Prediction of batch heat transfer coefficients for pseudoplastic fluids ...

29
In both Newtonian and non-Newtoni~D
fluids the shear
rates flere found to be directly proportional to the agitator
speed.
There seemed to be an impeller diameter effect 'tv-hich
was greater for Newtonian than for non-Newtonian fluids.
The shear rate at a given distance from the impeller is
slightly greater as the impeller diameter is increased.
For dilatant fluids the effect might be even greater.
In the laminar region (NR~ - 7.0) the al110Ullt of fluid
movement is much greater for Ne1-vtonian fluids than for the
pseudoplastics at the same rotational speed, a.nd flO1~
extends
almost to the periphery of the tank for the NevJtonians
vJhile flow is circular and is confined to the region of
the impeller for the non-Newtonian fluids.
In the first half of the transition region (NR~
about
10.3) fluid turnover begins for the Ne,-vtonian fluids and
mixing is carried out by the transport and blending.
The
radial veloci ty increases 14i th rotational speed quite
rapidly. However, for the pseudoplastics the movement is
still confined to the center and does not extend to the
edges of the baffles until the Reynolds number reaches 28.
At a Reynolds number of 78 the floH is 1>Jell into the
transition region and the radial velocity component of the
pseudoplastic fluids is high and there l.s an infloVling
vertical component..
Tll.e flo"V>J patterns for the NevJtonian
fluids are similar but the vertical inflm-.r is s lightly less