Experimental investigation and optimal performance assessment of four volumetric expanders (scroll, screw, piston and roots) tested in a small-scale organic Rankine cycle system.

Abstract The aim of this paper is to facilitate the selection of the expander for a small-scale organic Rankine cycle based on an experimental comparison of a piston, a screw, a scroll and a roots expander. First, based on a literature review, a comparison between these four technologies of volumetric expansion machines is performed. Afterward, four displacement expanders [2–4 kW] are tested on two similar small-scale ORC unit with fluid R245fa. The maximum effective isentropic efficiencies measured are 53% for the piston expander and the screw expander, 76% for the variable-speed scroll and 48% for the roots machine. However, these performances do not reflect the highest efficiencies achievable by each expander: the test-rig presents experimental limitations in terms of mass flow rate and pressure drop (among others) that restricts the achievable operating conditions. The calibration of semi-empirical models based on the measurements allows to overcome this issue and to predict the isentropic efficiency in optimal conditions despite the limitations of the test-rigs. Based on experimental results, extrapolated prediction of the semi-empirical model and practical considerations, some guidelines are drawn to help the reader to select properly a volumetric expander. Highlights • Experimental investigation of the performance of a roots, a scroll, a piston and a screw expander. • Show how a semi-empirical simulation model could be generalized and used to simulate 4 different expander technologies. • Extrapolation of the expander performance in optimal conditions to maximize the isentropic efficiency. • Establishment of a table to help engineers selecting the most appropriate technology depending on the application. [ABSTRACT FROM AUTHOR]