Parametric optimization and performance analysis of zeotropic mixtures for an organic Rankine cycle driven by low-medium temperature geothermal fluids

• Mixtures of HFCs/HCs and HFOs/HCs are investigated as working fluids.
• Performance of R245fa/R600a (0.9/0.1) is considered more preferable.
• Maximum net power output corresponds to an optimal mixture ratio.
• An optimal evaporating temperature exists.

The selection of working fluids is one of the important approaches to optimize the performance of an organic Rankine cycle (ORC). In order to select appropriate working fluids, zeotropic mixtures were investigated in this paper by theoretical analysis and detailed numerical simulation. Since the flame retardancy of fluoride can overcome the strong flammability of HCs, the mixtures of HFCs and HFOs with HCs were particularly investigated. The influences of 10 groups of mixtures on the performance of ORC were analyzed. The results show that the maximum net power output of the ORC using each mixture corresponds to an optimal mixture ratio that gives a highest temperature glide. In addition, an optimal evaporating temperature exists. It was found that R245fa/R600a (0.9/0.1) was the most preferable mixture among the working fluids within the scope of this research.