Understanding the physics of water evaporation from saline porous media is important in many processes such as soil salinity, terrestrial ecosystem functioning, vegetation and crop production, biological activities in vadose zone, and CO2 sequestration. Precipitation of salt is one of the possible outcomes of the evaporation process from saline porous media which may either enhance or interrupt the desired process depending on the localization and pattern of the precipitated salt. In the present study X-ray micro tomography was used to study the 3D dynamics and patterns of salt deposition in drying porous media under different boundary conditions and the effects of salt concentration, particle size distribution and shape of grains on the precipitation patterns and dynamics at pore-scale have been investigated. Evaporation process from porous media involves preferential invasion of large pores on the surface while the fine pores remain saturated serving as the evaporation sites to supply the evaporative demand. This results in increasing salt concentration in fine pores during evaporation. Precipitation starts when salt concentration exceeds the solubility limit in the preferential evaporation sites. At the early stages, the precipitation rate increases with time until all evaporation sites at the surface reach the solubility limit and turn into the precipitation sites. This is followed by a constant rate of precipitation proportional to the evaporation rate. We show that the formation of salt crust at the surface does not immediately interrupt the evaporation process due to the porous nature of the precipitated salt investigated using the scanning electron microscopy. Also, our results confirmed the formation of discrete efflorescence at the surface of porous media due to the presence of pores with different sizes. Distribution of these fine pores on the surface directly influences the patterns of salt precipitation and thickness of the salt crust such that in the media with more fine pores, precipitated salt forms a thinner crust as the solute transferred to the surface is distributed among more evaporation sites. In contrast, in the media with fewer evaporation sites at the surface the salt crust will be more discrete but thicker. A simple equation is also proposed to estimate the evolution if the thickness of the salt crust on the surface of porous media. Our results provide new insights regarding the physics of salt precipitation and its complex dynamics in porous media during evaporation.

Afin de mieux comprendre la stabilité des mousses de verre, des expériences à l'échelle d'une bulle et d'un film vertical sont réalisées pour différentes composition de verre, viscosité, taille de bulle, et gaz à l'intérieur de la bulle. L'épaisseur du film au-dessus de la bulle est mesurée par interférence optique et décroît exponentiellement avec le temps sous l'effet des forces de pesanteur et capillaires. Le temps de vie de la bulle doit être divisé en deux étapes. En premier, le taux d'amincissement dépend du nombre de Bond. Ensuite, un écoulement contraire est observé aux fortes températures pour les verres sodo-sili-calcite. Ce phénomène également observé pour des films verticaux et s'explique par des écoulements Marangoni dus à l'évaporation de substances telles que le sodium qui engendre des variations de composition et de tension de surface. Des petites bulles sont crées à la surface libre lors de l'éclatement de grosses bulles à la surface d'un verre fondu faiblement visqueux / For investigating glass foams stability, experiments with a single bubble rising towards the free surface of molten glass and with vertical films are performed for several values of glass chemical composition, viscosity, bubble size and gas nature. The glass lamella on top of the bubble is observed by video-recording and its thickness evolution is measured by optical interferometry. The lamella thins as a result of buoyancy and capillary forces and then it ruptures. Actually the lamella thinning occurs in two steps. In the first step, the drainage is regular and the thinning rate depends on Bond number. In the second step a backward flow is observed above 1200°C for ordinary soda-lime-silica glass, which is explained as Marangoni counter flow due to evaporation of volatile species such as sodium. As the lamella ruptures tiny bubbles are created by the rupture of bubble lamella on the free surface for large bubbles and low viscosity of the melt

Orientador: Jose Teixeira Filho / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agrícola / Made available in DSpace on 2018-08-14T15:58:35Z (GMT). No. of bitstreams: 1 Castilho_CamilaPrazeresGoncalvesde_D.pdf: 1491834 bytes, checksum: 834593c3472a9aa69686f15dfcfd5ffd (MD5) Previous issue date: 2005 / Resumo: O estudo dos mecanismos hidrológicos bem como a determinação das disponibilidades hídricas em bacias hidrográficas fornecem condições para avaliação dos recursos hídricos. O modelo semi-distribuído de transformação de chuva em vazão TOPMODEL tem sido, mundialmente utilizado por pesquisadores, desde seu desenvolvimento em 1979. O trabalho desenvolvido utilizou o TOPMODEL para simular o comportamento hidrológico de uma bacia rural com área de 4,6km2, cultivada predominantemente com cana-de-açúcar, localizada na região do município de Limeira-SP. O modelo foi aplicado em duas fases: isoladamente e acoplado a um modelo de interceptação de chuva pela cobertura vegetal, considerando duas hipóteses (H1 e H2) para a distribuição da precipitação interceptada ao longo do tempo. Na hipótese H1, a precipitação interceptada (PP) é distribuída uniformemente ao longo do tempo, sendo que cada valor de precipitação ao longo do tempo do evento em análise é multiplicado por um coeficiente de correção j, calculado por meio da relação entre a precipitação interceptada e incidente. Na hipótese H2, a quantidade total de precipitação interceptada (PP) durante o evento analisado é subtraída do primeiro valor de chuva do evento (P1), ou, dos primeiros valores caso PP seja maior que Pn. A aplicação do modelo TOPMODEL isoladamente apresentou valor médio de eficiência de Nash e Sucliffe de 50,8%, sendo a variação média entre valores de vazão máxima observada e simulada igual a 0,6%. Quando foi considerada a hipótese H1, esses valores foram: 41,3% e -2,5%, respectivamente. Para a hipótese H2, os valores foram 48,6% e -2,0%. Os resultados mostraram que a utilização do modelo TOPMODEL em conjunto ao modelo de interceptação vegetal apresentaram-se muito próximos aos obtidos considerando o TOPMODEL em suas condições originais, e ainda produz melhora na qualidade da informação a respeito do comportamento hidrológico da bacia. / Abstract: The study of hydrological mechanisms as well as determination of available water in watersheds provides conditions for assessment of water resources. The semi-distributed model of rainfall transformation into flow TOPMODEL has been widely used by researchers, since its development in 1979. This paper describes the use of TOPMODEL to simulate the hydrological behavior of a rural watershed with an area of 4.6 km2, mainly cultivated with sugar cane, located in the city of Limeira, in the State of São Paulo. The model was implemented in two phases: isolated and coupled with a model of rainfall interception by vegetation, considering two hypotheses (H1 and H2) for the distribution of precipitation intercepted over time. In hypothesis H1, the intercepted precipitation (PP) is evenly distributed over time, and each value of rainfall over time of the event in question is multiplied by a coefficient of correction a, calculated using the relationship between the intercepted and incident precipitation. In hypothesis H2, the total amount of intercepted precipitation (PP) during the event analyzed is subtracted from the first value of the rainfall event (P1) or from the first amounts, in case PP is greater than Pn. / Doutorado / Agua e Solo / Doutor em Engenharia Agrícola

Orientador: Giselle Maria Marchi Baron / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba / Made available in DSpace on 2018-08-26T22:21:22Z (GMT). No. of bitstreams: 1 Araujo_LarissaSgarbosaNapoleaode_D.pdf: 2549367 bytes, checksum: e7199299128873b8a98a1902b9a67070 (MD5) Previous issue date: 2015 / Resumo: O resumo, na íntegra, poderá ser visualizado no texto completo da tese digital / Abstract: The complete Abstract is available with the full electronic digital thesis or dissertation / Doutorado / Dentística / Doutora em Clínica Odontológica

O solo fornece suporte e atua como reservatório de água para as plantas, promovendo condições fundamentais ao crescimento de raízes e à dinâmica da água e nutrientes. O conhecimento de suas propriedades hidráulicas, como a curva retenção da água, é de grande importância na descrição e predição dos processos de transporte da água e solutos. O objetivo deste trabalho foi determinar a curva de retenção pelo método tradicional dos funis e câmaras de pressão de ar com placa porosa, pelo método de campo utilizando tensiômetros e pelo método da evaporação da água em amostra de solo no laboratório munida de tensiômetro. O solo utilizado para estudo foi classificado como Nitossolo Vermelho eutrófico de textura argilosa, e estava sendo cultivado com café há mais de 10 anos. A comparação entre as curvas obtidas pelos três métodos indicou que o método da evaporação diferiu estatisticamente do método do funil e câmara e foi estatisticamente idêntico ao método do tensiômetro a campo. Por sua facilidade de execução, baixo custo e rapidez na determinação da curva de retenção até a tensão de aproximadamente 100 kPa, o método da evaporação aqui apresentado é uma boa opção de utilização. Com relação ao método do tensiômetro no campo, embora mais realístico, é muito trabalhoso. / Soil provides support and acts as a water reservoir to plants, promoting essential conditions to root growth and to water and nutrient dynamics. The understanding of its hydraulic properties, like the water retention curve, is of great importance for the description and prediction of the processes of water and solute transport. The objective of this study was to determine soil water retention curve through the traditional method using porous plate funnel and pressure chamber, through the field method using tensiometers and through the water evaporation in soil sample with tensiometer in the laboratory. The studied soil was classified as clayey Rhodic Hapludox, which had been cultivated with coffee for more than 10 years. The comparison of curves obtained through the three methods indicated that the evaporation method was statistically different from the method using funnel and chamber, and statistically equal to the method of tensiometers at field. For its easy execution, low cost and quickness to determine soil water retention curve until the tension of about 100 kPa, the evaportation method presented here is a feasible option. As for the method of tensiometers at field, although it is more realistic, it is very laborious.

L'objectif de cette étude est de concevoir un système de refroidissement passif au sein d'un data center. La solution qui a été choisie est la boucle thermosiphon, combinant le free cooling et le refroidissement par changement de phase. Cette technologie offre de la simplicité et de la compacité. De plus, en l'associant avec des échangeurs de chaleur à micro-canaux, elle est capable d'absorber de grandes quantités de flux de chaleur avec un faible débit du réfrigérant. La boucle thermosiphon est composée d'un évaporateur à mini-canaux et à courants parallèles, d'un condenseur à air, d'un riser et d'un downcomer. Un prototype expérimental a été construit afin de caractériser les transferts de chaleur entre le réfrigérant et la chaleur créée. Des études expérimentales sont introduites. L'influence du taux de chargement et de la puissance électrique est détaillée et analysée. En parallèle, un modèle numérique a été développé pour prédire les caractéristiques du réfrigérant en fonction des paramètres géométriques et climatiques. Une comparaison avec les résultats expérimentaux est également effectuée. Enfin, la boucle thermosiphon est améliorée avec l'ajout d'un second évaporateur. Les tests sont effectués avec des puissances plus importantes. Une nouvelle conception d'une boucle thermosiphon et les limites du prototype sont présentées. / The objective of this study is to build a passive cooling system in a data center. The chosen solution is the loop thermosyphon, combining free cooling and two-phase cooling. This technology offers simplicity and compactness. Furthermore, by associating with micro-channels heat exchangers, it is able to remove higher heat fluxes while working with smaller mass flow rate of coolant. The thermosyphon is composed by mini-channel parallel-flow evaporator, an air condenser, a riser and a downcomer. The experimental setup has been built to characterize the heat transfer between the working fluid and the provided heat. An experimental study is introduced. The effect of the fill ratio and the input power is specified and analyzed. In parallel, a numerical model has been developed to predict the fluid properties in function of geometrical and climatic parameters. A comparison between experimental and numerical results is also carried out. Finally, the loop thermosyphon is upgraded with a second mini-channel parallel flow evaporator. Tests are conducted with huger heat flux. A new design of loop thermosyphon and the limits of the prototype are introduced.

No description available.

Proper disposal of industrial brine has been a critical environmental challenge. Driven by the even-tightening environment protection regulations, the Zero-Liquid-Discharge (ZLD) has gradually become mandatory option for brine disposal, but its application is limited by the intensive energy consumption. The recent development of solar crystallizer provides a new strategy to achieve ZLD brine disposal. However, the research on solar crystallizer, employing photothermal material to convert solar energy to heat for interfacial brine evaporation and crystallization, is still at the early stage. This dissertation thoroughly investigated the solar crystallizer-based ZLD technology in a broad scientific and application context. The scaling formation while treating real brine, which has been the major barrier to the application of solar crystallizer, was confirmed first with a solar crystallizer device. With a rational designed anti-scaling mechanism, the scaling-free crystallization behavior and stable high water evaporation rate of 2.42 kg m-2 h-1 was achieved when treating real seawater brine. After verifying the feasibility of solar crystallizer towards real brine treatment, its performance was further improved by integrating convective airflow, which provided considerable environmental energy for water evaporation. Both experiment results and COMSOL simulation results confirmed that the maximum environmental energy harvesting can be achieved with the proper size of solar crystallizer. At last, this dissertation pioneered a novel concept of integrating adsorption process into solar crystallizer for simultaneously ZLD brine treatment and potassium extraction. Owing to the special ion concentration behavior of solar crystallizer, the adsorption capacity and selectivity coefficient of absorbent was enhanced by 19.5% and 48.8%, respectively, comparing with traditional bulk adsorption. This dissertation potentially unlocks a new generation of ZLD technology with low carbon footprint and source recovery. More research efforts will be inspired on its applications in real scenarios.

The diploma thesis is focused on the investigation of the effect of zinc release during ferritic sintering on the permeability/inductance of ferrite ceramics. The theoretical part deals with the position of ferrites among other ceramic materials. It describes the basic characteristics of ferrites, their crystal structure and finally the problems that are directly related to their production and which fundamentally affect the magnetic properties of ferrites. In the second part of the work, the influence of the temperature and time of sintering and the position of the cores in the furnace during firing on the loss of zinc from the sample and subsequently on the electromagnetic properties of the prepared test specimens from industrial raw material mixtures was investigated. These are initial experiments, which will be followed by further research aimed at eliminating the problem of zinc loss in the production of Mn-Zn ferrites.

This thesis deals with preparation of organic molecular thin film compounds and its properties like morphology and purity. The vapour deposition was used for thin films preparation, because used materials are very few soluble. Thin films properties were characterized with the infrared spectroscopy (FTIR) and scanning electron microscope. There are described basics of infrared spectroscopy, spectra measurement and interpretation in the theoretical part. Process of thin film preparation is also described in this part. In the experimental part are described used vacuum technology and measuring instruments, process of sample measurement and there is the list of studied materials. 12 derivates of diketopyrrolopyrrols (DPP) were studied in this thesis. Diketopyrrolopyrroles (DPP) and its derivates have interesting chemical and physical properties, expecting wide range of applications, especially in electronics industry.