The effects of actively pulsing reactant flow rates into solid polymer electrolyte fuel cells were investigated in this thesis. First, work was conducted to determine the magnitude of voltage response to pulsed reactant flow on a direct hydrogen proton exchange membrane (PEM) cell. The effects of pulsed reactant flow into a direct methanol fuel cell (DMFC) were then considered. The PEM work showed substantially greater response to pulsed air flow than to pulsed fuel flow. It was found that several parameters affect the magnitude of cell response to active flow control (AFC). Increasing current load, increasing the magnitude of flow oscillation, decreasing the frequency of oscillation, and decreasing the average level of excess reactant supplied were found to maximize both the level of voltage oscillations and the decrease in cell power from steady state performance. Greater response to pulsed oxidant flow is believed to have been observed due to effects brought about by changes in membrane humidity. In contrast, pulsed fuel flow showed the greatest response in the study of DMFC technology. In this case, time averaged cell voltage was found to increase as the time averaged fuel flow rate was reduced. The increase in average cell power is the result of a reduction in methanol crossover; sustainable increases of up to 6% in power output were measured. The parameters found to effect the increase in cell power observed include the frequency of oscillation and the time-averaged NOSfuel. Pulsed air flow on the DMFC did not show any such rise in voltage, supporting the hypothesis that a reduction in methanol crossover is the phenomenon which brings about enhanced performance.

Proton exchange membrane (PEM) fuel cells, with low operating temperatures and high power density, are a reasonable candidate for use in mobile power generation. One large drawback to their use is that their fuel reformer requires not only fuel but also water, thereby requiring two separate reservoirs to be available. PEM fuel cells exhaust enough water in their oxidant stream to potentially meet the needs of the fuel reformer. If this water could be recovered and routed to the fuel reformer it would markedly increase the portability of PEM fuel cells. The goal of this research was to test a previously designed axial flow moisture separator. The separator was employed in a test bed which utilized compressed, heated air mixed with steam to simulate the oxidant exhaust conditions of a 25 kW PEM fuel cell. The simulated exhaust was saturated with water. The mixture was expanded through the turbine side of an automotive turbocharger, which dropped the temperature and pressure of the mixture, causing water to condense, making it available for separation. The humid air mixture was passed over an axial flow centrifugal separator and water was removed from the flow. The separator was tested in a variety of conditions with and without passing chilled water through the separator. The axial separator was tested independently, with a flow straightener preceding it, and with a commercially available centrifugal moisture separator in series following it. It was shown that cooling makes a significant impact on the separation rate while adding a flow straightener does not. Separation efficiencies of 19% on average were experienced without cooling, while efficiencies of 50% were experienced with 3.1 kW of cooling. The separation efficiency of the two moisture separators combined was found to be 31.7% which is 165% that of the axial separator alone under uncooled conditions.

PEM (Proton Exchange Membrane) fuel cell is one of the most important green energy, because it has high energy density, lifetime, small and light.etc advantages. Nafion , the major material for PEM now, However, has some disadvantages such as high cost ($600¡V1000/m2) and limited choices for operation temperature about 25¢J~80¢J. Consequently, there is an increasing interest in the development of alternative ionomer membranes with lower cost, and higher proton conductivity, and that are more easily processed. Here we present polymeric membranes made of sulfonic Poly(arylene ether)s (PAEs) which is achieved by nucleophilic displacement reactions of dihalo or dinitro compounds with alkali metal bisphenolates and direct polymer sulfonation was carried out in heterogeneous media using chlorosulfonic acid as both solvent and sulfonating agent. In our PAEs which has high Tg values about 225¡ã250¢XC depends on the barriers to rotation along the main polymer chain. And weight losses above 500 ¢XC by thermogravimetric (TGA) analysis, indicative of their high thermal stability. After FTIR analysis we preparation sulfonated polymer successfully by using chlorosulfonic acid as sulfonating agent. Thermogravimetric analysis (TGA) studies were carried out to investigate the thermal stability of sulfonated PAEs (Td≈ 500¢XC). The proton conductivity of polymer s(DFB+M3) sulfonated with chlorosulfonic acid about 10-6¡ã10-7S cm-1 .Compared with Nafion membrane measured in the same condition, the conductivity of our membrane is smaller than 3~4 order. In the future, it is possible to improve the conductivity of our membrane with optimization.

Fuel cells are expected to play an important role in future power generation. However, significant technical challenges remain and the commercial breakthrough of fuel cells is hindered by the high price of fuel cell components. As is well known, the fuel cells do not provide the robust source characteristics required to effectively follow the load during significant load steps and they have limited overload-handling capability. Further, the performance of the fuel cell is significantly degraded when the CO (Carbon Monoxide) is contained in the hydrogen fuel. In this thesis several new approaches to improve the performance of PEM based fuel cell power systems are discussed. In the first section an impedance model of the Proton Exchange Membrane Fuel Cell Stack (PEMFCS) is first proposed. This equivalent circuit model of the fuel cell stack is derived by a frequency response analysis (FRA) technique to evaluate the effects of the ripple current generated by the power-conditioning unit. Experimental results are presented to show the effects of the ripple currents. In the second section, a fuel cell powered UPS (Uninterruptible Power Supply) system is proposed. In this approach, two PEM Fuel Cell modules along with suitable DC/DC and DC/AC power electronic converter modules are employed. A Supercapacitor module is also employed to compensate for instantaneous power fluctuations including overload and to overcome the slow dynamics of the fuel processor such as reformers. A complete design example for a 1-kVA system is presented. In the third section, an advanced power converter topology is proposed to significantly improve the CO tolerance on PEM based fuel cell power systems. An additional two-stage dc-dc converter with a supercapacitor module is connected to the fuel cell to draw a low frequency (0.5Hz) pulsating current of the specific amplitude (20-30[A]) from the fuel cell stack. CO on the catalyst surface can be electro-oxidized by using this technique, and thereby the CO tolerance of the system can be significantly improved. Simulation and experimental results show the validity and feasibility of the proposed scheme.

The development of a control-oriented dynamic relative humidity model for a polymer electrolyte membrane (PEM) fuel cell stack is presented. This model is integrated with a first law based thermal model, which tracks energy flow within four defined control volumes in the fuel cell; the cathode channel, anode channel, coolant channel, and fuel cell stack body. Energy and mass conservation equations are developed for each control volume. On top of mass conservation, electro-drag and osmosis models were also implemented within the model to account for the major modes of vapor transfer through the membrane between the anode and cathode. Requisite alterations to the thermal model as well as mass flow rate calculations are also discussed. Initially, the model utilized a single lumped control volume for the calculation of all values each channel (anode and cathode). This lumped value method is computationally inexpensive, and makes the model optimal for control design. However, investigation of the mass-based Biot number showed the need for greater granularity along the length of the channels to properly capture the relative humidity dynamics. In order to improve the resolution of the model, while still minimizing the computation expense, the model was subdivided into a series of lumped value models. The cathode channel was the point of focus as it is the major concern from a controls perspective. This method captures the proper trends found in far more complex CFD models, while still maintaining a quick calculation time. Different levels are subdivision (3 and 6 submodels) are investigated, and the differences discussed. Particularly, temperature range, relative humidity range, the effect on the modeled voltage, and calculation time are compared. This control-oriented model is low order and based on lumped parameters, which makes the computational expense low. Formulation of this model enables the development of control algorithms to achieve optimal thermal and water management. / text

No description available.

Water electrolysis is one of the first methods used to generate hydrogen and is thus not considered to be a new technology. With advances in proton exchange membrane technology and the global tendency to implement renewable energy, the technology of water electrolysis by implementation of proton exchange membrane as solid electrolyte has developed into a major field of research over the last decade. To gain an understanding of different components of the electrolyser it is best to conduct a performance analysis based on hydrogen production rates and polarisation curves. The study aim was to compare the technologies of membrane electrode assembly with gas diffusion electrode and the proton exchange membranes of Nafion® and polybenzimidazole in a commercial water electrolyser. To determine which of the components are best suited for the process a laboratory scale electrolyser was to be used to replicate the commercially scaled performance. The effect of feed water contaminants on electrolyser performance was also investigated by introducing iron and magnesium salt solutions and aqueous methanol solutions in the feed reservoir. Components to be tested included different PEM types as well as the base component on which the electrocatalyst layer is applied. The proton exchange membranes compared were standard Nafion® N117 and polybenzimidazole meta-sulfone sulfonated polyphenyl sulfone (PBI-sPSU). A laboratory scale electrolyser from Giner Electrochemical Systems was utilised where different components were tested and compared with one another. Experimental results with commercial membrane electrode assemblies and gas diffusion electrodes demonstrated the influence of temperature on electrolyser performance for the proton exchange membranes, where energy efficiency increased with temperature. The effect of pressure was insignificant over the selected pressure range. Comparison of membrane electrode assembly and gas diffusion electrode technologies showed enhanced performance from MEA technology, this was most likely due to superior electrocatalyst contact with the PEM. Results of synthesised Nafion® N117 and PBI-sPSU MEA showed increased performance for PBI-sPSU, but it was found to be more susceptible to damage under severe conditions. The effect of metal cations in the supply reservoir exhibited reduced energy efficiencies and increased specific energy consumption for the test duration. Treatment with sulphuric acid was found to partially restore membrane electrode assembly performance, though it is believed that permanent damage was inflicted on the membrane electrode assembly electrocatalyst. Use of aqueous methanol solutions were found to increase electrolyser performance. It was also found that aqueous methanol electrolysis occurs at lower current densities, whereas a combination of aqueous methanol and water electrolysis occurred at higher current densities depending on the concentration of methanol. / Thesis (MIng (Chemical Engineering))--North-West University, Potchefstroom Campus, 2013.

Water electrolysis is one of the first methods used to generate hydrogen and is thus not considered to be a new technology. With advances in proton exchange membrane technology and the global tendency to implement renewable energy, the technology of water electrolysis by implementation of proton exchange membrane as solid electrolyte has developed into a major field of research over the last decade. To gain an understanding of different components of the electrolyser it is best to conduct a performance analysis based on hydrogen production rates and polarisation curves. The study aim was to compare the technologies of membrane electrode assembly with gas diffusion electrode and the proton exchange membranes of Nafion® and polybenzimidazole in a commercial water electrolyser. To determine which of the components are best suited for the process a laboratory scale electrolyser was to be used to replicate the commercially scaled performance. The effect of feed water contaminants on electrolyser performance was also investigated by introducing iron and magnesium salt solutions and aqueous methanol solutions in the feed reservoir. Components to be tested included different PEM types as well as the base component on which the electrocatalyst layer is applied. The proton exchange membranes compared were standard Nafion® N117 and polybenzimidazole meta-sulfone sulfonated polyphenyl sulfone (PBI-sPSU). A laboratory scale electrolyser from Giner Electrochemical Systems was utilised where different components were tested and compared with one another. Experimental results with commercial membrane electrode assemblies and gas diffusion electrodes demonstrated the influence of temperature on electrolyser performance for the proton exchange membranes, where energy efficiency increased with temperature. The effect of pressure was insignificant over the selected pressure range. Comparison of membrane electrode assembly and gas diffusion electrode technologies showed enhanced performance from MEA technology, this was most likely due to superior electrocatalyst contact with the PEM. Results of synthesised Nafion® N117 and PBI-sPSU MEA showed increased performance for PBI-sPSU, but it was found to be more susceptible to damage under severe conditions. The effect of metal cations in the supply reservoir exhibited reduced energy efficiencies and increased specific energy consumption for the test duration. Treatment with sulphuric acid was found to partially restore membrane electrode assembly performance, though it is believed that permanent damage was inflicted on the membrane electrode assembly electrocatalyst. Use of aqueous methanol solutions were found to increase electrolyser performance. It was also found that aqueous methanol electrolysis occurs at lower current densities, whereas a combination of aqueous methanol and water electrolysis occurred at higher current densities depending on the concentration of methanol. / Thesis (MIng (Chemical Engineering))--North-West University, Potchefstroom Campus, 2013.

Είναι γνωστό ότι οι απαιτήσεις σε ηλεκτρική ενέργεια συνεχώς αυξάνονται, όπως αυξάνεται και η ανάγκη για παραγωγή όσο το δυνατόν οικονομικότερης και καθαρότερης ενέργειας. Γι’ αυτό τα συστήματα κατανεμημένης παραγωγής διαδραματίζουν όλο και σημαντικότερο ρόλο για τον ενεργειακό μηχανικό. Μία τεχνολογία που συνεχώς κερδίζει έδαφος είναι αυτή των κυττάρων καυσίμου (fuel cells). Η παρούσα διπλωματική εργασία εξετάζει τη λειτουργία των fuel cells, παρουσιάζοντας τις βασικές αρχές λειτουργίας τους, παραθέτοντας ένα εγχειρίδιο χρήσης μιας βιομηχανικής εφαρμογής (βασισμένο στο αυθεντικό manual της εταιρίας) και μελετά τη μεταβατική συμπεριφορά της εφαρμογής αυτής με πειραματικό τρόπο. Στο πρώτο κομμάτι της εργασίας παρουσιάζονται οι βασικές αρχές λειτουργίας των fuel cells. Υδρογόνο και οξυγόνο χρησιμοποιούνται ως είσοδοι και στην έξοδο του κυττάρου έχουμε ρεύμα και νερό. Η χρήση του υδρογόνου ως καύσιμο αναμένεται να επεκταθεί πολύ στο μέλλον λόγω του ότι είναι πρακτικά ανεξάντλητο, αν και οι τρόποι παραγωγής του είναι ακόμα υπό συνεχή προσπάθεια βελτιστοποίησης. Τα κύτταρα καυσίμου είναι μια καθαρή πηγή ενέργειας, αφού έχει θεωρητικά μηδενικές εκπομπές ρύπων, ενώ ο βαθμός απόδοσής τους είναι μεγαλύτερος από αυτόν των μηχανών εσωτερικής καύσης. Επίσης, είναι γενικά απλές κατασκευές, με μικρές εκπομπές θορύβου και γενικά η λειτουργία τους δεν εξαρτάται ιδιαίτερα από τις γεωγραφικές συνθήκες. Όλοι αυτοί οι λόγοι τα καθιστούν ιδανικά για την κάλυψη ενεργειακών αναγκών σε φορητές εφαρμογές, στην ηλεκτρική αυτοκίνηση και φυσικά ως μέρος των συστημάτων κατανεμημένης παραγωγής. Το κύριο μειονέκτημα των κυττάρων καυσίμου είναι το κόστος τους, που ως τώρα δυσκολεύει την παραγωγή βιομηχανικών εφαρμογών ευρείας χρήσης. Επίσης, οι απαιτήσεις ασφάλειας που αφορούν στο πεπιεσμένο υδρογόνο είναι ένα ακόμα θέμα που χρίζει προσοχής και μελέτης. Η βιομηχανική εφαρμογή που χρησιμοποιήθηκε για το πειραματικό μέρος της εργασίας είναι το Nexa Power Module της εταιρίας Ballard. Αυτή είναι μία μονάδα παραγωγής DC ισχύος, που χρησιμοποιεί μία συστοιχία κυττάρων καυσίμου τεχνολογίας ΡΕΜ (Proton Exchange Membrane). Αυτή είναι η πιο απλή και διαδεδομένη κατηγορία fuel cells. Στην παρούσα εργασία παρατίθεται ένα εγχειρίδιο χρήσης της συγκεκριμένης μονάδας. Περιγράφονται αναλυτικά ο σχεδιασμός και η λειτουργία της, ενώ παρέχονται τεχνικές διευκρινήσεις, χαρακτηριστικά λειτουργίας, καθώς και οι απαραίτητοι κανόνες ασφάλειας που πρέπει να τηρούνται. Ιδιαίτερη προσοχή πρέπει να δοθεί στο κομμάτι της ασφάλειας. Το υδρογόνο αν βρεθεί σε μεγάλες συγκεντρώσεις μπορεί να δεσμεύσει το οξυγόνο του αέρα και να προκαλέσει ασφυξία, ενώ είναι αναφλέξιμο και εκρηκτικό. Είναι συνεπώς ένα επικίνδυνο αέριο (ειδικά όταν βρίσκεται σε πεπιεσμένη μορφή) και η χρήση του απαιτεί πείρα και μεγάλη προσοχή. Το εγχειρίδιο αυτό αποτελεί ένα πολύ καλό εργαλείο για την πλήρη κατανόηση του τρόπου λειτουργίας ενός ολοκληρωμένου συστήματος παραγωγής ενέργειας με κύτταρα καυσίμου, καθώς περιγράφει με λεπτομέρεια τη λειτουργία όλων των βοηθητικών υποσυστημάτων που είναι απαραίτητα για τη λειτουργία μιας κυψέλης υδρογόνου. Επίσης συνίσταται η ανάγνωσή του για τη χρήση στο εργαστήριο από μελλοντικούς ερευνητές. Το τελευταίο κομμάτι της εργασίας είναι η πειραματική μελέτη της μεταβατικής απόκρισης του Nexa Power Module. Μετρήθηκαν οι χρόνοι ανάληψης και απόρριψης φορτίου για διαφορετικές τιμές φορτίων και θερμοκρασίας λειτουργίας. Τα παρακάτω διαγράμματα παρατίθενται ενδεικτικά και δείχνουν τη μορφή των αποτελεσμάτων για την ανάληψη φορτίου. Από τις μετρήσεις φάνηκε ότι η μεταβατική απόκριση της μονάδας εξαρτάται σε σημαντικό βαθμό από τη θερμοκρασία. Επίσης, σημαντική είναι και η εξάρτηση της απόκρισης της μονάδας από το μέγεθος του φορτίου που αυτή αναλαμβάνει ή απορρίπτει. Η ικανότητα των κυττάρων καυσίμου να αποκρίνονται με ταχύτητα και αξιοπιστία σε μεταβολές φορτίων είναι απαραίτητη για τη μελλοντική χρήση τους, τόσο σε φορητές εφαρμογές όσο και ως μέρη των συστημάτων κατανεμημένης παραγωγής. Συνεπώς τα συμπεράσματα αυτά είναι πολύ σημαντικά και πρέπει να ληφθούν υπόψη κατά το σχεδιασμό συστημάτων με κύτταρα καυσίμου. / It is well known that the demands for electrical power are constantly increasing as well as the need for cheap and clean energy sources. This is why Distributed Generation has become a very important field of electric engineering. Fuel Cells, as a part of DG technologies, are constantly gaining ground and have known great development through the last two decades. This essay studies fuel cell operation attributes in three chapters. In the first one, the basic working principles of fuel cell technology are presented. The second chapter includes a user’s manual of an integrated fuel cell system and the third is an experimental study of the transient response of this system. In the first chapter of this essay, basic working principles of fuel cell technology are presented. Hydrogen and oxygen are the inputs of a fuel cell system and electrical current and water are the outputs. The usage of hydrogen as fuel is expected to expand in the future because it’s a practically infinite source, even though its production procedures are yet to be improved. Fuel cell systems are a clean energy source since they have theoretically zero emissions, while their efficiency is greater than combustion engines. Also, they are constructions of great simplicity, with low noise emissions and their operation is not affected by geographic factors. All these reasons make fuel cell systems ideal as an energy source on portable devices, vehicular applications and of course as a part of DG systems. The main disadvantage of fuel cells is their cost that still holds back the production of commercial use applications. Also, safety matters that mainly concern compressed hydrogen, should be examined. The commercial application that was used for the experimental study of the essay is Ballard Nexa Power Module. This is an integrated system that provides unregulated DC power and uses a PEM (Proton Exchange Membrane) fuel cell stack. PEM fuel cells are the simplest and most well known fuel cell systems. In this essay a user’s manual for this application is included. This manual describes system design and operation. It provides technical product specifications, performance characteristics and interface requirements for installation and operation. Important safety information is also included. Special attention should be paid on the safety part. Hydrogen met in large concentrations, can displace oxygen in the air and cause asphyxia, while it’s flammable and explosive. Thus, it’s a very dangerous gas (especially in compressed form) and its use requires experience and great attention. This manual is very useful for the reader to understand the way an integrated fuel cell system works, since it describes in detail the operation of all subsystems required for a fuel cell stack to work with efficiency and safety. Future operators are advised to review its contents before operating Nexa Power Module in the lab. The last chapter of this essay includes the experimental study of Nexa Power Module transient response. The time needed by the module to support and reject a load was measured for different loads and several values of stack’s temperature. The figures that follow are presented indicatively and show the form of the results for load support. The results showed that the system’s transient response is very much affected by operation temperature. Also, the response is related to the load that the stack will support or reject. Fuel cell systems’ ability to respond fast and reliably to load changes is critical for their future use, especially for portable applications or parts of distributed generation systems. Consequently, these results are of great importance and should be examined when designing a fuel cell system.

Tese (doutorado)—Universidade de Brasília, Instituto de Ciências Sociais, Departamento de Antropologia, Programa de Pós-graduação em Antropologia Social, 2015. / Submitted by Fernanda Percia França (fernandafranca@bce.unb.br) on 2016-06-06T18:12:12Z No. of bitstreams: 1 2015_SimoneMirandaSoares.pdf: 5221131 bytes, checksum: 81583c84ccfd8e1abea9ba5859353e52 (MD5) / Approved for entry into archive by Raquel Viana(raquelviana@bce.unb.br) on 2016-06-14T20:16:35Z (GMT) No. of bitstreams: 1 2015_SimoneMirandaSoares.pdf: 5221131 bytes, checksum: 81583c84ccfd8e1abea9ba5859353e52 (MD5) / Made available in DSpace on 2016-06-14T20:16:35Z (GMT). No. of bitstreams: 1 2015_SimoneMirandaSoares.pdf: 5221131 bytes, checksum: 81583c84ccfd8e1abea9ba5859353e52 (MD5) / Esta pesquisa trata das transformações ocorridas na carpintaria naval maranhense a partir de um conjunto de eventos e intervenções operadas desde uma pesquisa pioneira que, nos anos 1980, inventariou os modelos de embarcações típicas e seus processos construtivos. O Projeto Embarcações do Maranhão (PEM), coordenado pelo engenheiro mineiro, Luís Phelipe Andrés, registrou os estaleiros, os operários navais, as técnicas de construção e os tipos de barcos de madeira encontrados no estado. Os esforços desta pesquisa repercutiram ao ponto de incentivar a construção do CVT Estaleiro Escola do Sítio Tamancão em São Luís/MA. Esta escola de técnicas possui como missão a transmissão dos saberes e conhecimentos do mestre carpinteiro naval. As ações e efeitos do PEM e as experiências como aluna do Curso de Construção de Embarcações Artesanais compõem os dados de campo que figuram este texto. A partir destes eventos, busco seguir o barco neste processo de transformações e alterações que ocorrem tanto no objeto técnico quanto nas pessoas envolvidas com os fenômenos aqui apresentados. Acompanho os desdobramentos dessa série de acontecimentos a fim de compreender como o barco abarca estas existências. / This research discuss about the changes that took place in Maranhão shipbuilding from a set of events and interventions operated from a pioneering research in the 1980s, inventoried models of typical boats and their construction processes. The Maranhão Vessels Project (EMP), coordinated by the mining engineer, Luís Phelipe Andrés, recorded the shipyards, naval workers, the construction techniques and types of wooden boats found in the state. The efforts of this research had repercussions far as to encourage the construction of CVT Shipyard Tamancão Site School in São Luís/MA. This school techniques has as its mission the transmission of knowledge and expertise of the master shipwright. The actions and effects of PEM and experiences as a student of the Craft Construction Course make up the field of data contained this text. From these events, we try to follow the boat in this process of transformations and changes that occur in both the technical object as the people involved with the phenomena presented here. Follow the developments of this series of events in order to understand how the boat embraces these stocks.