Theoretical Analysis And Experimental Research Of Self-cascading Heat Pump Systems

The structure improvement of self cascade heat pump system is mainly studied in this paper.Research contents include:Energy analysis and thermodynamic calculation of the auto cascade heat pump system;Numerical simulation of evaporation tube;Optimization and improvement of condenser;Experimental study of auto cascade heat pump system.Firstly,experimental system to do the analysis and calculation of energy cycle,The calculation results show that,for auto cascade heat pump systems,the energy loss is mainly concentrated in the compressor,throttle body,evaporator and condenser.To reduce the energy loss of compressor considering the difficulty,proposed the use of electronic expansion valve throttling mechanism instead of thermal expansion valve and heat exchanger to improve the energy efficiency of the throttle mechanism to improve the program.Secondly,the evaporation in a single U tube is simulated.Based on the possible problems in the actual evaporator,the evaporation of pure R23 refrigerant and the R23 mixed refrigerant containing 8%R134a of mass fraction were numerically simulated.Simulation results show that:When pure R23 refrigerant evaporates in the tube,bubbly flow,slug flow and annular flow appear in the flow regime.For the R23 mixed refrigerant containing 8%R134a,the simulation results show that the evaporation rate in the tube is obviously lower than that in the pure R23 refrigerant.The reason for this phenomenon is that:The mixed refrigerant is easier to achieve the complete suppression state of nucleate boiling than pure refrigerant,the evaporation of the volatile components at the interface results in an increase in the saturation temperature of the scoring interface,reduce the effective temperature difference that provides heat for bubble growth,at the same time,the mass transfer resistance of the mixture slows the growth rate of the bubble,weakens the nucleate boiling,leads to the inhibition of the mixture more easily,and leads to the deterioration of heat transfer.It is decided to use a rectifying device instead of a steam liquid separator to improve the heat transfer effect of the evaporator.According to the non azeotropic mixture refrigerant in the heat when the heat transfer coefficient of this phenomenon is lower than the heat transfer effect of pure refrigerants,this paper presents experimental scheme on the condenser to add a separator to improve the heat exchange effect of the condenser and the mixed refrigerant fullyseparated,based on the experimental scheme,set up the experiment table.Finally,the load and no-load when there is no separator and refrigerant temperature of different proportion of different measuring points is measured,and the auto cascade system with two stage compression,jet enthalpy system was compared and observed the changes of flow patterns in the condenser.Get the main conclusions:The maximum temperature difference of heat transfer and heat transfer after separation of non azeotropic refrigerants with pinch phenomenon has been effectively suppressed,the effect of heat transfer and mass transfer resistance is greatly reduced,at the same time through the heat exchanger and condenser refrigerant separator after the heat transfer back to the beginning,the refrigerant steam can directly contact with the pipe wall to improve the heat transfer coefficient,and combined with the actual observed pattern was verified.Compared with other systems,the self cascade system is superior to several other systems in terms of cooling capacity,power and cooling coefficient...