Date of Award

1985

Degree Type

Thesis

Degree Name

Master of Science in Chemical Engineering (MSChE)

Department

Chemical Engineering

First Advisor

Donald J. Gray

Abstract

An investigation into the influence of suspended glass particles on bubble diameter, gas holdup, and interfacial area in an agitated tank

(May, 1985)

Paul M. Randall, B.S. University of Massachusetts

M.S. University of Rhode Island

Directed by: Dr. Donald J. Gray

Design of three-phase, gas-slurry, reactors is of continual interest and intrigue to the chemical engineer. The interest stems from the importance of gas-slurry reactors in the chemical, biochemical, and pharmaceutical industry. The intrigue is in the unknown (or poorly understood) relationships among key design variable that are potentially important to developing truly optimum equipment.

Developing methods for a more rational design of an agitated gas-slurry reactor requires experimentation. Without preliminary experimentation it is almost impossible to determine bubble diameter and gas holdup. Design and scaleup of gas-slurry reactors are based on mass transfer rate models which require knowledge of the average bubble size and volume fraction occupied by the gas in the dispersion. To date, there is very little information on the effect of solids on bubble size in gas-slurry reactors.

An investigation was conducted to determine the influence of suspended glass particles on bubble diameter, gas holdup, and interfacial area. The experiments were conducted in a 45.72 cm diameter flat bottom plexiglass tank. A new measuring technique was developed to determine local gas holdup and bubble sizes using the light transmission method. Interfacial area can then be calculated by using the well known relationship a = 6G/DB.

Consistently, experimental results show significant decreases in bubble diameter, gas holdup and correspondingly a decrease interfacial area with the initial addition of 25 μm glass particles (.3 wt %). When more solids are added (further decreases are observed but not in the same order of magnitude decreases as the initial addition of solids. Overall, gas holdup decreased by 10-40%, mean bubble size decreased by 5-20%, and interfacial area decreased by 6-23%.

The results are interpreted in terms of more bubble coalesces taking place with particles versus no solids so that bubbles are larger, faster rising which would reduce the gas holdup. The fact that the bubbles are also smaller appears to be due to the reduction in the gas holdup since all the data can be correlated together into one equation.

Larger particles (70 μm, 200 μm) are observed to have little effect on holdup or bubble size and tend to move more independently from the liquid.

Linear correlations of the data resulted in some dependences of the bubble diameter which agree with work of Shinnar and Calderbank in the coalescence controlled regions.

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