A two-level diagnostic baroclinic model is constructed for the purpose of examining the role of latent heat release in the production of vertical motion and rainfall. Incorporated in the model are terrain and frictional inflow effects and a variable level of non-divergence. The computations are carried out on a 300 point standard rectangular grid covering the North American continent. [...]

A caractérisation de l'écoulement, du transfert de chaleur et de masse lors du déplacement de gouttelettes de diamètre inferieur au millimètre dans un milieu extérieur font l'objet de notre étude. La première partie présente l'état de l'art des connaissances théoriques et expérimentales des comportements aérodynamiques ainsi que les mécanismes de transfert thermiques et massiques intervenant entre une phase dispersée et une phase continue. La deuxième partie est consacrée à l'étude du phénomène d'évaporation d'une gouttelette mono-dispersée en chute libre dans l'air. Pour cela, nous avons réalisé un dispositif expérimental. Les mesures, nous permettent de prédire l'évaporation de la gouttelette en fonction des caractéristiques physico-chimiques et de l'hygrométrie du milieu extérieur. Pour la modélisation du transfert de chaleur et de masse nous avons utilisé un modèle simple qui tient en compte du couplage entre le mouvement et les phénomènes de transferts, validé dans une précédente étude au sein du laboratoire. Un bon accord est observé. La troisième partie traite de la simulation numérique de l'interaction entre les particules sphériques dans un régime laminaire. Tout d'abord, nous avons proposé et validé un modèle simple qui ne tient pas en compte des phénomènes d'interaction. Les résultats obtenus sont en concordance avec la littérature. Par la suite, nous avons étudié l'interaction entre trois particules identiques et co-alignées. Ce modèle tient compte de la nature de la particule, du nombre du Reynolds et de la distance de séparation. Nous avons validé ce travail par une comparaison avec une étude précédente que nous avons généralisé. La dernière partie est cernée sur l'étude de la dispersion des gouttelettes dans un écoulement turbulent homogène et isotrope. Pour cela, nous avons proposé un modèle Lagrangien de suivi des trajectoires. La production de la turbulence est assurée par une condition de turbulence de grille. Nous avons considéré que les caractéristiques moyennes de l'écoulement fluide sont connues. La sélection des fluctuations de vitesse turbulente est assurée par une méthode probabiliste gaussienne que nous avons développée. La fluctuation est conservée durant un certain temps lié à turbulence, elle est renouvelée au cours du calcul. Ce renouvellement est donné par le temps caractéristique de turbulence.

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Western boreal peatlands have diverse ground covers of Sphagnum and brown mosses that have important hydrological controls on peatland-atmosphere interactions. Since peatland mosses are non-vascular, their shoot structural morphologies and community growth forms affect the storage and fluxes of water that are critical for maintaining productivity and evaporative functions. While many of the mechanisms of capillary rise are fairly well understood for Sphagnum mosses, there is less information on the water dynamics in communities of Tomenthypnum nitens, a dominant brown moss species in northern rich fens. This study investigated how the different hydrophysical characteristics of moss and peat profiles of T. nitens from a rich fen and intermixed Sphagnum angustifolium and Sphagnum magellanicum, from a poor fen affect capillary flow and water retention to support evaporation and productivity; and how different groundwater and atmospheric sources of water affected these processes. Laboratory investigations indicated volumetric water content and gross ecosystem productivity decrease with water table depth for both mosses without the advent of precipitation, with Sphagnum capitula retaining 10-20% more water than T. nitens due to its moss structure and pore connectivity with the water table. Consequently, Sphagnum capillary rise was sufficient to sustain both high pore-water pressures for evaporation and high water content for productivity at all water table depths due to a gradual shift in average water-retaining pore sizes with depth. The structure of T. nitens moss turfs, consisting of live shoots and a basal layer of old, partially decomposed shoots sometimes overlying well-decomposed peat makes capillary rise more difficult, requiring extremely low matric pressures at the surface, sometimes causing desiccation of the uppermost portions of moss shoots, and hence reduced productivity. Additional nocturnal sources of atmospheric water from dew, distillation, and vapour fluxes provide small, but potentially critical sources of water to rewet desiccated moss shoots for early morning productivity for both T. nitens and Sphagnum mosses. Investigations in the field, however, indicated that with frequent precipitation to rewet the moss and the turf base to refill large pores, evaporative demands at the T. nitens moss canopy could drive capillary flow from the water table to maintain adequate θ for productivity. T. nitens mosses also can grow in turfs disconnected from the underlying iii peat, so that the basal layer temporarily retains water from precipitation for capillary rise. Thus, while capillary connection of the T. nitens moss turf with the underlying peat and water table is not critical to maintain productivity, it grows in a relatively large range of elevations from the water table, compared to Sphagnum and feather mosses. Rewetting of the capitula and the raising of the water table by precipitation provided higher water matric pressures within the moss matrix, and along with high evaporative demands, provided the mechanisms for sufficient capillary flow for productivity. Thus, Sphagnum could grow in habitats far from the water table like feather mosses, although the latter did not require capillary rise for productivity. Furthermore, disequilibrium between water vapour and liquid in the pores of T. nitens in the near-surface suggested pressures calculated with the Kelvin equation may not provide an accurate characterization of actual matric pressures in the moss. However, as the disequilibrium is caused by vapour pressure gradients between the moss and the atmosphere, it is likely a driving factor that helps maintain vapour and capillary water fluxes to provide moisture for T. nitens and other mosses. These results illustrate hydrological mechanisms that explain how moss growth form and habitat are linked. As such, the Sphagnum and T. nitens mosses are well adapted to maintain capillary in their poorly drained habitats in western boreal peatlands.

Reservoir storage is essential for developing dependable water supplies and is a major component of the river system water budget. The storage contents of reservoirs fluctuate greatly with variations in water use and climatic conditions that range from severe multiple-year droughts to floods. Water surface evaporation typically represents a major component of the reservoir water budget. This thesis investigates the effects of evaporation and potential reductions in this evaporation on the water supply capabilities of reservoirs in Texas. As part of this research, a literature review based assessment of capabilities for reducing reservoir evaporation using monolayer films and other methods was performed. The literature review assessment provides an overview of past evaporation suppression studies performed using monolayer films and other evaporation suppression technologies including water shades and covers. The overview provides a summary on monolayer film application techniques, environmental impacts, operational and material costs, evaluation methods, and achievable evaporation reduction rates. This research project quantifies the impact of reservoir evaporation on water supply availability/reliability by using the Texas Water Availability Modeling (WAM) System which consists of the Water Rights Analysis Package (WRAP) and 21 sets of WRAP input files covering the 23 river basins of the state, a geographic information system (GIS), and contains over 8,000 water rights permits, which include 3,435 reservoirs. The impact of evaporation on water supply availability/reliability was evaluated by performing several analyses in which evaporation rates are reduced by specified percentages starting when storage levels drop below certain trigger percentages of reservoir storage capacity.

Nanomaterials are currently attracting billions of dollars in research funding and are entering such diverse fields as the computing, communications, life science and energy sectors. The growing popularity of nanomaterials demands a comprehensive understanding of the means by which such materials can be produced including the effects of physical and chemical factors. One method of forming inorganic nanomaterials is the sol-gel process; a low temperature process combining the benefits of glass and plastics technology. Whilst the research community has ascertained that gravity is important and appears to affect the sol-gel process, no coherent picture of the role of gravity on the sol-gel process has been proposed. The flexibility of the sol-gel process, and the promise it holds for creating products as diverse as hydrogen fuel cell membranes through to protective coatings for space vehicles, make it an important area of study. This thesis addressed a fundamental gap in the scientific knowledge concerned with the sol-gel process: how and why does gravity affect the sol-gel process? The nanomaterial chosen for study was a xerogel, a dense compound with a high surface area which finds applications in high temperature ceramics, energy saving coatings, molecular filtration and thin film sensors. The xerogel was produced from an acid catalysed sol. 2ml samples of the sol were subjected to reduced, normal and high gravity levels, and the resultant xerogels were characterised through liquid and solid state NMR and nitrogen adsorption/desorption techniques. Viscosity and pH measurements were also recorded. Reduced gravity conditions were provided by NASA’s KC-135 aircraft which is capable of creating a 25 second window of 1x10−2 gravities. A centrifuge was utilised to simulate increased gravity environments and xerogels were formed between 2 and 70 gravities. Analysis of the results led to two major contributions to this field of scientific endeavour. It was concluded that (1) gravity affected the reaction pathways of the sol-gel process and (2) gravity directly altered the molecular structure of xerogels The second contribution was determined through the NMR studies, where it was shown that a reduction in gravity resulted in a molecular structure composed of extended branches of cyclic compounds. Due to a decrease in convection in reduced gravity the molecular structure of the sample was dominated by cyclisation. In terrestrial and high gravity the molecular structure grew through both bimolecularisation and cyclisation reactions. Thus the gravity level also determined the reaction pathway available within the sol by creating a more or less convective environment. This created a structure composed of cyclics (rings) and chains. As gelation and drying of the sol occurred there was a loss in Q4 group amount. Chains, having a higher energy configuration than rings, underwent repolymerisation. Short chains formed which reacted end-to-end to form small, stable rings. The rings packed together more closely within the liquid sol and delayed the formation of a spanning cluster. The greater the gravity level, the greater the extent of bimolecularisation reactions contributing to chain formation, in turn allowing a greater degree of repolymerisation of the molecular structure. Thus gel times increased as the gravity level increased. Again gravity directly affected the reaction pathway of the sol-gel process. In reduced gravity the sol gelled very quickly due to the formation of a cyclic structure which was not capable of repolymerisation. The final contribution of this thesis was the proposal of a mechanistic model. The model depicted the ffect of gravity on the formation of the molecular structure of a xerogel.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Abdel-Khalik, Said; Committee Member: Ammar, Mostafa H.; Committee Member: Ghiaasiaan, S. Mostafa; Committee Member: Hertel, Nolan E.; Committee Member: Liu, Yingjie.

Thesis (Ph. D.)--University of Washington, 1995. / Vita. Includes bibliographical references (leaves [187]-197).

Thesis (Ph. D.)--Carleton University, 1996. / Also available in electronic format on the Internet.

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