ASME MFC-72016: Measurement of Gas Flow by Means of Critical Flow Venturis and Critical Flow Nozzles
John D. Wright, Aaron N. Johnson
This Standard applies only to the steady flow of single-phase gases through critical flow venturis, CFVs, of shapes specified herein (also sometimes referred to as critical flow nozzles or critical flow venturi nozzles). This document applies to critical flow venturis with diverging sections on the downstream side of the throat. When a critical flow nozzle, CFN, (no diverging section) is discussed, it will be explicitly noted. This Standard specifies the method of use (installation and operating conditions) of CFVs. This standard also gives information necessary for calculating the mass flow of the gas and its associated uncertainty. This Standard applies only to CFVs and CFNs in which the flow is critical. Critical flow exists when the mass flow through the CFV is the maximum possible for the existing upstream conditions. At critical flow or choked conditions, the average gas velocity at the CFV throat closely approximates the local sonic velocity.