Reduced Contact Time Research Articles

Effect of Asymmetry on the Contact Time of Droplet Impact on Superhydrophobic Cylindrical Surfaces.

Reducing the contact time during the droplet impact on the surface is crucial for anti-icing, self-cleaning, and heat transfer optimization applications. This study aims to minimize the contact time by modifying the surface curvature to create an asymmetric impact process. Our experiments showed that the increase in Weber numbers (We) and the decrease in the ratio of surface diameter to droplet diameter (D*) intensify the asymmetry of the impact process, yielding four distinct rebound modes. Low asymmetry observes the liquid retract toward the central point (Rebound Modes 1 and 2), whereas high asymmetry yields a wing-like rebound (Rebound Modes 3 and 4). In Rebound Mode 1, increased asymmetry would lead to more extended contact due to the prolonged waiting period. Conversely, the reduction in contact time in Rebound Mode 2 occurs due to increased asymmetry with no waiting period. For Rebound Modes 3 and 4, the retraction time could be divided into three stages, generated by two liquid detachment modes from the surface. Analysis reveals that an increased asymmetry would reduce the retraction time during the first stage but prolong it during the third stage, with no significant effects on the second. Four correlations, each pertaining to a distinct impact mode, are proposed based on these analyses to describe the contact time concerning We and D* for droplets impacting a superhydrophobic cylindrical surface.

Droplet impact dynamics on a flexible superhydrophobic cantilever wire mesh

Droplet impact on fixed permeable surfaces has many applications, including spray formation, coating deposition, and filtration processes. The present research studies the droplet and beam dynamics during the water droplet impact on the flexible superhydrophobic cantilever mesh, and the results are compared with the impact on a fixed-fixed superhydrophobic mesh. The effects of beam flexibility (droplet impact point), mesh opening size, and impact velocity on the rebound behavior of droplets, spreading diameter, contact time, beam deflection, and frequency were investigated. Although the contact time is reduced compared to the rigid surface, the well-known pancake rebound is not observed anymore on the cantilever beam. Therefore, the contact time reduction is not as pronounced as the fixed mesh for the cantilever beam. The spreading time and maximum spreading diameter decreased as the impact distance from the fixed point increased due to the reduced transmitted energy to the beam. However, the retraction time is affected by both beam dynamics and liquid penetration. Therefore, the shortest contact time depends not only on the oscillation and frequency of the beam and droplet but also on the liquid penetration. Moreover, the results prove that by defining an appropriate maximum spreading ratio, it becomes independent of the impact point. Finally, the beam deflection and frequency, in addition to the maximum spreading diameter of the droplet are modeled theoretically.

Hospital pharmacists', doctors' and nurses' perceptions of intra- and inter- professional communication in the context of electronic prescribing and medication administration systems: A qualitative study.

Effective, integrated and coordinated communication is essential in providing high quality patient care. Little prior research has detailed the impact of electronic prescribing and medication administration (ePMA) systems on healthcare professionals' (HCPs') communication. We investigated hospital pharmacists', doctors' and nurses' perceptions of how ePMA systems have affected, or are expected to affect, the way they communicate with each other in an inpatient setting. A qualitative study in three English NHS hospitals: two used different inpatient ePMA systems, and one used paper-based prescribing. We conducted focus groups with pharmacists, and semi-structured individual interviews with doctors and nurses. Transcribed data were analysed inductively using thematic analysis. Nine focus groups, three at each hospital, were conducted with pharmacists with different levels of seniority (58 pharmacists in total). Fourteen doctors and twelve nurses took part in individual interviews. Four themes were generated: modes of communication, reduced pharmacist visibility, system limitations, and future aspirations for ePMA. Whether working with ePMA or paper-based systems, all participants preferred to communicate face-to-face to facilitate collaborative discussions regarding patient care. Participants perceived that ePMA reduced contact time with patients. Pharmacists perceived that both their physical ward presence and their written communication on medication charts had reduced since introduction of ePMA. Doctors felt they were now less likely to ask pharmacists questions due to pharmacists' reduced physical presence on the ward. Hardware and software limitations were identified by all HCPs, with suggestions made for future developments to better support communication. ePMA does not necessarily support communication among HCPs. Pharmacists and doctors were also concerned that ePMA reduces communication between themselves and their patients. Hospital managers should ensure sufficient hardware for HCPs, including pharmacists, to conduct their work in clinical areas, and work with ePMA system suppliers to develop ways of enhancing, rather than inhibiting, communication.

Biomechanical changes identified during a marathon race among high-school aged runners

BackgroundDespite the increasing popularity of endurance running competitions among adolescent runners, there is currently limited information regarding expected biomechanical changes across the duration of a long-distance running event, and the relationship between young runners’ biomechanics and running performance. Wearable technology offers an ecological means to continuously assess runners’ biomechanical data during outdoor running competitions. Research questionDo adolescent athletes adopt changes in sensor-derived biomechanics throughout a marathon race, and are there relationships between race performance and biomechanical features among young marathoners? MethodsFourteen high-school aged runners (9 M, 5 F; age: 16 ± 1 years, height: 170.8 ± 7.5 cm; mass: 63.6 ± 9.4 kg) wore lace-mounted sensors to record step-by-step biomechanics during a marathon race. Official race segment completion times were extracted across 5 race segments (5-K, 15-K, Half Marathon [21.1-K], 35-K, Marathon [42.2-K]). Within-participant repeated measures of covariance (pace) were conducted to assess changes in biomechanics across the race, with Bonferroni post-hoc comparisons. Pearson’s r correlations were performed to assess the relationship between race finish times and biomechanics. ResultsPace was significantly slower (p-range: 0.002–0.005), contact times significantly longer, and stride lengths significantly shorter in the final segment compared to middle segments (p-range: 0.003–0.004). The rate of shock accumulation was significantly higher in the final race segment compared to the first three segments (p-range: 0.001–0.002). Moderate relationships existed between finish times and pace (r = −0.63), stride length (r = −0.62), and contact time (r = 0.51). SignificanceAdolescent runners altered their gait patterns in the final marathon segment compared to earlier segments. Spatiotemporal measures were moderately correlated with race finish times, suggesting a link between faster run pace, increased stride lengths, and reduced contact time for improved running performance during an endurance race.

Behavioral responses of dairy cows and their calves to gradual or abrupt weaning and separation when managed in full- or part-time cow-calf contact systems

There is growing interest in managing cow and calf together for a prolonged period, but concerns remain about how best to wean and separate the cow and calf to minimize stress. One approach is to progressively reduce suckling opportunity over time, as in nature. There is also interest in part-time contact (suckling for part of the day) to improve milk yield for the farmer and potentially reduce stress at weaning and separation. The primary objective of this study was to compare the behavioral responses of dairy cows to gradual or abrupt weaning and separation, when managed either full or part time with their calves; a secondary focus was the vocal responses of calves under these management conditions. In a 3 × 2 factorial design (n = 14/ treatment), dairy cows and their calves (n = 84 in 7 blocks of 12 cow-calf pairs) were assigned to one of 3 dam-contact treatments at birth: (1) full-time contact between the dam and calf, apart from milking times (total 23 h/d) (2) part-time contact between the dam and calf, between morning and afternoon milking only (total 10 h/d); (3) no contact, where the dam and calf were separated after leaving the maternity pen and had no further contact. At wk 8, one of 2 weaning treatments was assigned: (1) gradual weaning by reduced contact time (50%, then 25% of original dam-contact time in wk 8 and 9, respectively), or gradually reduced milk allowance for no-contact calves (50%, then 25% of estimated 12-L milk intake in wk 8 and 9, respectively) until complete milk removal and dam-calf separation at wk 10; (2) abrupt weaning where milk removal occurred simultaneously with dam-calf separation at wk 10, or only milk removal for no-contact calves. Overall, part-time contact did not reduce weaning and separation distress for cows or calves for either weaning method. Part-time cows showed reduced behavioral responses to separation (greater lying time and less searching behavior), especially on the day of and 24 h after separation, but they showed a similarly strong vocal response to separation as full-time cows. Part-time calves made substantially more high-pitched vocalizations than full-time calves at 24 h after separation. Furthermore, gradual weaning by reducing contact time did not seem to better prepare cows or calves for complete milk removal and separation; most behavioral and vocal responses occurred on the day of separation for gradual-weaning cows and calves, but 24 h later, the reverse occurred for abrupt-weaning cows and there was no difference between gradual- and abrupt-weaning calves. Our results suggest that part-time contact and gradual-weaning conditions likely resulted in hunger and expectation for reunion, which together may have exaggerated behavioral responses at separation. Temporary daily separations may not have increased independence of cow and calf, and the gradual-weaning method here may not have reduced milk intake by calves. These elements are important criteria to facilitate the weaning process, so future work should explore ways to gradually reduce milk intake and promote social independence of cow and calf to minimize weaning distress.

Droplet impact on a rapidly spinning superhydrophobic surface: Shortened contact time and reduced collision force

Despite extensive research on the impact of motionless superhydrophobic surfaces, the understanding of droplet impact behavior on spinning superhydrophobic surfaces had been limited and not adequately explored. Here, we used the template method to create a low-cost, low-adhesion, and highly water-repellent layered superhydrophobic surface. By employing a combination of experimental observations and simulation techniques, we successfully determined the contact time and collision force. Building upon these findings, our study further delved into the dynamics of droplet impact on both the center and eccentric of a spinning superhydrophobic surface. In the case where the droplet impacted at a distance of 5 mm from the center of rotation, we observed a significant reduction in contact time by 36.4 % and a decrease in the maximum collision force by 22.5 %. This could be attributed to the spinning motion of the superhydrophobic surface, which exerted frictional force on the droplet. Our findings provided a strong theoretical foundation for achieving better water repellency by combining spinning solids with superhydrophobic surfaces.

Behavioral deficits after mild traumatic brain injury by fluid percussion in rats

Mild traumatic brain injury (TBI) can lead to various disorders, encompassing cognitive and psychiatric complications. While pre-clinical studies have long investigated behavioral alterations, the fluid percussion injury (FPI) model still lacks a comprehensive behavioral battery that includes psychiatric-like disorders. To address this gap, we conducted multiple behavioral tasks over two months in adult male Wistar rats, focusing on mild FPI. Statistical analyses revealed that both naive and sham animals exhibited an increase in sweet liquid consumption over time. In contrast, the TBI group did not show any temporal changes, although mild FPI did induce a statistically significant decrease in sucrose consumption compared to control groups during the chronic phase. Additionally, social interaction tasks indicated reduced contact time in TBI animals. The elevated plus maze task demonstrated an increase in open-arm exploration following fluid percussion. Nonetheless, no significant differences were observed in the acute and chronic phases for the forced swim and light–dark box tasks. Evaluation of three distinct memory tasks in the chronic phase revealed that mild FPI led to long-term memory deficits, as assessed by the object recognition task, while the surgical procedure itself resulted in short-term spatial memory deficits, as evaluated by the Y-maze task. Conversely, working memory remained unaffected in the water maze task. Collectively, these findings provide a nuanced characterization of behavioral deficits induced by mild FPI.

Droplet impact dynamics on superhydrophobic surfaces with convex hemispherical shapes

Functional solid surfaces that can realize rapid shedding of liquid droplets have received significant research interest due to their close relevance to many industrial applications. Droplet impact on superhydrophobic surfaces with point-like protrusions has been demonstrated to take off as rings, which alters droplet impact dynamics and thus reduces contact time compared to flat surfaces. However, the essential role of the size ratio of protrusion-to-droplet (λ) for droplets impinging on such surface is rarely considered. Here, we numerically investigate droplet impact on superhydrophobic surfaces with convex hemispherical shapes using a phase-field model coupled with dynamic contact angles. The postimpact outcome regimes occurring for varied λ and Weber number (We) values, spanning 0 ≤ λ ≤ 1.44 and 0.69 ≤ We ≤ 33.68, are mapped on a We−λ diagram. Three distinct dynamic behaviours of droplet impact are identified: contactless bouncing, conventional bouncing, and ring bouncing. Detailed comparative analyses of these impact outcomes are also presented, including the evolution of droplet morphology, impact force, maximum impact pressure, pressure distribution, and velocity vector distribution. The results reveal a previously unknown phenomenon in contactless bouncing, where the impact force exhibits an initial increase followed by a subsequent decrease, while the maximum impact pressure remains approximately constant. Annular rotating retraction results in a longer contact time. Breakup occurs near the necked area, inducing a part of the droplet to depart from the surface as a jet. In addition, it is observed that the dimensionless maximum wetting area becomes independent of the λ and follows a scaling law of 0.67We3/5 if the We exceeds 2.75. Ring bouncing exclusively occurs within the range of 0.24 ≤ λ ≤ 0.96 and We ≥ 24.74, resulting in an approximate 50 % reduction in non-dimensional contact time compared to conventional bouncing. These findings favor the understanding of the underlying mechanisms governing droplet impact and thereby provide available guidance to the design of superhydrophobic surfaces.

Self-Adaptive Droplet Bouncing on a Dual Gradient Surface.

Rapid detachment of impacting droplets from underlying substrate is highly preferred for mass, momentum, and energy exchange in many practical applications. Driven by this, the past several years have witnessed a surge in engineering macrotexture to reduce solid-liquid contact time. Despite these advances, these strategies in reducing contact time necessitate the elegant control of either the spatial location for droplet contact or the range of impacting velocity. Here, this work circumvents these limitations by designing a dual gradient surface consisting of a vertical spacing gradient made of tapered pillar arrays and a lateral curvature gradient characterized as macroscopic convex. This design enables the impacting droplets to self-adapt to asymmetric or pancake bouncing mode accordingly, which renders significant contact time reduction (up to ≈70%) for a broad range of impacting velocities (≈0.4-1.4 ms-1 ) irrespective of the spatial impacting location. This new design provides a new insight for designing liquid-repellent surfaces, and offers opportunities for applications including dropwise condensation, energy conversion, and anti-icing.

Мобільні інструменти просування товарів

Mobile tools for product promotion play an important role in the marketing strategies of enterprises. The personality and constant presence of mobile devices ensures quick communication with target consumers. Therefore, it is important to study the possi­bilities of using mobile marketing tools to implement the strategic tasks of the marketing mix. The aim of the article is to reveal the role of mobile tools in the promotion of goods and to substantiate the areas of coordination of the marketing mix with the digital capabilities of the enterprise. The research was conducted using methods of analysis and synthesis, empirical, hypothesis testing, system-structural analysis, comparison, and graphic represen­tation. Mobile marketing tools were analyzed, the advantages of using mobile promotion tools for expanding the target audience were revealed. The evolution of the marketing mix has been studied and the connection with alternative components has been established. It has been proven that the adaptation of marketing communications to the approp­riate mobile tools for product promotion ensures the reduction of contact time with consumers and the acceleration of their purchase decisions.

Continuous Biosorption of Pb2+ with Bamboo Shoots (Bambusa spp.) using Aspen Adsorption® Process Simulation Software

The health risks impact of heavy metal contamination in the environment has prompted researchers to study its mitigation in an efficient and cost-friendly approach. Recently, simulated continuous biosorption using agricultural wastes is gaining popularity because it offers cheaper and faster alternative study methods using efficient large-scale removal of lead, which is known to cause adverse effects even at low concentrations. Bamboo shoots (Bambusa spp.), a delicacy known in Southeast Asia, are recognized worldwide, but the inedible sheath husks are thrown. This study evaluated the continuous Pb2+ biosorption performance of Bambusa spp. using Aspen Adsorption V8.4 by varying bed height, influent concentration, and volumetric flow rate. Linear driving force model was used to simplify, according to a separate batch biosorption study, ion exchange mechanism and Langmuir isotherm for equilibrium conditions. The backward differencing method was used to solve the resulting differential equation. Results showed that increasing the volumetric flowrate from 4.00x10-5 to 8.00x10-5 m3/s, the bed height from 0.2 to 1.0 m, and influent concentration from 80 to 120 ppm resulted in changes in the breakthrough time by a factor of 0,5, 4.0, and 0.67 respectively. Analysis of the breakthrough curves showed that increasing volumetric flow rate shortens breakthrough time due to reduced contact time, and increasing Pb2+ concentration facilitated ion exchange by increasing concentration difference. Bed height provides more binding sites available hence, higher Pb2+ removal.

The World's First Acne Dysbiosis-like Model of Human 3D Ex Vivo Sebaceous Gland Colonized with Cutibacterium acnes and Staphylococcus epidermidis.

Acne-prone skin is associated with dysbiosis involving Cutibacterium acnes (C. acnes) and Staphylococcus epidermidis (S. epidermidis) causing increased seborrhea in sebaceous glands (SG) and inflammation. Human primary sebocytes were cultivated using 1.106 UFC/mL C. acnes Type IA (facial acne, ATCC6919) and/or 1.105 UFC/mL S. epidermidis (unknown origin, ATCC12228) for 48 h in our SEB4GLN-optimized media without antibiotics. Bacteria and sebocytes were enumerated and assessed to determine their viability. Lipid production was imaged and quantified via Nile Red staining. SG with hair follicles were microdissected from healthy skin and cultured using 1.105 UFC/mL C. acnes Type 1A and/or 1.104 UFC/mL S. epidermidis (wild-type facial skin strain) through prior fixation and immunostaining for MC5R, C. acnes and nuclei (DAPI) via Z-stack confocal microscopy bioimaging (Leica SP5X & FIJI software, Version 2.9.0). C. acnes growth was not impacted when co-cultivated with sebocytes (2D) or SG (3D) models. Phylotype IA stimulated sebocyte lipid production, which had no impact on viability. The S. epidermidis reference strain overproliferated, inducing sebocyte mortality. For 3D SG model, culture conditions were optimized using a wild-type facial skin strain at a lower concentration, 1:10 ratio to C. acnes, reduced contact time, sequential inoculation and rinsing step. Bioimaging revealed strong C. acnes labeling in the active areas of the pilosebaceous unit. S. epidermidis formed biofilm, which was distributed across the SG via non-specific fluorescence imaging. We developed an innovative model of a sebaceous gland that mimics acne-prone skin with lipid overproduction and virulent phylotype IA C. acnes inoculation.

Two modes of contact‐time reduction in the impact of particle‐coated droplets on superhydrophobic surfaces

AbstractReducing the contact time during droplet impact is essential for many scientific and industrial applications, such as self‐cleaning, anti‐icing, heat transfer, and condensation. This paper reports contact‐time reduction by coating droplets with micro–nano hydrophobic particles. Such particle‐coated droplets are known as liquid marbles (LM). LM impact on superhydrophobic surfaces reveals two different modes of contact‐time reduction. For lower impact energies, the reduced adhesion of LM with the surface is responsible for a reduction of up to 21%. Contact‐time reduction in this regime is found to be independent of particle size but dependent on the solid fraction of LM. However, a fragmentation‐based contact‐time reduction is observed for larger particle sizes and higher impact energies. Here, the reduction is as high as 65%. Such fragmentation occurs because the spreading LM lamella breaks when its thickness becomes similar to particle dimensions. Our findings reveal the potential of LM as a novel approach to reduce contact time during droplet impact, with implications for various scientific and industrial applications.

What Controls the Hole Formation of Nanodroplets: Hydrodynamic or Thermodynamic Instability?

Using molecular dynamics simulations, we investigate the air hole formation of water nanodroplets impacting hydrophilic to hydrophobic surfaces in the range of static contact angles from 30° to 140° with different initial surface temperatures ranging from 300 to 1000 K. We show that the hole dynamics of nanodroplets are different from those observed in millimeter-sized droplets. The hole formation can be observed on smooth surfaces for nanodroplets; however, it only occurs on nonsmooth surfaces for millimeter-sized droplets. We clarify that the hole formation of nanodroplets is triggered by a nucleated vapor bubble due to thermodynamic instability, whereas it is initiated by air bubble entrapment during impact due to hydrodynamic instability for millimeter-sized droplets. The hole formation of nanodroplets relies heavily on the surface temperature and surface wettability, because the nucleated vapor bubble more easily occurs and grows on the surface with high initial temperatures and hydrophobic surfaces. Based on the thermal stability analysis, a criterion is developed to predict the hole formation of nanodroplets, which verifies the dependence of hole formation on the surface temperature and wettability. Furthermore, we show that the ring-bouncing of nanodroplets is triggered by the nucleated vapor bubble. We clarify the reasons for the reduced contact time of nanodroplets caused by the ring-bouncing.

Spatial heterogeneity and infection patterns on epidemic transmission disclosed by a combined contact-dependent dynamics and compartmental model.

Epidemics, such as COVID-19, have caused significant harm to human society worldwide. A better understanding of epidemic transmission dynamics can contribute to more efficient prevention and control measures. Compartmental models, which assume homogeneous mixing of the population, have been widely used in the study of epidemic transmission dynamics, while agent-based models rely on a network definition for individuals. In this study, we developed a real-scale contact-dependent dynamic (CDD) model and combined it with the traditional susceptible-exposed-infectious-recovered (SEIR) compartment model. By considering individual random movement and disease spread, our simulations using the CDD-SEIR model reveal that the distribution of agent types in the community exhibits spatial heterogeneity. The estimated basic reproduction number R0 depends on group mobility, increasing logarithmically in strongly heterogeneous cases and saturating in weakly heterogeneous conditions. Notably, R0 is approximately independent of virus virulence when group mobility is low. We also show that transmission through small amounts of long-term contact is possible due to short-term contact patterns. The dependence of R0 on environment and individual movement patterns implies that reduced contact time and vaccination policies can significantly reduce the virus transmission capacity in situations where the virus is highly transmissible (i.e., R0 is relatively large). This work provides new insights into how individual movement patterns affect virus spreading and how to protect people more efficiently.

Contact time of nanodroplets obliquely impacting nanopillar-arrayed superhydrophobic surfaces: A molecular dynamics study

On nanopillar-arrayed superhydrophobic surfaces, the contact time of oblique nanodroplet impacts is for the first time investigated via molecular dynamics simulations. Here, oblique nanodroplet impacts are triggered by nanodroplets impacting superhydrophobic surfaces under various impact angles, α. The simulation results show that owing to the non-axisymmetry of spreading factors on nanopillar-arrayed superhydrophobic surfaces, the contact time of oblique nanodroplet impacts is always less on nanopillar-arrayed rather than smooth superhydrophobic surfaces under same impact angles. As the impact angle is increased from 5° to 65°, that is, under different impact conditions, the non-axisymmetry is more remarkable as α > 35° instead of α < 35° at the low, medium, and high normal Weber numbers, Wen. Hence, the contact time is sharp as α > 35° and then slowly reduced as α < 35° at the low, medium, and high Wen, at which the drastically increased sliding length as α > 35° further promotes the rapid reduction in contact time. As the impact angle is constant at 35°, the non-axisymmetry is more remarkable as h/w < 1 instead of h/w > 1 as the aspect ratio of nanopillars, h/w, is increased, that is, under different surface conditions. Hence, the contact time is sharp as h/w < 1 and then slowly reduced as h/w > 1 at the low, medium, and high Wen, at which the drastically reduced sliding length as h/w > 1 further hinders the rapid reduction in contact time.

Continuous densification of wood with a belt press: the process and properties of the surface-densified wood

ABSTRACT Thermo-mechanical densification of sawn timber results in improved mechanical properties, but densified wood remains a fairly expensive niche product, partially because of high-cost batch processing. Densification in a continuous process could address this problem and was shown to be possible in previous research. The outcomes were limited to proofs-of-concept, partially due to insufficient cooling capabilities of the used densification equipment, resulting in high spring-back. Therefore, a novel continuous process using a belt press to densify full-sized sawn timber has been conceived. The press ensures almost constant contact between the wood and the heating and cooling elements. The study aimed to analyse how the processing temperature, speed and compression ratio affected the density profile, spring-back, set-recovery, Brinell hardness, and bending properties. Results showed a density increase concentrated close beneath the surface in contact with the heating element and approx. 20% spring-back. Belt speeds above 2 m min−1 caused higher spring-back due to the reduced contact time between the wood and the heating element. Brinell hardness increased by up to 250% at a compression ratio of 27% while bending properties were unaffected. Belt temperature and speed were shown to be critical factors to consider for the future optimisation of the belt-press process.

Dynamics and heat transfer of water droplets impacting on heated surfaces: The role of surface structures in Leidenfrost point

Textured surface has shown great potential in inhibiting Leidenfrost phenomenon for the thermal management of high heat flux devices. Although diverse textured surfaces have been designed to achieve multi-fold increases in Leidenfrost point, the dominant physical mechanism of different surface structures remains elusive. In this study, three aluminum-based surfaces including bare aluminum surface, superhydrophilic micro/nanostructured surface, superhydrophilic macro-pillar arrayed surface are fabricated by simple, low-cost methods. The effects of surface structures with various scales on Leidenfrost point and the dynamic characteristics of water droplets are elucidated. The experimental results indicate that micro/nanostructures cause intermittent liquid-solid contact and trigger more vapor dispersion into micro/nanocavities. A thicker vapor layer generated above micro/nanostructures reduces the vapor pressure that supports the droplet and increases Leidenfrost point from 188 ℃ (for bare aluminum surface) to 428 ℃. A higher Leidenfrost point over 500 ℃ (the maximum heating temperature) is achieved by macro-pillar arrayed surface due to strong capillary wicking and high permeability. Theoretical models that integrate the influence of surface structures on Leidenfrost point are established through balancing vapor pressure with capillary pressure and gravitational pressure. The prediction of present model shows good agreement with the experimental results. Impact and heat transfer regime maps are also provided, where a unique explosive bouncing with a significant reduction in contact time and an extended temperature span of transition boiling are observed on structured surfaces. Furthermore, macrostructures are found to induce a larger and longer liquid-solid contact, thus demonstrating an excellent cooling capability in the transition boiling.

Impact force of ring bouncing on superhydrophobic surface with a bead

The impingement of drops on superhydrophobic surfaces with macrotextures would result in a reduced contact time, which is crucial in applications, such as anti-icing and anti-frost. We experimentally investigate the impact force and deformation of a water drop falling on superhydrophobic surfaces decorated with a water-repellent bead by employing a high-sensitivity force transducer and high-speed cameras operated in synchrony. The drop falling on the water-repellent bead bounces off in the form of a liquid ring when the Weber number We > 37, and this leads to a shorter contact time compared with an impingement on a flat surface. Four regimes, referred to as the air cavity, column jet, intact ring, and splashing, are identified based on the characteristics of drop deformation and peak forces. Two predominant peaks are identified in the force curves in most cases. The first peak originates from the momentum change of the inertial impact; the second peak in the first two regimes originates from the momentum change of the Worthington jet, while that in the last two regimes originates from the momentum change of the bouncing ring. Furthermore, a third peak appears when the oscillation of the lifting drop reattaches the substrate at a moderate Weber number. We investigate the drop dynamics in different regimes and theoretically explain the We dependence of peak force related to bouncing in the intact-ring regime. The discoveries obtained in this study will advance our understanding of the dynamics of drop impingement on superhydrophobic surfaces with macrotextures for reducing the contact time.

Impact dynamics of droplets on the well-designed wrinkled surfaces: Enhancement of bounding ability

Designing the nanostructured substrates with efficiently executing self-cleaning functions such as anti-icing, anti-fogging, anti-flaming, and anti-corrosion is always a hot scientific research topic and plays an essential role in practical applications. Herein, a novel substrate decorated with wrinkled structures is investigated. Results show that it has a large improvement in the reduction of contact time compared with the smooth substrate, and could affect the critical velocity of transition between retraction rebound and non-reaction transition. Effects of geometrical parameters of the wrinkled structures on droplet rebounding ability are detailed discussed, such as angles, intervals, and arrangement gradient. Most importantly, a well-designed substrate decorated with wrinkled structures and two confinement walls is proposed, which is found that the contact time could be largely reduced due to the limitation of spreading behaviors of the impacting droplets resulting from the heavy restriction effect of the confined walls. The findings of this work are expected to provide potential implications for many multidisciplinary fields, such as aerospace engineering, industrial manufacturing, interfacial heat transfer, environment, energy storage, and so forth.