Investigation of star wheel tooth tip surface conjugate to groove bottom in the single screw compressor

Abstract

The single screw compressor (SSC) has demonstrated promising applications in hydrogen compression, oil-free air compression, and refrigeration systems due to its advantages of low vibration and low noise. Improving SSC efficiency would further promote its adoption. Studies indicate that leakage at the star wheel tooth tip accounts for more than 40% of the total leakage loss, significantly impacting volumetric efficiency. This is largely attributed to the relatively large size of the leakage channel at the tooth tip, exacerbated by the fact that the tooth tip surface is currently not conjugate to the groove bottom surface. In existing designs, the tooth tip is typically designed as a cylindrical surface with a radius equal to that of the star wheel, while the groove bottom is an hourglass surface generated by rotating an arc around the screw shaft. In this article, an hourglass-shaped groove bottom surface is used to generate a tooth tip surface that satisfies the conjugate principle. It is found that the resulting tooth tip surface is not cylindrical. Instead, it is formed by two cross-sectional arcs derived from the hourglass groove bottom: one arc lies in the transverse plane through the star wheel shaft, and the other is the intersection curve between the groove bottom and the cylindrical screw surface. This approach minimizes clearance at the tooth tip. For an SSC with a capacity of 20 m³/min, the average clearance at any point on the tooth tip can be reduced by 34%, and the leakage can be reduced by 18.4%.