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20 mins
Experimental investigation of four volumetric expanders
Olivier Dumont, Rémi Dickes, Vincent Lemort
Session: Session 2B: Small Scale Systems (1)
Session starts: Wednesday 13 September, 14:20
Presentation starts: 15:20
Room: Building 27 - Lecture room 02

Olivier Dumont (University of Liège)
Rémi Dickes (University of Liège)
Vincent Lemort (Université de Liège)

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 and two scroll expanders. First, based on a literature review, a comparison between these three technologies of volumetric expansion machines - namely piston, screw and scroll expanders – is performed. Following that, four displacement expanders (~2kWe) are tested in a small-scale ORC using R245fa as working fluid: a variable speed swatch-plate piston prototype, an oil-free twin-screw, a modified lubricated hermetic scroll compressor operating at a constant speed, and finally a variable-speed modified scroll compressor. The machines performance are compared in terms of isentropic efficiency and filling factor. The maximum isentropic efficiencies achieved are 53% for the piston expander and the screw expander, 76% for the variable speed scroll and 81 % for the constant speed scroll machine. However, these performances are not representative because of the limitations of the test-rig in terms of mass flow rate and pressure drop. The utilization of semi-empirical models calibrated with the measurements allows to predict the isentropic efficiency in optimal conditions without the limitations of the test-rig. When selecting an expander, other considerations than efficiency have to be taken into account such as the flexibility, the working conditions and the compactness of the expansion device. Based on the experimental results and these practical considerations, some guidelines are drawn to help the reader selecting a volumetric expander.