Study On The Performance Of The Water Vapor Heat Pump System

At present,there are a large amount of low-grade waste heat below 65℃in life and production.Due to the low grade,it is difficult to recycle,resulting in this part of low-grade waste heat often discharged directly into the environment,causing a lot of energy waste and affecting the environmental heat.This paper proposes a heat pump system using water as the working medium,which uses the good thermal performance and environmental protection characteristics of water to improve the quality recovery of low-grade waste heat.By establishing a thermodynamic model for the system and using MATLAB software,the effects of water spray temperature,evaporation temperature,and condensation temperature on the performance of the system are analyzed;in order to expand the application range of the steam heat pump,a steam heat pump combined with other working fluids is proposed The cascade system and the thermodynamic model and simulation process of the cascade system are established.The performance changes of the cascade system when different working fluids are combined with the steam heat pump are analyzed.Finally,the performance of the steam heat pump system in actual operation is verified through experiments.This paper has studied the steam heat pump system through theoretical calculations and experiments.(1)The core component of the water vapor heat pump system is the compressor.In view of the problem that the water vapor is larger than the volume when the temperature is low and the compressor exhaust temperature is high,this paper selects the screw compressor that is not sensitive to wet compression as the system compressor The effects of different water injection temperatures(saturated steam temperature at the water injection location)on the screw compressor discharge temperature,water injection mass flow rate,water injection ratio,condenser heat release,compressor power consumption,and system EER are analyzed.The results show that there is the best water spray temperature,so that the overall performance of the system is the best.(2)At the optimum water spray temperature,the specific volume of water vapor at an evaporation temperature of 30℃to 60℃,the amount of heat absorbed by the evaporator,the mass flow rate at the inlet of the evaporator,the mass flow rate of the compressor suction,the power consumption of the compressor,the condenser Changes in heat and system EER.The results show that the maximum EER of the system is 3.1 when the evaporation temperature is 60℃.Due to the compressor discharge temperature,it is recommended to use multi-stage water spray when the evaporation temperature is less than50℃to ensure the safe operation of the compressor.(3)When the evaporation temperature is 60℃,the changes of evaporator inlet mass flow rate,evaporator heat absorption,compressor power consumption,pressure ratio,condenser heat output and system EER are analyzed when the condensation temperature is 80℃～110℃.The results show that as the condensing temperature ri-ses,the system EER decreases from 5.86 to 2.15,and the system performance is sti ll considerable when the temperature is raised to 50℃.(4)In order to expand the range of waste heat recovery and increase the temp-erature range,this paper selects 7 common heat pump working fluids as low-tempe-rature working fluids,forms a cascade system with a steam heat pump,and analyz-es the low-temperature evaporation temperature to low-temperature pressure ratio and low-temperature compression The influence of the power consumption low-temperat-ure performance coefficient EER_d,the water vapor heat pump cascade system perfo-rmance coefficient EER_f,the different low-temperature condensation temperature and other cascade system performance.The analysis results show that under the premise of considering the environmental protection of the working medium and the energy saving of the system,it is better to choose R717 as the low-temperature working medium;at the same time,considering the pressure ratio,compressor exhaust tempe-rature,compressor lubricating oil and other issues,the low temperature is recomme-nded The condensation temperature should not exceed 65℃.(5)To verify the analysis results of the steam heat pump system,a separate st-udy was conducted.The water vapor heat pump experimental system uses a twin s-crew compressor with water jet.When the condensation temperature is 102℃,the ac-tual performance of the water vapor heat pump system with an evaporation temp-erature between 50℃and 60℃is studied.The experimental results show that:Water spray effectively controls the discharge temperature of the twins-crew compressor below the alarm temperature of the compressor;the volumetric e-fficiency and the maximum adiabatic internal efficiency are:0.514,0.435,and the EER increases fro m 1.74 to 2.46,showing good system performance.The comparison between the ex-perimental results and theoretical calculations shows that the ther-modynamic model of the steam heat pump system is in good agreement with the experimental results.As a green environmental protection system,water vapor heat pump can effectively recover low-grade waste heat,which is of great significance for energy saving and emission reduction.