Flow Detectors
STEAM FLOW DETECTION
Since steam is considered to be a gas, changes in pressure and temperature greatly affect its
density. Equations 4-5 and 4-6 list the fundamental relationship for volumetric flow and mass
flow.
(4-5)
and
(4-6)
m
Vr
where
= volumetric flow
K = constant relating to the ratio of pipe to orifice
h = differential pressure
r = density
= mass flow
m
It is possible to substitute for density in the relationship using Equation 4-7.
(4-7)
r
pm
Rq
where
r = density
p = upstream pressure
m = molecular weight of the gas
q = absolute temperature
R = gas constant
By substituting for density, the values are used by the electronic circuit to calculate the density
automatically. Since steam temperature is relatively constant in most steam systems, upstream
pressure is the only variable in the above equation that changes as the system operates. If the
other variables are hardwired, measuring the system pressure is all that is required for the
electronics to calculate the fluid’s density.
Rev. 0
Page 13
IC-04
