Study On The Inter-stage Injection Release And Defrost Characteristics Of Two-stage Compression Heat Pump System

At present,China's"three north"area is gradually promoting the air source heat pump heating technology under the policy of"coal to electricity".However,there will be some problems when the air-source heat pump is operated at low temperature,such as the increase of the compression ratio,the increase of the exhaust temperature,the decrease of heating performance,"frost",etc.Those problems limit its further application.The intermediate injection combined with two-stage compression technology can improve the low temperature adaptability of air source heat pump,but the problem of"frosting"is still to be improved.Therefore,in order to improve the two-stage compression heat pump system's low temperature adaptability,this paper puts forward a new type of inter-stage release defrosting cycle.Based on this cycle,matching relations between inter-stage release parameters and compressor capacity,inter-stage parameters of dynamic characteristics and influences inter-stage release parameters on the performance of the system were analyzed through experimental test and simulation.First of all,considered the two characteristics of variable capacity and inter-stage injection,a two-stage compression heat pump system with continuous heating defrosting is proposed.In addition,a two-stage compression heat pump experiment platform with the characteristics of the inter-stage release was set up.The experimental system adopts frequency conversion compressor,and the mass flow of injection and discharge loop is regulated by electronic expansion valve?What's more experimental system can simulate multiple evaporation and condensation conditions.Secondly,based on the rolling rotor compressor's structure features and operation characteristics,the compressor process is divided into four stages,which could be divided into16 coupling process of high and low-pressure compressor running mode.Combined with the compressor,throttle and heat exchanger's model,constructed the inter-stage release characteristics of two-stage compression heat pump system simulation model.The deviation between simulation results and the experimental test results of-10%¹2%.Thirdly,based on the experimental test and the simulation model,this paper analyzed how release parameters effects the performance of two-stage compression heat pump system with no inter-stage injection.This paper analyzes relationship between the high and low-pressure compressor capacity ratio and the amount of release.Under the benchmark conditions,when compressor capacity ratio capacity was 2.82,if the m_pumpump value increases by 0.001kg/s,then the inter mediate pressure will decrease by 25kPa,middle temperature will decrease by 1.5?.maximum COP corresponding?value increases along with the augment of release mass.Finally,based on the simulation,this paper analyzes the influences of the inter-stage release parameters on the intermediate control volume of thermodynamic parameters,points out that the two-stage compression is not a continuous compression process,and thermodynamic parameters in the control volume have the fluctuation performances which is minor to the time-average value,owing to the compressor asynchronism,the exhaust intermission and the difference in the input and output mass flow rate of the intermediate control volume system.However,the process of inter-stage release does not affect the operation cycle of the compressor,but it has certain influence on the compressor compression process of the system,which increases the fluctuation performances of the middle control volume.At the same time,analyzed under the different inter-staged release parameters,the change rule of inter-stage parameters the influence of the inter-stage parameters and the system performance.It is pointed out that inter-stage release mass is not much influence on the injection enthalpy and mass but has a great influence on the performance of the system.Under the same amount of injection,each inter-stage release mass increase of 0.001kg/s was added,the heat capacity and COP decreased by 3%⁶%,8%¹3%.When constant emission system exists the optimal injection quantity and the optimal injection quantity increases with the amount of emission increases gradually,when the release mass increased from 0.001 to 0.003 kg/s,the optimal COP of the injection volume changes from0.0022 kg/s to around 0.0043 kg/s.