Many inquiries have been made, theoretically and experimentally, into the hold-up in a wetted wall tower without gas flow. Most of the results of experimental studies are said to satisfy the theoretical relation obtained by Nusselt who analysed the flow of liquid film, but in view of the precision of measurements in these studies it is to be doubted whether this conclusion holds true or not. It should be rather noted that Kirkbride and Friedman et al. recognized the generation of waves on the surface of liquid film where Re
L>8.
On the other hand no researches have been made about a tower with gas flow because the suitable method for measurements was lacking.
The authors performed experiments with a new accurate method, the so-called balancing tower method. The towers used are shown in Table 1, and the liquids employed are water, soapless soap solution and millet-jelly solution. The results obtained are summarized as follows.
In the case without gas flow,
(i) The unsteady state parts of flow which existed at either end of the tower could be neglected when the length of the tower reached to about 250cm.
(ii) The influence of diameter on the thickness of liquid film might be represented by the term (1-2h/d)
1/3 regardless of the flow pattern.
(iii) The plot of h(1-2h/d)
1/3 vs. Re
L showed three different aspects according to the values of ReL as shown in Figs. 4 and 5. Where ReL was small the data agreed with Nusselt's theoretical line N represented by eq. (2). This region might by considered to be a complete laminar flow region. As ReL grew larger, the plots deviated downwards from the line N. In this region the generation of waves was observed and seemed to have some influence on the flow pattern, and the effects of the surface tension and viscosity of liquid were very significant. The data were well correlated with eq. (9). This region could be named a pseudo-laminar flow region. Eqs. (10) or (11) gave the criterion whether the flow was laminar or pseudo-laminar. In the region of large value of Re
L, the flow was fully turbulent and the influence of the surface tension of liquid diminished as in Fig. 6. Eq. (12) enabled one to predict the correlation in this region.
In the case with concurrent gas flow the following results were obtained.
(iv) When the liquid flows downwards in laminar film on a vertical surface, the ratio of the thickness of liquid film with countercurrent gas flow to that without gas flow, h/h
0, is theoretically given by eq. (16). The data obtained were compared with this equation as shown in Figs. 8, 9 and 10. The plots scattered on account of the low precision of measurements but mostly deviated downwards from the theoretical lines. The deviation appeared to be caused by the waves which were visible on the liquid surface, and the degree of deviation decreased with decrease of the surface tension of liquid and with increase of the viscosity. The ratio h/h
0 was expected to be smaller in turbulent flow than in laminar flow.
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