Research On Cold Storage And Release Characteristics Of Multi-stage Phase Change Cold Storage Unit

Cool storage air-conditioning technology can effectively adjust the phenomenon of unbalanced electricity load between day and night,thereby improving power generation efficiency and improving the safety of power grid operation.one of them.However,in the process of cold storage and cold release,the temperature change of the refrigerant will affect the phase change rate of the phase change material,thereby affecting the rate of cold storage and cold release.Therefore,the idea of multi-stage phase transition cold storage was put forward and attracted scholars’ attention and research.In this paper,a squarecolumn shell-and-tube multi-stage phase change cold storage unit is proposed,and the cold storage/release characteristics of the cold storage unit are studied by numerical simulation and experimental methods.In this study,three different phase change materials with phase change temperatures of 5.5℃,7℃,and 8℃ were selected as filling materials for cooling storage units,which were referred to as PCM1,PCM2,and PCM3,respectively.A multi-stage phase change cold storage unit model is established,and PCM1,PCM2,and PCM3 are filled in the cold storage unit in turn according to the flow direction of the refrigerant.The simulation and experiment were carried out under the condition that the inlet flow rate of the coolant was 0.5 m/s and the temperature was 2℃,and the experimental results were in good agreement with the simulation results.Based on the above,the effects of different heat exchange tube materials,refrigerant inlet temperature and flow rate on the cold storage/release characteristics of the cold storage unit were simulated and studied.The results show that in the process of cold storage and release,for the single-stage phase change cold storage unit filled with the same PCM,there will be no phase change region at the outlet of the carrier fluid.The use of multi-stage PCM phase change cold storage unit can make all levels of PCM undergo phase change at the same time,effectively reducing the area without phase change;in addition,the total time required for the storage and release cycle of separately filling PCM1,2,and 3 conditions is 19319s.,20586s,19458s,and the total time required for the multi-stage PCM cold storage and release cycle is the shortest,which is 18742s.The maximum energy storage efficiency per unit time is 42.21 kJ/h,The performance of the multi-stage cold storage unit is better than that of the single-stage cold storage unit in a complete cold storage and release cycle.Regarding the material of the heat exchange tube,the cold storage unit with plexiglass(PMMA)as the heat exchange tube has the smallest cold storage capacity per unit time,which is 33.35 kJ/h.The cold storage unit with aluminum tube as the heat exchange tube has a larger cold storage capacity per unit time,which is 39.87 kJ/h.The cool storage unit with copper tube as heat exchange tube has the largest cool storage capacity per unit time,which is 41.70 kJ/h.The cold storage unit with aluminum tubes and copper tubes as heat exchange tubes has very little difference in the amount of cold storage per unit time.When selecting the tube material of the cold storage unit,the metal pipe should be selected first to improve the cold storage efficiency of the cold storage unit.During cold storage,the inlet flow rate of the refrigerant is 0.1 m/s,and when the inlet temperature decreases from 3℃ to 1℃,the cooling capacity per unit time increases by 40.0%;when the inlet temperature of the refrigerant is 2℃,the flow rate increases from 0.1 m/s When it reaches 0.3 m/s,the cold storage capacity per unit time increases by 32.9%.When releasing cooling,the inlet flow rate of the refrigerant is 0.1 m/s.When the inlet temperature increases from 12℃ to 14℃,the amount of cooling released per unit time increases by 30%.The inlet temperature of the carrier refrigerant is 12℃ and the flow rate is 0.1 m/s.When it increases to 0.3 m/s,the cooling capacity per unit time increases by 24.3%.The refrigerant inlet temperature has a greater influence on the cooling capacity per unit time than the refrigerant flow rate.The research results of this paper can provide a reference for the design of the regenerator.