The shear rate distribution in the model mixer, the Brabender Farinograph,
is non-homogenous and varies with the relative positions of the sigma blade
s, which rotate at differential speeds. The non-invasive technique of Laser
-Doppler Anemometry (LDA) was used to determine velocity and shear rate dis
tributions in the mixer. A two-dimensional argon-ion Laser-Doppler Anemomet
er was used to obtain three-dimensional velocity measurements in the model
mixer with optically clear model fluids (Corn syrup, CMC, and Carbopol-940
seeded with polystyrene DVB microspheres). Local velocity gradient data obt
ained using infinitesimal movements of the traverse were used to calculate
the shear rate distribution in the model mixer. The shear rate was found to
be a function of blade geometry, blade position, and location. Shear rate
values ranged from 0 to 400 s(-1). Based on these data, a predictive equati
on for shear rate in the model mixer was developed. (C) 2000 Elsevier Scien
ce Ltd. All rights reserved.