interface.Apart from this,while maintaining the stable supercooling characteristics of liquid hydrated salt,two phase change energy storage devices based on different crystallization triggering methods(dry ice,liquid nitrogen trigger)of hydrated salt were designed,fabricated and tested.The results show that liquid nitrogen would be a more preferred option for triggering crystallization of hydrated salts due to its short triggering time,high crystallization efficiency and better exothermic effect.If the stability of the use of liquid nitrogen and the flexibility of the use of low-temperature materials can be further improved,the advantages of the phase change energy storage crystallization trigger device will be exerted to a greater extent,and its application value will be improved.