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In this study, mixing is identified to be the most crucial step during the pre-processing process of extruded food and feed stocks. This study therefore aimed to investigate different mixing techniques in an effort to identify the most effective method and its feasibility to pilot plant application for food extrusion processing. The study furthermore considered the methods of mixing with the view to incorporating the identified method in a standard portable cargo container. The research included an investigation and the design of an inexpensive pre-processing control system that would also save space in such applications where storing facilities for ingredients are housed. After investigating different mixing solutions, a V-blender was identified to be a feasible option. It is suggested that by adding a third leg to the V-blender, to obtain what is dubbed as a “Y”-blender, the effectiveness of mixing would be improved upon - not only in the specified application but with respect to mixing in general. In order to evaluate and compare the effectiveness of the mixers, rapid prototyping models of a V- and a Y- blender, with capacities of about 7.6 litres each, were produced from medium density fibreboard (MDF) with the aid of a laser cutter. It was found that, for a recipe consisting of 87% fine yellow maize, 12.75% fine sugar and 0.25% colorant, the effectiveness of mixing within the V-blender was greatly influenced by the level to which it was filled. This was not the case for the Y-blender. This therefore suggested that a Y-blender is the ideal solution for the given application. A layout of a pre-processing system that fits in a standard shipping container and can accommodate six funnel-shaped raw material storage bins with a feed conveyor leading to a Y-blender is designed and a rapid prototyping model of the most vital components of the system is produced. A novel control system using the IOIO USB controller coupled to an Andriod device is developed and this sub-system, with dedicated software, is coupled to the prototyped pre-processing set-up and operated successfully. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2014

The research undertaken for this Ph.D. thesis concerns the dispersion of solutes in sinuous open channel flows. The aim of the work is to address the void in knowledge and understanding of mixing and transport processes in natural watercourses. The influences of plan form curvature and non-uniform cross sectional shape on transverse and longitudinal mixing are specifically addressed. Experimental work was undertaken on the Flood Channel Facility at HR Wallingford Ltd. This involved creating a pseudo natural sand channel within the concrete meander plan form of the facility, and then stabilising the form. Tracer studies using instantaneous injection to investigate longitudinal mixing and continuous point source release to study transverse mixing were performed. Fluorescent tracer was used. Measurement was by six Turner Design Field Fluorometers in pump through mode and these were digitally logged. Detailed hydrodynamic measurements were made using a two-dimensional Laser Doppler Anemometer (LDA) fitted with a 14mm fibre-flow probe. The resulting data has undergone robust analysis and detailed interpretation. The conclusions are that the dominant processes in mixing, in the natural channel form studied, are shear effects. Simple equations for the prediction of flow fields have been investigated and validated against LDA measurements. It has been possible to make accurate predictions of the transverse and longitudinal mixing coefficients from the predicted flow fields. These predictions have been shown valid for the variations in mixing coefficients over the meander cycle and with discharge.

Decomposition of organic matter is a critical component in global biogeochemical cycling. While decomposition rates have been robustly predicted for mesic systems, modeling decomposition dynamics in drylands has proven to be problematic, reflecting a need to account for processes that may be unique to dryland systems: low and spatially variable vegetation cover, high rates of soil movement, and high levels of radiant energy exposure at the soil surface. Recent empirical evidence suggests that the discrepancies between measured and predicted decomposition rates in drylands may be due to the greater influence of abiotic drivers, such as soil-litter mixing (SLM) and solar radiation, on plant litter decomposition relative to more mesic systems. UV-driven photodegradation may dominate until SLM reaches a threshold, at which point litter is shielded from radiation and microbial processes become predominant. The overarching goal of this dissertation was to examine the influence of SLM and solar radiation on decomposition of foliar and woody plant litter in a dryland ecosystem undergoing woody plant encroachment. A series of four complimentary experiments sought to quantify the effects of these abiotic drivers on decomposition in relation to variables such as vegetation patch type (e.g., beneath a shrub canopy, in a grass patch, on bare ground), radiant energy regime (e.g., full sun vs. shade), geomorphic surface (e.g., sandy, Holocene-age vs. clay-rich, Pleistocene-age soils), seasonality of litter fall (e.g., summer vs. winter), and litter quality (e.g., grass, shrub leaf, woody). Results indicate that interactions between SLM and photodegradation are complex and mediated by variations in ground cover which influence the local radiant energy environment and the movement of soil across the landscape by wind and water. Decomposition rates were significantly influenced by SLM, UV radiation, radiant energy regime, vegetation structure, and initial litter quality. While these results confirmed the importance of SLM and photodegradation as dryland decomposition drivers, they also reinforced the need for additional research to further clarify the relative importance of these processes under field conditions, particularly the interplay between UV radiation and SLM and their relative influence on biotic and abiotic decomposition processes. Given the changes in climate and vegetation projected for drylands, it is critical to further elucidate the influence of these processes on dryland biogeochemical cycling, as their effects may be magnified or dampened under future conditions. A deeper understanding of the processes driving biogeochemical cycling that may be unique to systems undergoing shifts in plant lifeform composition will allow us to better account for the fate of carbon in these globally important ecosystems.

Sistemas multifásicos reativos, como as argamassas, vêm sendo bastante estudados e explorados das mais diversas formas ao longo dos anos. A mistura é uma das etapas do processamento (mistura, transporte e aplicação) desses sistemas que, devido à aparente simplicidade operacional tem sido de certa forma negligenciada. A qualidade da mistura exerce influência direta no comportamento reológico e nas propriedades no estado endurecido. Nesse contexto, os objetivos da pesquisa consistem em avaliar a influência de parâmetros que interferem no comportamento de mistura (tempo, taxa de adição de água e velocidade de mistura do equipamento), no intuito de entender o fenômeno físico envolvido, sugerindo técnicas de análise para estudá-los e propor procedimentos (sequência de introdução dos materiais) mais adequados para a mistura de argamassas em laboratório. O trabalho de pesquisa compreende duas etapas. A primeira trata da avaliação dos parâmetros que influenciam a mistura de argamassas (cimento, cal, filer e areia) com e sem aditivo dispersante (policarboxilato de sódio) e, estabelece técnicas de análise da curva de mistura, obtida no reômetro rotacional tipo planetário desenvolvido na POLI-USP. A segunda etapa estuda diferentes procedimentos de mistura de argamassas em laboratório, na Hobart, e os compara com o procedimento da ABNT NBR13276/2005. No estado fresco emprega-se a reometria rotacional (curva de mistura + ciclos de cisalhamento) e squeeze-flow (na segunda etapa do trabalho) para avaliação do comportamento reológico. No estado endurecido, as propriedades mecânicas são verificadas por meio de resistência à tração por compressão diametral, módulo de elasticidade dinâmico e porosidade. Os resultados obtidos na primeira etapa, indicam que a técnica empregada na análise das curvas mostra ser apropriada para avaliar o fenômeno físico envolvido na dispersão e homogeneização das partículas do sistema durante a mistura. Na segunda etapa, o estudo de diferentes procedimentos de mistura em laboratório, aponta que introduzir o líquido nos materiais sólidos, nas condições analisadas, tende a produzir sistemas mais fluidos. Dependendo da composição dos sistemas, estes podem ser mais ou menos suscetíveis ao processo de mistura. E, por fim, no estado endurecido, as propriedades avaliadas indicam que um processo de mistura adequado conduz a resultados satisfatórios no material endurecido, com redução da porosidade e melhor desempenho do produto final. / Multiphase reactive systems, such as mortars, have been extensively studied in many different ways over the years. The mixture is one of the processing steps (mixing, transport, application) of these systems that due to its apparent operational simplicity, has been somewhat neglected. The quality of the mixing process has a direct influence on the rheological behavior and on the properties in the hardened state. In this context, the objectives of the research are to assess the influence of experimental parameters that affect the mixing behavior (time, water addition rate and rotation speed) in order to understand the physical phenomena involved, and to develop analysis methodology and propose procedures (sequence of mixing) best suited for mixing mortar in the laboratory. The research comprises two steps; the first part is the evaluation of the influence of experimental parameters on mixing behavior of mortars (cement, lime, filler, sand) with and without additive (sodium polycarboxylate) and the establishment of a methodology to analyze the mixing curve obtained in planetary rotational rheometer developed on POLI-USP, and the second stage studies different procedures for mixing mortars in laboratory, on Hobart, and compares them with the current ABNT NBR13276/2005 standard procedure. In the fresh state rotational rheometer (mixing curve + shear cycles) and squeeze-flow (in the second stage of research) are used for rheological characterization, while mechanical properties were verified by splitting tensile strength, dynamic modulus of elasticity and porosity. The results obtained in the first step indicates that the technique employed for the analysis of the curves is suitable for evaluating the physical phenomena involved in the dispersion and homogenization of the particles during mixing. In the second step, the study of different mixing procedures in the laboratory indicates that introducing the water in the solids tends to produce more fluid systems. The mixing behavior of the systems depends on their mix design (composition). Finally, in the hardened state, properties evaluated indicated that a suitable mixing process leads to satisfactory results with reduced porosity and better final performance of the products.

Shelf seas occupy only 7% in area and less than 0.5% in volume of the entire ocean, but they play an important role in the carbon cycle by taking about 20% - 50% of all the CO2 absorbed by the ocean. Diapycnal mixing is a key process in transporting nutrients, carbon, water mass etc. between the surface and the lower mixed layers in a seasonally stratified shelf sea. The identification and quantification of the processes responsible for driving diapycnal mixing in seasonally stratified seas are the subjects worth study. Early researchers have examined the correlation between enhanced bulk shear and the wind. The bulk shear is defined as the average of the shear in two defined layers which are either side of the thermocline. However the contribution from the barotropic tide has generally been neglected. This study examines two stages of the evolution of water column stratification: the spring development stage and the autumn break down stage. Rotary spectral analysis shows that the shear across thermocline corresponds to different drivers when the water stratification is different. At the spring development stage, the shear across the thermocline corresponds to near-inertial oscillations, which are related to wind. Whilst at the autumn break down stage, the shear across thermocline relates to both the near-inertial oscillations and the barotropic tide. Thus, in contraction to earlier research, our research suggests that the barotropic tide is another dominant driver in the generation of shear. However not all observations can be explained by the wind or barotropic tide. The additional consideration of the baroclinic tide helps explain the signal of an odd shear spike observed in the northern North Sea, which occurred during a period of weak shear production by the wind and barotropic tide. A 1D two-layer vertical dynamic numerical model and a 1D turbulence closure numerical model were applied to investigate the impact of wind and barotropic tide on shear, respectively. In addition, the impacts of hydrographic conditions on the driver of shear were considered. Coherence analysis was applied to examine the similarity of constituents (in frequency domain) between the modelled shear production and the observations. The model sensitivity analysis demonstrates that the switch of driver of shear is highly related to the depth ratio, which is the ratio of thermocline depth over water depth.