Study of a Rotary Vane Expander for the Transcritical CO2 Cycle—Part I: Experimental Investigation

This paper presents the experimental investigation of a double acting rotary vane expander for work recovery in the transcritical CO2 cycle and focuses on the design improvements for leakage and friction within the expander. The bench tests were carried out to investigate the leakage and friction distributions within the expander. The test results showed that the end gaps caused the major leakage within the improved expander prototype, while the friction losses associated with the vanes—especially due to the springs in the slots—were dominant and accounted for about 70% of the total friction losses. By comparing the pressure-rotation angle diagrams of the improved prototype with the original one, the effects of adding springs in the slots and arranging sealing vanes at the sealing arc on the thermodynamic processes were analyzed. It was shown that the tight contact between the vanes and cylinder wall owing to the springs had a significant improvement on the thermodynamic processes in that the cycle duration resumed being normal and the expander demonstrated a reasonable expansion process. By putting springs in the vane slots and arranging the sealing vane in the cylinder at the sealing arc, the volumetric efficiency increased from 17% to 30%, and the isentropic efficiency improved from 9% to 23%, resulting in a maximum coefficient of performance COP improvement of 14.2% compared with the throttling cycle under the same test conditions.

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