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Author: Julie Elizabeth Steinbrenner Publisher: Stanford University ISBN: Category : Languages : en Pages : 149
Book Description
Proton exchange membrane (PEM) fuel cells show promise as CO2-free energy-conversion devices. Predictions show that reducing the size of the gas delivery channels could improve the efficiency and power density of PEM fuel cells, however the expected benefits of reduced channel sizes have not been realized due to flooding by water generated at the cathode. Channels with small dimensions exhibit an increased propensity toward flooding as surface tension forces become significant when compared with viscous, inertial, and pressure forces. This study characterizes the distinct two-phase flow profiles that result from the interplay of these forces. We investigate fundamental water-gas interactions in silicon channels of various hydraulic diameters and cross-sectional aspect ratios using a high-contrast fluorescent imaging technique. Then, we develop a test structure to study the evolution of two-phase flow structures in a microchannel geometry designed to mimic conditions in a fuel cell channel -- a 60-cm long channel with distributed water introduction through a porous gas diffusion layer (GDL) on one wall. Finally, we present considerations for the implementation of spinning-disk confocal microscopy to provide three-dimensional (3D) visualization of two-phase flow structures which may provide insight into key flow transitions that were observed during high-speed fluorescent flow visualization. By characterizing and modeling two-phase flow in various microchannel geometries and under a large range of flow conditions, these studies provide insight that enables the improved design of microchannels for two-phase flow in fuel cells and other practical devices.
Author: Julie Elizabeth Steinbrenner Publisher: Stanford University ISBN: Category : Languages : en Pages : 149
Book Description
Proton exchange membrane (PEM) fuel cells show promise as CO2-free energy-conversion devices. Predictions show that reducing the size of the gas delivery channels could improve the efficiency and power density of PEM fuel cells, however the expected benefits of reduced channel sizes have not been realized due to flooding by water generated at the cathode. Channels with small dimensions exhibit an increased propensity toward flooding as surface tension forces become significant when compared with viscous, inertial, and pressure forces. This study characterizes the distinct two-phase flow profiles that result from the interplay of these forces. We investigate fundamental water-gas interactions in silicon channels of various hydraulic diameters and cross-sectional aspect ratios using a high-contrast fluorescent imaging technique. Then, we develop a test structure to study the evolution of two-phase flow structures in a microchannel geometry designed to mimic conditions in a fuel cell channel -- a 60-cm long channel with distributed water introduction through a porous gas diffusion layer (GDL) on one wall. Finally, we present considerations for the implementation of spinning-disk confocal microscopy to provide three-dimensional (3D) visualization of two-phase flow structures which may provide insight into key flow transitions that were observed during high-speed fluorescent flow visualization. By characterizing and modeling two-phase flow in various microchannel geometries and under a large range of flow conditions, these studies provide insight that enables the improved design of microchannels for two-phase flow in fuel cells and other practical devices.
Author: Julie Elizabeth Steinbrenner Publisher: ISBN: Category : Languages : en Pages :
Book Description
Proton exchange membrane (PEM) fuel cells show promise as CO2-free energy-conversion devices. Predictions show that reducing the size of the gas delivery channels could improve the efficiency and power density of PEM fuel cells, however the expected benefits of reduced channel sizes have not been realized due to flooding by water generated at the cathode. Channels with small dimensions exhibit an increased propensity toward flooding as surface tension forces become significant when compared with viscous, inertial, and pressure forces. This study characterizes the distinct two-phase flow profiles that result from the interplay of these forces. We investigate fundamental water-gas interactions in silicon channels of various hydraulic diameters and cross-sectional aspect ratios using a high-contrast fluorescent imaging technique. Then, we develop a test structure to study the evolution of two-phase flow structures in a microchannel geometry designed to mimic conditions in a fuel cell channel -- a 60-cm long channel with distributed water introduction through a porous gas diffusion layer (GDL) on one wall. Finally, we present considerations for the implementation of spinning-disk confocal microscopy to provide three-dimensional (3D) visualization of two-phase flow structures which may provide insight into key flow transitions that were observed during high-speed fluorescent flow visualization. By characterizing and modeling two-phase flow in various microchannel geometries and under a large range of flow conditions, these studies provide insight that enables the improved design of microchannels for two-phase flow in fuel cells and other practical devices.
Author: Michael Grimm Publisher: ISBN: Category : Proton exchange membrane fuel cells Languages : en Pages : 154
Book Description
"Modern energy concerns have resulted in the necessity to create and understand alternative energy sources and develop systems to effectively utilize them. One such source is hydrogen, which can be utilized in a Proton Exchange Membrane Fuel Cell (PEMFC). This fuel cell has moved to the forefront for adaptability to the automotive industry. With this increased prominence the understanding of two-phase flow phenomena within the anode and cathode channels is needed. Much research has been performed in the area of two-phase flow within macro, mini, and micro-channels of both circular and rectangular cross-sections. However r previous research has been performed with a constant water and air introduction at the beginning of the channel. In a PEMFC water is introduced periodically along the length of the channel, resulting in more water at the end of the channel than at the beginning. A situation arises where the two-phase flow phenomena of the channel changes with distance, and the pressure drop model needs to be modified for the instantaneous flow phenomena. Previous studies have attempted to provide transition equations between the observed flow regimes, and several approaches have been taken. The two-phase flow in the gas channels of proton exchange membrane fuel cell (PEMFC) is studies with an ex-situ setup using a gas diffusion layer (GDL) as the sidewall of the channel. Air is introduced at the channel inlet with continuous uniform water introduction through the GDL. This is different from that use din two-phase studies reported in literature, where the air/water system is introduced at the inlet of the channel simultaneously. The GDL is compressed between the gas channels and the water changers to simulate PEMFC conditions. Superficial velocity for air and water ranged from 33 to 3962 (make m/s) and .02 to .2 (make m/s) respectively. The ex-situ cell was run in both vertical and horizontal orientations, with two GDLs (Baseline and SGL25BC) and three channel treatments (hydrophobic, hydrophilic, and untreated Lexan). The flow regime is observed at different locations along the channel and is expressed as a function of the superficial air and water velocities. Flow regime criteria are developed and validated against the range of ex-situ data observations. A new pressure drop calculation scheme is developed in order to account for the variation of water formations along the channel. Pressure drop models are developed for specific flow regimes and validated against experimental data. The final model is able to predict the pressure drop of experimental data within 8%"--Abstract.
Author: Jinyong Kim Publisher: ISBN: Category : Languages : en Pages :
Book Description
Water management is of paramount importance for improving the performances of proton exchange membrane fuel cells (PEMFCs). Fuel cell channel design plays the most significant role in not only water management but also species transport for electro-chemical reactions. To enhance the performance and durability of PEMFCs, uniform and high oxygen concentration at catalyst layer should be ensured. Unlike conventional PEMFCs, new generation PEMFCs (i.e. Toyota Mirai) maximize their performance by optimizing both macroscopic flow fields and configurations of micro-structures (i.e. baffle, blockages, obstacles). For a new generation of PEMFC technologies, macroscopic modeling of physical phenomena involved in micro-scale two-phase flow of 3D complex flow-fields (i.e. 3D fine-mesh flow-fields of Toyota Mirai) are crucial for large-scale fuel cell simulation.By making an analogy between flow-fields of PEMFCs and porous media, which is so-called porous media approach, two-phase flow models for flow-fields of PEMFCs are developed to numerically investigate and capture various macroscopic and microscopic two-phase flow behavior in flow-fields of PEMFCs. First, flow inertial effects in 3D complex flow-fields on macroscale and microscale two-phase behavior are investigated by considering Forchheimers inertial effect on two-phase flow. It is found that the Forchheimers effect plays a dominant role on liquid water removal and oxygen transport in 3D complex flow-fields of PEMFCs.Second, liquid water re-distributions caused by micro-pore structures attached to bi-polar plates of PEMFCs with 3D complex flow-fields are explored by a macroscopic modeling approach accounting for a capillary effect. It is revealed that the micro porous structures, which is macroscopically viewed as secondary porous media, can improve liquid water management and oxygen diffusion if the permeability of secondary porous media is above a threshold.Third, a two-phase flow model based on porous media approach is suggested to capture the effect of different micro-scale two-phase flow regime (slug, droplet/film, mist flow) in flow channels into a macroscopic PEMFC model. The macroscopic PEMFC model is then applied to explore the effect of two-phase flow regime in micro-channels on cell performance. It is found that flow mal-distribution can be alleviated as the two-phase regime changes from slug, droplet/film to mist flow.
Author: S. Kakaç Publisher: Springer Science & Business Media ISBN: 1402082959 Category : Science Languages : en Pages : 436
Book Description
This volume contains an archival record of the NATO Advanced Institute on Mini – Micro Fuel Cells – Fundamental and Applications held in Çesme – Izmir, Turkey, July 22–August 3, 2007. The ASIs are intended to be a high-level teaching activity in scientific and technical areas of current concern. In this volume, the reader may find interesting chapters on Mini- Micro Fuel Cells with fundamentals and applications. In recent years, fu- cell development, modeling and performance analysis has received much attention due to their potential for distributed power which is a critical issue for energy security and the environmental protection. Small fuel cells for portable applications are important for the security. The portable devices (many electronic and wireless) operated by fuel cells for providing all-day power, are very valuable for the security, for defense and in the war against terrorism. Many companies in NATO and non-NATO countries have concentrated to promote the fuel cell industry. Many universities with industrial partners committed to the idea of working together to develop fuel cells. As tech- logy advanced in the 1980s and beyond, many government organizations joined in spending money on fuel-cell research. In recent years, interest in using fuel cells to power portable electronic devices and other small equipment (cell phones, mobile phones, lab-tops, they are used as micro power source in biological applications) has increased partly due to the promise of fuel cells having higher energy density.
Author: Tim Zhao Publisher: Academic Press ISBN: 0080878873 Category : Technology & Engineering Languages : en Pages : 312
Book Description
Today's consumers of portable electronics consumers are demanding devices not only deliver more power but also work healthy for the environment. This fact alone has lead major corporations like Intel, BIC, Duracell and Microsoft to believe that Microfuel Cells could be the next-generation power source for electronic products. Compact and readable, Microfuels Principles and Applications, offers engineers and product designers a reference unsurpassed by any other in the market. The book starts with a clear and rigorous exposition of the fundamentals engineering principles governing energy conversion for small electronic devices, followed by self-contained chapters concerning applications. The authors provide original points of view on all types of commercially available micro fuel cells types, including micro proton exchange membrane fuel cells, micro direct methanol fuel cells, micro solid oxide fuel cells and micro bio-fuel cells. The book also contains a detailed introduction to the fabrication of the components and the assembly of the system, making it a valuable reference both in terms of its application to product design and understanding micro engineering principles. An overview of the micro fuel cell systems and applications A detailed introduction to the fabrication of the components and the assembly of the system Original points of view on prospects of micro fuel cells
Author: Dennis Y.C. Leung Publisher: CRC Press ISBN: 1315815079 Category : Science Languages : en Pages : 337
Book Description
Fuel cells are clean and efficient energy conversion devices expected to be the next generation power source. During more than 17 decades of research and development, various types of fuel cells have been developed with a view to meet the different energy demands and application requirements. Scientists have devoted a great deal of time and effort
Author: Dmitri Bessarabov Publisher: Academic Press ISBN: 0081028318 Category : Science Languages : en Pages : 140
Book Description
PEM Water Electrolysis, a volume in the Hydrogen Energy and Fuel Cell Primers series presents the most recent advances in the field. It brings together information that has thus far been scattered in many different sources under one single title, making it a useful reference for industry professionals, researchers and graduate students. Volumes One and Two allow readers to identify technology gaps for commercially viable PEM electrolysis systems for energy applications and examine the fundamentals of PEM electrolysis and selected research topics that are top of mind for the academic and industry community, such as gas cross-over and AST protocols. The book lays the foundation for the exploration of the current industrial trends for PEM electrolysis, such as power to gas application and a strong focus on the current trends in the application of PEM electrolysis associated with energy storage. Presents the fundamentals and most current knowledge in proton exchange membrane water electrolyzers Explores the technology gaps and challenges for commercial deployment of PEM water electrolysis technologies Includes unconventional systems, such as ozone generators Brings together information from many different sources under one single title, making it a useful reference for industry professionals, researchers and graduate students alike
Author: Kaushik Saha Publisher: Springer ISBN: 9811332568 Category : Technology & Engineering Languages : en Pages : 400
Book Description
This book focuses on the two-phase flow problems relevant in the automotive and power generation sectors. It includes fundamental studies on liquid–gas two-phase interactions, nucleate and film boiling, condensation, cavitation, suspension flows as well as the latest developments in the field of two-phase problems pertaining to power generation systems. It also discusses the latest analytical, numerical and experimental techniques for investigating the role of two-phase flows in performance analysis of devices like combustion engines, gas turbines, nuclear reactors and fuel cells. The wide scope of applications of this topic makes this book of interest to researchers and professionals alike.
Author: Satish Kandlikar Publisher: Elsevier ISBN: 9780080445274 Category : Science Languages : en Pages : 492
Book Description
&Quot;This book explores flow through passages with hydraulic diameters from about 1 [mu]m to 3 mm, covering the range of minichannels and microchannels. Design equations along with solved examples and practice problems are also included to serve the needs of practicing engineers and students in a graduate course."--BOOK JACKET.
Author: Julie Elizabeth Steinbrenner
Author: Julie Elizabeth Steinbrenner
Author: Julie Elizabeth Steinbrenner
Author: Michael Grimm
Author: Jinyong Kim
Author: S. Kakaç
Author: Tim Zhao
Author: Dennis Y.C. Leung
Author: Dmitri Bessarabov
Author: Kaushik Saha
Author: Satish Kandlikar