Low Shear Conditions Research Articles

Dissipative Heating Effects and End Corrections for Viscous Newtonian Flow in High Shear Capillary Tube Viscometry

The effect of dissipation heating on the apparent viscosity measured in capillary tube viscometry is described in this paper. Conditions of low Reynolds number and high shear are assumed. End corrections to the tube flow, found to be 3π/16 times the diameter of the tube, are incorporated. The flow curves show decreasing apparent viscosity when the shear stress increases. The configuration of the flow curves plotted in logarithmic presentation are found to be identical for fluids with Newtonian behavior. Convection is the predominant mechanism in removal of the heat in short capillary tube. The estimated upper bound for the shear stress obtainable in short length capillary tubes appears to be of the order of magnitude of 10 MPa limited primarily by the pressure drop associated with the constant end correction from the flat ended inlet and exit of the tube.

Glutaraldehyde fixation and the mechanism of erythrocyte agglutination by concanavalin a and soybean agglutinin

To evaluate the importance of lectin receptor mobility and clustering for enhanced cell agglutinability, the effect of glutaraldehyde fixation on the agglutinability of human erythrocytes by concanavalin A and soybean agglutinin was investigated. Agglutinability was evaluated in unperturbed Microtiter ® plates. Fixation increased slightly the agglutinability of the erythrocytes by both lectins. Fixation did not alter trypsin-enhanced agglutinability. Furthermore, when fixed erythrocytes were trypsinized, their agglutinability increased to the level of unfixed, trypsinized erythrocytes. The kinetics of agglutination of fixed and unfixed erythrocytes were monitored in an electronic particle counter. The shear forces associated with the kinetic experiments diminished fixed-cell to fixed-cell agglutination, i.e., both lectins gave slower kinetics of agglutination with fixed erythrocytes than with unfixed erythrocytes. In contrast, the kinetics of concanavalin A-mediated agglutination of trypsinized-fixed erythrocytes mixed with equal numbers of trypsinized-unfixed erythrocytes were indistinguishable from the rapid kinetics of agglutination of trypsinizedunfixed erythrocytes alone. Light microscopy revealed aggregates composed of fixed and unfixed erythrocytes. We conclude that glutaraldehyde fixation does not diminish the agglutinability of human erythrocytes under low-shear conditions. Our results indicate that the enhanced agglutination of trypsinized erythrocytes is not dependent on clustering of lectin receptors. The disruption of agglutination of fixed erythrocytes by shear forces that do not disrupt agglutination of fixed erythrocytes with unfixed erythrocytes suggests that the rigidity of the fixed erythrocyte may prevent stable aggregate formation by fixed erythrocytes alone.

19] Rotating cylinder viscometers

The floating rotor viscometer has found widespread use for studying the viscosity of deoxyribonucleic acid (DNA) solutions under conditions of low shear and for examining different types of non-Newtonian behavior, such as the increase or decrease in viscosity with change in shearing force or time of shear. In the past few years, this viscometer has also been used to study the shear-dependent viscosity of certain protein solutions. The viscosity of a solution, measured in poises, is simply the ratio of the shear stress exerted on the solution, in dynes/cm 2 , divided by the shear rate, in sec –1 . Rotating cylinder viscometers can either fix the shear stress and measure the shear rate or fix the shear rate and measure the shear stress. The latter type includes viscometers where either the inner or the outer cylinder is rotated, and the stress on the opposing cylinder is measured directly. These viscometers are usually complicated in construction and are designed for specific applications. Some incorporate a guard ring for circumventing the problem of surface films when working with protein-containing solutions. Others measure the rheological properties of blood by providing special geometries so that normal stresses and time-dependent phenomena can be investigated.

Solutions of drag‐reducing polymers—diameter effect and rheological properties

AbstractSolutions (0.5% by weight) of two high molecular weight drag‐reducing polymers, a polyethylene oxide and an acrylamide copolymer having anionic functionality, were prepared under low and high shear conditions. Rheological measurements demonstrated that high shear preparation causes a decrease in the size of the polymer units, the effect being markedly greater for the polyethylene oxide.These solutions were diluted to 25 ppm and drag reduction measured in 0.047‐in. and 0.93‐in. diameter test sections. The method of solution preparation showed no significant effect in the small tube measurements. In the large tube, however, low shear solution preparation led to drag reductions comparable to those found in the small tube, while high shear preparation gave markedly lower drag reductions. These results are discussed in terms of polymer supermolecular structure.

Plasma Injection and Trapping in a Caulked Stuffed Cusp Magnetic Field

A minimum-average-B-stable toroidal magnetic well with high shear is obtained from the combined fields of a solenoid, axial conductors, and an internal ring conductor. Results of measurements of the injection and trapping of high-energy plasma from a coaxial gun are described. The confinement times are dependent on both particle energy and magnetic field. The density e-folding time is independent of the ion velocity under conditions of low shear and well depth. As they are increased the e-folding time varies roughly as 1/vi2. Trapped 0.9-keV plasma decays with an e-folding time that increases by a factor of 6 to 110 μsec as shear and magnetic well depth increase. The initial density of the plasma (0.5 to 3 keV) is ∼ 5 × 1011 cm−3 for field magnitudes resulting in a 40-μsec lifetime of 0.9-keV deuterons. This lifetime is independent of density over the range from ∼ 5 × 1011 cm−3 to 109 cm−3. The range of magnetic field magnitude is limited by the decreasing amount of plasma injected from the gun with increasing magnetic fields. The maximum lifetime of 110 μsec is commensurate with the combined effects of the ∼ 370 μsec support lifetime, a calculated ∼ 1000-μsec charge exchange time, and an anomalous lifetime of ∼ 190 μsec. A search for fluctuating electric fields that might be associated with such an anomalous loss shows the presence of low-amplitude 2-MHz oscillations but their possible role as a loss mechanism is not identified.

The viscosity of tamm-horsfall mucoprotein and its relation to cystic fibrosis

1. 1. The viscosity of the urinary mucoprotein of Tamm and Horsfall has been studied in order to investigate physicochemical differences, if any, between this material from normal and from fibrocystic children. 2. 2. Viscosity has been measured in a rotating cylinder viscometer under conditions of low shear. The intrinsic viscosity [η] = lim C→0 (η rel−I) C g/100 ml of mucoprotein obtained from normal children has been found to be in the range 50–120 dl/g, which is the same as that previously reported for normal adult material. 3. 3. Tamm-Horsfall mucoprotein from fibrocystic children has been studied in parallel with the normal material, and it has been shown that there is no difference in [η] between normal and fibrocystic mucoprotein. 4. 4. The effect of storage as a dilute solution of ⩽ 0.05 mg/ml followed by reconcentration for both normal and fibrocystic material is to bring about a marked reduction in viscosity at all concentrations, together with a small increase in sedimentation coefficient. This is consistent with disentanglement of the macromolecules occurring on dilution .