Enclosure Effects

The Semenov criticality diagrams for fire growth are useful to understand the complex interactions of the fire growth mechanisms with the enclosure effects. These diagrams can be used qualitatively, but might also be the bases of simple quantitative graphical solutions. 

Operability. Hidden costs may result from changes in the way a process operates as a result of a control. For example, enclosure and isolation may diminish the abiUty of workers to observe the process. Upsets and dismptions resulting from this loss of intelligence are expensive and generate resistance to the use of these controls, no matter how effective. 

To reduce the amount of dust produced, water can be added to the abrasive from a circular water sprayer around the no22le. Chemical corrosion inhibitors must be dissolved in the water to prevent flash msting of the steel. Newer methods to reduce dust include the use of ice, soHd carbon dioxide (dry ice), or plastic beads as abrasives. Blasting with dry ice is inexpensive and effective, but the accumulation of carbon dioxide must be avoided in enclosures. Plastic beads are inexpensive, but the cutting efficiency is low and paint removal is slow the beads can be cleaned of paint particles and reused. 

Though this is a quartic equation, it is capable of explicit solution because of the absence of second and third degree terms. Trial-and-error enters, however, because (GSi)r and are mild functions of Tg and related Te, respectively, and aprehminary guess of Tg is necessaiy. An ambiguity can exist in interpretation of terms. If part of the enclosure surface consists of screen tubes over the chamber-gas exit to a convection section, radiative transfer to those tubes is included in the chamber energy balance, but convection is not, because it has no effect on chamber gas temperature. 

Material characteristics, both chemical and physical, should be considered, especially flowabihty. Abrasiveness, friability, and lump size are also important. Chemical effects (e.g., the effect of oil on rubber or of acids on metal) may dictate the structural materials out of which conveyor components are fabricated. Moisture or oxidation effects from exposure to the atmosphere may be harmful to the material being conveyed and require total enclosure of the conveyor or even an artificial atmosphere. Obviously, certain types of conveyors lend themselves to such special requirements better than others. 

For the theory of neutralization of the magnetic effect on the conductor in a non-magnetic shielding, refer to the continuous enclosures for isolated phase bus systems discussed in Section 31.2.2. As a result of non-magnetic shielding there will be no saturation of the iron core and the V-I characteristic of the reactor will remain almost linear. 

To contain the proximity effect, in the metallic structures existing in the vicinity, it is essential that the IPB enclosures be at least 300 mm from tdl structures exi,sting parallel and 1.30 mm existing across the enclosures. A distance of 300 mm is sufficient to contain the proximity effect in view of the substantially reduced magnetic field in the space. 

X (p in Q cm) as in Table 30.1 /= frequency of the system in Hz p = effective permeability of the medium in which the field exists (aluminium in the present case), and will depend upon the electric field induced in the enclosure... 

The part of the bus enclosure installed outdoors is exposed to solar radiation which is a cause of additional heat gain by the enclosure. ANSI C-37.24 has provided a basis to determine its effect in terms of heat generated as follows ... 

By forced convection The factors that can influence the temperature of the enclosure, installed outdoors are wind and snow, other than forced cooling. But their effect on actual cooling may be small. Sometimes this happens and sometimes not. It is better to ignore this effect when estimating various thermal effects. Natural convection and radiation will take account of this. 

In fact, it is the solar effect that is causing the maximum heat. The factors considered for the solar effect are also highly conservative. Nevertheless, a canopy over the outdoor part is advisable in the above case. This will ensure the same size of enclosure for the outdoor as well as the indoor parts and also eliminate the requirement for a thicker enclosure or a forced cooling arrangement. Now there will be no direct solar radiation over the bus system and the total solar effect can be eliminated, except for substituting the indoor ambient temperature of 48 C with the maximum outdoor temperature for the outdoor part of the bus system. 

If we can overcome the solar effect, the size of the conductor and the enclosure can be reduced to economize their costs. Another exercise with reduced dimensions will be necessary for this until the most economical sections are established. 

A, = effective surface of radiation per foot of enclosure length in square inches... 

Dwight, H.B., Some proximity effects formulae for bus enclosures , Trans. IEEE. 83, December 1167-1172 (1964). 

In Section 14.6 we have provided a brief account of such disturbances as well as the recommended tests and procedures to verify the suitability of critical enclosures and bus systems for locations that are earthquake-prone. For this the user is required to provide the manufacturer with the intensity of seismic effects at site of the installation in the form of response spectra (RS). (See Section 14.6.)... 

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