Performance optimization of organic Rankin cycle (ORC) based on comparative study of Box –Behnken and central Composite design methods

In this paper, with the aid of thermodynamic modeling of Organic Rankin Cycle (ORC), the effect of some parameters on the thermal efficiency and input heat of ORC is examined using design of experiment method. By this technique, along with the Backward Elimination Regression model, the values of thermal efficiency and input heat of ORC are introduced as a function of effective parameters. For this purpose, first, by comparing the two methods of surface response and selecting the central composite design procedure, the values of response functions were computed based on the input variables. The numerical values derived from these functions resulting from RSM central composite design are in good agreement with published theoretical results in literatures. The results show that among the effective parameters, turbine inlet temperature values, turbine isentropic efficiency , and mass flow ratio have most significant effect on thermal efficiency and also for input heat to ORC the most effective parameters are flow rate of working fluid, condenser temperature and input temperature of ORC's turbine. In order to numerical optimization according to the operating conditions of real cycles based on the desirability function and the central composite design procedure, it was revealed that the thermal efficiency is close to 36% for the heat input of 130 kW.