Surfactant effect on path instability of a rising bubble

2013 ◽  
Vol 738 ◽  
pp. 124-142 ◽  
Author(s):  
Yoshiyuki Tagawa ◽  
Shu Takagi ◽  
Yoichiro Matsumoto
Keyword(s):  
Shear Stress ◽  
High Speed ◽  
Lift Force ◽  
Surfactant Concentration ◽  
Bubble Surface ◽  
Surface Velocity ◽  
Helical Motion ◽  
Dimensionless Numbers ◽  
Surfactant Effect ◽  
Aspect Ratios

AbstractWe report results from the first systematic experiments for investigating surfactant effects on path instability of an air bubble rising in quiescent water. The addition of surfactant to a gas–water system causes a non-uniform distribution of surfactant concentration along the bubble surface, resulting in variations in the gas–water boundary condition from zero shear stress to non-zero shear stress due to the Marangoni effect. This leads to retarded surface velocity and ends up with immobilization of the bubble surface with increasing surfactant concentration, where the drag corresponds to that of a solid sphere of the same size. Using two high-speed cameras and vertical traverse systems, we measure three-dimensional trajectories, velocities and aspect ratios of a millimetre-sized bubble simultaneously for ${\sim }1~\mathrm{m} $. Experimental parameters are the diameter of the bubble and the surfactant concentration of 1-Pentanol or Triton X-100. We explore the surfactant effect on the drag and lift forces acting on the bubble in helical motion. While the drag force monotonically increases with the surfactant concentration as expected, the lift force shows a non-monotonic behaviour. Nevertheless, the direction of the lift force in a reference frame that rotates with the bubble along its trajectory is kept almost constant. We also observe the transient trajectory starting from helical motion to zigzag, which has never been reported in the case of purified water. The instantaneous amplitude and frequency of the transient motion agree with those of the motion regarded as steady. Finally the bubble motions are categorized as straight/helical/zigzag and experimentally examined in the field of two dimensionless numbers: Reynolds number $\mathit{Re}\in $ [300 900] and the normalized drag coefficient ${ C}_{D}^{\ast } $ which represents the slip condition. Remarkably it is found that the motions of a bubble with the intermediate slip conditions between free-slip and no-slip are helical for a broad range of $\mathit{Re}$.

High Flow Rate Micro Orifice Dispersion of Gas-Liquid Flow

2015 ◽  
Author(s):  
Alexander Tollkoetter ◽  
Norbert Kockmann ◽  
Florian Schirmbeck ◽  
Jens Wesholowski
Keyword(s):  
Flow Rate ◽  
High Speed ◽  
Bubbly Flow ◽  
Bubble Surface ◽  
Reduced Pressure ◽  
Aspect Ratios ◽  
Specific Contact ◽  
Break Up ◽  
Bubble Sizes ◽  
Gas Liquid Flow

The flow of microbubbles in millichannels with typical dimensions in the range of few millimeters offers a reduced pressure loss with simultaneous large specific contact surface. By flowing through micro orifices, the transformation of pressure into kinetic energy creates a desired secondary flow pattern, which results in continuous dispersion. Differences in velocity and pressure act on the phase boundary of the bubbles and lead to deformations and break-up. In this work, bubble dispersion and bubbly flow in different orifices and channel modules with widths up to 7 mm are studied experimentally and by CFD simulations. The effect of the orifice dimensions on bubble sizes are evaluated for hydraulic diameters of 0.25 to 0.5 mm with different aspect ratios. Several channel structures are analyzed to offer less coalescence and larger residence times. The modules are arranged in a holder and are fixed under a view glass for optical characterization via high-speed camera. Volume flow rates of 10 to 250 mL/min are studied with various phase ratios. Bubble diameters are generated in the range of less than 0.1 to 0.7 mm with narrow size distributions depending on the entire flow rate through the device. The first break-up point is shifted closer to the outlet of the orifices for increasing velocities and smaller hydraulic diameters, but the whole break-up region stays nearly constant for each orifice indicating stronger velocity oscillations acting on the bubble surface. Generally, a linear relation of smaller bubble diameters with larger energy input was identified. Opening angles of the orifices above 6° resulted in flow detachments and recirculation zones around the effluent jet. Independence of the Reynolds number was determined contrary to existing literature models. Flow detachment and coalescence in curves was avoided by an additional bend within the curve based on systematically varied geometrical dimensions.

The effects of surfactant on the multiscale structure of bubbly flows

2008 ◽  
Vol 366 (1873) ◽  
pp. 2117-2129 ◽  
Author(s):  
Shu Takagi ◽  
Toshiyuki Ogasawara ◽  
Yoichiro Matsumoto
Keyword(s):  
Shear Stress ◽  
Lift Force ◽  
Bubbly Flow ◽  
Marangoni Effect ◽  
Surface Concentration ◽  
Bubble Surface ◽  
Drastic Change ◽  
Contaminated Water ◽  
Lateral Migration ◽  
Rear Part

It is well known that a bubble in contaminated water rises much slower than one in purified water, and the rising velocity in a contaminated system can be less than half that in a purified system. This phenomenon is explained by the so-called Marangoni effect caused by surfactant adsorption on the bubble surface. In other words, while a bubble is rising, there exists a surface concentration distribution of surfactant along the bubble surface because the adsorbed surfactant is swept off from the front part and accumulates in the rear part by advection. Owing to this surfactant accumulation in the rear part, a variation of surface tension appears along the surface and this causes a tangential shear stress on the bubble surface. This shear stress results in the decrease in the rising velocity of the bubble in contaminated liquid. More interestingly, this Marangoni effect influences not only the bubble's rising velocity but also its lateral migration in the presence of mean shear. Together, these influences cause a drastic change of the whole bubbly flow structures. In this paper, we discuss some experimental results related to this drastic change in bubbly flow structure. We show that bubble clustering phenomena are observed in an upward bubbly channel flow under certain conditions of surfactant concentrations. This cluster disappears with an increase in the concentration. We explain this phenomenon by reference to the lift force acting on a bubble in aqueous surfactant solutions. It is shown that the shear-induced lift force acting on a contaminated bubble of 1 mm size can be much smaller than that on a clean bubble.

scholarly journals Assessing Machine Learning versus a Mathematical Model to Estimate the Transverse Shear Stress Distribution in a Rectangular Channel

Mathematics ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 596
Author(s):  
Babak Lashkar-Ara ◽  
Niloofar Kalantari ◽  
Zohreh Sheikh Khozani ◽  
Amir Mosavi
Keyword(s):  
Shear Stress ◽  
Stress Distribution ◽  
Fuzzy Inference ◽  
Rectangular Channel ◽  
Tsallis Entropy ◽  
Shear Stress Distribution ◽  
Data Series ◽  
Shear Stresses ◽  
Inference System ◽  
Aspect Ratios

One of the most important subjects of hydraulic engineering is the reliable estimation of the transverse distribution in the rectangular channel of bed and wall shear stresses. This study makes use of the Tsallis entropy, genetic programming (GP) and adaptive neuro-fuzzy inference system (ANFIS) methods to assess the shear stress distribution (SSD) in the rectangular channel. To evaluate the results of the Tsallis entropy, GP and ANFIS models, laboratory observations were used in which shear stress was measured using an optimized Preston tube. This is then used to measure the SSD in various aspect ratios in the rectangular channel. To investigate the shear stress percentage, 10 data series with a total of 112 different data for were used. The results of the sensitivity analysis show that the most influential parameter for the SSD in smooth rectangular channel is the dimensionless parameter B/H, Where the transverse coordinate is B, and the flow depth is H. With the parameters (b/B), (B/H) for the bed and (z/H), (B/H) for the wall as inputs, the modeling of the GP was better than the other one. Based on the analysis, it can be concluded that the use of GP and ANFIS algorithms is more effective in estimating shear stress in smooth rectangular channels than the Tsallis entropy-based equations.

Aluminum Reflow Sputtering

MRS Bulletin ◽  
1995 ◽  
Vol 20 (11) ◽  
pp. 53-56 ◽  
Author(s):  
Kuniko Kikuta
Keyword(s):  
Integrated Circuit ◽  
High Speed ◽  
Lower Cost ◽  
High Reliability ◽  
Device Fabrication ◽  
Damascene Process ◽  
Aspect Ratios ◽  
Multi Level ◽  
Poor Adhesion ◽  
Lower Resistivity

The scaling of integrated-circuit device dimensions in the horizontal direction has caused an increase in aspect ratios of contact holes and vias without a corresponding scaledown in vertical dimensions. Conventional sputtering has become unreliable for handling higher aspect-ratio via/contact holes because of its poor step coverage. Several studies have attempted to overcome this problem by using W-CVD and reflow technology. The W-CVD is used for practical device fabrications. However, this technique has several problems such as poor adhesion to SiO2, poor W surface morphology, greater resistivity than Al, and the need of an etch-back process.Al reflow technology using a conventional DC magnetron sputtering system can simplify device-fabrication processes and achieve high reliability without Al/W interfaces. In particular, the Al reflow technology is profitable for multi-level interconnections in combination with a damascene process by using Al chemical mechanical polishing (CMP). These interconnections are necessary for miniaturized and high-speed devices because they provide lower resistivity than W and simplify fabrication processes, resulting in lower cost.This article describes recent Al reflow sputtering technologies as well as application of via and interconnect metallization.

scholarly journals Mathematical modelling of the overflowing cylinder experiment

2003 ◽  
Vol 474 ◽  
pp. 275-298 ◽  
Author(s):  
P. D. HOWELL ◽  
C. J. W. BREWARD
Keyword(s):  
Free Surface ◽  
Surfactant Concentration ◽  
Dynamic Properties ◽  
Vertical Cylinder ◽  
Surfactant Solution ◽  
Surface Concentration ◽  
Experimental Results ◽  
Surface Velocity ◽  
Experimental Apparatus ◽  
Finite Distance

The overflowing cylinder (OFC) is an experimental apparatus designed to generate a controlled straining flow at a free surface, whose dynamic properties may then be investigated. Surfactant solution is pumped up slowly through a vertical cylinder. On reaching the top, the liquid forms a flat free surface which expands radially before over flowing down the side of the cylinder. The velocity, surface tension and surfactant concentration on the expanding free surface are measured using a variety of non-invasive techniques.A mathematical model for the OFC has been previously derived by Breward et al. (2001) and shown to give satisfactory agreement with experimental results. However, a puzzling indeterminacy in the model renders it unable to predict one scalar parameter (e.g. the surfactant concentration at the centre of the cylinder), which must be therefore be taken from the experiments.In this paper we analyse the OFC model asymptotically and numerically. We show that solutions typically develop one of two possible singularities. In the first, the surface concentration of surfactant reaches zero a finite distance from the cylinder axis, while the surface velocity tends to infinity there. In the second, the surfactant concentration is exponentially large and a stagnation point forms just inside the rim of the cylinder. We propose a criterion for selecting the free parameter, based on the elimination of both singularities, and show that it leads to good agreement with experimental results.

Application of R/S Rheometer in Low Temperature Drilling Fluid Rheology Determination

2012 ◽  
Vol 490-495 ◽  
pp. 3114-3118
Author(s):  
Xiao Ling Jiang ◽  
Zong Ming Lei ◽  
Kai Wei
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Low Temperature ◽  
High Speed ◽  
Drilling Fluid ◽  
Drilling Fluids ◽  
Rheological Parameter ◽  
Fluid Temperature ◽  
Fluid Rheology ◽  
Rotary Viscometer

With six-speed rotary viscometer measuring the rheology of drilling fluid at low temperature, during the high-speed process, the drilling fluid temperature is not constant at low temperature, which leads to the inaccuracy in rheological measurement. When R/S rheometer is used cooperating with constant low-temperature box , the temperature remains stable during the process of determining the drilling fluid rheology under low temperature. The R/S rheometer and the six-speed rotational viscometer are both coaxial rotational viscometers, but they work in different ways and the two cylindrical clearance between them are different.How to make two viscometer determination result can maintain consistent?The experimental results show that, The use of R/S rheometer, with the shear rate for 900s-1 shear stress values instead of six speed rotary viscometer shear rate for 1022s-1 shear stress values.Then use two-point formula to calculate rheological parameters.The R/S rheometer rheological parameter variation with temperature has a good linear relationship,Can better reflect the rheological properties of drilling fluids with low temperature changerule

Modeling Reichardt’s Formula for Eddy-Viscosity in the Fluid Film of Tilting Pad Thrust Bearings

2017 ◽  
Author(s):  
Xin Deng ◽  
Brian Weaver ◽  
Cori Watson ◽  
Michael Branagan ◽  
Houston Wood ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Turbulence Model ◽  
High Speed ◽  
Eddy Viscosity ◽  
The Other ◽  
Fluid Film ◽  
Suitable Model ◽  
Velocity Gradients ◽  
Wall Shear

Oil-lubricated bearings are widely used in high speed rotating machines such as those used in the aerospace and automotive industries that often require this type of lubrication. However, environmental issues and risk-adverse operations have made water lubricated bearings increasingly popular. Due to different viscosity properties between oil and water, the low viscosity of water increases Reynolds numbers drastically and therefore makes water-lubricated bearings prone to turbulence effects. The turbulence model is affected by eddy-viscosity, while eddy-viscosity depends on wall shear stress. Therefore, effective wall shear stress modeling is necessary in producing an accurate turbulence model. Improving the accuracy and efficiency of methodologies of modeling eddy-viscosity in the turbulence model is important, especially considering the increasingly popular application of water-lubricated bearings and also the traditional oil-lubricated bearings in high speed machinery. This purpose of this paper is to study the sensitivity of using different methodologies of solving eddy-viscosity for turbulence modeling. Eddy-viscosity together with flow viscosity form the effective viscosity, which is the coefficient of the shear stress in the film. The turbulence model and Reynolds equation are bound together to solve when hydrodynamic analysis is performed, therefore improving the accuracy of the turbulence model is also vital to improving a bearing model’s ability to predict film pressure values, which will determine the velocity and velocity gradients in the film. The velocity gradients in the film are the other term determining the shear stress. In this paper, three approaches applying Reichardt’s formula were used to model eddy-viscosity in the fluid film. These methods are for determining where one wall’s effects begin and the other wall’s effects end. Trying to find a suitable model to capture the wall’s effects of these bearings, with aim to improve the accuracy of the turbulence model, would be of high value to the bearing industry. The results of this study could aid in improving future designs and models of both oil and water lubricated bearings.

Development and Optimization of Mathematical Model of High Speed Planing Dynamics

2015 ◽  
Author(s):  
Prin Kanyoo ◽  
Dominic J. Taunton ◽  
James I. R. Blake
Keyword(s):  
Relative Velocity ◽  
High Speed ◽  
Lift Force ◽  
Hydrodynamic Pressure ◽  
Physical Nature ◽  
Ship Motions ◽  
Additional Contribution ◽  
Forward Speed ◽  
Planing Craft ◽  
Hydrostatic Force

The primary difference between a planing craft and a displacement ship is that the predominant force to support the conventional or displacement craft is hydrostatic force or buoyancy. While in the case of planing craft, the buoyancy cedes this role to hydrodynamic lift force caused by flow and pressure characteristics occurring when it is travelling at high forward speed. However, the magnitude of hydrostatic force is still significant that cannot be completely neglected. Due to the high forward speed and trim angle, the flow around and under the planing hull experiences change of momentum and leads to the appearance of lift force according to the 2ndlaw of Newton. In other words, there is a relative velocity between the craft hull and the wave orbital motion that causes hydrodynamic pressure generating hydrodynamic lift force act on the hull surface. Then, in case of behaviors in waves, an additional contribution of ship motions is necessary to be considered in the relative velocity, resulting in nonlinear characteristic of its physical nature.

PRESSURE DISTRIBUTION DUE TO STERN TAB DEFLECTION AT MODEL SCALE

2021 ◽  
Vol 157 (A1) ◽  
Author(s):  
T Arnold ◽  
J Lavroff ◽  
M R Davis
Keyword(s):  
Pressure Distribution ◽  
High Speed ◽  
Lift Force ◽  
Force Measurement ◽  
Maximum Pressure ◽  
Model Scale ◽  
Measure Model ◽  
Overall Resistance ◽  
Hydraulics Laboratory ◽  
The University

Trim tabs form an important part of motion control systems on high-speed watercraft. By altering the pitch angle, significant improvements in propulsion efficiency can be achieved by reducing overall resistance. For a ship in heavy seas, trim tabs can also be used to reduce structural loads by changing the vessel orientation in response to encountered waves. In this study, trials have been conducted in the University of Tasmania hydraulics laboratory using a closed- circuit water tunnel to measure model scale trim tab forces. The model scale system replicates the stern tabs on the full- scale INCAT Tasmania 112 m high-speed wave-piercer catamaran. The model was designed for total lift force measurement and pressure tappings allowed for pressures to be measured at fixed locations on the underside of the hull and tab. This investigation examines the pressures at various flow velocities and tab deflection angles for the case of horizontal vessel trim. A simplified two-dimensional CFD model of the hull and tab has also been analysed using ANSYS CFX software. The results of model tests and CFD indicate that the maximum pressure occurs in the vicinity of the tab hinge and that the pressure distribution is long-tailed in the direction forward of the hinge. This accounts for the location of the resultant lift force, which is found to act forward of the tab hinge.

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