1,149 research outputs found
The State of the Art in Fuel Cell Condition Monitoring and Maintenance
Fuel cell vehicles are considered to be a viable solution to problems such as carbon emissions and fuel shortages for road transport. Proton Exchange Membrane (PEM) Fuel Cells are mainly used in this purpose because they can run at low temperatures and have a simple structure. Yet to make this technology commercially viable, there are still many hurdles to overcome. Apart from the high cost of fuel cell systems, high maintenance costs and short lifecycle are two main issues need to be addressed. The main purpose of this paper is to review the issues affecting the reliability and lifespan of fuel cells and present the state of the art in fuel cell condition monitoring and maintenance. The Structure of PEM fuel cell is introduced and examples of its application in a variety of applications are presented. The fault modes including membrane flooding/drying, fuel/gas starvation, physical defects of membrane, and catalyst poisoning are listed and assessed for their impact. Then the relationship between causes, faults, symptoms and long term implications of fault conditions are summarized. Finally the state of the art in PEM fuel cell condition monitoring and maintenance is reviewed and conclusions are drawn regarding suggested maintenance strategies and the optimal structure for an integrated, cost effective condition monitoring and maintenance management system
Design of LTCC-based Ceramic Structure for Chemical Microreactor
The design of ceramic chemical microreactor for the production of hydrogen needed in portable polymer-electrolyte membrane (PEM) fuel cells is presented. The microreactor was developed for the steam reforming of liquid fuels with water into hydrogen. The complex three-dimensional ceramic structure of the microreactor includes evaporator(s), mixer(s), reformer and combustor. Low-temperature co-fired ceramic (LTCC) technology was used to fabricate the ceramic structures with buried cavities and channels, and thick-film technology was used to make electrical heaters, temperature sensors and pressure sensors. The final 3D ceramic structure consists of 45 LTCC tapes. The dimensions of the structure are 75 Ć 41 Ć 9 mm3 and the weight is about 73 g
Fabrication of a Flexible Micro Temperature Sensor for Micro Reformer Applications
Micro reformers still face obstacles in minimizing their size, decreasing the concentration of CO, conversion efficiency and the feasibility of integrated fabrication with fuel cells. By using a micro temperature sensor fabricated on a stainless steel-based micro reformer, this work attempts to measure the inner temperature and increase the conversion efficiency. Micro temperature sensors on a stainless steel substrate are fabricated using micro-electro-mechanical systems (MEMS) and then placed separately inside the micro reformer. Micro temperature sensors are characterized by their higher accuracy and sensitivity than those of a conventional thermocouple. To the best of our knowledge, micro temperature sensors have not been embedded before in micro reformers and commercial products, therefore, this work presents a novel approach to integrating micro temperature sensors in a stainless steel-based micro reformer in order to evaluate inner local temperature distributions and enhance reformer performance
Microfluidics and Nanofluidics Handbook
The Microfluidics and Nanofluidics Handbook: Two-Volume Set comprehensively captures the cross-disciplinary breadth of the fields of micro- and nanofluidics, which encompass the biological sciences, chemistry, physics and engineering applications. To fill the knowledge gap between engineering and the basic sciences, the editors pulled together key individuals, well known in their respective areas, to author chapters that help graduate students, scientists, and practicing engineers understand the overall area of microfluidics and nanofluidics. Topics covered include Finite Volume Method for Numerical Simulation Lattice Boltzmann Method and Its Applications in Microfluidics Microparticle and Nanoparticle Manipulation Methane Solubility Enhancement in Water Confined to Nanoscale Pores Volume Two: Fabrication, Implementation, and Applications focuses on topics related to experimental and numerical methods. It also covers fabrication and applications in a variety of areas, from aerospace to biological systems. Reflecting the inherent nature of microfluidics and nanofluidics, the book includes as much interdisciplinary knowledge as possible. It provides the fundamental science background for newcomers and advanced techniques and concepts for experienced researchers and professionals
Energy autonomous systems : future trends in devices, technology, and systems
The rapid evolution of electronic devices since the beginning of the nanoelectronics era has brought about exceptional computational power in an ever shrinking system footprint. This has enabled among others the wealth of nomadic battery powered wireless systems (smart phones, mp3 players, GPS, ā¦) that society currently enjoys. Emerging integration technologies enabling even smaller volumes and the associated increased functional density may bring about a new revolution in systems targeting wearable healthcare, wellness, lifestyle and industrial monitoring applications
Application of electro-active biofilms
The concept of an electro-active biofilm (EAB) has recently emerged from a few studies that discovered that certain bacteria which form biofilms on conductive materials can achieve a direct electrochemical connection with the electrode surface using it as electron exchanger, without the aid of mediators. This electro-catalytic property of biofilms has been clearly related to the presence of some specific strains that are able to exchange electrons with solid substrata (eg Geobacter sulfurreducens and Rhodoferax ferrireducens). EABs can be obtained principally from natural sites such as soils or seawater and freshwater sediments or from samples collected from a wide range of different microbially rich environments (sewage sludge, activated sludge, or industrial and domestic effluents). The capability of some microorganisms to connect their metabolisms directly in an external electrical power supply is very exciting and extensive research is in progress on exploring the possibilities of EABs applications. Indeed, the best known application is probably the microbial fuel cell technology that is capable of turning biomass into electrical energy. Nevertheless, EABs coated onto electrodes have recently become popular in other fields like bioremediation, biosynthesis processes, biosensor design, and biohydrogen production
Factors influencing fuel cell life and a method of assessment for state of health
Philosophiae Doctor - PhDProton exchange membrane fuel cells (PEMFC) converts chemical energy from the electrochemical reaction of oxygen and hydrogen into electrical while emitting heat, oxygen depleted air (ODA) and water as by-products. The by-products have useful functions in aircrafts, such as heat that can be used for ice prevention, deoxygenated air for fire retardation and drinkable water for use on board. Consequently, the PEMFC is also studied to optimize recovery of the useful products. Despite the progress made, durability and reliability remain key challenges to the fuel cell technology. One of the reasons for this is the limited understanding of PEMFC behaviour in the aeronautic environment.
The aim of this thesis was to define a comprehensive non-intrusive diagnostic technique that provides real time diagnostics on the PEMFC State of Health (SoH). The framework of the study involved determining factors that have direct influence on fuel cell life in aeronautic environment through a literature survey, examining the effects of the factors by subjecting the PEMFC to simulated conditions, establishing measurable parameters reflective of the factors and defining the diagnostic tool based on literature review and this thesis finding
Rapid Prototyping of Microfluidic Devices:Realization of Magnetic Micropumps, Fuel Cells and Protein Preconcentrators
With the growing importance of miniaturized energy applications and the development of micro Total Analysis Systems (Ī¼TAS), we have realized microfluidic devices, namely, magnetic micropumps, microfluidic fuel cells and membrane-based protein preconcentrators, all having high application potential in future. The choice of rapid prototyping microfabrication technologies and the selection of affordable materials are important aspects, when thinking of commercialization. Thus, we have employed powder blasting, polymer molding and assembly technologies during devices fabrication throughout the thesis. The first type of microfluidic device that we present is a poly(methyl methacrylate) (PMMA) ball-valve micropump with two different designs of the electromagnetic actuator, as optimized by the finite element method. The integration of a permanent magnet in a flexible polydimethylsiloxane (PDMS) membrane, which is clamped into PMMA structure, is proposed for providing a large stroke of the pumping membrane, making the micropump bubble-tolerant and self-priming Focusing on low power consumption for Ī¼TAS integration, another type of magnetic micropump with active valves is realized. It consists of a microfluidic chamber structure in glass that is assembled with a PDMS sheet, which comprises two valving membranes and a central actuation membrane, having each an integrated permanent magnet that is peristaltically actuated by a rotating arc-shaped permanent magnets assembly. A lumped circuit model is developed to predict and describe the frequency-dependent flow rate behavior for this type of pump. Powder blasting and PDMS molding rapid prototyping technologies are employed for realization of these two types of micropumps. Fuel cells with fluid delivery and removal options, having chemical reaction sites and electrode structures that can be realized in a microfluidic format, have high potential for applications. Therefore, microfluidic direct methanol fuel cells with embedded ion- permselective medium are studied and such type of fuel cell is realized by integrating a narrow Nafion strip in a molded elastomeric structure. A mechanical clamping assembly technology enables leakage-free operation and stable performance. The characterization reveals its output power density, using H2O2-based oxidant, is among the high-performance direct methanol fuel cells in microscale. Re-using the technology of the fuel cell chip, with its particular ion-permselective Nafion membrane and assembly method, we also have developed a protein preconcentrator with high purification performance. Our device can preconcentrate negatively charged biomolecules located at the anodic compartment side of the Nafion strip within only a few minutes with a high preconcentration factor. Moreover, a complex microfluidic finite element model is proposed to study and understand the physics of the preconcentration effect. Finally, we conclude the thesis with an outlook on future developments based on our work of the project and on the assembly technologies for microfluidic device integration
NASA Tech Briefs, July 2002
Topics include: a technology focus sensors, software, electronic components and systems, materials, mechanics, machinery/automation, manufacturing, bio-medical, physical sciences, information sciences, book and reports, and a special section of Photonics Tech Briefs
Physics-based prognostic modelling of filter clogging phenomena
In industry, contaminant filtration is a common process to achieve a desired level of purification, since contaminants in liquids such as fuel may lead to performance drop and rapid wear propagation. Generally, clogging of filter phenomena is the primary failure mode leading to the replacement or cleansing of filter. Cascading failures and weak performance of the system are the unfortunate outcomes due to a clogged filter. Even though filtration and clogging phenomena and their effects of several observable parameters have been studied for quite some time in the literature, progression of clogging and its use for prognostics purposes have not been addressed yet. In this work, a physics based clogging progression model is presented. The proposed model that bases on a well-known pressure drop equation is able to model three phases of the clogging phenomena, last of which has not been modelled in the literature yet. In addition, the presented model is integrated with particle filters to predict the future clogging levels and to estimate the remaining useful life of fuel filters. The presented model has been implemented on the data collected from an experimental rig in the lab environment. In the rig, pressure drop across the filter, flow rate, and filter mesh images are recorded throughout the accelerated degradation experiments. The presented physics based model has been applied to the data obtained from the rig. The remaining useful lives of the filters used in the experimental rig have been reported in the paper. The results show that the presented methodology provides significantly accurate and precise prognostic results
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