Evaluation and selection of dry and isentropic working fluids based on their pump performance in small-scale organic Rankine cycle

Abstract

• A trapezoid model used to represent the power consumption of pump is established. • The perfection of Organic Rankine Cycle relative to the Carnot cycle is analyzed. • The deviation between the real and ideal gas behavior is obtained. • The optimal condensation temperature of each working fluids is determined. • Their suitable pump types are determined. The circulation pump is an important element limiting the development of small-scale Organic Rankine Cycle system which may have a negative efficiency when the power consumption of the pump is considered and if a suitable pump that corresponds to the working fluid is not properly selected. Based on the consideration mentioned above, in this paper, a trapezoid used to represent the power consumption of the pump and a triangle used to represent the degree of subcooling of the working fluid are defined. Using these two models, the perfection of Organic Rankine Cycle at the optimal condensation temperature relative to the Carnot cycle within the same temperature limitation is analyzed when 69 dry and isentropic working fluids are used in Organic Rankine Cycle. The deviation between the real and ideal gas behavior of each working fluid is also obtained. On this basis, the optimal condensation temperature of each dry and isentropic working fluid is determined. Moreover, the applicability of each organic working fluid in Organic Rankine Cycle is discussed from the viewpoint of pump performance. 36 working fluids are suitable and 33 ones not suitable for the application in small-scale Organic Rankine Cycle system. Suitable pump types corresponding to applicable organic working fluids are also analyzed and determined. The graphic method proposed in this paper and the findings about pump performance can provide reference for the operation of practical Organic Rankine Cycle.