Falling films fluid mechanics

Dukler, A. E., 1960, Fluid Mechanics and Heat Transfer in Vertical Falling Film Systems, AIChE Chem. Eng. Prog. Sym Ser. 56(30) 1—10. (3)... 

Since we do not want to consider the fluid mechanics of this reactor in detah, we will assume that the hquid falls with a constant average velocity and forms a hquid film of thickness R — R, with / j the radius in the tube at the surface of the hquid film. If these assumphons hold, then and R — i j are independent of the position z in the tube of length L (actually the height, since the tube must be vertical). Similarly, if the hquid film thickness is constant, then the cross section occupied by the gas is constant, and the velocity of the gas is also independent of z if the density of the gas is constant. These distances are sketched in Figure 12-8. 

Falling Films When a liquid is distributed uniformly around the periphery at the top of a vertical tube (either inside or outside) and allowed to fall down the tube wall by the influence of gravity, the fluid does not fill the tube but rather flows as a thin layer. Similarly, when a liquid is applied uniformly to the outside and top of a horizontal tube, it flows in layer form around the periphery and falls off the bottom. In both these cases the mechanism is called gravity flow of liquid layers or falling films. 

Dukler, A.E. Fluid mechanics and heat transfer in vertical falling film systems, Chem. Eng. Prog. Symp. Ser. 56 (1960) 1-10... 

Shkadov, V. Y., and Sisoev, G. M. (2000b). Wavy falling liquid films theory and computation instead of physical experiment. In Chang, H.-C., ed., lUTAM Symposium on Nonlinear Waves in Multi-Phase Flow, volume 57 of Fluid Mechanics and Its Applications, 1-10. Notre Dame, USA Notre Dame University. 

Preliminary concentration of the whey to 50-55% dry matter in falling-film evaporating systems (thermal or mechanical vapor compression), followed by spray drying (one step or two step with subsequent vibraton fluid bed). 

Theories of antifoam mechanism appear to fall into two broad categories those that concern modification of surface tension gradients and those that concern formation of capillary instabilities in foam films. Theories that concern surface tension gradients appear to be rather speculative. Some of these theories attribute antifoam action to the generation of a surface tension gradient that supposedly drives fluid... 

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