Averaged Dynamics of Fluids near the Oscillating Interface in a Hele-Shaw Cell

The steady flow in a Hele-Shaw cell filled with fluids with a high viscosity contrast in the presence of fluid oscillations is experimentally studied.The control of oscillatory dynamics of multiphase systems with interfaces is a challenging technological problem.We consider miscible(water and glycerol)and immiscible(water and high-viscosity silicone oil PMS-1000)fluids under subsonic oscillations perpendicular to the interface.Observations show that the interface shape depends on the amplitude and frequency of oscillations.The interface is undisturbed only in the absence of oscillations.Under small amplitudes,the interface between water and glycerol widens due to mixing.When the critical amplitude is reached,the interface becomes unstable to the fingering instability:Aqueous fingers penetrate the high-viscosity glycerol and induce intensive mixing of miscible fluids and associated decay of the instability.After the disappearance of the fingers,the interface takes a U-shape in the central part of the cell.A similar effect is observed for immiscible fluids:The oscillating interface tends to bend to the side of a high-viscosity fluid.Again,when the critical amplitude is reached,the fingering instability arises at the convex interface.This paper focuses on the causes of bending of the initially undisturbed interface between miscible or immiscible fluids.For this purpose,we measure the steady flow velocity near the interface and in the bulk of a high-viscosity fluid using Particle Image Velocimetry(PIV).

Topographic variation and fluid flow characteristics in rough contact interface

Understanding flow characteristics of fluid near rough contact is important for the design of fluid-based lubrication and basic of tribology physics.In this study,the spreading and seepage processes of anhydrous ethanol in the interface between glass and rough PDMS are observed by a homemade optical in-situ tester.Digital image processing technology and numerical simulation software are adapted to identify and extract the topological properties of interface and thin fluid flow characteristics.Particular attention is paid to the dynamic evolution of the contact interface morphology under different stresses,the distribution of microchannels in the interface,the spreading characteristics of the fluid in contact interface,as well as the mechanical driving mechanism.Original surface morphology and the contact stress have a significant impact on the interface topography and the distribution of interfacial microchannels,which shows that the feature lengths of the microchannels,the spreading area and the spreading rate of the fluid are inversely proportional to the load.And the flow path of the fluid in the interface is mainly divided into three stages:along the wall of the island,generating liquid bridges,and moving from the tip side to the root side in the wedge-shaped channel.The main mechanical mechanism of liquid flow in the interface is the equilibrium between the capillary force that drives the liquid spreading and viscous resistance of solid wall to liquid.In addition,the phenomenon of“trapped air”occurs during the flow process due to the irregular characteristics of the microchannel.This study lays a certain theoretical foundation for the research of microscopic flow behavior of the liquid in the rough contact interface,the friction and lubrication of the mechanical system,and the sealing mechanism.

Oscillatory squeeze flow through an Oldroyd-B fluid-saturated porous layer

This study deals with the analytical investigation of oscillatory squeeze film flow through a Brinkman viscoelastic Oldroyd-B fluid-saturated porous layer subject to two vertically harmonically oscillatory disks.The validity of the present proposed analytical solutions is first demonstrated for the Newtonian fluids when bothΛ_(1)andΛ_(2)tend to zero by comparison with the previous literature.Results demonstrate that an increase in the elasticity parameterΛ_(1)correlates with a rise in axial velocities,indicating that the relaxation timeΛ_(1)facilitates enhanced squeeze flow.In the case of squeeze film flow in porous layers,low oscillating frequencies exert minimal effects on axial velocities,independent of variations in the viscoelasticity parameterΛ_(1).However,at higher oscillating frequencies,axial velocities escalate with increasing the viscoelasticity parameterΛ_(1).Furthermore,the retardation timeΛ_(2)of the viscoelastic fluid shows no significant effect on the axial velocity,regardless of oscillating frequency changes in both pure fluids and porous layers.

Dynamics of Low-Viscosity Liquids Interface in an Unevenly Rotating Vertical Layer

The behavior of two immiscible low-viscosity liquids differing in density and viscosity in a vertical flat layer undergoing modulated rotation is experimentally studied.The layer has a circular axisymmetric boundary.In the absence of modulation of the rotation speed,the interphase boundary has the shape of a short axisymmetric cylinder.A new effect has been discovered,under the influence of rotation speed modulation,the interface takes on a new dynamic equilibrium state.A more viscous liquid covers the end boundaries of the layer in the form of thin films,which have the shape of round spots of almost constant radius;with increasing amplitude of the velocity modulation,the wetting boundary expands.It is found that upon reaching the critical amplitude of oscillations,the film of a viscous liquid loses stability,and the outer edge of the wetting spot collapses and takes on a feathery structure.It is shown that this threshold is caused by the development of the Kelvin-Helmholtz oscillatory instability of the film.The spreading radius of a spot of light viscous liquid and its stability are studied depending on the rotation rate,amplitude,and frequency of rotation speed modulation.The discovered averaged effects are determined by different oscillatory interaction of fluids with the end-walls of the cell,due to different viscosities.The effect of films forming can find application in technological processes to intensify mass transfer at interphase boundaries.

Finite Difference Approach on Magnetohydrodynamic Stratified Fluid Flow Past Vertically Accelerated Plate in Porous Media with Viscous Dissipation

This study intends to evaluate the influence of temperature stratification on an unsteady fluid flow past an accelerated vertical plate in the existence of viscous dissipation.It is assumed that the medium under study is a grey,non-scattered fluid that both fascinates and transmits radiation.The leading equations are discretized using the finite differencemethod(FDM).UsingMATLABsoftware,the impacts of flowfactors on flowfields are revealed with particular examples in graphs and a table.In this regard,FDM results show that the velocity and temperature gradients increase with an increase of Eckert number.Furthermore,tables of the data indicate the influence of flow-contributing factors on the skin friction coefficients,and Nusselt numbers.When comparing constant and variable flow regimes,the constant flow regime has greater values for the nondimensional skin friction coefficient.This research is both innovative and fascinating since it has the potential to expand our understanding of fluid dynamics and to improve many different sectors.

The Effects of Thermal Radiation and Viscous Dissipation on the Stagnation Point Flow of a Micropolar Fluid over a Permeable Stretching Sheet in the Presence of Porous Dissipation

In this paper,the effects of thermal radiation and viscous dissipation on the stagnation–point flow of a micropolar fluid over a permeable stretching sheet with suction and injection are analyzed and discussed.A suitable similarity transformation is used to convert the governing nonlinear partial differential equations into a system of nonlinear ordinary differential equations,which are then solved numerically by a fourth–order Runge–Kutta method.It is found that the linear fluid velocity decreases with the enhancement of the porosity,boundary,and suction parameters.Conversely,it increases with the micropolar and injection parameters.The angular velocity grows with the boundary,porosity,and suction parameters,whereas it is reduced if the micropolar and injection parameters become larger.It is concluded that the thermal boundary layer extension increases with the injection parameter and decreases with the suction parameter.

Progress in molecular-simulation-based research on the effects of interface-induced fluid microstructures on flow resistance

In modern chemical engineering processes, solid interface involvement is the most important component of process intensification techniques, such as nanoporous membrane separation and heterogeneous catalysis. The fundamental mechanism underlying interfacial transport remains incompletely understood given the complexity of heterogeneous interfacial molecular interactions and the high nonideality of the fluid involved. Thus, understanding the effects of interface-induced fluid microstructures on flow resistance is the first step in further understanding interfacial transport. Molecular simulation has become an indispensable method for the investigation of fluid microstructure and flow resistance. Here, we reviewed the recent research progress of our group and the latest relevant works to elucidate the contribution of interface-induced fluid microstructures to flow resistance.We specifically focused on water, ionic aqueous solutions, and alcohol–water mixtures given the ubiquity of these fluid systems in modern chemical engineering processes. We discussed the effects of the interfaceinduced hydrogen bond networks of water molecules, the ionic hydration of ionic aqueous solutions, and the spatial distributions of alcohol and alcohol–water mixtures on flow resistance on the basis of the distinctive characteristics of different fluid systems.

Physicochemical properties and structure of fluid at nano-/micro-interface:Progress in simulation and experimental study

In modern chemical engineering processes, the involvement of solid/fluid interface is the most important component of process intensification techniques, such as confined membrane separation and catalysis. In the review, we summarized the research progress of the latest theoretical and experimental works to elucidate the contribution of interface to the fluid properties and structures at nano-and micro-scale. We mainly focused on water, alcohol aqueous solution, and ionic liquids, because they are classical systems in interfacial science and/or widely involved in the industrialization process. Surface-induced fluids were observed in all reviewed systems and played a critical role in physicochemical properties and structures of outside fluid. It can even be regarded as a new interface, when the adsorption layer has a strong interaction with the solid surface. Finally, we proposed a perspective on scientific challenges in the modern chemical engineering processes and outlined future prospects.

Seismoelectric wave propagation modeling in a borehole in water-saturated porous medium having an electrochemical interface

Water-saturated porous media often exhibit a seismoelectric effect due to the existence of an electrical double layer and a relative flow of pore fluid. Here we consider the seismoelectric waves in an open borehole surrounded by water-saturated porous formation which exhibits discontinuity of electrochemical properties at a cylindrical interface. We carefully analyze the seismoelectric interface response since these signals show sensitivity to contrasts in electrochemical properties across an interface. Both coupled and approximate methods are used to compute borehole seismoelectric fields. The simulation results show that the radiated electromagnetic wave from the electrochemical interface is generated due to the change of salinity in pore fluid in the porous formation. However, the elastic properties of the formation remain unchanged across such an electrochemical interface. As a result it is difficult to recognize such a change in electrochemical properties using only elastic waves. Therefore, the seismoelectric interface response is potentially used to detect the changes of the electrochemical properties in the formation.

Mechanisms of salt rejection at the ice-liquid interface during the freezing of pore fluids in the seasonal frozen soil area

Seasonal frozen soil accounts for about 53.50%of the land area in China.Frozen soil is a complex multiphase system where ice,water,soil,and air coexist.The distribution and migration of salts in frozen soil during soil freezing are notably different from those in unfrozen soil areas.However,little knowledge is available about the process and mechanisms of salt migration in frozen soil.This study explores the mechanisms of salt migration at the ice-liquid interface during the freezing of pore fluids through batch experiments.The results are as follows.The solute concentrations of liquid and solid phases at the ice-liquid interface(C*_(L),C*_(S))gradually increased at the initial stage of freezing and remained approximately constant at the middle stage.As the ice-liquid interface advanced toward the system boundary,the diffusion of the liquid phase was blocked but the ice phase continued rejecting salts.As a result,C*_(L)and C*_(S)rapidly increased at the final stage of freezing.The distribution characteristics of solutes in ice and the liquid phases before C*_(L)and C*_(S)became steady were mainly affected by the freezing temperature,initial concentrations,and particle-size distribution of media(quartz sand and kaolin).In detail,the lower the freezing temperature and the better the particle-size distribution of media,the higher the solute proportion in the ice phase at the initial stage of freezing.Meanwhile,the increase in concentration first promoted but then inhibited the increase of solutes in the ice phase.These results have insights and scientific significance for the tackling of climate change,the environmental protection of groundwater and soil,and infrastructure protection such as roads,among other things.

Binary fluids in mesoporous materials: Phase separation studied by NMR relaxation and diffusion

Relaxation and diffusion measurements were carried out on single and binary liquids filling the pore space of controlled porous glass Vycor with an average pore size of about 4 nm.The dispersion of the longitudinal relaxation time Tr is discussed as a means to identify liquid-surface interaction based on existing models developed for metal-free glass surfaces.In addition,the change of T1 and T2 with respect to their bulk values is discussed,in particular T2 serves as a probe for the strength of molecular interactions.As the native glass surface is polar and contains a large amount of hydroxyl groups,a pronounced interaction of polar and protic adsorbate liquids is expected;however,the T dispersion,and the corresponding reduction of T2,are also observed for non-polar liquids such as alkanes and cyclohexane.Deuterated liquids are employed for simplifying data analysis in binary systems,but also for separating the respective contributions of intra-and intermolecular interactions to the overall relaxation rate.Despite the lack of paramagnetic impurities in the glass material,H and 2H relaxation dispersions of equivalent molecules are frequently found to differ from each other,suggesting intermolecular relaxation mechanisms for the'H nuclei.The variation of the T dispersion when comparing single and binary systems gives clear evidence for the preferential adsorption of one of the two liquids,suggesting complete phase separation in several cases.Measurement of the apparent tortuosity by self-diffusion experiments supports the concept of a local variation of sample composition within the porespace.

In-situ building of multiscale porous NiFeZn/NiZn-Ni heterojunction for superior overall water splitting

The development of efficient nonprecious bifunctional electrocatalysts for water electrolysis is crucial to enhance the sluggish kinetics of the oxygen evolution reaction(OER)and hydrogen evolution reaction(HER).A self-supporting,multiscale porous NiFeZn/NiZn-Ni catalyst with a triple interface heterojunction on nickel foam(NF)(NiFeZn/NiZn-Ni/NF)was in-situ fabricated using an electroplating-annealing-etching strategy.The unique multiinterface engineering and three-dimensional porous scaffold significantly modify the mass transport and electron interaction,resulting in superior bifunctional electrocatalytic performance for water splitting.The NiFeZn/NiZn-Ni/NF catalyst demonstrates low overpotentials of 187 m V for HER and 320 mV for OER at a current density of 600 mA/cm^(2),along with high durability over 150 h in alkaline solution.Furthermore,an electrolytic cell assembled with NiFeZn/NiZn-Ni/NF as both the cathode and anode achieves the current densities of 600 and 1000 m A/cm^(2) at cell voltages of 1.796 and 1.901 V,respectively,maintaining the high stability at 50 mA/cm^(2) for over 100 h.These findings highlight the potential of NiFeZn/NiZn-Ni/NF as a cost-effective and highly efficient bifunctional electrocatalyst for overall water splitting.

Influence of Drilling Fluid Components on Shear Strength at Cement-aquifuge Interface in Coalbed Methane Wells

The hydraulic fracturing is still an effective technology for the exploitation of coalbed methane （CBM）. However, after the hydraulic fracturing operation, the high water cut or sudden water flooding of CBM well usually occurs due to upward migration of bottom water, which is called water channeling （water inrush）. This problem has been severely limiting the hydraulic fracturing effect of CBM wells. Some studies show that the aquifuge and cement paste themselves will not crush under hydraulic fracturing pressure. Water channeling often occurs at cement- aquifuge interface （CAI）.

NUMERICAL SIMULATION ON MULTI-FLUID INTERFACES

Enhancement of two fluid mixing was numerically studied by tracking the multi fluid interfaces. Level set equations were used to capture the interfaces, and flow field was obtained by upwind TVD scheme to solve 2D Eulerian equations. The boundary conditions at interface of two fluids are determined by Ghost fluid method (GFM). The distributions of fluid parameters, such as pressure and density, were got at different time steps. The results show that the method presented in this paper can track the density discontinuity perfectly. Superior to previous results, the density discontinuity remains sharper. Also, the mixing of fluids can be greatly enhanced by setting disturbances along the initial fluid interfaces.

NUMERICAL STUDY OF TWO INTERFACE METHODS FOR COMPRESSIBLE MULTI-FLUID FLOWS

Two interface capturing methods are studied for multi fluid flows, governed by the stiffened gas equation of state. The mixture type interface capturing algorithm uses a simple volume fraction model Euler equations written in a quasi conservative form, which is solved by a standard high resolution piecewise parabolic method (PPM) with multi fluid Riemann solver. The level set interface capturing method uses a narrow band ghost fluid method (GFM) with no numerical smearing. Several examples are presented and compared for one and two dimensions, which show the feasibility of the two methods applied to various multi fluid problems.

Molecular Dynamics Simulations of the Interface between Porous and Fused Silica

Molecular dynamics simulations are performed to gain insights into the structural and vibrational properties of interface between porous and fused silica.The Si–O bonds formed in the interface exhibit the same lengths as the bulk material, whereas the coordination defects in the interface are at an intermediate level as compared with the dense and porous structures.Clustered bonds are identified from the interface, which are associated with the reorganization of the silica surface.The bond angle distributions show that the O–Si–O bond angles keep the average value of 109°, whereas the Si–O–Si angles of the interface present in a similar manner to those in porous silica.Despite the slight structural differences, similarities in the vibrations are observed, which could further demonstrate the stability of porous silica films coated on the fused silica.

Transport diffuse interface model for simulation of solid-fluid interaction

For solid-fluid interaction, one of the phase-density equations in diffuse interface models is degenerated to a "0 = 0" equation when the volume fraction of a certain phase takes the value of zero or unity. This is because the conservative variables in phasedensity equations include volume fractions. The degeneracy can be avoided by adding an artificial quantity of another material into the pure phase. However, nonphysical waves,such as shear waves in fluids, are introduced by the artificial treatment. In this paper,a transport diffuse interface model, which is able to treat zero/unity volume fractions, is presented for solid-fluid interaction. In the proposed model, a new formulation for phase densities is derived, which is unrelated to volume fractions. Consequently, the new model is able to handle zero/unity volume fractions, and nonphysical waves caused by artificial volume fractions are prevented. One-dimensional and two-dimensional numerical tests demonstrate that more accurate results can be obtained by the proposed model.

Effect of Porous Copper Pore Density on Joint Interface:Microstructure and Mechanical Analysis

The effect of the pore density of porous copper(Cu)on brazed Cu/porous Cu was investigated.A filler with a composition of Cu⁃9.0Sn⁃7.0Ni⁃6.0P(Sn:Tin;Ni:Nickel;P:Phosphorus)and porous Cu with pore densities of 15 pores per inch(PPI),25 PPI,and 50 PPI were employed.The joint strength of Cu/porous Cu was evaluated with shear tests at different brazing temperatures.Characterizations of the joint interface and fractured surface were achieved with scanning electron microscope(SEM),energy dispersive X⁃ray spectroscopy(EDX),and X⁃ray diffraction(XRD).The micro⁃hardness test of Cu/porous Cu joint interface showed a high hardness value(HV)for 50 PPI porous Cu.This result was in line with its low shear strength.It was proved that the joint strength of Cu/porous Cu is dependent on the pore density of the porous Cu structure and brittle phases of Cu_(3)P and Ni_(3)P in the brazed interface.

Mathematical Modeling of Porous Medium for Sound Absorption Simulations II: Wave Propagation and Interface Conditions

The application of porous medium has a myriad of applications in different industries: automotive, aerospace, civil (commercial, residential), environmental noise control, and biomedical. In the past, design questions involving porous material were addressed with seat-of-the-pants decisions that led to multiple/iterative prototypes and experiments that were costly and time consuming. The objective, in this series of publications pertaining to porous medium, is to establish tools that will lead to effective and accurate simulations involving porous medium. In this third installment of this series the focus is on establishing the constitutive equations using tensors and then applying Transfer Matrix Method (TMM) to calculate diffuse field Transmission Loss (TL) across structures that comprises of layers of different porous medium. The constitutive equations are obtained by relating information regarding the micro-structure make-up to macro level properties. In order to apply the TMM, the equations for wave propagation across different mediums need to be developed and in turn represent these propagation properties in a matrix format. Additionally, the boundary condition between each layer type is defined in order to ensure numerical stability. The author’s current research effort is running simulations for the automotive industry to predict NVH environments. Therefore, TL calculations pertaining to the materials that are utilized in the interior of automobiles are used, in this paper, as a test bed for the developed analytical tools. Case in point, the TL for a multi-layered material consisting of one panel and two different layers of foam is calculated and compared to experimental data. Future publication goals will be to apply these tools in the biomedical field;an example will be to model and run simulations of different organs like the liver and lungs that are po-rous in nature.

Monolithic approach to thermal fluid-structure interaction withnonconforming interfaces

This paper presents a monolithic approach to the thermal fluidstructure interaction （FSI） with nonconforming interfaces. The thermal viscous flow is governed by the Boussinesq approximation and the incompressible NavierStokes equations. The motion of the fluid domain is accounted for by an arbitrary LagrangianEulerian （ALE） strategy. A pseudosolid formulation is used to manage the deformation of the fluid do main. The structure is described by the geometrically nonlinear thermoelastic dynamics. An efficient data transfer strategy based on the Gauss points is proposed to guarantee the equilibrium of the stresses and heat along the interface. The resulting strongly coupled set of nonlinear equations for the fluid, solution procedure. A numerical example efficiency of the methodology. structure, and heat is solved by a monolithic is presented to demonstrate the robustness and