Drop Spreading Research Articles

Water-in-oil emulsion drop-wall impact: Effect of viscosity and water particles on slip length over an oleophilic surface

The study is focused on the numerical simulation of the boundary slip of a water-in-oil (W/O) emulsion along an oleophilic surface in a 2D axisymmetric formulation of the Navier–Stokes equations for an incompressible laminar flow. Drops of emulsions with a volume fraction of the dispersed phase of 0.04–0.34 collide with a smooth glass wall at initial velocities of 1.2–3.6 m/s; the motion of the interface between the liquid and gas phases is resolved by the level set method. The influence of the wall wettability by oily liquids is demonstrated by varying the static contact angle up to 0.5° and by considering the dynamic one as a function of the empirically measured contact line velocity of the liquid drop according to Tanner's law. Numerical simulation of emulsion drop spreading dynamics reveals that the boundary slip of a heterogeneous liquid along a smooth oleophilic wall is different from that of a homogeneous. The temporal changes in the average viscous stress allowed the illustration of the interrelated effects of emulsion viscosity and the presence of disperse phase particles on the boundary slip of a heterogeneous liquid and its motion in the viscous boundary layer. The analytical expression evaluating the slip length for an arbitrary W/O emulsion was derived using the effective properties of the liquid. In testing the expression, the values of the maximum spreading factor of drops of an arbitrary W/O emulsion predicted by numerical simulation correspond to those determined from experiments at a moderate error of 7.4%.

Fractal interface of a spreading drop and maximum entropy production principle

The viscous spreading of a small liquid drop on a surface, where moving interface changes from circular to fractal, starting at a certain size, is considered. Based on the maximum entropy production principle, the analytical relation between the critical size of the morphological stability of a circular drop and the fractal dimension of the structure that appears during spreading is obtained for the first time. An experiment on the spreading of ink on a surface covered with acrylic paint quantitatively confirmed the validity of this relation.

Effect of Monodisperse Coal Particles on the Maximum Drop Spreading after Impact on a Solid Wall

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.

Rapid prediction of cementitious initial sorptivity via surface wettability

The tendency of cementitious systems to absorb and transmit liquid through capillary pores is often characterized by initial sorptivity, which is an important indicator of long-term durability. However, sorptivity measurements, which are based on the continuous mass change of specimens exposed to water, are labor-intensive (up to 6 h of continuous measurements). Here, we exploit the fundamental surface-wetting characteristics of cementitious systems to estimate their sorptivity in a rapid fashion, i.e., in a matter of few minutes. In a series of 63 distinct paste systems of varying w/c ratios (0.4–0.8), subject to a range of curing periods (1–7d), we establish strong correlations (adjusted R2 ≥ 0.9) between the initial sorptivity (~6 h) and dynamics of drop spreading (contact angle ~0.5 s, drop residence time <10 min). These results elucidate rapid pathways in estimating initial sorptivity and durability of a broad variety of hydrated cementitious matrices.

Modeling inkjet dots from drop spreading, absorption and evaporation – An engineering approach

Spreading and absorption of small liquid drops on porous substrates is of interest in a number of fields ranging from additive manufacturing and composite processing to inkjet printing. In inkjet printing, spreading and absorption processes determine the final area of a printed dot, which is decisive for print quality in terms of coverage and resolution. However, it is not fully understood how substrate and liquid properties influence the involved physical processes and the resultant printed dot area. In this work, the printed dot area of overall 140 paper-liquid pairings representative for the operational window of an inkjet printer is evaluated. The results are explained by a simple model including spreading, absorption, and evaporation. The surface tension and viscosity of the liquids, as well as the pore size and polarity of the substrates were varied systematically to represent the range of uncoated paper-liquid pairings applicable for inkjet printing. Results show that the printed dot area mainly depends on the wettability of the liquid-substrate pairing followed by penetration speed. Evaporation and volume reduction due to roughness filling had little impact. The modeling results are in line with empirical observations showing that the dot area is closely related to the contact angle.

Water drop impacts on regular micropillar arrays: Asymmetric spreading

Eye-catching shapes are produced when water drops land vertically and spread on horizontal surfaces with micropillars arranged in regular square arrays. The positions of protrusions and fingers are often determined by the microstructure design and may be produced repeatably, which suggests possible manufacturing and analytical applications. This paper uses high-speed imaging of droplet shapes following impact to record and analyze asymmetries as drop spreading reaches its maximum extent. The range of experimental parameters used produced results varying (often non-monotonically) from symmetric spreading to many fingers. Impact Weber numbers (We) were systematically adjusted between 50 and 250, while surface microstructures featured circular (◯) and square (□) cross-sectional pillars of width d = 20 μm; height h = 15, 22, or 30 μm; and pitch p = 40, 60, or 80 μm. Many observed trends correlate with the extent of the fully wet impact region, including a general increase in asymmetry with We, p, and for □ rather than ◯ pillars. More detailed understanding of asymmetry mechanisms is also developed. For example, protrusions may be nucleated by jetting in directions of high gas flow within 100 μs of impact. A new analysis of gas flow under the drop, which accounts for Laplace pressure, explains anomalous spreading and asymmetry measurements. Reduced spreading velocity is identified as the cause of finger suppression where the microstructure is wet.

К ОБОСНОВАНИЮ УПРАВЛЯЕМЫХ ПАРАМЕТРОВ ВЫСЕВАЮЩЕГО АППАРАТА ЭЛЕКТРИФИЦИРОВАННОЙ СЕЯЛКИ

An important aspect influencing the provision of a given seeding rate is the interaction of seeds with the mechanism of the double ejector under various operating modes of the sowing unit. The study of the interaction of seeds with structural elements of the sowing machine, taking into account their physical and mechanical properties, will allow us to evaluate the efficiency of seed placement at various speeds of the sowing unit and develop automatic control systems for the mechanism of the twin ejector. The purpose of the study is to determine the statistical characteristics of the distribution of seeds depending on the position of the twin ejector and the rotational speed of the sowing disc and to determine the optimal values of these parameters. The design and operating parameters of the sowing machine were determined using the methodology of planning a multifactorial experiment. A second-order planning matrix based on two-factor Box-Wilson plans was used. Lisbon soybeans were used for research. The speed of the meter disk was varied from 15 rpm (low level) to 55 rpm (high level). The position of the seed ejector was set so that the suction hole was blocked halfway (lower level) to a fully open hole (upper level). The coefficient of variation of the time intervals between the ejection of seeds from the sowing apparatus and the crushing of seeds were chosen as optimization criteria. The regression equations that adequately describe the seeding process under study were obtained from the results of the experiments. Installed. that the control factors should be within the following limits: the rotational speed of the seeding disc should be from 15 to 35 rpm, and the position of the excess seed remover should provide overlapping of the holes by 10 - 35%, while the coefficient of variation will be less than 33%, and the crushing of seeds less than 1 %. The data obtained can be used to develop a control algorithm for the automatic regulator of the position of the twin ejector, depending on the speed of the sowing unit.

GEOMETRIC CLAMPING PLATE DIMENSIONS OF THE IMPROVED OF GRAIN SEEDER COULTER SZ-3,6

The article notes that the improvement of operating tools of sowing machines is a solution to one of the many tasks of increasing crop yields. It is also noted that a two-disc coulter and its inherent advantages and disadvantages have been widely used on sowing machines, and the final sowing operation is considered the most important for seeds, since it creates conditions for their germination and further development.&#x0D; Significant factors affecting the germination and development of plants after sowing with seeders equipped with disc coulters are given, one of which is the tight contact of seeds with the bottom groove with a loose surface layer.&#x0D; The scheme for improving a two-disc coulter with pressure plate installed in the inter-disc space is proposed, and the details of the coulters are maximally unified with the coulters of grain seeders of the type SZ-3.6, mass-produced by domestic manufacturers. The pressure plate, moving together with the coulter, crushes small soil lumps with the inclined part and pushes the seeds into the bottom groove with a horizontal shank, ensuring their tight contact with the soil. A method for determining the main geometric parameters of the pressure plate depending on external forces acting from the soil is proposed, the dependence of the characteristics of the cross-section of the plate on the geometric dimension is given

Effect of gravity on the spreading of a droplet deposited by liquid needle deposition technique

This study represents an experimental investigation, complemented with a mathematical model, to decipher the effect of gravity on the spreading dynamics of a water droplet. For the theoretical discussion, an overall energy balance approach is adopted to explain the droplet spreading under both microgravity (μg) and terrestrial gravity condition. Besides explaining the mechanism of the droplet spreading under microgravity condition achieved during the parabolic flight, a technique with a detailed experimental set-up has also been developed for the successful deposition of droplet. A rational understanding is formulated through experimental investigation and theoretical analysis, which allows us to distinguish the transient variation of the spreading of a droplet, between microgravity and terrestrial gravity condition. The spreading of the droplet is predicted by the non-linear overall energy balance equation, which accounts for the operating parameters in the form of non-dimensional groups like Reynolds number ({{{rm{Re}}}}), Weber number (We) and Bond number (Bo). To distinctly identify the difference in the drop spreading at terrestrial and microgravity conditions, the Bo with transient gravitational field obtained through the on-board accelerometer is considered. The obtained theoretical results are further corroborated by experimental results which are obtained from the parabolic flight.

Drop impact dynamics on the hydrophobic leaf surface of an aquatic plant: a case study of Pistia stratiotes.

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.

Parametric Analysis &amp; Design Structure of Hydraulic Seed System

This paper is bases on the design and manufacturing of the sowing machine based on hydraulic principle named as ‘Hydraulic Seed Sowing Machine’. The machine is very efficient in working and will be able to easily sow the seeds like (bajra, rice, Val, gram, groundnut, pea, maize, groundnut, etc.). The machine is following the conditions such as – It operates on a permanent raised bed of 100 cm width which can sow seeds with fertilizer in 5 rows at 25 cm approximately apart. Seeds - bajra, rice, Val, gram, groundnut, pea, maize, groundnut, etc. Mechanism is preferably impact dibber and it make very thin slit of max depth of 30-40 cm. It covers the seeds after sowing and be operated by 1-2 people either 1 hp power motor or manually and sow 0.6 to 1 ha in approximately 6 hours. Hydraulic Seed Sowing Machine is Potential of being self-driven to get higher speed

New emulsion electrospun biodegradable fibers and films PLA/PVP, containing green synthesized hydrozincite – Antibacterial and photocatalytic activity

New Poly(lactic acid)/Polyvinylpyrrolidone, containing green synthesized Hydrozincite (GHZ) emulsion electrospun fibers and drop spread films possessing antibacterial and photocatalytic activity were prepared. The PLA/PVP/GHZ films possess higher photocatalytic efficiency towards Malachite Green (MG) dye discoloration (85%) than that of the fibers (62%). The films demonstrate better antibacterial activity to E. coli K-12 with about 6.58 Log CFU/ml in comparison with fibers which expressed about 2.20 Log CFU/ml reduction for 120 h contact.

Nonequilibrium configurations of swelling polymer brush layers induced by spreading drops of weakly volatile oil.

Polymer brush layers are responsive materials that swell in contact with good solvents and their vapors. We deposit drops of an almost completely wetting volatile oil onto an oleophilic polymer brush layer and follow the response of the system upon simultaneous exposure to both liquid and vapor. Interferometric imaging shows that a halo of partly swollen polymer brush layer forms ahead of the moving contact line. The swelling dynamics of this halo is controlled by a subtle balance of direct imbibition from the drop into the brush layer and vapor phase transport and can lead to very long-lived transient swelling profiles as well as nonequilibrium configurations involving thickness gradients in a stationary state. A gradient dynamics model based on a free energy functional with three coupled fields is developed and numerically solved. It describes experimental observations and reveals how local evaporation and condensation conspire to stabilize the inhomogeneous nonequilibrium stationary swelling profiles. A quantitative comparison of experiments and calculations provides access to the solvent diffusion coefficient within the brush layer. Overall, the results highlight the-presumably generally applicable-crucial role of vapor phase transport in dynamic wetting phenomena involving volatile liquids on swelling functional surfaces.

Solar Powered Seed Sowing Machine

Solar Powered Seed Sowing Machine

Spray impact onto a hot solid substrate: Film boiling suppression by lubricant addition

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.

Engulfment of a drop on solids coated by thin and thick fluid films

When an aqueous drop contacts an immiscible oil film, it displays complex interfacial dynamics. When the spreading factor is positive, upon contact, the oil spreads onto the drop's liquid–air interface, first forming a liquid bridge whose curvature drives an apparent drop spreading motion and later engulfs the drop. We study this flow using both three-phase lattice Boltzmann simulations based on the conservative phase field model, and experiments. Inertially and viscously limited dynamics are explored using the Ohnesorge number $Oh$ and the ratio between the film height $H$ and the initial drop radius $R$ . Both regimes show that the radial growth of the liquid bridge $r$ is fairly insensitive to the film height $H$ , and scales with time $T$ as $r\sim T^{1/2}$ for $Oh\ll 1$ , and as $r\sim T^{2/5}$ for $Oh\gg 1$ . For $Oh\gg 1$ , we show experimentally that this immiscible liquid bridge growth is analogous with the miscible drop–film coalescence case. Contrary to the growth of the liquid bridge, however, we find that the late-time engulfment dynamics and final interface profiles are significantly affected by the ratio $H/R$ .

Drop impact phenomena and spray cooling on hot nanotextured surfaces of various architectures and dynamic wettability

Spray cooling has been used to quench metal slabs during casting, cool nuclear reactors, suppress accidental fires, and remove heat from high-power density electronics. In particular, the miniaturization of electronic devices inevitably results in an increased power density or heat flux on the microelectronics surfaces and poses a threat of a thermal shutdown of such devices when cooling is insufficient. Surface nanotexturing effectively augments additional liquid-to-substrate surface area, thereby increasing cooling capability, as well as an effective heat transfer coefficient. In spray cooling, surface dynamic wettability also affects drop impact dynamics and subsequent coolant evaporation on a hot surface. Herein, we introduced various nanotextured surfaces and affected dynamic wettability using the so-called thorny-devil nanofibers, nickel nanocones, Teflon and titania nanoparticles, and zinc nanowires. The effect of these different nanoscale architectures on drop impact phenomena and subsequent evaporative cooling was investigated. These nanotextured surfaces were fabricated using various deposition methods, including electrospinning, electroplating, supersonic spraying, aerosol deposition, and chemical bath deposition. We found that the surface with greater dynamic wettability related to the hydrodynamic focusing considerably improved the heat removal capability by furthering the Leidenfrost limit and facilitating drop spreading. In particular, the thorny-devil nanofiber surface yielded the highest heat flux at all ranges of the Reynolds and Weber numbers. Spray cooling on a model electronic kit also confirmed that the thorny-devil nanofibers were most effective in cooling the surface of the model kit during multiple cycles of water spraying.

Determination of Performance of No-Till Seeder and Stubble Cutting Prototype

One of the most common problems in maize production is the management of plant residues. Small agricultural enterprises, which cannot allocate capital for acquiring stalk cutting machines for their operation, face many technical problems in preparing the sowing bed for the products that will be planted after maize. Stalks of maize that cannot be shredded adequately and on time cause machinery to clog, prevent the preparation of a proper sowing bed, increase fuel consumption and increase costs. The aim of this study is to compare the no-till sowing machine prototype and stalk cutting machine prototype with the classical stalk cutter in terms of some management values. The prototype stubble cutting machine used in the study was manufactured with a cylindrical structure and equipped with 24 cutting blades 1 cm thick and 8 cm wide. İn addition, the prototype stubble cutting machine used in the study was manufactured with a cylindrical structure and equipped with 24 cutting blades 1 cm thick and 8 cm wide. İn addition, the no-till seeder prototype was manufactured as a bucket-type seed hopper equipped with granular fertilizer capable of sowing four rows. It was concluded that the stubble cutting machine prototypes resulted in less fuel consumption with lower penetration resistance when compared with the classical stalk shredder.

Electrically driven heartbeat effect of gallium-based liquid metal on a ratchet.

The realization of the liquid metal heartbeat effect shows better controllability under non-periodic stimuli than spontaneous oscillation or periodic stimuli. However, adjusting the liquid metal heartbeat performance, drop spreading area, and frequency, solely by the magnitude of the voltage, has great limitations. Here, we demonstrate that the eGaIn drop can beat inside graphite ring electrodes under DC voltage in alkaline solutions on ratchet substrates. These sawtooth structures provide asymmetric textures which influence liquid metal deformation during the beating of the heart. We achieved heartbeat frequencies from 2.7 to 4.8Hz, a 100% increase in the tunable frequency range compared to that on a flat surface. The oxidative spreading of the eGaIn drop on the ratchet substrate shows that the drop penetrates into the grooves of the sawtooth structure. Moreover, we investigated the physical mechanisms affecting the eGaIn heartbeat frequency and the influence on the spreading area of the eGaIn drop at various sawtooth sizes and orientations. These findings not only enhance our understanding of droplet manipulation on sawtooth-structured surfaces but also facilitate the design of microfluidic pump systems.

Climate-smart technologies for reducing water footprints in different cropland ecosystems: a meso analysis

Water footprints (WFs) in crop production are an ecological measurement of water utilization that represents the cumulative groundwater quantum consumed within a region (district/state or country) to produce the crops. WFs in crop production have great significance for ecosystem’s sustainability, as high WFs are posing a serious challenge for the scientists and presents researchable issues for reducing WFs for increased crop water productivity. Crop need based approaches and improved climate smart technologies (CSTs) instead of conventional approaches help in reducing the irrigation water use without compromising crop yields. In view of global warming, need to reduce the water intake in agricultural production has been thought as an urgently sustainable issue. Amongst various crops of South Asia, rice–wheat cropping system extensively cultivated on ~ 12.5 million ha (Mha), has large WFs. A large scale field experimentation suggested several permissible techniques having overwhelming significance for reducing WFs in crop production. Amongst the several CSTs, laser levelers for precision leveling, cultivars with short duration rice varieties, delayed transplanting of rice seedlings, soil matric potential (or tensiometer) based irrigation scheduling, direct drilling of rice seeds, crop establishment on permanent beds, mechanical rice seedling transplanting, and crop diversification through oilseed/pulses has considerable significance in water saving and decreased WFs. Nonetheless, all technologies are not universally efficient in reducing WFs, and depend up on several factors of which soil texture and climatic conditions are the major determinants. For feeding the burgeoning population and to sustain and/or increased food production, technological focus should be on widespread adoption of technologies which aims at reduced WFs either by decreasing water loss from the leaf and/or soil. The present review deals with WFs in crop production, and the technologies to enhance irrigation water productivity and ecosystems’ sustainability of predominant cropping system of South Asia, particularly in water-harassed regions.