Hot water thermal energy stores have the potential to improve and extend the performance of many kinds of energy system. Waperature stratification in the store is likely to affect the system's efficiency. A basic but accurate computer model of the hot water store under various inlet flow conditions is a requisite means of assesiing promising applications of hot water storage by system computer simulation techniques. A microprocessor-controlled test facility has been constructed to evaluate the performance of a 3m 3 hot water store under a wide range of inlet flow conditions, using a temperature step input approach. Three types of inlet/outlet ports have been examined: horizontal, vertical and distributors. The results show that two distinct regions evolve within the store: a fully-mixed region adjacent to the inlet port and a region of smooth 'plug-flow' in the remaining volume of the store. The performance of the store is shown to be defined by the initial depth of the fully-mixed region which in turn is seen to be closely related to the buoyancy and momentum fluxes of the inlet flow. The behAviour of the store and the evident correlations have enabled a one-dimensional computer model of the store to be developed, taking into account the turbulent mixing, vertical heat conduction and heat losses to the surrounding areas. The model has been successfully validated against the results from the step input experiments. The model has been integrated into a computer simulated central heating system which incorporates a hot water store. Predictions have been made, using the simulation, of the energy savings which may be achieved with the use of storage in comparison to a conventional system, and an assessment has been made of the economic viability of the application.

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主催：JST/CREST，Vrije University, ALTERRA, IBPC

abstract: Water resource management is becoming increasingly burdened by uncertain and fluctuating conditions resulting from climate change and population growth which place increased demands on already strained resources. Innovative water management schemes are necessary to address the reality of available water supplies. One such approach is the substitution of trade in virtual water for the use of local water supplies. This study provides a review of existing work in the use of virtual water and water footprint methods. Virtual water trade has been shown to be a successful method for addressing water scarcity and decreasing overall water consumption by shifting high water consumptive processes to wetter regions. These results however assume that all water resource supplies are equivalent regardless of physical location and they do not tie directly to economic markets. In this study we introduce a new mathematical framework, Embedded Resource Accounting (ERA), which is a synthesis of several different analytical methods presently used to quantify and describe human interactions with the economy and the natural environment. We define the specifics of the ERA framework in a generic context for the analysis of embedded resource trade in a way that links directly with the economics of that trade. Acknowledging the cyclical nature of water and the abundance of actual water resources on Earth, this study addresses fresh water availability within a given region. That is to say, the quantities of fresh water supplies annually available at acceptable quality for anthropogenic uses. The results of this research provide useful tools for water resource managers and policy makers to inform decision making on, (1) reallocation of local available fresh water resources, and (2) strategic supplementation of those resources with outside fresh water resources via the import of virtual water. / Dissertation/Thesis / Ph.D. Civil and Environmental Engineering 2013

L’Afrique de l’Ouest est particulièrement exposée aux changements climatiques et anthropiques qui exercent une pression croissante sur les ressources hydriques et végétales, dont la bonne gestion constitue un enjeu scientifique majeur. Plus particulièrement, il devient indispensable de mieux comprendre les échanges d’énergie et de matière au sein du continuum surface-atmosphère qui régissent une bonne partie du cycle hydrologique et du développement de la végétation. À cet égard, l’évapotranspiration constitue une variable clé à l’interface surface-atmosphère car elle recycle la plus grande partie des précipitations vers l’atmosphère et assure le couplage des cycles de l’eau et de l’énergie. En Afrique de l'Ouest, les connaissances actuelles sur ce processus restent limitées car elles reposent principalement sur des mesures de terrain représentatives de petites échelles spatiales, ou sur des modèles de surface complexes, dont l’importance des jeux de données qu’ils requièrent limite leur application. Dans ce contexte, ce travail de thèse vise à améliorer notre connaissance de la variabilité spatiotemporelle de l'évapotranspiration, en analysant le potentiel de la télédétection pour son estimation en Afrique de l'Ouest. L'approche proposée repose sur une comparaison des produits d'évapotranspiration par télédétection disponibles et la proposition d’une nouvelle méthode permettant la génération de nouveaux produits. L’étude a été menée sur trois sites de méso-échelle (~ 104 km2) fournissant un échantillon des conditions éco-climatiques rencontrées en Afrique de l’Ouest, avec du Nord au Sud : le Nord-Sahel (au centre-est Mali), le Sud-Sahel (au sud-ouest Niger) et la zone soudanienne (au nord Bénin). Une méthode d’estimation de l’évapotranspiration journalière par télédétection et de son incertitude épistémique, nommée EVASPA S-SEBI Sahel (E3S), a été élaborée. E3S a été appliqué sur les trois sites d’étude à partir de données issues des capteurs MODIS à bord des satellites TERRA et AQUA. Les estimations journalières d’évapotranspiration ont été évaluées par rapport aux observations pluriannuelles acquises par l’Observatoire AMMA-CATCH. Cette étude souligne le potentiel d’E3S pour l’estimation de l’évapotranspiration journalière en Afrique de l’Ouest. Toutefois, ces estimations restent soumises aux aléas de la mesure satellite (qualité des images, couvert nuageux, angle de visée trop grand) et sont donc ponctuées de lacunes. Ces travaux de thèse proposent également de nouvelles méthodes de reconstruction de séries d’évapotranspiration journalières via la combinaison d’estimations multi-résolution et multi-source. Cette étude montre la pertinence de ces approches de reconstruction par rapport aux méthodes d’interpolation standards utilisées dans la littérature. Les approches proposées permettent notamment de mieux retranscrire la réponse des surfaces terrestres aux séquences d’assèchement du sol entre deux épisodes pluvieux. Les nouveaux produits générés ont été introduit dans l’exercice d’inter-comparaison incluant huit autres produits disponibles en Afrique de l’Ouest à diverses résolutions spatio-temporelles. Ces produits ont été évalués à différentes échelles spatiales et temporelles par rapport aux mesures locales et aux simulations spatialisées de vingt modèles de surface générées dans le cadre de l’expérience ALMIP2. Cette étude met en évidence la forte variabilité inter-produit, en particulier au Sahel. Elle souligne par ailleurs l’importance de la prise en compte d’une information liée au stress hydrique dans la génération des produits d’évapotranspiration. La résolution kilométrique des produits E3S leur fournit un avantage indéniable concernant la description de la variabilité spatiale des flux d’évapotranspiration par rapport à d’autres produits à faible résolution. Les produits nouvellement générés présentent un potentiel évident pour de futures études à caractère éco-hydrologique et hydrogéologique au Sahel. / West Africa is particularly vulnerable to climate and human-induced changes, exerting increasing pressure on water and plant resources. Sound management of the latter requires substantial scientific progress. In particular, it is essential to better understand energy and matter exchanges through the surface-atmosphere continuum, which are a major driver of the hydrological cycle and of vegetation development. In this respect, evapotranspiration is a key variable, as most of precipitation returns to the atmosphere by evapotranspiration and as it couples the water and energy cycles. In West Africa, current knowledge of this process is still limited because it is mainly based on field measurements that are representative of small spatial scales, or on land surface models that would require considerably more data than available in this region. In this context, this thesis work aims at improving our knowledge of the spatiotemporal variability of evapotranspiration, by analyzing the potential of remote sensing to estimate evapotranspiration in West Africa. The proposed approach is based on an inter-comparison of available remote sensing evapotranspiration products and on the proposal of a new method to generate new estimation products. The study was carried out over three mesoscale sites (~ 104 km2) providing a sample of the eco-climatic conditions encountered in West Africa, namely from North to South: the North-Sahel (in East-Central Mali), the South-Sahel (in South-West Niger) and the Sudanian zone (in North Benin). An improved remote sensing method for estimating daily evapotranspiration and its epistemic uncertainty named EVASPA S-SEBI Sahel (E3S) was developed. E3S was applied to the three study sites using data from the MODIS sensors onboard TERRA and AQUA satellites. Daily evapotranspiration estimates were evaluated against pluriannual observations acquired by the AMMA-CATCH Observatory. This study highlights the potential of E3S for estimating daily evapotranspiration in West Africa. However, these estimates are still subject to hazards of satellite measurements (image quality, cloud cover, large satellite view angle) and are therefore discontinuous. This thesis work also proposes new methods for reconstructing continuous daily evapotranspiration series by the combination of multi-resolution and multi-source estimations. The study shows the capabilities of these reconstruction approaches compared to the standard interpolation methods usually found in the literature. In particular, the proposed approaches allow better depicting the response of terrestrial surfaces to soil drying sequences between rainfall events. The newly generated evapotranspiration products were included in the product inter-comparison together with eight other products available in West Africa at various spatial and temporal resolutions. These products were evaluated at different spatial and temporal scales against local measurements and spatially distributed simulations by twenty land surface models from the ALMIP2 experiment. This study highlights the high inter-product variability especially in the Sahel. It also emphasizes the importance of taking into account information related to water stress in the generation of evapotranspiration products. The kilometric resolution of E3S products gives them a clear advantage in terms of description of the spatial variability of evapotranspiration flux compared to other coarse resolution products. The newly generated products show clear potential for future eco-hydrological and hydrogeological studies in the Sahel.

Thesis (Master of Engineering in Chemical Engineering)--Cape Peninsula University of Technology, 2018. / Globally, water is considered an essential resource as it sustains human, animal and plant life. Water is not only essential for all forms of life but imperative for economic growth. The world’s population is increasing at a disquieting rate, which will result in an increased demand for fresh water and food security. The agricultural industry is the main consumer of global freshwater and utilises fertilisers in order to meet food demands. The demand for water in South Africa (SA) has increased considerably due to the rapid expansion of the agricultural industry, and of the municipal and industrial sectors. Agricultural developments in SA are affected greatly as the country is facing a current drought crisis as a result of low rainfall and large water demands. With an abundance of saline water globally, desalinisation will be a major contributor to solving the global freshwater crisis. With limited fresh water resources accompanied by the agricultural industry as a major consumer, alternative measures are required to desalinate water specifically for agricultural use. Forward osmosis (FO) is a membrane technology that gained interest over the past decade because it has several advantages over pressure-driven membrane processes such as reverse osmosis (RO). FO technology is based on the natural osmotic process which is driven by a concentration gradient between two solutions separated by a semi-permeable membrane. Naturally, water will permeate through the membrane from a solution of low solute concentration or low osmotic pressure (OP) known as a feed solution (FS) to a solution of a higher concentration or higher OP also known as a draw solution (DS). Whilst various research studies have contributed to several advances in FO, several process limitations such as reverse solute flux (RSF), concentration polarisation (CP) and membrane fouling remain problematic, hindering FO for large-scale applications. Further investigation is therefore warranted and crucial in order to understand how to mitigate these limitations to develop/improve future processes. The aim of this study was to evaluate a fertiliser-drawn forward osmosis (FDFO) system by investigating the effects of membrane orientation, system flow rate, DS concentration, and membrane fouling on an FDFO systems performance and energy consumption. The FS used was synthetic brackish water with a sodium chloride (NaCl) content of 5 g/L whereas a potassium chloride (KCl) synthetic fertiliser was used as a DS. The membrane utilised was a cellulose triacetate (CTA) membrane and was tested in forward osmosis mode (FO mode) and pressure retarded osmosis mode (PRO mode) whilst the system flow rate was adjusted between 100, 200 and 400 mL/min. Additionally, the DS concentration was altered from 0.5, 1 and 2 M KCl, respectively. Experiments were performed using a bench scale FO setup which comprised of an i) FO membrane cell, ii) a double head variable peristaltic pump for transporting FS and DS’s respectively, iii) a digital scale to measure the mass of the DS, iv) a magnetic stirrer to agitate the FS, v) two reservoirs for the FS and DS, respectively, vi) a digital multiparameter meter to determine FS electrical conductivity (EC) and vii) a digital electrical multimeter to measure system energy consumption. Each experiment comprised of seven steps i) pre-FDFO membrane control, ii) membrane cleaning, iii) FDFO experiment, iv) post-FDFO membrane control, v) membrane cleaning, vi) membrane damage dye identification and vii) membrane cleaning. Pre- and post-FDFO membrane control experiments operated for 5 h whilst each membrane cleaning procedure operated for 30 min. The FDFO experiment operated for 24 h whilst the membrane damage dye identification operated until a minimum of 10 mL water was recovered. The process parameter which largely contributed to a beneficial system performance and specific energy consumption (SEC) was the increase in DS concentration. Water fluxes increased approximately threefold from a DS concentration increase from 0.5 to 1 M, followed by an additional 30 to 50 % rise in water flux at a DS concentration increase 1 to 2 M. SEC decreased by 58 and 53 % for FO and PRO modes, respectively, with a DS concentration increase from 0.5 to 1 M. An additional 35 and 37 % SEC reduction for FO and PRO modes was obtained for a DS concentration increase from 1 to 2 M. Altering the membrane from FO to PRO did not contribute to a beneficial system performance nor did it improve SEC. However, at a DS concentration of 0,5 M, the PRO mode obtained a 5.3 % greater water recovery compared to the FO mode. Conversely, at a DS concentration of 1 and 2 M, the FO mode achieved 5.4 and 7.0 % greater water recoveries compared to the PRO mode. The increase in flow rate also did not increase system performance significantly, however, a fluctuation in system SEC was observed. Throughout the study, no membrane fouling was observed, however, possible minute traces of membrane fouling could be observed from the membrane surface electron microscope (SEM) images. Additionally, minor changes in post- FDFO membrane control water recovery results were noticed which support the possible occurrence of membrane fouling during the FDFO experiment.

A major challenge to cold regions hydrology and northern water resources management lies in predicting runoff dynamically in the context of warming-induced changes to the rates and patterns of ground thaw and drainage. Meeting this challenge requires new knowledge of the mechanisms and rates of ground thaw and their implications to water drainage and storage patterns and processes. The study carries out to evaluate the concept of energy-based runoff in the perspective of ground heat flux, soil thaw and liquid moisture content, tortuosity of snow-free area, preferential flow and discharge of the hillslope. Based on field measurements, coupled energy and water flow is simulated in the Area of Interest (AOI) with a half-hour time interval by the distributed hydrological model, GEOtop. In the field, the saturated hydraulic conductivity varies exponentially between the superficial organic layer and the underlying mineral layer. In the simulation, the parameters of the soil physical properties are input by fourteen uneven layers below the ground surface. Starting from the initially frozen state, the process of soil thaw is simulated with dynamic variables such as soil liquid moisture and ice content, hydraulic conductivity, thermal conductivity and heat capacity. The simulated frost table depths are validated by 44-point measurements and the simulation of point soil temperature is also compared to data measured in an excavated soil pit. As a result, the frost table topography is dominated by both the snow-free pattern and the energy fluxes on the ground surface. The rate and magnitude of runoff derived from snow drift and the ice content of frozen soil is greatly influenced by the frost table topography. According to the simulation, the frost table depth is closely regressed with the ground surface temperature by a power function. As soil thawing progresses, ground heat flux reduces gradually and the rate of soil thaw becomes small when the frost table descends. Along with the snow-free area expanding, the average soil moisture of the AOI increases prior to that time when the average frost table is less than 25 cm deep. The snow-free patches expand heterogeneously in the AOI, which causes the spatial and temporal variation of hydraulic conductivity due to the non-uniform frost table depth. According to the simulation, the transit time of the flow through the AOI decreases to the shortest span on May 13 with the average frost table of 10 cm. Before this date, the time lag between snowmelt percolation and slope runoff is about 8-10 hours; while after this date, the time lag is no more than 5 hours. The pattern of the preferential flow in the AOI highly depends on the frost table topography. When the snow-free patches are widely scattered and the average frost table is between 0 and 10 cm, the preferential flow paths are inhibited. With soil thaw progresses, the preferential flow paths are prominent with the largest single contributing area occurring when the average frost table is between 10 cm to 15 cm. When the average frost table reaches 25 cm, the importance of preferential flow is not apparent, and matrix flow prevails.

A major challenge to cold regions hydrology and northern water resources management lies in predicting runoff dynamically in the context of warming-induced changes to the rates and patterns of ground thaw and drainage. Meeting this challenge requires new knowledge of the mechanisms and rates of ground thaw and their implications to water drainage and storage patterns and processes. The study carries out to evaluate the concept of energy-based runoff in the perspective of ground heat flux, soil thaw and liquid moisture content, tortuosity of snow-free area, preferential flow and discharge of the hillslope. Based on field measurements, coupled energy and water flow is simulated in the Area of Interest (AOI) with a half-hour time interval by the distributed hydrological model, GEOtop. In the field, the saturated hydraulic conductivity varies exponentially between the superficial organic layer and the underlying mineral layer. In the simulation, the parameters of the soil physical properties are input by fourteen uneven layers below the ground surface. Starting from the initially frozen state, the process of soil thaw is simulated with dynamic variables such as soil liquid moisture and ice content, hydraulic conductivity, thermal conductivity and heat capacity. The simulated frost table depths are validated by 44-point measurements and the simulation of point soil temperature is also compared to data measured in an excavated soil pit. As a result, the frost table topography is dominated by both the snow-free pattern and the energy fluxes on the ground surface. The rate and magnitude of runoff derived from snow drift and the ice content of frozen soil is greatly influenced by the frost table topography. According to the simulation, the frost table depth is closely regressed with the ground surface temperature by a power function. As soil thawing progresses, ground heat flux reduces gradually and the rate of soil thaw becomes small when the frost table descends. Along with the snow-free area expanding, the average soil moisture of the AOI increases prior to that time when the average frost table is less than 25 cm deep. The snow-free patches expand heterogeneously in the AOI, which causes the spatial and temporal variation of hydraulic conductivity due to the non-uniform frost table depth. According to the simulation, the transit time of the flow through the AOI decreases to the shortest span on May 13 with the average frost table of 10 cm. Before this date, the time lag between snowmelt percolation and slope runoff is about 8-10 hours; while after this date, the time lag is no more than 5 hours. The pattern of the preferential flow in the AOI highly depends on the frost table topography. When the snow-free patches are widely scattered and the average frost table is between 0 and 10 cm, the preferential flow paths are inhibited. With soil thaw progresses, the preferential flow paths are prominent with the largest single contributing area occurring when the average frost table is between 10 cm to 15 cm. When the average frost table reaches 25 cm, the importance of preferential flow is not apparent, and matrix flow prevails.

主催：JST/CREST，Vrije University, ALTERRA, IBPC

No description available.