Transient heat transfer and droplet dynamics during dropwise condensation on lubricant-infused surfaces

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Vapor condensation is ubiquitous in nature and in many industrial applications, including power generation, air conditioning, and water harvesting. Commonly water condenses as a thick (~mm) film, acting as a thermal barrier to heat transfer. In contrast, dropwise condensation, in which the condensate forms discrete droplets, can lead to an order-of-magnitude improvement in heat transfer performance compared to the filmwise mode. So-called lubricant-infused surfaces (LIS), which consist of a microporous surface infused with a thin oil layer, promote dropwise condensation, and can consequently lead to smaller and more efficient energy and water harvesting systems. However, the widespread implementation of LIS in commercial applications is limited due an incomplete understanding of droplet-lubricant interactions, droplet nucleation and growth, and lubricant drainage. This project elucidates these dynamics, and studies their influence on condensation heat transfer rates. Furthermore, this project fosters interest in science and help overcome the barriers for women and underrepresented minorities entering the field of engineering via outreach programs at a local girls-only middle school and summer research internships for talented high school students.This integrated experimental and mathematical research project provides a comprehensive understanding of the relationship of heat transfer, phase change, and fluid dynamics during condensation on lubricant-infused surfaces. It overcomes previous limitations that hindered the direct observation and quantification of nucleation and heat transfer during dropwise condensation by combining high-speed imaging with high-resolution microscopy. Mathematical modeling complements experiments to develop predictive tools and design criteria for condensation heat transfer enhancement. Specifically, the three main research aims are: (1) Determine the nucleation rate density on lubricant-infused surfaces, (2) Measure the contributions of phase change and forced convection from sweeping droplets on overall heat transfer rates using high-speed infrared imaging, and (3) Quantify the effect of cloaking on droplet growth via direct accretion.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.