Types of Fluid

Contents

What is Fluid?

A Fluid is a substance that has a tendency to flow. Example – Gases and Liquids

These fluids can be classified into two categories.

1. Newtonian Fluid
2. Non-Newtonian Fluid

Non- Newtonian Fluids

What are Non-Newtonian Fluids?

Non-Newtonian Fluids are the types of fluids that 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 that depend on the type of fluid and condition of flow.

Non- Newtonian Fluids Types

The Non-Newtonian Fluids are further categorized as-

Time-Dependent
• Thixotropic Fluids
• Rheopectic Fluids
Time-Independent
• Dilatant Fluids
• Bingham Plastic Fluids
• Pseudo plastic Fluids

Non-Newtonian Fluids Conditions

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), Adiabatic Bulk Modulus

Let us first understand about Bulk Modulus (K).

The Bulk Modulus (K) of any substance is basically the amount of resistance it can withstand on compression.

${\displaystyle K =-V{\frac{dP}{dV}}}$

Compressibility (β)

What is Compressibility?

• It is the inverse of Bulk Modulus of Elasticity.

β = 1/k = -dv/(v × dp)

v = volume

Isothermal Bulk Modulus (kT)

What is Isothermal Bulk Modulus?

kT = Pfinal = Ρrt