Droplet Condensation Research Articles

Preparation and initial condensation characteristics of superhydrophobic coating based on nano-SiO2 particles

Superhydrophobic surfaces can effectively inhibit the growth of droplets and reduce attachment, thus inhibiting the formation of frost. In this paper, using dimethyldimethoxysilane-modified silica nanoparticles, a superhydrophobic coating with a contact angle of 165.73 ± 1° and a rolling angle of 2 ± 1° was successfully prepared by the secondary spraying method, and the chemical composition of the substrate and the surface morphology of the coating were characterized by means of FT-IR, EDS, and SEM. A visualization test rig was constructed to investigate the condensation droplet growth characteristics on the superhydrophobic surface across various tilt angles (0°to 90°), cold surface temperatures (-1 ℃ to 5 ℃), and humidity levels (45% to 75%). The experimental results revealed that as the tilt angle increases, the forces acting on the condensed droplets change, resulting in a higher frequency of droplet merging, jumping, and slipping. Furthermore, a decrease in cold surface temperature accelerates the growth of condensed droplets. Under varying humidity conditions, droplets on the superhydrophobic surface nucleate and grow more rapidly in high humidity environments, where they exhibit a larger coverage area despite having a relatively small mean radius.

Long-Term Resistance to Phase Change-Induced Wetting Transition on Biphilic Armored Superhydrophobic Surfaces.

Material surfaces maintaining a liquid super-repellent is crucial in fields such as anti-fouling, drag reduction, and heat transfer. Superhydrophobic surfaces provide an effective approach but suffer from phase change-induced wetting transitions, hindering their practical applications. In this work, Biphilic armored superhydrophobic surfaces (BASS) are designed by integrating hydrophilic interconnected surface frames with superhydrophobic nanostructures. The hydrophilic top of the frame provides spatial selectivity for condensate droplet nucleation, and superhydrophobic nanostructures enable staying dry. Further growth, coalescence, jumping, and roll-off of the condensate droplets on BASS, show remarkable resistance to phase change-induced wetting transition. It still maintains stable superhydrophobicity when exposed to 100°C of steam for 240 h, at least two orders of magnitude improvement over traditional superhydrophobic surfaces. Such a designing BASS provides an effective approach to address the phase change-induced wetting transition, thereby extending the practical application in the fields of condensation heat transfer, anti-fouling, and fluid transportation of superhydrophobic surfaces.

Enhancing condensation droplets removal on tube through periodic ultrasonic vibration

Enhancing condensation droplets removal on tube through periodic ultrasonic vibration

Solar-Driven Thin Air Gap Membrane Distillation with a Slippery Condensing Surface.

Membrane-based desalination is essential for mitigating global water scarcity; yet, the process is energy-intensive and heavily reliant on fossil fuels, resulting in substantial carbon emissions. To address the challenges of treating seawater, produced water, brackish groundwater, and wastewater, we have developed a thin air gap membrane distillation (AGMD) system featuring a novel slippery condensing surface. The quasi-liquid slippery surface facilitates efficient condensate water droplet removal, allowing for the implementation of a 1 mm thin air gap. This advancement has led to a 2-fold increase in permeate flux without lowering the thermal efficiency while preventing permeate flooding. Furthermore, the thin AGMD system, employing a cost-effective zirconium nitride/poly(vinylidene fluoride) (ZrN-PVDF) composite membrane, has been demonstrated for solar-driven desalination. Experimental results indicate that reducing the air gap from 2 to 1 mm enhances the permeate flux by 150%.

Assessment of the impact of intensification of heat exchange processes in heaters on power unit efficiency

In various spheres of modern industry, including power engineering, the issue of low efficiency of operation of heatexchange equipment, where condensation of vapour-gas media occurs, is a significant concern. It is known that one of the effective ways of solving this problem is intensification of heat exchange processes by transitioning from the traditional film condensation mode to the droplet condensation mode. A promising and technically straightforward way to achieve the droplet mode of condensation is a method based on the treatment of heat-exchange surfaces using a surfactant – octadecylamine (ODA). The analysis of studies, in which results of experimental research and industrial implementation are given, has shown that application of the specified method in conditions of condensation of water steam promotes formation of a stable droplet mode of condensation; as a result, the heat transfer coefficient on the steam side can more than double.Equally important and interesting is the question of how the efficiency of heat exchangers impacts the overall efficiency of complex systems, in which they operate. In this study, we examined the effect of the operational efficiency of network and regenerative heaters on the energy efficiency and economic performance of a power unit based on steam turbine unit T-110-12,8-3 operating in the heat recovery mode. To this end, we calculated the thermal scheme under various operating conditions of these heat exchangers and determined several key efficiency indicators, including the fuel heat utilisation factor (HUF) and electrical efficiency (EE). It is revealed that intensification of heat-exchange processes by a factor of 2 in horizontal delivery water heaters (HDWH) or in low-pressure heaters (LPH) significantly enhances the efficiency indicators of the power unit as a whole. At the same time, as the analysis of calculation results showed, the greatest benefits are realized when this measure is implemented in HDWH.

Nanoscale wettability characterization—Interpreting droplet morphological evolution in nanopores

AbstractNanoscale wettability, crucial for various disciplines in science and engineering, challenges traditional theory, particularly the Young's equation. This study proposes and validates a modified format of the Young's equation under nano‐confinement and, for the first time, the nano‐confined droplet morphological evolution and transition are investigated from thermodynamic theories and molecular dynamics simulation. The morphologies of droplets in nano‐silts, identified as double‐cap, single‐cap, and bridge‐shaped, underscore the critical roles of line tension and nano‐confinement in characterizing wetting behavior. In hydrophobic nano‐slits, droplets transition from the double‐cap to the single‐cap shape at the critical point of = 0.31 and to bridge shape at the critical point of = 0.40. Moreover, the relative width of the neck region in the bridge‐shaped droplets is found to stabilize at ratio of 1.8. Particularly, linear relationships have been established between the droplet contact angle and the parameter , which identify condensation and breakage of droplets within hydrophobic nano‐slits. This model effectively characterizes nanoscale wettability, with precise droplet behavior predictions, which could be beneficial to enhance nano‐fluid dynamics understanding and its applications in science and engineering.

Ultra-Slippery Hydrophilic Surfaces by Hybrid Monolayers.

Slippery solid surfaces with low droplet contact angle hysteresis (CAH) are crucial for applications in thermal management, energy harvesting, and environmental remediation. Traditionally, reducing CAH has been achieved by enhancing surface homogeneity. This work challenges this conventional approach by developing slippery yet hydrophilic surfaces through hybrid monolayers composed of hydrophilic polyethylene glycol (PEG)-silane and hydrophobic alkyl-silane molecules. These hybrid surfaces exhibited exceptionally low CAH (<2°), outperforming well-established homogeneous slippery surfaces. Molecular structural analyses suggested that the remarkable slipperiness is due to a unique spatially staggered molecular configuration, where longer PEG chains shield shorter alkyl chains, thus creating additional free volume while ensuring surface coverage. This was supported by the observation of decreased CAH with increasing temperature, highlighting the role of grafted chain mobility in enhancing slipperiness by self-smoothing and fluid-like behaviors. Furthermore, condensation experiments demonstrated the exceptional performance of the hydrophilic slippery surfaces in dew harvesting due to superior condensation nucleation, droplet coalescence, and self-sweeping efficiency. These findings offer a novel paradigm for designing advanced slippery surfaces and provide valuable insights into the molecular mechanisms governing dynamic wetting.

Full-angle light out-coupling enhancement of quantum dot light-emitting diodes by Mie-scattering micro-lens arrays

High efficiency, high brightness, and long-life quantum dot light-emitting diodes (QLEDs) are crucial for realizing integrated display and lighting applications. However, about 80% of the light is confined inside the device with substrate mode, waveguide mode, and plasma mode, which greatly weakens the brightness, efficiency and lifetime of the device. Here, a quasi-periodic concave template with large area was fabricated through the spontaneous condensation of droplets on the substrate surface. Based on the quasi-periodic template, SiO2 micro-lens arrays (SiO2-MLAs) Mie scattering composite structure was fabricated by imprinting on a SiO2-nanosphere thin film, which significantly improved light out-coupling at full angles with optimized quasi-Lambertian luminescence characteristics. In comparison to the planar QLED with state-of-the-art, the external quantum efficiency (EQE) demonstrated a qualitative improvement (>20%). Accordingly, the EQE, luminance (L), T50 lifetime (reduce to half brightness) of the green QLEDs with SiO2-MLAs structure have been optimized by 22%, 28%, 31%, and up to 24.21%, 381962.6 cd/m2, 111335 h, respectively. This strategy provides valuable insights into mass-producing and utilizing SiO2-MLA Mie scattering composite structures to boost QLED performance in high-efficiency display and lighting applications.

Эффект интенсивного окисления сероводорода дымовых газов содорегенерационного котла при производстве целлюлозы

Despite the transition to the Swedish technology for regenerating black liquor from pulp production plants, even in those regions of Russia where the standard daily average levels of hydrogen sulfide and methyl mercaptan in the air of populated areas have been achieved, a number of problems remain with emissions of reduced sulfur. In many cities, onetime concentrations of reduced sulfur, especially at night, may exceed the permissible ones. In addition to flue gas emissions from soda recovery boilers, there are other, less intensive sources of harmful emissions in the cooking, evaporation and wood-chemical workshops, in the causticization and lime regeneration workshops, there are emissions from unorganized sources and from the open surface of wastewater treatment facilities. The population living near such plants feels the unpleasant odor of methyl mercaptan. This study has aimed to develop a new technology for reducing gas emissions of reduced sulfur into the environment, applicaple for different sources. The results of testing an industrial installation for purification of gas emissions from a soda recovery boiler in a scrubber with nozzle irrigation have been presented. Based on the measurements of the technological parameters of the operation mode of the gas purification plant and the determination of the composition of the irrigation solution, the analysis of the results obtained has been performed. During the tests, a high degree of hydrogen sulfide capture at a low pH value has been achieved. It has been established that hydrogen sulfide has been captured as a result of its oxidation before entering the irrigation solution in fine droplets of condensate formed on micron-sized particles of sulfate and sodium carbonate. The results of this study have been compared with the results of the studies conducted by Stanford University and the P.P. Shirshov Institute of Oceanology of the Russian Academy of Sciences. The possibility of hydrogen peroxide formation under our test conditions in the surface layer of fine droplets formed during the condensation of water vapour on dust particles has been analyzed. The suposed cause of the obtained effect has been determined to be the thermomechanical deformation of the surface layer of the droplets.

Pyramid floating solar still with enhanced condensation surfaces operating under actual weather conditions

The potential solution offered by floating solar still (FSS) to water scarcity confronts challenges associated with condensate droplet loss and structural instability under oceanic and swaying condition. A novel pyramid FSS with reduced wettability surfaces (silicon nano-coated) was proposed, utilizing central symmetry structure of pyramid to reinforce the stability and adopting nano-coated surfaces to enhance the condensation. A 4-day outdoor experiment was conducted to evaluate the performance. The highest yield of nano-coated FSS was 1.017 kg/m2/d under an accumulated irradiation of 15.166 MJ/m2/d, which was 16.76 % higher than that of uncoated FSS. Furthermore, the yield of nano-coated FSS was 0.949 kg/m2/d in the river experiment, showing a significant improvement. Next, the enhancement of nano-coated surface on droplet collection was numerically analyzed, showing that the condensation droplets could retain their complete shape until detachment. In contrast, the detachment process on the uncoated surface involved a separation of neck, leaving a residue of liquid behind. Quantitative analysis showed longer movement distances and faster travel velocities for droplets on the nano-coated surface, and these two improvements could facilitate condensate collection. Furthermore, the cost analysis reveals a CPL of 0.129 $/L for the proposed FSS, suggesting its affordability for off-grid communities.

Spontaneous continuous multiple jump of condensate droplets on superhydrophobic surface with hierarchical micro-nano structures

When two or more droplets coalesce on a superhydrophobic surface, the released surface energy will partially convert into kinetic energy, resulting in droplet jump from substrate surface. In this paper, a kind of superhydrophobic surface with hierarchical papillary micro-nano structures was fabricated to facilitate droplets coalescence-induced jump. The surface is easy to prepare without complex process. Different from single jump, a kind of spontaneous continuous multiple jump was observed on this kind of superhydrophobic surface. The influences of continuous multiple jump on condensation nucleation rate and water collection rate are investigated and a theoretical model is adopted to determine energy conversion efficiency of continuous multiple jump. The results find that continuous multiple jump makes large droplets to move spontaneously, and improves performance of superhydrophobic surface to maintain dropwise condensation even under a high subcooling. With condensing, the continuous multiple jump becomes more frequent. The average condensation nucleation rate is 303 % higher than those of surfaces without hierarchical micro-nano structures. The water collection rate on superhydrophobic surface is 2 times higher than those without hierarchical micro-nano structures. The energy conversion efficiency of continuous multiple jump is two times higher than that of single jump. This study provides a potential direction for heat transfer enhancement of condensation and self-cleaning.

Dropwise condensation on subcooled micropillar surfaces with 3D lattice Boltzmann method

In this investigation, an alternative geometric formula is proposed to address the force between fluid nodes and fluid ghost nodes, with the aid of which the contact angles can be varied in the range of 48.3°∼131.9°. This formula is applied to the three-dimensional double-distributed thermal lattice Boltzmann method being proved to be accurate and reliable by single droplet condensation. The effects brought by varying micropillar size on the kinetic properties of condensed droplets, including nucleation, growth, coalescence and jumping, are investigated in detail. The results show that the droplet wetting state tends to be the suspended Cassie state as the width and spacing of the micropillars are decreased, and the condensed droplets can merge and jump off the micropillar surface. In the meantime, the average droplet number increases, the average diameter and the diameter of dominant droplets decrease, thus reducing the condensate coverage. When the micropillar spacing is small, increasing the micropillar height results in the condensed droplet state being changed from Wenzel to Cassie state, and the percentage of small droplets also increases. Instead, when the micropillar spacing is large, by increasing micropillar height, droplets can nucleate in the middle of micropillars, and the percentage of large droplets is improved due to increased heat transfer area. In this study, the surface self-cleaning capability is strongest with the combination of dimensionless pillar height 0.4, spacing 0.1 and width 0.1, which reduces the condensate coverage by 66 % compared to its plain competitor.

Investigating the effect of environmental conditions and surface type on condensation heat transfer coefficient and droplet departure time

This study investigates the impact of surface characteristics—hydrophilic (copper) and hydrophobic (Teflon-coated copper) surfaces—and environmental conditions such as relative humidity (RH) ranging from 80 % to 96 %, temperature differences (DT) from 4 °C to 10 °C, and airflow velocities (V) from 2 to 8 m/s during 180 min on humid air condensation heat transfer coefficient (HTC) and droplet departure time. The research utilizes a Design of Experiments (DOE) strategy, utilizing the Response Surface Methodology (RSM) paired with a Central Composite Design (CCD) to evaluate the influence of these parameters and provide a correlation relationship between the HTC of each surface and the applied environmental conditions. Hydrophilic surfaces generally exhibited higher average HTCs than hydrophobic ones. However, at a temperature difference of 10 °C, relative humidity of 96 %, and air velocities of 2 and 8 m/s, hydrophilic surfaces significantly decreased HTC due to a condensation regime transition from dropwise to filmwise. The highest recorded average HTC was 1.16 and 1.13 kW/m2°C on the hydrophobic surface under these conditions. The temperature difference had the most significant effect on increasing the HTC. Additionally, it was observed that the relative humidity played a more critical role than the flow velocity. There is a similar process for droplet exit, with the difference that in some experiments, the heat flux of hydrophobic surfaces was slightly higher than that of hydrophilic surfaces. Still, the drop fell on it later and left the surface because of the nature of the hydrophobic surface, which prevents droplets from spreading and coalescence with other droplets.

Study on the Oil-Water Separation Performance of Axial-Flow Hydrocyclone Enhanced by Condensate Bubbles

Abstract Produced water is the main by-product of the oilfield extraction process. Due to its high emulsification degree and density close to water, micron oil droplets are inefficiently separated by ordinary cyclone, and it is difficult to meet the standards of external discharge and reinjection after treatment. In this study, micron bubbles were prepared by mixing hydrocarbon components as gas and passed into the cyclone separator to enhance the oil-water separation effect. After the bubbles entered the cyclone, due to the pressure environment inside, the heavier components in the bubbles were found to condense and precipitate from the bubble surface, while the lighter components did not undergo phase change. The heavy hydrocarbons condense and spread out in the bubble and form a condensate film, because the condensate and oil droplets belong to the hydrocarbon homologue is easier to capture the oil droplets. This technology realizes the modification of lipophilic and hydrophobic surface of the bubbles. After the oil removal experiments found that the traditional axial cyclone separator separation of 65%, through the ordinary bubble assisted separation efficiency of 74%, and through the preparation of condensate bubbles to enhance flotation can be raised to 89% of the oil removal efficiency. Therefore, the condensate bubble-enhanced cyclone separator oil-water separation has a good application prospect.

Supercooled condensation droplets sliding on frost: Origin and anti-frosting effect observed on Cotinus coggygria leaf

Fascinated by the purple color, water-repellent, and self-cleaning properties of Cotinus coggygria Scop. leaves, we studied their morphology, wetting, and condensation frosting. Wax nanotubules confer high contact angles, enabling coalescence-induced condensation droplet (out-of-plane) jumping, which, as known, contributes to slowing down frost. Another type of movement-this time in-plane-becomes predominant in reducing the frosting velocity ( ) within a sub-cooling temperature range. Specifically, supercooled droplets slide toward the frost bridges upon contact, moving in the opposite direction to frost propagation. Between -11 and -2°C, Sliding on Frost (SoF) shifts from being rare to very frequent, reducing from approximately 4 to 1, respectively. Using high-speed microscopy, we observed that the advancing contact angle of supercooled water on ice decreases with temperature. We describe the primary role of this behavior in SoF with a model that accounts for the forces involved and explains the observed transition.

Micro segment analysis and machine learning prediction for thermal-hydraulic parameters of propane condensation flow in a PCHE straight channel

In the LNG regasification process, the printed circuit heat exchangers(PCHE) is an ideal choice for vaporizer, with propane as the intermediate working medium in the hot side of PCHE. In this work, numerical simulations of propane condensation flow and heat transfer at different operating parameters was carried out in a semi-circular straight channel of PCHE. The micro-segment analysis method was used to present the local heat transfer coefficient and pressure drop in the channel. The results indicate that the propane condensation process can be divided into three stages: the “constant temperature condensation stage” in the droplet condensation state, the “varying temperature condensation stage” in the film condensation state, and the “subcooled stage” in the liquid phase state. Different operating parameters can affect the start and end position of each stage, as well as the parameter values in the same state. An artificial neural network method was used to predict the local heat transfer coefficient and pressure drop, with the predicting error of less than 5 % and 10 % respectively. This study provides a machine learning method to accurately predict the flow and heat transfer parameters for propane condensation flow in PCHE channel and valuable for future design of LNG vaporizer.

Edge-affected droplet dynamic and subsequent frost growth characteristics for horizontal cold plate under different humidity levels

Frosting widely exists in engineering applications and mostly has negative impacts. To better avoid or utilize frosting, more micro and systematic investigations into the frosting mechanisms are necessary. In this study, the combined effect of humidity and plate edge on droplet dynamic and the subsequent frost growth characteristics of a horizontal cold plate is experimentally investigated. The results show that the difference in the durations of droplet condensation stage between edge-affected and unaffected regions is little, and both decrease from around 480 to 43 s when relative humidity (RH) increases from 30% to 80%. In contrast, the difference in the durations of droplet freezing stage between edge-affected and unaffected regions is significant. The former is around 9 s at all humidity levels, while the latter decreases from around 100 s to 40 s when RH increases from 30% to 80%. Meanwhile, the average equivalent droplet diameters in the edge-affected region are 87.3 × 10−3–122.1 × 10−3 mm, which are 31.0 × 10−3–45.5 × 10−3 mm larger than in the unaffected region. The frost layer surface roughness at 80% RH is smaller than others due to the frost crystal reverse melting. This paper can help better understand the frosting mechanism from a microscopic scale and guide the accurate prediction of frost formation.

Enhancing Photoswitchable Wetting Properties of Hydrophobic Porous Spiropyran Copolymer Surfaces Through Surface Roughness Engineering

AbstractSurfaces with photoswitchable wettability are of great interest for various applications such as smart coatings or liquid condensation. The photochromic ring opening reaction of spiropyran (SP) to merocyanine (MC) implies a high dipole moment change, making it interesting for photo‐controlled wetting properties. In addition to the material chemistry, surface wettability is influenced by the surface topography. Porous SP copolymers with various micro‐/nanostructures, that is, different submicron roughness, are fabricated via polymerization‐induced phase separation. The influence of the surface topography on the photoswitchable wetting properties is studied. Surfaces with arithmetic mean roughness (Sa) below 150 nm exhibited a maximum static contact angle (SCA) photoswitch up to 16° from 124 ± 6° to 108 ± 4° upon UV exposure. While superhydrophobic surfaces with higher Sa (157 – 608 nm) showed an insignificant SCA switch. The latter surfaces have a SCA above 150° and low CA hysteresis indicating small and insufficient contact with SP/MC surface asperities for the switch. With the optimized surfaces, photo‐controlled water condensation is studied on microscale and showed that the condensate droplets merged faster, and formed larger droplets pinned to the original contact lines on surfaces switched to the less hydrophobic state.

Preparation of Aluminum-Based Superhydrophobic Surfaces for Fog Collection by Bioinspired Sarracenia Microstructures.

Freshwater shortage is a growing problem. Inspired by the Sarracenia trichome fog-trapping and ultrafast water-transport structure, a series of hierarchical textured surfaces with high-low ribs with different wettabilities was prepared based on laser processing combined with dip modification. Through fog-collection performance tests, it was found that the samples with superhydrophobicity and low adhesion had the best fog-collection effect. In addition, it was observed that the fog-collection process of different microstructured samples was significantly different, and it was analysed that the fog-collection process was composed of two aspects: directional condensation and directional transport of droplets, which were affected by the low ribs number and rib height ratio. A design parameter was given to create the Sarracenia trichome-like structure to achieve a fast water transport mode. This study provides a good reference for the development and preparation of fog-collection surfaces.

Self-draining microchannel surface structure for droplet condensation with controlled droplet radius distribution

Surface dewetting is technically important in industrial applications, particularly where phase change processes are involved. We present an intrinsically driven water-permeable microchannel surface system. It has two important advantages: its self-draining capability to remove surface droplets and its ability to limit both the maximum size of droplets condensing on the surface and the thickness of the water film in the microchannel system. This results in a reduction in the overall thermal resistance of the condensate on the cooled surface. We have successfully applied this surface drainage concept to water condensation. An improved condensation efficiency of 5%–9% has been achieved operating the device in an environmental chamber (60% relative humidity, 30 °C chamber temperature, 6 °C cooling temperature) without any optimization of the stable surface structure involved.