Turbulence in falling liquid films

Abstract

On the basis of fluid dynamic and heat transfer studies on falling‐film towers by various investigators, it has been commonly accepted by most workers that the liquid flow is essentially streamline in nature for liquid‐film Reynolds numbers under 1,800 to 2,000; conseuquently it would be expected that the rate of physical gas absorption in such liquid films could be predicted directly from a knowledge of molecular diffusion rates. Measurements of the absorption of pure gases in falling liquid films at low Reynolds numbers substantiated the findings of other investigators that the mass transfer rates were manyfold greater than could have been predicted if molecular diffusion were the only transfer process. Increased interfacial area due to rippling of the liquid films could not account for the large increase in mass transfer rates found, and experiments with the addition of a dye stream to the liquid at the freer interface indicated turbulence. Dissolution rates of slightly soluble solids coated on the tube wall to liquid films were measured and showed that the liquid film was not in laminar flow even for Reynolds numbers as low as 300. An explanation is proposed which resolves these apparently conflicting results between momentum and heat and mass transfer, based on the fact that mass transfer measurements provide a more sensitive test for the presence of turbulence than do momentum or heat transfer measurements.

Parameters affecting maximum fluid transport in large aperture fractures

“…Even without the effect of the delivery port geometry, free surfaces on vertical walls are inherently unstable and easily form waviness. These waves impact transport velocity and pressure gradients within the fluid and possibly affect fracture-matrix transfer [40].…”

Mass transfer from a soluble solid sphere

“…Thus there seems no reason why the analogy should not apply in these cases, and most experimentaI evidence suggests that it does. However, as a result of a study of wettedwall columns, Stirba and Hurt (29) suggest that the analogy may apply only under very strictly controlled conditions. They propose that since mass is transferred by the movement of specific molecules rather than by collisions and is the slowest of the three transfer processes, it is the most susceptible to alight degrees of turbulence.…”

A numerical study of mass transfer in free falling wavy films

“…M:iss transfer rates were determined either by weighing thc plaic before and after the experiments or by measuring the outlei bulk concentration of the fluid. Stirba and Hurt (1955) attempted to relate the increa& transfer rate due to the waves to a universal eddy ditfusivrt? Experiments in 2 m long tubes coated with organic acids owr lengths from 1 to I .5 m showed apparent diffusivities ranging from three to twenty times the molecular ditrusivity, depending on the Reynolds and Schmidt numbers.…”