Calculating Power Draw for Dynamic Mixers
One of the key parameters regarding mixers is their power consumption. This quantity is important because the energy absorbed by the mixer is directly transferred to the fluid being mixed through the impellers. If the applied energy is below a certain threshold, either mixing will not occur effectively, or the homogenization time will be longer than necessary. On the other hand, if the mixing energy exceeds a certain limit, it can result in energy wastage and, in some cases, lead to the destruction of the mixture in shear sensitive fluids.
The present essay focuses on calculating the power consumption of mixers in turbulent flow regimes and does not cover laminar flow regimes.
The power consumption in dynamic mixers is calculated using the following equation:
P: The power consumption of the mixer, measured in watts or joules per second (W).
Np: The power number which is a dimensionless quantity derived from the geometric shape of the impeller and is independent of impeller diameter.
𝜌: The density of the fluid being mixed, measured in kilograms per cubic meter (KG/m3).
N: The rotational speed of the impeller, measured in revolutions per second (RPS).
D: The diameter of the impeller, measured in meter (m).
Key Considerations for Dynamic Mixer Power Calculations
- The power consumption formula indicates that rotational speed has an exponent of three. Doubling speed therefore results in an eightfold power increase.
- Similarly, the impeller diameter term has an exponent of five. Doubling diameter thus leads to a thirty-twofold power rise.
- It is important to note that viscosity effects are excluded as turbulent flow is presumed. Consequently, viscosity variations will not impact calculated power consumption.
