admix - mixing and blending

8/10/2019 ADMIX - Mixing and Blending

1/8March 2001 PROCESSINGs 2001 Mixing, Blending & Size Reduction Handbook 1

The 2001Mixing,

Blendingand SizeReduction

Handbook

High shear mixingadvances for foods,pharmaceuticals, cosmetics

p. 2

Mixing scale-upspeeds new productsto market

p. 5

A Putman Publication A supplement to Processing

IN

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ID

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The 2001Mixing,

Blendingand SizeReduction

Handbook


2/82 PROCESSINGs 2000 Mixing, Blending & Size Reduction Handbook

High shear mixing equipment has been used inhygienic processing industries over the past twodecades. The equipment that was first developed tohandle these difficult-to-dissolve formulas has con-sistently been improved upon to allow for less wear-ing parts, quicker processing, and easier cleaning.These changes have allowed for even more applica-

tions that once required expensive homogenizers, lowflow colloid mills, high upkeep liqui-processors, andother high-powered equipment. Beyond its applica-bility in high viscosity creams and lotions and meattenderizers, high shear mixing is now used withoutmaintenance issues in such areas as the reconstitutionof milk powder, high temperature processes, and thedissolving of abrasive materials, such as TiO2.

Background

High shear mixers are an important tool for dispersing solidsinto liquids, emulsifying immiscible liquids, breaking down

solids and agglomerates,and other applications in which low

speed agitation is often not sufficient.One of the character-

istics that make high shear mixers different from traditional

low-to-moderate speed agitators is the use of high speed

motors,operating from 3600 rpm to as high as 10,000 rpm.

High speed mixers typically provide a very high degree of

shear and a low

level of pumping

and circulation.

Shear is produced

through a combi-nation of hydraulic

forces, as the mix-

ing head turns at

very high speeds,

and by mechanical

forces, as particles

split when contact-

ing the edges of the

mixing blades, or

when forced

through slots, ports

or orifices.

The Evolution of the Mixing Heads of Today

The first few high shear mixing heads developed could

be classified as either an open-disk impeller type or a

closed rotor-stator type.These worked great with respect

to shear, but have limitations in other areas.

Special impellers such as an open-disk type rely mostly

on hydraulic shear rather than mechanical and cannot beused for large batches without very high energy require-

ments.Open-disk mixers utilize a flat disk ranging in diam-

eter from 10 to 30 and saw teeth on the perimeter.

They are designed to

promote high shear

and particle reduc-

tion at moderate cir-

culation rates, but

they require very

high tip speeds (up

to 80 to 90 fps) for

total effectiveness.Open-disk high

shear mixers have

found wide applica-

tion in the paint and

coating industry and

related markets.

Unfortunately, the

saw teethare worn down with products containing abra-

sives and require replacement frequently.

The closed rotating rotor-stator type of mixers relies on

somewhat different technology. The high shear rotor

develops a pressure differential immediately below therotor and the process material, causing the product to be

continuously drawn from the bottom of the vessel and

into the mixing head. Once the product enters the mix-

ing head, it is forced through the restricted openings of

the stator, where mechanical shear causes further particle

reduction. Most rotor-stator devices utilize a deflection

plate somewhere above the mixing head to create the

proper circulation pattern dictated by the process.These

units can operate effectively at lower tip speeds (50 to 60

fps) and therefore require less power than open-disk types.

They can be difficult to clean and do not provide enough

pumping on their own to mix very viscous products.

High shear mixing advances

for foods, pharmaceuticals, cosmetics

High shear disperser/dissolver

High shear emulsifier


3/8


4/84 PROCESSINGs 2000 Mixing, Blending & Size Reduction Handbook

contents enough times to cause complete, homogenous

blending

Scale-up can generally be achieved by maintaining

equal ratios on all three parameters and typical values

used are listed below.

Scale-up with continuous mixers is done within theenlarging of the mechanical design, and different sizes are

chosen based on required flow rates.

High Shear Technology in Sanitary Industries

Cosmetics

High shear mixers have been present in the cosmetics

industry for years dealing with the rapid growth of viscous,

exotic liquid makeup, face creams, and lipsticks.They were

and still are useful tools in dispersing talc to produce anultrasmooth, lump-free product.

The new design improvements allow for the dispersing of

metal oxides and abrasives without a worry about having to

frequently replace wearing

parts.Titanium Dioxide and

Calcium Carbonate can be

dispersed for use in lotions,

creams,and sunscreens.

Any high temperature

processes can be done with-

out a concern, such as the

preparation of hair gel.Hairconditioner can be made

smoother and more consis-

tent than ever, reports one

cosmetics manufacturer

using a new axial and radial stage in-line mixer.

Difficult viscosity building ingredients such as

Carbopol, Methocel, and many other gums are

quickly dispersed and 100% hydrated in room temperature

water for use in shampoos and other products.These solu-

tions can be prepared easily in high concentrations with-

out any clumps.A major cosmetic/personal care manufac-

turer was able to reduce water phase mix times with poly-mer gums from two hours to 15 minutes with the upgrade

from a low speed agitator to a fixed rotor and stator mixer.

The emulsion droplet size reduction that Rotor-Stator

mixers are capable of makes them a necessary tool when

preparing shelf-stable lotions. Other common applications

include hair dyes, liquid mascara, and perm solutions

because of the difficult-to-mix ingredients.

Food and Beverage

One of the most important advancements in high shear

technology is the ability to quickly dissolve stabilizing and

thickening agents, such as pectin and carrageenin, with

considerably less power and faster process times.A major

tomato company was able to reduce power requirements

from 150 hp to 40 hp for paste thin-down applications in

750-gallon batches. A confection manufacturer was able

to increase the solid content of a slurry from 78% to 85%and higher with the use of a fixed rotor and stator mixer.

Further modifications have allowed high shear mixers to

also be used in the dairy industry. Fixed rotor-stator mixers

and sanitary in-line mixers can be used for the reconstitu-

tion of milk powder or making sweetened condensed milk

without bacteria and cleaning concerns.Developments have

also been made to reduce the air incorporation with those

products to produce a uniform product with minimal foam.

Pharmaceutical

The new developments within high shear have led to

more sanitary equipment, which now meet the require-

ments of pharmaceutical facilities.They are a much-wel-

comed addition with the ability to process ingredi-

ents for ointments, antibiotics, stomach medicine,

coatings, etc.Pharmaceutical processing applications

using Aluminum Hydroxide and Zinc Oxide can be

mixed smoothly.

Not only can colloid mills and low speed agitators

be replaced for faster mixing times and less power,but

also homogenizers and other, less effective high shear

mixers.A major pharmaceutical manufacturer was ableto go from having a high shear and low speed agitator

in a vessel,to just one fixed rotor and stator high speed

mixer.This head has such excellent pumping capabili-

ties that it can mix even the thickest fluids by itself.

Other Applications

High shear equipment can also be used for non-sanitary

applications. Rotor-stator units have been successfully

applied in the addition of high viscosity, difficult-to-dis-

perse polymer additives, used to enhance the elasticity of

asphalt and rubber compounds.Rotor-stator units are also being used within the

petroleum industry when difficult-to-wet-out polymers

are added into invert mud for improved drilling of oil

wells. In addition, dramatic results have been reported in

tertiary oil recovery operations where high shear tech-

nology is employed to disperse additives into oil fields.

The new high shear devices can be applied in any pro-

cessing area desiring lower power requirements, faster

mix times, less maintenance, and product consistency.

Article written by Gretchen Ames, Applications Engineer,

Admix, Inc.

How it works


5/8March 2001 PROCESSINGs 2001 Mixing, Blending & Size Reduction Handbook 5

Scale-up of mixing machin-

ery has become a key issue

with sanitary processors as

development times have been

reduced and new products are

brought to market at very quickspeeds. Testing formulations in

small beakers or 5 gallon pails is

often the only testing done on

some products, and a leap of

faith is taken that a process will

scale-up to large tanks with sim-

ilar results. A technical report

detailing how to succeed with

the scale-up of mixers from a 3

liter beaker up to a 1000 gallon

(or larger) production vessel has

been released.This is an excerpt of the full article and focuses on

scaling of high shear mixers only. Scale-up of high shear

mixers is a particularly challenging issue as many of the

variables typically observed with low speed agitators do

not apply.The most cr itical parameters that may be used

for conducting small-scale tests and resizing similar

machinery for the full-scale application are discussed in

order of their importance.

1. IntensityThis parameter is related to bulk fluid velocity as

practiced by some agitation companies, and is expressedin feet per second (fps). Intensity takes into account the

process fluid velocity, pumping rate, volume of the ves-

sel, and the distance traveled by particles or molecules in

the batch. Intensity values can range from a low of 3 to

a high of 30 or more, with an average value from 8 to

12.These averagevalues roughly equate to bulk veloc-

ities in the 40 to 60 fps range, considered quite vigorous

for low speed agitation.

Helpful Hint: If no other parameter is avail-

able, scaling the Intensity would provide a bet-

ter than 90% success in the full scale.

2. Tip SpeedTip speed is the peripheral

velocity of the mixing head, as

opposed to the bulk fluid veloci-

ty. Most high speed mixing appli-

cations can be completed with atip speed of 35 to 60 fps. Tip

speed only considers the speed of

the mixer and the rotor diameter,

and ignores the impact of viscosi-

ty, volume and specific gravity on

fluid behavior. For this reason, tip

speed is a useful tool, but is not

sufficient by itself to ensure 100%

scale-up success.

Helpful Hint: High tip

speeds are critical for maxi-mum particle and droplet size reduction.

3. Tank TurnoversTank turnover is a measure of how effective a mixers

pumping rate is relative to turning a batch over a particu-

lar number of times a minute. In order to make this cal-

culation, the pumping rate of the mixer is divided by the

volume of the batch. Tank turnover is a widely used

parameter for scaling low speed turbine agitators, but has

not been sufficiently used by most high shear mixer sup-

pliers.This is understandable as the geometry of most high

shear mixers is not designed to provide high flow or

pumping rates, but instead focuses on shear capabilities.

For small vessels (under 30 gallons) where the shearhead

can provide enough flow, as limited as it may be, it is still

adequate to circulate the fluid volume to eventually pro-duce the desired mix. The difficulty in scaling becomes

Sanitary in-line high shear mixers help move products to market.

A leap of faith is takenthat a process will scale-up

to large tanks with similar results.

Mixing scale-up speedsnew products to marketFour helpful hints to scale-up high shear batch and in-line mixers


6/8

dramatically evident as these same low flow high shear

mixers are placed into much larger vessels where lack of

pumping and product turnover eventually causes the

process material to freeze up whereby there is little vis-

ible motion.This is especially problematic with high vis-

cosity, thixotropic or other non-Newtonian materials

using gums, thickeners,or stabilizers.Look for a high shearmixing device that features an upper or lower high flow

impeller to help drive the process fluid through the mix-

ing head many times a minute, ensuring quicker homo-

geneity and more predictable scale-up.

Helpful Hint:While Intensity and Tip Speed

should be scaled completely proportional, the

number of Tank Turnovers is going to be far

greater with the lab mixer than with the pro-

duction mixer. The objective, therefore, is to

reach the minimum required turnover value

in the large tank rather than try to match the

lab mixer.

4. Geometric Similarity (D/T)It is desirable to match the ratio of mixing head

diameter to tank diameter as you progress from the lab

vessel to the full size production vessel.This ensures that

the flow control profile observed is similar in both

vessels, such that there are no obvious dead zones or

unmixed areas of the larger vessel.

Helpful Hint: A minimum D/T of 0.1 is

desirable for most high speed applications, i.e.,a 6" mix head within a 60" tank diameter.

What Batch Sizes Are Best for Scale-Up?Most lower viscosity mixing applications, scaling from

a 1 gallon (2 liter) beaker to a larger 100 to 200 gallon pro-

duction vessel, can be safely and accurately accomplished

using the above methods. For moderate to high viscosity

fluids, or where production batches exceed 250 gallons,

the manufacturer highly recommends an intermediatestep in the scale-up process.Typically, this would be a 5 to

10 gallon batch size, available as a pilot plant model

either at the mixing

companys lab or at

the users location.

When working with

both a high viscosity

product and a produc-

tion volume greater

than 750 gallons, an

additional scale-up

test as large as 100 to150 gallons is recom-

mended. While three

smaller scale tests may

seem excessive and

time consuming,it is a

small price to pay for

ensuring 100% accu-

racy and scalability in the larger,substantially more expen-

sive full scale production vessel.

Scale-Up of In-Line Mixers

Closed loop continuous flow in-line mixers, as well asthose used to recirculate through a batch process, are

6 PROCESSINGs 2001 Mixing, Blending & Size Reduction Handbook March 2001

One-gallon benchtop for initial scale

Tip Speed

Low Shear 10-30 fps High Shear 40-60 fps

Geometric Similarity (D/T)

Low Speed/Shear 0.25-0.60

High Speed/Shear 0.10-0.20

Tank Turnovers (minimum)

Low Viscosity (1-100 cps),under 250 gallons 4-6 turns/min

High Viscosity (500-5000 cps),

under 250 gallons 2-4 turns/min

Low Viscosity (1-100 cps),

from 250-500 gallons 2-4 turns/min

High Viscosity (500-5000 cps),

from 250-500 gallons 1-2 turns/min

Bulk Fluid Velocity / Intensity

BFV Intensity

Very slow to mild flow, relatively mixable components, or high viscosity 24-35 ft/min 5-7 Fairly vigorous mixing, sufficient for most applications 35-47 ft/min 7-9

Vigorous mixing, for difficult applications 47-59 ft/min 9-12

Extremely violent mixing, for very difficult applications 59-88 ft/min 12-17

Summary of typical operating conditions


7/8

becoming successful in sanitary processing. In-line high

shear mixers are fast,provide consistent results, and are easy

to add on to an existing process or production line.While

scale-up of these mixing devices is not as difficult as with

batch mixers, it still needs to be considered.Selection of a

high shear in-line mixer is primarily based on the required

flow or transfer rate dictated by the production line. Mostin-line mixers are offered in various sizes to cover the typ-

ical flow rates (from 10 to 300 gpm) utilized by most

plants.Tip speed must also be considered, and here again,

most in-line mixers provide tip speeds ranging from 40 to

90 fps or higher.There is a challenge in scaling in-line high

shear mixer surfaces when process viscosities are greater

than 5000 cps, or where the application requires the addi-

tion of powders for in-line wetting out, dispersion and

hydration.With higher viscosity process streams, flow rate

through the mixer can be drastically reduced, thus reduc-

ing the flow velocity and probably affecting the outcome

of the mixture. Higher flows can be generated with theaddition of an upstream pump to feed the process fluid

at a higher velocity into the in-line mixer.Therefore, flow

velocity presents a third parameter which needs checking

while scaling up,as the hydraulic shearprovided by high

velocities will improve both particle and droplet size

reduction and distribution.To ensure consistency of parti-

cle analysis in varying flow and velocity ranges, a scale-up

program that incorporates flow velocity, pumping capaci-

ty, tip speed, viscosity and density is necessary.

These hints on successful scale-up were supplied by Admix, Inc.

Further information is available at www. admix.com or800.466.2369.

March 2001 PROCESSINGs 2001 Mixing, Blending & Size Reduction Handbook 7

Bench-top studies are conducted with assurance of scale-up results.

AdmixtureThe Newsletter of Mixing

Technology for Sanitary Processors

Admixture is a quarter-

ly publication offeringuseful information

regarding primary

ingredients, production

and mixing technology.

Our objective is to pro-

vide our customers

with the most innova-

tive technology and

expertise available in

todays marketplace. We

identify and review

mixing applications and offer solutions to reduce costwhile increasing yield, quality and shelf life. Learn how

the Admix Advantage can improve your process! Call

today to request the latest issue of Admixture, the

Newsletter of Mixing Technology for Sanitary

Processors!

DYNASHEARSanitary In-Line High Shear Mixer

Admix, Inc. recently introduced the DynaShear

Sanitary In-Line High Shear Mixer. The DynaShear

represents the latest technology for sanitary in-line

continuous processing. The DynaShear will blend,dissolve, disperse and emulsify both miscible and

immiscible fluids. It is the first in-line mixer featuring

a dual stage, tandem head design combining the ben-

efits of both axial and radial rotor-stator technolo-

gy...creating excellent shear and flow capability. A sin-

gle pass through the DynaShear provides product

quality typical of multiple passes within conventional

mixers. The result is a processing unit with droplet

and particle size reduction capability of 2-3 microns

or less while providing flow capabilities that are sub-

stantially higher than existing in-line mixers and shear

pumps.

N e w P r o d u c t s


8/8

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