Flow recirculation in microfluidic T-junctions and bends

Flow recirculation occurs in the outlets of a dividing T-junction of square cross-section when the inlet Reynolds number Re exceeds a critical value Re_c ≈ 350 [1]. The recirculation zones can trap particles, which has important implications to the physics and engineering of inertial microfluidics. We investigate such flow phenomenon using novel glass microfluidic T-junction devices [2]. First, by micro-particle image velocimetry, we show the formation of two counter-rotating Dean vortices in the channel cross-section. Then, by a method that enables high-contrast imaging of recirculating streamlines, we visualize the complete structure of the recirculation zone for Re > Re_c. By varying the ratio of flowrate in the two outlets, we effectively decouple the swirl from the rate of vorticity decay. We demonstrate that even slight outflow imbalances can significantly alter both Re_c and the structure of the recirculation zones. Finally, we show that similar flow recirculation also occurs in sharp microfluidic bends.

1. Ault J T et al. (2016) Phys Rev Lett 117: 084501

2. Chan S T et al. (2018) Phys Rev Fluids 3: 072201(R)