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Gas Compressors 133

where
γ go = specific weight of standard air (0.0765 lb/scf or 12 N/scm)
v go = minimum required velocity of air under standard conditions
(50 ft/s or 15.24 m/s)
The kinetic energy of 1 standard cubic foot of air moving at a velocity
of 50 ft/s is

E go = 1 0:0765 2 3 3
2 32:2 ð50Þ ≈ 3ft-lb/ft ½143 J/m Š
If the carrying capacity of gas at the point of interest in the borehole
is equivalent to the carrying power of the velocity of standard air, the
following relationship must hold:
γ γ
1 g v = 1 go 2 (6.41)
2
2 g g 2 g v go
where
3
γ g = specific weight of in situ gas, lb/ft or N/m 3
v g = velocity of in situ gas, ft/s or m/s

The specific weight of gas in Eq. (6.41) can be expressed as a function
of in situ pressure and temperature based on the ideal gas law:

S g P
γ = (6.42)
g
53:3T
The volumetric in situ flow rate of gas can be determined based on
Eq. (6.39):
Q g = P o T Q go (6.43)
T o P
Dividing Eq. (6.43) by the cross-sectional area of the flow path yields
an expression for in situ gas velocity in U.S. engineering units as

v g = ð14:7Þð144Þð144ÞTQ go (6.44)
ð60Þð520ÞPA

or
TQ go
v g = 9:77 (6.45)
PA