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Gulan U.,Institute of Environmental Engineering | Turkoglu H.,Gazi University
Strojarstvo | Year: 2010

In this study, fluid flow and concentration distribution on the cathode side of a Proton Exchange Membrane Fuel Cell were numerically analyzed. The problem domain consists of a cathode gas flow channel, cathode gas diffusion layer and cathode catalyst layer. The governing equations, continuity, momentum and concentration equations were discritized by the control volume method and solved using a computer program based on SIMPLE algorithm. Simulations were made for different values of gas diffusion layer porosity, catalyst layer porosity and the ratio of the cathode gas diffusion layer thickness to the gas flow channel height. Using the results of these simulations, the effects of these parameters on flow, oxygen concentration and current density distribution were analyzed. It is observed that increasing the porosities of the gas diffusion layer and catalyst layer increases the current and power densities. The increase in the porosity of the gas diffusion layer also increases the oxygen concentration in both gas diffusion and catalyst layers but decreases the oxygen concentration in gas flow channel. Simulations also showed that increasing porosity of the catalyst layer increases the oxygen concentration in a catalyst layer but decreases the oxygen concentration in a gas flow channel and gas diffusion layer. It is also seen that the effect of the gas diffusion layer porosity is more dominant on cell performance compared to the catalyst layer porosity. The analysis of the effect of the ratio of the cathode gas diffusion layer thickness to the gas flow channel height on the cell performance showed that the increasing ratio of the cathode gas diffusion layer thickness to the gas flow channel height decreases the current and power densities. An analysis of the data obtained from simulations also shows that increasing the ratio of the cathode gas diffusion layer thickness to the gas flow channel height increases the oxygen concentration in the gas flow channel but decreases the oxygen concentration in both gas diffusion and catalyst layers. Source


Piatek Z.,Czestochowa University of Technology | Piatek Z.,Institute of Environmental Engineering | Kusiak D.,Czestochowa University of Technology | Kusiak D.,Institute of Industrial Electrotechnics | Szczegielniak T.,Czestochowa University of Technology
Przeglad Elektrotechniczny | Year: 2010

In the paper all components of total magnetic field in the screen and onto its internal and external surface as a function variables r and Θ of cylindrical coordinates were calculated. Total current density induced in the screen of flat high current busduct was taken into account. Total magnetic field of screen is defined according to the reverse reaction between eddy currents and this field is an elliptical, rotating field. In the article it was compared with the magnetic field of the unscreened flat three-phase high current busduct. Source


Fatichi S.,University of Florence | Fatichi S.,University of Michigan | Fatichi S.,Institute of Environmental Engineering | Ivanov V.Y.,University of Michigan | Caporali E.,University of Florence
Journal of Advances in Modeling Earth Systems | Year: 2012

An ecohydrological model Tethys-Chloris (T&C) described in the companion paper is applied to two semiarid systems characterized by different climate and vegetation cover conditions. The Lucky Hills watershed in Arizona represents a typical small, "unit-source" catchment of a desert shrub system of the U.S. southwest. Two nested basins of the Reynolds Creek Experimental watershed (Idaho, U.S.A.), the Reynolds Creek Mountain East and Tollgate catchments, are representative of a semiarid cold climate with seasonal snow cover. Both exhibit a highly non-uniform vegetation cover. A range of ecohydrological metrics of the long-term model performance is presented to highlight the model capabilities in reproducing hydrological and vegetation dynamics both at the plot and the watershed scales. A diverse set of observations is used to confirm the simulated dynamics. Highly satisfactory results are obtained without significant (or any) calibration efforts despite the large phase-space dimensionality of the model, the uncertainty of imposed boundary conditions, and limited data availability. It is argued that a significant investment into the model design based on the description of physical, biophysical, and ecological processes leads to such a consistent simulation skill. The simulated patterns mimic the outcome of hydrological and vegetation dynamics with high realism, as confirmed from spatially distributed remote sensing data. Further community efforts are warranted to address the issue of thorough quantitative assessment. The current lack of appropriate data hampers the development and testing of process-based ecohydrological models. It is further argued that the mechanistic nature of the T&C model can be valuable for designing virtual experiments and developing questions of scientific inquiry at a range of spatiotemporal scales. Copyright © 2012 by the American Geophysical Union. Source


Fatichi S.,University of Florence | Fatichi S.,University of Michigan | Fatichi S.,Institute of Environmental Engineering | Ivanov V.Y.,University of Michigan | Caporali E.,University of Florence
Journal of Advances in Modeling Earth Systems | Year: 2012

Numerous studies have explored the role of vegetation in controlling and mediating hydrological states and fluxes at the level of individual processes, which has led to improvements in our understanding of plot-scale dynamics. Relatively less effort has been directed toward spatially-explicit studies of vegetation-hydrology interactions at larger scales of a landscape. Only few continuous, process-oriented ecohydrological models had been proposed with structures of varying complexity. This study contributes to their further evolution and presents a novel ecohydrological model, Tethys-Chloris. The model synthesizes the state-of-the-art knowledge on individual processes and coupling mechanisms drawn from the disciplines of hydrology, plant physiology, and ecology. Specifically, the model reproduces all essential components of the hydrological cycle: it resolves the mass and energy budgets in the atmospheric surface layer at the hourly scale, while representing up to two layers of vegetation; it includes a module of snowpack evolution; it describes the saturated and unsaturated soil water dynamics, processes of runoff generation and flow routing. The component of vegetation dynamics parameterizes life cycle processes of different plant functional types, including photosynthesis, phenology, carbon allocation, and tissue turnover. This study presents a confirmation of the long-term, plot-scale model performance by simulating two types of ecosystems corresponding to different climate conditions. A consistent and highly satisfactory model skill in reproducing the energy and water budgets as well as physiological cycles of plants with minimum calibration overhead is demonstrated. Furthermore, these applications demonstrate that the model permits the identification of data types and observation frequencies crucial for appropriate evaluation of modeled dynamics. More importantly, through a synthesis of a wide array of process representations, the model ensures that climate, soil, vegetation, and topography collectively identify essential modes controlling ecohydrological systems, i.e., that satisfactory performance is a result of appropriate mimicking of internal processes. Copyright © 2012 by the American Geophysical Union. Source


Krolikowska J.,Cracow University of Technology | Debowska B.,Cracow University of Technology | Krolikowski A.,Institute of Environmental Engineering
Environmental Engineering IV - Proceedings of the Conference on Environmental Engineering IV | Year: 2013

This work is devoted to the problems of operating a vacuum sewer system. The presented results are based on the authors' own research and data from scientific sources. The analysis included in this work relates to the failure of vacuum sewer system components and the operating costs of such systems, which are governed primarily by the electricity consumption. © 2013 Taylor & Francis Group. Source

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