Homogeneous mixing of liquids in microchannels is well known and characterized for simple channel geometries, such as Y- or T-shaped mixers. Also meandering mixing channels, in which Dean vortices are generated, are often employed to achieve rapid mixing of liquids. A CFD study was performed to increase the mixing performance in the contacting and first mixing element. Dean vortices in the inlet channels increase the mixing quality for Re numbers in the range from 20 to 200 together with S-shaped mixing elements. Mixing quality is significantly increased by a factor of 2 to more than 5 compared to a T-shaped mixer. The residence time distribution is a further important parameter, which is investigated in this contribution.
Particle transport in a laminar tube flow at low Reynolds numbers leads to accumulation of particles at specific equilibrium radii. The equilibrium radius depends on the particle size. Small particles find their equilibrium radius near the wall and large particles near the tube axis. During their radial migration to the equilibrium position, the particles move in axial direction with the flow. In an experimental setup, the axial equilibrium distance is measurement for several tube Reynolds numbers. The axial equilibrium distance is the distance a particle migrates in the flow direction, until it reaches its radial equilibrium position. The results are compared with CFD‐simulations of single particle movement in a laminar tube flow.
The validity of Darcy’s law at very low Reynolds numbers is discussed controversially in literature, as some authors propose a pre–Darcy flow regime below some critical Reynolds number. The scope of this work is to investigate this problem experimentally. Therefore, a packing of glass spheres is perfused by different glycerin–water solutions. A linear behaviour between the flow velocity and the pressure drop through the packed spheres is found in the complete investigated range of Reynolds number $${Re}_{d'}$$ Re d ′ , based on the mean-pore diameter $$d'$$ d ′ and mean-pore velocity $$v'$$ v ′ with $$10^{-9} \le {Re}_{d'} \le 10^{-1}$$ 10 - 9 ≤ Re d ′ ≤ 10 - 1 . This contradicts the results of different authors like Fand et al. (1987) or Kececioglu and Jiang (1994), postulating a pre–Darcy regime for $${Re}_{d'} \le 2.8 \cdot 10^{-6}$$ Re d ′ ≤ 2.8 · 10 - 6 or $${Re}_{d'} \le 0.13$$ Re d ′ ≤ 0.13 , respectively. Graphical abstract
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