(170a) Revisiting the Relationships between Power, Flow and Momentum for Impellers in Agitated Vessels

The relationship between impeller Flow and Power numbers has been reported as (Herbert et al. (Chemie. Technik., 1994); Nienow (Chem, Eng. Sci., 1997)):

Fl = 0.77 Po^1/3

This suggests that there is no effect of impeller diameter in this relationship.

Brown (MIXING XXII, 2010) has suggested that:

Fl = 0.72 Po^1/4

And Marchado et al. (AIChEJ, 2012) reported that the Flow number reduced by ~11 % for pitched-blade turbines when the diameters reduced from T/2 to T/3 with negligible change in Power number.

Also, both Brown and Marchado define a Momentum number and that:

Mo = 1.45 Fl^1/2

Which should imply that, indeed, Fl ∼ Po^1/4

In this presentation the relationship between Flow and Momentum numbers with Power number and the impeller to tank diameter ratio will be re-examined and the effect on measures of impeller efficiency will be discussed.

Another question that will be addressed is the relationship between blend and circulation times in an agitated vessel and the exponent on the impeller to tank diameter ratio in blend time correlations.