Selection of prospective working fluid candidates for subcritical OR evaporators

Abstract

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.The trade-off between lower grade waste heat sources and thermal efficiencies of evaporators using refrigerants is an important in subcritical organic Rankine cycles (ORCs). Although the heat transfer performances of many refrigerants have been reported in various studies, there are relatively low amount of studies focusing on temperature and pressure ranges relevant to evaporators for subcritical ORCs. Therefore there is a necessity for new studies that would meet the current needs and fill the gaps in literature. For this purpose, the present study aims to contribute to the revealing and concretizing the lack of information about working fluids for ORC evaporators operating under subcritical conditions. An extensive literature survey is made for deducing the proper working fluids, by means of including both the older and new generation refrigerants. The thermo-hydraulic, environmental, safety and physical properties of 10 refrigerants with zero Ozone Depletion Potentials (ODP) and low Global Warming Potentials (GWP) such as R134a, R245fa, R365mfc, R245ca, R1234ze, R1233zd, Solkatherm® SES36, R1234yf, DR-2 and HDR-14 are discussed, where R134a was taken as reference for evaluation. The best candidates for future research for evaporators for subcritical ORC are proposed, by taking the two-phase heat transfer coefficients and pressure drops into consideration.