Rheology

Question 1

Rheology

Answer 1

Deformation and flow of matter

Question 2

Viscosity

Answer 2

Resistance to flow

Question 3

How are rheological properties measured

Answer 3

Rheometer
A force is applied to a material and the rate of flow is measured

Question 4

Shear rate equation

Answer 4

Velocity of top layer (m s-1) / height of cube (m)

Question 5

Shear stress equation

Answer 5

Applied force (N) / area of top layer (m2)

Question 6

Viscosity ratio

Answer 6

Shear stress over shear rate

Question 7

Newtonian

Answer 7

Viscosity of a material is independent of the applied shear stress

Question 8

Non Newtonian

Answer 8

Viscosity of a material changes with the applied shear stress

Question 9

Why is flocculating agents added

Answer 9

To prevent slow settling to form loosely bound aggregates (flocs) to ensure uniform doses

Question 10

Dilatant

Answer 10

Viscosity increases with applied stress

Question 11

Plastic and pseudo plastic

Answer 11

Viscosity reduces with applied stress

Question 12

Shear thinning

Answer 12

Gradient gets shallower with increasing stress

Question 13

Plastic of Bingham flow

Answer 13

Minimum shear stress must be applied before a material will flow, below this the material is elastic

Question 14

Pseudoplastic flow

Answer 14

Material flows as soon as shear stress applied

Gums, paste, creams

Question 15

Shear thickening

Answer 15

Gradient gets steeper with increasing stress

Question 16

Shear rates

Answer 16

Low shear rates= particles are separated, liquid acts as a lubricant

At high shear rates= particles clump together, liquid no longer a lubricant and viscosity increases

Question 17

Time dependent pseudoplastic flow (thixotrophy)

Answer 17

Different shear rates before and after shear stress is applied and removed
Greater after removal

Question 18

Time dependent dilatant flow (rheopexy)

Answer 18

Different shear rates before and after shear stress is applied and removed
Less after removal