1,721,142 research outputs found
Water recovery from HAT cycle exhaust gas: A possible solution for reducing stack temperature problems
No full textFor several years the injection of steam into the combustion chamber has represented a common way to improve the performance of gas turbine power plants, increasing both the power output and the efficiency and reducing, at the same time, NOx emissions. Starting from the first STeam Injected Gas turbine (GE STIG) cycles, several types of gas turbine cycle with steam or water injection (dual fluid cycles) have been proposed. Among them, the most interesting results were obtained with the Cheng and the humid air turbine (HAT) cycles. In particular, the HAT cycle (which is a gas turbine cycle featuring intercooled compression, an air-water mixing evaporator before the combustion chamber, and a recovery system for the exhaust gases) has been identified as a promising way to generate electric power at high efficiency, low cost and with a system that is simple compared with the combined cycles (Stecco et al. and Gallo et al.). However the associated water consumption, about 1210-2420 m3 per day for a 100 MW unit, continues to represent a significant drawback to the spread of the HAT cycle, as well as of other steam injected cycles. In fact, such a high spread water consumption means high operational costs for water treatment, eventual legislative restrictions limiting the use of water, not to mention the environmental impact of the depletion of water resources. Some different solutions to those problems have been proposed, such as the introduction of a mixing exchanger (Bettagli and Facchini), or of a surface exchanger (Bombarda, Bidini et al.) on the exhaust of the cycle to recover water and heat from the flue gases. Further cooling of the exhaust gases, which is necessary to condense the stream fraction, lowers the stack temperature so much that the stack draft may become too low to prevent sufficient diffusion of the emission; this is one of the main drawbacks for large-scale water and heat recovery. One of the possible solutions is the introduction an induced draft fan (IDF), the other is recuperative heating of the exhaust gases after the condenser. The aim of this paper is to estimate the cycle performance with an IDF placed between the turbine and the stack
Power Pipe: an Algorithm for Analysis for Single Phase, Steady State, Pipe Networks with Second-Degree Boundary Conditions
No full textIn this paper, an algorithm is described for the resolution of pipe networks with input and output conditions defined by pressure-flowrate correlations. The procedure and the main characteristics of the software are described. The method is particularly suited for solving pipe networks with boundary
conditions defined by pressure-flowrate second degree curves and during off-design operation. The code works with single-phase compressible and incompressible flow and a variety of fluids, including steam-gas mixtures. Heat transfer is also calculated for pipe elements and controls for steam condensation in steam or steam-gas networks are present. An application to a geothermal steam network power plant is included with comparison with experimental data
How the Water Section in the HAT Cycle can be an Efficient Power Output Modulator
No full textAfter a long period during which theoretical analyses were presented on evaporative gas turbine cycles, such as the HAT (Humid Air Turbine) and CHAT (Cascaded Humid Air Turbine), the first experimental plant with water recovery is currently under construction at the Lund Institute of Technology in Sweden. The pilot plant is due to start in evaporative mode in May 1998, and this represents the first step for the validation of the humid air turbine concept. One of the main points of interest is the power modulation which should be possible controlling the evaporated water flow rate. If the whole compressed air flow rate is introduced into the evaporator the possibilities to vary its water content are scarce if the temperatures in the recuperator are not changed. A solution to this problem has been patented by Vattenfall AB, and consists in bypassing a fraction of the air entering the evaporator directly into the recuperator. In this paper a detailed study of the different evaporation modes is presented from the point of view of both the first and second law analysis. The thermodynamic analysis will also be compared with the operational flexibility that the by-pass solution offers. Applications to some commercial turbines, which are most suited to use in HAT cycle mode, will also be presented
Elementi di psicologia dei gruppi
No full textNonostante gran parte della nostra esistenza sia in qualche modo contrassegnata dall'appartenenza a diversi gruppi, dentro e attraverso i quali cresciamo, lavoriamo, impariamo, giochiamo, l'interesse scientifico verso di essi, e ancor di più il loro studio e utilizzo, sono stati segnati da non poche resistenze, ambiguità e pregiudizi che non hanno pari nella storia delle discipline psicologiche.
La letteratura sui rapporti individuo-gruppo, individuo-società e sui problemi d'identità connessi con questi termini è molto vasta e spazia dalla sociologia alla psicologia, dall'antropologia al diritto. Grazie ai contributi di grandi studiosi afferenti ad aree della psicologia apparentemente differenti tra loro, è stato possibile sottolineare la natura profondamente sociale (gruppale) dell'uomo, superare la presunta dicotomia ontologica tra individuo e gruppo, considerare il gruppo straordinario strumento di sviluppo e trasformazione degli individui, spazio mentale e fisico in cui la convivenza con gli altri consente di soddisfare bisogni soggettivi e plurali, di valorizzare la propria autenticità, nell'incontro con la diversità. "Per comprendere l'intimità e la distinzione tra l'individuo e il gruppo - afferma Solomon Asch - dobbiamo cogliere l'insolito processo che dà vita ai gruppi a livello umano. è un processo nel quale i singoli assumono una parte straordinaria, mettendoci di fronte a un tipo di rapporto parte-tutto che non ha riscontri in natura...
Ciascuna persona è un centro di forze per il gruppo."
è su queste basi concettuali ed epistemologiche che il testo intende muoversi: un'analisi non riduttiva, articolata e multiforme dei possibili ambiti applicativi del gruppo psicologico, che, per poter essere compreso e soprattutto utilizzato, ha bisogno di diversi vertici osservativi che si soccorrano reciprocamente
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
Organizzazioni del potere o potere delle organizzazioni? Un contributo di ricerca per la misurazione del sentimento del potere mediante il Leadership Opinion Questionnaire di Fleishman.
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