Manabu Iguchi

Measurement of bubble characteristics in a molten iron bath at 1600 °C using an electroresistivity probe

A two-needle, electroresistivity probe was developed to measure bubble characteristics such as gas holdup, bubble frequency, and bubble rising velocity in a molten iron bath at 1600 °C. The probe’s electrode was made of a 0.5-mm platinum wire coated with ZrO2 cement and an outer coat of alumina as insulator. The life of this probe at 1600 °C was 15 to 20 minutes, making it possible to systematically measure bubble characteristics. The measured values of the bubble characteristics were compared with their respective empirical correlations derived from cold model experiments. Good agreement between the measured values and the empirical correlations was seen for each bubble characteristic. This electroresistivity probe allows us to measure bubble characteristics in actual metallurgical reactors with gas injection at high bath temperatures.

Bubble and liquid flow characteristics in a vertical bubbling jet

Abstract A vertical bubbling jet was formed in a cylindrical water bath by injecting air from a centric single-hole nozzle. Bubble characteristics, such as gas holdup (void fraction), bubble frequency, mean bubble rising velocity, mean chord length, were measured using a two-needle electro-resistivity probe. In addition, liquid flow characteristics, represented by the axial mean velocity, rms values of axial and radial turbulence components, Reynolds shear stress, effective kinematic viscosity, skewness and flatness factors for axial and radial turbulence components, were measured with a two-dimensional laser Doppler velocimeter. The flow field in the bubbling jet was essentially classified into two regions with respect to the axial distance from the nozzle exit. One is located near the nozzle where the inertia force of injected gas plays an important role. The other is located far from the nozzle in which the buoyancy force of bubbles governs the flow. In this study the experimental results of liquid flow characteristics in the latter region were compared with those for a single-phase round jet. Turbulence production in the bubbling jet was found to mainly occur in the wake of bubbles and to be approximately two times as large as the turbulence production in the single-phase round jet. The turbulence structures for the two jets also were different from each other.

Structure of turbulent round bubbling jet generated by premixed gas and liquid injection

Abstract An air water mixture was injected into a cylindrical water bath through a single-hole bottom nozzle to generate a vertical turbulent bubbling jet. A parameter called jet volume fraction, defined as the ratio of the air flow rate to the total flow rate of air and water, was introduced to specify the bubbling jet. The jet volume fraction was raised from zero to approximately 0.5 in order to study the effects of bubble concentration on the mean flow and turbulence characteristics in the water phase. Bubble diameters were roughly 2 mm and almost independent of the jet volume fraction. Water velocity measurements were made using a two-channel laser Doppler velocimeter. The effect of the jet volume fraction on the axial mean velocity of water was relatively weak, whereas the turbulence characteristics were significantly modulated. Turbulence production was enhanced with an increase in the jet volume fraction. The skewness and flatness factors, however, were not influenced by bubbles and agreed well with their respective values for single-phase free jets. Simplified methods of correlating the axial mean velocity, the root-mean-square values of the axial and radial turbulence components and Reynolds shear stress were proposed.

Simultaneous measurement of liquid and bubble velocities in a cylindrical bath subject to centric bottom gas injection

Abstract A vertical bubbling jet was generated in a cylindrical bath by injecting air cA vertical bubbling jet was generated in a cylindrical bath by injecting air bubble and liquid in the vertical bubbling jet were measured simultaneously using an electro-resistivity probe and a two-dimensional laser Doppler velocimeter. The output signal of the LDV was processed on a personal computer at a sampling frequency of 2 kHz. Hold signals were eliminated. Discrimination of the bubble and liquid velocities was made by referring to the output signal of the electro-resistivity probe. The accuracy of the present velocity measurement of bubbles and liquid was found to be satisfactory from a comparison with results obtained using an image processing technique for high-speed video pictures, a laser void meter or a two-dimensional electro-resistivity probe.

Velocity and turbulence measurements in a cylindrical bath subject to centric bottom gas injection

Laser Doppler velocimeter (LDV) measurements were made to clarify the fluid flow behavior in a bath subject to centric bottom gas injection. Correlations of the axial mean velocity and turbulence components in the gas-liquid two-phase flow region,i.e., in the bubbling jet region, were proposed as functions of the inner diameter of nozzle, gas flow rate, and densities of gas and liquid. Measured values of the flow rate, momentum, and kinetic energy of water rising upward were approximated satisfactorily by these empirical correlations. In addition, the Reynolds shear stress was calculated and compared with measured values.

Water model experiment on the liquid flow behavior in a bottom blown bath with top layer

Water model experiments were performed to study the effect of top slag on the mean flow and turbulence characteristics in a steel bath agitated by bottom gas injection. The slag was modeled by silicone oil with a density of 0.968 g/cm3 and a kinematic viscosity 100 times larger than that of water at 25 °C. Velocity measurements were made using a two-dimensional (2-D) laser Doppler velocimeter (LDV) in the absence of swirl motions. The output signals of the LDV system were processed on a personal computer to obtain the axial and radial mean velocity components, the root-mean-square (rms) values of the axial and radial turbulence fluctuations, the Reynolds shear stress, and the turbulence production for two cases with and without top slag. The bubbling jet (or the bubble dispersion) region was localized near the centerline of the bath by the presence of the top oil layer. The mean flow and turbulence motions in the recirculation region located outside the bubbling jet region were also suppressed significantly by the top layer. This result could be attributed to the entrainment of top slag into steel in a real system.

Bubble and liquid flow characteristics in a cylindrical bath during swirl motion of bubbling jet

Gas injection into a cylindrical bath through a centric bottom nozzle causes a swirl motion like rotary sloshing. Conditions indicating the initiation and cessation of the swirl motion have been made clear by many researchers. So far, the effect of the swirl motion on transport phenomena in the bath is not clear yet. The present study was made to clarify the bubble characteristics (void fraction, bubble frequency) and liquid flow characteristics (mean velocity, turbulence intensity, Reynolds shear stress) during swirl motion of bubbling jet. These two characteristics were investigated using an electro-resistivity probe and a two-dimensional LDV, respectively.

Model Study of Bubble and Liquid-Flow Characteristics in a Bottom Blown Bath under Reduced Pressure

Gas injection techniques are widely used in metals refining processes. Pressure on the bath surface of reactors is sometimes highly reduced to enhance the efficiency of refining. Many fundamental and practical investigations have been made to clarify the effects of reduced surface pressure on the mixing time and reaction rates of decarburization or desulfurization in the bath. However, details of these effects are not fully understood yet. Since the mixing time and chemical reaction rates are closely associated with fluid flow phenomena in the bath, information on, for example, the total surface area of bubbles rising in the bath and liquid flow induced by the buoyancy force of the bubbles should be accumulated as much as possible. In this study, the so-called water-model experiments were carried out to reveal the effects of reduced surface pressure on the bubble and liquidflow characteristics using a two-needle electroresistivity probe and a two-dimensional laser Doppler velocimeter. At an axial position near the nozzle, each bubble expanded to a volume corresponding to the hydrostatic pressure. The bubble and liquid-flow characteristics in the axial region located farther than this axial position were found to be approximately the same as those obtained under an atmospheric surface pressure.

The structure of turbulence in pulsatile pipe flows

This paper describes the fundamental feature of pulsatile transitional and fully turbulent pipe flows. First, the effect of pulsation on the behavior of turbulent slugs in the developing region of circular pipe is clarified. Second, the distributions of turbulence intensity and Reynolds shear stress in fully turbulent pulsatile pipe flow are compared with their respective distributions in fully turbulent steady pipe flow. Generation region of turbulence and radial propagation time of the turbulence are determined from these distributions. Finally the turbulence structure in pulsatile pipe flows with and without relaminarization, i. e., reverse transition, is made clear by means of the conditional sampling method based on the four quadrant classification.

The mechanism of thermal accretion (mushroom) formation and the bubble and flow characteristics during cold gas injection

Abstract The thermal accretion (or mushroom) which is formed around the tuyere in steelmaking plants was simulated by a cold model and its formation process was observed. Single- and multi-hole nozzles were used for gas injection. The multi-hole nozzle was an artificial mushroom-like nozzle. The bubble and flow characteristics were investigated using an electrical resistivity probe and the laser Doppler velocimeter system. The process of thermal accretion formation consists of the following three stages: (1) generation of a core; (2) separation of the core and regeneration of another core; and (3) steady growth of the accretion. The shape of the thermal accretion and the bubble characteristics changed with each stage, depending on the thermal conductivity of the material of the nozzle. The bubble and liquid flow characteristics for the multi-hole nozzle were examined in comparison with those for the single-hole nozzle. The following results were obtained: (1) the bubbling jet generated by the multi-hole nozzle spread more widely in the radial direction than that generated by the single-hole nozzle; and (2) the circulation flow rate for the former nozzle was 33% larger than that for the latter nozzle.