A study of the vane dynamics in a rotary vane expander for the transcritical CO2 refrigeration cycle

Abstract

Because of the loss of contact between the vane tip and the cylinder wall, excessive gas leakage existed in the rotary vane expander, which was developed to replace the throttling valve to improve the coefficient of performance of the transcritical CO2 refrigeration cycle. The mathematical model of the vane dynamics was established to analyse the vane movement in two different cases depending on whether the vane contacted the cylinder wall or not. From the recorded pressures, instead of assumed ones in the slots, the forces acting on the vane were analysed and the vane movement in the slot, as well as the contact state between the vane and the cylinder wall, was described quantitatively. The dynamics model was validated with the vane movement data recorded by a high-speed video. The results showed that the two adjacent vanes presented different movement behaviours. Both vanes left the cylinder wall because of the impact of the charging gas, but while one vane could rebound quickly back to and maintain contact with the cylinder wall, the adjacent vane did not contact the cylinder wall throughout most of the angles until the rotation angle reached ∼ 70°. Arranging springs in the slot underneath the vane proved to be beneficial in maintaining a tight contact between the vane and the cylinder wall and thus improve the working processes of the expander. Compared with the gas forces on the vane, the centrifugal force was much smaller and therefore had negligible influence on the vane movement.