Mixing Basics

7/18/2019 Mixing Basics

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3/12/20

Mixing and Blendingliquids, solids and gases into

Agenda for todays seminar

• Application of Power to Fluids – Formulae

• Energy Considerations & Applications

• Illustrations & Devices used for Blending

• Static Mixers and their applications

• Mixing with Compressed Air or Liquid

• Mechanical Agitator Design

• Side Bottom and Submersible Mixers

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• Q&A – Wrap Up and CEU Certificates



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The first mixer

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Common beginnings

• Porridge and soups were first mixed from theo om up o en e nu r en s an avours rom

the meat into the new additions

• Poor folks couldn't afford to start a fresh pot everyday so they blended the old into the new

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Beer and Wine kick start civilization

• Nomads got tired of travelling after discoveringt e secret oney ee tree an mea – sucrose& yeast = relaxation

• The success of herding and hunting gave wayto agriculture and vegetarians.

• Next thing you know they all want universal

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Government takes hold

• Soon more and more nomads came to the cityor ree eer an wine

• Taxes were levied to pay for the wheat andbarley and grapes

• Houses had to be built to protect the people..... mortar and mud mixers were invented to

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brewers and cooks



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Mixing 101 – History

• Food processing, mining, pulp & paper ,cosmetics harmaceuticals etroleum owerand chemical processing industries developedunique impellers for many applications......

• Many were for batch processes & simpleblending of 2-3 components

• Continuous flow processes require some

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eren ypes o ag a on

Mixing Pictures

• In order to choose the right equipment , youneed to understand the mixin needs and timeframe.

• Develop a visual image of what needs to bedone to satisfy the process goal

• Place your application into a mixing class tostart the process of selection

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5 Application Classes

• Liquid – Solid

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• Miscible Liquids

• Immiscible Liquids

• Fluid Motion

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Liquid - Solid

• Dissolving a solid into a liquid

• Describe the solids –powders,rocks,dense,fluffy,sticky,crystals

• Describe the power needed- just off bottom, ½way up the tank til reaction or completeuniformity for continuous pumping to another

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tank



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Gas Liquid

• Dispersion of a gas into a liquid

• Absorption of a liquid into a gas

• Describe the density and viscosity of the liquidto understand power needs

• Describe the amount of miscibility the gas hasin the liquid, whether it takes along time to

'

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Immiscible Liquids

• Explain the two components or more and theirviscosities and rheolo ies var

• Is it a blend like salad dressing or a finishedend product like mayonaaissee orshampoo.....emulsions and drop size data

• Is it a mass transfer operation like hexanedecaffinization of coffee or solvent extraction

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rom o ....• Is it mixing polymer into water for flocculation

or dewatering



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Fluid Motion

• Describe pumping capacity of impeller anden time require

• Explain the inlet and outlet port locations andside forces if velocities are high

• Is their heat transfer to accomplish like mixingcold water and warm water

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a CT tank ?

Tank and Impeller concepts

• The perfect tank is a cube – so describe howi erent your requirements are.....

• Tall and skinny, fat and short, round withconical bottoms, horizontal with a long sideratio ?

• Is it above ground , below ground... egress an

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,maintenance... or not ?

• Concrete , glass, FRP, stainless or steel ???



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Impellers or is it non-contact

• Radial flow impellers pump out from the tipstowar t e tan wa s

• Axial flow impellers pump down from theturbine or up toward the top

• Can you use a motive liquid stream or air toblend instead of sticking metal parts into the

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Tank Geometry

• Need height, length and width or diameter

• Open or closed top

• Side bottom or top entry point

• Injector locations

• Mixer location – center or offcenter

• Mixer angle for vortexing or not

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• Baffle locations if any..........



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Process Requirement

• 10 minute blend time – or 30 seconds

• Uniform temp at outlet within 30 min

• pH within +/- 0.1 log

• Conductivity or dissolved solids concentration

• Streaming current value stable

• UV level correct

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Feed Characteristics

• Density or specific gravity of components

• Temperature

• Viscosity

• Corrosivity / pH level

• Volume ratios

• % solids level

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• Settleability

• %Volatile solids

• Ash content



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Degree of Mixing

• Mild, moderate or violent agitation.....

• How to define these terms, swirling , splashingmoving rippling, vortexing......

• How about a Scale from 1-10

• Call it Chemscale & define it a the range from6-60 feet per minute

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• u u e oc y ~ an mo on or manyturbulent flow applications

Computational Fluid Mechanics

• CFM is a powerful tool that is used to mathematically model fluid flowsof different agitator/impeller designs in mixing tanks.

• Mixing of single and multi-phase fluids in stirred tank reactors is acommon operation in many industries.

• Understanding the fluid flow in these tanks is critical for equipmentdesign, scale-up, process control and economic factors.

• CFM models allow you to see what is taking place in the mixing vessel.The results enable an engineer to select the best agitator design to

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o a n e es re process per ormance.• Rectangular and side-entering agitated tanks as well as turbulent and

laminar flow static mixers can all be successfully evaluated



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Graphic Analysis

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Digital Particle Image Velocimetry (DPIV)

• An Argon-Ion laser light sheet illuminates fluorescent, neutrally buoyantparticles. A CCD camera captures the images, then an advanced timings stem and a com uter with ima e board freezes and di itizes theimages. The picture below shows the motion of fluorescent particlesilluminated by a sheet of Argon-Ion laser light.

• The particles (60 micrometers) are small and neutrally buoyant, so theyfollow the liquid flow. The tank is equipped with a pitched-blade turbine.The particle motion is filmed with a CCD camera. The velocity field is thenextracted from the digitized images using cross-correlation software.Armed with this information, engineers can better design agitators.

• DPIV technology has the capability of measuring the entire fluid velocity

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e n a an a mos ns an aneous y ma ng poss e o s u y arge-scale, time-dependent phenomena in the tank.

• The color shows the local, time-averaged velocity. Fast-moving regionsare colored red and slow-moving regions are colored blue. The pitched-blade turbine creates a mixed axial/radial flow pattern. The highestvelocities are found at the impeller blade tip. The velocities at the liquidsurface are an order of magnitude lower.



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DPIV images

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DPIV graph

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Laser Doppler Anemometry

• (LDA) is widely recognized as the best method of non-intrusivelydetermining mean velocity and turbulence data with pinpoint accuracyusin the Dantec FlowLite turnke measurement s stem to determinevelocities in stirred tanks and static mixers.

• The measurement technique relies on the physical fact that when twolaser beams of the same wavelength cross, an interference pattern ofbright and dark fringes is formed.

• As a single particle passes through the intersection of two such laserbeams, it reflects light at certain frequencies which depends only on thevelocity of the particle and the fringe spacing.

• Appropriate optical collection and data analysis enable highly accurate

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velocity measurements within extremely small volumes of fluid. Withinminutes, thousands of particles may pass through the measurement

volume, enabling an accurate determination of velocity at that point

Laser Doppler Anemometry

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Laser Induced Fluorescence

• One of the most challenging problems in fundamental diagnostics is directly

measuring mixedness.

• Limiting factors in traditional mixing systems include the intrusion of probesand the number of probes required to statistically determine mixedness.

• Laser Induced Fluorescence (LIF) is a measurement technique which enablesthe user to gain a fundamental understanding of mixing in a straightforwardfashion.

• Materials such as rhodamine or uranine will fluoresce when struck by light ofcertain wavelengths. We use this property to track the path and diffusion ofinjectants in agitated vessels and static mixers.

• A laser beam is spread into a sheet of coherent light which is projectedthrough a clear pipe or vessel. When fluorescent material is struck by thelight, it scatters light at a higher wavelength than the laser wavelength. The

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scattere g t may e capture on v eo or on a CCD camera rect y n eto a computer. These digital images may be analyzed to determine uniformity.

• One of the benefits of such an analysis is that both qualitative andquantitative assessment of mixing may be gained simultaneously.

• In static mixer systems, we have used this information to calculate acoefficient of variation while in stirred tanks, blend times have beenmeasured. In either circumstance, the user also gains a generalunderstanding of the mixing mechanisms.

L.I.F. images

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Shear Rate and Impeller style

• Impeller type and size affect tip speed

• Blade ratio & angle of attack affect shear

• RPM obviously controls this effect the most

• Time for an equation ?

• P ~ Q x H x density

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• P = powerdraw

• Q = flow or pumping capacity• H = Velocity head

Power draw vs Speed

• P ~ N3 where N = RPM

• P ~ D5 where D = impeller diameter

• P = N3 x D5 x s.g.

• All of the above vary with impeller type

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Time Release design review

• Dropping red dyeinto a pitchedblade turbine withbaffles in acircular tank

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Power Number

• Each impeller design has a unique flow vspower draw character

• Blades 12 inch long and 4 inches high

• Attached to hub at 45 degrees, 30 degrees or90 degrees will have different Hp draw at thesame RPM

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• Power # = 1.523 x1013x P / N3 D5 x s.g.



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Blade design optimization

• Using a novelexograp ic contour

plot system tomodel the impeller.....

• Run the simulationand shazam ....

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• out comes the

perfect turbine foryour application

Laboratory analysis

• Once the system isselected, you cantake the impeller tothe lab to confirmthe simulation withactual torque,thrust, speed and

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power drawmeasurements



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Sizing guidelines

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Laser Light Spectrum Velocimetry

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Reynolds Number / Flow Regime

• Laminar , transitional & turbulent flow

• Viscosity effect increases drag on impeller tankwalls and baffles > H[ draw

• Viscosity ratios 1000/1

• Volume ratios 100/1

• Nre = 10.754 x N x D2 x s.g. / u

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Impeller Power #s

• Rushton turbine ~ 5.75

• Bar turbine ~ 0.61

• Anchor impeller ~ 52

• 1.5/1 pitch prop ~ 0.87

• 45o pitch blade ~ 0.53

• Hydrofoils ~ 0.2 – 0.3 (3 or 4 blade)

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Reynolds number values

• N re < 10 = laminar creeping flow

• N re 10-100 = smooth laminar flow withoutstriations

• toothpaste extrusion

• N re >100 = transitional flow

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• N re > 1000 = turbulent flow

• Splashing brook / whitewater



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Various types of mixers

• Top entering – overhung shaft

• Side entering – angled mount

• Portable - air driven clamp on

• –

• Submersible gear driven – banana blade

• Submersible direct drive – wall pump

• Static or mechanical - in-line types

• Jet mixers – pod or manifold style

• Pumped recirc flow mixer / aspirators

• Pneumatic draft tube or bubble plate airlift

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• –

• Engineered pipe grid /check valve hydraulic designs

• Hyperbolic bottom mount circulators• Rotating arm or ball spray type agitators

• Screw auger counter - rotating double drives

Applications and Energyconsiderations

• Efficiency is now..... time to consider all

engines in lieu of electric motors

• Solar powered circulator mixers for waterstorage tanks in the distribution system

• Impeller conversions to reduce Hp orenhance process performance

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• Installation modifications to improvemaintenance and optimize equipment life



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Simple blending example

• 1975 Cl2 Contact chamber has a 5 Hp topentering mixer with drip feed lines

• p onver o arger - mpe er

• Opt B ) Change to same size A 310 turbine

• Opt C ) Convert to aspirating wet mixer

• Opt D ) Add static inline mixer before tank

• Opt E ) Use jet reactor mixer tube instead

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• Opt F ) Go to contract operations - retire

Applications for water andwastewater plants• Rapid mixers

• Flocculators

• Carbon soda ash or lime slurr makedown

• Lime softening clarifloc tanks

• Inline finished water adjustment

• Ferric chloride and polymer storage

• Draft tube ballast recirc systems

• Anaerobic digestor mixing

• Mudwell and sludge storage tanks

•

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• PH adjustment

• Surface Aeration or submerged turbine oxygenation

• Chlorine contact / CT basins



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Specialized Services

• ATTADs mixer aerators• SBR systems

• Pre-Oxidation of Fe/Mn/As

• Lagoon & Oxyditch Mixer Aerators

• Sidestream Ozonation Reactors

• Scum Storage & Homogenizers

• Foam Entrainment Mixers

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• Dewatering Feed Mixers

TOP ENTERING

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JET MIXER

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Aspirating Mixer

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Draft Tube Mixer

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Hyperbolic Mixer

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Submersible Mixer

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Static Mixer

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Portable Mixers

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Mechanical Inliner

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Polymer makedown systemsTYPICAL LAYOUTTYPICAL LAYOUT

5 4 . 0 0

C A L I B R A T I O NC O L U M N

P R I M A R Y D I L U T I O N

W A T E R S Y S T E M

N E M A 4 X

C O N T R O L P A N E L

H y B l e n d P O L Y M E R

M I X I N G C H A M B E R

R U G G E D O P E N S K I D

D E S I G N ( 3 0 4 S . S . )

Q U I C K - C H E C KP O L Y M E R C H E C K V A L V E

3 4 . 0 01 4 . 0 0

O P T I O N A L S E C O N D A R YD I L U T I O N W A T E R S Y S T E M

( E X P A N D E D F L O W R A N G E )

P O L Y M E R M E T E R I N G P U M P

( P R O G R E S S I V E C A V I T Y

P U M P S H O W N )

Sludge Recirculators

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Flocculators

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Walking Beam & Turbine Type

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Lime Slurry Makedown Mixers

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Soda Ash or Carbon system mixers

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Silo feeding a dry chemical makeSilo feeding a dry chemical make--down tankdown tank

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Floating scum control mixers

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2 speed SBR mixer aerator

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Pure Oxygen Mixing

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Airlift mixing

• Compressed

accumulatorplate formslarge bubblesto lift and mixtank contents

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TWAS Shear-tube Mixer

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Inline sludge mixers

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Mixing Basics

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