1,721,537 research outputs found
Numerical analysis of heat removal enhancement with extended surfaces
No full textThe problem of heat removal is a major issue in modern industry. The reasons for researching in this field are both to increase the performances of the target systems and to reduce the damages that high temperatures can cause. The present trend in high-tech production processes is to seek better performances by means of smaller devices. Aiming at this, it becomes necessary that all the components of the system examined are designed to supply the best possible performance. This paper faces the problem of optimising fins to enhance heat removal. The analysis so conjugates geometrical and thermo-fluid mechanical aspects. The starting point of this activity was a research, based on the Bejan's Constructal Theory, which focused on heat removal enhancement from high temperature surfaces through T-shaped fins. Initially, the same system was here numerically investigated using a CFD code. The performances computed were very similar to the reference ones. This validation allowed to apply the method to new configurations, so to develop systems further on optimised, able to remove higher thermal fluxes in the same processes. Y-shaped profiles were consequently examined, obtained by varying the angle between the two arms of the original T. The idea of performance optimisation as proposed in the reference work, was initially based on the maximisation of the dimensionless thermal conductance. This was here widened to a new definition taking into account thermal efficiency as another parameter of evaluation. It was, in fact, observed that the width reduction, typical of Y-shaped profiles with respect to T-shaped ones, enhance efficiency significantly.This new approach to heat removal optimisation suggested the realisation of arrays with multiple Y-shaped fins. Each array had the same width of the corresponding optimised T-shaped fin. This choice allowed immediate comparisons, so to evaluate the actual performance enhancements typical of multiple-fin configurations, with respect to previous configurations
Thermofluid dynamic performances numerical-constructal analysis of heat exchangers with standard and optimized profiles
No full textA Bejan’s Constructal Theory approach to the overall optimization of heat exchanging finned modules with air in forced convection and laminar flow condition
No full textNumerical analysis on heat removal from Y-shaped fins: efficiency and volume occupied for a new approach to performance optimisation
No full textThis paper faces the problem of geometric optimisation for exchanger profiles with innovative shapes. In particular it was analysed the Y shape, keeping the dimensionless thermal conductance as reference parameter like in the thematic technical literature. The use of suitable geometrical constraints allows wide comparisons with papers in literature using different kinds of geometries.The methodological approach here chosen is numerical and utilises a CFD software. The geometries examined are obtained by varying the angle between the two arms of the Y, starting from the T-shaped profile that allows the best performances, as obtained in a previous work. Results show that the new shape proposed for the fins, together with the assessment of the horizontal width, leads to a novel performance evaluation criterion
Fuzzy Norms, Default Reasoning and Equilibrium Selection in Games under Unforeseen Contingencies
Full text linkLIUC PAPERS 104, Etica, diritto ed economia, 6-aprile 2002 (2 edizione). This paper concerns the role that norms play in the emergence and selection of equilibrium points seen as social conventions under unforeseen contingencies – that is in the emergence of regularities of behaviour which are self-enforcing and effectively adhered to by limited rational agents due to their self-policing incentives. We define two version of a basic demand game such that in each of them players know that a given solution (norm) is shared knowledge (the Nash product and the typical non cooperative solution of a DP – both coinciding to equilibrium points of the demand game). The basic incomplete knowledge situation is then introduced by assuming that a move of Nature selects states of world where one of the two versions of the basic game will be played. However some of the states of the world that nature may choose are unforeseen. Thus players, when nature has made its choice, will face states that they ex post know to occurs, but that are vaguely described in terms of their ex ante knowledge about the rules of the game. Unforeseen contingencies are then modelled as states that can belong to events defined in terms of the ex ante base of knowledge only through fuzzy membership functions. Players must decide which strategy to play under this characteristic lack of clear information, i.e. under vagueness on the game they are going to play. Their information is resumed by a fuzzy measure of membership that induces a possibility distribution but does not allow them a shared knowledge of the norms (solution), which is played in the given game. Consequently there is no basis at this stage to infer that everybody know that a given equilibrium will be played and to conclude that a player must use his best response belonging to a given equilibrium solution. A default reasoning process here enters the scene, based on the reformulation of default logic in terms of possibility theory given - after Zadeh - by Dubois, Prade and Benferhat. At the first step of the recursive reasoning process, each player's first hypothetical choice, given the basic vague knowledge about the game they are going to play, is calculated in term of a fuzzy expected utility function - where fuzzy utility is considered in conjunction with a possibility measure on unforeseen states. At the second step, each player must guess the simultaneous reasoning process performed by the counterpart. Maybe fallibly, each player attributes by default to the other player his own scheme or reasoning, because it seems to himself the most “normal course of facts” - since he does not know about any falsification of this scheme of reasoning. This is provided by encoding the knowledge base that players have on the game and their default rules of inference - enunciates like “normally players own such information” or “normally a player who owns such information plays strategy such and such in a game like this” - by the formulae of a formal language on which we are able to induce a possibility ordering. The ordering will represent constraints on what the players believe as the “normal course of facts”, which are imposed by the default rules that extends the players' base of knowledge. Then, at the third step we may calculate each player second hypothetical choice given the reconstruction of the other player symmetrical reasoning and the ensuing new possibility assignment on the counterpart's action under any game in each state. This carries to a new best response for each of them in fuzzy expected utility terms. Iterating the procedure will not change the set of predicted choices. So that we can conclude that the default-possibilistic reasoning will stabilize in a couple of strategy choices that constitutes one of the basic games' equilibrium points. We end up by suggesting that the resulting equilibrium will be supported by what in default logic is called the extension of a given theory - which is characterised as a fixed point - obtained by iterately applying to it the set of accepted defaults, without introducing a contradiction. Is to be noted that default logic is non-monotonic, and allows for mistakes and revisions, which seems to belong to the very nature of bounded rationality
A Fuzzy Logic and Default Reasoning Model of Social Norms and Equilibrium Selection in Games under Unforeseen Contingenies
No full textThis paper focuses on the role that social norms play in the selection of equilibrium points seen as social conventions under unforeseen contingencies — that is, their role in the emergence of regularities of behavior which are self-enforcing and effectively adhered to by bounded rational agents due to their self-policing incentives. Differently stated, given a set of game situations imperfectly described, we want to understand how general and abstract norms provide at least the starting point for a norm-based equilibrium selection reasoning procedure which in the end will be able to determine which equilibrium point, belonging to perfectly described games, will be played as the unique solution of each imperfectly described game. In order to solve such a problem we introduce a selection process based on the reformulation of default logic in terms of possibility theor
recensione della mostra: La Collezione Borgia. Curiosità e tesori da ogni parte del mondo
No full textLa recensione della mostra è realizzata seguendo un percorso dedicato agli oggetti arabi (monete, manoscritti, metalli, ....) che facevano parte della collezione del cardinale Stefano Borgia, mettendo in luce il valore delle vestigia arabe da questi raccolte e l'interesse per il mondo arabo che già alla fine del Setteento animava il suo spirito.The review of the exhibition is made following a path dedicated to the Arab objects (coins, manuscripts, metals, ....) that were part of the collection of Cardinal Stefano Borgia, highlighting the value of Arab vestiges collected by them and interest for the Arab world since the end of Setteento animated her spirit
A CFD application to optimize T-shaped fins: comparisons to the Constructal theory's results
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