Test of Fluid Dynamics - SupBiotech 2021 PDF

Test of Fluid Dynamics - SupBiotech 2021 Rq : all questions can have several correct answers 1 - Give practical applications of super-hydrophobic or super-oleophobic surfaces. a : water-proof textiles b : underwater bubble generators c : anti-fouling surfaces d : self-clean...

Test of Fluid Dynamics - SupBiotech 2021 Rq : all questions can have several correct answers 1 - Give practical applications of super-hydrophobic or super-oleophobic surfaces. a : water-proof textiles b : underwater bubble generators c : anti-fouling surfaces d : self-cleaning surfaces e : spreading of pesticides on plant leaves 2 - In which phenomena we can « feel » the action of surface tension at a macroscopic level ? a : the slow-down of liquid sliding down a vertical plate b : the walk of small insects on top of water pools c : the spherical shape of oil drops into water d : the mixing between two liquids in a micro channel e : the impregnation of soils with water 3 - Give an estimation of the Reynolds number associated with the fall of a glass bead of 1 cm at velocity 10 cm/s in water. a : About 10-3 L = 1 cm b : About 1 U = 10 cm/s c : About 100 Density of water, ρ = 1000 kg/m³ Dynamic viscosity of water, η = 10^-3 Pa.s d : About 1000 4 - Give an estimation of the Reynolds number associated to the rise of liquid into a thin capillary of radius 100 microns. The value of the characteristic velocity value will be guessed from common sense. Radius of the capillary, r = 100 microns = 0.0001 m a : About 100 Diameter of the capillary, L = 0.0002 m b : About 10 Characteristic velocity, U = 1 mm/s = 0.001 m/s c : About 0.1 Density of the liquid, ρ = 1000 kg/m³ d : About 10-4 Dynamic viscosity of the liquid, η = 10^-3 Pa.s 5 - In the rising of liquids in capillary tubes : a : the height of rise is independent on the surface tension b : the height of rise is inversely proportional to the tube radius c : the height of rise is proportional to the tube radius d : the height of rise would be zero in a space shuttle e : the height of rise can take negative values 6 - Tick the assertions which are true for a laminar cylindrical pipe flow (Poiseuille flow) : a : the velocity profile is parabolic and the velocity is maximal on the cylinder axis b : the flow is always governed by viscosity c : the velocity is zero along the cylinder walls d : when the pipe length is multiplied by two, all other parameters kept constant, the flow- rate remains the same. e : the flow-rate is inversely proportional to the cube of the channel radius 7 - What are the typical situations where the flows are mainly ruled by viscous forces ? a : imbibition of a porous soil b : swimming of bacteria c : sedimentation of powder particles d : impact of water drops on surfaces e : fall of a centimetre-size glass sphere within water f : flow of blood in the aorta g : movement of a glacier within a valley h : lift of a solid by an air bearing 8 - What are the operations and applications which are especially suitable in microfluidic channels ? a : conveying of yield-stress fluids b : blood sample bio-analysis c : preparation of emulsions d : atomisation of liquids e : tumor cell sorting f : heat exchangers 9 - In the following rheometric curves, obtained with a suspension of particles and a Couette rheometer (internal cylinder in rotation in the fluid), the Torque is plotted versus angular velocity Ω and the liquid viscosity is plotted versus shear rate, for several volumes fractions of particles ɸ. By analysing the plots, give the assertions which seem true : a : the viscosity increases with volume fraction b : the fluid is shear-thickenning at small shear-rate c : the fluid is shear-thickenning at large shear-rate d : the viscosity diverges beyond a threshold in shear-rate 10 - How can we define the rheology of the fluid besides ? a : it is non-newtonian b : it is shear-thickening c : it is viscoelastic d : it is a yield-stress fluid e : it is newtonian 11 When a solid sphere of several centimetres radius freely falls in the air : a : the Archimedes (buoyancy) force is negligible b : the terminal velocity is proportional to the radius of the sphere c : the terminal velocity is proportional to square of the radius of the sphere d : the Reynolds number is much larger than one e : the terminal velocity is inversely proportional to the air density f : the main force opposing gravity is due to the viscosity of air The last questions are about the paper « The plasma protein fibrinogen stabilizes clusters of red blood cells in microcapillary flows » 12 - Give an approximate value of the Reynolds number and shear-rate 𝛾 in the experimental microfluidic cell (capillary radius 12 microns) : a : Re = 12 and 𝛾 = 800 s-1 b : Re = 0.012 and 𝛾 = 80-1 c : Re = 1.2x10-4 and 𝛾 = 8-1 13 - What are the effects of the concentration of fibrinogen in the properties of blood ? a : the higher the concentration, the higher the viscosity for any shear-rate b : the effect of fibrinogen concentration is stronger for high shear-rate c : the effect of shear-rate is stronger for small fibrinogen concentration d : the RCB aggregates are energetically more favorable at higher fibrinogen concentration 14 - What is the action of dextran in the blood suspension ? a : the dextran allows to span larger values of shear-rate b : the RBC cluster formation is better observed for intermediate dextran concentration c : high dextran concentration promotes the formation of clusters d : addition of dextran does not allows to observe clusters of more than 5 RBCs 15 - What are the advantages of the microfluidic cell (figure 1b) used in the experiments a : it allows to span a large range of Reynolds number for the flow b : it allows a clear visualisation of individual RBCs and clusters c : it allows high shear-rate comparatively to real physiological situations d : it allows to see the behaviour of hardened indéformable RBCs e : it allows to operate at well controlled flow-rate 16 - In your opinion, what would be the next steps of such a study a : to improve visualisation b : to explore ranges with higher shear-rate c : to cover micro channel walls with endothelial cells to modify the wall adhesion d : to determine the velocity profile around clusters and individual RBCs