Bubble injection

Ida M, Naoe T, Futakawa M (2007) Suppression of cavitation inception by gas bubble injection A numerical study focusing on bubble-bubble interaction. Phys Rev E 76 046309... 

In its passage through a water column, a bubble acts as an interface between the liquid and vapour phases, and as such collects surface-active dissolved materials as well as colloidal micelles on its surface. Thus in a well-aerated layer of water, the upper levels will become progressively enriched in-surface-active materials. In the open ocean, an equilibrium undoubtedly exists between the materials carried downward by bubble injection from breaking waves and those carried upward by rising bubbles. In the laboratory, however, this effect will enrich the surface layer with organic materials. 

For cracker catalyst (d = 55 (im, density = 950 kg/m3) fluidised by air, values of umb/umf of up to 2.8 have been found by Davies and Richardson(45). During the course of this work it was found that there is a minimum size of bubble which is stable. Small bubbles injected into a non-bubbling bed tend to become assimilated in the dense phase, whilst, on the other hand, larger bubbles tend to grow at the expense of the gas flow in the dense phase. If a bubble larger than the critical size is injected into an expanded bed, the bed will initially expand by an amount equal to the volume of the injected bubble. When, however, the bubble breaks the surface, the bed will fall back below the level existing before injection and will therefore have acquired a reduced voidage. 

The balance between relative rates of aerobic respiration and water movement were considered in Section 4.3.4. We saw that a subsurfece concentration minimum, the oxygen minimum zone (OMZ), is a common characteristic of vertical profiles of dissolved oxygen and is produced by in situ respiration. Waters with O2 concentrations less than 2.0 ppm are termed hypoxic The term anoxic is applied to conditions when O2 is absent. (Some oceanographers use the term suboxic to refer to conditions where O2 concentrations fall below 0.2 ppm but are still detectable.) As illustrated by Figure 4.21b, this water column is hypoxic in the OMZ. The dissolved oxygen concentrations are presented as % saturations in Figure 4.21c. With the exception of the mixed layer, the water column is undersaturated with respect to dissolved oxygen with the most intense undersaturations present in mid-depths. Surface supersaturations are the result of O2 input from photosynthesis and bubble injection. 

Boundary layer models take a similar approach but attempt to extend the parameterization of gas exchange to individual micrometeorological processes including transfer of heat (solar radiation effects including the cool skin), momentum (friction, waves, bubble injection, current shear), and other effects such as rainfall and chemical enhancements arising from reaction with water. 

In 1990 there was strong interest in data storage devices which exploited trains of small bubbles injected into a garnet film the presence or absence of a bubble representing the binary-coded information. Bubble memories offered the advantage of non-volatility but are now commercially unimportant because of inadequate access speed. 

A few simple differences in the properties of immiscible phases make possible their relative displacement. Most simply, if the phases have different densities they will automatically acquire a relative motion in a gravitational field. Thus in adsorptive bubble separation methods, bubbles injected into a column of liquid rise toward the upper surface. Separation occurs by combining the relative enrichment of components at the bubble interface with the continuous displacement of bubbles through the liquid [33-35]. 

The DOM has been extensively and successfully applied to photocatalytic reactors by the Santa Fe (Argentina) group (see Cassano and Alfano 2000, and references therein) and verified against experimental results (Brandi et al., 1999 Romero et al., 2003). Also Trujillo et al. (2007) have recently used a variant of the DOM, called finite volume scheme to model the effect of air bubbles injected in a fixed catalyst reactor. 

The bubble injection method of contact angle measurement utilizes a sessile bubble below the surface that is immersed in water. It is nearly impossible to measure the sessile bubble contact angle on top surface of a sample immersed in water, of which contact angle is to be measured, because the buoyancy works in the direction to lift the bubble. Although the two methods should yield the identical contact angle, the values obtained by the two methods could deviate significantly depending on the solubility of air in water and the perturbability of the surface by water as described in the previous chapters. 

The observed supersaturation was attributed to bubble injection from the overlying atmosphere (Nakayama et al., 2002). 

Boundaries and global mass conservation impose important constraints on the interstitial velocity. To relate these concepts to experimental measurements described later we focus on bounded channel flows generated by a stream of speed U through a cloud of bubbles injected into a channel and moving vertically with a speed v. When the average separation between the bodies is small relative to the separation of the channel walls, the dipole field and average flow is equivalent to a distributed dipole moment, and averaging (7.34) over the whole volume yields,... 

Marrucci G (1969) A Theory of Coalescence. Chem Eng Sci 24(6) 975-985 Martinez-Bazan C, Montanes JL, Lasheras JC (1999) On the breakup of an air bubble injected into a fully developed turbulent flow. Part 1. Breakup frequency. J Fluid Mech 401 157-182... 

Figure 13.9 illustrates some of the important observations from the gas tracer experiments in the commercial plant. First of all, these experiments confirmed the key CFD prediction that the major part of the gas injected at the middle does indeed largely rise sideways, that is, mostly near the wall rather than through the middle. Second, the rise velocity of the bubbles injected at the side was observed... 

Let us consider experimental results obtained for an ethanol-C02 exchange. Figure 14a shows CO2 bubbles injected into pure ethanol solvent. Compared with ethanol droplets injected into pure CO2 under the same conditions (Figure 4a), the mass transfer is much more intense, and the concentration gradients are greater than those for a relatively slow evaporation of ethanol drops into the supercritical phase. In fact, this process is so intense that deformation and surface instability of the bubbles are clearly visible in... 

Figure 14 Images obtained by means of laser interferometry showing the behavior of CO2 bubbles injected into ethanol for (a) pure solvent and (b) solvent saturated with CO2 T = 363.15 K, P = 8 MPa, the bubble diameter is about 1.6 mm. The interferometric fringes show intensive mass transfer in the solvent...

Martinez-Bazan, C., Montanes, J. L. Lasheras, J. C. 1999 Qn the breakup of an air bubble injected into a fully developed turbulent flow part 2. Size PDF of the resulting daughter bubbles. Journal of Fluid Mechanics 401, 183-207. 

From a starting point of equilibrium with the atmosphere (100% saturation), both helium and argon saturations increase as a result of bubbles injected from breaking waves. Ice formation increases the saturation of argon and decreases the saturation of helium, whereas ice melting has the opposite effect. 

Fig. 1. Processes that influence transfer of gases across the natural air-water interface. Some of these include wind shear, waves, Langmuir circulation, turbulent mixing, and bubbles injected by breaking waves. In addition, films of organic surface active materials reduce direct gas transfer through the air water interface and through bubble surfaces...

This is a report on an outstanding experimental study of the behavior of bubbles injected into pools through quencher orifices. 

Figure 4.9 Coupling PIV with DIA for a single bubble injected into a fluidized bed at incipient fluidization conditions (A) original recorded digital image, (B) PIV velocity field without correction, (C) phase separation by DIA, and (D) instantaneous flow field after PIV-DIA correction. Reprinted from Laverman etal. (2008) with permission from John Wiley and Sons.

The gas flow rates have been controlled with Brooks MFCs. For CO2 injection, a piston with adjustable volume has been used that allows fast injection of a measured amount of CO2 via a nozzle (d= 0.004 m) into the bed. Glass beads (dpartide = 400-600 pm, density = 2525 kg/m ) are fluidized by dried N2, (M if= 0.206 m/s). CO2 is fiUed in a piston at a certain prepressure via a three-way valve (V2 in Fig. 4.56). For fast bubble injection, CO2 inside the piston is then compressed by air at high pressure (6 bar) for fast bubble injection. CO2 at high pressure is subsequently released into the column through a solenoid valve (Vs) opened in 0.01 s. The amount ofC02 injected is determined by different pressure before and after injection and the volume of CO2 filled to the piston. The injection velocity depends on the amount of tracer gas and the injection time. 

In this section, the new analytical technique is applied to study the mass exchange coefficient from bubble-to-emulsion phase in bubbHng fluidized beds for a case of a single bubble injection from the bottom distributor into a... 

Figure 4.59 Snapshots of the tracer gas concentration profile inside the bubble at different times after bubble injection (snapshots are taken every 0.01 s with an injection velocity of 17 m/s). CO2 concentration is presented in mol/l. Reprinted from Dang et al. (2013) with permission from Elsevier.

The latest achievements include the development of a noninvasive measurement technique that allows to measure the gas-phase concentration profile of a CO2 jet injected in a N2 fluidized bed, via the extinction of the IR signal through the bed. This requires the combination of a high speed for the visual and IR spectrum. Ultimately, it has been shown that the bubble-to-emulsion phase mass transfer can be obtained experimentally via bubble injection. 

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