Types of Fluids

Types of Fluids 

               The fluids may be classified into the following five types :

 l. Ideal fluid
2. Real fluid

          3. Newtonian fluid

                         4. Non-Newtonian fluid and

              5. Ideal plastic fluid. 

1. Ideal Fluid

         A fluid, which is incompressible and is having no viscosity, is known as an ideal fluid. Ideal fluid is only an imaginary fluid as all the fluids which exist have some viscosity.

2. Real Fluid

         A fluid, which possesses viscosity, is known as real fluid. All the fluids in actual practice are real fluids.

3. Newtonian Fluid

         A real fluid, in which the shear  stress is directly proportional to the rate of shear strain is known as a Newtonian fluid. CLICK HERE

4. Non-Newtonian Fluid

             A real fluid, in which the shear stress is not proportional to the rate of shear strain (or velocity gradient), known as a Non-Newtonian fluid.

5. Ideal Plastic Fluid

             A fluid in which shear stress is more than the yield value and shear stress is proportional to the rate of shear strain (or velocity gradient), is known  as ideal plastic fluid.

Newton’s Law of Viscosity

             It states that the shear stress (t) on a fluid element layer is directly proportional to the rate of shear strain. The constant of proportionality is called the coefficient of viscosity. Mathematically, it is expressed as

𝜏 = μ du / dy

Fluids which obey the above relation are known as Newtonian fluids and the fluids which do not obey the above relation are called Non-Newtonian fluids.

Non-Newtonian Fluids

             Non-Newtonian Fluids are again divided in five types:

i) Dilatant

          ii) Pseudo Plastic

    iii) Rheopectic

            iv) Bingham Plastic

    v) Thixotropic

          The shear stress for a Non-Newtonian Fluid can be measured by the following formula - 

𝜏 = μ (du / dy)^n + B   CLICK HERE

i)Dilatant

        Here n>1 and B=0 and this type of fluid is also named as shear thickening fluid. eg- sugar in water, quick sand etc.

ii)Pseudo Plastic

       Here n<1 and B=0 and this type of fluid is also named as shear thinning fluid. eg- paint, blood, milk etc.

iii)Rheopectic

      Here n>1 but B is not equal to zero. eg- gypsum paste, lubricants etc.

iv)Bingham Plastic

       Here n=1 but B is not equal to zero. eg- toothpaste, sewage sludge etc.

v)Thixotropic

       Here n<1 and B is not equal to zero. eg- ink, ketchup etc.