Thermodynamic And Experimental Study Of Organic Rankine Cycle For Low-grade Heat Source Utilization

As one of the most useful technology for low-grade heat source utilization, Organic Rankine Cycle (ORC) get the attention of the scientific researchers. Working fluid selection and experimental study are very important on the ORC power generation technology.Considering safety, environmental protection and physical properties of working fluid, R245fa, R245ca, R123 are selected from twelve kinds of working fluid:R245fa, R123, R113, R114, R22, R134a, R245ca, R227ea, RC318, R141b, R236fa, R124. Then establishing thermodynamic model to carry out theoretical studies, exploring the influence of ORC system performance by superheat, subcooling, evaporation and condensation temperature. The results show that R123 has better thermal properties.On the basis of the existing thermodynamic theory analysis, designing and building the ORC system test platform, using R123 as cycle refrigerant of the system, useing the scroll expander, and conducting experimental study at the fixed heat source temperature 140℃. Experiental platform has two operating modes:constant flow and constant torque.Through the analysis of dynamic characteristics of the two operating modes, ORC system has regular and rapid response characteristics and can reach a new equilibrium state. It can be seen that the experimental platform has good operating characteristics. ORC system for Through analysis of steady performance of ORC system, it can be drawn from the following results:1) Condenser outlet always have a greater degree of subcooling, in a range of 15.86 ～20.77℃;2) the minimum superheat of expander outlet is 30.06℃, it can be considered to install regenerator to recover part of energy to improve thermal efficiency;3) The maximum output power of expander is 2350 W, the real efficiency of the expander in the range between 41.33%-59.69%, the maximum shaft power and maximum efficiency of expander does not occur synchronously;4) The system thermal efficiency decreases 0.69%～0.95% when considering the pump consumption, the system maximum thermal efficiency is 6.39%.Combined with theoretical analysis and experimental results shows that it can improve the thermal efficiency of the system through increase the evaporation temperature or decreasing the condensing temperature under the constant efficiency of pump and expander. But both efficiency is not constant in actual operation, therefore, we should select the most suitable pump and the expander according to operating conditions and match the parameters of the equipment of the system reasonably to improve the thermal efficiency and the power generation performance of ORC system.