Detailed analysis of an endoreversible fuel cell : Maximum power and optimal operating temperature determination

Producing useful electrical work in consuming chemical energy, the fuel cell have to reject heat to its surrounding. However, as it occurs for any other type of engine, this thermal energy cannot be exchanged in an isothermal way in finite time through finite areas. As it was already done for various types of systems, we study the fuel cell within the finite time thermodynamics framework and define an endoreversible fuel cell. Considering different types of heat transfer laws, we obtain an optimal value of the operating temperature, corresponding to a maximum produced power. This analysis is a first step of a thermodynamical approach of design of thermal management devices, taking into account performances of the whole system.Comment: 15 pages, 10 figure

Finite time analysis of an endoreversible fuel cell

The aim of this paper consists in a detailed thermodynamical description of a fuel cell, using finite time thermodynamics (FTT). Starting from the comparison beetween a reversible fuel cell and a Carnot heat engine driven by a perfect chemical reaction, we remind that – contrary to a common opinion – both systems have the same thermodynamical performances. Thereby, we evolve the comparison beetween these two systems to the area of finite time thermodynamics. The main results is the definition of an endoreversible fuel cell characterized by a maximum-power efficiency

Analysis of the thermal variations in a moving pantograph strip using an electro-thermal simulation tool and validating by experimental tests

The performance of the pantograph-catenary system is very significant in supplying reliable electrical power for the operation of trains. Many problems arise due to the increase in temperature inside the pantograph strip. More research works have been done to study the temperature extrema of the system but it is quite difficult to obtain the experimental values during a real-time train operation. Moreover, performing experimental tests needs a representative test bench of the system or a real train. This is challenging owing to the time and availability of materials and taking into account the number of physical phenomena to control and measure. To address this problem, the authors of this study present an electro-thermal modeling tool. The heat sources which characterize the system are analyzed to generate a heat equation formulation. This equation is solved with the finite differences numerical method in order to obtain the temperature distribution in the pantograph strip. In addition, some specifications such as computation time or required memory are taken into account. More precisely, mathematical and numerical optimizations are proposed to improve these specifications. The tool is validated by comparing the simulated results with the experimental tests obtained from a test bench located at POLIMI (Polytechnico Di Milano, Milan). Finally, thermal interpretations as well as relative gap analyses are done in different situations

An experimental investigation of the thermal behaviour of a moving pantograph's strip

In a railway system, electrical power supply is ensured by a sliding contact between the catenary wire and the pantograph collector strip. The contact between the two interfaced materials involves many physical phenomena which generate a temperature increase of the strip-wire system and its related deterioration. Determination of the temperature distribution in the contact strip is complex and in this paper, we propose an experimentally study of all the different parameters that contribute to the temperature increase of the strip. The tests were carried out on a test bench able to reproduce the electromechanical sliding contact between the collector strip and the contact wire and so the associated wear. Specific thermal instrumentation was created to accurately visualize all the thermal phenomena in the strip. The results show the temperature distribution in the strip for many configurations of the entry parameters such as: electrical current, applyed contact force, train velocity, stagger motion amplitude, air flow velocity and material type. Finally, an analyse of all the collected results is done and many conlusions can be assumed, namely: - The Joule effect induced by the electrical current circulation into an electrical contact resistance, as well as the temperature increase due to friction are the most important heat productions of the system. - The intern thermal parameters of the collector strip caracterise the thermal evolution of the system. The analyse of specific numbers such as solid Peclet number, system response time or thermal diffusivity allows some basic principles related to the material quality in function of the train power supply strains. - Thermal peaks appear in particular times and positions. Such phenomena give a glimpse, from a thermal point of view of the worse phases during a train travel

A New Experimental Method to Determine the Sorption Isotherm of a Liquid in a Porous Medium

International audienceSorption from the vapor phase is an important factor controlling the transport of volatile organic compounds (VOCs) in the vadose zone. Therefore, an accurate description of sorption behavior is essential to predict the ultimate fate of contaminants. Several measurement tech- niques are available in the case of water, however, when dealing with VOCs, the determination of sorption characteristics generally relies on gas chromatography. To avoid some drawbacks associated with this technology, we propose a new method to determine the sorption isotherm of any liquid compounds adsorbed in a soil. This method is based on standard and costless transducers (gas pressure, temperature) leading to a simple and transportable experimental de- vice. A numerical estimation underlines the good accuracy and this technique is validated on two examples. Eventually, this method is applied to determine the sorption isotherm of three liquid compounds (water, heptane and trichloroethylene) in a clayey soil