1,720,964 research outputs found
Simulation Studies on GAX and GAX Hybrid Absorption refrigeration cycles
No full textThe interest in the absorption refrigeration systems continuously grows in many applications as they can exploit either waste heat or both traditional fuels and renewables (natural gas, sun, geothermal, biomass) as primary energy. Among several configurations of absorption cycles the GAX (Generator/Absorber/heat eXchanger) one plays an important role and allows to achieve good energy efficiencies of energy utilization with no relevant increase in system complexity. Here the analytical models of both GAX and GAX Hybrid (GAX-H) absorption cycles using
ammonia–water mixture as working fluid are presented. Developed in Matlab R2010a, they simulate mass and energy conservation laws in each system component. The thermodynamic properties of ammonia-water solution are calculated based on the equations by Ziegler and
Trepp, on the equations of state by Schultz and on the explicit relations for the bubble point and the dew point temperatures by El-Sayed and Tribus. The developed models were run to investigate the influence on the overall cycles’ performance of the generator, the condenser and the evaporator temperatures, of the absorber pressure and of the heat exchanger effectiveness. Results show the general trends of the efficiency of the cycles and allow the comparison between GAX-H and GAX cycles. When a pressure ratio of 1.5 between the absorber and
evaporator pressure is maintained, the GAX-H COP (Coefficient Of Performance) is 50% and 32% higher than the conventional GAX cycle one operating with a degassing range of 0.2, 0.3 respectively
Impianti Integrati Solari e Geotermici: un’Analisi Prestazionale
No full textFacendo uso dell’ambiente di programmazione TRNSYS, si è condotta un’analisi sulle prestazioni di impianti integrati solare-geotermico utilizzati per la produzione di acqua sanitaria e per la climatizzazione invernale. Il caso di studio di partenza è quello di un’abitazione mono-familiare sita a Brindisi. Creati e testati, dapprima in maniera separata, i modelli di impianti solare e geotermico sono, poi, stati integrati nell’ottica di utilizzare l’acqua calda proveniente dal collettore solare termico nel circuito idronico di scambio a terreno della pompa di calore per mantenerne alta la temperatura di evaporazione. Per questa applicazione, i miglioramenti in termini di consumi e di efficienza dell’impianto prodotti con l’approccio integrato si sono rivelati più ridotti delle attese. Gli studi hanno, in seguito, riguardato le prestazioni dell’impianto integrato in diverse configurazioni caratterizzate da differenti proporzioni tra la superficie dei collettori solari e l’accumulo termico. Lo stesso modello è stato poi applicato a utenze del tipo ufficio con risultati più incoraggianti
Modeling and simulation of a gas absorption heat pump
No full textRising energy costs, increasing requirements in terms of home energy efficiency and greater environmental awareness have brought about great interest in gas absorption heat pumps (GAHP). These systems provide high thermal comfort combined with high energy efficiency and CO2 reductions when compared to state of the art condensing boilers. The gas absorption heat pump uses primary energy (natural gas) directly, which means that it does not require highly exergetic electricity as driving energy for the heat pump process. The gas absorption heat pump subject of this paper uses outside air as renewable heat source. Modeling and simulation is applied in order to gain insight into the main characteristics of the GAHP thermodynamic cycle. The paper presents a modular, steady-state model for the simulation of an air sourced gas absorption heat pump operating with an ammonia-water mixture. The GAHP refrigerant circuit is designed as a GAX cycle (Generator Absorber heat eXchanger) which boosts the efficiency of the unit by recovering the heat that is released from the absorption process. Modeling is based on heat and mass balances for each component. Investigation the cycle performance requires calculation of the thermodynamic properties of the ammonia-water solution. The model uses the equations presented by Ziegler and Trepp (1984), based on the equations of state provided by Schultz (1971). The bubble point temperature and the dew point temperature are computed from the explicit relationship developed by El-Sayed and Tribus (1985).
The model was implemented in MODELICA/DYMOLA. It calculates the heat pump heating power as a function of the water temperature at the inlet and outlet at different outdoor air temperatures. The results are compared with some manufacturer data reported in the open literature. In general a very good agreement between the simulation
results and the experimental data is found. The model is then used to investigate the influence of important design and operating parameters on the performance of the gas absorption heat pump
La figura cinematografica e l'emozione
No full textIl saggio mette in relazione gli ultimi sviluppi della riflessione di Raymond Bellour sull’emozione spettatoriale e il dibattito sul binomio discorso-figura negli studi di cinema. In questo modo sostiene che uno dei meriti del lavoro di Bellour è quello di offrire una base psicologica e una possibile soluzione a un importante problema dell’estetica contemporanea come quello del figurale
Il testo a-specifico e l'agire
No full textIl saggio lavora sul tema dell’indissociabilità di pensiero e azione, cogliendola in una serie di elaborazioni artistiche e teoriche (Godard, Ejzenstejn, Bellour), nonché nelle acquisizioni degli studi di antropologia e psicologia del Novecento.
In questa prospettiva, uno dei testi di cui l’interpretazione deve tenere conto – e perfino il testo che da quell’interpretazione dovrebbe essere privilegiato - è l’ipertesto che si forma nella mente dello spettatore e che risulta costituito dalle tante “illuminazioni”, dalle tante “accensioni” che si depositano nella memoria individuale e collettiva (in dipendenza dall’insieme delle esperienze di cui il soggetto è stato protagonista, e tra queste quelle estetiche) e che va a definire quelli che Bateson chiama “ethos gruppali”, Stern “affetti vitali”, Bowlby “modelli operativi interni”, Weiss “egoicizzazione” delle “riproduzioni autoplastiche”, Ruggieri “decodifica imitativa”, Casadio “pattern mimico-espressivi corporei” e “codifica ‘empatica’ dell’opera d’arte”. Un ipertesto, questa la conclusione del saggio, che è direttamente implicato nell’agire e la cui interpretazione non può avvenire che attraverso un autentico lavoro sperimentale interdisciplinar
The Diffusion Absorption Refrigerator operation and performance
No full textThis chapter focuses on the Diffusion Absorption Refrigerator (DAR) cycle and describes a new advanced thermodynamic model which allows good predictions of the chiller performance in terms of efficiency and cooling capacity, starting from a precise evaluation of the thermo-physical properties of the working mixture at each point of the circuit. A steady state thermodynamic analytical model of the thermal pump driving the DAR is also included. In addition, the experimental validation of the model, performed on a prototype built coupling a domestic 750 W-magnetron with a small purposely modified commercial DAR to activate the thermal pump, is here included: a maximum mismatch of 2.32% in the weak mixture mass flow rate and lower than 5% in COP between the predicted and measured data were found
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
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