On the Equivalent Diameter Approach to Prediction of Rarefied Gas Flow in Noncircular Tubes

Abstract

The feasibility of using a new characteristic dimension (equivalent diameter) is explored for predicting rarefied flows in noncircular tubes. A conclusion is that a single characteristic dimension is not necessarily appropriate. However, a normalized equivalent diameter does appear to give good relative descriptions of noncircular passages. In addition, a simplified equation based on the Weber equation is proposed. Coefficients in this equation include the variability of the characteristic dimension, and are determined by matching with three analytical solutions spanning the rarefied regimes. Significant computer time is saved and predictions are as accurate as the matching values. The classical hydraulic diameter appears to be the best characteristic dimension to use for correlating the predicted data.