Typical power requirements are in the range of 10 HP per 100 gallons of product.
Of all the "Rules of Thumb" the issues resulting from this pose the most severe issues. While not difficult to calculate, Blade Horsepower, does not correlate well to a simple Volume to power relation. Most disperser manufacuters' rely on a modification of the agitator horsepower relationship:
Np the power number varies with blade type and Reynolds Number.
The mixer power equation works well for predicting power requirements, however, as batch size grows power requirements tend to fall below the 10 hp per 100 gallon rule of thumb. While it is true that retaining all the same ratios a 2 gallon batch will draw more power per gallon than a 2000 gallon batch, typically we need to perform a given amount of work on a product to achieve the desired results. Resulting designs typically require longer batch times with increased volume.
To offset this, we can move to narrower tanks and multiple blades to improve batch times.