Pseudoplastic liquids, mixing

Takahashi K., Yokota T, Konno H., Mixing of pseudoplastic liquid in a vessel equipped with a variety of helical ribbon impellers, J. Chem. Engng. Japan 21 (1988) 1, p. 63-68... 

For suspension of free-settling particles, circulation of pseudoplastic slurries, and heat transfer or mixing of miscible liquids to obtain uniformity, a speed of 350 or 420 r/min should be stipulated. For dispersion of dry particles in liquids or for rapid initial mixing of liquid reactants in a vessel, an 1150- or 1750- r/min propeller should be used at a distance Df/4 above the vessel bottom. A second propeller can be added to the shaft at a depth Da below the liquid surface if the submergence of floating liquids or particulate solids is otherwise inadequate. Such propeller mixers are readily available up to 2.2 kW (3 hp) for off-center sloped-shaft mounting. 

The mixing power of a Rushton turbine with 6 flat blades and with 6 blades concavely curved in the direction of rotation was measured in pure and in gassed liquid of Newtonian and non-Newtonian (pseudoplastic and viscoelastic) behaviour [660]. The results were plotted as P/Pq = /(Q) and proved that the concave turbine used only 1/5 to 1/3 of the power at the same Q. In [709] power characteristics of turbine stirrers wirh 6 different shapes of concave blades are presented in the same form P/Pq = f Q). 

The pumps, metering, mixing and application systems must be adapted to the viscosity of both the components. The viscosities of the two components should be similar in order to get a good mixing effect a very liquid product could not be mixed efficiently with a very thick product. Rheology, of course, must be also adapted the products may be pseudoplastic, thixotropic but never dilatant (for these definitions, refer to Chapter 2 in Volume 1 Technical Characteristics of Adhesives and Sealants ). 

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