PI: Chanwoo Park Institution: University of Nevada, Reno
Advances in electronic, and energy systems require more efficient cooling to effectively manage high heat fluxes and large heat dissipation. Because of its superior cooling capabilities with low thermal resistances, phase change heat transfer is the preferred method to remove such demanding heat loads at isothermal conditions to avoid thermally induced damage. Meniscus thin-film evaporation is a fundamental phenomenon commonly found in phase change processes such as bubble growth and departure in pool boiling, slug and annular flows in flow boiling, wick boiling in capillary porous structures, and falling-film evaporation. The extended meniscus (Greek for crescent) is a curved liquid region near a three-phase (gas-liquid-solid) contact line which undergoes a drastic change in its liquid film thickness?from nano to micro to macro-scales. The extended meniscus is divided into three distinctive regions: (i) the adsorbed layer [region of intermolecular-bonding forces between liquid and solid molecules of a thickness < O(10 nm)], (ii) the thin-film evaporating region [disjoining-pressure-dominant region of a thickness > O(100 nm)] where evaporation predominantly occurs due to the small thermal resistance of the thin liquid film and (iii) the intrinsic meniscus [capillary-pressure-dominant region of a thickness > O(100 µm)]. For meniscus thin-film evaporation enhancement, a fundamental understanding of interplaying multi-scale moving meniscus and solid surface morphology is warranted. This project will study the meniscus thin-film evaporation enhancement using hierarchical multi-scale tri (nano, micro and macro) porous media ? (i) macro-scale surface modulation of (ii) micro-scale porous structures (e.g., interconnected particles or wires) with (iii) nano- and micro-scale surface morphology (e.g., second-tier surfaces) and specifically investigate micro-scale meniscus topology and dynamics in micro-scale capillary gaps, and meso-scale meniscus thin-film evaporation assisted by macro-scale liquid distribution and transport.
This hierarchical multi-scale approach, common in nature but rare in engineering, will provide a unique opportunity to delve into three-length-scale system designs and fabrication, combining nano-, meso- and macro-scale analyses for complex interfacial and phase-change processes. The insight gained from this research will advance a variety of emerging applications such as solar-powered point-of-use portable water desalinators using membrane distillation, bio-heat transfer from hyperthermia implants for cauterizing tumors, lab-on-a-chip, nano-fluidics, functional surfaces, miniature cooling systems of microthrust-powered satellites, and nano thermal?diode which rely on multi-scale and multi-physics processes of adsorption/desorption/diffusion, spreading, wetting, phase change and interfacial instability
