Numerical Investigation of the Hydrodynamic Focusing Phenomena in a Microflow Cytometer

Abstract

Simulations were performed to study the 2-D hydrodynamic focusing phenomena in a microflow cytometer. The hydrodynamic focusing phenomenon was studied by varying the velocities of both the sample and the sheath flows flowing through the center and the outer channel of a microflow cytometer. The geometries studied include both 2D and axisymmetric ones. Velocity ratios (velocity of sheath to sample flow ratio) were varied from 5 to 70 and the results include the change in the focusing width. Discrete phase model (DPM) of ANSYS FLUENT was used to inject particles with different sizes along the sample flow and their trajectories were tracked. The focusing characteristic of non-Newtonian fluids in comparison with Newtonian fluids was also studied. The predicted focusing widths tend to decrease with the increase in the velocity ratio. A focusing width less than 10 m can be achieved by increasing the velocity ratio to 70. It is also observed that the focusing ratio is the function of flow rate ratio and depends on the geometry of the sample flow. The trajectory of the particles in the cytometer is tracked and the results confirm the hydrodynamic focusing of the sample flow as the particles moved in a single file in the horizontal X-Y plane toward the detection region. The focusing width was calculated for velocity ratios of 5, 15, and 70 for both non-Newtonian and Newtonian fluids and the results revealed only slight deviation in the focusing widths.