Horizontal film

Figure 10-126. Horizontal film type cooler or condenser.

Horizontal Film or Cascade Drip-Coolers—Atmospheric... 

Initially devised to measure interactions in single soap films (air/water/air) [8], the TFB technique has been progressively improved and its application has been broadened to emulsion films (oil/water/oil) [ 12] and asymmetric films (air/water/oil or air/water/solid) [13,14]. In a classical setup, a thin porous glass disk is fused on the side to a capillary tube and a small hole is drilled in the center of the disk. The liquid solution fills the disk, part of the capillary, and a thin horizontal film is formed across the hole. The disk is enclosed in a hermetically sealed box, with the capillary tube exposed to a constant reference pressure Pr. Under the effect of the pressure difference AP between the box and the reference, the... 

Fig. 1, Calculated lines of constant velocity in a water film flowing near the comer of a rectangular glass channel at 30° to the horizontal film thickness far from side wall is 1 mm. (F7).

Krotov and Rusanov [96-98] have proposed an apparatus with a horizontal film. Here the frame is made of four platinum wires of 40 pm in diameter and 120 mm in length. The frame area, respectively, the film area can vary from zero to 140 cm2. The film is isolated from the bulk solution and drops of the solution are introduced by a special device. In order to obtain a film with uniform initial thickness, it is stirred by the intensive horizontal air stream. 

During drainage of larger circular horizontal films (r > 200 pm) more complex phenomena have been observed (Fig. 3.10) [29,73]. 

The existence of channels in microscopic circular horizontal films can be registered with the microinterferometric method of Scheludko-Exerowa (see Chapter 2) that plots the photocurrent/time curve. Each time when a channel passes through the place of photometry there appears a kink in this curve. 

Under certain conditions aqueous electrolyte solutions form foam films of equilibrium thickness. For a microscopic horizontal film this thickness is determined by the positive component of disjoining pressure (FU) which depends on the potential of the diffuse electric layer at the foam film/air(gas) interface. 

The values of CBF differ slightly since they were obtained by different techniques vertical films in a frame put into a horizontal X-ray diffractometer [341,342] and horizontal film (Fig. 2.21) in a synchrotron ray diffractometer [343], The data presented in the above table confirm the concepts established from previous investigation about the structure of both types of black films a sandwich model of two adsorption layers of amphiphile molecules with an aqueous core in between (for CBF) and bilayer of amphiphile molecules in which molecules of the solvent are incorporated (for NBF). The bilayer structure of NBF has been confirmed [344] for films from aqueous solutions of C]2E6 obtained in the measuring cell shown in Fig. 2.21. Their thickness of 6 nm found is less than the double length of the amphiphile molecule. 

Visual observations of film thinning in a coarsely dispersed foam from 2% Nekal solution have shown [78] that at first colourless thick films are formed. After 20 s the vertical films reach thickness of about 0.1 mm (in the thicker part about 0.8 mm) and after 5 min become black (thickness less than 15 nm). Horizontal films, however, thin much slower. 

Liquid horizontal films are always rupture resistant when their thickness exceeds a certain value hi, given by ... 

Most quantitative studies on foams have been carried out using foam films. As discussed above, microscopic horizontal films were studied by Scheludko and... 

Agitated horizontal film (votator) usually to condition foodsmffs, crystallize, and react. Especially for viscous feed. OK for foaming, fouling, crystal formation, and suspended solids. Viscosities >2000 mPa s. Relative to agitated film retention time of 1 1 and volume 1 1. Overall heat transfer coefficient 2 kW/m °C, decreasing with increasing viscosity 3 to 12 kW/m. See also evaporation, Section 16.11.4.1. 

Agitated horizontal film (votator) thin liquids U = 2.2 to 4 kW/m -°C viscous hhns U =... 

Surface Forces. Surface forces can be measured with thin film balances where freely suspended horizontal films are submitted to controlled pressures. If the film drainage has been smooth enough, so that no early rupture has occurred, a regime where interactions between the two sides of the film become significant can be attained this is in a thickness region of about 100 nm and less. Typical interactions are van der Waals forces (attractive) and electrostatic forces (repulsive). Short range forces (steric, hydration) are also present. 

Figure 13.16(b) shows an area of a lower grain boundary which includes a high density of defects. The lower horizontal film extends to the right while the film on the step flank extends to the left. The lower film is again much more... 

The stability of aqueous films in air, sterically stabilized by poly(vinyl alcohol), have been investigated by Lyklema and van Vliet (1978). Small horizontal films were formed inside a glass ring. Hydrostatic suction could be applied to the films by lowering (or raising) a container with polymer solutions, which was connected to the film. 

Ballotini Method ISOiSil). Small glass beads are poured onto a horizontal film surface. After 10 s the panel is inclined and brushed lightly. The coating is surface-dry if all the spheres can be... 

Similar conclusions were found by Houpert and Hamrock, Ref. 11, where EHL calculations were performed on nonsmooth surfaces. Fig. 9, for example, shows the steady state film thickness and pressure distribution calculated on a roller having a tranverse bump. Because in the calculations all deformations are put on one surface only (instead of being shared between the two surfaces), the bump seemed completely flattened, leading to a parallel and horizontal film separation. In a later study, elastic calculations and EHL calculations performed on a 3-D contact having longitudinal roughness will lead to... 

Most quantitative studies on film drainage have been carried out using small, horizontal films, as described in detail by Scheludko and co-workers [2-4]. Figure 8.2 illustrates the measuring cell for studying microscopic foam films. 

Most quantitative studies on foams have been carried out using foam films. As discussed above, microscopic horizontal films were studied by Scheludko and coworkers [2-4]. A schematic representation of the set-up used to study horizontal foam films is given in Figure 8.2. The foam thickness was determined by interferometry. Studies on vertical films were carried out by Mysels and collaborators... 

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