Optimization Of Phase Change Heat Storage Device And Its Application In Heating System

Heat storage technology is widely used in the energy field,which can effectively reduce energy waste and overcome the intermittency and volatility of clean energy to a certain extent.It plays an important role in many fields.Due to the advantages of phase change materials such as high energy storage density,easy matching and easy control,the research and application of phase change heat storage technology is widely concerned.At the same time,the difference between peak and valley of electric power consumption is becoming more and more serious.To solve this problem,the high latent heat value of phase change materials can be used to store the electric energy in the form of heat in the low electricity price period and release the heat in the peak stage,so as to achieve the purpose of peak shifting and valley filling.Firstly,a heat exchange tube in the heat exchanger is cut off as the research object to compare and analyze the influence of three phase change materials,stearic acid,barium hydroxide octahydrate and sodium acetate trihydrate,and their operating conditions on the comprehensive thermal performance of phase change heat storage unit.The research object is simplified as a 3D casing physical model,and the numerical simulation method is used for calculation.The results show that in the heat storage stage,compared with stearic acid,the modified barium hydroxide octahydrate and sodium acetate trihydrate can save 57.84%and 58.84% time.When the inlet temperature of heat transfer fluid increased from 358.15 K to 373.15 K,the complete melting time of stearic acid,barium hydroxide octahydrate and sodium acetate trihydrate decreased by 37.76%,35.43% and 21.52%.When the inlet velocity of heat exchange fluid increased from 0.5 m/s to 2.0 m/s,the complete melting time of stearic acid,barium hydroxide octahydrate and sodium acetate trihydrate is shortened by12.25%,45.68% and 45.49%.Secondly,annular fins,spiral fins and longitudinal fins are established,and the influence of three types of fins on shortening the melting time of phase change materials is compared and analyzed.The finned tube is further optimized according to its influence on heat transfer,which makes the temperature distribution in the heat accumulator more uniform during melting.The results show that the melting time of annular finned tube heat storage unit is the shortest,which can shorten the melting time by 73.11% compared with that of single tube heat storage unit.Compared with the heat storage unit of the same diameter finned tube,the temperature unevenness of the variable diameter finned tube with the fin area increasing from top to bottom is reduced to 0.03,but the melting time of the variable diameter finned tube is extended by 3.93%.Finally,a phase-change heat storage heating system is designed and built.The performance indexes of heat storage,heat storage and heat release rate,heat storage and heat release efficiency,exergic efficiency and so on were analyzed by experiments.Combined with the local building structure,the heating demand of the heating room is calculated.The heat storage capacity of the system is 100 k Wh,the heat storage time is 4.5 h,the heat storage rate is about 18 k W,the heat release rate is 85 k Wh,and the heat release rate is about 21 k W.The heat storage efficiency is 70 % and the effective energy release efficiency is 83 %.Overall exergic efficiency of thermal accumulator was about 17.5 %,while exergic efficiency is about 14 % and 78.89 %.The heating system proposed in this paper can use latent heat storage capacity of phase change materials for heating,effectively regulate indoor temperature,and rationally utilize peaking and valley electricity price,which provides theoretical support and design basis for the application of heat storage heating system in practical engineering.