4-16
Brooks
®
Model 5851E
Section 4 Maintenance
Installation and Operation Manual
X-TMF-5851E-MFC-eng
Part Number: 541B104AAG
November, 2008
Where:
Q
NITROGEN
=
Nitrogen equivalent flow rate (sccm)
Q
GAS
=
Desired flow rate of the gas (sccm)
NITROGEN
=
Density of Nitrogen at 70°F
GAS
=
Density of the gas (taken at customer temperature)
SG
GAS
=
Specific gravity of the gas (taken at customer
temperature)
Refer to Table 4-3 for densities.
Example:
Q
gas
=
2,000 sccm
gas
=
.269
Nitrogen
gas
Q
Nitrogen
=
Nitrogen
=
2,000 x .269
=
538 sccm Nitrogen
In order to calculate the orifice conversion factor when using a gas mixture,
the following formula must be used:
Orifice
Conversion
Factor 1
P
1
Orifice
Conversion =
Factor
Mixture
+ P
2
Orifice
Conversion
Factor 2
100
Orifice
Conversion
Factor n
+ P
n
Where
P
1
=
percentage by volume of gas 1
P
2
=
percentage by volume of gas 2
P
n
=
percentage by volume of gas n
Example: Find the Nitrogen equivalent for 20 slpm of a 20% Helium and
80% Chlorine gas mixture.
Orifice
Conversion
=
20(.378)
+
80(1.598)
Factor
100
Mixture
Q
Nitrogen
=
Q
gas
(orifice conversion factor)
=
20 x 1.439
=
28.78 slpm Nitrogen
2. If inlet and outlet pressures are given in gauge pressure (psig) add 14.7
to convert to absolute pressure (psia).
Q
GAS
x
