基于变窄点温差法的有机朗肯循环工质热物性与循环性能的研究

Research on Thermal Physical Property and Cycle Performance of Organic Rankine Cycle Based on Variable Pinch Point Temperature Difference

对基于有机朗肯循环的车用汽油机余热能回收利用系统进行了研究。根据试验所采用的蒸发器在MATLAB中建立了循环系统模型,采用变窄点温差的方法,计算分析了28种工质在不同蒸发压力下热物性与循环性能的关系。结果表明:工质的窄点温差随工质蒸发压力变化而变化,在蒸发压力从0.5MPa升至2.5MPa过程中,窄点温差变化均接近30℃,需要在变窄点温差的基础上比较工质热物性与循环性能的关系;临界温度越高的工质其循环效率相对越低;在不同的蒸发压力下,均存在蒸发温度与临界温度之比的最优区间,在此区间内的工质循环效率最高,且该区间随压力的升高而右移;在所给定的入口条件下,湿工质的循环功率最高,等熵工质其次,干工质输出功率最小。

Exhaust energy recovery （EER） from a light-duty gasoline engine based on organic Rankine cycle system was investigated. A circulation system model was established in MATLAB based on a heat exchanger used for the investigation. With variable pinch point temperature difference （PPTD）, the relationship of thermal physical property and cycle performance of 28 working fluids was calculated and analyzed. The results show that the PPTD changes with different evaporation pressures. With the pressure changing from 0.5 to 3.5 MPa, the PPTD varies by nearly 30℃. Therefore the PPTD change should be considered in the calculation. Relatively, the fluid with a higher critical temperature has a lower cycling efficiency. A region of optimal ratio of evaporation temperature and critical temperature exists in which the fluids have higher efficiencies than other regions, and it moves towards right with the increase of evaporation pressure. Wet fluids have the highest power output followed by isentropic fluids, and dry fluids produce the lowest one under given conditions.