A review of scroll expander geometries and their performance

Scroll expanders are currently attracting interest for integration in small scale organic Rankine cycle (ORC) waste heat recovery applications and have been subject to significant research over the last two decades. The most common geometrical design uses a scroll profile generated by the involute of a circle with a constant wall thickness. A major disadvantage of this approach is that the increase of the geometric expansion ratio is constrained, since it is accompanied with a large increase in the scroll profile length and is associated with a decreased efficiency. In this paper, the published literature related to scroll expander geometry is reviewed. Investigations regarding the influence of varying scroll geometrical parameters on the performance of scroll expanders with a constant wall thickness are first examined. The use of variable wall thicknesses and their effects on the performance are then considered. Finally, the impact of scroll expander geometries using unconventional scroll profiles and scroll tip shape variations on the performance is discussed and summarised. The major conclusion to be drawn from this review is that scroll expanders with variable wall thickness scrolls should be further designed and developed. It is possible to increase the geometric expansion ratio without increasing the length of the scroll profiles. CFD simulations are a promising tool to illustrate and understand the non-uniform and asymmetric inner flow and temperature fields. The related benefits could lead to scroll devices with variable wall thickness not only improving the performance of organic Rankine cycle (ORC) systems but also opening a broad new field of applications such as refrigeration cycles and other power cycles where a high pressure ratio is preferred.