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Two Phase Flow Phenomena In Fuel Cell Microchannels
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Book Synopsis Two-phase Flow Phenomena in Fuel Cell Microchannels by : Julie Elizabeth Steinbrenner
Download or read book Two-phase Flow Phenomena in Fuel Cell Microchannels written by Julie Elizabeth Steinbrenner and published by Stanford University. This book was released on 2011 with total page 149 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Two-phase Flow Phenomena in Fuel Cell Microchannels by : Julie Elizabeth Steinbrenner
Download or read book Two-phase Flow Phenomena in Fuel Cell Microchannels written by Julie Elizabeth Steinbrenner and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Modeling Pressure Drop of Two-phase Gas/liquid Flow in PEM Fuel Cell Channels by : Michael Grimm
Download or read book Modeling Pressure Drop of Two-phase Gas/liquid Flow in PEM Fuel Cell Channels written by Michael Grimm and published by . This book was released on 2011 with total page 154 pages. Available in PDF, EPUB and Kindle. Book excerpt: "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.
Book Synopsis Modeling Micro- and Macro-Scale Two-Phase Flow in 3D Flow Channels of Proton Exchange Membrane Fuel Cells by : Jinyong Kim
Download or read book Modeling Micro- and Macro-Scale Two-Phase Flow in 3D Flow Channels of Proton Exchange Membrane Fuel Cells written by Jinyong Kim and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Mini-Micro Fuel Cells written by S. Kakaç and published by Springer Science & Business Media. This book was released on 2008-04-10 with total page 436 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Micro Fuel Cells written by Tim Zhao and published by Academic Press. This book was released on 2009-07-07 with total page 312 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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
Book Synopsis PEM Water Electrolysis by : Dmitri Bessarabov
Download or read book PEM Water Electrolysis written by Dmitri Bessarabov and published by Academic Press. This book was released on 2018-07-23 with total page 178 pages. Available in PDF, EPUB and Kindle. Book excerpt: Hydrogen Energy and Fuel Cell Primers is a series of concise books that present those coming into this broad and multidisciplinary field the most recent advances in each of its particular topics. Its volumes bring together information that has thus far been scattered in many different sources under one single title, which makes them a useful reference for industry professionals, researchers and graduate students, especially those starting in a new topic of research. These volumes, PEM Water Electrolysis vol 1 and 2, allows these readers to identify the technology gaps for the development of commercially viable PEM electrolysis systems for energy applications. This primer examines the fundamentals of PEM electrolysis and selected research topics that are currently subject of attention by academic and industry community, such as gas cross-over and AST protocols. This lays the foundation for the exploration of the current industrial trends for PEM electrolysis, such as power to gas application, are discussed, with strong focus on the current trends in the application of PEM electrolysis associated with energy storage. These include durability aspects of PEM electrolysis systems and components, accelerated stress test protocols, manufacturing aspects of large-scale electrolyzers and components, gas crossover problems in PEM electrolyzer safety, and challenges associated with high-current density operation of PEM electrolyzers. A technology development matrix for systems and components requirements will also be covered, as well as unconventional PEM water electrolysis systems, such as ozone generators 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
Book Synopsis Micro & Nano-Engineering of Fuel Cells by : Dennis Y.C. Leung
Download or read book Micro & Nano-Engineering of Fuel Cells written by Dennis Y.C. Leung and published by CRC Press. This book was released on 2015-04-24 with total page 337 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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
Book Synopsis Two-Phase Flow for Automotive and Power Generation Sectors by : Kaushik Saha
Download or read book Two-Phase Flow for Automotive and Power Generation Sectors written by Kaushik Saha and published by Springer. This book was released on 2018-11-03 with total page 398 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Phase Separation in Two-phase Microfluidic Heat Exchangers by : Milnes P. David
Download or read book Phase Separation in Two-phase Microfluidic Heat Exchangers written by Milnes P. David and published by Stanford University. This book was released on 2011 with total page 151 pages. Available in PDF, EPUB and Kindle. Book excerpt: Two-phase microfluidic heat exchangers have the potential to meet the large heat dissipation demands of high power electronics and computing systems. Two-phase cooling systems face practical challenges brought on by the growth and advection of the vapor phase in the confined geometries, which lead to large pressure drops, increased thermal resistance and the formation of detrimental flow instabilities. One proposed solution to these issues is phase separation, whereby the vapor is locally separated from the two-phase flow through a porous hydrophobic membrane. This dissertation describes a series of studies conducted to develop an understanding of the factors that influence vapor separation and its impact on the hydraulic and thermal characteristics of two-phase heat exchangers. Flow phenomena are a critical component in developing this understanding of phase separation. High speed visualization of adiabatic and diabatic vaporizing flows was carried out in a single 124[Mu]m by 98[Mu]m copper microchannel with a 65[Mu]m thick, 220nm pore diameter hydrophobic PTFE membrane wall. During adiabatic air-water flow, wavy-stratified and stratified flow dominated lower liquid velocities, while plug and annular type flows dominated at the higher velocities. Analysis found that air removal could be improved by increasing the venting area, increasing the trans-membrane pressure or using thinner, high permeability membranes. Diabatic water-vapor experiments with mass flux velocities of 140 and 340 kg/s-m2 and exit qualities up to 20% found that stratified type flows dominate at lower mass fluxes while cyclical churn-annular flow became more prevalent at the higher mass-flux and quality. The observed flow regimes are hypothesized to play a significant role in determining the pressure drop and heat transfer coefficient during flow boiling. To study the impact of various geometric and membrane factors on the performance of a phase separating microchannel heat exchanger dissipating 100W of heat, a numerical model incorporating vapor separation and transport during two-phase flow boiling in a microchannel was developed. The impact of substrate thermal conductivity and thickness, membrane permeability and thickness, liquid channel density, liquid and vent channel diameter and vent-to-liquid channel diameter ratio was studied and compared for a standard non-venting heat exchanger, a vapor venting heat exchanger and a non-venting heat exchanger occupying the same increased volume as the venting heat exchanger. The numerical study found that the venting heat exchanger had improved pressure drop and device temperatures for all tested conditions when compared against a standard heat exchanger but only under very limited conditions when compared against the volumetrically equivalent non-venting heat exchanger. The study indicates that the best venting heat exchanger performance is achieved when the membrane conductance is of the same order or higher than that of the microchannel; this can be achieved through the use of thin high permeability membranes coupled with small hydraulic diameter microchannels. Finally, a study was conducted to explore the fabrication methods to build a vapor separating heat exchanger and to quantify the operating performance of multichannel silicon and copper phase separating devices. A copper parallel microchannel heat exchanger with nineteen 130[Mu]m square microchannels was built and tested at heat fluxes of up to 820 kW/m2 and water mass fluxes of between 102 and 420 kg/s-m2. Normalized pressure drop was improved by as much as 60% and average substrate temperature by a maximum of 4.4°C between the non-venting control and vapor venting device under similar operating conditions. Comparison between the experimental results and simulation predictions found higher than expected pressure drop improvements at higher mass fluxes and poorer heat transfer coefficients at the lowest mass flux. Based on the flow phenomena study these discrepancies are believed to be due to the mass flux and vapor quality dependent two-phase flow structures. The encouraging experimental and numerical results motivate further study into phase separation methods, materials and flow physics. The development of a high performance phase separating heat exchanger, with the thermal benefits of two-phase boiling flow and the hydraulic benefits of single-phase liquid flow, would strongly enable the adoption and application of two-phase heat exchangers to provide effective and efficient cooling for next generation high power computing systems.
Book Synopsis Heat Transfer and Fluid Flow in Minichannels and Microchannels by : Satish Kandlikar
Download or read book Heat Transfer and Fluid Flow in Minichannels and Microchannels written by Satish Kandlikar and published by Elsevier. This book was released on 2006 with total page 492 pages. Available in PDF, EPUB and Kindle. Book excerpt: &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.
Book Synopsis Encyclopedia Of Two-phase Heat Transfer And Flow Iii: Macro And Micro Flow Boiling And Numerical Modeling Fundamentals (A 4-volume Set) by : Thome John R
Download or read book Encyclopedia Of Two-phase Heat Transfer And Flow Iii: Macro And Micro Flow Boiling And Numerical Modeling Fundamentals (A 4-volume Set) written by Thome John R and published by World Scientific. This book was released on 2018-03-13 with total page 1460 pages. Available in PDF, EPUB and Kindle. Book excerpt: Set III of this encyclopedia is a new addition to the previous Sets I and II. It contains 26 invited chapters from international specialists on the topics of numerical modeling of two-phase flows and evaporation, fundamentals of evaporation and condensation in microchannels and macrochannels, development and testing of micro two-phase cooling systems for electronics, and various special topics (surface wetting effects, microfin tubes, two-phase flow vibration across tube bundles). The chapters are written both by renowned university researchers and by well-known engineers from leading corporate research laboratories. Numerous 'must read' chapters cover the fundamentals of research and engineering practice on boiling, condensation and two-phase flows, two-phase heat transfer equipment, electronics cooling systems, case studies and so forth. Set III constitutes a 'must have' reference together with Sets I and II for thermal engineering researchers and practitioners.
Book Synopsis Basic Transport Phenomena in Materials Engineering by : Manabu Iguchi
Download or read book Basic Transport Phenomena in Materials Engineering written by Manabu Iguchi and published by Springer Science & Business Media. This book was released on 2013-09-12 with total page 269 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents the basic theory and experimental techniques of transport phenomena in materials processing operations. Such fundamental knowledge is highly useful for researchers and engineers in the field to improve the efficiency of conventional processes or develop novel technology. Divided into four parts, the book comprises 11 chapters describing the principles of momentum transfer, heat transfer, and mass transfer in single phase and multiphase systems. Each chapter includes examples with solutions and exercises to facilitate students’ learning. Diagnostic problems are also provided at the end of each part to assess students’ comprehension of the material. The book is aimed primarily at students in materials science and engineering. However, it can also serve as a useful reference text in chemical engineering as well as an introductory transport phenomena text in mechanical engineering. In addition, researchers and engineers engaged in materials processing operations will find the material useful for the design of experiments and mathematical models in transport phenomena. This volume contains unique features not usually found in traditional transport phenomena texts. It integrates experimental techniques and theory, both of which are required to adequately solve the inherently complex problems in materials processing operations. It takes a holistic approach by considering both single and multiphase systems, augmented with specific practical examples. There is a discussion of flow and heat transfer in microscale systems, which is relevant to the design of modern processes such as fuel cells and compact heat exchangers. Also described are auxiliary relationships including turbulence modeling, interfacial phenomena, rheology, and particulate systems, which are critical to many materials processing operations.
Book Synopsis Proceedings of the 8th International Conference on Nanochannels, Microchannels and Minichannels, 2010 by :
Download or read book Proceedings of the 8th International Conference on Nanochannels, Microchannels and Minichannels, 2010 written by and published by . This book was released on 2011 with total page 1784 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Microchannel Phase Change Transport Phenomena by : Sujoy Kumar Saha
Download or read book Microchannel Phase Change Transport Phenomena written by Sujoy Kumar Saha and published by Butterworth-Heinemann. This book was released on 2015-09-27 with total page 358 pages. Available in PDF, EPUB and Kindle. Book excerpt: Microchannel Heat transfer is the cooling application of high power density microchips in the CPU system, micropower systems and many other large scale thermal systems requiring effective cooling capacity. This book offers the latest research and recommended models on the microsize cooling system which not only significantly reduces the weight load, but also enhances the capability to remove much greater amount of heat than any of large scale cooling systems. A detailed reference in microchannel phase change (boiling and condensation) including recommended models and correlations for various requirements such as pressure loss, and heat transfer coefficient. Researchers, engineers, designers and students will benefit from the collated, state-of-the-art of the research put together in this book and its systematic, addressing all the relevant issues and providing a good reference for solving problems of critical analysis. Up-to-date information will help delineate further research direction in the microchannel heat transfer The latest modeling information and recommendations will help in design method and purpose
Book Synopsis Proceedings of the ASME Heat Transfer Division by :
Download or read book Proceedings of the ASME Heat Transfer Division written by and published by . This book was released on 2002 with total page 274 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Two Phase Flow and Heat Transfer in Microchannels by : Rashid Ali
Download or read book Two Phase Flow and Heat Transfer in Microchannels written by Rashid Ali and published by LAP Lambert Academic Publishing. This book was released on 2011-09 with total page 160 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book explains some interesting phenomena in two-phase flow and heat transfer in microchannels. The microchannel technology is an emerging technology that finds many interesting applications in industry and academic research. Miniaturization of scientific and industrial components is the motivation to carry out the microchannel research. Microchannel technology offers many advantages in automotive heat transfer, in microelectronics for removal of high heat fluxes.The research in macro channels have been carried out for a long period now but still two-phase in macro and especially in microchannels is very complicated phenomena. As such the results found for macro scale channels are not directly applicable and can not be extrapolated to micro scale channels. This book gives some insight into main differences between a micro and macro scale channel and some governing phenomena in two-phase flow and heat transfer are highlighted.
