Curved microchannels with inner wall expansion–contraction array for particle focusing

To enhance focusing performance, we proposed an integrated microchannel with expansion–contraction arrays (ECA) on the inner wall of the curved microchannel (CIECA) and compared it with a straight microchannel with ECA (SECA) as well as the traditional integrated microchannel of ECA on the outer wall of the curved channel (COECA). We investigated the particle-focusing mechanisms in these microchannels through a combination of experiments and numerical simulations. The proposed integrated microchannel demonstrates significant improvements in focusing performance compared to SECA and COECA, which is attributed to its consistent Dean flow. In contrast, COECA shows the poorest performance because of inconsistent Dean flow. The focusing width in the proposed integrated microchannel is reduced to 1/3 of that in COECA and 1/2 of that in SECA. Furthermore, the focusing performance of CIECA improves as the Reynolds number increases, eventually forming a single trajectory when the Reynolds number (at contraction) reaches 83.33. Finally, the impact of particle size on focusing performance was investigated through numerical simulations. The focusing performance of the CIECA is the best in these three microchannels. In CIECA, as the particle size increases, the focusing width initially decreases and then increases. Among them, 8 and 10 μm particles can achieve complete focusing. This study serves as a crucial reference for comprehending and enhancing particle focusing through the synergy of multi-Dean flow.