scholarly journals Air Entrainment in the Developing Flow Region of Plunging Jets—Part 2: Experimental

1997 ◽  
Vol 119 (3) ◽  
pp. 603-608 ◽  
Author(s):  
P. D. Cummings ◽  
H. Chanson
Keyword(s):  
Shear Layer ◽  
Flow Region ◽  
Air Entrainment ◽  
Chord Length ◽  
Strong Interactions ◽  
Air Bubbles ◽  
Air Concentration ◽  
Air Bubble ◽  
Wide Range ◽  
Bubble Sizes

When a water jet impinges a pool of water at rest, air bubbles may be entrained and carried away below the pool free surface: this process is called plunging jet entrainment. The study presents new experimental data obtained with a vertical supported jet. Distributions of air concentration and mean air-water velocity, and bubble chord length distributions measured in the developing shear layer are presented. The results indicate that the distributions of void fraction follow closely analytical solution of the diffusion equation. Further, the momentum shear layer and the air bubble diffusion layer do not coincide. Chord length data show a wide range of air bubble sizes and overall the experimental results suggest strong interactions between the entrained air bubbles and the momentum transfer mechanisms.

scholarly journals Three-Dimensional Aerators: Characteristics of the Air Bubbles

Water ◽  
2018 ◽  
Vol 10 (10) ◽  
pp. 1430
Author(s):  
Shuai Li ◽  
Jianmin Zhang ◽  
Xiaoqing Chen ◽  
Jiangang Chen
Keyword(s):  
Three Dimensional ◽  
Flow Region ◽  
Air Entrainment ◽  
Chord Length ◽  
Air Concentration ◽  
Bubble Frequency ◽  
Cross Sectional ◽  
Frequency Distributions ◽  
Air Bubble ◽  
Flow Features

Three-dimensional aerators are often used in hydraulic structures to prevent cavitation damage via enhanced air entrainment. However, the mechanisms of aeration and bubble dispersion along the developing shear flow region on such aerators remain unclear. A double-tip conductivity probe is employed in present experimental study to investigate the air concentration, bubble count rate, and bubble size downstream of a three-dimensional aerator involving various approach-flow features and geometric parameters. The results show that the cross-sectional distribution of the air bubble frequency is in accordance with the Gaussian distribution, and the relationship between the air concentration and bubble frequency obeys a quasi-parabolic law. The air bubble frequency reaches an apex at an air concentration (C) of approximately 50% and decreases to zero as C = 0% and C = 100%. The relative location of the air-bubble frequency apex is 0.210, 0.326 and 0.283 times the thickness of the layers at the upper, lower and side nappes, respectively. The air bubble chord length decreases gradually from the air water interface to the core area. The air concentration increases exponentially with the bubble chord length. The air bubble frequency distributions can be fit well using a “modified” gamma distribution function.

scholarly journals MODIFICATION EQUATIONS OF AIR BUBBLES DISTRIBUTIONS AT SELF-AIR ENTRAINMENT CONDITION

2020 ◽  
Vol 82 (2) ◽  
Author(s):  
Yeri Sutopo ◽  
Budi S. Wignyosukarto ◽  
Bambang Yulistyanto ◽  
Istiarto Istiarto ◽  
Nor Hayati Abdul Hamid
Keyword(s):  
Concentration Distribution ◽  
Vertical Direction ◽  
Air Entrainment ◽  
Experimental Results ◽  
Air Bubbles ◽  
Air Concentration ◽  
Air Bubble ◽  
Discharge Water ◽  
Flow Surface ◽  
Imagej Software

The Chanson’s equation for distribution of air bubbles in vertical direction in the developing zone at self-air entrainment condition is used when the air bubbles concentration at the flow surface is 90%. Otherwise, if this condition is not satisfying, then the equations of Straub and Anderson can be used. The results of these two equations are not similar with experimental results. Therefore, these two equations need to be modified accordingly. These modification equations can also be used to predict the air bubbles distributions in vertical direction. Hence, the main objective of this study is to modify these equations for vertical air concentration distribution in the developing zone and validate them with experimental results. The steep channel in the form of flume with 10 m long, 0.2 m wide and 0.4 m high with slopes varies between 20° and 25° were used in this experimental work. The discharge water was 9 l/s, 12 l/s and 21 l/s with Froude numbers between 6.9 to 8.0. The Thomson weir (V Notch) was used to calibrate the discharge flow of water. A set of video cameras was used to record the motion pictures of the air bubbles. The air bubble was analyzed using Ulead Video Studio 11 software program equipped with Imagej software. The results of this study indicates that the modifications of equations of Straub and Anderson were the equation air concentration distribution (C) in the underlying zone value was 0.647 m at 20° slope of channel bed, the equation air concentration distribution (C) in the underlying zone the value was 0.542 m at 25° slope and the equation in the mixing zone remained the same. The original Chanson equation was modified mainly in terms of the hyperbolic tangent (tanh) equation which originally had a power of 2 while the modification was 0.8; and the Ce was 0.9 sin α, whereas at the modified Chanson’s equation, Ce was converted into Ce= 0.6 sin α.

Flow over a stepped chute with and without macro-roughness elements

2004 ◽  
Vol 31 (5) ◽  
pp. 880-891 ◽  
Author(s):  
Mehmet Ali Kökpinar
Keyword(s):  
Water Flow ◽  
High Speed ◽  
Length Distribution ◽  
Air Entrainment ◽  
Air Concentration ◽  
Bubble Frequency ◽  
Two Phase ◽  
Air Bubble ◽  
Roughness Elements ◽  
Stepped Chute

High-speed two-phase flows over a 30° stepped flume were experimentally investigated using macro-roughness elements. The roughness elements included combinations of steps and horizontal strips. Local values of air concentration, air bubble frequency, and mean chord lengths were measured by a fiber-optical instrumentation system in the air–water flow region. The range of unit discharge of water was varied from 0.06 to 0.20 m2/s. Three step configurations were studied: (i) without macro-roughness elements, (ii) with macro-roughness elements on each step, and (iii) with macro-roughness elements on each second step (AMR configuration). The results were compared in terms of onset flow conditions and internal air–water flow parameters such as local air concentration, mean air bubble chord length distribution, and air bubble frequency in the skimming flow regime. It was observed that the AMR configuration produced the maximum free-surface aeration among the other configurations. This alternative step geometry has potential for less cavitation damage than conventional step geometry because of the greater air entrainment.Key words: stepped chute, air-entrainment, air-water flow properties, macro-roughness elements, skimming flow.

Shock-Excited Pulsations of Large Air Bubbles in Water

1974 ◽  
Vol 96 (4) ◽  
pp. 389-393 ◽  
Author(s):  
F. B. Jensen
Keyword(s):  
Shock Wave ◽  
Thermal Behavior ◽  
Bubble Size ◽  
Air Bubbles ◽  
Pressure Measurements ◽  
Photographic Recording ◽  
Attenuation Effect ◽  
Air Bubble ◽  
Direct Pressure ◽  
Bubble Sizes

The interaction between an air bubble in water (d0 = 10–30 mm) and a shock wave generated by a small detonator (0.8 g) is studied. On the basis of direct pressure measurements inside pulsating bubbles and simultaneous photographic recording of the diameter variations, the overall thermal behavior of the gas in the bubbles is determined. It is found that the pulsation process is nearly adiabatic for the bubble sizes considered. The measured maximum pressures inside pulsating bubbles are given as a function of bubble size and distance from the explosion. From these results, the total energy absorbed by a bubble is calculated as a measure of the attenuation effect of a single bubble on a shock wave.

scholarly journals On the breakup of an air bubble injected into a fully developed turbulent flow. Part 1. Breakup frequency

1999 ◽  
Vol 401 ◽  
pp. 157-182 ◽  
Author(s):  
C. MARTÍNEZ-BAZÁN ◽  
J. L. MONTAÑÉS ◽  
J. C. LASHERAS
Keyword(s):  
Bubble Size ◽  
Critical Diameter ◽  
Air Bubble ◽  
Wide Range ◽  
Fully Developed Turbulent Flow ◽  
Flow Part ◽  
Bubble Sizes ◽  
Rate Of Dissipation ◽  
Processing Techniques ◽  
Good Agreement

The transient evolution of the bubble-size probability density functions resulting from the breakup of an air bubble injected into a fully developed turbulent water ow has been measured experimentally using phase Doppler particle sizing (PDPA) and image processing techniques. These measurements were used to determine the breakup frequency of the bubbles as a function of their size and of the critical diameter Dc defined as Dc = 1.26 (σ/ρ)3/5ε−2/5, where ε is the rate of dissipation per unit mass and per unit time of the underlying turbulence. A phenomenological model is proposed showing the existence of two distinct bubble size regimes. For bubbles of sizes comparable to Dc, the breakup frequency is shown to increase as (σ/ρ)−2/5ε−3/5 √D/Dc−1, while for large bubbles whose sizes are greater than 1.63Dc, it decreases with the bubble size as ε1/3D−2/3. The model is shown to be in good agreement with measurements performed over a wide range of bubble sizes and turbulence intensities.

scholarly journals Air Entrainment in the Developing Flow Region of Plunging Jets—Part 1: Theoretical Development

1997 ◽  
Vol 119 (3) ◽  
pp. 597-602 ◽  
Author(s):  
P. D. Cummings ◽  
H. Chanson
Keyword(s):  
Flow Region ◽  
Air Entrainment ◽  
Theoretical Development ◽  
Liquid Jets ◽  
Two Dimensional ◽  
Air Bubble ◽  
Developing Flow ◽  
Jet Impact ◽  
Plunging Jets ◽  
Advective Diffusion

Air-water bubbly flows are encountered in many engineering applications. One type of air-water shear flows is the developing flow region of a plunging jet. The mechanisms of air entrainment by plunging liquid jets are discussed in the light of new experimental evidence. Then the air bubble diffusion is analyzed analytically in the near-flow field of both circular and two-dimensional plunging jets. The theoretical developments are compared with existing circular plunging jet data and new experiments performed with a two-dimensional vertical supported jet. The study highlights two mechanisms of air entrainment at the plunge point depending upon the jet impact velocity and results suggest that the dispersion of air bubbles within the shear layer is primarily an advective diffusion process.

scholarly journals Studies of Two-Phase Flow at a Chute Aerator with Experiments and CFD Modelling

2016 ◽  
Vol 2016 ◽  
pp. 1-11 ◽  
Author(s):  
Penghua Teng ◽  
James Yang ◽  
Michael Pfister
Keyword(s):  
Two Phase Flow ◽  
Fluid Model ◽  
Air Entrainment ◽  
Phase Flow ◽  
Air Concentration ◽  
Cfd Modelling ◽  
Two Phase ◽  
Air Bubble ◽  
Two Fluid Model ◽  
Two Fluid

The chute aerator of a spillway is a structure in such a sense that air is, in the intense emulsification, entrained into the high-velocity water flow. Correctly predicting the air entrainment and two-phase flow pattern at the aerator would contribute to reliable spillway operation. Based on experimental data, 2D numerical simulations are preformed to predict streamwise air concentrations in the aerated flow, in which a two-fluid model is used. Depending on the air bubble size, relatively good agreement is seen with the experiments in the air cavity zone. The simulations give rise to higher air concentration downstream of the cavity, which is presumably due to underestimation of the interfacial forces in the two-fluid model.

scholarly journals An extension of Fuhrboter's studies for wave height: a theoretical study

1970 ◽  
Vol 34 (2) ◽  
pp. 115-122
Author(s):  
Azizur Rahman ◽  
MST Kamrunnaher ◽  
Ashabul Hoque
Keyword(s):  
Key Words ◽  
Wave Height ◽  
Theoretical Study ◽  
Air Entrainment ◽  
Air Bubbles ◽  
Air Bubble ◽  
Bubble Entrainment ◽  
Air Bubble Entrainment ◽  
Spilling Breakers ◽  
Academy Of Sciences

This theoretical study extends Fuhrboter's work and includes the effects of air bubble entrainment. Result shows that there is a correlation between the sudden reductions of wave height and entrained of air bubbles into the water. Moreover, the study reveals that air entrainment occurs very short way in plunging breakers comparatively to spilling breakers. Key words: Fuhrboter's studies; Wave height; Theoretical study DOI: 10.3329/jbas.v34i2.6855Journal of Bangladesh Academy of Sciences, Vol. 34, No. 2, 115-122, 2010

scholarly journals Experimental Investigations of Free-Surface Aeration in the Developing Flow of Two-Dimensional Water Jets

1998 ◽  
Vol 120 (4) ◽  
pp. 738-744 ◽  
Author(s):  
T. Brattberg ◽  
H. Chanson ◽  
L. Toombes
Keyword(s):  
Free Surface ◽  
Flow Region ◽  
Air Entrainment ◽  
Experimental Investigations ◽  
Two Dimensional ◽  
Air Bubble ◽  
Surface Aeration ◽  
Water Jets ◽  
Developing Flow ◽  
Air Diffusion

Turbulent water jets discharging into the atmosphere are often characterized by a substantial amount of free-surface aeration. The effects can be detrimental or beneficial. In any case, the knowledge of the air entrainment mechanisms is essential for an optimum design. New experimental data are presented in the developing flow region of two-dimensional water jets discharging into air. The results indicate that the air diffusion takes place rapidly downstream of the nozzle and it is nearly independent of the momentum transfer process. Further, the distribution of air bubble frequency may be related to the air content distribution by a parabolic relationship.

scholarly journals Effect of cannulation site on emboli travel during cardiac surgery

2021 ◽  
Vol 16 (1) ◽  
Author(s):  
Mira Puthettu ◽  
Stijn Vandenberghe ◽  
Stefanos Demertzis
Keyword(s):  
Cardiac Surgery ◽  
In Vitro Study ◽  
Blood Stream ◽  
Air Bubbles ◽  
Arterial Tree ◽  
Air Bubble ◽  
Cannulation Site ◽  
The Brain

Abstract Background During cardiac surgery, micro-air emboli regularly enter the blood stream and can cause cognitive impairment or stroke. It is not clearly understood whether the most threatening air emboli are generated by the heart-lung machine (HLM) or by the blood-air contact when opening the heart. We performed an in vitro study to assess, for the two sources, air emboli distribution in the arterial tree, especially in the brain region, during cardiac surgery with different cannulation sites. Methods A model of the arterial tree was 3D printed and included in a hydraulic circuit, divided such that flow going to the brain was separated from the rest of the circuit. Air micro-emboli were injected either in the HLM (“ECC Bubbles”) or in the mock left ventricle (“Heart Bubbles”) to simulate the two sources. Emboli distribution was measured with an ultrasonic bubble counter. Five repetitions were performed for each combination of injection site and cannulation site, where air bubble counts and volumes were recorded. Air bubbles were separated in three categories based on size. Results For both injection sites, it was possible to identify statistically significant differences between cannulation sites. For ECC Bubbles, axillary cannulation led to a higher amount of air bubbles in the brain with medium-sized bubbles. For Heart Bubbles, aortic cannulation showed a significantly bigger embolic load in the brain with large bubbles. Conclusions These preliminary in vitro findings showed that air embolic load in the brain may be dependent on the cannulation site, which deserves further in vivo exploration.

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