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High-Speed Surface Plasmon Resonance (SPR) Reflectance Imaging of Drop Coalescence during Condensation and Evaporation

[+] Author and Article Information
Vinaykumar Konduru

Michigan Technological University
vkonduru@mtu.edu

Dong Hwan Shin

Michigan Technological University
dshin@mtu.edu

Jeffrey S. Allen

Michigan Technological University
jstallen@mtu.edu

Chang Kyoung Choi

Michigan Technological University
cchoi@mtu.edu

Seong Hyuk Lee

Chung-Ang University
shlee89@cau.ac.kr

Young-Ki Choi

Chung-Ang University
ykchoi@cau.ac.kr

Sosan Cheon

Seoul National University
cjsthtks@snu.ac.kr

Kenneth D. Kihm

University of Tennessee
kkihm@ut.edu

1Corresponding author.

J. Heat Transfer 138(8), 080903 (Jul 08, 2016) (1 page) Paper No: HT-16-1205; doi: 10.1115/1.4033819 History: Received April 15, 2016; Revised April 27, 2016

Abstract

Drop condensation and coalescence is visualized using high-speed Surface Plasmon Resonance (SPR) reflectance microscopy. SPR microscopy is a label-free technique that can characterize thin films (less than 1µm) by detecting the changes in the refractive index of the test medium. The sensing surface is a 50 nm thick gold film on a 2.5 nm thick Ti layer is deposited on a borosilicate substrate. P-polarized monochromatic light (632 nm) is incident on the gold film in a total internal reflection mode. Free electrons in the gold film are excited by the incident light when a resonance condition is met. The result is a decrease in the reflected intensity. Resonance depends upon wavelength, incident angle, and refractive index of prism and test medium. To induce condensation, a water bridge is created between the SPR gold film and an ITO coated glass slide. When the ITO coated slide is heated water evaporates from the bridge and condenses on the gold film. The sequence of images on the process of droplet deposition and drop coalescence are captured at 1500 frames per second. Experiments were conducted at an SPR angle of 44o, which is slightly above the minimum intensity angle for air at 43.8o. Therefore, the brightest and darkest regions correspond to the areas on the gold film covered with bulk water and a very thin film of water, respectively. The thickness of the film is proportional to the intensity of reflected light.

Copyright © 2016 by ASME
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