| Since entering the 21 st century,the scale of cold storage built in China has been increasing with the development of national economy,while the energy consumption of cold storage operation in the total energy consumption of the building has further increased,the key to realize energy-saving operation of cold storage system is to improve the evaporator refrigeration performance,if the structure of evaporator has been determined,its refrigeration capacity is mainly affected by the liquid supply method and the frosting situation of the tube wall.This thesis is firstly based on the self-developed virtual simulation experiment software,through 3D solid modeling simulation to study the distribution of various components and pipes of cold storage refrigeration system,and also analyze the operation performance of different liquid supply method refrigeration system and the operation process of hot gas defrosting.For the pump-supplied liquid refrigeration system,this thesis optimizes the optimal pump-supplied liquid cycle multiplier with the objective of maximizing the energy efficiency ratio（EER）of the refrigeration system,taking into account the influence of the pressure drop of the refrigerant in the evaporator and the return tube on the operation performance of the refrigeration system;at the same time,the hot gas defrosting and defrosting process of the top-row tube evaporator is simulated and analyzed;the main contents and results of the study are as follows:（1）Development and application of cold storage virtual simulation experiment software.The software can realize the simulation experiment analysis of cold storage direct expansion liquid supply refrigeration system,gravity liquid supply refrigeration system and liquid pump liquid supply refrigeration system as well as analyze and calculate the optimal intermediate temperature of two-stage compression refrigeration cycle,and at the same time,the process of hot gas defrosting of cold storage can be standardized.The operation principle of three different liquid supply methods of cold storage evaporator is analyzed in combination with the software,and the effect of superheat on the COP of refrigeration cycle is also derived by comparing and analyzing the direct expansion liquid supply and liquid pump liquid supply.expansion type liquid supply increased by 2.3%.（2）The pump-supplied evaporator in-tube refrigerant boiling flow pressure drop model,in-tube convective surface heat transfer model and total heat transfer model were established for the refrigeration system using liquid pump supply as the research object,and the rationality of the models was verified by comparing with the experimental database,and the comparison results showed that the Chisholm correlation and the Muller-Steinhagen-Heck correlation had higher correlation for the predicted values of in-tube boiling flow pressure drop of refrigerants R717 and R22,respectively,and the Shah correlation had higher correlation for the predicted values of in-tube boiling convective surface heat transfer coefficients of the above two refrigerants.Based on the established model,the Matlab programming language was used for programming calculations to analyze the factors affecting the variation of boiling flow pressure drop of refrigerant in the tube,and to reveal the influence of liquid pump supply multiplication rate on the convective heat transfer coefficient in the refrigerant tube.Under the same mass flow rate,R717 has a larger pressure drop during the boiling flow in the tube,and the pressure drop increases more obviously as the mass flow rate increases;increasing the liquid pump supply multiplier can improve the convective heat transfer coefficient on the surface of the refrigerant in the tube,and the overall convective surface heat transfer coefficient in the tube of R717 is higher than that of R22,but the change of the total heat transfer coefficient K with the supply multiplier of the evaporator is lower than that of R22.（3）Combined with the energy consumption model of the refrigeration system using liquid pump supply,a freezing room with a fixed refrigeration load in the cold storage system was calculated and analyzed to explore the changes of the total refrigeration capacity,operating energy consumption and energy efficiency ratio（EER）of the refrigeration system with the liquid supply multiplier.The optimal cycle multiplier of R22 is higher than that of R717,indicating that the charge of R22 in the refrigeration system is larger under the same refrigeration load.Through comparative analysis,this thesis proposes optimization measures for the optimal cycle multiplier of R717 and R22 refrigeration systems,reducing the original design reference value from 5 times to 2 times and 3 times respectively,the reference value compared to the optimal cycle multiplier has minimal impact on the change in cooling capacity,but compared to the original system can reduce the R717 charge by 60% and the R22 charge by 40% respectively.（4）The frost melting process on the surface of the exhaust tube evaporator of a cold room with R717 refrigerant was simulated and analyzed during hot gas frost melting.A 3D model of the evaporator is established,and the solidification/melting model in ANSYS CFD is used to analyze the proportion of liquid water after melting the frost layer on the outer wall of the coil to determine the speed of melting time under different gas delivery speeds.The simulation results show that as the melting time increases,the liquid phase distribution rate of the melted frost layer on the outer surface of the exhaust pipe increases gradually from the inlet end to the outlet end,and the effect of different hot gas flow rates of the refrigerant inside the tube on the defrosting time is compared and analyzed,and it is concluded that the refrigerant gas flow rate inside the tube affects the hot gas defrosting effect under the perspective of considering only the heat transfer of the frost,and the larger the refrigerant flow rate inside the tube,the shorter the defrosting time in a reasonable range. |
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