Thin agitated falling film

T iquid films, whether in the form of natural falling films or in the more advanced form of mechanically agitated films in thin-film apparatus, offer convenient conditions for the solution of many difficult processing problems because of the films favorable surface-to-volume ratio and good heat transfer. This is especially so with an agitated film between heating wall and film. The agitated-film principle has previously found its broadest application in thin-film evaporators. 

Figure 2. Comparison between mean film thickness of falling and agitated films in a thin-film apparatus, expressed as a function of peripheral load and viscosity. Curves I, 2, and 3, falling film according to Equation 1 curve 1° and 2°, agitated film in the thin-film apparatus...

Figure 14. Increase of the intrinsic viscosity during the polycondensation reaction of polyester as a function of the residence time. Comparison between free-falling-film reactor (13) and agitated thin-film machine...

Figure 15. Final polycondensation of polyester. Comparison between horizontal rigid film, free-falling film, and agitated thin film in a high viscosity machine (Luwa Filmtruder)...

First, the overall mass transfer coefRcient k a of the microreactor was estimated to be 3-8 s [43]. For intensified gas liquid contactors, kj a can reach 3 s while bubble columns and agitated tanks do not exceed 0.2 s Reducing the flow rate and, accordingly, the liquid film thickness is a means of further increasing kj a, which is limited, however, by liquid dry-out at very thin films. Despite such large mass transfer coefficients, gas-liquid microreactors such as the falling film device may still operate between mass transfer and kinetic control regimes, as fundamental simulation studies on the carbon dioxide absorption have demonstrated [44]. Distinct concentration profiles in the liquid, and even gas, phase are predicted. 

Fig. 7.4-5 Combination of a falling film evaporator and an agitated thin-film evaporator...

Agitated thin-film evaporators with a falling, revolving liquid film (Fig. 2-18) are often used in molecular distillation. The film is 0.1-1 mm thick, with a mean residence time ranging from 10 s-10 min and a... 

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