Bubble Flow Characteristics Research Articles

Bubble and liquid flow characteristics in a wood’s metal bath stirred by bottom helium gas injection

A model study was carried out to elucidate bubble and liquid flow characteristics in the reactor of metals refining processes stirred by gas injection. Wood’s metal with a melting temperature of 70 °C was used as the model of molten metal. Helium gas was injected into the bath through a centered single-hole bottom nozzle to form a vertical bubbling jet along the centerline of the bath. The bubble characteristics specified by gas holdup, bubble frequency, and so on were measured using a two-needle electroresistivity probe, and the liquid flow characteristics, such as the axial and radial mean velocity components, were measured with a magnet probe. In the axial region far from the nozzle exit, where the disintegration of rising bubbles takes place and the radial distribution of gas holdup follows a Gaussian distribution, the axial mean velocity and turbulence components of liquid flow in the vertical direction are predicted approximately by empirical correlations derived originally for a water-air system, although the physical properties of the two systems are significantly different from each other. Under these same conditions, those turbulent parameters in high-temperature metals refining processes should thus be accurately predicted by the same empirical correlations.

Flow characteristics of horizontal bubbly pipe flow

Contrary to Kocamustafaougullari et al's conclusions, their experimental void and velocity profiles for horizontal bubbly flow are in fact compatible with a relationship assumed by Beattie between local void fraction and local velocity. Moreover, predictions based on the assumption (an independence of velocity profile on void profile and equations for (i) voidage profile, (ii) a two-phase “universal” velocity profile, (iii) a two-phase version of the smooth tube friction factor equation and (iv) average void fraction) are also supported by results of the experimental study. Some apparent inconsistencies in the data were uncovered while assessing their compatibility with the theory.

Bubble and liquid flow characteristics in a vertical bubbling jet

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.

Axial development of interfacial area and void concentration profiles measured by double-sensor probe method

Interfacial area concentration is an important parameter in modeling the interfacial transfer terms in the two-fluid model. In this paper, the local geometric and statistical characteristics of upward co-current dispersed bubbly flow in a pipe have been studied both at the entrance ( L D = 8 ) and at a region far away from the entrance ( L D = 60 ). The test section was a 5.08 cm i.d. and 375 cm long Lucite pipe. Four liquid flow rates ranging from 0.1 to 1.0 m s −1 were used in combination with four different gas injection rates ranging from 0.02 to 0.1 m s −1. A double-sensor probe was employed to measure the radial profiles of void fraction, interfacial area concentration, Sauter mean diameter, bubble velocity and bubble frequency. The wall peak of the void fraction profile was established within a short distance from the entrance. The flow characteristics changed very little from the entrance region to the fully developed region except for the flow case of j 1 = 0.1 m s −1. The area averaged flow quantities were also presented.

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.

Bubbly flows through a converging–diverging nozzle

Characteristics of bubbly flow through a vertical, two-dimensional, converging–diverging nozzle are investigated theoretically and experimentally. First, a new model equation of motion governing a dispersed bubble phase is proposed. This is compared in detail with those proposed previously by several researchers. Next, hyperbolicity of the resultant systems of governing equations for the bubbly flow is investigated in detail. Numerical simulations of bubbly flows through a converging–diverging nozzle are carried out by using the proposed system of model equations. In order to check the validity of the numerical results and then the proposed system, they are compared with the experiments which were performed previously in the authors’ laboratory in a water–nitrogen blow-down facility. It will be shown that the numerical results obtained by using the proposed system of model equations agree well with the experiments.

Technical note a gas-liquid drift-flux model for flotation columns

It is shown that since the flow characteristics of bubbles are dissimilar to those of solids in flotation columns, the gas-liquid drift-flux, J g1, is significantly different from the solid-liquid drift-flux, J s1, in two-phase systems. This is attributed to the fact that unlike the motion of solid spheres in water, the ascent of bubbles is influenced by their virtual mass, arrangement in a swarm, and most importantly, the presence of surfactants which are required in column flotation operations.

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

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.

Mechanistic model for onset velocity prediction for regime transition from bubbling to turbulent fluidization

An earlier study revealed a flow regime transition mechanism in that as the bubble flow characteristics vary from the coalesced to breakup conditions, the prevailing flow regime undergoes transition from bubbling to turbulent fluidization. On the basis of this mechanism, a mathematical model is developed to account for the onset velocity for this regime transition. Comparisons of the model prediction with the experimental data are also made

Flow Characteristics of Bubbles in a Single-Layer Gas-SolidFluidized Bed.

A single-layer gas-solid fluidized bed is developed by setting two glass plates vertically with a spacing space of which is slightly greater than the diameter of the particles. The behavior of gas bubbles is observed in detail by introducing high shutter-speed video cameras with 1/2000 s exposure time and an image analyzer.It is found that the rising velocity of bubbles in the single-layer fluidized bed is almost the same as that in the ordinary two-dimensional fluidized bed. The effect of gas velocity and height from the distributor on bubble growth is almost the same as in the three-dimensional fluidized bed despite its extremely small bed width.

Fluctuation characteristics of bubbly liquid flow in converging-diverging nozzle

The pressure fluctuation characteristics in bubbly liquid flow in a converging-diverging nozzle are interpreted on the basis of the previous theoretical results concerning the possible wave modes in bubbly liquid flow and their properties. The experiment is performed in a visual blowdown facility using water and nitrogen gas. The intensity and power spectrum density of the pressure fluctuations are measured, as well as the velocities of liquid and bubbles, the void fraction and the chord length of bubbles. All the fluctuation characteristics and their relation with the main stream condition are compatible with the theoretical predictions. The instability of the convection mode in the presence of the velocity slip and the cut off of the propagation modes in moderate frequency are demonstrated.

Effect of bubble size on internal characteristics of upward bubble flow.

Bubble flow characteristics were investigated experimentally in nitrogen gas-water in a spuare channel using a laser Doppler anemometer and a double-sensor conductance probe under the same flow rate conditions. The size of the bubbles was controlled by changing the mixing conditions and by adding a surface active agent to water. Thus, four sets of experiments were conducted. Experimental results show that the reduction in bubble size flattens the gas-phase distribution and increases the number density of bubbles. The reduction in bubble size leads to a decrease in turbulence and an increase in water and bubble velocities, but an extreme reduction does not bring about a further increase in both velocities, although it leads to a further decrease in turbulence. Turbulence suppression was observed in layer-type bubble flows. This type of flow has a peculiar profile of water velocity.

On the Characteristics of Bubble Flow with Low Void Fraction in a Two-Dimensional Convergent-Divergent Nozzle

On the Characteristics of Bubble Flow with Low Void Fraction in a Two-Dimensional Convergent-Divergent Nozzle