Performance Study On Two Stage Tube-In-Tube Gas Cooler Of CO₂ Heat Pump

As Global Warming and ozone depletion, environmental issues get more and more people’s attention. The refrigerant CO2 which global warm potential is 1, and the ozone depletion potential is 0. So the CO2 heat pump has been highly regarded in the world. How to improve the CO2 heat pump heating efficiency across the critical circulation system become the research emphasis of people. Gas cooler as the key components of the transcritical carbon dioxide cycle heat pump, the heat transfer effect directly affects the performance of the whole system.Tube-in-tube gas cooler because of its advantages of compact structure and high heat transfer efficiency, are widely used in the heat pump system. Research on heat transfer characteristics of the new type of two-stage tube-in-tube gas cooler, the high temperature of CO2 heat pump energy saving operation, the design of the new type of two-stage tube-in-tube gas cooler and application has important significance.From the two aspects of structure characteristics and heat transfer characteristics of CO2 transcritical cycle system in a variety of gas cooler were analyzed. To find out their advantages and disadvantages, and according to the existing across the CO2 transcritical cycle system with the research status of tube-in-tube gas cooler. Put forward the CO2 heat pump use a new type of two-stage tube-in-tube gas cooler, and the structure design and heat transfer characteristics were detailed introduction.Established a new type of two-stage tube-in-tube gas cooler thermodynamic simulation model. In this paper, by using the model, from the structural parameters and operational parameters on the two-stage tube-in-tube gas cooler simulation study is made on the influence of heat transfer performance. The results showed that:Under the condition of little change in the flow, can be adjusted through pipe diameter on both sides of the heat transfer coefficient is to increase the overall heat transfer coefficient; Intermediate node location selection should make the first level including live refrigerant pressure heat peaks, while making the first level heat transfer coefficient is larger; as the gas cooler outlet temperature is reduced, the area of the gas cooler are also needed to increase, when the outlet temperature of the refrigerant is already low, just in order to reduce the CO2 outlet temperature to increase in heat, need additional heat transfer area is not cost-effective; Refrigerant pressure increases to the gas cooler heat transfer, but the compressor input power increases, when the increase in quantity of heat is not enough to compensate the input power of the compressor for an additional, the system COP will drop, so there is an optimal pressure makes the increase in heat, system COP optimal. Finally, according to the results of the secondary cooling tube gas cooler optimization suggestions.Set up a experimental facility to used for the two-stage tube-in-tube gas cooler test, and designed the orthogonal experiment. According to the orthogonal experiment scheme, factors affecting the refrigerant water’s entrance temperature, the flow mass of water, the flow mass of refrigerant and pressure of the primary and secondary are ordered. The impact on the system heat, refrigerant pressure have the greatest influence, the water’s entrance temperature affect second, refrigerant mass flow rate affect third, The quality of the water flow influence relative to a minimum. Impact on the refrigerant pressure drop of the refrigerant flow mass have the greatest impact, the refrigerant pressure impact secondly, the water’s entrance temperature affect the third, the quality of the water flow relative to the minimum. And through the control variable method to quantitative understanding of the single factor effect the performance of the two-stage tube-in-tube gas cooler. The results show that:low water temperature, large refrigerant mass flow and high pressure is advantageous to the gas coller heat transfer, but consider the COP of the system, refrigerant mass flow rate and pressure there is an optimal value, causing the system COP optimal.