Search

Surface tension plays a central role in the mechanical behavior of soft materials such as gels. Elastocapillary deformation of elastic graded substrates is ubiquitous in soft materials. In this work, the effect of a partially wetting sessile liquid droplet on the elastocapillary deformation of a soft elastic graded substrate is studied. The modulus is assumed to have an exponential form along the thickness direction. By applying the Fourier transformation, a mixed boundary-value problem is reduced into a dual integral equation. The numerical results show that the surface displacement is strongly affected by the inhomogeneity of the material. The study of the wetting properties of gel substrates is essential for both understanding the wetting phenomena of gels and developing gels for applications as soft actuators and sensors that can be used in wearable electronics and soft robotics. [ABSTRACT FROM AUTHOR]

We study global minimizers of a functional modeling the free energy of thin liquid layers over a solid substrate under the combined effect of surface, gravitational, and intermolecular potentials. When the latter ones have a mild repulsive singularity at short ranges, global minimizers are compactly supported and display a microscopic contact angle of π / 2 . Depending on the form of the potential, the macroscopic shape can either be droplet-like or pancake-like, with a transition profile between the two at zero spreading coefficient for purely repulsive potentials. These results generalize, complete, and give mathematical rigor to de Gennes’ formal discussion of spreading equilibria. Uniqueness and non-uniqueness phenomena are also discussed. [ABSTRACT FROM AUTHOR]

In the present investigation, the effect of the disposition of the drip irrigation laterals on the potato yield was evaluated, using the partial drying of roots SPR, replacing a sheet of water of 100 and 50% of the evapotranspiration of the crop ETc. The experimental design was made based on the Completely Random Factorial Design considering two factors: (a) types of lateral arrangement (T-1 parallel arrangement and T-2 linear arrangement) and (b) irrigation types (100% ETc SPR1 and 50% ETc SPR2), obtaining four treatments as a result. The application of the SPR was carried out in two periods: the first, between days 20-29 after planting (during growth) and the second, between days 76-94 after planting (during maturity). Total and commercial yield as well as water productivity were evaluated. The results show that the type of irrigation had a greater incidence in the total yield of the crop with yields between 61 and 64 t/ha, while the disposition factor had a greater incidence in the commercial yield with yields between 51 and 60 t/ha. Water use efficiency varied between 38 and 47 kg/m3.

We carried out a comprehensive molecular simulation to investigate the evolution of the excess isotherms and the isosteric heat with respect to temperature for argon adsorption on strong and weak substrates. The temperature ranges from well below the bulk triple point temperature to above the bulk critical temperature to show the first- (second-) order transitions and the state of the system at the bulk coexistence pressure P0, whether it is non-wetting, partial wetting or complete wetting (preceded by pre-wetting). It is found that the key parameter that affects the dependence of the transitions on temperature and the state of the system at P0 is the relative difference between the isosteric heat and the heat of sublimation (or condensation). For strong substrates, the state of the system changes from partial wetting to complete wetting when the temperature crosses the bulk triple point temperature, and for temperatures well below the bulk triple point the 2D-condensation occurs in the first and second (and possible higher) layers. For weak substrates, the state of the system changes from non-wetting to complete wetting when the temperature crosses the wetting temperature TW, which is specific to the substrate. For temperatures greater than TW, complete wetting in weak substrates only occurs at pressures close to the bulk coexistence pressure P0 via the initial stage of clustering (unfavourable adsorption), followed by a pre-wetting (known as thin-to-thick transition), and this is reflected in the increase of the isosteric heat from a value less than the heat of condensation λ and approaching λ as the pressure tends to P0. [ABSTRACT FROM AUTHOR]

Adsorption mechanism of ethanol on graphite is comprehensively investigated with a combined experimental measurements and computer simulation. The unique feature of the interplay of clustering and molecular layering of ethanol is highlighted, and ethanol serves as an ideal adsorbate because it behaves as a species intermediate between simple gases and water. For simple gases such as argon and krypton, molecular layering is a dominant mechanism for temperatures above their bulk triple point temperatures, while for water the mechanism of clustering is the dominant one. The intermediate feature of ethanol lies in the ethyl group that interacts with graphite while the hydroxyl group induces intermolecular interactions which are stronger than the adsorbate-graphite interaction. It is this strong intermolecular interaction that leads to two-stage mechanism of monolayer formation, with discrete cluster formation and growth in the form of oligomers (dominantly in tetramers and pentamers), followed by the coalescence of growing clusters. The interplay of clustering and coalescence of growing clusters depends on temperature, and for low temperature at 190 K, a bilayer formation was observed with network of hydrogen bonding holding two adsorbate layers, exposing the ethyl groups to the gas phase. As the temperature is increased to 298 K, the hydroxyl groups are no longer limited to the interlayer region between the first and second adsorbate layers but have the freedom to expose themselves to the gas phase, which results in multilayering of the third and higher layers. [Display omitted] • Partial wetting of ethanol for temperatures above its bulk triple point temperature. • Bilayer formation of ethanol on graphite surface. • An interlayer hydrogen-bonding network within the bilayer. [ABSTRACT FROM AUTHOR]

The article deals with the cavitation phenomenon affected by full and partial wetting of the wall. For the numerical computation of flow in the Laval nozzle the Schnerr-Sauer cavitation model was tested and was used for cavitation research of flow within the nozzle considering partial surface wetting. The coefficient of wetting for various materials was determined using experimental, theoretical and numerical methods of fluid flow due to partial surface wetting.

Graphical abstract Abstract Hypothesis Rotational Brownian diffusions of colloidal particles at a fluid interface play important roles in particle self-assembly and in surface microrheology. Recent experiments on translational Brownian motion of spherical particles at the air-water interface show a significant slowing down of the translational diffusion with respect to the hydrodynamic predictions (Boniello et al., 2015). For the rotational diffusions of partially wetted colloids, slowing down of the particle dynamics can be also expected. Experiments Here, the rotational dynamics of Janus colloids at the air-water interface have been experimentally investigated using optical microscopy. Bright field and fluorescent microscopies have been used to measure the in-plane and out-of-plane particle rotational diffusions exploiting the Janus geometry of the colloids we fabricated. Findings Our results show a severe slowing down of the rotational diffusion D r, ⊥ connected to the contact line motion and wetting-dewetting dynamics occurring on particle regions located at opposite liquid wedges. A slowing down of the particle rotational diffusion about an axis parallel to the interfacial normal D r, || was also observed. Contact line fluctuations due to partial wetting dynamics lead to a rotational line friction that we have modelled in order to describe our results. [ABSTRACT FROM AUTHOR]

Highlights • A droplet actuation and manipulation mechanism using freely available surface energy is demonstrated without using external force. • The presented technique can avoid unwanted secondary effects due to external actuation. • Droplet transportation using experimental selective painting surface is validated with lattice Boltzmann model. • A new approach to design lab-on-chip using micro-pillar surface is discussed in LBM framework. Abstract In the digital microfluidic systems, the droplet actuation and control in a chip is an important requirement. Usually, to actuate any droplet operation, an external energy needs to be supplied. We have demonstrated the utilization of the freely available surface energy by the suitable design of partial wetting surfaces to actuate and perform various droplet operations like splitting, transportation and merging. This approach would help us to realize on-chip droplet operations without applying external force like pressure, electric field or magnetic field with required control. The partial wetting surface and interface are synthesized using a selective painting technique and basic operations such as impingement, spreading and transportation are demonstrated. These dynamic properties of the droplet are modelled and analyzed with a multiphase lattice Boltzmann method (LBM). The partial wetting study of droplet dynamics is demonstrated using chemical gradient and structural gradient. The modelling results show good agreement with the experimental study, thus LBM can be used as tool for analyzing such chip designs. Further a microfluidic chip is designed with partial wetting surfaces chemically and by the placement of micro-pillars and basic on-chip operations such as splitting, merging and transportation are illustrated using LBM. [ABSTRACT FROM AUTHOR]

Spontaneous capillary flow (SCF) in microchannels occurs for specific geometrical and wetting conditions. When the channel walls form corner angles with the channel bottom, liquid filaments may form in the corners. These capillary filaments are often called Concus-Finn (CF) filaments, and they can theoretically spread infinitely.In this work we consider rectangular open U-grooves of varying cross-section width, and we theoretically determine the flow conditions as a function of the aspect ratio of the channel and the liquid-solid contact angle. These flow conditions are numerically checked. Especially, we analyze the configurations where precursor capillary filaments form. We show that these filaments can be metastable, i.e. disappear into a bulk capillary flow if the proper conditions are met. A diagram of the flow regimes is deduced from theoretical developments and checked using numerical modeling.

• Derivation of two-dimensional Green's Function for Spherical Laplacian. • Use of multi-precision arithmetic for evaluation of Green's Function. • Evaluation of computation time for combination of pre-conditioners and Krylov methods. • PETSc based numerical calculations and comparison with Finite Difference Method (FDM). • Robustness of the Green's Function based approach over FDM is shown. The solution of the two-dimensional spherical diffusion equation inside the catalyst particle is proposed using Green's Function Method (GFM). A Green's Function was derived using Eigenfunction expansion in the polar direction and considering jump discontinuity in the radial direction. The advantage of using multi-precision arithmetic in the evaluation of Green's Function has been demonstrated. A pre-computed value of Green's Function at a selected precision level was used to calculate the concentration profile inside the fully and partially wetted spherical catalyst particle geometry. The non-linear kinetic rate expression-based formulation for concentration profile calculation gives rise to non-linear equations. These non-linear equations were solved in PETSc (Balay et al., 2017) using various combinations of linear pre-conditioners and Krylov methods. A comparison with the Finite Difference Method (FDM) formulation is presented, and the advantage of the proposed GFM-based formulation for convergence and reduction in computation time is demonstrated. [ABSTRACT FROM AUTHOR]

The spreading of small liquid drops over thin and thick porous layers (dry or saturated with the same liquid) is discussed in the case of both complete wetting (silicone oils of different viscosities over nitrocellulose membranes and blood over a filter paper) and partial wetting (aqueous SDS (Sodium dodecyl sulfate) solutions of different concentrations and blood over partially wetted substrates). Filter paper and nitrocellulose membranes of different porosity and different average pore size were used as a model of thin porous layers, sponges, glass and metal filters were used as a model of thick porous substrates. Spreading of both Newtonian and non-Newtonian liquid are considered below. In the case of complete wetting, two spreading regimes were found (i) the fast spreading regime, when imbibition is not important and (ii) the second slow regime when imbibition dominates. As a result of these two competing processes, the radius of the drop goes through a maximum value over time. A system of two differential equations was derived in the case of complete wetting for both Newtonian and non-Newtonian liquids to describe the evolution with time of radii of both the drop base and the wetted region inside the porous layer. The deduced system of differential equations does not include any fitting parameter. Experiments were carried out by the spreading of silicone oil drops over various dry microfiltration membranes (permeable in both normal and tangential directions) and blood over dry filter paper. The time evolution of the radii of both the drop base and the wetted region inside the porous layer were monitored. All experimental data fell on two universal curves if appropriate scales are used with a plot of the dimensionless radii of the drop base and of the wetted region inside the porous layer on dimensionless time. The predicted theoretical relationships are two universal curves accounting quite satisfactorily for the experimental data. According to the theory prediction, (i) the dynamic contact angle dependence on the same dimensionless time as before should be a universal function and (ii) the dynamic contact angle should change rapidly over an initial short stage of spreading and should remain a constant value over the duration of the rest of the spreading process. The constancy of the contact angle on this stage has nothing to do with hysteresis of the contact angle: there is no hysteresis in the system under investigation in the case of complete wetting. These conclusions again are in good agreement with experimental observations in the case of complete wetting for both Newtonian and non-Newtonian liquids. Addition of surfactant to aqueous solutions, as expected, improve spreading over porous substrates and, in some cases, results in switching from partial to complete wetting. It was shown that for the spreading of surfactant solutions on thick porous substrates there is a minimum contact angle after which the droplet rapidly absorbs into the substrate. Unfortunately, a theory of spreading/imbibition over thick porous substrates is still to be developed. However, it was shown that the dimensionless time dependences of both contact angle and spreading radius of the droplet on thick porous material fall on to a universal curve in the case of complete wetting.

Considering the increasing amount of data for communication and infotainment applications, fabrication of optical networks and bus systems is a challenging task for production engineering. A two-step manufacturing process for polymer optical waveguides is presented. By improving the highly efficient flexographic printing technology by laser functionalization of the printing tool in combination with a subsequent spray application, high-quality waveguides are accomplished. By adjusting the resulting surface energy of the foil substrate in the first fabrication process, the spray application achieved high-aspect ratio waveguides with a low attenuation of 0.2dB/cm at 850 nm. [ABSTRACT FROM AUTHOR]

This work presents a two-dimensional analytical solution of the governing differential equation for falling film vapour-absorption around a plain horizontal tube. The solution of the species transport equation gives the LiBr mass fraction distribution within the liquid absorptive film flowing along the tube surface and can be used to characterize the mass transfer performance of falling film absorbers or generators. By means of the inclusion of partial wetting effects at reduced solution mass flowrates, this study obtains an analytical expression of the mass transfer coefficient of these devices applicable over an extended range of operative conditions. The hypotheses of small penetration for physical absorption and constant heat flux condition are applied at the film interface to reach a closed-form solution. Fourier method is used to solve the problem and the eigenvalues obtained from the characteristic equation depend on Lewis number, Biot number and the dimensionless heat of absorption. Given the boundary condition at the wall, the two-dimensional mass fraction field of the laminar film can be expressed analytically as a function of Schmidt, Reynolds numbers, the tube dimensionless diameter and the ratio of the wetted area to the total exchange surface. Finally, mass transfer coefficient and absorbed mass flux are locally and globally investigated as functions of the influent dimensionless groups to clarify their effects on the physical process and screen the potentiality of the model. Results show notable qualitative and quantitative agreement with previous numerical solutions and experimental results from previous literature. This model constitutes a widely applicable and time-saving tool for actual system simulations, design and control. [ABSTRACT FROM AUTHOR]

Partial wetting surfaces and its influence on the droplet movement of micro and nano scale being contemplated for many useful applications. The dynamics of the droplet usually analyzed with a multiphase lattice Boltzmann method (LBM). In this paper, the influence of partial wetting surface on the dynamics of droplet is systematically analyzed for various cases. Splitting of droplets due to chemical gradient of the surface is studied and analyses of splitting time for various widths of the strips for different Weber numbers are computed. With the proposed model one can tune the splitting volume and time by carefully choosing a strip width and droplet position. The droplet spreading on chemically heterogeneous surfaces shows that the spreading can be controlled not only by parameters of Weber number but also by tuning strip width ratio. The transportation of the droplet from hydrophobic surface to hydrophilic surface due to chemical gradient is simulated and analyzed using our hybrid thermodynamic-image processing technique. The results prove that with the progress of time the surface free energy decreases with increase in spreading area. Finally, the transportation of a droplet on microstructure gradient is demonstrated. The model explains the temporal behaviour of droplet during the spreading, recoiling and translation along with tracking of contact angle hysteresis phenomenon. [ABSTRACT FROM AUTHOR]

This work reports that a partially wet phase can compatibilize and toughen a co-continuous PLA/PA11 blend. Four different polymers: PBS, PBAT, EMA and EMA-GMA are examined for their capacity to partially wet the PLA/PA11 interface in a melt-blending process. All the blends exhibit a partial wetting morphology, but offer very different compatibilization efficacies and toughening effects. EMA-GMA demonstrates the best compatibilization effect as it reduces the co-continuous thickness to 5–6 μm, which is about half that of the original binary PLA/PA11 blend, followed by EMA while PBS and PBAT result in the least changes in morphology and properties. Despite the enhanced compatibilization effect obtained with EMA-GMA, it is the self-assembled droplets of EMA at the PLA/PA11 interface which result in a major increase in the ductility of the blend with an elongation at break of 260% as compared to 4% for the binary blend. A substantial increase in the notched Izod impact strength is also achieved with partially wet droplets of EMA with a value of 73 J/m, a four-fold increase as compared to the impact strength of the pure PLA and the PLA/PA11 binary blend. This difference is attributed to the limited internal cavitation of the very fine droplets of EMA-GMA at the interface whereas the blends with partially wet EMA demonstrate significant interfacial cavitation after the impact fracture test. This work shows that self-assembled rubbery EMA droplets at a co-continuous PLA/PA11 interface combine to compatibilize the system, improve interfacial adhesion and interfacially cavitate through the continuous system upon fracture. The percolation of the stress field around these interfacially cavitated partially wet droplets results in the shear yielding of the matrix and a significant toughening effect ensues. These results indicate the potential of partially wet droplets to compatibilize and toughen co-continuous structures. [ABSTRACT FROM AUTHOR]

To understand the thin film evaporation in a partial wetting system, water morphology near the receding contact line driven by evaporation has been investigated experimentally. A state-of-the-art tapping-mode atomic force microscopy (TM-AFM) was used to obtain the nanoscale film profile. The test section first reached equilibrium in an enclosed chamber. Then a small amount of heat was supplied to increase the gas temperature to achieve an environmental heating. The droplet was evaporating and the receding velocity of the contact line was below 20 nm/s. The film profiles were found following the macroscopic profile, which was about linear, till about 2 nm thickness from the contact line which was already the limitation of the measurement. The results indicate that the microscopic contact angle at nanoscale was approximately equal to the optically detected macroscopic contact angle under this weak environmental heating. [ABSTRACT FROM AUTHOR]

Single-phase as well as two-phase fluid flows inside mini/micro-channels and capillary tubes are of practical importance in many miniaturized engineering systems. While several issues related to single-phase transport are fairly well understood, two-phase systems still pose challenges for engineering design. The presence of gas-liquid interfaces, dominance of surface forces, moving contact lines, wettability, dynamic contact angle hysteresis and flow in confined geometries are some of the unique features of two-phase systems, which manifest into complex transport phenomena. While Taylor plug/bubble flow is a fairly common flow pattern in several micro-fluidic devices operating at low Bond number, the ensuing transport characteristics are complex and still not fully discerned. This review paper aims at highlighting the nuances and features of a unit cell of a Taylor plug flow, especially focusing on partially wetting systems, which are more common in engineering applications. Emphasis is given to a 'unit cell' flow system consisting of an isolated liquid Taylor plug with adjacent gas phase, confined in a capillary tube. Such a seemingly simple flow condition poses considerable challenges for discerning and modelling local thermo-hydrodynamic transport coefficients. Relevant background information and fundamentals are carefully scrutinized while summarizing the state-of-the-art. The role of wettability and dissipation near the contact line is highlighted via available experimental and simulation results. Local momentum and heat transfer exchange processes during the motion of an isolated plug of partially wetting liquid moving inside a capillary tube are delineated. [ABSTRACT FROM AUTHOR]

Membrane distillation (MD) is promising for many applications such as seawater desalination. Designing membranes with high vapor flux is preferred to achieve high efficiency. However, understanding of effects of the membrane interfacial wetting properties on the vapor flux in MD is still missing. Here, elucidating this effect by theoretical and experimental tools is presented. Three interfacial wetting properties are identified, namely slip vs. non-slip, wetting vs. non-wetting and rough evaporation interface. While superhydrophobic surfaces of the membrane offer slippage of fluid, the effect of the slip condition has little effect on the heat and mass transfer in MD due to the relatively small slip length. When the fluid penetrates into and wets the membrane, the vapor flux increases due to the shortened vapor transport distance although the stagnant penetration layer hinders heat transfer. The rough evaporation interface with increased evaporation area does not necessarily significantly increase vapor flux. The rough evaporation problem can be reduced to an equivalent partial wetting problem with a certain wetting depth. This work clarifies the role of membrane interfacial wetting properties in vapor flux variation, which provides guidance for future membrane interfacial design to enhance vapor flux in MD. • Three interfacial wetting properties were identified in membrane distillation (MD). • Superhydrophobicity contributes little to vapor flux enhancement in MD. • Partial wetting of the membrane will increase vapor flux in MD. • Rough evaporation interface can be reduced to the partial wetting problem. [ABSTRACT FROM AUTHOR]

We report new analytical solutions for the thickness profile of partially wetting two-dimensional droplets. The model includes the effects of capillarity and both short- and long-range molecular forces. We analyze the dependence of the maximum thickness, the contact angle, and the cross-sectional area on the height of the nanometric precursor film that surrounds the droplet. We found asymptotic expressions for the thickness profile and for the contact angles for large and small droplets. The results are compared to those obtained previously for polar liquids. The analytical solutions found here are useful to assess the validity of the hypothesis and the semi-analytical solutions proposed in the literature. In addition, these solutions enable the inference of information about the molecular potential from the measured steady profiles. [ABSTRACT FROM AUTHOR]

We experimentally investigated the mobilization process of a partially wetting droplet in a pore doublet model. The process, involving contact line movement, liquid film generation, and interface deformation, has not been fully understood and modeled. In equilibrium, the droplet sat in one of the capillary tubes of the pore doublet, and the contact lines of the droplet were pinned with nonzero contact angles. The droplet was subject to pressure differences that were generated by pumping the continuous liquid into the pore doublet at different flow rates. At low flow rates, the droplet moved with sliding contact lines, and the shapes of the droplet’s menisci roughly resembled spherical caps. When the flow rate increased, the velocity of the droplet increased, and the shapes of the liquid-liquid interfaces changed dramatically forming finger-like structures and films. Once films form, the classical Young–Laplace equation, which assumes a spherical interface, is not sufficient to describe droplet mobilization and the corresponding pressure drops. The films ruptured as the droplet moved forward, and a certain amount of droplet liquid was left behind. When the flow rates reached a certain level, the droplet snapped off from the tube wall and rolled while being surrounded by thin films formed by the continuous liquid. [ABSTRACT FROM AUTHOR]

In wet granulation and particle coating, it is important to accurately predict the liquid dispersion for process optimisation and quality assurance. In this work, a new contact dispersion model is proposed by taking into account the partial wetting of particle surfaces, which is incorporated into the Discrete Element Method (DEM). In the proposed model, individual particle surfaces are sub-divided and the liquid redistribution between these sub-divided surfaces are tracked with time. The proposed model is applied to simulate a spray drum where liquid is sprayed to initially dry particles, and the liquid dispersion rate is compared with the results obtained from the Shi and McCarthy model ( Shi and McCarthy, 2008 ), which is one of the pioneering models for contact liquid dispersion in DEM. It is found that the Shi and McCarthy model gives faster liquid dispersion when highly viscous liquid is used, whilst the results are largely comparable in the low viscosity case. [ABSTRACT FROM AUTHOR]

The properties of the interface of two immiscible fluids play an important role in several processes such as membrane supported liquid extraction, enhance oil recovery, aquifer remediation, etc. In this paper the spatial distribution of two immiscible liquids in non-dispersive contact via a porous media is studied by using numerical simulations. The simulations are carried at pore-scale by minimizing the total interfacial energy using the simulated annealing method. This technique allows us to compute the spatial distribution of fluids in the pores without assuming the geometry of the solid or the interface. The studied solids are made of randomly packed spheres either monodispersed or bi-dispersed. The effect of pore size distribution, tortuosity, porosity and contact angle on the liquid–liquid interface extent and geometry is analyzed. The simulations demonstrate that liquid–liquid interface follows a simple linear correlation with the contact angle. At low contact angle the wetting phase extents into the non-wetting phase forming pendular liquid bridges. The continuity of the phases is evaluated. The liquid–liquid interface is mostly continuous for all the contact angles. [ABSTRACT FROM AUTHOR]

Evaporative triple contact lines are far from well understood, which is especially true for partial wetting. In the present work we obtain the water film profile down to about 1 nm from the contact line, through a state-of-the-art tapping-mode atomic force microscopy (TM-AFM). The test section is enclosed and the measurements are conducted under equilibrium state. The results show that the liquid surface is straight downward to the substrate. The microscopic contact angle is therefore identical to the macroscopic counterpart, which greatly facilitates the thin film modeling. The linearity of the equilibrium thin films is important for the comprehensive understanding of contact line region. [ABSTRACT FROM AUTHOR]

The paper reports an experimental study to understand the evaporation mechanism of a partially wetting isolated liquid plug (methanol) of length L moving inside a long, dry, horizontal circular glass capillary tube (ID = 1.5 mm). The plug (with specified range of non-dimensional L / D ratios) is pushed from rest by controlled injection of air from one side, till a quasi-steady terminal plug velocity is achieved in the adiabatic section (non-heated length) of the capillary tube. Under such conditions, the drainage of thin-film occurring at the receding interface and its subsequent dewetting is well predicted by existing literature. The plug is then allowed to move through the heated section maintained at constant wall temperature (lesser than the saturation temperature of methanol). The drained film now starts evaporating rapidly, drastically affecting the bulk transport behavior. High resolution videography, coupled with laser confocal microscopy provides vital bulk as well as local information, including time-varying plug length, film thickness and local dewetting behavior near the contact line. Experimental results obtained for different wall temperatures and different initial L / D ratios of liquid plug suggests that the Taylor’s law for predicting drainage characteristics under adiabatic flow conditions is valid, even for cases where there is a continuous evaporation of thin-film. The study thus provides a framework for modeling evaporative flux based on simple hydrodynamic theory of film drainage. [ABSTRACT FROM AUTHOR]

We propose a lattice Boltzmann approach for simulating contact angle phenomena in multiphase fluid systems. Boundary conditions for partially-wetted walls are introduced using the moment method. The algorithm with our boundary conditions allows for a maximum density ratio of 200000 for neutral wetting. The achievable density ratio decreases as the contact angle departs from 90°, but remains of the order ℴ(102) for all but extreme contact angles. In all simulations an excellent agreement between the simulated and nominal contact angles is observed. [ABSTRACT FROM AUTHOR]

Falling film drain water heat recovery (DWHR) systems are single pass, vented heat exchangers. The heat from the drain water is transferred through the DWHR system to the incoming cold mains water, recovering otherwise wasted energy. This article discusses the theory behind DWHR systems, and examines how drain-side wetting affects performance. It also describes the apparatus built by the Solar Thermal Research Laboratory (STRL), at the University of Waterloo, for testing the effectiveness of DWHR systems. The results show that as the flow rate increases, the effectiveness of the DWHR pipe decreases. The data also indicates that there is a Critical Flow Rate (CFR) below which the performance of a DWHR pipe cannot be extrapolated. The inability to extrapolate is due to the incoming drain water not repeatedly wetting the same amount of area on the pipe's interior wall. This CFR is dependent on the diameter and interior surface characteristics of the pipe. [ABSTRACT FROM AUTHOR]

Abstract: The coarsening of polymer mixtures is an important route towards major morphology modification in multiphase polymer systems. To date however the coarsening of ternary systems has not been significantly examined. In this study the phase coarsening mechanism via annealing for partial wetting, and complete wetting morphologies in ternary polymer blends is characterized. This is a route towards the examination of interfacial coarsening in polymer blends since ternary partially wet systems involve the presence of interfacial droplets while completely wet ternary systems are comprised of a complete interfacial layer. A partial wetting type of morphology is obtained for polybutylene succinate (PBS)/poly(lactic acid) (PLA)/polycaprolactone (PCL). Three different compositions for that system with composition ratios of ϕ (PBS/PLA) = 1.5; ϕ (PBS/PLA) = 3; and ϕ (PBS/PLA) = 10 are prepared to show the effect of the concentration of the self-assembled PLA droplets located at the interface of PBS/PCL. As the concentration of PLA decreases, the growth rate of the PLA phase during the annealing process sharply decreases due to a significant increase of the “surface to volume ratio” of the PLA droplets required in order to cover the interface. In this case, due to the short inter-droplet distances between PLA droplets at the interface, coalescence is controlled by the drainage time. This mechanism is confirmed by the observation of a linear relationship between the third power of droplet size and annealing time. For the 37.5%PBS/12.5%PLA/50%PCL blend, the conservation of interfacial-angles confirms that the annealing time has no effect on the angle values between phases, as predicted by Harkins spreading theory. The annealing process for complete wetting is studied at four compositions for an HDPE/PS/PCL blend where the PS phase is located as a continuous layer at the interface of co-continuous HDPE/PCL. In 33.3%HDPE/33.3%PS/33.3%PCL after 30 min of annealing, the PS phase thickness increases 49 times from 2.3 μm to 112 μm. Even for very low concentrations of 3%PS, a high coarsening rate of 0.0039 μm/s is observed. This sharp linear increase in PS phase size implies a capillary pressure mechanism and an impeded growth of Tomotika-like capillaries for all three phases that cause a confinement effect for coarsening of the middle PS phase. [Copyright &y& Elsevier]

The focus of this paper is to model a three-phase packed bed reactor where a phase is evolving as a result of reaction, such as in Fischer–Tropsch synthesis. In such systems, there is a strong two-way coupling between the hydrodynamics and the overall reaction kinetics. The hydrodynamics is affected by the amount of phase evolution and the amount of phase evolution in turn determines the local transport resistances, which in turn determine the local net rates of reaction. A reactor scale model incorporating species balance equation for the species in the gas and liquid phases, an overall energy balance and a pellet scale model accounting for partial wetting were used to complete the theoretical picture of the system. In the absence of local knowledge of transport effects, global correlations were used “locally” to predict the local hydrodynamics in the reactor. [ABSTRACT FROM PUBLISHER]

Abstract: Membrane gas absorption technology is a promising alternative to conventional technologies for the mitigation of acid gases. In this study, simultaneous removal of SO2 and CO2 from coal-fired flue gas was carried out in a polypropylene hollow fiber membrane contactor using aqueous monoethanolamine as the absorbent. The influences of liquid and gas flow rates on the simultaneous absorption performance of CO2 and SO2 were investigated. The experimental results indicated that the membrane contactor could eliminate these two sour gases simultaneously and effectively. Absorption of SO2 and CO2 was enhanced by the increase in liquid flow rate and decrease in gas flow rate. It was observed that a small amount of SO2 in the flue gas had a slight influence on the absorption of CO2. In addition, the membrane contactor was operated continuously for two weeks to evaluate its duration performance. The results showed that the CO2 mass transfer rate was decreased significantly with the operating time due to partial wetting of membrane pores. After 14days of continuous operation, the CO2 mass transfer rate of the wetted membrane contactor was decreased by 41% but could be retrieved to 86% of the fresh one by increasing the gas phase pressure. [Copyright &y& Elsevier]

Abstract: The membrane wetting by amine absorbents results in performance deterioration of membrane gas absorption system for CO2 post-combustion capture. To solve this problem, in this study, the polypropylene membrane fiber was modified by depositing a rough layer on the surface to improve its hydrophobicity. Weighing the coating homogeneity, hydrophobicity and modification process efficiency, the mixture of cyclohexanone and MEK system was considered as the best non-solvent. The contact angle increased dramatically from 122° to 158° by the modification, thereby obtaining superhydrophobic membrane surface. The membrane–absorbent interaction results demonstrated that the modification treatment effectively enhanced the stability and maintained the superhydrophobicity of fibers contacting with the absorbent. In addition, continuous CO2 absorption experiments for up to 20days were carried out in untreated and modified polypropylene hollow fiber membrane contactors, using 1molL−1 MEA solution as the absorbent. The long-term system operation results indicated that, even though additional mass transfer resistance was introduced by the surface coating, the modified polypropylene hollow fiber membrane contactor was still technically feasible for CO2 capture from the power stations. [Copyright &y& Elsevier]

The kinetics of partial wetting was investigated for the case of spreading of cylindrical and axisymmetric drops over a horizontal solid surface under the action of capillary forces. The Brochard-Wyart and de Gennes (1992) relation, having a cut off of molecular size below which the continuum theory breaks down, is used to provide a dynamic contact angle boundary condition. The dynamic contact angle relation and the viscous dissipation are shown to be valid even in the case of axisymmetric spreading when using the approximation of a wedge flow pattern near the leading edge. To obtain an analytical solution for the dynamics of spreading, the departure of the outer region solution from the spherical cap profile, near the inflection point, was neglected, and the accuracy of the approximation was examined. The analytical solution obtained is a powerseries expression. Simple short-time and long-time asymptotic solutions are also provided. The model for the dynamics of partial wetting does not require any fitting parameter. The results are found to agree favorably with the available published experimental data even at dynamic contact angles as large as about 90°, which is beyond the range of applicability of the lubrication theory. The model matches very closely the dynamics of spreading obtained with a previous model by Chebbi (2010), in which a numerically similarity solution was used to account for the deviation from the spherical cap profile near the inflection point. [ABSTRACT FROM AUTHOR]

Abstract: Partial wetting in a ternary polymer blend is the thermodynamic state where all three phases meet at a three-phase line of contact. Pickering emulsions, where solid particles situate at the interface of two other phases is a classic example of this state. This paper studies the presence of partial wetting in PE/PP/PS and in PE/PP/PC ternary polymer blends and examines, in particular, the influence of polyethylene viscosity on PS droplet formation at the PE/PP interface. Quantitative analysis of PS droplet growth and coverage at the PE/PP interface during static annealing were obtained by image analysis. A new approach was established to estimate the co-continuous PE/PP coarsening rate and was found to be in agreement with previous studies. In this work it is shown that the polyethylene viscosity can be of significant importance in ternary partial wetting when the interfacial driving force for partial wetting is weak and viscosity directly affects the quantity and size of PS droplets at the interface during annealing. The equilibrium between droplet stability at the interface, as predicted by spreading theory, and the interfacial mobility generated by coarsening determines the PS droplet size and surface coverage at the PE/PP interface. A ternary PE/PP/PC system, which displays a strong partial wetting driving force, was also investigated. The morphology of the blend system studied demonstrated a clear dominance of partial wetting over complete wetting. [Copyright &y& Elsevier]

Abstract: Hydrodynamics and transport phenomena inside Trickle Bed Reactors are strongly modified when superficial liquid velocity is not sufficient to insure a perfect wetting of catalyst particles. For this reason, the impact of partial wetting on catalyst effectiveness has been widely studied in past, in case of isothermal reactions. Heat transfer limitations, inside or outside catalyst particles, have also been investigated, but only in case of total wetting. In the present study, the effect of partial wetting is quantified numerically for various kinetics, mass and heat transfer limitations. When possible, an analogy is proposed between 1D and 2D models of particles. Robust rules are proposed to take into account for partial wetting in 1D-radial models of particles. The case of partial evaporation inside catalyst pores is also studied. Evaporation phenomena is approximated following a simple approach. Performed calculations show that the effect of partial wetting can affect very strongly catalyst effectiveness factors, especially in case of evaporation in the pores. The use of 1D approximations gives a good prediction of the global catalyst efficiency, as far as boundary conditions are symmetric between heat and mass transfer. Otherwise, 1D models are not relevant anymore. [Copyright &y& Elsevier]

Abstract: A numerical “macroscopic-scale” method for static (including hysteresis) and moving contact lines for partially wetting liquids is presented. The numerical method is based on the implementation of a “sub-grid” description of the contact line that consists in imposing the apparent angle for static and moving contact lines. The numerical simulations are validated against several well controlled bi-dimensional situations: the equilibrium shape of a drop released on a hydrophobic or hydrophilic wall, the axisymmetric spreading of a drop for a partially wetting liquid, the migration of a drop placed on a inclined wall and submitted to a Couette or Poiseuille flow. [Copyright &y& Elsevier]

Abstract: A mathematical model was developed to simulate the concentration profile in a gas absorption membrane (GAM) system. Carbon dioxide (CO2) absorption into an aqueous solution of monoethanolamine (MEA) was investigated in the GAM system. Three GAM modules were potted with polytetrafluoroethylene (PTFE) membranes and connected in series to measure CO2 concentration and CO2 loading profiles along the length of the GAM system. The model predictions for CO2 concentration and CO2 loading profiles along the length of GAM column were in excellent agreement with the experimental results. The average absolute deviation between the model and experimental results was 1.49%. The Wilson plot method was used to determine the membrane resistance, which was compared with a theoretical membrane resistance. It was found that the membrane mass transfer resistance calculated using the Wilson plot method could predict the CO2 concentration profile with a higher accuracy than the theoretical method. Partial membrane wetting was modeled to investigate the effect of membrane mass transfer resistance on the absorption performance and the overall mass transfer coefficient. The results showed that an acceptable membrane wetting for CO2 absorption in MEA solutions in GAM systems was 40%. A higher lean solution temperature increased the membrane wetting in the GAM system. The membrane mass transfer resistance in completely liquid-filled membrane pores accounted for 92% of overall mass transfer resistance. [Copyright &y& Elsevier]

Capillary solutions have long existed for the control of liquid inventories in spacecraft fluid systems such as liquid propellants, cryogens and thermal fluids for temperature control. Such large length scale, ‘low-gravity,’ capillary systems exploit container geometry and fluid properties—primarily wetting—to passively locate or transport fluids to desired positions for a variety of purposes. Such methods have only been confidently established if the wetting conditions are known and favorable. In this paper, several of the significant challenges for ‘capillary solutions’ to low-gravity multiphase fluids management aboard spacecraft are briefly reviewed in light of applications common to life support systems that emphasize the impact of the widely varying wetting properties typical of aqueous systems. A restrictive though no less typifying example of passive phase separation in a urine collection system is highlighted that identifies key design considerations potentially met by predominately capillary solutions. Sample results from novel scale model prototype testing aboard a NASA low-g aircraft are presented that support the various design considerations. [ABSTRACT FROM AUTHOR]

Abstract: Selective absorption into a liquid is a widespread method to separate and concentrate sulfur dioxide from gas emissions, reducing air pollution and environmental risks. Process intensification can be performed first by the substitution of the equipment (e.g. scrubbers) for a membrane device to avoid drops dragging, and second by the substitution of the absorption solvent (e.g. N,N-dimethylaniline) for ionic liquids to avoid solvent volatilization. According to this intensification, a zero solvent emission process has been developed. The ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate is used as the absorption solvent and the results are compared to the N,N-dimethylaniline results. A ceramic hollow fibre module is the membrane device where the sulfur dioxide absorption takes place. A gas stream with a typical composition of roasting effluents flows through the shell side and the absorption liquid flows counter currently by the inside of the hollow fibres. The influence of carbon dioxide in the absorption is also evaluated and the overall mass transfer coefficients are calculated. The difference between the estimated mass transfer coefficients and the experimental results for both solvents is discussed assuming partial wetting of the membrane. [Copyright &y& Elsevier]

Abstract: This paper reports a new numerical scheme of the lattice Boltzmann method for calculating liquid droplet behaviour on particle wetting surfaces typically for the system of liquid–gas of a large density ratio. The method combines the existing models of Inamuro et al. [T. Inamuro, T. Ogata, S. Tajima, N. Konishi, A lattice Boltzmann method for incompressible two-phase flows with large density differences, J. Comput. Phys. 198 (2004) 628–644] and Briant et al. [A.J. Briant, P. Papatzacos, J.M. Yeomans, Lattice Boltzmann simulations of contact line motion in a liquid–gas system, Philos. Trans. Roy. Soc. London A 360 (2002) 485–495; A.J. Briant, A.J. Wagner, J.M. Yeomans, Lattice Boltzmann simulations of contact line motion: I. Liquid–gas systems. Phys. Rev. E 69 (2004) 031602; A.J. Briant, J.M. Yeomans, Lattice Boltzmann simulations of contact line motion: II. Binary fluids, Phys. Rev. E 69 (2004) 031603] and has developed novel treatment for partial wetting boundaries which involve droplets spreading on a hydrophobic surface combined with the surface of relative low contact angles and strips of relative high contact angles. The interaction between the fluid–fluid interface and the partial wetting wall has been typically considered. Applying the current method, the dynamics of liquid drops on uniform and heterogeneous wetting walls are simulated numerically. The results of the simulation agree well with those of theoretical prediction and show that the present LBM can be used as a reliable way to study fluidic control on heterogeneous surfaces and other wetting related subjects. [Copyright &y& Elsevier]

The classic hydrodynamic wetting theory leads to a linear relationship between spreading speed and the capillary force, being determined only by the surface tension of the liquid and its viscosity. Both equilibrium and dynamic processes of wetting are important in adhesion phenomena. The theory appears to be in good agreement with the results generated from experiments conducted on the spreading of poly(dimethylsiloxane) (PDMS) on soda-lime glass substrate and fails to account for the behavior of other liquids. In this study, the spreading kinetics of four different liquids (hexadecane, undecane, glycerol and water) was determined on three different solids, namely, soda-lime glass, poly(methyl methacrylate) (PMMA) and polystyrene (PS). Droplets from the same liquid allowed to spread under identical conditions on three different substrates produce distinctly different behaviors. The results show that the equilibrium contact angles are qualitatively ranked in accordance with the critical surface tension of wetting (γc) of the respective solid, i.e., high-γc solids caused the low surface tension liquids to assume the least equilibrium spreading (largest contact angle). On the other end, low-γc solids with the lowest surface tension liquid produce the most wetting (smallest contact angle). The results suggest that equilibrium spreading could be explained on the basis of the axiom 'like wets like'; in other words, polar surfaces tend to be wetted by polar liquids and vice versa. [ABSTRACT FROM AUTHOR]

The capillary imbibition of aqueous surfactant solutions into dry porous substrates is investigated from both theoretical and experimental points of view in the case of partial wetting. Cylindrical capillaries are used as a model of porous media to study the problem. It is shown that if the mean pore size is below a critical value, then the permeability of the porous medium is not influenced by the presence of surfactants whatever the value of the concentration: the imbibition front moves exactly in the same way as in the case of the imbibition of pure water. The critical radius is determined by the adsorption of the surfactant molecules onto the inner surface of the pores. If the mean pore size is larger than the critical value, then the permeability increases with increasing surfactant concentration. These theoretical conclusions are in agreement with the experimental observations. [Copyright &y& Elsevier]

We report an experimental investigation on advancing contact lines of large drops spreading on chemically patterned surfaces. The model substrates were prepared using microphotolithography allowing precise control of the position and the size of the wettability patterns. Experiments were performed exploring different surface geometries: from ordered to disordered fields of defects and from low to high surface densities. The shape of the contact line between two isolated defects was investigated as a function of the distance. Portions of the contact line on the defects and on the matrix were studied during spreading experiments and were related to the apparent contact angles measured from the final thickness of the drops. A modified Cassie equation based on the line fraction of defects is proposed. [Copyright &y& Elsevier]

Physical mechanisms are discussed and crude mathematical models with lumped parameters are developed, which explain the authors recent experimental data , concerning temperature hysteresis and multiplicity phenomena for α-methylstyrene (AMS) liquid–vapor hydrogenation on a single catalyst pellet. The interplay between endothermic vaporization and exothermic vapor phase reaction is elucidated. The results of this study may help to develop more sophisticated models and theory of hot spots formation and runaway phenomena in trickle-bed reactors. [Copyright &y& Elsevier]