Experimental Testing of an Organic Rankine Cycle with Scroll-type Expander

An organic Rankine cycle (ORC) is a power cycle employing an organic working fluid. The term ORC is also applied generally to any Rankine cycle with a lowg rade heat source (80° - 300 o C). Because ORC are often employed in smallscale applications, use of positi ve displacement equipment is favored over the centrifugal units used in largescale power plants. A key feature of a positive displacement expander is its builtin v olume ratio. An ORC with a scrolltype expander is studied exper imentally. Data for steady state tests of the ORC are presented according to a proposed steady state standard. It is shown that the adiabatic efficiency of the expander can be fully characterized by its filling factor and the expansion volume ratio imposed across it. In particular, the peak adiabatic efficiency occurs near a filling factor of unity and an expansion volume ratio near the builtin volum e ratio of the expander. The influence of the expander's performance on cycle efficiency is considered. A procedure is presented which allows prediction of cycle performance based on knowledge of the expander efficiency versus expansion volume ratio, cycle operating conditions, and working fluid. Using this procedure, an optimal expander can be chosen for a set of cycle operating conditions based on its peak efficiency and builtin volume ratio.