NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
Measurement of an Evaporating Drop on a Reflective SubstrateA figure depicts an apparatus that simultaneously records magnified ordinary top-view video images and laser shadowgraph video images of a sessile drop on a flat, horizontal substrate that can be opaque or translucent and is at least partially specularly reflective. The diameter, contact angle, and rate of evaporation of the drop as functions of time can be calculated from the apparent diameters of the drop in sequences of the images acquired at known time intervals, and the shadowgrams that contain flow patterns indicative of thermocapillary convection (if any) within the drop. These time-dependent parameters and flow patterns are important for understanding the physical processes involved in the spreading and evaporation of drops. The apparatus includes a source of white light and a laser (both omitted from the figure), which are used to form the ordinary image and the shadowgram, respectively. Charge-coupled-device (CCD) camera 1 (with zoom) acquires the ordinary video images, while CCD camera 2 acquires the shadowgrams. With respect to the portion of laser light specularly reflected from the substrate, the drop acts as a plano-convex lens, focusing the laser beam to a shadowgram on the projection screen in front of CCD camera 2. The equations for calculating the diameter, contact angle, and rate of evaporation of the drop are readily derived on the basis of Snell s law of refraction and the geometry of the optics.
Document ID
20110016832
Acquisition Source
Glenn Research Center
Document Type
Other - NASA Tech Brief
Authors
Chao, David F.
(NASA Glenn Research Center Cleveland, OH, United States)
Zhang, Nengli
(Ohio Aerospace Inst. Cleveland, OH, United States)
Date Acquired
August 25, 2013
Publication Date
June 1, 2004
Publication Information
Publication: NASA Tech Briefs, June 2004
Subject Category
Instrumentation And Photography
Report/Patent Number
LEW-17301
Distribution Limits
Public
Copyright
Public Use Permitted.
No Preview Available