Formation Of Liquid Bridges Research Articles

Dynamic analysis of adsorbate behavior in nanopores: Liquid bridge formation, cavitation, and contact angle evaluation via molecular dynamics simulations

To explore the internal transport mechanisms and evolutionary processes within nanopore, molecular dynamic simulations were employed to explore the formation of liquid bridges and the evolution of menisci. The adsorption–desorption isotherms were obtained, and the dynamic behavior of the adsorbate was analyzed. Results revealed two distinct processes governing the behavior of the adsorbate within nanopore. At low pressure ratios, a molecular adsorption layer initially grows continuously on the pore surface. As the pressure ratio increases, an additional mechanism emerges, characterized by the formation of a liquid bridge near the nanopore mouth. This leads to pore filling as the liquid bridge expands and retreats towards the pore’s closed end. During desorption, cavitation occurs, which can be characterized as an activation process. Once initiated, cavitation intensifies, progressively increasing the number of cavities. The convergence of these cavities undermines the stability of the liquid bridge, ultimately resulting in its collapse and the rapid evaporation of the adsorbate molecules. Additionally, we further calculated the contact angle at the vapor–liquid interface using the Kelvin equation. The results indicated a deviation of less than 5 % compared to our simulations, suggesting that the Kelvin equation is applicable for materials with pore sizes of at least 3.6 nm.

Dedusting and inhibition of methane-coal dust hybrid explosion by ultrafine water mist containing SDS surfactant

The dust reduction and inhibition effects of ultrafine water mist containing SDS anionic surfactant on methane-coal dust explosion were experimentally investigated. Compared with pure ultrafine water mist, the Pmax and (dP/dt) max of 0.5% SDS water mist were reduced by 9.18% and 27.2%, respectively, and the explosion induction period was prolonged from 102 ms to 205 ms. SDS water mist can effectively inhibit the intensity and propagation of the flame, forming the formation of irregular fronts and unevenly colored orange flames after multiple extinguishments in the explosion induction period. In addition, the addition of SDS surfactant promotes the formation of liquid bridges between water mist and coal dust particles. The contact angle of coal dust is reduced by 38.9% and the sink time is reduced to 30 ms. This paper presents a new direction and choice for achieving simultaneous dust reduction and explosion suppression in coal mines.

Modes of Nanodroplet Formation and Growth on an Ultrathin Water Film.

Using nanobubbles as geometrical confinements, we create a thin water film (∼10 nm) in a graphene liquid cell and investigate the evolution of its instability at the nanoscale under transmission electron microscopy. The breakdown of the water films, resulting in the subsequent formation and growth of nanodroplets, is visualized and generalized into different modes. We identified distinct droplet formation and growth modes by analyzing the dynamic processes involving 61 droplets and 110 liquid bridges within 31 Graphene Liquid Cells (GLCs). Droplet formation is influenced by their positions in GLCs, taking on a semicircular shape at the edge and a circular shape in the middle. Growth modes include liquid mass transfer driven by Plateau-Rayleigh instability and merging processes in and out-of-plane of the graphene interface. Droplet growth can lead to the formation of liquid bridges for which we obtain multiview projections. Data analysis reveals the general dynamics of liquid bridges, including drawing liquids from neighboring residual water films, merging with surrounding droplets, and merging with other liquid bridges. Our experimental observations provide insights into fluid transport at the nanoscale.

Factors Influencing Food Powder Flowability

The flowability of food powders is a critical determinant of their processing efficiency, product quality, and overall operational success. This review delves into the intricacies of powder flowability, elucidating the factors that govern it and exploring various methods for its evaluation and enhancement. Particle size and distribution, particle shape, surface properties, moisture content, and storage conditions stand as the key determinants of powder flowability. Finer powders, with their increased interparticle cohesive forces, tend to exhibit poorer flowability. Particle shape also plays a role, with irregular or elongated particles flowing less readily than spherical ones. Surface properties influence interparticle friction, thereby impacting flow behavior. Moisture content significantly affects flowability, as increased moisture can lead to liquid bridge formation, hindering powder movement. Storage temperature, on the other hand, generally enhances powder flow due to reduced interparticle cohesive forces at higher temperatures. This highlights the need to understand the factors influencing food powder flowability and to employ appropriate evaluation strategies for optimizing food powder processing efficiency, product quality, and overall production success.

Rebound dynamics of two droplets asymmetrically impacting single-ridge superhydrophobic surfaces

On a single-ridge superhydrophobic surface, the rebound dynamics of double droplet impacts is investigated via lattice Boltzmann method (LBM) simulations, where one droplet is on the left of macro-ridges, whereas the other droplet being on the top of macro-ridges, leading to the asymmetrical impact of double droplets. The simulation results show that under different impact conditions of various Weber numbers, that is, at low, moderate and high Weber numbers, the rebound regime of double droplet impacts always consists of the complete-coalescence-rebound (CCR), partial-coalescence-rebound (PCR) and coalescence-split-rebound (CSR) regimes. Under these three rebound regimes, the contact time of double droplet impacts is always reduced by the increased We, as the center-to-center distances in the horizontal and vertical directions, Lx and Lz, are constant. At constant Lx and We, the contact time of double droplet impacts on single-ridge superhydrophobic surfaces is increased by the increased Lz because of the earlier formation of liquid bridges at larger Lz. But under different impact conditions of various center-to-center distances in the horizontal direction, that is, at the increased Lx, the rebound regime of double droplet impacts is not always composed of the CCR, PCR and CSR regimes at low, moderate and high Weber numbers. At constant We and Lz, both coalescence strength and rebound regime are significantly affected by the increased Lx for double droplet impacts. So that the contact time of double droplet impacts on singe-ridge superhydrophobic surfaces depends on the center-to-center distance in the horizontal direction, that is, in the x- direction.

Experimental investigations of liquid bridge rupture between a sphere and a spherical concave

The formation and rupture of liquid bridges between solid surfaces have widespread applications in micro gripping, self-alignment, and particles wetting. The axisymmetric liquid bridge rupture between a sphere and a spherical concave is systematically investigated in this study. Detailed analysis was conducted to examine the effects of the radius ratio, liquid bridge volume, and contact angles on the rupture distance and transfer ratio. When the radius ratio is smaller than 2, it exerts a substantial impact on the rupture distance and transfer ratio. The experimental studies support the effectiveness of the simulation modeling based on a minimal energy approach. Theoretical findings of the shooting method and simulated results exhibit great agreement. The maximum absolute errors for rupture distance and transfer ratio were 0.001 and 0.0175, respectively. The simulated and theoretical results are helpful to predict the rupture distance and transfer ratio.

Effect of Wax on Cohesive Behavior of Gas Hydrate under High Pressure

In the deep-sea crude oil pipeline, the formation of hydrates and the deposition of wax will cause pipeline blockage under adverse conditions. Moreover, the interaction of wax and hydrates will lead to a higher tendency of pipeline blockage, which will pose a huge threat to the transportation of crude oil on the sea floor. In order to clarify the effect of wax on cohesive behavior of gas hydrate, the gas hydrate particles were used as experimental particles to measure the adhesion force between particles in the wax-free system and the wax-containing system directly, and then, the effect of wax on the adhesion force between particles was compared and analyzed. The results showed that wax can destroy the shell structure of hydrate particles, resulting in easier formation of liquid bridges and significantly enhanced adhesion force. Therefore, the adhesion force in the wax-containing system would be significantly greater than that in the wax-free system. In addition, by comparing the adhesion force of different hydrate particles in contact with wax particles, it was found that under high pressure, the precipitation of wax may first cause the agglomeration of CH4 hydrate. Finally, by analyzing the adhesion force and particle morphology at different wax concentrations, the influence mechanism of wax on hydrate cohesion behavior was proposed. This study provides a theoretical basis for eliminating or reducing the blockage of deep-sea crude oil pipelines.

Sintering inhibition and oil-absorption properties of calcined coal-series kaolin

AbstractIn this study, aluminium fluoride trihydrate (AlF3⋅3H2O) was used to inhibit the sintering of calcined coal-series kaolin (CCSK). In addition, the oil absorption properties of CCSK were studied. The particle-size distribution, specific surface area and porosity of the samples were investigated as a function of calcination temperature and the addition of AlF3⋅3H2O. Moreover, the ability of AlF3⋅3H2O to improve the oil absorption of CCSK was explored. The morphology, structure and phase composition of the specimens were investigated using scanning electron microscopy and X-ray diffraction. The phase transition during heating of the samples was studied using thermogravimetric analysis. The preparation with 10 wt.% AlF3⋅3H2O had the optimal sintering inhibition effect on CCSK at 1000°C. The release of SiF4 gas during heating and the formation of mullite whiskers on the particle surface caused by AlF3⋅3H2O moderated the formation of molten-phase liquid bridges between particles and inhibited sintering of the raw material powder. Furthermore, the formation of submicron mullite whiskers on the surface of the CCSK particles enhanced the oil-absorption properties of the sample significantly.

Predicting the thermal conductivity of unsaturated soils considering wetting behavior: A meso‑scale study

Unsaturated soils are three-phase porous materials that consist of the solid phase, the liquid phase and the gas phase. While accurate predictions to the thermal conductivity of unsaturated soils are crucial for the analysis and design of geothermal systems, the distribution characteristics of the different phases can also significantly affect the thermal performance. In addition, the fact that soils are heterogeneous materials also adds to the challenges in the evaluation of the thermal conductivity of unsaturated soils. In this paper, a methodology is proposed to calculate the thermal conductivity of unsaturated soils. This methodology starts from identifying representative soil parameters based on microscopy images of soil specimens. The meso‑structures that consist of the different phases are then reconstructed in a finite-element model based on the identified characteristics. The Monte-Carlo-based finite-element analyses are then carried out to calculate the thermal conductivity of unsaturated soils while considering the wetting behavior between the solid and liquid phases, which is characterized using the hydrophilia coefficient. After validating the methodology using both the experimental and numerical results reported in the literature, a parametric analysis is conducted. The results indicate that a high quartz content improves the heat transfer, but the quartz content does not affect the heat transfer skeleton. Furthermore, an increase in the solid content and degree of saturation results in an increase in the density of the heat transfer skeleton, which leads to enhanced heat transfer efficiency. A reduction in the hydrophilia coefficient and the formation of liquid-bridges have a similar effect. Last, the effects of wetting are more evident in soils with high porosity and a low degree of saturation.

Agglomeration behavior of the dense medium in a gas–solid separation fluidized bed

In this study, the atomic force microscopy (AFM) was used to measure the micro-forces between different particles and study the influence of different operating parameters on the formation of particle clusters in the gas–solid fluidized bed separation process. In this way, the mechanism of liquid bridge formation and fracture can be elucidated, thereby providing a theoretical basis for inhibiting the formation of particle clusters. The results indicated that for relative humidity (RH) < 40%, the extrusion liquid bridge is the dominant factor for the formation of the particle liquid bridge, and the liquid film thickness, h, and liquid film volume, Vsq, vary linearly with RH; however, once the RH is > 40%, these relationships become nonlinear. The adhesion force between magnetite powder particles was found to be the largest and that between pulverized coal particles was found to be the smallest, with the mixture of the two particle types being in between. Further, the adhesion between particles increased monotonically with RH, while showing a maximum value with increasing particle separation. A theoretical analysis of the critical fracture distance, Drupture*, of the particle liquid bridge showed that, as the liquid bridge volume, V*, and contact angle, θ, increase, Drupture* gradually increases, but its rate of increase rate. The theoretical analysis was found to be largely consistent with the experimental data, only deviating at low RH.

Effectiveness of organic solvents for recovering collapsed PDMS micropillar arrays.

Polydimethylsiloxane (PDMS) micropillar arrays are widely used in research labs and engineering fields as analytical tools for various purposes. When the micropillar length or density surpasses a critical value, micropillars tend to collapse with each other and become unusable. Restoring collapsed PDMS micropillars typically involves the use of low surface tension solvents and ultrasound sonication, but such approach has received little success to date. In this work, we examined the effectiveness of different types of solvents for restoring collapsed PDMS micropillar arrays and show that the swelling ratio of PDMS in selected solvents constitutes an important factor in the effectiveness of restoring collapsed PDMS micropillars. Our results could be a promoter in recycling PDMS micropillar arrays and achieving economic and social benefits.

Influence of moisture content on die filling of pharmaceutical powders

Flow performance of pharmaceutical powders dictates various manufacturing processes, such as blending, filling and tableting, and is determined by not only material properties but also environmental conditions, such as relative humidity and temperature. In this study, the effect of moisture content on flow performance of two commonly used pharmaceutical excipients (mannitol and dicalcium phosphate anhydrous) during die filling was investigated. A rotary die filling system was employed and the die filling efficiency was assessed using the concept of critical filling velocity. Powder flowability was also characterised using a dynamic flow tester and a shear cell tester. It was found that, with increasing moisture content, the flow parameters, including the basic flow energy, the average pressure drop and the cohesion, increased first and then decreased from a maximum at 50% relative humidity (RH). For both mannitol and dicalcium phosphate anhydrous (DCPA), when the relative humidity is high (say >50%) and the cohesion due to the formation of liquid bridges dominates, the critical filling velocity increases as the moisture content increases. While at a low relative humidity (e.g. 15%), a strong electrostatic attraction between particles was observed, which has a significant impact on the flow properties and the die filling performance of the powders.

Comparing wire-mesh sensor with neutron radiography for measurement of liquid fraction in foam

The liquid fraction of foam is an important quantity in engineering process control and essential to interpret foam rheology. Established measurement tools for the liquid fraction of foam, such as optical measurement or radiography techniques as well as weighing the foam, are mostly laboratory-based, whereas conductivity-based measurements are limited to the global measurement without detailed spatial information of liquid fraction. In this work, which combines both types of measurement techniques, the conductivity-based wire-mesh sensor is compared with neutron radiography. We found a linear dependency between the liquid fraction of the foam and the wire-mesh readings with a statistical deviation less than 15%. However, the wire-mesh sensor systematically overestimates the liquid fraction, which we attribute to liquid bridge formation between the wires.

Magnet-actuated loading of magnetic conductive high-viscosity droplets

The dispensing resolution of high-viscosity magnetic conductive adhesives is essential for the bonding of magnetic components. Here, a novel magnet-actuated loading method based on transfer printing is proposed. The core of the loading method is the forming and breaking of a cone-shaped liquid bridge. The complete loading process is simulated using a computational fluid dynamic technique. With the homemade device and electromagnetic needle-stamp, the loading process is experimentally investigated. According to the results, magnetic flux intensity, viscous force, and surface tension together dominate the formation of the cone-shaped liquid bridge from an adhesive film. For the formed cone-shaped liquid bridge, its geometry size is dominated by magnetic flux intensity, which is controlled by the variation of the initial distance between the needle-stamp and the adhesive film. As the initial distance decreases, the top area of the liquid bridge on the needle-stamp correspondingly increases and the adhesive effect on the needle-stamp gradually strengthens. After the liquid bridge breaking, the volume of loaded droplets adhering to the needle-stamp gradually increases from about 0.11 to 1.41 nL with the standard deviations less than 0.08. Moreover, these loaded droplets are transferred to the substrate by the microforce feedback, and a transferred droplet with a minimum area of about 0.01 mm2 is obtained. The presented method gets rid of the limitation of submicron needle-stamps, realizes the loading of sub-nL high-viscosity droplets, and has great potential in microdispensing and other related techniques.

Evaluation of Time Consolidation Effect of Pharmaceutical Powders.

We aim to perform a systematic study of the time consolidation effect, i.e. the reduction of powder flowability resulting from at-rest storage, on a diverse array of pharmaceutical powders under different stress, humidity, and length of time. A ring shear cell-based methodology was employed. An instantaneous flow function was obtained, followed immediately by at-rest consolidation at precisely controlled humidity, stress, and duration. The consolidated powder was then subjected to shear-cell measurement. The difference in flowability between the immediate and consolidated specimens were attributed to the time consolidation effect. Among the six excipients tested, three exhibited time consolidation at varying extents. Citric acid and starch underwent time consolidation only at high relative humidity (RH = 75%), promoted by vapor condensation and liquid bridge formation. For both materials, the flowability decreased with time, and the extent of time consolidation was not sensitive to the stress applied (0.4-2kPa). Importantly, mannitol was found to time consolidate under both 50% and 75% RH. Given time, mannitol formed cake, giving rise to flow function below unity. Inverse gas chromatography analysis indicated that mannitol possesses high total surface energy among known pharmaceutical powders. While time consolidation is prevalent among pharmaceutical powders, most can be mitigated by controlling the RH to below 75%. Notably, for materials possessing high surface energy, such as mannitol, time consolidation could occur at ambient humidity. Therefore, it is desirable to consider in-depth time consolidation evaluation for high surface energy powders, e.g. those subjected to milling or of amorphous nature.

Effect of Surfactants with Different Hydrophilic–Lipophilic Balance on the Cohesive Force between Cyclopentane Hydrate Particles

Effective control of the cohesive force between hydrate particles is the key to prevent their aggregation, which then causes pipeline blockage. The hydrophilic–lipophilic balance (HLB) value of surfactants was proposed as an important parameter for the evaluation and design of hydrate anti-agglomerants. A microscopic manipulation method was used to measure the cohesive forces between cyclopentane hydrate particles in the presence of Tween and Span series surfactants with different HLB values; moreover, the measured cohesive force was compared with the results of calculations based on the liquid bridge force model. Combined with the surface morphology and wettability of the hydrate particles, we analyzed the mechanism by which surfactants with different HLB values influence the cohesion between hydrate particles. The results show that for both Tween (hydrophilic, HLB &gt; 10) and Span (hydrophobic, HLB &lt; 10) surfactants, the cohesive force between cyclopentane hydrate particles decreased with decreasing HLB. The experimental results were in good agreement with the results of calculations based on the liquid bridge force model. The cohesive force between hydrate particles increased with increasing concentration of Tween surfactants, while in the case of the Span series, the cohesive force decreased with increasing surfactant concentration. In the formation process of cyclopentane hydrate particles, the aggregation of low-HLB surfactant molecules at the oil–water or gas–water interface increases the surface roughness and hydrophobicity of the hydrate particles and inhibits the formation of liquid bridges between particles, thus reducing the cohesion between particles. Therefore, the hydrate aggregation and the associated blockage risks can be reduced.

Solid bulk cargo liquefaction: Stability of liquid bridges

This work focuses on investigating the correlation between the evolution of liquid bridges and moisture migration in solid bulk cargo liquefaction. We experimentally investigate the stability of liquid bridges in static and dynamic particles. The liquid-holding capacity of static particles is determined, and the formation and fracturing of liquid bridges are related to the particle distribution and particle radius. The spacing of the bottom particles determines the maximum liquid-holding capacity, while the space between the upper particles and the bottom particles determines the fracture position. The particles with larger radii have an increased liquid-holding capacity and a low volumetric moisture content, which confirms that cargo that consists entirely of large particles would be apt to have seepage and would not liquefy. Moisture migration for pendular and funicular liquid bridges during stretching and squeezing is captured. We indicate that the fusion behavior of liquid bridges is an important inducement for moisture migration, and it dramatically decreases the liquid-holding capacity. The findings suggest that cargo with low water content would still cause liquefaction, and that the water content should be reduced further for the safe transport of solid bulk cargo.

The Effective Thermal Conductivity of Unsaturated Porous Media Deduced by Pore-Scale SPH Simulation

The smoothed particle hydrodynamics (SPH) method was employed to simulate the heat transfer process in porous media at the pore scale. The effective thermal conductivity of a porous medium can be predicted through a simulation experiment of SPH. The accuracy of the SPH simulation experiment was verified by comparing the predicted values with reference values for ideal homogeneous media and multiphase layered media. 3D simulation experiments were implemented in granular media generated by the PFC method. Based on the SPH framework, a concise method was proposed to produce unsaturated media by simulating the wetting process in dry media. This approach approximates the formation of liquid bridges and water films on granules. Through simulation experiments, the empirical formula of the variation in thermal conductivity with the degree of saturation was tested. The results showed that the reciprocal of the normalized thermal conductivity and the reciprocal of the saturation are linearly related, which is in line with the empirical formula proposed by Cote and Konrad.

One-Step Fabrication of Hot-Water-Repellent Surfaces.

Hot-water repellency is of great challenge on traditional superhydrophobic surfaces due to the condensation of tiny droplets within the cavities of surface textures, which builds liquid bridges to connect the substrate and hot water and thus destroys the surface water-repellence performance. For the unique structural features and scales, current approaches to fabricate surfaces with hot-water repellency are always complicated and modified by fluorocarbon. Here, we propose a facile and fluorine-free one-step vapor-deposition method for fabricating excellent hot-water-repellent surfaces, which at room temperature even repel water droplets of temperature up to 90 °C as well as other normal-temperature droplets with surface tension higher than 48.4 mN/m. We show that whether the unique hot-water repellency is achieved depends on a trade-off between the solid–liquid contact time and hot-vapor condensation time, which determines the probability of formation of liquid bridges between the substrate and hot-water. Moreover, the designed surfaces exhibit excellent self-cleaning performance in some specific situations, such as oil medium, hot water and condensation environments. We envision that this facile and fluorine-free strategy for fabricating excellent hot-water-repellent surfaces could be valuable in popularizing their practical applications.

CFD modeling of droplet permeability in fluidized beds

The deposition of droplets of size [5–22] μm on the surface of particles in a gas–solid fluidized bed has been investigated employing a one-way coupled CFD-DEM modeling. In this approach the gas phase is solved as a continuum and the free-droplets are solved as Lagrangian objects, while solid particles are assumed to be stationary and act as an obstacle for the fluid flow.In this way, it was possible to calculate the deposition factor, defined as the ratio of droplets deposited on the surface of the particles to the number of droplets injected into the domain as a function of the droplet Stokes number and particle Reynolds number. An empirical correlation was developed that describes the deposition factor as a function of the operating conditions, which is valid for the inertial regime where effects of Brownian motion can be neglected.The final goal of this investigation is to employ the developed correlation in a larger scale CFD-DEM model describing a polymerization fluidized bed reactor operated in condensed mode, i.e. by injecting liquid into the gas–solid suspension through the gas distributor plate or via nozzles in order to improve the heat management. In this kind of modeling the free-droplets phase is described as a continuum and the deposition rate of droplets determines the amount of liquid on the particle surface, which affects for the hydrodynamic (i.e. formation of liquid bridges between particles) and thermal behavior (i.e. liquid evaporation, kinetic and subsequent cooling effect) of the system.