Viscous resuspension of droplets

Using absorbance measurements through a Couette cell containing an emulsion of buoyant droplets, volume fraction profiles are measured at various shear rates. These viscous resuspension experiments allow a direct determination of the normal stress in the vorticity direction in connection with the suspension balance model that has been developed for suspensions of solid particles. The results unambigously show that the normal viscosity responsible for the shear-induced migration of the droplets is independent on the capillary number, implying that particle deformation does not play a major role. It is similar to that of rigid particles at volume fractions below 40% but much smaller at higher ones.

Automated summary

Using absorbance measurements and a Couette cell, the volume fraction profiles of buoyant droplets were measured, and the normal stress in the vorticity direction was directly determined. It was found that the normal viscosity responsible for shear-induced droplet migration is independent of the capillary number.