Partitioned Enclosures

Physical Separation. In addition to providing electrical isolation, it is necessary to provide physical separation to ensure the non-hazardous circuits can not degrade the intrinsically safe portion of the circuits. This can be accomplished by planning the physical layout to incorporate the use of distance, enclosures, partitions, separate raceways, and insulation. The final physical layout selected should meet or exceed the requirements of Chapter 3, Sections 1, 2, 3, and 4 of NFPA 493. 

Let us now analyze the more complex shielding application of Figure 7.12(a), which illustrates a rectangular enclosure partitioned by two equal horizontal PEC walls. In the front plane, there is a centered (20 x 5) cm horizontal aperture. The dimensions are a = b = 60 cm, d = 120 cm, / = 70 cm, w = 2 cm, and the excitation is launched by a vertical coaxially fed monopole. Due to the nonstandard operators of (3.43), the domain is discretized into the coarse grid of30 x 60 x 30 cells with Ax = Ay = Az = 2 cm and At = 30.567 ps. In the area of the aperture, spatial derivatives are computed by the fictitious-point technique of Section 2.4.5, whereas the DRP schemes of Section 2.5.3 are also utilized. Figure 7.12(b) displays the shielding efficiency defined as the ratio of the electric field amplitude evaluated in front of... 

Wall, enclosure, partition = a physical system idealized as a surface forming the common boundary of two different systems. The walls that completely enclose a system are called enclosures. Walls separating the subsystems of a composite system arc called partitions. 

Electrical and optical connections between two flameproof enclosures separated by a partition wall are made by the insertion of (multiple) cable bushings or fibre bushings in an opening or thread of the partition wall. This technique is identical with the means of connection between e - and d -compartments (see Section 6.7.2, Table 6.19, and Section 6.7.6, Fig. 6.70, and, in addition, Fig. 6.84). 

Zone Methodology and Conventions For a transparent medium, no more than E = M(M —1)/2 of the M2 elements of the ss array are unique. Further, surface zones are characterized into two generic types. Source-sink zones are defined as those for which temperature is specified and whose radiative flux Q, is to be determined. For flux zones, conversely, these conditions are reversed. When both types of zone are present in an enclosure, Eq. (5-118) may be partitioned to produce a more efficient computational algorithm. Let A/ M t M. represent the total number of surface zones where A/ is the number of source-sink zones and Mf is the number of flux zones. The flux zones are the last to be numbered. Equation (5-118) is then partitioned as follows ... 

The fallacy of this view arises in conjunction with a concept of adiabatic processes. Adiabatic enclosures are ideal partitions which separate regions of thermodynamic interest from the remainder of the universe in particular, no heat transfer of any type can occur across those boundaries. In the present example, however, the walls of the container are in intimate contact with the gas which is being compressed. Thus, these walls cannot be considered as part of the adiabatic partition which separates the container plus contents from the remainder of the universe. 

Now, assume this gas isothermally fills an enclosure made of gray surfaces. The resulting enclosure problems can be treated by replacing the gas with a transparent solid partition with negligible reflectivity. 

Having reduced the problems of lumped gas radiation to enclosure problems with transparent partitions, we proceed next to problems of distributed gas radiation. 

The lower vapour pressure of these compounds means their concentration in ambient air will also be low. If explosives are contained in an enclosure with cool surfaces the vapour concentration may be even lower than saturated values due to partitioning effects. The saturated equilibrium ambient air concentration of TNT, RDX, and PETN as a function of ambient temperature is shown in Figure 4. At room temperature there are approximately 100 picograms of TNT per mL available for detection. NG and DNT have even higher concentrations available for detection. Flowever, PETN and RDX produce less than 1 picogram per mL and hence are much more difficult to detect as vapours. For these compounds it is easier to use a wipe to extract material from surfaces and then to desorb thermally the compounds as vapours into the detection system. 

Enclosure problems (Fig. 4.1c) arise when a solid surface completely envelops a cavity containing a fluid and, possibly, interior solids. This section is concerned with heat transfer by natural convection within such enclosures. Problems without interior solids include the heat transfer between the various surfaces of a rectangular cavity or a cylindrical cavity. These problems, along with problems with interior solids including heat transfer between concentric or eccentric cylinders and spheres and enclosures with partitions, are discussed in the following sections. Property values (including P) in this section are to be taken at Tm = (Th+ TC)I2. 

Classification of Partitions. Partitions are relatively thin, solid walls mounted inside the enclosure, as for example in Fig. 4.33. The partitions are passive in the sense that neither their temperature nor heat flux is prescribed. Depending on their extent and orientation, such partitions can have profound effect on the heat transfer. Partitions can be classified in various ways. Complete partitions run continuously from one side to another partial partitions have... 

M. W. Nansteel and R. Greif, An Investigation of Natural Convection in Enclosures With TVre>- and Three-Dimensional Partitions, Int. J. Heat Mass Transfer (27/4) 561-571,1984. 

The test enclosure (77 by 74 by 30 cm) had two chambers separated from each other by a solid metal partition. The front chamber (45 by 74 cm) was connected to the rear chamber (32 by 74 cm) by a small opening (5 by 5 cm) to allow passage of the female vole. Males were tethered in the front chamber such that a female could interact with either male without physical interference from the opposing male. The rear chamber was a neutral chamber. Food and water were provided ad libitum to each male and in the rear chamber. A long photoperiod of 14L 10D and ambient temperature of 24 2°C was maintained throughout the experiment. Each trio of voles was monitored for 84 h. As the videotapes are reviewed, the duration of all physical contacts between a female and each stimulus male and occurrences of copulation are scored for hours 40 to 75, a time period when females are expected to have achieved estrous and to have pair-bonded. To date, we have scored data for seven females. 

Load bearing exterior walls Party and fire walls Literior bearing walls it enclosures it corridors/ fire partitions Shafls... 

Where PVC insulated and sheathed cables are concealed in walls, floors or partitions, they must be provided with a box incorporating an earth terminal at each outlet position. PVC cables do not react chemically with plaster, as do some cables, and consequently PVC cables may be buried under plaster. Further protection by channel or conduit is only necessary if mechanical protection from nails or screws is required or to protect them from the plasterer s trowel. However, lET Regulation 522.6.101 now tells us that where PVC cables are to be embedded in a wall or partition at a depth of less than 50 mm they should be run along one of the permitted routes shown in Fig. 3.45. Figure 3.44 shows a typical PVC installation. To identify the most probable cable routes, lET Regulation 522.6.201 tells us that outside a zone formed by a 150mm border all around a wall edge, cables can only be run horizontally or vertically to a point or accessory if they are contained in a substantial earthed enclosure, such as a conduit, which can withstand nail penetration, as shown in Fig. 3.45. 

Separation with a non-IS conductor by use of approved insulating partition extended within 1.5 mm within enclosure. 

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