Experimental Evaluation and Comparison of Organic Rankine Cycle Using Mixture of R245fa/R141b Under Different Operating Conditions

Abstract

The performance of organic Rankine cycle (ORC) is mainly influenced by the operating conditions and working fluids. A small-scale ORC experimental apparatus with a scroll expander is established. This work aims to investigate the thermodynamic performance of ORC system under different rotational speeds, turbine inlet pressure and cooling water flow rates. Meanwhile, the performance of pure and mixture fluids, including R245fa, R141b, 0.25R245fa/0.75R141b, 0.5R245fa/0.5R141b and 0.75R245fa/0.25R141b, is experimentally compared to determine a suitable working fluid. The experimental results show that the shaft power, thermal efficiency and exergy efficiency gradually increase with the growth of turbine inlet pressure and cooling water flow rate. However, the ORC system will obtain lower thermal efficiency and exergy efficiency at higher rotational speeds. Mixed fluid can produce more shaft power than pure fluid, and the mass fraction of R245fa/R141b to achieve the best thermodynamic performance is 0.25/0.75. When the cooling water flow rate is 0.6m 3 /h, the maximum shaft power, thermal efficiency and exergy efficiency of 0.25R245fa/0.75R141b are 813 W, 5.63% and 24.18% respectively, which are 14.5%, 19.3% and 18.4% higher than R245fa. Under different operating conditions, the ranges of isentropic efficiency and mechanic efficiency of scroll expander are 47.5-58.9% and 85.6%-99.6, respectively.