1,721,304 research outputs found
Numerical modelling of a PV-T collector working as evaporator in a solar assisted heat pump
Full text linkA numerical study of a PV-T collector working as an evaporator for a solar assisted heat pump is presented. The work has been realized in the framework of the SolairHP project for the study of a reversible dual source heat pump. The main objective is to increase the seasonal coefficient of performance of the heat pump compared to an air source heat pump and reduce the overall electrical consumption by including a solar collector-evaporator. A mathematical steady state model of the solar evaporator device has been realized in Matlab environment: it considers the energy and mass fluxes in three dimensions by working a discretization of the main surfaces of the PV sandwich and of the absorber plate (roll-bond plate). The input of the model are the ambient conditions (irradiance components and air temperature), the thermodynamic conditions of the refrigerant at the inlet (enthalpy and mass flowrate) and the circuitation. The main results of the model are the electric and thermal efficiency, the conditions of the refrigerant all along the channels and the temperature distribution on the PV-T surfaces. The numerical model has been used in the design procedure of the solar evaporators to be coupled to a 8 kW heat pump working with R32. A preliminary seasonal analysis on the PV-T evaporator has been realized in order to evaluate the advantage of the dual source system
Modello Monodimensionale di Previsione delle Prestazioni Fuori Progetto di una Turbina Radiale
No full textExperimental and numerical study of an evaporator with integrated latent heat storage for a compressed air dryer
No full textIn the current work, a latent heat storage system with organic phase change material is integrated in a plate-and-fin evaporator for air dehumidification, embedded in a refrigerated compressed air dryer. The effect of the phase change material type, evaporator geometry and dew point range on the fluctuations of the air temperature at the evaporator outlet and on the compressor cycle duration is experimentally investigated at partial loads. The addition of a paraffin phase change material allows to keep the air dew point temperature variations within the desired range at partial loads and to cut the energy consumption at the compressor up to 40% at 30% partial load. A two-dimensional model for simulating the dynamic behaviour of the plate-and-fin evaporator with latent heat storage is developed in Matlab®. The model aims at predicting the temporal variations of the dew point and phase change material temperatures inside the evaporator and the compressor ON/OFF cycle durations. The numerical results are compared with the experimental data, showing that the model is able to reproduce the performance of the evaporator at partial loads. A parametric study is carried out to analize the effect of the evaporator geometry and type of phase change material on the system performance
Convective condensation at low mass flux: Effect of turbulence and tube orientation on the heat transfer
No full textIt is well proved in the literature that gravity affects in-tube condensation heat transfer at low mass flux.
Nevertheless very limited data are taken at low mass flux when changing tube orientation, despite the
many practical applications. In this paper, convective condensation inside a 3.4 mm inner diameter tube
is investigated in horizontal and vertical downflow using R134a as the working fluid. The experiments are
performed at low mass flux, between 50 kg m-2 s-1 and 200 kg m-2 s-1, which are usually the less investigated
despite the relevance of gravity force at such low velocities. The condensation heat transfer coefficient
in vertical downflow can be as low as half the value in horizontal flow at the same operating
conditions, since gravity acts for the thinning of the liquid film in the horizontal tube. In vertical downflow,
the heat transfer coefficients show an early effect of turbulence, thus a new transition criterion is
here proposed. Criteria for predicting the relevance of channel orientation on the heat transfer coefficient
are also assessed
Experimental measurements on the effect of a modulating ejector in a transcritical CO2 system
No full textCOMPARATIVE ANALYSIS OF TWO-PHASE THERMOSYPHONS SOLAR COLLECTORS
No full textThis paper deals with two-phase thermosyphons used in glazed flat plate solar collectors. It analyses the performance of thermosyphons solar collectors by means of a steady-state mathematical model based on the lumped capacitance method. The model simulates the thermal behaviour of a single tube and of the whole collector at various operating conditions.
The present mathematical model has been validated experimentally using data taken on a copper thermosyphon. A test section has been set up, which is made of a single ended copper thermosyphon, where the input power at the evaporator is supplied by an electrical heater.
The validated model is finally applied to an analysis of two-phase thermosyphons solar collectors with variable configuration
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
Condensation heat transfer of non-azeotropic mixtures inside channels
Full text linkBinary or ternary blends of hydroflourocarbons (HFCs) and hydrofluoroolefins (HFOs) are recently emerging as possible substitutes for the high GWP (Global Warming Potential) fluids currently employed in refrigeration and air-conditioning industry. In the present paper, heat transfer coefficients of a ternary mixture of R1234yf, R32 and CO2, ASHRAE designation R455A, 75.5/21.5/3.0 by mass composition, have been measured during condensation inside a minichannel having a 0.96 mm internal diameter and in a conventional tube with 8.0 mm diameter. Tests have been performed at 40°C mean saturation temperature. The present experimental database is used to assess available predicting correlations for condensation of mixtures, providing information on the applicability of available models
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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