Potential anomaly separation and archeological site localization using genetically trained multi-level cellular neural networks

In this paper, a supervised algorithm for the evaluation of geophysical sites using a multi-level cellular neural network (ML-CNN) is introduced, developed, and applied to real data. ML-CNN is a stochastic image processing technique based on template optimization using neighborhood relationships of the pixels. The separation/enhancement and border detection performance of the proposed method is evaluated by various interesting real applications. A genetic algorithm is used in the optimization of CNN templates. The first application is concerned with the separation of potential field data of the Dumluca chromite region, which is one of the rich reserves of Turkey; in this context, the classical approach to the gravity anomaly separation method is one of the main problems in geophysics. The other application is the border detection of archeological ruins of the Hittite Empire in Turkey. The Hittite civilization sites located at the Sivas-Altinyayla region of Turkey are among the most important archeological sites in history, one reason among others being that written documentation was first produced by this civilization

3-dimensional analysis of the effect of semi cylindirical blocks in flow channels on pem fuel cell performance

Bu tezde, anot ve katot gaz akış kanallarına farklı boyutlarda yarı silindirik engeller yerleştirilerek, tek bir hücreden oluşan proton aktaran membran yakıt pilinin (PEMFC) ANSYS-FLUENT PEMFC modülü kullanılarak analizi yapılmıştır. Analiz sonuçları literatürdeki benzer çalışmalarla karşılaştırılmış ve uyum içinde olduğu görülmüştür. PEMFC iki taraftan oluşmaktadır, bir tarafı anot diğer tarafı katottur. Anot ve katot ise; akım toplama plakası, gaz kanalı, gaz difüzyon tabakası ve katalizör tabakasının bulunduğu dört kısımdan oluşmaktadır. Anot ve katotun arasında membran bulunmaktadır. Anot ve katot gaz difüzyon tabakaları, iki katalizör tabakası ve membran, Membran Elektrot Çiftini (MEÇ) oluşturmaktadır. Fiziksel model anot ve katot gaz kanalları içerisine yerleştirilen farklı yarıçap (r=0,40 0,49 mm) ve sayıdaki yarı silindirik bloklardan oluşmaktadır. Yarıçap ve blokların sayısı, blokların toplam kesit alanı sabit kalacak şekilde seçilmiştir. Bu problemin çözümü için, kütle, momentum, enerji, türler ve faz potansiyelinin korunumu dikkate alınmıştır. ANSYS FLUENT PEMFC modülünde yakıt pili içindeki elektrokimyasal eşitlikler, hidrojenin oksidasyonu ve oksijenin indirgenme hızına bağlı olarak çözülmüştür. İki farklı kalınlık değerinde belirlenen MEÇ için PEMFC modelleri incelenmiştir. Düz gaz akış kanallı PEMFC modeli geometrisi için çalışma basıncının akım yoğunluğuna etkileri bu iki MEÇ (MEÇ-1 ve MEÇ-2) kullanılarak analiz edilmiştir. Bütün incelenen durumlar için sıcaklık şartları, anot ve katot gaz kanalı giriş çıkışlarıyla birlikte yakıt pilinin alt ve üst dış yüzeylerinde sabit olarak alınmıştır. Hız, sıcaklık, hidrojen ve oksijenin kütle kesri dağılımları ile ilgili sonuçlar, ana gaz akış yönünde iki boyutlu olarak sunulmuştur. Ayrıca hidrojenin kütle kesri değişimleri ana akışa dik kesitlerde (giriş, orta ve çıkış) alınan dağılımlarla iki boyutlu olarak incelenmiştir. Analizi yapılan her bir durum için kutuplaşma eğrileri oluşturulmuş ve gaz akış kanallarına konulan engellerin kutuplaşma eğrileri üzerine olan etkileri incelenmiştir. Bu çalışmada ele alınan engelli kanal geometrisi sonuçlarına göre, blokların toplam kesit alanı sabit kalacak şekilde engel sayısı arttırıldığında maksimum akım yoğunluğu değerlerinde %14,5'e varan iyileştirmeler elde edilebilmektedir.This thesis covers the analysis of a single-cell proton exchange membrane fuel cell (PEMFC) with different sized semi-cylindrical blocks in both anode and cathode gas flow channels by using ANSYS FLUENT PEMFC module. The results of the analysis are compared and a good agreement has been obtained with similar studies in the literature. PEMFC is made up of two sides, one anode and one cathode, each of which include four layers. Each side consists of a current collector, gas channel, gas diffusion layer and catalyst layer. There exists a membrane between the anode and cathode sides. These anode and cathode gas diffusion layers, the two catalyst layers, and the membrane compose the Membrane Electrode Assembly (MEA). Physical model consists of semi-cylindrical blocks with different radii (r=0,40 - 0,49 mm) and in various numbers that are located inside the anode and cathode gas channels. The radius and the number of blocks are selected such that the total cross sectional area of blocks is constant. For this purpose, basic principles such as conservation of mass, momentum, energy, species, and phase potential are considered. In ANSYS FLUENT PEMFC module, electrochemical equations depending on hydrogen oxidation and oxygen reduction rates are solved. MEAs are implemented in the PEMFC models and analyzed for two different thickness values. The PEMFC model is examined for the geometry of straight gas flow channel and the effects of operating pressure on current density are investigated for these two MEAs (MEA-1 and MEA-2). For all analyzed cases, the temperature condition is assumed to be constant at the anode and cathode gas channel inlet-outlet, as well as the upper and lower external surfaces of the fuel cell. The result of velocity, temperature, hydrogen and oxygen mass fraction distributions are presented along the gas flow main direction. Furthermore, hydrogen mass fraction distributions are analyzed at the cross sections (inlet, mid-way, outlet) perpendicular to the main flow direction. Polarization curves are obtained for each case and the effects of blocks on the variation of these curves are examined. According to the results of blocked channel geometries, improvements can be achieved in the values of maximum current density up to 14,5% when the number of blocks is increased for the same total cross sectional area of blocks

Investigation of the Effect of Stoichiometry Ratio on Two-Cell PEM Fuel Cell Stack Performance

The importance of fossil fuels has increased with the use of steam energy in industry. But especially in recent days, the problem of global warming is being felt seriously in the world. The most important reason for this problem is harmful emissions caused by burning fossil fuels. The world has turned to various alternative energy sources in order to eliminate this problem. Interest in PEM fuel cells, which are among alternative the energy converters, has been increasing. In this study, the effect of stoichiometry ratio on the performance of two-cell PEM fuel cell stack was analyzed numerically. Two fuel cells each with an active area of 5.4 cm2 were connected in series, and the gas flow channels were determined in parallel and stacked. Numerical analysis was performed with five different stoichiometry ratios (1.5, 2, 2.5, 3, and 3.5) at various cell voltage values (1 V, 1.2 V, 1.4 V, 1.6 V, 1.8 V). Polarization and power-current density curves were obtained for five different stoichiometry ratio values. In addition, in order to see the effect of the stoichiometry ratio on a constant voltage, temperature distribution of the membrane, the anode and the cathode mass fraction distributions formed by four different stoichiometric ratios at 1 Volt, where the maximum amount of power is obtained. With this study, it was observed that current density increased with the improvement in the stoichiometric ratio and the amount of this increment continued to decrease. The highest power value was obtained at the stoichiometric ratio of 3.5 and 1 V potential difference value. However, with the increasing stoichiometric ratio, it was concluded that hydrogen and oxygen distributions became more homogeneous in the anode and cathode channels while a limited increase in membrane temperature occurred

Gas flow field with obstacles for PEM fuel cells at different operating conditions

In proton exchange membrane fuel cells (PEMFCs) laminar flow inside anode and cathode gas channels can be disrupted by using obstacles. By arranging these obstacles near to the exit of the gas channels concentration losses due to hydrogen and oxygen consumption inside the channel will be decreased. Using a three dimensional computational model, numerical simulations are performed to investigate performance of PEMFCs containing obstacles in the anode and cathode gas flow channels. These simulations were conducted at different operating conditions (stoichiometry, relative humidity and temperature) to clarify the effects of the obstacles at specified conditions. The simulations show that the obstacles inside the gas flow channels improve the concentration distribution along the channels and the transport of the reactant gases through the gas diffusion layer (GDL). As a result, the electrochemical reaction is improved and higher cell voltage is obtained at high current densities.JRC.F.2-Energy Conversion and Storage Technologie

Numerical Analysis of Two Units PEM Fuel Cell Stack

The fact that the industrial factor progresses to the point where the fossil energy sources such as petroleum natural gas, which constitute a large part of human’s energy needs, move to the point of decreasing and exhausting day by day, and the increasing damage caused by the resources used for energy production leads the scientists to alternative energy sources. Fuel oil application, one of these alternative energy sources, draws attention. In this study, PEM fuel cell stack is analyzed by numerically. Two PEM fuel cells are turned into stack, each of which has 5.4 cm2 active area, by connecting in series. Reactants of anode and cathode flow direction is preferred parallel. PEM fuel cells are accepted as operating conditions of 70oC and 1 atm. Power values of this designed stack is calculated and presented in the study. Electrical power values of one and two PEMFCs are presented in graphics

Gözenekli metal yataklarda hidrojen soğurulmasının sayısal modellenmesi

Gözenekli metal yataklarda hidrojen gazının soğurulması, iki boyutlu olarak ısı ve kütle transferi yönünden silindirik koordinatlarda analiz edilmiştir. Yüksek soğutma oranı için eş merkezli iki silindir arasındaki gözenekli metal ortam seçilmiştir ve metal yatak, iç ve dış yüzeylerden akışkan ile soğutulmuştur. Gözenekli metal ortam olarak, $LaNi_5$ metal yatak seçildi ve hidrojen soğurulması sayısal olarak analiz edilmiştir. Radyal ve eksenel yönlerde metal hidrid sıcaklık değişimleri ve hidrojen/metal oranları bir Sayısal Akışkanlar Mekaniği (SAD) programı kullanılarak hesaplanmıştır. Hidrid oluşumu soğuk yüzeyler üzerinde daha hızlı şekilde meydana geldiği görülmüştür. Sonuçlar literatürde verilen farklı geometrilerdeki sonuçlar ile karşılaştırılmıştır.Two dimensional heat and mass transfer are analyzed for hydrogen absorption in a porous metal bed using cylindrical coordinates. For high cooling rates an annular geometry is selected for the porous metal bed, and the bed is cooled by fluid on both internal and external surfaces. Absorption process is analyzed numerically for the porous $LaNi_5$ metal bed. The variations of the metal hydride temperature and hydrogen/metal atomic ratio are calculated in the radial and axial directions by using a Computational Fluid Dynamics (CFD) program. It has been found that hydride formation takes places near the cold boundaries. The results were also compared with the numerical outcomes given in the literature for different geometries