Brooks Instrument 5850i - Manual (Page 44)

Brooks ® Model 5850i
4-16
Section 4 Maintenance Installation and Operation Manual
X-TMF-5850i-MFC-eng
Part Number: 541B108AAG
December, 2008
Example: What is the air equivalent flow rate of 2000 sccm Hydrogen?
In order to calculate the orifice conversion factor when using a gas mixture,
the following formula must be used:
Where P1 = percentage by volume of gas 1
P2 = percentage by volume of gas 2
Pn = percentage by volume of gas n
Example: Find the Air equivalent flow for 20 slpm of a 20% Helium
and 80% Chlorine gas mixture.
Q
AIR
= Q
gas
(orifice conversion factor)
= 20 x 1.417
= 28.34 slpm air
2. If inlet and outlet pressures are given in gauge pressure (psig)
add14.7 to convert to absolute pressure (psia).
Outlet Pressure — 30 psig + 14.7 = 44.7 psia
Inlet Pressure — 50 psig + 14.7 = 64.7 psia
3. Determine Critical Pressure Drop
Critical pressure drop occurs when the outlet pressure (psia) is less
than half the inlet pressure (psia) or
P outlet < P inlet
2
If these conditions exist, the pressure drop (
Δp) should be calculated as
follows: