Enclosure, conditions

Enclosure conditions, such as obstructing objects and confinement. 

Non-Black-Surface Enclosures In the following discussion we are concerned with enclosures containing gray sources and sinks, radiatively adiabatic surfaces, and no absorbing gas. The calculation of interchange between a source and a sink under conditions involving successive multiple reflections from other source-sink surfaces in the... 

Environmental Enclosures Enclosures for valve accessories are sometimes required to provide protection from specific environmental conditions. The National Electrical Manufacturers Association (NEMA) provides descriptions and test methods for equipment used in specific environmental conditions in NEMA 250. Protection against rain, windblown dust, hose-directed water, and external ice formation are examples of environmental conditions that are covered by NEMA standards. 

Fire or explosion hazards require special motor enclosures. Hazards include combustible gases and vapors such as gasoline dust such as coal, flour, or metals that can explode when suspended in air and fibers such as textile lint. The land of motor enclosure used depends on the type of hazard, the type and size of motor, and the probability of a hazardous condition occurring. Some available enclosures are explosionproof motors, which can withstand an internal explosion force-ventilated motors cooled with air from a safe location and totallv enclosed motors cooled bv air-to-water heat exchangers and pressurized with safe air, instrument air, or inert gas,... 

This is a location which is not permanently contaminated but is likely to be prone to fire hazards during processing, storage or handling of explosive gases, chemical vapour or volatile liquids, although under careful and controlled conditions. Eor such locations in addition to a flame- or explosion-proof enclosure, type Ex. d, an increased... 

Surface temperature should not exceed the ignition temperature noted in Table 7.6 for a particular temperature class under any conditions of operation. There is no limit to the temperature rise to the permissible limits for a particular class of insulation of windings or other parts of the machine, except the limiting surface temperature as in Table 7.6. For such an application, a normal 1P 55 enclosure may also be employed. 

We have defined the various types of enclosures adopted by various manufacturers to suit different locations and environmental conditions in Tables 1.10 and 1.11. Here we briefly discuss methods for testing these enclosures to check their compliance with defined requirements. 

In such conditions, it is important that adequate care is taken to construct the bus enclosure lo weather the outdoor conditions such as by providing a canopy on the top and special paint treatment on the outdoor part. It is also recommended to seal off the indoor from the outdoor part to prevent the eflecl of rainwater, dust and temperature and other weather conditions on the indoor part. This can be achieved by providing seal-off bushings, one on... 

As discussed later, the enclosure of an IPB may carry induced currents up to 95% of the current through the main conductors. Accordingly, the enclosure is designed to carry longitudinal parasitic currents up to 90-95% of the rated current of the main busbars. The cross-sectional area of the enclosure is therefore maintained almost equal to and even more than the main conductors to account for the dissipation of heat of the main conductors through the enclosure only, unless an additional forced cooling system is also adopted. The outdoors part of the enclosure exposed to atmospheric conditions is also subjected to solar radiation. Provision must be made to dissipate this additional heat, from the enclosure. 

The continuous current rating of a bus system can be defined by the current at which a steady-state thermal condition can be reached. It is a balance between the enclosure and the conductor s heat gain and heat loss. If this temperature is more than the permissible steady-state thermal limit it must be reduced to the desired level by increasing the size of the conductor or the enclosure or both, or by adopting forced cooling. Otherwise the rating of the bus system will have to be reduced accordingly. 

The outdoor part of the enclosure has to perform more onerous duties as it has to withstand weather conditions and also absorb solar radiation. It has also to dissipate the heat of the conductor in addition to its own. It is therefore possible that the surface area of enclosure so chosen may have to be increased, and this will be revealed during thermal calculations which are carried out to check its suitability. 

The selection of the motor enclosure type involves not only economics but also assessment of two factors area hazard classification and other area operation conditions. 

Operating conditions that also must be considered in selecting the enclosure type are exposure to airborne dust, dirt and moisture, the possibility of corrosive dust or vapors in the area, and the expected maximum ambient temperature. 

The vendor shall be responsible for the selection of proper range, pressure rating, materials of construction and electrical enclosure based on process conditions and electrical area classification. All instruments and controls shall be in accordance with Specification ME-0-JN400. 

The scope of this chapter is to show how to select a strategy and to make calculations to provide efficient room air conditioning for an industrial enclosure. Design examples for simplified scenarios include different ways to condition industrial halls. 

In order to analyze the conditions for air conditioning, the following information must be specified for the industrial enclosure ... 

For small-scale laboratory work, the exhaust surface is often made as a separate section added to the side of a table or put into a large hole in a table. These tables usually have a sheet metal surface that is resistant to the chemicals used and is easily cleaned. Many circular holes are cut into the metal surface to allow for airflow. This perforation makes the pressure difference over the table quite high and at the same time gives an even distribution of the airflow over the entire surface. These types of exhaust surfaces could be formed to suit different working conditions, e.g., the surface could be made to fit into a sink or to be placed below and around a balance. Using side walls that are not too high, on three or four sides, transforms the table to a partial enclosure, which increases... 

Under normal operating conditions the worker will be situated outside the enclosure. The operator will enter the hood only with his or her hands/arms. During the setting up of equipment it may be necessary to enter the enclosure, but entry should be kept to a minimum and, whenever possible, before the emission of contaminant has commenced. 

Working conditions outside the enclosure are drastically improved. 

If acceptable working conditions must be maintained in the enclosure during furnace operation, attention must be given to internal airflow patterns, i.e., minimization of fume recirculation in the enclosure. 

For enclosures, velocity measurements, in the plane of the opening, offer a quick check on the design conditions. Fiowever, the opening velocity is not a direct measure of the ability of an enclosure to provide personnel protection. Other measures of efficiency are required and depend on use of the enclosure. In the case of safety cabinets and laboratory hoods, allowance factors for protection and leakage are applied to ensure complete safety when in use. 

The highly resolved velocity profile can be mapped in the vicinity of solid boundaries such as the walls of a room and in the entire enclosure, providing relevant data for CFD boundary conditions. These data form a basis for verification of CFD results and for improvement of CFD codes. 

Air quality The concentration of one or more pollutants in the air, measured in either ppm or pg m . It may be related to pollution sources inside an enclosure or outdoor air. Temperature and moisture conditions may also be considered. 

Mixed flow, actual An actual flow pattern in an enclosure resulting in the air being mixed to such an extent that conditions are almost the same at every point in the occupied zone. 

Although transformers suitable for other industrial installations are generally suitable for producing applications, certain options may be desirable— primarily due to environmental considerations. At locations subject to harsh environmental conditions, and particularly at locations subject to washdown with high-pressure hoses, non-ventilated enclosures are desirable, if not necessary. Likewise, at locations subjected to salt water and salt-laden air, it often is desirable to specify copper windings and lead wires. Most manufacturers provide standard units with aluminum windings and lead wires. Even if aluminum coils are used, it is almost always desirable to require stranded copper lead wires. This will lessen corrosion and loose terminal problems when transformers arc interconnected to the facility electrical system with copper conductors. If the transformers are to be installed outdoors in corrosive environments, cases should be of corrosion-resistant material (e.g., stainless steel) or be provided with an exterior coating suitable for the location. 

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