AFD7 Agitation and Mixing

Applied Fluid Dynamics
AFD7 Agitation and Mixing
Chemical Engineering Guy
www.ChemicalEngineeringGuy.com

AFD7 Overview

Textbook, Reference and Bibliography

• Chapters:
– No Information Available 
Applied Fluid Mechanics. Robert
Mott 6th Edition

• Section 2: Fluid Mechanics
– CH9: Agitation & Mixing of Liquids
• Agitation of Liquids
• Circulation, Vel., Power Consumption…
• Blending and Mixing
Unit Operation of Chemical
Engineering. McCabe 7th Edition

AFD7 Block Overview
• Section 1: Agitation and Mixing Theory
– Agitation vs. Mixing
– Overview of Equipment
• Section 2: Design of Mixing Equipment
– Power Number
– Power Requirement
• Section 3: Static Mixers
– Basic Principle
• Section 4: Software Modeling

Section 1: Agitation and Mixing Theory

Scope
• Agitation of Newtonian-liquids
– low-moderate viscosity
– Liquid-gas dispersions
– Liquid-Solid Suspension
• Not included
– Viscous material
– Pastes
– Dry solids

Introduction
• Agitation, Mixing, Blending
• Industrial Application
– Reactors
– Agitation Tank
– Preparation Tank
– Mixers

Agitation vs. Mixing
• Agitation: specific and designed movement of
a liquid.
• Mixing: non-specific and random movement
of a liquid

Agitation
• Momentum Transport Operation
Objective:
– Promote Mass Transfer
• Suspension of solids in liquids
• Blending of miscible liquids
• Gas dispersion
• Blending of immiscible liquids to form
emulsions or suspensión
– Promote Heat Transfer
• Increase Area
• Increase mass flows

Agitation Tank
• The Impeller is the most important
part
• The motor rotates the shaft/impeller
• Baffles are many times added to
improve mixing
• Circular tip
• A level Indicator is also included
• Inlet/Outlet Pipe

Common Equipment
• Impeller
– Propellers
– Paddles
– Turbines
• Baffles
• Tanks/Container

Impeller
• Impeller Types:
– Propellers
– Paddles
– Turbines
• Axial Flow Impeller
– Parallel Direction
• Radial Flow Impeller
– Tangencial Direction

Impeller Type: Paddle

Impeller: Double Helix (High Visc.)

Radial vs. Axial Agitation

Axial Agitation

Radial Agitation

Tank/Container

Baffles

Level Indicator/Sensor
• Mechanical
• Pneumatic
• Ultrasonic
• Magnetic

Level Indicator/Sensor

Flow Patterns
• Swirling
• Vortex
• Death Point
• Eddies
• Stagnation

Flow Patterns  Swirling

End of Section 1: Agitation and Mixing Theory

Section 2: Design of Equipment

Design Equations
• Now we set equations for the Design
– Dimension of Equipment
– Distance between parts
– Agitation Requirements
– Power

Design Equations

Design Equations
• J  Baffle Size
• H  Height
• Da  Imp. Diameter
• E/C  Free Height
• Dt  Tank Diameter
• L  Impeller Size
• W Impeller Height

Design Equations
• Typical Proportion

Design Equations
• Number of Baffles
– 4
– No more than 8
• Number of Impeller Blades
– 4-16 Operative Range
– 6 or 8 are common
• Impeller Equations
– Similar to Centrifugal Pumps

Flow Number
• Is an dimensionless number
– Comes from a mathematical model
– Blade Velocity, Tangential velocity,
N = rotational speed (1/h)
Q = volumetric flow rate (m3/h)
Da = Impeller diameter (m)

Flow Number
• Common Flow Number Values
• Disk NQ= 1.30
• High Efficiency NQ= 0.47

Need More Problems?
Check out the COURSE
• Courses
Applied Fluid Dynamics
Part1: Incompressible Flow
You’ll get SOLVED Problems, Quizzes, Slides, and
much more!

Power Consumption
• Solve for q
• Substitute for
– Kinetic Energy  V2
– Mass Flow  kg/s
• You should get this equation…
Check out “Power
Consumption” form CH7,
Section 2.
McCabe Reference

Power Consumption
• We will use empirical/experimental correlations
for Power Requirements based mainly in the
velocity of the impeller
• Note that Power is Function of
• Gravity(g)
• Viscosity of the liquid (miu)
• Density of fluid (rho)
• Impeller’s Diameter (Da)
• Shape Factor (Si)
• Rotational speed RPM (n)

Power Consumption
• Solving for Power, you get this

Power Consumption
• The Power Number, Np, is similar to the
friction factor or the Drag Coefficient
– Drag Force vs. Inertial Stress
– Flow of momentum associated to the bulk velocity

Specification of Impellers “Si”
• The Shape Factor
– S1 = Da/Dt
– S2 = E/Dt
– S3 = L/Da
– S4 = W/Da
– S5 = J/Dt
– S6 = H/Dt

Power Consumption
Baffled Agitation Tank  Six-Blade Turbine + x Baffles
Multiply by Froude Number

Power Consumption
Baffled Agitation Tank  Three-Blade Propeller + x Baffles

Power Consumption

Required Power (Laminar Flow)
• Density is NOT a factor
• KL depends on impeller Geometry + Tank
Geometry
• Found in Tables and Data bases
• The formula 

Required Power (Laminar Flow)
• Np = KL/Re
• P = Np*N*Da2*rho

KL and KT Data
L = Laminar
T = Turbulent
NOTE: KL>KT

Required Power (Turbulent Flow)
• Density IS a factor
• KL depends on impeller Geometry + Tank
Geometry
• Found in Tables and Data bases
• The formula 

Required Power Exercise
Ct.
Values

Power Consumption  Froude Number
• Froude’s Number Equation

Flow number Exercise
• Recommended Flow Number Ex.
– McCabe Ex 9.1

Newtonian vs. Non-Newtonian Fluids
• Recall that we are studying Newtonian Fluids!
• There are correlations for Non-Newtonian as
well!

Newtonian vs. Non-Newtonian Fluids

Time of Mixing!
• We now introduce the concept of time of
mixing
• We will also use Adimensional Numbers!
• Time = seconds
• Angular Velocity = 1/sec
• N*t = sec/sec = adimensional!

Time of Mixing!
• We will use the concept of ft
• Ft is the mixing-time Factor

Time of Mixing!
• Ft is constant when Re> 10^5
• Fr number may be ignored = 1

Agitated Vessels Time Factor
• Different Equipment (Time vs. Re)

Turbine Agitated Vessel Time Factor
• Only valid for Turbine agitated vessels

Time for Six-Blade Turbine
• For the specific case of a six bladed turbine
• You may assume the mixing-time factor as:
– 4.3

Time of Mixing Exercise
• Recommended Study Exercise
– Ex 9.3

End of Section 2: Design of Equipment

Section 3: Static Mixers

Static Mixers
• AKA Motionless Mixers
• May be used in non-viscous liquids
• Avoid Viscous Flow!

Static Mixers
• Design
• Twisted Design
• Ratio D:L must be
• 5-10x min
• 50-100x recommended operation

End of Section 3: Static Mixers

Section 4: Software Modeling

Common Software
• COMSOL Multiphysics Inc ®
• Aspen Plus ®
• Aspen HYSYS ®
• Solid Works ®

COMSOL Multiphysics

SolidWorks

End Section 4: Software Modeling

End of AFD7
• By now you should know:
– Importance of Agitation and Mixing
– Difference Between Agitation and Mixing
– Common Applications
– Common Equipment used in the Industry
– Pattern and Fluid forms (eddies, whirlpools, vortex, etc.)
– Design of Equipment (dimension, type, etc…)
– Power Requirements
– Basic knowledge on Static Mixers
– General Software used to model Agitators + Mixers

Questions and Problems
• Check out the SOLVED & EXPLAINED problems
and exercises!
– Don’t let this for later…
• All problems and exercises are solved in the
next webpage
– www.ChemicalEngineeringGuy.com
• Courses
– Applied Fluid Dynamics  Part1: Incompressible Flow

Contact Information!
• Get extra information here!
– Directly on the WebPage:
• www.ChemicalEngineeringGuy.com/courses
– FB page:
• www.facebook.com/Chemical.Engineering.Guy
– My Twitter:
• www.twitter.com/ChemEngGuy
– Contact me by e-mail:
• Contact@ChemicalEngineeringGuy.com

AFD7 Agitation and Mixing

Recomendados

Recomendados

Mais conteúdo relacionado

Mais procurados

Mais procurados (20)

Semelhante a AFD7 Agitation and Mixing

Semelhante a AFD7 Agitation and Mixing (20)

Mais de Chemical Engineering Guy

Mais de Chemical Engineering Guy (20)

Último

Último (20)

AFD7 Agitation and Mixing