四种跨临界CO_2压缩式热泵系统的热力性能研究

Study on thermodynamic performance of four different types of transcritical CO_2 compression heat pump systems

CO2是具有很大潜力的天然替代工质之一,CO2跨临界循环放热过程中具有较大温度滑移,与水侧温升过程相匹配,因此适合用于热泵热水器系统。国内外学者提出了许多提高跨临界CO2循环效率的方法,其中包括引入回热器、喷射器等设备,从不同角度对比分析在常规跨临界CO2热泵系统中引入回热器、喷射器后系统的性能变化。本文在前人工作的基础上,建立相关热力学计算模型,并进一步对四种不同形式的跨临界CO2热泵系统(常规跨临界CO2热泵系统(TCHS)、带回热器的跨临界CO2热泵系统(TCHSI)、带喷射器的跨临界CO2热泵系统(TCHSE)及带喷射器与回热器的跨临界CO2热泵系统(TCHSEI))的性能进行研究,对比分析排气压力一定的情况下四种循环的热力性能;从最优排气压力的角度出发,分析对比不同系统中气冷器出口温度变化对系统最优排气压力和制热系数的影响,以及喷射器等熵效率对系统性能的影响。以上研究为CO2压缩式热泵系统的实用化进展奠定良好的理论基础。

CO2 is one of the most promising natural alternative refrigerants. Because of its large temperature change in the transcritical cycle and matching the temperature lifting process of water side, CO2 is a suitable refrigerant for heat pump water heater system. Domestic and foreign scholars have proposed lots of methods of improving the transcritical CO2 cycle＇s efficiency,including introducing internal heat exchanger and ejector, etc. , and contrastively analyzed the performance change of conventional transcritical CO2 heat pump system after including introducing internal heat exchanger and ejector from different aspects. Thermodynamic models are built up on the basis of previous work. Further theoretical investigations are carried out on the performances of four different types of transcritical CO2 heat pump systems.the conventional transcritical CO2 heat pump system （TCHS）, transcritical CO2 heat pump system with internal heat exchanger （TCHSI）, transcritical CO2 heat pump system with ejector （TCHSE） and transcritical CO2 heat pump system with both internal exchanger and ejector （TCHSEI）,and their thermodynamic performances under a certain discharge pressure are compared and analyzed. In the view of optimal discharge pressure, impacts of gas cooler outlet temperature on both optimal discharge pressure and COP,and impacts of ejector isentropic efficiency on system performance are compared and analyzed. The research above lays a solid foundation for practical use of transcritical CO2 heat pump system.