Publications (4)2.43 Total impact
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ABSTRACT: In this paper, equivalent electric circuit models of a commercial 1.2-kW proton exchange membrane (PEM) fuel cell stack are proposed based on AC impedance studies. The PEM fuel cell stack was operated using room air and pure hydrogen (99.995%). Using electrochemical impedance spectroscopy (EIS) technique, impedance data were collected in the laboratory under various loading conditions. Impedance data were analyzed and circuit models developed using basic circuit elements like resistors and inductors, and distributed elements such as Warburg and constant-phase elements. A nonlinear least-square fitting technique is employed to obtain the circuit parameters by fitting a curve to the experimental impedance data. Two circuit models of the fuel cell, one for low and one for high currents are proposed. The average ohmic resistance for the whole stack is estimated to be 41 mΩ. Double-layer capacitances are determined at anode and cathode at various current densities. As expected, cathode charge transfer resistance turns out to be much higher than the anode charge transfer resistance because of slower kinetics of the oxygen reduction reaction. At higher load currents, a significant increase in mass transfer resistance as well as low-frequency inductive effects is observed. These low-frequency inductive effects are recognized and modeled in the fuel cell models of this work. Finally, a semiquantitative analysis was used to determine the contribution of individual performance factors to the overall fuel cell voltage drop. The transient response of the fuel cell circuit models is simulated using MATLAB/Simulink and their performance is validated by comparison with experimental data.IEEE Transactions on Energy Conversion 10/2010; · 2.43 Impact Factor
- Journal of Fuel Cell Science and Technology - J FUEL CELL SCI TECHNOL. 01/2010; 7(3).
Conference Proceeding: Hydrogen dew point control in renewable energy systems using thermoelectric coolers[show abstract] [hide abstract]
ABSTRACT: This paper describes a system, utilizing the Peltier effect, to reduce and control the dew point of hydrogen gas by water condensation and desublimation using thermoelectric coolers and water cooled heat sinks. The design is compared to a two-tube desiccant-drying system used in some commercial proton exchange membrane electrolyzer systems. The desiccant system in the water electrolyzer consumes roughly 0.2 kg per day of hydrogen product gas (corresponding to 3.4 kWh per kg of hydrogen based on the higher heating value) to maintain the two desiccant beds. Thermodynamic modeling was performed to determine the appropriate sizing for the thermoelectric coolers and water-cooled heat sinks for a 1 Nm<sup>3</sup> hr <sup>-1</sup> hydrogen flow rate to obtain a theoretical dew point of -35 degC. The potential benefits and energy consumed by the thermoelectric approach (3.05 kWh per kg of hydrogen) is compared to the hydrogen loss of the desiccant system. The thermoelectric cooler-based system has the ability to control the dew point to match the variable flow rate of hydrogen in a renewable electrolysis system.Power and Energy Society General Meeting - Conversion and Delivery of Electrical Energy in the 21st Century, 2008 IEEE; 08/2008
Conference Proceeding: Improvement of the orthogonal code convolution capabilities using FPGA implementation[show abstract] [hide abstract]
ABSTRACT: When data is stored, compressed, or communicated through a media such as cable or air, sources of noise and other parameters such as EMI, crosstalk, and distance can considerably affect the reliability of these data. Error detection and correction techniques are therefore required. Orthogonal Code is one of the codes that can detect errors and correct corrupted data. An n-bit orthogonal code has n/2 is and n/2 0s. In a previous work these properties have been exploited to detect and correct errors. In this paper we present a new methodology to enhance error detection capabilities of the orthogonal code. The technique was implemented experimentally using field programmable gate arrays (FPGA). The results show that the proposed technique improves the detection capabilities of the orthogonal code by approximately 50%, resulting in 99.9% error detection, and corrects as predicted up to (n/4-1) bits of error in the received impaired code with bandwidth efficiency.Electro/Information Technology, 2007 IEEE International Conference on; 06/2007