Masamichi Sano

Effect of Process Parameters on Ultrasonic Separation of Dispersed Particles in Liquid

The effects of process parameters on ultrasonic separation of dispersed particles in a liquid using a standing-plane-wave field are discussed on the basis of experimental and theoretical results. Numerical solution of the equation of motion of a fine particle in a standing-wave field indicates that the inertia term can be neglected during conventional ultrasonic separation of fine particles. Analytical solutions for the particle speed, the position at which particles are coagulated, and the minimum power for separation, have then been derived to incorporate key process parameters. Experiments are carried out to observe transitional coagulation of polystyrene particles in an aqueous sugar solution with the incidence of standing ultrasonic plane wave, in terms of the density difference as well as the acoustic energy density exerted. Experimental results agree well with the theoretical predictions. The time required for coagulating and for the separation of particles is shortened in the case that particles coalesce.

Cold Model Study on Mg Desulfurization of Hot Metal Under Mechanical Stirring

The new method of in-situ desulfurization with mechanical stirring of new type impellers was introduced, in which the bubble’s dispersion and disintegration of magnesium vapor were the key to boosting the desulfurization efficiency and increasing the utilization rate of magnesium. Effects of different new type of impellers on bubble dispersion and disintegration were studied through bubble image analysis, gas-liquid mass transfer, and power consumption levels of different impeller structures. The results showed that the sloped swept-back blade impeller-2 produces optimal bubble’s dispersion and disintegration, as well as higher volumetric mass transfer coefficient and CO2 gas utilization while consuming the least power. Numerical simulation result with Fluent software also showed that the sloped swept-back blade impeler-2 has higher turbulent kinetic energy and better velocity distribution than the other two impellers.

Mechanical stirring for highly efficient gas injection refining

Abstract In gas injection refining processes, wide dispersion of small bubbles in the bath is indispensable for high refining efficiency. Eccentric mechanical stirring with unidirectional impeller rotation was tested using a water model for pursuing better bubble disintegration and dispersion. Effects of various factors on bubble disintegration and dispersion were investigated. These factors were stirring mode, eccentricity and rotation speed, nozzle structure, nozzle immersion depth, and gas flow rate. Gas injection from a nozzle at the end of the impeller shaft and from an immersed lance was studied. Under eccentric stirring, a vortex was formed away from the shaft. Small bubbles were produced in the strong turbulence or high shear stress field near the rotating impeller and moved in the direction to the vortex keeping up with the macroscopic flow induced by the mechanical stirring. Thus small bubbles could disperse widely in the bath under eccentric stirring with unidirectional rotation.

Bubble Formation from Nonwetted Slot Nozzles

Abstract Experiments examining gas injection and bubble formation from nonwetted slot nozzles are presented in this work. Gas was injected into water and mercury. Slot nozzles used for the water model experiments were made of Teflon plates which are not wetted by water. The slot lengths were 50 mm and 200 mm, and the slot widths were between 0.05 mm and 1 mm. For mercury model experiments, a slot nozzle was made of acrylic resin. The slot length and width were 80 mm and 0.05 mm, respectively. The size of the bubbles and the number of bubble sources were measured from pictures taken with a high speed video camera. It was found that the bubbles formed at a series of sources distributed along the slot length where each source acted like a nonwetted orifice. The number of bubble sources were less than observed previously for gas injection through welted slot nozzles. The source spacing was attributed to RayleighTaylor instability. The measured bubble size was explained well by a simple dynamic model for a point source orifice. The line of bubble formation sites along the slot can generate a wide bubble plume which may offer high efficiency for metal refining processes.

Effect of Sound Waves on Decarburization Rate of Fe-C Melt

Sound waves have the ability to propagate through a gas phase and, thus, to supply the acoustic energy from a sound generator to materials being processed. This offers an attractive tool, for example, for controlling the rates of interfacial reactions in steelmaking processes. This study investigates the kinetics of decarburization in molten Fe-C alloys, the surface of which was exposed to sound waves and Ar-O2 gas blown onto the melt surface. The main emphasis is placed on clarifying effects of sound frequency, sound pressure, and gas flow rate. A series of water model experiments and numerical simulations are also performed to explain the results of high-temperature experiments and to elucidate the mechanism of sound wave application. This is explained by two phenomena that occur simultaneously: (1) turbulization of Ar-O2 gas flow by sound wave above the melt surface and (2) motion and agitation of the melt surface when exposed to sound wave. It is found that sound waves can both accelerate and inhibit the decarburization rate depending on the Ar-O2 gas flow rate and the presence of oxide film on the melt surface. The effect of sound waves is clearly observed only at higher sound pressures on resonance frequencies, which are defined by geometrical features of the experimental setup. The resonance phenomenon makes it difficult to separate the effect of sound frequency from that of sound pressure under the present experimental conditions.

Effect of gas injection on the behavior of slag foaming with smelting reduction of iron oxide by graphite

The effect of gas injection on slag foaming with smelting reduction of iron oxide from molten CaO-Li 2 O-SiO 2 -Al 2 O 3 slag systems is investigated under argon atmosphere at 1573K. Two slag compositions with basicity (=(N CaO +N Li2O )/N SiO2 ; N: molar fraction) 1.0 and 2.0 are chosen. The initial iron oxide concentration is changed from 3 to 10 mass%. A graphite tube, which is 40mm in length and 10mm in outer diameter, is employed as a reductant. The rotation speed of the graphite tube is from 1.67 to 15 s -1 . Injection gas (Ar or CO) flow rate is varied between 0.33×10 -6 and 6.67×10 -6 Nm 3 /s. The slag foaming is evaluated by gas holdup, e. It is found that slag foaming behavior is affected by gas injection in the case of the slag with a composition of 38.4%CaO-20.5%Li 2 O-41.1%Si02, in which the reaction is controlled by mass transfer. Gas holdup at first increases and then decreases slightly with the increase in gas injection flow rate. This result is discussed on the basis of the reaction kinetics and physical behavior of bubbles. Reaction rate constant increases with the increase in gas injection flow rate. On the other hand, bubble coalescence is also enhanced by gas injection. The net effect of gas injection on slag foaming is the result of two opposing effects of (1) enhancement of gas evolution accompanied by increased rate of the reaction and (2) bubble coalescence in the foamed slag. But in the case of the slag with a composition of 57.9%SiO 2 -28.1%Li 2 O-14.0%Al 2 O 3 , in which chemical reaction is the rate controlling step, no foaming phenomenon is observed even under the condition that gas is injected. The present experimental results of slag foaming can be fitted using a drift-flux model.