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The mass transfer between immiscible two liquid phases can be greatly accelerated by bubbling gas through a reactor. Therefore, the physical phenomenon occurring during passage of a rising bubble through an immiscible two-liquid interface is of particular interest. The passage of the bubble through the oil (upper phase)/water (lower phase) interface starts with an upward lifting of the interface, and the bubble attracts a column of the water phase upwards keeping a film of the water phase around itself. In this chapter, particular remark is given to the influence of different interface tensions retracting water film, after the water film ruptured, which lays on the interface between air and silicone oil. Unlike the previous studies on the rupture of a single liquid film in a gas which is pulled due to the identical surface tension, this system can form concentric ripples on the outer interface of the water film (oil/water interface) around the bubble due to the weak interface tension. Then, numerous microwater droplets break out from the fully grown ripples. Also, index matching visualization and Computational Fluid Dynamics (CFD) sheds light on the instantaneous behavior on the bubble surface to make clear the still vague phenomenon. Furthermore, this chapter shows an oppositely charged oil/water interface makes more and finer droplets than the original experiment in the absence of the voltage.

An explanation is given on visualization techniques used in cold model experiments for refining processes agitated by gas injection. The topics include bubble generation methods, a typical experimental setup, choice of seeding particles, and image analyses. Various types of bubble generation methods have been proposed in order to meet requirement of researchers and engineers engaged in materials engineering. Most of them are briefly reviewed in this chapter. A previously used experimental setup is introduced for particle image velocimetry measurements of a flow in a bottom-blown bath. Scattering and tracking characteristics are explained for the choice of seeding particles. Finally, some algorithms for particle tracking velocimetry (PTV) are reviewed.

In a steelmaking process, micro particles such as calcium oxide (CaO, desulphurization chemical) are effectively injected into a molten iron bath and dispersed in the whole bath to enhance the efficiency of desulphurization or dephosphorization. However, the injected particles attract gas bubbles due to poor wettability with molten iron so that the dispersion in the bath could be inhibited. To achieve the effective dispersion of the injected particles, the dynamics of air cavity formed behind the particle entering the bath needs to be investigated. This chapter begins with the fundamentals of wettability about Young’s equation and models of Wenzel and Cassie–Baxter, Contact angle hysteresis. And then, we address the surface roughness on the coated plate of water-repellent material, the slip boundary condition related to Navier’s model, water entry problem of a coated sphere and circular cylinder. In addition, the bound motion of a water drop on an inclined plate coated of the water-repellent material.

Bubbles generated successively at the exit of a single-hole nozzle rise upwards independently without any interactions when the gas flow rate through the nozzle is very low. Coalescence of bubbles and breakup of a bubble become to take place near the nozzle exit with an increase in the gas flow rate. As a result, many small bubbles and droplets are produced there. Meanwhile, multi-nozzle gas injection operations are employed in the real materials processes at high temperatures. Three or four nozzles are usually settled on the bottom wall of the reactor. A bubbling jet is formed above every nozzle. Interactions occur among the bubbling jets under certain conditions through the Coanda effect. In this chapter, some topics in relation to bubble interactions are introduced.

Liquid sloshing sometimes takes place due to interactions between a liquid and a structure. The sloshing of fuel tank in an aircraft or a ship could affect the performance of control systems, and it is thereby desirable to avoid external vibration at the eigenfrequency of the liquid. The theory of liquid sloshing dynamics in partially filled container has been addressed, starting with the pioneering work of Lamb [6] who obtained the harmonic solution of the sloshing with a small amplitude. Since then, the sloshing dynamics with a finite amplitude has been provided for various container geometries. Self-induced rotary sloshing can be observed in a partially liquid-filled cylindrical container having an inlet jet and drain nozzles on the bottom. The inlet jet is injected into the liquid through an inlet nozzle and the same quantity of liquid as the injected one is synchronously drained through outlet nozzles at the bottom so that the liquid volume in the container can be kept constant. The inlet jet impinges on the free surface and then a surface swell is formed. After the injection of the jet, pressure fluctuations generated by the surface swell result in periodical surface oscillations. Also, the self-induced sloshing can be caused by a gas injection instead of the liquid injection. The self-induced rotary sloshing has been utilized in some industrial fields such as a snow melting system and an organic wastewater disposal facility. In these practical applications, the injected jet is replaced by an air bubble jet or an ozone–air mixture jet. For the purpose of the removal of organic materials contained in contaminated sediment and wastewater in coastal marine areas, the present authors now attempt to apply the self-induced rotary sloshing in a bottomless condition. In the system, the rotary sloshing plays a predominant role in the promotion of chemical reaction. Furthermore, the jet-induced rotary sloshing could enhance the chemical reaction in a continuous steel refining process.

Molten steel is solidified in the mold of a continuous casting process after refining. A tundish and an immersion nozzle are installed upstream of the mold. Nonmetallic inclusions and fine bubbles still remaining in the molten steel are designed to be removed in the tundish. The immersion nozzle equipped with a sliding gate is used for controlling the molten steel flow rate and induce uniform molten steel flow in the mold. Mold powder is continuously supplied on the meniscus of the mold for lubrication and so on. Many problems however arise in the continuous casting process. The most serious problem is entrapment of mold powder into the molten steel flow in the mold. The quality of steel products is significantly lowered due to the entrapment. Details of the problems and solution methods will be explained in this chapter.

The mass transfer between immiscible two-liquid phases can be greatly enhanced by bubbling gas through a reactor. Numerous micro water droplets breaking out from a ruptured water film around a rising bubble through the oil (upper phase)/water (lower phase) interface were demonstrated in the preceding paper (Uemura T., Ueda Y. and Iguchi M., Europhys. Lett., 92(2010)34004). In this letter, we attempt to oppositely charge the oil and water layers, taking into account the findings of the preliminary study (Uemura T., Ueda Y. and Iguchi M., J. Visualization, 13(2010)85). As a result, this study successfully produces more and finer water droplets than the preceding experiments.

For multiphase flow simulations, accurate evaluation of interfacial tension is an important issue, so a front-tracking method which tracks the interface explicitly by marker elements is expected to be very useful. In the front-tracking method, however, treating the elements in 3D space is very tedious. To eliminate this problem, a front-tracking method without connectivity called level contour reconstruction method (LCRM) has been developed. However, the volume conservation property of the method is not so good. In this study, three techniques in reconstruction process of the LCRM are proposed and evaluated for several curvature spheres. As the result, the proposed method shows very high volume conservation property even for 2-grid diameter sphere. And also shape of a single deformable bubble and merging of two bubbles are reasonably expressed.

This paper virtually demonstrates an air cavity formed by a superhydrophobic low-density sphere entering into water with the use of a high-speed camera. Unlike the previous results for a high-density sphere, the low-density sphere pinches off the resulting air cavity at the shorter depth before the cavity has fully grown, and attracts minimal air on the rear surface due to rapid deceleration of the sphere in water. The analytical model previously proposed on the time evolution of the cavity shape is thus shown to be no longer valid for the low-density sphere.

An adaptive stereoscopic-PIV system has been constructed for flow analyses around a cylinder body (length = 60 mm, diameter = 10 mm, polystyrene). The body is floated by the swirling flows in a vertical pipe with a length of 1100 mm and an inner diameter of 100 mm. Four optical sensors (LEDs) were installed onto the pipe wall to detect the posture of the cylinder body. The constructed stereoscopic-PIV system is activated by the signals of the optical sensors when the cylinder is in the upright posture. The measurement system consists of two cameras, a Nd-Yag laser, and a host computer. Flow characteristics around the floating cylinder body and the motional characteristics of the body itself are investigated when the body is in the upright posture. It has been verified that the motion of the floating cylinder becomes stable when the azimuthal velocity component (W component) of the swirl flow is maintained at stable states.

When air is injected vertically upwards into a water-filled cylindrical vessel through a J-shaped lance, two types of swirl motions of the water in the vessel appear under specific conditions: shallow-water wave type and deep-water wave type. The swirl motions are similar to the rotary slashing. The deep-water wave type of swirl motion has high mixing ability. Small solid particles placed on the bottom of the cylindrical vessel can be lifted up into the bath through an effect of the swirl motion. The lifting behaviors of the particles can be classified into two types depending on the aspect ratio of the bath.

In the first part of this paper, sub-pixel displacement detection methods in particle image velocimetry (PIV) measurements were discussed. Some schemes for calculating the spatial gradient in a gradient method, which is one of sub-pixel displacement detection methods, were evaluated. It was found that the second order central finite difference scheme tends to underestimate the gradient of the tracer-particle’s intensity. Consequently it leads to an overestimation of sub-pixel displacements. A first-frame upstream and second-frame downstream finite difference scheme was then proposed and evaluated for one-dimensional flow measurements. Furthermore, the proposed difference scheme was extended to apply to two-dimensional flows. It was shown that taking the direction of the sub-pixel correction into account and using fewer adjacent pixels are important for PIV images consisting of small tracer particle images. Finally, a robust procedure for the execution of the gradient method was proposed, which can eliminate the effect of noises. It was found that the proposed scheme is not only highly accurate but is highly robust to noise.

Holography technique can be used for 3D measurement of particle positions. However, in general in-line holography, accurate determination of the object’s position in the optical axis direction is difficult. In order to overcome this defect, we proposed a two-views recording technique combined with a digital in-line holography. The two-views recording is executed by only one camera with the assistance of one mirror, capturing the real image of a particle and the mirror image of the same particle simultaneously. This method keeps simplicity of optical alignment and is free from a difficult calibration of multiple cameras. It was confirmed that the proposed technique can reduce the uncertainty in the depth direction to about 1 pixel. For application of this method to micro-PIV, magnified recording is desired. In this paper, magnified holograms were also taken through a lens. It was confirmed that the uncertainty in the optical-axis direction can be reduced to a few pixels by the proposed technique for the magnified holograms.

In this study, a front-tracking (FT) method combined with a solver for the interfacial transport of surfactant is proposed to analyze interfacial flows affected by contamination. Because the interfaces are expressed explicitly in the FT method, the advection-diffusion equation on the interface can be treated easily and can be solved with high accuracy. In this study, a scheme that completely conserves the total amount of surfactant was constructed. Numerical simulations of a water drop sinking in silicone oil were performed, taking into account the Marangoni effect caused by concentrations. The effects of three parameters—a damping coefficient of interfacial tension, a diffusion coefficient, and the total amount of surfactant—were evaluated. Calculated results were compared with experimental results and were in very good agreement with variables including the stagnant cap size, the flow separation point, and the peak of shear stress. We can therefore expect that our simulations can estimate the conditions of surfactant at the interfaces.

Velocity fields of a spot vortex flow that happens spontaneously in the turbulent flow in a bubbling vessel are measured by using an improved defocus method. A new method is developed by improving the defocus method that can measure three-dimensional position of particles using a single camera.Performance of the new method is expanded in measurement range and in applicability to dense distribution of particles by introducing a color separation technique to the method. The spatial resolution of the method is less than 0.5mm in z-direction at the measurement distance of 380 mm.

本研究では，旋回流搬送装置設計の第一段階として，ＴｙｐｅＡ，ＴｙｐｅＢおよびＴｙｐｅＣの３種類の旋回流発生装置を試作した．そして，各装置を比較検討するために，鉛直パイプ内の速度分布を３Ｄ－ＰＩＶで可視化計測し，得られた速度分布の2次元ベクトル画像に対して，モーダルウェーブレットによる多重解像度解析を行った．

Two kinds of swirling flow are generated in a main vertical pipe by using two kinds of air inlets. A rod-like material is put into the main vertical pipe. Four optical sensors are attached to the main vertical pipe. When the rod-like material is sensed by the four optical sensors, laser sheet is irradiated and the image is obtained by 3D-PIV. It means the posture of the rod-like material is upright and rotating with orientation. However, when the rod-like material is sensed by the two optical sensors, it means the posture of the rod-like material is not upright and rotating without orientation. Two images obtained by the above-mentioned were compared to derive the condition for the rod-like material to rotate at the constant height in the main vertical pipe, and the flow field around the rod-like material is analyzed time mean velocity and time mean turbulence level.

本研究では，モーダルウェーブレット変換と離散ウェーブレット変換を比較し，前者の有効性，ならびにモーダルウェーブレット変換の各基底関数を比較検討し，最適な基底関数を選択することを目的とした。 模擬ＰＩＶ画像, および標準画像に対して , モーダルウェーブレット変換，および離散ウェーブレット変換をそれぞれ施し，加算多重解像度解析結果から，基底関数の比較検討を行った．モーダルウェーブレット変換の基底関数にはノイマン型，ディリクレ型，およびグリーン関数型を用い，離散ウェーブレット変換の基底関数にはＤＡＵＢＥＣＨＩＥＳ４次基底を用いた． 模擬ＰＩＶ画像，標準画像の解析結果より ，本研究においては，総合的に考えると，モーダルウェーブレット変換の最適基底関数は ，ノイマン型であると思われる．

In this paper, a front-tracking (FT) method combined with a solver of interfacial transport of surfactant was proposed in order to resolve interfacial flows affected by contamination. In the FT method, because the interfaces are presented explicitly, advection-diffusion equation on the interface can be easily treated and can be solved highly accurately. In this study, a scheme which conserves the total mass completely was constructed and proposed. Numerical simulations of a water drop sinking in silicone oil were performed taking the Marangoni effect into account. The effects of three parameters, damping coefficient of interfacial tension, diffusion coefficient and total mass, were evaluated. Calculated results were compared with PTV measurements and were in very good agreement with them in the points of stagnant cap size, flow separation point, peak of shear stress and so on. So, we can expect that our simulations can estimate the conditions of surfactant on the interfaces, which is very difficult to be measured.

In order to make the X-ray micro-PIV technique as a common technology, the alternative X-ray source to Synchrotron Radiation (SR) facility is indispensable. The characteristics of micro-focus X-ray (MFX) source are examined for the micro-PIV. The MFX source seems better than the SR, in respect of the availability, the flexibility for PIV systems, and image enlargement. X-ray PIV is the only method that provides us with a method to realize three-dimensional micro-PIV measuring flows in complex channels. The spatial resolution, intensities, and imaging methods are discussed. Three dimensional shape of a spiral shape of fine metal wire is reconstructed from a two-dimensional micro-focus X-ray picture.

Some X-ray imaging techniques are examined for a feasibility study for micro-PIV in this study. There are three X-ray imaging method, the absorption contrast method, the refraction contrast method, and the phase contrast method. The first one is a common method but its spatial resolution is rather poor. The 2nd method corresponds to the Schlieren method that utilizes refraction of parallel light. The characteristics of the method, edge enhancement, can be effective in extracting tracer images. The third method is a kind of holography methods, and this method can record fine tracer particles.Among the three methods, the second and the third method are seemed to be applicable to PIV imaging, and those methods need a parallel X-ray. The Spring8, the synchrotron radiation facility in Harima, is utilized. There are some methods to realize phase contrast image, most of them requires ultra-high precision in optical alignment. In the present study, though a coherent source is indispensable, the simplest and robust holography method, the inline holography, is used to take phase contrast pictures.

Two kinds of swirling flow are generated in a main vertical pipe by using two kinds of air inlets. A rod-like material is put into the main vertical pipe. Four optical sensors are attached to the main vertical pipe. When the rod-like material is sensed by the four optical sensors, laser sheet is irradiated and the image is obtained by 3D-PIV. It means the posture of the rod-like material is upright and rotating with orientation. However, when the rod-like material is sensed by the two optical sensors, it means the posture of the rod-like material is not upright and rotating without orientation. Two images obtained by the above-mentioned were compared to derive the condition for the rod-like material to rotate at the constant height in the main vertical pipe, and the flow field around the rod-like material is analyzed by modal wavelet transform.

In order to measure three dimensional multiphase flows in a micro scale space, the stereo micro PIV method using synchrotron radiation X-ray is expected to be developed. Selection of tracer particles, and imaging method are discussed in this paper. A stereo matching technique for parallel projected stereo pictures is also examined.

For stereo measurement, diffraction grating is used for laser light division into two rays. Direction of divided rays depends on only wavelength of light and the interval of grid lines. The advantage of stereo measurement using this idea is that an optical adjustment is extremely easy because the stereo arrangement angle is fixed. This paper describes effects of optical performance and position of diffraction grating on quality of stereo image and accuracy of measurement.

Some calculation schemes of spatial gradient for the spatio-temporal derivative method, which was used for sub-pixel displacement detection in PIV measurements, were evaluated. It was found that the second-order central finite difference scheme tends to underestimate the gradient of tracer-particle's intensity, so that it leads to overestimation of sub-pixel displacements. In this study, a combined upstream and downstream finite difference scheme was proposed and evaluated for one-dimensional flow measurements. Furthermore, the proposed scheme was modified for two-dimensional flow. Two important things for small tracer particle PIV images were shown : 1) the direction of the sub-pixel correction should be taken into account, 2) distant pixels should not be used. It was found that the proposed scheme has high accuracy even if images contain some noises.

In this paper, it was explained that the "proper" fewer-point difference scheme, which is used in the spatio-temporal derivative method for PIV sub-pixel analysis, is more advantageous than the method using many points. In the spatio-temporal derivative method, there is possibility that noisy pixels, which badly affect the measurement accuracy, can be eliminated by the feature of the method itself. So a robust algorithm utilizing that feature was proposed and evaluated by using artificial images. It was shown that the proposed method has very high accuracy and is robust to noise.

A new high-speed super-resolution PIV was proposed using characteristic pixel selection to accelerate the successive abandonment (SA) with recursive window subdivision. The performance and applicability of the proposed PIV were evaluated. In the SA calculation with the characteristic pixel selection, 1000 candidates are narrowed down to only one at over 50% of the measurement points, and the number of error vectors is reduced because the difference between the cumulative intensities of a correct candidate and of other ones becomes clear due to the characteristics of selected pixels. In all recursive processes, error checks are carefully performed using the summation of the distribution of the cumulative intensity difference distribution, which is suitable for the SA method. In a comparison of the time per velocity vector, the present super-resolution PIV was shown to be 10 times faster than the former ordinary resolution PIV. Another feature of the present super-resolution PIV is that the velocity vectors are obtained in the region very close to the image boundaries and masked regions by using the recursive algorithm.

This paper visually demonstrates instantaneous behavior of ripples propagating on the surface of a rising bubble through an oil/water interface. This experiment uses potassium iodide (KI) 31 wt% as refractive index matching material which makes the water phase invisible. As a result, the generated micro droplets, which are shown in the preceding paper (Uemura et al. in Europhys Lett 92:34004, 2010), cannot be visible in the present results, and therefore the droplets are positively confirmed to be made of water.Graphical Abstract[IMAGE]

This paper deals with the experiment to obtain quantitative information about conditions of the interface between a water drop and surrounding oil. Velocity distributions in very close region of the interface are measured by introducing a new illumination technique and a telecentric lens. It enables precise measurements of velocity distributions in the close region to the interface. Although the measured velocity distributions exhibit strong influence from the solid wall of an experimental tube, the coincidence of inner and outside velocities on the interface is clearly confirmed for the clean interface. The shearing stresses on the interface, which are proportional to the velocity gradient normal to the interface, clearly show conditions of contaminated interface, which can be divided into two parts. From front stagnation point to somewhere near a separation point, the distribution of shearing stresses is well coincide with that of the Hadamard’s analytical solution, while the distribution on the latter part of the interface shows quite different feature, which is supposed to be strongly influenced by contamination of the surface.

PIV techniques have been developed for one and half decades. The techniques have been applied to many kinds of fluid phenomena as its potential increases. High potential hardware such as a YAG laser, High resolutionWe have high power lasers for ideal illumination, which can be controlled to emit spatially and temporally defined light pulses, high power computers, various kinds of non-standard video cameras, and tracers. Measurement objects range from micro scale objects to actual airplanes. A velocity range expands from micron per seconds to beyond sonic velocity.Accelerated improvements in performances of hardware have changed PIV techniques. Applications of PIV to micron scale flows and multi-phase flows are shown in the paper.Some issues for further expansion of the applications are discussed in the end of the paper; Special remarks are made for the motion measurement moving objects of flexible structures.

Three-dimensional X-ray velocimetry with micrometer-level resolution is demonstrated., A direct measurement of three-dimensional X-ray velocimetry with micrometer spatial resolution is presented. The key to this development is the use of a Laue crystal as an X-ray beam splitter and mirror. Three-dimensional flow velocities in a 0.4 mm-diameter tubing were recorded, with

This paper virtually presents induced behavior of an oppositely charged oil–water interface with the use of a high-speed camera. The elevation behavior of an oil–water interface is demonstrated experimentally, using a transparent acrylic cylindrical container (176 mm in inner diameter, 450 mm in height) with the bottom half (100 mm) filled with deionized water and the top half (between 50 and 150 mm) with an immiscible oil (viscosity 1 or 5 cSt). Copper fragments are inserted into each liquid (at top and bottom) to serve as electrodes, i.e., the oil layer is negatively charged, and the water layer is positively charged. A high-DC-voltage power supply provides potential difference of the order between about 1 and 30 kV. As a result, three kinds of behavior are observed, i.e.: (1) rotary motion on the interface in lower electric field supplied about E = 0.013 kV/mm; (2) fluctuation on the interface in medium electric field supplied about E = 0.021 kV/mm; (3) elevation of the interface in higher electric field supplied between E = 0.04 and 0.65 kV/mm (which depends on the depth of the oil layer).