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![Schematic depictions of different modes of condensation. (a) Filmwise condensation (FWC) where the condensate forms a continuous liquid film on a chemically clean (high surface energy) surface. The wall is maintained at a lower temperature (Tw\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$T_{{\text{w}}}$$\end{document}) than the surrounding saturated vapor (Tsat\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$T_{{{\text{sat}}}}$$\end{document}). The temperature and velocity profiles are shown for laminar film condensation where the flow-rate based Reynolds number is < 30. (b) Dropwise condensation (DWC) on hydrophobic (low surface energy) surface. It is essential for dropwise condensation that some promoter material, for example organic compound, be present on the surface. Periodic removal of large droplets clears the surface for renewed droplet nucleation and growth. (c) Inverse opal condensation (IOC) on a porous inverse opal structure. Condensate seeps into the porous structure by displacing the air in the pores. Preferential condensate transport through high hydraulic conductivity micro cracks improves the heat transfer rate. (d) Condensation on a slippery liquid-infused porous surface (SLIPS). The porous interstices are impregnated with a chemically matched oil. Compared to DWC, droplets depart with smaller radius and higher frequency in SLIPS condensation.](publication/351781513/figure/fig1/AS:1026496139390977@1621747159389/Schematic-depictions-of-different-modes-of-condensation-a-Filmwise-condensation-FWC.png)
Schematic depictions of different modes of condensation. (a) Filmwise condensation (FWC) where the condensate forms a continuous liquid film on a chemically clean (high surface energy) surface. The wall is maintained at a lower temperature (Tw\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$T_{{\text{w}}}$$\end{document}) than the surrounding saturated vapor (Tsat\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$T_{{{\text{sat}}}}$$\end{document}). The temperature and velocity profiles are shown for laminar film condensation where the flow-rate based Reynolds number is < 30. (b) Dropwise condensation (DWC) on hydrophobic (low surface energy) surface. It is essential for dropwise condensation that some promoter material, for example organic compound, be present on the surface. Periodic removal of large droplets clears the surface for renewed droplet nucleation and growth. (c) Inverse opal condensation (IOC) on a porous inverse opal structure. Condensate seeps into the porous structure by displacing the air in the pores. Preferential condensate transport through high hydraulic conductivity micro cracks improves the heat transfer rate. (d) Condensation on a slippery liquid-infused porous surface (SLIPS). The porous interstices are impregnated with a chemically matched oil. Compared to DWC, droplets depart with smaller radius and higher frequency in SLIPS condensation.
Source publication
Phase-change condensation is commonplace in nature and industry. Since the 1930s, it is well understood that vapor condenses in filmwise mode on clean metallic surfaces whereas it condenses by forming discrete droplets on surfaces coated with a promoter material. In both filmwise and dropwise modes, the condensate is removed when gravity overcomes...
Citations
... When a rough hydrophobic surface is studied, the selection between the Wenzel and Cassie-Baxter models depends on the droplet contact angle on a smooth surface and the roughness [11]. Specifically, the critical contact angle, θ crit , is calculated with Eq. 5 and is used to predict the wetting mode [12,13]. ...
This study investigates the impact of combined texturing by micromachining and chemical functionalization on the wetting behavior and water condensation on stainless steel 304. The transition from Wenzel to Cassie-Baxter or impregnated Cassie-Baxter regimes is investigated. Understanding this transition is critical for advancing surface engineering, as it enables precise control over wetting behavior for various applications. Herein, we report on the wire EDM (wEDM) machining on stainless steel 304 to produce two distinct microstructure patterns with directional canals or pyramidal structure, and their performance in water condensation. These patterns significantly impact water condensation performance. wEDM is employed to create surface roughness, followed by phosphoric acid treatment and chemical functionalization with trichloro-1H,1H,2H,2H-perfluorooctyl silane. Contact angle measurements reveal a synergistic effect between groove direction and silane coating, leading to hydrophobic surfaces and dropwise water condensation. Specimens with directional canals exhibit a contact angle of 150°, while specimens with pyramidal structures exhibit 151o. Roll-off angle experiments showcased distinct behavior among specimens featuring canals or pyramidal structures. Specimens with canals exhibit notably lower roll-off angles compared to both flat surfaces and those with pyramidal patterns, leading to a dependence of roll-off angles on the orientation of canals. In humid environments, micromachined specimens exhibit superior water condensation capability compared to untreated SS304 surfaces. Chemically functionalized grooved specimens present larger condensate droplet diameters than flat surfaces. An enhancement in water condensation and a sevenfold higher latent heat transfer coefficient is reported. Specimens with chemical functionalization achieve corrosion protection with an efficiency reaching 82.9%.
... Cassie-Baxter models depends on the droplet contact angle on a smooth surface and the roughness [11]. Specifically, the critical contact angle, θcrit, calculated with eq. 5 and is used to predict the wetting mode [12,13]. ...
This study investigates the impact of combined texturing by micromachining and chemical functionalization on the wetting behavior and water condensation of a metallic surface. The transition from the Wenzel to Cassie-Baxter or impregnated Cassie-Baxter regimes was unveiled. Initially, grooved stainless steel 304 specimens displayed hydrophobic wetting in the Wenzel mode. The chemical functionalization with silane triggered a remarkable shift that was not observed in non-textured by micromachining samples. Thus contact angles surged, facilitating a transition to the Cassie-Baxter state for directional canal specimens and the impregnated Cassie-Baxter state for those with pyramidal patterns. Roll-off angle experiments showcased distinct behavior among specimens featuring canals or pyramidal structures. Specimens with canals exhibited notably lower roll-off angles compared to both flat surfaces and those with pyramidal patterns. Notably, the orientation of canals influenced these angles, with vertically aligned canals demonstrating reduced roll-off angles. In humid environments, micro-machined surfaces exhibited superior water condensation capabilities compared to untreated flat SS304 surfaces. Remarkably, chemically functionalized grooved specimens presented larger condensate droplet diameters than flat surfaces. Consequently a remarkable enhancement in water condensation and a 7 fold higher latent heat transfer coefficient is reported.
... Recently, there is much interest in understanding droplet condensation on lubricated surfaces [10][11][12][13][14] for enhanced heat-transfer and water-collection applications [10,[15][16][17]. Water droplets are highly mobile on lubricated surfaces [18][19][20] because the lubricant film (typically silicone or fluorinated oils) prevents direct contact of the droplet with the underlying solid substrate [21,22]. ...
Recently, there is much interest in droplet condensation on soft or liquid or liquidlike substrates. Droplets can deform soft and liquid interfaces resulting in a wealth of phenomena not observed on hard, solid surfaces (e.g., increased nucleation, interdroplet attraction). Here, we describe a unique collective motion of condensate water droplets that emerges spontaneously when a solid substrate is covered with a thin oil film. Droplets move first in a serpentine, self-avoiding fashion before transitioning to circular motions. We show that this self-propulsion (with speeds in the 0.1-1 mm s −1 range) is fueled by the interfacial energy release upon merging with newly condensed but much smaller droplets. The resultant collective motion spans multiple length scales from submillimeter to several centimeters, with potentially important heat-transfer and water-harvesting applications.
... More recently, there is much interest in understanding droplet condensation on lubricated surfaces [10][11][12][13][14] for enhanced heat-transfer and water-collection applications [10,[15][16][17]. Water droplets are highly mobile on lubricated surfaces [18][19][20], because the presence of a stable lubricant film (typically silicone or fluorinated oils) prevents direct contact of the droplet with the underlying solid substrate and hence eliminates contact-line pinning [21,22]. ...
Recently, there is much interest in droplet condensation on soft or liquid/liquid-like substrates. Droplets can deform soft and liquid interfaces resulting in a wealth of phenomena not observed on hard, solid surfaces (e.g., increased nucleation, inter-droplet attraction). Here, we describe a unique complex collective motion of condensate water droplets that emerges spontaneously when a solid substrate is covered with a thin oil film. Droplets move first in a serpentine, self-avoiding fashion before transitioning to circular motions. We show that this self-propulsion (with speeds in the 0.1–1 mm s−1 range) is fuelled by the interfacial energy release upon merging with newly condensed but much smaller droplets. The resultant collective motion spans multiple length scales from submillimetre to several centimetres, with potentially important heat-transfer and water-harvesting applications.
... More recently, there is much interest in understanding droplet condensation on lubricated surfaces [10][11][12][13][14] for enhanced heat-transfer and water-collection applications [10,[15][16][17]. Water droplets are highly mobile on lubricated surfaces [18][19][20], because the presence of a stable lubricant film (typically silicone or fluorinated oils) prevents direct contact of the droplet with the underlying solid substrate and hence eliminates contact-line pinning [21,22]. ...
This is a winning entry to the recently concluded APS DFD Gallery of Fluid motions (https://gfm.aps.org/). See https://www.youtube.com/watch?v=wpfYZJEEvhU
... Holden et al. (1987) found that during condensation of steam on horizontal tubes, the steamside heat transfer coefficient can be enhanced five to ten times through the use of organic polymer coatings which is responsible for an increase in condensate droplet contact angle. Adera et al. (2021) conducted experiments on copper tube coated with silica inverse opal structures and found that high hydraulic conductivity through the cracks in the porous silica (offered hydrophilic region for drainage) promoted rapid condensate transport that is helpful for condensation heat transfer. Surface roughness plays an important role in condensation heat transfer since it dictates water droplet contact-angle hysteresis which affects condensate removal from the surface and hence condensation rates. ...
Steam condensation plays a critical role as an accidental safety measure in the passive containment cooling system of a nuclear power plant. Zinc-silicate epoxy-coated mild steel plate is widely used for steel containment or as liner material for steel lined concrete containment of nuclear reactor. The purpose of the coating is mainly to increase the corrosion resistance of mild steel liner. However, high condensation rate is of utmost importance to prevent large pressure and temperature buildups within the nuclear reactor in case of a loss of coolant accident (LOCA) and maintain necessary safety margin. In this work, the effect of the epoxy coating on mild steel liner during vapor condensation in humid air environment has been investigated. Both as-purchased, uncoated (bare) and epoxy-coated mild steel plates have been used as condenser surfaces. A wide range of heat fluxes are realized by carrying out condensation experiments both under natural and forced convection scenarios. It is found that the epoxy-coated condenser plates show lower contact-angle hysteresis and hence promote better droplet mobility and condensate drainage from the surface. However, measurements reveal that the overall condensation rate on the epoxy-coated surfaces is less than that on uncoated mild steel plate. Our study shows that the lower nucleation density coupled with the additional thermal resistance due to the coating thickness causes lower condensation rates on the epoxy-coated mild steel surface. Results of the study are relevant for benchmarking reactor thermal hydraulics codes for realistic simulations of containment pressure under accident scenarios.
... Corrosion issue of condensing surfaces can be addressed either by the incorporation of expensive metals as engineering materials exhibiting low corrosion rates or by applying functional coatings to protect a much more cost-efficient base material. Ceramic or thinner coatings are able to provide protection in metal substrates at extreme conditions or both protect and modify the wetting properties at the same time of the condensing interface [7][8][9][10][11][12]. ...
The study of water condensation phenomena is important in order to evaluate the performance of materials and coatings employed in the fabrication of waste heat recovery units including heat exchangers, heat pipes, condensing economizers and related functional surfaces. Fast evaluation of lab-scale samples is important during research and development of coatings for wetting phenomena under controlled, reproducible, and stable humidity and temperature conditions of both sample and environment. To study these effects, we report on the construction of a lab-scale condensation chamber, along with its evaluation and benchmarking with superhydrophobic coatings on stainless steel using perfluorooctyl silane (PFOTS). A working unit has been successfully fabricated and applied in a highly responsive device capable of recording the condensation performance of flat specimens under controlled conditions. Sample temperature was maintained with 0.10 °C deviation. The humidity response time of the chamber is 17.2 s per degree of RH% while the maximum relative humidity variation is +/- 3.2%RH. The unit successfully delivered valuable data over hydrophillic, hydrophobic and superhydrophobic surfaces. Data useful for studying open research issues such the relationship of contact angle and condensation phenomena.
... Larger droplets can then be removed by gravity by overcoming surface tension forces. This process clears the surface and allows re-nucleation, growth, and departure of condensate droplets that will lead to substantial improvements in the heat transfer coefficient 42,43 . ...
Droplets residing on textured oil-impregnated surfaces form a wetting ridge due to the imbalance of interfacial forces at the contact line, leading to a wealth of phenomena not seen on traditional lotus-leaf-inspired non-wetting surfaces. Here, we show that the wetting ridge leads to long-range attraction between millimeter-sized droplets, which coalesce in three distinct stages: droplet attraction, lubricant draining, and droplet merging. Our experiments and model show that the magnitude of the velocity and acceleration at which droplets approach each other horizontally is the same as the vertical oil rise velocity and acceleration in the wetting ridge. Moreover, the droplet coalescence mechanism can be modeled using the classical mass-spring system. The insights gained from this work will inform future fundamental studies on remote droplet interaction on textured oil-impregnated surfaces for optimizing water harvesting and condensation heat transfer.
... The F-DLC coating provides a conformal, pinhole free, adherent solution for the rational design of multiple layers that can enable enhanced condensation heat transfer (Fig. 3) condensation heat transfer results are not unique, showing similar performance with previously developed hydrophobic materials 5,21,27,28 . However, the potential durability of F-DLC when compared to classical hydrophobic coatings makes it beneficial. ...
Seventy percent of global electricity is generated by steam-cycle power plants. A hydrophobic condenser surface within these plants could boost overall cycle efficiency by 2%. In 2022, this enhancement equates to an additional electrical power generation of 1000 TWh annually, or 83% of the global solar electricity production. Furthermore, this efficiency increase reduces CO2 emissions by 460 million tons /year with a decreased use of 2 trillion gallons of cooling water per year. However, the main challenge with hydrophobic surfaces is their poor durability. Here, we show that solid microscale-thick fluorinated diamond-like carbon (F-DLC) possesses mechanical and thermal properties that ensure durability in moist, abrasive, and thermally harsh conditions. The F-DLC coating achieves this without relying on atmospheric interactions, infused lubricants, self-healing strategies, or sacrificial surface designs. Through tailored substrate adhesion and multilayer deposition, we develop a pinhole-free F-DLC coating with low surface energy and comparable Young’s modulus to metals. In a three-year steam condensation experiment, the F-DLC coating maintains hydrophobicity, resulting in sustained and improved dropwise condensation on multiple metallic substrates. Our findings provide a promising solution to hydrophobic material fragility and can enhance the sustainability of renewable and non-renewable energy sources.
... When silane is used to chemically functionalize the inverse opal structure and silicone oil is used to permeate it, vapor condense will happen and highly mobile water droplets will develop that leave at a reduced length scale (see Figure 17d). This precipitation is known as SLIPS condensation, which can increase the rate of heat transfer by cutting the departure radius by almost 50% [12]. Condensate was discharged vertically downward in all but IOC situations where gravity won out over anchoring forces. ...
... However, the condensation was carried through the fissures preferentially in an axial orientation during IOC. The condensate only migrated axially to the right or to the left, which is determined by the shape, size, and direction of the crack [12]. ...
In this paper, by studying the characteristics of the bionic surface with pattern wettability, the process of its efficient dehumidification and atomization is explored. This paper briefly introduces the importance of dehumidification and physicochemical and the market demand, and also introduces the properties of superhydrophobic materials. The theoretical part mainly describes the basic principle of superhydrophobicity and the Wenzel and Cassie-Baxter models. Subsequently, natural and synthetic superhydrophobic surfaces are introduced, involving Namib beetles, butterfly wings, and so on. The final article points out that superhydrophobic surfaces can be used in numerous fields, especially in fog collection. However, the improvement of durability is the focus of attention for superhydrophobic surfaces. In future research, attention needs to be paid to the use of materials and the efficiency of fog collection.
