1,720,977 research outputs found
CONSIDERAZIONI SU CICLI CON IRREVERSIBILITA' MECCANICHE INTERNE [Consideration on the Cycles with Internal Irreversibilities of Mechanical Nature]
No full textStarting from the fundamental relations relying upon the first and second law of thermodynamics, the cycles with no overall external work are examined in this paper. The restricted conditions to which such systems must satisfy under pre-defined assumptions, are determined. Some of these cycles, which exhibit internal irreversibilities of mechanical nature (cicli dissipativi) are studied in detail; as an instance of application for cycles with a recirculating fluid, the case of the single-phase thermosyphon is analyzed
CICLI DISSIPATIVI E TUBI DI CALORE.
No full textThe behavior of the device known as ′′heat pipe′′ is studied using an irreversible cycle with no overall extgernal work. This cycle has been carefully described in T, S diagram, examining the thermodynamics of capillary phenomena. Starting from this analysis, the following are described: a ′′internal characteristics′′ , due to the thermodynamics and fluid dynamics of the device; an ′′external characteristic′′ defined by the external heat transfer conditions
OSSERVAZIONI SU TUBI DI CALORE A MEDIA TEMPERATURA [Observations on Heat Pipes at Medium Temperatures]
No full textAfter a short review of the current status of studies on this subject, the paper describes an analytical optimization method. Experimental apparatus is described and results of tests of a heat pipe operating with water up to the temperature of about 150 C are presented. In particular, the effect of condenser parameters on the heat transfer is investigated
GRAVITY HEAT PIPES AS GEOTHERMAL CONVECTORS
No full textDesign of and tests on a gravity heat pipe transmitting up to 25 kW thermal power from a surface aquifer in a volcanic area are described. This includes laboratory tests on a single pipe immersed in a thermostatically controlled water sink, which enabled determination of overall pipe conductance, and is followed by details of the design and construction of a full scale device
CONSIDERAZIONI SUGLI SCAMBIATORI INDIRETTI A TUBI DI CALORE
No full textHeat pipe heat exchangers are typically made of finned pipes which transfer the heat between two fluids in counterflow: these fluids are completely separated. The effectiveness of these indirect type exchangers has been studied as a function of the classical parameters of heat transfer (NTU method). The temperature profiles of the heat exchanger, have been analyzed. A detailed comparison with the classical liquid coupled indirect type exchangers has been made for the first time
Il termosifone bifase impiegato quale dissipatore di calore per diodi e tiristori di potenza
No full textThis work deals with a two-phase thermosyphon applied to cooling power electronic components. The difference between a typical heat sink with thermal gradient and one with a two-phase thermosyphon is shown. On the basis of general design criteria, a cooling device of this type for a 1. 0 kw thyristor has been realized. Heat transfer performance of this dissipator has been experimentally determined: the thermal resistance of about 0. 025 degree C/W, obtained by using this radiator with forced convection in air, is very similar to that offered by the devices employing water in forced convectio
DIMENSIONAMENTO DI UN GEOTERMOCONVETTORE: SOLUZIONI, CRITERI E METODI DI CALCOLO
No full textOn the basis of studies carried out during the Progetto Finalizzato Energetica 2, an unconventional system for heat extraction from a geothermal aquifer without fluid withdrawal has been conceived and developed. In the system a special two-phase thermosyphon, called a geothermal convector (GTC), is used. This device operates with a downhole evaporator and a condenser at the ground level. In this paper the problems of this application are described: the fundamental elements for determining the device performance and the thermal design criteria are reported. Moreover, a method for designing the system for activating the geothermal fluid convection inside the well is given. Finally, to exemplify the possible results of this design procedure, a GTC prototype, in an advanced stage of realization, is described
Sistema di Raffreddamento Passivo di Celle Solari per un Concentratore Cilindro-Parabolico
No full textTHE GEYSER EFFECT IN A TWO-PHASE THERMOSYPHON
No full textAn interesting phenomenon, which was observed during experimental research work carried out on a two-phase thermosyphon with water as the working fluid, is described. The phenomenon is a pulsed boiling at low pressure and was called the ′′Geyser Effect′′ . The heat transfer coefficient at the thermosyphon evaporator has been measured and a functional law, which links this coefficient with the pressure and the specific thermal flux, is proposed
VALUTAZIONI SPERIMENTALI E TEORICHE DI GRADIENTI TERMICI IN UN TRAVELLING GRADIENT RIG
No full textAfter a brief exposition of the scope of the traveling gradient method, a heat pipe employed as a thermostat in a ′′Traveling Gradient Rig′′ is described. Experimental results of temperature distribution along the axis of a thermocouple with maximum gradients of about 27 degree K/mm are reported. Their shape and slope is analyzed theoretically
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