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Real Gas Corrections for High Beta Ratio Critical Flow Venturi (CFV) Installations.



Aaron N. Johnson, Eric W. Lemmon


For almost 50 years flow measurement applications using critical flow venturis (CFVs) have relied exclusively on the critical flow function (C*) to correct for viral effects. This work shows that C* does not account for all real gas effects. For high beta ratio (> 0.25) CFV installations, virial effects can result in significant mass flow errors even after C* corrections have been made. These errors are attributed to the idealized thermodynamic models (ITMs) used to calculate the stagnation temperature and pressure. The errors in the stagnation temperature and pressure cause errors in C*, and ultimately in the CFV mass flow. For methane gas the mass flow errors exceeded 0.1 % for =0.5 at 10 MPa, and are larger than 0.3 % for =0.6 at 20 MPa. This manuscript presents a model that compensates for all virial effects for up to 0.6. Comparisons of the virial model (VM) and the idealized thermodynamic models (ITMs) are shown for methane up to 20 MPa. We incorporated this new model into the REFPROP thermodynamic program so that complete virial corrections can be applied to any user defined gas. We expect that this new model will enable high beta ratio CFV installations to be used reliably at lower uncertainty.
Proceedings Title
9th International Symposium on Fluid Flow Measurement (ISFFM)
Conference Dates
April 15-17, 2015
Conference Location
Arlington, VA
Conference Title
International Symposium on Fluid Flow Measurement (ISFFM)


Real Gas Corrections in CFVs, Viral Corrections in CFVs, Critical Flow Function, Critical Flow Venturis, CFVs, Sonic Nozzles


Johnson, A. and Lemmon, E. (2015), Real Gas Corrections for High Beta Ratio Critical Flow Venturi (CFV) Installations., 9th International Symposium on Fluid Flow Measurement (ISFFM), Arlington, VA, [online], (Accessed July 17, 2024)


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Created April 17, 2015, Updated February 19, 2017