调节传热窄点以提升有机朗肯循环性能的分析

依据热源温度与工质临界温度之间的关系，有机朗肯循环（ORC）的循环性能呈现有极值的优化工况或单调递增两种现象，并且后者优于前者。引起这种差异的主要原因是加热过程中传热窄点位置的不同，导致循环的加热量不同。由此，本文提出调节ORC中加热过程的传热窄点位置，以提高循环的加热量和净输出功。并构建一种喷射式有机朗肯循环（EORC），研究证明如何实现加热过程的传热窄点位置调节以提高循环性能。此调节还增强了传热的匹配性，或降低了传热的不可逆性。结果表明：热源水温度100~160℃范围内，采用R245fa，EORC的最大净输出功比ORC提高了34.99%~22.57%。EORC中，热源水温度120℃下，混合工质R134a/R245fa（0.7∶0.3）的最大净输出功比纯工质R245fa和R134a分别提高了7.12%和9.45%。

Analysis of adjusting pinch point of heat transfer to improve the performance of organic Rankine cycle

Thermal performance of organic Rankine cycle (ORC) exists optimum condition with the maximum or monotonic increase according to the temperature relation between low grade heat source and the critical temperature of working fluids. Performance with monotonic increase is better than that with optimum condition.This difference is caused by the location of the pinch point of heat transfer (PPHT) in the heating process, which causes the difference of the heat addition in the ORC. Based on this consideration,a new approach of adjusting PPHT in the heating process is proposed in order to increase the heat addition and net power output of the cycle. Accordingly, a configuration of ORC with ejector (EORC) is designed to demonstrate the adjustment of the PPHT to improve the thermal performance. Moreover, this adjustment of PPHT can enhance the matching of heat transfer of the heating process, or reduces the irreversibility of the heat transfer. Results show that the increment of the maximum net power output with R245fa can reach 34.99% to 22.57% in heating water temperature range of 100℃ to 160℃ by EORC compared with ORC. At heating water temperature 120℃, the maximum net power output of mixture R134a/R245fa (0.7∶0.3) is 7.12% and 9.45% higher than that of R245fa and R134a in EORC, respectively.