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The injection molding process is one of the most widely used methods for polymer processing in mass production. Three critical factors in this process include the type of polymer, injection molding machines, and processing molds. Polypropylene (PP) is a widely used semi-crystalline polymer due to its favorable flow characteristics, including a high melt flow index and the absence of a need for a mold temperature controller. Additionally, PP exhibits good elongation and toughness, making it suitable for applications such as box hinges. However, its tensile strength is a limitation; thus, glass fiber is added to enhance this property. It is important to note that the incorporation of glass fiber increases the viscosity of PP. Multi-cavity molds are commonly employed to achieve cost-effective and efficient mass production. The filling challenges associated with geometrically balanced layouts are well documented in the literature. These issues arise due to the varying shear rates of the melt in the runner. High shear rate melts lead to high melt temperatures, which decrease melt viscosity and facilitate easier flow. Consequently, this results in an imbalanced filling phenomenon. This study examines the impact of runner size, gate size, polymer viscosity, and molding process on the filling imbalanced problem in multi-cavity injection molds. Tensile bar injection molding was performed using conventional injection molding (CIM) and microcellular injection molding (MIM) techniques. The tensile properties of the imbalanced multi-cavity molds were analyzed. Flow length within the cavity served as an indicator of the filling imbalance. Additionally, computer simulations were conducted to assess the shear rate's effect on the runner's melt temperature. The results indicated that small runner and gate sizes exacerbate the filling imbalance. Conversely, glass fiber-filled polymer composites also contribute to increased filling imbalance. However, foamed polymers can mitigate the filling imbalance phenomenon. [ABSTRACT FROM AUTHOR]

AbstractTiO2 nanoparticles were synthesized using the reduction precipitation method, verified by powder x-ray diffraction (PXRD) with an average crystallite size of 62 nm and an average particle size of 135 nm from SEM images. Rheological studies of brake fluid with nanoparticle additives revealed that while the fluid generally maintains consistent behavior, a 2 wt.% concentration showed non-Newtonian behavior at 120 °C. Viscosity increased slightly with nanoparticle addition and decreased with rising temperature, with the 0.5 wt.% sample demonstrating the most notable increase of 18.18% at 120 °C. At 30 °C, the 1 wt.% sample exhibited a 4.06% increase. The observed viscosity changes are attributed to higher internal shear stress and the need to manage dispersion solid elements. The Herschel-Bulkley model was effective in predicting sample behavior, and all samples conformed to Reynolds’ equation μ0=be−aT. This research indicates that TiO2 nanoparticles can be effectively used as brake fluid additives, offering potential benefits for high-temperature applications in vehicles. Further optimization using mathematical models such as response surface methodology (RSM) is suggested for improved performance. [ABSTRACT FROM AUTHOR]

Highlights Poly(butylene adipate‐co‐terephthalate) with or without thermoplastic starch is often used as a biodegradable matrix in composites reinforced with 5 and 10 wt% of either microfibrillated cellulose or cellulose nanocrystals. If dispersion of the fillers is well studied, their orientation in melt blended composites requires further understanding. In this study, the effect of a controlled shear rate on the orientation of the filler was investigated to understand how shear rate affects orientation and how orientation affects mechanical properties of the composites. To this end, composites prepared by melt mixing and then compressed were taken as a reference state of low orientation. On the contrary, to orient the fillers, extrusion through a slit die with a determined shear rate was carried out. Results of tensile tests, microscopic observations, atomic force microscopy and dynamic mechanical analysis in the melt showed that orientation of fillers in the flow axis was possible for shear rates higher than 13 s−1. The orientated samples presented enhanced mechanical properties in the elastic domain as opposed to unoriented samples. In general, orientation of fillers leads to uniaxial stiffness at lower filler content with much better ductility. However, this was observed only on samples for which the percolation of the filler was not obtained in the unoriented state, otherwise, orientation proved to be detrimental to the elastic mechanical properties because of the rupture in the formed network. Orientation can be controlled during processing. Sufficient shear rate is required. Orientation improves mechanical properties. Orientation might have a negative effect on rigidity in case of existing network. [ABSTRACT FROM AUTHOR]

BACKGROUND: The biological properties of silicone elastomers such as polydimethylsiloxane (PDMS) have widespread use in biomedicine for soft tissue implants, contact lenses, soft robots, and many other small medical devices, due to its exceptional biocompatibility. Additive manufacturing of soft materials still has significant challenges even with major advancements that have occurred in development of these technologies for customized medical devices and tissue engineering. OBJECTIVE: The aim of this study was to develop a mathematical model of tangential stress in relation to shear stress, shear rate, 3D printing pressure and velocity, for non-Newtonian gels and fluids that are used as materials for 3D printing. METHOD: This study used FENE (finitely extensible nonlinear elastic model) model, for non-Newtonian gels and fluids to define the dependences between tangential stress, velocity, and pressure, considering viscosity, shear stress and shear rates as governing factors in soft materials friction and adhesion. Experimental samples were fabricated as showcases, by SLA and FDM 3D printing technologies: elastic polymer samples with properties resembling elastic properties of PDMS and thermoplastic polyurethane (TPU) samples. Experimental 3D printing parameters were used in the developed analytical solution to analyse the relationships between governing influential factors (tangential stress, printing pressure, printing speed, shear rate and friction coefficient). Maple software was used for numerical modelling. RESULTS: Analytical model applied on a printed elastic polymer, at low shear rates, exhibited numerical values of tangential stress of 0.208–0.216 N m - 2 at printing velocities of 0.9 to 1.2 mm s - 1, while the coefficient of friction was as low as 0.09–0.16. These values were in accordance with experimental data in literature. Printing pressure did not significantly influence tangential stress, whereas it was slightly influenced by shear rate changes. Friction coefficient linearly increased with tangential stress. CONCLUSION: Simple analytical model of friction for elastic polymer in SLA 3D printing showed good correspondence with experimental literature data for low shear rates, thus indicating possibility to use it for prediction of printing parameters towards desired dimensional accuracy of printed objects. Further development of this analytical model should enable other shear rate regimes, as well as additional soft materials and printing parameters. [ABSTRACT FROM AUTHOR]

The shear mechanical parameters of coal are important parameters for analyzing the deformation and stability of coal. In order to study the shear characteristics of straight joints of coal under different normal stress and shear rate conditions, the shear numerical simulation and laboratory test were carried out to study the influence of normal stress and shear rate on the shear characteristics of straight joints of coal. The results show that the shear strength of joints decreases with the increase of shear rate, and increases with the increase of normal stress. The higher the normal stress, the greater the influence of shear rate on the shear strength of joints. Shear stiffness is positively correlated with normal stress and negatively correlated with shear rate. When the shear rate reaches a certain value, the influence of shear stiffness is not obvious. The increase of shear rate makes the simulated joints more prone to shear slip, which is easy to cause coal and rock dynamic disasters. This phenomenon is more serious in high normal stress.

The aim of the study was to determine the shear strength of mineral and anthropogenic soil of similar grain size as a function of the applied shear rate and water saturation. Stability calculations using the finite element method of the road embankment model were also carried out to demonstrate the variation in factor of safety values depending on the adopted values of the angle of internal friction and cohesion. The tests were carried out in a direct shear apparatus in a 100 x 100 mm box with a sample height of 20.5 mm. The samples were formed directly in the apparatus box at optimum moisture content until a compaction index of IS = 1.00 was obtained. Tests were carried out under conditions without and with water saturation at shear rates of 0.01, 0.05, 0.1, 0.5 and 1.0 mm•min–1 until 18% horizontal displacement was achieved. The results showed that the effect of shear rate on the strength parameters was not unequivocal and was much smaller than the changes caused by saturation of samples. An increase in shear rate resulted in small changes in the angle of internal friction with a tendency towards a decrease. In contrast, cohesion varied over a much larger range with increasing shear rate, with an apparent initial decrease and subsequent increase. The saturation of the samples resulted in a decrease in the angle of internal friction of the cohesive soil and an increase for the ash-slag mixture. The cohesion of both soils decreased. The results obtained from the road embankment model stability calculations confirmed that soil saturation had a greater influence on the factor of safety values obtained than the shear rate.

We have found that the unique particle properties of fly ash can be applied to the modification of shear thickening fluid. In this paper, rheological properties and microscopic thickening mechanism of fly ash/silicon-based shear thickening fluid (subsequently abbreviated as FA/SiO2-STF) are studied. Ultrasonic technology and mechanical stirring method were used to prepare FA/SiO2-STF with different mass fractions of fly ash, and then rheometer was used to carry out steady-state rheological testing for FA/SiO2-STF, and 4%FA/SiO2-STF dynamic rheological test and temperature sensitivity testing, respectively. The thickening mechanism of FA/SiO2-STF was analyzed by scanning electron microscope. The rheological test results show that the FA/SiO2-STF with 4% fly ash content exhibits remarkable shear thickening effect. Finally, the relationship between the viscosity and shear rate of FA/SiO2-STF is numerically described by a mathematical model, which can accurately reflect the viscosity thickening effect. [ABSTRACT FROM AUTHOR]

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Due to the high rate of the development of housing, transportation and hydraulic engineering construction in the last hundred years, the study of the phenomenon of creep of clay soils has become a subject of scientific research. In the study, experimental investigations of clay soil were conducted using a simple shear device in kinematic loading mode, aimed at examining the influence of shear rate on the viscosity coefficient of the clay soil and its strength characteristics. The tests were performed at four different shear rates and three different vertical load values. Based on the results of experimental and theoretical studies, the viscosity coefficients of clay soil were obtained, and a new rheological equation was proposed, which simultaneously takes into account the influence of Coulomb friction, structural cohesion, cohesion of water–colloidal bonds and viscous resistance of the soil. It has been shown that the shear rate has a significant impact on the viscosity coefficient of clay soil, and the viscosity coefficient itself is a variable quantity, depending both on the magnitude of the applied load and the duration of its application. The obtained results can be used for further improvement of methods for calculating the settlement of structures over time, as well as for predicting the time until the bearing capacity of foundation soils is exhausted. [ABSTRACT FROM AUTHOR]

The global population growth and increasing energy demand pose challenges to the Oil and Gas industry, leading to increased exploration and production in offshore and deep-sea areas. Offshore oilfields in colder regions produce crude oils with higher wax content, causing wax deposition and flow assurance issues in pipelines. Nanoparticle inhibitors can mitigate wax deposition in pipelines. In this study, the performance of zinc oxide nanoparticle is evaluated by measurement of degree of viscosity reduction and wax deposition of a Niger Delta crude oil sample. Wax deposition is determined by cold finger technique. 10g of zinc oxide (ZnO) nanoparticle is mixed in 500mL of crude oil sample. From this experiment, it was observed that at 2rpm (revolutions per minute), the degree of viscosity reduction (DVR) was 31% at 10°C and 3% at 15%. Increase in crude oil temperature enhanced the viscosity of the blank sample and the sample blended with ZnO nanoparticle. However, at lower temperatures of 10 and 15C, the viscosity of the blank crude increased. higher, indicating a poor performance of ZnO on the viscosity of the crude oil sample. The addition of 10g of ZnO nanoparticle had more cumulative wax deposit of 16.76g than the blank crude having a cumulative wax deposit in the cold finger as 14.32g. This implies that 10g nano ZnO did not prevent or reduce the wax deposition in the cold finger, but it was efficient at improving the viscosity and flowability of the Niger Delta crude sample. [ABSTRACT FROM AUTHOR]

A systematic analytical study of the mathematical properties of the previously constructed nonlinear model for shear flow of thixotropic viscoelastic-plastic media, which takes into account the mutual influence of the deformation process and structure evolution, is continued. A set of two nonlinear differential equations describing the processes of shear at a constant rate and stress relaxation is obtained. Equation set describing creep is derived; a general solution of the Cauchy problem for the set is constructed in an explicit form (the equations of the families of creep, and structuredness curves are derived). For arbitrary six material parameters and (increasing) material function that govern the model, basic properties of the families stress-strain curves at constant strain rates, stress relaxation curves and creep curves generated by the model, and the features of structuredness evolution under these types of loading are analytically studied. The dependences of these curves on time, shear rate, stress level, initial strain, and initial structuredness of the material, as well as on the material parameters and function of the model, are studied. Several indicators of the applicability of the model are found which are convenient to check with experimental data. It was examined what effects typical for viscoelastic-plastic media can be described by the model and what unusual effects (unusual properties) are generated by a change in structuredness in comparison with typical stress-strain curves, relaxation curves, and creep curves of structurally stable materials. In particular, it is proved that creep curves always increase in time and have oblique asymptote, and structuredness under constant stress is always monotonous (unlike other loading modes), but can decrease or increase depending on the relation between the stress level and initial structuredness. The same condition controls creep curves to be convex up or down: at a certain (calculated) critical load creep curves change from convexity up (under smaller loads) to convexity down, and the structuredness becomes ascending instead of descending. The analysis proved the ability of the model to describe behavior of not only liquid-like viscoelastoplastic media, but also solid-like (thickening, hardening, hardened) media: creep, relaxation, recovery, a number of typical properties of experimental relaxation curves, creep and stress-strain curves, strain rate and strain hardening, flow under constant stress and so on. [ABSTRACT FROM AUTHOR]

Understanding the shear responses of discontinuities with different joint wall strengths (DDJS) under varying shear rates is crucial for evaluating slope dynamic stability in the Three Gorges Reservoir region, China. In this study, direct shear tests were performed on discontinuity replicas featuring three distinct wall strength combinations under three normal stress levels and four shear rates. The investigation explored the rate-dependent shear behaviors of DDJS and their underlying failure mechanisms. Tested results show consistent shear stress behavior under different shear rates for each configuration, with intensified surface damage observed at higher shear rates. Shear stiffness exhibits a decreasing trend with increasing shear rate, particularly under higher normal stress. Peak shear strength decreases non-linearly with the increase in shear rate, with this decrease being less pronounced at higher shear rates. Noted that the variation of peak shear strength versus shear rate remains roughly consistent under various normal loadings. Importantly, the negative shear rate dependence on shear stiffness and peak shear strength diminishes with the increase in discontinuity wall strength difference. Based on experimental observations, a new failure criterion with the inclusion of shear rates was developed to estimate the peak shear strengths of DDJS, further validated by experimental data available in the literature. [ABSTRACT FROM AUTHOR]

The object of the research is an intergranular friction model for use in discrete-element modeling of the mechanical behavior of granular materials under static and dynamic conditions. As in this approach grains are modeled by independent elements interacting through contact forces, the selection of contact force models, and in particular for the tangential component (friction), represents the most important task in obtaining the most realistic macroscopic behavior. There are many friction models that work well in dynamic regimes, but fail to model mechanical behavior in static or quasi-static regimes. In this work, an intergranular friction model is proposed based on Coulomb’s regularized friction model, which takes into account the stick-slip phenomenon that appears at low sliding speeds at the contact. Three different examples are designed and modeled in order to demonstrate the robustness of the model in different situations including static, quasi-static and dynamic regimes. The first is a basic example consisting of the translational motion of a grain on a planar surface with a relatively low constant velocity. This example allowed to capture the stick-slip phenomenon. The second represents a grain subjected to its own weight and supported essentially by frictional forces. This example shows that the model works well in both quasi-static and static regimes. The third example consists of a grain sliding on a plate and subjected to accelerated motion. It showed the effect of friction velocity on the occurrence of stick-slip, as well as the evolution of friction force with sliding velocity. The obtained results demonstrated that the model effectively captures shear behavior in the different regimes. It could therefore be used in discrete element modeling of granular materials under both static and dynamic conditions. As in this work, the model is formulated in 2D, it would be interesting to develop a general 3D formulation so that it can be easily applied in 3D modeling. [ABSTRACT FROM AUTHOR]

The shear mechanical behavior is regarded as an essential factor affecting the stability of the surrounding rocks in underground engineering. The shear strength and failure mechanisms of layered rock are significantly affected by the foliation angles. Direct shear tests were conducted on cubic slate samples with foliation angles of 0°, 30°, 45°, 60°, and 90°. The effect of foliation angles on failure patterns, acoustic emission (AE) characteristics, and shear strength parameters was analyzed. Based on AE characteristics, the slate failure process could be divided into four stages: quiet period, step-like increasing period, dramatic increasing period, and remission period. A new empirical expression of cohesion for layered rock was proposed, which was compared with linear and sinusoidal cohesion expressions based on the results made by this paper and previous experiments. The comparative analysis demonstrated that the new expression has better prediction ability than other expressions. The proposed empirical equation was used for direct shear simulations with the combined finite-discrete element method (FDEM), and it was found to align well with the experimental results. Considering both computational efficiency and accuracy, it was recommended to use a shear rate of 0.01 m/s for FDEM to carry out direct shear simulations. To balance the relationship between the number of elements and the simulation results in the direct shear simulations, the recommended element size is 1 mm.

BACKGROUND: Several conventional studies focused on platelet pinocytosis for possible utilization as drug delivery systems. Although platelet pinocytosis is important in such utilization, the impact of the shear rate on pinocytosis is unclear. OBJECTIVE: Our objective was to investigate the relationship between shear rate and platelet pinocytosis in vitro. In addition, this study addressed the change in platelet aggregation reactivity with adenosine diphosphate (ADP) stimulation after pinocytosis. METHOD: Porcine platelet-rich plasma was mixed with fluorescein isothiocyanate (FITC)-conjugated dextran and incubated for 15 min under shear conditions of 0, 500, and 1500 s-1. After incubation, confocal microscopic scanning and three-dimensional rendering were performed to confirm the internalization of FITC-dextran into platelets. The amount of FITC-dextran accumulated via platelet pinocytosis was compared using flow cytometry at each shear rate. In addition, light transmission aggregometry by ADP stimulation was applied to platelets after pinocytosis. RESULTS: The amount of intracellular FITC-dextran increased with higher shear rates. Platelets with increased amounts of intracellular FITC-dextran did not show changes in the aggregation reactivity to ADP. CONCLUSIONS: A higher shear rate promotes platelet pinocytosis, but enhanced pinocytosis does not affect aggregation sensitivity, which is stimulated by ADP. [ABSTRACT FROM AUTHOR]

Diatomites, or natural soils containing diatoms are found in the marine environment all over the world. Diatomites tend to have skeleton microstructures, resulting in unique rheological behaviors. In marine areas, the rheological behavior of diatomite significantly contributes to geohazards, especially submarine landslides. Predicting and preventing submarine landslides require a profound understanding of the rheological characteristics of diatomites. Therefore, to assess the rheological characteristics of diatomite with different diatom and water contents, we prepared different diatom-kaolin mixtures (diatom contents ranging from 0 to 100% and water contents from 66.8% to 640 %) and subjected them to rheological shearing tests. The Herschel-Bulkley model and the Cheng's model were used to analyze the critical rheological parameters (i.e., dynamic and static yield stresses) and the flow behaviors of the samples. The results show that kaolin mixed with 20% diatoms exhibits the highest value in yield stress. Also, the addition of diatoms alters the microstructure of kaolin which may lead to static yield at low water content and shear thickening at high water content. This study offers valuable references regarding critical rheological parameters and flow regimes for simulating submarine landslides in regions covered by natural sediments containing diatoms. [ABSTRACT FROM AUTHOR]

Exploring the mechanical response of rock joint subjected to dynamic shear load is essential for revealing the mechanism of dynamic disasters in jointed rock masses. Using an impact-induced direct-shear method, a series of dynamic shear experiments were conducted on artificial granite joints with regularly undulating interface. The dynamic friction coefficient of joint was first obtained from planar jointed granite specimens before the dynamic shear strength and shear displacement of the regularly undulating joints were tested. During the test, the effects of normal stress and shear rate were both considered. The results show that when the shear velocity ranges from 1 to 9 m/s, the dynamic friction coefficient of the planar joint is negatively correlated with shear velocity, and decreases by at least 50% compared with that under quasi-static condition. The rate dependence of shear strength appears opposite for granite joints with undulating angles of 11.3° and 26.6°, respectively. A shear strength model for rock joint with an undulating angle of 11.3° is then suggested based on the test results. During impact shear sliding, the maximum shear displacement of the joint is linearly negatively related to the initial normal stress. While, non-driven sliding may occur under low normal stress and high impact velocity, which leads to a large magnitude of shear slip. Highlights: The shear strength and shear displacement of rock joints are tested with shear rate ranging from 1 to 9 m/s. The rate dependence of shear strength appears opposite for rock joints with sharp and gentle undulation and a shear strength model is suggested. Besides impact-driven sliding, the non-driven sliding may also occur in the joint under low normal stress and high impact velocity. [ABSTRACT FROM AUTHOR]

The aim of the study was to determine the shear strength of mineral and anthropogenic soil of similar grain size as a function of the applied shear rate and water saturation. Stability calculations using the finite element method of the road embankment model were also carried out to demonstrate the variation in factor of safety values depending on the adopted values of the angle of internal friction and cohesion. The tests were carried out in a direct shear apparatus in a 100 × 100 mm box with a sample height of 20.5 mm. The samples were formed directly in the apparatus box at optimum moisture content until a compaction index of IS = 1.00 was obtained. Tests were carried out under conditions without and with water saturation at shear rates of 0.01, 0.05, 0.1, 0.5 and 1.0 mm·min-1 until 18% horizontal displacement was achieved. The results showed that the effect of shear rate on the strength parameters was not unequivocal and was much smaller than the changes caused by saturation of samples. An increase in shear rate resulted in small changes in the angle of internal friction with a tendency towards a decrease. In contrast, cohesion varied over a much larger range with increasing shear rate, with an apparent initial decrease and subsequent increase. The saturation of the samples resulted in a decrease in the angle of internal friction of the cohesive soil and an increase for the ash-slag mixture. The cohesion of both soils decreased. The results obtained from the road embankment model stability calculations confirmed that soil saturation had a greater influence on the factor of safety values obtained than the shear rate. [ABSTRACT FROM AUTHOR]

The investigation of the in-plane shear behavior of prepreg is crucial for understanding the generation of wrinkles of preforms in advanced composite manufacturing processes, such as automated fiber placement and thermoforming. Despite this significance, there is currently no standardized test method for characterizing uncured unidirectional (UD) prepreg. This paper introduces a ±45° off-axis tensile test designed to assess the in-plane shear behavior of UD carbon fiber-reinforced epoxy prepreg (CF/epoxy). Digital image correlation (DIC) was employed to quantitatively track the strains in three dimensions and the shear angle evolution during the stretching process. The influences of the temperature and stretching rate on the in-plane shear behavior of the prepreg were further investigated. The results reveal that four shear characteristic zones and wrinkling behaviors are clearly distinguished. The actual in-plane shear angle is significantly lower than the theoretical value due to fiber constraints from both the in-plane and out-of-plane aspects. When the off-axis tensile displacement (d) is less than 15.6 mm, the ±45° specimens primarily exhibit macroscale in-plane shear behavior, induced by interlaminar interface shear between the +45° ply and −45° ply at the mesoscale. The shear angle increases linearly with the d. However, when d > 15.6 mm, fiber squeezing and wrinkling begin to occur. When d > 29 mm, the in-plane shear disappears in the completely sheared zone (A). The reduction in the resin viscosity of the CF/epoxy prepreg caused by increased temperature is identified as the primary factor in lowering the in-plane shear force resistance, followed by the effect of the increasing resin curing degree. Higher shear rates can lead to a substantial increase in shear forces, eventually causing cracking failure in the prepreg. The findings demonstrate the feasibility of the test method for predicting and extracting uncured prepreg in-plane shear behaviors and the strain-rate and temperature dependency of the material response. [ABSTRACT FROM AUTHOR]

A systematic analytical study of the mathematical properties of the previously constructed nonlinear model of the shear flow of thixotropic viscoelastic-plastic media, which takes into account the mutual influence of the deformation process and structure evolution, is carried out. A set of two nonlinear differential equations describing shear at a constant rate and stress relaxation was obtained. Assuming six material parameters and an (increasing) material function that control the model are arbitrary, the basic properties of the families of stress-strain curves at constant strain rates, stress relaxation curves (Part 2) and creep curves (Part 3) generated by the model, and the features of the evolution of the structuredness under these types of loading were analytically studied. The dependences of these curves on time, shear rate, stress level, initial strain and initial structuredness of material (for example, degree of physical crosslinking), as well as on material parameters and function governing the model, were studied. Several indicators of the model applicability are found, which are convenient to check with experimental data. It was examined what effects typical for viscoelastic-plastic media can be described by the model and what unusual effects (properties) are generated by structuredness changes in comparison to typical stress-strain, relaxation and creep curves of structurally stable materials. The analysis proved the ability of the model to describe behavior of not only liquid-like viscoelastoplastic media, but also solid-like (thickening, hardening, hardened) media: the effects of creep, relaxation, recovery, a number of typical properties of experimental relaxation curves, creep and stress-strain curves at a constant rate, strain rate and strain hardening, flow under constant stress, etc. The first part of the article is devoted to formulation of the model and preparation of basis for the second part: the proof of the uniqueness and stability of the equilibrium point of the nonlinear equations set, analytical study of the equilibrium point dependence on all material parameters, possible types of phase portraits and the properties of integral and phase curves of the model. [ABSTRACT FROM AUTHOR]

The injection molding process is one of the most widely used methods for polymer processing in mass production. Three critical factors in this process include the type of polymer, injection molding machines, and processing molds. Polypropylene (PP) is a widely used semi-crystalline polymer due to its favorable flow characteristics, including a high melt flow index and the absence of a need for a mold temperature controller. Additionally, PP exhibits good elongation and toughness, making it suitable for applications such as box hinges. However, its tensile strength is a limitation; thus, glass fiber is added to enhance this property. It is important to note that the incorporation of glass fiber increases the viscosity of PP. Multi-cavity molds are commonly employed to achieve cost-effective and efficient mass production. The filling challenges associated with geometrically balanced layouts are well documented in the literature. These issues arise due to the varying shear rates of the melt in the runner. High shear rate melts lead to high melt temperatures, which decrease melt viscosity and facilitate easier flow. Consequently, this results in an imbalanced filling phenomenon. This study examines the impact of runner size, gate size, polymer viscosity, and molding process on the filling imbalanced problem in multi-cavity injection molds. Tensile bar injection molding was performed using conventional injection molding (CIM) and microcellular injection molding (MIM) techniques. The tensile properties of the imbalanced multi-cavity molds were analyzed. Flow length within the cavity served as an indicator of the filling imbalance. Additionally, computer simulations were conducted to assess the shear rate’s effect on the runner’s melt temperature. The results indicated that small runner and gate sizes exacerbate the filling imbalance. Conversely, glass fiber-filled polymer composites also contribute to increased filling imbalance. However, foamed polymers can mitigate the filling imbalance phenomenon.

Thrombosis is the main reason for the failure of ventricular assist devices (VADs). It has been acknowledged that the platelet activation induced by the nonphysiological blood flow leads to the increased thrombotic risk. However, due to the complicated influence of the VADs' flow field and the difficulty in real‐time in situ observation, the mechanisms and process of thrombus formation in VADs remain unclear. In this work, the process of thrombus formation in VADs in vitro experiments is observed. The thrombus is found to form on the middle of the inlet guide vanes first and it is mainly caused by the immediate activation of platelets induced by the high shear rate of the flow field around the vanes and also affected by the rotation of the impeller. Then, subsequent thrombus is found in the tail of guide vanes and around the axle journal, where the blood flow is stagnated and the platelets are activated by the accumulated bioagonists. These findings clarify that the thrombus formed on the inlet guide vanes and the axle journal are dominated by two different mechanisms. This work provides unique insights into the initial formation of the thrombus on VADs and helps to reduce the thrombotic risk. [ABSTRACT FROM AUTHOR]

Inspiratory resistance training (IRT) yields significant reductions in resting blood pressure and improves vascular endothelial function. Our objective was to quantify the acute effects of IRT on brachial artery flow‐mediated dilation (FMD) and shear rates (SRs) in healthy men and women. Twenty young adults (22.9 ± 3.4 years; 10 male, 10 female) completed a single bout of IRT or Rest condition in a randomized crossover design. Brachial artery FMD was performed before, 10 min after, and 40 min after the assigned condition. Brachial artery blood flow velocities were collected during IRT, separated by breathing cycle phase, and converted into SRs. FMD improved 10 min post‐IRT (+1.86 ± 0.61%; p = 0.025) but returned to baseline by 40 min post‐IRT (p = 0.002). Anterograde SR decreased by 10% and retrograde SR increased 102% during resisted inspiration, relative to baseline SR (p < 0.001). Anterograde SR increased by 7% in men and women (p < 0.001) and retrograde SR decreased by 12% in women but not men (p = 0.022) during unresisted expiration, relative to baseline SR. A single bout of IRT elicits a transient enhancement in FMD in both men and women. Acute IRT‐related enhancements in SRs may contribute to sustained improvements in FMD that have been reported previously. [ABSTRACT FROM AUTHOR]

Shear thickening fluids (STFs) have gained attention for their capacity to increase viscosity with higher shear rates, rendering them solid-like under high-impact conditions. This reversibility renders STFs valuable for diverse applications, particularly in defense systems. Preceding our study, mechanical hurdles, such as aggregation and blending issues, hindered efficient utilization. Our research presents an innovative method for STF synthesis using polyethylene glycol and SiO2 nanoparticles. Significantly, we employed a hot plate and oil bath to remove ethanol from the STF, a distinctive aspect of our approach. We also systematically explored the impact of temperature and the dispersion weight fraction of fumed silica nanoparticles on crucial rheological parameters, encompassing viscosity, shear rate, storage modulus (G′), and loss modulus (G″). As temperatures increased, the critical shear rate also rose, while viscosity decreased. Additionally, we observed a significant enhancement in thickening behavior with higher SiO2 concentrations in STFs. For instance, the peak viscosity of 15 wt% STF decreased by approximately 69.47% from 20 to 40 °C and by approximately 89.92% from 20 to 60 °C. This study highlights the unique rheological properties of STFs. [ABSTRACT FROM AUTHOR]

High-frequency components such as microprocessors, transistors, antennas, voltage-controlled oscillators, and many others generate a large amount of heat. In the absence of satisfactory cooling, these components may suffer damage or even destruction. Therefore, it is important to find effective ways to cool these components. A possible solution is to use oil-based magnetic fluids. Magnetic fluids contain magnetic particles dispersed in oil, and their properties, including viscosity, affect their cooling capabilities. Viscosity can be changed by adding various additives or by adjusting the concentration of magnetic particles. The advantage of using oil-based magnetic fluids for cooling is that they allow for precise dosing and control of the amount of fluid applied to the component, reducing thermal losses and increasing cooling efficiency. In addition, oil-based magnetic fluids can also act as a dielectric, reducing electrical noise and increasing electromagnetic compatibility with the components. Analyzing the heating rate of magnetic fluids consisting of mineral oils in an alternating magnetic field with a frequency of 500 kHz, we have shown the capability of controlling thermal losses by adjusting the viscosity of the carrier liquid. [ABSTRACT FROM AUTHOR]

Mayonnaise is a widely used emulsion-like food that is popular for its flavor properties. However, the modern trend of healthy eating requires a reduction in the calorie content of this product, which means an oil content decrease. Such emulsion systems require the solution of increased problems associated with the stabilization of their spatial structure. It is known that the size of droplets as a microstructural characteristic depends on the stability of the emulsion and correlates with the rheological properties of emulsions. Thus, the study of these characteristics becomes one of the important factors in predicting the properties of emulsions being developed with different natures of the main ingredients. The purpose of this study was a preliminary chemometric analysis of data on acidity and rheological and microstructural characteristics of commercial mayonnaises containing from 25 to 76% oils (sunflower, rapeseed and olive) in order to predict the effect of the main ingredients of the recipe on textural characteristics. Rheological data were analyzed within the framework of a structural representation based on the generalized Casson's model. The nine standardized parameters were grouped using multivariate statistical methodology techniques such as principal component analysis and hierarchical cluster analysis. The experimental flow curves demonstrated pseudoplastic behavior, which is typical for such emulsion systems. The three factors of multivariate factor analysis can explain 72.5% of the variability. In the first factor, the most important variables (with the highest loads) were Casson's model coefficient of the aggregation degree, the static yield stress and the average droplet size. In the second factor, the highest loadings were the oil content and Casson's model coefficient, which indicate a tendency to form an infinitely large droplet aggregate. The pattern captured by PCA is confirmed by HCA analysis data. Rheology combined with microstructural characteristics can be used as a tool to evaluate the effect of ingredients in mayonnaise and mayonnaise sauces on textural properties. This information is important for formulation in cases using alternative ingredients. [ABSTRACT FROM AUTHOR]

Simple Summary: Blood viscosity, an essential hemorheological parameter, signifies the inherent resistance encountered during blood circulation within blood vessels. Assessing whole blood viscosity stands as an early diagnostic modality for an array of vascular conditions, encompassing cardiovascular, cerebrovascular, and microvascular ailments. Given the intricate challenge of early-stage diagnosis using conventional blood tests, blood viscosity emerges as a tool to gauge disease susceptibility. Recently, scanning capillary viscometers that can obtain blood viscosity values for a wide range of shear rates through a single measurement have been widely used. Using this, this study aimed to establish reference intervals in cats, representative companion animals, for further hemorheological study and the veterinary clinical field. The outcomes of this study yield essential reference intervals for normal whole blood viscosity in healthy feline subjects, encompassing a wide range of shear rates that hitherto lacked comprehensive establishment. Whole blood viscosity, a hemorheological factor, is currently used for diagnosis, as it is correlated with various vascular diseases that are difficult to diagnose early with a general blood test. It was determined that it was necessary to set reference intervals for further studies and utilization of whole blood viscosity in cats, a representative companion animal, and this study was conducted. Fifty healthy cats were recruited for the study, and whole blood viscosity, complete blood count, and serum chemistry tests were performed. The reference intervals of whole blood viscosity were 15.169 to 43.684 cP at a shear rate of 1 s−1 reflecting diastole, and 3.524 to 5.544 cP at a shear rate of 300 s−1 reflecting systole. Red blood cells, hematocrit, hemoglobin, white blood cells, and neutrophils in the complete blood count, and total protein, albumin, globulin, and cholesterol in the serum chemistry were significantly correlated with whole blood viscosity. The results of this study set the reference intervals of whole blood viscosity for healthy cats in a wide shear rate range that has not yet been fully established, and its correlation with other blood indicators investigated. [ABSTRACT FROM AUTHOR]

Higher shear rate possessing homogeneous shear thickening fluids were synthesized using monodispersed silica nanoparticles and polyethylene glycol (PEG). Novel homogeneous methodology was developed for the synthesis of shear thickening fluids using monodispersed silica nanoparticles and PEG. Shear rate of shear thickening fluids (STF) was determined using rheometer at room temperature. The normal shear rate was observed in the range of 100 to 1200 s−1, whereas higher shear rate 2000 s−1 was obtained using monodispersed silica nanoparticles, PEG and shear rate enhancer. Monodispersed silica nanoparticles were synthesized in a typical one-pot using modified Stober's method at room temperature. Precursors were used for the synthesis of monodispersed silica nanoparticles such as tetraethyl orthosilicate (TEOS), ethanol, deionized water and ammonia as catalyst. Particle size of monodispersed silica nanoparticles was in the range of 100–1200 nm, and particle size distribution was varied from 0.000 to 0.221. Synthesis of monodispersed silica nanoparticles was studied by various parameters, namely effect of TEOS concentration, grade of ethyl alcohol, ammonia concentration and water concentration. TEOS concentration effect shows particle size and particle size distribution increases with increase in concentration of TEOS. Even though concentration of TEOS was increased up to 5 times the observation was same for all particle sizes such as 100, 300 and 500 nm. Particularly in the case of 300 nm monodispersed silica nanoparticle synthesis, as TEOS concentration was increased from 1 to 5X (5 times) the particle size was increased from 331.7, 447.8, 497.0, 512.0 and 531.7 nm and particle size distribution was 0.005, 0.000, 0.006, 0.007 and 0.089, respectively. The effect of grade of ethyl alcohol illustrates that Indian rectified spirit shows almost similar results with respect to China make ethyl alcohol. Comparative study of China and Indian rectified spirit shows silica nanoparticle size was 174.6 and 174.2 nm, and particle size distribution was 0.065 and 0.071, respectively. Ammonia concentration effect explains particle size and particle size distribution increases with increase in concentration of ammonia. Water concentration effect shows particle size and particle size distribution increases with increase in concentration of ammonia. Comparative data of water concentration effect for 1316 and 1974 mL shows particle size were 321.7 and 488.0 nm, and particle size distribution was 0.083 and 0.05, respectively, under similar conditions. Morphological studies displayed the shape of the silica nanoparticles was spherical, monodispersed and isolated. A typical TEM image of monodispersed silica nanoparticles for 500 nm was observed with extremely low polydispersity, i.e., 0.000. It is very difficult to get such a type of excellent photograph of monodispersity by Stober's method particularly on large scale. Rheology study of homogeneous shear thickening fluids studied by varying the parameters such as composition of silica nanoparticles with PEG, effect of amount of solvent, effect of refluxing time, effect of additive with respect to the mol. wt. of PEG and effect of additive such as Tannin. All these parameters of STF explored with respect to the shear rate and shear viscosity. Effect of ethanol amount on STF demonstrates the shear rate increases with increase in amount of solvent. Effect of refluxing time on STF exhibits the shear rate increases with increase in refluxing time. Effect of composition based on 500 nm monodispersed silica nanoparticles and PEG 200 with respect to 60:40, 65:35 and 70:30 composition was studied and the results predict that shear rate increases with increase in silica percentage in composition, i.e., 118, 265 and 1200 s−1 for 60:40, 65:35 and 70:30 composition, respectively, whereas maximum viscosity decreases with increase in silica content, i.e., 2.559, 1.420 and 1.200 Pa.s for 60:40, 65:35 and 70:30 composition, respectively. Effect of additive on shear rate and shear viscosity illustrates that shear rate decreases with increase in additive percentage in composition, whereas maximum viscosity increases with increase in additive content. Effect of additives on shear rate and shear viscosity was performed using 65:35 composition with respect to PEG 200 along with PEG 6000 shows shear rate was decreased from 142 to 6.42 s−1 and maximum viscosity was increased from 56.1 to 571.0 Pa.s when the quantity of PEG 6000 was doubled. In general, additive decreases shear rate and increases shear viscosity (maximum). But effect of Tannin as an additive on 500 nm monodispersed silica nanoparticles with PEG 200 using 70:30 composition showed enormous increase in shear rate, i.e., 2000 s−1. This is anomalous behavior of additive was observed. [ABSTRACT FROM AUTHOR]

Thrombosis is a vascular disease associated with severe risks such as heart attack and stroke. Extensive research has been conducted worldwide to identify the underlying causes of thrombus formation due to its potential implications. Many thrombosis studies have investigated hemodynamic effects by assuming blood as a single-phase fluid. However, since the behavior of blood is greatly influenced by red blood cells (RBCs), it is necessary to analyze blood as a mixture (two-phase). In this paper, computational fluid dynamics (CFD) was performed assuming that blood is a two-phase fluid composed of plasma and RBCs. In addition, microchannels with circular cross-sections similar to human blood vessels were fabricated and used for blood experiments. The thrombus formed in the microchannel was visualized using image processing technology. Three-dimensional models incorporating the visualized thrombus were created and utilized to investigate the physical factors affecting the thrombus surface. In conditions where the shear rates were too high, the thrombus did not grow because of the drag force. Thrombus overcame the drag force and grew in areas with reduced shear stress. Also, the volume fraction of plasma calculated by the two-phase fluid model increased after the apex of stenosis and behind the thrombus. Thrombus growth was identified in areas with increased plasma volume fraction. [ABSTRACT FROM AUTHOR]

Due to the high rate of the development of housing, transportation and hydraulic engineering construction in the last hundred years, the study of the phenomenon of creep of clay soils has become a subject of scientific research. In the study, experimental investigations of clay soil were conducted using a simple shear device in kinematic loading mode, aimed at examining the influence of shear rate on the viscosity coefficient of the clay soil and its strength characteristics. The tests were performed at four different shear rates and three different vertical load values. Based on the results of experimental and theoretical studies, the viscosity coefficients of clay soil were obtained, and a new rheological equation was proposed, which simultaneously takes into account the influence of Coulomb friction, structural cohesion, cohesion of water–colloidal bonds and viscous resistance of the soil. It has been shown that the shear rate has a significant impact on the viscosity coefficient of clay soil, and the viscosity coefficient itself is a variable quantity, depending both on the magnitude of the applied load and the duration of its application. The obtained results can be used for further improvement of methods for calculating the settlement of structures over time, as well as for predicting the time until the bearing capacity of foundation soils is exhausted.

Abstract To evaluate shear stress influence on ex vivo expansion of hematopoietic cell lineages for clinical application, in this study, human pro-monocytic cell (namely U937 cell line) was selected as a hematopoietic stem cell (HSC) model and cultured in suspension mode at two different agitation rates (50, 100 rpm) in the stirred bioreactor. At the agitation rate of 50 rpm, the cells achieved higher expansion folds (27.4 fold) with minimal morphological changes as well as apoptotic cell death, while at 100 rpm the expansion fold decreased after 5-day of culture in suspension culture in comparison with static culture and reached 24.5 fold at the end of the culture. The results of glucose consumption and lactate production were also in agreement with the data of fold expansion and indicated the preference of culture in the stirred bioreactor when agitated at 50 rpm. This study indicated the stirred bioreactor system with an agitation rate of 50 rpm and surface aeration may be used as a potential dynamic culture system for clinical applications of hematopoietic cell lineage. The current experiments shed data related to the effect of shear stress on human U937 cells, as a hematopoietic cell model, to set a protocol for expansion of HSCs for biomedical applications.

The shear strength of sand-foam mixtures plays a crucial role in ensuring successful earth pressure balance (EPB) shield tunneling. Since the sand-foam mixtures are constantly sheared by the cutterhead and the screw conveyor with varied rotation speeds during tunneling, it is non-trivial to investigate the effect of shear rates on the undrained shear strength of sand-foam mixtures under chamber pressures to extend the understanding on the tunneling process. This study conducted a series of pressurized vane shear tests to investigate the role of shear rates on the peak and residual strengths of sand-foam mixtures at different pore states. Different from the shear-rate characteristics of natural sands or clay, the results showed that the peak strength of sand-foam mixtures under high vertical total stress (σv ≥ 200 kPa) and low foam injection ratio (FIR ≤ 30%) decreased with the increase in shear rate. Otherwise, the peak strength was not measurably affected by shear rates. The sand-foam mixtures in the residual state resembled low-viscous fluid with yield stress and the residual strength increased slightly with shear rates. In addition, the peak and residual strengths were approximately linear with vertical effective stress regardless of the total stress and FIR. The peak effective internal friction angle remained almost invariant in a low shear rate (γ˙

Abstract Inspiratory resistance training (IRT) yields significant reductions in resting blood pressure and improves vascular endothelial function. Our objective was to quantify the acute effects of IRT on brachial artery flow‐mediated dilation (FMD) and shear rates (SRs) in healthy men and women. Twenty young adults (22.9 ± 3.4 years; 10 male, 10 female) completed a single bout of IRT or Rest condition in a randomized crossover design. Brachial artery FMD was performed before, 10 min after, and 40 min after the assigned condition. Brachial artery blood flow velocities were collected during IRT, separated by breathing cycle phase, and converted into SRs. FMD improved 10 min post‐IRT (+1.86 ± 0.61%; p = 0.025) but returned to baseline by 40 min post‐IRT (p = 0.002). Anterograde SR decreased by 10% and retrograde SR increased 102% during resisted inspiration, relative to baseline SR (p

Abstract Thrombosis is the main reason for the failure of ventricular assist devices (VADs). It has been acknowledged that the platelet activation induced by the nonphysiological blood flow leads to the increased thrombotic risk. However, due to the complicated influence of the VADs’ flow field and the difficulty in real‐time in situ observation, the mechanisms and process of thrombus formation in VADs remain unclear. In this work, the process of thrombus formation in VADs in vitro experiments is observed. The thrombus is found to form on the middle of the inlet guide vanes first and it is mainly caused by the immediate activation of platelets induced by the high shear rate of the flow field around the vanes and also affected by the rotation of the impeller. Then, subsequent thrombus is found in the tail of guide vanes and around the axle journal, where the blood flow is stagnated and the platelets are activated by the accumulated bioagonists. These findings clarify that the thrombus formed on the inlet guide vanes and the axle journal are dominated by two different mechanisms. This work provides unique insights into the initial formation of the thrombus on VADs and helps to reduce the thrombotic risk.

Introduction: Iliac vein compression syndrome (IVCS) is present in over 20% of the population and is associated with left leg pain, swelling, and thrombosis. IVCS symptoms are thought to be induced by altered pelvic hemodynamics, however, there currently exists a knowledge gap on the hemodynamic differences between IVCS and healthy patients. To elucidate those differences, we carried out a patient-specific, computational modeling comparative study.Methods: Computed tomography and ultrasound velocity and area data were used to build and validate computational models for a cohort of IVCS (N = 4, Subject group) and control (N = 4, Control group) patients. Flow, cross-sectional area, and shear rate were compared between the right common iliac vein (RCIV) and left common iliac vein (LCIV) for each group and between the Subject and Control groups for the same vessel.Results: For the IVCS patients, LCIV mean shear rate was higher than RCIV mean shear rate (550 ± 103 s−1 vs. 113 ± 48 s−1, p = 0.0009). Furthermore, LCIV mean shear rate was higher in the Subject group than in the Control group (550 ± 103 s−1 vs. 75 ± 37 s−1, p = 0.0001). Lastly, the LCIV/RCIV shear rate ratio was 4.6 times greater in the Subject group than in the Control group (6.56 ± 0.9 vs. 1.43 ± 0.6, p = 0.00008).Discussion: Our analyses revealed that IVCS patients have elevated shear rates which may explain a higher thrombosis risk and suggest that their thrombus initiation process may share aspects of arterial thrombosis. We have identified hemodynamic metrics that revealed profound differences between IVCS patients and Controls, and between RCIV and LCIV in the IVCS patients. Based on these metrics, we propose that non-invasive measurement of shear rate may aid with stratification of patients with moderate compression in which treatment is highly variable. More investigation is needed to assess the prognostic value of shear rate and shear rate ratio as clinical metrics and to understand the mechanisms of thrombus formation in IVCS patients.

By loading Cross model and Oldroyd-B model with User-defined Function (UDF) program, a method to simulate the extrusion flow of viscoelastic non-Newtonian fluid in Fluent software was proposed. In the homogeneous solution of Polyethylene terephthalate (PET) and supercritical CO2, the microscopic bubble growth kinetics model was coupled with the Population Balance Module (PBM), analysis effect of shear rate on bubble nucleation and growth, numerically simulated of the nucleation and growth of bubbles in the extrusion die of PET microcellular foam sheet. Through analysis, the bubble size distribution is more uniform under the condition of 60° template convergence angle. The larger the extrusion speed, the wider the uniform distribution range of bubble density at the outlet position. The initial concentration of CO2 has the greatest impact on the bubble density. Increasing the initial concentration of CO2 can improve the bubble density, but appropriately reducing the initial concentration of CO2 can improve the effective distribution range of bubble density of foam sheet. [ABSTRACT FROM AUTHOR]

Inspiratory muscle strength training (IMST) has shown potential to improve both respiratory and cardiovascular function in health and disease. Less is known about acute hemodynamic responses to a single IMST session, therefore we assessed upper and lower limb blood flow via Doppler ultrasound in the brachial and popliteal arteries, respectively. Mean, anterograde, and retrograde blood flow (BF) and shear rate (SR) were assessed relative to baseline during low-intensity (15% maximal inspiratory pressure - PImax) and high-intensity (75% PImax) IMST. During low-intensity IMST, popliteal BF and SR were reduced by -10%, and brachial BF and SR were reduced by -40%. During high-intensity IMST, popliteal BF and SR were reduced by -20%, and brachial BF and SR were reduced by -35%. BF and SR responses were not statistically different between low-intensity and high-intensity training for either blood vessel (P > 0.05). In addition, anterograde BF and SR were significantly decreased in the brachial artery for both low-intensity and high-intensity training (P < 0.05), but not the popliteal artery (P > 0.05). Finally, during IMST retrograde BF and SR were significantly increased in both the upper and lower limbs during low-intensity and high-intensity training (P < 0.05). These data provide novel insight into the acute BF and SR responses to a single bout of IMST and may enhance our understanding of the mechanism(s) by which IMST imparts its beneficial chronic effects on cardiovascular function. NEW & NOTEWORTHY Herein, we demonstrate for the first time that upper and lower limb blood flow and shear rate patterns are altered during a single bout of IMST, at low- and high-intensity training. Specifically, anterograde blood flow and shear rate are significantly reduced in the brachial artery, whereas retrograde blood flow is significantly elevated in both the brachial and popliteal arteries. These findings provide insight into the vascular impact of IMST, which may inform future mechanistic studies. [ABSTRACT FROM AUTHOR]

Reverse electrodialysis (RED) is one of the technologies used to harness 'Blue Energy', which is generated from the controlled separation of ions between salt water and fresh water through cation and anion exchange membranes (CEM/AEM) stack with end electrodes. The spacers present in between CEM and AEM allows the flow of salt and fresh water significantly affecting the fouling and concentration polarization in the RED cell. The present work focuses on improvement in flow path design, which may be used in place of mesh spacers in order to reduce pressure drop and enhance shear stress on the surface of the membrane to reduce concentration polarization. A three‐dimensional direct numerical simulation of the Navier–Stokes equation is conducted using Fluent 14.0 to analyze four different flow field designs, including serpentine, criss‐cross, rhombus, diamond, and standard mesh spacers. The simulation predicted closely the experimental data on pressure drop for the mesh spacers available in the literature. The present study points out that the diamond type flow field design, which combines characteristics of mesh spacers and flow field plates, gives lesser pressure drop per unit length with the increase in velocity within the same range of shear stress generated in mesh spacers. In other words, net power density of RED would improve with the use of diamond type spacer flow field with the decrease in concentration polarization loss and pumping power density. [ABSTRACT FROM AUTHOR]

Although there are many methods and instruments for measuring viscosity, it is still difficult to determine a reliable value of the dynamic viscosity of complex chemicals such as paraffins and fatty acids. This is due to the complex and heterogeneous structure of these compounds in the case of commercial products. On the other hand, the measuring instrument should be selected very carefully, including its measuring principle and measuring range. This paper presents results of viscosity measurements of three organic PCMs (phase change materials) obtained in four different research institutions. Commercial products: paraffin, myristic acid (97%) and mixture of palmitic acid (55%) and stearic acid (45%) were selected as PCMs. Four different viscometers, namely Fungilab V-Pad, Rheotest LK 2.2, Rheometer Anton Paar MCR 102, and Brookfield DV-II + Pro have been used to determine temperature dependent dynamic viscosity of the tested PCMs. Using a large database of present measurement results, correlations were developed to calculate the dynamic viscosity of fatty acids and paraffins, which predict the experimental data within a band of ±20%. [ABSTRACT FROM AUTHOR]

The shear rate is an important factor that influences the shear mechanical properties of rock joints. In this paper, constant normal load (CNL) direct shear tests at different shear rates ( v s = 0.2–5.0 mm/min) were performed on rock joint specimens to investigate the shear behavior and failure modes under various joint roughness coefficients (JRC = 6.071–17.212), joint wall compressive strengths (JCS = 9.36–25.86 MPa), and normal stresses (σn = 0.936–2.586 MPa). The experimental results indicated that the peak shear strength gradually decreased, the peak shear displacement increased and the residual shear strength decreased with increasing shear rate. The experimental findings suggested that with an increasing JRC and a decreasing JCS and σn, the peak shear strength and peak shear displacement were greatly influenced by the shear rate. Additionally, shear-off and wear failure modes were observed in this research and were both intensified by increasing shear rates. However, the failure mode tended to change from wear to shear-off as the shear rate increased, and this phenomenon was enhanced when JRC, JCS, and σn decreased. A modified new shear strength correlation model that related vs and valid values of JRC, JCS, and σn was developed to estimate the shear strength of rock joints. The predicted results indicated that the newly proposed model performed better than the existing models. Highlights: The influence of the shear rate on the valid values of joint roughness coefficients, joint wall compressive strengths, and normal stresses was evaluated. The evolution of the mechanical behavior and failure modes of rock joints related to the shear rate was investigated. A shear strength correlation model that related to shear rate was proposed to estimate the shear strength of rock joints. [ABSTRACT FROM AUTHOR]

Non-edible oils hold great potential as a viable feedstock for bio-lubricant production. Among these oils, castor oil stands out due to its unique hydroxyl group structure. Castor oil finds applications in various fields such as lubrication, dielectrics, and heat transfer. This study focused on investigating the dynamic viscosity and thermal conductivity of castor oil and graphene nanoplatelets/castor oil nanofluids. The nanofluids were synthesized through a two-step process involving the combination of graphene nanoplatelets crystal powder with pure castor oil. Morphological and crystallographic analyses revealed platelet-shaped graphene nanoplatelets with a prominent (002) reflection. Dynamic viscosity measurements were performed using a rheometer at temperatures ranging from 40 °C to 100 °C, and thermal conductivity assessments were conducted using the Modified Transient Plane Source technique from 30 °C to 70 °C. Investigation revealed that as temperature increased, the nanofluids exhibited a significant decrease in dynamic viscosity. Conversely, the dynamic viscosity increased moderately with higher concentrations of graphene nanoplatelets. Importantly, the addition of graphene nanoplatelets did not disrupt the Newtonian flow behavior of castor oil. Furthermore, the study demonstrated a remarkable enhancement in thermal conductivity with increasing concentrations of graphene nanoplatelets. This enhancement can be attributed to the high conductivity of graphene nanoplatelets. Overall, biodegradable graphene nanoplatelets/castor oil nanofluid present promising prospects as an advanced lubricating oil with superior heat transfer properties. This research contributes to the understanding and utilization of nanofluids for effective thermal management applications. [ABSTRACT FROM AUTHOR]

The hydrodynamics of airlift bioreactors, which offer an interesting alternative to conventional stirred-tank bioreactors, has generally been evaluated using experimental approaches, requiring time, energy, and reagents. However, computational fluid dynamics (CFD) has emerged as an important and valuable tool for the analysis and design of these devices, saving time and experimental effort, while providing a large amount of information. In this study, four geometries of a square cross-section 10-L split airlift bioreactor operating with distilled water were simulated using CFD, and the hydrodynamics variables gas hold-up and liquid velocity were evaluated. CFD satisfactorily predicted the hydrodynamic parameters, when compared to experimental data, allowing adequate prediction of the shear rate distribution in airlift bioreactors. The results indicated that different shear rate distributions were obtained by geometric modifications in the bioreactor, showing that its design should be considered to satisfy different specific bioprocess requirements. [ABSTRACT FROM AUTHOR]

The viscosity of fluid plays a major role in the flow dynamics of microchannels. Viscous drag and shear forces are the primary tractions for microfluidic fluid flow. Capillary blood vessels with a few microns diameter are impacted by the rheology of blood flowing through their conduits. Hence, regenerated capillaries should be able to withstand such impacts. Consequently, there is a need to understand the flow physics of culture media through the lumen of the substrate as it is one of the vital promoting factors for vasculogenesis under optimal shear conditions at the endothelial lining of the regenerated vessel. Simultaneously, considering the diffusive role of capillaries for ion exchange with the surrounding tissue, capillaries have been found to reorient themselves in serpentine form for modulating the flow conditions while developing sustainable shear stress. In the current study, S-shaped (S1) and delta-shaped (S2) serpentine models of capillaries were considered to evaluate the shear stress distribution and the oscillatory shear index (OSI) and relative residual time (RRT) of the derivatives throughout the channel (due to the phenomena of near-wall stress fluctuation), along with the influence of culture media rheology on wall stress parameters. The non-Newtonian power-law formulation was implemented for defining rheological viscosity of the culture media. The flow actuation of the media was considered to be sinusoidal and physiological, realizing the pulsatile blood flow behavior in the circulatory network. A distinct difference in shear stress distributions was observed in both the serpentine models. The S1 model showed higher change in shear stress in comparison to the S2 model. Furthermore, the non-Newtonian viscosity formulation was found to produce more sustainable shear stress near the serpentine walls compared to the Newtonian formulation fluid, emphasizing the influence of rheology on stress generation. Further, cell viability improved in the bending regions of serpentine channels compared to the long run section of the same channel. [ABSTRACT FROM AUTHOR]

Investigating the shear strength characteristics of sliding zone soil is crucial for evaluating slope safety and stability. This paper discusses the shear strength characteristics of Lishi loess and N2 laterite in the sliding zone under different influencing factors based on in-suit multiple shear tests, and the shear strength characteristics of Lishi loess were contrasted and analyzed based on field and laboratory tests. The results indicated a favorable correlation between the shear strength of soil samples and normal stress. The shear strength attenuation of clay-rich N2 laterite was much larger than that of sand-rich Lishi loess with the increase of the shear stage. Importantly, the mutation points of the shear rate corresponding to the peak stress of soil samples were obtained, which can be used as a symbol to judge the transfixion of the shear plane. Moreover, the stress-strain characteristics of Lishi loess under the same normal load were diverse as a result of the different experimental methods, and the residual strength characteristics for the two tests also varied substantially. Notably, the Lishi loess in the field test has a more stable residual strength than the laboratory direct shear test conducted. The findings can aid in the comprehension of the mechanical behavior of loess and laterite on the Loess Plateau. [ABSTRACT FROM AUTHOR]

Despite the dozens of earlier research verifications, the contribution of shearing of molten metallic alloys during their solidification to grain formation is still ambiguous. Also, modeling of this phenomenon has received very little attention. Experiments were conducted in this study to investigate the effect of the shear rate on the density, size, and shape factor of the formed grains up to a solid fraction of 0.15 for the solidifying A356 aluminum alloy in the coaxial cylinder viscometer. The rheology of the formed semisolid slurry was studied as well. Results exhibited morphological evolution and grain refinement. The grain number density increased from 5 × 108 m−3 in the absence of melt shearing to reach 4 × 109 m−3 at the shear rate of 250 s−1. Also, the shape factor was improved to reach 0.78. Based on the experimental investigations, the grain number density under shearing was correlated to the shear rate and the grain number density in the absence of shearing via an empirical formula. A shear-dependent grain multiplication factor was deduced. The alloy exhibited a shear-thinning behavior where the viscosity obeyed the power law with a constant and an exponent of 0.9264 and 0.468, respectively. Moreover, the measured data were fitted to several proposed viscosity models and the model of Hirai et al. showed the best fit; therefore, it was recommended for predicting the viscosity of semisolid slurries. [ABSTRACT FROM AUTHOR]