跨临界CO_2蒸气压缩-引射制冷循环的性能分析

Performance of ejector-expansion transcritical CO_2 vapor compression refrigeration cycle

CO2跨临界基本循环由于节流损失较大使其能效比较低,采用引射器替换节流阀可以回收部分膨胀功,进而提高循环的性能系数。针对跨临界CO2压缩-引射制冷循环建立了热力学模型,考虑了引射器喷嘴出口与蒸发器之间的压力差异,并分析了吸入压差值、气体冷却器压力、气体冷却器出口温度、蒸发温度及蒸发器出口过热度对循环性能的影响。结果表明:在一定工况下存在一最佳吸入压差,使引射器提升压力值和循环COP提高率达到最大值,典型空调工况下最佳吸入压差约为0.34 MPa。吸入压差的取值对引射系数和循环最优排气压力值影响很小。

The basic transcritical CO2 systems exhibits low energy efficiency owing to the large throttling losses. Replacing the throttle valve with an ejector is an effective measure for recovering some of the lost energy of the expansion process, thus im proving the cycle performance. A thermodynamic model of the ejector expansion transcritical CO2 refrigeration cycle was developed. The pressure drop between the evaporator and the outlet of the motive nozzle was taken into account in the model. Effects of parameters, such as the suction pressure drop, gas cooler pressure, gas cooler outlet temperature, evaporator temperature and evaporator outlet superheat on the cycle performance Were analyzed. The results showed that there exits an optimum suction pres- sure drop which gives a maximum recovered pressure or COP improvement rate under a specified condition. The optimum suction pressure drop is about 0.34 MPa under the typical air conditioning working conditions. The value of suction pressure drop has less influence on the ejector entrainment ratio and the optimal gas cooler pressure of the cycle.