Non- Newtonian Fluids
- 1 Non- Newtonian Fluids
- 1.1 Conditions for different Non-Newtonian Fluids
- 1.2 Compressibility (β), Isothermal Bulk Modulus (kT) and Adiabatic Bulk Modulus
These types of fluids do not obey Newton’s Law of viscosity. The relation between Shear Stress and Velocity gradient is given by the following formula-
τ = A (du/dy)n + B
Here A and B are constants which depend on the type of fluid and condition of flow.
Conditions for different Non-Newtonian Fluids
For Dilatant Fluids
- n > 1; and B = 0
- Ex- Butter, Quicksand
For Bingham Plastic Fluids
- n = 1; and B ≠ 0
- These fluids always have certain minimum shear stress before yielding.
- Ex- toothpaste, gel, sewage sludge etc.
For Pseudoplastic Fluids
- n < 1 ; and B = 0
- Ex- Paints, Blood, Paper pulp, Lipsticks, Rubber solution etc.
For Thixotropic Fluids
- n < 1; and B ≠ 0
- Viscosity increases with time.
- Ex- Enamel, Printers Ink etc.
For Rheopectic Fluids
- Viscosity decreases with time.
- Ex- Gypsum solution in water, etc.
Compressibility (β), Isothermal Bulk Modulus (kT) and Adiabatic Bulk Modulus
- It is the inverse of Bulk Modulus of Elasticity.
β = 1/k = -dv/(v × dp)
v = volume
Isothermal Bulk Modulus (kT)
kT = Pfinal = Ρrt
Adiabatic Bulk Modulus
ka = ϒ × Pfinal
ϒ = Cp/Cv