Ultrascalable Three-Tier Hierarchical Nanoengineered Surfaces for Optimized Boiling

Abstract

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.

Endoscopic Visualization of Contact Line Dynamics during Pool Boiling on Capillary‐Activated Copper Microchannels

“…Although increasing q ″ leads to increased bubble nucleation density, the average bubble departure diameter and frequency remain independent of q ″. [ 41,53 ] Therefore, analysis of the contact line dynamics at lower q ″ reflects the heat transfer mechanisms occurring at higher q ″.…”

“…In addition, for some porous surfaces having micro/nanostructures, the micro/nanostructures could enhance capillary and disjoining pressure, thus driving the liquid from the surrounding microlayer region into the structures. [ 53,57–59 ] In this case, the three‐phase contact line transforms to a three‐phase contact area, and the calculation of contact line length loses its significance. Future models are needed to clarify the contact line length on non‐porous structured surfaces and contact areas on porous structured surfaces with consideration of these effects on pool boiling performance.…”

Laser Surface Engineering for Boiling Heat Transfer Applications

“…The main enhancement approach, therefore, is based on the modification (functionalization) of the boiling surface in order to achieve a lower surface temperature at the onset of boiling, alongside increasing the density of active nucleation sites, limiting the bubble growth and finally delaying the dry-out as much as possible. Surface modification methods, thoroughly summarized in recent reviews [15,16], mostly include mechanical machining [17][18][19], sintering [9,20,21], electrodeposition [22][23][24][25][26], sputtering [27], oxidation [28,29], growth of nanowires and nanotubes [30][31][32][33], (nanoparticle) coatings [34,35], micro-/nanoelectromechanical techniques [36][37][38][39] or combinations of the above methods [40][41][42][43][44][45]. Usual drawbacks of the employed techniques are expensive production, mechanical and/or thermal instability of surfaces, problematic scale-up and difficult implementation on real threedimensional surface geometries.…”

Coupling droplets/bubbles with a liquid film for enhancing phase-change heat transfer

“…The critical heat flux (CHF) and HTC of phase-change heat transfer on the micro/nano-structured surfaces have been increased to several times higher than that of the smooth surface under some specific conditions, e.g. , enhanced boiling CHFs of 200-400 W/cm 2 and condensation HTCs of 100 kW/m 2 K ( Li et al., 2019 ; Wen et al., 2017a ). Most of the recent strategies have been focused on reducing the effective thermal resistance of the fluids in contact with the solid surface, e.g.…”