Effect Of Particle Wettability Research Articles

A numerical study on the effect of particle surface wettability on homogeneous and heterogeneous condensation processes in supersonic flows

Supersonic separators are an emerging device for processing natural gas impurities. Natural gas contains solid particulate impurities in addition to gaseous impurities, which can trigger heterogeneous condensation within the supersonic separator. There is a lack of research on the effect of particle wettability on supersonic condensation flow, although there have been studies on the effect of particle surface wettability on heterogeneous condensation in this area. Therefore, in this paper, the supersonic condensation flow is modeled considering the contact angle, and the effects of particle contact angle on heterogeneous condensation and homogeneous condensation are investigated separately. The results show that homogeneous condensation is inhibited and heterogeneous condensation is promoted by decreasing the particle contact angle. The reason is the smaller contact angle leads to the reduction of the free energy barrier for heterogeneous nucleation, which makes the conditions for heterogeneous nucleation lower and condensation more likely to occur.

Molecular dynamics study of water molecules nucleation for fine particle removal: Effects of wettability and aggregation modes and comparison with experiment

Water vapor nucleation on particle's surface plays an important role in dust removal, cloud formation, and particle measurement. However, the selectivity of nucleation sites and the nucleation characteristic of water molecule on the particle's surface are still unclear, especially for the aggregated particles. In this paper, the effects of particle wettability and aggregation modes on the selectivity of nucleation sites and the nucleation characteristics were investigated using molecular dynamics simulation. The results were compared with our earlier experimental findings. It illustrates how the contact angle of clusters, the growth velocity, and the growth duration are all influenced by the interaction coefficient between water and particles. Moreover, the nucleation sites of water molecules on the particle aggregation surface exhibit a definite selectivity. The primary indicator of this selectivity is the preferential nucleation of water molecules at the interfaces of linear chain aggregation particles, at the inner side of non-linear chain aggregation particles, and at the centers of ring aggregation. These results are in good agreement with our previous experimental findings. More significantly, additional research has revealed that subcritical-size clusters typically aggregate on two-particle surfaces spacing when the spacing smaller than the critical cluster size.

Effects of particle wettability and water moisture on separation efficiency and drop size distribution of particle-laden droplets in oil

Solid/oil separation is widely used in various industrial fields. Conventional methods can effectively separate solids with large particle sizes from oil media; however, removing fine solids using these methods remains challenging. Researchers have attempted to remove fine particles by applying wettability modification, interface capture, and sedimentation, but these methods have several disadvantages and exhibit low efficiency. The relationship between wettability, solid removal rate, and drop size distribution variation of particle-laden droplets remains unclear. Herein, we propose the application of a centrifugal field to enhance the water-based “forth flotation” and investigate its separation characteristics experimentally. Separation experiments under gravity and centrifugal conditions were performed, and the sedimentation of particle-laden droplets dispersed in oil was conducted. The effects of wettability and initial water moisture on separation efficiency were explored, and the solid/oil separation mechanism was analyzed. The variation in the drop size distribution under different conditions was evaluated, and a mathematical relation for predicting the initial average drop size of particle-laden droplets was fitted. In addition, the fitted mathematical expression can be utilized to predict the initial average drop size of particle-laden droplets.

A reusable electret filter media based on water droplet charging/cleaning

Electret filter media has been considered as the most effective and economical filtration material due to its additional electrostatic filtration effect. However, the regeneration and recycling of electret filter media is a great challenge, as its stored charge would dissipate during filtration process, resulting in a significant efficiency reduction after cleaning. To address this problem, based on liquid–solid contact electrification (C-E) theory and self-cleaning property of hydrophobic surface, we successfully designed and fabricated a reusable PTFE electret filter membrane. After water droplets charging/cleaning, the surface charge of the membrane can be recovered to 100–110%, and the pressure drop can be restored to > 93%, exhibiting an excellent regeneration performance. Then the effect of particle wettability on cleaning performance was investigated. The hydrophilic PM2.5 on hydrophobic surface was found to be easier to clean by droplets rolling than the hydrophobic PM2.5 due to its stronger adhesion to the droplets. Furthermore, based on the theory of ion transfer at the solid–liquid interface, the charge evolution of the hydrophobic PTFE surface during the triboelectric electrification of water droplets was modeled. The rate of ion transfer between water droplets and hydrophobic surfaces depends linearly on the actual liquid–solid contact area. The charge saturation value of a solid surface is related to its ionic binding sites and the dielectric properties. The study promotes the development of reusable electret filters, and advances the understanding of the triboelectric properties of droplets on hydrophobic surfaces.

Effects of Particle Combinations With Different Wettability on Foam Structure and Stability

Particle addition is an important method to prepare foam metal, and it is of great significance to clarify the mechanism of particle stabilizing liquid metal foam. In this paper, ethanol-water solution system is used to simulate liquid melt foam. By changing the wettability of particles to adjust the distribution position of particles in foam, two types of particles with different wettability are added, which are mixed and optimized in a certain proportion to improve the foam stability as much as possible. The main mechanism is that the large wetting angle particles at the gas-liquid interface to slow down the gas migration, while small wetting angle particles exist in the liquid film, which can reduce the liquid drainage velocity. The experimental results show that the effect of particle wettability on foam structure is greater than that on viscosity enhancement. The particles with large wetting angle are beneficial to the formation and stability of foam, and the particles with small wetting angle cannot stabilize the foam alone. The effect of two types of particle combinations with different wettability on foam stability is better than that of single type of particle. Considering the height and uniformity of the foam structure, the optimal particle combination is finally obtained.

Effect of Particle Wettability and Particle Concentration on the Enzymatic Dehydration of n‐Octanaloxime in Pickering Emulsions

AbstractPickering emulsion systems have emerged as platforms for the synthesis of organic molecules in biphasic biocatalysis. Herein, the catalytic performance was evaluated for biotransformation using whole cells exemplified for the dehydration of n‐octanaloxime to n‐octanenitrile catalysed by an aldoxime dehydratase (OxdB) overexpressed in E. coli. This study was carried out in Pickering emulsions stabilised solely with silica particles of different hydrophobicity. We correlate, for the first time, the properties of the emulsions with the conversion of the reaction, thus gaining an insight into the impact of the particle wettability and particle concentration. When comparing two emulsions of different type with similar stability and droplet diameter, the oil‐in‐water (o/w) system displayed a higher conversion than the water‐in‐oil (w/o) system, despite the conversion in both cases being higher than that in a “classic” two‐phase system. Furthermore, an increase in particle concentration prior to emulsification resulted in an increase of the interfacial area and hence a higher conversion.

Effect of Particle Wettability and Particle Concentration on the Enzymatic Dehydration of n-Octanaloxime in Pickering Emulsions.

Pickering emulsion systems have emerged as platforms for the synthesis of organic molecules in biphasic biocatalysis. Herein, the catalytic performance was evaluated for biotransformation using whole cells exemplified for the dehydration of n‐octanaloxime to n‐octanenitrile catalysed by an aldoxime dehydratase (OxdB) overexpressed in E. coli. This study was carried out in Pickering emulsions stabilised solely with silica particles of different hydrophobicity. We correlate, for the first time, the properties of the emulsions with the conversion of the reaction, thus gaining an insight into the impact of the particle wettability and particle concentration. When comparing two emulsions of different type with similar stability and droplet diameter, the oil‐in‐water (o/w) system displayed a higher conversion than the water‐in‐oil (w/o) system, despite the conversion in both cases being higher than that in a “classic” two‐phase system. Furthermore, an increase in particle concentration prior to emulsification resulted in an increase of the interfacial area and hence a higher conversion.

Effect of particle wettability on the hydrodynamics of three-phase fluidized beds subject to foaming

The effect of particle wettability on the hydrodynamics of gas-liquid-solid fluidized beds was studied in a cold-flow laboratory-model system. Average phase hold-ups in both three-phase and two-phase (freeboard) regions were measured in systems comprising hydrophobic or hydrophilic glass beads using water or 5 wt% aqueous solution of ethanol as the liquid phase, representing a coalescing (non-foaming) and a non-coalescing (foaming) system, respectively. Compared to hydrophilic particles, the lower gas hold-up observed with hydrophobic particles in the three-phase region is consistent with a greater average bubble size. This is explained by attachment of bubbles to hydrophobic particles and the formation of bubble-particle agglomerates with reduced ability to effect bubble break-up. Gas hold-up in the freeboard region is also lower in systems with hydrohobic particles, as is the steady foam thickness above the freeboard region in a foaming system. The experimental observations are quantitatively consistent with published models of the dynamics of foam formation.

The effect of particle wettability on the of rheology particulate suspensions with capillary force

We examined the dependence of the rheology of capillary suspensions on particle wettability using model ternary liquid/liquid/particle mixtures. Experiments were conducted using silica particles suspended in a majority liquid phase, to which a small minority of a second liquid was added. Silane modification was used to realize three different particle wettabilities ranging from particles being fully-wettable by the minority fluid, to being almost completely non-wettable by the minority liquid. In all three cases, the ternary suspensions showed solid-like behavior, with the yield stress and modulus decreasing as particles became less wettable towards the minority fluid. In all three cases, the minority liquid was found to induce particle aggregation into percolating networks which are responsible for the solid-like rheology. Our results suggest two reasons why the solid-like properties of such suspensions diminish as the particles become less wetting by the minority fluid: because particle network relies on multi-particle capillary clusters (rather than pair-wise meniscus binding), and because a certain fraction of particles become too non-wettable to participate in the network.

An analysis on heterogeneous bubble nucleation around a nanoparticle based on density functional approach

Density functional analyses are performed to study bubble nucleation around a nanoparticle submerged in a supersaturated LJ/s fluid in this paper. Two heterogeneous nucleation modes, i.e. core-shell mode and spherical cap mode, are considered. The minimal free energy path (MFEP) of these two nucleation modes are obtained. Effects of particle wettability and supersaturation of the bulk liquid on heterogeneous nucleation are studied. It is found that the energy barrier of the spherical cap mode nucleation is lower than that of core-shell mode nucleation. However, the difference between energy barriers of the two heterogeneous nucleation modes approaches zero when the particle becomes strongly solvophobic. The disappearance of nucleation barrier is observed for strongly solvophobic particles at high supersaturation.

The effect of particle wettability on the stick-slip motion of the contact line.

Contact line dynamics is crucial in determining the deposition patterns of evaporating colloidal droplets. Using high-speed interferometry, we directly observe the stick-slip motion of the contact line in situ and are able to resolve the instantaneous shape of the inkjet-printed, evaporating pico-liter drops containing nanoparticles of varying wettability. Integrated with post-mortem optical profilometry of the deposition patterns, the instantaneous particle volume fraction and hence the particle deposition rate can be determined. The results show that the stick-slip motion of the contact line is a strong function of the particle wettability. While the stick-slip motion is observed for nanoparticles that are less hydrophilic (i.e., particle contact angle θ ≈ 74° at the water-air interface), which results in a multiring deposition, a continuous receding of the contact line is observed for more hydrophilic nanoparticles (i.e., θ ≈ 34°), which leaves a single-ring pattern. A model is developed to predict the number of particles required to pin the contact line based on the force balance of the hydrodynamic drag, interparticle interactions, and surface tension acting on the particles near the contact line with varying particle wettability. A three-fold increase in the number of particles required for pinning is predicted when the particle wettability increases from the wetting angle of θ ≈ 74° to θ ≈ 34°. This finding explains why particles with greater wettability form a single-ring pattern and those with lower wettability form a multi-ring pattern. In addition, the particle deposition rate is found to depend on the particle wettability and vary with time.

Effect of particle wettability on particle-particle adhesion of colliding particles through droplet

In wet granulation processes, a liquid bridge formed between particles is not static but dynamic due to continuous motion of the particles. Therefore, understanding of the particle-particle adhesion by a dynamic liquid bridge is an important issue. We here conducted a direct numerical simulation of the particle-particle adhesion by a dynamic liquid bridge. The particle-particle adhesion of two colliding particles through a droplet on a particle surface was simulated. In particular, effect of particle wettability on a critical velocity for the particle adhesion (i.e., adhesiveness of the two colliding particles) was investigated. It was found that the critical velocity for the particle adhesion non-monotonically changed with the particle wettability. The critical velocity exhibited a local maximum with an increase in the contact angle, while the static liquid bridge force monotonically decreases with an increase in the contact angle. We revealed that a combined effect of the liquid bridge deformation and instantaneous liquid bridge force results in the non-monotonic dependence on the particle wettability.

Particle Zips: Vertical Emulsion Films with Particle Monolayers at Their Surfaces

Vertical emulsion films with particle monolayers at their surfaces have been studied by direct microscope observations. The effects of particle wettability and surface coverage on the structure and stability of water films in octane and octane films in water have been investigated. Monodisperse silica particles (3 microm in diameter) hydrophobized to different extents have been used. It is found that the structure and stability of emulsion films strongly depend on the film type (water-in-oil or oil-in-water), the particle contact angle, the interactions between particles from the same and the opposite monolayer, and the monolayer density. Stable films are observed only when the particle wettability fulfills the condition for stable particle bridges--in agreement with the concept that hydrophilic particles can give stable oil-in-water emulsions, whereas hydrophobic ones give water-in-oil emulsions. In the case of water films with dilute disordered monolayers at their surfaces, the hydrophilic particles are expelled from the film center toward its periphery, giving a dimple surrounded by a ring of particles bridging the film surfaces. In contrast, the thinning of octane films with dilute ordered monolayers at their surfaces finally leads to the spontaneous formation of a dense crystalline monolayer of hydrophobic particles bridging both surfaces at the center of the film. The behaviors of water and octane films with dense close-packed particle monolayers at their surfaces are very similar. In both cases, a transition from bilayer to bridging monolayer is observed at rather low capillary pressures. The implications of the above finding for particle stabilized emulsions are discussed.

Some Effects of Particle Wettability in Agitated Solid‐Gas‐Liquid Systems: Gas‐Liquid Mass Transfer and the Dispersion of Floating Solids

AbstractTwo‐ and three‐phase systems have been studied using particles that are water‐wetted and denser than water and with similar sized, small floating particles, both wetted and non‐wetted. The parameters investigated have been the agitator speed required to disperse the different types of particles under sparged and non‐sparged conditions and rates of gas‐liquid mass transfer. With the wetted, dense particles, only at concentrations of > ∼20% w/w did the kLa fall significantly (by ∼20 to 30%) whilst solid suspension followed the trends of earlier work. With the less dense particles, even with < ∼1% w/w that were not wetted, it was very difficult to disperse them throughout the liquid phase, though up‐pumping impellers were more effective than radial. In addition, bubble size significantly increased and kLa fell by a factor of 2 to 3. With the wetted, less dense ones up to 2% w/w, uniform dispersion was achieved even at much lower speeds and kLa did not change compared to the case without solids.

The effect of particle wettability on the accuracy of determination of particle sizes by the supersaturation variation technique

The effect of particle wettability on the accuracy of determination of particle sizes by the supersaturation variation technique

Role of particle wettability in capture by a suspension-feeding crab ( Emerita talpoida )

Suspension feeders sometimes depend on adhesion between particle and collector to capture food. If food particles have different adhesive properties than other particles, food could be passively selected by adhesive mechanisms. In this regard, the effect of particle wettability on adhesion to artificial and natural collectors was studied. First, the adhesion of glass particles to artificial collectors, both varying in wettability, was assessed to determine if wettability influenced adhesion in seawater. The adhesive force between glass particles and artificial collectors was measured by increasing the force pulling particles away from the collector until 50% of the particles fell off the collector. Adhesion increased as particle wettability decreased. Next, glass particles were used to determine if the antennal collector of the suspension-feeding mole crab Emerita talpoida captured particles based on particle wettability. 0.5 to 10 and 15 to 25 μm particles were suspended in a recirculating flow tank filled with seawater, and ablated antennae were exposed to this flow, after which the captured particles were counted. Results for the 0.5 to 10 μm particles confirmed predictions based on results from artificial collectors; particle capture increased as particle wettability decreased. The 15 to 25 μm particles may have been captured by sieving, and consequently did not follow predictions based on adhesion. Passive selection of particles based upon wettability differences can occur.

Structure formation and interaction of silanized glass beads at water-fluid interfaces: a redispersability study

Abstract The aggregation and spreading of silanized glass microspheres (diameter: 62–74 μm) were investigated at water (electrolyte)-fluid interfaces by evaporating hexane or chloroform from the water surface. Redispersion of aggregates was attributed to non-equilibrium interfacial tension at the water-fluid interface in the final stage of evaporation. The effect of particle wettability on this phenomenon was studied. Two different hydrophobic samples (Sample A: Θwater/air=77 ± 1°; Sample B: Θwater/air=44 ±1°) were prepared for experiments. Two-liquid wettability of particles was also characterized by contact angles (Sample A: Θ water hexane = 100 ± 4 °; Sample B: Θ water hexane = 57 ± 3 °) by means of which the colloid and capillary pair-potential energies have been calculated. In every case the aggregation yielded well-packed aggregates at the water-organic liquid interface, but spreading experiments showed that while the aggregate of the lower hydrophobic sample could disperse into little clusters or single particles, the higher hydrophobic particles remained together in the final stage of organic liquid evaporation. The speed and extent of redispersion of the lower hydrophobic sample were found to be dependent on the spreading liquids (hexane or chloroform), but the electrolyte (KCl) content of the subphase could not influence the process. The aggregates of higher hydrophobic particles could be redispersed in neither case investigated. It was proposed, on the basis of the calculated interparticle energies, that the higher hydrophobic particles could come into direct contact during the organic liquid evaporation due to the strong “immersion-type” capillary and hydrophobic attractive interactions. We characterized the dispersing ability of the spreading liquids used by a parameter (“dispersing energy”: 25.1 mN m−1 for hexane; 46.8 mN m−1 for chloroform) which could be calculated from a supposed interfacial tension difference at the water-air interface arising during the final stage of organic liquid evaporation. These values were compared with the “pull-off energy” (≈90 mN m−1) obtained earlier for silanized glass surfaces [J.L. Parker and P.M. Claesson, Langmuir, 10 (1994) 635]. The results confirmed the above suggestion that hydrophobic spheres (Sample A) can reach a situation in which the strong adhesion between them can hinder their redispersion and, furthermore, made it reasonable to assume that the aggregates of lower hydrophobic particles (Sample B) could be redispersed better if chloroform was used as spreading liquid.

Capture of hydrophilic and hydrophobic particles by condensing and evaporating water droplets

A linear theory was developed for the motion of aerosol particles somewhat larger than a fluid mean free path in a non-stationary, nonuniform fluid. The special case of viscous flow around a condensing water drop was examined. The influence of fluid nonuniformity on the aerosol particle concentration gradient adjacent to the drop surface was evaluated from experimental data, as was the effect of particle wettability on capture efficiency.