CAREER: Condensation-Driven Phase-Transitioning Surfaces

University Of Illinois At Chicago, Chicago IL

Investigators

Abstract

Condensation plays a pivotal role in countless natural and industrial activities, such as in cloud formation, electronic cooling, power generation, emulsion formation, water harvesting, and materials development. Promotion dropwise condensation on surfaces (instead of a liquid film) can result in significant savings in energy and cost in many applications like those mentioned above. In recent years, hydrophobic, superhydrophobic and liquid infused surfaces have been tested to promote dropwise condensation. However, the performance of such surfaces can get compromised easily by a variety of debilitating mechanisms such as random droplet nucleation within textures (leading to eventual film formation), surface flooding at high humidity, organic contamination, and surface degradation. The goal of this CAREER project is to understand condensation on a class of existing materials that can undergo phase-transition due to condensation itself. Such materials possess several beneficial attributes of solid and liquid surfaces that could be the key to overcome many of the challenges faced by the existing superhydrophobic or liquid infused surfaces. Investigation of condensation on such materials could also clarify the long-standing questions on the fundamentals surrounding phase-change, such as the role of substrate thermal conductivity, condensation rate and relative humidity on the growth of droplets and heat-transfer rates. Results from this research will be integrated with educational activities that seek to increase women/underrepresented-minority student participation in engineering via undergraduate (UG) student recruitment for water harvesting via condensation, and engagement with high-school (HS) students through university outreach program (UIC-CHANCE). The scientific objectives of this CAREER project is to discover new fundamental knowledge to inform development of coatings for condensation applications based on surfaces that undergo phase-transitions during condensation. This goal will be accomplished by performing comprehensive studies to understand water droplet interactions with phase-transitioning surfaces in absence/presence of condensation to determine the relation between nanoscale transport phenomena (e.g. temperature distribution below/around droplets) and the resulting macroscopic effects (reduced droplet adhesion, delayed droplet freezing on highly subcooled substrate (<<0 oC)) as a function of phase-transition material properties (such as their solid-state surface structure, water miscibility, thermal properties), thermodynamic conditions (the degree of subcooling and relative humidity) and interfacial properties using conventional (optical/IR microscopy) & advanced diagnostic tools (Environmental Scanning Electron Microscopy, X-Ray Phase Contrast Microscopy). As part of such investigations, a new methodology will be developed to measure temperature distribution in the condensing surface beneath droplets with nanoscale spatial resolution. The correlations established from experimental measurements and theoretical models will be supplemented with numerical simulations to elucidate the fundamentals of condensation on the special phase-transitioning surfaces. 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.