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ISSN Online: 2379-1748

ISBN Flash Drive: 978-1-56700-518-9

5th Thermal and Fluids Engineering Conference (TFEC)
April, 5-8, 2020, New Orleans, LA, USA

Determining micro droplet profile using internal reflection interference

Get access (open in a new tab) pages 109-113
DOI: 10.1615/TFEC2020.mns.031997


We introduce an optical diagnostics to determine the dual-surface profile of liquid droplet using internal reflection interferometry. A coherent laser beam is internally reflected on the air/liquid interface of a sessile droplet placed on a prism-based substrate to produce an interference fringe on a screen far from the substrate. The reflected laser rays consist of the reflection from the center spherical droplet profile and the one from the lower hyperbola-like droplet profile. The reflected rays are interfered each other to form the interference fringes. Ray tracing simulation is conducted using a custom-designed computer program. The simulation shows that the interfering rays reflected near the inflection point produce the outer-most fringes of the concentric interference pattern on the screen, and the reflected rays from the apex of the spherical profile and the contact line of the lower hyperbola-like profile construct the fringes at the center of the interference patterns. The simulated results are compared with the experimental observation to show a good agreement in the number and the location of the fringes and the radius of the outer-most-fringe where the number of the fringes is dependent on the droplet thickness and the radius of the fringe depends on the contact angle of the droplet. This result provides a new measurement technique to determine the morphological features of very small microdroplet such as the thickness (< a few micron thickness), the contact angle (< a few degree), and the dualsurface profile.