Interface Position Research Articles

Controllable preparation of double emulsion droplets in a dual-coaxial microfluidic device

This article investigates the formation process of double emulsions, controlling their sizes, and manipulating the encapsulation process in a three nested microcapillary tube configuration. In the proposed geometry, as a result of the interaction of liquids using dripping instability, double emulsions are generated. Governing equations are discretized using the finite-element method utilizing COMSOL Multiphysics 5.4 software, employing axisymmetric assumption, and the interface position is tracked by solving additional transport equations of the phase-field method. Influence of phase flow rates in the form of inner phase Weber number, Wein, intermediate phase capillary number, Caint, and outer phase capillary number, Caout, are studied on the flow regimes and characteristics of double emulsions. Results exhibit that the outer phase flow rate has the most influence among other phase flow rates. Additionally, three distinct regimes, named single emulsion, decussate, and double emulsion, are observed by changing intermediate phase flow rare. Furthermore, satellite droplets are detected at relatively high flow rates of the outer phase due to the second instability induced by the continuous phase to the intermediate phase jet. A comparison between the formation frequency of the present study with some similar works, including both capillary-based and channel-based devices, unveils that the existing configuration has a higher throughput of double emulsion generation in a broad range of flow rates.

Direct numerical simulation of evaporation and condensation with the geometric VOF method and a sharp-interface phase-change model

The paper describes a coupling of the geometric Volume-of-Fluid (VOF) method with a sharp-interface phase-change model for Cartesian and axisymmetric grids. Both the interfacial position and the temperature field are resolved with subgrid accuracy. Species transport with implicit diffusion is considered in the gas phase. The numerical implementation of the method developed here is described in detail, as well as its coupling with the incompressible Navier-Stokes solver PSI-BOIL, which features a hybrid, finite-volume/finite-difference approach based on a fixed, rectangular grid. Several verification cases have been undertaken to ensure correct implementation of the method in the code and to evaluate its performance. These include simulations of the Stefan problem, sucking problem and bubble growth in superheated liquid. In all cases, very good agreement with the analytical solution has been reached and grid convergence has been demonstrated. Simulations of evaporating and condensing rising bubbles, for which high-quality measured data are available, are also presented to serve as validation tests. Reasonable agreement of simulation results with experimental data has been recorded and applicability of the method to problems without inherent symmetry and featuring turbulence is shown. This work represents the first successful application of a geometric VOF method coupled with a sharp-interface phase-change model and species transport to non-trivial problems. The achieved performance of our algorithm in the verification and validation exercise represents an important step in the development of multiphase codes capable of accurately resolving complex three-dimensional multiphase flows.

Existence of global steady subsonic Euler flows with collision through 2D infinitely long nozzles

In this paper, we study the global existence of steady subsonic flows with collision, where the collision is caused by a confluence of two semi‐infinitely incoming flows that are nonmiscible steady subsonic irrotational Euler flows come from two different infinitely nozzles. First, we prove that when the total flux of two incoming flows is less that the critical mass flux, there exists a unique global smooth subsonic flow with collision. Meanwhile, the interface between two flows is a smooth free interface, which is determined uniquely by the mass fluxes of incoming flows. Second, by using the blowup argument, we establish the asymptotic behaviors for the stream function. Finally, we prove that the position of free interface can be determined uniquely by the mass fluxes of incoming flows. Moreover, we establish the monotonicity of the relation between the position of free interface and the mass fluxes of incoming flows.

Automatic identification of rock formation interface based on borehole imaging

ABSTRACT Borehole imaging, one of the main methods of rock formation detection, is widely used in mining, tunnels, petroleum, and other fields of engineering. However, the method of manually identifying the characteristic of rock formation based on borehole imaging is greatly affected by subjective factors. For example, it should be noted that when the rock layer color is similar, the position of the rock interface may be different. In this paper, a method of quantitatively describing the characteristics of the rock formation is proposed, and the automatic recognition of the rock interface is realized. Firstly, the calculation method of rock dip angle and position based on borehole image with 360° wall surface development is proposed. Secondly, the three-dimensional distribution characteristics of the gray values of the rock layer are used to quantitatively describe the characteristics of the rock layer. Finally, an automatic recognition method of rock formation interface based on change-point detection algorithm is proposed. In addition, the recognition effect of the rock formation interface is analyzed by experiments and applied in the field. Research shows that, compared with method two, method one can determine the rock inclination. But its anti-interference ability is poor. Method two can better determine the position of the rock interface. The method is of great significance to the intelligent development of the borehole imaging system and promotes safe, efficient, and sustainable mining in coal mines.

Validated Guidelines for Simulating Centrifugal Blood Pumps

Rotary blood pumps (RBPs) employed as ventricular assist devices are developed to support the ventricles of patients suffering from heart failure. Computational Fluid Dynamics (CFD) is frequently used to predict the performance and haemocompatibility of these pumps during development, however different simulation techniques employed by various research groups result in inconsistent predictions. This inconsistency is further compounded by the lack of standardised model validation, thus it is difficult to determine which simulation techniques are accurate. To address these problems, the US Food and Drug Administration (FDA) proposed a simplified centrifugal RBP benchmark model. The aim of this paper was to determine simulation settings capable of producing accurate predictions using the published FDA results for validation. This paper considers several studies to investigate the impact of simulation options on the prediction of pressure and flow velocities. These included evaluation of the mesh density and interface position through steady simulations as well as time step size and turbulence models (k-ε realizable, k-ω SST, k-ω SST Intermittency, RSM ω-based, SAS and SBES) using a sliding mesh approach. The most accurate steady simulation using the k-ω turbulence model predicted the pressure to within 5% of experimental results, however experienced issues with unphysical velocity fields. A more computationally expensive transient simulation that used the Stress-Blended Eddy Simulation (SBES) turbulence model provided a more accurate prediction of the velocity field and pressure rise to within experimental variation. The findings of the study strongly suggest that SBES can be used to better predict RBP performance in the early development phase.

Inferring incompressible two-phase flow fields from the interface motion using physics-informed neural networks

In this work, physics-informed neural networks are applied to incompressible two-phase flow problems. We investigate the forward problem, where the governing equations are solved from initial and boundary conditions, as well as the inverse problem, where continuous velocity and pressure fields are inferred from scattered-time data on the interface position. We employ a volume of fluid approach, i.e. the auxiliary variable here is the volume fraction of the fluids within each phase. For the forward problem, we solve the two-phase Couette and Poiseuille flow. For the inverse problem, three classical test cases for two-phase modeling are investigated: (i) drop in a shear flow, (ii) oscillating drop and (iii) rising bubble. Data of the interface position over time is generated by numerical simulation. An effective way to distribute spatial training points to fit the interface, i.e. the volume fraction field, and the residual points is proposed. Furthermore, we show that appropriate weighting of losses associated with the residual of the partial differential equations is crucial for successful training. The benefit of using adaptive activation functions is evaluated for both the forward and inverse problem.

Dynamics of domain boundaries at metal-organic interfaces.

Domain boundaries are a determining factor in the performance of organic electronic devices since they can trap mobile charge carriers. We point out the possibility of time-dependent motion of these boundaries and suggest that their thermal fluctuations can be a source of dynamic disorder in organic films. In particular, we study the C8-BTBT monolayer films with several different domain boundaries. After characterizing the crystallography and diversity of structures in the first layer of C8-BTBT on Au(111), we focus on quantifying the domain boundary fluctuations in the saturated monolayer. We find that the mean squared displacement of the boundary position grows linearly with time at early times but tends to saturate after about 7 s. This behavior is ascribed to confined diffusion of the interface position based on fits and numerical integration of a Langevin equation for the interface motion.

Experimental investigation of the effect of inclination angle on the performance of phase change material based finned heat sink

This paper presents an experimental study to investigate the effect of inclination angle on the thermal performance of phase change material (PCM) based heat sinks without and with plate fins. Paraffin wax with melting temperature range 58–62 °C is used as PCM. Three different heat flux values such as 1.3, 2.0 and 2.7 kW/m2 are chosen to analyze the effect of heat flux variation on the melting of PCM. Also, tests are carried out with various angles of inclination from 0o to 90o at increments of 15o. The solid-liquid interface position is studied through photographic observation. Effect of angle of inclination and heat flux values on the operating and melting time has been reported. It has been observed that the operating time is relatively not dependent on the angle of inclination for the unfinned heat sink without PCM and three finned heat sink filled with PCM. The increase in operating time with the decrease in inclination angle from 90o to 0o is found to be 66%, 45% and 43% for PCM based unfinned, one finned and two finned heat sinks, respectively at set point temperature (SPT) = 75 °C and a heat flux of 2.0 kW/m2. Also, the melting time is found to decreases by 44% for unfinned heat sink and 30% for finned heat sinks with the reduction in inclination angle from 90o to 0o.

Effects of Asymmetric Boundary Conditions on Freezing Process of Raw Potatoes with Variable Thermophysical Properties

In this paper, the effects of asymmetric boundary conditions encountered in refrigerators on the freezing process of raw potatoes were investigated in order to improve their preservation and extend their shelf life. A 2D numerical model, based on experimentally determined temperature-dependent thermophysical properties of potatoes, was first developed using COMSOL Multiphysics software in order to thermally characterize a potato during freezing process. This potato, having a square cross-section of various edge lengths (40 mm and 50 mm), was placed on a meshed surface and subjected to a coolant (air) flow of temperature −40 $$^{\circ }$$ C and different velocities (ranging between 0 m $$\cdot$$ s $$^{-1}$$ and 8 m $$\cdot$$ s $$^{-1}$$ ) from its top, left, and right sides. The evolutions over time of the temperature distribution and the soft–solid interface position in the potato were determined and analyzed. The developed model was then validated thanks to experiments carried out in the same conditions considered in the numerical simulations. An analytical model of the literature was finally established and the obtained results showed an acceptable agreement with the experimental data.

Nanochannel‐Based Interfacial Memristor: Electrokinetic Analysis of the Frequency Characteristics

AbstractAs a novel class of memristors, nanochannel‐based interfacial memristors in polydimethylsiloxane offer great flexibility and low cost. With practical attributes of novel transport phenomenon in nanofluidics, analysis of the physical properties and operational mechanisms in such memristor devices is possible. Made of pure soft‐matter materials, this type of device exhibits facile tuning of device conductance via the modification of solution interface positions. Under continuous sweep voltage, a typical hysteresis loop for a memristor can be observed. In this article, the dynamic frequency characteristics of this device is measured, which is regarded as a typical memristor characteristic as previously predicted. However, the physical mechanism behind such memristive behaviors and frequency characteristics is seldomly reported. Generalizing conventional physical models, here a comprehensive model including continuous voltage changes and surface tension modifications is proposed, which is able to predict the interface position changes and explain the conductance switching and frequency property experimentally observed in the device. Provided with a probable explanation of the physical mechanism behind this class of device, the model can serve as a candidate method in designing new nanochannel‐based structures or materials, aiming at more novel functionalities in neuromorphic computation.

Towards implementation of PDE control for Stefan system: Input-to-state stability and sampled-data design

The Stefan system is a representative model for a liquid–solid phase change which describes the dynamics of a material’s temperature profile and the liquid–solid interface position. Our previous work designed a boundary feedback control to stabilize the phase interface position modeled by the Stefan system. This paper resolves two issues our previous work did not study, that are, the robustness analysis under the unknown heat loss and the digital control action. First, we introduce the one-phase Stefan problem with a heat loss by modeling a 1-D diffusion Partial Differential Equation (PDE) dynamics of the liquid temperature and the interface position governed by an Ordinary Differential Equation (ODE) with a time-varying disturbance. We focus on the closed-loop system under the control law proposed in our previous work, and show an estimate of L2 norm in a sense of Input-to-State Stability (ISS) with respect to the unknown heat loss. Second, we consider the sampled-data control of the one-phase Stefan problem without the heat loss, by applying Zero-Order-Hold (ZOH) to the control law in our previous work. We prove that the closed-loop system under the sampled-data control law satisfies the global exponential stability in the spatial L2 norm. Analogous ISS result for the two-phase Stefan problem which incorporates the dynamics of the solid phase is also obtained. Numerical simulation verifies our theoretical results for showing the robust performance under the heat loss and the digital control implemented to vary at each sampling time.

Correction to 'Climate-driven benthic invertebrate activity and biogeochemical functioning across the Barents Sea polar front'.

You have accessMoreSectionsView PDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmail Cite this article Solan Martin, Ward Ellie R., Wood Christina L., Reed Adam J., Grange Laura J. and Godbold Jasmin A. 2021Correction to ‘Climate-driven benthic invertebrate activity and biogeochemical functioning across the Barents Sea polar front’Phil. Trans. R. Soc. A.3792020043820200438http://doi.org/10.1098/rsta.2020.0438SectionYou have accessCorrectionCorrection to ‘Climate-driven benthic invertebrate activity and biogeochemical functioning across the Barents Sea polar front’ Martin Solan Martin Solan Google Scholar Find this author on PubMed Search for more papers by this author , Ellie R. Ward Ellie R. Ward Google Scholar Find this author on PubMed Search for more papers by this author , Christina L. Wood Christina L. Wood Google Scholar Find this author on PubMed Search for more papers by this author , Adam J. Reed Adam J. Reed Google Scholar Find this author on PubMed Search for more papers by this author , Laura J. Grange Laura J. Grange Google Scholar Find this author on PubMed Search for more papers by this author and Jasmin A. Godbold Jasmin A. Godbold Google Scholar Find this author on PubMed Search for more papers by this author Martin Solan Martin Solan Google Scholar Find this author on PubMed Search for more papers by this author , Ellie R. Ward Ellie R. Ward Google Scholar Find this author on PubMed Search for more papers by this author , Christina L. Wood Christina L. Wood Google Scholar Find this author on PubMed Search for more papers by this author , Adam J. Reed Adam J. Reed Google Scholar Find this author on PubMed Search for more papers by this author , Laura J. Grange Laura J. Grange Google Scholar Find this author on PubMed Search for more papers by this author and Jasmin A. Godbold Jasmin A. Godbold Google Scholar Find this author on PubMed Search for more papers by this author Published:01 March 2021https://doi.org/10.1098/rsta.2020.0438See original article.Climate-driven benthic invertebrate activity and biogeochemical functioning across the Barents Sea polar frontPhil. Trans. R. Soc. A378, 20190365 (Published online 31 August 2020) (doi:10.1098/rsta.2019.0365)In the original version of this article, the data for station Xs were missing from figure 2. This has now been corrected.Figure 2. The effects of station and year on mean (s.e., n = 4) bioturbation activity as indicated by (a) surface boundary roughness, (b) mean mixed depth, f−SPILmean, (c) maximum mixed depth, f−SPILmax and (d) ventilatory behaviour, [Br− ] for stations B13–B17 in 2017 (black) and stations B13–B17 and Xs in 2018 (grey). For [Br− ], negative values indicate increased bioirrigation. In panels (b) and (c), dashed lines indicate the position of the sediment-water interface. In panel (d), the dotted line indicates no change in [Br− ]. Sediment profile images and associated luminophore distribution profiles are presented in electronic supplementary material, figures S5–S12.Download figureOpen in new tabDownload PowerPoint Previous Article FiguresRelatedReferencesDetailsRelated articlesClimate-driven benthic invertebrate activity and biogeochemical functioning across the Barents Sea polar frontAug 31, 2020, 12:00:00 AMPhilosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences This Issue19 April 2021Volume 379Issue 2195Discussion meeting issue ‘Intensification of short-duration rainfall extremes and implications for flash flood risks’ organised and edited by Hayley Fowler, Conrad Wasko and Andreas F. Prein Article InformationDOI:https://doi.org/10.1098/rsta.2020.0438Published by:Royal SocietyPrint ISSN:1364-503XOnline ISSN:1471-2962History: Published online01/03/2021Published in print19/04/2021 License:© 2021 The Author(s)Published by the Royal Society. All rights reserved. Citations and impact Subjectsbiogeochemistry

Solving phase change problems via a precise time-domain expanding boundary element method combined with the level set method

Phase change problems are investigated numerically in this study. A combined precise time-domain expanding boundary element method (PTEBEM) and the level set method is proposed. The PTEBEM is employed on one hand to solve the temporal-spatial field partial differential equations of the transient heat transfer problem. The radial integral method is used to transform the domain integral of the governing equation into a boundary integral. On the other hand, the level set method which is widely used to track crack trajectories is here employed to handle the complicated topological changing during phase change, to record the position of material phase interface during moving, merging or slipping. The formed numerical framework is further enhanced for higher stability. To demonstrate the accuracy and robustness of the proposed method, a few examples are provided.

Structural parameter study on stress intensity factors of interfacial crack in thermal barrier coatings

Cracks on the wave-shaped interface between the top coating (TC) layer and the bonding coating (BC) layer of thermal barrier coatings (TBCs) are unavoidable during manufacture and operation, which may reduce the strength of the TBCs under thermal shock. A model with curved crack on the wave-shaped interface is established, and the influences of structural parameters, including the porosity, the distribution of pores and thickness of the TC layer, the interface roughness and position of crack tip on the wave-shaped interface, on the stress intensity factors (SIFs) of the cracks during thermal shock are numerically studied with the finite element method (FEM). According to the microstructure of the TBCs, the shape of a pore is assumed to be elliptical, and the pores are randomly distributed in the TC layer. A program is developed to automatically generate the distribution of pores. The variation laws of the stress intensity factors (SIFs), KI and KII, of the curved interfacial crack under various structural parameters are obtained and analyzed, which may provide an instruction for the design of the TBCs.

Interface-dependent tunable elastic interface states in soft metamaterials

Elastic interface states, which are usually generated at the interface of two connected domains with opposite topological invariant, have been successfully demonstrated in periodic structures. Therefore, the interface states determined by the position of interface between two domain walls in one-dimensional elastic systems are rarely reported, which were mainly restricted by the mirror-symmetric geometry of the unit cell. Jointing interface-dependent interface states were mostly implemented with analogs of quantum valley Hall effects in two-dimensional systems. Herein, we first observe two types of elastic interface states simultaneously occurred in one-dimensional combined metamaterials, where two interface modes separately located at two connected domain walls and they can be actively tuned simply through deforming two components on two sides. Flexible and versatile frequency shift and switch on–off characteristics of combination of two interface modes are demonstrated, which may be employed in the multifunctional elastic wave filters, tunable energy harvesting, and elastography devices. Our primitive cell of the soft metamaterial, which breaks the inversion symmetry along the horizontal direction, may be generalized to realize tunable elastic valley Hall edge states.

Optical Tracking of the Interfacial Dynamics of Single SARS-CoV-2 Pseudoviruses.

The frequent detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA in healthcare environments, accommodations, and wastewater has attracted great attention to the risk of viral transmission by environmental fomites. However, the process of SARS-CoV-2 adsorption to exposed surfaces in high-risk environments remains unclear. In this study, we investigated the interfacial dynamics of single SARS-CoV-2 pseudoviruses with plasmonic imaging technology. Through the use of this technique, which has high spatial and temporal resolution, we tracked the collision of viruses at a surface and differentiated their stable adsorption and transient adsorption. We determined the effect of the electrostatic force on virus adhesion by correlating the solution and surface chemistry with the interfacial diffusion velocity and equilibrium position. Viral adsorption was found to be enhanced in real scenarios, such as in simulated saliva. This work not only describes a plasmonic imaging method to examine the interfacial dynamics of a single virus but also provides direct measurements of the factors that regulate the interfacial adsorption of SARS-CoV-2 pseudovirus. Such information is valuable for understanding virus transport and environmental transmission and even for designing anticontamination surfaces.

On the Transient Atomic/Heat Diffusion in Cylinders and Spheres with Phase Change: A Method to Derive Closed-Form Solutions

Analytical solutions for the transient single-phase and two-phase inward solid-state diffusion and solidification applied to the radial cylindrical and spherical geometries are proposed. Both solutions are developed from the differential equation that treats these phenomena in Cartesian coordinates, which are modified by geometric correlations and suitable changes of variables to achieve closed-form solutions. The modified differential equations are solved by using two well-known closed-form solutions based on the error function, and then equations are obtained to analyze the diffusion interface position as a function of time and position in cylinders and spheres. These exact correlations are inserted into the closed-form solutions for the slab and are used to update the roots for each radial position of the moving boundary interface. The predictions provided by the proposed analytical solutions are validated against the results of a numerical approach. Finally, a comparative study of diffusion in slabs, cylinders, and spheres is also presented for single-phase and two-phase solid-state diffusion and solidification, which shows the importance of the effects imposed by the radial cylindrical and spherical curvatures with respect to the Cartesian coordinate system in the process kinetics. The analytical model is proved to be general, as far as, a semi-infinite solution for diffusion problems with phase change exists in the form of the error function, which enables exact closed-form analytical solutions to be derived, by updating the root at each radial position the moving boundary interface.

Experimental study of miscibility of liquids in binary droplet collisions

The paper presents experimental research findings on binary collisions of droplets of water, glycerol and surfactant solutions containing fluorophore and a dye to record the position and form of the droplet-droplet interface at the moment of collision. The fluorophore used in the first droplet was Rhodamine B with a concentration of 1,000 μg/l. The gel dye concentration in the second droplet was 0.5 vol%. The integral characteristics of droplet miscibility were investigated by analyzing changes in the fluorescence intensity of liquid when recording laser-induced fluorescence effects. Droplets were illuminated by a system of spotlights and a continuous wave laser. Droplet collisions were captured by a high-speed video camera. The conditions were recorded for the formation of a droplet-droplet interface with different geometry while varying the dimensions, velocities, trajectories and impact angles. After processing the video frames, we plotted collision regime maps, calculated the ratios of free surface areas of liquid before and after droplet breakup, and determined the characteristics of secondary fragments. In particular, fragments of the target and projectile, as well as mixed fragments were distinguished. The fluorescence of two initial droplets and the droplet formed from their coalescence was recorded. We established the characteristics of the near-surface layer deformation of two colliding droplets and rates of liquid miscibility, as well as times of complete miscibility of droplets during coalescence.

Real Time Predictions of VGF-GaAs Growth Dynamics by LSTM Neural Networks

The aim of this study was to assess the aptitude of the recurrent Long Short-Term Memory (LSTM) neural networks for fast and accurate predictions of process dynamics in vertical-gradient-freeze growth of gallium arsenide crystals (VGF-GaAs) using datasets generated by numerical transient simulations. Real time predictions of the temperatures and solid–liquid interface position in GaAs are crucial for control applications and for process visualization, i.e., for generation of digital twins. In the reported study, an LSTM network was trained on 1950 datasets with 2 external inputs and 6 outputs. Based on network performance criteria and training results, LSTMs showed the very accurate predictions of the VGF-GaAs growth process with median root-mean-square-error (RMSE) values of 2 × 10−3. This deep learning method achieved a superior predictive accuracy and timeliness compared with more traditional Nonlinear AutoRegressive eXogenous (NARX) recurrent networks.

Effects of Total Thermal Balance on the Thermal Energy Absorbed or Released by a High-Temperature Phase Change Material.

Front tracking and enthalpy methods used to study phase change processes are based on a local thermal energy balance at the liquid–solid interface where mass accommodation methods are also used to account for the density change during the phase transition. Recently, it has been shown that a local thermal balance at the interface does not reproduce the thermodynamic equilibrium in adiabatic systems. Total thermal balance through the entire liquid–solid system can predict the correct thermodynamic equilibrium values of melted (solidified) mass, system size, and interface position. In this work, total thermal balance is applied to systems with isothermal–adiabatic boundary conditions to estimate the sensible and latent heat stored (released) by and salts which are used as high-temperature phase change materials. Relative percent differences between the solutions obtained with a local thermal balance at the interface and a total thermal balance for the thermal energy absorbed or released by high-temperature phase change materials are obtained. According to the total thermal balance proposed, a correction to the liquid–solid interface dynamics is introduced, which accounts for an extra amount of energy absorbed or released during the phase transition. It is shown that melting or solidification rates are modified by using a total thermal balance through the entire system. Finally, the numerical and semi-analytical methods illustrate that volume changes and the fraction of melted (solidified) solid (liquid) estimated through a local thermal balance at the interface are not invariant in adiabatic systems. The invariance of numerical and semi-analytical solutions in adiabatic systems is significantly improved through the proposed model.