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Introduction to Viscometry and
Rheology, Basics, Rotational
Testing
Basic Seminar
Applied Rheology
2
Contents
Definition of basic rheological parameters
Viscosity and elasticity
Deformation, shear stress and shear rate
Parameters changing viscosity
Temperature, time and pressure
Newtonian and Non-Newtonian flow behavior
Yield stress
Thixotropic and rheopectic flow behavior
3
(Spring) (Dashpot)
Real Systems
Definition of basic rheological parameters
Viscosity and elasticity
Rotation and Oscillation Rotation and Oscillation
Viscosity Elasticity
4
Viscosity (dynamic) [Pa∙s]
Shear stress [Pa]
Deformation [-]
Shear rate [1/s].
Calculation of the dynamic viscosity
· =
Definition of basic rheological parameters
5
y
A
F v
y
x
= F
A = Pa
N
m2
Force
Area =
= dv
dy =
d
dt =
m
s·m
1 s
·
= x y Distance
Displacement =
m
m
Calculation of the dynamic viscosity
Definition of basic rheological parameters
6
Viscosity Shear rate
Shear stress =
Torque Md · Shear factor A
Rotational speed · Shear factor M
= .
Definitionen rheologischer Größen Definition of basic rheological parameters
Calculation of the dynamic viscosity
7
Definitionen rheologischer Größen
Experimental determination of the viscosity
Absolute Measurement
Relative Measurement
The geometry factors A and M can be calculated for the sensor
(Certificate from the manufacture)
The geometry factors A und M can not be calculated for the sensor
(e.q. Brookfield)
Definition of basic rheological parameters
8
= Dynamic (shear-)viscosity [Pa∙s] = /
1 Pa∙s = 1000 mPa∙s
1 mPa∙s = 1cP (centi Poise)
= Shear stress [Pa]
= Shear rate [1/s]
Units of viscosity
.
.
Definition of basic rheological parameters
9
= Kinematic Viscosity [mm2/s] = /
1 mm2/s = 1 cSt (centi Stokes)
= Density [kg/m3]
rel = Relative Viscosity [-] rel = 1/ 2
e.q. HAAKE-Unit
Units of viscosity
Definition of basic rheological parameters
10
* = Complex
dynamic
(oscillatory-) viscosity [Pa∙s]
1 Pa∙s = 1000 mPa∙s
1 mPa∙s = 1 cP (centi Poise)
G* = Complex modulus [Pa]
= Angular frequency [rad/s]
i = Imaginary Unit (= -1)
* = G*/i∙
Units of viscosity
Definition of basic rheological parameters
11
e = Extensional viscosity [Pa∙s] e = ( 22- 11)/
= Rate of deformation [1/s]
.
.
Units of viscosity
Definition of basic rheological parameters
12
Contents
Parameters changing viscosity
Temperature, time and pressure
13
Chem./physical composition = f ( S )
Temperature = f ( T )
Pressure = f ( p )
Shear rate = f ( )
Time = f ( t ) Shear time, relaxation time
Miscelaneous e.g. electric, magnetic fiel intensity
Viscosity should always be indicated togehter with the relevant influencing
parameters
Einflussgrößen auf die Viskosität
Viscosity is not a constant
e.q.: = 1,4 Pa∙s (20°C, 100 s-1, after 1 min pre-shear 200 s-1)
.
Parameters changing viscosity
14
-20 -10 0 10 20
T [°C]
101
102
103
104
30 -30
At 20 °C: ( / )/ T = 0.0504 1/K
Temperature dependence of a mineral oil
Parameters changing viscosity [m
Pa∙s
]
15
Viscosity of fluids measured at 20°C
Water
Fruit juice, wine
Saccharose-solution
Coffee cream
Olive oil
Honey
Bitumen
Fluid Viscosity [mPa∙s]
1
2 - 5
6 (40 g in 100 ml Wasser)
10
100
10 000
100 000 000
Parameters changing viscosity
16
Pressure depence of viscosity of cruede oil
0 100 200 300 400 500 600 700 800 900 1000 0.1
1.0
[P
as]
Viscosity curve at 15 bar
Viscosity curve at
atmosheric pressure
[1/s] .
Increase of the viscosity of 20 % with a
pressure increase of 15 bar
Parameters changing viscosity
17
Contents
Newtonian and non-Newtonian flow behavior
18
log shear rate .
Slope of 1
Shear rate
Parameters changing viscosity
The viscosity is not a
function of the applied
shear rate.
≠ f(
Newtonian flow behavior
Water
Mineral oil
Bitumen
log
vis
co
sit
y
log
sh
ear
str
ess
19
.
Viscosity curve: = f ( ) .
Shear rate
Parameters changing viscosity
log shear rate .
Slope of 1
Slope > -0.82
Almost every polymer
containing fluid
(melts and solutions)
Shear thinning behavior
Shower gel
Skin cream
Mayonnaise
Aka pseudoplastic flow
behavior
log
vis
co
sit
y
log
sh
ear
str
ess
20
Dis-aggregation Deformation
Newtonsches und nicht-Newtonsches Fließverhalten
Shear thinning flow behavior
Orientation
Ridgid rods
Liquid crystal Polymeric fluids Emulsions Suspensions
Extension
Rest state
Sheared
Newtonian and Non-Newtonian flow behavior
Random coils Droplets Particles
21
Sedimentation
Storage,
shelf live
Transport
Producing paint
Applying paint
Consistency in
the can
Brushing,
spraying, rolling
Levelling
10-4
10-3
10-2
10-1
100
101
102
103
104
10-1
100
101
102
103
shear rates [1/s] .
Shear rates for different paint applications
Newtonian and Non-Newtonian flow behavior
vis
co
sit
y
[
Pa∙s
]
22
Applications and typical shear rates
10-6 - 10-4
10-6 - 10-4
10-1 – 101
100 – 102
101 – 102
101 – 102
101 - 103
101 - 104
103 - 104
Sedimentation
Phase separation
Levelling, running
Extrusion
Dip coating
Chewing
Pumping, stirring
Brushing
Spraying
Application .
Shear rate [s-1]
Newtonian and Non-Newtonian flow behavior
23
log shear rate .
Dilatant flow behavior
PVC-plastisol
Clay dispersions
Quicksand
Newtonian and Non-Newtonian flow behavior
log
vis
co
sit
y
log
sh
ear
str
ess
24
Contents
Yield stress
25
Shear stress
Yield stress
Microscopic picture
The yield stress 0 is the shear stress required , to
overcome elastic behavior and
obtain stationary flow behavior
26
Bingham flow behavior
shear rate .
0
Extrapolation of the flow curve
Mortar
Yield stress
log
vis
co
sit
y
log
sh
ear
str
ess
27
Plastic flow behavior
shear rate [1/s] .
0
Extrapolation of the flow curve
Chocolate
Tooth paste
Printing ink
Yield stress
log
vis
co
sit
y
log
sh
ear
str
ess
28
Flow behavior
Newton = ·
Bingham = 0 + ·
Shear thinning = K · n (n < 1) Ostwald de Waele
Plastic = 0 + K · n Herschel-Bulkley, Casson
Dilatant = K · n (n > 1)
.
.
.
.
.
Mathematic models
29
Fließverhalten
Overview
log shear rate
log
sh
ear
str
ess
. lo
g v
isco
sit
y
log shear rate .
Newtonian
Shear thinning
Dilatant
Plastic
Bingham
Flow behavior
30
Contents
Thixotropic and rheopectic flow behavior
31
Network-structure
Scherzeitabhängiges Fließverhalten
Decrease of viscosity as a function of time under shear
100% recovery as a function of time without shearing
Primary-Particles Agglomerates
Agglomerates
Thixotropy
Thixotropic and rheopectic flow behavior
32
Recording of initial state (low shear stress, shear rate or oscillation)
Disaggregation at constant shear rate (e.g. 100 1/s) until a constant level
is reached
Re-aggregation (low shear stress, shear rate or oscillation)
Scherzeitabhängiges Fließverhalten
Determination
Ramp up, (peak hold) and ramp down
Hysteresis area as a measure for thixotropy
Time curve
Thixotropic-Loop
Thixotropic and rheopectic flow behavior
33
Scherzeitabhängiges Fließverhalten
Time curve and structure recovery
Thixotropic and rheopectic flow behavior
Range 1
Initial State
Range 2
Disaggregation
Range 3
Reaggregation
time t
Rotation
(Oscillation)
0 .
Rotation
(Oscillation)
0 .
Rotation
>> 0 .
t1 t2
log
vis
co
sit
y
34
Scherzeitabhängiges Fließverhalten
Thixotropic loop
Thixotropic and rheopectic flow behavior
shear rate [1/s] .
peak hold
• fresh building material
sh
ear
str
ess
vis
co
sit
y
35
Scherzeitabhängiges Fließverhalten
Rheopexy
Thixotropic and rheopectic flow behavior
shear rate [1/s] .
• Dispersions with high concentration of solids (e.g. Latex)
Real Rheopexy is not observed often
double check whether an artifact is observed
sh
ear
str
ess
vis
co
sit
y
36
Flow behavior
Newtonian flow behavior: f ( )
Non-Newtonian Flow behavior: = f ( )
Bingham (yield stress)
Shear thinning (pseudoplastic)
Plastic (yield stress)
Dilatant (shear thickening)
Time dependant flow behavior: = f (t, )
Thixotropy
Rheopexy
.
.
.
Conclusions
37
Any Questions?
Thank you for your attention!