Publisher Summary This chapter studies fluid–flow characteristics of liquids in layers, with and without a superimposed gas velocity. The types of turbulence in layers need to be investigated and also the nature of a laminar layer containing ripples. As regards the theoretical studies of film flow, it is shown in the chapter that it is possible to predict quite accurately the flow behavior in the smooth laminar flow regime of the film; unfortunately, this flow regime is not of great practical importance. The Kapitsa theory for wavy film flow appears to apply over only a very limited part of the total wavy flow regime. Several new experimental techniques for the study of film flow have been developed. Film flow is a special case of two-phase flow. It takes place along a solid surface of some sort, with only one free surface. The second phase in contact with the free surface of the film may be either a gas or a second liquid, which may be at rest or in motion relative to the solid surface on which the film flows. Film flow is distinguished from other forms of two-phase flow by the presence of large interfaces of basically simple geometrical configuration. Two-phase flows are also often further classified as single-component. The occurrence and applications of film flow in modern technology are numerous and important.

The Flow of Liquids in Thin Films

Mass transfer equations are derived and compared with dissolution experiments of C6H5COOH-H2O and Cu-H2SO4-K2Cr2O7 systems on single spheres (6 different sizes from 3/4" to 3"). In region I (long contact time with smooth laminar film), Sh converges Sh=1.608 (GaSc/Pe*)1/3 or k=2.01 D√δ(δ: mean film thickness) and increases with decreasing volumetric flow rate Q. In region II (short contact time with smooth laminar film), Sh converges Sh=0.716 Pe*1/9(GaSc)2/9The transition from region I to II occurs around Pe*/(GaSc)1/4≤10. In region III (short contact time with wavy film surface), Sh increases with Pe* to the 1/3 - 1/2 power and is substantially higher than that in region II. A generalized short contact time equation using the measured local film thickness δ Sh=0.501 Pe*1/3{∫π0(d/δ)sinθdθ}2/3is valid in this region. Thus, main cause for enhancement in Sh is the reduction in film thickness relevant to the wave formation. The II-III transition is somewhere between wave inception and wave coverage flow rates. In the above, Sh=kd/D, Pe*=Q/dD and Ga=gd3/v2, in which k is based on a log-mean driving force.

https://www.jstage.jst.go.jp/article/jcej1968/7/1/7_1_19/_pdf

Solid-liquid mass transfer in falling liquid films on single spheres

A study of the effect of liquid maldistribution on the performance of a gas absorber is reported. The experimental work was carried out using the carbon dioxide-water system in a simulated packed column consisting of an ordered array of spheres. This device has been shown to closely approximate the behaviour of an actual column and permits the artificial manipulation of the liquid distribution. The results indicate that maldistribution causes only a small decrease in the mass transfer coefficient at low liquid flow rates, and has almost no effect at higher flows. A proposed iterative procedure for calculating the effect is presented.



On preente les resultats d'une etude de l'effet d'une mauvaise distribution d'un liquide sur le rendement d'un absorbeur de gaz. On a fait le travail experimental, en employant le systeme anhydride carbonique-eau, dans une colonne simulee garnie et formee de spheres disposees en rangees. On a constate que le dit dispositif reproduisait tres approximativement le comportement d'une colonne normale et permettait de manipuler artificiellement la distribution du liquide. Les resultats ont indique que la mauvaise distribution du liquide ne produisait qu'une faible diminution du coefficient de transfert de masse, lorsque les debits du liquide etaient faibles, et qu'il etait presque sans effet lorsque les ecoulements etaient eleves. On presente une methode iterative qu'on propose pour calculer l'effet en question.

The effect of liquid maldistribution on the performance of a packed tower absorber

This work was undertaken to clarify the mechanism of mass transfer into a liquid film flowing over the surface of a sphere and to see whether liquid is mixed completely or not at the points of juncture between the spheres connected in a vertical row. Experiments were performed on the absorption of pure carbon dioxide by water with and without a wetting agent, in columns containing 1, 3 and 5 spheres, respectively.Experimental data for single sphere are shown in Figs. 3 and 4, and those for multiple sphere in Fig. 6, as the plot of the HL values against the Reynolds number on logarithmic coordinates. Results with single sphere were in good agreement with the theoretical equation based on the assumptions of unsteady-state diffusion and parabolic velocity distribution in the liquid film, as shown in Fig. 5. The addition of a wetting agent caused no change in the absorption rate in the case of single sphere, and the HL values for both the runs with and without agent were the same.Fig. 7 shows the correlation among the results obtained with multiple sphere, when pure water was used as a solvent. Good agreement was obtained between the data and the theoretical equation, derived from the assumption that the mixing of the liquid was complete at the points of juncture between the spheres. Fig. 8 shows a similar plot of the data obtained by Yoshida and Koyanagi.7)When a wetting agent was added to water, the values of HL were higher than those for pure water and increased with the number of spheres, as shown in Fig. 9. The data obtained by authors and those by Lynn, Straatemeier and Kramers5) were in fairly good agreement with the theoretical equation based on the assumption that there was no mixing of the liquid as it flew from one sphere to the next.

https://www.jstage.jst.go.jp/article/kakoronbunshu1953/23/8/23_8_513/_pdf

H. Hikita

Papers

Mass Transfer into Liquid Film Flowing over Spheres