Drop Motion Research Articles

An Enhanced Forwarding Method based on Intelligent Water Drops Algorithm in Named Data Network

Although Named Data Network (NDN) has made a bright future in Internet for high volume of requests by many users, how to send a request package (I-Pkt) consciously from the consumer to the Producer and returning the data package (D-Pkt) inversely is still one of its most important challenges. According to the recent limited researches, using service quality parameters beside an optimization algorithm like ant colony to find the optimal path has been an appropriate response to solve this problem. Not considering the service quality parameters sufficiently to find an optimal path is a problem to be focused more on. In line with this, this study has addressed the Intelligent Water Drops (IWD) optimization algorithm. In this algorithm, the best possible path based on many parameters related to path quality like cost, delay and number of steps taken by the package (I-Pkt) will be selected. In other words, the water drop movement tries to find the optimal path through the amount of soil collection in the path or the velocity rate. The results of simulating in ndnSIM simulator show that comparing the ant colony, it has improved in cost parameter on average by 23%, in hit ratio parameter by 24% and in hop count parameter by 13%. The general result is increasing service level quality in NDNs.

Morphological characteristics of the drop on the travelling substrate with a sharp stepped configuration

The shape of a drop on a partially wetting substrate strongly depends on not only its wetting velocity but also the surface characteristics of the substrate. The unexpected deformation or even breakup of the drop on the heterogeneous travelling substrate is a common phenomenon and needs to be carefully controlled in industrial processes. In this work, we designed an experiment to investigate the morphological characteristics of the drop on the substrate with a sharp stepped configuration. We experimentally studied the entire process of the drop motion on the substrate with a vertical-edged stepped structure and subdivided it into three stages: the collision stage, the inserting stage, and the stretching stage. For the collision stage, substrate velocity was determined as an important factor influencing the tail of the drop before and after the collision. For the inserting stage, it was found that the liquid is transferred to the pre-inserting zone with the reduced gap height due to the squeezing, resulting in an increase in the tail length; it was verified that the tail lengths vary with the position of the stepped frame by assuming that the drop volume is constant and the tail is simplified as a cone. For the stretching stage, three types of drop tails were observed by balancing the motion of the constraint tail in two directions: the one along the substrate movement and the one for anti-constraint of the stepped configuration; we experimentally analyzed the three types of drop tails and found that they are related to the substrate velocity, the gap height, and the height of stepped configuration.

Lattice Boltzmann simulation of drop splitting in a fractal tree-like microchannel

Fractal tree-like microchannel is advantageous to faster emulsification and droplet production in microchannels. Although computer simulation is becoming a powerful tool for design and optimization, precise treatment of a large number of walls in fractal tree-like microchannel is troublesome. The numerical roughness caused by traditional bounce-back boundary condition may accumulate and generate large errors in flow pattern recognization. In this paper, an approach integrating Immersed Boundary Method (IBM), Phase-Field Model (PFM) and Lattice Boltzmann Method (LBM) is developed, aiming to accurately simulate droplet splitting in fractal tree-like microchannel system involving surfactants and wetting boundary walls. Then the operating conditions including capillary number, flow rate ratio and wetting boundary conditions were optimized. We found that the capillary number in 0.02 ∼ 0.05 and flow rate ratio in 1/3.6 – 1/9 can accelerate emulsification. Hydrophobic-lipophilic walls generate a slug-like water drop of bullet shape and thin oil film between the drop and walls, facilitating drop movement in microchannel. The effects of surfactant, Marangoni stress and interfacial tension force on droplet splitting were investigated. The contact walls at the corner and forks resist the surfactant migration, and therefore enrich surfactant at the upstream end of drop interface, leading to uneven distribution of interfacial tension. The breaking interfaces and the interfaces contacting with wall or fork are subjected to opposite reaction of Marangoni stress and tend to be thinner and finally deform or break.

Numerical study of microfluidic emulsion dynamics under the influence of heterogeneous surface wettability

Surface wettability plays a vital role in various natural phenomena and technical applications, such as coating, printing, membrane technology, microfluidic devices, and porous media flow. We numerically investigate the dynamics and stability of liquid–liquid dispersion flowing in a microfluidic channel with heterogeneous surface wettability, using a conservative phase-field lattice Boltzmann method. First, we validate the implementation of the wetting boundary conditions. We then perform three-dimensional simulations of a single drop motion immersed in another immiscible liquid in a square microchannel with alternating surface wettability: hydrophilic, hydrophobic, and again hydrophilic sections. The viscosity of the dispersed liquid (oil) is ten times higher than that of the continuous one (water), while the two liquids have equal densities. Depending on the drop length and Capillary number, calculated based on the drop velocity and the dynamic viscosity of the continuous phase, four different flow patterns are observed when the drop passes through the hydrophobic section. The distinct flow patterns include passing without any changes in drop shape or dynamics, adhesion of the dispersed liquid to the walls, phase inversion (i.e., water becomes the dispersed phase), and drop breakage. These outcomes are in close agreement with the experimental data. A detailed explanation of the choice of the numerical parameters is presented. The critical aspect of capturing the observed drop behavior is introducing an intervening thin-film of the continuous phase of at least three diffuse interface thicknesses (between the drop and channel walls).

Modelling of Water Drop Movement and Distribution in No Wind and Windy Conditions for Different Nozzle Sizes

A numerical model was developed to determine the water drop movement and mean droplet size diameter at any distance from a sprinkler as a function of nozzle size and pressure. Droplet size data from 4, 5, 6, and 7 mm nozzle sizes verified the model. Data for model prediction were generated throughout lab experiments. The results demonstrated that the correlation between the observed and predicted droplet size diameter values for all the nozzle sizes and pressures is quite good. Nozzle size and pressure had a major influence on droplet size. Higher pressure produced smaller droplets over the entire application profile. The wetted distance downwind from the sprinkler increased as wind velocity increased, for example at a constant working pressure of 300 kPa, at wind speeds of 3.5 m/s and 4.5 m/s, 20% and 32% of the total volume exceeded the wet radius respectively. Larger droplets (3.9–4.5 mm), accounting for 3.6% and 6.3% of the total number of distributed droplets, respectively. The model can also predict the droplet size distribution at any wind direction overall the irrigated pattern.

Flow and Drop Transport Along Liquid-Infused Surfaces

Liquid-infused surfaces (LISs) are composite solid–liquid surfaces with remarkable features such as liquid repellency, self-healing, and the suppression of fouling. This review focuses on the fluid mechanics on LISs, that is, the interaction of surfaces with a flow field and the behavior of drops on such surfaces. LISs can be characterized by an effective slip length that is closely related to their drag reduction property, which makes them suitable for several applications, especially for turbulent flows. Drag reduction, however, is compromised by failure mechanisms such as the drainage of lubricant from surface textures. The flow field can also sculpt the lubricant layer in a coupled self-organization process. For drops, the lubricant reduces drop pinning and increases drop mobility, but also results in a wetting ridge and the associated concept of an apparent contact angle. Design of LIS wettability and topography can induce low-friction drop motion, and drops can dynamically shape the lubricant ridges and film thickness.

Modeling the behavior of direct current electromagnetic forces acting on a drop of liquid metal during electroslag remelting

The article presents mathematical and computer modeling of the behavior of liquid electrode metal drops during the process of electroslag remelting (ESP) at a constant current source. The study of the effect of electric field created by direct current allowed us to show the deviation of the drop trajectory from the electrode axis. The flow of electrons and drops of the electrode metal are exposed to electromagnetic forces, which leads to their displacement relative to the remelted electrode axis. This effect entails destabilization of the liquid metal bath and crystal heterogeneity. In turn, the use of external influence on the flow of ESR process can make it possible to stabilize the liquid metal bath even with the use of direct current. Centrifugal forces can act as such forces. They can arise when implementing the technology with the consumable electrode rotation around its own axis. To establish the optimal parameters of rotation speed, it is necessary to estimate the magnitude of impact of the magnetic field that occurs during direct current remelting process. The modeling was carried out using the Ansys Fluent 16.0 software package on the example of remelting 12Kh18N10T steel under the flux ANF-6. The algorithm for calculating of Ansys Fluent is based on the finite element method. In this paper, the mathematical apparatus was not changed and was used in its initial form. The method of magnetic induction was used. The database of information about the ongoing process was built on a grid of finite elements with certain, but sufficient level of adequacy and quality. Each element contains information about the model at a given point, specified for this modeling process. We have revealed the change in the trajectory of the electrode metal drop by electric field from the opposite direction along which the drop flows. The average length of the path traversed by liquid metal drop from the mold axis to the inner surface is from 5 to 15 cm. The motion of an electrode metal drop without an external magnetic field was simulated. This simulation made it possible to determine (estimate) the direction of movement of electrode metal drops and the indicator of necessary external force to stabilize the liquid metal bath during ESP process at direct current equal to 0.067 N.

Surface acoustic waves as control actuator for drop removal from solid surface

Several types of research are performed on flow control and this fact highlights the importance of this topic. Over the last two decades, actuators based on acoustic waves have attracted much attention and have been used in widespread applications from mixing to pumping. This paper reveals the effects of some control parameters such as wave amplitude and wave frequency on the dynamical behavior of a sessile drop in order to change the flow characteristics. For this purpose, the removal of water from surfaces and drop movement against gravity are considered. Flow dynamics is simulated using lattice Boltzmann method. The results show that the drop can be removed from the surface in a short period of time (about one-tenth of the normal time) without moving upstream. In the microgravity condition, the dynamical behaviors of drop are affected by Bond number. There is a critical Bond number, when the Bond number is less than this parameter, drop slides on the wall. In this situation, when the wave amplitude is set to be 2.5 nm, the drop is pinned to the wall. If the wave amplitude is increased, the drop moves against gravity. Also, when the Bond number is greater than its critical value, we only can stop or remove the drop using the SAW.

Исследование газоводяных составов ультрадисперсного распыла для установок пожаротушения

The analysis of information about domestic and foreign installations of the volumetric fire-extinguishing with gas-water compositions is carried out. Pneumoacoustic sprayers of original design were developed, which make it possible to obtain a gas-water composition containing fire-extinguishing gas and water droplets of the ultrafine spray (10–60 microns). It is shown that gas-water compositions combine the advantages of fire-extinguishing gas and fine-sprayed water, since the volumetric method of gas fire-extinguishing and the cooling effect of water are preserved. The deposition (movement) of drops of the gas-water composition occurs together with the fire-extinguishing gas; therefore, the gas-water composition of the ultra-dispersed spray can be conventionally considered as a whole, i.e., new extinguishing agent. It is noted that the most promising is the application of gas-water compositions in the extinguishing of solid smoldering materials. In this case, when designing domestic fire-extinguishing installations, the amount of gas can be reduced by 20% or more, and the elimination of smoldering can be achieved by cooling with water from the gas-water composition. At the same time, the fire-extinguishing environment suitable for breathing for at least 3 minutes is formed in the room. The influence of gas in the gas-water composition on the dispersion of water droplets is studied. The sedimentation rate of water droplets in the gas-water composition was estimated. The droplet dispersion was measured by laser diffraction using the Malvern Spraytec system. It is shown that the substitution of nitrogen for argon or gas composition Argonite in the gas-water composition does not significantly affect the dispersion of droplets. Sedimentation of ultrafine spray water droplets in the volume of the room occurs within a few minutes. Nitrogen has the best characteristics for use in the gas-water compositions. Conducted studies make it possible to conclude that the installations based on domestic gas-water compositions allow for import substitution of the foreign analogues certified in Russia.

The post-impact dynamics of drop rebound on inclined hydrophobic surfaces of various wettabilities

In this work, the post-impact drop motions of the rebound regime on inclined hydrophobic surfaces are investigated using a numerical technique. The effects of impact velocity (Vi = 0.5–1.5 m/s), drop diameter (D0 = 1.0–2.5 mm), surface wettability (θeq = 120°–160°), and inclined angle (α = 0°–80°) on the post-impact regimes, contact time (tc) and spreading time (ts), nondimensionalized maximum spreading diameter (Ds_max*), and drop displacement prior to the rebound (ld_final) are examined and analyzed, some of which exhibit markedly different outcomes at α = 80° compared to α≤ 60°. It has been discovered that the rebound regime occurs in most impact conditions at θeq = 160° and 140° but transitions to sliding for all α = 80° cases at θeq = 120°. When α≤ 60°, tc and ts of θeq = 160° and 140° are very close and hardly affected by Vi and α, which are generally smaller than those of α = 80°, resulting from the rapid decline of the normal impact velocity that diminishes drop deformation and prolongs drop sliding motion. Ds_max* is barely influenced by θeq but increases with Vi and D0 and decreases when α increases owing to a greater normal inertial force. ld_final generally increases with Vi, D0, and α but with different mechanisms. More importantly, the nondimensionalized parameters tc*, Ds_max*, and ld_final* are found to scale with the normal or tangential Weber numbers according to the power law, while the exponents vary with θeq and α.

Development and evaluation of a computer based test for anatomy radiographic course examination

The assessment of the anatomical radiography course is to measure the student’s ability to identify anatomy on radiographic images. Conventional paper tests have used radiographic images. The limitations of this method are the number of radiographic films and the time-consuming assessment process. This study aimed to develop a computer-based test (CBT) to multiply the instruments, store pictures, and speed up the assessment time. The CBT software can reproduce radiographic images using digital files and a feature to add overlay markers. The placement of markers is done intuitively via a user interface with drag and drop motion recognition. The CBT software also provides features for instrument bank, instrument selection and management for exams, a relational database for examinee identities and exam entries, and automatic grading. CBT development uses the Waterfall Software Life Cycle (SDLC), with black-box testing using the normal value equivalent partition method. The CBT usability test was carried out by measuring user perceptions (5 administrators and 60 students) and comparing them with conventional methods at the 95% significance level. Research time decreased significantly during instrument preparation and the assessment process. User perceptions show that 76% of students and 85% of managers give positive assessments. There is no difference between conventional and CBT assessments with a p-value = 0.067 (p-value > 0.05) so that CBT is very potential to be used as a substitute for conventional paper-based tests in examining anatomical radiography courses.

Determining minimum fluidization velocity in magnetized fluidized bed with Geldart-B particles

This work aimed to solve the controversies about defining and determining the minimum fluidization velocity (Umf) in the magnetized fluidized bed (MFB). It should be defined rigorously from the physics behind the secondary phenomena such as bed pressure drop and particle motion. Since Umf demarcates the transition from the fixed-bed to the fluidization flow regime, it could not be determined from the ΔPb–Ug↓ curve but could from the ΔPb–Ug↑ curve. Moreover, the initial fixed bed for measuring this curve must meet its definition. For the MFB with purely magnetizable particles, it could be obtained via decreasing Ug gradually from full fluidization to zero at H = 0 kA/m to minimize the wedging effect. For the MFB with magnetizable and nonmagnetizable particles, such a decrease of Ug should be quick to simultaneously minimize the wedging effect and segregation. The as-determined Umf remained invariant with H in both types of MFBs.

Algorithm for flow of highly-concentrated emulsions through a narrow constriction

A multipole-accelerated 3D boundary-integral algorithm is developed to model pressure-driven flow of a highly-concentrated emulsion of many deformable drops through a periodic channel with tight constrictions. The drops are monodisperse, free from surfactant, and the Reynolds number is small for Stokes equations to apply. The channel surface consists of four solid panels: front and back parallel to each other, and band-like top and bottom panels with an arbitrary profile. The algorithm is for arbitrary channel aspect ratios, but the results are obtained for extreme cases, when the channel depth (front-back distance) is the same as the minimum channel height and both can be much smaller than the non-deformed drop diameter, making the drops flow as a monolayer. Strong hydrodynamic interactions (especially, drop-wall) necessitate very high surface resolutions combined with novel desingularization tools for the boundary integrals. Multipole acceleration gives, at least, two orders of magnitude gain over direct summations and facilitates long-time simulations, with many drop rearrangements. Examples for homoviscous emulsions with 40-92 drops in two types of channels at 80-90% drop volume fractions and different capillary numbers demonstrate single-file drop motion intermittent with pairs or triplets of drops in the constriction. Such squeezing interactions can result in extreme drop elongations, but are still not sufficient to promote breakup for the channel geometries, capillary numbers and drop confinements considered. Integral properties (the entire drop-phase and constriction flow velocities) are also analyzed.

Динамические характеристики скорости истечения жидкости из форсунок в струйных газопромывателях целлюлозного производства

It is shown that the modern development of pulp production technology is associated with the development of gas-liquid systems equipment. Such equipment provides the main technological processes of pulp cooking and regeneration of chemical reagents. Furthermore, this equipment, designed to recover chemical reagents and reduce their emissions into the environment, is part of the technological process. The use of scrubbers in pulp production has an advantage over many other industries, since it uses a closed liquor regeneration cycle. Currently, studies of the processes occurring in scrubbers of different types are becoming more numerous and fundamental. This paper is devoted to the development of jet scrubbers. These devices have a number of properties that do not have scrubbers of other types. They do not create resistance to the gas flow in the flue; they have a gravitational property due to ejection. Only jet scrubbers create the necessary conditions for the stability of the gas flow and have a jet effect that allows to significantly increase the efficiency of emissions cleaning. To implement the jet effect and intensify the technological equipment operation it is required to describe transfer processes in jet scrubbers with regard to polydisperse structure of drop flow and features of liquid splitting up into drops by centrifugal-jet nozzles. Scientific works devoted to the problem of realization of the jet effect showed the need to study the dynamics of liquid splitting in centrifugal-jet nozzles, which create a drop-filled jet with a large opening angle. The research purpose is to study the speed of the initial movement of drops in the area immediately after the splitting section of the continuous jet of liquid flowing from the nozzle. A photographic technique with two spark lamps was used for the experiment. At the same time, the distribution of irrigation density was controlled. The results of measuring the distributions of absolute speed of drops and irrigation density were compared with each other and the function of liquid speed distribution in the cross section of the gas-liquid jet of the jet scrubber was determined. Based on the obtained data, a theoretical model was developed to determine the initial speed of drops of centrifugal jet nozzles, an indicator required for the development of new jet scrubbers. The results can be applied to improve the technological processes of pulp production.

The Terminal Velocity of Axisymmetric Cloud Drops and Raindrops Evaluated by the Immersed Boundary Method

AbstractThe terminal velocity of cloud drops and raindrops used in numerical model calculations can significantly affect weather predictions. Current formulations rely on laboratory experiments made in the 1940s and 1960s. Because these experiments were performed only at typical environmental conditions of 20°C and 1013 hPa, parameterizations have been introduced to deduce the terminal velocity aloft without rigorous evaluation. In this study, an incompressible two-phase flow direct numerical simulation model is used to calculate the free-falling motion of axisymmetric drops with diameters between 0.025 and 0.5 mm to study the terminal fall velocity. Simulated terminal fall velocities of free-falling drops at 20°C and 1013 hPa agree within 3.2% with the previous empirical parameterization (Beard formula), and 4.5% with existing laboratory data in the diameter range between 0.3 and 0.5 mm. The velocities converge to the analytic Hadamard–Rybczynski solution within 2% for small Reynolds numbers, demonstrating the robustness of our simulations. Simulations under various atmospheric conditions show that existing empirical parameterizations that account for the air density dependence of the terminal velocity have errors up to 11.8% under the conditions examined in this study. We propose a new empirical formula that describes the air density dependence of the terminal velocity. It is also shown that the falling speed of a small drop is not sensitive to shape oscillation, and the terminal velocity decreases by only less than 1.3% when the axis ratio increases by 12% with reduced surface tension. Internal circulation within falling drops is also presented and compared with previous studies.

Small-Scale Condensation Simulation on Complicated Surface

<p indent=0mm>Vapor condensation is a typical phenomenon in the nature, whose realistic simulation is of great significance to virtual reality, video effects, game entertainment, etc. Traditional physically-based methods failed to preserve the small-scale details during condensation. A novel hybrid framework combining smoothed particle hydrodynamics and adaptive fluid implicit particle method is proposed. The heat transfer of air is modeled with smoothed particle hydrodynamics, with phase transition controlled by relative humidity and dew point. The fluid implicit particle method is combined with an octree-based adaptive grid to achieve high-resolution details of small-scale drops. Finally, surface tension, adhesion and resistance are introduced to simulate the motion of drops on complicated surfaces realistically. It is demonstrated that proposed method provides plausible results of condensation on intricate surfaces efficiently through several experiments.

Correlations between air drag and movement of water droplets in fibrous media

The movement of dispersed liquid drops in fibrous media occurs in many industrial applications, such as in filtration of liquid aerosols. The process can be complex and challenging to model for predictive purposes in filter design. Often the industry relies upon experimental comparisons between filter media to determine suitable media for specific applications. Correlations for predicting drop behaviors, such as drop movement and coalescence, in filter media can reduce experimental efforts by providing a tool to estimate media performances that narrows the range of media for experimental comparison.This work in this paper focused on movement of drops due to the drag force of the flowing gas phase. A simple force balance and introduction of drag coefficient led to a correlation for estimating the drag coefficient for the average movement of drops in fiber media. Experiments were conducted to detect the movements of water drops and parameters fitted to the correlation. Experimental observations showed that the drops did not move until the drag force exceeded a minimum. A correlation was developed to relate the Reynolds number of the gas flow through the porous medium that caused the drop to move.The minimum Reynolds number correlation provides a prediction of the size of drops that can be expected to move in a fiber medium for a given flow rate of gas. The drag coefficient correlation provides for a calculation of the average velocity of the moving drops through the fiber medium. The correlations are limited to motions of single drops and do not account for other drop behaviors such as coalescence or channel flow. This work extends prior works that developed similar correlations for drops on single fibers and on surfaces of fiber mats.

A two-dimensional numerical model for the sliding motion of liquid drops by the particle finite element method

Liquid drops sliding on surfaces are ubiquitous both in the natural and industrial world. The prediction of such drop motions has far-reaching implications in many fields of application, including microfluidics, phase change heat transfer, or coating technology. We present a numerical model based on the particle finite element method for the prediction of the sliding motion of liquid drops. The model includes the effect of a retention force which acts in the vicinity of the drop's contact line. This effect is found to be essential to obtain realistic spatiotemporal evolution of the drop. Thus far limited to two-dimensional simulations, the proposed model is validated by using experimental data found in the published literature, covering a wide range of drop size and physical properties. The numerical results are found to be mesh-independent and in good agreement with the experiments.

Interfacial phenomena between molten iron and molten slag\u2013Effect of nitrogen on the Marangoni convection

In order to investigate the influence of the surface-active element on the interfacial phenomena between molten iron and molten Al2O3-CaO-SiO2 slag, a mildly surface-active element, nitrogen, was introduced, and the interfacial phenomena were directly observed using an X-ray sessile drop method. The multiphysics model was employed to calculate the velocity of the Marangoni convection caused by the surface/interfacial tension gradient along with the contour of the sessile drop. Movement of the sessile drop was observed in the experiment, and the driving force of the movement was discussed from the distribution of surface tension active element viewpoint. The calculated velocity of the Marangoni convection in the droplet was reasonably agreed with the literature data for the metal-gas system, and thus, the same model was applied for the metal-slag system. The velocity of the Marangoni convection for the metal-slag system becomes ten times lower compared to that of metal-gas system.Graphical abstract

The vortex-driven dynamics of droplets within droplets

Understanding the fluid-structure interaction is crucial for an optimal design and manufacturing of soft mesoscale materials. Multi-core emulsions are a class of soft fluids assembled from cluster configurations of deformable oil-water double droplets (cores), often employed as building-blocks for the realisation of devices of interest in bio-technology, such as drug-delivery, tissue engineering and regenerative medicine. Here, we study the physics of multi-core emulsions flowing in microfluidic channels and report numerical evidence of a surprisingly rich variety of driven non-equilibrium states (NES), whose formation is caused by a dipolar fluid vortex triggered by the sheared structure of the flow carrier within the microchannel. The observed dynamic regimes range from long-lived NES at low core-area fraction, characterised by a planetary-like motion of the internal drops, to short-lived ones at high core-area fraction, in which a pre-chaotic motion results from multi-body collisions of inner drops, as combined with self-consistent hydrodynamic interactions. The onset of pre-chaotic behavior is marked by transitions of the cores from one vortex to another, a process that we interpret as manifestations of the system to maximize its entropy by filling voids, as they arise dynamically within the capsule.