Particle motions in low-Reynolds number pressure-driven flows through converging–diverging microchannels

Particle motions were experimentally studied in low-Reynolds number pressure-driven flows through converging–diverging microchannels. The whole process of particle acceleration and deceleration close to the bottom channel wall through the converging and diverging sections was visualized. We find that the ratio of the particle velocity in the throat to that in the straight channel is decreased when particles move closer to either sidewall. This ratio is, however, insensitive to the particle size. Both phenomena are well explained with the ratio of fluid velocity at the particle centers in the two regions. It is also found that the particle velocity ratio increases when particles move slower, and the underlying reason may need further investigation.