Influence of turbulence on surface reaeration

Some numerical methods are briefly described for determining vertical diffusion coefficients as a function of vertical coordinate in a turbulence vessel where there are no net velocities. It is planned to use this turbulence vessel and these numerical methods to study in detail the mechanics of diffusion of a substance (analogous to oxygen) which is absorbed at the free surface. A hot-film anemometer is to be used to make direct measurement of turbulence parameters affecting the diffusion process. The anemometer has been calibrated in water which was in solid body rotation. Some of t>he difficulties experienced with the hot-film sensor and the corrective measures which were used are discussed. Preliminary diffusion tests have been made in the turbulence vessel where turbulence is generated by vertically oscillating screens made of expanded metal. Some values of the vertical diffusion coefficient have been calculated from the data for two of these preliminary runs. Plans call for making more detailed diffusion studies and for making direct turbulence measurements in studying surface reaeration.U.S. Department of the InteriorU.S. Geological SurveyOpe

Effects of oxygen demand on surface reaeration

An extensive literature review is presented pointing out that the transport or diffusion of dissolved oxygen in the thin region or film immediately below the water surface is the most critical region in determining the oxygen absorption rate. Literature on the effects of sodium sulfite and biochemical oxygen demand (BOD) is also reviewed. The surface film is actually an oxygen boundary layer. This concept is supported by the definition of a boundary layer, by reaeration experiments, and by analogy with other mass and heat transfer problems. Thus, it should be expected that the film or boundary layer thickness changes with Schmidt number as well as mixing conditions and that the transport through the film can be represented by a diffusion model., as in other boundary layer problems. Temperature measurements were made to allow the calculation of the diffusion coefficient in the thermal boundary layer or film in a situation analogous to the reaeration problem. The results indicate that the diffusion coefficient is approximately equal to the molecular diffusivity even when turbulence is present. Using the boundary layer and diffusion model, analytical solutions are presented for the vertical concentration distribution both in the turbulent film and below the film for various situations involving no oxygen demand, sulfite, or BOD. The solutions substantiate that the concentration distribution is essentially linear in the film even in the unsteady absorption problem both with no oxygen demand and with BOD. The degree of approximation involved in making certain simplifying assumptions is demonstrated. The solutions show that the oxygen demand per se of the BOD does not affect the absorption rate, but the possibility is left open for other effects, such as physical influences, to affect the absorption rate. The solutions for the effects of sulfite in increasing the absorption rate are in general agreement with available data. Experiments were performed at 2°C and at 20°C to evaluate the effects of BOD on reaeration rates. For both temperatures, the reaeration rates were about 1.5 times the rate for pure water. Since biological activity is almost non-existent at 2°C, the increase must have been due to the physical presence of the organisms.U.S. Department of the InteriorU.S. Geological SurveyOpe

Some data on diffusion and turbulence in relation to reaeration

Heat was used as a tracer to determine diffusion rates immediately below the free surface both in the "film" region and in the remainder of the water in a mixing vessel. The results tend to indicate that a diffusion model can be used to represent the downward transport of a substance which is being absorbed at the free surface. Apparently, the diffusion coefficient in the "film" can be either equal to or greater than the molecular coefficient depending on the amount of mixing at the free surface. Hot film anemometry was used to determine turbulence characteristics from 1 in. to 0.006 in. below the free surface of a laboratory open channel flow. The energy spectra indicate no significant changes in the turbulence in this region. Thus, apparently turbulence exists right up to the free surface and in the "film" region. The amount of reliable data that was obtained was very limited.U.S. Department of the InteriorU.S. Geological SurveyOpe

Coevolution of Glauber-like Ising dynamics on typical networks

We consider coevolution of site status and link structures from two different initial networks: a one dimensional Ising chain and a scale free network. The dynamics is governed by a preassigned stability parameter $S$, and a rewiring factor $\phi$, that determines whether the Ising spin at the chosen site flips or whether the node gets rewired to another node in the system. This dynamics has also been studied with Ising spins distributed randomly among nodes which lie on a network with preferential attachment. We have observed the steady state average stability and magnetisation for both kinds of systems to have an idea about the effect of initial network topology. Although the average stability shows almost similar behaviour, the magnetisation depends on the initial condition we start from. Apart from the local dynamics, the global effect on the dynamics has also been studied. These parameters show interesting variations for different values of $S$ and $\phi$, which helps in determining the steady-state condition for a given substrate.Comment: 8 pages, 10 figure

Turbulent Jets in Crossing Pipe Flow (HES 30)

National Science Foundation Grant NSF-GK-24931unpublishednot peer reviewe

Laboratory Studies on the Hydrocarbon Gas Tracer Technique for Reaeration Measurement

U.S. Geological SurveyCenter for Water and the Environmen

Preliminary Investigation of Tracer Gas Reaeration Method for Shallow Bays

U.S. Department of the Interior Geological SurveyCenter for Water and the Environmen

Model for Transport of Floating Debris in the Ocean

U.S. Department of the Interior U.S. Geological Survey Grant No. 14-08-0001-G1728Center for Water and the Environmen

Literature Survey on Reaeration in Estuaries

Center for Water and the Environmen