Analysis of Profile and Unsteady Flow Performance of Variable Base Circle Radius Scroll Expander

To study the complex internal flow field variation and output characteristics of a variable base radius scroll expander,this paper uses dynamic mesh techniques and computational fluid dynamics(CFD)methods to perform transient numerical simulations of a variable base radius scroll expander.Analysis of the flow field in the working cavity of a variable base radius scroll expander at different spindle angles and the effect of different profiles,speeds and pressures on the output characteristics of the scroll expander.The results of the study show that due to the periodic blocking of the inlet by the orbiting scroll,the fluid hits the internal walls of the expander at different flow rates,with excessive mechanical losses,resulting in an uneven distribution of the internal flow field.At the same temperature,pressure and scroll plate diameter,the variable base radius scroll expander increases the output torque by 0.046 N·m,the output power by 9.634 W and the isentropic efficiency by 3.8%compared to the fixed base circle scroll expander.As the speed is inversely proportional to the output torque,the isentropic efficiency of the expander tends to increase and then decrease as the speed increases.The density of the fluid is directly proportional to the pressure over a range of pressures.As the pressure increases from 0.6 to 0.9 Mpa,the average mass flow rate and isentropic efficiency increase by 0.02357 kg/s,and 6.61%,respectively.

Analysis of a 1 kW organic Rankine cycle using a scroll expander for engine coolant and exhaust heat recovery

The development of engine waste heat recov- ery technologies attracts ever increasing interests due to the rising strict policy requirements and environmental con- cerns. This paper presented the study of engine coolant and exhaust heat recovery using organic Rankine cycle （ORC）. Eight working fluids were selected to evaluate and compare the performance of the integrated waste heat recovery system. Rather than the conventional engine ORC system mainly focusing on the utilization of exhaust energy, this work proposed to fully use the engine coolant energy by changing the designed parameters of the ORC system. The case study selected a small engine as the heat source to drive the ORC system using a scroll expander for power production. The evaluation results suggest that under the engine rated condition, the solution to fully recover the engine coolant energy can achieve a higher power generation performance than that of the conven- tional engine ORC system. The results suggest that adding a recuperator to the ORC system can potentially improve the system performance when the working fluids are dry and the overall dumped heat demand of the system can be reduced by 12% under optimal conditions. When the ORC evaporating and condensing temperature are respectivelyset at 85℃ and 30℃, the integrated engine waste heat recovery system can improve the overall system efficiency by 9.3% with R600, R600a or n-Pentane as the working fluid.

Experimental investigation on a small-scale ORC system with a pump driven by internal multi-potential

In this study,a novel organic Rankine cycle(ORC)based on a pump driven by internal multi-potential,i.e.,gravity-assisted thermally driven pump(GTP),is presented.The newly proposed cycle consists of a GTP,a condenser,an expander,and an evaporator.The GTP component is composed of three top-down organized units,and it drives the transport of liquid from the low-pressure condenser to the high-pressure evaporator by thermal energy and gravity.Such a component substitutes the conventional electricity-driven pump.Moreover,the modified scroll expander of the ORC-GTP system is experimentally studied,and the results show that the best conversion efficiency from shaft work to electricity and the best isentropic efficiency are 82.0%and 84.2%,respectively.The experimental setup of the ORC-GTP power system is built for low-grade thermal energy recovery.It is tested under the average evaporator outlet temperature of 96.4℃,106.1℃,and 108.8℃at the ambient temperature of around 25℃.The highest shaft work is achieved at 96.4℃evaporator outlet temperature,and the largest ratio of time lasting for power generation is 100%.Since the ORC-GTP system has much less sensible heat loss of the evaporator,the highest average thermal efficiency of the ORC-GTP reaches 3.57%,which is increased by 71.74%compared with the pumpless ORC system in the literature.