Environmental Engineering Reference
In-Depth Information
Flow Rate
q
= 275
.
Vd
2
,
where:
q
= flow rate in B/D
V
= superficial velocity in cm/s
d
= pipe ID in inches
A more complete set of conversion factors can be found in Appendix A.
Flow Regimes
If more than one fluid is flowing in the pipe, the flow regime becomes more com-
plex. For example, liquid and gas mixtures can form a number of flow regimes
depending on the relative amounts of each in the total flow pattern. These can be
categorized as:
Bubble flow: bubbles of gas in liquid
Slug flow: gas bubbles reach pipe ID
Froth flow: gas carries liquid froth with it
Mist flow: liquid carried as a mist in the gas
Figure
4.4
plots dimensionless liquid velocity against dimensionless gas velocity
and exhibits these various flow regimes. Note that, in general, the lighter phase in
the mixture travels fastest. Bubbles of gas in a glass of beer can be seen to rise
through the static liquid. Experiments show that the difference in velocity (slip
velocity) of two phases is generally related to their density difference. Typical
values for slip velocities are:
Oil-water mix: 20-30 ft/min
Oil-gas mix: 5-10 ft/min
Gas-water mix: 40-50 ft/min
Slip velocity as a function of density difference is shown in Fig.
4.5
. The sub-
scripts
hp
and
lp
refer to the heavy and light phases respectively.
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