Evaporation above plane surface

In order to estimate diying rates from Eq. (12-42) values of the empirical constants are required for the particular geometry under consideration. For flow parallel to plane plates, exponent n has been reported to range from 0.35 to 0.8 [Chu, Lane, and Conklin, Ind. E/ig. Chem., 45, 1856 (1953) Wenzel and White, Ind. Eng. Chem., 51, 275 (1958)]. The differences in exponent have been attributed to differences in flow pattern in the space above the evaporating surface. In the absence of apphcable specific data, the heat-transfer coefficient for the parallel-flow case can be taken, for estimating purposes, as... 

Fig. 47. Work function of the (110) facet of a tungsten field emitter at 300 K as a function of silver exposure. The authors interpret this data as follows Below an exposure treshold of about one ML, Ag adatoms migrate to the high-index facets that surround the W(llO) plane, and the emission properties are indistinguishable from those of the bare substrate. At 1 ML the adatoms invade the (110) plane, modifying the surface density of electron states and bringing about an abrupt increase in electron emission. Above 2 ML the additionally evaporated Ag atoms migrate again to the surrounding facets. From [95D].

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