Korea-Australia Rheology Journal最新文献

Circulating tumor cells (CTCs) detection has become one of the promising solutions for the early diagnosis of cancers. Thus, the separation of CTCs is of great importance in biomedical applications. In addition, microfluidic technology has been an attractive approach to the manipulation of biological cells. This study presents the parametric investigations relevant to the volumetric throughput of a microfluidic platform with the dielectrophoresis (DEP)-based cell manipulation technique for the continuous CTCs separation. A low potential voltage at an appropriate frequency was applied to slanted planar electrodes to separate CTCs from normal cells in blood samples due to mainly the cell size difference. The performance of the separation process was analyzed by evaluating the cell trajectories, purity, and recovery rates. Several inlet flow rates of buffer and cell sample fluid streams were examined. Various channel configurations with different outlet and height dimensions were also investigated to enhance the isolation of CTCs. During the simulation, the size and shape of cells were assumed as fixed-sized, solid spheres. The results showed that CTCs could be separated from blood cells, including white blood cells (WBCs), red blood cells (RBCs), and platelets (PLTs) with recovery and purity factors up to 100% at the cell sample throughput of 10 µL/min by utilizing a suitable microchannel design. The current study significantly contributes valuable insights into the design of the microchip devices to effectively and selectively isolate different cancerous cells in biofluids.

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Magnetically optimization of mini-MR damper with focused on MR fluid properties and damper construction is investigated using dissipative particle dynamics method as a molecular scale modeling technique. To select a suitable MR fluid, the effect of diameter and weight of magnetic particles on damping force of 10 N as set point is studied. The results show damping force increases by increasing diameter of magnetic particles and finally trends to a constant value while changes nonparabolic by enhancement of their weight. The results of studies on structural parameters of damper show that by increasing gap size of flow passage, damping force increases while enhancement in inner diameter of cylinder and piston length has reverse effect. Optimum design of MR damper completed by investigation on electrical coils in terms of their arrangement and step wise distribution of magnetic field strength as our major innovation. To optimum operating conditions of MR damper at minimum electrical energy consumption and hysteresis level, the scenario of three segment coils in length of 3, 5, and 7 mm at base relative magnetic strength of 40% with 15% difference in steps by utilizing 140CG MR fluid as agent fluid are selected.

A suspension of micro- or nano-magnetic particles dispersed in a nonmagnetic carrier medium is called a magnetorheological (MR) fluid. MR fluids are smart materials that undergo rapid and reversible changes in rheological properties under an external magnetic field. The rheological properties of MR fluids can be easily controlled through manipulation of the magnetic field strength. Because of their unique and fast reversible changes in rheological properties, MR fluids are widely used in various devices and structures. However, they suffer long-term stability (particle sedimentation) problems because of the density mismatch between the suspended magnetic particle and the liquid medium. In previous studies, researchers have expended great efforts to simultaneously improve the stability and performance of MR fluids. Nevertheless, a trade-off relationship exists between the stability and the performance of MR fluids, that is, as MR performance increases, stability decreases, and vice versa. In this review, we recapitulate the findings of our group's recent achievements and address the conflicting issues. Reviewing the various routes will provide clues to solving the trade-off problem and suggest a guideline for developing high-performance and highly stable MR fluids.

This paper presents an experimental study of the laminar flow of a non-Newtonian fluid through 75% (by area reduction) stenotic tubes. The fluid behaviour was described by the Herschel Bulkey non-Newtonian model. The non-Newtonian fluids were aqueous solutions of 0.1% Carbopol 940. Upstream flow conditions were steady and spanned a range of generalized Reynolds numbers Reg from 0.20 to 13.66. The velocity profiles were measured with a Laser Doppler Anemometry (LDA). This study allows us to see locally the influence of the geometry and the non-Newtonian character of the fluid on the velocity profiles, the pressure drops and flow resistance. From the experimental data, the frictional resistance decreases with increasing generalized Reynolds number Reg and resistance gave a weak value in a stenotic tube as compared to the flow in a simple tube. At the level of stenosis, a correlation relating of the Euler number to the generalized Reynolds number is developed. To compare the upstream and downstream parts of the stenosis, it is preferable to represent the pressure drops by the friction factor f. This factor f in upstream and downstream decreases linearly with the generalized Reynolds number Reg.

This study dealt with an experimental squeeze-flow test between two parallel disks and rheological measurements using a rotational rheometer of pure bitumen and bitumen mixed with 10 and 20 wt.% kaolin without slip condition. The experimental procedure of the homogeneous samples’ preparation was described. A steady-state and dynamic rheological analysis for pure bitumen and bitumen mixed with kaolin was detailed. Results show that pure bitumen and bitumen mixed with 10 wt.% kaolin at 26 °C correspond to a shear-thinning behavior. The effect of the kaolin particles becomes more critical at low shear rates than at high shear rates, where the matrix effect was dominant. The influence of temperature on bitumen mixed with 20 wt.% kaolin was investigated, and the obtained results show that the samples behave like a power-law model at 50 °C. Besides, the squeeze-flow test impact at an ambient temperature of 26 °C for pure bitumen and bitumen mixed with kaolin was also studied. Adding kaolin leads to a significant increase in viscosity and confirms the studied cases in the rheometry test at 26 °C. It was proven that pure bitumen and bitumen mixed with kaolin follow a power-law model at a specific range of shear rate. In particular, the decrease of the shear rate in bitumen mixed with 20 wt.% kaolin triggers the detection of the yield stress, which did not appear in the rheological measurements due to the applied deformation either in the shear and/or the elongational flow.

Transient behaviors of dual-layered patches for Newtonian liquids were numerically investigated in dual-layer slot coating processes for the first time using step-changed inlet flows. To further tune the leading and trailing edges in a patch cycle, startup and end lag times between the top and bottom layers were proposed, considering the flow state of a bottom-layer liquid in a coating bead region. Carefully chosen lag times significantly reduced the defects in the leading and trailing edges of a dual-layered patch. It was also found that a greater coating layer viscosity results in a greater amount of residue left on the die lips, which affects the next patch cycle.

We propose a new method to calculate relaxation time spectrum (RTS) and enable conversions between viscoelastic functions. The exact relations between the viscoelastic functions are simply derived using complex analysis of the higher-order derivative of those functions. Hence, a stable numerical differential method is demanded to obtain genuine solutions without the interference of errors due to numerical analysis. In this study, we adopted the double-logarithmic B-spline and its recursive relation to obtain higher-order derivative. The proposed algorithm is tested and compared with previous methods, using simulated and experimental data. When creep data obtained through experiments are converted to dynamic moduli, significant improvement in the terminal behavior is observed compared to the previous method because the Runge phenomenon is significantly reduced using a low-order polynomial. Moreover, the spectra obtained for experimental data are almost identical to those obtained through a previously verified algorithm. Thus, our results agree well with both simulated data and experimental data.

Magnetorheological (MR) fluid properties are essential in analyzing the performance of any MR fluid system. The fluid properties are dependent on shape, size, and magnetic saturation of the magnetic particles. Preliminary characteristics with SEM, particle size analysis (PSA), and vibration sample magnetometer (VSM) on carbonyl iron particles were performed to verify the particle’s feasibility to synthesize the MR fluid in a laboratory. Synthesis and characterization of MR fluids with particle concentrations (PC) of 10% (PC₁₀), 15% (PC₁₅), 20% (PC₂₀), 30% (PC₃₀), and 35% (PC₃₅) by volume are carried out. To show the inherent nonlinearity of the MR fluid, Herschel–Bulkley model is used. The relationship between sedimentation velocity, yield stress, and thermal conductivity is established as a function of particle concentration with experimental uncertainty of 6.15, 5, and 8.96%, respectively. Functional testing of PC₁₅ and PC₃₀ was carried out on an MR damper fabricated on dimensions obtained from the literature for the required size. The results indicate that damping force is 42% more in PC₃₀ than PC₁₅ at higher loading parameters. Finally, the saturation magnetization of the MR fluid depends not only on applied current but also on loading parameters when operating in the system.