Air Binding of Granular Media Filters

Air bubbles that form in water treatment filters create headloss and can form whenever the total dissolved gas pressure exceeds the local solution pressure. The location of potential bubble formation in filters can be predicted based on measurements of the clean bed headloss with depth, flow rate, and the influent total dissolved gas concentration. Bubble formation within filters can be reduced by increasing the pressure within the filter via greater submergence (water head above the media), lower hydraulic flow rate, or using a more porous media. Bubbles trapped in the bed can be released by “burping,” which can reduce the extent of headloss buildup. Burping is more significant at lower flow rates and within a lower density, higher porosity, hydrophobic anthracite layer.     

Prediction and Measurement of Bubble Formation in Water Treatment

Water utilities can experience problems from bubble formation during conventional treatment, including impaired particle settling, filter air binding, and measurement as false turbidity in filter effluent. Coagulation processes can cause supersaturation and bubble formation by converting bicarbonate alkalinity to carbon dioxide by acidification. A model was developed to predict potential bubble formation during coagulation, and its accuracy was confirmed using an apparatus designed to physically measure the actual volume of bubbles formed. Alum acted similar to hydrochloric acid for initializing bubble formation, and higher initial alkalinity, lower final solution pH, and increased mixing rate tended to increase bubble formation.     

Study on Mechanism of Large Bubble Formation in Slab Continuous Casting Mould with Argon Blowing

A physical model was established to study the mechanism of large bubble formation in a slab continuous casting mould with argon blowing and the effects of operation parameters on it were investigated. The results show that there are two mechanisms of large bubble formation, (i) the aggregation mechanism of bubbles at the upper tip of the nozzle port exit and (ii) the aggregation mechanism of bubbles during the floating process. The former just exists for a certain water flowrate when the gas flowrate is bigger than a certain value, while the latter always exists. Furthermore, the optimal gas flowrate to restrain the large bubble formation was presented by the physical model.     

Dissolved gas method of generating bubbles for potential use in ore flotation

Production and use of dissolved air bubbles were investigated with the purpose of improving the recovery of fine particles in ore flotation processes.The rate and extent of air dissolution were studied under different conditions of pressure, temperature, liquid volume, and gas-solid contact. The process of bubble formation by pressure release was also examined. Assessments made through dissolved oxygen measurements indicated that dissolution of air and the release of dissolved air could be achieved within a 1-minute period. Flotation tests carried out on a ?37 μm magnetite ore sample demonstrated superior results with dissolved gas bubbles compared to conventional bubbles.     

Characteristics of Iron Droplet Ejection Caused by Gas Bubble Bursting Under Reduced Pressure

 Abstract: Bursting of gas bubbles on the free surface of liquid iron produces iron droplets that are ejected into the surrounding atmosphere. The influence of the freeboard pressure on gas bubble bursting was investigated by collecting and measuring the formed droplets in water and in liquid iron systems. In water modelling it was observed that gas bubbles expanded markedly during the floating up when the freeboard was evacuated but the influence of the freeboard pressure on mass of ejection is not significant when the freeboard pressure varied from 0.01 to 0.1 MPa. On the other hand, in steel melt mass of ejection increased 2-3 times when the pressure was reduced from atmospheric pressure to 66.5 Pa.     

New method for simultaneous measurement of viscosity,density and surface tension of metallic melts at high temperatures

A new method for determination of the viscosity of metallic melts based on the measurement of the velocity of gas bubbles in the melt, is developed. Gas bubbles are produced at known depth through a capillary tube. The time needed by the bubble to reach the surface of the melt is measured with the help of a laser beam. The method is tested with reference metals (Sn, Pb, Cu). The results show that there is a large dependence of the bubble velocity on the viscosity although the diameter of the bubbles is large. The recorded pressure curve in the capillary tube during the bubble formation allows the measurement of the surface tension and the density of the metallic melt to be determined by using the method of the maximum bubble pressure.     

Nucleation of bubbles on a solidification front—experiment and analysis

The heterogeneous nucleation of bubbles on an advancing solidification front during the freezing of water containing a dissolved gas has been experimentally and analytically studied. The formation of bubbles resulting from supersaturation of liquids is commonly encountered in different fields such as heat transfer, manufacturing, and bioscience. In this work, the sizes of nucleating bubbles and the concentration profiles of dissolved oxygen and carbon dioxide gases in the water ahead of the solidification front have been measured. From successful comparisons between the measured and predicted critical radii of nucleating bubbles and distributions of dissolved gas content, the phenomena of heterogeneous nucleation in a binary weak solution during the freezing process are quantitatively confirmed. The results show that an increase in gas content at the solidification front in the liquid decreases the free-energy barrier and critical radii of bubbles that are formed on the solidification front. The sizes of the critical radii decrease and the number of nucleating bubbles increase in the early stage of solidification. As the solidification rates decrease at longer times, the content of the dissolved gas in the liquid on the advancing interface decreases and the critical radii of nucleating bubbles increase.     

Bubbling at high flow rates in inviscid and viscous liquids (slags)

The behavior of gas discharging into melts at high velocities but still in the bubbling regime has been investigated in a laboratory modeling study for constant flow conditions. Air or helium was injected through a vertical tuyere into water, zinc-chloride, and aqueous glycerol solutions. High speed cinematography and pressure measurements in the tuyere have been carried out simultaneously. Pressure fluctuations at the injection point were monitored and correlated to the mode of bubble formation. The effects of high gas flow rates and high liquid viscosities have been examined in particular. Flow rates were employed up to 10^-3 m³/s and viscosity to 0.5 Ns/m₂. In order to attain a high gas momentum, the tuyere diameter was only 3 x 10^-3 m. The experimental conditions and modeling liquids were chosen with special reference to the established practice of submerged gas injection to treat nonferrous slags. Such slags can be highly viscous. Bubble volume is smaller than that calculated from existing models such as those given by Davidson and Schüler10,11 due to the effect of gas momentum elongating the bubbles. On the other hand, viscosity tends to retard the bubble rise velocity, thus increasing volumes. To take elongation into account, a mathematical model is presented that assumes a prolate ellipsoidal shape of the bubbles. The unsteady potential flow equations for the liquid are solved for this case. Viscous effects are taken into account by noting that flow deviates from irrotational motion only in a thin boundary layer along the surface of the bubble. Thus, drag on the bubble can be obtained by calculating the viscous energy dissipation for potential flow past an ellipse. The time-dependent inertia coefficient for the ellipsoid is found by equating the vertical pressure increase inside and outside the bubble. This pressure change in the bubble is obtained by assuming that gas enters as a homogeneous jet and then calculating the stagnation pressure at the apex of the bubble.     

Relationship between venous bubbles and hemodynamic responses after decompression in pigs

We present a new pig model for studying relationships between venous gas bubbles and physiologic effects during and after decompression. Sixteen pigs were anesthetized to allow spontaneous breathing. Eight of them underwent a 30-min exposure to 5 bar (500 kPa) followed by a rapid decompression to 1 bar (2 bar/min); the remaining eight served as controls. The pigs were monitored for intravascular bubbles using a transesophageal echocardiographic transducer, and bubble count in the two-dimensional ultrasound image of the pulmonary artery was used as a measure of the number of venous gas bubbles. Effects on physiologic variables of the pulmonary and the systemic circulations were either measured or estimated. We detected venous bubbles in all pigs after decompression, but the interindividual variation was large. The time course of changes in the mean pulmonary artery pressure, in the pulmonary vascular resistance, in the arterial oxygen tension, and in the pulmonary shunt fraction followed the time course of the bubble count. In contrast, such a relationship to the number of venous gas bubbles was not found for the immediate increase in mean arterial pressure and for the changes in the other variables of the systemic circulation. We conclude that the number of venous gas bubbles, as evaluated by the bubble count in the ultrasound image of the pulmonary artery, is clearly related to changes in the variables of the pulmonary circulation in this pig model.     

Effects of pore diameter, bath surface pressure, and nozzle diameter on the bubble formation from a porous nozzle

The effects of the pore diameter, bath surface pressure, and nozzle diameter on the bubble formation from a porous bottom nozzle placed in a water bath and on the behavior of rising bubbles were investigated with still and high-speed video cameras and a two-needle electroresistivity probe. Three types of bubble dispersion patterns were observed with respect to gas flow rate, and they were named the low, medium, and high gas flow rate regimes. The transition boundaries between these gas flow rate regimes were expressed in terms of the superficial velocity at the nozzle exit, i.e., the volumetric gas flow rate per unit nozzle surface area. These transition boundaries were dependent on the pore diameter but hardly dependent on the bath surface pressure and the porous nozzle diameter. The characteristics of rising bubbles in each gas flow rate regime were investigated as functions of the three parameters.     

贫化电炉气液混合顶吹的气泡群形态及搅拌效果

针对贫化电炉还原油枪中气、油混合顶吹对渣层搅拌效果的研究,等比例制作贫化电炉水模型,进行气液混合喷吹实验。实验结果表明：顶吹气液两相混合射流在熔池中形成大小不一的气泡或气泡群,气泡本身的形变、破裂以及气泡间的团聚运动决定了油枪对熔池的搅拌效果。通过测量不同流量下气泡群尺寸的变化,分析气液流量混合比对熔池搅拌效果的影响。     

Investigation into the Total Dissolved Gas Dynamics of Wells Dam Using a Two-Phase Flow Model

Bubbles entrained by spilled water at hydroelectric projects increase the concentration of total dissolved gas (TDG), which may lead to gas bubble disease in fish. In this paper, the TDG dynamics downstream of Wells Dam are investigated using a two-phase flow model that accounts for the effect of the bubbles on the flow field. The TDG is calculated with a transport equation in which the source is the bubble/liquid mass transfer, a function of the gas volume fraction and bubble size. The model uses anisotropic turbulence modeling and includes attenuation of normal fluctuation at the free surface to capture the flow field and TDG mixing. The model is validated using velocity and TDG field data. Simulations under two plant operational configurations are performed to gain a better understanding of the effect of spill operations on the production, transport, and mixing of TDG. Model results indicate that concentrated spill releases create surface jets that result in the lowest TDG concentration downstream. On the other hand, spreading the spill release, with moderate flow through each gate, produces the highest TDG values downstream as a result of more air available for dissolution and smaller degasification at the free surface.     

Bubble Formation through Reaction at Liquid‐Liquid Interfaces

Slag foaming is an important phenomenon in steelmaking processes with both beneficial as well as negative effects. The present work is part of the wider project on the modelling of slag foaming, with special reference to dynamic conditions. Since bubble formation is the first step to foam formation, the present work was carried out in an attempt to simulate the bubble formation in slag/metal reactions in steelmaking processes by water‐modelling experiments. The bubble formation due to the gas produced through chemical reaction at the interface between oleic acid and sodium bicarbonate solution was systematically monitored. The chemical reaction rate was varied by varying the concentration of sodium bicarbonate. The bubbles were observed to be generated in the heavier aqueous phase just below the water‐oil interface. The bubbles penetrated the interface and escaped through the oil phase. The rate of the reaction was estimated from the volume of the gas that passed the water/oil interface. It was observed that the bubble formation and bubble growth mechanism were influenced by the reaction rate while the bubble size seemed to be unaffected by the reaction rate.     

Horizontal Injection of Gas–Liquid Mixtures in a Water Tank

Experiments were carried out to investigate the behavior of horizontal gas–liquid injection in a water tank. Measurements of bubble properties and mean liquid flow structure were obtained. The turbulence in the liquid phase appears to help generating bubbles with relatively uniform diameters of 1–4?mm. Both bubble properties and mean liquid flow structure depended on the gas volume fraction and the densimetric Froude number at the nozzle exit. It was found that the bubbles strongly affected the trajectory of the water jet, which behaved similarly to single-phase buoyant jets. However, at gas volume fractions smaller than about 0.15, the water jet completely separated from the bubble core. Bubble slip velocity was also found to be higher than the terminal velocity for isolated bubbles reported in the literature. Dimensionless correlations were proposed to describe bubble characteristics and the trajectory of the bubble plumes and water jets as a function of the gas volume fraction and the densimetric Froude number. Finally, applications of the results for aeration/mixing purposes are presented.     

Characterization of gas bubbles injected into molten metals under laminar flow conditions

Velocity and volume measurements of gas bubbles injected into liquid metals under laminar flow conditions (at the orifice) have been achieved. A novel experimental approach utilizing noises generated by bubbles was used to collect the necessary data. Argon gas was bubbled through tin, lead, and copper melts, and gas bubble formation frequencies (and hence bubble sizes) were determined. It was found that the bubble size generated for a particular orifice diameter was dependent upon the magnitudes of the orifice Froude and Weber numbers. Maximum formation frequencies increased slightly with decreasing orifice diameter, and the transition point from varying to constant frequency occurred at an orifice Weber number of approximately 0.44. Velocities of gas bubbles rising through the metals were greater than those previously reported for studies in which only one bubble was in the melt at any time. Effective drag coefficients of the rising bubbles were found to agree with data previously generated in aqueous systems. Formerly Graduate Student, Michigan Technological University     

Characterization of gas bubbles injected into molten metals under laminar flow conditions

Velocity and volume measurements of gas bubbles injected into liquid metals under laminar flow conditions (at the orifice) have been achieved. A novel experimental approach utilizing noises generated by bubbles was used to collect the necessary data. Argon gas was bubbled through tin, lead, and copper melts, and gas bubble formation frequencies (and hence bubble sizes) were determined. It was found that the bubble size generated for a particular orifice diameter was dependent upon the magnitudes of the orifice Froude and Weber numbers. Maximum formation frequencies increased slightly with decreasing orifice diameter, and the transition point from varying to constant frequency occurred at an orifice Weber number of approximately 0.44. Velocities of gas bubbles rising through the metals were greater than those previously reported for studies in which only one bubble was in the melt at any time. Effective drag coefficients of the rising bubbles were found to agree with data previously generated in aqueous systems. R. J. ANDREINI, Formerly Graduate Student, Michigan Technological University,     

Bubble formation during horizontal gas injection into downward-flowing liquid

Bubble formation during gas injection into turbulent downward-flowing water is studied using high-speed videos and mathematical models. The bubble size is determined during the initial stages of injection and is very important to turbulent multiphase flow in molten-metal processes. The effects of liquid velocity, gas-injection flow rate, injection hole diameter, and gas composition on the initial bubble-formation behavior have been investigated. Specifically, the bubble-shape evolution, contact angles, size, size range, and formation mode are measured. The bubble size is found to increase with increasing gas-injection flow rate and decreasing liquid velocity and is relatively independent of the gas injection hole size and gas composition. Bubble formation occurs in one of four different modes, depending on the liquid velocity and gas flow rate. Uniform-sized spherical bubbles form and detach from the gas injection hole in mode I for a low liquid speed and small gas flow rate. Modes III and IV occur for high-velocity liquid flows, where the injected gas elongates down along the wall and breaks up into uneven-sized bubbles. An analytical two-stage model is developed to predict the average bubble size, based on realistic force balances, and shows good agreement with measurements. Preliminary results of numerical simulations of bubble formation using a volume-of-fluid (VOF) model qualitatively match experimental observations, but more work is needed to reach a quantitative match. The analytical model is then used to estimate the size of the argon bubbles expected in liquid steel in tundish nozzles for conditions typical of continuous casting with a slide gate. The average argon bubble sizes generated in liquid steel are predicted to be larger than air bubbles in water for the same flow conditions. However, the differences lessen with increasing liquid velocity.     

Thermal rejection and growth of gas bubbles in electrodeposited nickel

In thick sections of a nickel electrodeposit annealed over the temperature range 200° to 1000°C, tiny (<100Å diam) gas bubbles were first observed after anneals at 500°C. Most of the hydrogen in the specimens was evolved before or during the formation of the bubbles. With increasing annealing treatment the gas bubbles coarsened, large grain-boundary bubbles developed, and significant swelling occurred. Bubble growth ceased at about 6 pct swelling during a 1000°C anneal. During annealing, considerable softening occurred in two stages, a rapid stage followed by a slow stage. Rapid softening constituted the largest portion of the total softening and is thought to be associated with redistribution of impurities and lattice defects, during which bubble nuclei are formed. Slow softening coincided with the appearance of visible bubbles, many of which were found to pin grown-in dislocations; coarsening of these bubbles is believed to cause slow softening. Deposits from certain types of plating baths are quite susceptible to swelling, and in these cases the degree of swelling increases strongly with increasing initial hardness of the deposits when some critical hardness is exceeded.