Gas-liquid mass transfer in rotating perforated-disc contactors

This paper presents a numerical model for predicting the performance of liquid-gas mass transfer in a rotating perforated-disc type contactor. The device consists of a cylindrical section situated between two 45-degree conical sections. A liquid flows downward by gravity while a stream of air moves upward by buoyancy thus forming a counter-current flow situation in the contactor. A gas dissolved in the liquid transfers into air bubbles which are sheared to a tiny size as they rise through the perforations on the rotating disc. Both laminar and turbulent flows are treated. Utilizing the velocity distribution [10,11] and bubble trajectory [12] as the basis, the interphase mass transfer performance of carbon dioxide in the water-air system is numerically determined. It is disclosed that in both laminar and turbulent flow cases, the rate of interphase mass transfer increases significantly with a reduction in bubble size. Rotational speed does not affect mass transfer in laminar flow but causes an exponential mass transfer enhancement in higher turbulent flows. There exists an optimum through-flow rate of the liquid for the best mass transfer performance depending on the initial bubble size and disc speed. Test results [9] provide a qualitative confirmation of the theory.