Solid-liquid Contact Area Research Articles

Direction-preferred liquid transportation on biomimetic hierarchical gradient microgrooves

Conventional understanding holds that droplets on microgrooves flow symmetrically toward both ends, which limits their utility in applications requiring direction-preferred droplet transport, such as vapor chambers. Inspired by the fog-collecting strategies of cactus spines, we propose a bioinspired hierarchical gradient microgroove (BHGM) that achieves the liquid transport in a preferred direction. By combining primary microgrooves with surface nanostructures, BHGM provides a strong initial driving force for liquid transport. Secondary microgrooves are introduced to increase the liquid–solid contact area, further enhancing capillary pressure. Additionally, gradient interfaces at structural discontinuities create unbalanced surface tension, driving direction-preferred liquid transport. This, in combination with the shape variation of the secondary grooves, regulates the meniscus and enables rapid and heterogeneous liquid movement. The BHGM demonstrates forward capillary wicking over a distance of up to 90 mm in just 12.5 s while reducing reverse wicking time by 53.7%. At the two gradient interfaces from bottom to top, speed reduction rates are only 7.7% and 2.3%, respectively. In addition, the BHGM maintains liquid transport capability even at bending angles of 90° and 120°. This hierarchical design enhances heterogeneous capillary transport efficiency while preserving scalability and adaptability, offering promising potential for practical applications, including improved thermal management in vapor chambers and more efficient fluid control in microfluidics.

Reconsideration on the maximum deformation of droplets impacting on solid surfaces

AbstractDroplet impact on solid surfaces is widely involved in diverse applications such as spray cooling, self‐cleaning, and hydrovoltaic technology. Maximum solid‒liquid contact area yielded by droplet spreading is one key parameter determining energy conversion between droplets and surfaces. However, for the maximum deformation of impact droplets, the contact length and droplet width are usually mixed indiscriminately, resulting in unignored prediction errors in the maximum contact area. Herein, we investigate and highlight the difference between the maximum contact length and maximum droplet width. The maximum droplet width is never smaller than the maximum contact length, and the difference appears once the contact angle exceeds 90° (which becomes more significant on superhydrophobic surfaces), regardless of impact velocities, liquid viscosities, and system scales (from macroscale to nanoscale). A theoretical model analyzing the structure of the spreading rim is proposed to demonstrate and quantitatively predict the above difference, agreeing well with experimental results. Based on molecular dynamics simulations, the theoretical analysis is further extended to the scenario of nanodroplets impacting on solid surfaces. Reconsideration on the maximum deformation of impact droplets underscores the often‐overlooked yet significant difference between maximum values of contact length and droplet width, which is crucial for applications involving droplet‒interface interactions.

Simulation and experimental investigation on kinetic and thermodynamic characteristics of liquid nitrogen droplets impacting superheated wall

Liquid nitrogen droplets impacting superheated wall is an essential phenomenon in cryogenic phase-change spray cooling. In this study, the Volume of Fluid (VOF) method was used to develop a numerical model to investigate the kinetic and thermodynamic characteristics of liquid nitrogen droplets impacting superheated wall. The experiment for the impact of liquid nitrogen droplets was conducted to validate the simulation. The findings indicate that liquid nitrogen droplets impacting superheated wall exhibit three boiling regimes: contact boiling, transition boiling, and film boiling. During contact boiling, as We increases, droplets undergo three modes sequentially: spreading, forming fingering-like structures, and fragmentation. During transition boiling and film boiling, as We increases, droplets exhibit spreading, splashing, and fragmentation. Increasing the wall temperature leads to the formation of vapor pockets and vapor film, which results in deteriorated heat transfer at the solid–liquid contact area, and meanwhile reducing the extent of droplet spreading. Increasing We promotes droplet spreading, reducing vapor pockets and vapor film thickness, increasing wetting area, and postpones the onset of heat transfer deterioration. Increasing the wall temperature and We both lead to a higher decreasing rate of liquid volume of droplet which indicates an intensified vaporization rate. The larger the contact angle of the wall, the less the droplet spreads, and the lower the heat transfer between the droplets and the wall.

Numerical investigation on the flow and heat transfer performances of a novel microchannel heat sink arranged with inclined pin fins

Abstract The advancement of microelectronics technology has led to an increased demand for heat dissipation in devices. In response to this challenge, microchannel heat sinks (MCHS) have been introduced as a viable solution. The heat dissipation capabilities of MCHS can be enhanced by adopting pin fins, which serve to augment the solid-liquid contact area and disrupt the fluid boundary layer. Most research on MCHSs with pin fins has concentrated on vertical pin fin configurations, with a comparatively limited investigation into inclined pin fins. To further enhance the thermal performance of MCHS with pin fins, this study presents a novel MCHS with inclined pin fins (MCHS-IPF). The flow and heat transfer characteristics under steady-state conditions were analyzed using three-dimensional numerical simulations. Additionally, geomet-ric optimization was conducted on the tilt angle (θ: 30° to 30°, excluding 0°) and the secondary flow channel width ratio (β) to achieve improved overall performance. The results show that the MCHS-IPF sig-nificantly enhances thermal dissipation capability compared to a conventional MCHS with vertical pin fins (MCHS-VPF). As the tilt angle remains constant, the heat dissipation capacity of MCHS-IPF improves with an increase in β. The MCHS-IPF with β = 0.6 and θ = 30° at Re = 600 shows a notable enhancement of 57.7% in the Nusselt number compared to the MCHS-VPF. This MCHS-IPF, also demonstrates superior overall performance in this study, achieving a maximum Performance Evaluation Criteria of 1.53, thereby establishing itself as the optimal structure.

Influence of microstructure on the wettability of tobacco leaves: a theoretical model and quantitative analysis

Wettability has widespread applications in everyday life such as waterproof clothing, moisture-proof materials, and self-cleaning surfaces. It is also a common phenomenon observed in plants like the lotus, where superhydrophobicity is primarily influenced by chemical composition and microstructure, with the latter playing the most critical role. In this paper, we explore how microstructure affects the wettability of tobacco leaves and examine the relationship between microstructure and contact angle. We select three different Roast tobacco leaves and use Neumann models and Owens-Wendt-Rabel-Kaelble (OWRK) models to calculate the surface energy, and the surface energy is between 28 and 31 mN/m and the Young’s contact angle is around 90°. Based on the Cassie–Baxter model, we develop theoretical models of venation and foliage for predicting contact angles. The results show that the surface of the tobacco leaves can transition from hydrophilic to hydrophobic by modifying the size of the surface microstructure. Also we develop a method that use SEM and ImageJ to predict contact angle on leaves by analyzing solid-liquid contact area. The results indicate that the discrepancy between the theoretical and experimental results is within 5%. These findings may provide a better understanding of the wettability in natural plants and may pave a new way of realizing surface fabrications with specific infiltrating properties in industries.

Sticky Superhydrophobic State.

It is common sense that the droplet is stickier to substrates with larger solid-liquid contact areas. Here, we report that this intuitive trend reverses for hollowed micropillars, where a decrease in solid-liquid contact area caused by an increase in the pore size of a pillar top leads to an increase in the droplet depinning force. As compared to relief of liquid-vapor interface distortion caused by the sliding of the contact line on filled pillars, the pore hinders the contact line sliding, hence leading to enhanced interface distortion and droplet adhesion. The droplet on hollowed micropillars is completely suspended above the vapor but inherently sticky. Hence, this counterintuitive phenomenon is termed as the sticky superhydrophobic state in contrast to the conventional superhydrophobic state with low adhesion. A model building upon the dynamics of the contact line and liquid-vapor interface, which successfully predicts the droplet depinning force on filled and hollowed pillars, is introduced.

Superhydrophobicity With Self-Adaptive Water Pressure Resistance and Adhesion of Pistia Stratiotes Leaf.

Superhydrophobic surfaces are promising for optimizing amphibious aircraft by minimizing water drag and adhesion. Achieving this involves ensuring these surfaces can resist high liquid pressure caused by deep water and fluid flow. Maximizing the solid-liquid contact area is a common strategy to improve liquid pressure resistance. However, this approach inevitably increases solid-liquid adhesion, making it challenging to guarantee a trade-off between the two wetting characteristics. Here, it is found that the Pistia stratiotes leaf exhibits superhydrophobicity with high water pressure resistance and low adhesion, attributed to its self-adaptive deformable microstructure with unique re-entrant features. Under pressure, these microstructures deform to increase the solid-liquid contact area, thereby enhancing water pressure resistance. The re-entrant features elevate the deformation threshold, enabling higher modulus microstructures to achieve adaptive response. This facilitates the recovery of deformed microstructures, restoring the air layer and maintaining low adhesion. Following these concepts, Pistia stratiotes leaf-inspired surfaces are fabricated, achieving an 183% improvement in water impact resistance and an ≈80% reduction in adhesion after overpressure compared to conventional superhydrophobic surfaces. The design principles inspired by Pistia stratiotes promise significant advancements in amphibious aircraft and other trans-media vehicles.

Wetting dynamics and heat transfer of droplet evaporation around boiling point: Facile manipulation by surface roughness

The evaporation of water–ethanol droplets on solid surfaces has vast potential for applications in thermal management, microfluidics, and biomedical sciences, while the approach of manipulating wetting dynamics and heat transfer of droplet evaporation around the boiling point remains open for investigations. The present study proposes a facile approach: fabricating solid surfaces with diverse roughness by sandpaper milling with different grit densities, which can alter the wetting and heat transfer characteristics of droplet evaporation. We discover that when the temperature of the heated surface exceeds the droplet boiling point, the existence of bubbles affects the solid–liquid wetting state; surface roughness alters the ability of bubble departure, thus determining the solid–liquid contact and the contact line retraction time. Consequently, in this case, the solid–liquid contact area and the heat absorbed from heated surfaces for droplets changes with surface roughness, altering the droplet evaporation time and the average heat flux at the solid–liquid interface. Bridged by droplet wetting dynamics, the heat transfer of droplet evaporation above the boiling point can be manipulated by adjusting surface roughness, offering a facile approach to tuning the process of droplet evaporation in the related industrial applications.

Droplet trampoline surface for regulating contact time of a bouncing droplet across a wide spectrum of Weber numbers verified by in-situ observation

The dynamic superhydrophobicity of metallic surfaces is crucial for anti-icing and anti-adhesion in the fields of aerospace and transportation. Generally, fabricating micro/nanostructures on metallic surfaces is an effective method for facilitating rapid detachment of droplets, and the micro/nanoscale composite structure can significantly reduce the solid–liquid contact area. Meanwhile, the exploration of the correlation between solid–liquid contact time and the spacing of microstructures across a wide range of Weber numbers is of great significance. In this study, it is observed that the contact time of a bouncing droplet on microstructures with small spacing exhibits a notable correlation with the Weber number. This observation challenges the prevailing understanding that the contact time of a bouncing droplet is commonly perceived as independent of the Weber number, equated to the impact velocity. Increasing the structure spacing appropriately proves advantageous in preventing pinning effect, consequently reducing the duration of solid–liquid contact. Subsequently, a regulatory diagram is generated to demonstrate the correlation between contact time and the dual dimensions of the structure spacing and Weber number. Specifically, a novel theory for predicting the contact time based on the Weber number has been established, which reveals the unconventional correlation and enriches the knowledge of droplet dynamics.

Effect of surface roughness on the liquid bridge between two rigid spheres

We aimed to investigate the impact of surface roughness on liquid bridges between spherical particles. Sandblasting was used to control the particle size and produce glass beads and plates with different surface roughness. First, by measuring the advancing and receding contact angles of droplets on different rough surfaces, we analyzed the effects of surface roughness on wettability and hysteresis. Next, we used a custom-made liquid-bridge stretching device to measure the capillary forces of the liquid bridges between spherical particles with different surface roughness values. A charge-coupled device camera acquisition system was set up to capture the morphological changes of the liquid bridge during stretching, and Image View software was used to extract the morphological parameters of the liquid bridge. Theoretically, we reasonably simplified and solved the differential equations for the liquid bridge morphology and used the Young–Laplace equation to calculate the theoretical capillary force of the liquid bridge, providing an in-depth analysis of the influence of surface roughness on the capillary force. Finally, we studied the impact of surface roughness on the volume ratio of the liquid bridge during static stretching and the residual liquid remaining after the liquid bridge breaks. Experimental results indicated that, as the surface roughness increased, the hydrophobicity and wettability hysteresis of the solid surface also increased. The increased hydrophobicity of the surface reduces the solid-liquid contact area of the liquid bridges between the particles, making it easier to form “columnar” or “convex” liquid bridges. Additionally, the enhanced wettability hysteresis causes the solid-liquid contact boundary to lag during the stretching of the liquid bridge, resulting in a decrease in the solid-liquid contact angle. These factors directly alter the geometric shape of liquid bridges during static stretching, thereby affecting capillary forces. Meanwhile, the increase in surface roughness weakens the effect of gravity on the morphology of the liquid bridge, resulting in less liquid mass remaining on the lower sphere after the liquid bridge breaks as the surface becomes rougher.

Ag-TiO2 Photovoltaic Synergistic Field-catalyzed Degradation Performance of Tetracycline

Background: Tetracycline (TC), a commonly used antibiotic, is extensively utilized in the medical sector, leading to a significant annual discharge of tetracycline effluent into the water system, which harms both human health and the environment. Objective: A novel technique was developed to address the issues of photogenerated carrier complexation and photocatalyst immobilization. Compared to traditional photocatalytic photoelectrodes, the suspended catalyst used in the photovoltaic synergy field is more stable and increases the solidliquid contact area between the catalyst and the pollutant. Methods: This paper uses sol-gel-prepared Ag-TiO2 materials for the photoelectric synergistic fieldcatalyzed degradation of TC. The study examined how the Ag doping ratio, calcination conditions, catalyst injection, pH, electrolytes, and electrolyte injection affected photoelectric synergistic fieldcatalyzed degradation. The experiments were performed in a photocomposite field with a constant 50 mA current and a 357 nm UV lamp for 60 minutes. The composites underwent characterization using XRD, TEM, and XPS techniques. Results: Ag-TiO2 photoelectric synergistic field-catalyzed reaction with 357 nm ultraviolet lamp irradiation for 60 min and a constant current of 50 mA degraded 5 mg/LTC under preparation conditions of molar doping ratio of Ti: Ag=100:0.5, roasting temperature of 500 °C, and roasting time of 2 h. The photoelectric synergistic field-catalyzed degradation process achieved a degradation rate of 90.49% for 5 mg/L TC, surpassing the combined degradation rates of electrocatalysis and photocatalysis. The quenching experiments demonstrated that the degradation rate of TC decreased from 90.49% in the absence of a quencher to 53.23%, 42.58%, and 74.52%. The presence of •OH had a more significant impact than h+ and •O2 -. Conclusion: The findings suggest that Ag-TiO2 significantly enhanced the efficacy of photoelectric synergistic field-catalyzed degradation and can be employed to treat high-saline and lowconcentration TC. This establishes a benchmark for using photoelectrocatalytic materials based on titanium in treating organic wastewater.

Numerical analysis of fluid flow and heat transfer characteristics in single crystal diamond microchannels with ribs and secondary channels

To meet the heat dissipation requirements of high-frequency and high-power electronic devices, single crystal diamond microchannels (SCD-MC) with secondary channels and rib combinations are proposed. The fluid flow and heat transfer characteristics in SCD-MC with various secondary channels and rectangular rib combinations are investigated through numerical simulations. The comprehensive performance and energy saving effect of the microchannel were evaluated by analyzing the factor of merit and entropy generation performance. The results show that the SCD-MC with secondary channels and rib combinations enhance fluid disturbance and increase the solid–liquid contact area, significantly improving heat transfer. When Reynolds number (Re) is 586, compared with the straight microchannel, the average temperature at the bottom of the SCD-MC with rectangular secondary channels and rectangular rib (Case 5) is reduced by 4.8 K, the heat transfer coefficient is increased by 209.8 %, and the factor of merit is improved by 89.2 %. The entropy generation augmentation number of the Case 5 microchannel was the minimum of 0.52, which has the highest energy saving effect. The factor of merit of the Case 5 microchannel exhibits a tendency to first increase and then decrease with the increase of the relative width of the secondary channel (Ψ), the relative width of the rib (Φ), and the relative position of the rib (Π). At Re = 586, Ψ = 0.933, Φ = 0.667, and Π = 0.5, the factor of merit of the Case 5 microchannel is 2.08, indicating the highest comprehensive performance. This finding provides new ideas and methods for the design and application of microchannel thermal management.

Superhydrophobic synergistic antibacterial ZrO2-based surfaces with tertiary hierarchical structures fabricated by femtosecond laser texturing and surface modification

Zirconia (ZrO2) is a hard and brittle dental implant material without anti-infective property. This work reports the preparation of a tertiary micro-nano hierarchical structure on a ZrO2 surface via femtosecond laser texturing combined with magnetron sputtering deposition of an Ag layer (Ag/ZrO2), aiming to achieve a superhydrophobic synergistic antibacterial effect. Laser-scanning pitch and Ag layer thickness were systematically optimized for obtaining the tertiary hierarchical structure. The wettabilities, antibacterial properties and durabilities of various ZrO2 and stearic acid modified Ag/ZrO2 (S-Ag/ZrO2) surfaces were further tested and comparatively analyzed. The results revealed that the optimal process parameters were a laser-scanning pitch of 30 μm and an Ag layer thickness of 100 nm. The as-obtained S-Ag/ZrO2 sample displayed a tertiary micro-nano hierarchical structure, which was featured by a periodic regular conical micro-convex structure covered with ZrO2 nano-protrusions and Ag nanoparticles. This structure could not only greatly reduce the solid-liquid contact area to achieve outstanding superhydrophobicity and durability, it could also sustainably release bacteria-killing Ag+ to obtain an antibacterial ratio of 95.1 % and ensure a long-term antibacterial effect. In addition, the optimal S-Ag/ZrO2 sample having this structure showed a PC12 cell survival rate of up to 81.75 %, demonstrating its good biocompatibility. This work may be of great inspiration and reference for the expansion of the use of ZrO2 in dentistry.

The optimization of roll-bond cold plate based on Taguchi-grey theory for server chips thermal management

The roll-bond cold plate, an economical and straightforward electronics liquid cooling approach, is highly promising to address the increasing electronics chip thermal management challenges. However, the roll-bond cold plate with staggered cellular flow channels, while having a sizable solid-liquid contact area and high heat dissipation potential, suffers from inadequate temperature uniformity and fluidity. This study addresses flow and temperature uniformity issues in current roll-bond cold plates by proposing a design—Direct Liquid Cooling Roll-Bond Plates (DLCRBP) tailored for high-performance server architectures. To investigate how regional combination, cellular diameter, and longitudinal spacing affect both thermal and flow performance, orthogonal experiments with diverse flow channel structures were conducted using the Taguchi-grey theory. COMSOL-based numerical simulation were used to analyze these experiment conditions. Multi-objective optimization, considering pressure drop, heat source temperature uniformity, and coolant temperature difference, was then performed using the grey correlation method. The optimized DLCRBP (A3B5C1) was fabricated, and its performance was compared with the staggered cellular DLCRBP (SCS), which is the control group without optimization, under various inlet flow velocities, heat source powers, and coolant inlet temperatures. Experimental comparisons illustrate that the optimized structure ensures outstanding temperature uniformity even at low inlet flow velocities. Specifically, at an inlet flow velocity of 0.2 m/s, the average and maximum temperature differences on the heat source's upper surface are 36.5 % and 75.3 % lower, respectively, compared to pre-optimization levels. Furthermore, A3B5C1's temperature uniformity improves with higher coolant inlet flow velocity and lower coolant inlet temperatures. At a coolant inlet flow velocity of 0.5 m/s or higher, A3B5C1 sustains the surface temperature of a 600 W chip below the thermal design's safe temperature of 77.8 °C, highlighting its enhanced performance.

Kinetics mechanism of pore pressure effect on CO2-water-rock interactions: An experimental study

Carbon capture, utilization and storage (CCUS) is an effective technology to reduce carbon dioxide (CO2) content in atmosphere, while due to the insufficient mastery of deterioration laws of reservoir rocks caused by CO2, the extensive application of carbon storage projects is hindered by the leakage risk. Therefore, it was aimed to study the kinetics mechanism of pore water pressure on CO2-water–rock interactions. First, the pressure effect on water–rock interactions was studied to obtain the relationship between ratio of solid–liquid contact area Ψ and pore pressure, and the controlling mechanism of Ψ on reaction rate ri was verified. On this basis, the pressure effect on CO2-water–rock interactions was further studied. Considering the effects on Ψ and solution acidity, the original CO2-applicable kinetics equation was modified to reduce the error of calculating reaction rate by 33.60% on average. Meanwhile, a forecast method was proposed for the reaction rate under different pressure conditions, and the average calculation error was 41.00% lower than that of original kinetics equation. After verifying the accuracy of these two theoretical methods to calculate reaction rate, the reliability to calculate porosity evolution process was further verified, and the calculation errors could be reduced by 29.52% and 31.81%, respectively.

Anti-icing polyurethane coating on glass fiber-reinforced plastics induced by femtosecond laser texturing

Polyurethane coating has been commonly used in aerospace and construction, and enhancing anti-icing capabilities in low temperatures is crucial for preventing mechanical failures and reducing energy consumption. Utilizing a superhydrophobic surface was considered an important option to improve anti-icing performance. In this study, femtosecond laser treatment has applied to polyurethane coating on glass fiber-reinforced plastic (GFRP) to transform from hydrophilic to superhydrophobic. Results have indicated that laser treatment significantly reduced the solid–liquid contact area compared to the original surface. The non-polar groups on the surface contributed greatly to the enhancement of hydrophobicity. In comparison to the original surface, the freezing temperature of droplets on the superhydrophobic surface with improved anti-icing performance was reduced from −4.5 °C to −9.2 °C, while the freezing time was extended from 65 s to 269 s. This improvement was attributed to the reduction of solid–liquid contact area, resulting in a low heat transfer rate and a low heterogeneous nucleation rate. Additionally, the laser-treated surface exhibited excellent self-cleaning effects, along with mechanical and chemical stability.

A simple strategy towards construction of copper foam-based robust superhydrophobic coating based on perpendicular nanopins for long-lasting delayed icing and reduced frosting

Icing/frosting poses a significant problem for materials used in everyday applications. In recent years, anti-icing methods utilizing superhydrophobic materials have become popular. These materials have superhydrophobic surfaces with air-solid composite structures, which can prevent icing/frosting by creating air cushions in the micro- and nano-scales of the rough structure. However, long-term protection of the substrate is challenging due to air leakage from the air cushion and the breakdown of the superhydrophobic coating. The use of superhydrophobic materials in cold environments is also greatly limited by this shortcoming. In this paper, superhydrophobic copper foam (SHS CF) was created by using electrochemical oxidation and impregnation techniques and subsequent modified by fluorosilane coupling agent on the copper foam surface to reduce surface particle activity through condensation reactions, achieving a superhydrophobicity with a water contact angle of up to 170±2°. Furthermore, gas was utilized to form a specific rough structure by combining with Cu(OH)2 micro-nanopins, leading to the development of long-lasting gas in SHS CF (LAG-SHS CF). The LAG-SHS CF exhibited impressive anti-frost characteristics, with a delayed icing time of approximately 2171 s. Notably, the SHS CF retained strong wetting capabilities and excellent resistance to abrasion, UV, acid, and alkali even after the removal of LAG, which was ascribed to the fact that the composite structure effectively reduces the solid-liquid contact area and has a high roughness. These properties provide a solid foundation for the application of LAG-SHS CF. The findings of this study contribute to the creation of new materials with anti-icing and anti-frost properties.

Preparation of mechanically durable superhydrophobic aluminum surfaces by LST/MAO and chemical modification

In this paper, a superhydrophobic surface with mechanical durability was prepared on 6061 aluminum (Al) alloy by combining laser surface texturing (LST) and micro-arc oxidation (MAO) techniques followed by chemical immersion treatment. The effects of processing on Al alloys with different texturing spacings on the surface morphology, roughness, surface wettability, and corrosion resistance of the subsequently formed composite coatings were analyzed. The results show that a superhydrophobic surface was obtained with the water contract angle (WCA) of 158.3 ° and the roll-off angle of 9.5 ° at a texture spacing of 300 μm. This was due to the fact that the surface microroughness texturization process created by LST on the surface increased the generation of surface nanostructures, and combined with the natural nanostructure possessed by MAO, unique " double " nanostructure was formed on the surface. This surface structure increased the area of fluoride attachment, reduced the solid-liquid contact area, and decreased the adhesion of droplets to the surface, resulting in higher hydrophobicity. Electrochemical corrosion experiment showed that the corrosion current density of LM-300 was 2 orders of magnitude lower than that of the LM-0 sample, clearly demonstrating better corrosion resistance. In addition, the prepared superhydrophobic surface presented excellent mechanical durability, and in the ceramic zirconia cyclic abrasion experiment, the superhydrophobic surface was able to withstand 61 cycles of abrasion at a pressure of about 2.5 kPa.

Effect of nanocavity geometry on nanoscale nucleate boiling heat transfer

In recent years, surfaces with nanocavities have been identified to considerably improve boiling heat transfer, that is highly promising for advanced thermal energy systems. To boost developments in nanostructured boiling surfaces, effects of nanocavity geometry on nucleate boiling at the nanoscale are systematically studied for the first time by utilizing molecular dynamics simulation. Three typical nanocavities with rectangular, semicircular, and triangular cross-sectional shapes are constructed, which have the identical width and depth (8 nm and 4 nm). Moreover, three representative wetting conditions corresponding to different solid-liquid interaction strengths are further considered to provide a comprehensive understanding of geometry effects. The results manifest that nanocavity geometry effect on nucleate boiling can be attributed to the differences in their solid-liquid contact area and solid-liquid interactions play a vital role in reinforcement effectiveness. When the solid-liquid interaction is sufficiently strong (energy coefficient equals 1.5, termed ultra-superhydrophilicity), variations in nanocavity geometries will induce remarkable effects on boiling performance. Among three geometric configurations, the rectangular nanocavity exhibits the highest heat transfer efficiency and achieves maximum boiling enhancement, including significant improvements in bubble nucleation and growth, as well as critical heat flux. This study provides an essential insight into nanoscale boiling reinforcement mechanism.

Laser-based fabrication of superwetting titanium alloy with enhanced corrosion and erosion-corrosion resistance

Titanium (Ti) alloy is vulnerable to erosion and corrosion effect of sea water in the application of marine equipment and prone to degradation and failure. In order to further enhance the erosion-corrosion resistance of Ti alloy, a laser-heat hybrid treatment is applied to fabricate superwetting Ti alloy surface. The surface morphology, chemical composition and surface wettability of Ti alloy before and after laser processing are characterized. The surface behaviors of the superwetting Ti alloy surface during corrosion and erosion-corrosion interaction are evaluated by electrochemical station and two-phase flow erosion equipment. The experimental results indicate that the periodic micro-bump structure induced by laser texturing and the low surface energy after heat treatment contribute to the surface wettability transformation into superhydrophobicity with the contact angle of 156.2°. Compared with the untreated Ti alloy surface, the laser-heat-treated superhydrophobic surface exhibits a smaller corrosion current density and a larger potential in NaCl solution, showing better corrosion resistance. The surface erosion-corrosion resistance has also been increased by 18% due to the decrease of solid-liquid contact area caused by air cavity of superhydrophobic surface. This can provide a solid laser-based fabrication method of Ti alloy for long-term and stable application in marine environment.