Ultrascalable Three-Tier Hierarchical Nanoengineered Surfaces for Optimized Boiling
mediaposted on 12.12.2019, 19:08 by Jiaqi Li, Wuchen Fu, Bohan Zhang, Gaohua Zhu, Nenad Miljkovic
Nanostructure-enhanced pool and flow boiling has the potential to increase the efficiency of a plethora of applications. Past studies have developed well-ordered, nonscalable structures to study the fundamental limitations of boiling such as bubble nucleation, growth, and departure, often in a serial manner without global optimization. Here, we develop a highly scalable, conformal, cost-effective, rapid, and tunable three-tier hierarchical surface deposition technique capable of holistically creating micropores, microscale dendritic clusters, and nanoparticles on arbitrary surfaces. We use this technique to investigate the pool boiling heat transfer performance with focus on the bubble departure diameter and frequency. By tuning the structure length scale, the pool boiling characteristics were optimized through a multipronged approach, including increasing nucleation site density (micropores), regulating bubble evolution behavior (dendritic structures), improving surface wickability (nanoscale particles and channels), and separating liquid and vapor pathways (micropores and micro/nanochannels). Ultrahigh critical heat fluxes (CHF) ≈400 W/cm2 were obtained, corresponding to an enhancement of ≈245% compared to smooth copper surfaces. To study in situ bubble departure and coalescence dynamics, we developed and used high-magnification in-liquid endoscopy. Our work reveals the existence of a linear relationship between the bubble departure diameter/frequency near the onset of nucleate boiling and CHF enhancement. Our study not only develops a highly scalable, conformal, and rapid micro/nanostructuring technique, it outlines design guidelines for the holistic optimization of boiling heat transfer for energy and water applications.
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Ultrascalable Three-Tier Hierarchical Nanoengineered Surfacessurface deposition techniqueheat transfersurface wickabilitybubble departure diameteroutlines design guidelinesvapor pathwaystunable three-tierOptimized Boiling Nanostructure-enhanced poolcopper surfacesheat transfer performancebubble evolution behaviorCHF enhancementbubble nucleationnonscalable structuresstructure length scalenucleation site densitymicroscale dendritic clusterswater applicationsconformalcoalescence dynamicsheat fluxesnanoscale particleshigh-magnification in-liquid endoscopyPast studiesoptimizationmicroporebubble departure