13,737 research outputs found
Fragmentation measurements with the FIRST experiment
No full textThe Phd thesis presented here documents the work performed within the FIRST collaboration. The research work was focused on the analysis of data collected for the interaction of a 12C beam at 400 MeV/nucleon on the thin targets. In particular I have dealt with the calibration of some detectors of the FIRST apparatus, the charge identification algorithm, the tracks reconstruction and the background studies. The results of this analysis work are the differential fragmentation cross sections, here presented, measured as a function of the fragment angle and kinetic energy in the forward angular region (θ . 6◦). Furthermore, I have also studied a possible upgrade of the FIRST experimental apparatus with an improved detector setup to enhance the fragments reconstruction and identification performances. In chapter 1 an introduction to particle therapy will be given and the mechanisms of interaction of ions with matter will be reviewed with a particular focus on the energy range of interest for particle therapy applications. Chapter 2 will deal with the nuclear fragmentation models and measurements. In chapter 3 the FIRST apparatus and the detector calibration strategies will be described. In chapter 4 the analysis techniques used for the reconstruction of fragment tracks in the forward angular region of FIRST and the results of the elemental and isotopic single differental cross sections with respect to angle and energy will be discussed. Finally, in chapter 5, a possible upgrade of the FIRST apparatus will be proposed
Performance assessment of a double-lift absorption prototype for low temperature refrigeration driven by low-grade heat
No full textThis work investigates the use of a water-ammonia double-lift absorption cycle for low temperature refrigeration driven by low-grade heat, as waste-heat or solar energy. Among the various double-lift cycles, the investigation focuses on the self-adapting two-pump series cycle, using water-ammonia as working pair. At first, by means of a numerical investigation, it is verified that an air cooled unit can operate with driving temperature of 90 °C, air temperature up to 32 °C and brine temperature down to −15 °C. Then, it is discussed how to modify an existing prototype to achieve the mentioned working conditions. The influence of the two restrictors of the refrigerant on the cycle behaviour is discussed in a qualitative manner, pointing out that the restrictor after the condenser sets the intermediate and low pressures and, consequently, the maximum allowed thermal lift. Finally, the prototype performances are experimentally assessed, confirming that the influence of the restrictor between high and intermediate pressure and pointing out that the use of a fixed restrictor prevents the full exploitation of the potential of the cycle. As a consequence, the use of a variable restrictor could represent an option for optimizing the appliance COP in a wide range of thermal lifts. © 2017 Elsevier Lt
A water-ammonia heat transformer to upgrade low-temperature waste heat
No full textA prototype water-ammonia absorption heat transformer has been built and thoroughly tested. Compared to water-salts mixtures, water-ammonia allows operating the machine in a lower temperature range, fostering recover of low-grade heat. Driving temperatures between 60 °C and 64 °C were tested, with condenser temperatures of 8–16 °C. The unit proved able to operate in a stable, reliable and repeatable way in this working range, achieving gross temperature lifts up to 25 °C and thermal COPs in the range 0.400–0.475. Useful effect up to 4.5 kW was achieved, with electric consumption always below 100 W
MABS validation through repeated execution and data mining analysis
No full textAgent Based Modelling is the most interesting and advanced approach for simulating a complex system: in a social context, the single parts and the whole are often very hard to describe in detail. Besides, there are agent based formalisms which allow to study the emergency of social behaviour with the creation and study of models, known as artificial societies. Thanks to the ever increasing computational power, it's been possible to use such models to create software, based on intelligent agents, which aggregate behaviour is complex and difficult to predict, and can be used in open and distributed systems. Data mining is born in the last decades in order to help users in finding useful knowledge from the otherwise overwhelming amount of data available nowadays from the web and the data collected every day by companies. Data Mining techniques can therefore be the keystone to reveal non-trivial knowledge expressed by the initial assumption used to build the micro-level of the model and the structure of the society of agents that emerged from the simulation
Analysis of gas-fired NH3-H2O generator with cross flow gas burner
No full textThis paper presents a model to simulate the combined heat and mass transfer processes that occur in a gas-fired generator of an ammonia water absorption heat pump. The model comprises three interconnected components: the gas furnace, the distillation column and the rectifier. The furnace is modeled like a well-stirred single volume. The distillation column and the rectifier are discretized along their axial dimension. Several heat transfer mechanisms are simultaneously solved: radiative and convective heat transfer between combustion products and generator finned surface, flow boiling and pool boiling in the two-phase ammonia water mixture inside the distillation column. The model is applied to operating conditions of interest in real applications. The generated outputs provide insight on the internal gradients, the quantification of gas furnace efficiency, and effectiveness of solution boiling and internal heat recovery. The model can be used for the simulation of absorption heat pumps with modulating gas burners. © 2015 Elsevier Ltd. All rights reserved
Experimental characterization of a newly developed air-source waterammonia gas absorption heat pumpfor residential applications
No full textModelling and experimental analysis of a GAX NH3-H2O gas-driven absorption heat pump
No full textThe experimental analysis of a gas-driven NH3-H2O heat pump whose cycle approaches the GAX concept is carried out. Full load operation is investigated by varying hot water temperatures and partial load operation is investigated by decreasing gas input down to 50% of the full load value. Numerical simulations bolster measurements accuracy and provide insight on the variation of cycle COP and Gas Utilization Efficiency (GUE), based on gross calorific value. A nearly constant GUE of about 1.5 is found for hot water temperatures lower than 50°C. The GUE steadily decreases above 50°C, reaching about 1.33 at 60°C. The COP varies more smoothly, from 1.73 at 45°C to 1.60 at 60°C. The GUE and COP reduction at 50% of the nominal gas input is 6.8% and 6.4%, respectively. Simulations suggest that performances at partial loads can improve if active control of solution mass flow rate is implemented. © 2016 Elsevier Ltd. and International Institute of Refrigeration. All rights reserved
Macchina termica
No full textMacchina termica (1) comprendente:
- una miscela refrigerante comprendente almeno un fluido ed un cofluido avente
volatilità inferiore alla volatilità del fluido;
- un condensatore (2);
- un compressore (3) che comprime ed invia al condensatore, mediante una linea
di alimentazione (4), flussi di vapore (V) della miscela refrigerante in cui il fluido è
presente in una concentrazione prevalente rispetto al cofluido, il condensatore
condensando almeno parzialmente i flussi di vapore (V) mediante cessione di calore
ad un primo fluido di scambio termico (F1);
- mezzi regolatori di flusso (10, 12, 14, 15) atti a immettere lungo la linea di
alimentazione (4), per essere miscelati con i flussi di vapore
nel condensatore, flussi liquidi (L) della miscela di refrigeranti in cui il cofluido è
presente in una concentrazione prevalente rispetto al fluido;
- un evaporatore (5) che riceve in ingresso flussi di miscela refrigerante usciti dal
condensatore, evapora in parte i flussi ricevuti mediante assorbimento di calore da
un secondo fluido di scambio termico (F2), ed emette flussi di miscela refrigerante
aventi una parte in fase di vapore arricchita di fluido ed una parte in fase liquida
arricchita di cofluido;
- un separatore di fasi (7) che riceve e separa tra loro, i flussi di miscela
refrigerante aventi una parte in fase di vapore ed una parte in fase liquida, la parte
di miscela in fase di vapore essendo destinata al compressore, la parte di miscela
in fase liquida essendo accumulata in un accumulatore (8) compreso nel o associato
al separatore di fasi. Il controllore (50) pilota anche uno o più tra i mezzi regolatori
di flusso in modo da variare la quantità di miscela in fase liquida arricchita di cofluido per
immettere flussi liquidi (L) lungo la linea di alimentazione (4)
Modeling and experimental validation of a tube-in-tube refrigerant cooled absorber
No full textA model for predicting heat and mass transfer and pressure drops occurring inside a tube-in-tube refrigerant cooled absorber (RCA) is developed. This heat exchanger is used as a low pressure absorber in a half-effect water-ammonia absorption chiller. The two-phase stream, resulting from the mixing at low pressure of the weak solution coming from the generator and the refrigerant leaving the evaporator, flows in the tube-in-tube annulus, while the stream of condensed refrigerant, throttled to a pressure level intermediate between condenser and evaporator pressures, flows counter-current in the internal tube. The RCA model is validated by comparing overall heat transfer duty, pressure drops on each stream and temperature axial profile in the annulus with experimental data. Results are in reasonable agreement with experiments in most of the analyzed cases, although some deviations exist in off-design operations. A sensitivity analysis of the model has shown that the measurement uncertainty of the inputs to the model does not affect the validity of the results
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