Effect of Channel Geometry on the Dynamics of a Water Droplet in a Microchannel

The objective of the present study is to investigate the effects of the microchannel geometry on the dynamic behaviour of liquid water emerging from a pore into a microchannel of a cross gas flow. The flow characteristics are resolved using the volume-of-fluid (VOF) method in conjunction with an interface tracking technique. A microchannel with dimensions of a typical proton exchange membrane fuel cell (PEMFC) gas channel (a square cross section of 250 μm in width) and a pore of 50 μm in diameter on the bottom wall is adopted as the baseline case. Simulations for microchannels of different cross sections, including trapezoid, upside-down trapezoid, triangle, rectangle, and rectangle with a arch bottom wall, are performed and the results are compared with the baseline case. The evolution of liquid water includes stages identified as emergence, growth, deformation, detachment, and remove. The simulations show that the cross section of the microchannel has significant impacts on the dynamics of the water droplet. The detachment time and diameter and the remove time of the water droplet are found to be in this order: triangle < trapezoid < rectangle with arch bottom wall < rectangle < upside-down trapezoid. The present study will advance our understanding in the transport of liquid water in a PEMFC where water is produced in the catalyst layer and flows through the pores of the porous electrode to the gas channel.