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RESEARCH PAPERS

Lattice Boltzmann Simulations of CO2 Bubble Dynamics at the Anode of a μDMFC

[+] Author and Article Information
K. Fei, C. H. Cheng

Department of Power Mechanical Engineering,  National Tsing Hua University, Hsinchu 30013, Taiwan

C. W. Hong

Department of Power Mechanical Engineering,  National Tsing Hua University, Hsinchu 30013, Taiwancwhong@pme.nthu.edu.tw

J. Fuel Cell Sci. Technol 3(2), 180-187 (Oct 20, 2005) (8 pages) doi:10.1115/1.2174067 History: Received July 15, 2005; Revised October 20, 2005

This paper presents the bubble transport phenomenon at the anode of a micro-direct methanol fuel cell (μDMFC) from a mesoscopic viewpoint. Carbon dioxide bubbles generated at the anode may block part of the catalyst/diffusion layer and also the flow channels that cause the μDMFC malfunction. Lattice-Boltzmann simulations were performed in this paper to simulate the two-phase flow in a microchannel with an orifice which emulates the bubble dynamics in a simplified porous diffusion layer and in the flow channel. A two-dimensional, nine-velocity model was established. The buoyancy force, the liquid-gas surface tension, and the fluid-solid wall interaction force were considered and they were treated as source terms in the momentum equation. Simulation results and parametric studies show that the pore size, the fluid stream flow rate, the bubble surface tension, and the hydrophilic effect between the fluid and the solid wall play the major roles in the bubble dynamics. Larger pore size, higher methanol stream flow rate, and greater hydrophilicity are preferred for bubble removal at the anode diffusion layer and also the flow channels of the μDMFC.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 2

The distribution functions at those boundary nodes: they are the inlet, outlet, left wall, and right wall, respectively (Solid lines represent known distribution functions; while dashed lines denote unknown distribution functions)

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Figure 3

Simulation domains (L=15.9μm, W=1.5μm) for the bubble flow in typical microchannels (a) case 1: no blocks; (b) case 2: a block is in the middle; and (c) case 3: blocks are on both sides (d represents the pore size or the gap between the blocks)

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Figure 4

Bubble flow in case 2 (methanol concentration: 5M; inlet flow rate: 0.0cm2∕s; hydrophilic wall; θ: the contact angle between the liquid/gas interface and the wall; the unit of the elapsed time t is in 10−3s or ms)

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Figure 5

Bubble flow in a horizontal microchannel (a) methanol concentration: 5M; inlet flow rate: 0.0cm2∕s; hydrophilic wall (θlower: The contact angle between the gas/liquid interface and the lower wall; θupper: the contact angle between the gas/liquid interface and the upper wall); (b) methanol concentration: 5M; inlet flow rate: 6.0×10−6cm2∕s; hydrophilic wall

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Figure 6

Bubble flow in case 3 (methanol concentration: 5M; inlet flow rate: 0.0cm2∕s; d=0.9μm; hydrophilic wall)

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Figure 7

Bubble flow in case 3 (methanol concentration: 5M; inlet flow rate: 1.5×10−6cm2∕s; d=0.9μm; hydrophilic wall)

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Figure 8

Bubble flow in case 3 (methanol concentration: 5M; inlet flow rate: 1.5×10−6cm2∕s; d=0.7μm; hydrophilic wall)

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Figure 9

Comparison of the bubble shape in hydrophilic channels (a)Gσ=−0.012, (b)Gσ=−0.004, (c)Gσ=0.004, and (d)Gσ=0.012 (methanol concentration: 5M; inlet flow rate: 1.5×10−6cm2∕s)

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Figure 10

Summary of bubble dynamics in the case 3 (methanol concentration: heavily spotted=1M; lightly spotted=5M; blank=10M)

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Figure 1

Unit cell of the D2Q9 model (two spatial dimensions, nine lattice velocities including the rest particle)

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