EFFECT OF MASS TRANSFER ON THE VELOCITY OF RISE OF BUBBLES IN WATER.

Journal/Book: Reprinted from Nature Vol. 190 No. 4777 pp. 687-688 May 20 1961. 1961;

Abstract: By Dr. J. H. LEONARD and PROF. G. HOUGHTON Department of Chemical Engineering University of Pittsburgh Pennsylvania ALTHOUGH Datta Napier and Newitt1 were the first to suggest that "mass transfer (from bubbles) may be accompanied by some retarding effect" no definite conclusions were reached in this respect from their experiments an carbon dioxide bubbles rising in water. In the present measurements both velocities of rise and mass transfer-rates for bubbles could be measured separately over short distances in a column of water. The apparatus used was a modification of that in which soluble bubbles were formed in a cup under mercury and allowed to rise up through a completely closed 'Pyrex' glass column (9 cm. internal diameter 270 cm. long) filled with water; the change in volume of each bubble was recorded by registering the position of a mercury meniscus in a horizontal capillary side-arm which provided the only opening to the atmosphere. By stretching a fine platinum wire through the capillary and connecting the wire to a bridge circuit it was possible to record the position of the mercury meniscus and hence the bubble volume on one channel of a high-speed Sanborn oscillograph. Although the principle was used earlier3'4 these earlier experimenters used high-speed photography to determine the volume of the bubble by photographing the position of the liquid meniscus in the capillary. However the present apparatus also differs from that of Houghton et al.2 in that the rising bubbles interrupt a series of light beams and photoelectric cells placed at intervals of 47 0 cm. up the column. As the bubble passed each light beam the change in light intensity was recorded on a second channel of the Sanborn oscillograph. In this way it was possible to determine the average bubble velocity and the average mass transfer-rate separately over each 47 0 cm. section of the column together with the corresponding average bubble diameter over the same section. In certain instances the velocities of rise obtained by the method described were also confirmed independently in a separate apparatus by forming the bubbles at jets of various sizes using a micrometer hypodermic syringe and then timing them over a 110 cm. length of column using a stopwatch and starting the measurements at a distance of 20 cm. from the jet (cf. ref. 5). ...

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