Apparent Slip Research Articles

Persistent slip observed in TiZrNbHfTa: A body-centered high-entropy cubic alloy

Slip properties of TiZrNbHfTa were evaluated to obtain ψ–χ relationships, where χ is defined as the angle between the maximum shear stress plane and (1¯01). ψ is defined as the angle between the apparent slip plane and (1¯01). Bending tests were conducted with micrometer-sized cantilevers fabricated from a single grain with a focused ion beam. Slip bands appear to be straight on a micrometer length-scale, as for Fe–Si alloys, which suggests a persistent slip. However, the ψ–χ relationship indicated that ψ is nearly the same as χ, suggesting that there is no persistent slip. Detailed observations with an atomic force microscope confirm that cross-slipping is so frequent at a sub-micrometer length-scale that the slip bands appear to be straight and the maximum shear stress plane is observed on a micrometer length-scale. Here, TiZrNbHfTa shows abnormally frequent cross-slipping, which is a novel characteristic of high-entropy body-centered cubic alloys.

Mesoscopic model framework for liquid slip in a confined parallel-plate flow channel

We investigated the liquid slip in a planar confined flow channel by proposing an exponentially decaying interaction force between fluid particles and two flat walls in the mesoscopic lattice Boltzmann model framework. In this way, we can explicitly link density profile, velocity profile, and apparent slip length with the mesoscale interaction parameters (force strength and decay length), and formulate the permeability-enhancement ratio as a function of two dimensionless numbers that indicate the role of interaction strength and interaction distance (relative to gap size of flow channel) in the slip-flow system.

Apparent wall slip effects on rheometric measurements of waxy gels

The effects of apparent wall slip on rheometric measurements of waxy gels are quantified for gels consisting of a macrocrystalline wax added in mineral oil in concentrations of 3.0 and 7.5 wt. %. The waxy gels are formed in situ in a stress-controlled rheometer, and rheological properties are then obtained. Seven different geometry configurations, including parallel plates, concentric cylinders, and vane, are employed. The surface roughness of the different geometries and wax crystals size are assessed to provide insight into the apparent wall slip phenomenon. In the presence of smooth surfaces, a decrease in approximately 80% in the measured yield stress value is observed in oscillatory tests, regardless of system composition. In addition, the storage modulus measurements are substantially different when obtained from smooth or grooved geometries. In creep experiments, the yield stress measurements decrease by 68%. As expected, apparent wall slip markedly affects the shape of the flow curves obtained, causing the appearance of kinks for smooth Couette geometry. Apparent slip velocities are calculated in the regime just above the yield stress, and it is found that for low concentrations apparent slip increases with concentration and decreases with the ratio between the shear stress and dynamic yield stress. The gathered results also demonstrate that the reproducibility of rheological measurements is improved by using geometries with grooved parts. By quantifying the effects of apparent wall slip on rheological measurements of waxy gels for different geometries, this work can provide useful information for the design of pipelines and oil transportation processes.

Experimental study of the solid circulation rate in a pressurized circulating fluidized bed

The solid circulation rate is essential for design of pressurized circulating fluidized beds (PCFBs). With increasing pressure from atmospheric pressure to a few bars, the gas density linearly increases with the pressure, which affects the gas–solid flow characteristics. In this work, experiments were performed at room temperature in a cold PCFB apparatus with a riser of 3.3m in height and 0.05m in diameter. The solid circulation rate was studied from 20 to 80kg/(m2·s) under various conditions with increasing pressure from 0.1 to 0.6MPa and fluidizing gas velocity from around 1.5 to 8.0m/s for different Geldart B group particles. Most of the conditions were in the flow regimes of core-annulus flow (CAF) only and CAF with a turbulent fluidized bed at the bottom. The trend of the apparent slip factor with the dimensionless slip velocity was similar at different pressures and for different average particle sizes, and it converged to an exponential function. An empirical equation was obtained by fitting the solid circulation rate with the operating parameters (particle transport velocity, particle volume fraction, Archimedes number, and Froude number), which is helpful for design and operation of PCFBs.

The microstructure of Carbopol in water under static and flow conditions and its effect on the yield stress

In this work, experimental observations of the microstructure of neutralized polyacrylic acid (Carbopol) in water by confocal microscopy under both static and flow conditions are presented. In the former case, a Carbopol-rich phase made by swollen particles dispersed in a water-rich continuous phase is found, so that the system will be henceforth referred to as a suspension, as long as particles are observed. The swollen particles form dendritic-like aggregates, which span the entire solution volume above a critical concentration. In such conditions, a percolated network can be formed, leading to the onset of a yield stress behavior. By separating the dispersed and continuous phase through centrifugation, we provide evidence of a miscibility gap in the phase behavior of Carbopol in water. When the Carbopol suspensions flow in a microfluidic capillary, a particle-concentrated plug core can be distinguished from a less concentrated layer corresponding to a steep velocity decrease. Confocal imaging also shows that the apparent slip found in Carbopol suspensions is due to a particle-concentrated near-wall region, where no flow is observed. Such flow-induced microstructure is responsible for the different nature of the yield stress values measured by classical rheometry and by flow velocimetry. While the yield stress measured by the former can be here related to the presence of a percolated network, the yield stress obtained from the velocity profile is due to the heterogeneous particle distribution along the capillary radius. These results provide a novel insight on the mechanisms governing yield stress in complex fluids.

Effects of elasticity and flow ramp up on kinetics of shear banding flow formation in wormlike micellar fluids

We report experiments on spatiotemporal evolution of the velocity profiles in shear-banding wormlike micelles upon inception of the flow in a Taylor–Couette (TC) cell. Both moderately entangled and highly entangled solutions are considered over a broad range of fluid elasticity E. Fluid elasticity, E = Wi/Re, characterizes the relative importance of the elastic to inertial effects. For both moderately and highly entangled solutions, upon inception of the shear, and during the stress decay period, fluid moves in the opposite direction to that of the imposed motion in a subset of the gap beyond critical thresholds of elasticity and flow ramp up rate, which depend on the fluid entanglement density. Surprisingly, beyond a second critical threshold of the fluid elasticity, the transient backflow disappears in moderately entangled solutions, highlighting the importance of the micellar entanglement on transient evolution of the flow in shear banding systems. More interestingly, we report the formation of multibanded quasisteady velocity profiles under certain conditions of fluid elasticity and flow ramp up rate. The multibanded profiles are characterized by a low shear band near the inner cylinder, a high shear band in the middle of the TC gap, and another low shear band near the outer cylinder. Finally, we show that the apparent wall slip at the inner cylinder of the TC cell is more pronounced for highly entangled solutions and decreases as the fluid elasticity increases. Experimental observations are compared with the existing simulations of the Vasquez–Cook–McKinley model, and several suggestions are made for future simulations.

Axial flow structure of solids holdup in an 18-m high-density CFB riser based on pressure measurements

The axial flow structure in a high-density CFB riser having a height of 18m is investigated on the basis of pressure measurements. Solids circulation rates reach 1400kg/(m2s) at superficial gas velocities of 5–9m/s and the apparent solids holdup exceeds 0.2, indicating high-density operations have been achieved. The apparent solids holdup increases with the solids circulation rate increasing and/or superficial gas velocity decreasing. Axial distributions of the apparent solids holdup have exponential shapes with denser regions at the bottom and more dilute regions in the upper part. The apparent slip velocity increases with the increasing solids holdup and reaches 14m/s, showing that there are more opportunities of cluster formation in high-density operation. Furthermore, the apparent slip velocity has a power relation with the apparent solids holdup under a wide range of operating conditions.

The Doll’s Gift

Brianna Beehler, “The Doll’s Gift: Ventriloquizing Bleak House” (pp. 24–49) This essay offers a new reading of the split narrative in Charles Dickens’s Bleak House (1852–53). Previous critics of the novel’s split narrative have primarily focused on the unequal knowledge and authority positions of the all-knowing third-person narrator and the unknowing first-person narrator, Esther Summerson. This division, however, does not fully account for the apparent slips and narrative exchanges between the two narrators, in which one narrator takes on the voice or knowledge position of the other. This essay takes up Robert Newsom’s suggestion that the only way to explain these “slips” is to conclude that Esther Summerson writes not only her own narration, but also that of the third-person narrator. However, the essay further argues that Esther uses the third-person narration to ventriloquize the voice of her mother, Lady Dedlock, in an effort to provide herself with the emotional support otherwise denied her. Readers may better understand Esther’s ventriloquism of the third-person narration by tracing how it mirrors her early daily ritual with her doll, in which she assumed both narrative positions at once. Object relations and gift theory further show how this dialogue creates a bond between the two narrations. Thus, characters and family structures that appear in the third-person narration and that may appear distant from Esther are actually her meditations on alternative maternal and familial relationships.

IN SITU MEASUREMENT OF TIRE PLY STEER BASED ON AN INTELLIGENT TIRE SYSTEM

ABSTRACT Ply steer is an inherent property of a belted tire, manifesting as the nonzero side force at a slip angle of zero, and it is thus an important design factor relevant to a vehicle's straight running, safety, and comfort. Although ply steer is a rolling contact phenomenon, there is a lack of approaches for direct measurement and modeling of tire ply steer force in motion. Thus, we developed an in situ measurement method for tire ply steer based on a recently proposed accelerometer-based intelligent tire system. This new measurement method is significant for three main reasons: it facilitates understanding of the inherent mechanism of ply steer for radial tires, it improves the intelligent tire's accuracy based on the accelerometer, and it provides an in situ measurement approach for tire ply steer. An accelerometer-based intelligent tire was developed to obtain acceleration measurements at different conditions in which the lateral behavior is of particular interest. Two unusual phenomena that have never been reported are observed: (1) lateral accelerations demonstrate asymmetrical behavior with respect to positive/negative slip angles and (2) lateral accelerations at zero slip angle still exist. It is hypothesized that the underlying reason for these two unusual phenomena is the ply steer–dependent kinematics, which can conversely be used to measure tire ply steer in situ. To this end, the mixed Lagrange–Euler approach for rolling contact kinematics is used to formulate tire lateral acceleration, which links both rigid motion and elastic displacement. It is clearly found that the lateral acceleration is proportional to the square of the rotating velocity and the second-order gradient of displacement. Based on this kinematic model, the features of lateral acceleration can be easily explained by tire ply steer, which manifests as the sinusoidal lateral deformation modes due to the coupling of the bending-twist deformation of the cord–rubber composites of the tire belt. The proposed hypothesis has been verified by finite element method simulations, and the experimental results prove that tire ply steer leads to the observed unusual lateral acceleration pattern. Thus, the quantitative value of ply steer could be measured in situ by integrating the obtained lateral acceleration and thus the apparent elastic slip angle, even under zero external wheel slip angle. In this manner, the intelligent tire system provides a direct measurement approach for tire ply in motion. In addition, the accuracy of the intelligent tire's algorithm might be improved by suitable modeling of the asymmetrical acceleration with respect to left/right slip based on the proposed hypothesis of ply steer–dependent kinematics.

Viscosity of API/fatty acid suspensions: Pitfalls during analysis.

This article describes how to obtain reliable data during rheological analysis of active pharmaceutical ingredient/fatty acid suspensions. These materials are specifically used for prilling, an innovative pharmaceutical technique for the production of a multiparticulate dosage form. Nevertheless, presented guidelines are applicable for a wide range of pharmaceutical suspensions. Reliable rheological results can only be obtained when being aware of artefacts, such as a non-continuous medium, sedimentation, apparent wall slip and protrusion flow. To comply with the continuum hypothesis at high phase volumes (≥25% w/w), the required gap-to-particle-size ratio may be larger than the generally accepted 10:1 ratio. Reproducible flow curves that are not disturbed by sedimentation during sample analysis can be obtained faster by varying the shear rate stepwise from high to low values. While apparent wall slip (at low shear rates) can be prevented via serrated instead of smooth plates, protrusion flow (at high shear rates) during measurements with serrated plates results in non-reliable data. Therefore, in general, high viscous suspensions with yield stress can be analysed with serrated plates, while low viscous suspensions without yield stress should be analysed with geometries having smooth surfaces. By following these guidelines, accurate rheological properties of pharmaceutical suspensions can be obtained.

Numerical simulation of pharyngeal bolus flow influenced by bolus viscosity and apparent slip.

Pharyngeal bolus flow was simulated numerically using a finite element method. The bolus liquids were X-ray medium, glucose, and thickener solutions. For a low-viscosity bolus, the simulation showed a reasonable agreement of bolus velocity with X-ray measurements. The influence of bolus density on swallowing velocity was investigated numerically. Although a higher density resulted in a higher bolus velocity, the increase in velocity was modest. When the bolus viscosity was high, it was necessary to apply the slip boundary condition to obtain an agreement for bolus velocity between the simulation and X-ray measurements. The simulations also showed that the method of characteristic shear rate proposed by Zhu et al., Journal of Texture Studies, 2014, 45, 430-439 is effective for predicting the bolus velocity for shear-thinning fluids. In order to discuss the effect of saliva lubrication and the physical meaning of the characteristic shear rate, an immiscible two-layer flow of the core and wall layer was analyzed theoretically by analogy with mesopharyngeal bolus flow. The characteristic shear rate enabled us to correlate the macroscopic flow behavior and the viscosity of the core layer fluid. Lubrication due to the wall layer caused the apparent slip and enhanced the transfer of viscous core fluid. For viscous fluid that presented a large apparent slip in the two-layer model, the slip boundary condition was needed in the swallowing simulation. The numerical simulation and model flow analysis revealed the usefulness of characteristic shear rate and the importance of saliva-layer lubrication in swallowing.

Thermocapillary stress and meniscus curvature effects on slip lengths in ridged microchannels

Pressure-driven flow in the presence of heat transfer through a microchannel patterned with parallel ridges is considered. The coupled effects of curvature and thermocapillary stress along the menisci are captured. Streamwise and transverse thermocapillary stresses along menisci cause the flow to be three-dimensional, but when the Reynolds number based on the transverse flow is small the streamwise and transverse flows decouple. In this limit, we solve the streamwise flow problem, i.e. that in the direction parallel to the ridges, using a suite of asymptotic limits and techniques – each previously shown to have wide ranges of validity thereby extending results by Hodes et al. (J. Fluid Mech., vol. 814, 2017, pp. 301–324) for a flat meniscus. First, we take the small-ridge-period limit, and then we account for the curvature of the menisci with two further complementary limits: (i) small meniscus curvature using boundary perturbation; (ii) arbitrary meniscus curvature but for small slip (or cavity) fractions using conformal mapping and the Poisson integral formula. Heating and cooling the liquid always degrade and enhance (apparent) slip, respectively, but their effect is greatest for large meniscus protrusions, with positive protrusion (into the liquid) being the most sensitive. For strong enough heating the solutions become complex, suggesting instability, with large positive protrusions transitioning first.

Compaction Dynamics during Progenitor Cell Self-Assembly Reveal Granular Mechanics

Summary We study the self-assembly dynamics of human progenitor cells in agarose microwells that are used for production of chondrogenic organoids. Using image analysis on time-lapse microscopy, we estimate the aggregate area in function of time for a large number of aggregates. In control conditions, the aggregate radius follows an exponential relaxation that is consistent with the dewetting dynamics of a liquid film. Upon introducing Y-27632 Rho kinase inhibitor, the compatibility with the liquid model is lost, and slowed-down relaxation dynamics are observed. We demonstrate that these aggregates behave as granular piles undergoing compaction, with density relaxation that follows a stretched exponential. Using simulations with an individual cell-based model, we construct a phase diagram of cell aggregates that suggests that the aggregate in presence of Rho kinase inhibitor approaches glass transition.

Electroosmosis of a viscoelastic fluid over non-uniformly charged surfaces: Effect of fluid relaxation and retardation time

We investigate the electroosmotic flow of a quasi-linear viscoelastic fluid over a surface having charge modulation in narrow confinements. We obtain analytical solutions using a combination of regular and matched asymptotic expansions in order to describe the viscoelastic flow field and apparent slip velocity besides pinpointing variations of the flow rate and ionic currents due to the surface charge modulation. We demonstrate excellent agreement between the asymptotic analytical solution for the flow field and the full numerical solution in the limiting condition of a thin electrical double layer and weakly viscoelastic fluid. For a wide range of flow governing parameters, we analyze the flow velocity, vortex dynamics, flow rates, and streaming current. We demonstrate that the magnitude of the observed electroosmotic slip velocity is more sensitive to the thickness of the electrical double layer rather than the viscoelasticity of the fluid. We have observed that the contribution of fluid elasticity is prominent in breaking the axial symmetry in the electroosmotic flow with the presence of periodic charge distributions, which is in contrast to the symmetric electroosmotic flow field of a Newtonian fluid over the same charge modulated walls. The results hold the key toward understanding the flow of biological fluids in microfluidic flows by leveraging electrokinetic transport over charge modulated surfaces. We believe that the results of net throughput, streaming current, and vortex dynamics will aid our understanding of the complex fluid behavior and microfluidic mixers.

Cyclic bond property of steel reinforced recycled concrete (SRRC) composite structure

For the composite structures consisting of the steel profile and recycled concrete, the interfacial bond property between steel and concrete is the most critical factor for the collaborative work. In order to study the interfacial bond property of steel reinforced recycled concrete (SRRC) structures, seven SRRC specimens were fabricated and then tested cyclically. The influences of replacement ratio of recycled aggregate and compressive strength of recycled concrete on the bond behavior of this combination were assessed by looking at failure patterns, hysteretic performance, backbone curves, characteristic loads and corresponding slip, bond strength degradation, and degradation mechanism. Test results showed that the replacement ratio of recycled aggregate dominates the onset of slip between steel and recycled concrete. The obvious pinching phenomenon appears on the hysteresis curves, indicating apparent slip characteristics between the steel profile and recycled concrete. As the chemical cementing force gradually loses effectiveness, the bond strength mainly relies on the friction to maintain the stress balance after the interfacial bond layer gradually crushes. Based on the experimental results, a simplified bond-slip model was proposed and divided into four parts, i.e. intact, hardening, degradation and failure stages, and the degradation mechanism corresponding to each segment was then analyzed in detail.

Characterization of velocity fluctuations and the transition from transient to steady state shear banding with and without pre-shear in a wormlike micelle solution under shear startup by Rheo-NMR

AbstractRheo-NMR velocimetry was used to study shear banding of a 6 wt.% cetylpyridinium chloride (CPCl) worm-like micelle solution under shear startup conditions with and without pre-shear. 1D velocity profiles across the fluid gap of a concentric cylinder Couette shear cell were measured every 1 s following shear startup for four different applied shear rates within the stress plateau. Fitting of the velocity profiles allowed calculation of the shear banding characteristics (shear rates in the high and low shear band, the interface position and apparent slip at the inner rotating wall) as the flow transitioned from transient to steady state regimes. Characteristic timescales to reach steady state were obtained and found to be similar for all shear banding characteristics. Timescales decreased with increasing applied shear rate. Large temporal fluctuations with time were also observed and Fourier transform of the time and velocity autocorrelation functions quantified the fluctuation frequencies. Frequencies corresponded to the elastically driven hydrodynamic instabilities,i.e.vortices, that are known to occur in the unstable high shear band and were dependent upon both applied shear rate and the pre-shear protocol.

Quaternary Displacement on the Joiner Ridge Fault, Eastern Arkansas

ABSTRACTThe New Madrid seismic zone of the central United States is an intraplate seismic zone with blind structures that are not seismically active but may pose seismic hazards. The Joiner ridge fault (JRF) is the 35‐kilometer‐long east‐bounding fault of the Joiner ridge blind horst located in eastern Arkansas ∼50 km northwest of Memphis, Tennessee. Shallow S‐wave (SH‐mode) seismic reflection profiles, continuous cores, and radiometric dating of Quaternary alluvium across the JRF reveal down‐to‐the‐east reverse faulting and folding of Eocene strata and overlying Quaternary Mississippi River alluvium. The base of the Quaternary alluvium has an age of 20.3 ka and is vertically displaced 12 m, resulting in an average slip rate of 0.6±0.1 mm/yr over the past 20.3 ka. The overlying upper Wisconsinan and Holocene alluvial facies are also displaced by the JRF. These facies increase in thickness across the JRF and were used to calculate late Wisconsinan and Holocene slip histories. The JRF slipped 7 m between 20.3 and 17.5 ka, 3 m between 12.3 and 11.5 ka, and 2 m between 11.5 and 8.9 ka. No apparent slip occurred on the JRF within the last 8.9 ka. This research illustrates that slip has been intermittent and that slip magnitudes on the JRF diminished through the late Wisconsinan and early Holocene.

Multiscale Apparent Permeability Model of Shale Nanopores Based on Fractal Theory

Based on fractal geometry theory, the Hagen–Poiseuille law, and the Langmuir adsorption law, this paper established a mathematical model of gas flow in nano-pores of shale, and deduced a new shale apparent permeability model. This model considers such flow mechanisms as pore size distribution, tortuosity, slippage effect, Knudsen diffusion, and surface extension of shale matrix. This model is closely related to the pore structure and size parameters of shale, and can better reflect the distribution characteristics of nano-pores in shale. The correctness of the model is verified by comparison with the classical experimental data. Finally, the influences of pressure, temperature, integral shape dimension of pore surface and tortuous fractal dimension on apparent permeability, slip flow, Knudsen diffusion and surface diffusion of shale gas transport mechanism on shale gas transport capacity are analyzed, and gas transport behaviors and rules in multi-scale shale pores are revealed. The proposed model is conducive to a more profound and clear understanding of the flow mechanism of shale gas nanopores.

Flow investigation of complex suspension electrodes for battery applications using ultrasound imaging velocimetry

Flow batteries using suspension electrodes are currently investigated due to their potentially high energy densities and individual scalability of capacity and power density. In contrast to batteries with statically contacted electrodes or conventional redox flow batteries, their performance depend significantly on the local flow conditions of the electrode suspension in the electrochemical cell. Hence, it is crucial to understand and model the complex flow characteristics of such solid-liquid suspensions.Detailed ultrasound flow measurements are combined with multidimensional modeling of the bulk rheology and wall interactions for opaque, thixotropic multiphase fluids in a real-world flow setup. The present flow investigations are conducted for zinc-air type of batteries using a gelled alkaline electrolyte with suspended microscopic zinc particles, however the utilized methods could be adapted to other complex suspension flows of interest. Due to the opacity of the suspension, an ultrasound flow mapping technique, the ultrasound imaging velocimetry (UIV), was applied. In a reference measurement using the model fluid glycerol, the UIV is validated by comparing the measured flow field to optical particle image velocimetry (PIV) measurements and a numerical simulation.In contrast to a Newtonian fluid, the gelled suspension with 8 vol.% particle loading exhibits significant time-dependent non-Newtonian flow characteristics with slip at the wall. While initially strongly sheared zones retain a comparatively low viscosity and allow for high velocity gradients, in areas with low initial shearing (e.g. in corners) the fluid structure is able to rebuild, resulting in a solid-like behavior. An in-depth understanding of the development and the extent of such zero-flow zones can be critical for reliable and efficient designs of the relevant fluidic structures. The measurement data of the zinc-electrolyte suspension flow were used as reference to estimate parameters for a computational fluid dynamics model considering the time-dependent, non-Newtonian rheology of the bulk fluid and the apparent slip at the walls. The simulation model is able to predict the main characteristics of the measured two-dimensional flow fields. Despite some uncertainties, the methods prove to be effective for investigating complex suspension flows and they can be applied to improve and optimize the corresponding fluidic structures, either in flow batteries with flowing suspension electrodes or other industrial applications, including the processing of polymers, minerals, cosmetics, food products, pharmaceuticals and ceramics.

Thermal transport due to liquid jet impingement on superhydrophobic surfaces with isotropic slip: Isoflux wall

Thermal transport due to a liquid water jet impinging an isoflux superhydrophobic surface with isotropic slip was modeled analytically. An integral analysis of the transport equations resulting in a system of ordinary differential equations was solved numerically. Impingement on superhydrophobic surfaces greatly reduces the heat transfer that occurs relative to a smooth surface due to gas trapped in cavities on the surface. This results in an apparent slip velocity and temperature jump at the surface. Local and average Nusselt numbers are presented as a function of radial position (0 to 45 jet radii), jet Reynolds number (3×103 to 1.5×104), liquid Prandtl number (2 to 11), normalized slip length (0 to 0.2), and normalized temperature jump length (0 to 0.2). All results are compared to classical (no-slip, no temperature jump) behavior on a smooth surface. Although local Nusselt numbers for the isoflux scenario are greater than the corresponding isothermal case, the difference in Nusselt number between these two heating conditions becomes negligible as the temperature jump length increases to quantities realizable on superhydrophobic surfaces. These results may be utilized to explore heat transfer degradation in applications where smooth surfaces are replaced by superhydrophobic surfaces to avoid fouling.