Sources of Bubbles

Decomposition of batch materials can produce extremely large quantities of gases such as CO2, SO3, NOx, H2O, etc. Reactions with metals in contact with the melt can generate oxygen, carbon dioxide, or hydrogen by electrolytic reactions. Corrosion of refractories can open previously closed pores to the melt, releasing the gas contained in those pores into the melt. Residual carbon in refractories, or carbide refractories such as SiC, can react with oxide melts to form CO2 or CO. The products of all of these reactions can agglomerate to form bubbles. 

Bubbles can also be formed by precipitation from the melt whenever supersaturation occurs for a specific gas. Since many gases have a large enthalpy of solution in glass forming melts, their solubility in these melts is a strong function of temperature. Species which alter their chemical form with temperature or changes in melt composition are particularly susceptible to precipitation from melts where they were previously soluble. Carbon dioxide, for example, is present in silica-rich melts as CO2 molecules, whereas it chemically reacts with alkali-rich 

Oxygen can also be released into melts by changes in the oxidation state of the surrounding atmosphere. Changes in oxidation state of polyvalent ions such as iron, chromium, manganese, etc. can alter the state of oxygen from chemically bound to physically dissolved molecules, as in the reaction  

Since the solubility of molecular oxygen is much less than that of chemically bound oxygen, supersaturation occurs and oxygen bubbles form during the reduction of polyvalent species. 

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Precipitation both in the form of rain and snow can produce bubbles on the sea (3). Bubbles from moderate rain intensities have diameters of less than 200 /xm, and those produced by snow are less than 100 /xm. However, since these bubbles are produced only in the upper few centimeters of the sea and only during the precipitation, they do not constitute the major source of bubbles in the sea. The precipitation of the continental aerosol into the sea has been suggested as a source of bubbles (50), but since this aerosol is composed of particles primarily less than 100 /xm diameter, and since water drops of 100 /xm diameter produce no bubbles when they fall into the sea (3), it is unlikely that the continental aerosol produces a significant quantity of bubbles. 

In no case should a liquid be boiled without the addition of a boiling aid. Bumping is stopped by adding to the liquid a source of bubble nuclei, such as a boiling chip, a platinum wire, or an ebullition tube. Boiling chips are most commonly used. They are small chips of clean hard porous plate or tile about 2 to 5 mm in diameter. The small pores induce smooth boiling. Platinum wire acts as a porous material supposedly because of dissolved gas. 

List and describe the 4 major sources of bubbles in glass forming melts. 

A significant problem in frontal polymerization is the formation of bubbles at the front. These bubbles affect the front velocity (Pojman et al., 1996b) and can cause voids in the final product. The high front temperature can cause boiling of some monomers at ambient pressures. The main source of bubbles in free-radical systems is the initiator, because all nitriles and peroxides produce volatile byproducts. The bubbles make a porous polymer, which may have less than optimal properties. 

The prediction is that steep sided cavities, with large contact angles (i.e., poor wetting) are likely to be the sources of bubble production. In well-wetted conditions, cavities are likely to be unimportant. 

There are three sources of bubbles. All thermal initiators (except for persulfates), produce volatile byproducts, such as CO2, methane, or acetone. It is an inherent problem with all commercially available peroxide or nitrile initiators. 

Another source of bubbles is dissolved gas and water in the monomer. Gases can be removed under vacuum but water is extremely difficult to remove from methacrylic acid and TGDMA. Less than 1 mg of water will result in 2 cm of water vapor at the front temperature of 200 ° G and 1 atm of pressure. The only certain solution to all three sources is to perform reactions under pressure. 

The computer subroutines for calculation of vapor-liquid equilibrium separations, including determination of bubble-point and dew-point temperatures and pressures, are described and listed in this Appendix. These are source routines written in American National Standard FORTRAN (FORTRAN IV), ANSI X3.9-1978, and, as such, should be compatible with most computer systems with FORTRAN IV compilers. Approximate storage requirements for these subroutines are given in Appendix J their execution times are strongly dependent on the separations being calculated but can be estimated (CDC 6400) from the times given for the thermodynamic subroutines they call (essentially all computation effort is in these thermodynamic subroutines). 

Steam is introduced at the base of the whiskey column through a sparger. Where economy is an important factor, as in a fuel alcohol plant, a calandtia is employed as the source of indirect heat. The diameter of the stiU, number of perforated and bubble cap plates, capacity of the doubler, and proof of distiUation are the critical factors that largely determine the characteristics of a whiskey. 

In ECS s 1986 repowefing project Babcock and Wilcox (B W) constmcted a bubbling-bed section to ECS s existing 125 MWe pulverized-coal furnace to produce 31.3 t/h of lime, usiag cmshed coal as the source of heat to calciae limestone ia the fluidized bed. A portion of the lime is drawn from the bed as bottom ash and a portion is collected as fly ash. Both portions are transferred to a cement (qv) plant adjacent to the boiler. The hot flue gas from the EBC flows iato the existing main pulverized-coal furnace, ia which a B W LIMB system was also iastaHed to absorb sulfur dioxide dufing those times when the EBC is not operating. 

Bubble Policy The bubble concept introduced under PSD provisions of the Clean Air Act Amendments of 1977 was formally proposed as EPA policy on Jan. 18, 1979, the final policy statement being issued on Dec. 11, 1979. The bubble pohcy allows a company to find the most efficient way to control a plant s emissions as a whole rather than by meeting individual point-source requirements. If it is found less expensive to tighten control of a pollutant at one point and relax controls at another, this woiild be possible as long as the total pollution from the plant woiild not exceed the sum of the current hmits on individual point sources of pollution in the plant. Properly apphed, this approach would promote greater economic efficiency and increased technological innovation. 

The evolution of gases, such as in dre example given above of dre formation of CO(g) in dre U airsfer of sulphur between carbon-saturated iron and a silicate slag, requires dre nucleation of bubbles before dre gas can be eliminated from the melt. The possibility of homogeneous nucleation seems unlikely, and the more probable source of gas bubbles would either be at the container ceramic walls, or on detached solid particles of the containing material which are... 

In high heat flux (heat transfer rate per unit area) boilers, such as power water tube (WT) boilers, the continued and more rapid convection of a steam bubble-water mixture away from the source of heat (bubbly flow), results in a gradual thinning of the water film at the heat-transfer surface. A point is eventually reached at which most of the flow is principally steam (but still contains entrained water droplets) and surface evaporation occurs. Flow patterns include intermediate flow (churn flow), annular flow, and mist flow (droplet flow). These various steam flow patterns are forms of convective boiling. 

Aluminum is the most abundant metallic element in the Earth s crust and, after oxygen and silicon, the third most abundant element (see Fig. 14.1). However, the aluminum content in most minerals is low, and the commercial source of aluminum, bauxite, is a hydrated, impure oxide, Al203-xH20, where x can range from 1 to 3. Bauxite ore, which is red from the iron oxides that it contains (Fig. 14.23), is processed to obtain alumina, A1203, in the Bayer process. In this process, the ore is first treated with aqueous sodium hydroxide, which dissolves the amphoteric alumina as the aluminate ion, Al(OH)4 (aq). Carbon dioxide is then bubbled through the solution to remove OH ions as HCO and to convert some of the aluminate ions into aluminum hydroxide, which precipitates. The aluminum hydroxide is removed and dehydrated to the oxide by heating to 1200°C. 

In the United States, methane is a major energy source used in many homes for cooking and heating of water and indoor air and water. It is commonly known that some power plants and industries use natural gas as a source of energy for generation of electricity and process heat and that this methane is a fossil fuel obtained from gas wells and transmitted throughout the country by gas pipelines. Most people also know that methane bubbles up from polluted swamps where sedimented plant matter is undergoing decomposition. Because of odors from swamps, and the odor due to natural gas additives, methane is incorrectly considered malodorous. 

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