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EFFECT OF SURFACTANTS ON THE GROWTH AND DEPARTURE OF
BUBBLES FROM SOLID SURFACES
by
Leslie B. King
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(MECHANICAL ENGINEERING)
December 2009
Copyright 2009 Leslie B. King
Object Description
| Title | Effect of surfactants on the growth and departure of bubbles from solid surfaces |
| Author | King, Leslie B. |
| Author email | lking@usc.edu; leslie.b.king@aero.org |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Mechanical Engineering |
| School | Viterbi School of Engineering |
| Date defended/completed | 2009-09-24 |
| Date submitted | 2009 |
| Restricted until | Unrestricted |
| Date published | 2009-11-02 |
| Advisor (committee chair) | Sadhal, Satwindar S. |
| Advisor (committee member) |
Redekopp, Larry Egolfopoulos, Fokion Yang, Bingen Shing, Katherine |
| Abstract | Bubbles are an important mass and energy transport mechanism and are present in many industrial systems. Boiling, fermentation, and aeration systems are a few examples where bubbles are key to mass and energy transport. In particular, there is scientific interest because of heat transfer fundamentals associated with the boiling phenomenon in various systems. Typically, bubbles form (nucleate) and grow on the crevices of solid surfaces. In a gravity field, they detach due to the presence of buoyancy. The process begins with simple growth after nucleation, followed by vertical elongation near the attachment point (necking phenomenon), and ending with detachment. Bubble formation time and departure size can influence the efficiency of these systems. It has been observed that a surfactant added to an ebullient flow field reduces the departure size of the bubble and the formation time. Although the surfactants being used cause a reduction in surface tension, the effect on departure size is opposite to that of a pure fluid with lower surface tension. To understand the reduction in bubble size, the flow field around the bubble together with surfactant transport is being studied. Bubble growth and departure models have been developed using computational fluid dynamics (CFD) with the Fluent package. Experiments have been conducted to capture the growth of the bubble with and without surfactants in deionized water using injected air to create a bubble in an isothermal system (instead of vapor bubbles as in boiling). This choice is made so as to isolate the effect of surfactant additives from thermal effects. Particle image velocimetry (PIV) test were also carried out to quantify the flow around a forming bubble. The results indicate that necking occurs more rapidly with a surfactant present. A surface tension gradient creates a tangential stress at the surface and causes it to move in the direction of the higher surface tension.; This movement causes the fluid in the neighborhood of the interface to move. This is called Marangoni convection. The fluid motion, in the bulk, therefore has both radial and tangential components. Final calculations have shown that the tangential velocity causes an increase in total pressure on the neck of the bubble. The additional force causes the neck to collapse more rapidly. |
| Keyword | bubbles; surfactant; surface tension gradient; mass transport; hydrodynamic forces |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m2707 |
| Rights | King, Leslie B. |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | http://www.usc.edu/isd/libraries/services/ask_a_librarian/email/ |
| Filename | etd-King-2488 |
| Archival file | uscthesesreloadpub_Volume40/etd-King-2488.pdf |
Description
| Title | Page 1 |
| Full text | EFFECT OF SURFACTANTS ON THE GROWTH AND DEPARTURE OF BUBBLES FROM SOLID SURFACES by Leslie B. King A Dissertation Presented to the FACULTY OF THE USC GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (MECHANICAL ENGINEERING) December 2009 Copyright 2009 Leslie B. King |
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