Effect of high beta values on mass flow through critical flow nozzles

In a previous work (Stewart et al., Flow Measurement and Instrumentation 10(1) (1999) 27–34) the authors presented improved calculations for the mass flow of a gas through a critical flow nozzle. The work in Stewart et al. is applicable only when the nozzle throat to pipe diameter ratio, β, is low (<0.15). Whilst it is preferable to use a critical flow nozzle with a low β, practical considerations may dictate otherwise. This work extends the calculations to include high β values, explaining the problems encountered in these situations and the procedure for calculating the mass flow accordingly. The same four gases are covered, dry CO₂-free air, nitrogen, argon, and methane. A new empirical correction factor for use with high β critical flow nozzles is presented which, when combined with the work in Stewart et al., provides an accurate yet simple method for calculating the mass flow of these gases through critical flow nozzles with a wide range of β values.