High Shear Mixers

High Shear Mixers

0 INTRODUCTION / PURPOSE
1 SCOPE
2 FIELD OF APPLICATION

3 DEFINITIONS

4 SELECTION OF MIXER TYPE
4.1 The Shrouded Turbine
4.2 Turbine Mixers
4.3 Unshrouded Agitators
4.4 In-Line Mixers
4.5 Ultrasonic Homogenizers

5 SHROUDED TURBINE DATA

5.1 Recommended Duties
5.2 Equipment Data

6 HIGH SPEED INTERNAL (TURBINE & VESSEL
COMBINED) MIXERS

6.1 Recommended Duties
6.2 Equipment Data

7 HIGH SPEED UNSHROUDED (SAWTOOTH) AGITATORS

7.1 Duties
7.2 Equipment Data

TABLES

1 POWER INSTALLED FOR TORRANCE SAWTOOTH
IMPELLERS FIGURES

1 SHROUDED TURBINE
2 TURBINE AND VESSEL COMBINED
3 SAWTOOTH MIXER
4 IN-LINE MIXER (OAKES)
5 ULTRASONIC EMULSIFIER IN-LINE
6 ROTOR STATOR GEOMETRIES

7 SAWTOOTH IMPELLER RANGE OF GEOMETRIES
(AFTER TORRANCE)

8 MIXER POWER CURVES

1. A,
CPT
CATALYST, PROCESS TECHNOLOGY
CONSULTANCY

Process Engineering Guide:

(GBHE-PEG-MIX-709

‘High Shear’ Mixers

supplied to U

2. FIELD OF APPLICATION

DEFINITIONS

‘SELECTION OF MIXER TYPE

The Shrouded Turbine
Turbine Mixers
Unshrouded Agitators
In-Line Mixers

Ulrasonic Homogenizers

‘SHROUDED TURBINE DATA

Recommended Duties,
Equipment Data

3. FIGURES

SHROUDED TURBINE
TURBINE AND VESSEL COMBINED
SAWTOOTH MIXER

IN-LINE MIXER (OAKES)

ULTRASONIC EMULSIFIER IN-LINE

ROTOR STATOR GEOMETRIES

SAWTOOTH IMPELLER RANGE OF GEOMETRIES
(AFTER TORRANCE),

MIXER POWER CURVES

4. re vulnerable to degradation in commercial hig
ation of polymers is used for viscosity control in the

short of the ideal; manufacturers
e able to supply such basic information as the power
nsumption of a mixer for a liquid of density greater than that of water.

1 SCOPE
This Process Engineering Guide helps the user to select Ihe appropriate mixer

type for the duly and then recommends
operation

5. FIGURE 1 SHROUDED TURBINE

6. 43 Unshrouded Agitators

Unshrouded agitators are often of the sawtooth disc type (see Figure 3 for an

example of the Torrance device). They are recommended for solids dispersion

requiring more than 15% w/w of solids. They can give problems with filter
nulsify liquid-liquid systems with a viscosity ratio

7. 44 In-Line Mixers

‘Some manufacturers make in-line versions of their shrouded mixers. Oakes Ltd
ondo Mix BV supply shrouded mixers with no batch equivalent.
Jakes mixer with its concentric rows of rotor and stator teeth should ensure
that fluid does not by-pass the active zones. Oakes and Mondo mixers are
particularly effective in the production of foams. Figure 4 illustrates an Oakes

FIGURE 4 IN-LINE MIXER (OAKES)

8. FIGURE 5 ULTRASONIC EMULSIFIER IN-LINE

5 SHROUDED TURBINE DATA
5.1 Recommended Duties

188 give the most intense extensional flow fields and are
recommended

) Emulsification

9. oft solids, eg: e d turbines to

give a homogeneous paste. They gi tense disruptive action and
uld be used whenever possible. Their use is however restricted by

their limited pumping action and by abrasion. Other d

recommended for solids concentrations in excess of 15%

Equipment Data

Rotor Stator Geometry

Typical geometries of the shrouded turbine mixers are shown in Figure 6.
The rotor discharges the fluid through the radial ports in the stator
lanufacturers supply ‘high shear and ‘high pumping’
fewer, larger ports to allow
s higher circulation rates.

10. DEFLECTOR
PLATE

ms STATOR

GREAVES

PORT

SILVERSON

11. Mixer Size for Standard Duties

For routine applications manufacturers should be approached. They should then
quote the size and power of a mixer for a particular duty. They are, however,
often reluctant to commit themselves to a mixing time and thus to throughput.
provided data for sizing impellers for batch emulsification and
which are Summarized by the dimensional equat

Impeller power in KW
Batch Volume in
ity in N sim? (for 0.01 < p = 30)

12. ing steps:

Using a small, variable speed laboratory mixer, establish the tip speed
needed to give the required process effect,

may not reach a full-scale tip speed,

From the laboratory resul y conditions for a trial with a 1 10 5
mixer in a batch up to 50 liters volume. This mixer will approximate
reasonably closely to the ful-scale geometry. A cooling coll would be
required for isothermal operation.

Calculate the full-scale batch mixing time to achieve the required end
result from:

viv + DID* WI

full-scale batch mixing time
‘small scale batch mixing time
full scale batch volume
‘smallseale batch volume
full-scale rotor diameter

‘small scale rotor width
number of blades in full scale ro
in smal

13. yer number for the same turbine sided in an undated

linear polymer of My of 400,000 or
‘additional power is dissipated in extensional flo
viscoelastic fluid is forced into the ‘nip' between the rotor and stator.

At present its not possible to predict the additional power di
been 2 hat predicted by the first term of equation 3. I is ther
ine additional torque be measured on a small-scale with the

14. M = M DID * nn"

full-scale torque
‘small-scale tor
ful-sc

= number of blades on full-scale rotor
scale rotor
Pumping Capacity

There are no published data on pumping capacities of shrouded turbine mix
The following tentative correlation is for a5 hp Greaves mixer:

() Bulk Mixing Times and Heat Transfer

No data are available for bulk mixing times and heat transfer, both of which are

15. 6 HIGH SPEED INTERNAL (TURBINE & VESSEL COMBINED) MIXERS

These machines tend to be sold in two performance ranges. The firs, typified by
the "Hydisperser, hi

operators to liquidize dispersible fiter cakes, often before spray drying. The
standard 'Hydisperser is ited with a back-swept vaned disc agitator (DIT =

in the base. The standard maximum tip speed is 11 m/s with W/D of 0.06-0.07 to
economize on power.

A cruciform baffle cage may be fited for lower viscosity applications and a
‘butterfly’ impeller of DIT = 0.65 is also available.

The second performance range includes the Baker Perkins 'Hynetic Mill and the
Bearsley & Piper Speed mixer’. These devices may incorporate mulling wheels
and are better regarded as colloid mills

6.1 Recommended Duties

(a) _ Solids Dispersion

16. packing of uniform spher
k can be as high as 1. il be lower than 1.6 for particles with a wide size

distribution. The limiting viscosity would be reached at 50%
05) with k = 1.6.

) Filler Cake Dispersion

ver 100 dispersible fiter cakes have been examined and all are liquidized at
ear rates of 300 ls or below. All these filer cakes may be dispersed by a high
speed internal mixer in the lower performance range (10-16 kW/m')

Equipment Data
le-Up

Trials, involving the manufacturer ofthe internal mixer, on small-scale machin
are advised, Manufacturers offer a product range of machines operating at a
constant maximum tip speed and scale up is by keeping t!

1d increasing the batch time in proportion of Ihe lr

17. Type agitators are used lo provide a
They do not off
although the op

ower Consumpt

The estimation of the agitator power should be the n
manufacturer. St ds and transients are likely to be more critical than the
power dissipa ersed batch and, in any event, a variable speed

elected. A power number (Po) of approximately 0.3 would be
expected for the abbreviated vaned disc in an unbalfled vessel at high Reynolds
number

Pumping Capa at Transfer and Bulk Mixing Times

The pumping capacity may be estimated for vaned discs of W/D = 0.065

Q=08N e

Mixing times will then be of the order of 3 times those expe tandard

18. a

(a) Solids Dispersion into Liquid

A major application of the sawtooth mixer
solids in a liquid resulting in a final batch vi

defining aggregate strengths. It is recommended that the agitator manufacturer

be consulted and that small-scale trials are performed in doubtful situatio
an break up large lumps of solid so that even in the more doubtful
could be used to prepare a feed for a colloid mil.

$ are effective at tip speeds greater than 20 m/s; GBHE prefer the

6 m/s. The recommended DIT ratios range from 0.25 in low vi
im?) batches to 0.5 in high N sim‘) applications. Figure 7
the preferred range of oth disc impellers in a

19. [rom strat
id from the base of the ves

FIGURE 7 SAWTOOTH IMPELLER RANGE OF GEOMETRIES (AFTER
TORRANCE)

20. igure 8 shows the relationship between Pc
y sawtooth and other high speed impell
mixer and a plain disc working in unbaffled vessels.

Hydraulic drives are usualy fitted and are recommended for application with
these limited power data as they cannot be overloaded and allow mixing s
to be changed in a batch.

A Paints manufacturer produced the power data shown in Table 1. The apparent
power numbers near 0.1 are because the two of the three mixers ar
ortex aerated conditions at the highest tip speeds. Using this

been able to replace the hydraulic drives with two speed electric motors wi
are easier to maintain. If overloaded (for example by an increase in velocity
which caus of vortex) the motor rips to the lower speed. The trip px
then be calculated from Figure 8. This procedure should only be attempted
tems of less than 3 N sim viscosity and then only in consultation with the

21. (©) Pumping Capacity, Heat Transfer and Bulk Mixing Times

An estimate of the radial pumping rate may be made from:

15ND

22. manufacturers

sawtooth impellers are more effective than plain or perforated di
reation of fine pigment dispersions. We have found that a circular sa
as a proprietary devi ispersion of pigment base. The
uy devices incorporate blade race oriented
ferentialy (along the direction of rotation) and these blades will be more

Shear Rates

for sawtooth impellers are caused by shear and elongational
flows. To determine the range over which peak shear rates apply, reference

‘ould be made to the GBHE Mixing and Agitation Manual, Sections D4.4 and
DAS.

24. Mixing of M qu
{referred to in 52 (f) and 6.1 (d))

GBHE-PEG-FLO-302 Interpretation and Correlation of Viscometric Data
(referred to in 6.1 (a))

OTHER GBHE DOCUMENTS

GBH Enterpri ing and Agitation Manual
(referred to in 52 (9), 6.2 (e) and 7.20).

25. GBH ENTERPRISES, LTD

VULCAN Catalyst Process

Technology Consultancy
Sales and Service

Gerard B. Hawkins
Managing Director, C.E.O.

‘Skype: GBHEnterprises
Office: 1-312-235-2610
Cell: [phone]

[email protected]
HawkinsGerard@amall com
"www gbhenterprises.com

uo ined. cor

plus 1oGBHEnlexprs

vrwrenalteneray.com E