In vitro hemorheological effects of parenteral agents used in peripheral arterial disease

Biro, Katalin,Sandor, Barbara,Toth, Andras,Koltai, Katalin,Papp, Judit,Rabai, Miklos,Toth, Kalman,Kesmarky, Gabor 한국유변학회 2014 Korea-Australia rheology journal Vol.26 No.2

Peripheral arterial disease (PAD) is a frequent manifestation of systemic atherosclerosis. In PAD hemorheological parameters were defined as risk factors in a number of studies and several therapeutic agents were tried in these conditions. Our study aims to investigate and compare the in vitro hemorheological effects of various drugs generally used in the parenteral treatment of intermittent claudication and critical limb ischemia. Blood samples of healthy male volunteers were incubated with iloprost, alprostadil, pentoxifylline, sulodexide or pentosan polysulfate at calculated therapeutic serum concentration. Hematocrit (Hct) was determined by microhematocrit centrifuge. Plasma and apparent whole blood viscosities (WBV) were evaluated by capillary viscometer. Red blood cell aggregation was measured by LORCA (laserassisted optical rotational cell analyzer) aggregometer, and LORCA ektacytometer was used for measuring erythrocyte deformability at $37^{\circ}C$. Iloprost, alprostadil, and pentoxifylline incubation did not have any significant effect on plasma and apparent WBV. Elongation index increased in samples incubated with alprostadil at low shear stresses 0.95 and 0.53 Pa (p < 0.05). Sulodexide significantly improved WBV and Hct/WBV ratio (p < 0.05). Incubation with pentosan polysulfate resulted in higher WBV, lower Hct/WBV ratio and deterioration in the aggregation parameters (p < 0.05). Sulodexide may have beneficial effect on a macrorheological parameter; alprostadil may improve a microrheological parameter. Hemorheological alterations could be important in PAD patients with hampered vasodilator capacity.

Numerical study of vortex shedding in viscoelastic flow past an unconfined square cylinder

Mahmood Norouzi,Seyed Rasoul Varedi,Mahdi Zamani 한국유변학회 2015 Korea-Australia rheology journal Vol.27 No.3

In this paper, the periodic viscoelastic shedding flow of Giesekus fluid past an unconfined square cylinder is investigated numerically for the first time. The global quantities such as lift coefficient, Strouhal number and the detailed kinetic and kinematic variables like normal stress differences and streamlines have been obtained in order to investigate the flow pattern of viscoelastic flow. The effects of Reynolds number and polymer concentrations have been clarified in the periodic viscoelastic flow regime. Our particular interest is the effect of mobility parameter on the stability of two dimensional viscoelastic flows past an unconfined square cylinder. To fulfill this aim, the mobility parameter has been increased from 0 to 0.5 for different polymer concentrations. Results reveal that mobility factor noticeably affects the amplitude of lift coefficient and shedding frequency more strongly at higher polymer concentrations

Dynamic measurement of stress optical behavior of three amorphous polymers

Inki Min,Kyunghwan Yoon 한국유변학회 2012 Korea-Australia rheology journal Vol.24 No.1

In the present study, rheo-optical and mechanical properties of three amorphous polymers, i.e., PS (polystyrene), PC(polycarbonate) and COC(cyclo olefin copolymer), widely used for optical products have been investigated. Accurate measurement of stress optical coefficients and elastic modulus data across the glass transition region are essential for predicting optical anisotropy in many injection molded optical products like pickup lenses and waveguide in LCD module since the final products have both flow and thermal history from the melt to glass. To obtain stress optical behavior in wide range of frequency and temperature including rubbery, glassy and glass transition regime, frequency sweep tests with extensional bar and shear sandwich tools were undertaken. As a result, glassy and melt extreme values of stress optical coefficient of PS and PC were evaluated as well as master plots in wide frequency region. The sign change of stress optical coefficient was shown clearly for PS as the frequency increased. On the other hand, the sign of stress optical coefficient over the whole frequency region is always positive for PC. For COC's of different composition, even though the glass transition temperature can vary, the stress optical coefficient of COC's with different composition stays almost constant at two extremes

Influence of viscosity modifying admixtures on the rheologicalbehavior of cement and mortar pastes

R. Bouras,A. Kaci,M. Chaouche 한국유변학회 2012 Korea-Australia rheology journal Vol.24 No.1

The influence of Viscosity-modifying admixtures (VMA) dosage rate on the steady state rheological properties, including the yield stress, fluid consistency index and flow behaviour index, of cementitious materials is considered experimentally. The investigation is undertaken both at cement paste and mortar scales. It is found that the rheological behaviour of the material is in general dependent upon shear-rate interval considered. At sufficiently low shear-rates the materials exhibit shear-thinning. This behaviour is attributed to flow-induced defloculation of the solid particles and VMA polymer disentanglement and alignment. At relatively high shear-rates the pastes becomes shear-thickening, due to repulsive interactions among the solid particles. There is a qualitative difference between the influence of VMA dosage at cement and mortar scales: at cement scale we obtain a monotonic increase of the yield stress, while at mortar scale there exists an optimum VMA dosage for which the yield stress is a minimum. The flow behaviour index exhibit a maximum in the case of cement pastes and monotonically decreases in the case of mortars. On the other hand, the fluid consistency index presents a minimum for both cement pastes and mortars.

Peristaltic flow of a Casson fluid in an annulus

P. Nagarani,A. Lewis 한국유변학회 2012 Korea-Australia rheology journal Vol.24 No.1

Peristaltic transport of a non-Newtonian fluid through the annular gap between two coaxial tubes is studied. We assumed that the inner tube is rigid whereas the outer tube has sinusoidal wave travelling down its wall. We modelled the flowing fluid as a Casson fluid to study the combined effects of yield stress (plug width) and annular gap on peristaltic transport. The flow is investigated in a wave frame of reference moving with velocity of the wave under long wavelength and low Reynolds number assumption. The expressions for velocity, stream function, pressure rise, flow rate and frictional force on inner and outer wall are obtained. Results are shown graphically and discussed in the results and discussion section. It is observed that yield stress and annular gap both have significant impact on the pressure rise, frictional resistance on the walls and on the formation and variation of trapped bolus.

Operability window of slot coating using viscocapillary model forCarreau-type coating liquids

Hyun Jung Koh,Ilyoung Kwon,정현욱,Jae Chun Hyun 한국유변학회 2012 Korea-Australia rheology journal Vol.24 No.2

Based on the simplified viscocapillary models for Newtonian and power-law coating liquids reported in Lee et al. (2011a), the one-dimensional (1-D) viscocapillary model for Carreau-type liquids containing zeroshear viscosity information has been developed for constructing the operability window in slot coating. Velocity distribution and position of upstream meniscus were numerically solved to determine onsets of leaking and bead break-up defects. The results obtained by 1-D model are quantitatively corroborated by two-dimensional (2-D) fluent calculations.

A comparison study on high-order bounded schemes:Flow of PTT-linear fluid in a lid-driven square cavity

Kerim Yapici 한국유변학회 2012 Korea-Australia rheology journal Vol.24 No.1

In this computational study, the convergence, stability and order of accuracy of several different numerical schemes are assessed and compared. All of the schemes considered were developed using a normalized variable diagram. Two test cases are considered: (1) two-dimensional steady incompressible laminar flow of a Newtonian fluid in a square lid-driven cavity; and (2) creeping flow of a PTT-linear fluid in a lid-driven square cavity. The governing equations are discretized to varying degrees of refinement using uniform grids, and solved by using the finite volume technique. The momentum interpolation method (MIM) is employed to evaluate the face velocity. Coupled mass and momentum conservation equations are solved through an iterative SIMPLE (Semi-Implicit Method for Pressure-Linked Equation) algorithm. Among the higher-order and bounded schemes considered in the present study, only the CLAM, COPLA, CUBISTA, NOTABLE, SMART and WACEB schemes provide a steady converged solution to the prescribed tolerance of 110-5 at all studied Weissenberg (We) numbers, using a very fine mesh structure. It is found that the CLAM, COPLA, CUBISTA, SMART and WACEB schemes provide about the same order of accuracy that is slightly higher than that of the NOTABLE scheme at low and high Weissenberg numbers. Moreover, flow structures formed in the cavity, i.e. primary vortex, are captured accurately up to We = 5 by all converged schemes.

The effects of particle concentration, ionic strength and shearing on themicrostructure of alumina nanorod suspensions

Seokwon Kim,김종엽 한국유변학회 2012 Korea-Australia rheology journal Vol.24 No.1

In the present study we investigated the microstructure of suspensions of alumina nanorods while varying particle loading and pH. The diameter and length of rod particles were 10 and 50nm, respectively and particle loading was varied from 1 to 5vol%. Using the optical microscopy, dynamic light scattering, Turbiscan and rheological measurement, we showed that the suspensions existed as weakly flocculated gels at pH = 4 while they became strongly flocculated gels when pH was 7 or 11. The cryo-SEM images confirmed that the rod suspensions had gel structures. Strong shearing by milling or sonication changed the microstructure to a certain degree but the basic honeycomb structure was maintained.

Relative viscosity of bimodal suspensions

Fuzhong Qi,Roger I. Tanner 한국유변학회 2011 Korea-Australia rheology journal Vol.23 No.2

A new differential (or multi-scale, mean field approach) model for the relative viscosity of bimodal suspensions is discussed in this paper. Solid spherical particles with a bimodal size distribution in a Newtonian solvent are considered. The problem of random close packing for a bidisperse system is studied. The bounds on volume fractions are given by 0.639<φ_(bm)<0.869, where the random close packing volume fraction for a monodisperse system, φ_(rcp)=0.639, is assumed. We propose that the bimodal suspension has a dominant large particle composition and that the small particles fill the empty spaces between the large particles. The model can therefore be based on the theory of monodisperse suspensions. The predictions of the relative viscosity for several bimodal suspensions given by the model are compared to experimental measurements. A reasonably good agreement is observed.

Analysis of drag effects on pulsatile blood flow in a right coronary artery by using Eulerian multiphase model

Fuat Yilmaz,Ahmet Ihsan Kutlar,Mehmet Yasar Gundogdu 한국유변학회 2011 Korea-Australia rheology journal Vol.23 No.2

The influence of the presence of neighboring entities on drag in blood flow where the dominating mechanisms are expected to be viscous, drag, and gravity forces is investigated in a 3-D anatomically realistic right coronary artery. A classical Eulerian multiphase model on the Fluent v6.3.26 platform is used to model pulsatile non-Newtonian blood flow. Two new drag models based on the mixture viscosity concept are developed by using the drag similarity criteria. In literature, drag models based on the mixture viscosity concept are only depended on volume fraction and show Newtonian viscosity effects on drag. However, mixture viscosity depends on the primary independent variables such as the volume fraction and the shear rate in most of the dispersed flows like blood flow. Non-Newtonian drag effects on red blood cell are so calculated by using these new volume fraction and the shear rate dependent drag models. Five different drag models including these new drag models are used to model the blood flow in this study to investigate the effectiveness of drag force model on blood flow.