20,056 research outputs found
Review of Molten-Salt Thermocline Tank Modeling for Solar Thermal Energy Storage
No full textMolten-salt thermocline tanks are a low-cost option for thermal energy storage in concentrating solar power systems. A review of previous experimental and numerical thermocline tank studies is performed to identify key issues associated with tank design and performance. Published models have shown that tank discharge performance improves with both larger tank height and smaller internal filler diameter due to increased thermal stratification and sustained outflow of molten salt with high thermal quality. For well-insulated (adiabatic) tanks, low molten-salt flow rates reduce the axial extent of the heat-exchange region and increase discharge efficiency. Under nonadiabatic conditions, low flow rates become detrimental to stratification due to the development of fluid recirculation zones inside the tank. For such tanks, higher flow rates reduce molten-salt residence time inside the tank and improve discharge efficiency. Despite the economic advantages of a thermocline tank, thermal ratcheting of the tank wall remains a significant design concern. The potential for thermal ratcheting is reduced through the inclusion of an internal thermal insulation layer between the molten salt and tank wall to diminish temperature oscillations along the tank wall. Future research directions are also pointed out, including combined analyses that consider the solar receiver and power generation blocks as well as optimization between performance and economic considerations
Social Designs: Tank Irrigation Technology and Agrarian Transformation in Karnataka, South India
No full textTank Irrigation of South India is largely considered “traditional”, “alternative”, or “appropriate” form of irrigation in the current academic and policy circles. Policy reforms have been underway in South India to rehabilitate tanks and hand them over to communities for management and maintenance. These efforts are guided by a premise that communities are better managers of natural resources. However, these efforts are not based on a careful inquiry about how internal power dynamics in the community results in inequitable distribution of the resource. Social Designs is based on a central argument that tank irrigation technology is shaped as a result of power relations in a particular historical, agrarian and social context. This technology as a matter of fact institutionalizes a particular pattern of resource utilization that favors only some users, and discriminates against some others. This book proposes that technological designs are socially shaped, and that through the means of technological designs society orders itself. By means of shaping and reproducing technology, a certain form of social organization or social arrangement is also reproduced. Extensive social anthropological research on tank irrigation technology and agrarian practices in Karnataka enriches this book. Shah has also drawn upon rich empirical material on the social and agrarian context of tank irrigation technology
A Cavitation Susceptibility Meter with Optical Cavitation Monitoring
No full textThis work is concerned with the design, development and operation of a Cavitation Susceptibility Meter based on the use of a venturi tube for the measurement of the content of active cavitation nuclei in water samples. The pressure at the ven-turi throat is determined from the upstream pressure and the local flow velocity without corrections for viscous effects because the flow possesses a lam-inar potential core in all operational conditions. The detection of cavitation and the measurement of the flow velocity are carried out optically. The apparatus comprises a Laser Doppler Velocimeter for the measurement of the flow velocity and the detection of cavitation, a custom-made electronic Signal Processor for real time generation and temporary storage of the data and a computerized system for the final acquistition and reduction of the collected data. The main considerations leading to the present design concept are illustrated and the implementation of the whole system is described. Finally, the results of application of the Cavitation Susceptibility Meter to measurement of the water quality of tap water samples are presented and critically discussed with reference to other similar or alternative methods of cavitation nuclei detection and to the current state of knowledge on cavitation inception
Evolution, present status and issues concerning small tank systems in Sri Lanka [Small tanks in Sri Lanka: evolution, present status and issues]
No full textTank irrigationHydrologyWater qualityIrrigation managementWater managementWater distributionWatershedsIrrigation designMaintenanceFarming systemsGovernmental interrelationsSmall scale systemsVillagesHistory
Food-web structure in relation to environmental gradients and predator-prey ratios in tank-bromeliad ecosystems
No full textLittle is known of how linkage patterns between species change along environmental gradients. The small, spatially discrete food webs inhabiting tank-bromeliads provide an excellent opportunity to analyse patterns of community diversity and food-web topology (connectance, linkage density, nestedness) in relation to key environmental variables (habitat size, detrital resource, incident radiation) and predators: prey ratios. We sampled 365 bromeliads in a wide range of understorey environments in French Guiana and used gut contents of invertebrates to draw the corresponding 365 connectance webs. At the bromeliad scale, habitat size (water volume) determined the number of species that constitute food-web nodes, the proportion of predators, and food-web topology. The number of species as well as the proportion of predators within bromeliads declined from open to forested habitats, where the volume of water collected by bromeliads was generally lower because of rainfall interception by the canopy. A core group of microorganisms and generalist detritivores remained relatively constant across environments. This suggests that (i) a highly-connected core ensures food-web stability and key ecosystem functions across environments, and (ii) larger deviations in food-web structures can be expected following disturbance if detritivores share traits that determine responses to environmental changes. While linkage density and nestedness were lower in bromeliads in the forest than in open areas, experiments are needed to confirm a trend for lower food-web stability in the understorey of primary forests
Evolution, present status and issues concerning small tank systems in Sri Lanka [Small tanks in Sri Lanka: evolution, present status and issues]
No full textTank irrigationSmall scale systemsHistoryIrrigation systemsDesignMaintenanceHydrologyPollutionIrrigation managementCultivationFarming systemsWells
Unsteady draining of a fluid from a circular tank
No full textThree-dimensional draining flow of a two-fluid system from a circular tank is considered. The two fluids are inviscid and incompressible, and are separated by a sharp interface. There is a circular hole positioned centrally in the bottom of the tank, so that the flow is axially symmetric. The mean position of the interface moves downwards as time progresses, and eventually a portion of the interface is withdrawn into the drain. For narrow drain holes of small radius, the interface above the centre of the drain is pulled down towards the hole. However, for drains of larger radius the portion of the interface above the drain edge is drawn down first, rather than the central section. Non-linear results are obtained with a novel spectral technique, and are also compared against the predictions of linearized theory. Unstable Rayleigh-Taylor type flows, in which the upper fluid is heavier than the lower one, are also discussed
Canada's new ice tank
No full textThe new refridgerated model basin, or ice tank, at the NRCC/IMD is described. Brief mention is made of the first projects to be conducted.NRC publication: Ye
An ant-plant mutualism induces shifts in the protist community structure of a tank-bromeliad
No full textAlthough ants may induce community-wide effects via changes in physical habitats in terrestrial environments, their influence on aquatic communities living in plant-held waters remains largely underexplored. The neotropical tank-bromeliad Aechmea mertensii (Bromeliaceae) occurs along forest edges in ant-gardens initiated by Camponotus femoratus or by Pachycondyla goeldii. Its leaves form wells that hold rainwater and provide suitable habitats for many aquatic organisms. We postulated that these ant-plant mutualisms indirectly affect the microbial community structure via changes in the environmental conditions experienced by the plants. To test this hypothesis, we analyzed the protist communities from 63 tank-bromeliads associated with either C. femoratus or P. goeldii (hereafter Cf-Aechmea and Pg-Aechmea) along a forest edge in French Guiana. For each plant, a large number of environmental variables (including habitat structure, food resources, incident radiation and the presence of aquatic invertebrates) were quantified to determine their relative importance in driving any observed differences across ant-associated plants. Pg-Aechmea are located in sun-exposed areas and hold low volumes of water and low amounts of detritus, whereas Cf-Aechmea are located in partially shaded areas and accumulate higher amounts of water and detritus. Protists (i.e., protozoa and algae) inhabiting Cf-Aechmea exhibit greater richness and abundances than those in Pg-Aechmea. Variations in detritus content, number of leaves, incident radiation, and the epiphyte richness of the ant-garden were the main factors explaining the variation in protist richness. A shift in the functional group composition of protists between bromeliads tended by different ant species suggested that mutualistic ants indirectly mediate changes in the microbial food web
'Chariots of Fire': The Evolution of Tank Technology, 1915-1945
No full textWe revisit the notion of technological trajectories by means of a detailed case-study of the evolution of tank technology between 1915 and 1945. We use principal component analysis to analyze the distribution of technological characteristics and how they map into specific service characteristics. We find that, despite the existence of differences in technical leadership, tank designs of different countries show a high degree of overlap and closeness along a common technological trajectory. In the conclusions, we speculate on whether this pattern can be explained by common heuristics that influenced the rate and direction of design activities or by doctrinal viewpoints influencing the development and use of tanks on the battlefield.Technological trajectories, Technological paradigms, Tanks.
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