Selection of working fluid mixtures for flexible Organic Rankine Cycles under operating variability through a systematic nonlinear sensitivity analysis approach

This work addresses the selection of working fluid mixtures in view of operating variability in solar Organic Ranking Cycles (ORC). A systematic sensitivity analysis procedure is proposed, which explicitly considers the impacts of working fluid and ORC design/operating decisions on the ability of the ORC to operate under conditions different from its nominal design settings. The method determines the effects of variability resulting from the simultaneous consideration of multiple system design and operating parameters on multiple ORC performance indicators. It further supports the identification of parameters with high influence in the overall ORC-working fluid performance and the quantification of the overall system sensitivity with respect to these parameters within a sensitivity index. The method is illustrated with several working fluid mixture candidates and supports identification of the mixtures with minimum sensitivity in operating variability and maximum overall ORC performance. The obtained results indicate that in order to avoid significant performance losses, variability should be systematically considered during the mixture selection. Mixture 70% 1,1,1-trifluoro-propane/1-Fluoromethoxy-propane exhibits the highest overall ORC performance and lowest sensitivity to variability. (C) 2015 Elsevier Ltd. All rights reserved.