Rehana Rahman

Date of Award

8-1-1984

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemical Engineering

Abstract

This thesis presents a study of void fraction when gas (air) is bubbled through a stagnant liquid (water) column in annular geometry. The apparatus used resembles an oil-well with a casing (outer tube) of 6.5 inch inside diameter, and it stood eight feet high. Three different sizes of replace able tubing (inner tube), ranging in outside diameter from 2.38 to 4.49 inches, were used to investigate the effect of annular diameters on void fraction. Superficial gas veloci ty, which is the single most important variable in determin ing void fraction, was varied from 0.015 to 0.60 ft/sec. The column temperature did not deviate much from 70° F and the column was open to the atmosphere.

Void fraction data gathered at four different sections (i.e., at different heights) of this column indicated strong influence of liquid height (from gas inlet) on void frac tion. A column eighteen feet tall with a 5 inch casing was constructed to gather void fraction data unaffected by liq uid height. Experiments conducted with this column (and tubings having 2.785 inches and 3.50 inches outside diame ter) did show the absence of entrance effects beyond nine feet from the gas inlet. These void fraction ( ) data were correlated with superficial gas velocity(u^) by a modified Zuber and Hench equation: Eg = Ug/(Aug+B) The parameter A was found to increase slightly and linearly with the inner tube diameter. The parameter B includes the single bubble rise velocity. The single bubble rise veloci ty was found to follow the Edger correlation, increasing slightly with the equivalent diameter (casing inside diame ter minus tubing outside diameter) of the channel.

Visual observation indicated the existence of slug flow whenever void fraction exceeded a value of 0.25 in all chan nels. These void fraction data were correlated by an equa tion suggested by Wallis (and similar in form to the Zuber- Hench Equation). The value of the parameter A was again found to increase slightly with the equivalent diameter of the channel. However, the dependence of void fraction on annular diameter, for both bubbly and slug flow, was found to be relatively small.

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