The Influence of Tank Geometry on the Oxygen
Transfer Capabilities of Mechanical Surface Aerators
R.A. KORMAN1K, Manager
C.B. GRIMES, Industrial Group Leader
Water Quality Control Division
Envirex, Inc., a Rexnord Company
Waukesha, Wisconsin 53168
T.C. ROONEY, Unit Manager
K.A. PIETILA, Engineer Technician
Corporate Research and Development Group
Rexnord, Inc.
Milwaukee, Wisconsin 53201
INTRODUCTION
One of the most controversial areas with respect to the design and application of
surface mechanical aerators is the determination of oxygen transfer rates at "standard
conditions." In the determination of these transfer rates at standard conditions, there are
two areas of real concern: 1) The actual testing procedures and techniques employed as well
as statistics associated with the interpretation of the raw data; and 2) The relationship
which exists between the aerator transfer rate and test tank geometry; that is, tank volume,
surface area and depth.
The actual test procedures and interpretation of the raw test data have been discussed
in detail by Boyle, et al (1). Using their work as a guide, a program was initiated to determine
the effects of test basin geometry on the oxygen transfer rates of surface mechanical
aerators.
HISTORY
Since about 1964 Eckenfelder (2) and others have promoted the idea that the oxygen
transfer rate of a surface mechanical aerator at standard conditions, N0, is a function of the
basin volume in which the tests were conducted. Figure 1 summarizes some of the work of
many investigators who have been involved in determining the efficiencies of surface
mechanical aerators. Up to this date, N0 (lbs 02 transferred per NpHp-HR) has been
correlated to a basin volume as defined by Pv, Hp per 1000 gal. of test basin volume.
From Figure 1 it has been shown that a straight line relationship can be established
between N0 and Pv with a fair degree of data scatter. This relationship has been defined as
follows (2).
N0 = Ns + KPV (1)
Where
Ns = oxygen transferred under standard conditions due to the liquid spray,
lbs 02/NpHp-HR.
K   = constant for the aeration device, slope of the lines in Figure 1.
The term Ns is the intercept of the line at the ordinate as shown in Figure 1 and is that
portion of the total oxygen transferred (N0) which is derived from the pumping of the liquid
by the aerator through the air.
Since a fair degree of scatter of data exists between N0 and Pv, and since the major
source of oxygen is transferred at the water surface, a testing program was initiated to determine the relationship of oxygen transfer rates using Hp/surface area, Pa (HP/100 sqft)
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