Comparison of Different Working Fluids Operation for Basic and Modified Organic Rankine Cycles (ORCs)

This paper presents a theoretical framework for selecting of appropriate working fluids for basic Organic Rankine Cycle (ORC) and three modified ORCs based on their thermodynamic properties. A comprehensive thermodynamics analysis is done for basic ORC, modified ORC incorporating turbine bleeding, regenerative ORC, and ORC incorporating both turbine bleeding and regeneration using 8 different working fluids (R113,R141b, n-pentane, R123, R245fa, R600, isobutane, R236fa). Among these analyzed working fluids, R113 and R236fa present the highest and lowest thermal efficiency. The thermal efficiency can be much higher when the modified ORC incorporating both turbine bleeding and regeneration is used. Of course, among of the presented working fluids, there are environmentally-friendly working fluids, too, which can be a good choice for the environmentally consideration issues. At the end, we will also present a parametric study for crucial parameters in the cycle. With this study, we can find a specific range for the evaporator pressure in which the condenser duty and net produced power will be minimum and maximum, respectively. In fact, we will present an optimum value for the pressure of evaporator using different working fluids for the purpose of the condenser duty minimization and the net produced power maximization. The optimum value for the pressure of the evaporator in this case will range from 2.778 to 3.656 MPa.