Conditions, of enclosure

By putting i successively 1, 2. .. c we thus obtain c equations which give the final state of a closed system in terms of the initial state. These are called the conditions of enclosure. 

For such a state to exist it is necessary that the equations (29.12) shall be compatible with the so-called conditions of enclosure (29.11). As we shall prove, this is not possible unless the variables in (29.9) have values satisfying certain conditions. If these conditions are satisfied the state defined by (29.9) is called an indifferent state. 

The above demonstration can be generalized immediately to all bivariant systems since for such systems the number of conditions of enclosure (29.108) is always, as in the above example, ( + r ) and this... 

For the c conditions of enclosure (29.108) to be compatible in an indifferent state, it is necessary and sufficient that the initial masses... 

Extreme situations may require heat exchangers or air conditioning of enclosures. Also, consider locating the entire control system in a separate room adjacent to the controlled machinery. 

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. 

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. 

A Type 6 enclosure is suitable for application where the equipment may be subject to temporary submersion. The design of the enclosure will depend upon the specific conditions of pressure and time. It is also dust tight and sleet (ice) resistant. 

Although the use of enclosures is conceptually the simplest approach, some particular problems arise in their use in studies of NH3 loss. These are associated with the chemical reactivity of the gas, particularly its reactivity with water, and to the strong influence of environmental factors on the volatilization process (11). Matching conditions within the enclosure to those prevailing outside is a difficult task and much of the data obtained using enclosures is open to question. However, the problems associated with enclosures can be overcome if the air speed through the enclosure is controllable to within the same range as that of wind speed at the experimental site (9, 12). 

Applications. The kinds of motors that are being used successfully with particular kinds of. chemical process equipment are identified in Table 4.1. As many as five kinds of AC motors are shown in some instances. The choice may be influenced by economic considerations or local experience or personal preference. In this area, the process engineer is well advised to enlist help from electrical experts. A checklist of basic data that a supplier of a motor must know is in Table 4.2. The kind of enclosure may be specified on the last line, operating conditions. 

To compare with this method, the heat of reaction calculated by REITP-2 8 9 , the combustion rate at the time of ignition under open conditions 3 3 3 0 in the IMO combustion rate tests 3 0 3 2 > and the combustion rate under conditions of partial enclosure 11 4 in the TNO deflagration tests 9 5> are shown along with variations in the composition of the mixtures in Fig.3.49. 

Table 7.1 Pressurization - p - according to EN 50016/2nd edition and IEC 60079-2/4th edition. Conditions of release for combustible substances and oxygen from a containment system into the pressurized enclosure...

---