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

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11-<br />

rotat~s at va~ious spe~ds and the resultant to~que om the<br />

bob is measUl1'ed.. In othel'" models val'!'ious tOl'"ques lU'Pe applied<br />

to th~ bob and the resultant speed <strong>of</strong> the bob ~easured. The<br />

viscomet~r ~sed<br />

in this work was oOMposed <strong>of</strong> a bob drivem by<br />

a sync~onous motor at a eomst~t val~e <strong>of</strong> RPM~ (Eigh~<br />

diffel'"ent speeds weF'e possible) .. The tOl"'que required to<br />

attain the desired speed was measured ..<br />

wall <strong>of</strong> the bob is<br />

(2-5<br />

wher~ Ts is the torque required to rotate the bob ..<br />

Rb is the radius <strong>of</strong> ~e bob.<br />

hb is the height <strong>of</strong> the bob ..<br />

The shear 1 rate in ~e annular space between the bob ~d<br />

cup depends upon the ratio <strong>of</strong> the radius <strong>of</strong> th~<br />

cup to tine<br />

bob, s, the angular speed <strong>of</strong> the bob, and the fluid parameters ..<br />

FOF Bingh&m plastics the relati0nanips are given by Fitch (64),<br />

Wilkinson (213), Green (79), and V~ Wazer (196).<br />

For power<br />

law <strong>fluids</strong>, Y,.:pieger and MaPon (100) developed an equation fop<br />

the she~ ratewhieh is valid to a m~~ cup to bob radius<br />

ratio <strong>of</strong> 1 .. 2 ..<br />

D .. K, (~,,-/) +Ji Z<br />

(~,,-/)2J<br />

[ 1+ ~ /hV 1 (oJ)<br />

(2-6<br />

(2-7

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