A study on the single screw expander with exhaust kinetic energy utilization in organic Rankine cycle conditions

Abstract

Using high-performance expanders is one of the keys to improve the efficiency of Organic Rankine Cycle (ORC). However, in large expansion ratio conditions, the performance deterioration caused by under-expansion seriously affects the performances of the ORC. For single-screw expanders, it is possible to utilize the kinetic energy of the screw groove exhaust to produce extra power. But there is still a lack of theoretical support for optimizing the exhaust kinetic energy utilization process of this new expander at present. Therefore, the energy conversion mechanism of Single Screw Expander with exhaust Kinetic energy Utilization (SSEKU) was investigated in this paper, and a mathematical model of SSEKU was developed to investigate the energy conversion mechanisms and predict the performances. The results show that introducing exhaust kinetic energy utilization process in single screw expander can reduce under-expansion losses effectively, and the effects in large size expanders were stronger than that in small scale machines. It was also found that the maximum increase in isentropic efficiency was 3.01, 5.47, and 9.38 percentage points for the expander with a screw diameter of 117 mm, 200 mm, and 350 mm, respectively.