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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04.11.2014 Views

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.3S The effect of using a 10"1 (0,,1.4-) exponent for the viscosi ty ratio also increases the error 1"hen comparing the eight inch by one inch paddle data (geometrically similar to Chilton) with Chilton's (39) correlation. Comparing the date to Chilton's equation there is an average error ofl: 16.3 percent. Uhl recalculated Chiltonts data and claLms that the exponent of the viscosity ratio should be 0 .. 2.4- instead of 0.14. Using l;'hl! s modification of Chilton I s equation there is an average deviation of± 11.1 percent between the predicted and measured Nusselt numbers. The results are plotted in Figure 6-2. The points are fairly evenly distributed along the line of perfect agreement. It ,,,ould be expected that the meaS1.U'ed values vJOuld be about 10 to 20 percent above the predicted values since Chilton did not use baffles. However, Chilton measL~ed the wall temperature at only one position, just opposite the impeller. This '--Tould lead to a measured driving force l--Thich lIms less than the actual value, causing the calculated Husselt nu.mbers to be greater than they should be. Naturally the correlation based on this data would predict Nusselt numbers which are too high. The propeller data were compared w~th Brown's (32) correlation and are plotted in FigLU'e 6-3. The average deviation is 26 .. 9 percent and thus the fit is not very good. ROV-lever, Brown t s correlation is only based on limited data,

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