TAILORING HEAT TRANSFER SURFACES
Recent research has reported that material characteristics at a heated or cooled surface affect thermal-hydraulic phenomena and thus can affect heat/energy system performance and safety. In our previous work, systematically designed experiments have been conducted to quantify surface characteristic effects, such as thermal conductivity, surface structure change, and surface wetting heterogeneity for actual heat transfer systems. Basic understanding of the surface effects on thermal-hydraulics can be used to describe actual phenomena in prototypical industry conditions. In addition, my research interest seeks to develop an engineered high-performance heat transfer material surface by tailoring surface compositional and physical characteristics for thermal components. We have established collaborations with material scientists to develop practical approaches for advanced surfaces having improved heat transfer capabilities and enhanced material reliability.
Boiling on tailored surfaces
Thanks to high heat transfer characteristics, boiling is extensively used in various industries and applications. In boiling, there are four different boiling regimes with three boiling transition points (ONB- Onset of Nucleate Boiling, CHF-Critical Heat Flux, MHF-Minimum Heat Flux), and the thing is that each regime has totally different heat transfer characteristics. Therefore, predicting and manipulating the boiling transition points for its purpose are the most important capabilities to design advanced heat and energy transfer systems.
Recent studies report that the effects of surface characteristics on boiling could be significant when micro/nano-fabrication methods are used but details are not well understood so far. In this regard, our team is trying to reveal the underlying physics of boiling phenomena on nano/micro-structured or wetting controlled surface to develop engineered surface having high heat transfer performance.
Condensation on engineered surfaces
Superhydrophobic surfaces have been investigated widely due to their useful properties that include self-repelling, anti-sticking, anti-fouling, and self-cleaning characteristics. These are important for condensation heat transfer. However, recent studies report that superhydrophobic surfaces lose their useful characteristics at high supersaturated water vapor conditions although they have superhydrophobic properties under atmospheric conditions. Researchers have reported that condensed water fills the surface structures and that the wetted structures are responsible for the loss of superhydrophobicity. A droplet was stickier on the surface filled with liquid rather than a hydrophobic smooth surface because it filled with liquid. Our previous study investigated the mechanism by which superhydrophobic characteristics disappear on a hydrophobic micro/nano-structured surfaces as the surrounding conditions change and proposed guidelines for sustaining the novel properties based on theoretical and experimental investigations.
Based on the understanding, currently, we are engineering a hierarchical superhydrophobic surface promoting coalescence-induced jumping to increase the efficiency of condensation.
