Viscosity and Fluid Behaviour Flashcards
(31 cards)
Solution
homogeneous mix of two or more substances (solute in solvent) chemically combined into the same phase. E.g salt water
Dispersion
heterogeneous mix of two or more substances in different phases that are immiscible in one another. E.g. mud, cement slurry, fog
Colloid
heterogeneous mixed of a dispersed phase as small particles immiscible in a continuous phase. E.g. paint, blood, milk
Suspension
Colloidal dispersion with larger particles, tend to settle. E.g. orange juice, cement, cosmetics with suspended particles
Emulsion
homogeneous mix of two or more phases that are usually immiscible in one another. Not thermodynamically stable, need SA. E.g. mayonnaise, moisturiser
What is Newtonian liquid
follows Newton’s law: viscosity is a constant proportionality between shear stress and rate.
What properties do Newtonian liquids show
steady and simple flow, not affected by shear stress or rate
What is non-Newtonian liquid
doesn’t follow Newton’s law as viscosity depends on shear rate or stress applied.
What properties do non-Newtonian liquids show
Dilatant (shear thickening) or pseudoplastic (shear thinning)
Dilatant fluids
Thicken (increase viscosity) when shear force is applied. E.g. oobleck, protective gear gels, shock absorbers
Pseudoplastic fluids
Thin (decrease viscosity) when shear force is applied. E.g. tomato sauce, shampoo, paint
Bingham plastics
Viscoplastic behaves as rigid body at low stress but viscous fluid at high stress
What is shear stress
T = F/A = N/m2 = Pa
deformation of material caused by shear force.
What is shear force
force applied in parallel to the surface of a material in N
What is shear rate
y. = v/h = 1/s
how fast a fluid flows under shear
What is shear strain
y = ()x/h
displacement of material due to shear
Viscosity
n = T/y. = Pa s
fluids resistance to flow due to internal friction.
Relationship between viscosity, shear stress and rate
T = n x y.
Newtonian: n is constant so linear
non: dependent on change of n with shear
What is rheology
the measure of movement and deformation of materials
What is rheology measured with
rheometers or viscometers can measure viscosity, G’, G”, yield stress, LVE ranges, shear stress and rate
What is G’
storage modulus describes elastic portion of energy in a material. Energy that is stored and used later to reform the material.
G’ = G*cos>
What is G”
loss modulus describes viscous portion of energy dissipated when material deforms.
G” = G*sin>
What is G
shear modulus describes materials stiffness when deformed by shear force
G = T/y.
What is G*
complex modulus is the entire viscoelastic behaviour of a sample
