| This paper mainly discusses the application and performance of the natural working fluid CO2in heat pump and refrigeration systems. Preliminary, the influences of different parameters on the transcritical CO2system is concluded through the experimental study. It studies on the characteristics of the water source CO2heat pump system cycle, which lays at the basis of the theoretical and empirical for the design of the air source transcritical CO2refrigeration system test bench. It has played effectively guiding and facilitating role for future system development, optimization and improvement.Firstly, through the software simulation calculation and comparison of different refrigerant thermodynamic properties have been discussed. The CO2refrigerant has the highest per unit volume of cooling capacity and liquid/vapor thermal conductivity, the lowest viscosity and surface tension in the nucleate boiling. Next, the paper uses thermodynamic formula deduced the relational, such as transcritical CO2cycle performance, the system operating pressure of the best COP and the loss of expansion. The result show that:the suction superheat temperature, gas cooler outlet temperature, system high side pressure and the isentropic efficiency, which are the main parameters of performance impact. It also discusses the control strategy of system high pressure operation, which proposes a bypass valve with dual expansion and the intermediate liquid receiver in the transcritical CO2system.Secondly, the paper introduces the transcritical CO2water source heat pump system test bench. The experimental research on cycle characteristics of the system, such as the influence of heat pump system with dual throttle intermediate reservoir on the pressure fluctuation and temperature, the effect of high side pressure changes in the system, the intermediate heat exchangers affect system performance, the heat dispersion measure test research on heat exchanger efficiency, which have been discussed and analyzed. Finally, the paper describes the build process of refrigeration test air source CO2, the air source transcritical CO2refrigerant system is built in the laboratory and the components are also introduced, including the computing and parts of the system thermodynamic cycle model simulation, the refrigeration systems, fan systems, data acquisition, and electronic control systems. We developed a dual expansion with regenerator gas liquid bypass and intermediate accumulator air source transcritical CO2refrigeration system test bench. The experimental studies on the charging amount of the new system have been discussed.The results show that:(1) For the1.5P transcritical CO2water source heat pump system, after the pressure balanced reservoir affects, the outlet temperature of low pressure side expansion valve is1℃/MPa.(2) The COPH rise4.4%, when the source temperature increase5℃; On the contrary is the COP drop6.8%, when the sink temperature increase5℃. The source temperature has great influence on the temperature of outlet chilled water, and the outlet temperature of cooling water alter within0.7-0.9℃per5℃change in sink temperature.(3) The intermediate liquid receiver and dual expansion with the bypass valve intermediate gas injection has improved the transcritical CO2refrigeration capacity. The charge of the air source test bench reasonable is about2.1kg, the system equilibrium pressure is4.375MPa, the refrigerant filling fraction is0.45standard. |
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