Session: Government Agency Student Posters

Paper Number: 173342

Dynamic Optical Measurement of Evaporating Liquid Films 

Evaporating thin liquid films frequently show instabilities at nano- and micro-scales, significantly affecting thermal transport, fluid dynamics, and interfacial behavior in a wide range of technologies. These include microelectromechanical systems (MEMS), advanced cooling solutions for electronics, lab-on-chip platforms, and even atmospheric water transport mechanisms. The motivation for this research stems from the need to better understand and control phase change dynamics in confined geometries, where competing thermal and mechanical forces interact in complex, non-linear ways. Despite the promising potential of phase change processes to deliver high-efficiency thermal management, especially at the nanoscale, a lack of fundamental understanding, particularly near the contact line region, hinders the predictive design of next-generation thermal systems. This study aims to investigate the dynamic stability of evaporating thin liquid films and their coupled influence on macroscopic contact line motion. Specific attention is given to the role of evaporative cooling, capillary effects, disjoining pressure, and thermal gradients in driving spontaneous oscillations or rupture of the liquid film. The core contribution of this work lies in the development of a novel experimental platform capable of resolving both film thickness and wall temperature fields simultaneously with high spatial and temporal resolution. The experimental setup consists of a confined volatile liquid film sandwiched between a transparent upper disk and a heated Silicon Carbide (SiC) wafer. To capture the film's thermomechanical response, two complementary optical diagnostics are employed. Monochromatic reflectivity-based interferometry is used to measure film thickness variations and capture mechanical effects such as capillary and disjoining pressure. Simultaneously, an Optical Interference Contactless Thermometry (OICT) technique is used to map wall temperature fields. OICT exploits the temperature-sensitive refractive index of SiC to produce interference patterns that can be quantitatively interpreted to reveal localized thermal gradients. This dual-interferometric approach allows for dynamic, co-located visualization of interfacial phenomena, enabling the identification of transient instabilities that emerge during evaporation. Preliminary experiments reveal oscillatory behaviors in both film thickness and wall temperature near the contact line, highlighting strong coupling between mechanical deformation and latent heat-driven cooling. These instabilities are found to arise under specific thermal boundary conditions and are influenced by factors such as film curvature and confinement. By bridging the gap between nanoscale film physics and macroscale contact line behavior, the insights gained from this study contribute to the fundamental understanding of phase change processes under confinement. Ultimately, the results are expected to inform the design of high-performance thermal systems that leverage controlled instabilities and localized phase change for enhanced energy efficiency and spatially resolved heat control.

Presenting Author: Saaras Pakanati University of Cincinnati

Presenting Author Biography: I am an undergraduate student majoring in Mechanical Engineering with a minor in Mathematics at the University of Cincinnati. I conduct research at the UC Lab for Interfacial Dynamics (UCLID), focusing on phase change phenomenon through both simulation and experimentation. My current projects include developing a multiscale model to simulate evaporation in cryogenic fuels and building a dual optical interferometry setup to investigate thermo-mechanical instabilities in evaporating liquid films.

Authors:

Amirhosein Sarchami University of Cincinnati
Saaras Pakanati University of Cincinnati
Kishan Bellur University of Cincinnati