Showing papers on "Air entrainment published in 1984"

Stabilization of extremely lightweight aggregate concrete.

Abstract: Method of producing monolithic mainly cementbound concrete in the density range of 650-1300 kg/m3, preferably of 800-1200 kg/m3 with substantially good placing properties both for building in situ and prefabrication. The concrete consists of cement mortar with an air-void volume of 7-18 % of the total concrete volume and aggregate consisting of lightweight organic or inorganic material. The smaller particles of the aggregate should be spherical, exceptionally lightweight, hydrophobic and durable against deformation in order to reduce the water content without changing the consistency of the concrete. The production of concrete is based on the aggregate having a continuous distribution of particle size within which the particle density decreases with decreased particle size, that during mixing small as well as big air-voids are created with strengthened and thickened bubble walls, that the thixotropy of the cement paste is strengthened and that air bubbles are replaced with an equivalent volume of sand particles in excess of those which are needed for the creation of air bubbles. The effects are achieved with multifunctional polymer microparticles on which different surfactant systems have been adsorbed. Air bubbles with their thickened walls as well as the most lightweight aggregate particles reduce the difference in density between the continuous medium and the air bubbles - aggregate particles.

Local air entrainment and detrainment

Abstract: Air and water are usually well separated by gravity due to their extreme difference in specific weight. Whenever they are mixed, however, they give rise to a very complex two-phase flow situation. The hydraulic engineer is often faced with the problem of estimating the effects of entrained air upon the flow, because this may be essential for the safe operation of a hydraulic structure.The predominant mechanism in generating airwater mixtures is the inclusion of air at the surface of flowing water. The mechanics of free-surface flow may lead to ambient surface aeration in high-speed flows, or - even at moderate flow velocities - to flow configurations with localized air entrainment, which includes inadvertent self-aeration as well as such specific flow systems in which surface aeration is forced.

Entrapment and Transport of Bubbles by Plunging Water

Abstract: Free surface penetration by plunging water gives rise to air entrainment and transport of bubbles in the submerged flows. Photography has revealed the bubbles are initially transported in discrete clusters. This behaviour has been attributed to bubble entrapment by shear vortices (i.e. large eddies) travelling in the edge of the jet. Our aim here is to address the more important mechanisms behind this phenomenon. Some main elements are described of a theoretical model for the motion of a small spherical bubble in quite general non-uniform and unsteady flows at high Reynolds number. The model predictions of bubble entrapment by line vortex flow are shown to agree rather well with the results of an experimental test in which small bubbles are released into the flow produced by a spinning rod. We are developing a computer simulation of the motions of these model bubbles using discrete vortices to model the unsteady shear vortex flows near the edge of a submerged jet. Preliminary results demonstrate bubble entrapment by the travelling zones of concentrated vorticity.

Powder spray gun and powder spray method

Abstract: A powder spray gun and method of spraying powder are disclosed wherein an air flow amplifier is contained within the gun and is operable to draw ambient air into the gun and to impact air entrained powder passing through the gun with a high velocity stream of compressed air so as to accelerate the velocity of powder emitted from the gun.

Gravity Spreading and Air Entrainment by Heavy Gases Instantaneously Released in a Calm Atmosphere

Abstract: Measurements of gravity spreading and dilution of right circular cylindrical volumes of dense gas released instantaneously in still air are described. Effects of volume released (34, 54, and 135 liters), initial density (2.19, 2.95, and 4.27 relative to air), and initial volume height-to-diameter ratio (0.4, 1.0, and 1.6) are reported. Ground level peak gas concentrations measured are compared with previously reported smaller scale experimental measurements, and scaling relationships are demonstrated.

Calculation of the air-capturing ability of a flow behind an aerator ledge

Abstract: Aerators are used for saturating the bottom layers of a flow with air, which is an effective measure for controlling cavitation erosion, and they also provide intense oxygen enrichment of the water. An aerator usually consists of a device providing separation of the flow from solid boundaries (ledge, ski-jump bucket, or their combination along with a groove) and a system ventilating the separation zone. The air can enter under the nappe through flow separation regions near the side walls and behind piers or through special air ducts, as for example, on the San Roque chute spillway. The main difficulty when calculating aerators is a determination of the air-capturing ability of the flow. It is necessary to know the discharge of the air entrained by the flow as a function of the vacuum in the space under the nappe, since these parameters are the initial ones for calculating the air ducts. The authors present here the calculation of the air-capturing ability of a flow behind an aerator ledge.

Hydronic room heating device

Abstract: A hydronic room heating device in the form of a baseboard heating panel of air entrained concrete with concrete radiating fins molded on the back of the panel with an upper concrete heating element section positioned to allow air flow past the fins upwardly and out through the opening between the upper element and the panel using low temperature heated water from solar heated systems.

Experimental Studies of Surface Wave Breaking and Air Entrainment

Abstract: Results of recent experiments and theory have shown that steep water waves are subject to three-dimensional instabilities that lead to breaking, turbulence and bubble generation by air entrainment. Three-dimensional breaking waves and bubble trajectories are shown here in photographs that give evidence that the plunging faces of breakers generate and entrain air bubbles. Bubbles are often injected to depths exceeding the wave height and larger bubbles rupture at the surface within a wave period. The implications of these processes in air-sea gas exchanges is briefly discussed.

Superplasticized flowing concrete: durability properties

Abstract: Synopsis This second paper reporting the investigation undertaken into the properties of superplasticized highworkability concrete describes the freezing-and-thawing and wetting-and-drying durabili...

I. Mixing in doorway flows. II. Entrainment in fire plumes

Abstract: The motion of hot combustion products through a burning structure plays a dominant role in fixing the spread of the fire and the spread of toxic gases. The first part of this report is concerned with the effect of door geometry on the rate of turbulent mixing between the hot and cold layers near a doorway. The second part of the report deals with the entrainment rates in the near field of a buoyant diffusion methane flame. In the study of the motion of the hot combustion products near a doorway, the gas in the burning room is assumed to be divided into two homogeneous layers--the ceiling layer which contains the hot combustion products and the floor layer which contains the denser fresh air. Temperature and carbon dioxide measurements are taken from a half-scale room which uses a pump and furnace to simulate the entrainment and heating of the fresh air by the fire plume. The mass transfer rates are calculated from these measurements and are found to be a function of a Richardson number that uses the interface height measured from the floor as the characteristic length and the average inflow velocity of fresh air as the characteristic velocity. This form for Ri(0) is derived from an analysis based on Taylor's entrainment hypothesis. For a given fire size, i.e., for a given mass flow of fresh air into the room, the effect of reducing the door area is to reduce the value of Ri(0), and hence increase the mixing rate in the room. The door height is found to be a much stronger influence on the mixing rate and interface height than the door width. The entrainment rates of fresh air in the near field of a buoyant diffusion methane flame whose flames extend well above the interface between the hot gas layer and the fresh air layer are measured for several interface heights. In the experiments, the ceiling layer-fire plume interaction is simulated by placing a large steel hood over an axisymmetric burner. The hood may be raised or lowered to change the interface height. The entrainment measurements are obtained from a chemical analysis of a dried sample of combustion products taken from the ceiling layer. The measured species concentrations are compared with the theoretical equilibrium composition of the ceiling layer gas. For a given interface height, the ceiling layer gas temperature is found to be a linear function of the fuel-air ratio up to the stoichiometric fuel-air ratio. Increasing the fuel-air ratio above the stoichiometric value did not change the gas temperature significantly. This maximum temperature is observed to decrease with interface height. The air entrainment rates are found to be a weak function of the fuel-air ratio at very low elevations of the interface.

Factors Affecting Apparent Plume‐Rise Entrainment

Abstract: Field measurements for 466 cases of plume rise from moderately sized sources were statistically analyzed for the ability of source and plume parameters to explain variations in the apparent entrainment coefficient used in the two-thirds law. The average value of the entrainment coefficient was 0.83, which was significantly greater than the 0.6 value characterizing entrainment caused by vertical rise of a bent-over plume and conventionally used by the USEPA. Correlation analyses demonstrated that increased coefficient values were most strongly associated with plumes that could not escape the stack wake, which increased entrainment and exerted a downward body force on the plume. Using an entrainment coefficient equal to 0.6 causes plume rise to be overestimated and ground-level concentration to be underestimated.