变冷凝环境条件下基于准二级膨胀单螺杆膨胀机的有机朗肯循环性能优化

Optimization on the Performances of Organic Rankine Cycle With Quasi Two-stage Single Screw Expander Under Variable Condensing Ambient Conditions

冷凝环境条件的季节性变化会对有机朗肯循环系统的性能和膨胀机的运行工况产生重大的影响。采用新型准二级膨胀单螺杆膨胀机是确保有机朗肯循环系统实现跨季节高效运行的有效举措。该文通过建立准二级膨胀单螺杆膨胀机和变冷凝环境条件下有机朗肯循环系统的耦合模型,揭示了冷凝环境条件、准二级膨胀单螺杆膨胀机的性能和有机朗肯循环最佳工况点之间的关联机理。同时,对准二级膨胀单螺杆膨胀机的内容积比进行优化分析。结果表明:引入速度膨胀过程可以降低膨胀机的最优内容积比,提高膨胀机的最佳等熵效率,其中最优内容积比从6.0降低到4.86,此时对应的最佳等熵效率从0.679增加至0.692。循环净功率和净效率均存在最优值,当湿球温度为5℃,内容积比为4.0时,循环净功率最高达13.87kW,内容积比为8.0时,循环净效率最高达12.66%;利用准二级膨胀单螺杆膨胀机可以显著提升变冷凝环境条件下有机朗肯循环系统的性能,系统最大净功率和最大净效率分别提升了4.51%和0.59%。

The seasonal variations in condensing ambient conditions have a significant impact on the performance of the organic Rankine cycle system and the operating conditions of the expander.Using a new single screw expander with quasi two-stage expansion is an excellent way to ensure efficient cross-season operation of organic Rankine cycle under variable condensing ambient conditions.In this paper,a coupled model of quasi two-stage expansion single-screw expander and organic Rankine cycle system under variable condensing ambient conditions is developed to reveal the relationships of condensing environment conditions,single-screw expander performance and optimal operating point of organic Rankine cycle.At the same time,the inner volume ratio of quasi two-stage single screw expander is optimized.The results show that the introduction of velocity expansion process can reduce the optimal inner volume ratio of the expander and improve the optimal isentropic efficiency of the expander.The optimal inner volume ratio decreases from 6.0 to 4.86,and the corresponding optimal isentropic efficiency increases from 0.679 to 0.692.The net power and the net efficiency of ORC both have optimal values.The net power is up to 13.87kW when the wet bulb temperature is 5℃ with the inner volume ratio of 4.0,and the net efficiency is up to 12.66% when the inner volume ratio is 8.0.The maximum net power and net efficiency of ORC can be improved by 4.51% and 0.59% respectively by using the new single screw expander with quasi two-stage expansion.