Abstract
Organic Rankine Cycle (ORC) is a system that uses working fluids with hydrocarbon components instead of water and generates power from the heat recovery of different heat sources. In this study, the exergy analysis of a simple ORC, which produces electrical energy with the help a geothermal source (125°C), was performed. R123, R152a, R245fa and R600a were determined as the fluids to be used in the Cycle. In this analysis, which was carried out according to the pinch point temperature differences (5-20°C) in the evaporator, the exergy performance of the cycle components was evaluated for the geothermal resource unit flow rate and the variation of the exergy efficiency of the system was calculated. With the increase of the pinch point temperature difference in the evaporator, the decrease of the system’s exergy efficiency became maximal (11.7%) with the use of R152a as a refrigerant and the loss in the system’s exergy efficiency became minimal (9.03%) with the use of R123 as a refrigerant.
Highlights
The Rankine cycle is a thermodynamic cycle that converts heat energy into work and water is used as the working fluid in this cycle
In the exergy analysis made with the help of parameters given in Table 1, point 1 is taken 8°C higher than the evaporation temperature in the evaporator so that refrigerant could be superheated steam in the turbine inlet
For the geothermal resource unit flow rate, the change of the flow rates of different refrigerants is shown in Figure 2, which are used in the cycle depending on the pinch point temperature difference in the evaporator
Summary
The Rankine cycle is a thermodynamic cycle that converts heat energy into work and water is used as the working fluid in this cycle. Many studies have shown that; among the hydrocarbon compound organic fluids used in the ORC systems, the ones that have higher molecular mass, low critical temperature and pressure and that are dry and isentropic in the meantime are more appropriate [1,2,3,4,5]. Wang et al [6] investigated the performance of the ORC systems, which work around the critical range, in terms of thermodynamics. Akkaya [9] examined an Organic Rankine Cycle based power generation system, which uses the thermal energy of exhausted gases from an industrial plant. Gao et al [13] examined the performance of solar based organic Rankine cycle through the various working conditions like inlet pressure and temperature of the turbine. Mago et al [14] analysed the performance of some working fluids under different heat source temperatures and indicated that the boiling point of the working fluids has a strong influence on the system thermal efficiency
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