Modeling and Experimental Investigation on the Internal Leakage in a CO_2 Rotary Vane Expander

摘要

A rotary vane expander has been developed to replace the throttling valve for improving the COP of transcritical CO_2 refrigeration system. Due to the serious internal leakage, the expander efficiency is not satisfactory. This paper presents the theoretical and experimental investigation on the internal leakage in a rotary vane expander prototype. Firstly, the leakage flow rate through the internal leakage paths with varied clearances were measured under various pressure differences as the expander was static. Then, the nozzle and friction pipe model was used to simulate the flow in the leakage gaps for calculating the leakage flow rate, and the commercial CFD software FLUENT was used to solve the equations in the model. Finally, the calculation results were compared with the experimental data. It was shown that the leakage through the seal arc between the cylinder and rotor is dominant and the percentage is 41%. The leakage through the end surface gaps accounts for 32% and the other leakage was mainly associated with the vane. The rotation speed has little influence on the leakage flow rate, though the volumetric efficiency increases with the speed directly. The seal arc length and the gap clearance has a remarkable effect on the leakage flow rate. Springs put in the vane slot were proven to be able to help the vane contact with the cylinder tightly. The increasing rotational speed can improve the volumetric efficiency of the expander to the value of 60% at the rotational speed of 3000 rpm.