Research On The Thermal Performance Of Ba?OH?₂·8H₂O And Numerial Simulation During Heat Exchange

The development and utilization of the renewable energy which include solar energy can effectively promote the diversification of Chinese energy structure and can achieve sustainable development of energy.As a clean and efficient energy,solar energy has been widely used in various fields.In order to improve the utilization efficiency of solar energy,a variety of storage devices should be studied,so thermal storage technology is the key technology of solar energy utilization.Methods for reducing the Ba?OH?₂·8H₂O undercooling degree and phase separation were studied in this article.The heat storage device,using Ba?OH?₂·8H₂O as thermal storage material,was designed and heat transfer performance was analyzed by numerical simulation technology.As many as 5 kinds of nucleating agents and 3 kinds of thickening agents were selected through the‘Edison Method'.The undercooling was measured by using the step cooling curve method,and the nucleating agent and thickening agent which can effectively reduce the undercooling of Ba?OH?₂·8H₂O were selected.Influence of the cooling rate?water cooling and air cooling?,nucleating agent content?mass fraction of 0.5%,1.5%,2.5%?,cooling mode?ultrasonic oscillation?on Ba?OH?₂·8H₂O undercooling and phase separation was studied in turn.In addition,thermal cycling stability of Ba?OH?₂·8H₂O was analyzed after 50,100,150,200times of thermal cycling experiments.Through the methods of comparative and theoretical analysis,a type of heat exchanger was selected according to the thermal physical properties and flow characteristics of Ba?OH?₂·8H₂O,and the corresponding heat storage device was designed at the same time.And then the packaging materials,pipe materials,thermal insulation materials and heat transfer media,which have a good compatibility with Ba?OH?₂·8H₂O,were chosen by order.The size parameters of the heat exchanger were determined by mathematical calculation,and the total heat transfer area was9.95×10⁵mm²,which provided a reference for the actual construction of the heat storage device.The changes of the temperature field and solid-liquid interface were analyzed by numerical simulation method?CFD?,and then heat transfer performance of the heat storage device was comprehensive analyzed.The factors that affect the heat transfer enhancement were theoretically analyzed through the heat transfer equation,and then the numerical simulation method was used to study the influence of each factor on the heat transfer process.Firstly,the relationship between the temperature and the heat transfer efficiency was studied by increasing the temperature difference between the heat storage system and the initial temperature of the heat transfer medium.Then the heat transfer efficiency of heat transfer surface with or without fin for heat storage system were studied,and the heat transfer enhancement effect of fin?high,thick,fin spacing?with different sizes was focus studied by using the control variable method.The results show that the heat transfer efficiency of the system can be improved when the fin size was 12mm high,2mm thick and 30mm spacing.In the end,the influence of heat transfer medium at different inlet velocity on the heat transfer efficiency was analyzed.According to the simulation results,for the heat storage device,the most appropriate inlet flow rate of heat transfer medium is 0.1m/s.The comprehensive analysis of the Ba?OH?₂·8H₂O phase change thermal storage material shows that Ba?OH?₂·8H₂O is an excellent solar thermal storage material with good heat storage capacity and thermal cycling stability.