Influence Of Shear Rate Research Articles

A constitutive model for bentonite–water mixture and the effect of wall slip boundary conditions on its mechanical response

This paper presents the development of a constitutive model for describing the nonlinear viscoelastic behavior of deep-seabed sediments. To quantify the nonlinear response, shear rheological tests are carried out on deep-sea sediments substitute at different shear rates. These substitute samples are prepared by mixing bentonite with water based on the in-situ vane shear strength of deep-sea sediments. A compressible viscoelastic fluid model is formulated based on the thermodynamic framework developed by Rajagopal and Srinivasa (2000) to describe the experimental response of bentonite–water mixture. Experimental responses indicate that the effects of slip are significant in the shear rheometry of bentonite–water mixture. Hence a slip model is proposed, which relates the shear stress to slip velocity at the wall and the imposed shear rate values. The slip boundary conditions coupled with the viscoelastic model is validated using experimental data and is observed to be in good agreement. Further, the influence of shear rate on interfacial slip has been numerically analyzed and slip effects are found to be significant in defining rheological behavior with increasing shear rates.

Effect of shear rate on floc characteristics and concentration factors for the harvesting of Chlorella vulgaris using coagulation-flocculation-sedimentation

Coagulation-based separation has been increasingly applied to microalgal harvesting because of its competitive cost and high scalability. The characteristics of flocs formed during coagulation/flocculation are critical for efficient harvesting. However, few studies have been devoted to systematically investigating the structural characteristics of microalgal flocs and their influences on subsequent settling performance. In this paper, the dynamic mean size and fractal dimension, strength, regrowth and settling performance of Al3+ coagulated Chlorella vulgaris flocs were characterized at various flocculation shear rates. The influence of shear rate on floc characteristics was revealed. An appropriate shear rate (9 s−1) produced more desirable microalgal flocs (in terms of size and compactness), with better settling performance and a higher concentration factor, than higher or lower shear rates, favoring their separation and subsequent harvesting. At this condition, the concentration factor reached 13.50, which was a 177.21% improvement over the 4.87 reached at a low shear rate.

Relationship between processing parameters and aging with the rheological behaviour of SBS modified bitumen

The influence of shear rate and mixing time and, simulated long-term aging as a function of frequency and temperature on the rheological behaviour of SBS modified bitumen was evaluated from oscillatory rheology measurements. Complex shear modulus (G*) and phase angle (δ) values were measured and Master curves, Black diagrams and Cole-Cole plots constructed in an attempt to assess the effects of mixing conditions (i.e. short term aging) and long term aging on the rheological characteristics of SBS modified bitumen. Rutting (G*/sin(δ)) parameters were calculated to obtain the performance grade (PG) temperatures of each modified bitumen. It was observed that higher shear rates and longer mixing times promote oxidative aging of the SBS modified samples relative to neat bitumen and have higher activation energies for flow and temperature susceptibility. Additionally, for the same shear rate and mixing time a similar level of compatibility between SBS and bitumen is obtained.

Preparation of methyl methacrylate-maleic anhydride copolymers via reactive extrusion by regulating the trommsdorff effect

In this study, the influence of shear rate on the Trommsdorff effect was investigated using rotational rheometer and torque rheometer firstly, then the bulk copolymerization of methyl methacrylate (MMA) and maleic anhydride (MAH) were carried out via two connected twin-screw extruders. Based on the assumption of utilizing the Trommsdorff effect, new monomers were continually added during the copolymerization process. The results indicated that the polymerization rate was greatly accelerated and copolymers with high molecular weight and narrow distribution were obtained. Under the high temperature and high pressure in extruder, the copolymerization of MMA and MAH approached to the ideal copolymerization, which was different from the solution copolymerization. Compared with the homo-polymethyl methacrylate, the Tg and Td50 of the copolymer was respectively increased by 12 °C and 24 °C while maleic anhydride units were uniformly distributed in the MMA-MAH copolymer. The flexural strength and modulus increased by 8.2% and 20%, respectively. The high efficiency and environment friendly of reactive extrusion technology provide a way for the large-scale industrialization of MMA-MAH copolymer.

The Effect of Shear Rate on Aggregation and Fragmentation of Asphaltene Aggregates

This paper investigates the shear rate influence on asphaltene aggregation in heptane-toluene mixture through experiments and theoretical modeling at constant temperature and pressure. The experiments were performed within a Couette apparatus at different shear rates (129.14 – 1142.39 s−1). The size distributions of asphaltene aggregates in time were measured. In all tests, the average diameter of asphaltene aggregates initially increases up to a maximum and then decreases to a steady-state value. The existence of steady state size is believed to occur when the rates of aggregation and fragmentation become equal. A fractal population balance model was used and the aggregation kernel was assumed to be a linear combination of orthokinetic and perikinetic kernels. The Particle Swarm Optimization (PSO) algorithm was employed for estimating the model parameters including orthokinetic and perikinetic collision efficiencies, and , respectively, fractal dimension, , and breakage coefficient, . The results showed that the fractal dimension, the collision efficiency of orthokinetic mechanism and breakup rate coefficient increase with increasing of shear rate. However, the value of perikinetic collision efficiency decreases with the increase in shear rate. Totally, the effect of fluid shear on fragmentation was found to be higher than that on aggregation of asphaltene particles.GRAPHICAL ABSTRACT

Drag and Lift Forces Acting on a Sphere in Shear Flow of Power-Law Fluid

Laminar flow of a power-law fluid over a sphere is considered for unbounded shear flow. The Navier–Stokes equations with power-law viscosity are solved numerically using an in-house developed CFD package. Vorticities structures downstream of particle are suppressed for powerlaw fluid. The shear rate influence on drag force is negligible for power index close to unit, and the drag force appreciably decreases with falling power index. For small Reynolds numbers, the lift force coefficient monotonically decreases against the power index and exhibits an opposite behavior for moderate values of Reynolds numbers. The results of the parametric studies are used to derive correlations for the drag force and to detect the hydrodynamic differences from uniform flow. The investigation parameters varied within the following ranges: power-law index 0.3 ≤ n ≤ 1, Reynolds number 0 < Re ≤ 150, and dimensionless shear rate 0.05 ≤ s ≤ 0.4.

Effect of shear rate on primary nucleation of para-amino benzoic acid in solution under different fluid dynamic conditions

The influence of shear rate on the primary nucleation of para-amino benzoic acid in water has been investigated via a series of cooling crystallization experiments. For each experiment, we recorded the induction time at various temperatures and supersaturation ratios, employing two flow devices: a capillary tube in which the solution was divided into hundreds of monodisperse droplets and a set of stirred vials. The capillary tube was used to perform experiments in stagnant conditions (motionless droplets) and low shear rate conditions (flowing droplets), while the stirred vials were used to perform experiments at relatively high shear rates. In this way, a wide range of shear rates was investigated. Comparing the results obtained for the motionless and flowing droplets, we saw that the nucleation rate is significantly increased (by several orders of magnitude) by the shear field; however, when the shear rate increases beyond a certain level (stirred vials experiments), we observed a drop in the nucleation rate. Thus, the results demonstrate a non-monotonic dependence of primary nucleation rate on shear rate. Various mechanisms to explain the effect of shear on nucleation are quantitatively and qualitatively discussed; however, at present no definitive conclusion can be drawn to identify the controlling mechanism.

Effects of xanthan gum on the rheological properties of soy protein dispersion

This study focused on the effects of addition of xanthan gum (XG) on the rheological properties of soy protein isolate (SPI) solution. Three types of tests (steady shear test, strain sweep test, and frequency sweep test) were performed to figure out the influences of shear rate on the viscosity of the SPI-XG hybrid system, the effects of strain variable on the storage modulus of the hybrid system, and the effects of frequency on both the storage modulus and the loss modulus of the hybrid system, respectively. SPI-XG hybrid system showed more obvious shear-thinning properties compared to pure SPI and pure XG solution. Meanwhile, it was found that the critical point of hybrid system was highly related to the XG concentration. XG can postpone the critical point strain amplitude to a higher value, and the addition of XG can enhance the strain resistance of hybrid system. The concentration of XG influenced the viscoelastic frequency dependence of the hybrid system significantly and complicatedly. After the addition of XG, the correlation between G′ and frequency changed from negative to positive. Keywords: rheological property, soy protein isolate (SPI), xanthan gum (XG), temperature, frequency independence DOI: 10.25165/j.ijabe.20181102.3253 Citation: Bi C H, Gao F, Zhu Y D, Ji F, Zhang Y L, Li D, et al. Effects of xanthan gum on the rheological properties of soy protein dispersion. Int J Agric & Biol Eng, 2018; 11(2): 208–213.

Characterizing gas bubble size distribution of laboratory foamed cement using X-ray micro-CT

The objectives of this study are to use micro-computed tomography (micro-CT) to elucidate the influencing factors of the microstructure of laboratory foamed cement and develop statistical models to quantify the gas bubble size distributions. During this study, foamed cement slurries were prepared using sealed foam cement mixers at various operating conditions. The influences of shear rate, mixing energy, base cement slurry composition, blender geometry, and applied pressure on the gas bubble size distribution of set foamed cement were investigated. Test results indicate foam quality and gas pressure are the primary determining factors of gas bubble size in foamed cement. The gas bubble size in foamed cement produced by a sealed foam mixer approximately follows the normal distribution. For samples generated with a standard multiblade blender at atmospheric condition, the mean and standard deviation of gas bubble size distribution increase exponentially with increasing foam quality. A dramatic decrease in gas bubble size is observed with increasing gas pressure. On the other hand, variations in mixing energy, shear rate, base slurry composition, and blender geometry have relatively little effect on the microstructure of the foamed cement within the range investigated.

Experimental study of residual strength and the index of shear strength characteristics of clay soil

Using a ring shear apparatus, the variation in the residual strength characteristics of 21 groups of saturated clay soil samples were experimentally investigated, and the results are discussed in this paper. The clay soil samples had different plasticity indexes under 10 different consolidation conditions. The influences of shear rate, over-consolidation ratio, plasticity index, and multi-stage shear mode on the residual strength were investigated. New shear strength variation trend data and a corresponding equation for shear strength calculations as a function of plasticity index of soils under large deformation are presented. The experimental results indicate that 1) both the shear rate and over-consolidation ratio have a negligible influence on the residual strength; 2) the residual strength gradually decreases as the plasticity index increases; 3) the residual strength shows a significant nonlinearity with the normal stress when subjected to low- or high-levels of normal stress; 4) the internal friction angle of drained clay decreases as the plasticity index increases under large deformation. Finally, a formula is proposed to describe the relationship between the residual inner friction angle and plasticity index.

Carotid artery longitudinal wall motion: regulatory factors and implications for arterial health.

The carotid artery wall moves longitudinally along the length of the vessel, although little is known about what causes this motion, or what health information it represents. The overarching purpose of this dissertation was to investigate the regulation of carotid artery longitudinal wall motion (CALM) in humans, as well as how CALM can be used to infer information about arterial health. Through observational and experimental designs, we tested evidence for a structural ventricular-vascular coupling effect, which postulates that systolic anterograde CALM is influenced by the forward blood shear rate while systolic retrograde CALM is influenced by left ventricular rotation, although the data suggest a moderate influence of left ventricular rotation, and minimal influence of shear rate. In cross-sectional analyses, we demonstrated that diastolic CALM variables are better related to age and health status compared with systolic CALM displacement and that this relationship was independent of traditional measures of arterial stiffness. These experimental and observational results directed the use of diastolic CALM as a potential indicator of arterial health in subsequent studies, owing to the relative independence from systolic events. While there was no effect of 12 weeks of exercise training in healthy men on diastolic CALM variables, we observed increased systolic retrograde CALM and diastolic CALM acceleration in men with a history of resistance exercise training compared with sedentary men, suggesting an effect of habitual exercise training. Our novel findings suggest that CALM is regulated by a complex system, in part related to both arterial wall structure and ventricular-vascular coupling, and may have clinical value in complimenting measures of traditional arterial stiffness in humans. Future studies should examine whether local changes to arterial wall structure or indirect changes in regulatory control dictate differences in CALM with aging and with chronic exercise training, before integrating CALM into routine measurement of arterial health.

Study on Interface Formation and Microstructures Evolution of Metal Shear Extrusion Bonding

The static shear extrusion bonding experiment was carried out on the Q345 plates by the solid-state metal joining device with fast shearing. Meanwhile, based on the experimental and theoretical analysis, the influence of shear rate, the press quantity on the interface formation and microstructures evolution mechanism during shear extrusion bonding process were analyzed, and mechanical properties was investigated. The results show that with the increase of the press quantity, the interface formation divides into three stages, and the grain refinement is improved through dynamic recrystallization. The deformation work is provided by the bonding device, which is affected by shear rate. When the press quantity reaches 125%, the tensile strength of the specimens with high shear rate and low rate are 499.56MPa and 500.56MPa, respectively.

Mixed undifferentiated neuroendocrine tumor and exocrine adenocarcinoma of the pancreas in an adolescent

Segregation and mixing of granular materials are complex processes and are not fully understood. Motivated by industrial need, we performed a simulation using the discrete element method to study size segregation of a binary mixture of granular particles in a horizontal rotating drum. Particles of two different sizes were poured into the drum until it was 50% full. Shear-driven segregation was induced by rotating the side-plates of the drum in the opposite direction to that of the cylindrical wall. We found that radial segregation diminished in these systems but did not completely vanish. In an ordinary rotating drum, a radial core of smaller particles is formed in the center of the drum, surrounded by larger revolving particles. In our system, however, the smaller particles were found to migrate toward the side-plates. The shear from anti-spinning side-plates reduces the voidage and increases the bulk density. As such, smaller particles in the mixer tend to move to denser regions. We varied the shear by changing the coefficient of friction on the side-plates to study the influence of shear rate on this migration. We also compared the extent of radial segregation with stationary side-plates and with side-plates moving in different angular directions.

Numerical study of shear rate effect on unsteady flow separation from the surface of the square cylinder using structural bifurcation analysis

In this paper, an incompressible two-dimensional shear flow past a square cylinder problem is investigated numerically using a higher order compact finite difference scheme. Simulations are presented for three sets of Reynolds numbers, 100, 200, and 500, with various shear parameter (K) values ranging from 0.0 to 0.4. The purpose of the present study is to elaborate the influence of shear rate on the vortex shedding phenomenon behind the square cylinder. The results presented here show that the vortex shedding phenomenon strongly depends on Re as well as K. The strength and size of vortices shed behind the cylinder vary as a function of Re and K. When K is larger than a critical value, the vortex shedding phenomenon has completely disappeared depending on the Reynolds number. Apart from the numerical study, a thorough theoretical investigation has been done by using a topology based structural bifurcation analysis for unsteady flow separations from the walls of the cylinder. Through this analysis, we study the exact locations of the bifurcation points associated with secondary and tertiary vortices with appropriate non-dimensional time of occurrence. To the best of our knowledge, this is the first time, a topological aspect based structural bifurcation analysis has been done to understand the vortex shedding phenomenon and flow separation for this problem.

Analysis of the rheological behavior of Fe trimodal micro-nano powder feedstock in micro powder injection molding

The rheological behavior of Fe trimodal powder feedstock for μ-PIM was investigated using torque rheometer analysis. The feedstock was prepared by mixing Fe micropowder (~4μm) and nanopowder agglomerates containing discrete particles with sizes of ~300nm and ~30nm, with low viscosity wax-based binders. During the feedstock mixing, a significant increase in mixing torque was observed at powder content above 72vol% in the feedstock, indicating the critical powder loading. The results obtained from the torque rheometer experiment at selected powder loadings of 66–74vol% were used as fundamental rheological parameters including flow behavior index (n), flow activation energy (E), and general moldability index (αstv). In addition, the influence of shear rate, temperature, and powder loading on feedstock viscosity was evaluated. It was found that the feedstock with 72vol% powder loading exhibited the best rheological behavior with the highest moldability parameter and homogeneous microstructure. Due to the lack of research on the trimodal system in the field of powder metallurgy and powder technology, this paper provides the possibility of applying the trimodal powder mixture to a near net-shape production technique such as PIM.

Chai-Qin-Cheng-Qi decoction alleviates multiple organ dysfunction syndrome by upregulating Nrf2 in rodent models of acute pancreatitis and intestinal ischaemia-reperfusion injury

Segregation and mixing of granular materials are complex processes and are not fully understood. Motivated by industrial need, we performed a simulation using the discrete element method to study size segregation of a binary mixture of granular particles in a horizontal rotating drum. Particles of two different sizes were poured into the drum until it was 50% full. Shear-driven segregation was induced by rotating the side-plates of the drum in the opposite direction to that of the cylindrical wall. We found that radial segregation diminished in these systems but did not completely vanish. In an ordinary rotating drum, a radial core of smaller particles is formed in the center of the drum, surrounded by larger revolving particles. In our system, however, the smaller particles were found to migrate toward the side-plates. The shear from anti-spinning side-plates reduces the voidage and increases the bulk density. As such, smaller particles in the mixer tend to move to denser regions. We varied the shear by changing the coefficient of friction on the side-plates to study the influence of shear rate on this migration. We also compared the extent of radial segregation with stationary side-plates and with side-plates moving in different angular directions.

Two-phase mixture model for nanofluid turbulent flow and heat transfer: Effect of heterogeneous distribution of nanoparticles

In this work, a two-phase mixture model for evaluation of flow and heat transfer performance of SiO2/water nanofluids under turbulent flow was proposed by considering the heterogeneity of concentration due to crossed effect and the influences of shear rate, viscosity gradient, thermophoresis and Brownian motion on the diffusion of the nanoparticles. The effects of Peclet number, Reynolds number, nanoparticle size and nanofluid mean concentration on the distribution of nanoparticles have been evaluated. The values of thermal conductivity and viscosity as the main thermophysical properties of nanofluids changed across different layers of the liquid due to the heterogeneous distribution of concentration. It was observed that an increase in the Peclet number caused heterogeneity in the distribution of the properties. The achieved nanoparticle distribution has been implemented for analysis of nanofluid using two-phase mixture model. It was found that the effect of nanofluid concentration on the Nusselt number was more noticeable in lower Reynolds numbers due to the insignificant effect of flow momentum on heat transfer. The maximum of 43.9% enhancement in convection heat transfer was achieved by dispersion of 4% SiO2 nanoparticles inside DI-water at Re=25,000.

Seedling-growing tray made of rice straw for maize seedling transplantation and its shear mechanics test

Abstract: The plant-made seedling-growing tray cultivation technique is an effective way to improve maize yield and quality in China’s cold northern area. However, the corn seedling nursery carrier and tray cultivation technique has been proved poor in adaptability. After comparing several nursery carriers, a design for a plant-made seedling-growing tray that is suitable for maize transplantation was proposed in which rice straw was used as the primary raw material. The preparation method, processing and structural dimensions of the tray were investigated and designed, five types of plant-made seedling-growing trays with different formulations were proposed. The shear mechanical properties and the shear strength of the plant-made seedling-growing trays were tested to determine the shear force needed for cutting through trays prepared with increasing mass ratios of rice straw and the effect of the shearing rate on the shear strength. The results showed that at a shearing rate of 100 mm/min, the maximum shear force decreased gradually as the mass ratio of straw was increased and that the hardness of the tray decreased as its shear strength decreased. Under three shearing rates (100 mm/min, 200 mm/min and 500 mm/min) and a blade displacement of 10 mm, the shear force was the highest at the point at which the tray was cut through; the required shear force to cut through the tray then gradually decreased. Trays with the same straw composition showed no significant influence of shearing rate on the tray’s shear strength at shearing rates of 100 mm/min, 200 mm/min or 500 mm/min. This study describes a multi-tray, single-strip nursery carrier for use in plant-made seedling-growing tray cultivation and proposes a theoretical basis for the design of a rotary transplanting device, the key part of a maize plant-made seedling-growing tray transplanter. Keywords: maize seedling transplanting, seedling-nursery tray, preparation, shear force, shear strength, rice straw, mixing ratio DOI: 10.3965/j.ijabe.20160906.2222 Citation: Ma Y C, Zhang W, Wang C, Mao X, Zhang B, Wang H Y. Preparation of a seedling-growing tray made of rice straw for maize seedling transplantation and its shear mechanics test. Int J Agric & Biol Eng, 2016; 9(6): 44－55.

Discrete element method study of shear-driven granular segregation in a slowly rotating horizontal drum

Segregation and mixing of granular materials are complex processes and are not fully understood. Motivated by industrial need, we performed a simulation using the discrete element method to study size segregation of a binary mixture of granular particles in a horizontal rotating drum. Particles of two different sizes were poured into the drum until it was 50% full. Shear-driven segregation was induced by rotating the side-plates of the drum in the opposite direction to that of the cylindrical wall. We found that radial segregation diminished in these systems but did not completely vanish. In an ordinary rotating drum, a radial core of smaller particles is formed in the center of the drum, surrounded by larger revolving particles. In our system, however, the smaller particles were found to migrate toward the side-plates. The shear from anti-spinning side-plates reduces the voidage and increases the bulk density. As such, smaller particles in the mixer tend to move to denser regions. We varied the shear by changing the coefficient of friction on the side-plates to study the influence of shear rate on this migration. We also compared the extent of radial segregation with stationary side-plates and with side-plates moving in different angular directions.

Characterization of nanoparticle binding dynamics in microcirculation using an adhesion probability function

Quantitative understanding of nanoparticles transport and adhesion dynamic in microcirculation is very challenging due to complexity of fluid dynamics and imaging setup. In-vitro experiments within microfluidic channels showed the significant influence of shear rate, carrier size, particle-substrate chemistry and vessel geometry on particle deposition rate. However, there are few theoretical models that can accurately predict experimental results. We have developed a numerical model to predict nanoparticle transport and binding dynamics and verified with our previous in-vitro tests results. A binding probability function is used to simplify the carrier attachment and detachment processes. Our results showed that due to the complex dynamics of particle transport and adhesion mechanism, the correlation between binding probability and actual deposition rate is not linear. Using experimental data, it is shown that the binding probability of small particles changes slightly with shear rate whereas the chance of binding for big particles decreases exponentially with shear. Our particulate model also captured some phenomena that cannot be achieved by continuum approach such as accumulation of drug particles in close vicinity of vessel wall. In addition, the effects of channel geometry and antibody density on particle binding are discussed extensively. The results from our particulate approach agrees well with experimental data suggesting that it can be used as a simple, yet efficient predictive tool for studying drug carrier binding in microcirculation.