The motivation for the determination of the viscosity of polymer solutions in dense fluids at the critical polymer concentration stems from the need to understand the factors that influence the time scale of phase separation in systems that undergo spinodal decomposition upon a pressure quench. In a recent investigation of PDMS + CO₂ and PE + n-pentane where molecular weights of the polymers and the critical polymer concentrations were comparable, significant differences were observed in the time evolution of new phase growth. Among the reasons that contribute to the difference in phase separation kinetics is the viscosity of the solutions. This thesis has been carried out to experimentally demonstrate the differences in viscosities of solutions at their critical polymer concentration. Specifically, the thesis focused on the high-pressure density and viscosity of solutions of poly(dimethylsiloxane) (Mw = 93,700, Mw/Mn = 2.99) in supercritical carbon dioxide and of polyethylene (Mw = 121,000, Mw/Mn = 4.3) in near-critical n-pentane. The measurements have been carried out at the critical polymer concentrations, which is 5.5 wt % for solution of PDMS in CO2 and 5.75 wt % for solution of PE in n-pentane. For PDMS + CO₂ system, the measurements were conducted at 55, 70, 85 and 100 oC and pressures up to 50 MPa. For PE + n-pentane system, the measurements were conducted at 140 and 150 °C and again up to 50 MPa. All measurements were conducted in the one-phase homogenous regions. At these temperatures and pressures, the viscosities were observed to be in the range from 0.14 mPa.s to 0.22 mPa.s for PDMS + CO₂, and from 2.3 mPa.s to 4.6 mPa.s for PE + n-pentane systems. In both systems the viscosities increase with pressure and decrease with temperature. The temperature and pressure dependence could be described by Arrhenius type relationships in terms of flow activation energy (E#) and flow activation volume (V#) parameters. The flow activation energies in PDMS + CO₂ system were about 7 kJ/mol compared to about 18 kJ/mol for the PE + n-pentane system. The activation volumes were in the range 40-64 cm3/mol for PDMS + CO₂ system and 65-75 cm3/mol for the PE + n-pentane solution. The higher values of E# and V# represent the higher sensitivity of viscosity to temperature and pressure changes in the PE + n-pentane system. The viscosity data could also be correlated in terms of density using free-volume based Doolittle type equations. Density is shown to be an effective scaling parameter to describe T/P dependency of viscosity. The closed packed volumes suggested from density correlations were found to be around 0.33 cm³/g for the PDMS and 0.48 cm3/g for the PE systems. Comparison of the viscosity data in these systems with the data on the kinetics of pressure-induced phase separation confirms that the slower kinetics in the PE + n-pentane stems from the higher viscosity in this solution compared to the PDMS + CO₂ system, despite the similarity in the molecular weight of the polymer and the critical polymer concentrations. These viscosity and density measurements were conducted in a special falling-body type viscometer. In the course of this thesis a more reliable procedure for determining the terminal velocity of the falling sinker was implemented. This is based on the precise and more complete description of the position of the sinker with time with the aid of a set of linear variable differential transformers (LVDTs). The design of the new arrangement and procedure for terminal velocity determination and calibration procedures for the viscometer are also presented. The densities and viscosities are determined with an accuracy of ± 1 % and ± 5 % or better, respectively. / Master of Science

Yes / Ice cover formed on a river surface is a common natural phenomenon during winter season in cold high latitude northern regions. For the ice-covered river with compound cross-section, the interaction of the turbulence caused by the ice cover and the channel bed bottom affects the transverse mass and momentum exchange between the main channel and floodplains. In this study, laboratory experiments are performed to investigate the turbulent flow of a compound channel with shore ice covered on the floodplains. Results show that the shore ice resistance restricts the development of the water flow and creates a relatively strong shear layer near the edge of the ice-covered floodplain. The mean streamwise velocity in the main channel and on the ice-covered floodplains shows an opposite variation pattern along with the longitudinal distance and finally reaches the longitudinal uniformity. The mixing layer bounded by the velocity inflection point consists of two layers that evolve downstream to their respective fully developed states. The velocity inflection point and strong transverse shear near the interface in the fully developed profile generate the Kelvin-Helmholtz instability and horizontal coherent vortices. These coherent vortices induce quasi-periodic velocity oscillations, while the dominant frequency of the vortical energy is determined through the power spectral analysis. Subsequently, quadrant analysis is used in ascertaining the mechanism for the lateral momentum exchange, which exhibits the governing contributions of sweeps and ejections within the vortex center. Finally, an eddy viscosity model is presented to investigate the transverse momentum exchange. The presented model is well validated through comparison with measurements, whereas the constants α and β appeared in the model need to be further investigated. / National Natural Science Foundation of China (NSFC). Grant Numbers: 52020105006, 11872285: State Key Laboratory of Water Resources and Hydropower Engineering Science (WRHES), Wuhan University. Grant Number: 2018HLG01

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Additive manufacturing is a growing field dominated by printing processes that soften and re-solidify material, depositing this material layer by layer to form the printed shape. Increasingly, researchers are pursuing new materials to enable fabrication of a wider variety of associated capabilities. This includes fabrication with high-viscosity materials of many new classes of material compositions, such as doping for magnetic or electrically conducting polymers. These additives complicate the materials deposition process by requiring complex, non-linear calibration to synchronize these new candidate materials with the additive manufacturing software and hardware. In essence, additive manufacturing is highly dependent on identifying the delicate balance between materials properties, hardware, and software-which is currently realized via a time-consuming and costly iterative calibration process. This thesis is concerned with reducing this cost of calibration, in particular by providing a time-based metric based on material viscosity for material retraction at the conclusion of each extrusion. It presents a novel non-contact method of determining the material retraction rate (during reversal of extrusion), by measuring the variation in laser intensity resulting from the deformation of the material reservoir due to change in material pressure. Commercially available laser measurement systems cost more than $20,000 and are limited to 1 μm at a 300 ms (3 Hz) sampling rate. The experimental setup presented in this thesis costs less than $100 and is capable of taking measurements of 1 - 2 μm at a 0.535 ms (1870 Hz) sampling rate. For comparison, the stepper motor driving the material extruder operates at 0.667 ms (1500 Hz). Using this experimental setup, an inverse correlation is shown to exist between the viscosity of a material and the rate at which the material is retracted. Using this correlation and a simplified material analysis process, one can approximate the retraction time necessary to calibrate new materials, thereby significantly improving initial estimated calibration settings, and thus reducing the number of calibration iterations required to ready a new material for additive manufacturing. In addition, the insight provided into the material response can also be used as the basis for future research into minimizing the calibration process. / Master of Science / Additive manufacturing is a growing field with an ever-expanding base of materials used in the printing process. Two types of material gaining popularity in the commercial and academic communities are pastes and liquids. These materials require a different method of printing, and users need to take into account other considerations, such as viscosity and pressure, for their precise control. Traditionally, a new material would require a time consuming or costly calibration process to properly print. To decrease the investment required for calibration, this thesis presents a new non-contact method of measuring the pressure of the liquids using a laser to detect a dimensional change in the size of the container. This measurement technique enables an initial calibration estimate that is closer to the optimal setting, potentially allowing for better printing results when working with new materials for additive manufacturing.

The objective of this research work was to develop a methodology for experimentally estimating the interfacial properties at slag-metal interfaces. From previous experiments carried out in the division, it was decided to use surface active elements like sulfur or oxygen to trace any motion at the interface. For this purpose the following experimental investigations were carried out. Firstly the density of slag was estimated using the Archimedes Principle and the Sessile Drop technique. The density of the slag would give the molten slag height required for the surface active element to travel before reaching the slag-metal interface. Diffusivity measurements were uniquely designed in order to estimate the sulfur diffusion through slag media. It was for the first time that the chemical diffusivity was estimated from the concentration in the metal phase. Experiments carried out validated the models developed earlier. The density and diffusivity value of sulfur in the slag was used to accurately capture the time for sulfur to reach the slag-metal interface. The oscillations were identified by calculating the contact angle variations and the interfacial velocity was estimated from the change in the surface area of the liquid iron drop. The interfacial tension was estimated from the contact angles and the interfacial dilatational modulus was calculated. Based on cold model experiments using water as well as mercury, an equation of the dependence of the interfacial shear viscosity on the interfacial velocity and interfacial tension was established. This paved way for the estimation of the interfacial shear viscosity at the slag-metal interface. The present study is expected to have a strong impact on refining reactions in pyometallurgical industries where slag/metal interfaces play an important role. From a fundamental view point, this provides a deeper insight into interfacial phenomena and presents an experimental technique to quantify the same. / QC 20101130

Oats is a crop that contains a high amount of fiber, protein and fat, but like all other crops it contains mostly starch. In this study the focus has been oat flours and brans with different b-glucan content. The health benefits of b-glucan, a soluble fiber are well documented and a correlation between intake of b-glucan with high molecular weight and a low glycemic response has been observed. Food with a low glycemic index can lower the risk for diseases like type 2 diabetes, cardiovascular diseases and obesity. Also a connection between intake of b-glucan with high molecular weight and a reduction of LDL-cholesterol has been observed. b-glucans from oat absorb water and build a viscous gel, which make them an interesting component when developing new products, as a fat replacer in for example meat products and pastries. To optimize the use of flours and brans with a modified b-glucan content in new applications, the water absorption was measured with a method called Solvent Retention Capacity and the viscosity with a Rapid Viscosity Analyzer (RVA). The results showed that a higher amount of b-glucan in the flour or bran, a higher water holding capacity (WHC) was observed. The WHC for oat flour with a b-glucan content at 2% was calculated to 73±7%, while the WHC for oat bran with a b-glucan content at 28%, was calculated to a WHC of 880±45%. A comparison of different flours and brans indicates that dietary fiber, where b-glucan have the greatest impact on the WHC. The result from the RVA indicates that a flour with a combination of a high b-glucan content (0.24g) and high starch content (3.72g) leads to a high viscosity 12700 cP, compared to other flours or brans with either a lower b-glucan content (0.12g) or lower starch content (0.12g) gives lower final viscosity, 5390 and 780 cP. The result also indicates that other factors such as a smaller particle size and a higher temperature during the heating step (95°C instead of 64°C) might give a higher viscosity.

Les travaux présentés s’axent autour de 2 chapitres indépendants : - le 1er concerne l’étude rhéologique d’une formulation pour SMC sans fibres. Cette étude permet d’élaborer des lois de comportement rhéologique. Ces lois sont ensuite insérées dans un code de calcul de simulation numérique afin de prédire les efforts mis en jeu lors d’une compression. Ces données simulées sont comparées avec des données de compression obtenues expérimentalement. - le 2ème se penche sur l’étude d’un comportement rhéologique rare : la rhéopexie négative. La viscosité de l’échantillon dépend de l’histoire de cisaillement qui lui est appliquée. Ce comportement est très sensible à la composition du mélange, et fait intervenir 4 constituants. Dès lors que l’un d’eux est retiré, le phénomène disparaît. Le mélange étudié est constitué de produits classiquement utilisés pour la production de SMC. / The research presented is divided into 2 independents chapters: - the 1st one focuses on the rheological study of a fibreless formulation for SMC. This study allows us to write constitutive equations of the formulation. These equations are in turn implemented in a numerical simulation program, in order to predict the forces generated during a compression experiment. These simulated data are eventually compared with experimental data obtained during compression.- the 2nd chapter concerns the study of a rare rheological behaviour: the negative rheopexy. The viscosity of the sample depends on its shear history, in a very different way than a thixotropic sample’s viscosity would. This rheological behaviour is very component sensitive, and results from the interactions between 4 components. As soon as one of them is missing, the negative rheopexy disappears. The mixture studied is constituted of products traditionally used for the production of SMC.

The reliable prediction of turbulent non-equilibrium flows is of high academic and industrial interest in several engineering fields. Most turbulent flows are often predicted using single-time-scale Reynolds-Averaged-Navier-Stokes (RANS) turbulence models which assume the flows can be modelled through a single time or length scale which is an admittedly incorrect assumption. Therefore they are not expected to capture the lag in the response of the turbulence in non-equilibrium flows. In attempts to improve prediction of these flows, by taking into consideration some features of the turbulent kinetic energy spectrum, the multiple-time-scale models arose. A number of two-scale models have been proposed, but so far their use has been rather limited.This work thus focusses on the development of two-time-scale approaches. Two two-time-scale linear-eddy-viscosity models, referred to as NT1 and NT2 models, have been developed and the initial stages of the development of two-time-scale non-linear-eddy-viscosity models are also reported. The models' coefficients have been determined through asymptotic analysis of decaying grid turbulence, homogeneous shear flows and the flow in a boundary layer in local equilibrium. Three other important features of these models are that there is consistent partition of the large and the small scales for all above limiting cases, model sensitivity to the partition and production rate ratios and sensitivity of the eddy viscosity sensitive to the mean strain rates.The models developed have been tested through computations of a wide range of flows such as homogeneous shear and normally strained flows, fully developed channel flows, zero-pressure-gradient, adverse-pressure-gradient, favourable-pressure-gradient and oscillatory boundary layer flows, fully developed oscillatory and ramp up pipe flows and steady and pulsated backward-facing-step flows.The proposed NT1 and NT2 two-scale models have been shown to perform well in all test cases, being, among the benchmarked models tested, the models which best performed in the wide range of dimensionless shear values of homogeneous shear flows, the only linear-eddy-viscosity models which predicted well the turbulent kinetic energy in the normally strained cases and the only models which showed satisfactory sensitivity in predicting correctly the reattachment point in the unsteady backward facing step cases with different forcing frequencies. Although the development of the two-time-scale non-linear-eddy-viscosity models is still in progress, the interim versions proposed here have resulted in predictions of the Reynolds normal stresses similar to those of much more complex models in all test cases studied and in predictions of the turbulent kinetic energy in normally strained flows which are better than those of the other models tested in this study.

The aim of this diploma thesis is a description of viscosity as a physical characteristic of liquids, next a description of projecting different types of sewer systems (pressure sewer system, vacuum sewer system and gravity sewer system). There was a range of density and viscosity of wastewater experimentally determined. These values were compared with ordinary values used in practice. The practical part of this work consists of sampling wastewater from different types of sewer systems and various localities. Chemical-biological analysis was realized on those samples with defined density, then dynamic viscosity was measured by the rotary viscometer for various temperatures. Measured data are evaluated. Finally, a calculation related to the design of sewers was made.

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