Embedded self-circulation of liquid fuel for a micro direct methanol fuel cell Dennis Desheng Meng and Chang-Jin ‘ CJ ’ Kim Mechanical and Aerospace Engineering Department, University of California, Los Angeles (UCLA) MENS 2007 Teacher Cheng-Hsien Liu Teacher Cheng-Hsien Liu Reporter C.M Lee

outline Introduction Pumping by hydrophobic venting Fabrication and activation of uDMFC Verification of fuel citculation Conclusion

Introduction Portable consumer electroics : cell phones, GPS, digital cameras and laptop computers. More and more functions integrated into a single device, which demands small power source with higher energy density. Micro direct methanol fuel cell(  DMFC): much higher energy density than traditional batteries.

Issue: –Use external pump to deliver the fuel and push the gas bubble to downstream –An open tank (gas/liquid separator) can be used to release CO2 gas into the environment. New bubble-driven pumping mechanism Introduction

Pumping by hydrophobic venting Gas removal :Microscopic hydrophobic venting holes Allow the gas to pass through relatively undeterred while the liquid menisci block the liquid from following out Liquid can be restricted from leaking by its own meniscus

Pumping by hydrophobic venting New bubble-driven pumping mechanism –Utilizing hydrophobic venting Virtual check valve: provide a higher capillary pressure than the right meniscus does hydrophobic nanoporous embranes : providebubble is vented out without liquid loss

Fabrication and activation of uDMFC

Verification of fuel circulation

Conclusion A self-pumping mechanical was integrated into a  DMFC Reduced the system complexity by eliminating the gas/liquid separator and the external fuel pump

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