变热源工况下非共沸工质有机闪蒸循环热性能分析

Thermal Performance Analysis of Non-azeotropic Working Fluid Organic Flash Cycle Under Variable Heat Source Conditions

有机闪蒸循环(OFC)能有效利用中低温热能,非共沸工质的变温相变特性可以改善循环和换热器之间的匹配性。为了提高系统的循环性能,本文基于Matlab2018b构建了一种采用正丁烷/1,1,1,3,3-五氟丙烷(R600/R245fa)制冷剂非共沸混合工质的OFC热力学模型,以100℃~200℃地热水作为热源,研究了非共沸工质摩尔分数和热源温度对系统净输出功率、热效率、[火用]效率和总[火用]损的影响。结果表明:热源温度为200℃,R600摩尔分数为0.4时,系统净输出功率和热效率达到最大值,分别为48.92 kW和7.12%;当热源温度超过一定值,[火用]效率开始减小;热源温度为150℃,R600摩尔分数为0.4时,[火用]效率最大为32.44%。采用非共沸工质能有效提高系统净输出功率、热效率和[火用]效率,同时也能降低系统总[火用]损。

The organic flash cycle(OFC)can effectively utilize the heat energy at medium and low temperature,and the temperature-changing phase change characteristics of the non-azeotropic working fluid can improve the matching between the cycle and the heat exchanger.In order to improve the cycle performance of the system,based on Matlab2018b,an OFC thermodynamic model using n-butane/1,1,1,3,3-pentafluoropropane(R600/R245fa)refrigerant non-azeotropic mixture working medium was constructed.With 100℃~200℃geothermal water as the heat source,the effects of mole fraction of non-azeotropic working medium and heat source temperature on net power output,thermal efficiency,exergy efficiency and total exergy loss of the system were studied.The results show that when the heat source temperature is 200℃and the R600 mole fraction is 0.4,the net output power and thermal efficiency of the system reach the maximum value,which are 48.92 kW and 7.12%,respectively.When the heat source temperature exceeds a certain value,the exergy efficiency begins to decrease.When the heat source temperature was 150℃and R600 mole fraction was 0.4,the maximum exergy efficiency is 32.44%.The use of non-azeotropic working medium can effectively improve the net output power,thermal efficiency and exergy efficiency of the system,as well as reduce the overall exergy loss of the system.