Impact Of Shear Rate Research Articles

Lignin Purification from Mild Alkaline Sugarcane Extract via Membrane Filtration

In this study, the separation of lignin from a mild alkaline sugarcane bagasse extract was studied, and the impacts of different parameters on the filtration performance were evaluated. The tested parameters included transmembrane pressure (0.5–3.0 bar), shear rates (2831–22,696 s−1), temperature (20 and 40 °C), membrane molecular weight cut-off (5 and 10 kDa), and membrane material (polyethersulfone and polysulfone). During the filtration process, the permeate flux and all the main components of the extract were analyzed, including lignins (acid insoluble lignin and acid soluble lignin), sugars (xylose, arabinose, glucose, and galactose), total phenolic compounds, and phenolic acids (p-coumaric acid, ferulic acid, vanillin, and 4-hydroxybenzaldehyde). It was proved that the tested conditions had a great impact on the permeate flux and molecule retention rate. Increasing the temperature from 20 to 40 °C resulted in a much higher permeate flux for the 5 kDa PES membrane, and the impact of shear rate was greater at 40 °C for this membrane. Although the 5 kDa PES membrane could retain slightly more large molecules, i.e., acid-insoluble lignin and xylose, the 10 kDa membrane afforded greater phenolic acid removal capacity, leading to higher purity. For the 10 kDa PS membrane, the polarization layer began to form at TMP below 0.5 bar. This membrane had a lower retention rate for all molecules than the 10 kDa PES membrane.

Shear behavior of a two-component non-water reactive foamed polyurethane (TNFPU) grouting material under different stress levels

The two-component non-water reactive foamed polyurethane (TNFPU) material utilized in structural restoration scenarios may experience shear failure when subjected to multifaceted external factors, potentially culminating in structural instability or even failure. Consequently, it is imperative to conduct a thorough examination of the shear properties of TNFPU material. A series of direct shear tests were conducted to investigate the impact of factors such as density, normal stress, and shear rate on the shear properties of TNFPU material. These properties encompass shear strength, shear modulus, peak shear displacement, shear deformation, and shear dilation angle. The findings underscore the density and normal stress had more significant effects on the shear properties of TNFPU material. Conversely, the impact of shear rate on shear performance was relatively modest and exhibited a diminishing trend as density increased. Notably, a specific discovery emerged: the effects of density, normal stress, and shear rate on the shear properties of TNFPU displayed pronounced distinctions before and after reaching a critical density threshold of 0.51 g/cm³ . Furthermore, the study revealed a phenomenon of shear dilation and contraction transformation when the density or normal stress exceeded a certain critical value.

The Impact of Shear Rate on the Mechanical Behavior of Rock Joints Under Multiple-Influencing Factors

The Impact of Shear Rate on the Mechanical Behavior of Rock Joints Under Multiple-Influencing Factors

Impact of hydrodynamic conditions on the structure of clay-based tailings aggregates flocculated in freshwater and seawater

• Flocculation of clay-based tailing in industrial water and seawater was compared. • A number of the particles does not flocculate unless the shear rate increases. • The use of seawater led to a reduction in the size of aggregates. • The fractal dimension of aggregates decreases with increasing mixing intensity. The impact of shear rate on the structural properties of aggregates obtained during the flocculation of clay-based tailings with an anionic polyacrylamide was analyzed. The effects generated in industrial water (IW) and seawater (SW) were compared. Flocculation-sedimentation batch tests were performed to know aggregate size distribution, hindered settling rate, and internal structure of flocs expressed through their fractal dimension. The aggregate properties were characterized by the Focused Beam Reflectance Measurement (FBRM) and Particle Vision Microscope (PVM) techniques. The aggregate size distribution showed a bimodal behavior, where a portion of the particles does not flocculate properly unless the shear rate increases during flocculation. On the other hand, the size and quantity of coarse aggregates strongly depend on the mixing intensity. The use of seawater led to a reduction in the size of aggregates. It is suggested that this is a result of polymer coiling, which leads to a decreased ability to form polymeric bridges and thus less particle capture. The fractal dimension of aggregates shows that while the shear rate increases, the aggregates are less compact, with structures possibly more open and further away from a solid spherical body. The greatest reduction occurred in industrial water, related to the larger size of the structures in a low salinity environment.

Differential impact of shear rate in the cerebral and systemic circulation: implications for endothelial function.

Differential impact of shear rate in the cerebral and systemic circulation: implications for endothelial function.

Simultaneous assay of platelet adhesion at multiple shear rates within a single microfluidic channel

Cardiovascular diseases are currently the major causes of mortality in the world, especially in developed nations. As a predominant one, thrombosis is the platelet aggregation induced by a high shear rate. Platelet aggregation assay can clarify the occurrence mechanism of thrombosis, as well as be used as an important tool in the clinical diagnosis, personalized treatment, and screening of anticoagulants. Thus, relevant studies attracted considerable attention. As an important step in platelet aggregation, platelet adhesion and its detection also attract intensive concern. Thus, some analytical methods have been developed for platelet adhesion assay, and the impact of shear rate is one of the focuses. Compared with other devices, biosensors can give a more accurate result within a shorter time. Furthermore, some biosensors can achieve real-time analysis. However, only one or several shear rates can be tested at the same time, which may decrease the analytical efficiency. Meanwhile, in most cases, only the average platelet adhesion effect within a reactor is detected, and the impact of the distribution of shear rates is improperly neglected. In this study, a microfluidic device with a single channel is designed and fabricated for platelet adhesion assay. When the platelet-rich plasma flows through the collagen-modified sensing surface of the channel bottom, the interaction between platelets and collagen molecules on the entire surface can be simultaneously monitored by using a surface plasmon resonance imaging (SPRi) system. A gradient of the shear rate (0–546 s-1) could be formed within the channel by choosing a suitable depth-to-width ratio (1:5), so platelet adhesion at multiple shear rates could be monitored simultaneously. This method enables the measurement of the adhesion process of unlabeled platelets on the entire sensing surface, in vitro, at multiple shear rates. Such a system can obtain more accurate platelet adhesion result at a given shear rate than traditional methods. Furthermore, in an individual operation, platelet adhesion can be repeatedly tested at multiple points with an equal shear rate, so a much higher analytical efficiency can also be achieved.

Synergistic effects of shear flow and nucleating agents on the crystallization mechanisms of Poly (Lactic Acid)

This paper presents a study of the effects of microscopic particles of talc on the crystallization kinetics of PLA. Our study covers the quiescent conditions and the case where a shear flow is applied “short term shearing”. The incorporation of talc increases the crystallization rate; it enhances the nucleation mechanism through additional heterogeneous nuclei. The microstructure is highly affected by the addition of talc due to the increase of the number of nuclei (i.e. reduced crystalline size). The application of a shear flow increases the ability of PLA to crystallize even in the presence of talc particles. The impact of shear rate becomes dramatically important just after a critical shear rate of 0.1 s−1. It turns out that the shear rate enhances more the crystallization of PLA with talc than the pure PLA under quiescent conditions. Consequently, a supplementary contribution “synergistic effects” is responsible of the relative enhancement of the crystallization of PLA in the presence of shear flow and talc. With combining different experimental analysis techniques and modeling of the crystallization kinetics, the synergistically effects were quantified in terms of the nucleation density induced by the mutual interaction between shear flow and particles.

Size-cartography of orange juices foulant particles: Contribution to a better control of fouling during microfiltration

Despite the several advantages of microfiltration, applications of this separation technique in fruit juice industries have been challenged by its low economical productivity due to membrane fouling. Although several studies aimed to identify operating conditions (e.g. juice pretreatment, crossflow filtration mode, etc.) to achieve acceptable performances, only few studies focused on the fouling propensity of fruit juices and on the identification of their foulant compounds. The aim of this work was to evaluate the fouling behavior of two orange juices and focused on the identification of relevant size-classes of foulant particles. Lab-scale filtration tests were carried out in conjunction with juice size-fractionation with the aim of quantifying the resistance to filtration of the juices. Based on a resistance-in-series approach, size-cartographies of foulant particles that are juice and membrane-specific were built. These cartographies were provided for two mineral membranes M1.2 and M0.2 with different average pore diameters (1.2 and 0.2μm). M1.2 results showed that the fouling is mainly external for both juices and due to particles larger than 2µm. In contrast, results concerning M0.2 filtration tests showed that four different size-classes of fruit juices compounds are involved in different fouling mechanisms. Moreover, the hydraulic reversibility of the fouling mechanisms was evaluated through the impact of shear rate on the measured resistances. It was seen that the fouling was mainly reversible when M1.2 was used for both juices filtration while it was not the case when juices were filtered with M0.2. This information would be interesting to choose the appropriate strategy in order to enhance the microfiltration of these juices at large scale. Moreover, the proposed size-cartography strategy would greatly satisfy the industrial demand for practical tool to identify the different size-classes of compounds governing the overall membrane fouling.

Population balance modeling of activated sludge flocculation: Investigating the influence of Extracellular Polymeric Substances (EPS) content and zeta potential on flocculation dynamics

Abstract Modeling activated sludge flocculation via particle population balances has been used to investigate the floc size distribution (FSD). The impact of shear rate on the FSD has been stated in previous studies, but the quantitative effect of the Extracellular Polymeric Substance (EPS) content and zeta potential on the aggregation and breakage of activated sludge flocs need to be further investigated. This study defined the balance factor, i.e. the ratio of the breakage rate coefficient to the collision efficiency, to evaluate the combined effect of the EPS content and the zeta potential on the aggregation and breakage of activated sludge, and introduced a binomial breakage function for more probable daughter-particles distributions after the breakage of flocs. The flocculation dynamic parameters were found to be linearly related to the EPS content and the zeta potential. The flocculation balance factor decreased with the increase of EPS content and the decrease of absolute zeta potentials. Smaller flocculation balance factor means better flocculation ability of flocs, leading to larger mean-size flocs. The binomial breakage function parameter values varied from 0.79 to 1.78 for activated sludge flocs with different EPS content, from 0.87 to 1.19 (Al3+ addition) and from 0.96 to 1.93 (Ca2+ addition) for flocs with different zeta potentials, which suggests that the flocs might possess different breakage. Although the increase of EPS content is beneficial to the aggregation of larger flocs, the flocs with high EPS content are susceptible to large-scale fragmentation resulting in more smaller-daughter-particles. Lower absolute values of zeta potentials would promote flocculation, and the activated sludge flocs showed strong stability with Al3+ additions but weak stability with Ca2+ additions.

Thermal aggregation of whey proteins under shear stress

Processed food protein such as whey protein, used as hydrocolloid, is a possibility to impart specific structural and physical properties of food. The specific protein properties can be achieved by controlled denaturation or rather aggregation. The resulting aggregate structure and thereby the functional properties at the macroscopic scale depend strongly on the process conditions. Heating conditions, shear stress and material composition, determine the reaction kinetics as well as the resulting particle size distribution and the structure of the aggregates. These conditions often cannot be investigated separately in industrial processes. Therefore, the impact of shear rate, heating time and protein concentration on the particle characteristics was investigated by a rotational rheometer at 80 °C. By increasing the protein concentration (from 5 to 30% w/w), smaller more compact and stable aggregates were produced. This is due to the higher viscosity and the higher shear stress. The aggregates appearance changes from long and crystalline like structure to a spherical shape. The influence of shear rate is dependent on protein concentration. In suspension with 5% protein the aggregate size initially increases with increasing shear rates because of the predominant effect of increasing number of collisions; and decreases subsequently due to limitation of the particle growth. At high concentrations the size of the aggregates decreases with the shear rate, because of increasing shear stress. The size of whey protein aggregates can thus be regulated by the applied shear rate during processing.

Molecular Simulation of Poly-α-olefin Synthetic Lubricants: Impact of Molecular Architecture on Performance Properties

Equilibrium and nonequilibrium molecular dynamics simulations are performed at constant pressure and temperature on three structurally distinct poly-α-olefin (PAO) isomers representative of a major component in synthetic motor oil basestock. In agreement with empirical observations, the temperature dependence of viscosity, as characterized by the viscosity number (VN), is reduced as the degree of branching is lowered. A molecular-level explanation for this behavior is given in terms of the energy barriers for intramolecular reorientation. Other dynamic properties, such as the diffusivity and rate of tumbling, were also computed and found to have similar dependencies on temperature as the viscosity. Based on these calculations, it appears that PAO molecules with long, widely spaced branches should yield a higher VN than those with short, closely spaced branches. The impact of shear rate on PAO properties is also investigated. High shear rates and shear-thinning increases the VN because the behavior of the fluid is largely dominated by the flow field rather than by the thermodynamic state point. Contrary to what has been observed with linear alkanes, it is observed that molecular alignment with the flow field does not always correlate with enhanced shear-thinning. These observations are explained in terms of a competition between the shear forces responsible for aligning the molecules and intermolecular forces that resist shear-thinning. The results of the present work provide molecular-level explanations for the favorable lubricant properties exhibited by “star-like” molecules and suggest an important strategy for assisting in a more rational approach toward the development of improved lubricants and additives.