Relative performance of different shaped surface aeration tanks

Surface aeration experiments were conducted in tanks of length to width ratio (L/W) of 1.0, 1.5 and 2 and circular tanks to study their relative performance on oxygen transfer and energy consumption while re-aerating deoxygenated water. An identical geometric similarity of various linear dimensions of aerators, rotor blades and rotor diameter was maintained for all sizes and shapes of aeration tanks tested. Power consumed per unit volume concept to simulate the oxygen transfer coefficient k is found to be valid in all the three shapes of aerators. Simulation equations to predict the oxygen transfer coefficient k for any given dynamic parameter governing the theoretical power per unit volume, X were developed for rectangular tanks of L/W ratios equal to 1.5 and 2. Results were compared with simulation equations (correlating k and X) for square and circular tanks. Simulation criterion correlating the oxygen transfer coefficient k with actual and effective power consumption per unit volume for three shapes of tanks was developed in this paper. Energy consumption per unit volume of water was also analyzed. Examples illustrating the application of results are presented. It has been found that the circular tanks are the most energy efficient i.e., to produce maximum k for a given effective / actual input energy, followed by square tank, rectangular tank of L/W = 1.5 and rectangular tank of L/W = 2. This suggests that the circular tank gives a better performance as far as power requirements is concerned and hence better economy