Parametric investigation of working fluids for organic Rankine cycle applications

Abstract

This paper investigates working fluids for organic Rankine cycle (ORC) applications with a goal of identifying “ideal” working fluids for five renewable/alternative energy sources. It employs a methodology for screening and comparing with good engineering accuracy the thermodynamic performance potential of ORC operating with working fluids that are not well characterized experimentally or by high-accuracy equations of state. A wide range of “theoretical” working fluids are investigated with the goals to identify potential alternative working fluids and to guide future research and development efforts of working fluids. The “theoretical” working fluids investigated are described in terms of critical state properties, acentric factor, and ideal gas specific heat capacity at constant pressure and are obtained by parametrically varying each of these parameters. The performances of these “theoretical” working fluids are compared to the performances of several “real” working fluids. The study suggests a working fluid's critical temperature and its critical ideal gas molar heat capacity have the largest impact on the cycle efficiency and volumetric work output, with “ideal” working fluids for high efficiency possessing critical temperatures on the order of 100%–150% of the source temperature and possessing intermediate values of critical ideal gas molar heat capacity.