Gas-in-liquid emulsions

OCCURRENCE OF DILUTE GAS-IN-LIQUID EMULSIONS IN NATURAL WATERS... 

CONCENTRATED GAS-IN-LIQUID EMULSIONS IN ARTIFICIAL MEDIA. I. DEMONSTRATION BY LASER-LIGHT SCATTERING... 

This molecular argument may explain the earlier-described and repeatedly observed finding with concentrated gas-in-liquid emulsions (see Section 10.4) that, following a period of microbubble growth, the average hydrodynamic diameters (detected by photon correlation spectroscopy) of the microbubble and micellar populations simultaneously decreased. In such situations, microbubble fission may have occurred (following microbubble collision) and the surfactant molecules needed for the expanding... 

J.S. D Arrigo, Surfactant mixtures, stable gas-in-liquid emulsions, and methods for the production of such emulsions from said mixtures, United States Patent No. 4,684,479 (issued 1987). 

Vol. 19 Stable Gas-in-Liquid Emulsions Production in Natural Waters and Artificial Media Second Edition By J.S. D Arrigo... 

Stable gas-in-liquid emulsions, as found in natural waters or when modeled from natural micro bubbles using artificial media, are basically coated microbubbles and represent one more example of self-assembly in science. 

The surfactant-coated microbubbles described in this book range in size from nanoscale (i.e., submicron) to mesoscale (i.e., microns or micrometers), and fall into two categories. First, surfactant-stabilized natural microbubbles ( 0.5-100 pm in diameter), also referred to as dilute gas-in-liquid emulsions, are reviewed and analyzed in Chapters 1-8 of the book. Second, the synthetic or artificially coated microbubbles (from submicron to a few micrometers in diameter), also referred to as concentrated gas-in-liquid emulsions or as lipid-coated microbubbles, are described and their properties examined in detail in Chapters 9-15. 

Foams are agglomerations of gas bubbles separated from each other by thin films (5). Mainly, the problem is concerned with one class of colloidal systems —gas dispersed in liquid—but liquid dispersed in gas, solids dispersed in liquid (suspensions), and liquids dispersed in liquids (emulsions) cannot be ignored. The dispersion of a gas into a liquid must be studied and observed by the food technologist to improve the contact between the liquid and gas phases, the agitation of the liquid phase, and most important, the production of foam 10). 

As in the fluidized beds analysis (Section 3.8.3), a similar simplification has been made in Kunii-Levenspiel model for the material balances in the emulsion phase, where again the corresponding derivatives have been omitted (eqs. (3.529) and (3.530)). As in the case of liquid flow in trickle beds, the flow of the gas in the emulsion phase is considered too small and so the superficial velocities can be neglected. Thus, in trickle beds, from eq. (3.367),... 

Sections 10.2 and 9.1, respectively). Hence, the observed generation of a concentrated gas-in-liquid (macro)emulsion which interacts readily with simultaneously formed large (rodlike) micelles, using the above surfactant mixtures, is to be expected from and confirms such molecular packing considerations. 

A dispersion of liquid-in-gas-in-liquid in which a droplet of liquid is surrounded by a thin layer of gas that in turn is surrounded by bulk liquid. Example In an air-aqueous surfactant solution system this dispersion would be designated as water-in-air-in-water, or W/A/W, in fluid film terminology. A liquid-liquid analogy can be drawn with the structures of multiple emulsions. See also Fluid Film. 

Foam is a disperse system, consisting of gas bubWes, separated by liquid layers. Dispersion of gas in liquid in which the gas cortect is low and the thickness of liquid layers is commensurable to gas bubble size is called gas emulsion or spherical foam ( kugelsctiaiim by Manegold l l ). The shape of bubbles in die gas emulsion is spherical (if their size is not very big) and there is no contact between them. 

In emulsions the dispersed phase and the dispersion medium arc both fluids. The commonest examples arc those in which the two phases are oil and an aqueous medium. They may be of two distincL types a dispersion of fine oil droplets in an aqueous medium, an oU-in-waler (O/YV) emulsion, or of aqueous droplets in oil, a waler-in-ail (YV/O) emulsion. In some special cases a biconlinuous emulsion may he formed in which one phase forms a continuous network in the other. Recently, dilute pas-in-liquid emulsions (dispersions of fine gits bubbles in liquid) have been shown to exist in solutions of gas at high pressure in liquids (for example in carbonated drinks), from this point of view also an aerosol of liquid droplets may be regarded as a dilute liquid-ingas emulsion. 

Liquid continuous phase. Gas-in-liquid dispersions are the foams or the boiling liquids (Prud homme and Khan 1996, Exerova and Kruglyakov 1998). Liquid-in-liquid dispersions are usually called emulsions. The emulsions exist at room temperature when one of the liquids is immiscible or mutually immiscible in the other, e.g. water, hydrocarbon and fluorocarbon oils and liquid metals (Hg and Ga). Many raw materials and products in food and petroleum industries exist in the form of oil-in-water or water-in-oil emulsions (Shinoda and Friberg 1986, Sjoblom 1996, Binks 1998). The solid-in-liquid dispersions are termed suspensions or sols. The pastes, paints, dyes, some glues and gels are highly concentrated suspensions (Schramm 1996). 

ANSYS simulation enables engineers to study multiphase distribution, heat and mass transfer calculations, chemical kinetics and reaction of gas-liquid reactions. These include the design of plate columns, packed columns and bubble columns, a loop reactor and bioreactor development, gas-in-liquid dispersion studies and emulsion design. 

Foamed acid can be useful in increasing effective fracture length, as well as in improving contact in longer treatment intervals. Foamed acid is essentially a gas-in-add emulsion stabilized with a foaming agent. The amount of gas in the foam on a volume basis is called the quality for example, a foam composed of 70% gas and 30% liquid is a 70-quality foam. The gas phase is usually nitrogen, but CO can also be used. Most foamed acids are 60-75 quality. 

Phenomena at Liquid Interfaces. The area of contact between two phases is called the interface three phases can have only aline of contact, and only a point of mutual contact is possible between four or more phases. Combinations of phases encountered in surfactant systems are L—G, L—L—G, L—S—G, L—S—S—G, L—L, L—L—L, L—S—S, L—L—S—S—G, L—S, L—L—S, and L—L—S—G, where G = gas, L = liquid, and S = solid. An example of an L—L—S—G system is an aqueous surfactant solution containing an emulsified oil, suspended soHd, and entrained air (see Emulsions Foams). This embodies several conditions common to practical surfactant systems. First, because the surface area of a phase iacreases as particle size decreases, the emulsion, suspension, and entrained gas each have large areas of contact with the surfactant solution. Next, because iaterfaces can only exist between two phases, analysis of phenomena ia the L—L—S—G system breaks down iato a series of analyses, ie, surfactant solution to the emulsion, soHd, and gas. It is also apparent that the surfactant must be stabilizing the system by preventing contact between the emulsified oil and dispersed soHd. FiaaHy, the dispersed phases are ia equiUbrium with each other through their common equiUbrium with the surfactant solution. 

The choice of scale-up technique depends on the particular system. As a general guide, constant tip speed is used where suspended solids are involved, where heat is transferred to a coil or jacket, and for miscible liquids. Constant power per unit volume is used with immiscible liquids, emulsions, pastes and gas-liquid systems. Constant tip speed seems more appropriate in this case, and hence the rotor speed should be 0.66 Hz. The... 

---