The Experts below are selected from a list of 56898 Experts worldwide ranked by ideXlab platform
Junye Wang - One of the best experts on this subject based on the ideXlab platform.
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discrete approach for flow field designs of Parallel Channel configurations in fuel cells
International Journal of Hydrogen Energy, 2012Co-Authors: Junye Wang, Hualin WangAbstract:Abstract It is the major challenge to transform a laboratory scale production of fuel cells to an industrial scale one and to meet the requirements of throughput, operating life, low cost, reliability and high efficiency in R&D of fuel cells. Designs of uniform flow distribution are central to upscale fuel cells as well as to tackle critical issues of water, thermal and current management. However, in spite of our growing appreciation of designs of uniform flow distribution, there is little or no practical solution to ensure a uniform flow distribution across Channels of a cell and cells of a stack in designs of flow fields. The purpose of this paper was to develop a discrete approach to find a design that met requirements of flow distribution uniformity and pressure drop in Parallel Channel configurations with Z-type arrangement through adjustments of configurations and normalised structural parameters. Variation of the frictional and the momentum coefficients with flow velocities was incorporated into the flow distribution equation to improve modelling accuracy. We also developed procedure, measures and guideline for the designs of flow distribution and pressure drop to bridge knowledge gap between the generalised theory and industrial applications. The results showed that the present approach could provide the practical guideline to evaluate quantitatively performance of different layout configurations, structures, and flow conditions.
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pressure drop and flow distribution in Parallel Channel configurations of fuel cells u type arrangement
International Journal of Hydrogen Energy, 2008Co-Authors: Junye WangAbstract:A general theoretical model based on mass and momentum conservation has been developed to solve the flow distribution and the pressure drop in Z-type configurations of fuel cells. While existing models neglected either friction term or inertial term, the present model takes both of them into account. The governing equation of the Z-type arrangement was formulated to an inhomogeneous version of the U-type one. Thus, main existing models have been unified to one theoretical framework. The analytical solutions are fully explicit that they are easily used to predict pressure drop and flow distribution for Z-type layers or stacks and provide easy-to-use design guidance under a wide variety of combination of flow conditions and geometrical parameters to investigate the interactions among structures, operating conditions and manufacturing tolerance and to minimize the impact on stack operability. The results can also be used for the design guidance of flow distribution and pressure drop in other manifold systems, such as plate heat exchanges, plate solar collectors, distributors of fluidised bed and boiler headers.
Sennur Ulukus - One of the best experts on this subject based on the ideXlab platform.
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an outer bound for the gaussian mimo broadcast Channel with common and private messages
IEEE Transactions on Information Theory, 2012Co-Authors: Ersen Ekrem, Sennur UlukusAbstract:We consider the Gaussian multiple-input multiple-output (MIMO) broadcast Channel with common and private messages. We obtain an outer bound for the capacity region of this Channel. To this end, we show that a Parallel Gaussian broadcast Channel can be constructed from any given Gaussian MIMO broadcast Channel by using the generalized singular value decomposition and a relaxation on the power constraint for the Channel input. Due to this relaxation of the power constraint, the capacity region of the constructed Parallel Channel, which is known, provides an outer bound for the capacity region of the original Channel. We show that this outer bound is within a finite gap of the capacity region by comparing it with an achievable rate region that can be obtained either by using dirty-paper coding or by using a variation of the zero-forcing scheme.
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degrees of freedom region of the gaussian mimo broadcast Channel with common and private messages
arXiv: Information Theory, 2011Co-Authors: Ersen Ekrem, Sennur UlukusAbstract:We consider the Gaussian multiple-input multiple-output (MIMO) broadcast Channel with common and private messages. We obtain the degrees of freedom (DoF) region of this Channel. We first show that a Parallel Gaussian broadcast Channel with unmatched sub-Channels can be constructed from any given Gaussian MIMO broadcast Channel by using the generalized singular value decomposition (GSVD) and a relaxation on the power constraint for the Channel input, in a way that the capacity region of the constructed Parallel Channel provides an outer bound for the capacity region of the original Channel. The capacity region of the Parallel Gaussian broadcast Channel with unmatched sub-Channels is known, using which we obtain an explicit outer bound for the DoF region of the Gaussian MIMO broadcast Channel. We finally show that this outer bound for the DoF region can be attained both by the achievable scheme that uses a classical Gaussian coding for the common message and dirty-paper coding (DPC) for the private messages, as well as by a variation of the zero-forcing (ZF) scheme.
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degrees of freedom region of the gaussian mimo broadcast Channel with common and private messages
Global Communications Conference, 2010Co-Authors: Ersen Ekrem, Sennur UlukusAbstract:We obtain the degrees of freedom region of the Gaussian multiple-input multiple-output (MIMO) broadcast Channel with common and private messages. We first show that a Parallel Gaussian broadcast Channel with unmatched sub-Channels can be constructed from any given Gaussian MIMO broadcast Channel by using the generalized singular value decomposition (GSVD) and a relaxation on the power constraint for the Channel input, in a way that the capacity region of the constructed Parallel Channel provides an outer bound for the capacity region of the original Channel. The capacity region of the Parallel Gaussian broadcast Channel with unmatched sub-Channels is known, using which we obtain an explicit outer bound for the degrees of freedom region of the Gaussian MIMO broadcast Channel. We finally show that this outer bound for the degrees of freedom region can be attained by the achievable scheme that uses a classical Gaussian coding for the common message and dirty-paper coding (DPC) for the private messages.
Chi Pok Cheung - One of the best experts on this subject based on the ideXlab platform.
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enhanced gas flow uniformity across Parallel Channel cathode flow field of proton exchange membrane fuel cells
International Journal of Hydrogen Energy, 2017Co-Authors: Mohammad Sajid Hossain, Bahman Shabani, Chi Pok CheungAbstract:Abstract Distributing reactant gases uniformly within a cell to ensure proper delivery of reactants is one the crucial requirements for better performance of a Proton Exchange Membrane fuel cell (PEMFC). This investigation was focused on enhancing flow uniformity and distribution of cathode air in Parallel Channel flow field of a fuel cell. 2D Computational Fluid Dynamic (CFD) simulations (i.e. using ANSYS) were performed to solve continuity and momentum equations across the cathode flow field. Two main designs with modified headers that provide (i) Z-type, and (ii) combination of Z and U-types Parallel Channel configurations, were investigated for uniform distribution of gases. Our presented designs were able to allow 60–70% of total flow through frontal 80% of total gas flow field area which was just reversed case compared to conventional design where nearly 80% of flow passes through 20% of total area at the end portion of the gas flow field. Further improvement in flow distributions was observed by segmenting the flow field.
Stuart A. Young - One of the best experts on this subject based on the ideXlab platform.
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calipso lidar calibration algorithms part i nighttime 532 nm Parallel Channel and 532 nm perpendicular Channel
Journal of Atmospheric and Oceanic Technology, 2009Co-Authors: Kathleen A Powell, William H. Hunt, Chris A. Hostetler, Mark A Vaughan, Ralph Kuehn, Charles R. Trepte, Zhaoyan Liu, Kam-pui Lee, Raymond R. Rogers, Stuart A. YoungAbstract:Abstract The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) mission was launched in April 2006 and has continuously acquired collocated multisensor observations of the spatial and optical properties of clouds and aerosols in the earth’s atmosphere. The primary payload aboard CALIPSO is the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), which makes range-resolved measurements of elastic backscatter at 532 and 1064 nm and linear depolarization ratios at 532 nm. CALIOP measurements are important in reducing uncertainties that currently limit understanding of the global climate system, and it is essential that these measurements be accurately calibrated. This work describes the procedures used to calibrate the 532-nm measurements acquired during the nighttime portions of the CALIPSO orbits. Accurate nighttime calibration of the 532-nm Parallel-Channel data is fundamental to the success of the CALIOP measurement scheme, because the nighttime calibration is used to infer...
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calipso lidar calibration algorithms part i nighttime 532 nm Parallel Channel and 532 nm perpendicular Channel
Journal of Atmospheric and Oceanic Technology, 2009Co-Authors: Kathleen A Powell, William H. Hunt, Chris A. Hostetler, Mark A Vaughan, Ralph Kuehn, Charles R. Trepte, Zhaoyan Liu, Kam-pui Lee, Raymond R. Rogers, Stuart A. YoungAbstract:The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) mission was launched in April 2006 and has continuously acquired collocated multisensor observations of the spatial and optical properties of clouds and aerosols in the earth’s atmosphere. The primary payload aboard CALIPSO is the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), which makes range-resolved measurements of elastic backscatter at 532 and 1064 nm and linear depolarization ratios at 532 nm. CALIOP measurements are important in reducing uncertainties that currently limit understanding of the global climate system, and it is essential that these measurements be accurately calibrated. This work describes the procedures used to calibrate the 532-nm measurements acquired during the nighttimeportions of the CALIPSO orbits. Accurate nighttime calibration of the 532-nm Parallel-Channel data is fundamental to the success of the CALIOP measurement scheme, because the nighttime calibration is used to infer calibration across the day side of the orbits and all other Channels are calibrated relative to the 532-nm Parallel Channel. The theoretical basis of the molecular normalization technique as applied to space-based lidar measurements is reviewed, and a comprehensive overview of the calibration algorithm implementation is provided. Also included is a description of a data filtering procedure that detects and removes spurious high-energy events that would otherwise introduce large errors into the calibration. Error estimates are derived and comparisons are made to validation data acquired by the NASA airborne high‐spectral resolution lidar. Similar analyses are also presented for the 532-nm perpendicular-Channel calibration technique.
Abhijit P Deshpande - One of the best experts on this subject based on the ideXlab platform.
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pressure drop and flow distribution in multiple Parallel Channel configurations used in proton exchange membrane fuel cell stacks
Journal of Power Sources, 2006Co-Authors: S Maharudrayya, S Jayanti, Abhijit P DeshpandeAbstract:Single U- and Z-type Parallel-Channel configurations for gas distributor plates in planar fuel cells reduce the pressure drop but give rise to the problem of severe flow maldistribution wherein some of the Channels may be starved of the reactants. In this paper, previous analytical solutions obtained for single U- and Z-type flow configurations are extended to multiple U- and multiple Z-type flow configurations of interest to fuel cell applications. Algorithms to calculate flow distribution and pressure drop in multiple U- and Z-type flow configurations are developed. The results are validated by comparison with those obtained from three-dimensional computational fluid dynamics (CFD) simulations. It is found that there is a significant improvement in the flow distribution in some configurations without paying for extra pressure drop. The possibility of unmatched distribution on the cathode and the anodes sides is also highlighted. Careful design of the flow configuration is therefore necessary for optimum performance.
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flow distribution and pressure drop in Parallel Channel configurations of planar fuel cells
Journal of Power Sources, 2005Co-Authors: S Maharudrayya, S Jayanti, Abhijit P DeshpandeAbstract:Parallel-Channel configurations for gas-distributor plates of planar fuel cells reduce the pressure drop, but give rise to the problem of severe flow maldistribution wherein some of the Channels may be starved of the reactants. This study presents an analysis of the flow distribution through Parallel-Channel configurations. One-dimensional models based on mass and momentum balance equations in the inlet and exhaust gas headers are developed for Z- and U-type Parallel-Channel configurations. The resulting coupled ordinary differential equations are solved analytically to obtain closed-form solutions for the flow distribution in the individual Channels and for the pressure drop over the entire distributor plate. The models have been validated by comparing the results with those obtained from three-dimensional computational fluid dynamics (CFD) simulations. Application of the models to typical fuel-cell distributor plates shows that severe maldistribution of flow may arise in certain cases and that this can be avoided by careful choice of the dimensions of the headers and the Channels.
