Fluid Dynamics Test - SupBiotech 2021

Super-Hydrophobic and Super-Oleophobic Surfaces

• Practical applications include water-proof textiles, underwater bubble generators, anti-fouling surfaces, self-cleaning surfaces, and spreading of pesticides on plant leaves.

Surface Tension

• Phenomena where surface tension is visible at a macroscopic level include slow-down of liquid sliding down a vertical plate, insects walking on top of water pools, spherical shape of oil drops in water, and impregnation of soils with water.

Reynolds Number

• Estimation of Reynolds number for a 1 cm glass bead falling at 10 cm/s in water: about 100.
• Estimation of Reynolds number for liquid rising in a thin capillary of radius 100 microns: about 10.

Capillary Tubes

• Height of rise in capillary tubes is inversely proportional to the tube radius.
• Height of rise is not zero in a space shuttle.

Laminar Cylindrical Pipe Flow (Poiseuille Flow)

• Velocity profile is parabolic and maximal on the cylinder axis.
• Flow is governed by viscosity.
• Velocity is zero along the cylinder walls.

Typical Situations for Viscous Forces

• Flows mainly ruled by viscous forces include imbibition of a porous soil, swimming of bacteria, sedimentation of powder particles, and flow of blood in the aorta.

Microfluidic Channels

• Operations and applications suitable for microfluidic channels include conveying of yield-stress fluids, blood sample bio-analysis, preparation of emulsions, and tumor cell sorting.

Rheology of Fluids

• In a suspension of particles, viscosity increases with volume fraction and shows shear-thickening behavior at small shear rates.
• Rheology of a fluid can be defined as non-Newtonian, shear-thickening, viscoelastic, or yield-stress fluid.

Falling Solid Sphere in Air

• Archimedes force is negligible for a solid sphere falling in air.
• Terminal velocity is proportional to the square of the radius of the sphere.

Plasma Protein Fibrinogen in Microcapillary Flows

• Approximate value of Reynolds number and shear rate in the experimental microfluidic cell: Re = 0.012 and γ = 80-1.
• Effects of fibrinogen concentration on blood properties include increased viscosity for any shear rate and stronger effects for high shear rates.
• Dextran allows spanning larger values of shear rate and promotes cluster formation at intermediate concentrations.
• Advantages of the microfluidic cell include clear visualization of individual RBCs and clusters, high shear rates, and well-controlled flow rates.

Future Steps of the Study

• Next steps could include improving visualization, exploring higher shear rate ranges, coating micro channel walls with endothelial cells, and determining velocity profiles around clusters and individual RBCs.