As propriedades mecânicas de componentes metálicos são influenciadas pela microestrutura que muitas vezes é determinada pelo ciclo de tratamento térmico submetido. No tratamento térmico de têmpera de aço: água, óleos, soluções poliméricas e soluções salinas podem ser utilizados como meio de resfriamento que apresentam diferentes características nos mecanismos de resfriamentos. Por exemplo, quando a água é usada como um meio de resfriamento uma estável camada de vapor é formada ao redor do metal em alta temperatura, resultando em uma transferência de calor não uniforme durante o processo de resfriamento, que geralmente é responsável por distorções e falhas no material. A adição de sal pode reduzir ou inibir a formação da camada de vapor melhorando a uniformidade de transferência de calor durante o resfriamento. Este trabalho objetiva-se em investigar o desempenho em resfriamento de diferentes soluções iônicas (NaCl, NaOH, NaNO2, Na2SO4, NaHCO3) variando-se a concentração, temperatura (25, 35 e 45°C) e agitação do meio (0, 500 e 800 rpm) e a sua utilização na têmpera de um aço de baixa temperabilidade. A caracterização destes meios e a influência de fatores externos foi realizada por meio de curvas de resfriamento, taxa de resfriamento, coeficiente de transferência de calor e fluxo de calor. A resposta a têmpera foi realizada em um aço SAE 1045 nas condições menos severas de resfriamento e caracterizada pelas medidas de dureza e avaliação metalográfica. A utilização de soluções iônicas, em geral, mostrou-se ser efetiva na inibição da camada de vapor, no aumento da extração de calor elevando-se as taxas de resfriamento e mantendo-se um alto fluxo de calor durante a maior parte da queda de temperatura, o que resulta em uma homogeneidade de resfriamento capaz de evitar distorções. Essas soluções mostraram-se ser capazes de temperar o aço SAE 1045. / The mechanical properties of steel components are influenced by the microstructure that is determined by the heat treatment cycle. In the quenching of the steel: water, oil, aqueous polymer solutions and aqueous salt solutions (brine) can be used as quenchants that exhibit different characteristic on cooling mechanisms. For example: when water is used as the cooling media, a stable vapor film is formed around the hot component resulting in non-uniformity of surface heat transfer during the cooling process which is often responsible for distortion and cracking. Salt addition can reduce or inhibit vapor film formation enhancing the uniformity of heat transfer during the cooling. This work will investigate the cooling performance of different ionic solutions (NaCl, NaOH, NaNO2, Na2SO4, NaHCO3) varying concentration, temperature (25, 35 and 45°C) and agitation of the quenchants (0, 500 and 800 rpm) and their use on quenching a low hardenable steel. The description of these medium and the influence of external factors were made using cooling curves, cooling rates, heat transfer coefficients and heat flux. Samples of SAE 1045 steel were quenched and evaluated by hardness measures and metallography. The use of ionic solutions, in general, has proved to be effective in to inhibit the vapor blanket, to increase heat extraction and keeping a high heat flux during the most part of the drop of the temperature that results in a homogeneous cooling able to avoid distortions. These solutions were abele to quench SAE 1045 steel.

In this thesis, a numerical model for coupled heat and moisture transfer in a run around membrane energy exchanger (RAMEE) with a liquid desiccant as a coupling fluid is developed. The numerical model is two dimensional, transient and is formulated using the finite difference method with an implicit time discretization. The model for the case of only heat transfer for a single heat exchanger is compared to an available analytical solution and good agreement is obtained. It is shown that the discrepancy between the numerical and theoretical dimensionless bulk outlet temperature of the fluids is less than 4% during the transient period. The model is also validated for the case of simultaneous heat and moisture transfer using experimental data measured during the laboratory testing of a RAMEE system. The results for both sensible and latent effectiveness showed satisfactory agreement at different operating conditions. However, there are some discrepancies between the simulation and the experimental data during the transient times. It is proposed that these discrepancies may be due to experimental flow distribution problems within the exchanger. The maximum average absolute differences between the measured and simulated transient effectivenesses were 7.5% and 10.3% for summer and winter operating conditions, respectively.<p> The transient response of the RAMEE system for step changes in the inlet supply air temperature and humidity ratio is presented using the numerical model. In addition, the system quasi steady state operating conditions are predicted as the system approaches its steady state operating condition. The effect of various dimensionless parameters on the transient response is predicted separately. These included: the number of heat transfer units, thermal capacity ratio, heat loss/gain ratio, storage volume ratio and the normalized initial salt solution concentration. It is shown that the initial salt solution concentration and the storage volume of the salt solution have significant impacts on the transient response of the system and the heat loss/gain rates from/to the circulated fluid flow can change the system quasi steady effectiveness substantially. The detailed study of the transient performance of the RAMEE is useful to determine the transient response time of the system under different practical situations.

In this thesis, a numerical model for coupled heat and moisture transfer in a run around membrane energy exchanger (RAMEE) with a liquid desiccant as a coupling fluid is developed. The numerical model is two dimensional, transient and is formulated using the finite difference method with an implicit time discretization. The model for the case of only heat transfer for a single heat exchanger is compared to an available analytical solution and good agreement is obtained. It is shown that the discrepancy between the numerical and theoretical dimensionless bulk outlet temperature of the fluids is less than 4% during the transient period. The model is also validated for the case of simultaneous heat and moisture transfer using experimental data measured during the laboratory testing of a RAMEE system. The results for both sensible and latent effectiveness showed satisfactory agreement at different operating conditions. However, there are some discrepancies between the simulation and the experimental data during the transient times. It is proposed that these discrepancies may be due to experimental flow distribution problems within the exchanger. The maximum average absolute differences between the measured and simulated transient effectivenesses were 7.5% and 10.3% for summer and winter operating conditions, respectively.<p> The transient response of the RAMEE system for step changes in the inlet supply air temperature and humidity ratio is presented using the numerical model. In addition, the system quasi steady state operating conditions are predicted as the system approaches its steady state operating condition. The effect of various dimensionless parameters on the transient response is predicted separately. These included: the number of heat transfer units, thermal capacity ratio, heat loss/gain ratio, storage volume ratio and the normalized initial salt solution concentration. It is shown that the initial salt solution concentration and the storage volume of the salt solution have significant impacts on the transient response of the system and the heat loss/gain rates from/to the circulated fluid flow can change the system quasi steady effectiveness substantially. The detailed study of the transient performance of the RAMEE is useful to determine the transient response time of the system under different practical situations.

The rate and extent of syneresis (whey expulsion) strongly affects cheese composition and quality. During salting, curd syneresis is influenced by the combined effect of both osmotic pressure and protein hydration. Our objective is to examine how cheese composition and whey expulsion are influenced by dry salting curd at various intervals, levels, applications, and potassium chloride (KCl) substitution, or change in calcium or sodium level in test solution (i.e., whey-brine). Four sets of unsalted fresh Cheddar curds were salted with different methods, with at least 3 replicates of each set on separate days. Set A was salted with 30 g/kg NaCl over 3 applications, either 5 or 10 min apart. Set B was salted with 30, 25, and 20 g/kg NaCl over 3 applications 5 min apart. Set C was salted with 20 g/kg NaCl using 1, 2, or 3 applications. Set D received salt consisting of a 2:1 molar ratio of NaCl and KCl over 3 applications 5 min apart. Whey was collected every 5 or 10 min until 30 or 40 min after the start of salting and subsequently pressed for 3 h. Using 10-min intervals delayed whey syneresis but after pressing there was no significant influence on final cheese composition. Decreasing salt levels significantly reduced the amount of whey expelled prior to pressing and resulted in cheeses with higher moisture and slightly lower pH. Adding salt over different applications did not significantly affect cheese composition. Partial substitution with KCl did not affect the amount of whey expelled or cheese moisture composition. Salted milled Cheddar cheese curd was immersed at 22°C for 6 or 18 h in test solution, with the addition of 1, 5, 10, or 20 g/L calcium, and 15 g/L salt. After immersion, curd weight change, moisture, pH, sodium, serum calcium and total calcium levels were measured. When calcium levels in solution increased, curd moisture, pH, and weight gain decreased while serum and total calcium levels increased significantly. Similarly, unsalted milled Cheddar cheese curds were immersed at 22°C for 6 h in test solution with 30, 60, 90, or 120 g/L salt in addition to 6 g/L calcium. The salt level in solution was inversely proportional with weight change, moisture, and salt level of curd.

Les matériaux cimentaires peuvent se détériorer grandement lorsqu'ils sont soumis à des cycles de gel/dégel avec ou sans sels de déverglaçage. Ceci peut porter atteinte à la durabilité à long terme des bétons/mortiers dans les régions aux hivers froids. Laissant de côté les processus d'endommagement et de rupture mécanique à l'oeuvre dans de tels problèmes, ce mémoire de thèse est consacré aux phénomènes physiques et thermo-mécaniques accompagnant la solidification de l'eau dans des solides poreux cohésifs, avec une attention particulière aux «propriétés matériau» issues de l'hydratation du ciment et de l'évolution de la microstructure. Ce travail reprend la poromécanique des milieux poreux partiellement gelés telle que développée par Olivier Coussy, tout en lui adjoignant une analyse de l'effet de la fin de la surfusion (en volume, hors contribution capillaire) et de la présence de sels dans le liquide saturant l'espace poreux. Nous avons mesuré la température de fin de surfusion en fonction de la concentration en sel. Ceci nous permet ensuite de calculer l'angle de contact entre la glace et les parois des pores dans le cadre classique de la nucléation hétérogène : on trouve que cet angle diminue avec la concentration en sel. Nous montrons que la dilatation instantanée consécutive à la fin de la surfusion dépend de la structure poreuse puisque cette dernière détermine la teneur en glace dans l'espace poreux. À l'aide de la distribution de tailles de pores estimée par porosimétrie par intrusion de mercure, nous estimons le degré de saturation en glace en fonction de la température et de la concentration initiale en sel via la relation de Gibbs-Thomson. Nous avons mesuré la déformation d'échantilllons de pâte de ciment saturées. L'analyse poromécanique montre que la déformation dépend de la concentration initiale en sel et de la structure poreuse des pâtes de ciment. En utilisant la même approche expérimentale sur des pâtes de ciment sèches, nous trouvons que la porosité (avec ou sans vide d'air entraîné) influence significativement le coefficient d'expansion thermique du matériau. En ce qui concerne les pâtes de ciment saturées, les mesures expérimentales et l'approche poromécanique en condition drainée ou non-drainée montrent que le degré de saturation initiale en liquide des vides d'air entraîné a un impact important sur la déformation de l'échantillon avec la température / When subject to freezing/thawing cycles with or without deicing salt, cement-based materials can suffer severe damage, which raises the long term sustainability problem of concrete/mortar in cold regions. Leaving aside the precise fracture mechanics and damage processes in this kind of problem, this PhD deals with the physical and thermomechanical phenomena undergone by cohesive porous solids under freezing, with particular attention to the material properties arising from cement hydration and microstructure development. The present work revisits the poromechanics of freezing porous materials developed by Olivier Coussy. This gives the opportunity to add the effect of the bulk supercooling and of salt in the liquid saturating the porous space.We measured the relation between depressed temperature at the end of bulk supercooling and salt concentration. We then obtained that the contact angle between ice and pore wall by heterogeneous nucleation decreases as salt concentration increases. We showed that the instantaneous dilation at the end of bulk supercooling is related to the pore structure because the latter determines the in-pore ice content. Using the pore size distribution measured by mercury intrusion porosimetry, we estimated the ice saturation degree with temperature and NaCl solution at different concentration through the Gibbs-Thomson equation. We measured the deformation of saturated cement pastes. The poromechanical analyses show that the strains depend on the initial salt concentration and pore structure of our cement pastes. By the same experimental approach on dried cement pastes, we concluded that the porosity (with or without air voids) has significant influence on the thermal expansion coefficient of our cement pastes. We also performed measurements on the deformation of saturated air entrained cement pastes. The results obtained by both experiments and poromechanical analyses under drained and undrained conditions showed that the initial saturation degree in air-voids has significant influence on the deformation curves with temperature

A liquid-to-air membrane energy exchanger (LAMEE) is a novel flat-plate membrane-based energy exchanger where heat and moisture transfer between air and solution streams occurs through a semi-permeable membrane. The LAMEE consists of many air and solution flow channels, each separated by a membrane. A small-scale single-panel LAMEE consists of a single pair of neighboring air and solution channels. This PhD thesis focuses on developing, testing and modeling the small-scale single-panel LAMEE, and investigating the similarity between the small-scale LAMEE and a full-scale LAMEE. This PhD thesis presents a methodology to investigate similarity between small-scale and full-scale energy exchangers. A single-panel energy exchanger test (SPEET) facility is developed and built to measure the performance of the small-scale single-panel LAMEE under different test conditions. Also, the small-scale LAMEE is numerically modeled by solving coupled heat and mass transfer equations for the air, solution and membrane of the LAMEE. The effects of membrane vapor diffusion resistance and enhanced air side convective heat transfer coefficient are numerically investigated. The numerical model of the small-scale LAMEE is validated with the experimental data for summer test conditions, and effectiveness values agree within ±4% in most cases. Moreover, the effects of different heat and mass transfer directions, and salt solution types and concentrations are experimentally and numerically investigated. The results show that the LAMEE effectiveness is strongly affected by the heat and mass transfer directions but negligibly affected by salt solution type and concentration. The solution-side effectiveness for liquid-to-air membrane energy exchangers is introduced in this thesis for the first time. The results show that the solution-side effectiveness should be used to evaluate the sensible and total effectiveness of LAMEE regenerators. Finally, the similarity between the small-scale and full-scale LAMEEs is investigated experimentally and numerically. The results show that the small-scale LAMEE effectiveness results can be used to predict the performance of a full-scale LAMEE within ±2% to ±4% in most cases.

Submitted by Luciana Sebin (lusebin@ufscar.br) on 2016-10-05T13:14:46Z No. of bitstreams: 1 DissNBD.pdf: 2471615 bytes, checksum: a8204662dfb8062a11f60b9f5723d468 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-10-13T20:17:50Z (GMT) No. of bitstreams: 1 DissNBD.pdf: 2471615 bytes, checksum: a8204662dfb8062a11f60b9f5723d468 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-10-13T20:18:10Z (GMT) No. of bitstreams: 1 DissNBD.pdf: 2471615 bytes, checksum: a8204662dfb8062a11f60b9f5723d468 (MD5) / Made available in DSpace on 2016-10-13T20:18:20Z (GMT). No. of bitstreams: 1 DissNBD.pdf: 2471615 bytes, checksum: a8204662dfb8062a11f60b9f5723d468 (MD5) Previous issue date: 2016-02-26 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Paspalum is the most important genus of Poaceae family in the Americas, with about 330 species and occurs throughout Brazil, Bolivia, Paraguay, Argentina and Uruguay. In Brazil, except for the Pampa Biome, the use of species of this genus as a cultivated forage is still very small. Species of the informal group Plicatula are among the most promising Paspalum genotypes for forage quality. The majority of Paspalum accessions is tetraploid and apomitic. The sexual cytotypes are rare in the Plicatula group. To add features located in different accessions, it is necessary to cross sexual species in tetraploid level with apomictic genotypes that are interesting to breeding programs and select those that have better agronomic characteristics. For the occurence of hybridization, the flowering synchronization betwemn parents is essencial. An interesting tool for this is the cryopreservation of pollen. P. notatum, popularly known as bahiagrass, is a species from Notata group and is widely used in the United States as forage. Diploid and tetraploid accessions are observed in this species and, it is easy to obtain large amounts of pollen. The purpose of this study was to evaluate the cryopreservation of pollen of P. notatum, as a model for future conservation and synchronization of flowering of other species that are interesting for breeding program. The P. notatum pollen grains were collected in the field at Embrapa Southeast Livestock. Four dehydrating agents were tested (LiCl, MgCl2, NaOH and Silica gel) with three distinct periods of exposion (30, 60 and 120 minutes). After slow thawing, pollen grains were evaluated for viability by staining with tetrazolium solution 0.25% and in vivo germination by fluorescence. The viability of fresh pollen grains was also evaluated as a control. For comparison, pollen grains were stored in freezer and refrigerator conditions for a period of 10, 60, 120 and 180 days. The data showed that the dehydration of Paspalum notatum pollen with lithium chloride during 30 minutes and silica gel during 120 minutes was adequated for the conservation in liquid nitrogen and freezer as the viability of pollen after this treatment remained equal to the control. The pollen preservation in the refrigerator without dehydration since 10 days may be an alternative for short-term storage situations. Dehydration results with dehydrated magnesium chloride for 30 and 60 minutes and dehydrated sodium hydroxide for 60 and 120 9 minutes were also statistically similar to the control. The use of the tetrazolium sollution and in vivo germination were an effective technique to evaluate the viability of pollen grains after liquid nitrogen conservation. The use of tetrazolium was also efficient for the evaluation of pollen grains after storage in freezer and refrigerator. / Paspalum é o mais importante gênero da família Poaceae nas Américas, com cerca de 330 espécies e ocorre em todo Brasil, Bolívia, Paraguai, Argentina e Uruguai. No Brasil, a exceção do Bioma Pampa, o uso deste gênero como forrageira plantada ainda é muito pequeno. As espécies pertencentes ao grupo informal Plicatula são consideradas entre as mais promissoras pela qualidade forrageira. A grande maioria dos acessos de Paspalum é tetraplóide e apomítico. São raros os citotipos de espécies do grupo Plicatula sexuais. Para agregar características localizadas em acessos distintos, é necessário cruzar espécies sexuais já em nível tetraplóide com genótipos apomíticos promissores e selecionar os que tem melhores características agronômicas. Para isso, há a necessidade de sincronização de florescimento entre os genitores. Uma ferramenta interessante para isso é a criopreservação de pólen. A espécie P. notatum, conhecida popularmente como grama-batatais, do grupo informal Notata, é muito usada nos Estados Unidos para produção de forragem. Já foram observados acessos diplóides e tetraplóides dessa espécie, sendo fácil a obtenção de grande quantidade de pólen. A proposta desse trabalho foi estudar a criopreservação de pólen de P. notatum, como um modelo, para futuramente conservar e sincronizar o florescimento de outras espécies com características de interesse para o melhoramento. Os grãos de pólen de P. notatum foram coletados em campo na Embrapa Pecuária Sudeste. Foram testados quatro agentes de desidratação (LiCl, MgCl2, NaOH e sílica gel) e um tratamento sem desidratação, todos por três tempos distintos (30, 60 e 120 minutos). Após descongelamento lento, os grãos de pólen foram avaliados quanto à viabilidade por coloração com solução de tetrazólio 0,25% e por germinação in vivo via fluorescência. A viabilidade de grãos de pólen recém-colhidos também foi avaliada como controle. Para efeitos de comparação, foram armazenados grãos de pólen em condições de freezer e geladeira, por um período de 10, 60, 120 e 180 dias. Os dados demonstraram que a desidratação de pólen de Paspalum notatum com cloreto de lítio por 30 minutos e sílica gel por 120 minutos foi adequado no armazenamento em nitrogênio liquido e em freezer, pois a viabilidade permaneceu igual aos grãos de pólen recém-colhidos 7 (testemunha). A conservação de pólen em geladeira sem desidratação por até 10 dias pode ser uma alternativa em situações de armazenamento a curto prazo. A conservação de pólen em freezer por até 60 dias também pode ser uma alternativa, já que além dos tratamentos citados acima, resultados de desidratação com cloreto de magnésio desidratado por 30 e 60 minutos e hidróxido de sódio desidratado por 60 e 120 minutos também foram estatisticamente iguais a testemunha. O uso do corante de tetrazólio e da técnica de germinação in vivo foram eficientes para a avaliação da viabilidade de grãos de pólen após o armazenamento de nitrogênio líquido. O uso do corante de tetrazólio também foi eficiente para a avaliação dos grãos de pólen após o armazenamento em freezer e em geladeira.

Master of Public Health - MPH / This mini-thesis, assessed the use of ORT as a treatment for childhood diarrhoea in primary health care facilities in the Cape Metropole from the caregivers' perspective. Awareness and knowledge of oral rehydration therapy (ORT) and the preparation abilities of sugar salt solution (SSS) by caregivers of children younger than 5 years attending the health facilities were assessed. The availability of resources and utensils for the use of ORS packets and SSS and the accessibility to health facilities by caregivers were also determined. Using a cross sectional descriptive study design, a baseline situation review was carried out. Primary health care facilities in three heath districts namely; Khayelitsha, Nyanga and Oostenberg were purposely selected. Ninety-two caregivers in 12 facilities participated in the study. Basic analyses of quantitative data were done using Epi-Info 2002 software. Qualitative data were analysed manually. The study found that according to caregivers, all facilities used ORS packets as their immediate treatment for uncomplicated diarrhoea, and recommended sugar salt Diarrhoea Management in PHC Facilities solution as home treatment. Ninety-one percent of caregivers used ORT at home before they presented to the health facility.Of the caregivers who were advised by the health worker to use SSS at home, 60.7%, 55.8% and 60.2% in Oostenberg, Khayelitsha and Nyanga districts respectively remembered the correct ingredients and quantities to make the solution at home. Of those given ORS packets, 94.5%, 99.0% and 98.5% respectively, remembered the quantity of water to be mixed with each packet. Packets were found to be convenient and were preferred by many caregivers as compared to SSS. The advice or health education messages given to caregivers were often unclear, and there were language barriers in Brighton and Bloekombos clinics in the Oostenberg district. A litre bottle was available in 47% of caregivers' homes, 82 % had a teaspoon and all of them had access to running water. Twelve percent and 11 % admitted to not having sugar and salt respectively when they wanted to make SSS. Eighty-eight percent walked to the health facility and 12% used taxis or buses. The study concludes that ORT is widely used in primary health care facilities for diarrhoeal disease treatment, however caregiver's knowledge and preparation abilities of SSS is still limited. The resources and utensils to prepare ORT at home were fairly available in many homes, which makes SSS preparation at home feasible and acceptable.

Corrosion represents the single most frequent cause for product replacement or loss of product functionality with a 5% coat to the industrial revenue generation of any country in this dissertation the efficacy of using filled coatings as a protection coating are investigated. Fillers disrupt the polymer-substrate coating interfacial area and lead to poor adhesion. Conflicting benefits of increasing surface hardness and corrosion with long term durability through loss of adhesion to the substrate are investigated. The effects of filler type, filler concentration and exposure to harsh environments such as supercritical carbon dioxide on salt water corrosion are systematically investigated. The constants maintained in the design of experiments were the substrate, AISI-SAE 1018 steel substrate, and the corrosive fluid synthetic sea salt solution (4.2 wt%) and the polymer, Bismaleimide (BMI). Adhesion strength through pull-off, lap shear and shear peel tests were determined. Corrosion using Tafel plots and electrochemical impedance spectroscopy was conducted. Vickers hardness was used to determine mechanical strength of the coatings. SEM and optical microscopy were used to examine dispersion and coating integrity. A comparison of fillers such as alumina, silica, hexagonal boron nitride, and organophilic montmorillonite clay (OMMT) at different concentrations revealed OMMT to be most effective with the least decrease in adhesion from filler-substrate contact. Subsequently examining filler concentration, a 3 wt% OMMT was found to be most effective. A comparison of unmodified and modified BMI with 3 wt% OMMT exposed and not exposed to supercritical carbon dioxide showed that the BMI provided better corrosion protection; however, OMMT provided better wear, shear, and hardness performance.

No description available.