The sorting devices of microfluidic system have a passive method and an active one. Curved microchannels are often used in these systems due to secondary flows. Because sorting or mixing can be used with the secondary flow in these systems, it is necessary to clarify the characteristic of the secondary flow. In this study, we investigate behavior of particles in spiral rectangular microchannel, and effects of aspect ratio and of Dean number De on the particle sorting. We performed three-dimensional numerical simulations using the particle tracking method (PTM) to analyze the particle sorting. When particle density is larger than water density, it is found that good sorting is obtained in the case of 20 < De < 40. This tendency appears to be stronger if the aspect ratio is small.
