1996 Volume 29 Issue 1 Pages 51-58
The mixing of yield stress fluids with an anchor impeller is investigated numerically in the laminar regime using a three-dimensional finite element method. First, it is shown that the flow behavior is strongly influenced by the level of viscoplasticity and that mixing is rather inefficient in such a case. Next, correlations of the power number versus the Reynolds number are presented for different values of the Bingham number. In particular, it is established that the Metzner-Otto concept remains valid for fluid exhibiting a yield stress and that the Metzner and Otto constant (Ks) varies slightly over a wide range of Bingham numbers (Bi ≤ 75M). Finally, the 25-year old experimental findings of Nagata are reviewed and clarified.