Rheology

Question 1

Stress

Answer 1

Force per unit area that leads to deformation

Question 2

Strain

Answer 2

Resulting deformation

Question 3

Elastic

Answer 3

Material fully recovers when stress removed

Question 4

Viscosity

Answer 4

Internal resistance involved in the relative motion of one layer of molecules with respect to the next

Question 5

What happens to viscosity of a gas upon heating?

Answer 5

Viscosity increases due to increasing internal friction

Question 6

What happens to viscosity of a liquid upon heating?

Answer 6

Viscosity reduces as there is decreased contact

Question 7

Equation for dynamic viscosity

Answer 7

log(Π) = E/RT + logA

Question 8

Equation for relative viscosity

Answer 8

Πrel = Π1/Π2 = t1p1/t2p2

Question 9

Equation for relative viscosity when p1 ≅ p2

Answer 9

Πrel = t1/t2

Question 10

Equation for specific viscosity

Answer 10

Πspecific = Πrel - 1

Question 11

Equation for reduced viscosity

Answer 11

Πred = Πsp/c

Question 12

Intrinsic viscosity

Answer 12

Theoretical viscosity at 0 concentration

Question 13

How is intrinsic viscosity found?

Answer 13

Plot reduced viscosity against concentration. y-intercept is intrinsic viscosity

Question 14

3 types of non-newtonian flow

Answer 14

Plastic, pseudoplastic and dilatant

Question 15

What type of flow has a yield stress?

Answer 15

Plastic

Question 16

What is the apparent viscosity equation for newtonian fluids?

Answer 16

Πapp = shear stress/shear rate = σ/γ

Question 17

Why do plastic and pseudoplastic have their graph shape?

Answer 17

Shear thinning

Question 18

What is the power law when related to shear stress?

Answer 18

σ = Π’γ^n
Π’ = viscosity coefficient
γ = shear rate
n = rate index

Question 19

What is the power law in graphic form?

Answer 19

logσ = nLogγ + LogΠ’

Question 20

What is the value of n in newtonian flow?

Answer 20

n = 1

Question 21

What is the value of n in pseudoplastic flow?

Answer 21

n < 1

Question 22

What is the value of n in dilatant flow?

Answer 22

n > 1

Question 23

What is the value of n in plastic flow?

Answer 23

n < 1 and y intercept = σ0

Question 24

What are the units of viscosity?

Answer 24

Pa.s

Question 25

Equation for rotational viscometers

Answer 25

Π = T/kw T = torque w = speed of rotation k = constant

Question 26

Equation for falling sphere viscometer

Answer 26

v = 2a^2 g(σ-ρ) / 9n a = radius of ball σ = density of ball ρ = density of fluid Π = viscosity g = acceleration due to gravity

Question 27

What is thixotropy?

Answer 27

To change by tough

Question 28

What is the area inside the rheogram of a thixotropic fluid measuring?

Answer 28

Degree of breakdown

Question 29

Why does thixotropy show up on a rheogram?

Answer 29

Viscosity is usually measured by increasing shear rate from 0 to a maximum and then decreasing at the same rate. This creates an increasing and decreasing curve

Question 30

Strain equation

Answer 30

Strain = ΔL/L Strain = change in length/original length

Question 31

Strain percentage equation

Answer 31

Strain = ΔL/L x 100

Question 32

Rate of shear equation

Answer 32

Rate of shear = dv/dr