Origin of Surface-Driven Passive Liquid Flows

Yd, Sumith; Maroo, Shalabh C.

doi:10.1021/acs.langmuir.6b02117

Cited by 16 publications

(10 citation statements)

References 19 publications

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“…To investigate the possible momentum transport within the absorbed layer, mass flow is calculated along the surface coordinate, “ s ” (see Section B of the Supporting Information). Strikingly, an atomic level mass flow is apparent within the absorbed layer, as shown in Figure c, because of the solid–liquid surface tension gradient originating from the temperature gradient together with evaporation along the evaporator surface . The mass flow decreases continuously along the layer and vanishes at the end of the side wall, where actually two opposite molecular streams merge because of the periodic boundary condition.…”

Section: Results and Discussionmentioning

confidence: 99%

Atomic Scale Interfacial Transport at an Extended Evaporating Meniscus

2019

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Recent developments in fabrication techniques enabled the production of nano-andångström-scale conduits. While scientists are able to conduct experimental studies to demonstrate extreme evaporation rates from these capillaries, theoretical modeling of evaporation from a few nanometers or sub-nanometer meniscus interfaces, where adsorbed film, transition film and intrinsic region are intertwined, is absent in the literature. Using the computational setup constructed to identify the detailed profile of a nano-scale evaporating interface, we discovered the existence of lateral momentum transport within and associated net evaporation from adsorbed liquid layers, which are long believed to be at the equilibrium established between equal rates of evaporation and condensation. Contribution of evaporation from the adsorbed layer increases the effective evaporation area, reducing the excessively estimated evaporation flux values. This work takes the first step towards a comprehensive understanding of atomic/molecular scale interfacial transport at extended evaporating menisci. The modeling strategy used in this study opens an opportunity for computational experimentation of steadystate evaporation and condensation at liquid/vapor interfaces located in capillary nano-conduits.Capillary evaporation and the associated passive liquid flow are vital for numerous natural and artificial processes such as transpiration of water in plants, 1 solar steam generation, 2,3 water desalination, 4 microfluidic pumping, 5 and cooling of electronic and photonic devices. 6 Regardless of the process or the geometrical configuration, studies on evaporation focus on identification and characterization of heat transfer and flow dynamics in the vicinity of the contact line, the juncture of three phases of matter. Fig. 1a-c shows different evaporation processes schematically. Green dashed rectangles point out the liquid film distribution around the contact line, which is broadly composed of three multiscale regions as shown in Fig. 1d. Evaporation rate intensifies in evaporating thin film region due to the micro-scale liquid film thickness. The adsorbed nano-scale layer extending further is assumed to be non-evaporating due to the suppression of evaporation by strong long-range intermolecular forces. [7][8][9][10][11][12][13][14][15][16][17][18][19] While the kinetic theory of gases 20,21 is widely used to predict the theoretical maximum rate of evaporation, experiments have always calculated smaller heat fluxes than the kinetic limit. 22 However, two recent experimental studies have attracted the attention of scientific community by reporting evaporation fluxes one to two orders of magnitude higher than the prediction of kinetic theory. 23,24 These unexpectedly high flux values were attributed to the possible underestimation of evaporation area in the first study, 23 where the stretching of water meniscus over the flat surface adjacent to the channel mouth was speculated. On the other hand, the second study, 24 reported evaporation rates from a ...

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Section: Results and Discussionmentioning

confidence: 99%

Atomic Scale Interfacial Transport at an Extended Evaporating Meniscus

2019

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“…2. Increasing evaporation rates from the microlayer under a bubble has been found to increase the boiling performance as demonstrated by Kandlikar [12], Maroo [28], and Zou et al [29]. This can be achieved by increasing the microlayer volume under a growing bubble [8,11].…”

Section: Concept and Hypothesismentioning

confidence: 94%

Microscale Morphology Effects of Copper–Graphene Oxide Coatings on Pool Boiling Characteristics

Jaikumar

Rishi

Gupta

et al. 2017

Journal of Heat Transfer

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Enhanced pool boiling heat transfer, with simultaneous increase in critical heat flux (CHF) and heat transfer coefficient (HTC), is desired to improve overall system efficiency and reduce equipment size and cost. This paper focuses on combining graphene oxide (GO) and porous copper particles to generate microstructures based on their ability to enhance HTC, CHF, or both. Three pool boiling performance characteristics based on CHF improvements and wall superheat reductions are identified: Type I-reduction in wall superheat only, type II-increase in CHF only, and type III-increase in CHF with reduction in wall superheat at higher heat fluxes. Specific microscale morphologies were generated using (a) screen-printing and (b) electrodeposition techniques. In type-I, rapid bubble activity due to increased availability of nucleation cavities was seen to influence the reduction in the wall superheats, while no increase in CHF was noted. Roughnessaugmented wettability was found to be the driving mechanism in type-II enhancement, while wicking and increased nucleation site density were responsible for the enhancement in type-III. An HTC enhancement of $216% in type-I and a CHF improvement of $70% in type-II were achieved when compared to a plain copper surface with water. In type-III enhancement, a CHF of 2.2 MW/m 2 (1.8Â over a plain surface) with a HTC of 155 kW/m 2 C ($2.4Â over a plain surface) was obtained. Furthermore, close correlation between the boiling performance and the microscale surface morphology in these three categories has been identified.

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“…88 In microuidics, the generation of strong passive ows can be achieved by selecting a suitable surface and liquid combinations that can create the required solid-liquid surfacetension gradients. 89 Mathematical models are required to nalize the design of the channel, so Makhijani et al developed a numerical model to simulate the liquid lling due to the presence of surface tension in the liquid-air interface and demonstrated the application of disposable biochips for clinical diagnosis. It was mainly used for analysis and optimization to achieve the desired ow.…”

Section: Surface Tensionmentioning

confidence: 99%