Characterizing bubble penetration from a falling stream

The depth that bubbles will penetrate a receiving pool before rising due to buoyancy forces is an important phenomena in designing Low Head Oxygenator (LHO) devices, particularly in an indoor application where the available elevation between the top of the fish tank water column and the inside ceiling height is limited. The relationship between bubble loss and LHO geometry is unclear. If the submergence of the LHO is less than the bubble penetration depth, excessive escape of bubbles can increase operating costs substantially. A series of physical experiments were conducted using an elevated bucket with a single orifice to create a falling stream into a receiving pool. The primary variables of hydraulic head, hole diameter and fall height were varied over a practical range for such applications. Videotaping was used to analyze bubble penetration. Regression equations were developed to predict both bubble penetration and standard deviation associated with a specific set of operating conditions. The standard deviation regression equation can be used to predict the statistical variation in bubble penetration depth. Bubble penetration depth decreased as fall height was increased and became stable at a fall height of 50 cm. Bubble penetration increased as hole diameter was increased at all fall heights and hydraulic heads. An example is provided of how to predict bubble penetration depth to meet some user defined statistical confidence for maximum bubble penetration.