Liquid Spreading Research Articles

The thermo-viscous fingering instability of a cooling spreading liquid dome

We investigate a theoretical model of a molten viscous planar liquid dome spreading under gravity over an inclined substrate. The liquid in the dome cools as it spreads, losing its heat to the surrounding colder air and substrate. Coupled nonlinear evolution equations for the dome's thickness and temperature describing the spreading flow are derived employing the lubrication approximation. The coupling between the flow and cooling is via a temperature-dependent viscosity. For intermediate Péclet numbers, a new one-dimensional free surface shape is identified. In this solution, the hotter and more mobile liquid piles up behind the dome's colder and less mobile leading edge, forming a distinct elevated ridge at the flow front. The ridge solution is mapped in parameter space. The transverse stability of the one-dimensional ridge solution is investigated using linear stability analysis and numerical simulations. The existence of a thermo-viscous fingering instability is revealed. For this instability to occur, the presence of the ridge is shown to be necessary. Two-dimensional simulations confirm the stability analysis elucidating the underlying thermo-viscous mechanism.

Research on plated structure design in weft knitting seamless fabric and sweat management

During exercise, the degree of sweating in different parts of the body varies. The organization of different functions in different parts can be realized using weft knitting seamless technology. The advantage of this technology was that it can be one-piece woven, has high efficiency, offers environmental protection, provides superior wearing comfort, and facilitates the rapid response of sweat and sweat management in different parts. In this work, 9.33 tex/384 F yarn was selected as the face yarn, and 5.55 tex/24 F yarn was selected as the ground yarn, seven fabrics were designed using a combination of three basic plated loops. The effect of two factors, surface porosity and fabric tightness, on the sweat management performance of plated fabrics was investigated through experiments, including moisture management performance, liquid spreading performance, wicking performance, evaporation performance, air permeability and moisture permeability performance, etc. The results showed that the smaller the surface porosity of the fabric, the better the one-way transmission performance of the liquid. However, the larger the surface porosity, the easier the liquid plane diffusion was. The tightness of the yarn filling in the fabric was beneficial for the weft flow of the liquid. A certain degree of tightness was helpful for the unidirectional conduction of fluid, but both too tight and too loose fabrics were not conducive to fluid conduction. Studying the difference in performance caused by the surface porosity and the tightness of the fabric can provide some theoretical help for the design of weft-knit seamless sports products.

Analysis of high-speed drop impact onto deep liquid pool

The present work is devoted to the analysis of drop impact on a deep liquid pool, focusing on the high-energy splashing regimes caused by large raindrops at high velocities. Such cases are characterized by short time scales and complex mechanisms, thus they have received very little attention until now. The BASILISK open-source solver is used to perform three-dimensional direct numerical simulations. The capabilities of octree adaptive mesh refinement techniques enable capturing of the small-scale features of the flow, while the volume of fluid approach combined with a balanced-force surface-tension calculation is applied to advect the volume fraction of the liquids and reconstruct the interfaces. The numerical results compare well with experimental visualizations: both the evolution of crown and cavity, the emanation of ligaments, the formation of bubble canopy and the growth of a downward-moving spiral jet that pierces through the cavity bottom, are correctly reproduced. Reliable quantitative agreements are also obtained regarding the time evolution of rim positions, cavity dimensions and droplet distributions through an observation window. Furthermore, simulation gives access to various aspects of the internal flows, which allows us to better explain the observed physical phenomena. Details of the early-time dynamics of bubble ring entrapment and splashing performance, the formation/collapse of bubble canopy and the spreading of drop liquid are discussed. The statistics of droplet size show the bimodal distribution in time, corroborating distinct primary mechanisms of droplet production at different stages.

Spreading of a thin droplet on a soft substrate

A thin liquid droplet spreads on a soft viscoelastic substrate with arbitrary rheology. Lubrication theory is applied to the governing field equations in the liquid and solid domains, which are coupled through the free boundary at the solid–liquid interface, to derive a set of reduced equations that describe the spreading dynamics. Fourier transform techniques and the finite difference method are used to construct a solution for the dynamic liquid–gas and solid–liquid interface shapes, as well as the macroscopic contact angle. Substrate properties affect the spreading dynamics through the contact angle and internal droplet flow fields, and these mechanisms are revealed. Increased substrate softness increases the spreading rate, whereas increased viscoelasticity decreases the spreading rate. For the case of a purely elastic substrate, the spreading power-law exponent recovers Tanner's law in the rigid limit and increases with substrate softness.

Effects of in-nozzle liquid fuel vortex cavitation on characteristics of flow and spray: Numerical research

The current work studies the dynamics of vortex cavitation under various conditions, including the pressure and orifice number, and their effects on the nozzle flow and spray characteristics using a modified cavitation model considering the swirling flow. Its validation against experimental data has demonstrated a high precision of the code in terms of vortex cavitation inside the nozzles. The higher the inlet pressure, the higher the mass flow rate and discharge coefficient, but the weaker the vortex cavitation; while the vortex cavitation intensity decreases, the discharge coefficient increases and the mass flow rate is almost constant with increasing back pressure. Moreover, under the influence of vortex cavitation, the primary jet liquid spreading angle, spray penetration, and spray volume coefficient increase first and then decrease with increasing inlet pressure; with an increase of back pressure, however, the primary jet liquid spreading angle increases, the spray penetration vice versa. Additionally, once the inner well-organized large-scale longitudinal vortices are destroyed, the vortex cavitation will not incept, which induces a larger discharge coefficient and spray penetration, but a smaller primary jet liquid spreading angle as a result. The swirling flow in the multi-hole nozzle is inhibited; hence, vortex cavitation is difficult.

Eulerian simulations of local liquid distribution in a Trickle Bed: Effects of flow rates and liquid properties

We performed Eulerian simulations of gas–liquid flow in a Trickle Bed Reactor (TBR) to understand contributions of gas–liquid, gas–solid and liquid–solid interaction forces (F→GL,F→GS,F→LS), capillary-pressure (F→C) and mechanical-dispersion (F→D) forces to local liquid spreading and how their contributions change with changes in flow rates and physical properties. Further, we simulated effects of these parameters on pressure drop (ΔP), overall liquid hold-up (〈εL〉) and importantly on local liquid spreading and validated the predictions using measurements. We have shown that F→LS significantly contributes to local liquid spreading, ΔP and 〈εL〉, whereas F→D contributes marginally. The modified F→LS model led to satisfactory predictions of local liquid spreading, ΔP and 〈εL〉 for a wide range of fluid flow rates and physical properties and predictions are in a satisfactory agreement with the measurements. The present work is an important step in extending the CFD model for simulating reactions and heat effects in TBRs.

Shape and Stability of a Local Heat-Transfer Magnetofluid Coating on a Plate

Purpose. Investigate the shape and stability of a magnetic fluid coating on a flat surface in a non-uniform magnetic field of a permanent magnet.Methods. Magnetic fluids based on transformer oil MMT-44 and MMT-21 with saturation magnetization of 43.8 and 21.2 kA/m, respectively, were used in the experiments. A magnetic-fluid coating was formed on the surface of horizontal and vertical non-magnetic plates in a locally inhomogeneous magnetic field of permanent magnets. The source of the inhomogeneous magnetic field is a system of two rectangular magnets. The size of the magnetic system is 40×12×10 mm. The maximum values of the magnetic field strength and gradient reach 180 kA/m and 8∙104 kA/m2, respectively. The shape and stability of a sessile and suspended magnetic fluid coating were studied for various plate orientations.Results. The shape and stability of the magnetic fluid coating on horizontal and vertical plates are studied. The experimental dependences of the height and length of the coating on the volume of the magnetic fluid are established. It is established that the coating can have a certain maximum volume. When this volume is exceeded, the liquid spreads over the surface of the plate or a part of the liquid volume is separated. The limiting volume of the coating is determined by the magnetic characteristics of the ferrofluid and the magnetic field.Conclusion. The possibility of forming a sessile and suspended local magnetic fluid coating on horizontal and vertical plates is established. The height and length of the magnetic fluid coating on the plate depend on the volume of the magnetic fluid, as well as on the characteristics of the magnetic system and the magnetization of the magnetic fluid. The results obtained can be used in the formation of magnetic fluid coatings of cooled sections of heated surfaces.

Effect of contact angle on spreading of refrigerant mixture over the vertical cylinder

The paper presents 3D numerical modeling of spreading dynamics of R21 (mol. fraction: 0.9) and R114 refrigerant mixture film. We considered an outer flow along a round vertical cylinder at Reynolds numbers of 50 and 104 and contact angles of 10°, 30°, 50°, 70° and 90°. The simulation was performed in OpenFOAM software on the basis of the volume of fluid (VOF) method. Main simulated results are presented in the form of velocity fields of liquid that allow evaluating both wetting dynamics and local characteristics of the liquid film. We obtained that the contact angle has a key effect on the wetted area due to the change of liquid spreading modes over the cylinder. At that, we distinguished the following flow modes: the continuous film, the stable jet mode, the cascade jet mode, the mode of the massive jet, the jet-droplet mode and the drying mode. These modes are similar ones for horizontal tubes. In some flow modes over the vertical cylinder we demonstrated the existence of the noticeable transversal velocity at the wetting front, that leads to moving of jets sources, and the back liquid flow between jets, directed against gravity.

A numerical methodology to support the development of liquid adhesive spreading patterns on display bonding process

A numerical methodology was implemented to support the development of adhesive spreading patterns for the Optical Bonding (OB) material on display bonding process, in order to reduce the experimental trial and error effort, being this iterative process done mainly through numerical simulations. These simulations were performed using the commercial software Abaqus, more specifically the Abaqus/Explicit module, which includes the Coupled Eulerian-Lagrangian method (CEL), used in cases where extreme deformations of the material are observed. This way, it was possible to obtain a methodology capable of predicting the spreading behaviour of a predefined OB material pattern. These results were initially compared to experimental results for a simple validation case and later for two more complex real cases. The numerical approach developed provided results very close to what was observed in experimental tests. This methodology can be a useful tool to optimize OB material patterns for display bonding process, but the simulation time needed is still a concern to have in mind.

De-wetting of evaporating drops on regular patterns of triangular posts.

Directional wicking and spreading of liquids can be achieved by regular micro-patterns of specifically designed topographic features that break the reflection symmetry of the underlying pattern. The present study aims to understand the formation and stability of wetting films during the evaporation of volatile liquid drops on surfaces with a micro-pattern of triangular posts arranged in a rectangular lattice. Depending on the density and aspect ratio of the posts, we observe either spherical-cap shaped drops with a mobile three-phase contact line or the formation of circular or angular drops with a pinned three-phase contact line. Drops of the latter class eventually evolve into a liquid film extending to the initial footprint of the drop and a shrinking cap-shaped drop sitting on the film. The drop evolution is controlled by the density and aspect ratio of the posts, while no influence of the orientation of the triangular posts on the contact line mobility becomes evident. Our experiments corroborate previous results of systematic numerical energy minimization, predicting that conditions for a spontaneous retraction of a wicking liquid film depend weakly on the orientation of the film edge relative to the micro-pattern.

Dynamic and Quasi-static Droplet Penetration through Meshes.

We investigate experimentally the effects of pore size, surface wettability, and penetration mode on the characteristics of liquid penetration through meshes. Utilizing the impact of droplets and the hydrostatic pressure, we study water penetration through superhydrophobic, hydrophobic, superhydrophilic, and hydrophilic meshes with different uniform radii and pitch values of the pores. In the case of dynamic penetration enabled by the droplet impact, our results show that surface wettability has a negligible effect on either the threshold speed of the droplet penetration or the penetrating liquid mass. The threshold droplet speed is found to be mainly determined by the synergistic effects of global and local dynamic pressures of the impacting droplet, and a modified expression for the threshold droplet speed is proposed. For the quasi-static penetration based on the applied hydrostatic pressure, we find that surface wettability and pore pitch do not affect the penetration threshold pressure but do affect the pressure at which the liquid penetration ceases. This is due to the fact that under quasi-static conditions, the droplet liquid spreads out and merges with that at the adjacent pores on the mesh underside, affecting the wetted area and, hence, the capillary pressure resisting penetration.

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.

Effects of process parameters on the spreading morphology of disc surface and aluminium powder produced by centrifugal atomisation

ABSTRACT An apparatus was developed to study the effects of operating parameters on liquid spreading and particle size in centrifugal atomisation. Different areas of aluminium spreading on the surface of the rotary disc were observed, in which the diameter of the ‘Plane area’ showed a linear relationship with the rotational speed. The microscopic morphology of the aluminium powder samples was analysed by scanning electron microscopy (SEM). The variation of particle size distribution curve with rotational speed was explored, and the shape of the curve was changed from ‘Single-peak’ to ‘Double-peak’ when the rotating speed increased to a certain value. The effect of the fragmentation mode on the particle size distribution and median diameter was analysed. The variation of the median diameter of the powder with the rotating speed was obtained. The effect of different disc configurations on the particle size was obtained.

Bionic Jaw-Like Micro One-Way Valve for Rapid and Long-Distance Water Droplet Unidirectional Spreading.

A surface with asymmetric microstructures for self-driven directional spreading of liquid has attracted keen interest from researchers in recent years for its great application prospects. Inspired by the jaws of tiny insects, such as ants, a surface textured with novel jaw-like microstructures as micro one-way valves is reported. These microstructures are almost two-dimensional, thus being simple and easy to fabricate. Whereas surfaces with such jaw-like micro one-way valves exhibit amazing rapid and long-distance water droplet unidirectional spreading behaviors. The maximum forward-backward distance ratio of water droplets on surfaces with the optimized microstructures is about 14.5, almost twice those of previous research. The capillary attraction at the location of the mouth of the jaws and the pinning effect brought by the sharp edge of the jaws for the precursor film are analyzed and deduced as the main mechanisms. The findings open a promising avenue for 2D asymmetric microstructure design and effective self-driven liquid unidirectional spreading.

Wall reduction and heat transfer characteristics of captured iron ore particles during flash ironmaking process

ABSTRACT The wall reaction and heat transfer characteristics of captured particles in the flash ironmaking reactor are essential to the reduction degree and liquid phase flow. In-situ studies of near-wall reduction were conducted using a high-temperature hot-stage microscope. Furthermore, a mathematical model was established for analyzing heat and mass transfer in iron ore particles. Results showed that above 1642 K, haematite particles partially melted, forming a bilayer structure with a molten ring and unmolten core as the liquid intermediate product spread rapidly. Higher gas flowrates prolonged melting product diffusion time. The liquid intermediate product volume predicted by the mathematical model matched well with the experimental data. Computational analysis revealed fluctuating particle temperatures during the reaction process, with the degree influenced by the reaction rate. Fluctuations increased with higher CO gas flowrate, particle size, and gas temperature, with gas temperature being the most influential factor.

Numerical study on the effects of bund on liquid pool spreading and vapor dispersion after a catastrophic LNG tank failure

Liquefied natural gas (LNG) storage tanks are usually equipped with bunds to provide an additional layer of protection. However, the catastrophic failure of an LNG storage tank usually results in a bund overtopping. The overtopped LNG will evaporate rapidly at ground surface to form the flammable gas cloud. Previous studies have developed computational fluid dynamics (CFD) models to investigate the ability of bunds to retain liquids; However, the models were developed based on ambient liquid, ignoring the evaporation phenomena and vapor dispersion of LNG. In this work, a multiphase CFD model which integrated with the evaporation model was proposed to simulate the complete overtopping process (including LNG overtopping, LNG spread, LNG evaporation and vapor dispersion). The data from two field experiments were used to validate the model. In addition, this paper studied a case of catastrophic failure that derived from an industrial LNG Tank. The effect of the bund configurations on the wind flow field, the overtopping fraction, the spread of LNG and the dispersion of LNG vapor cloud was analyzed. The present work can help relevant personnel to better assess the engineering risks associated with catastrophic failure of storage tanks for decision making in the process safety framework.

Numerical study of the process of liquid droplets impacting the curved wall surface

The impact of droplets on the solid wall is a typical free surface flow phenomenon that widely exists in nature, industry, and daily life. According to the change of the droplet’s center thickness, the droplet, the spreading process of the droplet is usually divided into three unique stages: the initial droplet deformation stage, the inertia-dominated stage, and the viscosity-dominated stage with the increase of the impact time. The problem of the liquid droplet spreading under different impact conditions is simulated by the smoothed particle hydrodynamics (SPH) method. Firstly, the dynamic process of droplet spreading is simulated and compared with relevant experimental results to verify the effectiveness of the proposed method. Then, the effects of the Weber number and the diameter ratio of the droplet to the curved wall surface on the droplet’s maximum spreading diameter and central thickness were studied and analyzed. On this basis, the key coefficient in the existing relationship between the Weber number and maximum spreading diameter is fitted. Finally, the fitting equation of the center thickness and the impact time in the third stage of droplet spreading is assessed.

Directional Superspreading of Water Droplets on Grooved Hydrogel Surfaces for Open Microfluidic Platforms.

Directional liquid spreading has an irreplaceable role in applications such as microfluidic devices, disposable biosensors, and point-of-care diagnostics. However, how to achieve directional, rapid, and complete spreading (i.e., superspreading) of liquids without external energy input is a great challenge. Herein, inspired by the peristome surface of Nepenthes pitcher, the directional superspreading of water droplets on hydrogel surfaces with predesigned microchannels by using the synergistic effect of the liquid-like property of hydrogels and the guidance of anisotropic microstructures is reported. Compared with the smooth ones, hydrogel surfaces with isotropic microstructures can facilitate the superspreading of water droplets, which can be realized within 500ms in the absence of external forces. Furthermore, directional superspreading and the flow of water droplets are realized under the guidance of anisotropic microgrooves. Such a unique spreading behavior can also be observed on the hydrogel surfaces with various shaped microchannels, such as periodic, bent, shunted, divergent, and confluent morphologies, which have potential for the development of open microfluidic platforms for various healthcare-related applications.

Liquid Superspreading on Surface with Microhexagonal Structure Inspired by Rock‐Climbing Fish

The dynamic spreading mechanism of liquid on a specific surface is vital for understanding interface wetting and antifouling. Whereas, how to control the spreading process and accelerate the spreading speed is a major challenge. The rock‐climbing fish is characterized by its alepidote feature that lives in stream habitats dominated by strong currents. The mucus on its body surface plays a vital role in its adherence and maintenance of antifouling and antibacterial properties. However, the rapid, uniform, and efficient spreading mechanism of mucus on the fish body surface remains largely unknown. Herein, it is revealed that the surface of the rock‐climbing fish is overlaid fully by the microhexagonal texture structure. This hexagonal structure shows a superspreading effect on liquid diffusion, resulting from testing with bionic microfabrication inspired by the rock‐climbing fish. It is demonstrated that the microhexagonal‐textured surface can enhance liquid spreading quickly and evenly on the surface by regulating the moving contact line of the liquid. This kind of superspreading mechanism has great potential applications in the antifouling, electroencephalogram electrode interfaces, flexible skin sensors, and interfacial lubrication of underwater surfaces.

Cleaning testing of nineteenth-century plaster surface models with thin polyacrylamide-based gel layers attached to flexible polyethylene films

This paper explores the cleaning efficacy of polyethylene-supported 15-min photo-crosslinked poly (acrylamide-co-benzophenone) surface-attached gels (SAGs) on gypsum plaster surface models inspired by nineteenth-century casts. Cleaning tests were performed on plaster surface models with and without organic and inorganic coatings, which had been exposed to accelerated ageing by heat, humidity, and light after artificial soiling. The specific types of SAG systems were selected based on their water loading and dehydration capacities. The SAGs were loaded with customized solutions and applied on the plaster models for one minute. Cleaning efficacy was evaluated with visible reflectance, UV fluorescence photography, scanning electron microscopy, colorimetry, UV/Vis spectrophotometry, glossimetry, high resolution 3D microscopy, attenuated total reflection Fourier transform infrared spectroscopy and 2D Fourier transform infrared imaging. The SAGs provided fast and minimal wetting of the substrates, prevented excessive liquid spreading and allowed the effective liquid contact with the soiled gypsum plaster surface. A striking removal of soils from the gypsum plaster surface models was observed, which suggests convenient application of the SAG systems for the cleaning of historical plaster objects.