Liquid film, falling

The Leveque-type correlation, Eq. (26), has been used for mass-transfer from a liquid film falling under gravity (110, W13b), where it holds for Reynolds numbers in the laminar range, in spite of the presence of surface waves on the film. The latter caused small local oscillations of the mass-... 

Killion, J. D., and Garimella, S. (2003) A Review of Experimental Investigations of Absorption of Water Vapor in Liquid Films Falling over Horizontal Tubes, HVAC and R Research, Vol. 9(2), pp. 111-136. 

In vertical devices with condensation on the inside or on the outside of the tubes the condensed liquid-film falls under the influence of gravity. The thickness of the condensed liquid film increases in the direction of flow due to the increased liquid load caused by 435... 

The equations of fluid flow in region 4 are then similar to those of a liquid film falling around a cylinder ... 

I. A. Mudawwar, T. A. Incropera, and F. P. Incropera, Boiling Heat Transfer and Critical Heat Flux in Liquid Films Falling on Vertically-Mounted Heat Sources, Int. J. Heat Mass Transfer (30) 2083-2095,1987. 

Consider the idealized picture of a mass-transfer process based on the two-film theory as shown in Figure 7.27. The partial pressure profile in the gas film is linear, as called for by steady-state diffusion, but the concentration profile in the liquid film falls below a linear measure as a result of a first-order chemical reaction removing the absorbed gas. A normal mass balance over the differential segment dz (we may assume unit area normal to the direction of diffusion) produces a familiar result ... 

We make only one essential alteration in this interpretation the film on the surface of ice (in the course of premelting) consists of second liquid L2, not of ordinary liquid Li. In the light of this alteration becomes clearly, why the ice slippery considerably diminishes in the days of thaw this phenomenon is well known to the skaters. Indeed, in this case, the phase transition L2- Li happens in the surface film, and fluidity of the liquid film falls. 

Trifonov, Y., and Tzvelodub, O. Y. (1985). Nonlinear waves on the surface of a liquid film falling down a vertical plane. Zh. Prikl. Mekh. Tekh. Fiz. 5 15-19. 

Falling-film crystalhzation utilizes progressive freezing principles to purify melts and solutions. The technique estabhshed to practice the process is inherently cyclic. Figure 22-15 depicts the basic working concept. First a ciystalline layer is formed by subcoohng a liquid film... 

FIG. 23-25 Typ es of industrial gas/Hqiiid reactors, (a) Tray tower, (h) Packed, counter current, (c) Packed, parallel current, (d) Falling liquid film, (e) Spray tower, if) Bubble tower, (g) Venturi mixer, h) Static in line mixer, ( ) Tubular flow, (j) Stirred tank, (A,) Centrifugal pump, (/) Two-phase flow in horizontal tubes. 

Multistrand wire, close-knit in two layers, holds stable liquid film by surface tension. Falling films of liquid form expansive contact surface with rising vapor layers. 

Sinek and Young present a design procedure for predicting liquid-side falling film heat transfer coefficients within 20% and overall coefficients within 10%. 

P 12] A falling film micro reactor was applied for generating thin liquid films [6]. A reaction plate with 32 micro channels of channel width, depth and length of 600 pm, 300 pm and 66 mm, respectively, was used. Reaction plates made of pure nickel and iron were employed. The micro device was equipped with a quartz window transparent for the wavelength desired. A 1000 W xenon lamp was located in front of the window. The spectrum provided ranges from 190 to 2500 nm the maximum intensity of the lamp is given at about 800 nm. 

Dukler and Taitel, 1991b). The simplest configuration of annular flow is a vertical falling film with concurrent downward flow. Given information on interfacial shear and considering the film to be smooth, the film thickness and heat transfer coefficient between the wall and the liquid film can be predicted from the following basic equations (Dukler, 1960) ... 

Figure 3.35 Comparison of velocity fit examples of falling liquid film with peak/substrate — 3 ...

Simon, F. F., and Y. Y. Hsu, 1970, Thermocapillary Induced Breakdown of a Falling Liquid Film, NASA-TN-D-5624, NASA Lewis Res. Ctr., Cleveland, OH. (5)... 

If long distillation time is a problem, one can move to continuous distillation with conventional shell and tube heaters accompanied by a typical column bottom (often called a sump) which is a high temperature holdup, or better yet a short path evaporator (falling film, thin film, or wiped film) with usually a smaller receiver (called an accumulator in this case). The most chemical damage is in the thin liquid film at the heat transfer surface, so the short path evaporators do the least thermal damage. 

The temperature of a liquid metal stream discharged from the delivery tube prior to primary breakup can be calculated by integrating the energy equation in time. The cooling rate can be estimated from a cylinder cooling relation for the liquid jet-ligament breakup mechanism (with free-fall atomizers), or from a laminar flat plate boundary layer relation for the liquid film-sheet breakup mechanism (with close-coupled atomizers). 

The velocity u of the gas is strictly the velocity relative to the surface of the falling liquid film, though little error is introduced if it is taken as the superficial velocity in the column. 

Figure 12-13 A falling film catalytic wall reactor in which reactant in the gas must diffuse through a liquid film to react L...

The mathematical treatment of surfaces was developed much earlier than the direct examination of superficial films. It is based primarily upon the observed tendency of a volume of liquid to adopt when unconstrained a shape with a minimum surface. The property of having a minimum surface for a given volume is possessed by a sphere, and this shape is assumed by a free body of liquid. A falling raindrop is spherical upon this fact indeed is based the... 

It is striking that the lifetimes fall to very small values as the relative humidity (RH) approaches 50%. At larger values of RH, not only is the gas-phase concentration of water larger, but condensation to form an aqueous liquid film on surfaces becomes more important. One cannot distinguish from data whether NO, is itself being taken up into a liquid film, whether N20, is being removed, or whether both processes are occurring. 

Figure 12.22 shows the composition in terms of the weight percent HNO, and H2S04 as a function of temperature as solid SAT is cooled from 194 K under conditions corresponding to a pressure of 50 rnbar in an atmosphere containing 5 ppm HzO and an HNO, concentration of 10 ppb (Koop and Carslaw, 1996). Under these particular conditions, as the temperature falls below 192 K, the SAT is in equilibrium with a liquid film on the particle containing both HN03 and H20. The particular temperature at which SAT deliquesces is a function of the water vapor and gaseous nitric acid concentrations as shown in Fig. 12.23. As the temperature falls further and more HNO, and HzO are taken up into the liquid, the solid SAT dissolves completely, forming a ternary solution of the two acids and water. This solution can then act again to nucleate PSCs.

Another solution to Eq. (159) for the diffusion into a falling film with a flat velocity profile is obtained by taking into account the finite thickness of the liquid film 8 and its effect on the concentration profiles that is, the boundary conditions are taken to be... 

A very early application of liquid film flow in the chemical industry is mentioned in a patent of 1836 (G5) hydrogen chloride gas produced in the Leblanc soda process was absorbed by water films flowing over packings. Much later the film coolers and evaporators used in the German beet sugar industry inspired the earliest detailed theoretical and experimental studies of flow and heat transfer in falling films (CIO, N6, N7). Chemical engineering interest in film flow has increased rapidly in recent years. 

Experimental measurements of the wall shear stress exerted by a falling liquid film have been reported for the cases of film flow outside a vertical tube (B14) and in a channel of variable slope (F7). In both cases the experimental results in the zone of smooth laminar flow were in agreement... 

Fulford (F6), 1960 Brief review of heat and mass transfer to falling liquid films. 

A3. Allen, J. M., Some studies of falling liquid films. Ph.D. thesis, Manchester Coll. Sci. and Technology, England, 1962. 

Aeration can be accomplished by allowing the liquid to fall in a thin film or to be sprayed in the form of droplets in air at atmospheric pressure or the air, under pressure, may be bubbled into the liquid by means of a sparger, or other device that creates thousands of small bubbles, thus providing maximum contact area between the air and the liquid. 

SURFACE TENSION. Fluid surfaces exhibit certain features resembhng the properties of a stretched elastic membrane hence the term surface tension. Thus, one may lay a needle or a safety-razor blade upon the surface of water, and it will lie at rest in a shallow depression caused by its weight, much as if it were on a rubber air-cushion. A soap bubble, likewise, tends to contract, and actually creates a pressure inside, somewhat after the manner of a rubber balloon. The analogy is imperfect, however, since the tension in the rubber increases with the radius of the balloon, and the pressure inside, which would otherwise decrease, remains approximately constant while the liquid film tension remains constant and the pressure in the bubble falls off as the bubble is blown. 

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