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Rectangular tank surface aerators: scale up criteria and energy conservation
A. R. Rao and B. Kumar
Abstract
Surface aeration experiments were conducted in two types of rectangular tanks of aspect ratios i.e., length to width ratio (L/W) of 1.5 and 2 and developed simulation equations to correlate the oxygen transfer coefficient, k and power number, P_{0} with a parameter governing theoretical power per unit volume X. The parameter X is defined as equal to F^{4/3}R^{1/3}, where F and R are impellers' Froude and Reynolds numbers respectively). Results have shown that the P_{0} can not be simulated singularly with either Reynolds number, R or Froude number, F, which results in scaleeffects; there appears to be a need to incorporate the effects of both F and R. It was found that P_{0} is uniquely related to X for rectangular aeration tanks of both aspect ratios, however, such relationships are different depending upon the aspect ratios. It has been demonstrated that energy can be saved substantially if the aeration tanks are run at relatively higher input powers. It is also demonstrated that smaller sized tanks are more energy conservative and economical when compared to big sized tanks, while aerating the same volume of water, and at the same time by maintaining a constant input power in all the tanks irrespective of their size.
Keywords
Froude number, oxygen transfer coefficient, power number, power per unit volume, Reynolds number, surface aerators, water and wastewater treatment
