Water Surface Flow and Exchange Induced by a Bubble Plume

by K. Zic, Univ of Minnesota, Minneapolis, United States,
H. G. Stefan, Univ of Minnesota, Minneapolis, United States,

Abstract: Aeration is a common method to increase dissolved oxygen in the water of stratified (or non-stratified) lakes. In this method compressed air is injected at some depth, and gas is transferred from rising bubbles to the water, but there is also increased reaeration at the water surface due to the surface flow and turbulence induced by the bubble plume. Experiments were conducted in temperature stratified laboratory tanks simulating midsummer conditions in temperature lakes. The time evolution and the spatial distribution of water temperatures were measured. Of particular interest for surface transfer processes is the upwelling region induced by the bubble plume. Infrared photography of water surface temperatures showed the axisymmetrical nature of the flow. A distinct nearfield and farfield were visible on the surface. The radius of the nearfield was approximately equal to the depth at injection. A 2-D numerical turbulent flow model provided additional information about the flow field which would have been difficult to obtain from the experiments. The flow patterns were illustrated by means of the velocity vectors, streamlines and isotherms. No gas transfer rates were calculated or measured directly, but vertical turbulent heat fluxes w¯'T¯' in the highly agitated near-surface boundary layer can be related to turbulent gas fluxes w¯'C¯'. Using the analogy is advantageous since temperatures T' are more easily measured than gas concentrations C'.

Subject Headings: Water surface | Turbulent flow | Water flow | Plumes | Temperature measurement | Boundary layers | Water treatment | Overland flow

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