Date of Award

6-2011

Document Type

Open Access

Degree Name

Bachelor of Science

Department

Mechanical Engineering

First Advisor

Ann Anderson

Language

English

Keywords

drag, aerodynamics, aerogel, coating, particle

Abstract

The objective of this project was to determine if superhydrophobic aerogel-based surface coatings have an effect on hydrodynamic drag. Superhydrophobic aerogels were fabricated using Union College’s patented rapid supercritical extraction technique. These aerogels were crushed and combined with a perfluorinated ion-exchange membrane to create a superhydrophobic coating that can be painted on to surfaces. These coatings are 250% aerogel by weight to Nafion in solution, and exhibit an average contact angle with water of 160°. An investigation of the aerogel powders and films using a scanning electron microscope (SEM) revealed that the most successful films had an average aerogel material width of 50 μm, uniform distribution of aerogel material on the coated slide, and that the peaks of the aerogel material coming into contact with the water had a feathery, crystalline appearance. Three experiments were designed and conducted to determine if coating an object had an effect on the drag forces. The first experiment was a falling ball experiment, which examined the falling velocity of coated and uncoated balls gliding down an inclined surface. The second experiment used a rotational viscometer to examine the difference in torque required to rotate a spindle in water. The third experiment used particle image velocimetry (PIV) to examine the wake size of coated and uncoated cylinders in cross flow. For the conditions tested, no significant differences were observed between coated and uncoated surfaces. These experiments were performed at low Reynolds numbers (between 613 and 10,258), which are characterized by a combination of friction drag and pressure drag. Future work with these surfaces should include testing in flows of higher Reynolds numbers, as well as conducting experiments that examine pressure drag and friction drag separately.

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