Orifice Flow Calculation: Comparison Between Fluid Meter Applications — 6^th Edition 1971, ASME PTC 19.5-2004 and ISO 5167 2003

This paper presents a comparison between existing flow calculations that are currently in use by the authors’ company in its Test Data Reduction System (TDRS) and the latest ASME flow measurement standard. Equations for the current system are referenced from Flow Meter Applications – 6^th Edition 1971 [1] and updated equations are referenced from Flow measurement ASME PTC 19.5-2004 [2]. Comparisons were made between mass flow, expansion factor and orifice discharge coefficient calculations. The equations for mass flow and expansion remained unchanged between versions; however a variation in results exists between orifice discharge coefficients. For a diameter ratio, β range of 0.4 to 0.7, the updated 2004 equation for discharge coefficient provides a relatively small change over the 1971 equation. The 2004 equation was also found to be less sensitive to changes in pipe diameter and Reynolds number. A comparison between the ISO 5167 2003 and PTC 19.5-1971 flow calculations was also done. There was a significant difference in the calculation of expansion factor using ISO 5167 2003, which resulted in a significant mass flow variation between the two flow measurement standards.