Korea-Australia Rheology Journal最新文献

A mathematical model of physiological pulsatile flow of blood through a stenotic flexible artery in the presence of body acceleration is presented in this paper. Streaming blood is considered as a shear-thinning non-Newtonian fluid as proposed by Yeleswarapu (Evaluation of continuum models for characterizing the constitutive behaviour of blood, Ph.D. thesis, Dept. Mech. Eng., University of Pittsburgh, 1996), and a physiological pulsatile flow rate proposed by Pedrizzetti (J Fluid Mech 310:89–111, 1996) has been taken through the tube. Deformation of vessel wall is modelled as a function of flow rate. This computational study of an idealized model may bring some insights for realistic blood flow through a stenotic artery. The novelty of this work lies in the fact that realistic flow of blood through a stenosed artery has been studied as far as possible and a new idea has been provided to describe the arterial wall motion. Governing equations in cylindrical polar coordinates are solved using stream function–vorticity method. Behaviour of various flow quantities is investigated through a parametric study. It is noted that the degree of constriction and body acceleration have important impacts on the haemodynamic parameters such as wall shear stress, oscillatory shear index, and relative residence time. Increasing body acceleration enhances the peak value of wall shear stress, but reduces the oscillatory shear index and relative residence time. Almost 1/4th increase in length of flow separation is found when Froude number raises its value from 0.1 to 0.5, other parametric values remaining fixed. On the other hand, almost 50% increase in the magnitude of the peak value of wall pressure is found when the amplitude of body acceleration takes a value 0.4 (A = 0.4) compared to the without body acceleration case (A = 0). These results have a significant role.

The multiscale stochastic simulation method based on the marriage of the Brownian Configuration Field (BCF) and the Radial Basis Function mesh-free approximation for dilute fibre suspensions by our group, is further developed to simulate non-dilute fibre suspensions. For the present approach, the macro and micro processes proceeded at each time step are linked to each other by a fibre contributed stress formula associated with the used kinetic model. Due to the feature of non-dilute fibre suspensions, the interaction between fibres is introduced into the evolution equation to determine fibre configurations using the BCF method. The fibre stresses are then determined based on the fibre configuration fields using the Phan–Thien–Graham model. The efficiency of the simulation method is demonstrated by the analysis of the two challenging problems, the axisymmetric contraction and expansion flows, for a range of the fibre concentration from semi-dilute to concentrated regimes. Results evidenced by numerical experiments show that the present method would be potential in analysing and simulating various suspensions in food and medical industries.

The migration of ellipsoidal particles in bounded shear flow of Giesekus fluids is studied numerically using the direct forcing/fictitious domain method for the Weissenberg number ranging from 0.1 to 3.0, the mobility parameter α which quantifies the shear-thinning effect ranging from 0.1 to 0.7. The model and numerical method are validated by comparing the present results with available theoretical and numerical results in other literatures. The results show that the trajectory of particles depends on their initial orientation and vertical position, and the particle migration can be roughly classified into returning and passing pattern. The values of initial vertical position of particle corresponding to the separatrix between the returning and passing pattern decrease with increasing Weissenberg number regardless of the initial orientation of particle, and the shear thinning has the opposite effect. The evolution of particle orientation depends on the initial particle orientation. For the particles whose initial orientation is parallel to the shear plane, the particle rotates with the semi-major axis as radius in the shear plane. For the particles whose initial orientation is perpendicular to the shear plane, the particle rotates with the semi-minor axis as radius. For the particles whose initial orientation has a certain angle with the shear plane, the particle rotates with the vorticity axis and the orientation vector is gradually close to the vorticity vector. The evolution of the particle orientation becomes slow with increasing Wi whether it is in passing behavior or in returning behavior.

The sedimentation stability of Magnetorheological fluid (MRF) is one of the research hotspots in the academic field of magnetorheological science. Excellent sedimentation stability is of great significance for the preservation and application of MRF. Given many traditional methods of characterization of sedimentation stability, this paper proposes a new method to characterize the sedimentation stability of MRF based on the change of shear yield stress during the sedimentation process of MRF. Then, the key components of the self-made MRF shear yield stress test device were introduced in detail, and three different surfactants containing dodecyl benzoate, polyethylene glycol and oleic acid were prepared. And then used the device to test their effects on the sedimentation stability of MRF. The results showed that oleic acid has the best effect on improving the sedimentation stability. Finally, the change law of shear yield stress of MRF in the next 90 days was predicted successfully by fitting experimental data based on the least square method. By comparing the test value and fitting value of 60–75 days, the error of the best fitting result were within 3%, this showed the reliability of the predicted results.

The present study proposes a novel spiral-shaped micromixer to provide high mixing performance at low Reynolds numbers encountered in many microfluidic systems. The liquid mixing is analyzed with Reynolds numbers from 0.1 to 10, molecular diffusivities from 10⁻⁸ to 10⁻¹¹, and aspect ratios from 0.5 to 1.5. In the present simulations, the Dean number is not sufficient to cause the formation of primary rotating vortices. It is revealed that as the Reynolds number increases, the mixing performance is improved. The results demonstrate that the magnitude of ME/Δp (Pa⁻¹) is 0.236, 0.018, 0.011, 0.009, and 0.007 at Reynolds numbers of 0.1, 2, 5, 8, and 10, respectively indicating the high mixing performance of the proposed micromixer. It is found that the mixing efficiency is improved slightly with the molecular diffusivity. The mixing efficiency of the micromixer is 94.44, 93.76, 93.1, and 92.7% for molecular diffusivities of 10⁻⁸, 10⁻⁹, 10⁻¹⁰, and 10⁻¹¹ m²/s, respectively. In addition, the proposed micromixer reaches 99.5% for the aspect ratio of 1. Due to relatively high values of ME/Δp, the proposed micromixer with square cross-section can be suggested as a good candidate for biochemical applications.

We investigated the effects of silica nanoparticles (SiNPs) on the rheological properties and microstructures of polyvinyl alcohol (PVA)/silver nanowire (AgNW) suspensions. For PVA/AgNW suspensions without SiNPs, rheological percolation threshold was calculated using storage modulus determined by small amplitude oscillatory shear (SAOS) tests. Results from SAOS tests revealed that PVA/AgNW suspensions had two transition concentrations, which led to different structure developments. Storage modulus from large amplitude oscillatory shear (LAOS) tests showed double-step strain softening behavior at all AgNW concentrations tested, and elastic stress components, also obtained by LAOS tests, exhibited trends similar to storage modulus development. Furthermore, two distinguishable structures were observed when large strain amplitude shear was applied. When SiNPs were added to PVA/AgNW suspensions, the rheological properties of PVA/AgNW suspensions from SAOS tests increased. LAOS results showed storage modulus and elastic stress components of PVA/AgNW suspensions were dependent on AgNW concentration. Doublestep strain softening disappeared for PVA/AgNW suspensions containing SiNPs at low AgNW concentrations, whereas at high AgNW concentrations double-step strain softening behavior was observed.

This article intends to conduct an analytical simulation for the electroosmosis modulated peristaltic transport of ionic hybrid nano-liquid with Casson model through a symmetric vertical microchannel occupying a homogeneous porous material in the existence of the dominant magnetic field, Hall, and ion-slip currents. The hybrid nano-liquid is acquired by the suspension of silver and silicon dioxide nanoparticles into pure water. The wall slip and convective heating impacts are imposed. The Casson fluid (CF) model is adopted to mimic the rheological behaviour accounting for hybrid nano-liquid. Darcy’s law is applied to evaluate the impact of a porous medium. The Poisson-Boltzmann equation is engaged to accommodate the electric double layer (EDL) in the microchannel. Assumptions of low Reynolds number (LRN), long wavelength (LWL), and Debye-Hückel linearization (DHL) are undertaken to simplify the normalized constitutive equations. Closed-form solutions for the linearized dimensionless resulting equations are achieved by ND-solve code in Mathematica. For a comprehensive physical investigation of the problem under simulation, several graphs are furnished to evaluate the role of emerging thermal and physical parameters in developing the flow patterns and thermal characteristics. Outcomes envisage that Hall, ion-slip, and electro-osmotic parameters have a marked impact on the velocity of the ionic liquid. A decrement in the EDL thickness corresponds to an augmentation in the axial velocity profile in the locality of the channel walls. An increment in radiation parameter results in a demotion in the temperature profile. The pressure gradient is elevated with higher Hall and ion-slip parameters, thermal Grashof number, and electro-osmotic parameter, whereas it is dropped due to higher estimates of Hartmann number. The trapping phenomena under the flow factors are also outlined in brief. The bolus formation is deeply affected by Hall, ion-slip, and electro-osmotic parameters. Outcomes achieved here are expected to shed light on the design and analysis of electro-osmotic pumps, microchannel devices, water filtration and purification processes, DNA analyzers, nanoscale electro-fluid thruster designs in-space propulsion, and many more.

Nanocarbon materials are critical ingredients with unique properties in emerging materials. In this study, various carbon nanofillers, such as carbon nanotube (CNT), graphene oxide (GO), reduced GO wrapped by poly(styrene sulfonate) (PSS-RGO), and graphite nanoplatelet (GNP), were utilized to examine the effects of nanofiller types and surface treatments on the electrical and rheological properties of polystyrene (PS) nanocomposites prepared by latex-based process. The PS/CNT nanocomposites exhibited the most enhanced electrical and rheological properties among the composites evaluated. The PS/GO nanocomposites showed improved rheological properties and significantly increased electrical conductivity, despite the decrease in the intrinsic properties of graphene due to the change in hybridization from sp² to sp³ by strong acid treatment. Interestingly, they exhibited higher conductivity than PS/PSS-RGO due to the higher graphene moiety and the thermal reduction of GOs during compression molding. The PS/GNP nanocomposites showed marginal enhancement because GNP is a larger aggregate of graphene layers bonded by van der Waals force. The results of this study on the electrical and rheological properties, surface modification, and size and dispersion of conductive nanofillers in an insulating polymer matrix are beneficial for the development and application of electrically conductive nanocomposites.

Magnetorheological (MR) dampers are becoming popular smart devices with controllable higher damping properties. This paper presents an inclusive review of energy harvesting MR dampers. The classifications of energy harvesting MR dampers, operating principles, structural design, mathematical models, fluid models, experimental investigation, and applications are classified and reviewed. The regenerative MR dampers have self-power capability, and self-sensing capability to control higher performance and it is an important feature of regenerative MR dampers. The review indicates that regenerative MR dampers have enough power generation capacity to power MR dampers and higher damping performances. It has been found that a single-ended monotube regenerative MR (RMR) damper has maximum power generation capabilities than other RMR dampers.

Magneto-rheological (MR) dampers using MR fluids with controllable rheological properties are mainly utilized in automobiles, structures, electrical transmission lines, medical applications, agricultural engineering, and military equipment. This paper presents a comprehensive review of bypass MR dampers. The principles of operation, design structures, analytical models, experimental analysis, and applications of MR dampers are classified and reviewed. The bypass MR dampers have better MR fluid stability and sedimentation control compared to MR dampers. This is important for maintaining homogeneous magnetic flux distribution throughout the fluid area. The advantageous features of external bypass MR dampers over internal bypass dampers are the higher shear stress, the damping force controllability, and the higher damping force they can generate.