Indirect heat exchange at

In S/L dispersions with /Sp 0, the above concept does not apply with averaged material values, as Kwasniak [312] demonstrated on the basis of the material system polystyrene beads (dp = 0.3 mm)/water, see Fig. 7.10. In the left half of the figure the experimental data are evaluated in the above-discussed way for different 

The reason for this discrepancy lies in the fact, that in the layer close to the wall a separation of the dispersion occurs, as a result of which an almost homogeneous liquid phase exists in the boundary layer, whose heat transfer behavior corresponds to the physical properties of the continuous phase. If this is taken into consideration by incorporating the values of the continuous phase (index c) for k, h and and averaged values of p and p for the dispersion (index s), the following equation is obtained  

It is evident, that in S/I dispersions with Ap w 0, higher Nu values occur than in pure liquids or at Ap 0. This is explained by the rotation of particles close to the wall. 

In striking contradiction with the above-discussed experimental data, are measurements [358] of heat transfer for suspensions of macromolecular materials (copolymers with dp = 0.1-2 mm and p = 1054 or 1025 kg/m = 34%) in aqueous polyvinyl alcohol or gelatin solution of comparable density, in which a pitched-blade stirrer with 2 blades (h = 45° D/d = 2 h/d = 0.1) and an anchor stirrer with D/d = 1.07, h/d = 0.1 were utilized. The tank of D = 300 mm with a hemispherical bottom was not baffled. The result 

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