1,720,974 research outputs found
HIGH TEMPERATURE COMPACT HEAT EXCHANGERS:PERFORMANCE OF ADVANCED METALLIC RECUPERATORS FOR POWER PLANTS
Full text linkOTTIMIZZAZIONE DI SCAMBIATORI DI CALORE COMPATTI:SVILUPPO DI UN MODELLO DI CALCOLO PER IL DIMENSIONAMENTO TERMOFLUIDODINAMICO
No full textSCAMBIATORE DI CALORE AD ALTA TEMPERATURA PER IMPIANTI EFCC: DETERMINAZIONE TEORICA E NUMERICA DELLE PRESTAZIONI E DELL’EFFICIENZA
No full textThe heat-pump market in Italy: An in-depth economic study about the reasons for a still unexpressed potential
No full textIn this paper, the Italian heat-pump (HP) market is presented, with an overview over the past 10 years. In order to highlight market potential and barriers, a comparison is proposed between the economic performances of two different heating and domestic hot-water systems, air-to-water HPs and condensing boilers, based on several factors, such as energy costs, thermal loads, climatic conditions, HP-performance classes and some economic indicators such as the payback time and the interest rate. The results are presented in a parametric form, which may be profitably used for a comparative analysis with other European countries. The first part of the paper deals with the analysis of the current Italian HP market, to show its still unexpressed potential. The second part analyses the HP economic convenience with respect to the most commonly used heating technology, i.e. the gas boiler, under conditions typical of the Italian climate. The comparison is carried out in terms of two economic indicators: additional acceptable cost and net present value. The main results show that HP technology is economically competitive in most Italian climatic zones, with a strong dependence on the HP-performance class. In particular, if the best-performing class was adopted, economic gains would be guaranteed over the gas boiler, even with significant variations in the main influencing variables. Thus, the economic issue does not seem to be a limiting factor for HP technology diffusion, at least if the current incentives are maintained. Rather, some other barriers should be removed, such as the supply chain, the training of installation personnel and the final-user awareness
Motive flow calculation through ejectors for transcritical CO2 heat pumps. Comparison between new experimental data and predictive methods
No full textThe revival of CO2 as refrigerant is due to new restrictions in the use of current refrigerants in developed countries, as consequence of environmental policy agreements. An optimal design of each part is necessary to overcome the possible penalty in performance, and the use of ejectors instead of throttling valves can improve the performance. Especially for applications as CO2 HPs for space heating, the use of ejectors has been little investigated. The data collected in a cooperation project between ENEA (C.R. Casaccia) and Federico II University of Naples have been used to experimentally characterize several ejectors in terms of motive mass flow rate, both in transcritical CO2 conditions and not. A statistical comparison is presented in order to assess the reliability of predictive methods available in the open literature for choked flow conditions. © Published under licence by IOP Publishing Ltd
Experimental study on the drying power of a hot jet
No full textExperiments on the drying power of a hot jet, issued from commercial hairdryers, are reported in the paper. A
dedicated experimental apparatus was built and operated: measurements included the air flow rate, and the input
electrical power, while the jet average outlet temperature was derived from the energy balance. The drying power
was estimated by weighing a thin fabric patch before the test and after a prescribed amount of time. Results were
compared with available models of jet drying, showing considerable discrepancy especially for high values of
input power; the reasons for this discrepancy are at present not fully understood, but can likely be found in a
distribution of the temperature of the surface to be dried different from the expected one, that is the adiabatic
saturation.
Finally, the energetic balance of the system was introduced, and an attempt was made to define an energetic
efficiency of the appliance, on the basis of the energy actually spent for evaporation over the input electrical
power. The measured efficiency resulted to be strongly dependent on outlet temperature and weakly dependent
on flow rate, in agreement with the theoretical models
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