100/180 mm PAPERLESS GRAPHIC RECORDER: USER GUIDE
HA028910
Issue 13 Sep 16
User Guide
Page 116
4.3.11 FUNCTION (Cont.)
ROOT MASS FLOW
Note: The overall accuracy of a fl ow measurement installation depends on a number of factors
outside the control of the recorder manufacturer. For this reason, the recorder manufacturer takes
no responsibility for the accuracy of the results obtained using the mass fl ow equations imple-
mented in the maths pack.
The equation solved is:
where QM
t
= Mass fl ow (in kg/sec), at time ‘t’
K = Scaling factor (see below)
Rg = Specifi c gas constant in J/kg-K (see below)
Z = Compressibility factor (see below)
DeltaP
t
= Measured value across the orifi ce plate at time ‘t’
AbsP
t
= Absolute pressure of the fl uid at the up-stream tapping at time ‘t’ in kPa(A)
Temp = Temperature of the fl uid at the up-stream tapping in Kelvins
Scaling factor
This is determined from an assumed value of Qm at a known DeltaP, AbsP and Temp.
The value is chosen to give an output within the range low scale to high scale.
Specifi c gas constant The specifi c gas constant for any gas is available from published tables. For conven-
ience, the value for a number of common gases is given in
table 4.3.11a
, above.
Compressibility factor (Z-Factor)
Compressibility factor is a density-related measure of how far a particular gas devi-
ates from a ‘perfect’ gas under any set of temperature and pressure conditions, and
is given by the equation:
where: Z = Compressibility factor
P = Absolute pressure of the gas in kPa(A)
T = Absolute temperature of the gas (Kelvins)
%
= gas density at pressure P and temperature T (from published tables
QM
t
!
K
2
Rg
$
Z
$
DeltaP
t
$
AbsP
t
Temp
Z
!
P
T
$
1
%
