Numerical investigation of water droplet dynamics in a low-temperature fuel cell microchannel: Effect of channel geometry

The sensitivity of liquid water to geometry of cathode gas microchannel in low-temperature fuel cells is investigated numerically. The two-phase flow is resolved using 3D CFD simulations with the volume-of-fluid (VOF) method. Simulations for microchannels with different cross-sections, including rectangle with aspect ratios in a range of 0.1-2, trapezoid, upside-down trapezoid, triangle, rectangle with a curved bottom wall, and semicircle are compared. The 0.5 aspect ratio rectangle yields the longest detachment time and the largest detachment diameter, whereas the longest removal time occurs for the 0.25 aspect ratio case. With decreasing aspect ratio for the rectangle the pressure drop increases and the coverage ratio decreases. The 0.1 and 2 aspect ratios rectangles have the largest water saturation. For microchannels with different cross-sections, the detachment time, detachment diameter, and removal time of the water droplet are found to be in this order: triangle < trapezoid < rectangle with a curved bottom wall < rectangle < upside-down trapezoid. The friction coefficient increases by a factor of 2-4 in the presence of water. The upside-down trapezoid yields the maximum coverage ratio and water saturation, while the rectangle with a curved bottom wall results in the minimum values. (C) 2009 Elsevier B.V. All rights reserved.