Fluid selection and thermodynamic optimization of Organic Rankine Cycles for waste heat recovery applications
Session: Poster session & Welcome drinks
Session starts: Wednesday 13 September, 17:30
Roberto Agromayor (Norwegian University of Science and Technology (NTNU))
Organic Rankine Cycles are an effective and efficient manner to convert waste thermal energy into power. One of the advantages and challenges of this kind of cycles is that the most suitable working fluid and cycle configuration have to be selected for every application. Numerous fluids can be used in Organic Rankine cycles, including hydrocarbons, HCFCs, HFCs, siloxanes, alcohols or even mixtures of fluids. The selection of the working fluid is based on many different criteria including the thermodynamic match with the heat source and sink, chemical stability, environmental concerns, safety, or cost and it is not possible to find a single best fluid for a given application. For this reason, the fluid selection and cycle optimization is usually a compromise between different factors.
In this work an Organic Rankine Cycle is proposed for a waste heat recovery application where the heat source is a 10 kg/s mass flow rate of hot air at 250 oC and the heat sink is liquid water at 10 oC. 105 pure working fluids from the REFPROP library were considered and several criteria were used to screen out 71 of these fluids. A robust, steady state solver for cycles with and without regeneration was developed in MATLAB. The REFPROP libraries were linked to the solver to compute the thermodynamic properties of the working fluids. In order to select the most suitable fluids, a single objective thermodynamic optimization was performed using a genetic algorithm with the second law efficiency as objective function. The most important sources of irreversibility of the cycles were analysed and conclusions were drawn about the best fluid candidates and cycle configurations for this heat recovery application.