Selection of organic Rankine cycle working fluid based on unit-heat-exchange-area net power

GUO Mei-ru(郭美茹)^{1, 2}, ZHU Qi-di(朱启的)^{1, 2}, SUN Zhi-qiang(孙志强)^{1, 2}, ZHOU Tian(周天)^{1, 2}, ZHOU Jie-min(周孑民)^{1, 2}

(1. School of Energy Science and Engineering, Central South University, Changsha 410083, China;
2. Hunan Key Laboratory of Energy Conservation in Process Industry (Central South University),
Changsha 410083, China)

Abstract:To improve energy conversion efficiency, optimization of the working fluids in organic Rankine cycles (ORCs) was explored in the range of low-temperature heat sources. The concept of unit-heat-exchange-area (UHEA) net power, embodying the cost/performance ratio of an ORC system, was proposed as a new indicator to judge the suitability of ORC working fluids on a given condition. The heat exchange area was computed by an improved evaporator model without fixing the minimum temperature difference between working fluid and hot fluid, and the flow pattern transition during heat exchange was also taken into account. The maximum UHEA net powers obtained show that dry organic fluids are more suitable for ORCs than wet organic fluids to recover low-temperature heat. The organic fluid 1-butene is recommended if the inlet temperature of hot fluid is 353.15-363.15 K or 443.15-453.15 K, heptane is more suitable at 373.15-423.15 K, and R245ca is a good option at 483.15-503.15 K.

Key words:organic Rankine cycle (ORC); working fluid selection; net power; heat exchange area