Bubble Profile Research Articles

Adsorption layer characteristics of Triton surfactants: 4. Dynamic surface tension and dilational visco-elasticity of micellar solutions

The presence of micelles in the solution accelerates the adsorption dynamics of Tritons at the solution/air interface, depending on the micelle dissolution rate. Micellar solutions (at CMC and up to about 10× CMC) are studied by maximum bubble pressure tensiometry and oscillating bubble profile tensiometry. The dynamic surface tensions in the time range between 0.1 ms up to 50 s are analysed by a diffusion controlled mechanism. At very short times the effect of molecular reorientation of the Triton molecules at the surface is observed. The dilational elasticity data at low frequencies (0.005–0.2 Hz) provide good agreement with a respective model assuming a very fast micelle dissolution. While for Triton X-45 and X-100 a quantitative agreement with existing theories is observed, the results for Triton X-165 and X-405 agree only qualitatively. This discrepancy is obviously due to the respective composition of the technical surfactants and a quantitative understanding would require an accurate knowledge on the sample composition.

Adsorption layer characteristics of Triton surfactants: Part 2. Dynamic surface tension and adsorption

The adsorption kinetics of four Tritons (TX45, TX100, TX165 and TX405) was studied by using the complementary drop and bubble profile and maximum bubble pressure tensiometry methods. While TX45 and TX100 can be quantitatively described by a diffusion controlled adsorption mechanism, based on the reorientation model for describing the equilibrium state of adsorption, the results for TX165 and TX405 deviate significantly from this adsorption mechanism. With additional assumptions, such as a finite rate constant for the transition of adsorbed molecules between states of different molar area, and effects of the composition of the Triton samples by many compounds of different ethylene oxide chains, a much better description of the experimental data is possible.

Adsorption layer characteristics of Triton surfactants: 1. Surface tension and adsorption isotherms

The adsorption of the non-ionic surfactants Triton X-45, Triton X-100, Triton X-165, and Triton X-405 can be described by a reorientation model, assuming that molar area required by adsorbed molecules depends on the surface coverage. The surface tension isotherms we measured by drop and bubble profile tensiometry, where it was shown that at low surfactant bulk concentrations, significant differences in the measured equilibrium tensions are due to depletion effects from the volume of a single drop. This difference in equilibrium surface tensions, observed between data from drop and bubble experiments, is a good tool to determine the adsorbed amount from the total mass balance. An intersection point of all surface tension isotherms at about 1 μmol/l is explained by a respective displacement of the ethylene oxide chain from the interface by the hydrocarbon chain.

Buoyancy-driven motion of a gas bubble through viscous liquid in a round tube

The steady axisymmetric flow of viscous liquid relative to a gas bubble due to its buoyancy-driven motion in a round tube is computed by solving the nonlinear Navier–Stokes equations using a Galerkin finite-element method with a boundary-fitted mesh. When the bubble is relatively small compared with the tube size (e.g. the volume-equivalent radius of the bubble is less than a quarter of the tube radius R), the bubble exhibits similar behaviour to one moving in an extended liquid, developing a spherical-cap shape with increasing Reynolds number (Re) if the capillary number is not too small. The long-bubble (also known as a Taylor bubble) characteristics can be observed with bubbles of volume-equivalent radius greater than the tube radius, especially when the surface tension effect is relatively weak (e.g. for Weber number We greater than unity). The computed values of Froude number Fr for most cases agree well with the correlation formulae derived from experimental data for long bubbles, and even with (short) bubbles of volume-equivalent radius three-quarters of the tube radius. All of the computed surface profiles of long bubbles exhibit a prolate-like nose shape, yet various tail shapes can be obtained by adjusting the parameter values of Re and We. At large Weber number (e.g. We=10), the bubble tail forms a concave profile with a gas ‘cup’ developed at small Re and a ‘skirt’ at large Re with sharply curved rims. For We≤1, the bubble tail profile appears rounded without large local curvatures, although a slightly concave tail may develop at large Re. non-uniform annular film adjacent to the tube wall is commonly observed when Weber number is small, especially for bubbles of volume <3πR3, suggesting that the surface tension effect can play a complicated role. Nonetheless the computed value of Fr is found to be generally independent of the bubble length for bubbles of volume-equivalent radius greater than the tube radius. If the bubble length reaches about 2.5 tube radii, the value of its frontal radius becomes basically the same as that for long bubbles of much larger volume. An examination of the distribution of the z-component of traction along the bubble surface reveals the basic mechanism for long bubbles rising at a terminal velocity that is independent of bubble volume.

Surface Dilational Viscoelasticity of C14EO8 Micellar Solution Studied by Bubble Profile Analysis Tensiometry

The experimental dependences of viscoelasticity modulus and phase angle as a function of frequency for various C 14EO8 concentrations at the critical micelle concentration (cmc) of 7 micromol/L and far above the cmc (up to 70 x cmc) were studied using the buoyant bubble profile analysis method. With increasing C14EO8 concentration the viscoelasticity modulus decreases and the phase angle increases. At the highest surfactant concentrations, the phase angle was more than 45 degrees . For the theoretical description of the equilibrium surface tension isotherm and the limiting elasticity modulus, a combined theoretical model was used considering surface reorientation and molecular compression. To analyze the experimental dependencies of the viscoelasticity modulus and phase angle on frequency, a model proposed by Joos for fast micellar kinetics was applied. This theory agrees well with the experimental data of the viscoelasticity modulus obtained for all concentrations of the studied nonionic surfactant C14EO8.

Modeling Total Dissolved Gas Concentration Downstream of Spillways

Dams are often operated to facilitate downstream juvenile anadromous fish migration over the spillways, but such operation can cause high dissolved concentrations of oxygen and nitrogen that can be harmful to fish. The concentration of total dissolved gas (TDG) in the flow changes with distance downstream of the spillway crest and depends on the geometric configuration of the spillway and on hydraulic and operating conditions. A model is presented that simulates the physical processes of gas transfer with the goal of having an accurate and more widely applicable TDG model for plunging spillway discharges. Bubble transfer is dominant in the stilling basin, while water surface transfer is dominant downstream. Sensitivity analyses suggest which physical processes are important for accurate total dissolved gas predictions. Instantaneous bubble coalescence and breakup based upon local turbulence conditions is an appropriate assumption. Vertical bubble profiles do not need to be simulated in this type of model. Water surface roughness provides a significant increase to surface transfer. Tailwater depth is important to downstream TDG concentrations. Finally, a 10% difference in air entrained at the plunge point causes relatively minor differences in TDG of 1.4 and 3.1% at low and high discharges, respectively.

DNA denaturation bubbles at criticality

The equilibrium statistical properties of DNA denaturation bubbles are examined in detail within the framework of the Peyrard-Bishop-Dauxois model. Bubble formation in homogeneous DNA is found to depend crucially on the presence of nonlinear base-stacking interactions. Small bubbles extending over fewer than ten base pairs are associated with much larger free energies of formation per site than larger bubbles. As the critical temperature is approached, the free energy associated with further bubble growth becomes vanishingly small. An analysis of average displacement profiles of bubbles of varying sizes at different temperatures reveals almost identical scaled shapes in the absence of nonlinear stacking; nonlinear stacking leads to distinct scaled shapes of large and small bubbles.

Stability of Microbubbles under Variation of a Pressure Field

The shrinkage and growth of microbubbles coated by palmitic acid under variation of a pressure field are observed with a CCD camera. We investigate the influence of gas diffusion on the stability of microbubbles. It is shown that when the ambient liquid pressure increases, a tiny microbubble with a radius of about 5 μm shrinks accompanied with large surface depression, and does not return to the initial size even after the pressure is reduced. The depression suggests the formation of multilayers of surfactant on the bubble surface. A bubble model is constructed by taking the dynamic surface tension and the gas permeation resistance of surfactant layers into account. The simulations show that the hysteresis of the surface tension is an important factor in determining the bubble response to the pressure change; the bubble profiles in the experiments are simulated qualitatively by considering the hysteresis of the surface tension. Also, the simulations considering the variable permeation resistance are in good agreement with the experimental results. The results also show that the permeation resistance increases during bubble shrinkage and stabilizes the microbubble. The smaller the initial bubble radius becomes, the larger the permeation resistance becomes during bubble shrinkage. The present simulations support the experimental results that the surfactant multilayers are formed when the bubble is compressed under the pressure increase.

Adsorption behaviour of hen egg-white lysozyme at the air/water interface

The adsorption dynamics and equilibrium properties of hen egg-white lysozyme at the air/water interface is studied using bubble and drop profile analysis technique, ellipsometry and infrared reflection absorption spectroscopy (IRRAS). The set of equilibrium data can be described by a recently developed thermodynamic model. Using the equilibrium adsorption parameters the adsorption dynamics can be well described by a diffusion controlled mechanism at the lower concentrations and a mixed model at higher lysozyme concentrations where conformational changes in the surface layer become time determining.

Temperature effects in the blown Newtonian film.

The film blowing process, by which thin polymer films are manufactured, is modelled by highly nonlinear differential equations. Typically, analysis of these using numerical techniques leads to instabilities. Our earlier work used an iteration process to construct the film bubble profile and some associated quantities for the simplest case of a Newtonian film incorporating an axial temperature variation. Now we extend this to an investigation of the effects of variations in temperature parameters on the film radius, film fluid velocity, film thickness and overall temperature profiles. This information is of considerable use to investigators examining the film blowing process. References Shepherd J. J. and Bennett J. C., Interior layer structure in the Newtonian blown film, ANZIAM Journal 46(E), 2005, pp. C839-C853. http://anziamj.austms.org.au/V46/CTAC2004/Shep/ J. J. Shepherd, H. J. Connell and D. C. H. Tam, An interior layer in a film-blowing problem, Proceedings of the Fifth Biennial Engineering Mathematics and Applications Conference (EMAC2002), M. Pemberton, I. Turner, P. Jacobs (eds), The Institution of Engineers Australia, Brisbane, Queensland (2002), pp. 181--186. Bennett J. C. and Shepherd J. J., Analysis of the non-isothermal Newtonian model in the blown film process, ANZIAM Journal 47(E), 2006, pp. C325--C338. http://anziamj.austms.org.au/V47EMAC2005/Bennett/ X.-L. Luo, R. I. Tanner, A computer study of film blowing, Polymer Engineering and Science, Volume 25, Number 10, 1985, pp. 620--629. J. R. A. Pearson, Mechanics of Polymer Processing, Elsevier Applied Science Publishers, 1985. J. R. A. Pearson and C. J. S. Petrie, The flow of a tubular film. Part 2. Interpretation of the model and discussion of solutions, Journal of Fluid Mechanics, Volume 42, Part 3, 1970, pp. 609--625.

Adsorption of hen egg-white lysozyme at the air–water interface in presence of sodium dodecyl sulphate

The mixed adsorption layers of hen egg-white lysozyme/SDS for fixed protein concentration and varying surfactant concentrations at the air/water interface have been studied using bubble and drop profile analysis tensiometry and ellipsometry. The set of equilibrium and kinetic data are compared with thermodynamic and adsorption kinetic models developed recently. The parameters used for the mixed system are essentially those parameters obtained for the individual components. For a lower SDS concentrations the agreement with the model is good while in the transition region to a mainly surfactant controlled surface layer is poor.

Surface Dilational Rheology of Mixed Surfactants Layers at Liquid Interfaces

Experimental data on surface tension and dilational rheology for mixtures of two non-ionic surfactants (decyl and tetradecyl dimethyl phosphine oxide) are analyzed on the basis of a recently derived model. The chosen surfactant mixtures are suitable for studies of the dilational rheology at low frequencies, as provided by slow area oscillations in drop and bubble profile analysis tensiometry. The results show that the compressibility of adsorbed layers given by the parameter ε has negligible effect on the equilibrium adsorption behavior but have significant influence on the frequency dependence of the viscoelasticity modulus and phase angle. The model allows also satisfactory analysis of literature data obtained for mixed anionic (sodium dodecyl sulfate) and non-ionic (dodecanol) surfactant systems.

C 14EO 8 adsorption characteristics studied by drop and bubble profile tensiometry

The adsorption characteristics of the non-ionic surfactant C 14EO 8 studied by drop and bubble profile tensiometry at the solution/air interface is best described by a model that considers molecular reorientation and compressibility at high surface coverage. The comparison of the adsorption equilibrium at a single drop surface with that at the surface of a bubble formed in a large solution reservoir allows determining the adsorbed amount at the solution surface. The adsorption isotherm data are used to quantitatively describe the adsorption kinetics as well as the dilational elasticity and viscosity over the entire concentration range up to the CMC. It is shown that dilational rheology data are most sensitive to the physical models while the equilibrium surface tensions are less sensitive and can be described adequately also by a Frumkin model.

ICONE15-10779 A STUDY OF ULTRASONIC VELOCITY PROFILE MEASUREMENT ON BOILING TWO-PHASE FLOW

This paper describes the velocity profile measurement in boiling two-phase flow using pulse ultrasound. The high temperature transducer, which has an allowable temperature limit of 120℃, was developed, and the applicability to boiling two-phase flow under the atmospheric pressure was confirmed. In addition, for measurements of the velocity profiles, a Plexiglas wedge was used to incline the ultrasonic beam path in fluid. The intensity of the ultrasonic transmission through the wedge and the radiation angle were clarified by measuring the sound field, and the optimal angle of the wedge was found. In the boiling two-phase flow under the atmospheric pressure, the velocity profiles of vapor bubbles generated by a cartridge heater were measured by the ultrasonic Doppler method, and the possibility of the ultrasonic velocity profile measurement in boiling two-phase flow was confirmed.

1434 動的表面張力と気体の拡散抵抗を考慮したマイクロバブルの安定性解析(S38-2 気泡・粒子,S38 マイクロ・ナノフルイズ)

The influence of gas diffusion is investigated for two kinds of microbubbles. It is shown that a tiny microbubble shrinks accompanied with large surface depression, and does not return to the initial size even after the pressure is reduced. On the other hand, a large microbubble shrinks nearly spherically. The depression of bubble surface suggests the formation of multilayers of surfactant or lipid on bubble surface. A bubble model is also constructed by considering the dynamic surface tension and gas permeation resistance of surfactant or lipid layers. The experimental results are compared with simulations based on the model. The results show that the dynamic surface tension is a significant factor to determine the bubble profile. The results also show that the increase of the permeation resistance during bubble shrinkage stabilizes microbubbles.

Automatic measurement of surface tension from noisy images using a component labeling method

Automatic surface tension measurement of turbid liquids using a bubble method (e.g., pendant/captive bubble) or interfacial tension measurement of some liquid–liquid systems necessitates an image analysis scheme robust against noise. Measuring the surface tension of lung surfactant–polymer systems using the combination of axisymmetric drop shape analysis (ADSA) and a captive bubble is such an example. We have recently developed a sophisticated image analysis scheme featuring the combination of the Canny edge detector and a novel edge smoothing technique called axisymmetric liquid fluid interfaces-smoothing (ALFI-S). The Canny edge detector is highly noise-resistant and ALFI-S is efficient in further removing noise close to the bubble profile (i.e., adhering noise). However, the procedure of eliminating noise far away from the bubble profile (i.e., isolated noise) is still not satisfactory in the previous scheme. Here a component labeling method is developed to automatically remove isolated noise. Component labeling refers to the process of detecting connected objects in a digital image. Once labeling is completed, information, such as area, location and pixel intensity, of these separate objects can be obtained. Hence, component labeling can be used as a region-based segmentation technique that is capable of differentiating the bubble and the isolated noise. The new component labeling-based noise reduction method is used to analyze captive bubble images with different amounts of noise. It is found that with the help of the labeling procedure smooth edges can be detected with a simple set of user-specified parameters even from images with extensive noise. Combined with the previous image analysis scheme, the component labeling method significantly improves the effectiveness and reliability of ADSA in automatically measuring surface tension from noisy images.

Dynamic capillary pressure measurements in the short time range by applying a fast growing drop technique

The capillary pressure technique is the method of choice for any tensiometry measurements in microgravity, as all bubbles and drops have a spherical shape. A combination of fast drop formation based on a known constant liquid flow and fast data acquisition of measured capillary pressure gives access to dynamic interfacial tensions in the range of milliseconds. Also the maximum drop pressure method, an equivalent to the maximum bubble pressure technique as fastest dynamic surface tension method, can be practised by the same set-up. The technique was developed already 15 years ago [ii] and now further refined during the MAP FASES* supported by the European Space Agency [ii]. Besides a detailed description of the technical parameters, experimental results for emulsion relevant systems are presented. The set-up presented here is based on a commercial drop and bubble profile analysis tensiometer which appears to be a kind of in-situ technique for membrane emulsification processes. The instrumental set-up is suitable also for oscillating drop and bubble experiments up to frequencies of several hundreds Hz.

THE GAS-ASSISTED FLUID FLOW EXPELLED IN FRONT OF A LONG BUBBLE IN A CIRCULAR TUBE

This study investigates the steady-state flow field in a circular tube filled with a viscous fluid expelled by a long gas bubble. We use a finite difference method with successive over-relaxation in the computation of the viscous flow field. An empirical bubble profile is employed to simplify the computation of the interface shape between the gas and the viscous fluid. By varying the ratio of the bubble width to the diameter of the circular tube (λ), the numerical simulation shows three fluid flow patterns: the complete bypass flow, the recirculation flow and the transient flow. The transient flow is only observed in a limited λ range of √1/2 < λ < 0.7143 and isn’t clearly discussed in the previous studies. The variation of vorticity also is observed by the various sizes of λ.

Flow patterns in gas-assisted injection molding process in a channel

The flow field of a long bubble steadily expelling a viscous fluid confined by two closely located parallel plates is examined. In order to investigate the influence of bubble size on the flow field, a theoretical bubble profile is used to replace the complicated procedure for computing simultaneously the interface between the gas surface and fluid flows. The present study showed the two typical flow patterns and also a third flow pattern of the stagnation point moving in the region of the bubble tip front during transformation of the two typical flow patterns. The vorticity patterns are also drawn for various bubble profiles and are examined for their effect on the flow. The velocity field is also presented from two different viewpoints and the phenomena is examined. The stagnation point located on the center line between the bubble tip to the upstream is only found in the small range of \(2/3 <\lambda < 0.685\) in a channel, where λ is ratio of the bubble width to the distance between two parallel plates.

A231 超音波流速分布計を用いた沸騰二相流計測のためのセンサ開発と感度特性(超音波・電磁波による熱流体計測1)

This paper describes a fundamental study for UVP measurement of boiling two-phase flow. The ultrasonic sensor for transmitting and receiving ultrasonic pulse decreases the sensitivity with temperature rise, because the piezoelectric elements of the sensor loses the piezoelectric effect over Curie temperature. So the high-temperature ultrasonic sensor is required for boiling two-phase flow measurement. In this study, the ultrasonic sensor with allowable temperature limit of 120 degrees Celsius was produced by using the 1-3 composite oscillator, which has high sensitivity and has been used widely for fluid flow measurement. Using this ultrasonic sensor, the rising velocity profiles of vapor bubbles generated by a heater were measured by UVP monitor.