06/00145 Valveless piezoelectric micropump for fueldelivery in direct methanol fuel cell (DMFC) devices

Abstract

Presented in this dissertation is the study of a novel fuel delivery system combined with miniaturized direct methanol fuel cell (DMFC). The core component of this system is a valveless micropump driven by ring-type piezoelectric bending actuator. By applying an alternating electrical field across the actuator, the resultant reciprocating movement of the pump diaphragm can be converted into pumping effect. Nozzle/diffuser elements are used to direct the flow. To make the power system applicable for portable electronic devices, the micropump needs to meet some specific requirements: low power consumption but sufficient fuel flow rate. In this study, both theoretical and experimental methods have been used to investigate the effects of materials properties, actuator dimensions, driving voltage, driving frequency, nozzle/diffuser dimension, and other factors on the performance of the whole system. As a result, a viable design of micropump system for fuel delivery in DMFC devices has been achieved and some further improvements are suggested.In the beginning of this dissertation, the history, working principle, types, and current research status of both fuel cell and micropump are reviewed. Following this comprehensive introduction, the research objective to develop a novel portable power system that combines fuel cell technology and micropump technology is presented. To help design such a system, a series of analytical models are established to estimate the deflection, volume change, flow rate, and power iv consumption of the micropump. Both finite element method (FEM) and experimental method are applied to verify the models. Based on the analytical analysis, material properties and dimensions of the micropump actuator are optimized to obtain maximum flow rate and minimum power consumption. Later a separated micropump prototype has been fabricated and tested. It is observed that the performance of a DMFC device is improved by using this micropump to supply fuel. In addition, the electrochemical impedance analysis of this fuel cell device is conducted to try to understand the reasons for the performance improvement. Finally, the accomplishments of this study are summarized and future perspective is provided.v