# Fluid Statistics and Dynamics – Study Materials

0 Fluid Statistics and Dynamics – Study Materials

Generally matter exists in three states. They are,

1. Solid
2. Liquid &
3. Gas

Although different in many aspects, liquids and gases have a common characteristic in which they differ from solids. The liquid and as together called by the common term “fluids”.

A fluid is a substance which deforms continuously under the action of shear stress, in addition it has the following properties :

1. It is unable to retain any unsupported shape.
2. It flows under its own weight and takes the shape of any solid body with which it contained.
3. A fluid in equilibrium cannot sustain any shear.
4. It cannot regain its original shape on the removal of the shear force.
5. Shear stresses occur in fluids only when they are in motion.
6. Rate of strain is directly proportional to the applied stress.

Classification of fluids :

1. Ideal fluids & real or practical fluids.
2. Newtonian fluids and Non –Newtonian fluids.

Fluid properties :

1. Mass density (p)
2. Specific Volume (V)
3. Specific weight (W)
4. Specific gravity (S)
5. Surface Tension

Some important real life examples are :

1. Formation of water bubbles.
2. Formation of rain droplets.
3. Collection of dust particles on water surface.
4. A small needle can gently placed on the liquid surface without sinking.
5. Break up of liquid jets.
6. capillary rise and capillary siphoning.

Surface tension depends directly upon the inter molecular cohesion and hence the cohesion decreases with temperature rise, the surface tension also decreases with rise in temperature. It also depends upon the following factors.

1. Nature of the liquid.
2. Nature of the surrounding liquid.
3. Kinetic energy of the liquid.

FLOW DYNAMICS:

The science which deals with the geometry of motion of fluids without reference to the forces causing the motion is known as hydro kinematics or simply kinematics. The science deals with the action of the forces in producing or changing motion of fluids is known as hydro kinetics or simply kinetics. If the science deals both the kinematics and kinetics, it is known as fluid dynamics.

In this, the dynamic equation of fluid motion is obtained by applying Newton’s law of motion to a fluid element considered as a free body. In this study, the fluid is assumed as incompressible and non-viscous.

Minor Losses in pipe Flow:

1. Loss of energy due to sudden enlargement.
2. Loss of head due to sudden contraction.
3. Loss of energy at the entrance to the pipe.
4. Loss of energy at the exist from the pipe.
5. Loss of energy due to gradual contraction or enlargement.
6. Loss of energy due to an obstruction in a pipe.
7. Loss of energy in bends.
8. Loss of energy in various pipe fittings.