Metodologia para pré-seleção de fluidos de trabalho para ciclos Rankine orgânicos

Abstract

This work proposes a methodology to streamline the selection of fluids suitable for each application in an Organic Rankine Cycle. The simulations used fluids that allow the harvesting of energy remaining after the turbine using a regenerator. The simulations used three diesel engines with exhaust gas temperature at 775, 816, and 854 K and a geothermal source at 480 K. Simulations searched for the maximum recoverable power in the cycle, respecting the Pinch Point of the 10 K in both the evaporator and condenser. Considering the thermal efficiency and requested area for the three heat exchangers, the most suitable fluids for the diesel engine applications were benzene, toluene, n-hexane, and p-xylene, while HFE7100, fluoroketone, R245fa, and butene for the geothermal source. Temperature and pressure at the condenser outlet close to each other, with averages respectively at 0.02 and 0.004, were obtained through dimensionless with reference to the critical and saturated liquid at 0.9 atm points, for all applications studied. The maximum power recovered from the thermal sources at 480, 775, 816, and 854 K was obtained with dimensionless vaporization temperatures close to 0.51; 0.79; 0.81, and 0.86, respectively, with the corresponding dimensionless pressures close to 0.23; 0.58; 0.62, and 0.68, for all pre-selected fluids, indicating expected values increasing with the source temperature, proving the utility of the proposal. The presented proposal produced generalized temperature x entropy and pressure x enthalpy diagrams, capable of representing the thermodynamic cycle in an approximately overlapping way for all promising substances for a given application.