The magnitude of contaminant mass flux reduction associated with a specific amount of contaminant mass removed is a key consideration for evaluating the effectiveness of a source-zone remediation effort. Thus, there is great interest in characterizing, estimating and predicting relationships between mass flux reduction and mass removal. Intermediate-scale flow- cell experiments and published data for several field studies were examined to evaluate factors controlling the mass-flux-reduction/mass-removal relationship. Flow-cell experiments evaluated the impact of source-zone architecture and flow-field heterogeneity on mass-flux-reduction/mass-removal behavior. Significant reductions in mass flux occurred for systems wherein immiscible-liquid mass was present at both residual saturation and in high saturation pools. For a system with immiscible liquid present in multiple zones of different permeability, an increase in mass flux was observed for late stages of mass removal. Image analysis confirmed that the late stage increase in mass flux was attributed to changes in relative permeability. Early reductions in mass flux were also observed for systems wherein immiscible-liquid mass was poorly accessible to flowing water. End-point analysis, based on comparing masses and mass fluxes measured before and after a source-zone remediation effort, conducted for 21 field remediation projects ranged from slightly less than to slightly greater than one-to-one. Time-continuous analysis, based on continuous monitoring of mass removal and mass flux, performed for two sites illustrated the dependence of the mass-flux-reduction/mass-removal relationship on source-zone architecture and mass-transfer processes. Minimal mass flux reduction was observed for a system wherein mass removal was relatively efficient. Conversely, a significant degree of mass flux reduction was observed for a site wherein mass removal was inefficient. A simple mass-removal function was used to evaluate the measured data at both the intermediate and field scales. This function was unable to capture the complex behavior observed for some of the systems unless specific measurable system parameters were incorporated into the function. Finally, mathematical models of varying complexity used to simulate immiscible liquid dissolution illustrated the dependence of the calibrated dissolution rate coefficient on implicit and explicit consideration of larger-scale factors influencing immiscible liquid dissolution.

Minimal research has been conducted to examine dissolution and remediation of NAPL located in lower-permeability (K) media. The purpose of this research was to investigate dissolution of non-uniformly distributed residual NAPL located in lower-K media and how mass transfer was affected. Additionally, in situ chemical oxidation (ISCO) effectiveness using KMnO₄ in the laboratory and field was examined. A series of column and flow cell experiments were conducted with trichloroethene (TCE). For uniformly distributed residual NAPL control experiments, reduced interfacial pool area and resonance time were likely the most important mass transfer limitation. For non-uniformly distributed residual NAPL, by-pass flow attributed to reduced effective permeability was initially the most important factor affecting nonideal mass transfer. Dissolution times increased with physical heterogeneity due to bypass flow. Mass transfer was more non-ideal for non-uniformly distributed NAPL. Nonideal mass transfer was most pronounced for non-uniformly distributed NAPL in lower-K zones. NAPL location influences dissolution behavior and ultimately remediation. Mass flux reduction versus mass reduction comparisons for the experiments exhibited how mass transfer trends vary between systems. The effectiveness of KMnO₄ ISCO of residual TCE located in lower-K media was examined. KMnO₄ solution was flushed through a flow cell followed by water flushing to evaluate long-term mass flux behavior, which was then compared to a water-flush control. For water flushing following KMnO₄ flushing, mass flux was similar to the control experiment. However, since contaminant mass was reduced, the number of pore volumes required for complete TCE removal via water flushing was estimated to be reduced by half. 1,1-Dichloroethene (DCE) is thought to be located in lower permeability strata adjacent to the water table at the Samsonite Building Area. Eight injection wells were emplaced in the source zone area, with well screens spanning the vadose and saturated zones, and injected with ~250 kg of 1.7% KMnO₄ solution. Bench-scale studies using core material determined that DCE was readily degraded by KMnO₄, even at lower reagent concentrations (< 1 mM). The natural oxidant demand was determined to be 1.0 x 10⁻⁵ g of KMnO₄/g of sediment. Aqueous DCE levels dropped below detection after KMnO₄ solution was present.

An adaptive wing, a zero mass ux ow control device for low speed airfoil separation control, is investigated both experimentally and computationally at low speeds. The adaptive mechanism in the wings provides variable camber that can be actuated across a range of frequencies and amplitudes. Piezoelectric actuators are housed in a NACA 4415 airfoil with a chord length of :203 m. The entire adaptive wing assembly is then wrapped under a layer of latex membrane to provide a exible and smooth upper surface pro le. Experimental diagnostics include ow visualization, particle image velocimetry, as well as lift and drag measurements. The numerical simulation uses a 2D incompressible CFD code based on a nite-volume structured formulation with a chimera overset grid for the purpose of parallel computing. In the current study, the dimensionless speed range examined is 2:5 104 Re 1:5 105, where particular focus is given to Re 7:5 104, where Re = U` . All experiments and simulations are conducted in the range of attack angles from 0 24 and between reduced frequency values from 0 f+ 1:09, where f+ = f` U1 . Both experimental and computational results show that the region of separation is reduced when the actuation is turned on, thus enhancing aerodynamic e ciency. The maximum coe cient of lift increases by 26% when the reduced frequency, f+, is approximately :2, where the ow control mechanism appears to be most e ective. Phase-locked PIV and CFD vorticity plots reveal that the downward motion of the surface actuation decelerates the boundary ow and increases surface pressure, resulting in the formation of a series of cross-stream vortices that provides uid entrainment towards the suction surface, hence reducing separation.

L'objectif de ce travail est l'étude du procédé de pervaporation et plus particulièrement la compréhension des mécanismes de transfert de masse et de chaleur dans une membrane en polymère qualifiée de dense. Une meilleures compréhension des mécanismes permettrait de lever les verrous limitant le développement de ce procédé, comme les faibles flux de matière ainsi que l'origine et la quantité de chaleur nécessaire au transfert à travers la membrane. Pour cela, nous avons développé un dispositif expérimental qui permet de mesurer en simultané les densités de flux de matière et de chaleur. La configuration frontale statique de perméation du dispositif mis en place donne accès au profil de température du liquide d'alimentation. Ces données de température ont permis de calculer les densités de flux de chaleur engagées durant les expériences de pervaporation grâce à un calcul par méthode inverse couplé à une simulation STAR CCM+. La densité de flux de matière est mesurée par une nouvelle méthode. La nouvelle méthode utilise un capteur de pression situé dans le réservoir d'alimentation permettant de mesurer en continu la densité de flux de matière synchronisée avec la mesure des températures. Afin de simplifier au maximum les contraintes expérimentales, nous nous sommes restreints à la perméation de composés purs. La corrélation des deux flux mesurés nous a conduit à observer que la quantité de chaleur prise au fluide en amont pour pervaporer une unité de masse de liquide pur est inférieure à la quantité de chaleur nécessaire pour vaporiser ce même liquide. Elle représente 50 % de celle-ci dans le cas de l’eau et seulement 25 % dans le cas de l’éthanol. / The aim of this work is to study the pervaporation process and specifically to understand the mass and heat transport mechanisms in a dense polymeric membrane. A better understanding of these mechanisms would make it possible to improve the limiting parameters for the development of this process, such as the low mass fluxes as well as the origin and the quantity of heat required for transport through the membrane. In order to answer these questions, we have developed an experimental setup that allows simultaneous measurement of mass flux and heat flux density. The dead-end permeation of the setup developed gives access to the temperature profile of the liquid feed. These temperature data make possible the estimation of the heat flux densities engaged during the pervaporation experiments by means of an inverse computation coupled with a STAR CCM + simulation. The mass flux is measured by a new method in addition to the gravimetric method used as a reference. The new method uses a pressure sensor located in the feed tank to continuously measure the mass flux with 1Hz raw acquisition frequency synchronized with the temperature measurement. In order to simplify the experimental constraints, we applied only permeation of pure liquids. The correlation of the two fluxes (mass and heat density) measured led us to observe that the amount of heat taken to the feed side to pervaporate a unit mass of pure liquid is less than the amount of heat required to vaporize the same liquid. It represents 50% of it in the case of water and only 25% in the case of the ethanol.

No description available.

The phenomenon of plume persistence was observed for five federal Superfund sites by analysis of historical groundwater-withdrawal and contaminant-concentration data collected from long-term pump-and-treat operations. The potential factors contributing to plume persistence are generally recognized to include incomplete isolation of the source zone, permeability heterogeneity, well-field hydraulics, and non-ideal (rate-limited, nonlinear) desorption. However, the significance of each factor, especially the site-specific contribution is undetermined, which is very important for site development and management. One objective of this study is to quantify the impacts of different factors on mass-removal efficiency. Three-dimensional (3D) numerical models were used to simulate the impact of different well-field configurations on pump-and-treat mass removal. The relationship between reduction in contaminant mass discharge (CMDR) and mass removal (MR) was used as the metric to examine remediation efficiency. Results indicate that (1) even with effort to control the source, residual impact of source can still be a factor causing plume persistence, (2) the well-field configuration has a measurable impact on mass-removal efficiency, which can be muted by the influence of permeability heterogeneity, (3) in terms of permeability heterogeneity, both variance and correlation scale influence the overall mass-removal behavior, (4) the CMDR-MR relationship can be used to quantify the impacts of different factors on mass-removal efficiency at the plume scale. It has been recognized that the use of pump and treat for groundwater remediation will require many decades to attain site closure at most complex sites. Thus, monitored natural attenuation (MNA) and enhanced attenuation (EA) have been widely accepted as alternatives because of their lower cost and sustainable management for large, complex plumes. However, the planning and evaluation of MNA/EA applications require greater levels of characterization data than typically collected. Advanced, innovative methods are required to characterize specific attenuation processes and associated rates to evaluate the feasibility of MNA/EA. Contaminant elution and tracer (CET) tests have been proposed as one such advanced method. Another objective of this study is to investigate the use of modified well-field configurations to enhance the performance of CET tests to collect critical site-specific data that can be used to better delineate attenuation processes and quantify the associated rate coefficients. Three-dimensional numerical models were used to simulate the CET test with specific well-field configurations under different conditions. The results show that the CET test with a nested (two-couplet) well-field configuration can be used to characterize transport and attenuation processes by eliminating the impact of the surrounding plume. The results also show that applying select analytical mass-removal functions can be an efficient method for parameter estimation, as it does not require the use of mathematical transport modeling and does not require the attendant input data that are costly and time-consuming to obtain.

The Skelton Glacier is one of the many smaller outlet glaciers located in the Transantarctic Mountains, where it drains ice into the Ross Ice Shelf. These outlet glaciers are important when determining the past, present, and future state of the mass balance of the East Antarctic Ice Sheet. This research uses satellite imagery acquired over a period of 15 years to obtain a high resolution velocity field for the Skelton Glacier which is then used to calculate the mass flux and mass balance at ten flux gates along the glacier using the input-output method. The high resolution velocity field is combined with ice thickness data and accumulation data from other sources to obtain the total mass balance. The high resolution velocity field of the Skelton Glacier was created using European Remote-Sensing Satellite 1 and 2 (ERS-1/2) Synthetic Aperture Radar (SAR) data acquired in 1996 with the processing technique of SAR interferometry (InSAR). Because of the lack of differential InSAR pairs, new auxiliary data from the ICESat and TanDEM-X mission were included into the analysis. A velocity field was created at a spatial resolution of 50m which was validated with in situ GPS measurements from 2011/12, and compared to lower resolution velocity fields of the Skelton Glacier. The ice velocity field is at improved accuracy for this area compared to previous studies and is thought to be representative for the mean ice velocity. The analysis of ice flux at several flux gates allowed an improved error estimation of the applied technique to estimate the overall mass balance. Mass flux estimates along the glacier were calculated using the new velocity field and additional thickness data, which was then compared to two accumulation datasets to give mass balance estimates along the glacier at selected flux gates. The mass flux through the grounding line was found to be 1.2165 Gt a⁻¹, which needs to be balanced in a state of mass balance equilibrium by a mean annual snow accumulation of about 185 mm a⁻¹ water equivalent over the total catchment area determined with 6569 km². The mass balance at the grounding line is slightly negative, but the second flux gate is thought to be more representative of the mass balance, which is estimated to be 0.0441 Gt a⁻¹. Error analysis of the mass balance estimates found uncertainties in this data to be approximately 0.110 Gt a⁻¹. It is concluded from the analysis that further improvements in the overall mass balance estimate can be primarily obtained by a better knowledge of ice thickness and snow accumulation.

A great deal of work has been conducted on in-tube condensation in horizontal and vertical smooth tubes. The available literature points to mechanisms governing two-phase condensation heat transfer coefficients and pressure drops, which are directly linked to the local flow pattern for both horizontal and inclined configurations. However, the work has been limited to flow pattern observations, heat transfer, pressure drops and void fractions for both horizontal and inclined tubes at high mass fluxes. No work has been conducted on the analysis of the observed flow patterns and the effect of temperature difference between the average wall temperature and average saturation temperature for different inclination angles at mass fluxes of 100 kg/m2.s and below. The purpose of this study is to carry out a qualitative analysis of flow patterns, and show the effect of temperature difference on the heat transfer coefficient for inclination angles from +90° (upward flow) to -90° (downward flow) at mass fluxes below 100 kg/m2.s. An experimental set-up provided the measurements for the two-phase condensation of R-143a in a smooth tube with an inside diameter of 8.38 mm and a length of 1.5 m. The mass fluxes were 25 kg/m2.s to 100 kg/m2.s, the saturation temperature was 40 °C and the mean qualities were 0.1 to 0.9. A high-speed camera was used to visually analyse and determine the flow patterns for both the inlet and the outlet of the test section. Through the results, eight flow patterns were observed: stratified-wavy, stratified, wavy, wavy-churn, intermittent, churn, annular and wavy-annular. The maximum heat transfer was observed for downward flow between inclination angles of -15° and -30°. The Thome-Hajal flow pattern map correctly predicted horizontal flow patterns, but failed to predict most of the inclined flow patterns. Various flow pattern transitions were identified and proposed for all the investigated inclination angles in this study. Finally, the heat transfer coefficient was found to be dependent on quality, mass flux, temperature difference and inclination angle. / Dissertation (MSc)--University of Pretoria, 2016. / Mechanical and Aeronautical Engineering / MSc / Unrestricted

A Météo France, le modèle opérationnel AROME a une résolution horizontale de 2,5 km. L'augmentation des moyens de calcul permettra au prochain modèle opérationnel de tourner à des résolutions de l'ordre ou inférieures au kilomètre. Il entrera donc dans une gamme de résolution appelée zone grise de la turbulence. A ces échelles, les plus grandes structures turbulentes, qui étaient jusqu'alors entièrement sous-maille, devraient être en partie résolues. Cette thèse a permis de définir ce que les modèles devaient obtenir aux échelles kilométriques et sub-kilométriques, c'est-à-dire les parts sous-maille et résolue de référence de la turbulence dans la zone grise. Ces références ont été établies dans le cas de couches limites convectives en convection libre ou forcée, nuageuse ou non. Elles permettent de prouver qu'à hauteur de couche limite égale, les thermiques sont plus larges dans les couches surmontées de nuages. Elles indiquent surtout que, quelle que soit la configuration, les paramétrisations actuelles ne sont pas capables de reproduire la zone grise. Ces échelles demandent donc de développer une nouvelle paramétrisation de la turbulence. La représentation de la turbulence non locale est la part qu'il faut faire évoluer. Nous avons donc pris le parti de modifier le schéma de thermique en flux de masse. Pour étudier les structures cohérentes sous-maille de couche limite, nous avons créé une analyse conditionnelle permettant de circonscrire la part de thermique qui influence le schéma sous-maille en fonction de la résolution. Cet outil nous a permis de définir les caractéristiques des thermiques sous-maille dans la zone grise, mais également de vérifier à micro-échelle les hypothèses de méso-échelle des schémas en flux de masse. Nous avons démontré que toutes les hypothèses ne sont pas valables. Finalement nous avons établi le système d'équations d'un schéma en flux de masse qui fonctionne aux échelles kilométriques. / The turbulence is well-represented on grid coarser than 2 km. Indeed, in meso-scale models, the turbulence is entirely sub-grid. The turbulence is also well-represented at very high resolution (10 to 100 m) by LES models for which turbulence is mainly resolved. However we do not know which part of the turbulence should be resolved and which part of it should be parameterized when a model runs at kilometric scales, the so-called “Terra Incognita“ from Wyngaard (2004). Thanks to increasing computational resources, in a near future, limited area NWP models will reach grid spacings on the order of 1 km or even 500 m. The aim of this study is to develop a parameterization which will provide adequate turbulence to these new-generation, high-resolution models. At first, this study describes a new diagnostic based on LES, which clarifies which part of turbulence should be parameterized at kilometric scales. This reference called “partial similarity function“ is a precious tool to quantify the error made by atmospheric models when running at kilometric scales. These errors are quantified for a state-of-the-art meso-scale model (Méso-NH) with several turbulence mixing options : different mixing lengths, different dimensionalities, a K-gradient scheme or an EDMF approach (K-gradient with a mass-flux scheme). K-gradient turbulence schemes are unable to reproduce the counter-gradient zone. In the grey-zone, this characteristic has a disastrous effect. As the instability is too large, the boundary layer is mixed by the dynamic of the model and the resolved mixing is too strong. The counter-gradient zone can be reproduced by adding a mass-flux scheme to the K-gradient turbulence scheme (Pergaud et al. (2009)). However the mass-flux scheme in its original form only produces wholly subgrid thermals at a grid size for which boundary-layer thermals should be partly resolved. In this case, the subgrid mixing is too strong. So the question arises as what is a subgrid thermal in the “grey zone“, when the mesh contains one thermal at the most and a part of the thermal has to be resolved by the advection scheme of the model. A conditional sampling is defined in order to detect the subgrid part of the thermals. It allows to determine the characteristics of the subgrid thermals in the “grey zone“ and to find out which assumptions of the mass-flux schemes are not verified. In the light of this study, the mass-flux scheme equations are established by taking the thermal fraction and the resolved vertical velocity into account. Finally, the system of equations is closed. The new parameterization is valid in the grey zone.

Over the past century the study of gas exchange rates between the atmosphere and the ocean has received increased attention because of concern about the fate of greenhouse gases such as CO2 released into the atmosphere. Of interest is the oceanic uptake of CO2 in shallow water coastal regions as biological productivity in these regions is on average about three times larger than in the open ocean. It is well-known that in the absence of breaking surface waves, the water side turbulence controls gas transfer of sparingly soluble gases such as CO2 from the air to the water. The dependence of gas transfer on wind-driven shear turbulence and convection turbulence generated by surface cooling has been investigated previously by others. However, the effect of Langmuir turbulence generated by wave-current interaction has not been investigated before. More specifically, Langmuir turbulence is generated by the interaction of the wind-driven shear current with the Stokes drift velocity induced by surface gravity waves. In this dissertation, large-eddy simulations (LES) of wind-driven shallow water flows with Langmuir turbulence have been conducted and scalar transport and surface scalar transfer dynamics analyzed. The scalar represents the concentration of a dissolved gas such as CO2 in the water. In flows with Langmuir turbulence, the largest scales of the turbulence consist of full-depth Langmuir circulation (LC), parallel downwind-elongated, counter-rotating vortices acting as a secondary structure to the mean flow. LES guided by the full-depth LC field measurements of Gargett & Wells (2007) shows that Langmuir turbulence plays a major role in determining scalar transport throughout the entire water column and scalar transfer at the surface. Langmuir turbulence affects scalar transport and its surface transfer through 1. the full-depth homogenizing action of the large scale LC and 2. the near-surface vertical turbulence intensity induced by the Stokes drift velocity shear. Two key parameters controlling the extent of these two mechanisms are the dominant wavelength (λ) of the surface waves generating the turbulence and the turbulent Langmuir number, Lat , which is inversely proportional to wave forcing relative to wind forcing. Furthermore, LES representative of the field measurements of Gargett et al. (2004) shows that Langmuir turbulence increases transfer velocity (a measure of mass transfer efficiency across the air-water interface) dramatically with respect to shear-dominated turbulence. Finally, direct resolution of the surface mass transfer boundary layer allows for the LES to serve as a testing ground for bulk parameterizations of transfer velocity. Several wellestablished parameterizations are tested and a new parameterization based on Stokes drift velocity shear is proposed leading to encouraging results.