Bubble Separation Research Articles

Dynamics of two interacting bubbles in an acoustic field

This paper contains theoretical and experimental results on the relative motion of two pulsating spherical bubbles along their line of centres, in a liquid subjected to an acoustic field. The motion is caused only by the secondary Bjerknes forces. The linear theory for the secondary Bjerknes forces is modified by introducing a model for the coupling between the pulsations of the interfaces. The secondary effects introduced by this model are determined by the frequency indices of the bubbles, defined as the ratio of the forcing frequency to the resonance frequency of each bubble. The equations of motion are set up with the conservative Lagrangian formalism. This approach allows an analytical study of all the possible patterns of motion and the identification of the set of governing parameters: total energy and interaction coefficient. A pair of bubbles driven far from their resonance frequencies may attract or repel, depending on whether their frequency indices are respectively on the same side or on either side of unity. For forcing frequencies close to resonance, the proposed model predicts a new pattern of relative motion, namely a periodic motion (oscillations) around an equilibrium bubble separation. The experimental study identifies this new periodic pattern of motion, for acoustically levitated bubbles of nearly equal sizes, forced near their resonance frequency. A quantitative study on the variation of the relative velocity with the separation between the bubbles shows that the conservative model for the motion holds for large and moderate separations. The following information is reported: (a) a classification of the pairs of bubbles, based upon their phase difference in oscillations; (b) a model for the coupling of the pulsations of two bubbles; (c) formulas for the interaction force field of two pulsating bubbles, for all of the categories; (d) a study of all possible patterns of relative motion (collisions, scattering and oscillations), with their conditions of occurrence; (e) experimental data for two attracting bubbles; (f) experimental data for two oscillating bubbles.

Dissolved air precipitation/solvent sublation for oil-field produced water treatment

We report on the use of dissolved air precipitation (DAP) for bubble generation for use in solvent sublation bubble columns. Solvent sublation is a non-foaming adsorptive bubble separation distinguished by the presence of an immiscible layer on top of the water column which aids in the separation of hydrophobic compounds. The generation of very fine bubbles is necessary for effective separation. With DAP, air is saturated into water at a moderate pressure (480–820 kPa) in a packed column saturator. Then the pressure is released through a valve into the water column where the air precipitates, forming 60–100 μm diameter bubbles. Experiments were performed in a pilot-scale semi-batch bubble column using both aliphatic and aromatic hydrocarbons as test compounds in a simulated produced water. With a precipitated gas flow rate of 100 ml min −1 , 95% removal of dissolved octane was achieved with 25 min treatment time, and 75% removal of micro-disperse decane was achieved in 30 min. For dissolved ethylbenzene and toluene, 40% removal was achieved in 360 min at an air delivery rate of 60 ml min −1 , and 70% removal was achieved in the same period with an air delivery rate of 200 m lmin −1 . These results are explained in terms of the physical–chemical properties and removal mechanisms, and are compared to a mathematical model of the separation process.

NUCLEATE POOL BOILING FROM PLAIN AND ENHANCED SINGLE TUBE TO R12 AND R134a FOR AIR-CONDITIONING EVAPORATORS

Measurements of pool boiling heat transfer coefficients in pure R12 and R134a are reported for a plain tube (FYI) and three enhanced tubes: (Screen Matrix tube, (SM) and two integral finned tubes: Radial (RF) and longitudinal LF). The data were taken at saturation temperatures of -5, and 5 , and heat flux range from 2 x 103 to 104 W/m2. All enhanced tubes provide higher boiling coefficients than the plain tube does. The slopes of the boiling coefficient vs the heat flux curves for enhanced tubes are smaller than those for the plain tube, indicating the dominating effect of enhanced surfaces conditions. The mechanism describing the generation, growth and separation of bubbles for tested enhanced tubes was elaborated . The highest boiling coefficient was found to belong to the screen matrix tube , having the highest nucleation sites density. Additional achievement was observed when R134a was tested at the considered operating condition. Two correlations for predicting the boiling coefficients from the present considered surfaces were developed with satisfactory accuracy for the design of refrigerant flooded evaporators.

Deepwater Blowouts: Modeling for Oil Spill Contingency Planning, Monitoring, and Response

ABSTRACT This paper describes work in progress in the Environmental Engineering Division of SINTEF's Applied Chemistry Institute in Trondheim, Norway. The modeling work relies heavily on past and planned future field and laboratory work for calibration and verification data. Because these data remain incomplete, the results presented are tentative. The deepwater blowout model DeepBlow includes hydrate formation, gas dissolution, and separation of bubbles and oil droplets from the oil-gas-water plume as key processes which have been ignored in previous models, and which appear extremely important in determining the dynamics of the blowout plume. Time-variable vertical current profiles and the vertical density profile affect the depth of penetration of the plume. The oil droplet distribution in the blowout plume, combined with the above factors, determines to a large extent the time-varying footprint of the oil on the sea surface. Oil Spill Contingency And Response (OSCAR) model simulations demonstrate that mechanical response may be reasonably effective, or not, depending on the eventual correct values of key underlying parameters. Future field trials will be critical in establishing such values. The results demonstrate the usefulness of these models as tools for guidance of environmental monitoring and response activities during an actual blowout event.

Trends in catalytic reaction engineering

Catalytic reactions in multiphase systems are prevalent in production of fuels, bulk and specialty chemicals, pharmaceuticals, materials, food and feed, etc. Making useful products, at economical yields and selectivities, from the diverse chemistries in such a broad range of applications requires the ability to quantify the interplay of transport phenomena and kinetics. This is the domain of catalytic reaction engineering. In this paper the current state of the art of this discipline is briefly reviewed with the emphasis on describing the increased use of fundamentals in multiphase reactor modeling and scale-up. Packed beds, trickle beds, slurry bubble columns, simultaneous reaction and separation via catalytic distillation, membrane reactors and trickling solids adsorbent, as well as nonconventional multiphase reactor operations are discussed.

Hydrodynamic processes in dynamic bubble pressure experiments: Part 3. Oscillatory and aperiodic modes of pressure variation in the capillary

The effect of the process of bubble separation from the capillary tip on the hydrodynamic flow in maximum bubble pressure experiments is analysed. The existence of both aperiodic and oscillatory modes in the gas pressure distribution along a narrow capillary is predicted. The equations are derived which define the conditions for the transitions between the modes and describe the relationship between the pressure oscillation frequency and amplitude. The effect of fast pressure oscillations on a liquid meniscus after a bubble detachment is discussed on a qualitative basis. The possibility of a qualitatively different mechanism for overcoming the maximum bubble pressure is considered. Model experiments with capillaries of different lengths and diameters are performed for pure water. The results of these experiments agree with the theoretical predictions.

Special features of boiling of a slightly subcooled liquid

Slightly subcooled boiling is characterized by the fact that vapor bubbles that form at active sites on the heater surface grow continuously and, having attained a maximum size, separate and float. The frequency of bubble separation, which determines the rate of heat transfer, depends on the degree of subcooling of the boiling liquid.

Bubble fractionation of enantiomers from solution using molecularly imprinted polymers as collectors.

Adsorptive bubble separation methods have been used to enrich components from both heterogeneous and homogeneous solutions. These methods are particularly effective for processing large solution volumes at low cost. Previous work demonstrated that chiral, surface-active collectors could be used to enrich enantiomers from homogeneous solution in a foam fractionation process. In a significant extension of this work, the use of highly selective molecularly imprinted polymers (MIPs) and heterogeneous solutions for the bubble flotation of enantiomers was evaluated. The high selectivity and ease of recycling of the MIP make this a potentially powerful approach for process-scale separations from large-volume bulk solutions. New MIPs were produced with low swelling properties which allowed them to retain enantioselectivity after numerous recyclings.

The effect of capillary characteristics on the results of dynamic surface tension measurements using the maximum bubble pressure method

The dynamic surface tension of Triton X-100 solutions was measured using the maximum bubble pressure method (MBPM). The data obtained depended on the geometry and material of the capillaries employed. It is shown that reliable results are obtained with short capillaries of hydrophobic internal surfaces. The effect of the ratio of the bubble volume to measuring system volume on the measured dynamic surface tension is studied. Recommendations are given for the optimum choice of the capillary to be employed in the MBPM. High-speed video imaging is used for studying the hydrodynamics of the liquid meniscus after bubble separation in hydrophilic and hydrophobic capillaries.

Experimental investigation of a turbulent bubbly mixing layer

An experimental investigation of a turbulent air-water bubbly flow in a plane vertical mixing layer is presented. An important characteristic of this bubbly flow is that the slip velocity is of the same order of magnitude as the liquid velocity. For various inlet conditions of liquid velocity and void fraction, the distributions of velocity, turbulence intensity and void fraction were measured. The mean velocity fields in both phases present self-similar evolutions that preserve the main characteristics of single-phase mixing layer. The spreading rate of the mixing layer is found to be significantly greater in bubbly flow than in single-phase flow. Moreover, the global structure of the flow proved to be sensitive to void fraction contrast at the inlet. The void fraction distributions exhibit a pronounced peak in the wake of the splitter plate. This peak decreases in intensity and is displaced significantly in the lateral direction. The turbulence intensity is also greater in bubbly mixing layers: it is shown that this effect is related to the bubble drift velocity. A heuristic model for the separation of bubble and shear-induced velocity fluctuations is presented and discussed. Finally, it is observed that the RMS velocity of the gas phase results from combined effects of turbulent dispersion and self-induced fluctuating motions of the bubbles.

Displacement of horizontal layers by bubbles injected into fluidised beds

Mixing in bubbling gas-fluidised beds comes primarily from bubble motion through the particulate phase and this has previously been studied experimentally by examining the displacement of a marked layer of particles by rising bubbles. The reported experimental profiles show considerable variation in the distortion of the interface. In this work, the distortion of the interface by a two-dimensional bubble of initial radius a, rising inviscidly in a semi-infinite channel of width b, is examined theoretically and the results applied to the interpretation of experimental data from fluidised beds, assuming that the particulate phase may be modelled as an inviscid fluid. Two new contributions are considered: (i) the contribution from the injection of the bubble, and (ii) the effect of initial finite separation, z 0, of the bubble and marked layer. Numerical calculations and analytic expressions show that the distortion of the interface depends on z 0 b and not z 0 a . When z 0 b < 0.4 , the distortion of the interface is shown to be critically dependent on the initial separation of bubble and layer. The area between the final and initial position of the layer, the partial drift area (Eames et al., 1994, J. Fluid Mech. 275, 201–223), is equal to the area of the bubble's primary wake. A review of experimental results shows that many of the results were taken for z 0 b < 0.4 , even though z 0 a was large. Qualitative comparisons are made between theory and experiment which show some agreement.

MOTION OF INTERACTING GAS BUBBLES IN A VISCOUS LIQUID INCLUDING WALL EFFECTS AND EVAPORATION

The motion of single and multiple gas bubbles in an otherwise stationary liquid contained in a closed right vertical cylinder is investigated using a modified volume-of-fluid (VOF) method incorporating surface tension stresses. An isolated bubble was considered in a separate paper [4], where the initial bubble radius was small in comparison with that of the cylinder and watt effects were negligible. In this work the focus is on the interference effects during the motion of two initially spherical bubbles in a gravitational field, as well as the influence of the container wall on the bubble motion: the initial bubble diameter in the present study is more than half the cylinder diameter. The bubble size is also much larger than that required to satisfy the condition in which the gas can be treated as incompressible. In addition, the effect on bubble motion of the inclusion of evaporation at the gas-liquid interface as well as the bursting of a bubble through a five surface are considered. The modified VOF method used in this study is able to identify and physically treat features such as bubble deformation, cusp formation, breakup, and joining. Results are presented in a two-dimensional as well as a three-dimensional coordinate framework. The bubble motion and deformation are characterized by the Reynolds number, the Bond number, the density ratio, the viscosity ratio, the ratio of the cylinder radius to that of the initial bubble, and for interacting bubbles, the initial bubble separation.

Triggering basaltic volcanic eruptions by bubble-melt separation

Understanding the processes by which volcanic eruptions are triggered is crucial for volcanic hazard prediction and assessment. In intermediate and silicic magmas, where water is the dominant volatile phase1,2, 'second boiling' provides an effective eruption trigger1—as the magma cools and crystallizes, volatiles are increasingly concentrated in the residual melt where they eventually become saturated and are exsolved, thereby raising the magma pressure to the point of eruption1,2. In contrast, in basaltic magma chambers in which carbon dioxide is the dominant volatile phase, the effect of second boiling is to decrease the chamber pressure. But basaltic magmas are also relatively inviscid, so volatile bubbles can separate from the turbulently convecting melt to produce a foam layer at the chamber roof3,4: decompression of the rising bubbles can increase the chamber pressure and so trigger an eruption5,6. Here we model the complex competition between the processes of magma cooling and bubble ascent. We find that in basalt of very low viscosity (1–10Pas), bubble separation dominates and can increase the reservoir pressure by as much as 10 MPa (sufficient to trigger an eruption7) on timescales of 1–10 years, comparable to the duration of eruptive episodes at Kilauea volcano, Hawaii4,8.

Treatment of Textile Wastewater by Foam Flotation

Foam flotation (adsorptive bubble separation) experiments in a packed bed reactor were conducted to investigate the efficiency of this process in reducing the color, turbidity and chemical oxygen demand (COD) of the textile wastewater obtained from a dyeing and finishing plant. Both hexadecyltrimethylammonium bromide (HTA) and sodium lauryl sulfate (NLS) were tested as a potential collector agent for foam flotation. Experimental runs have been extensively performed to determine the effects of the wastewater pH, air flow rate and amount of collector agent employed on the nephalematic turbidity unit (NTU) and color reductions and COD removal. The experimental results were utilized to determine the optimum operating conditions of those variables. Chemical coagulation using polyaluminum chloride (PAC) and organic polymer was also tested to show whether this method has complementary effect on enhancing the treatment efficiency of foam flotation.

チタン合金精密鋳造時の凝固に及ぼす遠心力の影響

The melt flow and mold filling in precision casting of a Ti-6Al-4V alloy has been examined by casting trials, in which the molten alloy with an amount intentionally adjusted to be less than that for complete filling is poured into mold cavities under some centrifugal force. By rotation of the tree on the horizontal plane, the molten alloy flows into the mold cavities keeping contact with one of the vertical inside walls of a gate and a mold cavity. Solidification in the mold cavity proceeds mainly in a manner of directional solidification by accumulating the solidifying layer from the far end of a mold cavity where the centrifugal force is maximum to the gate at which the force is a minimum. The centrifugal force imposed on the melt enhances separation of gas bubbles which may evolve during pouring the melt into the mold cavity, reduces the number of gaseous defects to a level negligibly small at 30G, and improves mechanical properties of castparts. Detailed observation of the defects showed that dendrites appears at the bottom of porosity where the inter-dendritic melt is sucked to the half thickness side surface by solidification shrinkage. Micro segregation of solute in a dendrite tip seems to be caused not during solidification but during transformation from the β to α phase by mapping analysis.

Motion of Liquid around a Vapor Bubble in Saturated Pool Nucleate Boiling in Region of Interfered Bubble.

In order to elucidate the mechanism of saturated pool nucleate boiling in the region of the interfered bubble from a local viewpoint, flow visualization of liquid motion caused by the vapor bubble action was carried out. In this experiment, two hydrogen generating electrodes for supplying vapor bubbles were provided on the heating surface. Within the present study, liquid speed is accelerated through the behavior of the neighboring bubble. Liquid speed is mainly decided by liquid extrusion action due to vapor bubble growth and the entaild flow effect after separation of the vapor bubble.

Adsorption Behavior of Organic Substances onto Bubble Surface in Nonfoaming Bubble Separation.

The adsorption behavior of organic substances onto bubble surface in nonfoaming bubble separation was investigated. Experiments were conducted with a bubble column equipped with a droplet collector or a trap at its top. Crystal violet (CV) and humic acid (HA) were used as examples of surface-active substances. The amount adsorbed onto the bubble surface was calculated through the mass balance in the bubble column. Two adsorption parameters, equilibrium constant, K, and saturated surface density on bubble surface, γ, were determined for CV and HA, respectively, by fitting of the experimental results to a Langmuir-type isotherm. Using the value of K, γ and the intrinsic volumetric flow rate of droplets at the liquid-atmosphere interface, the variation of enriching ratio, E, with concentration of the solution was estimated and compared to the experimental results. The calculated E was in good accordance with the experimental ones for both CV and HA.

Harvesting of Saccharomyces cerevisiae using colloidal gas aphrons

AbstractAdsorptive bubble separation using Colloidal Gas Aphrons (CGA) can be used for harvesting of microorganisms. The effect of various operating parameters, for example pH, biomass loading, dispersed and continuous phase velocity, surfactant type and concentration, has been studied on the recovery of Saccharomyces cerevisiae. The operating conditions were optimised for maximum separation. The results obtained have been compared with the prediction of an model earlier.

Bubble Behaviors in Weakly Conductive Liquid Flow applied by an Electromagnetic Field under Microgravity Environment.

An air bubble separation and removal system is necessary, especially in space, for fluid processing devices. We have developed a new bubble separator for microgravity environments in which bubbles are pushed through a hydrophobic membrane by an electromagnetic body force. Our ground experiments using the separator model confirmed that air bubbles can be removed efficiently by an electromagnetic force. Subsequently, we carried out microgravity tests of 10-second duration in a drop shaft. In these tests, the effect of the electromagnetic force on bubble behavior was visually investigated and successfully recognized.

Application of nonfoaming bubble separation to enrichment of dilute dye solution.

Application of nonfoaming bubble separation to enrichment of dilute dye solution.