Experiment on pumpless Rankine-type cycle with scroll expander

The first experiment on a pumpless Rankine-type cycle (PRC) with a practical expander was performed to verify the feasibility of the PRC in power generation from low-grade heat sources. The PRC is an alternative to a Rankine cycle (RC) for lower output power and lower- and/or unstable temperature heat sources, where the conventional RC is rarely economically efficient owing to the low efficiency of the working fluid pump. The PRC mainly consists of a scroll expander, two heat exchangers, and switching valves for the expander and heat exchangers. A switching valves method that does not require the use of a working fluid pump is employed to control the PRC, hence avoiding problems such as cavitation caused by the working fluid pump. A mini-PRC experimental system showed that the PRC could successfully function with a scroll expander and produce actual power of 20 W. In addition, the PRC generated relatively larger net power than the conventional organic Rankine cycle in a very small output range.