Experimental evaluation of organic Rankine cycle using zeotropic mixture under different operation conditions

Abstract

The zeotropic mixture is a feasible way to improve the thermodynamics performance of organic Rankine cycle (ORC). A small-scale ORC experimental apparatus with a scroll expander was established. Then, the system performance using different zeotropic mixtures (including 0.75R245fa/0.25R141b, 0.5R245fa/0.5R141b and 0.25R245fa/0.75R141b) was tested and compared with the pure fluid of R245fa and R141b to determine whether the mixture fluid can improve the system performance. The experimental results show that the thermal efficiency and exergy efficiency of ORC system gradually increase with the increase of cooling water flow rate and the decrease of expander rotational speed. Under different working conditions, mixture fluids can produce more shaft power and have lower condenser exergy destruction than pure fluids. The zeotropic mixture is not always better than the pure fluid, while it can improve the thermal efficiency and exergy efficiency of the ORC system with an appropriate mass fraction. In the experiment, the best mass fraction of R245fa/R141b is 0.25/0.75, and its thermodynamic performance is significantly higher than that of R141b and R245fa. The maximum thermal efficiency and exergy efficiency of 0.25R245fa/0.75R141b are 5.58% and 23.2% respectively.