Performance analysis of a zeotropic mixture (R290/CO2) for trans-critical power cycle

Low critical temperature limits the application of CO2 trans-critical power cycle. The binary mixture of R290/CO2 has higher critical temperature. Using mixture fluid may solve the problem that subcritical CO2 is hardly condensed by conventional cooling water. In this article, theoretical analysis is executed to study the performance of the zeotropic mixture for trans-critical power cycle using low-grade liquid heat source with temperature of 200 °C. The results indicated that the problem that CO2 can't be condensed in power cycle by conventional cooling water can be solved by mixing R290 to CO2. Variation trend of outlet temperature of thermal oil in supercritical heater with heating pressure is determined by the composition of the mixture fluid. Gliding temperature causes the maximum outlet temperature of cooling water with the increase of mass fraction of R290. There are the maximum values for cycle thermal efficiency and net power output with the increase of supercritical heating pressure.

Graphical AbstractTheoretical study on a zeotropic mixture (R290–CO2) for trans-critical cycle is executed in this article. Some properties and cycle performance are provided. The first figure shows the T–S diagram for trans-critical power cycle using R290/CO2 (mass fraction: 0.5:0.5). In the figure, trans-critical power cycle is represented by the loop of 1-2-a-3-4-5-b-1. Variation of thermal oil temperature and cooling water temperature is also shown in the figure. The second figure shows the variation of net power output with heating pressure. Net power output is a very important performance for evaluating the cycle.Figure optionsDownload as PowerPoint slide