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

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

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6D and e directions and constant density, the equation becomes I A J(eA i£)_ 0 eJft - (3-7 In the system being considered the mechanical energy input is negligible compared to the heat transferred through the 1..Jal1s. The energy equation for this case is (21) d T 0tdT J/p (-'c;; ( d-c -;- J~ ";-;t ) 7 -f liz dT ) = J& oiL! J [; (3-8 The temperature gradients in the e direction are zero, and the temperature gradients in the z direction are also assumed zero.. Therefore equation 3-8 reduces to Equations 3-5, 3-7 and 3-9 thus describe the model (3-9 discussed above. These equations cannot be solved since the velocity and temperature gradients cannot be expressed analytically. However, the system can be characterized by solving the equations dimensionally. The follo-vring dimensionless variables are defined by Bird, et al. (21) as r-lH~ = ( riDs. ) (3-10 Z~:- = z/Ds. 0-11

61 Vr;> Jt.- ,,"Ii'\... ..", ::: (Vr/V) (3-12 Vz .. ~~ = Vz/V (3-13 p -li- p-p = Ie f/ Z 0 (3-14 t~=- -- tV/Da (3-15 T~~ T = - Too (3-16 Ts - %0 where V is a characteristic velocity which can be quantitatively evaluated. For an agitated vessel, NDa is such a velocity. Da is the diameter of the impeller and N is its rate of revolution .. Solving equations 3-10, 3-11, 3-12, 3-13 and 3-14 for the variables in equation 3-5 r = r~~~:"D a (3-17 z ... J~ z"Da (3-18 Vr :: V ~~-!~V r (3-19 V z = Vz·:"'V (3-20 p :: p~:. (e V2 ) + po (3-21 Equation 3-5 also has differential terms. Equation 3-22 is valid since it is an identity .. (3-22

61<br />

Vr;> Jt.- ,,"Ii'\...<br />

..", ::: (Vr/V) (3-12<br />

Vz .. ~~<br />

= Vz/V (3-13<br />

p<br />

-li-<br />

p-p<br />

= Ie f/ Z<br />

0<br />

(3-14<br />

t~=-<br />

-- tV/Da (3-15<br />

T~~ T<br />

=<br />

- Too (3-16<br />

Ts - %0<br />

where V is a characteristic velocity which can be quantitatively<br />

evaluated.<br />

For an agitated vessel, NDa is such a velocity.<br />

Da is the diameter <strong>of</strong> the impeller and N is its rate <strong>of</strong><br />

revolution ..<br />

Solving equations 3-10, 3-11, 3-12, 3-13 and 3-14 <strong>for</strong><br />

the variables in equation 3-5<br />

r = r~~~:"D a (3-17<br />

z ...<br />

J~<br />

z"Da (3-18<br />

Vr :: V ~~-!~V<br />

r (3-19<br />

V z = Vz·:"'V (3-20<br />

p :: p~:. (e V2 ) + po (3-21<br />

Equation 3-5 also has differential terms. Equation 3-22<br />

is valid since it is an identity ..<br />

(3-22

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