Investigation on a small-scale pumpless Organic Rankine Cycle (ORC) system driven by the low temperature heat source

Highlights: • A small-scale pumpless Organic Rankine Cycle (ORC) system is established. • The maximum power output is 232 W when the hot water inlet temperature is 95 °C. • The highest energy and exergy efficiency are 2.4% and 13.7%. • Pumpless ORC may become one alternative solution to low grade heat utilization. - Abstract: A small-scale pumpless Organic Rankine Cycle (ORC) system driven by the low temperature heat source is established to investigate the overall performance. Hot water temperature from 75 °C to 95 °C is adopted for performance analysis whereas the environmental temperature is about 25 °C. Refrigerant R245fa is selected as working fluid, and scroll expander is employed for power generation. One worth noting fact is that pumpless ORC system shows great potential for low temperature heat recovery. Experimental results indicate that the maximum power output is 232 W, which is obtained at 95 °C hot water inlet temperature. Correspondingly, the average power output is 204 W which is lasted for 6.6 min, revealing the high stability for power generation. For different hot water inlet temperature, the highest energy and exergy efficiency of the system are 2.4% and 13.7%. Besides, performance of novel pumpless ORC system is compared with that of our previous prototype. It shows a remarkable improvement in terms of power output, energy efficiency and exergy efficiency. Power generation process is able to keep constant for 95% of the cycle time. As a result, pumpless ORC may become an alternative solution to low grade heat utilization when compared with conventional small-scale ORC.