Thermodynamic Modeling and Optimal Operating Conditions of Organic Rankine Cycles (ORC) Independently of the Working Fluid (Pages: 9-22)

E. Saloux1,2, M. Sorin1, H. Nesreddine3 and A. Teyssedou2

1Department of Mechanical Engineering, Sherbrooke University, Québec, Canada; 2Nuclear Engineering Institute, Engineering Physics Department, Polytechnique Montréal, Québec, Canada; 3Energy Technology Laboratory, Hydro-Québec, Québec, Canada



The development of systems based on organic Rankine cycles (ORC) permits low- or high-grade heat to be converted into useful work. Nevertheless, in such systems, the selection of the organic fluid represents a critical step because it strongly depends on operating conditions. To this aim, in this paper, a thermodynamic model, which requires limited information (only about external heat and cold sources), is presented. The model, based on the equivalent temperature concept, is independent of both the nature of the working fluid and the isentropic efficiencies of the mechanical components. It allows an appropriate optimization problem, independent of the working organic fluid, to be formulated for finite source systems. Applied to a given case by using genetic algorithms, the optimal operating conditions are obtained in terms of equivalent temperatures and overall heat transfer coefficients. A method for determining the traditional parameters and for selecting the optimal working fluid is then tackled while the range of applications of the methodology is discussed in detail.

Keywords: Entropy, Equivalent temperature, Exergy analysis, Genetic algorithms, Optimization, Waste heat.