The nature of many powders, pigments and prills are to form into agglomerated lumps which often contain more than 50% air. This cluster of dry media is challenging to hydrate and break-up into an even mixture by traditional centrifugal agitation – this process can take many hours with poor results.
The high speed disperser was developed to offer positive vortex thrust drawing lumps, agglomerates and solids directly to the impeller tips. The cutting action of the blade and high tip speed reduces process time dramatically (and often achieves results not previously attained). The dispersion of these clusters containing air combined with a vortex would suggest aeration of product could be an issue, however this is not often a problem in lower viscosity products. Vacuum dispersers are suggested in higher viscosity processes to any overcome aeration issues. High viscosity processes may also need dual or triple action dispersers to prevent HSD cavitation in a viscous media. The addition of turbines and anchor scraper agitators delivers axial flow towards HSD whilst the anchor assists heat transfer, baffling and cleaning the vessel walls.
A triple action disperser offers flexible, high efficiency mixing when involving viscous fluid processes. Normal practice is to increase the sawtooth diameter to around a third (moderate viscosities) or a half (higher viscosities) of the vessel diameter to overcome the density of liquid in a HSD process – volumes over 500 litres this requires significant motor power and cost. A triple action mixer may only need a HSD impeller diameter 1/6th of the vessel diameter as the other turbine and anchor generate the mass flow needed in the vessel and force material into the path of the HSD blade. Clearly, benefits in aeration, thrust and heat transfer are also gained by operating a triple action mixer. Due to the HSD power reductions the cost of high speed sealing technology for large diameter shafts also saves further expense.