Resistance Characteristics of Surface Aerators

The resistance characteristics in terms of power consumption, interpreted in terms of Power number $\left(P_0\right)$ , of unbaffled surface aeration systems consisting of flat bladed impellers, were studied in two shapes of surface aerations tanks: square and circular. Experiments were conducted in three different sizes in each of the geometrically similar unbaffled square and circular surface aerators. Results have shown that the $P_0$ cannot be simulated singularly either with Reynolds number $\mathsf{R}$ or with Froude number as there are scale effects; hence there appears to be a need for incorporating the effects of both $\mathsf{R}$ and $\mathsf{F}$ . It is found that $P_0$ is uniquely related to a parameter $X$ $(={\mathsf{F}}^{4∕3}{\mathsf{R}}^{1∕3})$ , which is defined as a parameter governing the theoretical power per unit volume for both shapes of aeration tanks; however, such relationships are different for both shapes of aerators. Interestingly $P_0$ values are always higher in square surface aerators than in circular surface aerators, which suggests that the circular surface aerators require less power input than the square surface aerators. The usefulness of such correlations was demonstrated in estimating the power requirement while achieving a required oxygen transfer coefficient in surface aerators.