CAREER: Uncover contact line dynamics during thin film evaporation on micro/nano-engineered surfaces with combined velocimetry, thermometry, and interferometry

Computers and electronics with ever-increasing power densities have become an indispensable part of our daily life to support our learning, communication, driving, and other applications. Effective thermal management technologies are essential to cool these devices to a safe temperature to sustain their high performance. Thin film evaporation, based on continuous evaporation of very thin films of liquid coolant, is a promising cooling strategy due to its simple design, high cooling capacity, and high stability. By incorporating micro/nano-structures such as micro-pillars and nano-pores, the cooling capacity of thin film evaporation has been significantly improved in recent years but is still much lower than theory predictions, due to the lack of fundamental understanding, especially the detailed flow and thermal characteristics at microscopic and nanoscopic scales. This CAREER project seeks to study fluid flow and thermal transport processes at evaporating interfaces by accurately measuring the flow speed, film shape and temperature within thin coolant films that are typically a few micrometers thick. The knowledge gained will be integrated into educational and outreach activities by establishing a thermal-fluid instructional laboratory at Montana State University and creating educational materials targeting the general public and school children. The overarching goal of this project is to advance the fundamental understanding of the flow, thermal transport, and contact line dynamics at evaporating interfaces via quantifying 3D velocity fields, interface temperature, and interface profile, enabled by innovative experiments and modeling efforts. Specifically, the project team will (i) employ combined astigmatism particle tracking velocimetry, fluorescence thermometry and interference microscopy to perform measurements on micro-structured surfaces, (ii) quantify film temperature and meniscus dynamics within nanopores using nanoscale quantum dot thermometers and environmental scanning electron microscopy, and (iii) develop a microscale model for thin film evaporation on micro-structured surfaces with improved accuracy by incorporating Marangoni flows. The research will characterize the wicking dynamics, liquid-vapor interface temperature, curvature and meniscus dynamics of thin evaporating films with high spatial and temporal resolutions, which will allow precise determination of the accommodation coefficient and the quantification of Marangoni effects, thus filling in current knowledge gaps and informing the next generation of predictive tools. This project is jointly funded by the Thermal Transport Processes Program and the Established Program to Stimulate Competitive Research (EPSCoR). This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.