Surface temperature small components

Testing codes within the scenario of a fully developed fire are based on intermediate, large, or full-scale testing. Specimens are typically in the dimension of several square meters and often, real components such as building columns are tested, or the whole product in the case of gas bottles. Tests like the small-scale test furnace based on specimens of 500 mm x 500 mm are exceptions. Intensive flame application or the use of furnaces realizing standard time-temperature curves are used to simulate the characteristics of fully developed fires. Thus, in particular the heat impact of convection and the surface temperature are clearly greater than in the tests discussed earlier. The fire properties investigated are often resistance to fire, or the fire or temperature penetration. 

Consider two-dimensional laminar boundary layer flow over a flat isothermal surface. Very close to the surface, the velocity components are very small. If the pressure changes are assumed to be negligible in the flow being considered, derive an expression for the temperature distribution near the wall. Viscous dissipation effects should be included in the analysis. 

The analytical proof assumes that the radius of curvature of the surface is small compared with the thickness of the transition layer between two phases, otherwise the position arbitrarily chosen for XY is of appreciable importance.3 Gibbs proves that the temperature and chemical potentials of the components are uniform throughout the system when equilibrium exists but we shall take this here as self-evident, as indeed it is from a physical standpoint, considering that temperature and potentials are measures of the escaping tendencies of heat and of each component from the different phases, and therefore equalize themselves automatically. The pressures in the different phases are not, however, equal unless the surfaces are strictly plane, as was pointed out in Chap. I, 15. 

As a second main feature of intrinsic safety, current densities in thin internal wires and printed board wiring may increase up to some 102 A/mm2, and the surface temperature of small components may exceed the limits of T classification by far. 

The question remains why the other components, principally branched paraffins, are converted at all. Several explanations can be offered, none completely satisfactory. Not all the palladium is inside the zeolite cages but may be partially on external surfaces and nonzeolite components, amorphous material which is either the residue of incomplete crystallization or the product of zeolite decomposition in subsequent treatments. Since x-ray crystallinity is uniformly high, the amorphous component should be quite small. Branched paraffins can penetrate the zeolite surface far enough to be cracked. High temperature alters the selective adsorption properties of the zeolite, which were observed at low temperature. Offretite intergrowths provide enough surface in larger diameter pores partially to convert branched and cyclic molecules. There is some truth in all of these but we prefer the latter. 

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