Drainage of liquid films

Scheludko et al. [13,15,73,89,229,230] derived the Reynolds relation in a slightly generalised form and tested it experimentally. The agreement between experiment and theory was very reasonable. More recently, Chan and Horn [231] have used the surface force apparatus (SFA) and found that the Reynolds approach to hydrodynamic lubrication is very successful in describing the drainage of liquid films between smooth solid surfaces. 

The rate of thinning (drainage) of liquid films is drastically influenced by the rheological properties of the related adsorption layer. We will restrict ourselves to just a few examples. A detailed description of various sites of thin film problems is given for example by Ivanov (1988) and Hunter (1993). The immobilisation of a cylindrical plane film is a precondition for... 

As shown in Section 3.4. the rate of drainage of liquid films depends on surface rheological properties. This is valid for foam and emulsion films. However, the drainage of the films between fluid particles is only the first common step in stability, the DLVO theory controls films and films stabilised in the second minimum of the it/A- isotherm. 

As mentioned earlier, heavy oil produced by solution gas drive often displays marked foaminess in wellhead samples. This feature is not surprising because the two key factors needed for nonpolar foam stability are present in the heavy-oil system. The viscosity of the liquid phase (heavy oil) is high enough to retard drainage of liquid films by capillary... 

The drainage of liquid films between a solid-liquid and a liquid-fluid interface has been studied experimentally and theoretically [690-695, 702]. The formation of the dimple and the close distance at the rim hinders the liquid in the center to flow out As a consequence, surface forces indirectly influence the drainage time. A strong repulsion leads to a large film thickness in the rim and a fast drainage. Weak repulsion leads to a closely approaching rim and a slow drainage [697]. 

Groenveld, P. Drainage and Withdrawal of Liquid Films. AIChE J. 1971, 17, 489-490. 

Tallmadge, J. A. Gutfinger, C. Entrainment of Liquid Films Drainage, Withdrawal, and Removal. Ind. Eng. Chem. 1967, 59, 19-35. 

Contact time, drainage and rupture of liquid film... 

A high bulk liquid viscosity simply retards the rate of foam collapse. High surface viscosity, however, involves strong retardation of bulk liquid flow close to the surfaces and, consequently, the drainage of thick films is considerably more rapid than that of thin films, which facilitates the attainment of a uniform film thickness. 

The drainage of liquid from liquid lamellae separating bubbles in a foam. See also Fluid Film. 

J. A. Tallmadge and C. Gutfinger, Entrainment of liquid films. Drainage withdrawal and removal. Ind. Eng. Chem., 59 (1967) 19-34. 

If the continuous phase is a liquid, the main obstacle to coalescence is the drainage of the film of liquid in the small space in between the two particles. The efficiency is in these cases usually quantitied as a function (generally a negative exponential function) of the ratio of the characteristic time for droplet contact and film drainage. For example, in the case of small bubbles coalescing due to turbulent velocity fluctuations the coalescence kernel assumes the form (Buffo et al, 2012 Laakkonen et al, 2006 Petitti et al, 2010)... 

Attachment by sliding can be controlled by the drainage rate, which goes down with increasing retardation of liquid film surface by DAL. Thus, surface retardation by DAL is favourable because the unwanted action of centrifugal forces can be prevented. On the other hand, it hampers the drainage, which is unfavourable for flotation. 

Film Drainage The drainage of liquid from a lamella of liquid separating droplets or bubbles of another phase (i.e., in a foam or emulsion). Also termed thin film drainage. See also Fluid Film. 

Viscosity Opposes the drainage of liquid from the film. 

The behavior of thin liquid films formed between coalescing drops and bubbles has attracted considerable attention in an attempt to understand the stabilizing mechanisms of emulsions and foams. It is now generally recognized that the drainage of this film plays a crucial role in determining the stability of the dispersion. 

At lamella intersections the liquid is more bulky . Tree film pairs come together at an angle of 120°. These zones are called Plateau Boarders (J.J. Plateau, French Chemist 1861). Because of the pressure difference by diameter as well as symmetrical considerations, the vapour pressure is lower than in a lamella which results in a sucking effect towards Plateau zones, helping the drainage of liquid. 

It was established flieoretically (97, 133) that when the surfactant is dissolved in the drop phase (System II in Fig. 15) it remains uniformly distributed throughout the drop surface during film thinning, and interfacial tension gradients do not appear. This is the result of a powerful supply of surfactant, which is driven by convective diffusion from the bulk of the drops toward their surfaces. For that reason, the drainage of the film surfaces is not opposed by surface-tension gradients, and the rate of film thinning, Fjj, is the same as in the case of pure liquid phases (97, 133) ... 

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