Masters Theses

Date of Award

6-1986

Degree Type

Thesis

Degree Name

Master of Science

Major

Engineering Science

Major Professor

Carl J. Remenyik

Committee Members

Richard J. Jendrucko, John H. Forrester

Abstract

The incomplete understanding of bubble motion and fluid flow around bubbles when they are in contact with a solid surface indicates a need for further study. An experimental flow visualization investigation was undertaken to look at the flow around gravity-driven bubbles underneath an inclined plate. Nearly neutrally buoyant tracer particles, ranging from 88 μm to 150 μm in diameter, were dispersed in the camera's field of view in either plain water or a water-detergent solution. An air bubble of predetermined volume was released on the underside of the plate surface. A high speed motion picture camera filmed the bubble as it moved by the camera's field of view. Several different bubble volumes (10 cc, 40 cc, 70 cc, and 100 cc) were filmed at three plate angles (0.76°, 4.29°, and 7.83°).

A computer program was written to digitize the motion of individual tracer particles one at a time. The film was projected onto a graphics tablet that was linked to the computer terminal. By using this tablet and a stylus, a particle's coordinates were read into the computer frame by frame and stored in memory. Between 20 and 50 particle paths were traced for each bubble.

Four programs were written to plot the calculated displacement and velocity data in two different coordinate systems, namely, laboratory-fixed and bubble-fixed. In laboratory-fixed coordinates the bubble moves through the stationary fluid whereas in bubble-fixed coordinates the fluid moves past a stationary bubble. It was found that the bubble-fixed plots were easier to interpret because the particle paths were given with respect to the stationary bubble. The instantaneous velocity plots were of little use because the flow was turbulent and the plots became a chaotic assemblage of vectors pointing in all directions .

By comparing all of the bubble-fixed plots and subsets of these plots some characteristic patterns are seen.

The bubble surface becomes more randomly unsteady with increasing plate angle or bubble volume. This surface is more unsteady in plain water than in a water-detergent solution.

* The bottom surface of the bubble becomes flatter as the volume increases and tends to become horizontal. It also tends to become horizontal with decreasing plate angle. The bottom tends to be flatter in the water-detergent solution.

* The bubble height increases with increasing plate angle or bubble volume. For the same bubble volume and plate angle, the bubble height is greater when the bubble is in plain water.

* A brow at the front of the bubble protrudes to various degrees.

* The bubble velocity and the Reynolds number increase with increasing plate angle or bubble volume. Both the velocity and the Reynolds number have a greater value when the bubble is in plain water.

* A wake with various intensities of turbulence is observed behind each bubble.

* Tracer particles move down the front interface of all the bubbles. When in a water-detergent solution, this movement may be an artifact of the method used. Because of the finite size of the particles, the movement is probably opposite the flow at the front interface for the wate-rdetergent solution.

* Intensity and extent of the turbulent flow region increases with increasing plate angle or bubble volume.

* Rolling bubbles show one or more recirculating regions underneath the bubble, while sliding bubbles do not.

These type of bubbles need to be studied further to acquire a more complete picture of how their flows progress as they move up the inclined plate.

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