Changes in the NPL orifice conductance on a transition from molecular gas flow to transitional flow

Abstract

The conductance of an NPL orifice in the molecular regime is constant and can be exactly calculated from the geometric dimensions. For smaller Knudsen numbers the conductance increases and correction functions are employed to reduce the uncertainty in this range of pressures.

A suitable function has been chosen with one free parameter and the parameter was determined on the basis of the experimentally measured course of the conductance at the borderline between molecular and transitional flow.

Keywords

• NPL orifice
• transitional flow