EFFECT OF RED CELL RIGIDITY ON GAS TRANSPORT BY SHEARED FLOWING BLOOD†

By means of a blood flowing model the dependence of oxygen uptake by red blood cells (RBC) on the deformation of the RBC was investigated. The model allows measurements of oxygen transfer in flowing sheared blood. Simultaneously secondary flows can be produced, which enhances oxygen transfer rate of whole blood considerably. The model is applied to analyse the effect of an artificial rigidification of RBC on oxygen uptake by the cells.

A diminution of RBC deformations, obtained by an oxidation of membrane SH-groups, is shown to result in a decrease of O₂-uptake by RBC. This decrease is assumed to be due to a reduction of intracellular convection, which diminishes intracellular mixing of haemoglobin. Glutardialdehyde treatment results in an even higher decrease of oxygen uptake. In this case the complete lack of deformations of the RBC and of orientation in shear flow, which is typical for native RBC and is maintained in diamide RBC, is proposed to be responsible for this greater loss of O₂-uptake.

A shift of the O₂-saturation curves of RBC as a consequence of the chemical modifications is shown not to be responsible for the diamide and glutardialdehyde effects.     

EFFECT OF RED CELL RIGIDITY ON GAS TRANSPORT BY SHEARED FLOWING BLOOD†

By means of a blood flowing model the dependence of oxygen uptake by red blood cells (RBC) on the deformation of the RBC was investigated. The model allows measurements of oxygen transfer in flowing sheared blood. Simultaneously secondary flows can be produced, which enhances oxygen transfer rate of whole blood considerably. The model is applied to analyse the effect of an artificial rigidification of RBC on oxygen uptake by the cells.

A diminution of RBC deformations, obtained by an oxidation of membrane SH-groups, is shown to result in a decrease of O₂-uptake by RBC. This decrease is assumed to be due to a reduction of intracellular convection, which diminishes intracellular mixing of haemoglobin. Glutardialdehyde treatment results in an even higher decrease of oxygen uptake. In this case the complete lack of deformations of the RBC and of orientation in shear flow, which is typical for native RBC and is maintained in diamide RBC, is proposed to be responsible for this greater loss of O₂-uptake.

A shift of the O₂-saturation curves of RBC as a consequence of the chemical modifications is shown not to be responsible for the diamide and glutardialdehyde effects.     

RHEOLOGICAL PROPERTIES OF EMULSIONS OF OIL IN AQUEOUS NON-NEWTONIAN POLYMERIC MEDIA

The viscous flow behaviour of emulsions of oil in non-Newtonian Ellis model fluids (aqueous solutions of sodium carboxymethyl cellulose) has been studied experimentally. The addition of oil droplets to a non-Newtonian aqueous suspending media leads to an increase in the apparent viscosity of the emulsion system. The shape of the emulsion flow curves (apparent viscosity versus shear-stress plots) is found to be similar to that of the suspending media; consequently, the emulsion flow curves at various oil concentrations (0 to 70% by volume) are described adequately by the Ellis model. The relative viscosities of the emulsions of oil in non-Newtonian aqueous suspending media are significantly lower than those exhibited by emulsions of oil in Newtonian media.     

Influence of carrier fluid on the electrokinetic and rheological properties of shear thickening fluids

This paper presents a study on the influence of hydroxyl groups and oxygen atoms together with chain length and branching of carrier fluid on the rheological and electrokinetic properties of shear thickening fluid (STF). An STF is non-Newtonian fluid behaviour in which the increase of viscosity increases with the applied shear rate. Ethylene glycol, triethylene glycol, 1,3-propanediol, glycerin, poly(propylene glycol) of different molecular weight and poly(propylene glycol) triol were used as the carrier fluids (dispersants). Silica powder with an average particle size of 100 nm was used as the solid phase. Zeta potential, particle size distribution (by DLS technique), steady-state and dynamic rheological measurements were conducted. Experimental results indicate that a different amount of hydroxyl groups and oxygen atoms together with chain length and branching of carrier fluids have a significant influence on the intermolecular interactions thereby and on the rheological properties of suspensions. Depending on the composition, it is possible to control rheological properties. The use of a suitable carrier fluid allows the required pattern flow to be obtained, from Newtonian through shear thinning to shear thickening, given specific shear conditions.     

Characteristics of transient blood flow in MHVs with different maximum opening angles using fluid-structure interaction method

A numerical analysis has been performed to investigate the characteristics of two-dimensional transient blood flows interacting with the leaflet motion in a bileaflet mechanical heart valve with different maximum opening angles, located in the aortic position. Here, for one cycle of heartbeat the analysis has been carried out in the light of fluid-structure interaction since the blood flow and the leaflet motion are coupled with each other. Blood has been assumed to be a Newtonian and non-Newtonian fluid, where the Carreau model has been used for the simulation of non-Newtonian fluid. Physiologic ventricular and aortic pressure waveforms have been used as flow boundary conditions at the ventricle and the aorta. A finite volume computational fluid dynamics code and a finite element structure dynamics code have been used concurrently to solve the flow and the structure equations, respectively, where the two equations are strongly coupled. Flow fields, leaflet behavior, and shear stresses with time have been obtained. Also the discharge and the regurgitation flow rates have been calculated. The maximum shear stress, an important issue for valve hemodynamic analysis, has been found in the vicinity of the contact point where a leaflet contacts with housing in the final stage of the closing phase.     

VELOCITY PROFILES OF NEWTONIAN AND NON-NEWTONIAN TOROIDAL FLOWS MEASURED BY A LDA TECHNIQUE

Laser Doppler Anemomeiry was used to measure the primary (axial) and secondary (recirculating) velocity profiles in laminar flows of Newtonian (ethylene glycol) and non-Newtonian (aqueous solutions of CMC and PAA) liquids in curved tubes. Rheological characteristics of these liquids were measured using standard viscometric techniques (Haake and Mechanical Spectrometer). The effect of the shear-thinning viscosity is to flatten the axial velocity profile while enhancing the circulating flow close to the walls. On the other hand, the viscoelasticity reduces the extent of the secondary flow for all Dean numbers. This fact explains the reduction of laminar friction reported in the literature.

The primary and secondary velocity profiles, which appear to be the first ones ever published for the toroidal flows, are compared with the predictions of numerical simulation. The agreement is good when comparing the profiles of the axial flow but it is unsatisfactory for the secondary flows.     

挤出条件对聚苯乙烯熔体流动行为的影响

应用毛细管流变仪，考察了挤出条件对通用型聚苯乙烯（ＰＳ６６６）和高抗冲聚苯乙烯（ＰＳ４７０）熔体流动行为的影响，实验发现，后者的末端效应较前者显著，且其熔体的切性亦高于前者；而前者熔休的温粘性则高于后者，两试样熔体的剪切流动大体上服从幂律。此外，口型入口角对两试样熔体流动行为的影响是明显的。     

INTEGRATED LINEAR AND NONLINEAR VISCOELASTICITY OF DISCOTIC LIQUID CRYSTALS

Theory and simulation of steady, small-amplitude, and large-amplitude oscillatory capillary Poiseuille flow of discotic mesophases are presented, discussed, and used to provide an integrated framework to characterize the rheology of precursors used in the manufacturing of carbon super-fibers. The underlying microstructural changes responsible for the non-Newtonian rheology are presented and discussed, taking into account dynamic couplings between orientation and velocity fields. Proper scaling of viscoelastic material functions leads to superposition and hence provides a better fundamental understanding of flow processes in steady and oscillatory flows. The relations between shear-thinning behavior in steady flow, elastic storage in small-amplitude oscillatory shear, and flow enhancement in pulsatile flow are established.     

INTEGRATED LINEAR AND NONLINEAR VISCOELASTICITY OF DISCOTIC LIQUID CRYSTALS

Theory and simulation of steady, small-amplitude, and large-amplitude oscillatory capillary Poiseuille flow of discotic mesophases are presented, discussed, and used to provide an integrated framework to characterize the rheology of precursors used in the manufacturing of carbon super-fibers. The underlying microstructural changes responsible for the non-Newtonian rheology are presented and discussed, taking into account dynamic couplings between orientation and velocity fields. Proper scaling of viscoelastic material functions leads to superposition and hence provides a better fundamental understanding of flow processes in steady and oscillatory flows. The relations between shear-thinning behavior in steady flow, elastic storage in small-amplitude oscillatory shear, and flow enhancement in pulsatile flow are established.     

Flow properties of vacuum gas oil–low density polyethylene blends

In this paper, the viscous flow behaviour of Vacuum Gas Oil (VGO) with different fractions (0–10% wt.) of Low Density Polyethylene (LDPE) under dynamic shear has been investigated. Viscosimetry measurements of the blends at temperatures between 333 and 433 K using a BOHLIN Controlled Stress Rheometer, as well as compatibility studies using Differential Scanning Calorimetry (DSC) were carried out. The effects of the variation of the blends polymer content on the activation energy of flow has also been investigated. The results obtained reveal that the blends show Newtonian flow behaviour at higher temperatures for all polymer concentrations studied, while at lower temperatures and at higher polymer concentrations, they show non-Newtonian shear-thinning behaviour. Furthermore, at lower temperatures, these behaviours are more pronounced at lower shear rates than at higher shear rates. As the polymer content in the blend is increased, the shear viscosity increases, the flow behaviour index decreases, and the application of an Arrhenius type equation shows an increase in the activation energy of flow at the lower shear rates.     

水辅助熔体充模流动的熔体流痕

构建了用于研究水辅助熔体充模的仿真模具,采用红色和绿色着色剂作为示踪剂,通过水辅助着色的聚丙烯(PP)熔体在柱状模腔里充模,获得了能够反映熔体流动痕迹的样品。通过观察流痕,对水作用下熔体的充模流动进行了研究。实验结果表明:在一次穿透中,与注水喷嘴接触的高黏度熔体造成水从喷嘴射入熔体的不稳定,水的穿透导致模壁附近熔体可能产生回流现象,回流沿水的穿透方向呈减弱趋势。在二次穿透中,水前缘熔体黏度和黏度分布对水的穿透影响较大,熔体体积的收缩是近似线性的减小过程,熔体的剪切流动弱于一次穿透。实验中还发现,水前缘的熔体也会产生"喷泉流"。     

Rheo-optical investigations of highly concentrated polyurethane solutions for industrial processing into elastic fibres

On a large industrial scale, segmented polyurethanes are processed from solution in the dry spinning process to produce textile fibres. Rheo-optical investigations of the flow behaviour of polyurethane solutions enable new material functions to be determined and provide important information for processing. Proportional increases with shear rate were observed for the flow birefringence, Δn', and the orientation, ϕ. The polymer segments were more easily aligned in the direction of the shear field in more concentrated solutions than in dilute solutions. The same tendency was observed for samples with differing molar masses. An ideal standardisability for the temperature (in a window of 20 K) was found over the entire range of shear rate and, hence, the change in the Newtonian and non-Newtonian flow behaviour was also observed to be completely identical. Using the stress-optical rule, it was possible to determine the first normal stress difference. The stress-optical coefficient, C, was 2.6·10^–9 Pa^–1. The normal stress values lie in the range of accessible shear rates below the shear stress, but do, however, rapidly approach this value as the strain increases. Even at a shear rate of 100 s^–1 the viscoelasticity of a 17 wt.-% polyurethane solution is already significant. At a high shear rate the Weissenberg number, We, which is a measure of the viscoelasticity, has a constant limiting value that only depends on the power law exponent, n. Its values in the range of high shear rates mostly lie between 2 and 3 and are rarely (for the smallest n) above 3.     

MODELING OF CONCENTRATED LIQUID-SOLIDS FLOW IN PIPES DISPLAYING SHEAR-THINNING PHENOMENA

This paper describes our work in modeling concentrated liquid-solids flows in pipes. Based on our previous analyses, some concentrated liquid-solids suspension flows display shear-thinning rather than Newtonian phenomena. Therefore, we developed a new two-phase non-Newtonian power-law model that includes the effect of solids concentration on solids viscosity. With this new two-phase power-law solids-viscosity model, and with constitutive relationships for interfacial drag, virtual mass and shear lift forces, and solids partial-slip boundary conditions at the pipe walls, COMMIX-M is capable of analyzing concentrated three-dimensional liquid-solids flows.     

Non-Newtonian multi-phase flows: On drag reduction, pressure drop and liquid wall friction factor

The present work focuses on the non-Newtonian liquid drag reduction by gas injection. Two regimes are taken in consideration: fully stratified gas shear-thinning liquid flow and gas shear-thinning liquid slug flow regimes.Predictions of drag reduction ratio and holdup are presented for the stratified flow of gas and non-Newtonian Ostwald-de Waele liquid. Fully stratified flow is considered and the approach developed in Taitel and Dukler (1976) is used. For these regimes, CMC (CarboxyMethyl Cellulose) solution is used in order to investigate the behaviour of the gas and non-Newtonian liquids in horizontal pipes. Results have been reformulated and an extension to interfacial Andreussi and Persen (1987) correlation has been carried out for stratified regimes.For slug flow regimes, the mechanistic slug unit model is adopted in order to estimate the pressure gradients along the slug unit. The slug unit model is rearranged and reinterpreted as inviscid Burgers's equation for incompressible phases.For both stratified and slug flow regimes, three dimensional CFD (computational fluid dynamics) simulations were performed in order to compare the drag reduction ratio and pressure gradients. In stratified flows, CFD is also used in an attempt to evaluate the liquid wall friction factor and to compare the obtained values with those given by empirical standard correlations.     

ON THE SWELLING OF SUBMERGED JETS OF DILUTE AND SEMI-DILUTE POLYMER SOLUTIONS

Profound jet swelling is shown to exist when a dilute or semi-dilute solution of PEO (POLYOX WSR 301) is ejected from a capillary tube into a stagnant fluid. The jet swells up to ten times the diameter of the capillary tube depending on the shear rate in the tube and on the density difference between the ejected and the stagnant fluid. The diameter ratio (jet/tube) grows as the 1/3 power of the shear rate, regardless of the density difference, tube diameter and polymer concentration and provided the tube is long enough for the development of the flow profile. For SEPARAN AP 45 solutions, displaying a non-Newtonian behaviour in shear, it is shown that the 1/3 power law holds between the diameter ratio and the shear stress, instead of the shear rate. The analogy between the swelling behaviour of these dilute and semi-dilute polymer solutions and the one observed in concentrated solutions and melts is discussed. The possibility of utilizing the submerged jet technique to compute the polymer solution normal stresses is considered.     

ON THE SWELLING OF SUBMERGED JETS OF DILUTE AND SEMI-DILUTE POLYMER SOLUTIONS

Profound jet swelling is shown to exist when a dilute or semi-dilute solution of PEO (POLYOX WSR 301) is ejected from a capillary tube into a stagnant fluid. The jet swells up to ten times the diameter of the capillary tube depending on the shear rate in the tube and on the density difference between the ejected and the stagnant fluid. The diameter ratio (jet/tube) grows as the 1/3 power of the shear rate, regardless of the density difference, tube diameter and polymer concentration and provided the tube is long enough for the development of the flow profile. For SEPARAN AP 45 solutions, displaying a non-Newtonian behaviour in shear, it is shown that the 1/3 power law holds between the diameter ratio and the shear stress, instead of the shear rate. The analogy between the swelling behaviour of these dilute and semi-dilute polymer solutions and the one observed in concentrated solutions and melts is discussed. The possibility of utilizing the submerged jet technique to compute the polymer solution normal stresses is considered.     

衣架式模头设计理论及其流道数值模拟验证

按照微元法进行数学建模,以非牛顿流体在歧路管中的全展流动模型和在狭缝流道中的全展流动模型为理论基础,应用所有流径上压力降相等和歧路管内外壁剪切速率相等的设计准则,实现沿模头幅宽方向的流量分布均匀设计目标,并用Pro/E进行参数化建模和几何模型网格划分,最后采用Polyflow有限元软件对理论设计进行数值模拟验证,得到压力分布、速度场和壁面剪切速率.模拟结果表明:压力降符合较好,均匀性在宽幅方向上基本一致,剪切速率与设计准则相符.     

Rheological studies on Streptomyces fradiae ScF-5 in submerged fermentation

Studies on the rheology of Streptomyces fradiae ScF-5 in a 10-dm³ submerged fermenter for the production of intracellular glucose isomerase revealed that the apparent viscosity of the broth increased with increase in cell density up to 24 h and then declined while the density of the broth remained constant. The plot of shear stress versus shear rate at various fermentation periods showed the applicability of the Casson model. The yield stress and consistency index were found to increase gradually then decrease subsequently. In contrast, the flow behaviour index was less than unity and remained constant throughout the fermentation. The results contrast with the findings of other workers on the Newtonian and non-Newtonian character of fermentation broths and the applicability of the power law model to such systems.     

RHEOLOGY OF HIGHLY FLOCCULATED OIL IN WATER EMULSIONS

The viscous flow behavior of highly flocculated oil in water emulsions was studied experimentally using a co-axial cylinder viscometer. The aqueous phase of the emulsions consisted of a non-Newtonian solution of Carbopol-940 in tap water; the oil phase consisted of a Newtonian white mineral oil. The emulsions produced were very viscous and they appeared “gelled”. The shear stress/shear rate behavior of the emulsions was described by the Casson's model. The yield-stress in emulsions was found to depend upon the concentrations of the dispersed phase (oil) and the polymer. The yield-stress increased non-linearly with the dispersed phase concentration and it increased linearly with the polymer concentration