1,720,985 research outputs found
Definition and sensitivity analysis of a finite volume SOFC model for tubular cell geometry.
No full textA finite volume model of a solid oxide fuel cell has been developed. The model applies a detailed electrochemical and thermal analysis
to a tubular SOFC of given geometry, material properties and assigned input flows. Electrochemical modeling includes an evaluation of
ohmic, activation and diffusion losses as well as a kinetic model of hydrocarbon reactions, based on most recent literature experiences.
Internal heat exchange coefficients have been calculated with a specific fluid-dynamic finite volume analysis. The model is calibrated on
the available experimental data for atmospheric and pressurized tubular SOFCs, showing the capacity of predicting accurately the SOFC
operating conditions. The model generates total cell balances and internal cell profiles for any relevant thermodynamic or electrochemical
variable, giving the possibility of discussing the effects of different operating conditions on the internal FC behavior. A sensitivity analysis
is carried out to investigate the effects of different assumptions on a selection of key model parameters involved in the calculation of cell
losses, internal heat exchange process and reforming reactions. Among other results, it is shown that the importance of the adoption of
appropriate parameters for the evaluation of activation polarization, as well as the relevance of a kinetic model for reforming reactions
Energy performance and well-to-wheel analysis of different powertrain solutions for freight transportation
No full textIn this paper we compare energy performance and environmental impact of four nominal weight classes of commercial vehicles with different powertrain solutions: conventional diesel internal combustion engine (ICE), Plug-In Electric Vehicle (PHEV), Battery Electric Vehicle (BEV) and Plug-In Fuel Cell Vehicle (PFCV). First, the sizing of the various powertrain components is performed adopting a simplified calculation based on a rule-based model. Then, the energy performances are evaluated through simulation over different driving cycles carried out with a self-developed Matlab/Simulink® simulator tool based on a forward-looking approach, that implements a control strategy that targets the instant velocity specified by the driving cycle. We show that when the optimal control strategy based on the Pontryagin's Minimum Principle is adopted, the fuel consumption significantly reduces with respect to the simplified rule-based control strategy approach. Finally, the overall specific energy consumption and the corresponding greenhouse gases (GHG) emissions are evaluated by means of a well-to-wheel analysis, considering various possible scenarios, covering the main traditional and low emission solutions for production, transportation and distribution of diesel, electricity and hydrogen. As expected, the highest GHG emissions are obtained in case of fossil origin of the energy carrier, with maximum value of 270 gCO2/km/kg in case of 3.5 ton truck with traditional diesel ICE, due to the low powertrain efficiency compared to the other considered solutions. Moreover, both the specific primary energy consumption and GHG emissions proportionally reduce with tonnage, as a consequence of the progressive reduction of the fraction of the powertrain weight with respect to the total vehicle mass
Modelling of a 15-kW Electric Utility Vehicle and Range Assessment through Driving Cycle Analysis Based on GPS Experimental Data
No full textThe electrification of utility vehicles represents a promising solution to reduce the emissions in the urban context. Differently from traditional vehicles, they operate intermittently and generally follow routine driving cycles. In this paper, we model a 15-kW electric utility vehicle, adopting a backward-looking approach, widely used in literature to estimate the range of electric cars. The model requires a limited number of data, either supplied by the vehicle manufacturer or found in literature, as in case of the induction motor/generator efficiency and of the battery Peukert coefficient. The model can be used to assess the possibility of the vehicle to complete an assigned mission, as well as to optimize the vehicle's design and architecture. The model is validated on GPS data obtained through an experimental campaign where the electric utility vehicle was driven to depletion considering different routes, including the effect of slopes. A satisfactory correspondence with the experimental data was observed with maximum difference in the simulated average energy consumption lower than about 8%. Results of the simulations show that the range of the electric utility vehicle is about 110 km on urban flat cycle while it significantly reduces when slopes are included in portions of the routes
Electrification of compact off-highway vehicles—overview of the current state of the art and trends
Full text linkElectrified vehicles have undergone great evolution during the last decade because of the increasing attention paid on environmental sustainability, greenhouse gas emissions and air pollution. Emission regulations are becoming increasingly tight, and governments have been allocating multiple funds to facilitate the spreading of the so-called green mobility. In this context, steering towards electrified solutions not only for passenger vehicles, but also for compact off-highway vehicles extensively employed, for instance, on construction sites located in urban areas, warehouses, and greenhouses, is essential even if seldom considered. Moreover, the electrification of compact offhighway machinery may allow manufacturers to increase their expertise in and lower the costs of these alternative solutions, while gathering useful data to be applied in bigger and more remunerative off-highway vehicles. In fact, while electric automobiles are as of now real alternatives for buyers, off-highway vehicles, regardless of the application, are mostly in the research and experimental phase, with few of them already on the market. This delay, in comparison with the passenger automotive industry, is caused by different factors, mostly related to the different tasks of off-highway vehicles in terms of duty cycles, productivity performance parameters and user acceptability. The aim of this paper is to give an overview of the many aspects of the electrification of compact off-highway vehicles, to highlight the key differences between on-highway and off-highway vehicles and to summarize in a single source of information the multiple solutions investigated by researchers and manufacturers
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
A one dimensional solid oxide electrolyzer-fuel cell stack model and its application to the analysis of a high efficiency system for oxygen production.
No full textThis paper presents a finite difference one-dimensional(1D)model of a single unit SOFC–SOEC stack, a novel technology based on the integration of a solid oxide fuel cell (SOFC) and solid oxide electrolyzer (SOEC), and a promising candidate for the high efficiency production of oxygen and/or hydrogen,
especially for small scale applications.The model is applied to determine the performance of a SOFC–SOEC integrated system for oxygen production which has been previously analysed by means of a
simplified zero-dimensional or lumped volume approach.The improved 1D model is used to explore
the impact ofdifferent system configurations and operating conditions. It is shown that the simplified
approach previously used overestimates the performance of the system by up to 60%.Despite this, the
results presented here show an electricity consumption in optimized conditions in the range of 0.35–0.5 kWh/kgO2, still significantly lower than that of state of the art technology for small scale oxygen
production systems
Fluorobenzene as new working fluid for high-temperature heat pumps and organic Rankine cycles: Energy analysis and thermal stability test
Full text linkIndustrial high-temperature heat pumps and Organic Rankine Cycles play a pivotal role in reducing CO2 emissions of the industrial sector. While several eco-friendly refrigerants have been explored for subcritical heat pumps below 150 °C, above this threshold only a few fluids can be adopted. In this article, fluorobenzene (C6H5F) is proposed for the first time as a versatile working fluid suitable for both HTHP and ORC systems. Notably, it possesses a near-zero Global Warming Potential, null Ozone Depletion Potential, low cost, and low toxicity. The thermo-chemical stability of fluorobenzene is experimentally investigated with an advanced procedure, simulating the presence of the non-condensable-gases removal system in real plant operating conditions. The yearly rate of unimolecular decomposition is estimated less than 4 % at 350 °C, and even after 400 h of thermal stress no decomposition products have been detected in the liquid phase through Fourier Transform Infrared Spectroscopy. In a direct heat exchange case study, coupled with exhaust gases at 390 °C, fluorobenzene achieves a net power production higher than other commercial fluids adopted in high-temperature units. In subcritical two-stage throttling heat pump condensing at 180 °C fluorobenzene shows a good Coefficient of Performance of 3.25 at 100 °C temperature lift
Experimental isochoric apparatus for bubble points determination: Application to CO2 binary mixtures as advanced working fluids
Full text linkCarbon dioxide binary mixtures are increasingly considered as working fluids in transcritical power cycles, due to the capability to perform liquid-phase compression even at high environmental temperatures. However, a robust thermodynamic model is essential for optimal and reliable design conditions. It is widely recognised that fine-tuning the equation of state with experimental vapour-liquid equilibrium data of the mixture significantly enhances its reliability.In this work, a new apparatus dedicated to vapour-liquid equilibrium measurements of mixtures is presented. The proposed method consists of a constant-volume system, where bubble points are identified from the divergence of slope of the isochoric lines between the two-phase and liquid regions, in the temperature-pressure plane. The temperature and pressure limits of the apparatus are 503 K and 25 MPa.Bubble points of CO2 binary mixtures with hexafluorobenzene (C6F6) and n-pentane (C5H12) have been measured and compared with previous literature data for validation purposes. Then, the CO2 mixture with octafluorocyclobutane (c-C4F8) is experimentally studied, addressing a literature gap in bubble point data. The data are used to calibrate the thermodynamic model, leading to affordable design conditions of the power cycle compared to the non-optimised thermodynamics scenario, in a concentrated solar power tower plant
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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