1,721,028 research outputs found
Energy and exergy analysis of a geothermal heat pump air conditioning system
No full textThis paper considers the energy analysis of a heat pump system coupled to the ground by means of vertical exchangers, to verify which thermodynamic boundary conditions, in terms of thermal conductivity and diffusivity of the ground and the grout, make it competitive in comparison with other technologies harnessing atmospheric air as the heat source. The comparison is based on the maximum theoretical efficiency available in correspondence to the temperature effectively assumed by the thermal energy reservoirs in contact with the evaporator and the condenser during the operating conditions. The comparison of the two sources/sinks of heat, i.e. the ground and atmospheric air, represents the comparison between the time trend of the exergy of the two reservoirs required by an ideal GSHP and ASHP respectively. A fully transient heat transfer model able to handle on a time scale of a year or more and with a refinement of less than an hour is considered, since short term variations have significant effects on the overall performance of GSHP. In this paper the borehole heat transfer problem in the Laplace domain is solved for any trend and duration of thermal loads, taking into account an existing analytical approximation model of the full solution proposed by Lamarche and Beauchamp. A numerical inversion using the Inverse Discrete Fourier Transform is then applied to obtain the time domain solution. The method combines the flexibility and accuracy of the analytical model with the superior efficiency of the computational time offered by the numerical inversion if compared with that of methods based on the convolution scheme
The usefulness of artificial neural networks in predicting the outcome of hematopoietic stem cell transplantation: a crystal ball to foresee the future?
No full textMarginal condition for spontaneous oscillations of a thermoacoustic engine coupled with a piezoelectric element. Analytical ana experimental study
No full textThis paper deals with the problem to derive a marginal condition for the onset of spontaneous thermoacoustic oscillations of a gas in a circular tube, subject to a variable shape of the temperature gradient along the side wall, with one end rigidly closed and the other closed by a piezoelectric element converter. In this study the acoustic impedance of the piezo element is arbitrary in order to achieve marginal conditions between those exhibited with rigidly closed end, and those with end opened onto free atmosphere. Moreover, marginal condition is outlined adopting a variable shape of the temperature gradient with respect to the position of the stack along the tube. The solution includes all dissipative effects related to the compressive and shear viscosity and the heat transmission in the boundary layer at the side wall and end wall
Marginal condition for the onset of Thermoacoustic Piezo System oscillations with variable impedance and subject to variable temperature gradient
No full textThis paper deal with the problem to derive a marginal condition for the onset of spontaneous thermoacoustic oscillations of a gas in a circular tube, subject to a variable shape of the temperature gradient along the side wall, with one end rigidly closed and the other closed by a piezo electric element. In this study the acoustic impedance of the piezo element is arbitrary in order to achieve marginal conditions between those exhibited with rigidly closed end, and those with end opened onto free atmosphere. Moreover marginal condition is outlined adopting a variable shape of the temperature gradient respect to the position of the stack along the tube. The marginal condition is provided at the same time respect to variable piezo-impedance and variable position of the acoustic driver. The solution includes all dissipative effects related to the compressive and shear viscosity and the heat transmission in the boundary layer at the side wall and end wall. The formulation is given in the framework of the linear theory and the first order theory in the ratio of a boundary layer thickness to the tube radiu
Un Algoritmo per il calcolo del fabbisogno regionale di energia per il riscaldamento residenziale
No full textSolar Energy System in A Small Town Constituted of A Network of Photovoltaic Collectors to Produce Electricity for Homes and Hydrogen for Transport Services of Municipality
No full textThe supply of Energy resources to the villages located in inland and hilly regions, is disadvantageous both for the domestic and transport purposes. Because these conditions may produce the depopulation of the inland zone, a smart way to ease this inconvenience is to produce in situ electrical Energy for houses and fuel for cars, getting them from an available Energy source in the village, as the solar Energy. The only technology to produce hydrogen ecologically and to minimize CO2 emission, is through RES (Renewable Energy Sources). The solar energy plants must use the surfaces of buildings instead of occupying other green areas useful for agricultural activities. On this basis, we propose in this paper a demonstrative project for a village in Sardinia, consisting of photovoltaic collectors connected in a network, to provide electricity to homes and hydrogen for transport purposes
Energy analysis of a geothermal heat pump air conditioning system for regions with mild climates
No full textAssessment and comparison among prediction methods for the low frequency noise produced by wind turbines: Application to a case study
No full textThe present energy scenario leads to an acceleration in the development of the exploitation of renewable sources. Latest regulations impose higher and higher percentage shares of energy from renewable sources. The current technological advancement stresses the wind energy as an energy source endowed of a special reliability. The technology to take advantage of such a source is based on large size wind turbines, with a rated power of about 3 MW. Among the main environmental problems that have to be faced in planning a new wind farm, the acoustic impact stands out. It consists of the noise engendered by wind turbines with a special effect of the noise emitted at the low frequency spectrum. Recently Denmark has produced a new regulation which calls for specific procedures for the assessment of noise at low frequencies. Purpose of the present work to take stock of the procedures currently employed in the predictive study of the low frequency noise produced by wind turbines. The analysis was carried out by applying the expounded procedures to a real case situated in Sardinia. It concerns a wind farm formed with 21 large size turbines, where a comparison between the results obtained by applying the procedures of ISO 9613 and those provided for by the Danish regulation is show
Influenza sugli indici di valutazione dei requisiti acustici passivi in situ della misura del tempo di riverberazione
No full textA diversi anni dall’entrata in vigore del DPCM 5\12\97 si verificano sempre più casi di contenzioso fra venditore ed acquirente, talvolta basate su risultati differenti ottenuti in situ, nelle misure fatte eseguire dalle parti in causa. Il presente lavoro valuta come la misura del tempo di riverberazione in opera, eseguita in uno stesso ambiente, con l’utilizzo delle metodologie di misura basate sul rumore interrotto o sul rumore impulsivo, incida sugli indici di valutazione dei requisiti acustici passivi a seconda della tipologia di sorgenti utilizzate
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