Method for Estimating Wall Film Thickness and Velocity

C Method for Estimating Wall Film Thickness and Velocity 

In some special applications it is of value to be able to estimate certain physical characteristics of the film of liquid that is flowing down the walls of a gas/liquid cyclone. This includes the fraction of the cross-sectional area occupied by the gas and by the liquid wall film, the film velocity, residence time, and film thickness. Such information is of interest, for example, in performing heat transfer computations wherein the wall film is heated by an external steam jacket, or the film is cooled by an external chilled water enclosure. Knowledge of the film characteristics is also of value if one is interested in ensuring that a sufficient film velocity or thickness is maintained to keep solids from depositing upon the walls. Herein, we shall present a technique that is intended to provide an estimate of the wall film s flow characteristics. 

The model we develop in this appendix is thus based on a two-phase, cocurrent flow force balance that relates the cross-sectional liquid void fraction 

In most gas-liquid cyclone installations, the majority of all incoming liquid is deposited upon the walls immediately upon entry into the cyclone as a result of the mass loading effect alone. This is due to the relatively large size of the incoming liquid drops and also to the mass loading effect discussed in Sect. 13.6 above. 

In this model, the primary purpose of the centrifugal force field generated by the rotational motion imparted to the incoming feed stream is to convey and keep the liquid on the walls of the cyclone. Herein we shall assume that the gas and liquid phases spiral down the walls of the cyclone in a helical 

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C Method for Estimating Wall Film Thickness and Velocity 13.C.2 Friction Factors and Shear Stresses... 

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