Civil Engineering Reference
In-Depth Information
TABLE 9-7. Typical Design Values for Spray Aeration
Design Parameter
Value
Pressure ranges
1 to 10 psi (6.6 to 70 kPa)
Nozzle diameter
1.0 to 1.5 in. (2.5 to 3.8 cm)
Discharge rates
75-150 gpm at
10 psi
(
4.7-9.5 L / s at
69 kPa)
Nozzle spacing
2 to 12 ft (0.6 to 3.7 m)
Droplet diameter
2 to 10,000
m
Area required
50 to 150 ft
2
per mgd of capacity
head to be expended, the area allocated to aeration, and the degree of interference
between adjacent sprays. Key design parameters for the nozzles include
K
L
a
(mass transfer values available from manufacturers)
•
Droplet diameter
•
Time of exposure
•
The droplet diameter determines the area:volume ratio and is a major controlling
factor in the mass transfer rate. It is a function of the dispersing action of the nozzle
and generally ranges from 2 to 10,000
m. A smaller diameter will allow a higher
air-to-water ratio. However, the smaller nozzles are more susceptible to clogging, re-
sulting in higher maintenance requirements.
The time of exposure is dependent on the droplet's initial velocity and trajectory.
The initial velocity
V
of a drop emerging from an orifice or nozzle is given by
V
C
2
gh
v
where
V
initial velocity, ft / sec (m / s)
C
v
coefficient of velocity
g
acceleration of gravity, ft / sec
2
(m / sec
2
)
h
total head on nozzle, ft (m)
The total discharge
Q
from the nozzle is given by
Q
CA
2
gh
d
where
Q
nozzle discharge, ft
3
/ sec (L / sec)
C
d
coefficient of discharge
A
area of nozzle opening, ft
2
(m
2
)
g
acceleration of gravity, ft / sec
2
(m / sec
2
)
h
total head on nozzle, ft (m)
