Shear-induced particle migration in Couette and parallel-plate viscometers: NMR imaging and stress measurements

Abstract

Couette and parallel plate viscometers are two commonly used flow geometries to characterize shear viscosity of concentrated suspensions. In Couette flow, it is well documented that prolonged shearing causes a decrease in the apparent viscosity of concentrated suspensions due to shear-induced particle migration from the annulus region to the stagnant region under the bob. In this study, the technique of nuclear magnetic resonance imaging (NMRI) was used to measure the evolution of suspension concentration profiles in Couette and parallel-plate flow devices upon shearing. Neutrally buoyant suspensions of nearly monodisperse, non-Brownian spherical particles at a volume fraction of 0.5 in a Newtonian fluid were used. The same flow cells and suspensions were also used in a rheometer to measure the changes in shear stress under identical experimental conditions such that a direct comparison can be made between the stress and concentration data. For Couette flow, the NMRI data correlated very well with the stress measurements and directly confirmed the Leighton–Acrivos [J. Fluid. Mech. 181, 415 (1987)] shear-induced migration theory. In torsional flow between parallel plates, no detectable change was found in particle concentration in the radial direction, but some decrease in the apparent viscosity was observed. These results provide some important clues for developing and evaluating more general descriptions of particle migration for nonrectilinear shear flows.

Synergy between shear-induced migration and secondary flows on red blood cells transport in arteries: considerations on oxygen transport

“…Blood shows remarkable non-Newtonian effects primarily caused by RBC -RBC interactions and RBC -protein interactions: the aggregation and disaggregation of RBCs and their deformation dictate the value of viscosity [1,2]. A wide body of experimental evidence shows that flowing suspensions of rigid and deformable particles exhibit particle migration [3][4][5][6][7][8][9][10] with a general trend showing migration from regions of higher shear rate to regions of lower shear rate. RBCs also show this behaviour and their migration to the centre of micro and small vessels (micrometre to millimetre size) and the consequent segregation of PLTs near the wall has been the subject of intense study in the past years, both numerically [11][12][13][14] and experimentally [15][16][17].…”

Experimental Investigation of Shear-Induced Particle Migration in Steady-State Isothermic Extrusion

“…4) These experiments were for the determination of the material index, m, of the Krieger rheological model where φ c was assumed to be 0.68. However, for this present investigation, the fluid was non-Newtonian.…”

“…14) For the determination of the material constant, m in Equation (2), it is important to carry out experiments under the conditions that there is no or minimum particle migration. As it was shown that parallel-plate viscometer introduced little migration 4) , m was determined to be 0.82 using this testing method. Phillips et al 3) hypothesized that migration occured due to irreversibility in two-body interactions attributed to particle surface roughness, leading to constant empirical …”

“…The results showed particle accumulation and blunting of the velocity profile at the tube center. Chow et al 4) also employed this technique to measure the concentration profiles of neutrally buoyant suspensions of nearly monodisperse, non-Brownian spherical particles. Abbott et al 2) found that the particles migrated away from the inner cylinder and toward the outer wall where shear rate was lower using NMRI.…”

“…Particle migration in concentrated suspensions was studied by employing experimental techniques such as nuclear magnetic resonance imaging (NMRI) 2,4,5,6) and laser Doppler anemometry (LDA). 7,8,9) Using these techniques, they measured the particle concentration and velocity profiles in Newtonian flow suspensions.…”