The present study investigated the effect of dilute polymer solutions on the size, shape, and roughness of channels and holes, machined in metal and glass using a novel abrasive slurry-jet micro-machining (ASJM) apparatus. The apparatus consisted of a slurry pump and a pulsation damper connected to an open reservoir tank to generate a 140-micron turbulent jet containing 1 wt% 10-micron alumina particles. With the addition of 50 wppm of 8-M (million) molecular weight polyethylene oxide (PEO), the widths of the channels and diameters of holes machined in glass decreased by an average amount of 25%. These changes were accompanied by approximately a 20% decrease in depth and more V-shaped profiles compared with the U-shape of the reference channels and holes machined without additives. The present results demonstrate that a small amount of a high-molecular-weight polymer can significantly decrease the size of machined channels and holes for a given jet diameter.

The blood is a complex fluid that contains, in addition to water, cells, macro-molecules and a large number of smaller molecules. The physical properties of the blood are therefore the result of non-linear interactions of its constituents, which are influenced by the local flow field conditions. Hence, the local blood viscosity is a function of the local concentration of the blood constituents and the local flow field itself. This study considers the flow of blood-like fluids in generalised 90-degree bifurcating pipes and patient-specific arterial bifurcations relevant to the large aortic branches in humans. It is shown that the Red Blood Cell (RBC) distribution in the region of bifurcations may lead to large changes in the viscosity, with implications on the concentrations of the various cells in the blood plasma. This in turn implies that the flow in the near wall regions is more difficult to estimate and predict than that under the assumption of a homogeneous fluid. The rheological properties of blood are complex and are difficult to measure, since the results depend on the measuring equipment and the inherent flow conditions. We attempt to model the viscosity of water containing different volume fractions of non-deforming RBC-like particles in tubes. The apparent viscosities of the mixtures obtained from these model experiments have been compared to the predictions of the different rheological models found in the literature. The same rheological models have also been used in the different simulations, where the local RBC concentration and local shear rate are used in the viscosity models. The flow simulations account for the non-linearity due to coupling between the flow and fluid rheology. Furthermore, from a physiological perspective, it is shown that oscillatory wall shear stresses are affected by changes in RBC concentration in the regions of the bifurcation associated with atherogenesis. The intrinsic shear thinning rheological property of the blood, in conjunction with stagnation in separated flows, may be responsible for elevated temporal wall shear stress gradients (TWSSG) influencing endothelial cell behaviour, which has been postulated to play a role in the development of atherosclerosis. The blood-like fluid properties along with variations in the RBC concentration could also lead to variations in the developing flow structures in the larger arteries that could influence the work the heart has to bear. / <p>QC 20131206</p>

The UK Health & Safety Executive are responsible for advising on ways to ensure the safety of employees within the workplace. One of the main areas of concern is the potential problem of unwanted fire, and it has been identified that within the area of large-scale storage in warehouses, there is an uncertainty posed by large quantities of thermoplastic. Some forms of thermoplastic exhibit melt-flow behaviour when heated, and a large vertical array exposed to a fire may melt and ignite forming a pool fire in addition to a wall fire. This project is largely experimental, and aimed at quantifying the effect of a growing pool fire fuelled by a melting wall on overall fire growth rate. The pool fire has been found to increase melting and burning rates, producing a much faster growing fire. It has also been found that - 80% of flowing and burning material will enter a potential pool fire, with only 20 - 25% of total mass loss actually burning from the original array. During the project 400+ small-scale tests and several medium-scale experiments have been undertaken at both Edinburgh University and the HSE's Fire & Explosion Laboratory, Buxton. The experiments have confirmed the main parameters governing pool fire development are molecular weight degradation rate and mechanism, which control flow viscosity. There have also been investigations into other influences, the most significant of which was found to be flooring substrate. These parameters then form the basis of a simple 1-D model. A semi-infinite heat transfer approximation is used to determine temperature profile through a thermoplastic exposed to its own flame flux, with extrapolated temperature dependant material properties. The derived profile is then inserted into a gravity driven flow model, to produce estimates of flow rate and quantity for plastics undergoing either random or end chain scission thermal degradation processes. The model identifies property data which are required to permit its use as a hazard assessment tool.

Simulation of fresh concrete flow has spurged with the advent of Self-Compacting Concrete, SCC. The fresh concrete rheology must be compatible with the reinforced formwork geometry to ensure complete and reliable form filling with smooth concrete surfaces. Predicting flow behavior in the formwork and linking the required rheological parameters to flow tests performed on the site will ensure an optimization of the casting process. In this thesis, numerical simulation of concrete flow and particle behaviour is investigated, using both discrete as well as a continuous approach. Good correspondence was achieved with a Bingham material model used to simulate concrete laboratory tests (e.g. slump flow). It is known that aggregate properties such as size, shape and surface roughness as well as its grading curve affect fresh concrete properties. An increased share of non-spherical particles in concrete increases the level of yield stress, τ0, and plastic viscosity, µpl. The yield stress level may be decreased by adding superplasticizers, however, the plastic viscosity may not. An explanation for the behaviour of particles is sought after experimentally, analytically and numerically. Bingham parameter plastic viscosity is experimentally linked to particle shape. It was found that large particles orient themselves aligning their major axis with the fluid flow, whereas small particles in the colloidal range may rotate between larger particles. The rotation of crushed, non-spherical fine particles as well as particles of a few microns that agglomorate leads to an increased viscosity of the fluid. Generally, numerical simulation of large scale quantitative analyses are performed rather smoothly with the continuous approach. Smaller scale details and phenomena are better captured qualitatively with the discrete particle approach. As computer speed and capacity constantly evolves, simulation detail and sample volume will be allowed to increase. A future merging of the homogeneous fluid model with the particle approach to form particles in the fluid will feature the flow of concrete as the physical suspension that it represents. One single ellipsoidal particle in fluid was studied as a first step. / <p>QC 20150326</p>

Drop-on-demand (DOD) inkjet print-head has a major share of the market due to simplicity and feasibility of miniature system. The efficiency of droplet generation from DOD print-head is a result of several factors, include viscosity, surface tension, nozzle size, density, driving waveform (wave shape, frequency, and amplitude), etc. Key roles in the formation and behavior of liquid jets and drops combine three dimensionless groups: Reynolds number, Weber number and Ohnesorge number. These dimensionless groups provide some bounds to the “printability” of the liquid. Adequate understanding of these parameters is essential to improve the quality of droplets and provide guidelines for the process optimization. This thesis research describes the application of computational fluid dynamics (CFD) to simulate the creation and evolution process of droplet generation and transport of a highly viscous Newtonian fluid. The flow field is governed by unsteady Navier-Stokes equations. Volume of Fluid (VOF) model is used to solve this multi-phase (liquid-gas) problem.

<p>QC 20140902</p>

The focus of this thesis is optimal path planning. The path planning problem is posed as an optimal control problem, for which the viscosity solution to the static Hamilton-Jacobi-Bellman (HJB) equation is used to determine the optimal path. The Ordered Upwind Method (OUM) has been previously used to numerically approximate the viscosity solution of the static HJB equation for direction-dependent weights. The contributions of this thesis include an analytical bound on the convergence rate of the OUM for the boundary value problem to the viscosity solution of the HJB equation. The convergence result provided in this thesis is to our knowledge the tightest existing bound on the convergence order of OUM solutions to the viscosity solution of the static HJB equation. Only convergence without any guarantee of rate has been previously shown. Navigation functions are often used to provide controls to robots. These functions can suffer from local minima that are not also global minima, which correspond to the inability to find a path at those minima. Provided the weight function is positive, the viscosity solution to the static HJB equation cannot have local minima. Though this has been discussed in literature, a proof has not yet appeared. The solution of the HJB equation is shown in this work to have no local minima that is not also global. A path can be found using this method. Though finding the shortest path is often considered in optimal path planning, safe and energy efficient paths are required for rover path planning. Reducing instability risk based on tip-over axes and maximizing solar exposure are important to consider in achieving these goals. In addition to obstacle avoidance, soil risk and path length on terrain are considered. In particular, the tip-over instability risk is a direction-dependent criteria, for which accurate approximate solutions to the static HJB equation cannot be found using the simpler Fast Marching Method. An extension of the OUM to include a bi-directional search for the source-point path planning problem is also presented. The solution is found on a smaller region of the environment, containing the optimal path. Savings in computational time are observed. A comparison is made in the path planning problem in both timing and performance between a genetic algorithm rover path planner and OUM. A comparison in timing and number of updates required is made between OUM and several other algorithms that approximate the same static HJB equation. Finally, the OUM algorithm solving the boundary value problem is shown to converge numerically with the rate of the proven theoretical bound.

The purpose of this study was to investigate the velocity distribution through an annular bed packed randomly with equal sized spheres. Extensive research has been conducted on the velocity distribution inside packed beds packed with equal sized spheres, different sized spheres, deformed spheres, cylinders and Raschig-rings. A majority of these experimental and numerical studies focused on the cylindrical packed bed. These studies and numerical models are all confined to the velocity profile once the fluid flow is fully developed. The development of the velocity through the inlet region of the bed and the fluid flow redistribution in the outlet of the bed is thus neglected. The experimental investigation into the velocity distribution down stream of the annular packed bed of the HTTU indicated that the velocity profile was independent of the mass flow rate for a particle Reynolds number range of 439 £ Re £ 3453 . These velocity profiles did not represent the distribution of the axial velocity due to shortcomings associated with the single sensor hot wire anemometry system used to measure the velocity distribution. A numerical investigation, using the RANS CFD code STAR-CCM+®, into the velocity distribution downstream of an explicitly modelled bed of spheres indicated that the axial velocity distribution could be extracted from the experimental velocity profiles by using an adjustment factor of 0.801. This adjusted velocity profile was used in the verification of the implicit bed simulation model. The implicit bed simulation model was developed in STAR-CCM+®. The resistance of the spheres was modelled using the KTA (1981) pressure drop correlation and the structure of the bed was modelled using the porosity correlation proposed by Martin (1978), while the effective viscosity model of Giese et al. (1998), adjusted by a factor of 0.8, was used to model the velocity distribution in the near wall region. It was found that the structure in the inlet region of the bed, where two walls disturb the packing structure, can be modelled as the weighted average of the radial and axial porosity while the structure in the outlet regions can be modelled by letting the radial porosity increase linearly to unity. The basic shape of the velocity profile is established immediately when the fluid enters the bed. The amplitude of the velocity peaks however increase in magnitude until the velocity profile is fully developed at a distance approximately of five sphere diameters from the bed inlet. The profile remains constant throughout the bed until the outlet region of the bed is reached. In the outlet region a significant amount of fluid redistribution is observed. The amplitude of the velocity peaks is reduced and the position of the velocity peaks is shifted inwards towards the centre of the annular region. The fully developed velocity profile, predicted by the simulation model is in good agreement with profiles presented by amongst others Giese et al. (1998). The current model however also offers insight into the development of the profile through the inlet of the bed and the fluid redistribution, which occurs in the outlet region of the bed. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2010.

This thesis examines how the non-Newtonian characteristics of liquid hog manure affect the flow conditions within a steady-flow anaerobic digester. There are three main parts to this thesis. In the first part of this thesis, the physical properties of liquid hog manure and their variation with temperature and solids concentration are experimentally determined. Naturally¬¬-settled manure sampled from an outdoor storage lagoon is studied, and density, viscosity, and particle size distribution are measured. Hog manure with total solids concentrations of less than 3.6% exhibits Newtonian behaviour; manure between 3.6% and 6.5% total solids is pseudoplastic, and fits the power law; manure with more than 6.5% total solids exhibits non-Newtonian and time-dependent characteristics. The second part of this thesis investigates the flow of Newtonian and non-Newtonian fluids—represented by tap water and xanthan gum solution, respectively—within four lab-scale reactor geometries, using residence time distribution (RTD) experiments. The effect of reactor geometry, flow rate, and fluid viscosity are evaluated. In the third part of this thesis, flow conditions within lab-scale and pilot-scale anaerobic digester reactors are simulated using three-dimensional modeling techniques. The RTDs of lab-scale reactors as predicted by the 3D numerical models compare well to the experimental results. The 3D models are also validated using data from particle image velocimetry (PIV) experiments. Finally, the viscous properties of liquid hog manure at 3% and 8% total solids are incorporated into the models, and the results are evaluated.

The purpose of this study was to investigate the velocity distribution through an annular bed packed randomly with equal sized spheres. Extensive research has been conducted on the velocity distribution inside packed beds packed with equal sized spheres, different sized spheres, deformed spheres, cylinders and Raschig-rings. A majority of these experimental and numerical studies focused on the cylindrical packed bed. These studies and numerical models are all confined to the velocity profile once the fluid flow is fully developed. The development of the velocity through the inlet region of the bed and the fluid flow redistribution in the outlet of the bed is thus neglected. The experimental investigation into the velocity distribution down stream of the annular packed bed of the HTTU indicated that the velocity profile was independent of the mass flow rate for a particle Reynolds number range of 439 £ Re £ 3453 . These velocity profiles did not represent the distribution of the axial velocity due to shortcomings associated with the single sensor hot wire anemometry system used to measure the velocity distribution. A numerical investigation, using the RANS CFD code STAR-CCM+®, into the velocity distribution downstream of an explicitly modelled bed of spheres indicated that the axial velocity distribution could be extracted from the experimental velocity profiles by using an adjustment factor of 0.801. This adjusted velocity profile was used in the verification of the implicit bed simulation model. The implicit bed simulation model was developed in STAR-CCM+®. The resistance of the spheres was modelled using the KTA (1981) pressure drop correlation and the structure of the bed was modelled using the porosity correlation proposed by Martin (1978), while the effective viscosity model of Giese et al. (1998), adjusted by a factor of 0.8, was used to model the velocity distribution in the near wall region. It was found that the structure in the inlet region of the bed, where two walls disturb the packing structure, can be modelled as the weighted average of the radial and axial porosity while the structure in the outlet regions can be modelled by letting the radial porosity increase linearly to unity. The basic shape of the velocity profile is established immediately when the fluid enters the bed. The amplitude of the velocity peaks however increase in magnitude until the velocity profile is fully developed at a distance approximately of five sphere diameters from the bed inlet. The profile remains constant throughout the bed until the outlet region of the bed is reached. In the outlet region a significant amount of fluid redistribution is observed. The amplitude of the velocity peaks is reduced and the position of the velocity peaks is shifted inwards towards the centre of the annular region. The fully developed velocity profile, predicted by the simulation model is in good agreement with profiles presented by amongst others Giese et al. (1998). The current model however also offers insight into the development of the profile through the inlet of the bed and the fluid redistribution, which occurs in the outlet region of the bed. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2010.