Non Newtonian Fluids
Contents
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 NonNewtonian 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 (k_{T}) and Adiabatic Bulk Modulus
Compressibility (β)
 It is the inverse of Bulk Modulus of Elasticity.
β = 1/k = dv/(v × dp)
v = volume
Isothermal Bulk Modulus (k_{T})
k_{T} = P_{final} = Ρrt
Adiabatic Bulk Modulus
k_{a} = ϒ × P_{final}
ϒ = C_{p}/C_{v}