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Powder Mixing (main
# Types of mixers
# Mixing mechanisms
# Mixing time
# Mixing speed
# Mixing volume
# Mixing power
#Mixer loading # Discharge time
# Froude Number
# Coefficient of Variation
# Segregation / demixing
# Tip speed
# ATEX speed
# Mixer Bearing seals
# Mixer discharge valve
Powder mixing is based on the movement of the particles part of the recipe to be mixed. The movement can be of different type and different designs of mixers will correspond to different mixing principles.
Mixers are often classified thanks to the Froude number. This adimensional number will define the regime of mixing depending on its value.
Froude number is defined in equation 1 [Perry]:
Equation 1 : Froude number
It can be expressed in a more convenient form for powder mixers having a mixing element in equation 2:
Equation 2 : Froude number calculation for blender equipped with a mixing tool (ribbon, paddles...)
Froude number is comparing 2 forces : Fr = (forces other than gravity - mainly centrifugal) / gravity
If Fr < 1 it means that the gravity forces will be
stronger than the centrifugal forces, the powder will
remain settled in the mixer, moved, but not in a cloud
Among the common mixers used industrially for powder mixing, the table below is proposing a classification according to Froude number
Table 1 : Mixer classified according to their Froude number and mixing principle
Another type of classification could be proposed depending on the type of process where mixers are integrated : Batch or Continuous. If batch mixer probably represent the majority of the industrial applications, some types of mixers (paddle mixers) can be used in a continuous mode, which can be useful for some kind of processes.
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