Thermodynamic performance comparison between singlepressure and dual-pressure evaporation organic Rankine cycles for heat sources with outlet temperature limit

Organic Rankine cycle (ORC) is a widely used technology to generate power from renewable energy and waste heat. Dual-pressure evaporation cycle holds immense potential to be used in ORC systems because it can remarkably increase the heat-work conversion efficiency and improve the adaptability of ORC to heat sources with various characteristics. This study compared the thermodynamic performance of single-pressure and dual-pressure evaporation ORCs for heat sources with outlet temperature limit, based on five organic fluids. Effects of the heat source outlet temperature limit on the characteristics of dual-pressure evaporation ORC system were also discussed. Results show that the dual-pressure evaporation cycle can substantially increase the net power output by increasing system efficiency, and is beneficial to reduce the charge volume of organic fluid in the system, compared to the single-pressure evaporation cycle. The increments in net power output of dual-pressure evaporation cycle over the single-pressure evaporation cycle can be 4.9%, 8.3%, 10.8%, 12.8%, and 14.0% at most for R227ea, R1234ze(E), R600a, R245fa, and R601a, respectively. While, compared to heat sources without outlet temperature limit, the increment in net power output of dual-pressure evaporation cycle is remarkably lower for heat sources with outlet temperature limit.