Interface Position Research Articles

Dimensionless analysis on liquid–liquid two-phase flow patterns in a numbered-up microfluidic device

Flow patterns of six liquid–liquid systems in a numbered-up microfluidic set-up were studied in this work. Chloroform-water, butyl acetate-water, ethyl acetate-water, kerosene-water, butanol-water and octanol–water were chosen as test liquids. Three distinct flow regimes were observed in the parallelized microfluidic device: slug flow, droplet flow and parallel flow. A uniform flow distribution was achieved in the scaled-out microfluidic device for all observed flow regimes. Flow non-uniformity was determined based on both the volumetric flow rate and slug size/droplet size/interface position for each microchannel. The two-phase interface's position relative to the microchannel walls was considered a criterion for flow non-uniformity measurement in parallel flow. A comprehensive dimensionless analysis was also performed to determine which dimensionless numbers are appropriate for presenting universal flow maps. Re-0.31We0.41, We0.07Ca0.31, Re0.07Ca0.41, Ca0.5Oh-0.14, We0.25Oh0.31 and Re0.5Oh0.82 were identified as the suitable combinations of dimensionless numbers for proposing generalized flow pattern maps for the numbered-up set-up. For the slug and droplet flow regimes, slug and droplet length and velocity were also investigated.

Temperature distribution in coastal aquifers: Insights from groundwater modeling and field data

The temperature distribution in coastal aquifers is determined by the effect of different heat sources: surface water recharge, sea infiltration, and geothermal heat. In previous studies, the signal generated in groundwater by each source was individually studied, and in the case of geothermal heat, it was often not considered. This research is the first in considering all possible sources of heat in a coastal aquifer simultaneously by using a combination of field data and numerical modeling to present a reference model based on the characteristics of a real aquifer. The position of the freshwater-saltwater interface (FSI) and its effect on temperature distribution have been modeled considering variable-density flow, coupled heat and solute transport. This study broadens the theoretical knowledge of temperature distribution in coastal aquifers based on a sensitivity analysis of hydraulic and thermic parameters. Furthermore, a case study (the Motril-Salobreña aquifer) was modeled with field data calibration to test the applicability to real aquifers. The new insights gained through this study provide integrated knowledge of the temperature distribution in coastal areas and establish the basis for future research using heat as a tracer in seaside aquifers.

Effects of groove shape on microstructure and properties of resistance spot welding joints in WC-10Co/B318 steel

In resistance spot welding, groove shape has an important influence on joint performance. The groove shapes designed in this study are applied to a bimetal band-saw blade, which has theoretical and application value. Three groove shapes (straight, arc, and V-shaped) are designed on the backing bracket to weld WC-10Co and B318 steel. The welding process is imaged using a high-speed camera, and the distribution and change of heat in the welding process are compared and analyzed. The shear force, interfacial microstructure, and fracture surface are analyzed by shear tests, scanning electron microscopy, and energy-dispersive X-ray spectroscopy, and the relationship among the heat distribution, interfacial microstructure, and shear force is investigated. The results show that the reaction duration and temperature distribution at various interfacial positions of the different groove shapes are heterogenous, leading to an uneven interfacial reaction. For short welding time, the straight joint with heat concentrated in the center of the interface has larger deformation and so larger shear force. For long welding time, the reaction layer forms at the interface. At the straight joint interface, the η phase is distributed more and aggregates, thereby decreasing the shear force. At the other two joint interfaces, the distribution is more eutectic and the η phase is relatively dispersed, so the shear force is higher. The maximum shear forces of the joints are 1068.2 N (straight), 1138.1 N (arc), and 1231.7 N (V-shaped). For short welding time, the metallurgical reaction of the interface is insufficient, and the joint fractures at the interface. For long welding time, the fracture usually starts from the cracks on the WC-Co side, then propagates to the interfacial reaction layer, and finally fractures at the steel side. The appearance of cracks, reaction layer, extrusion, and inclusions reduces the shear force of the joint.

Shape Optimization of an Imperfect Interface: Steady-State Heat Diffusion

In the context of a diffusion equation, this work is devoted to a two-phase optimal design problem where the interface, separating the phases, is imperfect, meaning that the solution is discontinuous, while the normal flux is continuous and proportional to the jump of the solution. The shape derivative of an objective function with respect to the interface position is computed by the adjoint method. Numerical experiments are performed with the level set method and an exact remeshing algorithm so that the interface is captured by the mesh at each optimization iteration. Comparisons with a perfect interface are discussed in the setting of optimal design or inverse problems.

A Novel Measurement-Based Model for Calculating Diffusive Fluxes Across Substrate-Water Interfaces of Marine Aggregates, Sediments and Biofilms

Our understanding of the small-scale processes that drive global biogeochemical cycles and the Earth’s climate is dependent on accurate estimations of interfacial diffusive fluxes to and from biologically-active substrates in aquatic environments. In this study, we present a novel model approach for accurate calculations of diffusive fluxes of dissolved gases, nutrients, and solutes from concentration profiles measured across the substrate-water interfaces using microsensors. The model offers a robust computational scheme for automatized determination of the interface position and enables precise calculations of the interfacial diffusive fluxes simultaneously. In contrast to other methods, the new approach is not restricted to any particular substrate geometry, does not requirea prioridetermination of the interface position for the flux calculation, and, thus, reduces the uncertainties in calculated fluxes arising from partly subjective identification of the interface position. In addition, it is robust when applied to measured profiles containing scattered data points and insensitive to reasonable decreases of the spatial resolution of the data points. The latter feature allows for significantly reducing measurement time which is a crucial factor forin situexperiments.

Density functional for the lattice gas from fundamental measure theory.

We construct a density functional for the lattice gas or Ising model on square and cubic lattices based on lattice fundamental measure theory. To treat the nearest-neighbor attractions between the lattice gas particles, the model is mapped to a multicomponent model of hard particles with additional lattice polymers where effective attractions between particles arise from the depletion effect. The lattice polymers are further treated via the introduction of polymer clusters (labelled by the numbers of polymer they contain) such that the model becomes a multicomponent model of particles and polymer clusters with nonadditive hard interactions. The density functional for this nonadditive hard model is constructed with lattice fundamental measure theory. The resulting bulk phase diagram recovers the Bethe-Peierls approximation and planar interface tensions show a considerable improvement compared to the standard mean-field functional and are close to simulation results in three dimensions. We demonstrate the existence of planar interface solutions at chemical potentials away from coexistence when the equimolar interface position is constrained to arbitrary real values.

Solidification and melting model of phase change material with volumetric shrinkage/expansion void in an annulus

A one dimensional analytical model is proposed to analyze the solidification/melting of phase change materials (PCMs) incorporating the shrinkage/expansion void in an annulus. An air-PCM system is considered in this study. Paraffin wax is considered as PCM and filled inside the annulus, while air is considered inside the void. Separation of Variable method involving Bessel’s function is employed to obtain temperature distribution for air, solid and liquid domains and to locate interface positions. Stefan condition and mass conservation equation are used at the interfaces. Results obtained from the present model are found to be in good agreement with the existing test results. Effect of various parameters such as density ratio, end wall temperature, and radius ratio on the solidification/melting of PCM have been investigated. The solid-liquid interface moves 76.53% and 70.88% during solidification and 34.26% and 35.32% during melting for density ratio of 1 and 1.16, respectively during a time period of 1400 s. Shrinkage as well as solidification rate increases with decrease in cold wall temperature, increase of radius ratio and increase in Stefan number; while expansion as well as melting rate increases with increase in hot wall temperature, increase of radius ratio and increase in Stefan number.

Non-uniformity of intermetallic compounds and properties in inertia friction welded joints of 2A14 Al alloy to 304 stainless steel

Inertia friction welding (IFW) is attracting considerable attention in recent years for dissimilar metals joining such as aluminum (Al) alloy to stainless steel due to its ease to control heat input accurately. As a result of thermo-mechanical conditions, the microstructure at the friction interface, especially the brittle IMCs, is usually considered to be non-uniformly distributed. In the present study, the non-uniformity of IMCs at different interfacial regions in the IFWed joint and the diffusion bonded joint was comparatively studied by annealing experiments with tensile tests conducted accordingly for quantitatively evaluating the influence of IMCs thickness on the bonding properties. Following the heat treatment, unlike diffusion bonded joints, different growth behavior of IMCs at different interfacial positions of the IFWed joint was observed, which deviated with a varying degree from the parabolic diffusion law. The phenomenon indicated a non-uniform distribution of energy storage along friction interface after welding, resulting from the unique thermo-mechanical conditions in the friction welding process. Moreover, the highest bonding strength appeared at the central interface region where no obvious IMCs layer was founded in the as-welded joint, and a negative correlation between IMCs thickness layer and bonding strength was observed. Therefore, for designing a high-performance Al/steel IFWed joint, the distribution and the corresponding thickness of IMCs should be carefully considered.

Asymptotic stability of viscous shocks in the modular Burgers equation

Dynamics of viscous shocks is considered in the modular Burgers equation, where the time evolution becomes complicated due to singularities produced by the modular nonlinearity. We prove that the viscous shocks are asymptotically stable under odd and general perturbations. For the odd perturbations, the proof relies on the reduction of the modular Burgers equation to a linear diffusion equation on a half-line. For the general perturbations, the proof is developed by converting the time-evolution problem to a system of linear equations coupled with a nonlinear equation for the interface position. Exponential weights in space are imposed on the initial data of general perturbations in order to gain the asymptotic decay of perturbations in time. We give numerical illustrations of asymptotic stability of the viscous shocks under general perturbations.

Propulsion reversal in oscillating-bubble powered micro swimmer

A gaseous bubble trapped in a one-end-open tube generates a microstreaming flow when oscillated by externally excited acoustic waves, which has been proven as an effective propulsion force for underwater micro robots. The propulsion force is known to be a pushing force on the tube since the microstreaming flow is outgoing from the tube exit. This article reports that this microstreaming flow and thus propulsion direction can be reversed when the gas–liquid interface of the bubble is exposed outside of the tube, which is confirmed using two types of tubes: commercially available capillary tubes and microfabricated parylene tubes. This result implies that control of the interface position in the tube relative to the exit is critically important. As such, two methods are incorporated to control the position of the interface and thus the length of trapped bubble: neck structure at the tube exit and plasma treatment of the tube. The neck structures enable the three-phase contact line to pin at the neck, thus providing uniform bubble lengths and warranting consistent oscillation spectra and propulsion behaviors. However, the reversal in microstreaming flow and propulsion does not occur since the bubble interface with the neck structure still stays inside the tube. The plasma treatment makes the three-phase contact line pinned right at the tube exit such that the entire interface is exposed to the outside of the tube. In this case, the reversal in microstreaming and propulsion consistently occurs, which provides an additional option to control the propulsion and steering of micro swimmers powered by acoustically oscillating bubbles.

Synthesis of Polymer Janus Particles with Tunable Wettability Profiles as Potent Solid Surfactants to Promote Gas Delivery in Aqueous Reaction Media.

Janus particles exhibit a strong tendency to directionally assemble and segregate to interfaces and thus offer advantages as colloidal analogues of molecular surfactants to improve the stability of multiphasic mixtures. Investigation and application of the unique adsorption properties require synthetic procedures that enable careful design and reliable control over the particles’ asymmetric chemistry and wettability profiles with high morphological uniformity across a sample. Herein, we report on a novel one-step synthetic approach for the generation of amphiphilic polymer Janus particles with highly uniform and tunable wettability contrasts, which is based on using reconfigurable bi-phasic Janus emulsions as versatile particle scaffolds. Two phase-separated acrylate oils were used as the constituent droplet phases and transformed into their solidified Janus particle replicas via UV-induced radical polymerization. Using Janus emulsions as particle precursors offers the advantage that their internal droplet geometry can be fine-tuned by changing the force balance of surface tensions acting at the individual interfaces via surfactants or the volume ratio of the constituent phases. In addition, preassembled functional surfactants at the droplet interfaces can be locked in position upon polymerization, which enables both access toward postfunctionalization reaction schemes and the generation of highly uniform Janus particles with adjustable wettability profiles. Depending on the particle morphology and wettability, their interfacial position can be adjusted, which allows us to stabilize either air bubbles-in-water or water droplets-in-air (liquid marbles). Motivated by the interfacial activity of the particles and particularly the longevity of the resulting particle-stabilized air-in-water bubbles, we explored their ability to promote the delivery of oxygen inside a liquid-phase reaction medium, namely, for the heterogeneous Au-NP-mediated catalytic oxidation of d-glucose. We observed a 2.2-fold increase in the reaction rate attributed to the increase of the local concentration of oxygen around catalysts, thus showcasing a new strategy to overcome the limited solubility of gases in aqueous reaction media.

Homogenization of Composites with Extended General interfaces: Comprehensive Review and Unified Modeling

Abstract Interphase regions that form in heterogeneous materials through various underlying mechanisms such as poor mechanical or chemical adherence, roughness, and coating, play a crucial role in the response of the medium. A well- established strategy to capture a finite-thickness interphase behavior is to replace it with a zero-thickness interface model characterized by its own displacement and/or traction jumps, resulting in different interface models. The contributions to date dealing with interfaces commonly assume that the interface is located in the middle of its corresponding interphase. We revisit this assumption and introduce a universal interface model, wherein a unifying approach to the homogenization of heterogeneous materials embedding interfaces between their constituents is developed. The proposed novel interface model is universal in the sense that it can recover any of the classical interface models. Next, via incorporating this universal interface model into homogenization, we develop bounds and estimates for the overall moduli of fiber-reinforced and particle-reinforced composites as functions of the interface position and properties. Furthermore, we elaborate on the computational implications of this interface model. Finally, we carry out a comprehensive numerical study to highlight the influence of interface position, stiffness ratio and interface parameters on the overall properties of composites, where an excellent agreement between the analytical and computational results is observed. The developed interface-enhanced homogenization framework also successfully captures size effects, which are immediately relevant to emerging applications of nano-composites due their pronounced interface effects at small scales.

Energy localization and topological protection of a locally resonant topological metamaterial for robust vibration energy harvesting

During the past decade, metamaterial-based vibration energy harvesters (meta-VEHs) have been increasingly developed owing to the extraordinary characteristics of metamaterials, such as locally resonant bandgap, defect state, and wave focusing features. In this paper, the interface state, a feature recently found in topological metamaterials, is exploited for low-frequency vibration energy harvesting. The topological meta-VEH consists of two kinds of locally resonant metamaterials with different topological phases and a piezoelectric transducer being installed at the interface between these two metamaterials. First, the governing equations of the topological meta-VEH are established based on the mass–spring model. Subsequently, the dispersion relation of such a one-dimensional topological meta-VEH is obtained by applying Bloch's theorem. It is revealed that the interface mode can be attained in the low-frequency range through the band folding of the locally resonant metamaterial. Moreover, the finitely long model of this topological meta-VEH is built, and the transmittance response is calculated both analytically and numerically. Subsequently, the potential benefits of topological metamaterial, including wave localization and topological protection, are thoroughly investigated. It is found that the elastic energy in the interface state is localized at the interface position, resulting in a significant improvement in output power. Meanwhile, the topological protection property can significantly improve the robustness of the interface mode, thus achieving outstanding energy harvesting performance. Finally, to further enhance the energy harvesting performance, the stiffness tuning method and the defect enhancement method are proposed. It is found that integrating the defect mode and interface mode not only improves the output voltage but also achieves the capability of a highly robust energy harvesting.

Interface coupling model of Stefan phase change during thermal dissociation of natural gas hydrate

The thermal dissociation process that occurs in a natural gas hydrate is a Stefan phase-change problem with moving boundaries. Based on the integral form of a heat conduction model, for a continuous single-phase hydrate control volume, the energy conservation condition for interfacial coupling during the Stefan phase-change was built for the control volume of thermal dissociation of a natural gas hydrate with a sharp moving boundary. A Neumann solution of the Stefan phase-change model was obtained for the thermal dissociation in a semi-infinite natural gas hydrate reservoir, using Boltzmann similar variables. A unique solution for the Stefan model was found using a monotonic of the transcendental equation. An example analysis was used to verify, the monotonicity of the transcendental equation, and uniqueness of the solution of the Stefan model. The MATLAB program was used to study, the laws of temperature distribution, and dissociation frontal brim during the thermal dissociation process in a hydrate reservoir. Sensitivity fitting studies showed that, the solution of transcendental equation and interface position gradually increased, whereas, the depth penetrated and time penetrated gradually decreases with increasing temperature.

Anthropogenic nitrogen pollution in mangrove ecosystems along Dar es Salaam and Bagamoyo coasts in Tanzania

Mangroves are among the most productive coastal ecosystems; however, they are prone to anthropogenic pollution due to their land-sea interface position. We used stable nitrogen isotopes and spectrophotometric nitrate analysis to study the anthropogenic pollution in five mangrove ecosystems in Tanzania, including two polluted (Mzinga and Kizinga), one moderate (Kunduchi) and non-polluted (Mbegani and Ras Dege) sites. Also, we tested the suitability of mangrove leaves, roots, sediment, and gastropod as indicators of anthropogenic nitrogen pollution using stable δ15N isotope analysis. Results revealed higher than 10‰ δ15N values in all analysed components and the highest nitrate concentrations of 16.44 mg L−1 in the interstitial waters at the polluted sites, indicating anthropogenic nitrogen inputs. The δ15N enrichment increased in the order: non-polluted < moderate < polluted. The polluted sites are fed by freshwater creeks and probably receive high loads of domestic sewage from the surrounding communities, industries, and agricultural effluents. Therefore, to protect mangrove ecosystems, proper waste and wastewater management upstream are recommended.

Interface-position-dependent structure evolution and mechanical behavior of corrugated cold rolled Cu/Al clad plate: experiment and simulation

Abstract Cu/Al corrugated clad plates were prepared by the novel corrugated cold roll bonding (CCRB) process to investigate the stress states, microstructures and mechanical behaviors of the corrugated clad plate adjacent to various corrugated interface positions by experimental and numerical simulation methods. The results show that the CCRB process induces multiple “cross shear” zones in the rolling deformation zone. This greatly accelerates the plastic deformation of Cu layer and significantly diminishes the deformation difference between Cu and Al dissimilar metals with a result of the reduced warpage amplitude. Also, the microstructure at different positions is obviously different due to the various stress states and deformations. Especially at positions III (trough) and IV (front waist), the elongated grains and fine equiaxed grains are formed under the severe plastic deformation and the shear stress. And the ultimate tensile strength achieves a maximum value of 209.25 MPa at position III (trough), and does the minimum value of 182.43 MPa at position II (back waist). The strength of the Cu/Al corrugated clad plate is affected by both the dislocation strengthening and grain boundary strengthening. When the plastic deformation is severe, the dislocation strengthening mechanism is dominant in Cu matrix, while the fine-grain strengthening mechanism in Al matrix.

Mass-constrained basin basement mapping

The irregular interface model setting side by side two dense homogeneous media has found many applications in gravity-data exploration such as for petroleum and gas in sedimentary basins, groundwater resources in buried paleochannels, characterization of abandoned landfills, and variable regolith-depth mapping. Despite its simplicity and wide range of applicability, the determination of the interface position from inverting surface gravity data configures an ill-posed problem requiring specialized regularizing procedures to produce reliable results. Common approaches to obtain stable and reliable solutions require a judicious choice of regularizing functionals, each of them able to convey a desired geologic attribute that the unknown interface is expected to feature. In assuming a style that the unknown interface may have, a mathematical procedure is elected to convey such an attribute when the interface is mapped from gravity data inversion. We have developed a different approach to the interface mapping problem by imposing a common constraint that all model solutions must have, meanwhile preventing oscillations for the interface to be mapped. As a constraint that the solutions must have, we fix the volume or the cross section for 2D structures that the anomalous density structure has. This volume (or 2D cross section) is determined by applying the mass excess theorem to the measured gravity data and assuming as known the density contrast caused by the two media paired by the interface. We find that this simple formulation for the interface-mapping problem is effective in imaging a variety of basin styles without introducing specific information about the interface attributes. Our technique is applied to invert previously published gravity data in cases with good drillhole control or with a known interface.

The Influence of Liquid–Solid Interface Position and Shape on the Electromagnetic Forcing Parameter During Horizontal Solidification

The forcing parameter is an important value for determining the solidification conditions under electromagnetic impact. This parameter tends to change and affect the solidification conditions. The aim of this work is to investigate the influence of the liquid–solid interface position and deformation on the forcing parameter. Electromagnetic analysis by the finite element method, validated experimentally, was used as the main research tool. Horizontal solidification in the presence of a traveling magnetic field installation was chosen as the experimental setup. Various interface deformations were investigated, as well as its propagation. As a result of the calculation, the electromagnetic (EM) forcing parameter functions were obtained. It was determined that the liquid–solid interface propagation causes significant attenuation of the forcing parameter, as well as interface slope. The results were analyzed and approximated by analytical functions. These functions can be easily used to determine values for various solidification conditions and stages.

On an averaged model for immiscible two‐phase flow with surface tension and dynamic contact angle in a thin strip

AbstractWe consider a model for the flow of two immiscible fluids in a two‐dimensional thin strip of varying width. This represents an idealization of a pore in a porous medium. The interface separating the fluids forms a freely moving interface in contact with the wall and is driven by the fluid flow and surface tension. The contact‐line model incorporates Navier‐slip boundary conditions and a dynamic and possibly hysteretic contact angle law. We assume a scale separation between the typical width and the length of the thin strip. Based on asymptotic expansions, we derive effective models for the two‐phase flow. These models form a system of differential algebraic equations for the interface position and the total flux. The result is Darcy‐type equations for the flow, combined with a capillary pressure–saturation relationship involving dynamic effects. Finally, we provide some numerical examples to show the effect of a varying wall width, of the viscosity ratio, of the slip boundary condition as well as of having a dynamic contact angle law.

Experimental investigation on the melting characteristics of n-octadecane with electric field inside macrocapsule

Experiments on the melting characteristics of n-octadecane with electric field inside a cavity are carried out. The classical differentially heated cavity is considered to explore the effect of electric field on solid-liquid phase change heat transfer. The influence of the applied voltage's polarity and magnitude on the melting process of n-octadecane is investigated. The dynamic evolution of the liquid fraction and solid-liquid interface positions with melting time are reported. The velocity fields and electric current-voltage curves are also presented for understanding the physical mechanism. Results show that Coulomb force plays the central role in affecting the melting heat transfer process. The electric field would hinder or accelerate the melting process depending on the strength of electric field. When the applied voltage set to the right wall that is cold is larger than 10.0kV, the electric field would obviously accelerate the melting process. For a cavity with the length of 40.0 mm, the charge injection is hardly taken place when the maximum DC voltage of 20.0kV is applied, so the free charge carriers are mainly generated by conduction mechanism.