An examination of super dry working fluids used in regenerative organic Rankine cycles

Thermodynamic and economic performance of an Organic Rankine Cycle (ORC) system is closely related to the thermophysical properties of its organic working fluid. Super dry working fluids are especially suitable for regenerative ORC. Setting a recuperator in an ORC not only improves its thermodynamic performance, but also increases the investment cost of heat exchanger that accounts for the highest proportion in the whole ORC system. Based on the above consideration, this paper presents an examination of super dry working fluids used in regenerative ORC. The suitable super dry working fluid used in a regenerative ORC is determined and selected for common medium/low-temperature heat sources. Based on different types of heat sources, the optimal single-stage extraction pressure and extraction temperature of each super dry working fluid in regenerative ORC is determined according to the net power output and thermal efficiency of regenerative ORC, respectively. The results show that heptane may match the closed heat source best with an optimal extraction condition at 0.45 MPa and 478.64 K. While pentane, hexane, propylcyclohexane, undecane and o-xylene may match five different open heat sources. Their corresponding optimal extraction conditions are 0.85 MPa/408.78 K, 0.6 MPa/445.33 K, 0.35 MPa/570.22 K, 0.175 MPa/584.25 K and 0.4 MPa/544.32 K.