Effect Of Capillary Forces Research Articles

Optimization of the micro-textures on the cutting tool based on the penetration of the lubricant in the micro-textures

In recent years, surface textures in micron scale is introduced into the rake face of cutting tools to facilitate the lubricant penetration into the cutting area and improving the friction conditions between tool-chip contact area. The penetration process of lubricant into micro-textures introduced into the rake face of the cutting tool during machining process is analyzed through theory calculation, FEA analysis and penetration experiments. It is found that the initial penetration velocity increases as the size of the micro-texture decreases; However, due to the combined effect of capillary pressure and friction force, the penetration distance for micro-texture with larger size is longer than that for micro-texture with smaller size when the penetration distance is larger than 0.15 mm; micro-texture with smaller size is suitable for smaller chip width, 0.15 mm under the conditions in this study, and micro-texture with a larger size is more effective for large back engagement in consideration of lubricant penetration. Also, an optimum size of micro-texture on the rake face of cutting tools should take both lubricant penetration and strength of the cutting tool into consideration. The results of this study would benefit for the designation of micro-textures in the future.

Modeling the process of oil displacement by a heat carrier considering the capillary effect

The manuscript is aimed at improving the mathematical model of oil production in a heterogeneous environment with the use of a thermal mode of displacement considering the action of capillary effect. We have constructed an algorithm to solve numerically the respective nonlinear boundary value problem on multiphase filtering by introducing the function of quasi-potential and the respective, conjugated thereto, flow function . In this case, the quasi-potential is represented in the form thereby having essentially simplified the overall strategy to split the algorithm for solving the original problem.Owing to the algorithm, which is based on the ideas of methods for quasiconformal mapping and staged registration of parameters, we have carried out calculations of the hydrodynamic grid, velocity fields, temperature, saturation, taking into consideration the impact of a capillary effect and when ignoring it. In particular, the charts of saturation fields demonstrate a difference in the ratio of percentage content of a displacing fluid up to 15 % at temperatures above 80 °C, which explains the effect of capillary forces. Instead, at temperatures from 50 °С to 70 °С the difference is not noticeable, though at 50 °С and below the results of flooding slightly differ (to 5 %) for the worse in terms of the actual representation of the process. In this case, it is believed that the dynamic viscosities of phases change with a change in temperature, the fluid movement is slow and occurs without phase transitions, while functions of relative phase permeabilities and capillary pressure are the known and unambiguous saturation functions.Numerical calculations of multiphase non-isothermal filtering in the symmetry element at a five-point system of flooding have been presented. In this case, it was found that taking into account the capillary effect makes it possible to not only predict the location of stagnant zones, but also to more accurately estimate the time when a displacing reagent breaks through in an operational well in order to effectively perform respective waterproofing operations.

To the issue of the mechanism of cell migration

The paper presents the experimental and theoretical aspects of studying the migration of cancer cells through narrow microchannels when interacting with a chemical substance — an attractant. Chemical agents were injected directly from the respective separate reservoir via hydrostatic head. The presence of migration channels of different sizes allowed us to analyze the migration abilities inherent in the cells. Experimental studies on the migration of cancer cell lines were carried out using a microfluidic binary migration cell. It consists of two chambers 50 μm deep, connected by a series of narrow microchannels 10 μm high. The chambers are connected to the tanks from which cancer cells and activating media come. The model features smooth transitions from all tanks to microchannels to prevent accumulation of microbubbles and cells, the presence of a restrictive barrier between a chemoattractant container and a nutrient medium to reduce the effect of capillary forces, sealing the supply channels and cells with cells using a glass plate glued on top. In a series of experiments, the ability of epithelial-like cells of the metastatic prostate cancer DU145 to migrate in the migration microfluidic system developed by us was revealed. The nature of migration depends on the width of the channel and the location of the cells at the time of adding the chemical agent. In wider channels, cells adhere more slowly and are able to perform rolling movements. In narrower channels, the cells are spread over the glass. The mathematical model of concentration-capillary movement, which is a system of equations of the dynamics of an incompressible viscous fluid, written separately for the cell contents and for its environment, is considered as the basis for a theoretical study of cell migration.

Modeling Immiscible Two‐Phase Flow in Rough Fractures From Capillary to Viscous Fingering

AbstractWe develop an efficient computational model for simulating fluid invasion patterns emerging in variable aperture fractures. This two‐dimensional model takes into account the effect of capillary force on the fluid‐fluid interfaces and viscous pressure drop in both fluid phases. The pressure distribution is solved at each time step based on mass balance and local cubic law, considering an imposed pressure jump condition at the fluid‐fluid interface. This pressure jump corresponds to the Laplace pressure which includes both terms related to the out‐of‐plane (aperture‐spanning) curvature and to the in‐plane curvature. Simulating a configuration that emulates viscous fingering in two‐dimensional random porous media confirms that the model accounts properly for the role of viscous forces. Furthermore, direct comparison with previously obtained experimental results shows that the model reproduces the observed drainage patterns in a rough fracture reasonably well. The evolutions of tip location, the inlet pressures, and the invading phase fractal dimensions are analyzed to characterize the transition from capillary fingering to viscous fingering regimes. A radial injection scenario of immiscible invasion is also studied with varying modified capillary number and viscosity ratio, showing displacement patterns ranging from capillary fingering to viscous fingering to stable displacement. Such simulations using two contact angles show that the invading phase becomes more compact when the wetting condition changes from strong to weak drainage, as already observed in 2‐D porous media. The model can be used to bridge the gap in spatial scales of two‐phase flow between pore‐scale modeling approaches and the continuum Darcy‐scale models.

The effect of capillary and intermolecular forces on instability of the electrostatically actuated microbeam with T-shaped paddle in the presence of fringing field

• The mechanical behavior of a clamped–clamped microbeam with middle paddle is analyzed. • The pull in voltage declines and the deflection enlarges as the intermolecular forces increase. • Presence of the electrostatic force accelerated the instability resulting from the capillary force . • Fringing field effect considerably affected determination of the bifurcation points . The present study is aimed to investigate pull-in instability, static deformation, natural frequency, primary and subharmonic resonances in the clamped–clamped microbeam with middle T-shaped paddle in presence of electrostatic force, Casimir force, van der Waals force and fringing field effect; besides, it is focused on investigating the effect of capillary force on instability and adhesion considering the effects of middle layer elongation and axial force. The microbeam is modeled as an Euler Bernoulli beam. In order to solve the nonlinear equations, the Galerkin-based rank reduction method was used. The discretized equations are solved by the perturbation theory in the neighborhood of primary and subharmonic resonances. The obtained results showed that the van der Waals and Casimir forces had attractive nature and led to the increased static deformation as well as occurrence of the pull-in at lower voltages; besides, the effects of attraction in Casimir was more than that in van der Waals. Results showed that with increase in the dimensionless length, which is influenced by the capillary force, the maximum static deformation was increased as well, leading to instability in capillary coefficients. Furthermore, presence of the electrostatic force also accelerated the instability resulting from the capillary force. Effects of the axial force and elongation in the clamped state resulted in the reduced static deformation as well as delayed instability. It is shown that changing the Casimir and Van der Waals forces as well as the fringing field effect, in addition to causing changes in the voltage and range, considerably affected determination of the bifurcation points. To validate the analytical results, numerical simulation is performed.

Numerical study on inertial effects on liquid-vapor flow using lattice Boltzmann method

Liquid-vapor flow in porous media is studied in this article. To fulfill this goal, a double-distribution-function lattice Boltzmann (LB) model is proposed based on the separate-phase governing equations at the representative elementary volume (REV) scale. Importantly, besides the Darcy force and capillary force, which were commonly included in previous studies, the LB model in this article also considers the inertial force characterized by the Forchheimer term. This feature enables the model to offer an effective description of liquid-vapor flow in porous media at low, intermediate and even high flow rates. We validated the LB model by simulating a single-phase flow in porous media driven by a pressure difference and found its results are in good agreement with the available analytical solutions. We then applied the model to study water-vapor flow in a semi-infinite porous region bounded by an impermeable and heated wall. The numerical simulation reveals the flow and mass transfer characteristics under the compounding effects of inertial, Darcy and capillary forces. Through a comparison with the results given by the generalized Darcy’s law, our numerical results directly evidence that the inertial force is a dominating factor when a fluid passes through porous media at an intermediate or high flow rate.

Surfactant flooding in oil-wet micromodels with high permeability fractures

Recovery in carbonate reservoirs is challenging because they are often oil wet and highly fractured. Surfactant flooding has been proposed as a possible enhanced oil recovery method to address these problems. To better understand the mechanisms of oil recovery from oil-wet, fractured rocks using surfactants, we created oil-wet glass micromodels, traversed by a deep fracture (130 µm) and conducted surfactant spontaneous imbibition experiments and floods at typical reservoir flow rates (approximately 2 ft/day). We compared the effects of capillary, viscous, and gravity forces as well as wettability alteration. We show, by conducting spontaneous imbibition experiments with negligible gravity effects (inverse Bond number ∼105) and by analyzing the results using simple force balance calculations, that in our micromodels low IFT plays the key role in balancing the viscous, gravity, and surface forces and hence the dynamics of imbibition. To quantify the role of viscous forces, we present displacement experiments at low IFT (10−3 mN/m) where transverse viscous pressure gradients mobilize oil from the matrix into the fracture. These results help rationalize and quantify the contributions of gravity, wettability alteration, and viscous crossflow to the rate of matrix-fracture transfer at low-IFT conditions.

Decoupling the contributions to the enhancement of electrical conductivity in transparent silver nanowire/zinc oxide composite electrodes

Abstract Electrical properties of silver nanowire (AgNW)-based transparent electrodes have been improved without transmittance loss by forming a composite with zinc oxide (ZnO). Here, we identified the dominant effect responsible for the improvement of electrical conductivity of the transparent AgNW:ZnO composite electrodes by fabricating the AgNW:ZnO composite electrodes with different architectures and theoretically calculating the overall resistance of their equivalent circuits. Specifically, when we compared the overall resistances of the AgNW:ZnO electrodes with various architectures by experiment, the electrode with only the electrical bridge effect showed the lowest electrical resistance. In addition, while the theoretical overall resistances were comparable on changing the interconnect resistances between the silver nanowires in the equivalent circuits of all architectures, they decreased dramatically with the decreasing ZnO bridging resistance. Thus, it was concluded that the electrical bridge effect is more important than the capillary force effect which decreases the interconnect resistance between the silver nanowires for the enhancement of the electrical properties of AgNW:ZnO composite electrodes. It was also found that the AgNW:ZnO electrodes with only the electrical bridge effect showed better device performances when applied to optoelectronic devices such as organic photovoltaics.

Random loose packing of small particles with liquid cohesion

Random packing of wet grains is numerically investigated using a multiscale discrete element method. The cohesion between wet grains is evaluated by the Weber number, with which the macroscopic and microscopic properties of wet packing are compared with those of dry systems. The effect of capillary force on wet packing partially resembles that of van der Waals force on the dry adhesive packing, because both packing fraction (ϕ) and coordination number (Z) of wet packing decrease with increasing surface tension, following a Boltzmann‐like exponential decay that leads to a metastable state with ϕ ≈ 0.37 and Z ≈ 3.8. The decay processes of wet grains, however, are much faster than that of dry ones due to the additional liquid‐phase viscous dissipation. Moreover, in the cases of strong cohesion, the relationship between Z and ϕ can be well interpreted by the Edwards' ensemble theory, while those with weak cohesion follow an exponential formula instead. © 2018 American Institute of Chemical Engineers AIChE J, 65: 500–511, 2019

Numerical investigation of particle shape on mechanical behaviour of unsaturated granular soils using elliptical particles

The unsaturated soils mechanic is of significant importance for understanding and predicting the actual behavior of unsaturated soils in plenty of geo-environmental condition including tailing dams and earth dams during construction and operation, soil slopes, and shallow foundations. In this research, a micromechanical model for unsaturated assemblies composed of elliptical particles is presented so that the effect of capillary force, confining stress, and particle shape on unsaturated granular media behavior is analyzed in the pendular regime. As one of the early attempts, the toroidal liquid bridge for elliptical particles is studied in granular assemblies using modified ELLIPSE program, Discrete Element Method based program. The results show that although the strength of spherical particles grows when the saturated degree increases, the strength of elliptical particles rises and then decreases; however, the friction angle remains almost constant. Furthermore, the highest percentage of apparent-cohesion rise takes place at saturation degree of 10% at the highest eccentricity. As long as the eccentricity increases, the effect of capillary force on shear strength grows continuously. Not only do unsaturated assemblies contract more at low strains, but also they expand more after the phase transfer point at high stains. The assembly composed of particles with eccentricity of 0.15 has the highest coordination number. The coordination number constantly increases with the saturation degree for circular particles. In contrast, for elliptical particles assemblies, when degree of saturation increases, the coordination number increases at the beginning then drops.

Visualization Study on Thermo-Hydrodynamic Behaviors of a Flat Two-Phase Thermosyphon

The coupled effect of boiling and condensation inside a flat two-phase thermosyphon has a non-negligible influence on the two-phase fluid flow behavior and heat transfer process. Therefore, a flat two-phase thermosyphon with transparent wall was manufactured. Based on this device, a visualization experiment system was developed to study the vapor–liquid two-phase behaviors and thermal performance of the flat two-phase thermosyphon. A cross-shaped wick using copper mesh was embedded into the cavity of two-phase thermosyphon to improve the heat transfer performance. The effects of heat flux density, working medium, and wick structure on the thermal performance are examined and analyzed. The results indicated that a strong liquid disturbance is caused by the bubble motions, leading to the enhancement of both convective boiling and condensation heat transfer. More bubbles are generated as the heat flux increases; therefore, the disturbance of bubble motion on liquid pool and condensation film becomes stronger, resulting in better thermal performance of the flat two-phase thermosyphon. The addition of the wick inside the cavity effectively reduces the temperature oscillation of the evaporator wall. In addition, the wick structure provides backflow paths for the condensate owing to the effect of capillary force and enhances the vapor–liquid phase change heat transfer, resulting in the improvement of thermal performance for the flat two-phase thermosyphon.

Capillary flows along microchannels in the presence of magnetic field

To analytically determine liquid depth and velocity, we formulated a theoretical a capillary flow. The coupling effects of viscous force (Fv), capillary force (Fs), and electromagnetic force (Fm) were considered during the modeling process. Periodical electromagnetic force facilitates capillary flow in hydrophilic conditions, and velocity vibration synchronizes with electromagnetic force. A sufficiently high electromagnetic force was required for ensuring the upward movement of liquid front in hydrophobic conditions. Liquid depth was increased with the increase in magnetic field, damping factor, and angular frequency. The velocity peak was positively related to $$\mid \cos\theta \mid$$ and magnified with the increase in damping factor and angular frequency in hydrophilic conditions. However, variations in velocity in hydrophobic conditions experienced an initial forward instantaneous peak and became consistent with that of hydrophilic conditions because of electromagnetic force.

Electric and capillary instability of liquid rising between heated/cooled parallel plates and subjected to phase change: DC on perfect dielectric liquids

Based on Lucas–Washburn's seminal works, a simple model governing the flow inside a narrow channel, partly dipped into a large pool filled with a dielectric liquid, is presented. The channel walls are electrically polarized and can be warmer or cooler than the pool liquid using an appropriate heating and cooling device. The liquid dielectric constant is assumed varying linearly with temperature and evaporation or condensation can occur at the meniscus surface. Linear stability analysis is performed near the equilibrium position demonstrating various effects of dielectrophoretic, capillary, gravity and viscous forces. For the investigated liquid's volatility, it is shown that only sufficiently heated electrodes can exhibit instabilities about equilibrium position, whereas cooling these electrodes leads always to an asymptotically stable liquid motion. A numerical investigation is also performed on the transient regime showing either monotonic or damped oscillatory liquid motion depending on viscous, capillary and dielectric effects. If channel walls are heated and the electric field magnitude is above a specific and finite threshold, liquid can be pushed out of the gap, preventing reentrance. This effect can lead to undesirable walls dry-out that would be detrimental to two-phase heat transfer devices. A comparative survey is also performed on two liquids typically found in applications involving thermo-electrohydrodynamics, namely hfe-7100 and hfe-7300.

Effect of capillary pressure force on local liquid distribution in a trickle bed

Accurate prediction of the local liquid volume fraction (εL) distribution, an important process parameter that governs the performance of Trickle Bed Reactors (TBRs), is still a challenge. In the present work, Eulerian multi-fluid simulations of local εL distribution were performed in a laboratory-scale pseudo-3D (rectangular) and cylindrical TBR and the predictions were compared with the Electrical Resistance Tomography (ERT) measurements of Singh et al. (2017). The effect of formulation of capillary pressure force (F‾C) was investigated and it was found that -PC∇εL definition of F‾C preserved the functional relation between the capillary pressure (PC) and εL, and that εL∇PC definition of F‾C reversed the same. Through the simulations performed for the pseudo-3D column, we showed that the alteration in the functional relation severely affects the ability of F‾C=εL∇PC definition to predict the effects of particle diameter, gas and liquid flow rates. It was elucidated that such an alteration underpredicts F‾C and could necessitate the inclusion of additional dispersion forces for particles with small diameters. F‾C implemented as -PC∇εL provided satisfactory predictions of the steady-state local εL distribution for the bed pre-wetted with the pseudo-Kan pre-wetting method. However, the PC model required an empirical correction ([(dP/dthr)(εS)0.6]-13.957) to predict the steady-state local εL distribution in the bed pre-wetted using the Levec method. While the modified F‾C predicted the time-averaged local εL distribution satisfactorily for different liquid flow rates and liquid distributor configurations, it was seen that further reduction in F‾C was required to predict the dynamic liquid spreading behavior under synthetically created pulsing flow conditions.

Microgravity Investigation of Capillary Driven Imbibition

The goal of the present paper is to investigate the capillary driven filtration in porous media under microgravity conditions. New mathematical model that allows taking into account the blurring of the front due to the instability of the displacement that is developing at the front is proposed. The constants in the mathematical model were selected on the basis of the experimental data on imbibition into unsaturated porous media under microgravity conditions. The flow under the action of a combination of capillary forces and a constant pressure drop or a constant flux is considered. The effect of capillary forces and the type of wettability of the medium on the displacement process is studied. A criterion in which case the capillary effects are insignificant and can be neglected is established.

Magnetogravitodynamic Stability of Three Dimensional Streaming Velocities of Fluid Cylinder under the Effect of Capillary Force

Magnetogravitodynamic Stability of Three Dimensional Streaming Velocities of Fluid Cylinder under the Effect of Capillary Force

Finite volume solution for two-phase flow in a straight capillary

The problem of two-phase flow in straight capillaries of polygonal cross section displays many of the dynamic characteristics of rapid interfacial motions associated with pore-scale displacements in porous media. Fluid inertia is known to be important in these displacements but is usually ignored in network models commonly used to predict macroscopic flow properties. This study presents a numerical model for two-phase flow which describes the spatial and temporal evolution of the interface between the fluids. The model is based on an averaged Navier-Stokes equation and is shown to be successful in predicting the complex dynamics of both capillary rise in round capillaries and imbibition along the corners of polygonal capillaries. The model can form the basis for more realistic network models which capture the effect of capillary, viscous and inertial forces on pore-scale interfacial dynamics and consequent macroscopic flow properties.

Study on evaluation method of mud-pumping of cement concrete bridge deck pavement

Mud-pumping is one of major distresses of concrete bridge deck pavement, which not only influences the riding comfort of vehicles but also affects the appearance of bridge pavement and endangers the whole bridge structure. Although many methods have been used to assess the mud-pumping distress, most of them remain in the qualitative assessment. Relevant researches about testing methods and quantitative assessment approaches are seldom studied. In this paper, Initial Surface Absorption Test (ISAT), X-ray CT technology, and fractal theory are adopted to assess mud-pumping pavement and study the effect of capillary force on the mud-pumping distress. In addition, the influences of voids distribution characteristics on the capillary water absorption capability are discussed. The ISAT result shows that three significant parameters of mud-pumping cores, such as the capillary water absorption mass, the capillary water absorption coefficient, and the ratio of capillary voids to air voids, are markedly different from those of the non-pumped cores. The mud-pumping cores had a relatively higher void ratio of volume ≤ 0.1 mm3, and lower complexity of void. Quantitative evaluation indexes for mud-pumping distress are recommended by this paper.

Well productivity enhancement by applying nanofluids for wettability alteration

Water blocking is a frequent cause for gas productivity decline in unconventional and conventional fields. It is a result of the capillary end effect near the wellbore vicinity. It creates significant formation damage and decreases gas well productivity. The alteration of the rock wettability by nanofluids is an effective way to reduce water blockage and enhance gas production. Presently, several types of surfactants and nanofluids are used in the industry for contact angle alteration. In this study, we developed an analytical model and analysed the sensitivity to several parameters. After the treatment, the porous medium in the well vicinity (or along the core) will have a stepwise constant contact angle profile. We derive analytical models for compressible steady-state two-phase linear and axi-symmetric flows, accounting for the piecewise-constant contact angle and contact-angle-dependent capillary pressure and relative permeability. The modelling reveals a complex interplay between the competing effects of compressibility, viscous and capillary forces, which influence the optimal contact angle for treatment. The optimal contact angle for treatment will depend on the initial wettability of the formation, the water cut and the capillary-viscous ratio.

Experimental and theoretical analyses on the effect of physical properties and humidity of fly ash impacting on a flat surface

This study investigated the particle-wall collision characteristics of different fly ash particles against a flat surface under dry and humid conditions by experimental and theoretical analyses. The experiment could be applied to simulate the particle deposition in many engineering fields, such as electrostatic precipitators (ESPs), filtration, and agglomerates. The coal used are bituminous coal from Fushun, Liaoning Province (LN) and meager coal from Zhundong, Xinjiang Province (XJ), which are turned into fly ash particles with a diameter of approximately 7µm using a muffle furnace. The experimental system is designed for an aerosol inlet particle velocity range of 1–7m/s. A dynamic model is developed to calculate the damping coefficient, contact time, critical impact velocity, and contact displacement under both dry and humid conditions during impact. The results show that the normal restitution coeffcients decrease with increasing density, Young's modulus, and humid condition. Second, based on the dynamic model calculation, the damping coefficient and contact time are obtained with different impact velocities in a collision. The values of the damping coefficient and contact time are larger under humid conditions due to the effect of capillary force. Third, the critical impact velocity increases under humid condition. Finally, the maximum contact displacement versus the impact velocity and the change of total force and velocity versus the contact displacement during a collision are examined.