Gas dispersions

TATTERSON Fluid Mixing and Gas Dispersion in Agitated Tanks TATTERSON Scale-up of Industrial Mixing Processes VVILLIG Environmental TQM... 

Extra coarse 170-220 Filtration of very coarse materials. Gas dispersion, gas washing, and extractor beds. Support of other filter materials. 

If the gas-flow rate is increased, one eventuaHy observes a phase transition for the abovementioned regimes. Coalescence of the gas bubbles becomes important and a regime with both continuous gas and Hquid phases is reestabHshed, this time as a gas-flUed core surrounded by a predominantly Hquid annular film. Under these conditions there is usuaHy some gas dispersed as bubbles in the Hquid and some Hquid dispersed as droplets in the gas. The flow is then annular. Various qualifying adjectives maybe added to further characterize this regime. Thus there are semiannular, pulsing annular, and annular mist regimes. Over a wide variety of flow rates, the annular Hquid film covers the entire pipe waH. For very low Hquid-flow rates, however, there may be insufficient Hquid to wet the entire surface, giving rise to rivulet flow. 

Aerosols (qv) are very finely divided sprays having droplet diameters of l ndash 30 p.m. They are used almost entirely as space sprays for appHcation to enclosures, particularly against flying insects. Aerosols are most conveniendy appHed by the familiar Hquefted gas dispersion or bomb but can be generated on a larger scale by rotary atomi2ers or twin duid atomi2ers. 

G. B. Tatterson, Fluid Mixing and Gas Dispersion inMgitated Tanks, McGraw-HiU, Inc., New York, 1991. 

The physical mass-transfer rate of o2one into water is affected by the gaseous o2one concentration, temperature, pressure, gas dispersion, turbulence, mixing, and composition of the solution, ie, pH, ionic strength, and the presence of reactive substances. Mass transfer of gaseous o2one into... 

TATTERSON Fluid Mixing and Gas Dispersion in Agitated Tanks... 

D E Steinmeyer/ M A / M S / P.E., Distinguished Fellow, Monsanto Company Fellow, Amencan Institute of Chemical Engineers Member, Amencan Chemical Society. (Liquid-in-Gas Dispersion.s)... 

It should be noted that the fraction of column cross-sectional area available for gas dispersers (perforations, bubble caps) decreases when more than one downcomer is used. Thus, optimum design of the plate involves a balance between hquid-flow accommodation and effective use of cross section for gas flow. 

Historically the most common gas disperser for cross-flow plates has been the bubble cap. This device has a built-in seal which prevents liquid drainage at low gas-flow rates. Typical bubble caps are shown in Fig. 14-20. Gas flows up through a center riser, reverses flow under the cap, passes downward through the annulus between riser and cap, and finally passes into the liquid through a series of openings, or slots, in the lower side of the cap. 

Minimum allowable capacity of a column is determined by the need for effective dispersion and contacting of the phases. The types of plates differ in their ability to permit Tow flows of gas and liquid. A cross-flow sieve plate can operate at reduced gas flow down to a point where liquid drains through the perforations and gas dispersion is inadequate for good efficiency. Valve plates can be operated at veiy... 

Many experimental studies of entrainment have been made, but few of them have been made under actual distillation conditions. The studies are often questionable because they are hmited to the air-water system, and they do not use a realistic method for collecting and measuring the amount of entrainment. It is clear that the dominant variable affecting entrainment is gas velocity through the two-phase zone on the plate. Mechanisms of entrainment generation are discussed in the subsection Liquid-in-Gas Dispersions. ... 

Objectives of Gas Dispersion The dispersion of gas as bubbles in a liquid or in a plastic mass is effected for one of the following purposes (1) gas-liquid contacting (to promote absorption or stripping,... 

Methods of Gas Dispersion The problem of dispersing a gas in a liqmd may be attacked in several ways (1) The gas nubbles of the desired size or which grow to the desired size may be introduced directly into the liqmd (2) a volatile hquid may be vaporized by either decreasing the system pressure or increasing its temperature (3) a chemical reaction may produce a gas or (4) a massive bubble or stream of gas is disintegrated by fluid shear and/or turbulence in the liquid. 

Practical separation techniques for gases dispersed in liquids are discussed. Processes and methods for dispersing gas in hquid have been discussed earlier in this section, together with information for predicting the bubble size produced. Gas-in-hquid dispersions are also produced in chemical reactions and elec trochemic cells in which a gas is liberated. Such dispersions are likely to be much finer than those produced by the dispersion of a gas. Dispersions may also be uninten-tionaUy created in the vaporization of a hquid. 

Types of Gas-in-Liquid Dispersions Two types of dispersions exist. In one, gas bubbles produce an unstable dispersion which separates readily under the influence of gravity once the mixture has been removed from the influence of the dispersing force. Gas-hquid contacting means such as bubble towers and gas-dispersing agitators are typical examples of equipment producing such dispersions. More difficulties may result in separation when the gas is dispersed in the form of bubbles only a few micrometers in size. An example is the evolution of gas from a hquid in which it has been dissolved or released through chemical reaction such as electrolysis. Coalescence of the dispersed phase can be helpful in such circumstances. 

Daniel A Crowl/ Ph D / Profe.ssor of Chemical Engineering, Chemical Engineering Depaitment, Michigan Technological University Member, American Institute of Chemical Engineers, American Chemical Society. (Gas Dispersion)... 

Dust Explosions Static Electricity Hazards of Vacuum Hazards of Inert Gases Gas Dispersion... 

See also General References in Gas Dispersion in this section. 

Initial plume volume flux for dense gas dispersion, voliime/time Continuous release rate of material, mass/time Instantaneous release of material, mass Release duration, time T Absolute temperature, K... 

Introduction Gas dispersion (or vapor dispersion) is used to determine the consequences of a release of a toxic or flammable material. Typically, the calculations provide an estimate of the area affected and the average vapor concentrations expected. In order to make this determination, one must know the release rate of the gas (or the total quantity released) and the atmospheric conditions (wind speed, time of day, cloud cover). 

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