Title: Development of a silicon-based passive gas-liquid separation system for microscale direct methanol fuel cells

Authors: C.C. Hsieh, S.C. Yao, Yousef Alyousef

Addresses: Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA. ' Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA. ' Energy Research Institute, King Abdulaziz City for Science and Technology, Riyadh, Saudi Arabia

Abstract: The design, fabrication and performance characterisation of a passive gas-liquid separation system is presented in this paper. The gas-liquid separation system is silicon-based and its fabrication is compatible with the existing CMU design of the microscale direct methanol fuel cell (DMFC). Both gas and liquid separators consist of staggered arrays of etched-through holes fabricated by deep reactive ion etching (DRIE). The gas separator is coated with a thin layer of hydrophobic polymer to substantiate the gas-liquid separation. To visually characterise the system performance, the gas-liquid separation system is made on a single wafer with a glass plate bonded on the top to form a separation chamber with a narrow gap in between. Benzocyclobutene (BCB) is applied for the low-temperature bonding. The maximum pressure for the liquid leakage of the gas separators is experimentally determined and compared with the values predicted theoretically. Several successful gas-liquid separations are observed at liquid pressures between 14.2 cmH₂O and 22.7 cmH₂O, liquid flow rates between 0.705 cc/min and 1.786 cc/min, and CO₂ flow rates between 0.15160 cc/min to 0.20435 cc/min.

Keywords: direct methanol fuel cells; microscale DMFC; separation systems; two-phase flow; passive gas-liquid separation; bonding; silicon wafers; deep reactive ion etching; DRIE.

DOI: 10.1504/IJNM.2009.028106

International Journal of Nanomanufacturing, 2009 Vol.4 No.1/2/3/4, pp.13 - 25

Published online: 07 Sep 2009 *

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