1,720,969 research outputs found
New efficiency charts for the optimum design of axial flow turbines for organic Rankine cycles
No full textTurbine efficiency plays a key role in the design optimization of ORCs (organic Rankine cycles) and should be properly evaluated for an accurate estimate of the real power production. Its value is in general assumed as given in the design optimization procedure, without a check that it can be really achieved in the resulting working conditions. The peculiar properties of high molecular weight fluids markedly influence turbine design and ask for turbine design criteria specifically tailored to ORCs. In this work a meanline design procedure for single stage axial flow turbines is developed to find optimum turbine geometry and efficiency in a wide range of operating conditions. Unlike previous literature, real fluid properties and very recent loss models are implemented. The variation of the predicted turbine efficiency with loading coefficient, flow coefficient, specific speed and specific diameter is shown through new general maps that explicitly take into account the strong influence of compressibility and turbine size through the volumetric expansion ratio and size parameter, respectively. All these maps can be included in a general design optimization procedure of the ORC system to help select the optimum design point, overcoming any arbitrary assumptions on turbine efficiency
An insight into the similarity approach to predict the maximum efficiency of organic Rankine cycle turbines
No full textThis work deals with the prediction of the maximum efficiency achievable by turbines for Organic Rankine Cycle (ORC) systems by means of similarity principles. At present, this is a key topic in the preliminary design optimization procedures of these systems. The dimensional analysis applied to the most general ORC turbines scenario helps obtain the functional relationship between maximum turbine efficiency and the most relevant design variables within the general framework of the flow similarity. Aim of the work is to search for the less wide and more convenient set of independent similarity parameters to increase the accuracy of turbine efficiency data in the optimization of ORC systems. Results show that the strict flow similarity does not hold if the same design is used for different working fluids, because real gas compressibility effects cannot be disregarded for most of the fluids usually adopted in ORC systems. On the other hand, a “quasi-similarity” approach can be applied to the design of low volume expansion ratios ORC turbines using the size parameter (SP), volume expansion ratio (VR) and the compressibility factor (Z) as predictors of turbine efficiency. Accordingly, two original correlations for the SP-VR-Z map of optimized axial turbine stages are suggested
Manure drying optimization
No full textHorse manure is a poor feedstock whose energetic content is comparable to that of herbaceous biomass. However, it can be effectively burnt provided that it is previously desiccated, being its moisture content very high (60% wb). This work reports an experimental investigation to identify optimal conditions for horse manure drying in a bench-scale direct heating rotary drier, to be sequentially combined with its combustion. The relative impact of the variables affecting the drying rate is assessed by an extensive sensitivity analysis which addresses both the role of solid motion and the drying fluid. Results show that the effectiveness of the gas-solid contact has a remarkable effect on the moisture release rate, and the drying air temperature is the controlling parameter. Tests using flue gases as drying medium confirm that they can be profitably used, without significant loss of drying capacity, suggesting that combined drying and combustion is a viable option. Setting a target residual moisture at 30% wb, by sensitivity analysis the time required could be cut to 12 min, for a reference quantity of 1.2 kg, with a maximum moisture removal capacity of 70 (kg/h)/m(3). (C) 2022 Published by Elsevier Ltd
Emissions reduction from wood pellet stoves by uniform feeding
No full textThe instantaneous fuel-to-air ratio in pellet stoves may vary because of the feeding mechanism. The pellet feed flow rate variability of a standard screw feeder was quantitatively assessed with real-time measurements. Temporary excess or deficit of pellets commonly occur. The variability can be significantly reduced with a new feeder, by approx. 70%, both at nominal (full) and partial (half) load operation. The analysis of the instantaneous emissions reveals that the fuel feed instabilities cause temporary sub-optimal fuel-to-air ratio and, in turn, peaks of pollutants emissions. The impact on the emissions of a more regular pellet feeder is impressive. A reduction of CO emission by 46% and 37.5%, and of PM by 52% and 44% at nominal and partial load, respectively was measured. NOx emissions are less affected by a more uniform feed rate, being predominantly from fuel nitrogen
Effective energy exploitation from horse manure combustion
No full textWe investigated the exploitation of horse manure for energy recovery by combustion. First, the impact of the waste origin and management (storage conditions) was evaluated in terms of elemental analysis, moisture content, heating value, and ash melting temperature. Besides some carbon loss over the time, horse manure origin and management policy do not impact its profitable exploitation by combustion. More relevant, the ignition tests disproved the current industrial opinion that combustion of manure alone is difficult, without the addition of auxiliary fuel, like wood shavings. It has been demonstrated through ignition tests that the major limitation in manure combustion is just the high moisture content (approx. 60% w.b.). The study focused on overcoming the detrimental effect of the large moisture content, and specifically its removal efficiency. The latter requires the understanding of manure permeability which is determined by the bedding material and the stable management. Here we provide indications of the impact of the manure composition and its sample size on the efficiency of moisture removal, whose energy impact must be minimized for an effective energy recovery. The energy balance confirms that the total removal of 62% w.b. moisture reduces by 23% the potential energy content of the manure; this drying penalty on energy is largely offset by the dramatic improvement in reactivity of the residual solid fuel
Optimal decarbonization strategies for an industrial port area by using hydrogen as energy carrier
Full text linkThis article discusses possible strategies for decarbonizing the energy systems of an existing port. The approach consists in creating a complete superstructure that includes the use of renewable and fossil energy sources, the import or local production of hydrogen, vehicles and other equipment powered by Diesel, electricity or hydrogen and the associated refuelling and storage units. Two substructures are then identified, one including all these options, the other considering also the addition of the energy demand of an adjacent steel industry. The goal is to select from each of these two substructures the most cost-effective configurations for 2030 and 2050 that meet the emission targets for those years under different cost scenarios for the energy sources and conversion/storage units, obtained from the most reliable forecasts found in the literature. To this end, the minimum total cost of all the energy conversion and storage units plus the associated infrastructures is sought by setting up a Mixed Integer Linear Programming optimization problem, where integer variables handle the inclusion of the different generation and storage units and their activation in the operational phases. The comprehensive picture of possible solutions set allows identifying which options can most realistically be realized in the years to come in relation to the different assumed cost scenarios. Optimization results related to the scenario projected to 2030 indicate the key role played by Diesel hybrid and electric systems, while considering the most stringent, or much more stringent, scenarios for emissions in 2050, almost all vehicles energy demand and industry hydrogen demand is met by hydrogen imported as ammonia by ship
Plasma cell leukemia: first diagnostic approach in the laboratory|Leucemia plasmacellulare: primo inquadramento diagnostico in laboratorio
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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