Investigation On The Working Fluids Optimization And Power Generation Performance Of Pumpless Organic Rankine Cycle

With the problems of environmental issues and huge energy depletion,the energy saving and carbon emission reduction has drawn more attentions from researchers.The waste heat recovery from low temperature heat source will be an effective way to tackle these problems.Organic Rankine Cycle(ORC)has the characteristics of simple structure,high reliability and low maintain cost and relatively low driving temperature,thus it is considered as an effective way in waste heat recovery filed.But for the small-scale ORC system,the power consumed by the working fluid pump will decrease the energy efficiency of the system.To solve the problem,the pumpless ORC system is proposed.There is no working fluid pump in the pumpless ORC system.Thus,the energy efficiency of pumpless ORC system will increase compared with the conventional ORC system.For the pumpless ORC system,the investigation of this paper focuses on the selection and modification of the expander,the working fluid choices and study of the system performance in power generation.A scroll expander is adapted in the pumpless ORC system.The performance of scroll expander which converted for the Automotive air conditioning expander compressor is tested.Results show that the expander is applicable for the small-scale ORC system.Based on the properties of the refrigerants and the simulation results of the theoretical performance in the pumpless ORC system,the refrigerants of R245fa and R1233zd(E)are picked for experimental research.The low-grade heat source is simulated by an electric boiler.The temperature of the heat resource ranges from 75~oC to 100~oC with the interval of 5~oC.The cooling water inlet temperature is affected by the environmental temperature.Results show that when increasing heating water inlet temperature,the power output of the system rises up accordingly.For system with R245fa as the working fluid,the average power output increases from 90 W to 212 W when heating water temperature increases.The lowest energy efficiency and the highest energy efficiency are 2.1%and2.6%,respectively.The minimum and maximum exergy efficiency are12.62%and 14.1%accordingly.When R1233zd(E)is selected as the working fluid,the average power output increases from 62W to 127W when the heating water inlet temperature increases from 80~oC to 100~oC.The lowest energy efficiency is 2.7%at the heating water inlet temperature of 80~oC.The best performance is achieved with heating water inlet temperature of 95~oC.The exergy efficiency ranges from 16.1%to 17.1%under the conditions of different heating water inlet temperature.The influence of the loads is studied in the system.Results show that the power and current output increase when the loads increase under the condition of the constant heating water temperature,meanwhile the voltage output decreases.When increasing the number of loads,the rotation speed of expander and generator decrease,thus the volume flowrate of refrigerant reduce accordingly and the time lasts for power generation rise up finally.