(98f) An Alternative Formulation of the Standard Orifice Equation for Natural Gas and Pure Compounds

This paper presents a detailed analysis of the standard orifice equation reported in the American Gas Association (AGA) Report No. 3 using data for natural gas measured by the Southwest Research Institute (SRI), data for nitrogen measured by the National Institute of Standard and Technology (NIST), and air data from the Colorado Engineering Experiment Station, Inc (CEESI). It appears that the standard orifice equation does not fit satisfactorily all of the data. A bias of about 0.5% exists for the natural gas data and 4% for the air data. In this paper, an alternative scheme to determine the expansion factor coefficient leads to a single curve for all the data with an uncertainty of ±0.02% at 3ó. Finally, a simple fit for the discharge coefficient using the new expansion factor provides a correlation that fits the natural gas data within ±0.3%.