X-ray tomographic measurement of Taylor bubble shape for investigation of mass transfer coefficients

Several experimental and mathematical modelling studies have been done to quantify the effect of different parameters such as liquid properties, bubble velocity, bubble size and level of contamination of fluid on the liquid side mass transfer from gas bubbles to liquids and various correlations have been proposed. However, little attention has been paid to the influence of the pipe wall on mass transfer coefficient particularly for millimeter sized channels.

In this work, the absorption rate of a single Taylor bubble of carbon dioxide in water is investigated using a new technique in vertical channels. The liquid side mass transfer is studied by measuring the changes in the size of the bubble at constant pressure. The experiments cover a large range of initial Taylor bubble length varying from 6 to 24 mm. The channel is a glass channel with 6 mm hydraulic diameter and circular and square cross section. The bubble is continuously monitored by holding the bubble stationary using a downward flow of liquid. The method which is used to measure the variation of the bubble size is microfocus X-ray radioscopy and tomography.

The results show that by application of the radioscopy and tomography technique the evolution of the bubbles shape during mass transfer reliably can be measured. This technique was suitable for determining the three-dimensional shape of Taylor bubbles in channels and enabled the acquisition of a series of high-resolution radiographic images of nearly stationary Taylor bubbles. The processed images, which give volume (and also the interfacial area) of the bubble with high accuracy as a function of time, are used to evaluate the liquid side mass transfer between bubble and liquid.