Stable film

A notable characteristic of stable films is their resistance to mechanical disturbance. Gibbs [178] considered the important property to be the elasticity of the film E ... 

The magnesium nitride [12057-71 -5] produced does not form a stable film. If sufficient nitrogen is present this reaction can be self-sustaining. The nitride produced can react with water to form ammonia [7664-41 -7]. 

LB Films of Long-Chain Fatty Acids. LB films of saturated long-chain fatty acids have been studied since the inception of the LB technique. The most stable films of long-chain fatty acids are formed by cadmium arachidate deposited from a buffered CdCl2 subphase. These films, considered to be standards, have been widely used as spacer layers (23) and for examining new analytical techniques. Whereas the chains are tilted - 25° from the surface normal in the arachidic acid, CH2(CH2) gCOOH, films (24), it is nearly perpendicular to the surface in the cadmium arachidate films (25). 

Properties. Ethyl cellulose [9004-57-3] (EC) is a nonionic, organo-soluble, thermoplastic cellulose ether, having an ethyl DS in the range of 2.2-2.7. Actually, EC is water-soluble at DS 1.2, but only those products that are thermoplastic and soluble in organic solvents are of commercial importance, because of thek abiUty to form tough, stable films. Above a DS of about 2.5, EC is soluble in many nonpolar solvents. 

Banchero,J. T, G. E. Barker, and R. H. Boll, Stable Film Boiling of Liquid Oxygen Outside Single Horizontal Tubes and Wires, Chem. Eng. Prog. Sym. Series, No. 17, Heat Transfer— St. Louis, V. 51,p. 21, (1955). 

Fig. 4.42 Effect of pH on the rate of corrosion of zinc, A, rapid corrosion B, stable film — low corrosion rate C, rapid corrosion (after Roetheli, elal )...

The formation of a magnetite film, although highly desirable, is itself a form of corrosion. The effective protection of boiler surfaces requires the proper development of an adherent, nonporous, self-limited, and stable film. Under adverse conditions, however, such as when... 

Bromley, L. A. (1950) Chem. Eng. Prog. 46, 221. Heat transfer in stable film boding. 

Figure 1.1 Pool boiling regimes A-B, natural convection B-C, nucleate boiling C-D, partial film boiling D-E, stable film boiling.

Because the bubble population increases with heat flux, a point of peak flux may be reached in nucleate boiling where the outgoing bubbles jam the path of the incoming liquid. This phenomenon can be analyzed by the criterion of a Hemholtz instability (Zuber, 1958) and thus serves to predict the incipience of the boiling crisis (to be discussed in Sec. 2.4.4). Another hydrodynamic aspect of the boiling crisis, the incipience of stable film boiling, may be analyzed from the criterion for a Taylor instability (Zuber, 1961). 

Figure 2.16 Stable film boiling from a horizontal surface.

Annular flow. In annular flow there is a continuous liquid in an annulus along the wall and a continuous gas/vapor phase in the core. The gas core may contain entrained droplets—dispersed mist—while the discontinuous gas phase appears as bubbles in the annulus. This flow pattern occurs at high void fractions and high flow velocities. A special case of annular flow is that where there is a gas/vapor film along the wall and a liquid core in the center. This type is called inverse annular flow and appears only in subcooled stable film boiling (see Sec. 3.4.6.3)... 

The heat transfer mechanism of a vapor-liquid mixture in which the critical heat flux has been exceeded can be classified as partial or stable film boiling. The differ-... 

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