BUBBLE FORMATION AT A PUNCTURE IN A SUBMERGED RUBBER MEMBRANE

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Abstract
Very large enhancements in volumetric mass transfer coefficients have recently been reported using a new type of sparger which is comprised of a punctured rubber membrane. The punctured sheet has been reported to produce very uniform emulsions of small bubbles, which leads to large apparent increases in gas voidage and mass transfer area. Flooding(slugging) is presumably repressed owing to the “elastic hole” phenomenom whereby the rubber sheet balloons and expands as applied pressure increases. Under conditions of expansion, a puncture in the sheet also expands thereby mitigating the occurence of jetting. In the present effort, we study a single puncture in the center of circular rubber sheets of 2, 3, and 4 inch diameters. By measuring bubble frequency and flow rate, we compute average bubble size. These results for flow rates from 0.01 to 2.0 cc/sec suggest that bubble size is practically constant over a nearly two decades of flow rate, until a flow of around 0.5 cc/sec, thence bubbles tend to follow the empirical correlation of L. Davidson and Amick (1956) and the inviscid theory of J.F. Davidson and Schuler (1960) both of which predict bubble volume increases as the 6/5 power of flow. Using the “point source” model of J.F. Davidson for bubble growth, we include additional effects of surface tension to derive the required detachment-time. This leads to a theory which includes inertial, buoyancy and surface tension effects. The theory gives flow rate as a function of final bubble size and agrees quite well with the 180 experiments reported. The new theory approaches the inviscid models in the limit of large gas flow rates. Finally, we present results which clearly suggest that hole area increases linearly with increasing plenum chamber pressure.

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