Casson Viscosity Research Articles

Article

High-fat and skim-milk powders were produced under constant processing conditions from Spring and Autumn herd milks. The influence of the seasonal variation in protein and solid-fat contents at 10 o C of these milks on some properties of the milk powders was determined. The free-fat content and the median particle size of high-fat milk powders were significantly ( P< 0.05) affected by the protein content and solid-fat content of the milk. There was a curvilinear relationship between the median powder particle size and solid-fat content at 10 o C of the milks. Milk composition did not significantly affect the properties of the skim-milk powders studied. The results showed that it is pos- sible to predict the free-fat content of high-fat milk powders from the protein and solid-fat content of the milks used. Relationships between the spray-dried high-fat milk powder properties and the rheol- ogy of milk chocolate at the end of conching and its final hardness were then determined. Eleven spray-dried high-fat milk powders were blended with skim-milk powders to give a 26% fat ingredient for chocolate manufacture. The Casson viscosity (Pas) of the chocolate at 40 o C at the end of conching decreased as the free-fat content increased ( P< 0.01) and as the powder median particle size in- creased (P < 0.05). The Casson yield value (Pa) at 40 o C at the end of conching decreased (P < 0.01) as the solid fat content at 10 o C increased. The hardness of the tempered milk chocolate was significantly reduced as the free-fat content increased (P < 0.05) and as the particle size increased (P < 0.05). It was concluded that spray-dried high-fat milk powders with different properties can be used to make choc- olates with a range of viscosities and yield values for different end uses. Milk composition / milk powder composition / chocolate rheology

Application of a factorial design to the study of the flow behavior, spreadability and transparency of a Carbopol ETD 2020 gel. Part II

A factorial design (2 3) is applied to study the influence of three of the components of a cosmetic gel (the concentrations of Carbopol ETD 2020, ethanol and glycerine) on flow parameters (Casson's yield value ( τ c), Casson's viscosity ( η c) and apparent viscosity at 125 s −1 ( η ap. 125 s −1)), spreadability, and transparency. The first-order polynomial equation allowed by the model suitably accounts for the τ c and spreadability. Both depend on the concentrations of Carbopol and ethanol, and τ c also depends on the ethanol–glycerine interaction. The model explains to a certain extent the complex relationships that are established between the components and that influence η c y η ap. 125 s −1. Transparency is independent of the Carbopol concentration and it is also thought to be independent of the ethanol concentration. In addition, a high linear correlation has been found between the τ c and spreadability and other viscoelastic parameters of the gels that were previously determined (Int. J. Pharm. (2001)). The application of the technique of experimental design has been shown to be a very useful tool for formulating gels.

Effect of rheological properties of zircon-alumina suspensions on density of green casts

Rheological properties of aqueous suspensions (48 vol%) of zircon-alumina mixtures containing different amounts of polyelectrolyte as dispersant were studied. Slip casting in a plaster mold and pressure filtration at 8 MPa experiments were performed to correlate the rheological properties of the suspensions with the relative density of green casts. Flow curves fitted satisfactorily to the Casson model. The Casson viscosity values remained nearly constant whereas Casson yield stress parameter decreased to a minimum and then increased with increasing the amount of dispersant added. The influence of particle size distribution (PSD) of the powder mixtures on Casson yield stress parameter and on the minimum viscosity was also examined. Green densities increased as yield stress Casson parameter decreased. The mixture of alumina and zircon as fine and coarse powders produced bimodal PSD which maximized the green density of the compacts. Some weakly flocculated suspensions having low apparent viscosity and small yield stress produced casts with relatively high densification. This is attributed to a slight higher viscosity at low shear rates of these suspensions in which settling of particles and /or segregation of components can not occur.

Development and application of confocal scanning laser microscopy methods for studying the distribution of fat and protein in selected dairy products.

Confocal scanning laser microscopy (CSLM) methods were developed to identify fat and protein in cheeses milk chocolate and milk powders. Various fluorescent probes were assessed for their ability to label fat or protein in selected food products in situ. Dual labelling of fat and protein was made possible by using mixtures of probes. Selected probes and probe mixtures were then used to study (a) structure development of Mozzarella cheese during manufacture and ripening, and (b)) the distribution of fat and protein in milk chocolate made with milk powders containing varying levels of free fat. Microstructural changes in the protein and fat phases of Mozzarella cheese were observed at each major step in processing. Aggregation of renneted micelles occurred during curd formation; this was followed by amalgamation of the para-casein into linear fibres during plasticization. Following storage, the protein phase of the Mozzarella became more continuous; entrapping and isolating fat globules. Chocolate made with a high free-fat spray-dried powder blend showed a homogeneous fat distribution, similar to that of chocolate made with roller-dried milk. Chocolate made with whole milk powder containing 10 g free fat/100 fat showed a non-homogeneous fat distribution with some fat occluded within milk protein particles. These differences in fat distribution were related to Casson yield value and Casson viscosity of the chocolates.

RHEOLOGICAL PROPERTIES OF NONCOHESIVE APPLE DISPERSION WITH HELICAL AND VANE IMPELLERS: EFFECT OF CONCENTRATION AND PARTICLE SIZE

ABSTRACTThe proportionality constant, ks, between shear rate, γ, and agitation velocity, N, for a helical ribbon‐screw (HRS) agitator was 17.8. Using the HRS agitator, values of consistency index K and the flow behavior index n of 14 apple pulp suspensions at seven different solids concentrations and two average particle diameters 0.71 mm and 1.21 mm were determined; in addition, values of the Casson viscosity ηc and yield stress σOC were also calculated. The magnitudes of K increased and of n decreased with increase in pulp concentration. Experimental values of the vane yield stress, σOν, measured with a six‐blade vane increased with increase in pulp content. The values of σOC obtained using the Casson model were close to the experimental values σOν. The effect of particle size on the relative viscosity, ηr, was correlated with Peclet number.

Blood Flow around Hollow Fibers

In an artificial lung, blood is oxygenated and flows around a bundle of hollow fibers while gas flows inside the fiber. The objective of this study is to understand the hydrodynamics of three different fiber banks (inline square IS, staggered square SS and equilateral triangle ET) and to investigate the influence of both a Newtonian and non-Newtonian Casson viscosity model on the flow field. A two-dimensional finite element model for permanent, isothermal, laminar blood flow perpendicular to hollow fibers is used. All fibers are assumed identical, straight and parallel. Porosity ranges from 0.4 to 0.6 and Reynolds number varies from 1 to 60. For a given Re, ET generates less resistance than SS, the latter being comparable with IS. A lower porosity increases resistance. Non-Newtonian viscosity affects velocity patterns only at low Re (<0.5) and higher porosity (>0.5). Resistance at low Re is significantly elevated in the fiber banks due to an overall increase in viscosity. This model makes it possible to study the influence of geometry and viscosity on hydrodynamics in fiber banks and may aid in the optimization of hollow fiber artificial lung design.

Rheological Properties of Magnetite Suspensions

Rheological properties of aqueous suspensions of magnetite, varying in particle size distribution and solids content have been studied. Three models, the Bingham, the Herschel-Bulkley, and the Casson were found to describe the experimental flow curves quite well. The Casson model turned out to be very effective in describing the flow curves in a broad range of magnetite particle sizes (from d 63.2 = 30 μm resembling commercial magnetite down to a micronized magnetite with d 63.2 =2.7 μm), and over the solid content range from 5% to 25% by volume. The two rheological parameters obtained from the experimental data using the Casson model, the Casson yield stress and the Casson viscosity were evaluated, and it was concluded that while the Casson viscosity was nearly constant over the magnetite medium density range of 1.3 to 1.7 (5% to 20% by volume), the Casson yield stress varied in a predictable way with magnetite particle size and solids content.

Power Consumption Diagram for Wet Particle Kneader Mixers. In the Case that Rheological Properties for Wet Particles cannot be Measured.

A method to draw power consumption diagrams (Np-Re diagram) for kneader mixers dealing with wet particles which have a high particle content and a flow curve showing plastic fluid characteristics are proposed. The method requires only power consumption measurement of kneader mixers. Rheological properties measured with a rheometer are unnecessary.The proposed method was developed based on Nagata’s method, which was designed to draw Np-Re diagrams using the Metzner-Otto concept for mixing vessels containing a low-particle content.For drawing Np-Re diagrams, we used Casson equations and the Metzner-Otto method to represent the relationship between apparent viscosities and shear rate. The procedure of the present method is as follows. Firstly Np-Re diagrams for Newtonian fluids are made. Secondly, mixing power consumption is measured for wet particles by varying rotational speeds. Then ratios of yield stresses to the specific equipment factor of the kneader mixer, τc/B, and Casson viscosity, μc, are estimated. Finally Np-Re diagrams can be obtained using corrected Bingham numbers and impeller Reynolds numbers based on Casson viscosities. Then, we ascertained that an Np-Re diagram is determined solely by Reynolds numbers based on apparent viscosities, and the Np-Re diagrams drawn by the method in this study are independent of the kind of wet particles and the scale-up ratio of the kneader mixer.

Rheological Measurements on Settling Suspensions: Characterization of a Cyanide Leach Pulp

An elongated concentric cylinder cup and bob viscometer fixture was designed to study the rheological properties of unstable magnetite suspensions. The fixture and its use in characterizing the rheological properties of a cyanide leach slurry are described. The cyanide leach slurry exhibited yield shear thinning flow properties which were modeled using the Casson Equation. The flow properties were affected most by parameters that contributed to the yield stress. Increasing the solid content and pH and decreasing the particle size caused the yield stress to increase. Changes in parameters also affected the Casson viscosity. Increasing the solid content, pH (Ca(OH)2) and grind size increased the viscosity.

Rheological, Mass Transfer, and Mixing Characterization of Cellulase-Producing Trichoderma reesei Suspensions

Steady and dynamic shear measurements are utilized to characterize the rheological behavior of Trichoderma reesei RUT-C30 fungal suspensions during batch growth on xylose (soluble substrate) or cellulose (particulate solid substrate) at three different fermentor impeller speeds (250, 400, and 550 rpm). Biomass concentrations versus time were unimodal on xylose and bimodal on cellulose. This behavior is consistent with relatively rapid, early growth on easily metabolized growth medium components (yeast extract), followed by a second, slower growth phase due to hydrolysis of recalcitrant cellulose by increasing cellulase concentrations. Critical dissolved oxygen (DO) concentration for T. reesei growth on cellulose was found to be 0.073 mmol/L. The DO was kept above this level by supplementing the air feed with pure oxygen, implying that mass transfer limitations were not the cause of bimodal cell growth. Steady shear rheological data showed shear thinning behavior and a yield stress for all broth samples regardless of substrate. Casson and Herschel−Bulkley constitutive equations fit steady shear data well. Dynamic shear measurements on broth suspensions indicated “gel-like” behavior at low strains, with microstructural breakdown at larger displacements. Time variations of the Casson model parameters (yield stress and Casson viscosity) and dynamic moduli (elastic and viscous modulus) followed both cell mass and morphology: a single maximum in all rheological variables resulted when cells were grown on xylose or on cellulose at impeller speeds of 400 or 550 rpm, and dual maxima were observed for cellulose-grown cells at 250 rpm.

Rheological examination of material with cellular structure. 1. Communication: conventional examination of apple-material with cellular structure

Rehydrated material with cellular structure and alcohol insoluble substance may be regarded as concentrated suspension with viscoelastic properties. The rheological properties of disperse systems are determined on the basis of the material properties of the disperse phase apart from its concentration. The material properties of the disperse phase depend on the macrostructural parameters of the particles including the interactions occuring and the chemical structure of the cell wall. The material properties of the rehydrated material with cellular structure may be detected by means of classical rheological examinations and specifically systemizing their evaluation. The description of material with cellular structure with the aid of CASSON's model and the further investigation of the yield stress τ0 as a function of its concentration and of the effektive viscosity ηeff as a function of its concentration and shear rateγ seem to be established. If comprehensivly applied this method allows to interpret the rheological properties of the material with cellular structure in specific respect. The dominant linear dependence of the influencing variables yield stress, CASSON's viscosity and effectiv viscosity on concentration is especially remarkable.

Influence of Viscosity upon Characteristics of Magnetically Suspended Centrifugal Blood Pump and Indirect Measurement of Pressure and Flow Rate.

A magnetically suspended centrifugal blood pump has no mechanical friction, so its shaft torque is stable and almost linear to its motor current. Using this characteristic, the pump head and flow rate can be evaluated from motor current and rotating speed. However, pump characteristics depend on blood viscosity. Therefore, it is important that the change of blood viscosity can be calibrated. Reynolds number is defined using Casson's viscosity and rotating speed of the motor. Then the relationships of pump head versus flow rate and motor current versus flow rate indicate a slightly different Reynolds number dependence between blood and glycerol aqueous solutions. The indirect measurement of the pump head and flow rate from observed motor current and rotating speed was confirmed to have good accuracy and response.

Increased viscosity of erythrocyte suspension upon hemolysis

Viscous properties of partially hemolyzed erythrocyte suspensions were studied with a cone-plate viscometer. A Casson plot was successfully applied for analysis of the viscous properties. When the degree of hemolysis was increased, Casson viscosity (ŋc) of the partially hemolyzed erythrocyte suspensions increased, but the substitution of hemoglobin solution with the same O2-carrying capacity of hemolyzed fraction (containing ghost) reduced theŋc remarkably. The yield stress (fc) of the intact erythrocyte suspension increased with increasing hematocrit, but thefc of partially hemolyzed erythrocyte suspension was dependent on both hematocrit and the degree of hemolysis. The apparent viscosity (ŋa) of erythrocyte suspension was drastically increased with the slight hemolysis, and became maximum at a certain degree of hemolysis which was dependent on both total hemoglobin concentration and shear rate. Such influence of hemolysis on theŋa was also evident in the mixture of erythrocyte suspension and hemoglobin solution. These results suggest that the hemoglobin molecule plays a certain role in erythrocyte-erythrocyte interaction in their suspension, which modifies the viscosity.

虚血性心疾患患者におけるｃｏｅｎｚｙｍｅ Ｑ１０の血液レオロジーへの効果 血液粘度，赤血球膜抵抗，赤血球変形能についての検討

The effects of coenzyme Q10 (CoQ10) on blood rheology were studied in patients with ischemic heart disease. Twenty milligrams of CoQ10 was administrated per os three times daily (total dose 60 mg per day) for two months. Whole blood viscosity was measured at the shear rates of 37.5, 75, 150 and 375 sec-1 with a conplate type viscometer. Whole blood viscosity at each shear rate was decreased after administration of CoQ10. Casson viscosity and yield shear stress were calculated using the Casson plot method from the blood viscosity at each shear rate. Yield shear stress was significantly lowered after administration of CoQ10, while Casson viscosity was not significantly changed. Both the hemolysis starting point and hemolysis end point represented by mOsm were determined by means of the coil plant centrifuge method. These parameters, which reflect osmotic fragility of erythrocytes, showed significant decreases after administration of CoQ10. After the blood was diluted with a phosphate buffer solution, passage time through the Nuclepore membrane with a pore size of 5 μm was measured 10 min after the in vitro administration of CoQ10 of 5 μg. This passage time was significantly shortened after administration of CoQ10. There were no significant changes in hematocrit and fibrinogen after administration of CoQ10. These results show that administration of CoQ10 improves hemorheology in ischemic heart disease, and thus suggests that oxygen transport to heart muscle is increased by treatment of CoQ10.

ペースメーカー植込み前後の血小板機能と血液粘度

To evaluate the effect of pacemaker implantation on the cerebral embolization, we studied changes of platelet function and blood viscosity in patients with pacemaker implantation. Platelet count, mean platelet volume, platelet aggregation by ADP, epinephrine and collagen, plasma TXB2, plasma 6-Keto-PGF1α, blood viscosity and fibrinogen were measured before, at 1 week, at 2 weeks and at 3 weeks after implantation in 7 patients with sick sinus symdrome, 7 with complete AV block and 2 with bradycardiac atrial fibrillation. The modes of pacemakers were VVI in 8 and DDD in 8 patients.In results, 1) Platelet count decreased immediately after implantation, then recovered to the initial level, and stayed increased at 2 and 3 weeks after implantation. 2) Mean platelet volume stayed decreased at 1 week, 2 and 3 weeks after implantation. 3) Platelet aggregation by ADP and epinephrine increased at 2 weeks, and in some patients, stayed increased even at 3 weeks. Aggregation by collagen recovered to the initial level at 3 weeks. 4) Plasma TXB2 increased at 2 weeks, but plasma 6-Keto-PGF1α didn't change. 5) Fibrinogen and plasma viscosity increased at 1 week, and recovered to the initial level at 2 weeks. Casson's viscosity and yield shear stress revealed no change.Platelet function, plasma viscosity and fibrinogen increased transiently after implantation, but in some patients, platelet function stayed increased at 3 weeks after implantation. Some reports mentioned that changes platelet function after operation were transient and returned to the initial level within 1 month after operation. Then, it is necessary to follow up platelet function when it increases up to 1 month after implantation, because either the pacing lead or flow change by pacing might accelerate platelet function.

Rheology of Blood and Blood Vessels

Hereunder is presented a resume of the author's recent work on hemorheology.The problem concerns in the first place the influence of the plasmatic zone upon the relationship of the quantity of blood and its pressure flowing through minute vessels. When blood is regarded as a Bingham body with plastic viscosity ηB and yield value fB, the pressure-flow relationship is given in eq. (6) as P>pB/γ and in eq. (8) as P<pB/γ, where ξ=pB/P, pB=2LfB/R and γ=1-(δ/R). Here δ is the thickness of the plasmatic zone, R is the radius of the vessel, and P is the difference in pressure between two cross-sections at distance L. Similar pressure-flow relationships (11) and (13) were also obtained of the blood obeying Casson's equation with Casson viscosity ηc and Casson yield value fc.The problem concerns in the second place the flow behavior of blood in capillaries with permeable walls. Blood is regarded, for simplicity, as an incompressible Newtonian fluid with viscosity η, and an approximate solution of Navier-Stokes equation was obtained under the boundary conditions u=0 and v=k(p-α) at the wall. Here u and v are respectively the axial and radial component of velocity, p is the hydrostatic pressure, k is the permeability coefficient and α is a constant. Starling's law was assumed with regard to filtration and reabsorption of water. The streamlines are shown in Fig. 9. It is shown that the flow Q becomes minimum at a distance LΔα/Δp from the arterial end of the capillary, where L is the length of the capillary, Δα=pa-α and Δp=pa-pv. Here pa and pv are respectively the pressure at the arterial and venous end of the capillary. In case where filtration and reabsorption of water balance, Δα/Δp must be equal to 1/2, that is, α=(pa+pv)/2.The problem concerns lastly the circumferential tension T in a thick-walled blood vessel. The tension is given in T=p1r1'-p2r2', where r1' and r2' are respectively the inner and the outer radius of the vessel under the internal pressure p1 and the external pressure p2. The formula holds quite generally, irrespective of whether the wall is homogeneous or inhomogeneous, whether the wall is isotropic or anisotropic, whether the elasticity of the wall is Hookean or nonlinear. The distribution of the circumferential stress τ in the wall with Hookean elasticity was discussed in detail on the basis of classical theory of elasticity. It is shown that τ is not always positive throughout the wall even if p1 is greater than p2. Three cases actually occur: (a) τ is always positive throughout the wall, (b) τ is positive in the inner region, while it is negative in the outer region, and (c) τ is always negative throughout the wall. Introducing non-dimensional parameters difined by k=p1/p2 and s=r2/r1, sk-plane (s>1, k>1) can be divided by two curves k=(1+s2)/2 and k=2s2/(1+s2) into three regions A, B and C which correspond to the cases a, b and c, respectively. It is clear that the circumferential tension T is not always positive in more general cases.

Influence of anaesthetics in rheology of human blood.

Cyclopropane, halothane, and methoxyflurane were investigated for their effects on the viscometry of freshly drawn human blood (group O, Rh+). A total of 43 blood and 63 plasma samples containing specific anaesthetic agents were studied under controlled conditions of temperature, pH, Pco2, Po2, and red blood cell and plasma protein concentrations. A series of three cone plate viscometers, each with different shear rate ranges from 1500 to 6.75 sec.-1, was used. The Casson viscosity of blood and apparent plasma viscosity were determined from the slope of the shear stress-shear rate relationship plotted on a square root scale. Yield stress was determined by extrapolation from the shear stress axis intercept. Our findings indicate that the three anaesthetic agents, within concentrations equivalent to those used during clinical anaesthesia, caused no discernible effect on either yield stress or the apparent viscosity of blood or plasma. However, there was a marginal increase of the yield stress of blood with high concentrations of cyclopropane (above 20 mg.%) and a trend toward reduced plasma viscosity in all of the methoxyflurane samples.

Theoretical Studies on Hemorheology

In this paper are presented some reports of theoretical studies made on hemorheology which is the rheology of blood and blood vessels. The first problem is concerning the influence of the plasmatic zone upon the apparent viscosity of blood in capillaries. If the central core is treated as a Bingham body with the plastic viscosity ηB and the yield value τf, the volume of flow per unit time is obtained as follows.with γ=1-δ/R> and ξ=2Lτf/PR. Here R is the radius, P is the pressure difference between the two cross sections at a distance L, ηp is the viscosity of plasma, and δ is the thickness of the plasmatic zone.If we neglect small terms of order (δ/R)2, then the above equation becomes modified as follows.It is pointed out that the formula obtained by Baylissis not correct.If we consider that the central core obeys Casson's equation, we getwith ξ=2L τf/PR. ηc is the Casson viscosity and τf is the yield value. If we neglect small terms of order (δ/R)2, the above formula is reduced to that derived already by the author.The second problem is concerned with the elastic tension in thick-walled blood vessels in relation to the law of Laplace. Since some doubts have been expressed in physiological literature about the applicability of the law of Laplace to blood vessels, we have examined closely the elastic tension in the wall from the physical point of view. Let a thick-walled vessel be in equilibrium under the internal pressure p1 and the external pressure p2 and let the inner and the outer radius be denoted by r1', and r2', respectively. Then the circumferential tension Tc is exactly given by Tc=p1r1'-p2r2'.This relationship holds quite well generally, irrespective of whether the blood vessel wall has Hookean or rubber-like elasticity, whether the vessel wall is homogeneous or inhomogeneous, and whether the vessel wall is isotropic or anisotropic. Our formula is reduced to the law of Laplace for thin-walled blood vessels.

Viscometry of human blood for shear rates of 0-100,000 sec-1.

THE viscometry of human blood has been represented by a number of empirical equations. Their usefulness has been limited to relatively narrow ranges of shear rate. Among the equations suggested, Casson's equation has been used for calculating the shear strength of blood and for describing its viscometry at shear rates below 5 sec−1 (refs. 1 and 4) (equation 1): where τ is shear stress, γ is shear rate, K is Casson viscosity, C is shear strength of suspension.