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Fundamental Aspects of Surface Aerator Performance and Design J. R. McWHIRTER, Research Manager Mixing Equipment Company, Inc. Rochester, N. Y. INTRODUCTION Considerable effort during the past decade has been devoted to developing methods and techniques for measurement of the oxygenation capacity of aeration equipment. In spite of this effort, however, there seems to exist a significant degree of contradictory information and confusion in the literature. This paper discusses several common methods for determining the oxygenation or mass transfer capacity of surface aerators. Comparison of the applicability of these methods is made as well as specific problems relating to their use in evaluation of surface aeration equipment. Performance information concerning commercial aeration devices have been largely obtained using four common methods of measurement (1). Of these techniques, the most widely used are the unsteady-state aeration of pure tap water and the steady-state oxidation of sodium sulfite solution. In addition, however, both steady-state and unsteady-state aeration of activated sludge systems are reported. A new method which involves steady-state aeration of pure tap water will also be discussed. UNSTEADY-STATE AERATION OF PURE TAP WATER This method involves reaeration of pure tap water from which the dissolved oxygen has been previously removed. Removal of the dissolved oxygen may be accomplished by stripping with inert gas or chemical reaction with a stoichiometric amount of sodium sulfite. The hasic theory governing the rate of diffusion of oxygen from a gas to a liquid had been developed many times (1,2,3,4) and therefore will not be repeated. Equation (1) describes the unsteady-state transfer of oxygen which applies during the reaeration. ^ = ^KLa(c*-C) (1) dt W in which Kj^a = combined overall liquid phase mass transfer coefficient and inter- facial area, lbs, Og^Hr) (ppm) driving force c = bulk average dissolved oxygen concentration in liquid, ppm. c* = dissolved oxygen concentration in liquid in equilibrium with gas phase. W = mass of water, lbs t = aeration time, hrs The use of Equation (1) implies the following basic assumptions. 1. The primary resistance to mass transfer is in the liquid phase and the inter- facial liquid concentration can be taken to be essentially in equilibrium with the gas phase. 2. The entire liquid contents are instantaneously perfectly mixed and therefore of a uniform composition at any time, t. - 75 -
Object Description
Purdue Identification Number | ETRIWC196507 |
Title | Fundamental aspects of surface aerator performance and design |
Author | McWhirter, J. R. |
Date of Original | 1965 |
Conference Title | Proceedings of the twentieth Industrial Waste Conference |
Conference Front Matter (copy and paste) | http://earchives.lib.purdue.edu/u?/engext,12162 |
Extent of Original | p. 75-92 |
Series |
Engineering extension series no. 118 Engineering bulletin v. 49, no. 4 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital object copyright Purdue University. All rights reserved. |
Language | eng |
Type (DCMI) | text |
Format | JP2 |
Date Digitized | 2009-05-19 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Resolution | 300 ppi |
Color Depth | 8 bit |
Description
Title | page 75 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital object copyright Purdue University. All rights reserved. |
Language | eng |
Type (DCMI) | text |
Format | JP2 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Transcript | Fundamental Aspects of Surface Aerator Performance and Design J. R. McWHIRTER, Research Manager Mixing Equipment Company, Inc. Rochester, N. Y. INTRODUCTION Considerable effort during the past decade has been devoted to developing methods and techniques for measurement of the oxygenation capacity of aeration equipment. In spite of this effort, however, there seems to exist a significant degree of contradictory information and confusion in the literature. This paper discusses several common methods for determining the oxygenation or mass transfer capacity of surface aerators. Comparison of the applicability of these methods is made as well as specific problems relating to their use in evaluation of surface aeration equipment. Performance information concerning commercial aeration devices have been largely obtained using four common methods of measurement (1). Of these techniques, the most widely used are the unsteady-state aeration of pure tap water and the steady-state oxidation of sodium sulfite solution. In addition, however, both steady-state and unsteady-state aeration of activated sludge systems are reported. A new method which involves steady-state aeration of pure tap water will also be discussed. UNSTEADY-STATE AERATION OF PURE TAP WATER This method involves reaeration of pure tap water from which the dissolved oxygen has been previously removed. Removal of the dissolved oxygen may be accomplished by stripping with inert gas or chemical reaction with a stoichiometric amount of sodium sulfite. The hasic theory governing the rate of diffusion of oxygen from a gas to a liquid had been developed many times (1,2,3,4) and therefore will not be repeated. Equation (1) describes the unsteady-state transfer of oxygen which applies during the reaeration. ^ = ^KLa(c*-C) (1) dt W in which Kj^a = combined overall liquid phase mass transfer coefficient and inter- facial area, lbs, Og^Hr) (ppm) driving force c = bulk average dissolved oxygen concentration in liquid, ppm. c* = dissolved oxygen concentration in liquid in equilibrium with gas phase. W = mass of water, lbs t = aeration time, hrs The use of Equation (1) implies the following basic assumptions. 1. The primary resistance to mass transfer is in the liquid phase and the inter- facial liquid concentration can be taken to be essentially in equilibrium with the gas phase. 2. The entire liquid contents are instantaneously perfectly mixed and therefore of a uniform composition at any time, t. - 75 - |
Resolution | 300 ppi |
Color Depth | 8 bit |
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