Select Page Fig.- Types of Fluids

## Non- Newtonian Fluids

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

#### Compressibility (β)

• It is the inverse of Bulk Modulus of Elasticity.

β = 1/k = -dv/(v × dp)

v = volume

#### Isothermal Bulk Modulus (kT)

kT = Pfinal = Ρrt

ka = ϒ × Pfinal

ϒ = Cp/Cv