Reduced complexity models for water management and anode purge scheduling in DEA operation of PEMFCs

In this work, the dynamic behavior of Fuel Cell operation under Dead-Ended Anode conditions is shown. A DEA can be fed with dry hydrogen, since water crossing through the membrane is sufficient to humidify the fuel. The reduced requirements for inlet humidification yield a system with lower cost and weight compared to FCs with flow-through or recirculated anodes. The accumulation of water and nitrogen in the anode channel is first observed near the outlet. A stratified pattern develops in the channel where a hydrogen-rich area sits above a depleted region and is stabilized by the effect of gravity. A model is presented which describes the dynamic evolution of a blanketing N2 front in the anode channel and a hydrogen starved region. Understanding, modeling, and predicting the front evolution can reduce the H2 wasted during purges, avoid over drying the membrane, and mitigate degradation associated with hydrogen starved areas

Experimental validation of equilibria in fuel cells with dead-ended anodes

This paper investigates the nitrogen blanketing front during the dead-ended anode (DEA) operation of a PEM fuel cell. Surprisingly the dynamic evolution of nitrogen and water accumulation in the dead-ended anode (DEA) of a PEM fuel cell arrives to a steady-state suggesting the existence of equilibrium behavior. We use a multi-component model of the two-phase one-dimensional (along-the-channel) system behavior to analyze and exploit this phenomenon. Specifically, the model is first verified with experimental observations, and then utilized for showing the evolution towards equilibrium. The full order model is reduced to a second-order ordinary differential equation (ODE) with one state, which can be used to predict and amalyse the surprising but experimentally observed steady state DEA behavior

Nitrogen front evolution in purged polymer electrolyte membrane fuel cell with dead-ended anode

In this paper, we model and experimentally verify the evolution of liquid water and nitrogen fronts along the length of the anode channel in a proton exchange membrane fuel cell operating with a dead-ended anode that is fed by dry hydrogen. The accumulation of inert nitrogen and liquid water in the anode causes a voltage drop, which is recoverable by purging the anode. Experiments were designed to clarify the effect of N-2 blanketing, water plugging of the channels, and flooding of the gas diffusion layer. The observation of each phenomenon is facilitated by simultaneous gas chromatography measurements on samples extracted from the anode channel to measure the nitrogen content and neutron imaging to measure the liquid water distribution. A model of the accumulation is presented, which describes the dynamic evolution of a N-2 blanketing front in the anode channel leading to the development of a hydrogen starved region. The prediction of the voltage drop between purge cycles during nonwater plugging channel conditions is shown. The model is capable of describing both the two-sloped behavior of the voltage decay and the time at which the steeper slope begins by capturing the effect of H-2 concentration loss and the area of the H-2 starved region along the anode channel

IMPROVING THE EDUCATIONAL PRACTICE USING SIMULATIONS IN SCIENCE EDUCATION: THE CONTRIBUTION OF ALTHUSSER’S THEORY ON THE COGNITIVE PROCEDURE

This article discusses the relationship between the theory of Louis Althusser concerning the subjectivity of knowledge and the cognitive process and the effective use of educational computer simulations during Science Education and Science Teaching. Our first aim is to highlight the aspects of the cognitive process – according to Louis Althusser’s theory – that should be considered by teachers when they opt to utilize computer simulations in their classroom teaching in the subject of Science and Physics. Our second aim is to suggest ways in order to overcome the conceptual ambiguity, the misunderstandings and the misconceptions that sometimes students form while using simulation models on the computer. The research question being investigated here is the following: “What kind of learning outcomes might the use of computer simulations have concerning the acquisition and construction knowledge by students in the course of Science and Physics in the light of L. Althusser’s theory and what could teachers do so as to eliminate the potential risks of their use and to achieve better outcomes in the learning procedure?”. The utilization of computer simulations in Science Teaching sometimes make students think that the simulated object or phenomenon is identical in nature with the real one. However, the simulations do not constitute the “real objects” themselves; in contrary, they are the means to come closer to reality in order to study it thoroughly.  Article visualizations

CERN

As a team, we decided to elaborate on the CERN center for scientific research. We are going to refer to topics such as; the history of the institute, the countries that have participated in the foundation of CERN, the main projects that take place there and lastly the contribution of our country, Greece,  in the scientific research taking place there.

A Controllable Membrane-Type Humidifier for Fuel Cell Applications-Part I: Operation, Modeling and Experimental Validation

For temperature and humidity control of proton exchange membrane fuel cell (PEMFC) reactants, a membrane based external humidification system was designed and constructed. Here we develop and validate a physics based, low-order, control-oriented model of the external humidification system dynamics based on first principles. This model structure enables the application of feedback control for thermal and humidity management of the fuel cell reactants. The humidification strategy posed here deviates from standard internal humidifiers that are relatively compact and cheap but prohibit active humidity regulation and couple reactant humidity requirements to the PEMFC cooling demands. Additionally, in developing our model, we reduced the number of sensors required for feedback control by employing a dynamic physics based estimation of the air-vapor mixture relative humidity leaving the humidification system (supplied to the PEMFC) using temperature and pressure measurements. A simple and reproducible methodology is then employed for parameterizing the humidification system model using experimental data

Der Rahmenbeschluss über die Europäische Beweisanordnung

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.Peer Reviewe