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High potato damage and peeling rates have been caused by the potato loading and unloading bag device. It is also unclear on the impact damage. In this study, a potato loading and unloading bag device test bench was constructed to reduce and prevent losses. Two aspects were mainly taken to optimize the structure: the potato collection device and the unloading device. A mechanical structure was adopted with the dual buffering of buffer rollers and limiting rollers, in order to reduce the impact damage of potatoes during bagging; Furthermore, two limiting rollers of "gather caching and separate bagging" mode were used to achieve uninterrupted harvesting for the high bagging efficiency; The lifting slide of the bag unloading device adopted the technology of "gradually decreasing with weight" to control the drop height of potatoes during bagging within a specific range, thus avoiding damage that caused by excessive drop height of potatoes. The position of the buffer roller was adjusted to determine the optimal movement trajectory of the potato, and then minimize the damage during potato bagging. The severity of the impact between potatoes and buffer rollers was evaluated to calculate the maximum contact stress. The main parameters of key components were then determined, according to the main structure and working principle of the device. The impact theory was analyzed during potato bagging. The key influencing factors were clarified on the potato skin damage. RecurDyn and EDEM were coupled to simulate the stress situation of potatoes under roller buffering and non-roller buffering states. The maximum collision contact force of potato blocks with roller buffering was reduced to 263.566 N, compared to those without roller buffering. Taking the conveying speed, buffer roller diameter, and feeding amount as the experimental factors, while the potato damage rate and skin breakage rate as evaluation indicators, a three-factor three-level orthogonal experiment was conducted using Box-Behnken neutral combination design function in Design-Expert. Variance analysis was also performed to analyze the impact of the interaction of various experimental factors on the evaluation indicators using the response surface method (RSM). The working parameters were optimized to determine the optimal values of each parameter, according to actual working conditions. A series of experiments were conducted to verify using an electronic potato impact detector. The results showed that the potato damage rate and skin breaking rate were 0.82% and 1.14%, respectively, when the conveying speed was 0.96 m/s, the diameter of the buffer roller was 83mm, and the feeding amount was 26 t/h. The peak impact acceleration was smaller than the critical damage threshold of potato impact acceleration. At the same time, the impact acceleration at the last point was much smaller than the initial one. The relative errors between the measured and the theoretical values after parameter optimization were 4.06% and 0.4%, respectively. The intensity of the potato impact decreased in a manner like wave, where the impact weakened gradually. Therefore, the potato bagging and unloading device achieved the expected goal of potato collecting and reducing loss. Field experiments showed that the potato damage rates were 0.97%, 1.32%, and 1.58%, respectively, and the skin breaking rates were 1.34%, 1.53%, and 1.87%, respectively, when the harvesting speeds were 0.6, 0.8, and 1.0 m/s, respectively. The high performance was all met the national standards. [ABSTRACT FROM AUTHOR]

When a water drop is impinged upon a superhydrophobic surface with submillimetric surface structures, unconventional impact dynamics such as pancake-like bouncing and asymmetric drop spreading can occur. However, the fabrication of such surface structures often requires an unconventional fabrication approach, which is either time-consuming or costly. In this study, we propose a simple lithography-based approach to manufacture submillimetric cone-shaped pillars over a large area by taking advantage of a unique optical property of hydrogels: a change of refractive index after UV-curing. With an additional hydrophobic nanoparticle coating, we demonstrate that such structures can be used to reduce the contact time during drop impact and induce a drop rotation during rebound. Moreover, the flexibility of hydrogels enables the transfer of surface structures to non-planar substrates. [ABSTRACT FROM AUTHOR]

This paper investigates the modal parameter identification technique utilizing a drop impact load. A 12-DOF mathematical model of a Railway Vehicle System (RWVS) was constructed, followed by theoretical calculations, simulation analysis, and tests with four different drop impact loads. The responses to these loads were inspected through FFT, and the modal frequencies of the RWVS were determined by the Peak Picking (P-P) method. The simulation demonstrated that four types of drop impact loads can activate the bounce, pitch, and roll modes of the RWVS. The theoretical calculation and simulation analysis revealed that the maximum error of modal frequency identification is no greater than 6.5%. The experimental results verified that the drop impact excitation method can be used to identify the modal parameters of a complex railway vehicle system, which is highly beneficial for the design and verification of the vehicle structure. [ABSTRACT FROM AUTHOR]

An innovative metallic buffer consisting of series-connected hat-shaped entangled wire mesh damper (EWMD) and parallel springs are proposed in this work to enhance the reliability of engineering equipment. The impact response and the energy dissipation mechanism of hat-shaped EWMD under different quasi-static compression deformations (2–7 mm) and impact heights (100–200 mm) are investigated using experimental and numerical methods. The results demonstrate distinct stages in the quasi-static mechanical characteristics of hat-shaped EWMD, including stiffness softening, negative stiffness, and stiffness hardening. The loss factor gradually increases with increasing compression deformation before entering the stiffness hardening stage. Under impact loads, the hat-shaped EWMD exhibits optimal impact energy absorption when it enters the negative stiffness stage (150 mm), resulting in the best impact isolation effect of metallic buffer. However, the impact energy absorption significantly decreases when hat-shaped EWMD enters the stiffness hardening stage. Interestingly, quasi-static compression analysis after experiencing different impact loads reveals the disappearance of the negative stiffness phenomenon. Moreover, with increasing impact loads, the stiffness hardening point progressively shifts to an earlier stage.

During postharvest processing, mechanical damage caused by impact during drops significantly affects the product quality of 'Huangguan' pears. In this study, the potential influence on postharvest fruit quality of the pears was investigated, by subjecting them to drop from different heights (200 mm, 400 mm, and 600 mm) onto various surfaces (steel plates, wood panels, and HDPE plastics). The experiments were performed under controlled conditions of 20 ± 1 ℃ and 85 ± 5% relative humidity, with storage periods of 0 d, 5 d, 10 d, and 15 d. Physiological and biochemical parameters of 'Huangguan' pears were measured during storage, including weight loss rate, chromaticity values, ethylene production, respiration rate, hardness, titratable acid content (TAC), soluble solids content (SSC), and others. Results showed that with increasing drop height and storage time, weight loss rate, a* value, b* value, ethylene production, respiration rate, and TAC gradually increased, respectively. In contrast, L* value, hue angle (H°), hardness, and SSC decreased, respectively. The steel plates had a more significant impact on the changes in fruit quality indicators, compared with the no-drop test (the control group), wood panels, and HDPE plastics. This study contributes to optimizing mechanical equipment design during processing and provides substantial theoretical support for reducing damage. [ABSTRACT FROM AUTHOR]

ABSTRACTEfforts have been made to streamline the abstract as follows. If further changes are made we are concerned that the integrity of the content may be compromised. We hope you will understand. This study aimed to investigate the impact damage experienced by Pucheng crisp pears during various stages, including harvest, transportation, and processing. Drop impact tests were conducted on pears, considering drop height and collision contact material as factors influencing damage. The bruise area was used as an indicator for damage evaluation. Additionally, the pressure-sensitive film technique was employed to measure the contact stress distribution characteristics of Pucheng crisp pears after the drop impact. The relationship between contact stress distribution and damage area was examined, and the stress area range close to the damage area was determined. The results revealed that the damage area of pears increased linearly with the increasing drop height. Among the four contact materials, foam board exhibited the best cushioning properties, with a maximum safe drop height of 20 cm. The pressure distribution tended to follow a normal distribution, with a pressure range of 0.2-0.3 MPa covering the largest area, corresponding to the majority of the bruise area on the pears. Furthermore, the pressure area and average pressure were found to be related to the severity of bruising. When pears were dropped onto steel, rubber plate and corrugated board, for the former two the stress area exceeding 0.2 MPa closely approximated the damage area, with an average relative error of 7.2%. For the latter, the closest range was above 0.3 MPa, with an average relative error of 3.6%. However, when dropped onto foam board, the average relative error was 75%. This research provides valuable insights for designing packaging tools to minimize damage and serves as a theoretical basis for predicting and assessing pear bruise area using finite element analysis.

Slope incline is one of the factors affecting the soil water erosion process. Most of the work to date related to erosion has been on large-scale studies based on rainfall events or laboratory investigations with the use of simulators, where the displaced mass of soil was determined. However, there is a lack of studies providing information about splash erosion on slopes in relation to single-drop impact methodology, that allows for the examination of the basic processes of the phenomenon. Thus, the aim of this study was a quantitative description of the splash phenomenon on a simulated slope affected by a single drop impact, with respect to the influence of slope incline on the number of ejected particles and their characteristics. The investigation was carried out using three types of soil with different textures in moistened conditions (i.e. pressure head corresponding to 1.0 kPa) and three variants of slope incline: 5°, 15°, and 30°. A drop with a diameter of 4.2 mm was allowed to fall freely on soil surface with kinetic energy equal 1.42 mJ. The splash phenomenon was registered by a set of three synchronized high-speed cameras and combined with PTV software (Particle Tracking Velocimetry) to identify and track displaced particles. The methodology used made it possible to observe the course of the phenomenon and determine the following quantities: the number and size of ejected particles, ejection velocity and angle, displacement range, and also the contribution of the kinetic energy of the falling drop transferred to the ejected particles. The measured quantities were specified for the particles ejected in upslope and downslope directions. It was found that: (i) the interaction between different slope inclines and the particle size distribution of the soils influenced the surface conditions, which had a significant effect on the course of the splash phenomenon; (ii) the number of ejected particles decreased with the increasing slope, which was directly related to limited ejection in the upslope direction; (iii) the influence of slope incline was mostly visible in the ejection angle, range of displacement and sizes of ejected particles; (iv) the portion of the falling drop energy transferred to ejected particles decreased with increasing slope. The obtained results could enhance the development of physical models of splash erosion. A more thorough understanding and better recognition of the mechanisms governing this phenomenon at all stages could contribute to the development of more effective methods for protecting soil against erosion.

Using a mesh surface is a promising technique in oil-water separation applications. In this paper, we investigated the dynamic impact of a silicone oil drop with different viscosities on an oleophilic mesh experimentally, which will help to define the critical conditions of the oil-water separation process. Four impact regimes were observed by controlling the impact velocity: deposition, partial imbibition, pinch-off, and separation. Thresholds of deposition, partial imbibition, and separation regimes were estimated, by balancing the inertia, capillary, and viscous forces. During the deposition and partial imbibition phenomena, the maximum spreading ratio (β max) increases with the Weber number. In contrast, in the case of the separation phenomenon, no significant effect of the Weber number on β max has been observed. Based on energy balance, we predicted the maximum elongation length of the liquid under the mesh during the partial imbibition phenomenon; the predicted data agrees well with the experimental data. [ABSTRACT FROM AUTHOR]

Air entrapment in drop impact onto solid surfaces has riveted the attention of the scientific community since it could drastically influence heat rate and splat porosity in additive manufacturing or thermal spraying processes. Due to the limitations of experimental methods, numerical methods have been gaining popularity in probing into air entrapment dynamics. To that end, this paper developed a paralleled phase field model. The model couples the Navier–Stokes equations with the Cahn–Hilliard equation to capture the liquid–gas interface, and adopts the liquid fraction, defined all over the computational domain, to distinguish between solid and liquid. The model is discretized using a finite difference method on a half-staggered grid. The model was first compared with experimental data, achieving reasonable agreement. Afterward, it was applied to a couple of cases. The air entrapment process was captured entirely and the interaction between solidification and air entrapment was also given. It shows that under the parameters studied here air entrapment may occur twice, one in the impacting center in the form of a bubble and the other in the form of a bubble ring. Besides, the effect of phase field mobility on air entrapment was examined as well. [ABSTRACT FROM AUTHOR]

Pistia stratiotes is an aquatic plant with a complex structure that allows it to stay afloat. It grows quickly, and in large numbers becomes an undesirable plant as an invasive species. Describing the dynamics of a water drop splash on P. stratiotes leaves can contribute to increasing knowledge of its behavior and finding alternative methods for eradicating it or using it for the benefit of the environment. The non-wettable surface of P. stratiotes presents a complex structure—simple uniseriate trichomes and also ridges and veins. We analyzed the drop impact on a leaf placed on the water surface and recorded it by high-speed cameras. Based on the recordings, quantitative and qualitative analyses were performed. After impacting the leaf, the water drop spread until it reached its maximum surface area accompanied by the ejection of early droplets in the initial stage. Thereafter, three scenarios of water behavior were observed: (i) drop receding and stabilization; (ii) drop receding and ejection of late droplets formed in the later stage as an effect of elastic deformation of the leaf; and (iii) drop breaking apart and ejection of late droplets. The results indicated that the increasing kinetic energy of the impacting drops expressed by the Weber number and the complex leaf surface have an effect on the course of the splash. The simple uniseriate trichomes of the P. stratiotes leaf and the high energy of the falling drops were responsible for the formation and characteristics of the early droplets. The presence of ridges and veins and the leaf's mechanical response had an impact on the occurrence of late droplets. [ABSTRACT FROM AUTHOR]

Crop production and quality safety system have the potential to nurture human health and improve environmental sustainability. Providing a growing global population with sufficient and healthy food is an immediate challenge. However, this system largely depends on the spraying of agrochemicals. Crop leaves are covered with different microstructures, exhibiting distinct hydrophilic, hydrophobic, or even superhydrophobic wetting characteristics, thus leading to various deposition difficulties of sprayed droplets. Here, the relationship between wettability and surface microstructure in different crop leaves from biological and interfacial structural perspectives is systematically demonstrated. A relational model is proposed in which complex microstructures lead to stronger leaf hydrophobicity. And adding surfactant with a faster dynamically migrating velocity and reducing droplet size can improve agrochemical precise deposition. These contribute toward highly accurate and efficient targeted applications with fewer agrochemicals use and promote sustainable models of eco‐friendly agriculture systems. [ABSTRACT FROM AUTHOR]

Abstract Crop production and quality safety system have the potential to nurture human health and improve environmental sustainability. Providing a growing global population with sufficient and healthy food is an immediate challenge. However, this system largely depends on the spraying of agrochemicals. Crop leaves are covered with different microstructures, exhibiting distinct hydrophilic, hydrophobic, or even superhydrophobic wetting characteristics, thus leading to various deposition difficulties of sprayed droplets. Here, the relationship between wettability and surface microstructure in different crop leaves from biological and interfacial structural perspectives is systematically demonstrated. A relational model is proposed in which complex microstructures lead to stronger leaf hydrophobicity. And adding surfactant with a faster dynamically migrating velocity and reducing droplet size can improve agrochemical precise deposition. These contribute toward highly accurate and efficient targeted applications with fewer agrochemicals use and promote sustainable models of eco‐friendly agriculture systems.

The effect of coal hydrophilic particles in water-glycerol drops on the maximum diameter of spreading along a hydrophobic solid surface is experimentally studied by analyzing the velocity of internal flows by Particle Image Velocimetry (PIV). The grinding fineness of coal particles was 45–80 μm and 120–140 μm. Their concentration was 0.06 wt.% and 1 wt.%. The impact of particle-laden drops on a solid surface occurred at Weber numbers (We) from 30 to 120. It revealed the interrelated influence of We and the concentration of coal particles on changes in the maximum absolute velocity of internal flows in a drop within the kinetic and spreading phases of the drop-wall impact. It is explored the behavior of internal convective flows in the longitudinal section of a drop parallel to the plane of the solid wall. The kinetic energy of the translational motion of coal particles in a spreading drop compensates for the energy expended by the drop on sliding friction along the wall. At We = 120, the inertia-driven spreading of the particle-laden drop is mainly determined by the dynamics of the deformable Taylor rim. An increase in We contributes to more noticeable differences in the convection velocities in spreading drops. When the drop spreading diameter rises at the maximum velocity of internal flows, a growth of the maximum spreading diameter occurs. The presence of coal particles causes a general tendency to reduce drop spreading. [ABSTRACT FROM AUTHOR]

Production of conventional concrete leads to several negative impacts on the environment while the plastic waste concrete can effectively overcome the environmental issues and having better performance than conventional concrete. Therefore, this research presents the works in producing new concrete by replacing the fine aggregates in concrete by using a mixture of soft and hard plastic waste with different ratios density. In addition, this research also aims to evaluate the mechanical and physical properties of different ratios of fine aggregate plastic waste in producing a concrete. At the end of this research, a comparison is made between the optimum composition of plastic waste concrete and conventional concrete. This study is conducted by using SolidWorks software version 2021. The tests conducted include compressive strength test, drop test, and failure analysis. The results from the compressive strength test revealed that a force at 100kN with 20% plastic waste (Sample B) showed the highest stress (18.91 MPa). Meanwhile, from the drop height of 2.0m, the impact strength of Sample B showed the highest result with a value of 7.830 x106 N/m2. However, failure analysis results revealed that Sample B has more cracking than Sample A. From the study carried out, it can be summarised that an optimum replacement of 20% plastic waste as fine aggregates in a concrete gives the best performance is the most suitable option to be used as a replacement concrete in construction. [ABSTRACT FROM AUTHOR]

The interaction of a liquid drop with a copper surface is studied. The substrate is assumed to be superhydrophobic with a wetting angle of . Based on the volume of the drop, the Bond and Weber numbers are approximately 0.23 and 1.6, respectively. The temperature of the surface and the surrounding air is 298 K, and the temperature of the liquid drop is 5K lower. Simulation of conjugate heat transfer is performed using an axisymmetric coordinate system. The Kistler contact line model is used to determine the dynamic contact angle of a drop during spreading. The change in the shear stress on the substrate and the heat flux induced during the propagation of the drop as a function of time is studied. [ABSTRACT FROM AUTHOR]

The evolution of the falling drop substance transfer in a target fluid at rest was traced by high-speed video techniques. Two flow modes were studied: slow intrusive flow, when the KE of the drop was comparable or less than the available potential energy (APSE), and a fast impact flow, at a relatively high drop contact velocity. For the substance transfer visualization, a drop of alizarin ink solution at various concentrations was used. The use of transparent partially colored fluid allows tracing the drop matter motion in the bulk and on the fluid free surface. The traditional side and frontal view of flow patterns were registered and analyzed. In both flow modes, the substance of the drop partially remained on the free surface and partially went into the target fluid bulk, where it was distributed non-uniformly. In the intrusive mode, the drop substance partially remained on the surface, while the main mass of the drop flowed into the thickness of the target fluid, forming the lenticular colored domain. The intrusion was gradually transformed into an annular vortex. In the impact mode, the drop broke up into individual fibers during the coalescence, creating linear and reticular structures on the surface of the cavity and the crown. The flow patterns composed of individual fibers were rapidly rebuilt as the flow evolved and the splash emerged and decayed. The sizes of cavities and colored fluid domains were compared in different flow regimes as well. The total energy transfer and transformation impact on the flow structure formation and dynamics was revealed. [ABSTRACT FROM AUTHOR]

Predicting the dynamics of impacting drops is crucial in various industrial applications such as spray and inkjet technologies. Especially in painting technology, the entrapment of air bubbles greatly reduces the product quality. The formation of a thin air film in front of the moving contact line causes the entrapment of air bubbles in the spreading phase. To clarify the main forces acting at the gas-liquid interface that induce air bubbles entrapment, we investigate the contact line velocity of impacting drops by taking bottom view images using the total internal reflection (TIR) method. We used droplets of glycerol or glycerol-ethanol solutions and solid surfaces covered with either glycerol or silicone oil. Our results show the contact line velocity decreased rapidly at Tc when a thin air film was formed and settled down at a constant value Vconst after the formation of the air film. Furthermore, we revealed that drop viscosity affects Tc and Vconst . Moreover, we found that after Tc, the lubrication pressure of the air had the same order of magnitude as the viscous shear stress of the drop, which implied the importance of the air lubrication pressure. [ABSTRACT FROM AUTHOR]

Copyright of Japanese Journal of Multiphase Flow is the property of Japanese Journal of Multiphase Flow and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

An axisymmetric initial and boundary value problem regarding the impact of a liquid drop on a solid surface at constant speed is considered, for different contact angles. Mathematically, Navier–Stokes equations are used to describe the motion of each phase (liquid, air). A method of numerical solution is described, and sample calculations are presented. [ABSTRACT FROM AUTHOR]

Spray cooling of solid substrates is one of the methods used in various industrial processes such as forging, quenching or other metallurgical applications, electronics, pharmaceutical industry, medicine, or for cooling of powerful electrical devices. Spray cooling is governed by various hydrodynamic and thermodynamic processes, like drop impact, heat conduction in the substrate and convection in the spreading drops, and different regimes of boiling. The problem of modeling spray cooling becomes even more challenging if the liquid is multicomponent. The presence of components with various physicochemical properties (surfactants, binders, dispersed particles, etc.) can significantly affect the entire process of spray impact, as well as the outcome of the known cooling regimes and could lead to a formation of a thin deposited layer on the substrate. In this experimental study, spray impact onto a substrate, initially heated to temperatures significantly exceeding the liquid saturation point, is visualized using a high-speed video system. The heat transfer associated with spray impact is characterized using an array of thermocouples installed in a thick metal target. As a working fluid, a mixture of a distilled water and industrial white lubricant was used. It is observed that the presence of very small concentrations of lubricant augments the heat flux dramatically, particularly at high wall temperatures, at which usually film boiling is observed for spray cooling by using distilled water. Three main mechanisms lead to the increase of heat flux and shift of the Leidenfrost point. They are caused by the significant viscosity increase of the evaporating lubricant solutions, by an increase of the substrate wettability and by the emergence of stable liquid sheets between bubbles, preventing their coalescence and percolation of the vapor channels.

Efforts have been made to streamline the abstract as follows. If further changes are made we are concerned that the integrity of the content may be compromised. We hope you will understand. This study aimed to investigate the impact damage experienced by Pucheng crisp pears during various stages, including harvest, transportation, and processing. Drop impact tests were conducted on pears, considering drop height and collision contact material as factors influencing damage. The bruise area was used as an indicator for damage evaluation. Additionally, the pressure-sensitive film technique was employed to measure the contact stress distribution characteristics of Pucheng crisp pears after the drop impact. The relationship between contact stress distribution and damage area was examined, and the stress area range close to the damage area was determined. The results revealed that the damage area of pears increased linearly with the increasing drop height. Among the four contact materials, foam board exhibited the best cushioning properties, with a maximum safe drop height of 20 cm. The pressure distribution tended to follow a normal distribution, with a pressure range of 0.2-0.3 MPa covering the largest area, corresponding to the majority of the bruise area on the pears. Furthermore, the pressure area and average pressure were found to be related to the severity of bruising. When pears were dropped onto steel, rubber plate and corrugated board, for the former two the stress area exceeding 0.2 MPa closely approximated the damage area, with an average relative error of 7.2%. For the latter, the closest range was above 0.3 MPa, with an average relative error of 3.6%. However, when dropped onto foam board, the average relative error was 75%. This research provides valuable insights for designing packaging tools to minimize damage and serves as a theoretical basis for predicting and assessing pear bruise area using finite element analysis. [ABSTRACT FROM AUTHOR]

Water erosion is an unfavorable phenomenon causing soil degradation. One of the factors causing water erosion is heavy or prolonged rainfall, the first effect of which is the deformation of the soil surface and the formation of microcraters. This paper presents an overview of research methods allowing the study of microcraters as well as the process of their formation. A tabular summary of work on the measurements of various quantities describing the craters is presented. The said quantities are divided into three groups: (i) static quantities, (ii) dynamic quantities, and (iii) dimensionless parameters. The most important measurement methods used to study crater properties, such as (i) basic manual measurement methods, (ii) photography, (iii) high-speed imaging, (iv) profilometers, (v) 3D surface modelling, and (vi) computed tomography (CT) and its possibilities and limitations are discussed. The main challenges and prospects of research on soil surface deformation are also presented. [ABSTRACT FROM AUTHOR]

The impact of a drop onto a liquid film is relevant for many natural phenomena and industrial applications such as spray painting, inkjet printing, agricultural sprays, or spray cooling. In particular, the height of liquid remaining on the substrate after impact is of special interest for painting and coating but also for applications involving heat transfer from the wall. While much progress has been made in explaining the hydrodynamics of drop impact onto a liquid film of the same liquid, the physics of drop impact onto a wall film with different material properties is still not well understood. In this study, drop impact onto a very thin liquid film of another liquid is investigated. The thickness of the film remaining on a substrate after drop impact is measured using a chromatic-confocal line sensor. It is interesting that the residual film thickness does not depend on the initial thickness of the wall film, but strongly depends on its viscosity. A theoretical model for the flow in the drop and wall film is developed which accounts for the development of viscous boundary layers in both liquids. The theoretical predictions agree well with the experimental data. [ABSTRACT FROM AUTHOR]

The phenomenon that the drops impact the solid wall widely exists in industrial production. In this paper, the dynamic evolution of a single drop impacting a horizontal hydrophilic wire is explored through experiments and numerical simulation methods. Combined with the phenomena of spreading, retracting and breaking, the movement behavior law of the drop impacting the curved surface is analyzed. Furthermore, the effects of eccentricity, Weber number and wall wettability on drop impact spreading dynamics are studied. The results show that, with the increase of impact eccentricity, the drop impacting the wire appears symmetrical wrapping mode, asymmetrical wrapping mode, unilateral infiltration mode and partial wetting mode in turn. With the increase of the Weber number, the drop morphology appears in turn as spread-retracting, spread-splitting, spread-wrapping and spread-breaking modes when the axis of the drop impacts the wire. In addition, both eccentricity and Weber number have influence on the maximum spreading coefficient and the maximum spreading time. The wettability of wire has a significant effect on the spread-retracting behavior of drops. With the increase of hydrophilicity of wire, the peak dimensionless spreading area and spread-retracting stage of drops increase, and the retracting time is delayed.

The impact of a liquid drop on a granular medium is a common phenomenon in nature and engineering. The possible splashing droplets and ejected particles could pose a risk of pathogen transmission if the water source or granular medium is contaminated. This work studies the liquid drop impact on the granular medium using high-speed photography and considers the effects of liquid properties, drop impact characteristics, and granular medium properties. Four flow regimes, including direct penetration, prompt splashing, spreading, and corona splashing, are observed and a regime map is created to identify their thresholds. The spreading regime can eject a large number of particles, and the corona splashing regime can produce splashing droplets in addition to the ejected particles. For the splashing droplets, their median diameters and velocities are in the ranges 0.11 to 0.21 and 0.15 to 0.37 of the diameter and velocity of the impact drop, and their median splashing angles range from 14° to 27°. Two particle ejection mechanisms are observed, falling squeeze and forward collision, driven by the collapsing and forward spreading of the liquid lamella, respectively. The particles ejected by the latter mechanism have larger ejection velocities, angles and distances from the impact center, which can facilitate their long-range transmission. In addition, the process of spreading and retracting of the lamella formed by the drop impact is also studied, and it is found that the maximum spreading diameter of the lamella is proportional to the crater diameter. These results improve the understanding of the phenomenon after the drop impact on the granular medium and the characteristics of the splashing droplets and ejected particles, contributing to the prediction and risk assessment of contaminated particle transmission., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence that work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

We aimed to derive a phase diagram in the parameter space of wall temperature Tw and Weber number We for the spreading behaviors of water drops impacting a heated sapphire plate. Focusing on hydrodynamic instabilities, we performed drop impact experiments to investigate spreading behaviors with varying wall temperatures (Tw = 60 to 150 ℃) and Weber numbers (We = 29.5 to 443) using high-speed infrared (IR) imaging. A phase diagram was established accommodating three different regimes: the gentle spreading regime, rim instability regime, and contact-line instability regime. The gentle spreading regime occurs under low-We and low-Tw conditions. In this regime, the drop spreads while maintaining a round shape with no perturbations. With an increasing Weber number at any wall temperature, the spreading behavior undergoes a transition to the rim instability regime, where a finger like perturbation can be observed along the lamella rim of the spreading drop. For low-We and high-Tw conditions, instead of rim instability, we observed a transition to the contact-line instability regime, where finger like perturbations form along the contact line. Additionally, we explored the temperature dependency of the maximum spreading ratio, dimensionless perimeters, and number of fingers for the contact-line instability and rim instability regimes. The experimental results indicated that intense evaporation around the contact line has a significant impact on the growth of the observed hydrodynamic instabilities, leading to changes in spreading behaviors. To the best of our knowledge, ours is the first study to observe the contact line instability induced by thermal effects. Considering the occurrence of contact line instability only at high Tw values, we expect that intense evaporation around the contact line is a key factor in the underlying mechanism of contact line instability.

The effect of coal hydrophilic particles in water-glycerol drops on the maximum diameter of spreading along a hydrophobic solid surface is experimentally studied by analyzing the velocity of internal flows by Particle Image Velocimetry (PIV). The grinding fineness of coal particles was 45–80 μm and 120–140 μm. Their concentration was 0.06 wt.% and 1 wt.%. The impact of particle-laden drops on a solid surface occurred at Weber numbers (We) from 30 to 120. It revealed the interrelated influence of We and the concentration of coal particles on changes in the maximum absolute velocity of internal flows in a drop within the kinetic and spreading phases of the drop-wall impact. It is explored the behavior of internal convective flows in the longitudinal section of a drop parallel to the plane of the solid wall. The kinetic energy of the translational motion of coal particles in a spreading drop compensates for the energy expended by the drop on sliding friction along the wall. At We = 120, the inertia-driven spreading of the particle-laden drop is mainly determined by the dynamics of the deformable Taylor rim. An increase in We contributes to more noticeable differences in the convection velocities in spreading drops. When the drop spreading diameter rises at the maximum velocity of internal flows, a growth of the maximum spreading diameter occurs. The presence of coal particles causes a general tendency to reduce drop spreading.

The high-speed liquid impact on a dry wall is known to result in appearance of a shock wave propagating up the impacting liquid from the wall. In the first stage this wave remains attached to the wall whereas in the second stage it detaches from the wall, leading to lateral jetting of the liquid compressed by the shock wave. In the first stage the pressure maximum on the wall, just like the extremes of other impact characteristics (the compressed liquid velocity, the shock wave slope, etc.), is attained at the shock wave edge. In the course of the first stage this maximum grows although in the second stage its magnitude gradually decreases. In the present work, the pressure maxima and the extremes of other compressed liquid characteristics achieved in the course of the first stages of liquid impact on a liquid surface and a wall wetted by a thin liquid film are studied, using known Heymann's theory (J. Appl. Phys. 40, 1969) originally devoted to the liquid impact on a dry wall. Corresponding algebraic expressions for the compressed liquid characteristics at the impact area edge in the course of the first stage of liquid impact on a liquid surface and a wetted wall are derived. A variant with water as the involved liquids has been considered in detail. It is found that the impact characteristics in the case of impact on a liquid surface under the impact Mach number up to 1 are quite close to their values in the case of impact on a dry wall with half the impact angle and half the Mach number. In the case of a wall wetted with a very thin liquid film, the impact characteristics are close to those for a dry wall. It is shown that the derived expressions for the impact characteristics are useful for construction of the shock wave fronts during the first stage of liquid impact onto a liquid and a wetted wall. [ABSTRACT FROM AUTHOR]

Droplets within droplets occur in numerous situations in which two immiscible liquids interact, for instance, binary drop collisions or when a drop of one liquid impacts onto a film of a different liquid, ejecting secondary droplets containing both liquids. In the present study, an imaging technique for determining the volume fraction of each liquid component in such two-component droplets is introduced, in which multiple images of the same droplet at different times are used. The processing of these images is supported by a machine learning algorithm, which is taught using synthetically generated images and validated on droplets with known mixture fractions placed in an acoustic levitator. The application of the technique is demonstrated by measuring the volume fraction in splashed secondary droplets following the impact of a drop of one liquid onto a film of a different liquid. [ABSTRACT FROM AUTHOR]

Predicting the dynamics of an electrically charged drop impacting a solid surface is of great importance in various industrial applications such as spray coating and painting. An impacting drop decelerates immediately before the touch-down by the lubrication pressure of the intervening air. The pressure build-up forms a dimple resulting in the entrapment of bubbles under the drop. We measured and visualized the dimple and bubble formations using high-speed interferometry and back-light imaging techniques by focusing on the effect of the electrostatic charge on the surface deformation. We clarified that the dimple size decreased, and the kink of the dimple became more flattened with increasing the charge, which resulted in forming a micro-bubble band around a central bubble. By comparing the dimple profile obtained with interferometry and bubble images, we revealed that an air layer, thinner than 266 nm, raptures into small pieces forming a microbubble band while a thicker air layer collapses into a bubble. Replacing a substrate from conductive to dielectric hinders the decrease in dimple volume, confirming Maxwell stress acting between the drop bottom surface and the substrate plays a crucial role in determining the bubble entrapment. [ABSTRACT FROM AUTHOR]

Droplet impact may rupture a liquid film on a non-wettable surface. The formation of a stable dry spot has only been studied in the inviscid case. Here, we examine the break-up of viscous films, and demonstrate the importance and role of the viscous dissipation in both film and droplet. A new model was therefore proposed to predict the necessary droplet energy to create a dry spot. It also showed that the dissipation contribution in film dominates when the ratio of the thicknesses to drop diameter is larger than 7/4. [ABSTRACT FROM AUTHOR]

Drop impact on a dry substrate is ubiquitous in nature and industrial processes, including aircraft de-icing, ink-jet printing, microfluidics, and additive manufacturing. While the maximum spreading factor is crucial for controlling the efficiency of the majority of these processes, there is currently no comprehensive approach for predicting its value. In contrast to the traditional approach based on scaling laws and/or analytical models, this paper proposes a data-driven approach for estimating the maximum spreading factor using supervised machine learning (ML) algorithms such as linear regression, decision tree, random forest, and gradient boosting. For this purpose, a dataset of hundreds of experimental results from the literature and our own—spanning the last thirty years—is collected and analyzed. The dataset was divided into training and testing sets, each representing 70% and 30% of the input data, respectively. Subsequently, machine learning techniques were applied to relate the maximum spreading factor to relevant features such as flow controlling dimensionless numbers and substrate wettability. In the current study, the gradient boosting regression model, capable of handling structured high-dimensional data, is found to be the best-performing model, with an R2-score of more than 95%. Finally, the ML predictions agree well with the experimental data and are valid across a wide range of impact conditions. This work could pave the way for the development of a universal model for controlling droplet impact, enabling the optimization of a wide variety of industrial applications. [ABSTRACT FROM AUTHOR]

The combination of high-concentration solutions of hydrogen peroxide, known as High Test Peroxide (HTP), with the green fuel composed of tetramethylethylenediamine, dimethylaminoethanol, and methanol (TMEDA/DMEA/MeOH, 1:1:1 vol%), catalyzed by 1 wt% of copper chloride dihydrate, has significant potential for space hypergolic propulsion applications in terms of performance and safe operation. Besides the well-known and mature propulsion systems adopting liquid and solid propellants, gel propellants also present interesting characteristics that can be better explored to enable the creation of alternative propulsive systems. The present work employed HTP at 98 wt% with 6 wt% of fumed silica as a gelling agent to create gelled HTP (GHTP). Droplets of the green fuel impinged on a layer of GHTP placed over a glass slide, acting as a solid oxidizer, mimicked an element of a new hybrid gel/liquid hypergolic propulsion system. Data from infrared and visible light cameras enabled a detailed analysis of the dynamics of a reactive droplet impinging on a gelled oxidizer wall, as well as the heat release, ignition, and flame spread of the hypergolic GHTP/green fuel pair under open-air conditions. The heat release was observed to be distributed across concentric annular areas for both the fuel surrogate and the fuel with catalyst, before and after ignition, demonstrating a strong correlation with non-reactive droplet fluid dynamics, which was corroborated by spread diameter analysis processed from visible image data. Vapor and Ignition Delay Times (VDT and IDT) were found to be as low as 4 and 17 ms, respectively, for the highest droplet impact velocity and catalyst concentration. The reaction rate in the gas phase, considering the flame spread area, showed a dependency of both impact velocity and catalyst concentration, with the latter exhibiting a more pronounced and clear effect. The surface temperature ranges where first vaporization and ignition occurred were 60 °C ∼ 70 °C and 120 ∼ 170 °C, respectively, which is close to the boiling point of methanol and the auto-ignition temperature of TMEDA. This finding, along with the chemical mechanisms in the gas phase related to the presence of a catalyst in the fuel, may be important for hypergolic ignition. The relatively low ignition temperatures and the short ignition times represent additional advantages of the present hypergolic combination for propulsion applications. [Display omitted] • Potential use of gelled hydrogen peroxide in a gel/liquid hypergolic system. • A dimensionless time of 2 marks the shift in droplet/wall dynamics to reactive flow. • Vapor and Ignition Delay Times were found to be as low as 4 and 17 ms, respectively. • Flame spread showed dependency on both impact velocity and catalyst concentration. • Vapor and ignition detected at 60∼70°C and 120∼170°C on the surface, respectively. [ABSTRACT FROM AUTHOR]

Nanofiber surface coating is a promising method for the enhancement of heat transfer during spray cooling. In the present work, the drop dynamics as well as local and overall heat transfer during single drop impact onto a heated wall covered with a polyacrylonitrile (PAN) nanofiber mat are investigated to obtain insight into the mechanisms governing the heat transport enhancement. The influence of wall superheat, drop impact velocity, and mat thickness on the hydrodynamics and heat transfer from the heated wall to the fluid is studied. The experiments were conducted inside a temperature-controlled test cell with a pure vapor atmosphere maintained with refrigerant FC − 72 (perfluorohexane). The temperature field at the solid–fluid interface was observed with a high-speed infrared camera, and the heat flux field was derived by solving a three-dimensional transient heat conduction equation within the substrate. The presence of the nanofiber mat on the heater surface suppresses the drop receding phase due to the pinning of the contact line at the end of the spreading phase. Two different heat transfer scenarios are observed depending on the wall superheat and drop impact velocity: scenario (I), in which the liquid drop completely penetrated through the porous nanofiber mat and made contact with the heater surface; and scenario (II) in which the vapor produced inside the pores of the nanofiber mat prevented the liquid drop from touching the heater surface. In scenario (I), an up 450% heat flow enhancement during the sessile drop evaporation stage has been observed. In scenario (II), a 80% heat flow enhancement at this stage has been registered. • Wall heat flux during drop impact on nanomat-covered hot substrates is measured. • The drop receding phase is suppressed in the presence of nanofiber mat. • Heat transfer scenario is determined by impact velocity and wall superheat. • Heat transfer in sessile drop phase is significantly enhanced by using nanomats. • Heat transfer enhancement is high at high impact velocities, low wall superheats. [ABSTRACT FROM AUTHOR]

This study investigates the hydrodynamics and heat transfer of a droplet impinging on a heated superhydrophobic surface at low Weber numbers with subsequent bouncing through numerical simulations in the phase-field framework. These structure-resolved simulations take into consideration the entrapment of air during impingement on the micro-textured surface and effectively replicate the hydrodynamic behavior observed in corresponding experimental studies [1]. The simulation results indicate notable differences in air entrainment and heat transfer dynamics for the same contact angle under varying surface topography. This offers the potential to deliberately modify the dynamics of heat transfer by manipulating the surface topography without significantly altering the wetting behavior. Additionally, an attempt to substitute the structure-resolved boundary with a temperature boundary condition, which incorporates the void fraction and thermal conductivity of the involved fluids, has been observed to be insufficient to reproduce the temperature evolution due to the absence of wetting physics description. These findings suggest that the primary source of variations in heat transfer is the alteration in the contact area with the surface, rather than the local thermophysical properties of the air/water mixture. Consequently, for an accurate evaluation of heat transfer on textured surfaces, it is imperative to employ simulations that consider the resolved surface topography. • 3D simulations of droplets on heated surfaces with varying roughness were conducted using phase-field. • Textured surfaces with low roughness improve heat exchange over smooth ones due to larger contact area. • Textured surfaces with high roughness can either enhance or reduce cooling due to their wetting effect. [ABSTRACT FROM AUTHOR]

We investigate numerically the influence of thixotropic effects on the impact of a drop onto a thin film, a fundamental process in many technical systems. Direct numerical simulations are performed with a Volume-of-Fluid (VOF) method based multiphase flow solver whose capabilities are expanded in order to enable simulations of a thixotropic liquid. The thixotropic behavior is modeled by a rate kinetic equation for the structural integrity of the assumed microstructure of the liquid. The corresponding structural parameter is described by an additional VOF-variable. After a validation of the implementations, we vary systematically the two parameters of the thixotropic model for a selected impact scenario in order to identify thixotropic effects during the impact and on the overall impact morphology. The two parameters are the mutation number M u = t exp / t θ as the ratio of the experimental time scale to the time scale of the structural rebuilding and the parameter β , which describes the effectivity of the shear-induced structural disintegration. The parameter study leads to a regime map with three different regimes. For M u > 10 , the liquid behaves purely shear-thinning. High shear rates during the early stages of the impact lead to a low apparent viscosity at the crown base and to an enhanced crown growth. For M u < 0. 1 , the liquid behaves irreversible thixotropic or rheodestructing, respectively. Structural rebuilding is negligible and every deformation leads to a further disintegration of the microstructure. In this regime, a thin region of disintegrated microstructure develops within the liquid, spanning from the location of high shear stresses at the bottom into the crown rim. In between these two regimes, purely thixotropic effects become significant. A complex microstructure develops during the impact, in which features of both regimes occur combined, leading to a pronounced viscosity gradient along the crown wall. A comparison of the resulting maximum crown heights reveals that various combinations of M u and β values can lead to the same maximum crown height whereas the crown shapes prior to this point in time can be very different. [Display omitted] • Volume-of-Fluid framework for simulating multiphase flows with thixotropic liquid. • Influence of parameters of Moore's model on drop impact is studied systematically. • A thixotropic behavior of the liquid can inhibit the initial crown growth. • A derived regime map shows the influence of thixotropy on the maximum crown height. • Different model parameters can lead to same crown height but different initial growth. [ABSTRACT FROM AUTHOR]

[Display omitted] • Promoting droplets to fly off the surface is a key anti-icing strategy. • Droplet breakup is a prerequisite for droplets to fly off the surface. • Multi-scale ridged bionic structure promotes droplet breakup and fly-off. • Multi-scale ridged bionic structure inhibits SLD from freezing on the surface. The ice formed on aircraft as a result of the freezing of supercooled large droplets (SLD) presents a significant safety risk to flight safety. Mitigating or inhibiting SLD icing has attracted considerable attention from researchers. Although superhydrophobic surfaces have demonstrated potential in reducing contact time to achieve anti-icing, their effectiveness has been limited by the issue of droplets eventually staying and freezing on the horizontal surface after bouncing. To address this limitation, droplets breaking up and flying away from the surface is an effective method of preventing them from adhering to the surface, thereby enhancing the anti-icing performance of superhydrophobic surfaces. This study observed that droplets of high Weber numbers impacting barnyard grass break up into smaller droplets through liquid column disintegration and quickly fly away from the leaf. This behavior is attributed to the anisotropic spreading and retraction of the liquid film caused by the surface structure, resulting in the formation of a scattering liquid column that is more unstable than that of a droplet of the same volume. Additionally, SLD impacting a bionic surface inspired by barnyard grass also break up and fly away, leaving no ice on the bionic superhydrophobic surface, whereas those impacting a smooth superhydrophobic surface retract into spherical droplets that eventually freeze on the surface. This research contributes to the advancement of SLD anti-icing studies and provides a strategy and bionic structure to enhance anti-icing performance further. [ABSTRACT FROM AUTHOR]

The evolution of the falling drop substance transfer in a target fluid at rest was traced by high-speed video techniques. Two flow modes were studied: slow intrusive flow, when the KE of the drop was comparable or less than the available potential energy (APSE), and a fast impact flow, at a relatively high drop contact velocity. For the substance transfer visualization, a drop of alizarin ink solution at various concentrations was used. The use of transparent partially colored fluid allows tracing the drop matter motion in the bulk and on the fluid free surface. The traditional side and frontal view of flow patterns were registered and analyzed. In both flow modes, the substance of the drop partially remained on the free surface and partially went into the target fluid bulk, where it was distributed non-uniformly. In the intrusive mode, the drop substance partially remained on the surface, while the main mass of the drop flowed into the thickness of the target fluid, forming the lenticular colored domain. The intrusion was gradually transformed into an annular vortex. In the impact mode, the drop broke up into individual fibers during the coalescence, creating linear and reticular structures on the surface of the cavity and the crown. The flow patterns composed of individual fibers were rapidly rebuilt as the flow evolved and the splash emerged and decayed. The sizes of cavities and colored fluid domains were compared in different flow regimes as well. The total energy transfer and transformation impact on the flow structure formation and dynamics was revealed.

We aim to maintain as much control over the microstructure development during the manufacture of polyurethane foam with a specific density. As a result, the finished product contains the shock absorber's required characteristics. That is why polyurethane foam loaded with zinc oxide and silica must sustain the cellular structure and strengthen it. First, mechanical characterization was carried out utilizing a dynamic drop impact test conducted on locally developed and constructed equipment. Polyurethane foams' mechanical properties rely on their density, cell structure (size and shape), and the fraction of open or closed cells. Within the cell structure, the foam may be directed preferentially. Following that, Raman spectroscopy and SEM investigation to visualize the semi-opened cells of the cellular polymer. The cellular polymer appears to possess permanent, regular cellular structures with a high degree of reversibility in terms of overlap. [ABSTRACT FROM AUTHOR]

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