Thermal efficiency investigation for organic Rankine cycle and trilateral flash cycle using hydrofluoroether working fluids

Abstract

The thermal efficiency of the organic Rankine cycle (ORC) is higher than the trilateral flash cycle (TFC) using normal dry working fluids. On the contrary, the thermal efficiency of TFC outperforms the thermal efficiency of ORC by using super dry working fluids at specific conditions. This study aims to investigate thermal efficiency for TFC and ORC cycles using HFE7100 and HFE7500, classified as super dry working fluids. The effect of two techniques was studied on the thermal efficiency of ORC and TFC: the recuperator cycle (RORC and RTFC) with various ratios of effectiveness and the partial evaporator organic Rankine cycle (PE-ORC), with various ratios of vapor quality. The results indicated that the recuperative heat exchanger helps convert the super dry behavior to be like normal dry. Therefore, using HFE7100 required 0.2 effectiveness of recuperative heat exchanger, while for HFE7500, 0.4 effectiveness is needed. A partial evaporator cannot help convert the super dry's behavior to the normal dry fluid completely, while it has the crucial role of moving the intersection point towards critical temperatures (Tcr), which increases the range of heat source temperatures that assist super dry fluids to behave as normal dry fluids. However, PE-ORC can be a good competitor to TFC at vapor quality (x = 0.1, and x = 0.2) and (x = 0.1), and it has higher thermal efficiency than ORC at vapor quality (x = 0.9) and (x = 0.8 and x = 0.9) for HFE7100, and HFE7500 respectively.

Keywords

• Hydrofluoroether
• Subcritical cycles
• Thermal efficiency
• Partial evaporator
• Recuperator cycles