Capillarity Forces Research Articles

Vibration of structures containing compressible liquids with surface tension and sloshing effects. Reduced-order model

This paper deals with the development of the linear vibration of a general viscoelastic structure, with a local wall acoustic impedance, containing an inviscid compressible liquid (but with an additional volume dissipative term), with surface tension (capillarity) and sloshing effects, and neglecting the effects of internal gravity waves and the elastogravity operator. The sloshing problems of incompressible liquids with capillarity effects in elastic structures exhibit a major difficulty induced by the boundary contact conditions on the triple line because the capillarity forces are forces per unit length while the elastic forces are forces per unit surface. The proposed framework has the following novel features: (i) introducing a new appropriate boundary condition for the contact angle condition compatible with a deformable structure considered here as viscoelastic, (ii) considering a compressible liquid while incompressibility hypothesis is generally used for FSI problems including capillarity phenomena, and (iii) constructing a reduced-order model for the computational coupled problem.

Impact of capillarity forces on the steady-state self-organization in the thin chromium film on glass under laser irradiation

Metal films on transparent substrates are widely used for mask production in lithography, and lasers are frequently applied for their patterning. Steady self-organization of a chromium thin film on the glass substrate to parallel metal lines under irradiation with partially overlapping highly astigmatic nanosecond laser pulses above the ablation threshold has been observed. Transformations in a chromium film were investigated experimentally and numerically. The theoretical model of the steady self-organization is presented and discussed. It was demonstrated that the capillarity convection force was responsible for the transformation process in the molten metal. It was shown that the thermo-capillarity (Marangoni) shear stress and the stress originating from a variation in the radius of curvature along the structure were equally important in the case of the steady self-organization process.

Rainfall thresholds for landslide activity in Portugal: a state of the art

Rainfall is the most important physical process responsible for the landslide triggering in Portugal. Results obtained worldwide have shown that control of rainfall on landslides differs substantially depending upon landslide depth and kinematics and the affected material. Therefore, the critical rainfall conditions for failure are not the same for different types of landslides, and may be strongly influenced by regional geologic and geomorphologic conditions. Rapid debris flows are typically triggered by very intense showers concentrated in just a few hours, and shallow translational soil slips are usually triggered by intense precipitation falling within the 1–15 days long range. On the contrary, activity of deep-seated landslides of rotational, translational and complex types is related to periods of nearly constant rainfall, lasting from several weeks to several months. The different rainfall intensity–duration conditions are associated with different hydrologic mechanisms for slope failure. The generation of surface run-off and high peak discharges in first-order mountain catchments is a critical triggering mechanism for debris flows. The intense rainfall allows the rapid growth of pore water pressure and the drop of capillarity forces that sustain the apparent cohesion of thin soils. As a consequence, shallow soil slips occur within the soil material or at the contact with the underlying less permeable bedrock. Long lasting rainfall episodes enable the steady rise of the groundwater table and the development of positive pore water pressures into the soil. Consequently, deep-seated failures occur in relation to the reduction of shear strength of affected materials. In this work, we present the state of the art concerning the proposition of empirical rainfall thresholds in Portugal for different types of landslides observed in different zones of the country: the Lisbon region, the Douro Valley and the NW Mountains, and the Povoacao Municipality in Sao Miguel Island (Azores). The empirical thresholds applied in Portugal are based on the identification of past landslide events and include (i) the computation of antecedent rainfall threshold defined by linear regression, (ii) the normalization of rainfall by the mean annual precipitation, (iii) the definition of lower limit and upper limit rainfall thresholds and (iv) the definition of combined rainfall thresholds, which integrates the rainfall event and the antecedent rainfall for different time periods.

Analysis of bifurcations in a Bénard–Marangoni problem: Gravitational effects

This article studies the linear stability of a thermoconvective problem in an annular domain for different Bond (capillarity or buoyancy effects) and Biot (heat transfer) numbers for two set of Prandtl numbers (viscosity effects). The flow is heated from below, with a linear decreasing horizontal temperature profile from the inner to the outer wall. The top surface of the domain is open to the atmosphere and the two lateral walls are adiabatic. Different kind of competing solutions appear on localized zones of the Bond–Biot plane. The boundaries of these zones are made up of co-dimension two points. A co-dimension four point has been found for the first time. The main result found in this work is that in the range of low Prandtl number studied and in low-gravity conditions, capillarity forces control the instabilities of the flow, independently of the Prandtl number.

Structure of nanoscale gas bubbles in metals

A usual way to estimate the amount of gas in a bubble inside a metal is to assume thermodynamic equilibrium, i.e., the gas pressure P equals the capillarity force 2γ/R, with γ the surface energy of the host material and R the bubble radius; under this condition there is no driving force for vacancies to be emitted or absorbed by the bubble. In contrast to the common assumption that pressure inside a gas or fluid bubble is constant, we show that at the nanoscale this picture is no longer valid. P and density can no longer be defined as global quantities determined by an equation of state (EOS), but they become functions of position because the bubble develops a core-shell structure. We focus on He in Fe and solve the problem using both continuum mechanics and empirical potentials to find a quantitative measure of this effect. We point to the need of redefining an EOS for nanoscale gas bubbles in metals, which can be obtained via an average pressure inside the bubble. The resulting EOS, which is now size dependent, gives pressures that differ by a factor of two or more from the original EOS for bubble diameters of 1 nm and below.

Polyynes and flexible Si–H doped carbon nanoribbons by pulsed laser ablation of graphite in tetraethyl orthosilicate

Polyynes and graphene-based lamellae doped with both Si and H were synthesized simultaneously by pulsed laser ablation of bulk graphite in tetraethyl orthosilicate and characterized using optical spectroscopy and X-ray/electron diffraction. The polyyne molecules have long carbon chains (up to C16H2) to give multiple ultraviolet absorptions. The graphene-based lamellae were assembled as nanoribbons having hierarchical folds and dislocations due to wrinkle-to-fold transitions and imperfect attachment growth of the lamellae. A rather high fraction of sp3 bonds in the nanoribbons, as manifested by Raman shift, can be ascribed to capillarity force and Si–H solute trapping under the influence of particle size and lattice imperfections. The implications of the present composite phases on the natural dynamic occurrence and potential engineering applications are discussed.

A Calculation Model of Pull-Off Force with Edge-Effect

Based on the pull-off force calculation model with the liquid bridge capillarity force theory, analysis of the circumstance of the liquid bridge, puts forward an pull-off force calculation model with the consider of the edge effect. More experiment test results show, the model is effective and it can use for the exactitude calculate.

Direct numerical simulations of interface dynamics to link capillary pressure and total surface energy

The flow of two immiscible fluids through a porous medium depends on the complex interplay between gravity, capillarity, and viscous forces. The interaction between these forces and the geometry of the medium gives rise to a variety of complex flow regimes that are difficult to describe using continuum models. Although a number of pore-scale models have been employed, a careful investigation of the macroscopic effects of pore-scale processes requires methods based on conservation principles in order to reduce the number of modeling assumptions. In this work we perform direct numerical simulations of drainage by solving Navier–Stokes equations in the pore space and employing the Volume Of Fluid (VOF) method to track the evolution of the fluid–fluid interface. After demonstrating that the method is able to deal with large viscosity contrasts and model the transition from stable flow to viscous fingering, we focus on the macroscopic capillary pressure and we compare different definitions of this quantity under quasi-static and dynamic conditions. We show that the difference between the intrinsic phase-average pressures, which is commonly used as definition of Darcy-scale capillary pressure, is subject to several limitations and it is not accurate in presence of viscous effects or trapping. In contrast, a definition based on the variation of the total surface energy provides an accurate estimate of the macroscopic capillary pressure. This definition, which links the capillary pressure to its physical origin, allows a better separation of viscous effects and does not depend on the presence of trapped fluid clusters.

Liquid drainage from high-expansion (HiEx) aqueous foams during and after filling of a container

An aqueous foam drains interstitial liquid as it fills a container after an induction period. We obtain solutions of quasi-steady and volume-averaged conservation equations containing the moving foam front to describe the induction period and the subsequent drainage, respectively. The quasi-steady theory predicts that the induction period increases with decreasing foam injection velocity. After the induction period, the theory shows a constant liquid drainage rate when the foam front propagates at a constant velocity. The space-averaged liquid fraction of the foam decreases with time and reaches a constant (pseudo-steady state) value because of the drainage. The theory shows that the liquid drainage is significant when the foam injection velocity is less than or equal to the terminal velocity of the liquid in a channel (Plateau border), which is shown to depend on foam parameters including initial liquid volume fraction and bubble diameter. At large injection velocity, the theory predicts induction time and drainage rate corresponding to free drainage from stationary foams. We also present experiments measuring liquid drained from dry foams (high-expansion foams), which are generated by forcing air through a liquid-covered metal screen at bench-scale. The experimental data show significant liquid drainage during filling in good agreement with the theoretical predictions for foams with liquid volume fraction less than 0.01. After the container is filled with the foam and the foam addition is stopped, both the theory and experiments show that the drainage rate decreases exponentially with time until equilibrium between capillarity and gravitational forces is reached and drainage ceases to occur. Thus, the theory shows striking differences in drainage behavior during and after filling in agreement with the experimental data.

Synthesis of Dispersed Y<sub>2</sub>O<sub>3</sub> Nanopowder from Yttrium Stearate

Fine yttrium stearate powder was produced at a relatively low temperature using yttrium nitrate hexahydrate, ammonia and stearic acid as the raw materials. Dispersed Y2O3 nanopowder was synthesized by calcining the yttrium stearate. The formation mechanism of the precursor and the Y2O3 nanopowder was studied by means of XRD, TG-DTA, FT-IR, BET, FE-SEM and HR-TEM. Pure and dispersed Y2O3 nanopowder with an average particle size of 30 nm was produced by calcining the precursor at 600 °C. The particle size increases to about 60 nm with the increase of the calcination temperature to 1000 °C. In the preparation of Y2O3 from yttrium stearate, no water medium is involved, thus capillarity force and bridging of adjacent particles by hydrogen bonds can be avoided, resulting in good dispersion of the particles. The dispersed Y2O3 nanopowder prepared in this work has potential application in phosphors and transparent ceramic materials.

On the densification of cubic ZrO2 nanocondensates by capillarity force and turbostratic C–Si–H multiple shell

A turbostratic C–Si–H lamellar phase with 0.35–0.39nm interspacing and ZrO2 condensates having cubic (c), tetragonal and monoclinic structures stabilized by increasing particle size were synthesized by pulsed laser ablation on Zr plate in TEOS and characterized by X-ray/electron diffraction and optical spectroscopy. The c-ZrO2 phase ca. 10% denser than the ambient lattice was stabilized as 3–10nm sized cubo-octahedral nanoparticles but as abnormal large-sized (up to 30nm) ones when encapsulated by the C1−xSix:H multiple shell with defective graphite-like structure units to exert an effective compressive stress. The potential application of such core–shell nanostructure with enhanced binding of Zr and O ions and implication for natural dynamic occurrence of the C1−xSix:H phase are addressed.

Spontaneous bending of the coalesced α-Cr2O3 nanocondensates: implications for multilayer coating systems

Nanosized α-Cr2O3 bicrystals with a special boundary of mixed planes via (hkil)-specific coalescence were formed by pulsed laser ablation on Cr in oxygen atmosphere. Transmission electron microscopy observations indicated that the bicrystals consist of rhombic (denoted as r) and platy (denoted as p) parts with well-developed \( \left( {10\bar{1}\bar{2}} \right)_{\text{r}} \)//(0001)p interface and exact \( \left[ {{\bar{\text{2}}\text{2}}0\bar{1}} \right]_{\text{r}} //\left[ {{\bar{\text{1}}\text{1}}00} \right]_{\text{p}} \) alignment, where \( \left( {10\bar{1}\bar{2}} \right)_{\text{r}} \) belongs to a prevailed group nonequivalent to \( \left( {10\bar{1} 2} \right)_{\text{r}} \) due to the \( \bar{3} \)(inverse triad) operation. The nanoplate was significantly bent when anchored on the ledged \( \left( {10\bar{1} \bar{2} } \right)_{\text{r}} \) surface of the nanorhomb. The hoop stress by the combined factors of anchorage points, capillarity force, and lattice/thermal mismatch accounts for the bending of the nanoplate. Such understanding sheds light on the bending mechanism of more complicated multilayer coatings generally with residual stress via islands coalescence.

Spring-block approach for nanobristle patterns

A two dimensional spring-block type model is used to model capillarity driven self-organization of nanobristles. The model reveals the role of capillarity and electrostatic forces in the pattern formation mechanism. By taking into account the relevant interactions several type of experimentally observed patterns are qualitatively well reproduced. The model offers the possibility to generate on computer novel nanobristle based structures, offering hints for designing further experiments. In order to allow for experimental validation of the model through future experiments, the cell-size distribution of the simulated cellular pattern is also studied and an exponential form is predicted.

A new insight for reliable interpretation and design of injection tests

Injection/fall-off test is a viable alternative to the conventional production/build-up sequence since it eliminates surface emissions. However, the well test interpretation is complicated especially in oil reservoirs because of the presence of two mobile phases, the fluid originally in place (hydrocarbon) and the injected fluid (diesel, brine or nitrogen). Fluid saturations vary during the test and their distribution in time is governed by fluid mobilities and effective permeabilities; additionally, gravitational forces, thermal gradients and capillary pressures may also strongly affect the flow. As a consequence, the conventional analytical approach used to describe the pressure behavior is no longer applicable, and only numerical simulations can thoroughly describe the evolution of the saturation and pressure fields in the reservoir. A new near wellbore, axial simmetric numerical model was developed and implemented for properly designing and interpreting injection tests in both oil and gas reservoirs. The model accounts for all the aspects that can have an impact on fluid and pressure distribution. Simulation results are provided in terms of pressure, saturation and temperature profiles. The pressure and pressure derivative reservoir response obtained during injection tests were simulated for a large number of different scenarios. Simulation results demonstrated that capillarity and gravity forces can have a strong influence on the evolution of the saturation profile during the fall-off phase, but their impact on the test interpretation is negligible when a fully penetrating vertical well is considered. Conversely, the combined impact of thermal effects and of the shape of the permeability curves on the test interpretation results proved to be dramatic.

Laboratory Investigation of Free Fall Gravity Drainage in Fractured Porous Systems Using Unconsolidated Macromodels

Naturally fractured reservoirs (NFRs) contain a significant amount of the world's oil reserves. Oil recovery by gravity drainage in a NFR strongly depends on the capillary height of the porous medium. Capillarity and gravity forces are usually the major driving forces in NFRs. To address this issue, a series of flow visualization experiments were performed using unconsolidated packed models of rectangular geometry with two fractures on the side. Parametric sensitivity analyses were performed considering effects of different system parameters such as fracture aperture, matrix height and permeability, and fluid viscosity on liquid drainage rate. These experiments enabled us to capture some aspects of the flow communication between matrix block and fracture during gravity drainage. Results from this study showed that the rate of liquid flowing from matrix to fracture is proportional to the difference of liquid levels in the matrix and in the fracture (H f ― H m ). In addition, the characteristic rate and the maximum liquid drainage rate from these fractured models are determined for stable gravity-dominated processes. Also, it was concluded that the characteristic rate depends only on the dimensions of the fracture and properties of the test fluid, and not on the properties of the matrix. For a given fracture―matrix system with different initial liquid saturation conditions, it is observed that the production history can be correlated by plotting the fraction of recoverable liquid as a function of time. Furthermore, ultimate recovery factor and capillary threshold height can be correlated using dimensionless numbers such as the Bond number and the porosity ratio.

Influence of Water on Crack Self-Healing in Soda-Lime Silicate Glass

The self-healing behavior of radial cracks generated by Vickers indentation in float glass is analyzed when heat treated at 620°C under various atmospheres. Results evidence that two main driving forces influence radial crack evolution: release of residual stresses induced by initial indentation and capillary forces due to surface energy minimization. Depending on the viscosity level, viscous flow allows crack morphological changes driven by capillarity forces or not. Our results evidence that at 620°C, the viscosity of the glass surrounding cracks can be significantly reduced by water diffusion and glass hydrolysis, or increased by glass des-hydration, as a function of the humidity level of the furnace atmosphere. Hydration and des-hydration of glass are shown to play a major role in the crack morphology changes during healing, respectively, favoring or impeding morphological changes driven by capillarity forces.

Finite reservoir effect on capillary flow of microbead suspension in rectangular microchannels

The present study reports a theoretical investigation of capillary transport of microbead suspension in microfluidic channels with finite size reservoirs at the inlet. The reservoir-microchannel combination is often the case in Lab-on-a-Chip (LOC) where biomolecules are transported using capillary force. To demonstrate such finite reservoir effect, the reservoir is placed vertically above the microchannel. Under such condition, the pressure field expression at the rectangular microchannel inlet is deduced. Appropriate correlations for effective physical properties are used to account for the presence of microbeads in the working fluid, mimicking biomolecules in actual LOC. The non-dimensional governing equation for capillary flow with finite size reservoir is derived based on the balance among the surface, viscous and gravity forces acting on the fluid front. The numerical solution of governing equation is obtained to investigate the impact of several operating parameters on the flow front progression. It is observed that the aspect ratio of the microchannel and reservoir play vital roles in deciding the behavior and magnitude of flow front progression in the microfluidic channels. Capillarity and gravity force dominant regions during the progression is observed. The microchannel width and reservoir width decide the interplay between gravity and capillarity. Although higher fluid level in the reservoir has an added advantage for more gravitational head, the resistance from the reservoir makes the flow front progress slowly at the beginning of the capillary transport. It is also found that microbead volume fraction in the working fluid plays an important role in delaying the capillary transport under various operating conditions. Hence, it can be concluded that the use of reservoir at the inlet of microfluidic channels has an impact on the overall capillary transport of biomolecules in LOC devices.

X-ray radioscopy of liquid metal foams under microgravity

Results obtained from ground-based reference experiments, a parabolic flight campaign (PFC) and the sounding rocket MASER 11 campaign are presented. X-ray analysis that allows us to follow the entire foaming process in-situ, was employed for qualitative and quantitative analysis of local changes in density, pore size distribution and the frequency and location of cell wall rupture. In the PFC, we found that under microgravity imbibition of liquid metal into the foam due to capillarity forces dominates, and even a pre-existing gravity-induced drainage disappears. This effect could be observed specially after gravity transitions from 1.8 to 0 g. During MASER 11, a homogeneous wet collapsefree metal foam with round pores could be produced. Obviously, there was no gravity-induced drainage, but an unexpected strong coalescence rate was observed. We conclude that gravity-induced drainage is not the only factor that leads to cell wall rupture as previously assumed.

Shape-dependent local internal stress of α-Cr 2O 3 nanocrystal fabricated by pulsed laser ablation

The α-Cr 2O 3 single-crystal nanocondensates were fabricated by pulsed laser ablation in air and characterized by analytical electron microscopy regarding shape-dependent local internal stress of the anisotropic crystal. The nanocondensates formed predominantly as rhombohedra with well-developed { 0 1 1 ¯ 2 } surfaces and occasionally hexagonal plate with thin { 1 1 2 ¯ 0 } edges and blunt corners. Such nanocondensates showed Raman shift for the CrO 6 polyhedra, indicating a local compressive stress up to ca. 4 GPa on the average. Careful analysis of the lattice fringes revealed a local compressive stress (0.5% strain) at the thin edge of the hexagonal plates and a local tensile stress (0.3–1.0% strain) near the relaxed { 1 ¯ 0 1 2 } , { 1 0 1 ¯ 1 } , and (0 0 0 1) surfaces of truncated rhombohedra. The combined effects of nanosize, capillarity force at sharp edge, and specific surface relaxation account for the retention of a local internal compressive stress built up in an anisotropic crystal during a very rapid heating–cooling process.

Testing of Intrinsic Sorptivity for Liquid Infiltration into Initially Dry, Miller‐ Similar Silica Sands

The sorptivity (S) of a porous medium quantifies the effect of capillarity and surface forces on liquid infiltration. For infiltration into initially dry soil, S is dependent on three system attributes: the infiltrating liquid properties, the soil properties, and the maximum liquid content behind the infiltration front, θm Through the use of scaling analyses, a singular, dimensionless value of intrinsic sorptivity (S*) and an accompanying dimensionless Boltzmann transformation (Φ*) were previously derived that are independent of these system attributes for Miller‐similar materials. The existence of S* for different infiltrating liquid properties alone were tested by performing a series of experiments that examined the infiltration of either water or the aliphatic oil Soltrol 220 into an initially dry silica sand. This study extended that work to include testing of intrinsic sorptivity for different values of θm and different Miller‐similar soils. A series of 57 experiments examined the infiltration of water or Soltrol 220 into two Miller‐similar dry silica sands across a range of θm values. The results of these experiments, together with the previous ones, support the existence of S* for the experimental conditions investigated. A singular value of S* can be used to estimate sorptivity values for Miller‐similar media for a range of conditions. Likewise, Φ* can be used to generate a similarity profile for normalized liquid content in Miller‐similar media for different liquid types and θm values.