Abstract
We investigate the sedimentation of colloidal micro-spheres and red blood cells (RBCs) in non-Newtonian fluid - silicone oil with different viscosities. We use digital holographic microscopy (DHM) to obtain volumetric information of the sedimenting micro-objects. Especially, the numerical refocusing feature of DHM is used to extract the depth information of multiple particles moving inside the fluid. The effects of proximity to a flat wall and the non-Newtonian behavior on the sedimenting micro-spheres and RBCs are studied by trajectory analyzing and velocimetry. We observe that for lower viscosity values the proximity effect is more pronounced. The variation rate of the particle falling velocities versus their distance to the flat wall decreases by increasing the viscosity of the fluid. For RBCs, however, the decreasing of the velocity variations have a smoother trend. The experimental results verify the theoretical prediction that, similar to Newtonian case, a correction factor in Stokes’ law suffices for describing the wall effect.
Highlights
Several phenomena, in different scales, in biology, geology, and industry include settling of suspended particles in fluids
For the motion of micro-spheres near a flat wall in Newtonian fluids we have shown that the effect of a flat wall may be represented by multiplying a with the empirical results13,17. λh−1 is a power correction factor series of the ratio to the drag of the radius of a force, which was in agreement sedimenting micro-sphere (a) and its distance from the flat wall (h), and it is independent of the Reynolds number: λh−1
The numerical refocusing feature of digital holographic microscopy (DHM) is used in this research to extract the depth information of multiple particles falling inside the fluid
Summary
In different scales, in biology, geology, and industry include settling of suspended particles in fluids. 3D trajectories of several micro-particles (MPs) and RBCs, in different distances from the flat wall of the container within 5 s and in two different viscosities (100 mPa s and 8900 mPa s). The micro-particles and the RBCs falling at distances below few times of their sizes feel the presence of the wall as their settling velocities are hindered and they travel less trajectory within the same duration.
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