Plunging Water Jet Research Articles

突入水膜流による気泡の取り込み(OS6-2 流れの複合現象II 混相流)

突入水膜流による気泡の取り込み(OS6-2 流れの複合現象II 混相流)

Role of Nozzles with Air Holes in Air Entrainment by a Water Jet

Abstract When a water jet impinges a pool of water at rest, air bubbles may be entrained and carried a distance below the pool's surface. This process is called plunging water jet entrainment and aeration. This paper describes an experimental study of the air entrainment rate of circular nozzles with and without air holes, and in particular, the effect of varying numbers and positions of air holes and distance between the location of the air holes and nozzle exit. A negative pressure occurred due to the air holes on the circular nozzles. This phenomenon affected air entrainment. The differences in air entrainment rate were related to changes in the jet shape. It was demonstrated that the air entrainment rates of the circular nozzles with air holes were significantly higher than those of circular nozzles without air holes.

Study of the influence of air holes along length of convergent-divergent passage of a venturi device on aeration

One of the most cited water quality parameters in the freshwater hydrosphere is dissolved oxygen. The oxygen concentration in surface waters is a prime indicator of the quality of that water for human use as well as use by the aquatic biota. When a water jet impinges a pool of water at rest, air bubbles may be entrained and carried a way below the pool free surface. This process is called plunging water jet entrainment and aeration. In this paper, air entrainment rate and oxygen transfer efficiency of venturi device with air holes along the length of the convergent-divergent passage was studied experimentally, and in particular, the effect of varying numbers, positions, and open/close status of the air holes. A negative pressure drew air in through holes at the convergent-divergent passage of the venturi device. This phenomenon affected the water jet expansion, the air entrainment rate, and the bubble penetration depth and hence the oxygen transfer efficiency. It was demonstrated that the values of air entrainment rate and the oxygen transfer efficiency of the venturi device were significantly higher than those of the circular nozzle.

Acoustic resonances in the bubble plume formed by a plunging water jet

Experiments were performed to investigate the nearfield sound from an axisymmetric conical bubble plume formed by a continuous vertical freshwater jet as it penetrates the surface of a pool of fres...

The Effect of Nozzle Type on Air Entrainment by Plunging Water Jets

Abstract In this study, for the plunging water jet aeration system using various inclined nozzle types, bubble penetration depth, air entrainment rate, water jet expansion, effect of water jet circumference at impact point, oxygen transfer coefficient and oxygen transfer efficiency which changed depending on the water jet velocity, were researched in an air-water system. Numerous studies were conducted with circular nozzles. The present study describes new experiments performed with different nozzle types. Three types of nozzles were examined, i.e., those with circular, ellipse and rectangle duct with rounded ends. Experimental results showed that water jets produced with ellipse and rectangle duct with rounded ends nozzles have very different flow characteristics, entrainment patterns on free water jet surface, and submerged water jet region within the receiving tank. Higher air entrainment rate and oxygen transfer efficiency was observed in the rectangle duct with rounded ends nozzle due to water jet expansion. Bubble penetration depth, however, is lower for the rectangle duct with rounded ends nozzle than for the other nozzles. The ellipse nozzle provided the highest bubble penetration depth. These results showed that it is appropriate to use ellipse nozzle in aeration of deep pool and rectangle duct with rounded ends nozzle in the applications where high bubble concentration is desirable.

209 プランジングジェットによるエアレーションに関する研究(流体工学-噴流・希薄流体2)

209 プランジングジェットによるエアレーションに関する研究(流体工学-噴流・希薄流体2)

Low-frequency acoustic resonances in the bubble plume formed by a plunging water jet

As a jet of water penetrates a free water surface, air is entrained in the form of bubbles which produce sound by various mechanisms, including both individual and collective oscillations. The low-frequency acoustic emissions of the bubble clouds entrained and dispersed by vertical continuous and transient fresh water jets impinging from varying heights into a fresh water receiving pool in a large laboratory tank were studied both theoretically and experimentally for jet velocities ranging to about 10 m/s, and jet diameters of millimeter order. The acoustic signals were measured with hydrophones in different positions, amplified, and digitally sampled. The measured power spectra revealed well-defined, nonuniformly spaced resonance peaks at frequencies below about 1 kHz. A theory based on a conical bubble plume, with a nonuniform sound speed profile, acting as a resonant cavity predicts the frequencies of the resonance peaks and shows remarkable agreement with the experimentally measured values. Further, time-frequency analysis gives bubble size distributions and shows the driving source for the resonant cavity to be large secondary bubbles formed through coalescence, which become acoustically active through deformation or break-up as they are re-entrained by the downstream flow in a failed attempt to rise to the surface.

Control of Oil Spills In Fast-Water Currents—A Technology Assessment1

ABSTRACT A technology assessment was conducted to quantify the oil spill threat in fast waters, and then identify promising equipment and strategies for those threat scenarios. Recommendations are made to pursue methods, equipment, and training that show the most promise to improve response capabilities in currents from 1 to 6 knots. Containment and removal of oil spilled in rivers and coastal tidal regions where currents exceed 0.7 knots is difficult because many skimmers and conventional booming methods are not effective in fast currents. The oil will generally entrain and follow the water path under the boom or skimmer for faster currents unless it is tricked by a device for deflection, containment, or recovery. This can be accomplished using specialized equipment and strategies; however, properly trained response personnel are essential. The benefits and liabilities of high speed skimmers and specialized boom systems that use a number of techniques are summarized. Shallow-draft high-current boom can be used to deflect the oil to shore at steep angles where the currents are slowed by the rising shoreline and conventional skimmers can be effectively used. Promising deflection strategies are listed. Alternate containment and diversion techniques also presented include: pneumatic boom, horizontal air and water jets, plunging water jets, diversion paravanes, and floating paddle wheel.

Acoustic measurements of air entrainment by a plunging free water jet

Low-frequency acoustic emissions of a free plunging water jet were studied to determine the volumetric rate of gas transfer across the pool surface. At the studied jet velocities, up to 10 m/s, air bubbles are entrained at the interface and form well-defined bubble clouds penetrating up to 20 cm into the pool. The resulting biphasic region of the submerged jet was found to be an efficient acoustic resonator. The radiated sound field was recorded with hydrophones close to the region of the submerged jet and strong resonances were found below 1 kHz. The frequencies of the lowest modes were measured for a given jet diameter as a function of the jet velocity. The observed acoustic eigenfrequencies are unique functions of the jet velocity and the gas flux, independent of the details of the gas entrainment. This functional dependence was investigated both experimentally and theoretically, allowing an inversion of the acoustic data for the air flux across the interface as a function of the jet velocity. Reference measurements of the air flux were made to calibrate the inversions. Using this technique, measurements of the air flux were made for a variety of jet diameters, lengths, and velocities. [Work supported by ONR.]

Air entrapment and air bubble dispersion at two-dimensional plunging water jets

Air–water bubbly flows are encountered in numerous engineering applications. One type of air–water shear flow, the developing flow region of a plunging jet, is discussed in the light of new experimental evidence. Distributions of air concentration and mean air–water velocity, and bubble chord length distributions are presented for inflow velocities ranging from 2 to 8 m/s. The results indicate that the distributions of void fraction follow closely analytical solutions of the diffusion equation, as developed by Chanson (1995a Report, CH46/95, pp. 368, 1997 Report CH48/97). In air–water shear layers, the velocity distributions have the same shape as in monophase flows but the characteristic parameters of the shear layer differ from monophase flow results, because of the interactions between the entrained air bubbles and the turbulence.

Low-frequency acoustic emissions of a plunging water jet. Part II. Theory

A theory of low-frequency acoustic emissions of a plunging water jet is developed and presented. A plunging liquid jet impinging on a free liquid surface entrains air and produces a bubble cloud with a well-defined geometry. At low frequencies the resulting bubble cloud has a substantially lower sound speed than the surrounding single phase medium. The cloud is modeled as a conical resonant cavity having the apex at the plunging point, with nonuniform sound speed profile and acoustically hard boundaries. Analytical estimates for the eigenfrequencies, based on the wave equation and a simplified void fraction profile, provide insight into the dependence of the resonance frequencies on various system parameters. A more realistic numerical model that includes advection by the surrounding flow and a more appropriate void fraction profile gives remarkable agreement with measured values and scalings for the eigenfrequencies. Further improvements can be made by including turbulent transport and dissolution in the model but at the cost of including additional parameters. Considering the complicated nature of the system, very strong overall agreement of the presented models is found, thus allowing inversions to be performed for important quantities related to the gas transfer, such as the entrainment rate and the void fraction profile.

Low-frequency acoustic emissions of a plunging water jet. Part I. Experiment

Low-frequency acoustic emissions of bubble clouds entrained by a continuous fresh water jet were experimentally studied. Bubble clouds penetrating 10–20 cm deep into a 160-cm deep pool of fresh water were generated and dispersed by an impinging water stream of 1.6 mm diameter and velocities of up to 10 m/s. The sound field was recorded with small hydrophones at various positions close to the cloud as well as directly in the plume. At frequencies below 1 kHz the power spectral density exhibited a strong resonance structure. The observed resonance frequencies scale with the jet velocity as well as the air volume flux but are largely independent of the details of the air entrainment (e.g., nozzle geometry). Reference measurements in a much larger body of fresh water, a natural lake, are shown to exhibit the same resonances, indicating that wall reflections in the tank do not influence the values of the resonance frequencies. All observations are consistent with an interpretation of the bubble plume as a resonant cavity with a sound speed much smaller than in the surrounding medium.

Mean velocity and turbulence characteristics of water flow in the bubble dispersion region induced by plunging water jet

Water was injected vertically downward through a straight circular pipe onto a water bath contained in a cylindrical vessel. Three types of bubble dispersion patterns were observed with respect to the distance from the pipe exit to the undisturbed bath surface. When the distance was short, small bubbles were generated at the bath surface and they dispersed in the whole bath (type 1). On the other hand, when the distance was long, relatively large bubbles were generated and the bubble dispersion region was localized beneath the pipe exit (type 3). For an intermediate distance, the bubble dispersion patterns of the two types appeared simultaneously (type 2). We focused on types 1 and 3 and carried out LDV measurements to investigate the liquid motion in the bubble dispersion region. In the case of type 1, the mean velocity and turbulence characteristics were not affected by bubbles and agreed well with those for single-phase free jets, while the two characteristics for type 3 were influenced significantly by bubbles. The differences in the two characteristics between types 1 and 3 were found to be associated with turbulence production in the wake of bubbles.

Depth of penetration of bubbles entrained by a plunging water jet

A model is proposed to predict the depth of penetration of the air bubbles entrained by a round water jet impacting into a flat, liquid pool. This depth is shown to be determined only by the initial jet momentum and by the non-monotonic nature of the bubble terminal velocities as a function of their size. The model is shown to be in excellent agreement with measurements of the depth and width of penetration of the bubbles performed over a wide range of jet diameters, velocities, and plunging angles.

Penetration depth of bubble swarm entrained by a plunging water jet.

When a liquid jet plunges into a liquid, a submerged two-phase region like a cone is formed in the liquid. The penetration depth of the bubble swarm is one of the important parameters for the design of plunging jet absorbers. Several experimental correlations with respect to penetration depth have already been established by some other workers, such as Suciu and Smigelschi, Van de Donk and McKeogh and Ervine. Their equations were, however, based only on the term regarding the momentum of a jet. It is obvious from the authors' investigations that the penetration depth depends not only on the jet momentum but also on jet length, nozzle diameter and jet discharge angle. Taking into account these parameter dependences, we propose an experimental correlation for penetration depth in a wider range of application. Some comparisons between the authors' and other workers' results are also made

Comment on article: “Gas holdup and gas entrainment of a plunging water jet with a constant entrainment guide” Can. J. Chem. Eng. 66, 19–28 (1988)

Comment on article: “Gas holdup and gas entrainment of a plunging water jet with a constant entrainment guide” Can. J. Chem. Eng. 66, 19–28 (1988)

OXYGEN TRANSFER IN THE WATER-JET VESSEL

Abstract This is an investigation of the gas holdup and the volumetric mass transfer coefficient of a plunging water jet in an air-water system. We sound kLa to be directly proportional to gas holdup in two regions. For the first time, this has been clarified in the plunging liquid jet system. The volumetric mass transfer coefficient and the gas holdup have been well correlated in terms of the Froude number, liquid jet length, nozzle diameter and vessel diameter.

Gas holdup and gas entrainment of a plunging water jet with a constant entrainment guide

AbstractThe gas holdup and gas entrainment of a plunging liquid jet with a gas entrainment guide in an air‐water system was investigated. The measurement of the gas holdup was performed using an over‐flow method. The turbulent jet velocity calculated on an inside nozzle diameter in the range from 4.4‐26.5 m/s for this system has been used in our correlations. The gas holdup has been well correlated in terms of 1/H(v02 + 2gH1), H1 d0 and the gas entrainment in terms of 1/Hw(v02 + 2gH1), H1, d0. The jet power requirement was also obtained from experimental data.

Flow and oxygen transfer in a plunging water jet system using inclined short nozzles and performance characteristics of its system in aerobic treatment of wastewater

For the plunging water jet system using inclined short nozzles, the flow characteristics such as the bubble penetration depth and the gas entrainment rate, which changed depending on the jet velocity, the nozzle diameter, the jet length, and the jet angle were first evaluated in an air-water system. A comparable investigation between our results and those of existing studies used the long nozzles on those characteristics revealed that both the bubble penetration depth and the gas entrainment rate differed depending on the nozzle length; that is, the nozzle-length-to-diameter ratio L(N)/D(N) and that of these characteristics the gas entrainment rate affected considerably by its magnitude and tended to be high when the nozzle of a large L(N)/D(N) ratio was used. It was also confirmed from the oxygen transfer experiments that the transfer efficiency at low jet velocities in the present water jet system was not inferior to the ones of other types of existing aeration systems; that is, the utilization of this jet aeration system to a high rate reactor for wastewater treatment or fermentation was sufficiently possible. The applicability of the plunging jet aeration method to microbial processes was then examined. As a typical example of microbial processes to be tested, the continuous treatment of an organic wastewater using activated sludge microorganisms was carried out, and the performance and related problem when this type of aeration system was applied to such a microbial process were investigated. Experimental results showed that, when viewed from the removal ability of dissolved organic matters, the plunging jet aeration system was capable of treating a wastewater of considerable high loading without the rate of oxygen transfer becoming the biooxydation-rate-limiting factor. Special attention was necessary for the choice of the liquid pump to be employed, however, due to the increased amount of fine suspended solids in the treated water caused by the shearing action between sludge flocks and pump blades.

Erosion of unconsolidated gravel beds

In any riverbed degradation phenomenon, the vertical dimension of the deepest part of the scour hole is a pertinent parameter since all the other erosion parameters describing the configuration of the scour hole depend on its numerical value. Hence, it is necessary to be able to evaluate the maximum depth of the scour hole.For most practical situations, the impingement of submerged water jets on a granular riverbed occurs at an angle, and it is the object of this study to include the effects of obliqueness in the analysis. Some examples of the effects of impingement by water jets are the erosion problems caused by plunging water jets from hydraulic control structures as they discharge into the tail-water downstream.Basic to an understanding of the mechanism of local scour is the concept of "initiation of motion." Hence, the analytical study will use this concept to derive generalized relations that will link the incipient motion condition at the deepest point of the scour hole with the numerical value of the scoured depth. In addition, care was taken to ensure that only those hydraulic variables that are frequently used in hydraulic engineering design are included in the analysis in order to make the results useful to practicing engineers. Key words: local scour, maximum erosion, river bed, plunge basin, diving jets, energy dissipation, riverbed degradation.