Prediction of flow rates through an orifice at pressures corresponding to the transition between molecular and isentropic flow
Abstract
A model of compressible flow through an orifice, in the region of transition from free molecular to isentropic expansion flow, has been developed and tested for accuracy. The transitional or slip regime is defined as the conditions where molecular interactions are too many for free molecular flow modeling, yet not great enough for isentropic expansion flow modeling. Due to a lack of literature establishing a wellaccepted model for predicting transitional flow, it was felt such work would be beneficial. The model is nonlinear and cannot be satisfactorily linearized for a linear regression analysis. Consequently, a computer routine was developed which minimized the sum of the squares of the residual flow for the nonlinear model. The results indicate an average accuracy within 15% of the measured flow throughout the range of test conditions. Furthermore, the results of the regression analysis indicate that the transitional regime lies between Knudsen numbers of approximately 2 and 45.
 Publication:

Presented at the 32nd National Vacuum Symposium and Topical Conference
 Pub Date:
 1985
 Bibcode:
 1985avs..symp.....D
 Keywords:

 Compressible Flow;
 Flow Velocity;
 Orifice Flow;
 Orifices;
 Predictions;
 Regression Analysis;
 Slip Flow;
 Transition Flow;
 Accuracy;
 Computer Programs;
 Mathematical Models;
 Pressure;
 Fluid Mechanics and Heat Transfer