Entrainment horizontal liquid films

An interesting study of entrainment from horizontal liquid films has also been carried out by Van Rossum (VI). On the basis of a liquid film in laminar flow with a flat and smooth surface, he found that the mean actual film thickness was about 0.6 times the theoretical one. The critical Weber number corresponding to the onset of atomization was determined for five different liquids, with Weber number defined as... 

Entrainment studies have been relatively few, as pointed out earlier. Anderson and Mantzouranis (A3) used the results of measurements of entrainment (which was small in their work) to correct their calculated liquid film thickness, and thus obtained somewhat better agreement with experimental values. Wicks and Dukler (W2) measured entrainment in horizontal flow, and obtained a correlation for the amount of entrainment in terms of the Lockhart and Martinelli parameter, X. The entrainment parameter, R, of Wicks and Dukler is given by... 

Mass transfer controlled by diffusion in the gas phase (ammonia in water) has been studied by Anderson et al. (A5) for horizontal annular flow. In spite of the obvious analogy of this case with countercurrent wetted-wall towers, gas velocities in the cocurrent case exceed these used in any reported wetted-wall-tower investigations. In cocurrent annular flow, smooth liquid films free of ripples are not attainable, and entrainment and deposition of liquid droplets presents an additional transfer mechanism. By measuring solute concentrations of liquid in the film and in entrained drops, as well as flow rates, and by assuming absorption equilibrium between droplets and gas, Anderson et al. were able to separate the two contributing mechanisms of transfer. The agreement of their entrainment values (based on the assumption of transfer equilibrium in the droplets) with those of Wicks and Dukler (W2) was taken as supporting evidence for this supposition. 

Studies of heat and mass transfer to films and film condensation are considered only insofar as the results throw light on the flow behavior a brief review of such studies has been published elsewhere (F6). In addition, annular gas/liquid flow in horizontal ducts will not be considered here, since this is usually complicated by droplet entrainment. 

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