Thermodynamic Analysis and Working Fluid Selection of a Novel Cogeneration System Based on a Regenerative Organic Flash Cycle

Abstract

Recently proposed organic flash cycles maintain lower irreversibility in the evaporator than traditional organic Rankine cycles. This study presented a novel combined heat and power system that was based on a regenerative organic flash cycle, in order to improve thermal efficiency. Parametric analyses for the proposed combined heat and power system were carried out, using six working fluids, and performed with heat source temperatures and heat sink temperatures that ranged from 130 °C to 170 °C, and from 20 °C to 40 °C, respectively. The results showed that the preferable working fluid was altered, with a change in the operating condition. Isopentane, R1234ze(Z), R1233zd(E), and R245fa performed better at a cooling water temperature of 20 °C. The system that used R245fa showed more promising performance when the heat source temperatures were set to 150 °C and 160 °C. R365mfc was determined to be the best working fluid at a heat source temperature of 150 °C, and at cooling water temperatures of 30–40 °C. Finally, the analyses evaluated the year-round system performance on the basis of monthly ambient and water temperatures in Daegu, Korea, as the system’s parameters. Compared to the single regenerative organic flash cycle, the thermal efficiency of the novel system improved significantly, from 8.37 % to 32.80% in August, and to 74.34% in February.