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Infrared thermography investigation of an evaporating water/oil meniscus in confined geometry Xiang Liu, Lu Huang, Dan Guo, and Guoxin Xie Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.6b03482 • Publication Date (Web): 20 Dec 2016 Downloaded from http://pubs.acs.org on December 25, 2016

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Infrared thermography investigation of an evaporating water/oil meniscus in confined geometry

Xiang Liu1,2*, Lu Huang1,2, Dan Guo2* , Guoxin Xie2*

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National Institute of Metrology, Beijing 100029, China

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State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China

ACS Paragon Plus Environment

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KEYWORDS: water/oil droplet, diffusion and boiling, infrared, superheat, point contact confined space.

ABSTRACT: To simulate the heat and mass transfer in real heterogeneous systems, such as metal-production processes and lubrication, the point contact condition with the formation of narrowly confined liquid film and its surrounding meniscus is constructed to study the classical micro channel boiling problem in this work. Specifically, the evaporation and diffusion of the superheated water meniscus and water/oil droplet in the point contact geometry were investigated. Emphasis is put on the influence of the contact line transport behaviors on the nucleation and bubble dynamics in the confined meniscus. The observations suggested that superheat is the necessary condition for bubble formation and enough vapor supply is the necessary condition for bubble growth in the confined liquid. The oil film could significantly inhibit the evaporation and diffusion of water molecules in the superheat geometry. The water/oil droplet can exist for a long time even in the hot contact region, which could have sustained damages to the mechanical system suffering from water pollution. This work is of great significance to better understand the damage mechanism of the water pollution to the mechanical system.


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INTRODUCTION Heat and mass transfer in the confined geometry has attracted worldwide researchers as one of frontiers in the energy and thermal fluid science discipline, showing great significances in both understanding the fundamentals of transport phenomena at the microscale and promoting the development of new technologies such as micro energy systems, compact heat transfer devices, and cooling technology. 1-4 The problem is clearly of multiscale character. It is also complex, not only in its multiphysics content (fluid, solid, thermal physics), but also in the apparent presence of a multitude of potentially and highly interactive instability mechanisms (nucleation, contact line motion, and counter-current vapor–liquid flow). 5-9 In general, the micro channel was used as a confined space, and the geometrical size was experimentally demonstrated to have significant effect on the boiling, especially on the nucleation and bubble dynamics. The liquid temperature could be increased to much higher than the heterogeneous nucleation temperature of bubbles without detectable bubble formation in the micro channel. 4 The complex physicochemical phenomena occurring in the three phase contact line region of an evaporating meniscus is important to many applications involving phase change phenomena. The three phase contact line region accounts for the maximum evaporation and forms the most significant section of the evaporating meniscus, 10-13 but a monolayer oil film can greatly suppress the evaporation of water at the water-oil interface. 14-18 The resistance of an oil film to water transport isRF=L/Dk, where L is the film thickness and Dk is the permeability of the oil film to water, i.e., the product of the diffusion coefficient of water in oil, D, and the


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equilibrium partition coefficient of water in oil, k. Thus, if water has no solubility in the spread oil film, evaporation halts.17-18 Relatively little experimental research is available regarding the behaviors of three-phase contact lines under highly superheated conditions despite their importance in the modeling of a wide range of phenomena including drop evaporation, thin film stability, bubble nucleation, growth and departure during boiling. However, real systems where the confined heat and mass transfer occur, such as metalproduction processes and lubrication, are rarely uniform, adding complexity to the behaviors of the fluid. The point contact formed by a ball and plate configuration is a very simple system to mimic the real nonuniform condition for controlling the confined heat and mass transfer problem. In practice, many mechanical systems, for example, the bearings in hydraulic systems and offshore wind turbines, work in the point contact condition, suffering from the devastation of water contamination. 19 Because small amounts of water contamination to the lubricating oil lead to corrosion as well as accelerated abrasive and fatigue wear. Moreover, the operation temperature of the machine could be much higher than 100 ℃, and condensation usually takes place around the point contact area in moisture-rich environments, 20-22 particularly when the machine is frequently started and stopped. When the water droplet gets in contact with the lubricating oil capillary bridge between the contact pair, it could be absorbed into the oil capillary bridge completely to form a water/oil droplet. 23-25 Hence, it is important to investigate the confined heat and mass transfer behaviors of water and water/oil droplet, under the highly superheated point contact condition. For this specific problem, the objectives of this paper are to clarify the contact line transport mechanism under highly superheated conditions through experiments. The point contact


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condition with narrowly confined liquid film and its surrounding meniscus is constructed to mimic a degree of heterogeneity of a real system. The infrared technique has been used for a long time in heat transfer and fluid dynamics research. It can not only investigate the thermal properties like local temperature and heat flux, but also can distinguish the liquid and vapor phases based on their differences in IR transmissivity. 26-29 But, on the other hand, when some scholars use infrared thermal imaging technology to quantitative analysis of the boiling process, they may ignore the impact of the material transmissivity and treat the whole IR image as an accurate temperature field information. That will make some misunderstand. In this research, we were interested in how the small water meniscus behaved under highly superheated point contact condition, and the contact line transport behaviors at the edge of the meniscus when the contact line was connected with the atmosphere or cloaked by the oil ring. Finally, the influence of the contact line transport behaviors on the nucleation and bubble dynamics in the meniscus was investigated. MATERIALS AND METHODS Materials. For the experiments, n-hexadecane (purity 99%, Sigma Aldrich, Australia) and polyalkylene glycol ethers(PEG, J＆K, China) were used as the nonpolar and polar oil phases, respectively. Hexadecane is a non-polar alkane hydrocarbon, insoluble in water, and has a boiling point of 300 ℃. The PEG is slightly soluble in water, and has a boiling point higher than 300 ℃. Ultrapure deionized water obtained from a Milli-Q system, was used in all experiments. In particular, nanoscopically smooth ZrO2 ceramic ball(18.625 mm in diameter) and high polished sapphire disks(15cm in diameter and 2mm in thickness) were used as the ball and plate in the experiment. Their RMS roughnesses were 1.5 nm and 1.0 nm, measured with the AFM (Dimension V, VEECO, America).


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Preparation of materials. Experiments were performed at atmospheric pressure with deionized, degassed water as the working fluid. Prior to an experimental run, deionized water was boiled extensively inside a modified commercial water heater, which was used as a degassing chamber. Highly polished ZrO2 ceramic ball and high polished sapphire disk were pretreated by ultrasonication in acetone and ethanol for 5 minutes, respectively; followed by 10 minutes ultrasonication in distilled water (Milli-Q) to remove possible contaminants. Experimental setup. The schematic diagram of the experimental set is shown in Figure 1. It comprised a ball and disk configuration, and an ImageIR8325 infrared camera (InfraTec, Germany). In the experiment, the ball was supported by three bearings mounted on the top of a pedestal. The pedestal was mounted on one side of a lever; a weight was put on the other side of the lever to control the load applied. When the load was applied, the ball was able to contact the plate through an upward force provided by the counterweight through the lever, and a wedge-like gap formed between them. 5 µL water was injected into the gap firstly, and it formed an water capillary bridge around the contact region due to the spontaneous capillary imbibition. When the phase behavior of water/oil droplet was investigated, 5 µL oil was then injected into the gap to form a water/oil emulsion droplet. The ceramic ball was heated with a thermoelectric heater inserted into the bottom of the pedestal at controled power, while the sapphire disk was kept at room temperature. The behaviors of the water and water/oil meniscus were captured from above through the optically transparent sapphire disk with an ImageIR8325 infrared camera (InfraTec, Germany) at 100 frames per second. The spacial resolution of the camera is 10um. The depth of focus of the


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camera/lens is 1 mm, the field of view is 9.6mm×7.7mm. In all experiments, the load between the steel ball and the sapphire disk was 10 N, which corresponded to a maximum contact pressure of 500 MPa and a Hertzian contact radius of 80 µm. The air temperautre was 20 ℃, and the relative humidity was 30%.

Calibration of the IR images. In this experiment, the radiation was emitted from the hot surface of the ceramic ball, passing though the liquid film and sapphire window, and finally received by the IR camera. The temperature readings of the camera are based on the intensity of the radiation it received. However, water with 1 mm in thickness is sufficient to completely suppress any IR transmission in the MW spectral range.30 So it is impossible to use IR imaging to observe hot objects immersed in water. The transmissivity of water changed dramatically when the thickness is lower than 1mm, and this is the case in the present work. Sapphire disk and the water vapor have high IR transmissivity, the oil has only finite absorptivity of IR radiation. So the hot ceramic ball can be seen though the sapphire disk and the vapor bubble; the oil will appear “warmer” than the water meniscus, but actually they are at the same temperature. In this work, because the depth of focus of the camera/lens is 1 mm, larger than the gap between the disk and the ball (less than 200µm). The IR image of the water surface under the sapphire disk and the surface of the hot ceramic ball all can be captured clearly. The surface temperature of the ceramic ball uncovered by the liquid was calibrated and was set as an accurate temperature standard in the IR image. No quantitative data analysis was performed in the area covered by the liquid, but the temperature map could be used to distinguish different liquids and phases, and precisely located the interface based on the differences in transmissivity.


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A thermocouple was used to measure the surface temperatures of the hot ceramic ball, and calibrate the IR images. In order to get accurate IR images, the sapphire disk, which is transparent to infrared (IR) radiation between 3 and 5 µm and treated with anti-reflection coatings to obtain a total transmissivity higher than 90%, was chosen as the upper disk; the ZrO2 ceramic ball with the emissivity higher than 0.9 was chosen as the lower heated surface. The infrared camera calibration was performed by comparing the temperature given by the thermocouple placed on the ceramic ball and the camera reading. After the calibration, the emissivity of the whole field of view was set to 0.85, and the temperature difference between these two values was less than 0.3 ℃. Thanks to the calibration, the infrared image not only gave us the accurate temperature standard at the ceramic ball surface uncovered by the liquid, but also enabled us to distinguish the different liquids and phases, and precisely locate the interface based on the differences in transmissivity. RESULTS AND DISCUSSION Typical infrared images of water meniscus heated in the confined geometry Figure 2(a) shows the typical infrared images of water meniscus in the confined geometry. The pink area is the image of the ceramic ball uncovered by the liquid, which shows that the accurate temperature of the whole image is 32 ℃. The round blue area in the center is covered by a water meniscus. Although the water meniscus and the substrate would reach thermal equilibrium quickly, due to the high adsorption of the water to the IR radiation, 30 the apparent temperature of the water covered region in the infrared image is far lower than that of uncovered region. Because the radius of the ceramic ball was R=9.313 mm, and the radius of the water meniscus was r=1.875


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mm. So the gap width between the sapphire disk and the ceramic ball at the edge of the water meniscus was h = R − R 2 − r 2 = 200 µm . Because the thickness of the water meniscus decreases dramatically from 200 µm at the edge to a few nanometers at the center; the rate of its absorption of infrared radiation decreases with the thickness. Thus, the final apparent temperature of the water meniscus confined in the wedge gap between the ball and the plate gradually increases from edge toward the center, presenting a conical distribution as shown in the 3D image in figure 2(c). Although it could not get accurate temperature information from the water covered region, but the characteristic that the water film will absorb the IR radiation can be used to distinguish the phase behavior of the water meniscus confined in the hot point contact. As shown in Figure 2(a), a large number of regular blue spots start to emerge around the edge of the water meniscus when the substrate is 32 ℃. From the color it can be distinguished easily that the blue spots are the condensed droplets, which formed when the water vapor evaporated from the hot ceramic ball encountered the colder upper sapphire plate. Figure 2(b) shows the schematic diagram of this process. Further increase the temperature of the ceramic ball, if bubble emerged in the water meniscus, it will appear as a red hot circle in the thermal image due to its lower adsorption of infrared radiation from the hot substrate. Behaviors of superheated water meniscus in the confined geometry. In the field of lubrication, rolling bearings always work in alternating hot and cold environments, and the working temperature ranges from 80 ℃ to 200 ℃. In this part, the behaviors of superheated water meniscus in the confined geometry were investigated. The power input can be controlled, and the ceramic ball was heated and kept at certain stable temperatures from 30 ℃ to 200℃; then 5 µL water droplet was injected into the gap between the ball and the plate at each


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temperature. Due to the small volume of the water droplet, the temperature and the evaporating rate at its edge would reach a stable state immediately. Particular emphases were focused on the superheat needed for the bubble emergence inside the meniscus and the evaporating behaviors of the contact line at the edge of the meniscus. Because the water droplet is so small, the volume of it influence the area of the water meniscus and the number of the condensate droplets a lot. In this experiment, the volume of the water droplet was controlled carefully. For the experiment at the same temperature, the change of the number of condensate droplets is in the range of ±10%.. The ceramic ball was heated and then kept at some specified temperature. The number of condensing droplets around the water meniscus at different substrate temperatures is shown in Figure 3(a) and 3(b). The behavior of the condensing droplets could be divided into two stages in terms of the number and the size of the droplet. The first stage starts from emerging of the droplet at 30 ℃ to nearly 90 ℃; the second stage starts from 90 ℃ to 180 ℃. In the first stage, the ceramic ball was heated from room temperature to 90 ℃. The evaporation at the contact line increased with the increasing temperature, and the condensing droplet grew and merged with the droplets around to form larger droplet. The number of the droplet at the edge of the meniscus decreased, but the droplet volume increased dramatically. As shown in Figure 3, the maximum diameter of the condensing droplet increases from 50 µm at 30 ℃ to 300 µm at 90 ℃. Growing and merging are typical behaviors of the condensing droplets with the increasing evaporation in this stage. In the second stage, a dramatic turning point occurred when the temperature of the substrate reached near 100 ℃. The droplet of 500 µm in diameter “burst” and disappeared in the thermal image. Instant thermal image changes from picture B to C in Figure 3, and a number of small droplets occupy the original area where large droplets locate. The “burst” of the large droplet


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became a typical characteristic of the second stage. In order to study what happened at this moment, the evaporation and condensation of the superheated meniscus in the confined geometry was investigated using the high-speed shooting function. Figure 4 shows a “burst” process at the edge of the meniscus when the substrate is 145 ℃. At time zero the large droplet in the circle is very close to the meniscus; with the supplement of vapor from the contact line on the hot ceramic ball, the droplet gets in contact with the meniscus at this moment. The droplet was actually imbibed into the meniscus within 30 ms, clearing the surface of larger droplets and exposing fresh surface for nucleation of new droplets. The cycle of small droplets condensed around the contact line and large droplets imbibed into water meniscus happened dramatically during the second stage. At each temperature throughout the second stage, intense evaporation and condensation happened near the three phase contact line of the meniscus; the size and number distribution of the condensing droplet around the meniscus were very stable. These were the typical characteristics of the second stage different from those of the first stage. There were two typical phenomena worth noticing with respect to the evaporating meniscus in the second stage. One phenomenon was no obvious bubble formation and growth inside the superheated water meniscus. The whole boiling process has two stages including nucleation and bubble evolution. The critical nucleus radius values are commonly on the order of nanometers, which can not be captured by the IR camera in this research. As shown in Figure 5, small red vapor bubbles with 20 µm in diameter start can be seen inside the meniscus, but the bubble itself can’t be heated to grow even if the superheat of the ceramic ball was 80 K. It is well known that the liquid adjacent to the device surface must first be superheated by a few degrees above the saturation temperature in order to form the first bubble. But for the water meniscus confined in


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the 200 µm gap between the nanoscale smooth surface, the boiling is inhibited and much higher superheat is needed to form the first bubble. The second phenomenon was the intense evaporation and condensation at the contact line. The growth of a vapor bubble depends on the evaporation flux all around the bubble interface; but in this case, most of the vapor was spilled into the atmosphere and condensed into droplets. Hence, it is natural to speculate that vapor spill is the reason for the inhibition of bubble growth in the confined space. In order to confirm the speculation, two kinds of oil with different polarity and solubility were used as a barrier to control the diffusion intensity of the water molecules. Behaviors of water/oil droplet in the superheat geometry were investigated to further understand this problem. Effect of oil on the water diffusion capacity in the confined geometry. In this part, 5 µL deionized water droplet was injected into the gap to form a water meniscus first, then 5 µL oil was injected into the gap to from a water/oil emulsion droplet. The ceramic ball was heated with a thermoelectric heater attached at its bottom while the sapphire disk was kept at room temperature. n-hexadecane (C16H34, purity 99%, Sigma Aldrich, Australia) and polyalkylene glycol ethers(PEG, J＆K, China) were used as the nonpolar and polar oil phase respectively. The solubility of water in PEG is higher than that in n-hexadecane. The interfacial resistance is pertinent to condensation as well as evaporation, because the flux of evaporation is equal to that of condensation at equilibrium. The condensation coefficient is interpreted as the probability that a water molecule enters the liquid upon striking the surface, ranging from 0 to 1. The condensation coefficient for pure water surface is nearly unity, whereas it is reduced by 4 orders of magnitude when the water surface is covered with haxadecanol monolayer, and reduced by 23 orders of magnitude when the water surface is covered with PEG monolayer. 14,15


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The changes of the water/hexadecane droplet confined in the gradually heated geometry are shown in Figure 6. Hexadecane has nonpolar molecule; its boiling point is 286.8 ℃, and surface tension is 27.5 mN/m at 20 ℃. As shown in Figure 6, the ceramic ball was heated from room temperature to 180 ℃ within 35 min. When the substrate reaches 180 ℃, slow volatilization of the hexadecane with boiling point near 300 ℃ occurs. After 18 min, the width of the oil circle surrounding the water droplet reduces from 580 µm to 200 µm at 180 ℃. But it is very striking that the area of the water droplet with much lower boiling point does not change during the whole process, and no bubble formed inside the water meniscus. The evaporation and diffusion of the water molecules are greatly inhibited by the hexadecane surrounding it. Only when the substrate is 180 ℃, a small amount of condensed droplet can be seen at the lower right corner of the water/oil interface. The condensed droplet forms when the vapor generated at the edge of the evaporating water meniscus attempting to pass through the oil surrounded it. From the distance between the condensed droplet and the water/oil interface, it could be seen that only 50 µm thick hexadecane film could completely inhibit the evaporation and the diffusion of water molecules to atmosphere. This thickness is a small amount at the engineering perspective, so the inhibition is very significant. As can be seen from the above results, the nonpolar hexadecane has an enormous resistance on the diffusion of the water droplet inside it. Next the polar polyalkylene glycol ethers (PEG) is used as the oil phase, to explore what different phenomena would occur compared with the above results. PEG is a commonly used synthetic lubricant; the boiling point of the PEG is above 300 ℃, and surface tension is 30.5 mN/m at 20 ℃.


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Figure 7 shows the changes of the water/PEG droplet confined in the gradually heated geometry. No significant volatilization of PEG is observed when the substrate is near 200 ℃. When the substrate reaches 160 ℃, several bubbles appears in the water meniscus, and the bubble grows up with the increasing temperature. When the substrate reaches 180 ℃, a circle of condensing droplets form near the edge of the water meniscus. Two conclusions could be obtained from the above phenomena. First, the resistance of the PEG on the evaporation at the water/oil interface weakens compared with hexadecane, and more water vapor is produced during the whole process. Second, this resistance is still large enough that water vapor is all restricted in the water meniscus to supply the bubbles and make them grow. The bubbles in the water meniscus grow and move slowly to the water-oil interface. When the bubbles reach the water-oil interface, the bubble would pass though the oil circle quickly and release into atmosphere. Figure 8 shows the water/PEG droplet at the beginning of the heating and after 70 minutes’ heating. Relative to the water/hexadecane droplet, the diffusion capability of the water molecules in the PEG increases significantly. From the width of the condensing droplet in the oil ring, water molecules are able to diffuse 400 µm from the water-oil interface. Although bubbles have escaped from the confined water droplet, the size of the water droplet is almost unchanged compared to the start. Therefore, relative to the evaporation of the pure water droplet, the diffusion of the water molecules in the water/oil droplet has been significantly inhibited. Discussion. The geometrical size was experimentally demonstrated to have a significant effect on the boiling, especially on the nucleation and bubble dynamics. Besides the usual necessary conditions, such as superheat and nuclei, the scale of the liquid bulk should be large


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enough for bubbles to exist and grow in the liquid, or there is a minimum liquid bulk size that allows internal evaporation to occur and bubble to grow within the liquid. This critical scale was referred to “evaporating space” by Peng4. Only when the liquid bulk size is larger than this necessary evaporating space will boiling or nucleation occur with bubble growth in liquid. Apparently, the evaporating space is affected by the thermal boundary conditions of the liquid or the boundaries surrounding the liquid. In microstructures and very small channels/tubes, bubble formation and bursting boiling occur at very high superheat because of liquid space restriction and the lack of effective active nuclei. Peng proposed a nucleation criterion by superheat as4

∆Tsup ≥

4 ATs (v' '−v' )σ hlv Dh

(1)

where ∆Tsup is the superheat needed for bubble initiation, hlv is the enthalpy of liquid, Dh is the size of the micro channel, and A is an empirical constant, being experimentally evaluated as A ≈ 280 , Ts is the saturation temperature, v' ' and v' are specific volume of vapor and liquid, σ is

the surface tension of the liquid. Hence, one would observe increased liquid superheat needed to trigger visible bubble formation when the size of microchannel goes down. Based on the the above equation and the experiment result, Peng found that water confined in a 300 µm space needs 75 K superheat for visible bubble formation. In this work, the experiments also found that 80 K superheat is needed for the visible bubble formation in the water meniscus confined in the 200 µm gap, showing reasonably consistent with the peng’s work.


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The evaporation flux at the contact line also has been proved to have relation with the bubble growth inside the meniscus. In the evaporation process of the superheated pure water meniscus, large amount of vapor forms at the three phase contact line and escapes to the atmosphere. Therefore, the bubble inside the water meniscus could not get enough vapor to make them grow. As a result, it is natural to think that if the water meniscus could be sealed between the confined space, maybe the vapor formed at the three phase contact line could not escape to the atmosphere and the bubble could get enough vapor to make them grow. Luckily, the lubricating oil is an ideal material for that purpose. The condensation coefficient reduced by 4 orders of magnitude when the water surface is covered with haxadecanol monolayer, and reduced by 2-3 orders of magnitude when the water surface is covered with PEG monolayer.14,15 With the help of the behaviors of water/oil droplet in the superheat geometry, it is found that nonpolar hexadecane film could completely inhibit the evaporation and the diffusion of water molecules at the water/oil interface, and then there is no bubble formed inside the water meniscus. For polar PEG molecules, the inhibition of PEG on the evaporation of water molecules weakens, and more water vapor is produced during the whole process. But the resistance for water vapor to escape is also large that all the water vapor is restricted in the water meniscus to supple the bubbles and make them grow. Thus, superheat is the necessary condition for bubble formation and enough vapor supply is the necessary condition for bubble growth in the confined liquid. CONCLUSIONS


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Significant new insights have been gained from direct observations and quantifications of the evaporation and diffusion of the superheated water meniscus in the point contact geometry. The geometrical size and the intense evaporation at the contact line to the atmosphere could inhibit the boiling of the superheated meniscus. The significant inhibition of the oil film on the evaporation and diffusion of the water molecules in the superheat geometry has been found. superheat is the necessary condition for bubble formation and enough vapor supply is the necessary condition for bubble growth in the confined liquid. Because small amounts of water contamination to the lubricating oil lead to corrosion as well as accelerated abrasive and fatigue wear. In this experiment, the water/oil droplet can exist for a long time even in the hot contact region, which could have sustained damage to the mechanical systems use oil as the lubricant. This work is of great significance to better understand the damage mechanism of the water contamination to the mechanical system.


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AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. *E-mail: [email protected]. *E-mail: [email protected].

Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ACKNOWLEDGMENT The work is financially supported by the National Natural Science Foundation of China (Grant Nos. 51605460, 51375255, 51527901, and 51475440), and the China Postdoctoral Science Foundation (Grant No. 2016M591228).

REFERENCES 1. Li, J., & Cheng, P. Bubble cavitation in a microchannel. Int. J. Heat Mass Transfer 2004, 47, 2689-2698. 2. Li, J., & Peterson, G. P. Microscale heterogeneous boiling on smooth surfaces—from bubble nucleation to bubble dynamics. Int. J. Heat Mass Transfer 2005, 48, 4316-4332.


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3. Li, Y., & Homsy, G. M. Experimental study of vapor bubbles in small-sized channels. J. Colloid Interface Sci. 2008, 317, 235-240. 4. Peng, X. Micro Transport Phenomena During Boiling; Springer: Berlin, Heidelberg, 2011. 5. Wang, Y., & Khellil, S. Single bubble geometry evolution in micro-scale space. Int. J. Therm. Sci. 2013, 67, 31-40. 6. Kundan, A., et al. Thermocapillary phenomena and performance limitations of a wickless heat pipe in microgravity. Phys. Rev. Lett. 2015, 114, 146105. 7. Barber, J., Brutin, D., Sefiane, K., Gardarein, J. L., & Tadrist, L. Unsteady-state fluctuations analysis during bubble growth in a “rectangular” microchannel. Int. J. Heat Mass Transfer 2011, 54, 4784-4795. 8. Plawsky, J. L., & Wayner, P. C. Explosive nucleation in microgravity: the constrained vapor bubble experiment. Int. J. Heat Mass Transfer 2012, 55, 6473-6484. 9. Kundan, A., Plawsky, J. L., & Wayner, P. C. Thermophysical characteristics of a wickless heat pipe in microgravity-constrained vapor bubble experiment. Int. J. Heat Mass Transfer 2014, 78, 1105-1113. 10. Chatterjee, A., Plawsky, J. L., & Wayner, P. C. Disjoining pressure and capillarity in the constrained vapor bubble heat transfer system. Adv. Colloid Interface Sci. 2011, 168, 40-49. 11. Duan, C., Karnik, R., Lu, M. C., & Majumdar, A. Evaporation-induced cavitation in nanofluidic channels. Proc. Natl. Acad. Sci. U. S. A. 2012, 109, 3688-3693.


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12. Zhang, X., Lhuissier, H., Sun, C., & Lohse, D. Surface nanobubbles nucleate microdroplets. Phys. Rev. Lett. 2014, 112, 144503. 13. Raj, R., Kunkelmann, C., Stephan, P., Plawsky, J., & Kim, J. Contact line behavior for a highly wetting fluid under superheated conditions. Int. J. Heat Mass Transfer 2012, 55, 26642675. 14. Su, J. T., Duncan, P. B., Momaya, A., Jutila, A., & Needham, D. The effect of hydrogen bonding on the diffusion of water in n-alkanes and n-alcohols measured with a novel single microdroplet method. J. Chem. Phys. 2010, 132, 044506. 15. Sakaguchi, S., & Morita, A. Mass accommodation mechanism of water through monolayer films at water/vapor interface. J. Chem. Phys. 2012, 137, 064701. 16. Davies, J. F., Miles, R. E., Haddrell, A. E., & Reid, J. P. Influence of organic films on the evaporation and condensation of water in aerosol. Proc. Natl. Acad. Sci. U. S. A. 2013, 110, 8807-8812. 17. Cerretani, C. F., Ho, N. H., & Radke, C. J. Water-evaporation reduction by duplex films: application to the human tear film. Adv. Colloid Interface Sci. 2013, 197, 33-57. 18. Fellows, C. M., et al. Understanding the role of monolayers in retarding evaporation from water storage bodies. Chem. Phys. Lett. 2015, 623, 37-41. 19. Cyriac, F., Lugt, P. M., Bosman, R., & Venner, C. H. Impact of water on EHL film thickness of lubricating greases in rolling point contacts. Tribol. Lett. 2016, 61, 1-8. 20. Macner, A. M., Daniel, S., & Steen, P. H. Condensation on surface energy gradient shifts drop size distribution toward small drops. Langmuir 2014, 30, 1788-1798.


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21. Yarom, M., & Marmur, A. Vapor-liquid nucleation: the solid touch. Adv. Colloid Interface Sci. 2014, 222, 743-754. 22. Yasuoka, K., Gao, G. T., & Zeng, X. C. Molecular dynamics simulation of supersaturated vapor nucleation in slit pore. J. Chem. Phys. 2000, 112, 4279-4285. 23. Liu, X., Guo, D., Liu, S., Xie, G., & Luo, J. Interfacial dynamics and adhesion behaviors of water and oil droplets in confined geometry. Langmuir 2014, 30, 7695-7702. 24. Yang, Z., & Abbott, N. L. Spontaneous formation of water droplets at oil-solid interfaces. Langmuir 2010, 26, 13797-13804. 25. Anand, S., Paxson, A. T., Dhiman, R., Smith, J. D., & Varanasi, K. K. Enhanced condensation on lubricant-impregnated nanotextured surfaces. Acs Nano 2012, 6, 10122-10129. 26. Kim, H., & Buongiorno, J. Detection of liquid-vapor-solid triple contact line in two-phase heat transfer phenomena using high-speed infrared thermometry. Int. J. Multiphase Flow 2011, 37, 166-172. 27. Diana, A., Castillo, M., Steinberg, T., & Brutin, D. Asymmetric interface temperature during vapor bubble growth. Appl. Phys. Lett. 2013, 103, 031602. 28. X. Duan, B. Phillips, T. McKrell, & J. Buongiorno. Synchronized high-speed video, infrared thermometry, and particle image velocimetry data for validation of interface-tracking simulations of nucleate boiling phenomena. Exp. Heat Transfer 2013, 26, 169-197. 29. Buffone, C., Sefiane, K., Minetti, C., & Mamalis, D. Standing wave in evaporating meniscus detected by infrared thermography. Appl. Phys. Lett. 2015, 107, 041606.


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30. Vollmer, M., & Möllmann, K. P. Infrared Thermal Imaging: Fundamentals, Research and Applications; Wiley: KGaA, Weinheim, 2010.


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Figure 1. (a)Schematic of the experimental setup, (b)details of the water/oil meniscus confined between the ball and disk configuration. 2549x1196mm (72 x 72 DPI)


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Figure 2. (a) Typical 2D infrared image of water meniscus heated in the confined geometry, (b) the schematic diagram of the water vapor evaporated from the hot ceramic ball condensed under the colder upper sapphire plate, (c) typical 3D infrared image of water meniscus heated in the confined geometry. 2052x1335mm (72 x 72 DPI)


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Figure 3. Behaviors of the evaporating meniscus at different heating temperature. (a) Number of condensing droplets around the water meniscus at different substrate temperatures. (b) The droplet size distribution at typical temperature. (c) Thermal images at some key temperatures. 2159x2335mm (72 x 72 DPI)


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Figure 4. The instantaneous capillary imbibition process of the condensing droplet into the water meniscus when the substrate was 145 ℃. (Supplemental Dynamic Image 1) 1680x1237mm (72 x 72 DPI)


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Figure 5. Thermal image when the substrate was 180 ℃. (Supplemental Dynamic Image 2) 834x619mm (72 x 72 DPI)


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Figure 6. Changes of the water/hexadecane droplet confined in the gradually heated geometry. 1527x1127mm (72 x 72 DPI)


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Figure 7. Changes of the water/PEG droplet confined in the gradually heated geometry. 1541x1136mm (72 x 72 DPI)


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Figure 8. The water/PEG droplet at the beginning of the heating and after 70 minutes’ heating. 1525x570mm (72 x 72 DPI)


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Insert Table of Contents Graphic and Synopsis Here 1895x1530mm (72 x 72 DPI)


Infrared Thermography Investigation of an ... - ACS Publications

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