Effects of heat source temperature and mixture composition on the combined superiority of dual-pressure evaporation organic Rankine cycle and zeotropic mixtures

Dual-pressure evaporation cycle is an emerging cycle type in the organic Rankine cycle (ORC) that can remarkably reduce the irreversible loss during heat absorption process and improve the adaptability to various heat sources. Introduction of zeotropic mixtures in dual-pressure evaporation ORC presents great potential to further increase the heat-power conversion efficiency due to the variable phase-change temperature. This study investigated the dual-pressure evaporation ORC using isobutane/isopentane mixtures for heat sources of 100–200 °C. Effects of heat source temperature and mixture composition on the system thermodynamic performance were analyzed. Application potential and applicable ranges of introducing isobutane/isopentane mixtures in dual-pressure evaporation ORC were evaluated. Results showed that the introduction of zeotropic mixtures in dual-pressure evaporation ORC substantially increased the power output. The maximum power output of dual-pressure evaporation ORC using isobutane/isopentane mixtures could increase by 11.9% and 15.2% at most compared with those of using isobutane and isopentane, respectively. It could increase by 25.7% at most compared with that of single-pressure evaporation ORC using isobutane/isopentane mixtures. In terms of being introduced into dual-pressure evaporation ORC, the zeotropic mixture with a high critical temperature can generally achieve larger range in applicable heat source temperature and larger increment in the power output.