Experimental investigation on a small-scale ORC system with a pump driven by internal multi-potential

In this study, a novel organic Rankine cycle (ORC) based on a pump driven by internal multi-potential, i.e., gravity-assisted thermally driven pump (GTP), is presented. The newly proposed cycle consists of a GTP, a condenser, an expander, and an evaporator. The GTP component is composed of three top-down organized units, and it drives the transport of liquid from the low-pressure condenser to the high-pressure evaporator by thermal energy and gravity. Such a component substitutes the conventional electricity-driven pump. Moreover, the modified scroll expander of the ORC-GTP system is experimentally studied, and the results show that the best conversion efficiency from shaft work to electricity and the best isentropic efficiency are 82.0% and 84.2%, respectively. The experimental setup of the ORC-GTP power system is built for low-grade thermal energy recovery. It is tested under the average evaporator outlet temperature of 96.4°C, 106.1°C, and 108.8°C at the ambient temperature of around 25°C. The highest shaft work is achieved at 96.4°C evaporator outlet temperature, and the largest ratio of time lasting for power generation is 100%. Since the ORC-GTP system has much less sensible heat loss of the evaporator, the highest average thermal efficiency of the ORC-GTP reaches 3.57%, which is increased by 71.74% compared with the pumpless ORC system in the literature.