Oxygen Transfer Efficiency in Counter-and Co-Current Air-Water Flow

Abstract

Abstract This study was undertaken to determine the efficiency of oxygenation in different air-entrained water systems. Both co-current and counter-current air-water flow conditions were used in a closed-loop diffused aeration system, consisting of 4 in. diameter plexiglass U-Tube of variable height and a 4 1/2 × 2 × 1 1/2 ft water re-circulating reservoir at the top. Four separate systems were investigated: System I was a simple water column; System II used only diffused air for water circulation and for creating an upward co-current air-water flow; System III employed pumping for water circulation, with a control on water velocity such that counter-current air-water flow was maintained; System IV used pumping to circulate water with the water velocity made large enough to create a downward co-current air-water flow. The aeration devices were located at the bottom of one side of the U-Tube in Systems I, II and III and near the top in System IV. The operating conditions were varied by changing airflow rates, water depth, water flow rates, and diffuser location. The efficiency of different systems is compared in terms of the rate of oxygen transferred/unit power input, given in lb/KWhr. It is found that, within the limitations of this study. System III is the most efficient.