Shear Flow Field Research Articles

Constructing In situ microfibrillar PA6/PLA composites with high strength and high toughness by a strong shear flow field

In situ microfibrillar PA6/PLA composites (MFCs) with high strength and toughness were produced via a multistage stretching extrusion system. The PA6 microfibrils induced the growth of PLA crystals perpendicular to the PA6 microfibrils and significantly enhanced the mechanical properties of the MFCs. Notably, the PLA-9 sample with 9 wt% PA6 microfibrils achieved excellent tensile strength and elongation at break (79.1 MPa and 77.8 %, respectively), which were 1.3 and 13.4 times than those of neat PLA. During the tensile process, the PA6 microfibrils underwent plastic deformation accompanied by the detachment and fragmentation of the PLA lamellae.

Study on Wax Deposition Process of Crude Oil System under Shear Flow Field Conditions

Study on Wax Deposition Process of Crude Oil System under Shear Flow Field Conditions

Experimental study on the continuous preparation of high‐performance thermal conductivity CNTs/EG/SSBR composite based on the shear and elongation flow fields with the assistance of the silanization reaction

AbstractA self‐developed Serial Rubber Continuous Mixing Device (SRCMD) based on the shear and elongation flow fields was adopted to continuously prepare the carbon nanotubes (CNTs)/expanded graphite (EG)/Solution‐polymerized styrene butadiene rubber (SSBR) composite. Meanwhile, the silanization reaction between the Silica and Si69 was introduced to improve the performance of the CNTs/EG/SSBR composite. When comparing the sample prepared using the two‐stage mixing process based on the shear flow field in the internal mixer, the continuously prepared CNTs/EG/SSBR composite with 3 wt% CNTs and 15 wt% EG demonstrates a higher thermal conductivity of 1.32 W/m·K. At the same time, it exhibits significant advantages in terms of mechanical properties, processability and dispersion rating. In addition, the mechanism for the continuous preparation of CNTs/EG/SSBR composite was revealed through visual experiments. This study aims to achieve the real continuous production of high‐performance thermally conductive polymer composites to meet the urgent demand for thermal conductivity materials in 5G technology.Highlights Real continuous preparation of CNTs/EG/SSBR composite was realized. The silanization index of 92.26% between Silica and Si69 was achieved. Good silanization promotes the construction of thermal conductivity networks. High‐performance CNTs/EG/SSBR composite with low Payne effect was obtained.

The morphology of cell spheroids in simple shear flow

Cell spheroids are a widely used model to investigate cell-cell and cell-matrix interactions in a 3D microenvironment in vitro. Most research on cell spheroids has been focused on their response to various stimuli under static conditions. Recently, the effect of flow on cell spheroids has been investigated in the context of tumor invasion in interstitial space. In particular, microfluidic perfusion of cell spheroids embedded in a collagen matrix has been shown to modulate cell-cell adhesion and to represent a possible mechanism promoting tumor invasion by interstitial flow. However, studies on the effects of well-defined flow fields on cell spheroids are lacking in the literature. Here, we apply simple shear flow to cell spheroids in a parallel plate apparatus while observing their morphology by optical microscopy. By using image analysis techniques, we show that cell spheroids rotate under flow as rigid prolate ellipsoids. As time goes on, cells from the outer layer detach from the sheared cell spheroids and are carried away by the flow. Hence, the size of cell spheroids declines with time at a rate increasing with the external shear stress, which can be used to estimate cell-cell adhesion. The technique proposed in this work allows one to correlate flow-induced effects with microscopy imaging of cell spheroids in a well-established shear flow field, thus providing a method to obtain quantitative results which are relevant in the general field of mechanobiology.

Solvent-Dependent Dynamics of Cellulose Nanocrystals in Process-Relevant Flow Fields.

Flow-assisted alignment of anisotropic nanoparticles is a promising route for the bottom-up assembly of advanced materials with tunable properties. While aligning processes could be optimized by controlling factors such as solvent viscosity, flow deformation, and the structure of the particles themselves, it is necessary to understand the relationship between these factors and their effect on the final orientation. In this study, we investigated the flow of surface-charged cellulose nanocrystals (CNCs) with the shape of a rigid rod dispersed in water and propylene glycol (PG) in an isotropic tactoid state. In situ scanning small-angle X-ray scattering (SAXS) and rheo-optical flow-stop experiments were used to quantify the dynamics, orientation, and structure of the assigned system at the nanometer scale. The effects of both shear and extensional flow fields were revealed in a single experiment by using a flow-focusing channel geometry, which was used as a model flow for nanomaterial assembly. Due to the higher solvent viscosity, CNCs in PG showed much slower Brownian dynamics than CNCs in water and thus could be aligned at lower deformation rates. Moreover, CNCs in PG also formed a characteristic tactoid structure but with less ordering than CNCs in water owing to weaker electrostatic interactions. The results indicate that CNCs in water stay assembled in the mesoscale structure at moderate deformation rates but are broken up at higher flow rates, enhancing rotary diffusion and leading to lower overall alignment. Albeit being a study of cellulose nanoparticles, the fundamental interplay between imposed flow fields, Brownian motion, and electrostatic interactions likely apply to many other anisotropic colloidal systems.

Study on jetting droplet formation regime in a low-speed annular shear flow field

This study aims to explore the mechanism of droplet generation and the change rule of liquid bridge in an annular shear flow field. With the help of a two-phase system of continuous phase (deionized water)-dispersed phase (fluorescent oil), the process of droplet generation under the jetting mechanism was captured using a camera. By studying the effect of the dispersed phase flow rate on the length of the liquid bridge, it was found that the volume flow rate of the dispersed phase is positively correlated with the frequency of droplet formation and the droplet size, and that the distance of the liquid bridge is also positively correlated with the droplet size under the jetting mechanism. Besides, a prediction mechanism for the maximum stable droplet under the jetting mechanism is proposed based on the droplet formation process.

Conditions for Relativistic Magnetic Reconnection under the Presence of Shear Flow and Guide Field

The scaling of the relativistic reconnection outflow speed is studied in the presence of both shear flows parallel to the reconnecting magnetic fields and guide fields pointing out of the reconnection plane. In nonrelativistic reconnection, super-Alfvénic shear flows have been found to suppress reconnection. We extend the analytical model of this phenomenon to the relativistic regime and find similar behavior, which is confirmed by particle-in-cell simulations. Unlike the nonrelativistic limit, the addition of a guide field lowers the in-plane Alfvén velocity, contributing to slower outflow jets and the more efficient suppression of reconnection in strongly magnetized plasmas.

Droplet coalescence in coupled shear and electric fields: A molecular dynamics study

Water droplet coalescence in coupled flow and electric fields is a phenomenon extensively observed in petrochemical, microfluidic, and chemical synthesis processes; however, the existing research in this domain lacks the necessary depth. This paper employs a molecular dynamics approach to elucidate the microscopic mechanisms governing droplet aggregation in water-in-oil emulsions. The investigation spans various shear rates and droplet angles, considering droplet morphology and molecular interactions. The study reveals an interrelation between shear rate and droplet angle effects on droplet coalescence, both seeking to understand the impact of the flow field's shear effect on the electrocoalescence of water droplets. Increasing the shear rate proves advantageous to droplet aggregation up to a certain threshold; however, complete coalescence is hindered beyond the critical shear rate, γ = 7.5 × 109 s−1. Augmenting the droplet angle amplifies the shear force exerted by the flow field on the droplets, while diminishing the radial electric field force. Consequently, an optimal droplet angle of θ = 25° facilitates comprehensive droplet merging. The analysis of the coalescence process, interaction energy, charge density and radial distribution function shows that the approximate process of droplet motion is as follows: the shear effect drives the droplets to approach, and then the directional migration of charge and electrostatic attraction between water molecules drive the coalescence. The existence of a moderate shear effect enables complete droplet coalescence. This study offers theoretical guidance for the exploration of dynamic electrocoalescence technology.

Droplet electrohydrodynamic deformation in a shear flow field

The electrohydrodynamic deformation characteristics of a leaky dielectric droplet in combined shear flow field (SFF) and electric field (EF) are investigated by a three-dimensional numerical simulation. Based on the investigation, the cooperation and competition of the two fields on the droplet electrohydrodynamic deformation degree D and orientation angle ϕd are revealed. The influences of SFF strength, EF strength, viscosity, electrophysical parameters, and confinement degree on the droplet deformation morphologies are analyzed. Particularly, theoretical prediction models for droplet electrohydrodynamic deformation and rotation with consideration of domain confinement are proposed. It is found that the two fields collaborate with each other in promoting droplet deformation while they are competing or cooperating with each other in rotating the droplet when Ω > 0 and Ω < 0 (Ω is Taylor's deformation characteristic function). In addition, for a given condition, with increasing conductivity ratio R, the effect of permittivity ratio S turns to diminish and the droplet steady-state D and ϕd converge to a constant. Otherwise, a larger permittivity ratio S leads to a larger D and a smaller ϕd, respectively. The domain confinement promotes D when Ω > 0, while it first reduces D and then promotes it when Ω < 0. For the droplet orientation, the droplet is rotated to the EF direction with the increasing confinement degree when R < S, while it is rotated to the direction perpendicular to the EF when R > S. Furthermore, theoretical prediction models for droplet deformation and rotation with consideration of domain confinement are proposed, which are proved to be accurate and reliable based on the current simulation results and available data.

Predicting shear stress distribution on structural surfaces under internal solitary wave loading: A deep learning perspective

The density of the ocean varies unevenly along the vertical axis. In the presence of external disturbances, internal solitary waves (ISWs) are generated. The strong shear flow field induced by ISW seriously threatens the operational safety of marine structures. Therefore, it has become a hot spot to study the force law of marine structures in ISW. The existing studies are conducted when the ISW parameters are known. However, ISW is not visible in real situations, which leads to difficulties in obtaining ISW parameters. Therefore, it is of great engineering value to accomplish real-time force prediction of marine structures without knowing the ISW parameters in advance. To fill the gap, this study proposes a novel hydrodynamic prediction model with a sensor array as the sensing system and a deep learning algorithm as the decision-making system. The model successfully achieves accurate prediction of the shear stress on the cylinder in the ISW. In addition, a technique for optimizing sensor placement is proposed. This will help identify critical regions in the graphical representations to enhance exploration of flow field information. The results demonstrate that the prediction accuracy of the optimized sensor layout scheme surpasses that of randomly deployed sensors. As a result, this study will provide an important assurance for the safe operation of marine structures.

Progress of air flow field and fiber motion analysis in textile manufacturing process: a review

The control of air flow fields generated in the textile manufacturing process is important to fiber motion. With the expansion of textile applications and the challenges brought by carbon emissions, a series of fundamental research has been conducted on the control of various forms of air flow fields in textile processes. This paper reviews the research on air flow fields and fiber motion in textile processes over the past few decades, focusing on both experimental and numerical studies. The air flow field characteristics, fiber motion patterns, and corresponding control methods for vortex, jet and shear flow fields in the textile process are summarized. The results show that the air flow field and fiber motion are major factors affecting textile structure. These fundamental studies are of great significance in improving product quality, reducing energy consumption, and exploring novel applications.

Dynamic processes in the liquid crystal-water emulsion under shear flow and electric field

We present the results of experimental investigation of dynamical processes arising in liquid crystal-water emulsion under action of a decay shear flow and ac electric field. The 10 : 1 emulsion, consisting of the well-studied nematic mixture E7 and ionized water was prepared by usage of ultrasonic (29 kHz) mixer. It made possible to get a number of water droplets with the distribution of diameters in the range 2… 20μm. So, the slow decreasing of sizes of these instabilities resulted in corresponding slow motion of the attracted water droplets. The strong electric filled, which stabilized the initial homeotropic orientation of LC suppressed the flow induced instabilities and the slow motion of water droplets mentioned above. It also induced the aggregation of droplets in the vicinity of boundary between regions with strong field and free of field. So, combined action of shear flow and electric field can be effectively used for manipulation of the motion and interaction of water droplets. The obtained results are discussed within the existing theory of liquid crystals.

Simulation of Fountain Flow based on Molecular Dynamics Method

In this paper, numerical simulations of the fountain effect on the flow front of polymer dilute solutions are carried out based on molecular dynamics principles and the FENE dumbbell model. The Euler method is used to solve the constitutive equations of the mechanical model for the simple shear flow field and the dislocation equations of the dumbbell molecules, and subsequently obtain the tracer flow lines and the dumbbell distribution of the flow front. The results are used to calculate the stress field, analyze the rheological evolution law, study the effect of temperature and shear rate and other parameters on the model and analyze the effectiveness of the FENE dumbbell molecular model for the fountain effect. The study shows that due to the fountain effect the dumbbell molecules stretch more with increasing shear rate, the polymer stress at the flow front will show a complex change of stress overshoot and then stabilize, and the dumbbell molecules are oriented along the fountain flow line.

Experimental investigation and theoretical prediction of droplet breakup under a combined electric field and shear flow field

The electrohydrodynamic breakup of a droplet under a combined electric field (EF) and shear flow field (SFF) is experimentally investigated. The interface morphology characteristics of the droplet undergoing different breakup patterns are analyzed, and the interactions among electric forces, viscous forces, and interfacial tension during the droplet breakup process are also revealed. In addition, a diagram of droplet breakup patterns with different hydrodynamic and electric capillary numbers (Ca and CaE, respectively) is summarized. In particular, a prediction model for the criteria of droplet breakup under combined EF and SFF is proposed. The results indicate that three typical patterns of droplet breakup occur in turn with increasing CaE, i.e., satellite droplet detachment from a migrating droplet, a lobe detachment pattern, and a lobe disintegration pattern. As the Ca increases, the breakup pattern of satellite droplets detaching from the migrating droplet gradually disappears, and the critical CaE for droplet breakup decreases because the enhanced viscous force facilitates the detachment of the lobes from the mother droplet. Additionally, the breakup pattern of charged lobe disintegration occurs under a large CaE when the charge of the droplet reaches the Rayleigh limit. The critical CaE of the lobe disintegration breakup pattern decreases first and then increases with increasing Ca because the changes in droplet shape, interfacial tension, electrical potential energy, and fluid potential energy lead to a variation in the Rayleigh limit. Moreover, the breakup speeds of the three patterns are also altered by the strengths of the SFF and EF. Particularly, a reliable prediction model for the criterion of droplet breakup is proposed and compared with experimental data. This model provides a feasible approach for determining the criterion of droplet breakup through a very small amount of data for droplet-based applications.

Bidirectionally promoting assembly order for ultrastiff and highly thermally conductive graphene fibres

Macroscopic fibres assembled from two-dimensional (2D) nanosheets are new and impressing type of fibre materials besides those from one-dimensional (1D) polymers, such as graphene fibres. However, the preparation and property-enhancing technologies of these fibres follow those from 1D polymers by improving the orientation along the fibre axis, leading to non-optimized microstructures and low integrated performances. Here, we show a concept of bidirectionally promoting the assembly order, making graphene fibres achieve synergistically improved mechanical and thermal properties. Concentric arrangement of graphene oxide sheets in the cross-section and alignment along fibre axis are realized by multiple shear-flow fields, which bidirectionally promotes the sheet-order of graphene sheets in solid fibres, generates densified and crystalline graphitic structures, and produces graphene fibres with ultrahigh modulus (901 GPa) and thermal conductivity (1660 W m−1 K−1). We believe that the concept would enhance both scientific and technological cognition of the assembly process of 2D nanosheets.

Study on microstructure evolution of waxy crude oil emulsions under dynamic cooling conditions.

A rheo-microscopy in situ synchronous measurement system was utilized to investigate the dynamic behavior of water droplets in W/O waxy crude oil emulsions subjected to dynamic cooling conditions, the microstructural evolution of water droplets aggregates can be categorized into three stages based on the various forms of wax crystals. The results show that under the joint action of wax crystals and water droplets, the water droplets aggregation trend and complexity in the system are negatively correlated with the changes of temperature and shear rate, and the water droplets movement behavior is positively correlated with the changes of temperature and shear rate. As the temperature decreases, the minimum edge distance of water droplets decreases by a maximum of 32.1%, the specific surface area (SA) decreases by a maximum of 12.0%, and the fractal dimension increases by a maximum of 11.7%. As the shear rate increases, the minimum edge distance of water droplets increases by up to 27.9%, the specific surface area (SA) increases by up to 10.1%, and the fractal dimension decreases by up to 8.5%. Additionally, an analysis is conducted on the collision aggregation behavior of water droplets in shear flow field based on population balance theory.

CO2 Corrosion of X80 Steel under High Shear Flow Fields

Corrosion failure accidents owing to flow erosion and pipeline corrosion frequently occur during transportation. In this study, a high wall shear stress (WSS) experimental setup was established to conduct the online electrochemical corrosion test. The corrosion behavior of welded joints in NACE solution was studied by electrochemical experimental methods such as electrochemical impedance spectroscopy (EIS) and wire harness microelectrode (WBE). The results show that different areas of the welded joint show different corrosion phenomena in NACE solution. The weld metal (WM) has the significantly better corrosion resistance, while the base metal (BM) and heat-affected zone (HAZ) have worst corrosion resistance than WM. The current of the WM surface was cathodic current, while the current of the BM and HAZ surface were anode currents.

The effect of Navier slip on the rheology of a dilute two-dimensional suspension of plate-like particles

Through boundary integral simulations and asymptotic analysis, we investigate the effect of a finite Navier slip length on the rheological proprieties of a dilute two-dimensional suspension of plate-like particles in the creeping flow limit. Specifically, we study the effects of Navier slip, particle thickness and Péclet number on the effective shear viscosity and average normal stress difference of an isolated two-dimensional plate-like particle in an unbounded shear flow field. We find that Navier slip induces a significant reduction in the effective viscosity and increases the average normal stress difference. The effect of slip becomes more enhanced as the thickness of the particle decreases and as the Péclet number increases. Remarkably, the analysis suggests that it is theoretically possible for a dilute suspension of slip plate-like particles at high Péclet numbers to have a shear viscosity smaller than that of the suspending fluid.

Oil droplet migration in the coupling of electric field and nano-confined shearing flow field: A molecular dynamics study

Electrocoagulation (EC) has become one of the main oily wastewater treatment method due to its low cost, high efficiency, and deep purification capability. In this study, the nano-oil droplet migration and deformation behaviors at different Reynolds numbers (Re), electrocapillary numbers (CaE), component types and SPAN (span-80) concentrations were investigated by molecular dynamics (MD) simulations. The weak interactions between SPAN&SiO2 (silicon dioxide) and ASP (asphaltene) molecules were mainly electrostatic interactions. The tendencies of oil droplet moving along the negative and positive x-axis were enhanced with respectively increasing CaE and Re, and the electric force (FE) was approximately equal to the shear force (FS) at CaE = 152.59 Re. The shearing flow field dominantly affected the tilt angle (θ), while the electric field mainly influenced the deformation ratio (D). ASP molecules were susceptible to FE, while RES (Resin) &HEX (n-hexane) molecules were susceptible to FS. In addition, the presence of both SPAN and SiO2 molecules can improve the oil droplet stability. The results can potentially provide theoretical guidance for the optimization of EC device.

Numerical solution of coupled Cahn–Hilliard Navier–Stokes equations for two‐phase flows having variable density and viscosity

This work is concerned with the implementation of a decoupled diffuse interface approach for the numerical solution of two‐phase flows with a moving interface. The underlying two‐phase flow model consists of a mass‐preserving Cahn–Hilliard (CH) equation coupled with the incompressible Navier–Stokes equations (NSEs) through surface tension. Due to the higher order nonlinearity and stiff nature of the CH equation, its numerical solution is very challenging. We have used the decoupled pressure projection method for the numerical simulation of the governing equations. The spatial variables are discretized using the finite difference scheme on the staggered grids, while the explicit Euler method is used for time discretization. Four examples include the coalescence of inline rising bubbles, the obliques coalescence of two rising bubbles, and the deformation of single and two different‐sized bubbles in a shear flow field is numerically simulated. It is observed that the scheme is capable of tracking the interface accurately and respecting mass conservation and energy dissipation. Moreover, the scheme is efficient, easily implementable, energy stable, and fully decoupled.