Mist zone

Johnson, J.W. and Holloway, D.G. (1966) On the shape and size of the fracture zones on glass fracture surfaces, Phil. Mag. 14, 731. Also Microstructure of the mist zone on glass fracture surfaces, Phil. Mag. 17, 899. 

Figure 9.34 Scanning electron micrographs showing the tensile fracture surfaces of (a) neat polymer, (b) 10 phr NT-Al O, nanocomposites, and (c) 10 phr APTES-AI2O3 nanocomposites. A - mirror zone, B - mist zone, C - hackle zone. Reprinted from [97] with permission from Elsevier.

Thermal Process. In the manufacture of phosphoric acid from elemental phosphoms, white (yellow) phosphoms is burned in excess air, the resulting phosphoms pentoxide is hydrated, heats of combustion and hydration are removed, and the phosphoric acid mist collected. Within limits, the concentration of the product acid is controlled by the quantity of water added and the cooling capabiUties. Various process schemes deal with the problems of high combustion-zone temperatures, the reactivity of hot phosphoms pentoxide, the corrosive nature of hot phosphoric acid, and the difficulty of collecting fine phosphoric acid mist. The principal process types (Fig. 3) include the wetted-waH, water-cooled, or air-cooled combustion chamber, depending on the method used to protect the combustion chamber wall. 

The Bechtel confined zone dispersion (BCZ) process involves the injection of a fine slurry mist of pressure hydrated dolomitic lime or calcitic lime, using two-fluid atomizing nozzles. A demonstration at the 70 MWe Seward Station of the Pennsylvania Electric Co., performed in 15.2 m of ductwork with a 2.4-m by 3.4-m cross section, achieved a 50% removal of SO2 at a Ca S ratio around 1.1. 

FW supply and on-off/modulation mechanisms. The on-off supply of FW tends to create cold-zone stratification within the boiler, leading to reduced steam production rates and misting (fogging) in the steam space. Boiler plant designs that provide for the continuous provision of FW through a modulated FW supply prevent these problems. 

Objection has been raised to the use of DDT and chlordan in food establishments because of the possibility that mists may spread onto the product zone of equipment and onto surfaces of food or ingredient mixes. Experience has shown that the use of the paint spray nozzle effectively prevents this. As large a pressure is used as will lay a flat stream of liquid there is no mist and should be no drip. Admittedly, other sprays are used in baking establishments, and special precautions must be taken to keep DDT or chlordan solutions from being confused with these. 

South America has two major areas, separated by the Andes Mountain ridges, where arid and semi-arid zones dominate. In the barren, coastal Atacama desert of Peru and northern Chile, precipitation is extremely limited and comes as winter mists or drizzles. In the rain shadow east of the Andes in Argentina, arid zones are widespread. South America apparently has only a slightly greater proportion of dry zones than North America. 

The desolvation of the droplets is usually completed in the preheating zone. The mist of salt clotlets then fuses and evaporates or sublimes. This is critically dependent on the size and number of the particles, their composition and the flame mixture. As the absolute concentration of analyte in the flame is very small (< lO- atm), the saturated vapour pressure may not be exceeded even at temperatures below the melting point. 

Oil mists traveling at high velocity have been successfully photographed by Deryogen and Vlasenko (2V), who have provided a let-up zone in the direction of vision. Engel (3V) describes the photography of gas turbine sprays and suggests that a new nozzle should always be tested in the atmosphere prior to installation. 

Following the historical development of electrical engineering and explosion protection, zone classification was the objective of national standards and installation rules. Most of the leading industrial countries established an installation practice for chemical plants and the oil and gas industry with two or three zones for areas hazardous due to gas- or vapour-air mixtures and two zones for areas with hazardous dust-air mixtures. Apart from this philosophy, the coal mining industry in most countries tends to avoid an area classification and defines only one category of explosion protection ( firedamp-proof ). More recent standards or directives present a three-zone concept for areas endangered by combustible gas- (vapour-, mist-) air mixtures and dust-air mixtures in industrial plants (other than coal mines). 

II Classification system with three zones for areas hazardous due to combustible gas, vapour or mist (Ha) or due to combustible dust (lib). 

Ilia - areas in which an explosive atmosphere caused by mixtures of air with combustible gas, vapour or mist is present continuously or for long periods or frequently zone 0... 

Note The content of Table 2.2(a) describes the traditional classification (IEC standardization not incorporated). Until 1998 the USA and Canada adopted the three-zone concept for areas hazardous due to combustible gases, vapours and mist according to IEC 60079-10, in parallel with the content of Table 2.2(a). 

This concept incorporates three zones each for hazardous areas endangered by combustible gas- (vapour- mist-) air or dust-air mixtures. 

TGL 30042 has defined a four-zone concept for areas hazardous due to combustible gases, vapours and mists EG 1, comparable with zone 0 EG 2 and EG 3, covering zone 1 EG 4, comparable with zone 2. In contradiction to the majority of standards covering the zone 1 requirements with all types of protection such as flameproof enclosure, increased safety, pressurization, oil immersion, intrinsic safety, powder filling, EG 2 excludes the general application of, e.g., increased safety e, which has been the domain of EG 3. 

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