Internal friction theoretical models

As the results of Schwander and Cerf (188) and of Leray (180,181), which were obtained on samples of DNA from calf thymus, have been reproduced already in several review articles (1,3), the present discussion can be kept rather short. When the viscosity of the solvent (1.0 molar aquous solution of sodium chloride) is increased by replacing part of the water by glycerol, the behaviour of the initial slope of the extinction angle curve follows the qualitative pattern, as given by Fig. 5.10. At low solvent viscosities the molecules seem to behave like frozen molecules, at high solvent viscosities they seem to become flexible coils exhibiting internal friction. These results have been considered to prove the correctness of Cerf s theoretical model. 

A comparison of the theoretical prediction of boundary B for low-velocity pneumatic conveying with the experimental results from the test rig described in this paper is shown in Fig, 7. The input data required for the model include the particle density (897 kg m ), the voidage of bulk solid (0.391), the coefficient of friction between the particles and wall (0.23), the coefficient of particle internal friction (0.5) and pipeline diameter (60 mm). The agreement between Ae modelling results and the experiments is quite good and the model can be used for design and optimisation purposes. Also, the model described in this paper is able to represent the mechanism of slug formation. 

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