Mass Transfer in a Plunging Liquid Jet

Abstract

Plunging liquid jets are being increasingly used as mass transfer devices in wastewater and sewage treatment, chemical manufacture, and mineral flotation. The advantages of using plunging liquid jet bubble is their ability to produce very fine bubbles, typically less than 500 microns in diameter, without the need for small clearances, moving parts or mechanical seals which may block or fail in industrial situations, especially those involving solid suspensions. The effectiveness of mass transfer devices is commonly reported in terms of the volumetric mass transfer coefficient, k L a, with higher values indicating superior performance. One way of obtaining higher k L a values is to increase the specific interfacial area, a. This is achieved by either increasing the gas holdup, or decreasing the mean bubble size for a given gas/liquid flow ratio. A method for increasing the amount of interfacial area per unit volume in a plunging liquid jet bubble column is presented in this paper. A wire gauze was placed in the top section of the bubble column and its effects on (i) froth height, (ii) rate of gas entrainment, (iii) bubble size and (iii) operational stability were determined. It was found that the inclusion of the gauze screen resulted in smaller bubble size and higher gas entrainment rates for a given liquid jet power input. Moreover, the inclusion of the gauze significantly reduced fluctuations in the froth height resulting in improved operational stability.