Surface temperature limits

Hazardous area apparatus is classified according to the maximum surface temperature produced under fault conditions at an ambient temperature of 40 °C (104 °F) or as otherwise specified. Some desert locations may produce ambient temperatures higher than 40 °C (104 °F) and suitable adjustments must be made in these circumstances. 

Class II and Class III areas are for Dust and Fibers respectively, and are typically not extensively used in the hydrocarbon industries. 

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Special provisions are laid down in lEC 60079-0 and lEC 60079-1 for motors required for such locations in view of fluctuating degrees of humidity and temperature. Such locations are defined with a surface temperature limit of 150°C where coal dust can form a layer, or 450°C where it is not expected to form a layer. Otherwise, other details are generally the same as for flameproof motors type Ex d , according to lEC 60079-1. For variations in length of paths, gaps, widths, creepage and clearance distances, the reader should consult these Standards. 

Part 1-1 Electrical apparatus protected by enclosures and surface temperature limitation-Specification for apparatus... 

So, one effect of short-circuit arcs inside a flameproof enclosure may be heating or even melting the enclosure material and thus exceeding the surface temperature limitations or burning a hole in the enclosure - far away from the basic safety rules of flameproof enclosure - d... 

Two limits may possibly be reached during the primary drying stage. First, the surface temperature Ti(t, o) must not become too high because of the risk of thermal damage. Second, the temperature of the interface Tx must be kept well below the melting point. If the outer surface temperature limit (T coi) is encountered first as r,(t, o) is raised, the process is considered to be heat transfer controlled to increase the drying rate further, the thermal conductivity ki of the... 

The surface temperature limit of 85°C for Type B(U) packages under exclusive use, where potential damage to adjacent cargo can be well controlled, is required... 

Table 14.2 Electrical Apparatus Surface Temperature Limits...

PV limit is generally related to rubbing surface temperature limit. As such, PV limit decreases with increasing ambient temperature. The PV limits determined on any given tester geometry and ambient temperature can rank materials, but translation of test PV limits to other geometries is difficult. 

In summary, it has become quite clear that contact between two surfaces is limited to a small fraction of the apparent area, and, as one consequence of this, rather high local temperatures can develop during rubbing. Another consequence, discussed in more detail later, is that there are also rather high local pressures. Finally, there is direct evidence [7,8] that the two surfaces do not remain intact when sliding past each other. Microscopic examination of the track left by the slider shows gouges and irregular pits left in the softer metal... 

Catalyst Development. Traditional slurry polypropylene homopolymer processes suffered from formation of excessive amounts of low grade amorphous polymer and catalyst residues. Introduction of catalysts with up to 30-fold higher activity together with better temperature control have almost eliminated these problems (7). Although low reactor volume and available heat-transfer surfaces ultimately limit further productivity increases, these limitations are less restrictive with the introduction of more finely suspended metallocene catalysts and the emergence of industrial gas-phase fluid-bed polymerization processes. 

The membrane is usually made from one of several materials. Woven polyester or cotton, the most commonly used and least expensive material, is adequate for temperatures up to 150°C. Siatered plastic is used where a low cost, washable surface is desired. This material is temperature limited by the polymer material to about 60°C and the flow of some powders may cause a static charge build-up on the membrane that could be hazardous ia some operatioas. Wovea fiberglass fabric or porous ceramic block is used for temperatures up to about 425°C. Siatered stainless steel powder or bonded stainless mesh is used for corrosion resistance, and for temperatures up to 530 to 650°C. Additional information can be found ia the Hterature (38,39). 

Plastic Pipe In contrast to other piping materials, plastic pipe is free from internal and external corrosion, is easily cut and joined, and does not cause galvanic corrosion when coupled to other materials. Allowable stresses and upper temperature limits are low. Normal operation is in the creep range. Fluids for which a plastic is not suited penetrate and soften it rather than dissolve surface layers. Coefficients... 

Table 7.6 Temperature class and limiting surface temperature with regard to gas ignition...

Temperature class Ignition temperature (°C) Limiting surface temperature, (°C)... 

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. 

One limitation in the use of floor heating is the surface temperature of the floor. Most people will find a floor surface temperature of more than 25 °C uncomfortable. 

The response factors are characteristic for the layer buildup of the selected wall and are calculated before (by a preprocessor program) or at the beginning ol the simulation. Numerical reasons limit the time step to approximately 10 to 60 min, depending on the thickness and material properties of the wall layers. The method allows the calculation of surface temperatures and heat fluxes bur not the determination of the temperature distribution within the wall. Due to the precalculation of these response factors, the computer time for the simulation might be significantly reduced. 

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