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 ...
42 tween 0.25 and 0.58. L~~l had reported ~n 18 percent difference in Nusselt nu..l11bers for an impeller in hw different locations a..D.d a fev1 authors had mentioned that hi'>.:her heat transf~r rates Here achieved for certain impeller locations but the effect had not been studied qua.nti ta ti vely. The effect of height variation may have a considerable signific8~ce since changes in the impeller height cause minimal if not neglirible changes in pOHer requirements. The model proposed in Chapter 3 results in a dLmensionless equation which acclJ.rately characterizes the batch heat transfer system as sh01~m by the good fi t achieved. Thus the model itself may be inferred to be a fairly accurate portrayal of the :mechanismof heat transfer in an agitated vessel. To be more specific~ the center core of tIle fluid is in turbulent flm! Hi tll. thorough mixing of the fluj e3 in this region. In addi tion to tlJrbulence in the impeller region, the impel10r produces bulk fluid .flow, largely axial. This results in fluid flov~ alon!:. the cylindrical heat tra..Ylsfer surface in the vertical direction. At the wall surface the flu:td is motionless. There is a velocity gradient in the radial direction. Heat is transferred across the stagnant fluid layer at the Hall by conduction 8Jld is then transferred by diffusion and bulk floH into the turbulent core. TI'le controllinG factor in the rate of heat transfer is thus a stagnant layer at the Hall. An increase in the bulk rImA)" rate through the eye of the impeller (by increasine; im-
LfJ peller diameter, l,~idth, or speed) causes an increase in the velocity of the fluid near the lfJall.. This results in greater momentlL111 transfer in the radial direction Itli th a subsequent decrease in the thickness of t.c"I-J.e stagnant layer .. Comparison of Correlations * 1 .. w « ' p ... . _$ ",' -'1' 'M - -"- The data was correlated by equations representing tvw different approaches, theoretical and semi-empirical. The best equation of each type 1~ill be compared v,Ii th each other later in this chapter, but first their common characteristics v-rill be mentioned.. One characteristic is that they both revert to the cornmonly accepted correlations :for NeHtonian :fh:tids for the case of n equal to unity.. This is not the case lvi th ma..ny correlations, an eXE'uuple being the correlation of Blanchard and Chu (22) for the prediction of batch heat trans:fer coefficients. The accuracy of the cOl'"'relation in reproducing the experimental data is very good, the average error for all :fluids is in the ra..n8e of 9 to 14 percent Hi th the greatest average deviation being :for the most pseudoplastic fluid in the range of 13 to 20 percent. In no insta..nce is the average error o:f the correlation in representing the data greater than the error in the determination of the heat transfer coe:f:ficient. Both the theoretical and semi-empirical correlations are based on a more fundamental fO~Uldation than are the previous correlations :for the prediction of batch heat
- Page 103: and if' lO"V'l$' a sm.all amount of
- Page 106 and 107: 94- was about 40-45 ndmutes .. Tke
- Page 108 and 109: 96 vThere N is in rev./sec .. and S
- Page 110 and 111: 88 ql\fETI A = 6 T \--T -s L/kw (1+
- Page 112 and 113: I {)D The generalized Reynolds n~mb
- Page 114 and 115: 02. CHAPTER !2. RESUI,TS Many heat
- Page 116 and 117: 01 TABLE 5-2 sutn~U{Y OF ADDITIONAL
- Page 118 and 119: 108 the batch than the other ticJO
- Page 120 and 121: 108 optimum impeller heights were u
- Page 122 and 123: 10 I r "'" , •• ,'., "",' """",
- Page 124 and 125: 112 correlations for the prediction
- Page 126 and 127: TABLE 5 - 4 Correlation Constants A
- Page 128 and 129: 1/6 Table 5-5 and 5-6. A measure of
- Page 130 and 131: TABLE S - 6 IMPELLER Correlation Co
- Page 132 and 133: 120 greater than 2.0. In this case
- Page 134 and 135: 12.2
- Page 136 and 137: TABLE 5 - 9 CORRELATION E t (a/n +1
- Page 138 and 139: TABLE 5 - 10 IMPELLER Correlation C
- Page 140 and 141: TABLE 5 - 11 CORRELATION G (1.30/61
- Page 142 and 143: 1.30 of the substantial improvement
- Page 144 and 145: 1.3 2. The probable error in the ca
- Page 146 and 147: 134 .,;' : :: :::: : ~ !~. , " . .'
- Page 148 and 149: T." ••••••• ,_ .....
- Page 150 and 151: 38 the cooling of nitration liquors
- Page 152 and 153: 140 The average deviation of the me
- Page 156 and 157: 144 transfer coefficients to non-Ne
- Page 158 and 159: 16 of fit and it may t...herefore b
- Page 160 and 161: 148 'tvas insufficient data to eval
- Page 162 and 163: 50 A ::: Apr ... B ::: C p ::: CPr
- Page 164 and 165: 52. Q ::. Average heat transfer rat
- Page 166 and 167: Xc = Function of Reynolds nL:l.m.be
- Page 168 and 169: IS6 G REE:>{ ALPHABET 0 ::: Value o
- Page 170 and 171: 158 coefficient. Thus, for the wate
- Page 172 and 173: 160 , ., I .. : I :. '. • • !.
- Page 174 and 175: 162 I , . I . "I '1 I i I 1 I 1· '
- Page 176 and 177: 64 ncr --~iIluto e torque of the in
- Page 178 and 179: 166 rive different temperatures; ab
- Page 180 and 181: 168 TABLE A-4. SLOPE OF "LOG SHEAR
- Page 182 and 183: TABLE 11.-5 RHEOLOGICAL DATA FOR CA
- Page 184 and 185: TABLE A-5 (eollt. ) /12 o . 24;;& C
- Page 186 and 187: '11 The flow behavior index and flu
- Page 188 and 189: i .f.C ·F s o 6 1 6 I
- Page 190 and 191: · . . . " , · . :::11" ': "'" ~ .
- Page 192 and 193: 180 Tke thermal e€l1'!ciluetlvity
- Page 194 and 195: 182 Heat capacity data for 100% gly
- Page 196 and 197: IB4- wkiek ex~resses the aensity e
- Page 198 and 199: 186 Ts - Torque X :: Peree~t 0~ ful
- Page 200 and 201: Phase I Calcu13tiJ~ of Slope of !oG
- Page 202 and 203: 3 REAL). N. ti •• D 4 cN=N E'I'
LfJ<br />
peller diameter, l,~idth,<br />
or speed) causes an increase in<br />
the velocity <strong>of</strong> the fluid near the lfJall..<br />
This results in<br />
greater momentlL111 <strong>transfer</strong> in the radial direction Itli th a<br />
subsequent decrease in the thickness <strong>of</strong> t.c"I-J.e stagnant layer ..<br />
Comparison <strong>of</strong> Correlations<br />
* 1 .. w « ' p ... . _$ ",' -'1' 'M - -"-<br />
The data was correlated by equations representing tvw<br />
different approaches, theoretical and semi-empirical. The<br />
best equation <strong>of</strong> each type 1~ill<br />
be compared v,Ii th each other<br />
later in this chapter, but first their common characteristics<br />
v-rill be mentioned..<br />
One characteristic is that they both revert<br />
to the cornmonly accepted correlations :<strong>for</strong> NeHtonian<br />
:fh:tids <strong>for</strong> the case <strong>of</strong> n equal to unity..<br />
This is not the<br />
case lvi th ma..ny correlations, an eXE'uuple being the correlation<br />
<strong>of</strong> Blanchard and Chu (22) <strong>for</strong> the prediction <strong>of</strong> <strong>batch</strong> <strong>heat</strong><br />
trans:fer <strong>coefficients</strong>.<br />
The accuracy <strong>of</strong> the cOl'"'relation in reproducing the experimental<br />
data is very good, the average error <strong>for</strong> all :<strong>fluids</strong><br />
is in the ra..n8e <strong>of</strong> 9 to 14 percent Hi th the greatest average<br />
deviation being :<strong>for</strong> the most <strong>pseudoplastic</strong> fluid in the range<br />
<strong>of</strong> 13 to 20 percent. In no insta..nce is the average error<br />
o:f the correlation in representing the data greater than the<br />
error in the determination <strong>of</strong> the <strong>heat</strong> <strong>transfer</strong> coe:f:ficient.<br />
Both the theoretical and semi-empirical correlations<br />
are based on a more fundamental fO~Uldation<br />
than are the<br />
previous correlations :<strong>for</strong> the prediction <strong>of</strong> <strong>batch</strong> <strong>heat</strong>
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