Design and testing of an algebraic scroll expander for power generation from a waste heat recovery system

Abstract

A scroll expander was designed, fabricated, and tested as a power converting device in a waste heat recovery system fitted to the cooling system of internal combustion engine. An algebraic spiral was adopted as the base curve for the scroll wrap profile for the compact scroll design. A reduction of approximately 13.2% was accomplished in the scroll diameter, compared to conventional involute scroll. Additionally, numerical analysis on the expander performance showed that the performance of the designed algebraic scroll expander was about the same as that of a conventional scroll expander. The fabricated prototype was tested in a R134a Rankine cycle with a heat source of 20 kW. For the operating conditions of 20–26 bar and 90–93℃ at the expander inlet and 8–9 bar at the outlet, the expander produced a shaft power of 0.6–0.7 kW at an operating speed range of 1500–2000 r/min. This corresponded to an expander efficiency of 40–45%. The volumetric efficiency also increased as the expander speed increased, reaching to 80% at 2000 r/min. Furthermore, compared to the numerical simulation results, the mechanical efficiency from the test data was found to be considerably low as much as 30%.