Special Topics Modules in Pharmaceutical Engineering Ch E

Special Topics - Modules in Pharmaceutical Engineering Ch. E 702 Introduction to Mixing Equipment and Processes in Pharmaceutical Operations Piero M. Armenante © Ch. E 702 2008

Objectives n Become familiar with the principles of single and multiphase mixing in pharmaceutical processes n Analyze pharmaceutical processes or in which mixing is important n Provide basic tools to conduct process design analysis and scale-up of processes or in which mixing is important Piero M. Armenante Ch. E 702 2

Relevant Topics n Classification of Mixing Processes and Applications n Mixing Equipment n Liquid Mixing Fundamentals n Mixing and Blending in Low Viscosity Liquids n High Viscosity Mixing in Stirred Tanks n Mass Transfer and Mixing n Solid-Liquid Mixing Piero M. Armenante Ch. E 702 3

Relevant Topics (continued) n Liquid-Liquid Mixing n Gas-Liquid Mixing n Mixing and Chemical Reactions n Heat Transfer n Jet Mixing n In-Line Mixing n Mechanical Aspects of Mixing Systems n Special Topics and Applications Piero M. Armenante Ch. E 702 4

Classification of Mixing Processes and Applications Piero M. Armenante Ch. E 702

Instructional Objectives of This Section By the end of this section you will be able to: n Identify basic mixing classes n Develop an appreciation for the importance of mixing in industry n Provide examples of common pharmaceutical mixing processes Piero M. Armenante Ch. E 702 6

Definition of Mixing n Textbook definition: The term “mixing” refers to all those operations that tend to reduce nonuniformity in one or more of the properties of a material in bulk (e. g. , concentration, temperature) Piero M. Armenante Ch. E 702 7

Example of Mixing Tanks/Reactors Piero M. Armenante Ch. E 702 8

Definition of Fluid Mixing n “Fluid mixing” refers to mixing operations in which the continuous phase is a fluid n Although a gas can be used as a fluid (e. g. , fluidization) a liquid is typically the continuous phase in fluid mixing processes n In the rest of this course a liquid phase will always be the continuous phase Piero M. Armenante Ch. E 702 9

Single-Phase vs. Multiphase Mixing n Single-phase mixing refers to mixing of miscible fluids. This operations is typically called “blending” n Multiphase mixing refers to mixing immiscible phases, i. e. : qsolid-liquid mixing qliquid-liquid mixing qgas-liquid mixing Piero M. Armenante Ch. E 702 10

Importance of Mixing in the Pharmaceutical Industry n Mixing of a fluid with other media (solids, liquids) is an extremely common operation encountered in countless applications in the pharmaceutical industry n Many pharmaceutical processes require or are greatly enhanced by: q rapid homogenization of miscible components (in single phase systems) q intimate contact between two or more distinct phases (in multiphase systems) Piero M. Armenante Ch. E 702 11

Examples of Typical Pharmaceutical Mixing Applications n Blending n Precipitation and Crystallization n Chemical reaction n Fermentation n Solid-liquid suspension n Liquid-liquid emulsification n Gas sparging Piero M. Armenante Ch. E 702 12

Economic Impact of Mixing. Related Problems n The impact of poor mixing on industrial applications has been estimated to be at 1 -10 billion $/year (1989) n The additional economic impact associated with scale-up and start up problems, waste material and byproducts generation has not been estimated yet Piero M. Armenante Ch. E 702 13

Mixing as an Objective or a Means to an End n There are operations where mixing itself is the objective of the process n These operations are required to produce homogenization of a system or a product n Examples: q Blending of gasoline in large storage tanks q Dispersion of pigments in paint q Uniform and stable suspension of API particles in an oral liquid dosage form q Formation of stable liquid-liquid emulsions Piero M. Armenante Ch. E 702 14

Mixing as an Objective or a Means to an End n However, in most pharmaceutical processes involving mixing, mixing is just a means to achieve a process objective n In this case mixing is typically required to effectively conduct a primary process (NOT to be limited by mixing) Piero M. Armenante Ch. E 702 15

Mixing as an Objective or a Means to an End n Examples of processes possibly affected by mixing: q Dissolution of an intermediate in a stirred vessel prior to reaction (mass transfer) q Precipitation of API or intermediate (crystallization) q Minimization of impurity formation during synthesis of a drug product (parallel/consecutive homogeneous reaction) q Suspension of a catalyst during heterogeneous catalysis (mass transfer + heterogeneous reaction) q Preparation of nano/micro-particles or droplets of desired particle size distribution (particle size control) q Achievement of a uniform temperature in a crystallizer and temperature control (heat transfer) Piero M. Armenante Ch. E 702 16

Mixing as an Objective or a Means to an End n Mixing operation may involve: qsingle phase liquids (e. g. , blending of miscible solutions, fast chemical parallel reactions and impurity formation) qmultiphase systems (e. g. , solid dispersion/suspension, emulsification) n Mixing can improve both single-phase and mulpiphase processes Piero M. Armenante Ch. E 702 17

Mixing as a Means to an End n Example: interfacial mass transfer A Cinterface Cbulk k. L Piero M. Armenante Ch. E 702 18

Mixing as a Means to an End n Example: interfacial mass transfer n Mixing affects: q state of dispersion or suspension of the dispersed phase, i. e. , degree of macroscopic homogeneity of the dispersed phase throughout the continuous phase ( VL, DC) q specific interfacial area (av), and overall interfacial area (A) q mass transfer coefficient at the interface (k. L) Piero M. Armenante Ch. E 702 19

Mass Transfer Operations in Mixing Processes n All mass transfer processes are enhanced by: qhigh mass transfer coefficients qlarge interfacial area n Mixing can contribute to achieve both n However, most mixing operations are associated with the generation of interfacial (contact) area Piero M. Armenante Ch. E 702 20

Classification of Mixing Processes Piero M. Armenante Ch. E 702 21

Mass Transfer Operations in Mixing Processes Piero M. Armenante Ch. E 702 22

Reactions in Mixing Processes Piero M. Armenante Ch. E 702 23

Single vs. Multiple Mixing Requirements n Mixing problems can involve: qa single mixing requirement (e. g. , suspend solids) qmultiple simultaneous mixing requirements (e. g. , suspend solids, homogenize liquid phase, promote solidliquid mass transfer, transfer heat) n Even multiple requirements are typically satisfied by the use of a single impeller Piero M. Armenante Ch. E 702 24

Example of Multiple Mixing Requirements: Crystallizers In crystallizers a successful process depends on: qheat transfer (for supersaturation) qbulk blending (for homogenization) qsolids suspension (for crystal growth) qeffective mass transfer (for crystal growth) qpossible gas removal (boiling systems) Piero M. Armenante Ch. E 702 25

Critical Mixing Process n Whenever a process involving a mixing operation is analyzed one should ask: qis mixing a critical component of the process? qif multiple, simultaneous mixing requirements are present which one is the most critical? Piero M. Armenante Ch. E 702 26

Mixing Equipment Piero M. Armenante Ch. E 702

Instructional Objective of This Section By the end of this section you will be able to: n Identify basic types of mixing equipment n Describe main components of mixing equipment n Describe main features and characteristics of mixing equipment Piero M. Armenante Ch. E 702 28

Classification of Mixing Equipment Mixing is typically conducted with: n mechanically stirred tanks n jet mixed tanks n in-line dynamic mixers n in-line static mixers n high-shear mixing equipment n mixing equipment for highly viscous materials (e. g. , polymers) Piero M. Armenante Ch. E 702 29

Mechanically Stirred Tanks and Reactors Motor Gearbox Shaft Baffle Impeller Piero M. Armenante Ch. E 702 30

Drive (Motor-Gearbox) Assembly After Chemineer Piero M. Armenante Ch. E 702 31

Mechanically Stirred Tanks and Reactors: Symbols B H Cb D T Piero M. Armenante Ch. E 702 32

Mechanically Stirred Tanks and Reactors: Symbols H S 23 Cb S 12 T Piero M. Armenante Ch. E 702 33

Mechanically Stirred Tanks: Nomenclature n Tank shape = cylindrical (occasionally square cross section) n T = Internal diameter of tank n HT = Internal height of tank n H = Z = Liquid height n B = Baffle width Piero M. Armenante Ch. E 702 34

Mechanically Stirred Tanks : Other Geometric Characteristics n Shape of tank bottom (flat, dished, conical, hemispherical) n Baffle length (full, half) n Number of baffles n Baffle position n Gap between baffles and tank ( B) n Gap between baffles and tank bottom Piero M. Armenante Ch. E 702 35

Baffles n Baffles are typically introduced to prevent vortex formation and convert tangential (rotational) flow into axial (vertical) flow n Baffles are always used in turbulent flow systems (low viscosity fluids) n Baffles are not used in laminar flow (high viscosity fluids) Piero M. Armenante Ch. E 702 36

Baffles n Typically four baffles are used (occasionally three) in fully baffled tanks n In glass-lined tanks a single baffle placed midway between the tank wall and the impeller may be used n A gap between the baffles and the wall is introduced to prevent stagnation behind the baffles and accumulation of material (e. g. , solids) Piero M. Armenante Ch. E 702 37

Typical Baffle Arrangement in a Stirred Tank Baffle Piero M. Armenante Ch. E 702 38

Typical Baffle Arrangement in a Glass-Lined Tank De Dietrich Vessel Single Baffle Piero M. Armenante Ch. E 702 39

Baffles and Vortexing Baffled tank: No vortex Piero M. Armenante Unbaffled tank: Vortex Ch. E 702 40

The “Standard” Tank n H/T = 1 n D/T = 1/3 n C/D = 1 n B/T = 1/10 (academic) or 1/12 (industry) n Number of baffles = 4 n Baffle length = full n B/T =1/72 or 1/100 n Bottom shape = flat Piero M. Armenante Ch. E 702 41

Impellers After Oldshue, 1984 Piero M. Armenante Ch. E 702 42

Impeller Types Impeller can be classified as follows: n radial impellers (e. g, Rushton turbines, paddles, flat-blade turbines, Smith impellers) n axial impellers (e. g. , marine propellers, pitched-blade turbines, fluidfoil impellers such as HE-3 s, A 310 s) n close-clearance impeller (e. g. , anchors, helical ribbons, gates) Piero M. Armenante Ch. E 702 43

Radial Impellers n Radial impellers pump radially. n They are used primarily with lowviscosity liquids in baffled tanks. n Disk turbines can be used for gas dispersion. Piero M. Armenante Ch. E 702 44

Radial Impellers n Common types include: q. Rushton turbine (6 -blade disk turbine) qpaddle qflat-blade turbines qcurve-blade turbine qretreat-blade turbine q. Smith impeller Piero M. Armenante Ch. E 702 45

Examples of Radial Flow Impellers After Tatterson, 1991 Piero M. Armenante Ch. E 702 46

Examples of Radial Flow Impellers Disk Turbine (Rushton Turbine) Piero M. Armenante Ch. E 702 47

Examples of Radial Flow Impellers Flat-blade turbine (Source: Chemineer) Piero M. Armenante Ch. E 702 48

Example of Radial Flow Impeller for High Shear Applications R 500 Sawtooth Impeller (Source: Lightnin) Piero M. Armenante Ch. E 702 49

Example of Radial Flow Impeller for Gas Dispersion Concave-Blade Turbine (Smith Turbine) Piero M. Armenante Ch. E 702 50

Example of Radial Flow Impeller for Gas Dispersion Concave-Blade Turbine (Smith Turbine) Piero M. Armenante Ch. E 702 51

Flow Generated by Radial Impellers Piero M. Armenante Ch. E 702 52

Flow Generated by a Radial Impeller in a Stirred Tank After Tatterson, 1991 Piero M. Armenante Ch. E 702 53

Axial Impellers n Axial impellers pump primarily (but not exclusively) vertically, either upwards or downwards. n They are used mainly with lowviscosity liquids in baffled tanks. n They are typically used in a downpumping mode. n High-solidity impellers are used with gas. Piero M. Armenante Ch. E 702 54

Pitch Ratio in Axial Impellers n The pitch-to-diameter ratio (or “pitch ratio”) is the ratio of the distance the impeller would advance per rotation to the impeller diameter n In constant pitch impellers (e. g. , propellers) the angle of attach changes along the blade; in variable pitch impellers (e. g, 45° pitchedblade turbine) the angle is constant Piero M. Armenante Ch. E 702 55

Constant vs. Variable Pitch Constant Pitch (Variable angle of attack) Variable Pitch (Constant angle of attack) After Oldshue, 1984 Piero M. Armenante Ch. E 702 56

Axial Impellers n Common types include: qmarine propeller qpitched-blade turbine qfluidfoil impeller (e. g. , Chemineer HE 3, Lightning A-310) qhigh-solidity ratio impellers (e. g. , Prochem) Piero M. Armenante Ch. E 702 57

Examples of Axial Flow Impellers After Tatterson, 1991 Piero M. Armenante Ch. E 702 58

Examples of Axial Flow Impellers Pitched-Blade Turbine Piero M. Armenante Ch. E 702 59

Example of Axial Flow (Hydrofoil) Impeller Chemineer SC-3 Impeller Piero M. Armenante Ch. E 702 60

Example of Axial Flow (Hydrofoil) Impeller Chemineer HE-3 Impeller Piero M. Armenante Ch. E 702 61

Example of Axial Flow (Hydrofoil) Impeller Chemineer HE-3 Impeller Piero M. Armenante Ch. E 702 62

Example of Axial Flow (Hydrofoil) Impeller Maxflow W Impeller Piero M. Armenante Ch. E 702 63

Example of Glassed Impellers De Dietrich Glas. Lock System Piero M. Armenante Ch. E 702 64

Flow Generated by Axial Impellers Flow generated by true axial impellers (~propeller, A-310, HE-3) Piero M. Armenante Ch. E 702 Flow generated by mixed-flow impellers (e. g. , 45° pitchedblade turbine) 65

Flow Generated by an Axial Impeller in a Stirred Tank After Tatterson, 1991 Piero M. Armenante Ch. E 702 66

Close-Clearance Impellers n Close-clearance impellers are primarily used with high-viscosity fluids in unbaffled tanks. n Close-clearance impellers scrape fluid off the tank wall and off the impeller. n They generate a complex flow pattern and have a pumping action similar to that of a displacement pump. Piero M. Armenante Ch. E 702 67

Close-Clearance Impellers n Common close-clearance impeller types include: qanchors qhelical ribbons qgates qkneaders q. Z- and sigma-blade impellers Piero M. Armenante Ch. E 702 68

Examples of Close Clearance Impellers Anchor Impeller (Source: Chemineer) Piero M. Armenante Ch. E 702 69

Examples of Close Clearance Impellers After Oldshue, 1984 Piero M. Armenante Ch. E 702 70

Examples of Close Clearance Impellers After Oldshue, 1984 Piero M. Armenante Ch. E 702 71

Examples of Close Clearance Impellers Double Helical Ribbon Impeller (Source: Chemineer) Piero M. Armenante Ch. E 702 72

Examples of Close Clearance Impellers Auger Impeller (Source: Chemineer) Piero M. Armenante Ch. E 702 73

Examples of Close Clearance Impellers After Tatterson, 1991 Piero M. Armenante Ch. E 702 74

Examples of Close Clearance Agitation System Piero M. Armenante Ch. E 702 75

Blending Capabilities of Different Impellers Piero M. Armenante Ch. E 702 76

Characteristics of Common Radial Impellers n Rushton turbines (Disk turbine, R 100). Strong radial flow, high power consumption, significant shear, good for gas dispersion n Smith impeller. Similar in performance to Rushton turbine, but particularly well suited for gas dispersion Piero M. Armenante Ch. E 702 77

Characteristics of Common Radial Impellers n Paddles. Simple and inexpensive, medium-to-strong radial flow and shear, intermediate power consumption, good for simple applications at small-to-medium scales n Flat-blade turbines. Similar to paddles but with stronger radial flow power, consumption, and shear. Used in transition flow. Piero M. Armenante Ch. E 702 78

Characteristics of Common Radial Impellers n Curve-blade turbine. Similar to flatblade turbines n Retreat-blade impeller (Pfaudler, De Dietrich types). Simpler construction suitable for glass-lined vessels; reduced power and flow Piero M. Armenante Ch. E 702 79

Characteristics of Common Axial Impellers n Marine propeller (A-100). Oldest constant-pitched impeller, usually cast (cannot be easily inserted in a manhole), expensive, low power consumption, high pumping rate n Pitched-blade turbine (A-200). Very common, simple, usually 45°, effective for solid suspension; mixed flow; medium power consumption, good pumping rate Piero M. Armenante Ch. E 702 80

Characteristics of Common Axial Impellers n Fluidfoil impellers. Many types exist (Chemineer HE-3, Lightning A 310); expensive, near constant pitch for improved axial flow, low power consumption, high pumping rate n High-solidity ratio impellers. Many types exist (e. g. , Maxchem); low-tomedium power consumption, high pumping rate, “streamlined” Piero M. Armenante Ch. E 702 81

Characteristics of Common Close-Clearance Impellers n Anchor impellers (A-400). Good for blending and heat transfer for liquids with 5000 c. P < < 50, 000 c. P n Helical ribbon. Good for blending high viscosity liquids (up to 25· 106 c. P) n Gates. Used in large “squat” tanks. n Kneaders, Z- and sigma-blade impellers. Used to mix pastes Piero M. Armenante Ch. E 702 82

Impellers: Nomenclature n D = Impeller diameter n C = Impeller clearance off the tank bottom measured from the impeller center n Cb = Impeller clearance off the tank bottom measured from the bottom of the impeller n Sij = distance between i and j impellers Piero M. Armenante Ch. E 702 83

Impellers: Nomenclature n L = Impeller blade length n w = Impeller blade width n wb = Impeller blade width projected along the vertical axis n Sij = distance between impellers i and j n = Blade angle of attack (if constant) n Pitch Piero M. Armenante Ch. E 702 84

Rushton Turbine L/D=1/4 w/D=1/5 Disk diameter= 3/4·D or 2/3 ·D Piero M. Armenante Ch. E 702 85

45° Pitched-Blade Turbine Piero M. Armenante Ch. E 702 86

Typical Ranges for Geometric Variables n T = 0. 1 m to 10 m (0. 3’-33’) n H/T = 0. 3 to 1. 2 for single impeller systems n D/T = 1/5 to 2/3 n C/D 1 n B/T = 1/10 to 1/12 Piero M. Armenante Ch. E 702 87

Jet Mixers n Jet mixers rely on the use of a jet, i. e. , a stream of liquid injected at high velocity in the bulk of another miscible liquid. n This is typically achieved with an external recirculation pump n Jet mixers are used in: qtanks qtubes and pipes Piero M. Armenante Ch. E 702 88

Jet Mixer External recirculation line Pump Piero M. Armenante Ch. E 702 89

Jet Mixers in Tanks n Jet mixers are typically used in large tanks. n Jet mixers are used for blending purposes (e. g. , gasoline) or to suspend solids in unusual processes (e. g. , radioactive material slurry). n Typically one or more jets are placed at an angle to provide good recirculation. Piero M. Armenante Ch. E 702 90

Axial Jets in Mixing Tanks Poorly mixed zone Piero M. Armenante Ch. E 702 91

Angled Jets in Mixing Tanks Poorly mixed zone Piero M. Armenante Ch. E 702 92

In-Line Mixers n In-line mixers are small mixing devices placed in the same line where the materials to be mixed are flowing. n Two types of in-line mixers exist: qdynamic mixers, where the mixing energy is provided from the outside qstatic (motionless) mixers where the fluid itself provides the mixing energy Piero M. Armenante Ch. E 702 93

In-Line Dynamic Mixers n In-line dynamic mixers consist of small high-speed mixers placed inside a casing fed with a continuous stream of the materials to be mixed. n The residence time of in-line mixers is usually of the order of seconds. Piero M. Armenante Ch. E 702 94

Example of a Dynamic In-Line Mixer Piero M. Armenante Ch. E 702 95

Example of In-Line, High Shear, Homogenizing Mixer Greerco (Chemineer) Piero M. Armenante Ch. E 702 96

Example of a Two-Stage Rotor Stator for In-Line High Shear Mixer Greerco (Chemineer) Piero M. Armenante Ch. E 702 97

Applications of Dynamic In-Line Mixers After Oldshue, 1984 Piero M. Armenante Ch. E 702 98

In-Line Static Mixers n Static mixers consist of mirror image inserts (elements) placed inside a pipe, capable of altering the fluid flow, and rearranging the distribution of fluid elements across the pipe cross section. n Static mixers are only capable of homogenizing the content of the pipe across its cross section but not along its length. Piero M. Armenante Ch. E 702 99

Static Mixers Source: Chemineer Piero M. Armenante Ch. E 702 100

Classification of Static Mixers n Static mixers are classified according to the flow regime under which they operate. n Static mixers are available for: qlaminar flow qtransitional flow qturbulent flow Piero M. Armenante Ch. E 702 101

Static Mixers for Laminar Flow n In laminar flow the only mechanism for radial mixing is molecular diffusion. n Each element in a laminar static mixers typically produces spit and a rotation (90° or 180°) of the flow, which is then fed to the next element. n Such actions result in further sub-divisions of the flow and the generation of striations leading to mixing. Piero M. Armenante Ch. E 702 102

Static Helical Mixer for Laminar Flow After Myers et al. , Chem. Eng. June 1997 Piero M. Armenante Ch. E 702 103

Static Helical Mixer for Laminar Flow Piero M. Armenante Ch. E 702 104

Static Helical Mixer for Laminar Flow Piero M. Armenante Ch. E 702 105

Static Mixers for Turbulent Flow n In turbulent flow, turbulent eddies are responsible for radial mixing n Flow in open pipes produces radial mixing if enough pipe length is provided (at least 100 pipe diameters) n Static mixers for turbulent flow rely on vortex generation to produce mixing Piero M. Armenante Ch. E 702 106

Static Vortex Mixer for Turbulent Flow Piero M. Armenante Ch. E 702 107

Static Vortex Mixer for Turbulent Flow Source: Chemineer Piero M. Armenante Ch. E 702 108

Static Vortex Mixer for Turbulent Flow After Myers et al. , Chem. Eng. June 1997 Piero M. Armenante Ch. E 702 109

High-Shear Mixing Equipment n High-shear mixers are devices used to generate high velocity gradients across small distances (resulting in high shear stress and shear rates) in order to disperse, break up, or homogenize a second immiscible phase. n Different devices base on different physical mechanisms are used to produce high shear. Piero M. Armenante Ch. E 702 110

High-Shear Equipment High shear equipment include: n (high speed) rotor-stator devices n valve homogeneizers, such as: qvalve homogeneizers qultrasonic homogenizers Piero M. Armenante Ch. E 702 111

High-Speed, High-Shear Rotor-Stator Mixer n High-speed rotor-stator mixers are devices in which a rotor rotates at high speed inside a casing provided with slots. A small gap exists between the rotor and the stator. n As the liquid (and its dispersed phase) move through the rotor-stator assembly they are subjected to high shear, resulting in break up effects. Piero M. Armenante Ch. E 702 112

High-Speed, High-Shear Rotor-Stator Mixer Piero M. Armenante Ch. E 702 113

Example of High-Speed, High. Shear Rotor-Stator Mixer Silverson Machines, Inc. Piero M. Armenante Ch. E 702 114

Example of High-Speed, High. Shear Rotor-Stator Mixer Silverson Machines, Inc. Piero M. Armenante Ch. E 702 115

Example of High-Speed, High. Shear Rotor-Stator Mixer Silverson Machines, Inc. Piero M. Armenante Ch. E 702 116

Colloid Mills n Colloid mills are in-line machines designed to finely homogenize, disperse solids, and emulsify immiscible liquids n Mixing head consist of a rotor and a stator separated by an extremely small gap (0. 001 -0. 03 in. ) n Stirring speed are usually extremely high (2000 -14, 000 rpm) n Flow rates are usually small (as a result of the small rotor-stator gap) Piero M. Armenante Ch. E 702 117

Colloid Mill Greerco (Chemineer) Piero M. Armenante Ch. E 702 118

Colloid Mill Greerco (Chemineer) Piero M. Armenante Ch. E 702 119

Colloid Mill IKA® Piero M. Armenante Ch. E 702 120

Colloid Mill Greerco (Chemineer) Piero M. Armenante Ch. E 702 121

Valve Homogenizers n Valve homogenizers pump material at high pressure (30 -500 bar) through small orifices. n The high velocity in the orifices produces high shear. n The equipment operates in line and can be used to produce emulsions, dispersion, and suspensions. Piero M. Armenante Ch. E 702 122

Valve Homogenizer After Harnby et al. , 1985 Piero M. Armenante Ch. E 702 123

Example of Valve Homogenizer Five Star Technologies Piero M. Armenante Ch. E 702 124

Ultrasonic Homogenizers n Ultrasonic homogenizers pump material at high pressure (up to 150 bar) through a small orifice placed in front of a vibrating ultrasonic blade. n The high velocity in the orifice produces high shear, and the blade produces microcavitation that results in emulsions, dispersion, and suspensions of the dispersed phase. Piero M. Armenante Ch. E 702 125

Ultrasonic Homogenizer After Harnby et al. , 1985 Piero M. Armenante Ch. E 702 126

Basic Mechanisms in Laminar Flow Mixing n Laminar shear n Elongation and extensional flow n Distributive mixing n Molecular diffusion n Stresses in laminar flow Piero M. Armenante Ch. E 702 127

Mixing Equipment for Highly Viscous Materials Equipment for highly viscous material (such as pastes, dough, plastics) include: nkneaders nsingle-screw extruders ntwin-screw extruders Piero M. Armenante Ch. E 702 128

Double-Arm Kneader After Perry and Green, 1984 Piero M. Armenante Ch. E 702 129

Single-Screw Extruder Feed Hopper Die Piero M. Armenante Ch. E 702 130

Twin-Screw Extruder Piero M. Armenante Ch. E 702 131

Single-Screw Extruder Piero M. Armenante Ch. E 702 132

Screw Design to Enhance Mixing/Compounding Capability in Single Screw Extruders Piero M. Armenante Ch. E 702 133

Twin-Screw Extruder with Clam -Shell Barrel Design Piero M. Armenante Ch. E 702 134

Gear Mixing Elements in a Twin. Screw Extruder Piero M. Armenante Ch. E 702 135

Kneading Paddles in a Twin. Screw Extruder Piero M. Armenante Ch. E 702 136

Final Remarks About Impellers n No universal “optimal” impeller design exists n Each process needs to be analyzed to determine what are the controlling mechanisms n Impellers can be designed to optimize the process Piero M. Armenante Ch. E 702 137