Afin de modéliser correctement les phénomènes liés à l'évaporation, les numériciens souhaitent obtenir des mesures expérimentales fiables, leur permettant d'améliorer leurs modèles. A l'opposé, de nombreux industriels souhaitent pouvoir réaliser des mesures in situ, avec des techniques expérimentales appliquées aux conditions réelles.C'est dans ce cadre que s'est inscrite cette thèse. L'objectif principal, a été de démontrer la faisabilité, et la stabilité, de mesures en réfractométrie d'arc-en-ciel sur des gouttes uniques en écoulement afin d'obtenir le taux d'évaporation de ces gouttes.L'utilisation d'un dispositif dédié habituellement à la PIV a servi à réaliser des acquisitions de couples d'images, séparées par un délai temporel variable. Une méthode très fine de la mesure de variation de diamètre a été introduite, autorisant la mesure du taux d'évaporation instantané d'une goutte en écoulement par le biais du déphasage de la structure de ripple. / In order to model correctly the evaporation phenomenon, numerical simulations needs to work with reliable experimental data, allowing to improve the existing models. On the other side, industrialists needs to realize in situ measurements, with experimental techniques that apply to real conditions. This is the framework of this thesis. The main work has been to prove that measurements with rainbow refractometry on unique droplets in a flow were possible, obtain the evaporation rate from those measurements, and prove their stability.The use of a specific setup, most of the time used in PIV, allowed us to realize acquisitions of couple images with a temporal delay. A very fine method for the measurement of variation of diameter has been introduced, allowing the measurement of instantaneous evaporation rate of unique droplets in a flow, using the ripple structure phase shift.

An ancient technology of solar-driven water evaporation and distillation has recently been revived due to the concept of interfacial solar evaporation and the development of photothermal materials. There have been many research interests in improving solar light harvesting and solar-to-water evaporation efficiency within these systems, including new photothermal materials search, structural engineering, and thermal management. The application horizon of both solar-driven water evaporation and distillation has been broadly expanded beyond their conventional domain, including now wastewater treatment, seawater desalination, steam sterilization, electric generation, and chemicals/fuels productions. This dissertation focused on designing of photothermal materials and their applications to clean water production. More specifically: (1) a bi-layered porous rGO membrane with a polystyrene (PS) foam as the heat insulator was designed and proved to be effective for reducing heat conduction to the bulk water and to improve the solar-to-water evaporation efficiency, (2) a tandem-structured SiC-C ceramic monolith was prepared and demonstrated to be mechanically and chemically stable to withstand physical or chemical cleaning during long-term use in real seawater and wastewater, (3) in order to simultaneously treat the contaminated water and get clean distillate water, multi-functional SiC foam modified with mesoporous Au/TiO2 nanocomposites has been prepared, which was demonstrated to possess both photocatalytic reduction and oxidation abilities for complex wastewater treatment, and (4) when the water source was contaminated by VOCs, another efficient multi-functional photothermal material was designed with a honeycomb ceramic plate as the matrix material, and a CuFeMnO4 nanocomposite coating layer acting as both photothermal material and Fenton agent for VOCs removal. Therefore, the light absorption property of photothermal material could be improved by using a porous structure, tandem-structure, porous foam or 3D structure. The solar-to-water evaporation efficiency was improved by including a heat insulator and the reduction of the water channels’ dimension. The ceramic-based material showed potential for long-term use with high mechanical strength to endure physical cleaning. Multi-functional photothermal materials were successfully developed for complex wastewater treatment and clean water generation.

Experimental and theoretical simulations of a novel sustainable desalination process have been carried out. The simulated process consists of pumping seawater through a solar heater before flashing it under vacuum in an elevated chamber. The vacuum is passively created and then maintained by the hydrostatic balance between pressure inside the elevated flash chamber and outdoor atmospheric pressure. The experimental simulations were carried out using a pilot unit built to depict the proposed desalination system. Theoretical simulations were performed using a detailed computer code employing fundamental physical and thermodynamic laws to describe the separation process, complimented by experimentally based correlations to estimate physical properties of the involved species and operational parameters of the proposed system setting it apart from previous empirical desalination models. Experimental and theoretical simulation results matched well with one another, validating the developed model. Feasibility of the proposed system rapidly increased with flash temperature due to increased fresh water production and improved heat recovery. In addition, the proposed desalination system is naturally sustainable by solar radiation and gravity, making it very energy efficient.

The removal of vegetation and overburden changes the naturalwater purifying processes and thus decreases the groundwaterprotection in gravel pit areas. The sand and gravel depositsusedfor aggregate extraction in Sweden are also often valuablefor extraction of groundwater as a drinking water resource. TheSwedish legislation requires that gravel pits be restored afterthe cessation of extraction, the aim being to reestablishvegetation and to reinstate groundwater purifyingprocesses. The objective of this study was to improve our understandingof the processes governing groundwater protection andvegetation establishment so that these could be applied toimproving restoration methods for reestablishing naturalgroundwater protection. The focus was on the importance of soilphysical properties of the topsoil for vegetation establishmentand groundwater recharge. Actual field methods for restoration were reviewed.Conflicts between aggregate extraction and groundwaterinterests were common. In many cases the actual restorationcarried out differed from pre-planned specifications in permitdocumentation. Commonly available substrates that might be used forrestoration of gravel pits were investigated. The soils weredescribed as regards texture, organic content, porosity, waterretention and hydraulic conductivity. The way in which acombination of the water retention characteristic and theunsaturated conductivity influenced the behaviour of thesoil-plant-atmosphere system was demonstrated using aprocess-orientated simulation model. Plants with well-developedaboveground characteristics and shallow roots in particularexerted the highest requirements on the soil physicalproperties. Key words:groundwater protection, soil physicalproperties, CoupModel, unsaturated conductivity, waterretention, transpiration, soil evaporation

NR 20140805

The impact of long term management strategies of irrigation with saline water in semi-arid region of Gordonia, South Africa is the highest interest to optimize water consumption, soil conservation, and crop yield for sustainable water allocations to human food production and ecosystem without irreversible damages to soil and water body. An integrated ecosystem assimilation, in shape of soil-water storage model based on physical approach for 30-year simulation run defined in form of digital ecosystem modelling with help of CoupModel tool to assemble together the most important underlying processes of soil hydraulics, irrigation demands, leaching fraction, evapotranspiration, salt transport. Two scenarios of water management strategy; surface as traditional and drip as subsurface irrigation considered to apply water and salt into the ecosystem model. Gaining high food production for human with respect to ecosystem sustainability, in each water management scenario studied by evaluating general and detailed result from water and salt balance for the entire simulation period plus long term nitrogen and carbon turnover as crop yield indicator. Non-productive water losses, salt accumulation in root zone, carbon and nitrogen turnover, salt transport to aquifer via deep percolation observed thoroughly. Decline in crop yield due to water and salt stress, conducted by monitoring biomass production with respect to water consumption and soil osmotic pressure in root zone. Drip scenario had better functionality to perform less water wastage by decreasing soil evaporation as non-productive water loss almost 40 %, however productive water consumption decreased 20 % due to insufficient leaching fraction and also salt accumulation increased in root zone. Precipitation had a significant role to accomplish leaching deficiency and removing salt from root zone. Salt accumulation flushed out from root zone by more leaching, though resulting more water wastage and more possibility of salinization threatening beneath aquifer. Ecosystem in terms of soil-water and plant responding differently facing salinity in different water management practices and salt as source of pollution could either stabilized in soil by accumulating in root zone causing anthropogenic soil desertification or percolate to beneath aquifer resulting aquifer salinization.

>Magister Scientiae - MSc / Water is a fundamental resource and key in the provision of energy, food and health. However, water resources are currently under severe pressure as a consequence of climate change and variability, population growth and economic development. Two driving factors that affect the availability of water resources are land use land cover (LULC) change and climate variability. Increasing population influences both LULC change and climate variability by inducing changes in key hydrological parameters such as interception rates, evapotranspiration (ET), run-off, surface infiltration, soil moisture, water quality and groundwater availability thereby affecting the watershed hydrology. The effects of LULC change and climate variability on hydrologic parameters have been extensively studied.

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Philosophiae Doctor - PhD / Low- and medium-spin bands of 187Os have been studied using the AFRODITE array, following the 186W(4He,3n)187Os reaction at a beam energy of 37 MeV. The measurements of γ − γ coincidences, angular distribution ratios (RAD), polarization and γ-intensities were performed using eleven High Purity Germanium (HPGe) clover detectors. In the current work, all the previously known bands have been significantly extended and five new bands have been added to the level scheme. The observed bands are interpreted within the cranked shell model (CSM), cranked Nilsson-StrutinskyBogoliubov (CNSB) formalism and Quasiparticle-plus-Triaxial-Rotor (QTR) model. Systematic comparison of bands with the neighbouring isotopes has also been made. Comparison of the models with experimental data shows good agreement. The configurations of some of the previously observed bands have been modified. Most importantly, the coupling of 2+ γ band to the 11/2+[615] neutron configuration is observed for the first time.

Philosophiae Doctor - PhD / Orchard evapotranspiration (ET) is a complex flux which has been the subject of many studies. It often includes transpiration from the trees, cover crops and weeds, evaporation from the soil, mulches, and other orchard artefacts. Studies of evapotranspiration in orchards often quantify tree water use and soil evaporation, treating the water use from the understorey vegetation on the orchard floor as negligible. Therefore, there is a paucity of information; first about the water use of cover crops in general, and secondly about the contribution of cover crops to whole orchard ET. This information is important, especially in semi-arid regions like South Africa where water resources are already under great strain and the situation is predicted to worsen in future due to climate change.