Korea-Australia Rheology Journal最新文献

The double-lumen cannula (DLC) is the most critical component of extracorporeal membrane oxygenation (ECMO) because of its narrow cross-section, thereby developing the highest shear stress in the entire ECMO circuit. To measure blood damage in a DLC, the Eulerian approach is generally used without contemplating exposure time or history of blood exposure to shear stresses. Alternatively, Lagrangian approach has also been recently employed for a Newtonian blood flow through a DLC, thereby leaving a research gap on the impact of variable shear rate in case of non-Newtonian blood flow. In the present study, the hemodynamic performance of DLC is investigated using different non-Newtonian models by applying Lagrangian approach. Moreover, the motion of RBC was tracked inside the cannula to predict its behavior during the motion. The results showed that the return lumen had higher pressure, velocity, and shear stress values than other parts of the DLC. In addition, recirculation was observed due to the mixing of blood coming from different inlets and found increase with increasing flow rate of blood. Moreover, it was found that the blood damage increased with increasing flow rate. There was more blood damage in the Newtonian model than in the other non-Newtonian models at higher flow rates. However, the Carreau model showed more blood damage at lower flow rates than the other models. The Cross model showed DLC’s higher efficacy in delivering oxygenated blood to the tricuspid outlet because it showed the least blood damage among all other models. It was also concluded that the efficacy of the DLC to deliver oxygenated blood to the tricuspid outlet decreases with increasing blood flow rate.

The rheological and electrical properties of polyvinyl alcohol (PVA)/silver nanowire (AgNW) suspensions and films are investigated with increasing AgNW concentrations, employing AgNWs with two different aspect ratios, namely 714 and 1000 (referred to as Ag714 and Ag1000, respectively). To estimate the effect of the aspect ratio on the rheological and electrical percolation behavior, the linear rheological properties of suspensions and the electrical properties of the resulting films are systematically assessed. The microstructure of the suspensions and the surface morphology of the films are visualized using optical microscope (OM) and field emission scanning electron microscope (FE-SEM), respectively. Observations from OM analyses reveal that suspensions containing higher aspect ratio AgNW (Ag1000) exhibit larger flocculated clusters, resulting from the entanglement of the nanowires. As results, PVA/Ag1000 suspensions show higher linear viscoelasticity (as indicated by G′ and G″) when compared to PVA/Ag714 suspensions. However, unlike linear viscoelasticity, the electrical conductivities of PVA/Ag1000 films are lower than those of PVA/Ag714 films. This observation is attributed to the alignment of AgNWs during coating process providing substantial deformation and rapid alignment. Furthermore, SEM images of the films confirm the importance of retaining the flocculated clusters to achieve the desired electrical properties.

In this study, we investigated the electrorheological characteristics of a fibrous hydrated magnesium silicate, sepiolite suspension. The sepiolite nanoparticles were heat-treated between 150 and 900 °C, and 2 wt% sepiolite was dispersed in silicone oil. The structural change of the baked particles was analyzed. The effects of the particle loading and applied voltage were evaluated. It was found that the heat-treated sepiolite suspension showed relatively higher viscosity, storage modulus and loss modulus. In addition, as the applied voltage increased, the shear yield stress increased. When a 9 kV/mm direct current (DC) field was applied, a shear yield stress of 16.8 kPa was measured.

Yam is a vegetable that is widely grown around the world. Yam mucilage contains a high mucin concentration that can be useful for supporting the swallowing process. Although the shear and extensional rheology of yam mucilage is essential to its flow, they have not received much attention. Using a commercial rheometer and a filament stretching rheometer, the rheological properties of the mucilage in yam were examined. Yam mucilage exhibits shear-thinning behavior and viscoelastic behavior. In addition, yam mucilage also exhibits stretching phenomena and shows high extensional viscosity. However, the elasticity of yam mucilage decreased when the shear increased. The extensional rheological behavior of the yam mucilage can be predicted by two models, including the Giesekus model and global function. However, the agreement between the model and the experimental data decreases gradually when the Hencky strain increases, even though the model can predict the shear viscosity data well.

This paper presents a comprehensive review of the partitioned pipe mixer (PPM) and its design variants: the barrier-embedded partitioned pipe mixer (BPPM) and the groove-embedded partitioned pipe mixer (GPPM). These mixers utilize chaotic advection as their mixing mechanism in the laminar flow regime. The review first focuses on the flow and mixing characteristics of these mixers, considering the influence of the operating conditions and design variables. The advantages and flexibility of the BPPM and GPPM over the original PPM are highlighted. The investigation covers mixing performance in both the creeping and non-creeping flow regimes. In addition, this review examines the impact of thixotropy and fluid inertia on mixing performance of the mixers, revealing irregular trends. It emphasizes the importance of carefully considering thixotropy and inertia when selecting appropriate mixing protocols and operating conditions. Furthermore, the potential use of chaotic mixing by the BPPM in filtration processes is briefly reviewed. In conclusion, the review summarizes the limitations of the previous studies and suggesting future research directions. Further studies are expected to explore the potential of these types of mixers in improving mixing performance in various industries, particularly those dealing with rheologically complex fluids.

Graphical abstract

Interested in the previous work of Walters et al. (Korea Aust Rheol J 21:225–233, 2009) regarding the competing roles of extensional viscosity and normal stress differences in complex flows of elastic liquids, rheological studies rarely discuss the relationship between the shear and extension-induced first normal stress differences (N1S and N1E) within a mixed flow for a viscoelastic fluid. One, therefore, derives N1S and N1E related to Weissenberg’s number and Trouton’s ratio. The classic White–Metzner viscoelastic constitutive equation coupled with the recent GNF-X (Generalized Newtonian Fluid eXtended) weighted shear/extension viscosity has the potential to show the typical vortex growth in entry flow simulations. Based on the improved White–Metzner model, demonstrating the opposite effect of N1S and N1E with respect to strain rates is evident. N1S mainly dominates the shell layer near the wall boundary at high strain rates, whereas N1E controls the center core at low strain rates. In contraction flow simulations, the predicted slit-die velocity profile is in good agreement with experimental data. It is significant to conclude that N1E hinders flow and N1S facilitates flow. In addition, a comparison of extensional-thickening and extensional-thinning viscosity curves for the velocity profile is discussed herein.

In this study, we systematically investigate the rheological behavior and microstructure formation of the anode slurries containing silicon (Si), carbon black (CB), and carboxymethyl cellulose (CMC) from the perspective of interactions between the constituent components, aiming to provide a fundamental understanding of the dispersion characteristics of Si-based anode slurries. The CMC adsorbs onto both particles (CB/Si) but has different effects on the inter-particle interactions (CB–CB and Si–Si). It stabilizes the CB particles through electro-steric interactions, whereas it agglomerates the Si particles through bridging interactions, in aqueous medium. In the meanwhile, the CMC selectively adsorbs onto CB particles among the two particles. Therefore, at a CMC content lower than the optimum graft density where CB particles are adsorbed and saturated by CMC, it acts as a dispersant in the slurries. However, at a higher content, the CMC that remains after adsorption on CB particles adsorbs onto Si particles and acts as a flocculant for the particles in the slurries. The origin of selective adsorption is understood in terms of the driving forces for adsorption and the surface energy analysis. We anticipate our findings provide a useful guideline for the Si slurry design in terms of its dispersion and contribute to the development of Si anode technology.

Vortex growth is related to the extensional thickness viscosity of polymer melts flowing through contractions, whereas the shear thinning viscosity results in no significant vortex. The nonlinearity of extensional viscosity in relation to molecular architectures and additive composition compositions is usually more sensitive than shear viscosity. Recently, the proposed GNF-X (Generalized Newtonian Fluid eXtended) of the weighted shear/extensional viscosity has been incorporated in the state-of-the-art CFD (computational fluid dynamics) framework to show the extension-induced vortex growth. Using GNF-X, it is important to investigate the conflicting role of shear thinning and extensional thickening on vortex sizes in 3D (three-dimensional) contraction flow simulations for branched and filled polymers melts. In particular, one demonstrates that the long-branched polymers and fiber-filled polymers strongly increase the vortex size, which is consistent with the related experimental observations.

To study the overall rheological characteristics of the silicone oil-based ferrofluid, a chemical co-precipitation method was adopted for preparation, and transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) were used for characterization. The average size of Fe₃O₄ magnetic particles was 10.4 nm and the saturation magnetization of the ferrofluid was 5.98 emu/g. Then, the fluidity, magnetoviscous effect and viscoelasticity of the ferrofluid were studied using a rotational rheometer. The results showed obvious shear thinning of the silicone oil-based ferrofluid under an external magnetic field, and the yield stress of the ferrofluid could not be accurately obtained by fitting the flow curve with an H–B model at a continuous shear rate. A strong magnetoviscous effect could be observed at different shear rates and temperatures. The magnetoviscous parameter R increased with the increase of temperature and its variation decreased with the increase of shear rate. Moreover, based on the magnetic particle chain model and the viscosity–temperature characteristics of the base carrier liquid, different mechanisms of temperature influence on the magnetoviscous effect were analyzed. Finally, a discussion of the microstructure evolution mechanism of the ferrofluid in the modulus changing with frequency was presented through the viscoelastic analysis of the silicone oil-based ferrofluid.

In this work, a numerical model is carried out to investigate the magneto-hemodynamics of blood driven by an oscillating pressure gradient and exposed to a uniform magnetic field and an external body acceleration. The non-Newtonian nature of blood was taken into account using a time-dependent thixotropic model. Incompressible, axisymmetric, and laminar flow assumptions were used to simplify the non-linear partial differential equations. The velocity field and wall shear stress distribution are numerically solved using the finite difference method. The analytical solution of the velocity distribution of a fully developed pulsatile flow of a Newtonian fluid is used to validate the numerical solution. Further research is done into how structural traits, the average of the pressure gradient, body acceleration, and the magnetic field affect the magneto-hemodynamic properties of blood. The findings indicate how the various characteristics taken into account affected the blood's magneto-hemodynamic behavior in arteries.