Performance explorations of an organic Rankine cycle featured with separating and mixing composition of zeotropic mixture

Abstract

Organic Rankine cycle (ORC) working with zeotropic mixture is particularly attractive due to the performance enhancement. By applying composition adjustment, it can accommodate to various operating conditions without much penalty of performance. This paper implements a liquid-separation condenser (LSC) to separate composition of zeotropic mixture and uses a vapor-liquid ejector to accomplish the mixing process. A novel ORC (LEORC) is constructed with a feature of two operating modes. It has 3.66%, 8.48%, 5.41% and 6.15% higher net power generation (WNET) than an existing LSC-based ORC (LMZORC) with R245fa/R365mfc, R600/R1234ze(Z), R1234ze(Z)/R601 and R600a/R601 at a mass flow rate (ṁ2) of 10 kg/s, respectively. A parametrical study of ṁ2 and vapor quality for vapor-liquid separation (x) is carried out with R1234ze(Z)/R601 for two modes individually. It is found that WNET is maximized when the temperature difference of 5 °C is allocated in both evaporators. Finally, potential of LEORC is further explored by using Genetic Algorithm to optimize ṁ2, x and z2. The optimum performances are mapped under various inlet temperatures of heat source and heat sink. WNET of mode II could be improved by 14.2% relative to mode I. This study broadens new ways to adjust the composition of zeotropic mixture.