Effect of fluid dryness and critical temperature on trans-critical organic Rankine cycle

In this paper, the effect of fluid dryness (represented by xi = ds/dT, where T is temperature, s is entropy) and critical temperature on the trans-critical ORC performance is investigated. The thermal efficiency of fifty-two working fluids is examined at four typical heat source temperatures. The results show that the critical temperature and fluid dryness have a significant impact on the system thermal efficiency. At a specific heat source temperature, the thermal efficiency increases with increasing of fluid critical temperature, and decreases with increasing of fluid dryness. The exergy destructions contributed by evaporator and condenser dominate the total exergy loss of the system. The exergy loss induced by condenser is more sensitive to the variation of fluid dryness than that induced by evaporator. Suitable working fluids are proposed based on the comprehensive criteria of cycle performance, toxicity, flammability and environment friendliness. (C) 2019 Elsevier Ltd. All rights reserved.