Thermodynamic analysis and comparison of a novel dual-ejector based organic flash combined power and refrigeration cycle driven by the low-grade heat source

Abstract

This proposes a novel dual-ejector based organic flash combined power and refrigeration cycle, which replaces the two throttle valves with two ejectors for the basic flash cycle, to provide power and cooling simultaneously for users. Detailed mathematical models of the proposed system are built and validated. The preliminary analysis results show that the exergy efficiency reaches 45.59% under geothermal water at 150℃. Then a parametric analysis is conducted to investigate the effects of five key parameters on system performance. The results show that both an optimal flash pressure and an extraction pressure exist to maximize the exergy efficiency. Finally, the proposed cycle, the separated power and refrigeration cycle consisting of a basic organic flash cycle and an ejector refrigeration cycle, and the basic organic flash cycle are optimized and compared by examining seven different organic fluids such as R245fa, R141b, R123, R245ca, R601, R365mfc, and R600. The results show that the R245fa brings the highest exergy efficiency to both the proposed cycle and organic flash cycle among seven involved organic fluids. Compared with the basic organic flash cycle, the proposed cycle with R245fa has a 4.91% percentage point higher exergy efficiency, 10.44% higher net power output, and an extra 172.6 kW of refrigeration output. Meanwhile, the optimal exergy efficiency and net power output of the proposed cycle are 5.82–6.80% percentage point higher and 15.06–23.87% higher than those of the separated power and refrigeration cycle. An exergy analysis suggests that the throttling losses are indeed significantly reduced by replacing the throttle valves with the ejectors for the organic flash cycle.