Air Concentration Distribution Research Articles

Characteristics of Diffusion Mixing Process in an Unsteady Gas Jet.

The combustion process in internal combustion engine is dominated by turbulent mixing the injected fuel with the ambient air. Therefore, in order to realize the high efficiency and clean combustion, it is necessary to understand in detail phenomena concerning these turbulent mixing process. Then, as a fundamental work elucidating the mechanism of mixture formation in the turbulent flow field, the gas velocity inside the transient gas jet was measured by PIV method, the concentration distribution of the entrained air was measured by LIF method. In addition, with two fluorescence tracer method proposed in this study, it is possible to measure simultaneous characteristics of fuel and surrounding air flow and concentration distribution. As the result, there is the stronger inverse proportional relation between the change in the ambient concentration and that in the axial turbulence intensity against that in the radial turbulence intensity. The change in the radial turbulence intensity is larger than that in the axial turbulence intensity, as a consequence that in the concentration is larger.

Air-water flows in partially-filled conduits

Supercritical open channel flows are characterised by a large amount of “white waters”. Although free-surface aeration was investigated for steep chutes, flow aeration down partially-filled pipes received little attention. A re-analysis of partially-filled pipe data (VOLKART 1982,1985) is presented. The results indicate that the air concentration and velocity distributions can be estimated by simple expressions. The study provides new information for the design of storm waterways, sewers and tunnel spillways where flow aeration may occur.

Air bubble entrainment in open channels: Flow structure and bubble size distributions

At spillways and sewers, high-velocity open channel flows are characterised by free-surface aeration (i.e. 'white waters'). The air-water flow comprises a region of low-air-content (i.e. C < 0.3 to 0.4) with a bubbly flow structure, and a high-air-content region above characterised by air-water projections and foam structures. New experiments were performed in a 25-m long channel with a 4-degree slope. Measured air-water flow properties and bubble chord length distributions are described. The analysis of the new data provides information on the air concentration distributions, the distributions of mean air-water velocities and the bubble chord length distributions. The results indicate a broad spectrum of chord length sizes extending over several orders of magnitude. The cumulative distributions of chord lengths follow approximately a Log-Normal distribution while the bubble frequency distributions is related to the void fraction by a parabolic law.

AIR CONCENTRATION DISTRIBUTION DOWNSTREAM OF SPILLWAY AERATORS

ABSTRACT Laboratory experiments on the distribution of air concentration downstream of spillway aerators have been reported. These data along with those of earlier investigators on different shapes of aerators have been analysed to develop relationships for concentration distribution in terms of geometry and approach flow conditions. The analysis has also been used to evolve an approximate criterion for the spacing of aerators.

Air Concentration Distribution In Self-Aerated Flow

Air Concentration Distribution In Self-Aerated Flow

Air Concentration Distribution In Self-Aerated Flow

Air Concentration Distribution In Self-Aerated Flow

Air Concentration Distribution In Self-Aerated Flow

Abstract A criterion for the development length of self-aerated flow over a spillway has been obtained by analysis of published and new experimental data. The new data were collected on a spillway model having a lope of I(V):0.75(H). Because of the limited length (3 m) of the spillway model, the data collected during the present investigation correspond only to the developing region. The published data, however, correspond to both the developing and developed flow region . The slope of the spillway for the published data range from 7.5° to 75°. The scaling parameters used in the theory of Rao et al. [9] have been evaluated and empirical relations obtained for the e both in developing and developed region, thereby making the construction of air concentration profile possible for given spillway geometry and approach flow condition .

Air concentration distribution in self-aerated flow

Abstract A criterion for the development length of self-aerated flow over a spillway has been obtained by analysis of published and new experimental data. The new data were collected on a spillway model having a lope of I(V):0.75(H). Because of the limited length (3 m) of the spillway model, the data collected during the present investigation correspond only to the developing region. The published data, however, correspond to both the developing and developed flow region . The slope of the spillway for the published data range from 7.5° to 75°. The scaling parameters used in the theory of Rao et al. [9] have been evaluated and empirical relations obtained for the e both in developing and developed region, thereby making the construction of air concentration profile possible for given spillway geometry and approach flow condition .

Air concentration distribution in self-aerated flow

Air concentration distribution in self-aerated flow

An area source numerical model on atmospheric dispersion with chemical reaction and deposition

An atmospheric dispersion model for gaseous pollutants emitted from an area source is presented. The model is facilitated by the numerical solution (an implicit finite difference scheme) of the atmospheric diffusion equation with the coefficients of eddy diffusion and wind velocity taken as a function of vertical distance. Ground deposition of the pollutants is accommodated by applying absorptive boundary conditions at the ground surface. Chemical transport is also described by a simple linear decay term in the atmospheric diffusion equation. The ambient air concentration distribution is studied for variable atmospheric stability and surface roughness. The effect of dry deposition and chemical reaction rates is also analysed. The moderate computer time requirements make the model applicable for practical use.

Uniform Region of Self‐Aerated Flow

The measurement of air concentration and velocity obtained in the laboratory are compared with the recent prototype measurement obtained on Aviemore spillway. This comparison suggests that if a characteristic depth such as the depth at which the air concentration is 0.9 chosen then the averaged air concentration over this depth is only a function of the slope. Similarly the air concentration distribution is also determined by the slope. The velocity distribution determined in the laboratory and in the field are also compared and it is suggested that water velocity measurements are consistent with a universal velocity distribution. These with the Darcy friction factor computed from laboratory results lead to a simple method for predicting the design parameters in the uniform aerated flow at the end of a long spillway.

Measurements of Self-Aerated Flow on a Spillway

Measurements are made on the spillway on a 36-m high concrete gravity dam. The measurements include the point of inception, and the velocity distribution and air concentration distribution and bubble size in the developing region of the flow. The measurements show that there appears to be a universal velocity distribution which is independent of the mean air concentration for average air concentrations of between 0 and 0.5, and the air concentration becomes progressively more uniform with the distance downstream. However at 200 times the depth at the point on inception downstream of this point it is still growing. At 100 times the depth at the point of inception a significant air concentration has reached the spillway floor. A simplified formulae for computing the position and properties at the point of inception is also presented.

Developing Zone Characteristics in Aerated Flows

A knowlegde of air concentration distribution is very essential in the study of flow characteristics in the developing zone. The local mean air concentration along the flow is correlated with Froude number. The developing zone is classified into a dispersion zone and a diffusion zone based on the variation of wall concentration.

Self-Aerated Flow Characteristics in Wall Region

Characteristics of self-aerated flows in the wall region are studied. The distribution of velocity and air concentration in the wall turbulent zone is studied by dividing the wall turbulent zone into an inner and outer region according to the eddy viscosity distribution. It is shown that the inner region ceases to exist under certain conditions. Air concentration on the wall is estimated. The values of the Karman constant and Manning’s roughness coefficient show an increase in their value as air concentration increases. An estimation of the average velocity and the probable diameter of an air bubble shows a definite relation with mean air concentration in the wall region.

Self-Aerated Flow in Open Channels

Measurements of distribution of air concentration in self-aerated flows are presented. The experiments were made in a rough channel of sand-grain type surface at various slopes and discharges, and the data were used as a basis for study of the mechanism of entrainment of air and to relate the air content and distribution to the characteristics of the flow. The analysis of the data shows that the air distribution can be adequately described by relationships based on a simplified concept of turbulent transport and thus are functions of the flow characteristics. The maximum depth and the mean velocity are both shown to increase above those of a corresponding nonaerated flow.

Experiments on Self-Aerated Flow in Open Channels

Measurements of distribution of air concentration in self-aerated flows are presented in this paper. The experiments were made in a rough channel of sand-grain type surface at various slopes and discharges, and the data were used as a basis for study of the mechanism of entrainment of air and to relate the air content and distribution to the characteristics of the flow. The analysis of the data shows that the air distribution can be adequately described by relationships based upon a simplified concept of turbulent transport and thus are functions of the flow characteristics. The maximum depth and the mean velocity are both shown to increase above those of a corresponding nonaerated flow.