Mixer having a centrally disposed helical or anchor agitator and eccentrically disposed screw or blade agitator
A mixer having improved axial and radial mixing which retains good mixing time even during large viscosity changes, comprising a housing with at least one helical or anchor agitator located centrally in the housing in combination with at least one eccentrically arranged screw or blade agitator, preferably in mutual engagement, the combination of a helical agitator and a screw agitator enabling a much shorter mixing time as compared to a mixer having only a helical agitator without a screw agitator.
1. A device comprising at least a housing ( 1 ), at least two rotating agitators ( 2 ) and ( 3 ), wherein at least one of the agitators ( 2 ) is a helical or anchor agitator arranged centrally in the housing ( 1 ), and at least one of the other agitators ( 3 ) is an eccentrically arranged screw or blade agitator, and wherein the pitches, the rotary speeds and the outer diameters of the agitators satisfy the following mathematical relationship (I):
S
1
S
2
=
n
2
D
2
n
1
D
1
(
I
)
where n 1 and n 2 are the rotary speeds, D 1 and D 2 are the outer diameters and S 1 and S 2 are the pitches, respectively, of the at least one central and eccentric agitator.
2. The device as claimed in claim 1 , characterized in that at least one eccentric agitator ( 3 ) and at least one central agitator ( 2 ) are corotating or counter rotating.
3. The device as claimed in claim 1 , wherein said centrally arranged agitator is a helical agitator and said eccentrically arranged agitator is a screw agitator, and the eccentric screw agitator engages with the central helical agitator.
4. The device as claimed in claim 3 , wherein the engagement E is 30-99%.
5. The device as claimed in claim 4 , wherein said engagement E is 80-95%.
6. The device as claimed in claim 1 , wherein the number of flights for the helical or anchor agitator is two and the number of flights for the screw or blade agitator is one or two.
7. The device as claimed in claim 1 , wherein the number of flights for the helical or anchor agitator is two and the number of flights for the screw or blade agitator is one or two.
8. The device as claimed in claim 7 , wherein the central agitator is a helical agitator and the pitch S of the helical agitator is between 0.05 and infinity.
9. The device as claimed in claim 7 , wherein the central agitator is a helical agitator and the eccentric agitator is a screw agitator, and the rotary speed ratio of screw agitator to helical agitator is in the range between 5:1 and 1:1.
10. The device as claimed in claim 1 , wherein the vertical distance between a blade of the eccentric agitator and a blade below it of the engaged screw agitator is equal to x u and the distance between the same blade of the eccentric agitator and a blade above it of the engaged screw agitator is equal to x o , wherein the relative values of x u and x o are selected so that x u <<x o with the direction of transport induced by the helical agitator in the vicinity of the vessel wall going downwards (down-pumping action) and x o <<x u with the direction of flow of the induced by the helical agitator going upwards (up-pumping action).