Mixing time and power consumption during blending of cohesive food powders with a horizontal helical double-ribbon impeller

• Cohesive food powders mixing was analyzed considering their physical properties, impeller dimensions and operating conditions.
• Mixing times lower than 5 min were required to achieve 90% homogeneity for different impeller speeds.
• A dimensionless generalized correlation between power number and inverse cohesion number described impeller performance.

The mixing time and power consumption of a helical double-ribbon impeller during blending of normal corn starch and icing sugar were studied. The approach took into account representative physical, flow and frictional properties of individual components and a 50:50 (w:w) blend, operating conditions and impeller characteristic dimensions. Physical tests showed the powders to be cohesive, hyperfine/superfine, with fair to good flow properties and different internal friction coefficient. Operating conditions played an important role in mixing time. Power consumption data were correlated with relevant powder physical properties; bulk density (ρb) and friction coefficient (μi), system dimensions; impeller volume (VI) and length (LI), and operating conditions; load ratio (f) and impeller speed (N), by the relationship P = 0.21[(ρbμi)(VILI)(fN)g]. A dimensionless correlation between the power number (NP = P/ρbDo3N5) and the effective cohesion number (NCe = [ρbDo4N2/FC][Kp(f)/f]) was obtained for the impeller; NP decreased with increasing NCe.