MEMSdesign6 - DESIGN OF A PIEZOELECTRICALLY ACTUATED MICROVALVE FOR FLOW CONTROL IN FUEL CELLS by Ahmet Fatih Ayhan BS Mechanical Engineering

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DESIGN OF A PIEZOELECTRICALLY ACTUATED MICROVALVE FOR FLOW CONTROL IN FUEL CELLS by Ahmet Fatih Ayhan BS Mechanical Engineering, Middle East Technical University, 2000 Submitted to the Graduate Faculty of School of Engineering in partial fulfillment of the requirements for the degree of Master of Science in Mechanical Engineering University of Pittsburgh 2002
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ii UNIVERSITY OF PITTSBURGH SCHOOL OF ENGINEERING This thesis was presented By Ahmet Fatih Ayhan It was defended on 04/10/2002 and approved by Thesis Advisor: Jeffrey S. Vipperman, Ph. D.
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iii DESIGN OF A PIEZOELECTRICALLY ACTUATED MICROVALVE FOR FLOW CONTROL IN FUEL CELLS Ahmet Fatih Ayhan, MS University of Pittsburgh, 2002 This thesis presents a novel piezoelectrically actuated microvalve for flow control in fuel cells. A fuel cell is an electrochemical device, which directly converts chemical energy stored in a fuel (e.g. hydrogen) and an oxidizer (e.g. oxygen) directly into electrical energy. Poor flow distributions within the cell have been attributed to degraded performance and even damage. In this study, it is proposed to embed microvalves directly into the fuel cells to manage the gas flows and improve efficiency, performance, and reliability. The microvalve has four parts. The actuator is a piezoelectric trimorph which has two piezoelectric layers and one brass layer sandwiched between them and has dimensions of 20000 × 4000 × 290 microns. It also has a valve gate placed on the tip. For a 5-volt input, a deflection of 32 microns can be achieved in the trimorph tip, which is what modulates the flow through the valve. The valve design and analysis are complete. Maximum stress on the bender reaches up to 60 MPa when the fluidic and thermal forces are at their maximum. This maximum stress is below the tensile dynamic strength values of piezoelectric and brass layers used. A minimum factor of safety of 1.5 is obtained at 20 ° C. At the operating temperature, which is about 100 ° C
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iv the factor of safety is around 13. The drag and pressure forces are found to reduce the free deflection by only 0.2 microns whereas the thermal expansion forces increases the deflection almost by the same amount. Finally detailed fabrication plan and drawings were completed.
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v ACKNOWLEDGEMENTS “This thesis is dedicated to my sister Ayca Ayhan…” Firstly, I would like to thank my advisor Dr. Jeffrey S. Vipperman for his support, guidance and enthusiasm throughout this research. I would also like to acknowledge the support that I received from Dr. Qing-Ming Wang, Dr. William W. Clark and Dr. Dipo Onipede. I would like to thank all members of the Sound Systems and Structures Laboratory that I worked with during the course of this research. In particular, I would like to thank Deyu Li and Ilya Avdeev for their help.
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This note was uploaded on 02/08/2010 for the course MECHANICAL 6537 taught by Professor Stiharu during the Winter '10 term at Concordia Canada.

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MEMSdesign6 - DESIGN OF A PIEZOELECTRICALLY ACTUATED MICROVALVE FOR FLOW CONTROL IN FUEL CELLS by Ahmet Fatih Ayhan BS Mechanical Engineering

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