A Simultaneous Optimization of Working Fluid Design and System Parameters in Organic Rankine Cycle

The working fluid is the carrier of energy conversion in the organic Rankine cycle (ORC), and its matching with the cold and heat sources directly affects the performance of the ORC system. While the existing working fluid provides a limited improvement for the performance of the ORC system, the design of the novel working fluid is very important for improving the performance of the ORC. The modeling and solving method based on computer-aided molecular design (CAMD) for working fluid design and ORC system is simultaneously optimized, and the traditional CAMD model is improved. A mixed integer nonlinear mathematical programming (MINLP) model with the maximum output net power of ORC system as the optimization target is established, and the solving strategy is proposed. Based on 9 basic elements, 37 groups are selected and applied to the established simultaneous optimization model. The optimal working fluids under the conditions of heat source range of 353.15~463.15 K and cold source range of 293.15~298.15 K are obtained and compared with existing working fluids. The comparisons of net power by ORC show that the novel working fluid is 12.46% higher than the existing working fluids. A sensitivity analysis is performed on the thermodynamic properties such as critical temperature, critical pressure, boiling point temperature, specific heat capacity, density and relative molecular mass involved in calculating the ORC cycle performance.