The Dispersing Effect of the Dissolver Disc on Agglomerates
When the vanes of the disc are moved through the millbase at a high velocity,areas of higher and lower pressure are generated in front of and behind the vane.The alternating stress acting on the agglomerates in these areas facilitate their dispersion.In addition to this, a smashing impact should be considered for larger agglomerates being hit by the edges and the surfaces of the vanes.
However,a considerable share of the total dispersion work takes place at the surface of the dissolver disc.Due to the fast movement of the blade,a gradient of shear builds up on these surfaces in which the dispersion takes place.
The shear stress which acts particularly between the lower disc surface and the bottom of the container largely depends upon the distance between the two.The efficiency of the shear gradient may be enhanced by decreasing this separation since the shear rate within the gap is increased and since a higher rotational speed may be chosen due to the fact,that the change from laminar to turbulent flow takes place at higher rotational speeds.
When higher speeds are used, more mechanical power is introduced into the millbase. The best dispersion results are obtained with the highest possible mechanical power input,as long as the doughnut flow pattern (laminar flow)is maintained.The mechanical power is a product of rotational speed and momentum (torque) of the shaft.