二氧化碳及其混合工质跨临界朗肯循环热力学研究

Thermodynamic research on transcritical rankine cycle using CO2 and CO2-based mixtures

利用热力学仿真的方法,研究纯CO2及其与R32,R1270,R290,R161,R152a,R1234yf和R1234ze共7种有机工质组成的二元混合工质下循环的热效率和㶲效率。研究结果表明:有机工质添加比上限为70%,超过该比例时回热器热侧出口温度过高,导致循环变为朗肯循环;大部分混合工质热效率随一级透平入口压力p4增大而升高,其最佳再热入口压力p5在10~13 MPa范围内;研究工质中,CO2-R152a的回热再热循环热效率和㶲效率最高,较纯CO2循环分别提升16.16%和28.46%,这是因为其临界温度最高、临界压力最低导致系统做功更多、热损更少。

The thermodynamic simulation methods were used to study thermal/exergy efficiency of pure CO2 and its mixed working fluids composed of R32,R1270,R290,R161,R152a,R1234yf and R1234ze,which were organic working fluids.The results show the proportion of organic working fluids are 70%,because the outlet temperature of the hot side of the regenerator is too high when this ratio is exceeded,causing the cycle become Rankine cycle.Most of mixed working fluids increase the thermal efficiency with the increase of the inlet pressure p4,and the optimal inlet pressure p5 is in the range of 10-13 MPa.Among the working fluids,CO2-R152a has the highest thermal efficiency/exergy efficiency,which is 16.16%and 28.46%higher than that of the pure CO2 cycle.This is because the highest critical temperature and the lowest critical pressure lead to more system work and less heat loss.