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Über dieses Buch

This book presents a comprehensive review of particle image velocimetry (PIV) and particle tracking velocimetry (PTV) as tools for experimental fluid dynamics (EFD). It shares practical techniques for high-speed photography to accurately analyze multi-phase flows; in particular, it addresses the practical know-how involved in high-speed photography, including e.g. the proper setup for lights and illumination; optical systems to remove perspective distortion; and the density of tracer particles and their fluorescence in the context of PIV and PTV. In this regard, using the correct photographic technique plays a key role in the accurate analysis of the respective flow. Practical applications include bubble and liquid flow dynamics in materials processes agitated by gas injection at high temperatures, mixing phenomena due to jet-induced rotary sloshing, and wettability effects on the efficiency of the processes.





Chapter 1. Introduction

Removal of impurities and nonmetallic inclusions contained in molten metals is of essential importance for producing high-quality metal products. Such an operation is called refining. The refining can be effectively achieved by enhancing the opportunity for the impurities and nonmetallic inclusions to meet their respective refining agents carried into the reactor. Such requirement is satisfied when the bath of the reactor is strongly mixed. Mixing of the bath is usually done by injecting gas into the bath. A molten metal flow is induced in the bath through the gas-lift effect, and the flow contributes to the bath mixing. Consequently, information on the flow field in the bath is necessary for enhancing the efficiency of the conventional metal refining processes as well as for developing novel processes. Molten metals contained in the reactor of the real refining processes are not transparent, and their temperature is very high. In addition, the molten metal flows in the real refining processes are highly turbulent and unsteady in many cases. A full understanding of the real molten metal flows therefore is not easy. Cold model experiments are often chosen for investigating the molten metal flows. Flow visualization techniques are suitable for whole flow field measurements. In this chapter, an outline of the flow field in the bath of real materials processes at high temperatures is briefly introduced.
Tomomasa Uemura, Manabu Iguchi, Yoshiaki Ueda

Chapter 2. Fundamentals of Experimental Visualization

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.
Tomomasa Uemura, Manabu Iguchi, Yoshiaki Ueda

Applications—Multi-phase Flow and Its Visualized Examples in Materials Processing


Chapter 3. Visualization of Flow Induced by Bubble Dispersion

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.
Tomomasa Uemura, Manabu Iguchi, Yoshiaki Ueda

Chapter 4. Jet-Induced Rotary Sloshing in a Cylindrical Container

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.
Tomomasa Uemura, Manabu Iguchi, Yoshiaki Ueda

Chapter 5. Behavior of a Rising Bubble Through an Oil/Water Interface

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.
Tomomasa Uemura, Manabu Iguchi, Yoshiaki Ueda

Chapter 6. Continuous Casting of Molten Steel

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.
Tomomasa Uemura, Manabu Iguchi, Yoshiaki Ueda

Chapter 7. Wettability Problems in Materials Processing

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.
Tomomasa Uemura, Manabu Iguchi, Yoshiaki Ueda

Chapter 8. Miscellaneous Applications

This chapter consists of three topics on argon gas attachment to an immersion nozzle in the continuous casting process of steel, production of single-crystal silicon particles, and bubble removal from molten metals. Molten steel is introduced into a continuous casting mold through an immersion nozzle equipped with a sliding gate which controls the molten steel flow rate. Alumina (Al2O3) still contained in the steel preferably attaches to the inner wall of the immersion nozzle. As a result, the cross-sectional area changes with time and the flow rate of molten steel cannot be kept constant. In order to suppress the clogging of alumina, argon gas is introduced into the nozzle. The argon gas however attaches to the sliding gate and affects the flow rate and flow direction. Attachment patterns of argon gas will be explained. Spherical microsolar cells made of single-crystal silicon are expected to reduce the cost for generating solar energy. Conditions for producing high-quality single-crystal silicon will be introduced. Small bubbles contained in molten metals cause the pinhole defect, and hence, removal of the bubbles is one of the key technologies for producing clean metals. Bubble removal based on wettability effect will be introduced.
Tomomasa Uemura, Manabu Iguchi, Yoshiaki Ueda


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