Improved rotary vane expander for trans-critical CO2 cycle by introducing high-pressure gas into the vane slots

The loss of contact between the vane tip and cylinder wall was proven to cause a serious leakage and inefficient operation of the rotary vane expander, which was developed to replace the throttling valve in the trans-critical CO₂ refrigeration system. An improved structure was suggested by introducing high-pressure gas into the vane slots. This paper presents the experimental investigation of the improved prototype expander. By comparing the improved prototype with the original, focusing on the expander performance and the p-θ diagram as well as the vane movement, the effects of introducing high-pressure gas into the slots on the thermodynamic processes and performance were analyzed. The results showed that, by introducing the high-pressure gas into the vane slots, the volumetric efficiency was increased from 17% to 35%, and the isentropic efficiency improved from 15% to 45%, resulting in a maximum COP improvement of 27.2% compared to the throttling cycle under the same working conditions.