Thermal efficiency evaluation of an organic Rankine cycle with n-pentane as working fluid

In this study, the effect of evaporation pressure and superheating temperature on system performance was determined in the Organic Rankine Cycle (ORC) model designed using n-pentane fluid. EES (Engineering Equation Solver) software design using 9 different conditions have been identified. In the first model where the evaporation pressure was between 250 kPa and 400 kPa, the efficiency of ORC was determined under five different constant superheating temperatures. In the second model, the evaporation pressure was determined as 4 different constant values and the temperature of the superheating temperature was changed between 0 oC and 20 oC. N-pentane, which is widely used in ORC geothermal applications, has been determined as working fluid. Within the scope of geothermal applications, the heat source temperature is assumed to be constant at 120 °C. Condenser pinch point temperature difference is taken as 3 oC. As a result of the study, the data obtained from two different models were evaluated separately. When the superheating temperature is not applied, turbine work increases by 35% as the evaporation pressure rises from 250 kPa to 400 kPa. In addition, thermal efficiency also increased by 26%. When the evaporation pressure is constant at 250 kPa, the turbine work increased by 7.32% due to the increase of the superheating temperature from 0 oC to 20 oC. However, with the increase of heat input, thermal efficiency decreased by 1.38%. In the ORC system using N-pentane, it is stated that application of the superheating temperature reduces the performance. In the study, the highest thermal efficiency (12.59%) was achieved at the evaporation pressure of 400 kPa in the case of not applying superheating. The main purpose of this study was to evaluate the thermal efficiency of n-pentane fluid used in the geothermal applications of ORC under different evaporation pressure and overheating temperatures.