Experimental study on the influence of horizontal channel vibration on the mass transfer rate of bubbles in milli-channels

Millimeter-sized reactors have gained a great research interest from the industry and academia because of their advantages such as large interfacial area, high mass transfer rates, low pressure drop, and ease of scale-up over the conventional reactor technology. Optimization of the multiphase flow processes is one of main requirements of modern industry to achieve the higher efficiency and environment-friendly processes. A new design and technique for measurement of mass transfer rate of single bubbles in vibrating milli-channels is being developed with the claimed goal of process intensification [1].
In this study, the absorption rate of a single Taylor bubble of carbon dioxide in water is investigated using high resolution X-ray radiography technique in an oscillating vertical channel. The liquid-side mass transfer coefficient is calculated by measuring the changes in the size of the bubble at constant pressure. The channel is a glass pipe with 6 mm inside diameter and circular cross section. The glass channel is vibrated using a calibrated vibrator in horizontal direction. The amplitude and frequency of vibration is controlled by a wave generator accurately. The method which is used to measure the variation of the bubble size is X-ray radiography. This technique was qualified to disclose the three-dimensional shape of Taylor bubbles in capillary 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 coefficient between bubble and liquid using the mass conservation equation. The liquid phase is filtered-deionized water and the gas phase is carbon dixide.
The results for the short term dissolution of single carbon dioxide bubbles confirmed that the channel vibration causes to increase of mass transfer rate for single Taylor bubbles. The dissolution rate of bubbles increases as the frequency of vibration rises and there is a maximum value at the channel resonance frequency where large surface oscillation of bubbles exists. Furthermore, it was shown that the liquid-side mass transfer coefficient of dissolving bubbles grow up as the vibration amplitude of channel enlarges.