Study of Non-Newtonian viscosity and yield stress of blood in a scanning capillary-tube rheometer (A)

2021 ◽  
Author(s):  
Sangho Kim
Keyword(s):  
Yield Stress ◽  
Capillary Tube ◽  
Newtonian Viscosity

Capillary Flow of Yield-Stress Fluids in Microchannels

2006 ◽  
Author(s):  
V. Bertola
Keyword(s):  
Yield Stress ◽  
Flow Regime ◽  
Capillary Flow ◽  
Capillary Tube ◽  
Plug Flow ◽  
Wall Slip ◽  
Critical Distance ◽  
Tube Diameter ◽  
Force Balance ◽  
Theoretical Argument

The wicking of a model yield-stress fluid (hair-gel solution in water) in a capillary tube is studied experimentally. By changing the hair-gel concentration in the solution, the yield stress varied from 5 to 20 Pa. A simple force balance between capillary and viscous forces suggests that the fluid should stop flowing as soon as the wall shear stress reaches the yield value, at a critical distance from the inlet which is independent of the tube diameter. However, this theoretical argument is not confirmed by experiments, which show that the fluid moves well beyond the critical distance determined theoretically, and that there is a well-defined effect of the tube diameter. It is proposed that such behavior may be determined by wall slip, which causes the flow to switch from the Poiseuille flow regime to the plug flow regime.

High Shear Stress Behavior of Some Representative Lubricants

1975 ◽  
Vol 97 (3) ◽  
pp. 479-485 ◽  
Author(s):  
J. Jakobsen ◽  
W. O. Winer
Keyword(s):  
Shear Stress ◽  
Capillary Tube ◽  
Pressure Level ◽  
High Shear ◽  
Newtonian Viscosity ◽  
Constant Viscosity ◽  
Independent Behavior ◽  
End Corrections ◽  
Silicone Lubricant ◽  
Newtonian Behavior

Shear stress independent behavior was observed for representative, synthetic, nonblended lubricants to about 4.8 × 106 N/m2 (700 psi) shear stress in high pressure viscometric measurements. This shear stress is of the same magnitude as the shear stress in sliding elastohydrodynamic contacts. It is shown that dissipation heating is the only mechanism of importance in the generation of the deviations from constant viscosity as measured with capillary tube viscometric methods. The Newtonian end corrections for the capillary tubes were found to be constant for the nonblended, liquid lubricants. Newtonian behavior will be expected of the fluids in a high shear lubrication situation. Shear induced, nonliquid behavior was found for the silicone lubricant at about 106 N/m2 and for the polymer-blended mineral oil at about 104 N/m2 at a relatively low pressure level. The observations might provide a key to an understanding of the generation of the anomalous low elastohydrodynamic film thickness as found with these lubricants. The polymer-blended oil showed shear thinning effects. The apparent viscosity was found to increase (∼30 percent) with increasing shear stress in the range of the second Newtonian viscosity level.

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