Investigation of effective parameters on capturing particles by secondary flows in rectangular microchannels

In recent years, inertial microfluidics (the use of inertial forces in microchannels) have attracted much attention aiming particle separation. The advantage of this method over other methods of separation and enrichment is its high-throughput performance and inexpensiveness. In the present study, the purpose of enriching the fluid with particles greater than 15 microns in diameter accomplished by designing a rectangular microchannel with an array of contraction-expansion regions in which expansion regions (reservoirs) had the task of trapping larger particles. By using the finite element method and by solving the Navier-Stokes equations, streamlines and vortex shapes are obtained. It was observed that for inlet flow rates in the range of 0.25 to 0.5 milliliters per minute, the highest capture efficiency for particles larger than 10 microns in diameter occurred near 0.35 milliliters per minute. The effect of parameters such as channel height, number of reservoirs and the initial length of the contraction region on the capture efficiency was also measured. Finally, in order to approach the practical applications, the effect of viscosity change due to replacement of blood (Non-Newtonian fluid) instead of water was also investigated, which resulted in the formation of vortices at higher flow rates. In general, vortices created in the expansion region, whose intensity depends on the parameters mentioned above, play a dominant role in particle separation, while inertial lift forces appear as an initial guide