Abstract
This present work investigates experimentally the two-phase flow of ethanol and carbon dioxide in non-uniform microchannels to simulate the two-phase flow phenomenon on the flow channel of a micro direct methanol fuel cell in which CO2 bubble may regenerated due to methanol oxidation. The diverging and converging microchannels are fabricated in silicon wafer by bulk micromachining, and channel width a varied linearly was from 1575μm to 45μm for a converging channel, and from 35μm to 1475μm for a diverging one, while the channel depth is 69.5μm and 59.6μm for both channel. The volume flow rates of ethanol and carbon dioxide are controlled range from3.18×10-9m3/s to 1.638×10-8m3/s and from 1.5×10-8m3/s to 1.8×10-7m3/s,respectively. Single phase liquid flow and two-phase flow pressure drop through both types of channels are measured. Moreover, a high speed video camera is employed to capture two-phase flow pattern in both diverging and converging microchannels. The single phase liquid experiment, results investigate that the pressure drop of converging microchannels is 38.8 kPa higher than diverging microchannels at the largest liquid flow rate. The main reason may be an accelerated low in converging microchannels but a decelerated flow in diverging microchannels. In addition, two-phase pressure drop in the converging microchannel is found to be proportional to the gas at a given liquid volume flow rates. In diverging microchannels, the two-phase pressure drop hardly increases with the gas volume flow rate at a given liquid flow rate. In this study, the structure of microchannels influences two-phase flow patterns significantly. Several peculiar flow patterns are observed in converging micro-channel, including long and short slug flow, wavy flow, churn flow and annular flow. In diverging microchannels, mushrooms bubble flow, slug flow and merging churn flow, chestnut slug flow (a slug flow with sharp head bubble), are also observed except stable annular flow.