•We present a 3D coupled VOF and sharp interface-implicit IBM for multiphase flows.•Contact line dynamic is resolved by applying a contact angle boundary conditions.•Extensive validation cases are ...presented for static and dynamic contact angles.•The simulated contact line dynamics with and without using IBM are compared.•Pore-scale water flooding process through BCC and FCC structures are presented.
A numerical methodology is presented for simulating 3D multiphase flows through complex geometries on a non-body conformal Cartesian computational grid. A direct forcing implicit immersed boundary method (IBM) is used to sharply resolve complex geometries, employing the finite volume method (FVM) on a staggered grid. The fluid-fluid interface is tracked by a mass conservative sharp interface volume of fluid (VOF) method. Contact line dynamics at macroscopic length scale is simulated by imposing the apparent contact angle (static or dynamic) as a boundary condition at the three-phase contact line. The developed numerical methodology is validated for several test cases including the equilibrium shape of a droplet on flat and spherical surfaces, the temporal evolution of a droplet spreading on a flat surface. The obtained results show an excellent correspondence with those derived analytically or taken from literature. Furthermore, the present model is used to estimate, on a pore-scale, the residual oil remaining in idealized porous structures after water flooding, similar to the process used in enhanced oil recovery (EOR).
Amino acid surfactants (AASs) based on environmentally friendly biomasses have the characteristics of renewable, easy biodegradation, antibacterial and low toxicity, and have been widely used in ...daily chemicals, pharmaceuticals, and other fields. This study concerned the use of octanal and amino acids as raw materials. In addition, seven types of amino acid‐based surfactants, through Collins reagents, Wittig‐Hornor reaction, and aza‐Micheal addition reaction, and amino acid head groups were connected with the alkyl chain by the CN bond. The structures were confirmed by infrared spectroscopy (FT‐IR) and nuclear magnetic resonance spectroscopy (1HNMR). Its surface activity and adsorption properties are evaluated. The physical properties of amino acid‐based surfactants were tested by surface tension and dynamic contact angle. The results demonstrated that histidine‐based amino acid surfactant (C8His) has the lowest critical micelle concentration (CMC) and surface tension at CMC (γCMC), 0.39 mmol L−1 and 28.79 mN L−1, respectively. Amino acid residues contribute to reducing the critical micelle concentration of surfactant. The interfacial adsorption of glycine‐based amino acid surfactant (C8Gly) significantly improved with the increase in temperature, so the surface tension decreased significantly. In addition, sodium chloride could effectively enhance the interfacial adsorption, and the gas–liquid interfacial tension and contact angle of AASs decrease.
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Determining capillary pressures and permeation resistances of multiphase seepage in porous-type reservoirs is crucial. The dynamic contact angle (CA) is one of the critical parameters ...used to calculate capillary pressures and permeation resistances. Under reservoir conditions, dynamic CAs are rate-independent of the triple-phase contact line velocity. Calculating rate-independent dynamic CAs remains challenging and is the main focus of this paper.
An experimental system was designed to capture the dynamic CAs of liquid-fluid displacements in microscale polydimethylsiloxane (PDMS) microchannels. These microchannels were 20 × 80 μm or 20 × 40 μm in height and width. The capillary numbers (Ca) were controlled to satisfy the conditions of Ca < 4 × 10−5 for liquid-air displacements and Ca < 3.5 × 10−7 for liquid-liquid displacements.
Since pinning forces were consistent at the receding interface and the advancing interface, energy barriers exhibited symmetry. However, CA hysteresis exhibited asymmetry. Based on our experiments, a linear regime of hysteresis was developed and verified to be consistent with others’ experiments. The relation can be used to calculate hysteresis strengths and rate-independent CAs. This model was also compared with the fractal model. The hysteresis factor in this model can be derived using the Wenzel factor r and the Cassie fraction ϕs.
•High-temperature spreading of Al-Cu(l)/Ni(s) and Al-Ni(l)/Ni(s) was studied.•Significant dissolution reaction occurs between drops and solid substrate.•Precursor film formation is suppressed by the ...dissolution reaction.•Dissolution of solid atoms into the droplet correspond to spreading enhancement.•Spreading rate is controlled by the lattice constants.
The high-temperature spreading dynamics of Al-Cu(l)/Ni(s) and Al-Ni(l)/Ni(s) wetting systems was studied using molecular dynamics simulations. Accompanied with spreading, a significant dissolution reaction was noted to take place for the two studied systems. The dissolution reaction involves both diffusion of solid atoms into the droplet and incorporation of liquid atoms into the substrate. No precursor film is generated during spreading, since its formation is suppressed by the dissolution reaction. The dissolution reaction induces an enhanced spreading rate, and spreading becomes faster when droplets contain less Cu or Ni atoms. The dissolution of solid atoms into the droplet is faster than that of liquid atoms into the substrate, so that the dissolution of the former is the dominant driving force for the spreading enhancement. The spreading of Al-Cu droplets correlates with that of Al-Ni droplets so long as the Cu concentration in Al-Cu droplets is equal to the Ni concentration in Al-Ni droplets, since both Cu and Ni atoms have the identical lattice constants.
The determination of the dynamic contact angle is of significant interest for the characterization of the wettability of technical fibers and textiles in diverse fields of science and technology. ...There exist traditional methods for dynamic contact angle measurements of flat surfaces and of fibers with a uniform cross‐sectional shape along the fiber. So far, however, no method has been reported which is suitable for structured fibers, particularly for spindle‐knotted structured fibers of varying cross‐sections. This article describes a new method for measuring the dynamic contact angle for polydimethylsiloxane (PDMS) spindle‐knotted structured fibers. The method is an outcome of integrating the results obtained from experiments (applying force tensiometry) and a proposed theoretical model describing such fibers. The reliability and conformity of the results are shown by comparing the measured dynamic contacts angle of PDMS as spindle‐knot and as a flat surface. This method may pave the road for better wettability analysis of various structured fibers. It also allows to measure the local receding and advancing contact angles for macroscopic/microscopic structured fibers (especially when they are not accessible as flat surfaces) against the various test liquids.
A method is developed to measure the dynamic contact angle of PDMS spindle‐knotted structured fiber. The method is an outcome of integrating results from the experiment (force tensiometry) and the theoretical model based on the position‐dependent forces acting on the fiber, taking into account its non‐uniform structure. Generalizing the method is straightforward for other structured fibers to analyze their wettability.
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Measuring contact angles made by liquids around individual carbon fibers (CFs) using the Wilhelmy technique is a conventional method to evaluate their surface properties. However, ...despite its apparent simplicity, inaccurate measurements of capillary forces and wetted lengths, due to the fineness of the CFs, as well as an improper selection of probe liquids can lead to incorrect contact angle and surface energy calculations, leading to an erroneous characterization of their surface properties.
In this study, dynamic wetting experiments of individual CFs were performed in ethylene glycol, diiodomethane, and formamide based on the Wilhelmy method. Capillary forces exerted on the CFs were recorded and analyzed in detail to calculate reliable dynamic contact angles at different contact-line velocities. The molecular-kinetic theory (MKT) and hydrodynamic approach (HD) were then used to model the experimental data and to obtain static contact angles.
The analysis shows that the experimental data are in good agreement with the linear MKT suggesting that the dominant channel of energy dissipation at the contact line is the contact-line friction. From the predicted static advancing contact angle values, the surface energy components of the CFs could be obtained thus providing a way to characterize their interfacial properties and predict their compatibility with polymer matrices. This study furthermore points out the importance of choosing the correct combination of test fluids to obtain reliable surface energy results.
The development of the Molten Carbonate Fuel Cell, now 65 years old in its pure molten-salt cell embodiment, has spawned a remarkable variety of designs and technologies (gas-fed fuel cells, direct ...carbon fuel cells, solid oxide FC hybrids, CO2 concentrating/capture and hydrogen generating systems). Sometimes these new subsets are recycling ideas from earlier stages of fuel cell exploration - which extend quite far back. Since Grove's discovery in 1840, diversification of the fuel has been a persistent lure and challenge – which led to exploration of ionic melts. Much later, after the isolation and identification of solid-oxide conductors, the path to a purely carbonate cell became conceptually clear. Its history since then has had several critical points, of diversification and convergence. Like all energy technologies, it is forever at the mercy of the economics, and politics, of primary energy resources – the balance between fossil and renewable. Is MCFC a technology whose time has come … and gone? Such a view would ignore its strong chemical fundamentals, intrinsic to a future including biofuels. But controlling and stabilizing the morphology and wetting properties of MCFC materials is vital for another cycle of re-birth and flowering.
•Fuel cell development is multidisciplinary and attracts many due to simplicity of concept.•MCFC development shows traditional cycles of improvement, but may profit from 21st century functional-materials approach.•High-temperature fuel cell development has a natural fit with multiplicity of energy-conversion schemes.•Only experimentation yields information essential for MCFC electrode structure design, such as micro-scale gas evolution.•A new cycle of molten-carbonate technology may well be expected based on bio-carbon.
As a universal phenomenon in nature, capillary rise not only strongly influences the physical properties and industrial processes of powder materials but can also be applied as an important technique ...to measure their wettability. In this paper, molecular dynamics (MD) was implemented to investigate the capillary transport behavior of water flow through α-quartz nanochannels considering the channel height. The results showed that the Capillary rise method (CRM) with the classical Lucas-Washburn (L-W) equation may obtain an overestimated equilibrium contact angle, and the value decreases with increasing channel height. Through the introduction of the concepts of effective viscosity, slip length and dynamic contact angle, a modified L-W equation was proposed. The equilibrium contact angle calculated by the equation was more accurate and independent of channel size. Additionally, the pore-water can be divided into absorption water and capillary water. The upper bound of the absorption water density was determined to be 1.14 g/cm3.
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•Molecular dynamic is used to study the capillary rise behavior of water in quartz nanochannels.•The Washburn capillary rise technique may obtain an overvalued equilibrium contact angle.•A modified L-W equation is proposed showing a good agreement with the penetration rate.•The upper bound of adsorptive water density and thickness of water film is 1.14 g/cm3and 0.3 nm.
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