published_or_final_version / abstract / Physics / Doctoral / Doctor of Philosophy

This study focuses on the effect that particle properties (size, density and shape) have on fluidized bed hydrodynamics and entrainment rate. The experimental work was carried out using two Plexiglas columns having internal diameters of 0.05 m and 0.14 m respectively and a total height of 6 m from the gas distributor. The particle density was in the range 1300 to 4600 kg/m3, the Sauter mean diameter was in the range 23 to 60 um and the fines content (% < 22 um) was in the range 1 to 29 %. Particle shapes, which ranged from angular to spherical, were characterized by image analysis of SEM photographs. Air was used, as the fluidizing gas and the superficial velocity was kept constant at 0.38 m/s in the 0.05 m column. In the 0.14 m column it was varied in the range 0 to 0.8 m/s. The dense-phase voidage, bubble fraction and entrainment rate of the powders were measured at ambient conditions. In general it was found that the bubble fraction and entrainment rate increased with an increase in the superficial gas velocity. The dense phase voidage was found to increase with an increase in the fines content of the powder and it was only a weak function of the superficial gas velocity. Most importantly, it was found that angular-shaped particles had a higher dense phase voidage, a lower bubble fraction and a lower entrainment rate when compared to spherical-shaped particles having similar particle density and size. Possible reasons for the lower entrainment rate for the angular-shaped particles are given. The measured dense phase voidage, bubble fraction and entrainment flux was compared with predictions from published correlations and it was found that none of the correlations provided a good fit to the data obtained in this work and that different correlations predicted widely different entrainment rates for the same system. It is therefore recommended that literature correlations should be used with caution in the absence of experimental data. Empirical correlations for the dense phase voidage and bubble fraction are developed. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2007.

Effective monitoring and modelling of the marine environment is of importance to both the general public and the scientific community, but relies on the ability to obtain accurate measurements of suspended particle characteristics. Many instruments for measuring particles rely on optical and acoustic scattering from the particles and use this information to infer a particle size and concentration. However, assumptions such as spherical particles of a known composition are widely used, both in measurement technology and in numerical modelling. Various imaging techniques have shown great variability in the shape, size and composition of marine particles when measured within their natural environment. Subsequently, there is substantial uncertainty in the response of light scattering instruments to this diverse range of particles. In this study, a holographic camera was modified to simultaneously record in-focus images of marine particles with their forward angle scattering characteristics. This was achieved by combining both laser scattering and transmissometry with digital holography. The results from this system were compared with theoretical models of scattering from spherical particles within the intended size range of both instruments (15-500microns), with particle size information from both techniques agreeing well during these idealised conditions. The combined holographic and light scattering system was then used to investigate the response of the LISST-100 (Sequoia Scientific Inc.) to spherical particles with diameters extending beyond that intended by the instrument 250microns for type-B and 500microns for type-C derivatives), but that have been observed in-situ with imaging methods. This revealed an aliasing of single large particles into multiple smaller particles during the inversion of LISST-100 scattering into a particle size distribution. For spheres greater than the type-C instrument range, the inversion of scattering produces particle volume distributions that peak at varying sizes between 250-400microns. This key finding highlights the need for care to be taken when interpreting particle size distributions from the LISST-100 when there is potential for particles outside of its range limit. Natural particles, extracted from coastal waters, were then recorded by the combined laboratory system. These complex particles produced highly variable scattering properties which were contaminated by asymmetrical features within the azimuthal plane. This observation of strong azimuthal asymmetry is of concern for both measurements and models of optical properties that assume a symmetrical scattering function for natural particle populations. The azimuthal asymmetry in scattering contributed to additional variability in the response of the instrument in comparison to the holographic camera, which was also subjected to apparent particle break-up via segmentation during image processing. A discussion of holographic imaging and laser diffraction for characterising particles in-situ forms the final part of this thesis, which utilises data from a magnified holographic system that covers the same size range of the LISST-100. This final analysis demonstrated the need for future technology to accurately measure size distributions over a much larger range of sizes than is currently possible (e.g. &lt;2microns to 1000microns). In summary, three key factors were identified to cause an increase in the apparent number of small particles reported by the LISST-100: 1) contamination from scattering of particles larger than the intended size range of the instrument; 2) a decrease in refractive index (particle composition); 3) additional scattering from small sub-components of particle geometry. The standard holographic camera systems are capable of accurately obtaining particle size and concentration measurements that are comparable to other techniques such as the LISST-100. However, in situations where background illumination is poor, errors in the image processing routines can cause an apparent particle break-up due to incorrect binarisation. Despite this, the holographic method provides a unique and powerful mechanism that enables images of particles to be analysed within the context of their in-situ environment.

Master of Science / Food Science / Fadi Aramouni / Nutrition from whole grains has become an integral part of a healthy diet. Consumers are focused on adding fiber and whole grains to be healthy and want the benefits of whole grain with the taste and appearance of refined flour. A review of current commercial whole wheat flour in the marketplace indicated many options for food processors to use. However, many of these options required processing changes and added ingredients to provide the consumer with a quality product. A milling and baking study was done to compare commercially and experimentally milled whole wheat flours from both white and red wheat varieties. Both white and red wheat varieties were kept identity preserved. Experimental milling was done with a hammer mill and a roll stand to closely replicate the commercial milling process. Baking was done using a sponge and dough method to closely replicate commercial baking conditions. The results showed both particle size and wheat variety impact bake performance of whole wheat flour. The most significant impact appeared to be dependent on the variety of wheat being milled. The milling process also had an impact. As particle size decreased, bake functionality improved. However, some decreased functionality was seen when particle size became very fine. It was concluded that additional work on a commercial flour mill needed to be done to determine if an optimal particle size for milling whole wheat flour exists. Experimental milling equipment was not adequate enough to replicate particle size distributions of commercial whole wheat mills.

Master of Science / Department of Grain Science and Industry / Charles Stark / Experiments were conducted to evaluate particle size methodology and flow-ability of fractionated corn. The first experiment compared five variations of the current approved method to determine geometric mean diameter (d[subscript]gw) and geometric standard deviation (S[subscript]gw) described by ANSI/ASAE S319.4 “Method of determining and expressing fineness of feed materials by sieving”. This method controls many variables, including the suggested sample size and the type, number, and size of sieves. However, the method allows for variations in sieving time, sieve agitator inclusion, and the use of dispersing agent. The variations were tested with three grains (corn, wheat, and sorghum). There was no method × grain (P>0.05) interaction for d[subscript]gw, so it was removed. Ten minute sieving time with sieve agitators and dispersing agent resulted in the lowest d[subscript]gw and greatest S[subscript]gw (P<0.05). The second experiment evaluated particle size analysis on ground corn using a 3-sieve method with varying sieving time (30, 60, and 90 s) with the addition of dispersing agent. The sieving time for the 3-sieve method referred to the time sieves were hand shaken side to side. Ninety seconds sieving time with dispersing agent (0.25 g) resulted in the lowest d[subscript]gw (P<0.05). The 3-sieve method was not developed to calculate the S[subscript]gw, so means and main effects were not determined. Experiment three evaluated particle size and flow-ability by grinding corn at two moisture (10 and 12%) with three screenings levels (0, 2.5, and 5%). Results suggested cleaning corn prior to grinding with a roller mill does not change particle size or flow-ability. Experiment four continued the evaluation of flow-ability with corn ground to three target particle sizes (400, 500, and 600 µm) and fractionated into fine, medium, and coarse segments. Target particle size impacted d[subscript]gw, S[subscript]gw, and bulk density (P<0.05), prior to fractionation. Based on the results of this experiment, flow-ability can be improved if fine particles (<282 µm) are removed. Results of these experiments indicated that particle size analysis should use sieve agitators, dispersing agent, and 10 or 15 min sieving time for the standard 13-sieve method and 90 s sieving time with dispersing agent for the 3-sieve method.

O desempenho final das argamassas depende das matérias-primas e de suas proporções na formulação, pois estas determinam o comportamento do material na etapa de aplicação e a microestrutura final do material endurecido. Entre as patologias de revestimentos, a falha de aderência é um dos fenômenos mais freqüentes, sendo originada pela incompatibilidade entre o comportamento reológico da argamassa e a energia de lançamento utilizada, resultando em defeitos na interface argamassa substrato. A adequação das características reológicas das argamassas às solicitações envolvidas na aplicação fornece condições de processamento mais favoráveis para a obtenção das máximas propriedades finais do revestimento. Assim, o objetivo do trabalho é desenvolver critérios de formulação, baseados nas características das matérias-primas, nos modelos de empacotamento de partículas e nos comportamentos reológicos, de modo a obter um método de formulação de argamassas. O método de squeeze-flow foi desenvolvido com sucesso para avaliação reológica de argamassas, sendo as principais variáveis experimentais foram estudadas, assim como o efeito do tipo de mistura no comportamento reológico. Procedimento para quantificação da segregação pasta-agregado foi criado, tendo em vista o intenso efeito que este fenômeno exerce sobre o comportamento reológico em squeeze-flow, especialmente em baixas velocidades. Foi ainda comprovado que o squeeze-flow tem boa relação com a percepção do pedreiro, principalmente, nas etapas de lançamento e aperto. Diversas argamassas nacionais e européias foram caracterizadas, resultando em um mapeamento das características de formulação, do comportamento reológico e das propriedades no estado endurecido. Através da aplicação de conceitos de empacotamento e distância de separação de partículas, foi verificado que a otimização do empacotamento de agregados permite um melhor aproveitamento da pasta para promover argamassas com comportamento reológico mais adequado à aplicação ou com menor consumo de finos e água. As correlações estabelecidas entre as características no estado fluido e as propriedades no estado endurecido permitem prever o comportamento das propriedades no estado endurecido com boa confiabilidade. Por fim, são descritas diretrizes sistemáticas para a formulação de argamassas considerando requisitos de desempenho tanto no estado fresco quanto no endurecido. / The in-use performance of rendering mortars depends on the raw materials features and their content in the formulation, since they have major influence on the material behavior during emplacement, as well as, on its final properties. Adherence failure is one of the most frequent problems of this class of building materials, caused by the incompatibility between rheological behavior and the application process, generating mortar/substrate interface flaws. A rheological behavior more suitable to the application demands, provides appropriate conditions to obtain maximum final rendering properties. Therefore, the main goal of this work is to develop mix-design parameters based on raw materials features, particle packing models and rheological behavior, in order to create a mix-design method for mortars. Squeeze-flow technique was successfully adapted for the rheological evaluation of rendering mortars, and the most important experimental parameters were studied. The method is sensitive enough to measure rheological changes as a function of the mixing process applied. Considering that phase segregation plays an important role on the rheological behavior of concentrated suspensions especially at low speeds, a method was developed to measure paste-aggregate segregation. It was also established that the squeeze-flow agrees well with the workers perception during manual emplacement. Several Brazilian and European products were evaluated, and significant differences were determined on the formulation features, rheological behavior and hardened properties. Using models of particle packing and particle distance, it was verified that optimized packing of aggregates enhances rheological behavior and can also allow the reduction of water and fine particles consumption. The experimental relationships established between fresh characteristics, rheological behavior and final properties can be used to predict hardened features and properties with fair confidence. Lastly, mix-design suggestions are made considering both fresh and hardened performance.

O presente estudo visa dar luz sobre fenômenos ainda pouco explorados que ocorrem durante a estratificação em leitos de jigagem, bem como sobre novas possibilidades de aplicação da técnica. Por meio de testes com misturas de agregados em jigues hidráulico e pneumático descontínuos, foi pela primeira vez examinada a ocorrência de convecção granular em jigues. Os fatores envolvidos em sua formação e a influência sobre a estratificação foram analisados em detalhes. Do mesmo modo, foi examinada a influência da granulometria do leito sobre a estratificação em jigues pneumáticos e a possibilidade de uso do mesmo como um equipamento multi-separador. Os resultados revelam a existência de um fluxo ordenado e estacionário de partículas durante a pulsação do leito, ascendente na porção central e descendente nas bordas do jigue, de modo similar ao fluxo convectivo descritos na literatura para leitos vibrados mecanicamente. Este fluxo convectivo gerou uma distorção no rearranjo do leito estratificado, dando origem a um perfil horizontal de estratificação no qual as partículas leves se concentraram nas bordas e as partículas densas se concentraram preferencialmente na zona central dos estratos. Com base nos resultados, um mecanismo de formação do fluxo convectivo e um modelo preditivo do rearranjo do leito foram propostos. Observou-se também que a diminuição da granulometria e o aumento da distribuição de tamanho dos constituintes do leito teve um efeito positivo sobre a estratificação. Os resultados sugerem que isto pode estar em parte relacionado a maior compactação do leito quando da presença de partículas de menor tamanho. Também, resultados experimentais demonstraram a possibilidade de uso do jigue pneumático para realizar a operação conjunta de separação de materiais rochosos e não rochosos em um único estágio. O desempenho global na remoção de contaminantes não-rochosos foi similar ao de separadores pneumáticos e sistemas de "sorting" automático descritos na literatura. Ainda, a quantidade inicial de contaminantes no sistema teve um efeito desprezível sobre o desempenho. Os resultados obtidos, em particular aqueles relacionados à convecção granular, fornecem novas perspectivas a respeito dos fenômenos envolvidos na estratificação em jigues. Ainda, benefícios práticos podem ser extraídos a partir dos resultados da análise do efeito da granulometria sobre a estratificação e do uso de jigues pneumáticos como multi-separadores. / This study aims to shed some light on some unclear phenomena that occurs during particle stratification in jigs as well as on new possibilities of application of jigging technique. For the first time, the occurrence of granular convection in jigging beds was analyzed by considering the case of hydraulic and pneumatic jigs operating with mixtures of aggregates. The elements involved in the pattern formation and its influence on bed stratification were analyzed in detail. The influence of particle size distribution on bed stratification and the possibility of using pneumatic jigging as a multi-separator were also examined. The experimental results reveal the existence of a steady, ordered flow of particles over bed pulsation, in which particles move upward in the center of the jig bed and downward along the walls of the jig container, similarly to the circulation patterns reported in the literature. The convection gave rise to a distortion in the particle rearrangement, engendering the formation of a horizontal stratification profile in which light particles tended to be concentrated along the walls while dense particles tended to be concentrated preferentially in the center portion of the strata. On the basis of the experimental results, a mechanism of pattern formation and a prediction model were proposed. The results also revealed that the decrease of the particle size and the increase in the particle size distribution had a positive influence on stratification extent. It was suggested by the results that this behavior can be related to the higher bed compaction due to the presence of smaller particles in the bed. Also, experimental results indicated the technical feasibility of the combined use of pneumatic jigging for the removal undesired non-stony materials together with the bed stratification in only one single stage. The reported separation efficiency in the removal of low-density materials was comparable to those of air classifiers and automatic sorting systems. Also, the initial content of contaminants seemed to have a negligible effect on the separation performance. The results obtained, in particular those related to the granular convection, provides new perspectives about the phenomena involved in stratification by jigging. Moreover, practical benefits can be obtained from the results about the influence of particle size on bed stratification and about the usage of pneumatic jigging for multi-separation.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / by Mark V. Parish. / M.S.

Materiais complexos como porcelanas e porcelanatos tem suas propriedades maximizadas quando atingem altas densidades finais após a sinterização. Contudo, a sua formulação contém no mínimo quatro matérias- primas diferentes, sendo o caulim a maior parte, mas também contendo quartzo e feldspatos. A granulometria final da mistura é controlada por uma única etapa de moagem de todos os materiais misturados. O objetivo deste trabalho foi obter combinações de diferentes granulometrias de ortoclásio, albita e quartzo com uma única granulometria de caulim através de cálculos de máximo empacotamento com o objetivo de alcançar a máxima densidade a cru, mantendo-se uma única composição química final. Os resultados mostraram que utilizando o conceito de empacotamento de partículas e otimizando a distribuição granulométrica foi possível obter corpos de prova com maiores densidades finais, menor retração final, além de reduzir a temperatura de queima, o que impacta diretamente no custo de produção. / Complex materials such as porcelain and porcelain stoneware have maximized their properties when they reach high final densities after sintering. However, formulations contain at least four different raw materials, where the kaolin is the major constituent, but also quartz and feldspars. The final particle size of the mixture is controlled by a single step milling of all materials. The attempt of this paper is to make different combinations of particles size distributions of orthoclase, albite and quartz with a single particle size of kaolin by calculation of maximum packing in order to achieve maximum density crude keeping same final chemical composition. The results showed that using the concept of particle packing and optimizing the particle size distribution was possible to obtain specimens with higher density end, the lower total shrinkage, in addition to reducing the firing temperature, which directly impacts the cost of production.

In recent years, economic, social, and environmental factors have encouraged higher forage diets to be fed to dairy cows. Consequently, a better understanding of both the chemical and physical properties of dietary forage fiber is needed. Undigested neutral detergent fiber after 240 hours of fermentation (uNDF240) is the fiber residue remaining after 240 hours of in vitro fermentation and has only recently been defined. Physically effective neutral detergent fiber (peNDF) was defined about two decades ago and is the fraction of dietary fiber with a particle size (i.e., ≥1.18-mm screen) that stimulates chewing behavior, forms the rumen digesta mat, and is resistant to passage from the rumen. To-date, the relationship between these two dietary fiber measurements has not been evaluated. The overall goal of this thesis research was to quantitate the relationship between dietary uNDF240 and peNDF on feed intake, lactational performance, chewing behavior, and the ruminal environment of lactating Holstein dairy cows. The focal study (Chapter 2) investigated the effects of dietary uNDF240 (low or high) and peNDF (low or high) on lactating dairy cows. The four treatments were: 1) low uNDF240, low peNDF (8.8%, 20.1%; LULP; 2) low uNDF240, high peNDF (8.9%, 21.8%; LUHP); 3) high uNDF240, low peNDF (11.4%, 18.6%; HULP); and 4) high uNDF240, high peNDF (11.6%, 22.0%; HUHP). Additionally, a new descriptive term, physically effective uNDF240 (peuNDF240) was calculated as the product of the dietary physical effectiveness factor (pef; % of particles retained on ≥1.18-mm screen with dry sieving) and uNDF240 as a percentage of dry matter (DM). This new descriptive term aimed to integrate the effects of dietary particle size and NDF (in)digestibility. The dietary peuNDF240 concentrations were 5.4% (LULP), 5.8% (LUHP), 5.9% (HULP), and 7.1% (HUHP). The LULP treatment resulted in greater dry matter intake (DMI) and energy corrected milk (ECM), as well as more favorable chewing behavior (i.e., no effect on rumination but less time spent eating) in comparison to the HUHP diet. When comparing the same two treatments, total volatile fatty acid concentration was greater, mean ruminal pH was lower, and NDF turnover rate tended to be greater for the LULP treatment. Milk fat percentage was influenced by dietary uNDF240 with the high uNDF240 diets having an elevated percentage. The LUHP and HULP treatments often did not differ in animal response variables, such as DMI, ECM, mean ruminal pH, and chewing behavior, reflecting their similar dietary peuNDF240 concentration. Importantly, by reducing peNDF of the high uNDF240 treatments, DMI increased to an amount similar to the low uNDF240 treatments. Animal responses were consistently different between the LULP and HUHP treatments as expected: the low uNDF240 diet, chopped more finely, encouraged greater DMI than the high uNDF240 diet chopped coarsely. However, the LUHP and HULP diets with similar peuNDF240 often resulted in similar cow responses, even though the peuNDF240 was obtained differently for each diet. With these diets fed to high-producing cows, it appears that the integration of particle size and indigestibility of fiber using a peuNDF240 measurement is highly related to DMI, ECM yield, chewing behavior, and ruminal environment. In the future, this relationship may prove useful in predicting DMI of lactating dairy cows fed a range of diets differing in uNDF240 and particle size.