# Types of Fluids

Fluids are classified into the following types

**Ideal fluid:**A fluid said to be ideal if it is both incompressible and have no

**viscosity**. Its bulk modulus is infinite. It has no surface tension. Such fluid is only imaginary and does not exist in nature.

**Real fluid:**A fluid that possesses viscosity, finite compressibility and surface tension.

**Newtonian fluid:**A real fluid that obeys the

**Newton’s law of viscosity**. In this type of fluid shear stress is directly proportional to shear strain (or velocity gradient).

- For the Newtonian fluid coefficient of viscosity remain constant.

**Non-Newtonian fluid:**A real fluid that doesn't follow the Newton’s law of viscosity.

**Ideal plastic fluid:**A fluid in which shear stress must overcome a yield value and then shear stress is directly proportional to the rate of shear strain.

### Types of non-Newtonian fluids

In this kind of fluid, the relationship between shear stress and velocity gradient is given by the equationNon-Newtonian fluid classified into

**Time independent:**(i) Dilatant fluid (ii) Bingham fluid (iii) Pseudoplastic fluid

**Time-dependent:**(i) Thixotropic fluid (ii) Rheopectic fluid

**Dilatant fluids**

n > 1, B = 0

Also called shear thickening fluid

Eg. Quicksand, Butter

**Bingham fluid**

n = 1, B ≠ 0

Act like solid by withstanding a certain amount of stress without a change in strain.

Eg. Toothpaste, water suspension of clay, jellies

**Pseudoplastic fluid**

n < 1, B = 0

Eg. Paint, slurry, blood, milk

**Thixotropic fluids**

n < 1, B is a function of time, B = f(t)

Viscosity increases with time.

Eg. Enamels, printer ink

**Rheopectic fluids**

n > 1, B = f(t)

Viscosity decreases with time.

Eg. Gypsum solution

**Read:**

**-**Types of fluid flow

**-**Flow Lines - Pathlines, Streamlines, Streaklines, Timelines, Stream Tube