Koichi Terasaka

Bubble formation under constant-flow conditions

Abstract Bubble volumes and shapes formed from a constant-flow nozzle submerged in liquids were measured experimentally. By modifying the previous works, a new constant gas flow condition was proposed. A nonspherical bubble formation model under constant-flow conditions was developed, and the calculated volumes and shapes of bubbles agreed with both the present experimental results and the previous works.

Bubble formation at a nozzle submerged in viscous liquids having yield stress

Abstract The effects of operating conditions on bubble volume formed from a nozzle submerged in some viscous media with yield stress were experimentally investigated. Pressure fluctuations in the gas chamber accompanied by bubble formation as well as bubble growth curves were measured. By analysis of the time course of pressure change in the gas chamber, the dependency of the gas flow rate into the gas chamber and the chamber volume on the polytropic coefficient of gas in the gas chamber was discussed. To simulate the bubble formation at a single nozzle in a viscous medium having yield stress, the non-spherical bubble formation model was proposed. The calculated bubble volumes agreed relatively well with the experimental ones.

Ammonia absorption from a bubble expanding at a submerged orifice into water

Abstract To investigate the mechanism of gas absorption from a bubble containing soluble and insoluble components, a gaseous mixture of ammonia and nitrogen was bubbled into water. The growth curve, volume, surface area and shape of the growing bubbles were measured with parameters such as inlet gas composition, gas flow rate and gas chamber volume. The bubble volume decreased with the increasing composition of ammonia in a bubble, decreasing gas chamber volume and decreasing gas flow rate. To reasonably express the mass transfer from the bulk of a gas in a bubble to the bulk of a liquid, the overall mass transfer resistance was evaluated by the mass transfers in the gas phase, interface and liquid phase. The non-spherical bubble formation model combined with the overall mass transfer resistance estimated well experimental bubble shape, bubble volume at its detachment from an orifice, growth rate and mass transfer rate. Moreover, the change of concentration with bubble growth time and the fractional absorption during bubble formation were simulated.

Bubble formation at a single orifice in non-Newtonian liquids

Abstract The effects of various factors on the volumes and shapes of bubbles formed at a single orifice submerged in non-Newtonian liquids, such as physical properties of liquids, gas chamber volume, orifice diameter and gas flow rate were studied. To clarify the bubble formation mechanism, the bubble volume, bubble shape and gas chamber pressure during the bubble growth were measured simultaneously. A revised non-spherical bubble formation model was proposed to describe the bubble formation mechanism in non-Newtonian liquids. The bubble volume, bubble shape and pressure change in the gas chamber calculated by this model agreed well with the experimental results over a wide range of rheological characteristics of liquids.

Behavior of bubble formation in suspended solution for an elevated pressure system

The effects of various factors on the volumes of bubbles formed in suspended solutions under highly pressurized conditions, such as system pressure, orifice diameter, gas flow rate, gas chamber volume and solid particle concentration, were experimentally studied. A non-spherical bubble formation model considering the effects of solid particle concentration and the highly pressurized system is proposed in order to estimate bubble volumes.

Bubble formation in flowing liquid under reduced gravity

Abstract A great deal of research has been done regarding bubble formation from submerged orifices in liquids under the force of gravity for the design of gas-liquid or gas-liquid-solid contacting equipment. On the other hand, little research has been done concerning bubble formation under reduced gravity conditions. For the basic design of the chemical process systems or life-support systems in space stations and on other planets, it is important to clarify the effects of various factors on the volume and shape of bubbles formed at submerged orifices or nozzles under reduced gravity conditions. In order to disperse adequately bubbles in liquids for mass transfer or chemical reaction processes at relatively low gas flow rates under reduced gravity, it is necessary to force bubbles to become detached from nozzles by external forces. In this study, the liquid flow was used as the external force on bubble formation. The aim of this study is to clarify the behavior of bubble formation in flowing liquids under reduced gravity conditions. We experimentally investigated the effects of gas flow rate, liquid flow velocity, and liquid flow direction (cocurrent, countercurrent or cross-current flow) on bubble formation for a period of 1.2 s under reduced gravity conditions that were produced in the 10 m drop tower at the Hokkaido National Industrial Research Institute at Sapporo in Hokkaido. In order to describe theoretically the bubble formation in flowing liquids under reduced gravity conditions, a revised non-spherical bubble formation model was proposed and the calculated results of the bubble volume were compared with the experimental ones.

Behavior of bubbles formed from a submerged orifice under high system pressure

The effects of various factors on the volumes and shapes of bubbles formed at a single orifice under highly pressurized conditions, such as system pressure, orifice diameter, gas flow rate and gas chamber volume, were studied. To clarify the bubble formation mechanism, the bubble shape during the bubble formation and bubble volume were measured. The experimental results were compared with the calculated ones by the revised non-spherical bubble formation model presented by the authors and they agreed qualitatively well.

Mass Transfer in High-Pressure Bubble Columns with Organic Liquids

Oxygen desorption from organic liquids (ethanol (96%), 1-butanol, toluene) and water into nitrogen gas has been studied with an optical sensor. Gas hold-ups and volumetric mass transfer coefficients have been determined in the pressure range of 1-10 bar. In this range both quantities are found to increase with the gas density to the power of 0.24. However, by comparison with literature data and on theoretical grounds, the gas density effect can be shown to depend on the gas velocity and on gas density itself. The effect becomes negligible at gas velocities below 0.01 m/s and at gas densities below about 0.1 kg/m 3 .

Effect of irradiation distance on degradation of phenol using indirect ultrasonic irradiation method

Ultrasound is used as degradation of hazardous organic compounds. In this study, indirect ultrasonic irradiation method was applied to the degradation process of phenol, the model hazardous organic compound, and the effects of irradiation distance on radical generation and ultrasonic power were investigated. The chemical effect estimated by KI oxidation dosimetry and ultrasonic power measured by calorimetry fluctuated for the irradiation distance, and there was a relationship between the period of the fluctuation of ultrasonic effect and the wavelength of ultrasound. The degradation of phenol was considered to progress in the zero-order kinetics, before the decomposition conversion was less than 25%. Therefore, the simple kinetic model on degradation of phenol was proposed, and there was a linear relation in the degradation rate constant of phenol and the ultrasonic power inside the reactor. In addition, the kinetic model proposed in this study was applied to the former study. There was a linear relation in the degradation rate constant of phenol and ultrasonic energy in the range of frequency of 20-30 kHz in spite of the difference of equipment and sample volume. On the other hand, the degradation rate constant in the range of frequency of 200-800 kHz was much larger than that of 20-30 kHz in the same ultrasonic energy, and this behaviour was agreed with the former investigation about the dependence of ultrasonic frequency on chemical effect.

Development of a J-shaped pneumatic valve to control the solid particle circulation rate in a circulating fluidized bed

Abstract To design the two-stage catalytic oxychlorination process which is composed of two reactors utilizing a circulating fluidized bed with a pneumatic valve, it is necessary to control the circulation rate of the catalyst particles and to estimate the gas leakage between two reactors. For this process, a J-shaped pneumatic valve consisting of a downcomer, a horizontal pipe, a riser and two aeration gas inlets was utilized. In this study, the effects of the superficial gas velocities in the downcomer, the horizontal pipe and the riser and the pressure drop in the J-valve on both the mass flux of the solid particle and the gas entrainment with the particles were investigated. The opening or shutting down of the solid particle flow through the J-valve was performed by the control of the superficial gas velocity in the riser. When the valve is open, the mass flux of solid was controlled either by the superficial gas velocity in the downcomer at a constant pressure drop in the downcomer or by the pressure drop in the downcomer at a constant superficial gas velocity. The mass flux of solid was estimated well by a theoretical equation. The gas entrainment throughout a J-valve decreased with decreasing the downward gas velocity in the downcomer, whereas the gas entrainment occurred by not only the downward gas flow in the downcomer but also entrapment in the void in particles.