Doubling transistor count for every two years in a computer chip, transmitter and receiver (T/R) module of a phased-array antenna that demands higher power with smaller dimensions are all results of miniaturization in electronics packaging. These technologies nowadays depend on improvement of reliable high performance heat sink to perform in narrower volumes. Employing microchannels or open cell metal foam heat sinks are two recently developing promising methods of cooling high heat fluxes. Although recent studies especially on microchannels can give a rough estimate on performances of these two methods, since using metal foams as heat sinks is still needed further studies, a direct experimental comparison of heat exchanger performances of these two techniques is still needed especially for thermal design engineers to decide the method of cooling. For this study, microchannels with channel widths of 300 &micro / m, 420 &micro / m, 500 &micro / m and 900 &micro / m were produced. Also, 92% porous 10, 20 and 40 ppi 6101-T6 open cell aluminum metal foams with compression factors 1,2, and 3 that have the same finned volume of microchannels with exactly same dimensions were used to manufacture heat sinks with method of vacuum brazing. They all have tested under same conditions with volumetric flow rate ranging from 0,167 l/min to 1,33 l/min and 60 W of heat power. Channel height was 4 mm for all heat sinks and distilled water used as cooling fluid. After experiments, pressure drops and thermal resistances were compared with tabulated and graphical forms. Also, the use of metal foam and microchannel heat sinks were highlighted with their advantages and disadvantages for future projects.

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We investigate how the formation of heterogeneity and structures in flows through explicit porous microstructures depends upon the geometric and topological observables of the porous medium. Using direct numerical simulations of single-phase, isothermal, laminar fluid flow through realistic three-dimensional stochastically generated pore structures, hereafter referred to as pore spaces, the characteristics of the resulting steady state velocity fields are related to physical characteristics of the pore spaces. The results suggest that the spatially variable resistance offered by the geometry and topology of the pore space induces a highly heterogeneous fluid velocity field therein. Focus is placed on three different length scales: macroscopic (cm), mesoscopic (mm), and microscopic (microns). At the macroscopic length scale, volume averaging is used to relate porosity, mean hydraulic radius, and their product to the permeability of the pore space. At the mesoscopic scale, the effect of a medium's porosity on fluid particle trajectory attributes, such as passage time and tortuosity, is studied. At the final length scale, that of the microscopic in-pore fluid dynamics, finite time Lyapunov exponents are used to determine expanding, contracting, and hyperbolic regions in the flow field, which are then related to the local structure of the pore space. The results have implications to contaminant transport, mixing, and how chemical reactions are induced at the pore-scale. A description of the adopted numerical methods to simulate flow and generate the pore space are provided as well.

Two problems in the study of elastic filaments are considered.First, a reliable numerical algorithm is developed that candetermine the shape of a static elastic rod under a variety ofconditions. In this algorithm the governing equations are writtenentirely in terms of local coordinates and are discretized usingfinite differences. The algorithm has two significant advantages:firstly, it can be implemented for a wide variety of the boundaryconditions and, secondly, it enables the user to work with generalconstitutive relationships with only minor changes to thealgorithm. In the second problem a model is presented describingthe dynamics of an elastic tube conveying a fluid. First weanalyze instabilities that are present in a straight rod or tubeunder tension subject to increasing twist in the absence of afluid. As the twist is increased beyond a critical value, thefilament undergoes a twist-to-writhe bifurcation. A multiplescales expansion is used to derive nonlinear amplitude equationsto examine the dynamics of the elastic rod beyond the bifurcationthreshold. This problem is then reinvestigated for an elastic tubeconveying a fluid to study the effect of fluid flow on thetwist-to-writhe instability. A linear stability analysisdemonstrates that for an infinite rod the twist-to-writhethreshold is lowered by the presence of a fluid flow. Amplitudeequations are then derived from which the delay of bifurcation dueto finite tube length is determined. It is shown that the delayedbifurcation threshold depends delicately on the length of the tubeand that it can be either raised or lowered relative to thefluid-free case. The amplitude equations derived for the case of aconstant average fluid flux are compared to the case where theflux depends on the curvature. In this latter case it is shownthat inclusion of curvature results in small changes in some ofthe coefficients in the amplitude equations and has only a smalleffect on the post-bifurcation dynamics.

[pt] O presente trabalho tem como objetivo a modelagem de escoamentos através de meios porosos, sob o ponto de vista da Teoria Contínua de misturas. O fluido e o sólido, que compõe o meio poroso, são tratados como constituintes contínuos de uma mistura binária, onde não ocorrem reações químicas. Em todas as situações aqui tratadas o fluido é suposto Newtoniano e incompressível, enquanto o meio poroso é rígido, homogêneo e isotrópico. O trabalho pode ser dividido em duas partes principais. Na primeira são modelados escoamentos através de regiões contendo meios porosos saturados e regiões onde só existe o fluido. São discutidas condições de compatibilidade sobre as interfaces, que separam as regiões, e é estabelecido um modelo para escoamentos, nos quais não exista fluxo de massa através das interfaces. A segunda parte trata de escoamentos em meios porosos insaturados, onde é preciso se considerar o efeito de forças capilares. Nesta parte é estabelecido um modelo e são simuladas situações unidimensionais. São estudados vários casos entre eles o enchimento de uma placa porosa, com e sem efeitos de atrito e de forças gravitacionais. A obtenção de resultados, nestes casos, exige a solução numérica de um sistema hiperbólico não-linear de equações diferenciais. / [en] This work aims to a modelling of flow through a porous media based upon the Continuum Theory of Mixtures. The fluid and the solid, which composes the porous media, are assumed as continuous constituent of a binary mixture where chemical reactions do not occur. In all situations here considered, the fluid is assuned Newtonian and incompressíble, while the porous media is rigid, homogeneus and isotropic. This work can be divided in two main parts. In the first one, flows are modelled through regions containing saturated porous media and regions where there is nothing but the fluid. Conditions of compatibility in the interfaces that divide the regions are discussed and a flow modelling is stablished where there are no crosaflow through the interfaces. The second part is concerned with flows in unsaturated porous media, where the effect of capillery pressure is considered. In this Part a model is stablished and unidimensíonal situations are simulated. Several cases are studied and the filling-up of a porous plate is among them, with and without frictíon effect and gravitational forces. The obtainment of results, in such cases, requires the numeric solution of a non-linear hyperbolíc system of differential equations.

For many years tax jurisdictions have encountered challenges with the concept of the taxation of trusts. The trust concept itself conjures up thoughts of complexity. The development of the trust as a structure and the subsequent colonial influence on the development of trusts in Africa, resulted in different applications of the common law trust principle in tax legislation. This study explores the complexity of the trust tax legislation by way of a comparison of the legislation in selected Southern African Development Community (SADC) countries. The study applies a qualitative approach to compare the trust tax legislation of the selected SADC tax jurisdictions in an effort to assess the complexity involved in the taxation of trusts. The research methodology employed is doctrinal (black letter law) and includes an analysis of the legislation of the selected jurisdictions. The study reveals substantial similarities in the terminology used in the taxation of trusts in the selected jurisdictions. In comparing the legislation of the jurisdictions that make provision for the flow through principle with those of the jurisdictions that do not make provision for the flow through principle, a larger element of complexity in the legislation becomes apparent with wider legislative design differences. Additionally, jurisdictions that make provision for the flow through principle also introduce anti-avoidance legislation to curb the misuse of income attributed to the beneficiaries of trusts. This anti-avoidance legislation creates additional complexity in the legislation. / Dissertation (MCom (Taxation))--University of Pretoria, 2019. / Taxation / MCom Taxation / Unrestricted

Urban stormwater management is evolving toward sustainable approaches which rely on dispersed small-scale bioretention BMPs. One such BMP is the flow-through planter, commonly applied in areas where infiltration into in situ soil is restricted or not possible. A project was developed to evaluate 18, vertically scaled flow-through mesocosms. Three replicates of six treatments, including four soil mixtures containing varied percentages of sand, compost and topsoil, were tested for orthophosphate and nitrate removal, volume reduction capabilities, and peak flow attenuation through the application of a synthetic solution over a simulated 2-inch, Type II storm event. Runoff volume was significantly (p < 0.05) reduced compared to controls. Nutrient levels observed along the hydrograph at different time-steps and flow rates revealed patterns not apparent in cumulative results. The observation of preferential flow patterns along with variability in nutrient removal across treatments highlights the need for design modifications of flow-through facilities.

Abdominal pumping is a well-known behavior in insects, thought to function largely in respiratory processes. In particular, the abdominal pump is considered to produce ventilation of air in the tracheal system, but the mechanistic link between abdominal movement and flow of air is not well understood. In this thesis, we explore the relationship between the abdominal pump and ventilation of air using pupal and adult forms of the darkling beetle Zophobas morio. First, we investigated the mechanical linkage between abdominal pumping and active ventilation in pupae by simultaneously measuring abdominal movement, hemolymph pressure, CO2 emission, and deformation of tracheal tubes. This study revealed that pupae with low metabolic rates do indeed exhibit tracheal compression, which is coincident with abdominal pumping and pressure pulsation. However, more than 63% of the abdominal pumps and associated pressure pulsations did not lead to tracheal compression. This result can be explained by the status of the spiracles; when the system is closed, little compression in the tracheae can occur. Therefore, we conclude that abdominal pumping in insects does not necessarily lead to ventilation and may serve other functions, such as producing hemolymph flow for circulation. Insects have an open circulatory system, with flow driven largely by the small dorsal vessel. Within the open coelom, hemolymph pressure should be mostly uniform, suggesting that abdominal pumping does not produce hemolymph flows within the main body cavity. We tested this assumption by simultaneously measuring hemolymph pressure in different locations in the coelom. Within the abdomen and thorax, hemolymph pressure is nearly uniform, as expected. However, hemolymph pressures are significantly different between the abdomen and thorax. This suggests that the coelom is compartmentalized, and that abdominal pumping can induce hemolymph flow within the coelom. Throughout these experiments, we faced a common difficulty inherent to flow-through respirometry systems: they are incapable of providing direct, instantaneous measurement of gas concentration. Previous methods are not able to reconstitute the rapid dynamical changes in respiratory signals that are required for precise temporal analysis. Therefore, we developed two new methods to accurately recover instantaneous gas exchange signals, based on new models of the impulse response of the system. These methods enabled us to accurately recover fast- changing respiratory signals with a higher fidelity than previously possible. Using these methods, we demonstrate the synchronization of respiratory data with other physiologically relevant signals, such as pressure and abdominal movement. This research was supported by NSF grant #0938047 and the Virginia Tech Institute for Critical Technology and Applied Science (ICTAS). / Ph. D.