scholarly journals Measurement of the air bubble size and velocity from micro air bubble generation (MBG) in diesel using optical methods

2020 ◽  
Author(s):  
Bader A. Alfarraj ◽  
Abdullah M. Alkhedhair ◽  
Ahmed A. Al-Harbi ◽  
Wojciech Nowak ◽  
Saleh A. Alfaleh
Keyword(s):  
Size Distribution ◽  
Optical System ◽  
Bubble Size ◽  
Bubble Radius ◽  
Optical Methods ◽  
Objective Lens ◽  
Air Bubbles ◽  
Generation Process ◽  
Bubble Generation ◽  
Air Bubble

Abstract In this paper, we determine the bubble size and velocity from air bubble generation (MBG) in a diesel using optical methods. A KTM Series Pump was used to generate micro air bubbles in diesel. The air bubble radius and velocity measurements can be useful parameters to optimize the bubble generation process. Two optical systems were used for measurement air bubble sizes and their velocities in diesel. First, the optical system without an objective lens was used to determine the velocity of air bubbles in diesel. Another optical system with a 10× objective lens was used to obtain the size distribution of air bubbles generated in diesel. An available optical system with a 10× objective lens can detect a bubble diameter greater than 3.3 µm that air bubble images were processed using the ImageJ program. We measured the size distribution of air bubbles generated using the ImageJ program. The micro air bubble radius measured in diesel was found to be 6.26 µm in the sample after a month from air bubble generation. In addition, the particle image velocimetry (PIV) technique was used to measure the velocity field. Then, we used the OpenPIV program for PIV image processing. The highest velocity distribution was determined to be 90 mm/s for diesel without air bubbles and 20 mm/s for diesel with air bubbles after a month of the bubble generation.

scholarly journals Development of Bubble Characteristics on Chute Spillway Bottom

Water ◽  
2018 ◽  
Vol 10 (9) ◽  
pp. 1129
Author(s):  
Ruidi Bai ◽  
Chang Liu ◽  
Bingyang Feng ◽  
Shanjun Liu ◽  
Faxing Zhang
Keyword(s):  
Size Distribution ◽  
Bubble Size ◽  
Dissipation Rate ◽  
Bubble Diameter ◽  
Bubble Size Distribution ◽  
Impact Zone ◽  
Air Bubble ◽  
Air Supply ◽  
Bubble Characteristics ◽  
The Impact

Chute aerators introduce a large air discharge through air supply ducts to prevent cavitation erosion on spillways. There is not much information on the microcosmic air bubble characteristics near the chute bottom. This study was focused on examining the bottom air-water flow properties by performing a series of model tests that eliminated the upper aeration and illustrated the potential for bubble variation processes on the chute bottom. In comparison with the strong air detrainment in the impact zone, the bottom air bubble frequency decreased slightly. Observations showed that range of probability of the bubble chord length tended to decrease sharply in the impact zone and by a lesser extent in the equilibrium zone. A distinct mechanism to control the bubble size distribution, depending on bubble diameter, was proposed. For bubbles larger than about 1–2 mm, the bubble size distribution followed a—5/3 power-law scaling with diameter. Using the relationship between the local dissipation rate and bubble size, the bottom dissipation rate was found to increase along the chute bottom, and the corresponding Hinze scale showed a good agreement with the observations.

scholarly journals Numerical Simulation Study on Distribution of Bubble in Flow near Aerator Based on CFD-PBM Coupled Model in Tunnel

2021 ◽  
Vol 2021 ◽  
pp. 1-24
Author(s):  
Jiaming Lei ◽  
Jianmin Zhang ◽  
Lifang Zhang
Keyword(s):  
Size Distribution ◽  
Bubble Size ◽  
Numerical Models ◽  
Coupled Model ◽  
Bubble Size Distribution ◽  
Balance Model ◽  
Main Process ◽  
Air Bubbles ◽  
Air Concentration ◽  
Aerated Flow

The aerator can reduce erosion by mixing a large amount of air into the water in the solid wall area. The effectiveness of erosion reduction is mainly based on air concentration and its bubble size distribution. However, simultaneous simulation of the air concentration and its bubble size distribution in numerical simulations is still a hot and difficult area of research. Aiming at the downstream aerated flow of hydraulic aeration facilities, several numerical models, such as VOF, mixture, Euler, and Population Balance Model (PBM), are compared and verified by experiments. The results show that the CFD-PBM coupled model performs well compared to other conventional multiphase models. It can not only obtain the evolution law of the bubble distribution downstream of the aerator but also accurately simulate the recombination and evolution process of bubble aggregation and breakage. The Sauter mean diameter of the air bubbles in the aerated flow decreases along the way and eventually reaches a stable value. The bubble breakage is the main process in the development of the bubbles. It reveals the aeration law that the small air bubbles are closer to the bottom plate, while the large bubbles float up along the aerated flow, which provides a powerful support for the basic research on the mechanism of aeration and erosion reduction.

Acoustic wave propagation in air‐bubble curtains in water—Part I: History and theory

Geophysics ◽  
1982 ◽  
Vol 47 (3) ◽  
pp. 345-353 ◽  
Author(s):  
S. N. Domenico
Keyword(s):  
Wave Propagation ◽  
World War Ii ◽  
Acoustic Wave ◽  
Bubble Radius ◽  
Free Water ◽  
Air Bubbles ◽  
Frequency Range ◽  
World War ◽  
Acoustic Wave Propagation ◽  
Air Bubble

Air bubbles in water increase the compressibility several orders of magnitude above that in bubble‐free water, thereby greatly reducing the velocity and increasing attenuation of acoustic waves. The effect of air bubbles in water on acoustic wave propagation was studied extensively during World War II as part of an overall effort to apply underwater sound in submarine warfare. Currently, air bubble curtains are used to prevent damage of submerged structures (e.g., dams) by shock waves from submarine explosives. Also, air‐bubble curtains are used to reduce damage to water‐filled tanks in which metals are formed by explosives. Since World War II, research has progressed less feverishly in government and university laboratories. Published results of laboratory experiments generally confirm theoretical velocity and attenuation functions and demonstrate that these quantities are dependent principally upon frequency, bubble size, and fractional volume of air. Below the bubble resonant frequency and in the frequency range of marine energy sources, acoustic wave velocity is essentially independent of frequency and bubble radius, being well below the velocity in bubble‐free water. In this frequency range, attenuation increases with increasing frequency, decreasing bubble radius, and increasing fractional air volume.

scholarly journals Air entrainment and bubble statistics in breaking waves

2016 ◽  
Vol 801 ◽  
pp. 91-129 ◽  
Author(s):  
Luc Deike ◽  
W. Kendall Melville ◽  
Stéphane Popinet
Keyword(s):  
Size Distribution ◽  
Bubble Size ◽  
Dissipation Rate ◽  
Unit Length ◽  
Bubble Radius ◽  
Air Entrainment ◽  
Breaking Waves ◽  
Bubble Size Distribution ◽  
Breaking Wave ◽  
Bubble Plume

We investigate air entrainment and bubble statistics in three-dimensional breaking waves through novel direct numerical simulations of the two-phase air–water flow, resolving the length scales relevant for the bubble formation problem, the capillary length and the Hinze scale. The dissipation due to breaking is found to be in good agreement with previous experimental observations and inertial scaling arguments. The air entrainment properties and bubble size statistics are investigated for various initial characteristic wave slopes. For radii larger than the Hinze scale, the bubble size distribution, can be described by $N(r,t)=B(V_{0}/2{\rm\pi})({\it\varepsilon}(t-{\rm\Delta}{\it\tau})/Wg)r^{-10/3}r_{m}^{-2/3}$ during the active breaking stages, where ${\it\varepsilon}(t-{\rm\Delta}{\it\tau})$ is the time-dependent turbulent dissipation rate, with ${\rm\Delta}{\it\tau}$ the collapse time of the initial air pocket entrained by the breaking wave, $W$ a weighted vertical velocity of the bubble plume, $r_{m}$ the maximum bubble radius, $g$ gravity, $V_{0}$ the initial volume of air entrained, $r$ the bubble radius and $B$ a dimensionless constant. The active breaking time-averaged bubble size distribution is described by $\bar{N}(r)=B(1/2{\rm\pi})({\it\epsilon}_{l}L_{c}/Wg{\it\rho})r^{-10/3}r_{m}^{-2/3}$, where ${\it\epsilon}_{l}$ is the wave dissipation rate per unit length of breaking crest, ${\it\rho}$ the water density and $L_{c}$ the length of breaking crest. Finally, the averaged total volume of entrained air, $\bar{V}$, per breaking event can be simply related to ${\it\epsilon}_{l}$ by $\bar{V}=B({\it\epsilon}_{l}L_{c}/Wg{\it\rho})$, which leads to a relationship for a characteristic slope, $S$, of $\bar{V}\propto S^{5/2}$. We propose a phenomenological turbulent bubble break-up model based on earlier models and the balance between mechanical dissipation and work done against buoyancy forces. The model is consistent with the numerical results and existing experimental results.

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 Auto-Aspirated DAF Sparger Study on Flow Hydrodynamics, Bubble Generation and Aeration Efficiency

Processes ◽  
2020 ◽  
Vol 8 (11) ◽  
pp. 1498
Author(s):  
Dmitry Vladimirovich Gradov ◽  
Andrey Saren ◽  
Janne Kauppi ◽  
Kari Ullakko ◽  
Tuomas Koiranen
Keyword(s):  
Size Distribution ◽  
Water Flow ◽  
Flow Rate ◽  
Bubble Size ◽  
Transfer Rate ◽  
Pure Water ◽  
Water Flow Rate ◽  
Bubble Size Distribution ◽  
Bubble Generation ◽  
Aeration Efficiency

A novel auto-aspirated sparger is examined experimentally in a closed-loop reactor (CLR) at lab scale using particle image velocimetry, high-speed camera and oxygen mass transfer rate measurements. State-of-the-art 3D printing technology was utilized to develop the sparger design in stainless steel. An insignificant change in the bubble size distribution was observed along the aerated flow, proving the existence of a low coalescence rate in the constraint domain of the CLR pipeline. The studied sparger created macrobubbles evenly dispersed in space. In pure water, the produced bubble size distribution from 190 to 2500 μm is controlled by liquid flow rate. The bubble size dynamics exhibited a power-law function of water flow rate approaching a stable minimum bubble size, which was attributed to the ratio of the fast-growing energy of the bubble surface tension over the kinetic energy of the stream. Potentially, the stream energy can efficiently disperse higher gas flow rates. The oxygen transfer rate was rapid and depended on the water flow rate. The aeration efficiency below 0.4 kW/m3 was superior to the commonly used aerating apparatuses tested at lab scale. The efficient gas dissolution technology has potential in water treatment and carbon capture processes applications.

Factor Affecting Bubble Creation and Bubble Size

2011 ◽  
Author(s):  
Ammar A. T. Alkhalidi ◽  
Ryo S. Amano
Keyword(s):  
Flow Rate ◽  
Computational Fluid Dynamic ◽  
Bubble Size ◽  
Fluid Dynamic ◽  
Air Bubbles ◽  
Hole Size ◽  
Critical Factors ◽  
Water Pool ◽  
Factors Affecting ◽  
Air Bubble

This paper presents the factors affecting air bubble size when air is injected through a perforated membrane into a water pool. Critical factors that govern the size of air bubbles are the air pressure and the flow rate as well as the hole size of the diffuser membrane. In order to have a better understanding of how bubble size can be affected and what the most effecting conditions are, the study was conducted in a computational fluid dynamic (CFD) investigation, which was validated by the experimental results.

scholarly journals Comparison of Bubble Size Distributions Inferred from Acoustic, Optical Visualisation, and Laser Diffraction

2019 ◽  
Vol 3 (4) ◽  
pp. 65 ◽  
Author(s):  
Pratik D Desai ◽  
Woon Choon Ng ◽  
Michael J Hines ◽  
Yassir Riaz ◽  
Vaclav Tesar ◽  
...  
Keyword(s):  
Size Distribution ◽  
Bubble Size ◽  
Acoustic Method ◽  
Laser Diffraction ◽  
The Other ◽  
Optical Methods ◽  
Main Hypothesis ◽  
Advantages And Disadvantages ◽  
Bubble Cloud ◽  
Acoustic Methods

Bubble measurement has been widely discussed in the literature and comparison studies have been widely performed to validate the results obtained for various forms of bubble size inferences. This paper explores three methods used to obtain a bubble size distribution—optical detection, laser diffraction and acoustic inferences—for a bubble cloud. Each of these methods has advantages and disadvantages due to their intrinsic inference methodology or design flaws due to lack of specificity in measurement. It is clearly demonstrated that seeing bubbles and hearing them are substantially and quantitatively different. The main hypothesis being tested is that for a bubble cloud, acoustic methods are able to detect smaller bubbles compared to the other techniques, as acoustic measurements depend on an intrinsic bubble property, whereas photonics and optical methods are unable to “see” a smaller bubble that is behind a larger bubble. Acoustic methods provide a real-time size distribution for a bubble cloud, whereas for other techniques, appropriate adjustments or compromises must be made in order to arrive at robust data. Acoustic bubble spectrometry consistently records smaller bubbles that were not detected by the other techniques. The difference is largest for acoustic methods and optical methods, with size differences ranging from 5–79% in average bubble size. Differences in size between laser diffraction and optical methods ranged from 5–68%. The differences between laser diffraction and acoustic methods are less, and range between 0% (i.e., in agreement) up to 49%. There is a wider difference observed between the optical method, laser diffraction and acoustic methods whilst good agreement between laser diffraction and acoustic methods. The significant disagreement between laser diffraction and acoustic method (35% and 49%) demonstrates the hypothesis, as there is a higher proportion of smaller bubbles in these measurements (i.e., the smaller bubbles ‘hide’ during measurement via laser diffraction). This study, which shows that acoustic bubble spectrometry is able to detect smaller bubbles than laser diffraction and optical techniques. This is supported by heat and mass transfer studies that show enhanced performance due to increased interfacial area of microbubbles, compared to fine bubbles.

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