<p> Since Newton's definition of viscosity does not lead to a useful description of non-Newtonian flow, two other model liquids, the Maxwell liquid and the Prandtl-Eyring liquid are discussed. Equations describing the flow behaviour of these liquids in narrow capillaries are derived and discussed. </p> <p> A thorough analysis is given of corrections that are, or may be, necessary in capillary viscometry, and the influence of non-Newtonian flow on these corrections is discusses, both for cylindrical and spherical bulbs. </p> <p> The significance of measurements of non-Newtonian flow in dilute solutions of macromolecules is discussed in terms of recent theories. It is shown that a capillary viscometer has inherent limitations for such measurements, but that a properly designed capillary viscometer can give precise and reliable data at shear rates down to 50 sec^-1, provided that the system is not too shear-dependent. </p> <p> A new variable shear capillary viscometer-- a modification of the Ubbelohde suspended level viscometer-- is describes. It was designed to be rugged, convenient and precise, to eliminate or minimize the kinetic energy correction and surface tenison effects, and to permit dilution of a solution while in the instrument. Three different viscometers of this type have been constructed, calibrated and tested, and proved sound in design and convenient in use. </p> <p> The usefulness of the viscometers has been demonstrated in three diverse investigations: (i) the shear dependence in aqueous solutions of a high molecular weight dextran, (ii) the temperature dependence of the zero-shear intrinsic viscosity in a good solvent of a very high molecular weight fraction of polystrene, (iii) the shear dependence of the interaction coefficient k' in the systems polystyrene-toluene and poly(n-octyl-methacrylate). </p> / Thesis / Master of Science (MSc)

No description available.

We have designed and fabricated a biomicroviscometer platform for measurement of microflows of biological fluids. The biomicroviscometer combines an optically clear biocompatible polydimethylsiloxane (PDMS) channel with on-chip integrated microfluidic differential pressure sensors and capabilities of modular channel geometries. This setup allows for a direct measurement of the change in pressure and flow rate, increasing the overall accuracy of the measurement of viscosity and optical observation. We present an introduction of this combined method of measurement with different channel dimensions, using Newtonian and non Newtonian fluids, and the corresponding calculations. This measurement technique has potential applications in measuring rheological properties at the micro level to further blood disease analysis, and lab-on-a-chip fabrication and analysis.

Overend et al [68] designed a viscometer to measure the viscosity of slurries that have a tendency to settle. This viscometer consists of a rotating ribbed rotor surrounded by a stationary slotted sleeve; this system is then placed eccentrically within an inclined rotating bowl. It, is claimed that this overcomes most of the difficulties encountered when attempting to obtain accurate measurements for these types of mixtures. If the mixture being sheared within the annulus does not represent the true composition of the slurry being, tested then the results are expected to be inaccurate. The presence of sediment at the bottom of the rotor or the formation of large masses of particles within the flow domain will affect the accuracy of the measurements obtained. This dissertation studies the amount of flow through the slotted sleeve and the region, or regions, of low shear rate within the flow domain. Assuming that end-effects are unimportant and that the slurries can be replaced by a single-phase fluid, three two-dimensional models are proposed. These models are designed to capture the large-slot construction of the sleeve and the, approximate, non-Newtonian behaviour of the slurries. The first two models solve analytically (using a regular perturbation scheme) and numerically (using a finite volume method) the moderate-and large-Reynolds-number flow, and the third model uses a finite volume method to study the flow patterns developed by pseudoplastic fluids. The results show that the mixing of the slurry is expected to be enhanced by moving the concentric system (i.e., the rotor and the slotted sleeve) close to the rotating bowl and using low to moderate speeds for the rotor and bowl. In addition, when the cylinders rotate in the same directions, two (counter-rotating) eddies are present within the flow domain; whereas, only one eddy (rotating counter-clockwise) is ++ / present when the cylinders rotate in opposite directions. The presence of eddies in the former situation inhibits the flow through the sleeve; while, for moderate rotorspeeds, the flow through the sleeve is enhanced in the latter. When the slurry assumed pseudoplastic, we observe a region of low shear rate located near the dividing streamline present within the flow field. The distribution of shear rate within the flow field is shown to be affected by factors such as the rate of diffusion of the apparent viscosity and the value of the power law index. Therefore, this study suggests that for certain types of slurries, concentrations of particles exist within the domain and that the mixing of slurries can be impeded by the presence of eddies within the main flow field.

Real-time monitoring of fluid properties in tubular systems, such as viscosity, flow rate, and pressure, is essential for industries utilizing the liquid medium. Today such fluid characteristics are studied off-line using laboratory facilities that can provide accurate results. Nonetheless, it is inadequate to match the pace demanded by the industries. Therefore, off-line measurements are slow and ineffective. On the other hand, commercially available real-time monitoring sensors for fluid properties are generally large and bulky, generating considerable pressure reduction and energy loss in tubular systems. Furthermore, they produce significant and persistent damage to the tubular systems during the installation process because of their bulkiness. To address these challenges, industries have realigned their attention on non-destructive testing and noninvasive methodologies installed on the outer tubular surface to avoid flow disturbance and shutting systems for installations. Although, such monitoring sensors showed greater performance in monitoring and inspecting pipe health conditions, they are not effective for monitoring the properties of the fluids. It is limited to flowmeter applications and does not include fluid characteristics such as viscometers. Therefore, developing a convenient real-time integrated sensory system for monitoring different fluid properties in a tubular system is critical. In this dissertation, a fully compliant compact sensory system is designed, developed, examined and optimized for monitoring fluid properties in tubular architectures. The proposed sensor system consists of a physically flexible platform connected to the inner surface of tubes to adopt the different diameters and curvature shapes with unnoticeable flow disruption. Also, it utilizes the microchannel bridge to serve in the macro application inside pipe systems. It has an array of pressure sensors located bellow the microchannel as the primary measurement unit for the device. The dissertation is supported by simulation and modeling for a deeper understanding of the system behavior. In the last stage, the sensory module is integrated with electronics for a fully compliant stand-alone system.

<p> A new two-capillary absolute viscometer for the measurements of the viscosity of gases down to cryogenic temperatures and for moderate pressures up to 200 atm has been developed and described in this thesis.</p> <p> An experimental determination of the absolute viscosity of nitrogen at atmospheric pressure and in the temperature range 97.41-297.88°K is also reported. The maximum error of the smoothed data is believed to range from ±1% at highest temperatures to ±1.6% at the least favourable lowest temperatures.</p> <p> Data obtained in this work and those of previous workers have been correlated using integral equations postulated by Chapman-Enskog collision theory of dilute gases.</p> <p> Furthermore, viscosity measurements have been carried out for nitrogen at 42 and 84 atm and are presented in the thesis to confirm the applicability of the viscometer for high pressure work.</p> / Thesis / Master of Engineering (MEngr)

The flow behaviour of liquid metals (Sn, Pb and Sn-Pb eutectic) under different shearing conditions is investigated. Experiments were performed with two designs of concentric cylinder viscometers: rotating the inner cylinder (Searle) and rotating the outer cylinder (Couette). The latter technique is uncommon and the equipment was optimised with standard oils. The flow behaviour for the metals differs in the two systems. The curves of 'apparent' viscosity versus shear rate may be divided into two regimes: I. At lower shear rates (<200 s-1): a reduction of 'apparent' viscosity with shear was observed with both viscometers. It is suggested that the high density and high surface tension of the metals and eccentricity between the cylinders at low shear rates, leads to instabilities. Results at low shear rates were therefore discarded and further detailed analysis would be required for a fuller understanding of this behaviour. II. At higher shear rates: a steady, shear-independent behaviour of 'apparent' viscosity with shear rate is observed in the Couette system (upto 600 s-1) whereas in the Searle system the 'apparent' viscosity increases with shear rate (upto 2600 s-1). From hydrodynamic theory about Newtonian fluids, it is suggested that in the Searle type viscometer, the fluid is unstable and Taylor vortices are expected at low shear rates (~80 s-1). This gives rise to an increase in the 'apparent' viscosity with shear rate. Whereas, in the Couette type, the flow is more stable, resulting in a steady 'apparent' viscosity. This interpretation is consistent with liquid metals behaving as Newtonian fluids, but further research is required to confirm this. The author suggests further experiments, with the prime one being the investigation of the fluid with counter and co-rotation of the cylinders in order to observe more complex flows. The results are expected to have implications in the modelling of flow for liquid metal processes, especially the initiation of Taylor vortices under the unstable flow conditions produced by rotating the inner cylinder.

When cultivated properly in bioreactors, microalgae have been found to produce vast amounts of biomass. In the case of diatom cultivation where the organisms will fall out of suspension quite easily, paddle wheels or pumps are the primary means to maintain the necessary velocity in the raceway. This study will focus on the potentially harmful shear stress these devices may impart onto the organisms. The system used to impart shear stress to a diatom culture was a cone and plate viscometer. Cells were counted using a fluorescein diacetate staining method with a fluorescent and brightfield microscope. Under the white light all cells were visible while only the healthy cells were visible under fluorescent light. The sample was exposed to shear stress with the cone and plate viscometer at 6 Pascals for 10 minutes and compared against a non-sheared sample. For each sample, 5 pairs of white and fluorescent light images were captured, counted, and averaged. A non-sheared sample was paired with a sheared sample to calculate the decrease in cell viability. The slope was calculated from the plot of shear stress and cell viability for 9 strains. In each case shear stress resulted in a significant decrease in cell viability; however, there was no statistical difference between strains. While effective, this method would be impractical for a commercial algae cultivation facility as the viscometer in this study costs approximately $100,000. Therefore, tests were performed to determine if a rotary mixer could be substituted for the viscometer. The hypothesis was that the cell damage was a product of shear stress and exposure time. For the viscometer test, the shear exposure was 3600 Pa s. Two rotational mixer tests were performed, one at 1250 RPM for 7 hours and one at 313 RPM for 28 hours, providing the same 3600 Pa s shear exposure. After staining, cell viability decreased 35.62% and 11.07% in the 1250 RPM and 313 RPM test, respectively. This difference was significant compared to the 6.04% decrease in the viscometer test. The increased cell damage was attributed to turbulence in the mixer tests and the basis for further study.

Blood is a dense suspension of flexible red blood cells. In response to a background flow, these cells distribute themselves non-uniformly throughout the vessel. As a result, material properties that are well defined in homogeneous fluids, such as viscosity, are no longer so, and depend upon the flow geometry along with the particle properties. Using a simple model that accounts for the steady-state particle distribution in vessel flow, we derive an expression for the effective viscosity of blood and the suspension flow velocity field in a pressure-driven tube flow. <br /><br /> We derive the steady-state particle distribution from a conservation equation with convective flux arising from particle deformation in the flow. We then relate the particle microstructure to the overall flow through a generalized Newtonian stress-tensor, with the particle volume fraction appearing in the expression for the local viscosity. Comparing with experimental data, we show that the model quantitatively reproduces the observed rheology of blood in tube flow. <br /><br /> We reconsider the problem in an alternate geometry corresponding to the flow between two concentric cylinders. The steady-state particle distribution, suspension velocity field and the measured effective viscosity are all very different from their counterparts in tube flow, casting serious doubt upon the practice of using data from a Couette viscometer to parameterize constitutive models applied to vascular blood flow. <br /><br /> Finally, we calculate the effect of random fluctuations in the particle velocity on the averaged behaviour of the particle conservation equation. Using a smoothing method for linear stochastic differential equations, we derive a correction to the free Einstein-Stokes diffusion coeffcient that is due to the interaction of the particles with their neighbours.

Blood is a dense suspension of flexible red blood cells. In response to a background flow, these cells distribute themselves non-uniformly throughout the vessel. As a result, material properties that are well defined in homogeneous fluids, such as viscosity, are no longer so, and depend upon the flow geometry along with the particle properties. Using a simple model that accounts for the steady-state particle distribution in vessel flow, we derive an expression for the effective viscosity of blood and the suspension flow velocity field in a pressure-driven tube flow. <br /><br /> We derive the steady-state particle distribution from a conservation equation with convective flux arising from particle deformation in the flow. We then relate the particle microstructure to the overall flow through a generalized Newtonian stress-tensor, with the particle volume fraction appearing in the expression for the local viscosity. Comparing with experimental data, we show that the model quantitatively reproduces the observed rheology of blood in tube flow. <br /><br /> We reconsider the problem in an alternate geometry corresponding to the flow between two concentric cylinders. The steady-state particle distribution, suspension velocity field and the measured effective viscosity are all very different from their counterparts in tube flow, casting serious doubt upon the practice of using data from a Couette viscometer to parameterize constitutive models applied to vascular blood flow. <br /><br /> Finally, we calculate the effect of random fluctuations in the particle velocity on the averaged behaviour of the particle conservation equation. Using a smoothing method for linear stochastic differential equations, we derive a correction to the free Einstein-Stokes diffusion coeffcient that is due to the interaction of the particles with their neighbours.