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Mechanism of gas cell stability in bread makingSroan, Baninder Singh January 1900 (has links)
Doctor of Philosophy / Department of Grain Science and Industry / Finlay I. MacRitchie / Expansion of dough and hence breadmaking performance is postulated to depend on a dual mechanism for stabilization of inflating gas bubbles. Two flours were used in this study, one from the wheat variety Jagger (Jagger) and the other from a composite of soft wheat varieties (soft). The primary stabilizing mechanism is due to the gluten-starch matrix surrounding the bubble. The secondary mechanism operates when gas bubbles come into close contact during later proofing and early baking. When discontinuities occur in the gluten-starch matrix surrounding gas bubbles, thin liquid lamellae stabilized by adsorbed surface active compounds, provide a secondary stabilization.
A key parameter in the primary stabilizing dough film is thought to be the property of strain hardening. Jagger flour gave higher test-bake loaf volume than soft wheat flour and higher strain hardening index for dough. Rheological properties of doughs were varied by addition of protein fractions prepared by pH fractionation. Fractions were characterized by SE-HPLC and MALLS. The molecular weight distribution (MWD) of fractions progressively shifted to higher values as the pH of fractionations decreased. Mixograph peak development time paralleled the MWD. However, the strain hardening index and the test-bake loaf volume increased with increasing MWD up to a point (optimum), after which they declined. At a given strain rate the behavior at the optimum appeared to result from slippage of the maximum number of statistical segments between entanglements, without disrupting the entangled network of polymeric proteins. Shift of MWD to MW higher than the optimum results in a stronger network with reduced slippage through entanglement nodes, whereas a shift to lower MWs will decrease the strength of the network due to less number of entanglements per chain.
In order to study the secondary stabilizing mechanism, different lipid fractions were added incrementally to the defatted flours. No effects were observed on the rheological properties of the dough. However, large effects on the loaf volume were measured. The additives used were the total flour lipid and its polar and non polar fractions and the fatty acids palmitic, linoleic and myristic. Polar lipids and palmitic acid had positive or little effect on loaf volume respectively. Non polar lipid, linoleic and myristic acids had negative effects on loaf volume. 1
The different effects of the lipid fractions are thought to be related to the type of monolayer that is formed. Polar lipid and palmitic acid form condensed monolayers at the air/water interface whereas non polar lipid, linoleic and myristic acids form expanded monolayers.
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[pt] DESLOCAMENTO DE LÍQUIDOS VISCOELÁSTICOS EM TUBOS CAPILARES / [en] DISPLACEMENT OF VISCOELASTIC LIQUIDS IN CAPILLARY TUBESERICK FABRIZIO QUINTELLA ANDRADE COELHO 06 January 2006 (has links)
[pt] O deslocamento de um líquido em um tubo capilar pela
injeção de um gás
ocorre em muitas situações, tais como na recuperação
avançada de petróleo,
no revestimento de conversores catalíticos e na moldagem
assistida por
injeção de gás. Geralmente o líquido deslocado é uma
solução polimérica
ou uma dispersão, que é não Newtoniana. Forças
viscoelásticas alteram o
balanço de forças em várias partes do escoamento e,
conseqüentemente, alteram a eficiência do deslocamento,
isto é, mudam a quantidade de líquido deixada na parede do
capilar. Modelos de tais escoamentos devem se basear em
teorias que levem em consideração o comportamento
diferenciado de líquidos
com microestrutura complexa, tanto no cisalhamento quanto
na extensão.
Além do mais, escoamentos de deslocamento envolvem uma
superfície livre,
e o domínio no qual as equações diferenciais são
resolvidas é desconhecido a priori, fazendo parte da
solução. Estas duas características tornam o
problema extremamente complexo. Este problema foi estudado
aqui tanto
experimentalmente quanto teoricamente. Os experimentos
consistiram da
visualização do escoamento e medição da massa deslocada
pela passagem
de uma bolha de gás através de um tubo capilar preenchido
por um líquido
viscoelástico. Várias soluções de baixo peso molecular de
Polietileno Glicol
(PEG) e de alto peso molecular de Óxido de Polietileno
(PEO) em água
foram usadas a fim de avaliar os efeitos do comportamento
viscoelástico no
escoamento. As propriedades reológicas das soluções foram
avaliadas tanto
em cisalhamento quanto em extensão. Na análise teórica, o
escoamento com
superfície livre bidimensional próximo µa interface gás-
líquido foi modelado
usando três equações diferenciais constitutivas distintas
que aproximam o
comportamento viscoelástico de soluções poliméricas
diluídas, as quais são
os modelos Oldroyd-B, FENE-P e FENE-CR, juntamente com as
equações
de conservação de massa e de quantidade de movimento
linear. O sistema
de equações foi resolvido pelo Método dos Elementos
Finitos. O sistema
de equações algébricas não-lineares resultante foi
resolvido pelo método de
Newton. Os resultados mostram o efeito do caráter
viscoelástico do líquido
na forma da superfície livre e a espessura do filme
líquido deixado na parede. / [en] Displacement of a liquid in a capillary tube by gas
injection occurs in many
situations, like enhanced oil recovery, coating of
catalytic converters and
gas-assisted injection molding. Generally the liquid being
displaced is a
polymeric solution or dispersion, which is not Newtonian.
Viscoelastic forces alter the force balance in various
parts of the flow and consequently
change the amount of liquid left attached to the capillary
wall. Models of
such flows must rely on theories that can account for the
different behavior
of microstructured liquids in simple shear and extensional
flow. Moreover,
displacement flows involve a free surface, and the domain
where the differential equations are posed is unknown a
priori being part of the solution.
These two characteristics make the problem extremely
complex. This problem was analyzed here both by
experiments and theory. The experiments
consisted of flow visualization and measurement of mass
displaced by a gas
bubble in a capillary tube filled with a viscoelastic
liquid. Various solutions of low molecular weight
Polyethylene Glycol (PEG) and high molecular
weight Polyethylene Oxide (PEO) in water were used in
order to evaluate
the effect of viscoelastic behavior on the flow. The
rheological properties
of the solutions were evaluated both in simple shear and
predominantly
extensional flows. In the theoretical analysis, the two-
dimensional free surface flow near the gas-liquid
interface was modelled using three different
differential constitutive equations that approximate
viscoelastic behavior of
dilute polymer solutions, namely Oldroyd-B, FENE-P and
FENE-CR, together with momentum and continuity equations.
The equation system was
solved with the Finite Element Method. The resulting non-
linear system of
algebraic equations was solved by Newton`s method. The
results show the
effect of the viscoelastic character of the liquid on the
free surface shape
and the film thickness attached to the capillary wall.
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[en] REPRESENTATION OF RETROGRADE CONDENSATION: FROM DIGITAL PETROPHYSICS IN MICRO-PORES TO SIMULATION AT FIELD SCALE / [pt] REPRESENTAÇÃO DA CONDENSAÇÃO RETRÓGRADA: DA PETROFÍSICA DIGITAL EM MICROPOROS À SIMULAÇÃO EM ESCALA DE CAMPOMANOELA DUTRA CANOVA 23 January 2024 (has links)
[pt] Campos de petróleo com gás não associado do tipo gás condensado possuem
destaque pelo maior valor econômico agregado associado a seu recurso energético:
a expressiva quantidade de condensado produzida, além do próprio gás. Porém, tais
reservatórios possuem um comportamento termodinâmico particular, induzindo
mudanças de composição e, consequentemente, fase ao longo do processo de
produção por depleção. Nas condições de reservatório, por exemplo, pode ocorrer
o fenômeno chamado de condensate blockage, em que bancos de condensado se
formam, geralmente em regiões próximas aos poços, dificultando assim o
escoamento e afetando a produção de gás.
A fim de definirmos a melhor estratégia de gerenciamento de um projeto a
ser implementado ao longo da explotação desse tipo de reservatório, uma
ferramenta importante utilizada pelos engenheiros é a simulação numérica.
Especialmente relacionadas à representação do fenômeno físico-químico citado,
nas simulações se utilizam as curvas de permeabilidade relativa. Na realidade,
porém, existe uma certa limitação de representatividade do fenômeno nos ensaios
laboratoriais praticados pela indústria e os melhores insumos poderiam ser
fornecidos por simulações em rede de poros, com modelos que representem a sua
alteração com função das mudanças na tensão interfacial e na velocidade de
escoamento ao longo do reservatório.
A reprodução de uma simulação de escoamento em rede de poros para a
escala mais próxima possível em uma simulação de simulador comercial de
diferenças finitas é validada. Da simulação em rede de poros até a escala de campo
praticada nas simulações de reservatórios, uma metodologia de scale-up é proposta,
utilizando um processo de otimização, procurando ser fiel à curva de
permeabilidade relativa original, em escala de microporo, obtida simulando
fenomenologicamente o processo de condensação no reservatório, através de um
modelo que reproduza sua dependência com a velocidade desenvolvida pelas fases
em meio poroso.
A comparação de produtividades na escala de campo e na evolução da
saturação de condensado em regiões próximas aos poços foi apresentada para as
três curvas de permeabilidade relativa utilizadas. Os resultados mostram que a
metodologia proposta consegue ser mais fiel à influência da condensação no
reservatório sobre a produtividade dos poços quando comparada ao insumo de
curva de permeabilidade relativa de ensaio laboratorial que apresenta o condensado
mais móvel. / [en] Oil fields with non-associated gas like gas condensate type stand out due to
the higher added economic value associated with their energy resource: the
significant amount of condensate produced, in addition to the gas itself. However,
such reservoirs have a particular thermodynamic behavior, inducing changes in
composition and, consequently, phase throughout the depletion production process.
Under reservoir conditions, for example, the phenomenon called condensate
blockage may occur, in which bridges of condensate are formed, usually in regions
close to the wells, thus hindering flow and affecting gas production.
In order to define the best management strategy for a project to be
implemented throughout the exploitation of this type of reservoir, an important tool
used by engineers is numerical simulation. The relative permeability curves are
used in the simulations, especially related to the representation of the mentioned
physical phenomenon. In reality, however, there is a specific limitation of
representativeness of the phenomenon in the laboratory tests carried out by the
industry, and the best inputs could be provided by simulations in a pore network,
with models that represent its alteration as a function of changes in interfacial
tension and flow velocity along the reservoir.
The reproduction of a pore network flow simulation to the closest possible
scale in a commercial finite difference simulation is validated. From the pore
network simulation to the field scale practiced in reservoir simulations, a scale-up
methodology is proposed, using an optimization process, seeking to be faithful to
the original relative permeability curve, on a microporous scale, obtained by
simulating phenomenologically the condensation process in the reservoir, using a
model that reproduces its dependence on the velocity flow developed by the phases
in a porous medium.
The three relative permeability curves used were presented by comparing
productivities at the field scale and the evolution of condensate saturation in regions
close to the wells. The results show that the proposed methodology proves to be
more faithful to the influence of condensation in the reservoir on the productivity
of the wells when compared to the relative permeability curve input from the
laboratory test, which presents the condensate with more mobility.
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Étude des paramètres affectant le transfert d'oxygène dans les vinsChiciuc, Igor 07 December 2010 (has links)
La micro-oxygénation des vins, par la dispersion de bulles d’oxygène, est une pratique de plus en plus utilisée dans le domaine de l’œnologie. Cette technique n’est pas toujours convenablement maitrisée par manque de connaissances scientifiques sur les paramètres régissant le transfert de l’oxygène. La recherche s'est focalisée sur l'étude des coefficients de transfert en fonction des composés du vin (CO2, éthanol, sucrose, consommateurs d’oxygène) et des conditions opératoires (type de diffuseur, température, rapport entre hauteur et diamètre du contenant de liquide). Les résultats montrent que lors de la micro-oxygénation, le dioxyde de carbone dissous et le sucrose ont une incidence négative sur le transfert alors que la présence d’éthanol améliore le transfert. En ce qui concerne les conditions opératoires, l’augmentation de débit de gaz et l’augmentation de rapport entre la hauteur et le diamètre de la cuve de micro-oxygénation joue positivement sur le transfert d’oxygène La surface spécifique des bulles et le coefficient de transfert de matière ont pu être dissociés pour les vins. La nature tensio-active des composés du vin semble être un élément important sur le transfert de matière. Les connaissances acquises ont été appliquées à la micro-oxygénation au cours de deux étapes de l'élaboration des vins : la fermentation alcoolique avec la maitrise de l’apport d’oxygène et la simulation de la technique d’élevage en barrique par micro-oxygénation couplée à l’ajout de copeaux de bois. Une nouvelle approche concerne l'étude d'un contacteur membranaire qui permet le transfert d’oxygène par diffusion. / Micro-oxygenation of the wines, by the dispersion of oxygen bubbles, is a practice increasingly used in oenology. This technique is not always suitably controlled for lack of scientific knowledge on the parameters governing the transfer of oxygen. Research was focused on the study of transfer coefficients in function of wine components (CO2, ethanol, sucrose, consuming oxygen) and of operating conditions (type of diffuser, temperature, relationship between height and diameter of the container of liquid). The results show that during micro-oxygenation, the dissolved carbon dioxide and the sucrose have a negative incidence on the transfer whereas the presence of ethanol improves the transfer. As operating conditions are concerned, the increase in gas output and the increase in micro-oxygenation tank height/diameter ratio positively influence oxygen transfer. For wines, the specific surface of the bubbles and the mass transfer coefficient could be dissociated. The surfactant nature of wine components seems to be the most important factor in mass transfer. The knowledge so acquired was applied to micro-oxygenation during two stages of wine making: alcoholic fermentation with the oxygen yield control and the simulation of ageing technique in barrels coupled with the wood chips addition. A new approach relates to the study of a membrane contactor application allowing the oxygen transfer by diffusion.
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Modélisation et simulation des dispositifs de ventilation dans les stockages de déchets radioactifs / Modelling and simulation of ventilation devices in nuclear waste geological repositoriesZhang, Yumeng 17 December 2015 (has links)
L'objectif de cette thèse est de fournir des modèles et des outils de simulation pour décrire les échanges de masse entre les circuits de ventilation (galeries) et les milieux poreux des ouvrages souterrains d'enfouissement des déchets nucléaires. La modélisation prend en compte le couplage à l'interface poreux-galerie entre les écoulements liquide gaz compositionnels dans le milieu poreux constituant le stockage et les écoulements gazeux compositionnels dans le milieu galerie libre. / The objective of this thesis is to develop models and algorithms to simulate efficiently the mass exchanges occurring at the interface between the nuclear waste deep geological repositories and the ventilation excavated galleries. To model such physical processes, one needs to account in the porous medium for the flow of the liquid and gas phases including the vaporization of the water component in the gas phase and the dissolution of the gaseous components in the liquid phase. In the free flow region, a single phase gas free flow is considered assuming that the liquid phase is instantaneously vaporized at the interface. This gas free flow has to be compositional to account for the change of the relative humidity in the free flow region which has a strong feedback on the liquid flow rate at the interface.
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Passive Gas-Liquid Separation Using Hydrophobic Porous Polymer Membranes: A Study on the Effect of Operating Pressure on Membrane Area RequirementMaxwell, Taylor Patrick 01 January 2012 (has links)
The use of hydrophobic porous polymer membranes to vent unwanted gas bubbles from liquid streams is becoming increasingly more common in portable applications such as direct methanol fuel cells (DMFCs) and micro-fluidic cooling of electronic circuits. In order for these portable systems to keep up with the ever increasing demand of the mobile user, it is essential that auxiliary components, like gas-liquid separators (GLS), continue to decrease in weight and size. While there has been significant progress made in the field of membrane-based gas-liquid separation, the ability to miniaturize such devices has not been thoroughly addressed in the available literature. Thus, it was the purpose of this work to shed light on the scope of GLS miniaturization by examining how the amount porous membrane required to completely separate gas bubbles from a liquid stream varies with operating pressure. Two membrane characterization experiments were also employed to determine the permeability, k, and liquid entry pressure (LEP) of the membrane, which provided satisfying results. These parameters were then implemented into a mathematical model for predicting the theoretical membrane area required for a specified two-phase flow, and the results were compared to experimental values. It was shown that the drastically different surface properties of the wetted materials within the GLS device, namely polytetrafluoroethylene (PTFE) and acrylic, caused the actual membrane area requirement to be higher than the theoretical predictions by a constant amount. By analyzing the individual effects of gas and liquid flow, it was also shown that the membrane area requirement increased significantly when the liquid velocity exceeded an amount necessary to cause the flow regime to transition from wedging/slug flow to wavy/semi-annular flow.
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Synergistes jonesii, gen. nov., sp.nov.: A Rumen Bacterium That Degrades Toxic PyridinediolsAllison, Milton J., Mayberry, Wiliam R., Mcsweeney, Christopher S., Stahl, David A. 01 January 1992 (has links)
This study was conducted to identify and characterize rumen bacteria that are able to degrade the toxic compound, 3-hydroxy-4(lH)-pyridone (3,4 DHP), that is produced in the rumen from mimosine. Mimosine is a non-protein amino acid that is found in leaves and seeds of Leucaena leucocephala, a leguminous tree used as a forage crop for ruminants in the tropics, and degradation of 3,4 DHP by ruminal microbes is critical for protection of animals from leucaena toxicity. Microbes with this capacity are, however, not ubiquitous and microbial populations in the rumens of animals in some parts of the world are unable to metabolize 3,4 DHP. Four strains of obligately anaerobic, gram-negative, rod-shaped bacteria that degrade 3,4 DHP were isolated from rumen contents from a goat in Hawaii. The isolates do not ferment carbohydrates, but are able to use both 3,4 DHP and its isomer, 3-hydroxy-2(lH)-pyridone (2,3 DHP), as well as arginine and histidine as substrates for growth. Comparisons of the 16S rRNA sequence from one of these isolates with sequences from a widely diverse group of bacteria agree with other information indicating that these isolates do not fit into any existing taxon. Thus, we are hereby proposing a new genus and species designation, Synergistes jonesii, for these organisms.
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