10 APPENDIX
170
TITAN VERSA Operations and Maintenance Manual
LACO Technologies
Gas Flow Conversions
Gas Flow Conversions
To Convert From m
3
/sec
Liter/sec
m
3
/hr
CFM (feet
3
/min)
m
3
/sec
1
1.000
3,600
2.12 x 10
3
Liter/sec
0.001
1
3.6
2.12
m
3
/hr
2.78 x 10
-4
0.278
1
0.589
CFM (feet
3
/min)
4.72 x 10
-4
0.47
1.70
1
Leak Flow Regime
10.1.4.1.
Viscous vs. Molecular Flow Leaks
The flow regime encountered in leak testing is often di
ffi
cult to determine. It can,
however, be estimated by calculating the average mean free path of the gas
molecule (l) divided by the estimated leak path diameter (d). Use the following
guidelines to det
ermine the flow regime.
•
Viscous Flow
leaks typically occur in systems leaking at atmosphere or larger
pressures (l/d < 0.01). Viscous leaks are typically larger than 10-5 atm-cc/sec, but
can occur at lower leak rates.
•
Molecular Flow
leaks typically occur under vacuum conditions (l/d > 1.00).
Molecular leaks are typically smaller than 10-5 atm-cc/sec.
•
Transitional Flow
occurs between viscous and molecular flow regimes (0.01 < l/d <
1.00).
Helium Leak Rate vs. Other Gases
Convert to
Multiply Helium Leak Rate by:
Viscous Flow
Molecular Flow
Argon
0.883
0.316
Neon
0.626
0.447
Hydrogen
2.23
1.41
Nitrogen
1.12
0.374
Air
1.08
0.374
Water Vapor
2.09
0.469
