Enhanced Boiling Heat Transfer using Self-Actuated Nanobimorphs

Shin, Sangwoo; Choi, Geehong; Lee, Donghwi; Shim, Dong Il; Kim, Beom Seok; Kim, Kyung Min; Cho, Hyung Hee

doi:10.1021/acs.nanolett.8b02747

Cited by 38 publications

(13 citation statements)

References 23 publications

(44 reference statements)

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“…The model of transition for water calculated using Eq. ( 1) is also shown, where the dash dot line corresponds to a superheat of 30 K and the grey band corresponds to the superheat range of 15~45 K. these fluids reported in literature are also plotted for comparison, including evaporation of IPA [49] and water [36,38], and pool boiling of ethanol [46], FC-72 [48], and water [9,13,50].…”

Section: Discussionmentioning

confidence: 99%

“…The critical heat flux (CHF) in pool boiling represents the maximum heat flux that can be dissipated under safe operation conditions, which is usually on the order of 100 W cm -2 for a flat surface for water at the atmospheric pressure. Extensive efforts have been made to enhance the CHF and decrease the wall superheat using various strategies, including managing the bubble nucleation sites [5][6][7], increasing the surface wettability/capillarity using micro/nanostructures (which usually also increases the nucleation site density and provides a fin effect with an enhanced heat transfer area) [8,9], increasing the contact line length [10,11], providing separate liquid-vapor pathways for enhanced macroconvection [12,13], preventing bubble coalescence by pinning the contact line [14], and combination of multiple mechanisms stated above. Significant CHF enhancement has been demonstrated up to ~400 W cm -2 [15], but the CHF is still relatively low compared with flow boiling and other new configurations using water [16,17].…”

Section: Introductionmentioning

confidence: 99%

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Transition between thin film boiling and evaporation on nanoporous membranes near the kinetic limit

Wang

Shi

Chen

2020

International Journal of Heat and Mass Transfer

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Nanoporous structures including single nanopores and nanoporous membranes have beenutilized as a platform to study fundamental liquid-vapor phase change heat transfer (PCHT) processes as well as a promising candidate for high flux heat dissipation. Previously, we implemented nanoporous membranes to support a thin liquid film for boiling, which was termed "thin film boiling", and realized high heat transfer performance. Besides thin film boiling, thin film evaporation through nanoporous structures have also been demonstrated to achieve high heat flux, but these two mechanisms are usually considered two mutually exclusive regimes operated under vastly different conditions, and the factors dictating how close the PCHT process is to the kinetic limit are elusive. In this work, we utilized a unique transition between thin film boiling and evaporation through nanoporous membranes to clarify the factors determining the heat flux and heat transfer coefficient (HTC) with respect to the kinetic limit conditions. We unambiguously showed the controllable transition from boiling to evaporation, when the liquid receded into the nanopores and provided additional driving force from capillary pumping sustained in the nanoscale pores. We showed that this transition is universal and can be understood from a simple fluid transport model for all the four types of fluids we studied, which cover a wide span of surface tension (water, ethanol, IPA, FC-72). More importantly, PCHT conditions at the transition points between boiling and evaporation were close to those of the kinetic limit of all these fluids. However, further increase of the heat flux beyond the transition points led to decreasing HTC and deviation from the kinetic limit, which can be attributed to the increasing vapor resistance in the vapor space and inside the nanopores. This increasing vapor resistance was also confirmed by experiments on IPA with different vapor pressures. Our work could shed light on PCHT on nanoporous structures with respect to the kinetic limit, and could advance the development of high heat-flux heat dissipation devices, especially using dielectric fluids.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Transition between thin film boiling and evaporation on nanoporous membranes near the kinetic limit

Wang

Shi

Chen

2020

International Journal of Heat and Mass Transfer

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“…Through designing novel wicking structures with diverse materials, the efficiency of liquid transportation can be dramatically improved. In recent years, there is an increasing attention on developing advanced wicking structures because of their critical role in practical applications such as micro heat pipes, − nucleate boiling, − and water harvesting systems . The wicking structures reported previously can be divided into three categories: microscale, nanoscale, and hierarchical structures.…”

Section: Introductionmentioning

confidence: 99%

Superwicking on Nanoporous Micropillared Surfaces

Zheng

Choi

Sun

et al. 2020

ACS Appl. Mater. Interfaces

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Engineering surfaces with excellent wicking properties is of critical importance to a wide range of applications. Here, we report a facile method to create superhydrophilic nanoporous micropillared surfaces of silicon and their applicability to superwicking. Nanopores with a good control of the pore depth are realized over the entire surface of three-dimensional micropillar structures by electrochemical etching in hydrofluoric acid. After rinsing in hydrogen peroxide, the nanoporous micropillared surface shows superhydrophilicity with the superwicking effect. The entire spreading process of a water droplet on the superhydrophilic nanoporous micropillared surface is completed in less than 50 ms, with an average velocity of 91.2 mm/s, which is significantly faster than the other wicking surfaces reported. Owing to the presence of nanopores on the micropillar array, the wicking dynamics is distinct from the surfaces decorated only by micropillar arrays. The spreading dynamics of a water droplet shows two distinct processes simultaneously, including the capillary penetration between micropillars and the capillary imbibition into the nanopore’s interior. The wicking dynamics can be described by the two stages separated by the time when the contact line starts to recede. The transition between the two wicking regimes is due to the increasing effect of the imbibition of the bulk droplet by the nanopores. While a similar transition of the wicking dynamics is shown on the surfaces with different pore depths, the nanopore structure with a greater depth causes a greater amount of imbibition to slow down the spreading and promote superwicking.

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“…Other coating technologies involve atomic layer deposition, − oxidation, , chemical vapor deposition, ,− electrophoretic deposition, − etc. In addition, a wet/dry etching technique was used to fabricate micro pin fins, − micro cavities, and nanowires, − while a new emerging laser technique was also attempted to modify the boiling surfaces, obtaining micro pin fins − and micro cavities . Pool boiling of various liquids was experimentally investigated on the surfaces mentioned above, including SES36, HFE-7200, , FC-72, ,,, n-pentane, and water, and on other surfaces.…”

Section: Introductionmentioning

confidence: 99%

Nanoparticle-Assisted Pool Boiling Heat Transfer on Micro-Pin-Fin Surfaces

et al. 2021

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Boiling heat transfer intensification is of significant relevance to energy conversion and various cooling processes. This study aimed to enhance the saturated pool boiling of FC-72 (a dielectric liquid) by surface modifications and explore mechanisms of the enhancement. Specifically, circular and square micro pin fins were fabricated on silicon surfaces by dry etching and then copper nanoparticles were deposited on the micro-pin-fin surfaces by electrostatic deposition. Experimental results indicated that compared with a smooth surface, the micro pin fins increased the heat transfer coefficient and the critical heat flux by more than 200 and 65–83%, respectively, which were further enhanced by the nanoparticles up to 24% and more than 20%, respectively. Correspondingly, the enhancement mechanism was carefully explored by high-speed bubble visualizations, surface wickability measurements, and model analysis. It was quantitatively found that small bubble departure diameters with high bubble departure frequencies promoted high heat transfer coefficients. The wickability, which characterizes the ability of a liquid to rewet a surface, played an important role in determining the critical heat flux, but further analyses indicated that evaporation beneath bubbles was also essential and competition between the wicking and the evaporation finally triggered the critical heat flux.

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Enhanced Boiling Heat Transfer using Self-Actuated Nanobimorphs

Cited by 38 publications

References 23 publications

Transition between thin film boiling and evaporation on nanoporous membranes near the kinetic limit

Transition between thin film boiling and evaporation on nanoporous membranes near the kinetic limit

Superwicking on Nanoporous Micropillared Surfaces

Nanoparticle-Assisted Pool Boiling Heat Transfer on Micro-Pin-Fin Surfaces

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