1,614 research outputs found
The catalyst layer and its dimensionality – A look into its ingredients and how to characterize their effects
No full textTransport Properties of the Gas Diffusion Layer of PEM Fuel Cells
No full textNon-woven carbon paper is a porous material composed of carbon composite and is the preferred material for use as the gas diffusion layer (GDL) of polymer electrolyte membrane (PEM) fuel cells. This material is both chemically and mechanically stable and provides a free path for diffusion of reactants and removal of products and is electrically conductive for transport of electrons. The transport of species in the GDL has a direct effect on the overall reaction rate in the catalyst layer. Numerical simulation of these transport phenomena is dependent on the transport properties associated with each phenomenon. Most of the available correlations in literature for these properties have been formulated for spherical shell porous media, sand and rock, which are not representative of the structure of the GDL. Hence, the objective of this research work is to investigate the transport properties (diffusion coefficient, thermal conductivity, electrical conductivity, intrinsic and relative permeability and the capillary pressure) of the GDL using experimental and numerical techniques. In this thesis, a three-dimensional reconstruction of the complex, anisotropic structure of the GDL based on stochastic models is used to estimate its transport properties. To establish the validity of the numerical results, an extensive comparison is carried out against published and measured experimental data. It was found that the existing theoretical models result in inaccurate estimation of the transport properties, especially in neglecting the anisotropic nature of the layer. Due to the structure of the carbon paper GDL, it was found that the value of the transport properties in the in-plane direction are much higher than that in the through-plane direction. In the in-plane direction, the fibers are aligned in a more structured manner; hence, the resistance to mass transport is reduced. Based on the numerical results presented in this thesis, correlations of the transport properties are developed. Further, the structure of the carbon paper GDL is investigated using the method of standard porosimetry. The addition of Teflon was found have little effect on the overall pore volume at a pore radius of less than 3 micro meters. A transition region where the pore volume increased with the increase in pore radius was found to occur for a pore radius in the range 3<5.5 micro meters regardless of the PTFE content. Finally, the reduction of the overall pore volume was found to be proportional to the PTFE content. The diffusion coefficient is also measured in this thesis using a Loschmidt cell. The effect of temperature and PTFE loading on the overall diffusibility is examined. It was found that the temperature does not have an effect on the overall diffusibility of the GDL. This implies that the structure of the GDL is the main contributor to the resistance to gas diffusion in the GDL. A comparison between the measured diffusibility and that predicted by the existing available models in literature indicate that these models overpredict the diffusion coefficient of the GDL significantly. Finally, both the in-plane and through-plane thermal conductivity were measured using the method of monotonous heating. This method is a quasi-steady method; hence, it allows the measurement to be carried out for a wide range of temperatures. With this method, the phase transformation due to the presence of PTFE in the samples was investigated. Further, it was found that the through-plane thermal conductivity is much lower than its in-plane counterpart and has a different dependency on the temperature. Detailed investigation of the dependency of the thermal conductivity on the temperature suggests that the thermal expansion in the through-plane direction is positive while it is negative in the in-plane direction. This is an important finding in that it assists in further understanding of the structure of the carbon paper GDL. Finally, the thermal resistance in the through-plane direction due to fiber stacking was investigated and was shown to be dependent on both the temperature and compression pressure
Transfer of Mass and Heat in the Cathode of Polymer Electrolyte Membrane Fuel Cell
No full textThe need for alternative sources of energy with low to zero emissions has led to the development of polymer electrolyte membrane fuel cells. PEM fuel cells are electro-chemical devices that convert chemical energy to electricity by using hydrogen as the fuel and oxygen as the oxidant with water as the byproduct of this reaction. One of the major barriers to the commercialization of these cells is the losses that occur at the cathode due to the slow oxygen diffusion and sluggish electrochemical reaction, which are further amplified by the presence of liquid water. Numerous numerical and mathematical models are found in the literature, which investigate the transport phenomena in the cathode and their effects on the cell performance. In this thesis, the discussion of a two-dimensional, steady state, half cell model is put forward. The conservation equations for mass, momentum, species charge and energy are solved using the commercial software COMSOL Multiphysics. The conservation equations are applied to the cathode bipolar plate, gas diffusion layer and catalyst layer. The flow of gaseous species are assumed to be uniform in the channel. The catalyst layer is assumed to be composed of a uniform distribution of catalyst, liquid water, electrolyte, and void space. The Stefan-Maxwell equation is used to model the multi-species diffusion in the gas diffusion and catalyst layers. Due to the low relative species' velocity, the Darcy law is used to describe the transport of gas and liquid phases in the gas diffusion and catalyst layers. A serpentine flow field is used to distribute the oxidant over the active cathode electrode surface, with pressure loss in the flow direction along the channel. A sensitivity analysis is carried out to investigate the effects of pressure drop in the channel, permeability, inlet relative humidity and shoulder/channel ratio on the performance of the cell. Electron transport is shown to play an important role in determining the overall performance of the cathode. With a serpentine flow field, the oxygen consumption occurs more aggressively at the areas under the land since electrons are readily available at these areas. In addition, the reaction increases along the catalyst layer thickness and occurs more rapidly at the catalyst layer/membrane interface. The losses due to electron transport are much higher than those due to the proton transport. The sensitivity analysis put forward illustrated that with the increase of pressure drop along the channel flow field, the performance of the cell and liquid water removal are enhanced. Similarly, an increase in permeability of the porous material results in an increase in liquid water removal and cell performance. Further, the investigation of the inlet relative humidity effects revealed that the electrolyte conductivity has a significant effect on the performance up to a point. On a similar fashion, a decrease in shoulder/channel width ratio leads to an increase in performance and an increase in the leakage between neighboring channels. Finally, the addition of heat is shown to have a negative effect on the cell performance. Some recommendations can be drawn from the results of this thesis. It is recommended to develop a model to study the flow in the channel flow field in order to investigate the effects of the channel flow on the transport of species in the cell. Further, the geometry of the channel should be studied. Finally, the production of water should be analyzed. The analysis should be extended to investigate its production in vapor form only and its production as a mixture of vapor and liquid
Fuel Cells, Stacks and Systems. Electrochemical Energy Applications: Fuel Cells and Electrolysis
No full text
SISTEM PENGKONVERSI NADA LAGU DARI NOT BALOK MENJADI NADA PIANO
No full textABSTRAKSI: Semakin berkembangnya teknologi pengolahan citra dgital, banyak aplikasi pengolahan citra yang sangat bermanfaat untuk keperluan deteksi, konversi, sekuriti, dan lainnya. Sehingga banyak bidang yang menggunakan pengolahan citra sebagai teknologi dasar untuk membantu menyelesaikan berbagai permasalahan yang berkaitan dalam bidang tersebut.Dalam bidang musik, partitur merupakan suatu hal yang sangat penting. Partitur adalah alat bantu bagi seorang penyanyi atau musisi dalam bernyanyi atau memainkan alat musik. Partitur berisi susunan nada-nada yang harmonis yang disusun sedemikian rupa oleh pengarang. Oleh karena itu, untuk mendapatkan nada- nada yang harmonis, sangat dibutuhkan ketepatan dalam membaca not-not dalam partitur.Pada tugas akhir ini, dikembangkan suatu aplikasi untuk mengkonversikan not balok pada suatu data gambar yang berasal dari partitur keluaran sebuah software musescore, menjadi nada. Sistem ini dibuat dengan tujuan untuk optimasi terhadap pembacaan not balok yang biasanya dilakukan secara manual.Hasil yang diharapkan dari tugas ini adalah bagaimana sistem ini mampu mengkonversi not balok menjadi nada yang dengan menghasilkan performansi diatas 80 % .Kata Kunci : not balok, partitur, citra digital, scanning.ABSTRACT: The continued development of digital image processing technologies, many image processing applications are very useful for detection purposes, conversion, security, and others. So many fields that use image processing as a basic technology to help solve various problems related to the field.In the field of music, the score is a very important thing. Scores are an invaluable tool for a singer or musician in singing or playing musical instruments. Arrangement of the score contains a harmonic tones are arranged in such a way by the author. Therefore, to obtain a harmonious tunes, much-needed accuracy in reading the notes in the score.At this final project, developed an application to convert musical notes on an image data output from a software musescore to be a tone. The system is made with a view to optimization of reading musical notes that are usually done manually.The expected outcome of this task is how the system is able to convert musical notes to produce a tone with performance above 80%.Keyword: musical notes, sheet music, digital images, scanning
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