Surface Shear Rate Research Articles

Viscosity Flow Curves of Agar and the Bounded Ripening Growth Model of the Gelation Onset.

The gelation kinetics of agar aqueous solutions were studied by means of the viscosity flow curves using a coaxial Couette cylinder viscometer. The viscosity curves show an unusual sigmoidal trend or an exponential decay to a viscous steady state. An original theory of gelation kinetics was developed considering the coarsening of increasingly larger and more stable clusters due to Ostwald ripening and the breakup of clusters that were too large due to the instability of rotating large particles induced by the shear rate. The developed Bounded Ripening Growth model takes into account the trend of the viscosity curves by means of an autocatalytic process with negative feedback on aggregation according to the logistic kinetic equation, in which the constants k1(γ) and k-(ν) are governed by the surface tension and shear rate, respectively. A dimensionless equation based on the difference between the Weber number and the ratio of the inverse kinetic constant to forward constant, accounts for the behavior of the dispersed phase in equilibrium conditions or far from the hydrostatic equilibrium.

Comparative Analysis of Different Injection Molding Process Parameters through Injection Molding Flow Simulation for Various Gate Locations

This study deals with part quality concerning gate location on the part for injection molding. Through injection molding filling simulations, basic parameters such as injection pressure, bulk and surface temperature, shear rate, solidification, shrinkage, air entrapment, weld lines and others were analysed. The simulation was conducted on a fan blade model with Polycarbonate material. Polycarbonate is a commonly used polymer in the industry and is famous for its rigidity, strength-to-weight ratio and reliability in critical system. Simulation is done at six possible gate locations labelled A1 through A6. Injection molding filling simulations was performed to evaluate the performance of each gate location. Among the considered gate locations, gate A4 exhibited a considerably high pressure drop, while gate A5 exhibited a comparatively uniform pressure drop across the mould cavity, also gate A5 showed consistent and smooth filling along with uniform cooling implying less chance of defects. Gate A4 and A5 exhibit uniform distribution across the cavity in shear rate analysis. Gate locations A2, A3, A4, and A5 exhibited controlled solidification, indicating consistent part quality. However, Gate A6 exhibited problems with volume shrinkage, which requires process optimization. Gate A6 exhibited a significant reduction in air entrapment as compared to other gate locations.

Investigation of helical strut attached vena cava filter hemodynamic performanc

Hemodynamic performance of the Celect Platinum vena cava filter and the revised forms of it with helical flow inducer strut were studied with computational fluid dynamic software Ansys Fluent 18. The central velocity and shear stress increased but overall flow disturbance has been observed minimal level. Central velocity increases to 9.72% with Celect filter, by the single helical flow inducer strut the rate reaches to 14.69%, and with doubled form it reaches to 19.73%. The filter surface shear rate increases to 8.29% with the single helical flow inducer strut and increases 13.31% with doubled attachment. Increased velocity and shear stress on the filter may eliminate short term thrombus build-up problems by breaking the big size particulates with the high shearing forces. The new struts may also contribute to the ability of the filter to capture smaller clots, as well as to dissolve them from being bigger. Shear stress in the vein wall increases approximately 6.63% with the filter placement. It raises to 8.06% and 9.45% with single and double helical flow inducer strut attachment. Increased vein wall shear may reduce the recirculation and clotting in the vein wall and it may prevent the accumulation of clots. The increased shear stress on the filter may cause the migration problem, design improvements can minimize this risk. Helical flow inducer strut attachment can cause efficacy increase, and the flow are normalized.

The effect of surface roughness and shear rate during fall-cone calibration

The effect of surface roughness and shear rate during fall-cone calibration

Controlling Ultrafiltration Membrane Rejection via Shear-Aligned Deposition of Cellulose Nanocrystals from Aqueous Suspensions

Cellulose nanocrystals (CNCs) of 180 nm length and 8 nm diameter were deposited on porous supports by tangential flow filtration followed by salt permeation to form ultrafiltration membranes. At a high enough shear rate on the support surface, CNCs aligned in the direction of flow, showing a nematic order. The shear rates for transition to the nematic phase determined from rheology analysis, polarized optical microscopy, and membrane performance were consistent with one another, at ca. 10 s-1. Permeating an AlCl3 solution through the shear-aligned CNC deposit stabilized the CNC layer by screening repulsive electrostatic interactions, and the stable CNC layer was obtained. On changing the surface shear rate from 10 to 50 s-1, the order parameter of CNCs increased from 0.17 to 0.7 and the rejection for Blue Dextran (5 kDa) increased from 80.4 to 92.7% and that for β-lactoglobulin (18 kDa) increased from 89.6 to 95.4%. Hence, a simple and scalable method for controlling rejection properties of ultrafiltration membranes is developed, which uses aqueous CNC suspensions to form the selective layer.

Optimization of vibratory nanofiltration for sustainable coffee extract concentration via response surface methodology

ABSTRACT A vibratory nanofiltration (NF) system was investigated in the preconcentration of coffee extracts for soluble coffee production. Four different NF membranes were studied, among which the selected membrane (Trisep Microdyn TS80) rendered the highest permeate flux and rejection efficiencies. The vibratory NF operation also considerably improved permeate flux, rejection efficiencies, and reduced flux decline from those observed in crossflow (CF) operation. Further, the effects of applied transmembrane pressure (TMP) and module vibrational frequency (F) at corresponding displacement (d) were investigated via response surface methodology in conjunction with a Box-Behnken experimental design, as to their interactions on the performance of the vibratory NF operation. Mathematical models were statistically determined from multivariate regression analysis on permeate flux, maximum surface shear rate, permeate quality, and rejection efficiencies. These correlations were also used to determine optimum conditions (TMP = 3.79 MPa, F = 54.7 Hz, d = 3.18 cm) to process 25.4 g L−1 coffee extracts. The observed responses from experimental verification were found to be in good agreement with the predicted values obtained by the reduced regression models.

Modelling Acoustic Emissions induced by dynamic fluid-asperity shearing in hydrodynamic lubrication regime

This paper investigates the mechanism and characteristics of Acoustic Emission (AE) generated from the dynamic Fluid-Asperities Shearing (FAS) in the hydrodynamic lubrication (HL) regime. Firstly, a FAS model is derived to take into account the dynamic effect of surface asperities. Then, the influence of surface profiles, lubricants and operating conditions are illustrated on AE characteristics, i.e. magnitudes and frequency bandwidths. It has been found that the correlation length of surface roughness parameters and shear rate are two main factors affecting FAS behaviours and consequently AE characteristics. Finally, the corresponding experiments are carried out based on a rheometer rig, which validate the predictability of the model and new findings, paving the foundation for developing AE based monitoring techniques.

Doppler Imaging and Differential Rotation of σ2 Coronae Borealis Using SONG*

Abstract We present new Doppler images of both components of the double-lined binary σ 2 CrB, based on the high-resolution spectroscopic data collected during 11 nights in 2015 March–April. The observed spectra form two independent data sets with sufficient phase coverage. We apply the least-squares deconvolution to all observed spectra to obtain high signal-to-noise mean profiles, from which we derive the Doppler images of both components of σ 2 CrB simultaneously. The surfaces of both F9 and G0 components are dominated by pronounced polar spots. The F9 component exhibits a weak spot at latitude 30° and its mid-to-low latitudes are relatively featureless. The G0 star shows an extended spot structure at latitude 30°, and its surface spot coverage is larger than that of the F9 star, which suggests a higher level of magnetic activity. With the cross-correlation method, we derive a solar-like surface differential rotation on the G0 star of σ 2 CrB for the first time, and the surface shear rate is ΔΩ = 0.180 ± 0.004 rad days−1 and α = ΔΩ/Ωeq = 0.032 ± 0.001. We do not obtain a clear surface shear law for the F9 star due to the lack of mid-to-low latitude features, but detect a systematic longitude shift of high-latitude spots, which indicates a slower rotation with respect to the corotating frame.

The effect of surface roughness and shear rate during fall-cone calibration

The fall-cone test is one of the most popular methods used to characterise fine-grained soils. Traditionally, the fall-cone has been used to determine the liquid limit. However, the undrained shear strength of a given soil can be related to the penetration depth based on Hansbo's cone factor K. Specifically for the 30° cone, a wide number of different K values are reported in the literature, ranging from 0·5 to 1·33. It has been consistently argued that the cone surface roughness is one of the main reasons for the divergence. In the first part of this paper, four different cone surfaces were tested under similar conditions with three different soils; the experimental evidence shows that the cone surface roughness does not have a major effect on the fall-cone penetration. Instead, different shear rates during calibration procedures are mainly responsible for diverging K values. In the second part of the paper, experimental evidence from this work and that of several other authors are used to define an empirical expression to determine K. A Bayesian technique was used to quantify the uncertainty of the empirical parameters estimated during the process. The fitted results are reported with the relevant statistical uncertainty. It is expected that the proposed equation would provide engineers with a tool to better define a K value.

Flow-Accelerated Corrosion Characterization of Magnesium in NaCl Solution and a Case Study by Computational Fluid Dynamics Simulation

Magnesium as a light weight material is gaining significance in application such as automobiles. But magnesium is prone to higher corrosion rate than other structural materials such as steel and aluminum. Hence, it is important to characterize the corrosion rate of magnesium in various electrolytes. In this work, the magnesium samples were subjected to a flowing electrolyte such as NaCl in water solution for assessing the flow-accelerated corrosion (FAC) by weight loss method. Lab experiments were designed to correlate corrosion rate with the surface shear rate of the electrolyte near specimen surface. In a case study, the effect of flow on an ‘L’-shaped pipe bend in two dimensions made of magnesium was analyzed by CFD simulation to obtain shear rate along the inner and outer walls of the bend. Further, the locations in the bend with high FAC damage were identified.

Microbubble aeration enhances performance of vacuum membrane distillation desalination by alleviating membrane scaling

Membrane fouling, especially inorganic fouling due to salt crystal formation and deposition on the membrane surface, is still a major technical issue in membrane distillation (MD) applications. In this study, microbubble aeration (MBA) was included in a laboratory-scale vacuum membrane distillation (VMD) rig and its effect on a desalination process was examined. Without MBA, serious membrane scaling occurred during desalination of simulated high-salinity sea water (100 g.L−1 salt concentration), which resulted in a dramatic reduction of permeate flux to essentially zero after 120 min. Scanning electron microscopy showed that a layer of large cuboid salt crystals uniformly covered the membrane surface. However, membrane scaling was mitigated with the introduction of MBA, resulting in the improved VMD desalination performance, which was positively correlated with pump pressure in the microbubble (MB) generator. Results showed that the effective processing time of the VMD desalination processing cycle was respectively prolonged to 150, 180, and more than 300 and 360 min (cf. 120 min without MBA) when the pump pressure was respectively at 0.1, 0.2, 0.3 and 0.4 MPa, leading to the increase of cumulative water production. Further studies found that larger numbers of MBs of smaller size were produced at higher pump pressure, which are more beneficial for increasing water vapor production and alleviating salt precipitation. The difference in zeta potential between the MBs in distilled water (about −30 mV) and that in SW100 solution (about -2 mV) demonstrated that MBA not only effectively mitigated the negative effect of concentration polarization by enhancing the surface shear rate at the membrane surface, but also reduced salt precipitation probably due to the MBs attracting counterions to the gas-water interface. Finally, energy consumption analysis of the modified VMD desalination process revealed that MBA, while itself only adding about 3% to the total energy consumption at varied pump pressures, was able to improve the specific energy consumption, especially at higher pump pressures. Together, these results demonstrate that MBA is an effective way of improving the performance of VMD desalination of water.

Using Computational Fluid Dynamics to Compare Shear Rate and Turbulence in the TIM-Automated Gastric Compartment With USP Apparatus II

We use computational fluid dynamics to compare the shear rate and turbulence in an advanced in vitro gastric model (TIMagc) during its simulation of fasted state Migrating Motor Complex phases I and II, with the United States Pharmacopeia paddle dissolution apparatus II (USPII). A specific focus is placed on how shear rate in these apparatus affects erosion-based solid oral dosage forms. The study finds that tablet surface shear rates in TIMagc are strongly time dependant and fluctuate between 0.001 and 360 s−1. In USPII, tablet surface shear rates are approximately constant for a given paddle speed and increase linearly from 9 s−1 to 36 s−1 as the paddle speed is increased from 25 to 100 rpm. A strong linear relationship is observed between tablet surface shear rate and tablet erosion rate in USPII, whereas TIMagc shows highly variable behavior. The flow regimes present in each apparatus are compared to in vivo predictions using Reynolds number analysis. Reynolds numbers for flow in TIMagc lie predominantly within the predicted in vivo bounds (0.01-30), whereas Reynolds numbers for flow in USPII lie above the predicted upper bound when operating with paddle speeds as low as 25 rpm (33).

磁気混合流体を用いたホーニング加工特性と加工中の磁気クラスタの挙動

In this study, we proposed processing the inner surface of cylinder-like parts with a magnetic compound fluid (MCF). We determined the processing characteristics of material removal and the changes in surface roughness and shape accuracy. The processing tool was a round SUS bar with a permanent magnet inserted in it. Processing was performed by coaxial processing and eccentric processing. In the processing experiments, material removal and surface roughness were found to have peak values as the processing surface shear rate increased. An observation experiment was conducted to clarify the behavior of magnetic clusters during MCF processing. We clarified the shape and distribution of the clusters and the processing speeds at various rotation speeds of the processing tool. The magnetic clusters were found to expand with the existence region in material removal peak. Through the processing speed measurement experiment, it was clarified that the MCF exhibits elastic behavior during processing.

The impact of the surface macro-roughness on the surface shear stress and rate under the oblique linear cylindrical nozzle jet as pertinent to particles detachment

Particles mitigation and decontamination by impinging jets is commonly used in various engineering in both indoor and outdoor settings. The current research is concerned with advancing the understanding of the phenomena occurring under the specific linear cylindrical nozzle, as well as under the oblique linear nozzle in general. The numerical method is extensively validated using published experimental data before being applied to the configuration of interest. The results demonstrate large differences between the forward and leeward maximal shear stress and rate at the surface impacted by the oblique jet and the impact of the macro-roughness on their values.

Shear-enhanced microfiltration of microalgae in a vibrating membrane module

The performance of a vibratory shear-enhanced membrane process for dewatering of freshwater microalgae, Chlorella vulgaris, has been studied. Chlorella vulgaris is a potential renewable feedstock for biofuel and bioproduct production. The efficient dewatering of the algal biomass is crucial for scale-up and sustainable design. This dynamic filtration system achieves high shear rates desirable for microfiltration by high-frequency torsional oscillations of the membrane unit. A 0.05 µm (nominal pore size) polyethersulfone microfiltration membrane was evaluated for the separation of suspended algae (0.5–100 g/L). The effect of process parameters such as trans-membrane pressure, surface shear rate, and solute concentration on permeate flux was evaluated and quantified. Algal biomass mixtures were dewatered with high algae rejections for all studies. The effect of trans-membrane pressure on permeate flux showed a classic pattern of a pressure-controlled region at lower pressures transforming to a mass transfer gel layer-controlled region at higher pressures, with quicker transitions at higher algae feed concentrations. The shear rate at the membrane surface was varied by changing the vibrational frequency of the unit. Permeate flux values observed in dynamic filtration mode, compared to those in cross-flow filtration (CFF) mode, were greater by a factor of 4.2–4.9. This process could provide a greener alternative to conventional mechanical and thermal separation systems, as high values of permeate flux and separation efficiency can be maintained with an energy consumption of 1.6 kWh/m3 of water removed.

Heat transfer intensification and scaling mitigation in bubbling-enhanced membrane distillation for brine concentration

Membrane distillation (MD) technology is being extensively studied to address operational challenges such as undesired thermal efficiency and scaling phenomenon in recovering valuable solutes and minimizing brine disposal. This study has explored the working mechanisms of utilizing gas–liquid two-phase flow to enhance heat transfer and mitigate scaling formation in MD concentration process, based on the quantification of heat-transfer coefficients and local scaling-resistance associated with bubble size properties.With the aid of direct observation and statistical analysis on the bubble characteristics in a specially-designed direct contact MD (DCMD) module, it was found that the bubbles with small mean bubble size and narrow size distribution were preferred for creating even flow distribution, intensifying mixing and enhancing surface shear rate. Compared to non-bubbling DCMD, the heat-transfer coefficient and temperature polarization coefficient (TPC) reached up to 2.30- and 2.13-fold, respectively, at an optimal gas flowrate of 0.2Lmin−1. With the theoretical expressions for local scaling resistance derived based on the resistance-in-series model, the relative permeation flux (Jw/o|t=t1/Jw/o|t=0) in non-bubbling MD was quantified and found to rapidly decline by 65% as the concentration process progressed, consistent with the increasing trend of the ratio of local scaling resistance to the overall resistance (rfl/rov). Fortunately, the introduction of gas bubbles has shown benefits for supersaturation brine concentrating MD process – remarkably decreased the local-scaling resistance due to bubble-intensified shear stress and enhanced hydrodynamics. Also, the total water removal for the brine concentration process was significantly improved by 131% and the discharged brine volume was reduced accordingly at appropriately selected gas flow rates. Nevertheless, at inappropriately high gas flowrates, high energy consumption and potential fiber breakage should be avoided.

Operational characteristics of oscillatory micro-screen emulsifier: Coupling effects and energy dissipation

Production of oil in water (O/W) emulsion using oscillatory high porosity woven metal microscreen (WMMS) is investigated both experimentally and theoretically. The investigation included coupling effects of design and operating parameters on droplet size and distribution. Results demonstrate the ability to produce emulsions with predictable characteristics and to achieve high dispersed phase concentrations at low energy requirements. Increasing oscillation intensity resulted in smaller droplet size due to the increase in both surface shear and surfactant transfer rate to the droplets surface. The expansion rate of the later increased with increasing the dispersed phase flow resulting in faster surfactant depletion. Using bi-surfactants in both the continuous and dispersed phases resulted in smaller droplet size due to lower interfacial tension. Decreasing the emulsification channel width decreased droplet size due to the increase in the relative surface shear as well as the energy dissipation density. The presence of surface roughness resulted in smaller droplet sizes but had an adverse effect on the dispersion uniformity, which was also affected by lateral vibrations. Both led to localized energy dissipation and droplets breakage near the edges. An order of magnitude assessment of power consumption showed favourable energy requirement (kWh/m3) of the proposed approach compared to other techniques.

Hemodynamics and Flow Characteristics of a New Dialysis Port

Renal replacement therapy by hemodialysis requires a permanent vascular access. Implantable ports offer a potential alternative to standard vascular access strategies although their development is limited both in number and extent. We explored the fluid dynamics within two new percutaneous bone-anchored dialysis port prototypes, both by in vitro experiments and computer simulation. The new port is to be fixed to bone and allows the connection of a dialysis machine to a central venous catheter via a built-in valve. We found that the pressure drop induced by the two ports was between 20 and 50 mmHg at 500 ml/min, which is comparable with commercial catheter connectors (15-80 mmHg). We observed the formation of vortices in both geometries, and a shear rate in the physiological range (<10,000s-1), which is lower than maximal shear rates reported in commercial catheters (up to 13,000s-1). A difference in surface shear rate of 15% between the two ports was obtained.

Flux Characteristics of Oil Separation from O/W Emulsions using Highly Hydrophilic UF Membrane in Narrow Channel

Flux characteristics of oil separation from O/W emulsions using highly hydrophilic polymeric UF membrane has been investigated. The effect of using sub-millimeter filtration channel on both unsteady and steady state permeate flux is evaluated. The time-dependent flux characteristics indicated that membrane fouling has proceeded mainly according to the intermediate pore blocking mechanism modified for crossflow filtration. The steady state flux increased initially with the transmembrane pressure (TMP), then reached a plateau at a relatively low TMP of ∼15 kPa, beyond which a steady operation was achieved, and there were practically no advantages of increasing the TMP. The pressure independent limiting flux increased with increasing the crossflow velocity and was found to scale with the membrane surface shear rate to the power of 0.35. The data were modeled satisfactorily using a dimensionally consistent semi-empirical model with R2 value of 0.96.

Effect of PEGylation on Ligand-Based Targeting of Drug Carriers to the Vascular Wall in Blood Flow

The blood vessel wall plays a prominent role in the development of many life-threatening diseases and as such is an attractive target for treatment. To target diseased tissue, particulate drug carriers often have their surfaces modified with antibodies or epitopes specific to vascular wall-expressed molecules, along with poly(ethylene glycol) (PEG) to improve carrier blood circulation time. However, little is known about the effect of poly(ethylene glycol) on carrier adhesion dynamics-specifically in blood flow. Here we examine the influence of different molecular weight PEG spacers on particle adhesion in blood flow. Anti-ICAM-1 or Sialyl Lewis(a) were grafted onto polystyrene 2 μm and 500 nm spheres via PEG spacers and perfused in blood over activated endothelial cells at physiological shear conditions. PEG spacers were shown to improve, reduce, or have no effect on the binding density of targeted-carriers depending on the PEG surface conformation, shear rate, and targeting moiety.