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Low Viscosity Blending

Low-viscosity blending involves evaluation of the degree of uniformity required and the operating cycle.

There is a difference in performance, depending on whether the materials to be blended are added continuously and uniformly into the tank, with the tank originally in motion or whether the tank has become stratified during the filling application, and mixing must be accomplished with a stratified liquid level situation.

In general, blend time is reduced at constant mixer power with larger DIT ratios. The exponent on DIT with blend time is approximately -1.5, with the range observed experimentally of from 0.5 to 3.0. This leads to the fact that larger impellers running at slow speeds require less power than a small mixer running at high speed for the same blend time. In that case an evaluation is needed which relates capital cost of the equipment, represented by the torque required in the mixer drive which is usually greatest for the big impeller, versus the cost of horsepower, which is usually greatest for the small impeller. This leads to the concept of optimization of the economics of a particular process. In all cases, at least two or three mixers must be selected for the same blend time with different power and impeller diameter to carry out this evaluation. Mixers may be either top entering or side enter­ing. Again, a side-entering mixer requires more power and less capital dollars, and this must be evaluated in looking at practical equipment

Blending is the operation of combining components of different viscosities and/or densities to produce a material with uniform properties throughout, such that it will not separate with time.

We subdivide blending into two broad classifications;

Low Viscosity - < 50,000 cp
High Viscosity - > 50,000 cp

Blending is divided this way because different impellers are used in high viscosities vs. low viscosities. To be used only as a guideline in determining what types of impellers should be considered.

CHARACTERISTICS OF MATERIAL BEING BLENDED This includes the viscosities and densities of each component. The percent of each and the final viscosity and density. The greater the difference in viscosities and/or densities of the components, the more horsepower required. Also, the higher the final viscosity, the more horsepower required.