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Terminal velocity and drag reduction measurements on superhydrophobic spheres
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10.1063/1.3081420
/content/aip/journal/apl/94/6/10.1063/1.3081420
http://aip.metastore.ingenta.com/content/aip/journal/apl/94/6/10.1063/1.3081420
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Figures

Image of FIG. 1.
FIG. 1.

A sequence of three images [(a)–(c)] showing a comparison of settling in water of a 1.5 in. diameter acrylic sphere with three different surface coatings. Each image consists of a composite of three frames from three different experiments; the sequence of frames selected is the one corresponding to the median terminal velocity for that surface coating from a set of ten drop tank experiments. The object on the left in each image is an acrylic sphere with a thin layer coating of sieved sharp sand with grain sizes below . The object in the center in each image is the same acrylic sphere with its thin layer coating of sieved sharp sand, but with an additional coating of the HIREC superhydrophobic paint. The object on the right in each image is the same as in the center, but with an ethanol pretreatment to suppress the formation of a plastron.

Image of FIG. 2.
FIG. 2.

Terminal velocities (vertical components) measured for spheres with and without hydrophobic sand surface finishes. (a) Four spheres with 1 in. diameter and various surface finishes. The first group of four bars shows one sphere with the following sequence: (i) blank surface (unfilled bar), (ii) surface coated with sieved sand of below grain size (diagonal pattern bar), (iii) Granger’s Gore-Tex® waterproofing treated sand surface (shaded bar), and (iv) Granger’s Gore-Tex® waterproofing treated sand surface with ethanol pretreatment to prevent formation of a plastron (dotted bar); each bar represents the average terminal velocity from at least eight drop tank measurements. The second group of four bars is a replicate of the same sequence using a new sphere. The third group of four bars uses a superhydrophobic paint (HIREC-1450) to impart water repellency (lighter shaded bar) and the fourth group of four bars is a replicate of the same sequence using a new sphere. (b) and (c) are repeats of (a) using 1.5 and 2 inch diameter spheres, respectively. (d) Shows the terminal velocity in water (shaded bar) and then in water, but with an ethanol pretreatment to prevent the formation of a plastron (dotted bar), for two spheres of each diameter coated in commercially available superhydrophobic Magic Sand™.

Image of FIG. 3.
FIG. 3.

(a) Estimates from the data in Fig. 2 of the ratio of the drag coefficients with and without plastron using the terminal velocity measured with the plastron bearing sphere in water and the same sphere using an ethanol pretreatment to prevent the formation of a plastron. (b) Thickness of the plastron in water measured on sieved fractions of sand possessing: (i) a HIREC-1450 hydrophobic paint coating (diamonds), (ii) a Granger’s Gore-Tex® waterproofing (triangles), and (iii) commercially available superhydrophobic Magic Sand™ (squares).

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/content/aip/journal/apl/94/6/10.1063/1.3081420
2009-02-10
2014-04-19
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Terminal velocity and drag reduction measurements on superhydrophobic spheres
http://aip.metastore.ingenta.com/content/aip/journal/apl/94/6/10.1063/1.3081420
10.1063/1.3081420
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