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Description / Abstract:
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.