Theoretical and experimental studies were carried out with the aim of
developing an improved aeration device. Many of the aeration devices
currently in use contain fine pores, through which air is pumped to produce
small bubbles in the diameter range of 2 to 3 mm in water, the objective
being optimum performance in terms of mass transfer. Because of the very
small pore size, these devices are often subject to clogging, consequent
deterioration of efficiency and escalation of power requirements. The
development of the new aeration device, named the SAF diffuser, is an
attempt to generate bubbles of the optimum size range using relatively larger
orifices so that the diffuser clogging and the energy requirements can be
The SAF Diffuser comprises a vertical draft tube immersed in the water
body to be aerated. A buoyancy: induced flow is created within the tube by
injecting air through 0.5 mm diameter peripheral orifices located near the
inlet end. The induced flow exerts a drag force on the bubbles that are being
formed at the peripheral orifices. This drag force causes the bubble to detach,
from the orifice before it grows to the normal size attained in stagnant water.
Utilizing this concept, hole sbes that are larger than (about 15 times) those
used in conventional fine pore diffusers are possible. For a given air flowrate,
the induced velocity and hence the bubble size depends upon the tube
dimensions. This dependence provides a novel technique to control the bubble
Theoretical and experimental study of the air-water flow as well as the
mass transfer characteristics of the device were undertaken. Simple methods of
measuring the two phase flow parameters were developed. Through theoretical
analysis and experimentation, non-dimensional correlations to predict the
phase velocities within the device as well as the mass transfer characteristics
of the device were developed. The studies showed that for medium depth
applications, the device can operate with 10 to 20 percent higher aeration
efficiencies than conventional designs. Even higher efficiencies are possible in
the low depth applications typical in aquaculture.
Legislative Commission on Minnesota Resources; Metropolitan Waste Control Commission
Ramanathan, V.; Arndt, Roger E. A..
Experimental Development of a Novel Aeration Device.
St. Anthony Falls Hydraulic Laboratory.
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