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Fluid Flow > Question 1 - Non-Newtonian Fluids > Flashcards

Question 1 - Non-Newtonian Fluids Flashcards

1
Q

fluid does not follow Newton’s law: viscosity is not constant but dependant upon the shear rate

A

non-Newtonian fluids

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2
Q

shear viscosity for Newtonian fluid

A

ratio of shear strees to shear rat and hap netween the plates H.

τ = η𝛾

τ = shear stress
η = dynamic viscosity
𝛾 = shear rate

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3
Q

shear viscosity for non-Newtonian fluid

A

η=η𝛾
τ = η𝛾𝛾

τ = shear stress
η = dynamic viscosity
𝛾 = shear rate

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4
Q

viscosity decreases when increasing the shear rate.
These fluids display a constant-viscosity value of the viscosity at low shear rate values followed by a decrease of the viscosity when increasing further the shear rate

A

shear thinning

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5
Q

viscosity increases when increasing the shear rate.
These fluids display a constant viscosity value at low shear rate value is followed by an increase of the viscosity when increasing the shear rate.

A

shear thickening

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6
Q

Do not flow is the applied stress is below a critical threshold called yield stress. Above this critical stress, the fluids flow with a shear stress directly proportional to the shear rate

A

Bingham fluid

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7
Q

critical threshold of applied stress needed to make Bingham fluids flow

A

Yield Stress

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8
Q

Shear thinning: ________ decreases when increasing the shear rate.

A

viscosity

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9
Q

Shear thinning: viscosity decreases when increasing the ________.

A

shear rate

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10
Q

Power Law Model equation

A

η = K𝛾 ^(n-1)

η = dynamic viscosity
K = consistency
𝛾 = shear rate
n = power law index

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11
Q

What η represents

A

shear viscosity

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12
Q

What K represents in power law

A

consistency

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13
Q

What 𝛾 represents

A

Shear rate

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14
Q

What n represents in power law model

A

power law index

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15
Q

Cross Model equation

A

η = (η0 - η∞)/ 1+(K𝛾)^m

η = dynamic viscosity
η0 = zero-shear viscosity
η∞ = infinite shear viscosity
K = time constant
𝛾 = shear rate
m = dimensionless constant used to modulate the transition between the zero shear constant viscosity reion to the shear thinning region

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16
Q

What η∞ represents

A

infinite shear viscosity

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17
Q

What K represents in cross model

A

time constant

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18
Q

What η0 represents

A

zero-shear viscosity

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19
Q

What m represents in cross model

A

dimensionless constant used to modulate the transition between the zero shear constant viscosity reion to the shear thinning region

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20
Q

extension of the Cross model with one additional parameter
employed to better describe the transition between constant-viscosity and shear-thinning
region

A

Carreau - Yasuda model

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21
Q

Carreau-Yasuda model

A

η = (η0 - η∞)/ (1+(K𝛾)^a)^(n-1/n)

η = dynamic viscosity
η0 = zero-shear viscosity
η∞ = infinite shear viscosity
K = time constant
𝛾 = shear rate
n = dimensionless constant used to modulate the transition between the zero shear constant viscosity reion to the shear thinning region
a = additional parameter to smoothen the transition to shear thinning

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22
Q

Bingham model

A

τ = τy + 𝜂𝑝𝛾

np = plastic viscosity
τy = yield stress

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23
Q

polymers that do not present a charge on the chain itself

A

neutral polymers

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24
Q

polymers that carry electric charges on the chain

A

polyelectrolytes

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25
Q

poor solvents + neutral polymers

A

polymer collapses into dense coils

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26
Q

θ solvent + neutral polymers

A

intra-chain interactions are balanced by polymer-solvent interactions. Polymer conformation is a random coil

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27
Q

good solvent + neutral polymer

A

pollymers are swelled in solution. Polymer conformation is a swollen random coil

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28
Q

polyelectrolytes with no salt

A

charges on polymer exert steric repulsion and the polymer conformation is extended

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29
Q

Polyelectrolytes with salt

A

Electric interactions are screened or partially screened and the polymer conformation is in between extended and random coil

30
Q

dilute polymer regime

A

concentration of polymer in solution is so low that polymer chains do not interact with each other

31
Q

semi-dilute unentangled polymer regime

A

above a critical concentration value called overlapping concentration polymer chains begin to interact but they are yet to form entanglement

32
Q

semi-dilute entangled polymer regime

A

polymer chains start to form some entanglements

33
Q

entangled polymer regime

A

above a critical concentration value called entanglement concentration polymer chains are fully entangled

34
Q

Polyelectrolytes and neutral polymers could span different regimes due to their _____

A

conformation

35
Q

For a solution of polyelectrolytes with no salt the chain is _______

A

extended and therefore is easier to interact with surrounding chains

36
Q

For polyelectrolytes the addition of salt causes __

A

the screening of the electrostatic interactions on the chain and therefore the chain is free to assume a coil like shape

37
Q

refers to the capacity of a liquid to display both viscous and elastic properties

A

viscoelasticity

38
Q

Why do polymer solutions show shear thinning?

A
  • low values of shear rate, Flow fluid does not deform random coil due to elastic entropy
  • when molecular conformation of the random coil is constant the drag exerted the solution is constant
  • above a certain shear rate, the macromolecule is deformed
  • this causes a reduction in drag exerted by the liquid
  • the more the shear rate increases the more the polymer deforms thus causing a continuous reduction of the drag
39
Q

the difference between the stress along the flow direction and the one along the shear gradient direction

A

First normal stress difference

40
Q

the difference between the stress along the shear gradient direction and that along the vorticity direction

A

Second normal stress difference

41
Q

Equation for first normal stress difference

A

N1 = τxx - τyy

τxx = stress along flow direction
τyy =stress along the shear direction

42
Q

Equation for second normal stress difference

A

N2 = τyy - τzz

τyy = stress along the shear direction
τzz = stress along the vorticity direction

43
Q

fanning factor equation

44
Q

When is fanning factor used?

A

Power Law model Moody diagram

45
Q

polymers that do no present a charge on the chain itself

A

neutral polymers

46
Q

polymers that carry electric charges on the chain

A

polyelectrolytes

47
Q

The elastic components are quantified via:

A

the storage modulus G’
the viscous modulus G’’

48
Q

For low frequency values in the SAOS experiment

A

G’ ∝ ω
G’ ∝ ω^2

49
Q

What SAOS stands for

A

Small Angle Oscillatory Shear

50
Q

In this experiment, the sample is between to parallel plates. One oscillates which causes a constant small deformation to the sample, while the other is stationary.

A

Small Angle Oscillatory Shear experiment (SAOS)

51
Q

Re’ equation

A

Re’ = ρ V^n-1D^n / 32.17 K^n-1

Re’ =/= Re

52
Q

Hedstrom number equation

A

He = ρ D^2 τy / η

53
Q

What power law model uses ____ instead of Re

54
Q

Dimensionless number used in the Bingham moody diagram

A

Hedstrom number

Reynolds number used as well

55
Q

low values of________, Flow fluid does not deform random coil due to elastic entropy

A

shear rate

56
Q

low values of shear rate, Flow fluid does not deform random coil due to ________

A

elastic entropy

57
Q

when molecular conformation of the random coil is constant the ____ exerted the solution is constant

58
Q

when molecular conformation of the random coil is ____ the drag exerted the solution is constant

59
Q

when molecular conformation of the random coil is constant the drag exerted the solution is ____

60
Q

above a certain ____, the macromolecule is deformed

A

shear rate

61
Q

above a certain shear rate, the macromolecule is ____

62
Q

above a certain shear rate, the ________ is deformed

A

macromolecule

63
Q

why polyelectrolytes span different regimes to neutral polymers

A

they have different conformations

64
Q

What the addition of salt to polyelectrolytes does

A

causes the screening of the electrostatic interactions on the chain and therefore the chain is free to assume a coil like shape

65
Q

above a certain shear rate, the macromolecule is deformed. this causes a ____ in drag exerted by the liquid

66
Q

above a certain shear rate, the macromolecule is deformed. this causes a reduction in ____ exerted by the liquid

67
Q

above a certain shear rate, the macromolecule is deformed. this causes a reduction in drag exerted by the ____

68
Q

In turbulent region where the fluid is …… (0<n<1) the friction factor is lower than the one for a Newtonian liquid. This is drag reduction

Power Law Model

A

shear thinning

69
Q

In turbulent region where the fluid is shear thinning (0<n<1) the friction factor is …. than the one for a Newtonian liquid. This is drag reduction

70
Q

In turbulent region where the fluid is ….. (n>1) the friction factor is higher than the one for a Newtonian liquid.

A

shear thickening

71
Q

In turbulent region where the fluid is shear thickening (n>1) the friction factor is …. than the one for a Newtonian liquid.

Fluid Flow (2 decks)

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