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22 June 2000 Airflow control systems for miniature fuel cells
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The feasibility of utilizing piezoelectric actuators for air flow control of low-power fuel cells is assessed using an electromechanical model of the actuator and a steady-state model for compressible flow. Expressions for electromechanical efficiency are derived using one-dimensional transducer equations of a piezoelectric actuator coupled to the pressure- volume relationships for an ideal gas. The derivation demonstrates that the mechanical power output and electrical power requirements of the system are a function of the input- output force ratio, the input force normalized to the blocked force of the actuator, and the piezoelectric coupling coefficient. The mechanical efficiency of the closed cycle is constant at 28.6% and the electrical efficiency varies from less than 1% for a coupling coefficient of 0.1 to approximately 8% for a coupling coefficient of 0.5. Expressions for the force, displacement, and work performed during each process of the four-stroke cycle are derived. A numerical example of a 50 Watt fuel cell demonstrates that only 219 mW of real mechanical power is required to deliver the necessary air flow to the fuel cell. Operating frequencies are approximately 600 Hz for actuators with 1 mm free displacement. Dissipation in the power electronics is between 6 and 19 Watts for linear amplifiers but can be reduced to less than 2 Watts for more efficient switching-type power conditioners. This example demonstrates that piezoelectric actuators are a viable technology for fuel cell air flow control when they are used in conjunction with efficient power electronics.
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Donald J. Leo and Khalil Nasser "Airflow control systems for miniature fuel cells", Proc. SPIE 3985, Smart Structures and Materials 2000: Smart Structures and Integrated Systems, (22 June 2000);

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