Experimental Investigation Of Start-up Characteristic Of R744/R600a Heat Pump System

In recent years,the economy has developed rapidly,and the heat for building heating has increased year by year.It has been affected by energy and environmental issues such as the haze in the north and the gas shortage in the south.Traditional fossil fuels such as coal have been unable to meet the requirements.The heat pump system uses electricity as its energy source,which has become the protagonist in the coal conversion to northern China,energy saving in heat pump systems and replacement of environmental protection refrigerants,and has become the focus of current scholars at home and abroad.Research shows that each of the natural refrigerants R744 and R600 a has excellent environmental performance.The two refrigerants are mixed to form a non-azeotropic mixed refrigerant,which can complement each other,can achieve a good match with the temperature-slip between the heat-carrying fluids,improve the system efficiency,and the explosion characteristics can be improved.Suppressed.This paper takes natural R744/R600 a heat pump system as the research object,and conducts in-depth research on its start-up characteristics.The experimental study of the start-up process of the R744/R600 a heat pump system found that although the pressure,temperature,and power consumption of the mixed refrigerant fluid system fluctuate greatly,the settling time is shorter.This is because the addition of R744 makes the heat efficiency of the working medium.With the improvement,the system stability time is shortened,and the heat sink water temperature rises faster and reaches a stabilization time 440 s earlier than the pure refrigerant system.Because R744 increases the evaporation pressure,the instantaneous pressure ratio of the system gradually decreases during the start-up period and tends to be stable.When the heat sink water outlet temperature is 45℃,50℃,and 55℃,the system start-up process time is gradually increased to 1585 s,1385s,and 2105 s,respectively.The results of cold and hot start of the system show that a higher initial refrigerant temperatureis beneficial to shorten the system’s settling time and improve the stability of the system during start-up.In order to shorten the start-up time,this paper improved the start-up scheme of the mixed refrigerant system,controlled the initial flow of hot sink water,and raised the temperature of the working fluid quickly.As a result,it was found that the pressure and temperature of the system after start-up were faster than that of the unmodified improvement and reached stability.The time was shortened,in which the time taken for the outlet temperature of the heat sink water to stabilize was shortened by 560 s.In addition,the instantaneous pressure ratio achieved a substantial reduction in the stabilization time.This is due to the fact that the smaller heat sink water flow speeds up the temperature increase of the working fluid,shortens the uniform distribution time of the refrigerant,improves the heat transfer efficiency,and shortens the time for the instantaneous heating performance coefficient of the system and instantaneous heat gain to reach a stable level.