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Marangoni Films

It may not be realised that the unwetted walls above the stratified LNG will be covered with differential surface-tension-driven Marangoni films of ethane rich liquid up to the saturation temperature of ethane, and propane rich liquid up to the saturation temperature of propane. Ethane and propane rich droplets will run down the walls against the film flow and collect in the bottom of the tank, as an example of auto-stratification of a high density layer at the bottom of the tank. [Pg.106]

Cold instrumentation heads inside the tank will give incorrect readings if they are covered with Marangoni film. [Pg.106]


Film Elasticity The differential change in surface tension of a surface film with relative change in area. Also termed surface elasticity, dilata-tional elasticity, areal elasticity, compressional modulus, surface dilata-tional modulus, or modulus of surface elasticity. For fluid films, the surface tension of one surface is used. The Gibbs film (surface) elasticity is the equilibrium value. If the surface tension is dynamic (time-dependent) in character, then for nonequilibrium values, the term Marangoni film... [Pg.495]

Wang, K.H.T., Ludviksson, V., and Lightfoot, E.N., Hydrodynamic stability of Marangoni films. II. Preliminary analysis of the effect of interphase mass transfer, AIChE J., 17, 1402, 1971. [Pg.377]

The consequences of surface evaporation (T-x) values being different to published free-boiling, equilibrium values, means that vapour compositions of LNG and LPG in storage tanks are not a good guide to their liquid phase compositions. See also the consequences of Marangoni film flows up the tank walls in Sect. 6.4.4. [Pg.69]

Measurement of composition by liquid withdrawal through a capillary tube, followed by total evaporation and gas phase analysis, is extremely time consuming and expensive for any continuous monitoring programme to be maintained. Furthermore the accuracy will be plagued by the Marangoni film flows. [Pg.93]

Film Rupture. Another general mechanism by which foams evolve is the coalescence of neighboring bubbles via film mpture. This occurs if the nature of the surface-active components is such that the repulsive interactions and Marangoni flows are not sufficient to keep neighboring bubbles apart. Bubble coalescence can become more frequent as the foam drains and there is less Hquid to separate neighbors. Long-Hved foams can be easHy... [Pg.429]

In a foam where the films ate iaterconnected the related time-dependent Marangoni effect is mote relevant. A similar restoring force to expansion results because of transient decreases ia surface concentration (iacteases ia surface tension) caused by the finite rate of surfactant adsorption at the surface. [Pg.464]

Figure 1. Schematic diagram showing the possible mechanisms of thin film stabilization, (a) The Marangoni mechanism in surfactant films (b) The viscoelastic mechanism in protein-stabilized films (c) Instability in mixed component films. The thin films are shown in cross section and the aqueous interlamellar phase is shaded. Figure 1. Schematic diagram showing the possible mechanisms of thin film stabilization, (a) The Marangoni mechanism in surfactant films (b) The viscoelastic mechanism in protein-stabilized films (c) Instability in mixed component films. The thin films are shown in cross section and the aqueous interlamellar phase is shaded.
An improvement in foam stability was observed as R was increased to >0.15 (Figure 17). This was accompanied by the onset of surface diffusion of a-la in the adsorbed protein layer. This is significantly different compared to our observations with /8-lg, where the onset and increase in surface diffusion was accompanied with a decrease in foam stability. Fluorescence and surface tension measurements confirmed that a-la was still present in the adsorbed layer of the film up to R = 2.5. Thus, the enhancement of foam stability to levels in excess of that observed with a-la alone supports the presence of a synergistic effect between the protein and surfactant in this mixed system (i.e., the combined effect of the two components exceeds the sum of their individual effects). It is important to note that Tween 20 alone does not form a stable foam at concentrations <40 jtM [22], It is possible that a-la, which is a small protein (Mr = 14,800), is capable of stabilizing thin films by a Marangoni type mechanism [2] once a-la/a-la interactions have been broken down by competitive adsorption of Tween 20. [Pg.46]

It is also important that the emulsifier films have sufficient elasticity to enable recovery from local disturbances (see Gibbs-Marangoni effect page 274). [Pg.265]

An absence of the Gibbs-Marangoni effect is the main reason why pure liquids do not foam. It is also interesting, in this respect, to observe that foams from moderately concentrated solutions of soaps, detergents, etc., tend to be less stable than those formed from more dilute solutions. With the more concentrated solutions, the increase in surface tension which results from local thinning is more rapidly nullified by diffusion of surfactant from the bulk solution. The opposition to fluctuations in film thickness by corresponding fluctuations in surface tension is, therefore, less effective. [Pg.275]

In concentrated emulsions and foams the thin liquid films that separate the droplets or bubbles from each other are very important in determining the overall stability of the dispersion. In order to be able to withstand deformations without rupturing, a thin liquid film must be somewhat elastic. The surface chemical explanation for thin film elasticity comes from Marangoni and Gibbs (see Ref. [199]). When a surfactant-stabilized film undergoes sudden expansion, then immediately the expanded... [Pg.86]

Although many factors, such as film thickness and adsorption behaviour, have to be taken into account, the ability of a surfactant to reduce surface tension and contribute to surface elasticity are among the most important features of foam stabilization (see Section 5.4.2). The relation between Marangoni surface elasticity and foam stability [201,204,305,443] partially explains why some surfactants will act to promote foaming while others reduce foam stability (foam breakers or defoamers), and still others prevent foam formation in the first place (foam preventatives, foam inhibitors). Continued research into the dynamic physical properties of thin-liquid films and bubble surfaces is necessary to more fully understand foaming behaviour. Schramm et al. [306] discuss some of the factors that must be considered in the selection of practical foam-forming surfactants for industrial processes. [Pg.210]


See other pages where Marangoni Films is mentioned: [Pg.89]    [Pg.106]    [Pg.89]    [Pg.106]    [Pg.111]    [Pg.468]    [Pg.427]    [Pg.1442]    [Pg.234]    [Pg.370]    [Pg.370]    [Pg.28]    [Pg.149]    [Pg.36]    [Pg.166]    [Pg.43]    [Pg.34]    [Pg.122]    [Pg.122]    [Pg.298]    [Pg.9]    [Pg.23]    [Pg.25]    [Pg.25]    [Pg.127]    [Pg.141]    [Pg.275]    [Pg.275]    [Pg.276]    [Pg.117]    [Pg.87]    [Pg.87]    [Pg.512]    [Pg.512]    [Pg.516]    [Pg.35]   


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