ASME International

Measurement of Gas Flow by Means of Critical Flow Venturi Nozzles
 N MFC-7M

Annotation

SCOPE AND FIELD OF APPLICATION

This Standard applies only to the steady flow of single-phase gases and deals with devices for which direct calibration experiments have been made, sufficient in number and quantity to enable inherent systems of applicationst o be basedo n their resultsa nd coefficients to be given with certain predictable limits of uncertainty. The critical flow venturi nozzles dealt with can only beu sed within limitst hat ares pecified, for example nozzle throat to inlet diameter ratio and Reynolds number.

This Standards pecifies the geometry and methoodf use (installation and operating conditions) of critical flow venturi nozzles inserted in a system to determine the mass flow rate of the gas flowing through thsey stem. It also gives necessary information for calculating the flow rate and its associated uncertainty

This Standard applies only to venturi nozzles in which the flow is critical. Critical flow exists whent he mass flow rate through the venturnio zzle is the maximum possible for thee xisting upstream conditions. At critical flow or choked conditions, the average gas velocity at the nozzle throat closely approximates the local sonic velocity.

Information is given in this Standard for cases in which:

(a) the pipeline upstream of the venturi nozzle is of circular cross section; or

(b) it can be assumed that theirse a large space upstream of the venturi nozzle.

The venturi nozzles specified in this Standard are called primary devices. Other instruments for the measurement are known as secondary devices. This Standard covers primary devices; secondary devices will be mentioned only occasionally.