Analysis of air-bubble plumes

The air-bubble plume induced by the steady release of air into water has been analyzed with an integral technique based on the equations for conservation of mass, momentum and buoyancy. This approach has been widely used to study the behavior of submerged turbulent jets and plumes. The case of air-bubble induced flow, however, includes additional features. In this study the compressibility of the air and the differential velocity between the rising air bubbles, and the water are introduced as basic properties of the air-bubble plume in addition to a fundamental coefficient of entrainment and a turbulent Schmidt number characterizing the lateral spreading of the air bubbles. Theoretical solutions for two- and three-dimensional air-bubble systems in homogeneous, stagnant water are presented in both dimensional and normalized form and compared to existing experimental data. The further complication of a stratified environment is briefly discussed since this case is of great practical interest. This paper is to be considered as a progress report, as future experimental verification of various hypotheses is needed

Mixing of density-stratified impoundments with buoyant jets

This study is an investigation of the mixing of density-stratified impoundments by means of buoyant jets created by a pumping system. The deterioration of water quality which often occurs in density-stratified lakes and reservoirs may be counteracted by mixing. The physical aspects of the mixing process are the primary concern of this study, although several implications regarding changes in water quality are indicated. A simulation technique is developed to predict the time-history of changes in the density-depth profiles of an impoundment during mixing. The simulation model considers the impoundment closed to all external influences except those due to the pumping system. The impoundment is treated in a one-dimensional sense, except for the fluid mechanics of the three-dimensional jet and selective withdrawal of pumping system. The numerical solution to the governing equations predicts density profiles at successive time steps during mixing, given the initial density profile, the area-depth relation for the impoundment, the elevations of intake and jet discharge tubes, and the jet discharge and diameter. The changes due to mixing in the profiles of temperature and of a conservative, non-reacting tracer can be predicted also. The results of laboratory experiments and two field mixing experiments in which density-stratified impoundments were mixed using pumping systems show that the simulation technique predicts the response of the impoundment reasonably well. The results of a series of simulated mixing experiments for impoundments which have prismatic shapes and initially linear density profiles are given in dimensionless form. For these special conditions, the efficiency of the pumping system increased as the jet densimetric Froude number decreased, and the time required for complete mixing was a fraction of the characteristic time, T ≤ V-/Q (where V- is the impoundment volume included between intake and jet elevations and Q is the pumped discharge). Recommendations are made for the application of the generalized results and for the use of the simulation technique for lakes and reservoirs which are not closed systems

The potential impact of Ocean Thermal Energy Conversion (OTEC) on fisheries

The commercial development of ocean thermal energy conversion (OTEC) operations will involve some environmental perturbations for which there is no precedent experience. The pumping of very large volumes of warm surface water and cold deep water and its subsequent discharge will result in the impingement, entrainment, and redistribution of biota. Additional stresses to biota will be caused by biocide usage and temperature depressions. However, the artificial upwelling of nutrients associated with the pumping of cold deep water, and the artificial reef created by an OTEC plant may have positive effects on the local environment. Although more detailed information is needed to assess the net effect of an OTEC operation on fisheries, certain assumptions and calculations are made supporting the conclusion that the potential risk to fisheries is not significant enough to deter the early development of IDEe. It will be necessary to monitor a commercial-scale plant in order to remove many of the remaining uncertainties. (PDF file contains 39 pages.

Mathematical Simulation of Tidal Time-averages of Salinity and Velocity Profiles in Estuaries

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