Fluids:-
Fluid is a substance which is capable if flowering and deform continuously under the action of shearing stress.
Fluid may be divided into three types-
- Liquids
- Vapours
- Gasses.
- Liquids:-
Liquids offer great resistance to compression and aate not much affected by change of temperature.
Liquid are particularly incompatible.
Liquid can occupy definite volumes and can take the shape of the container.
2.3. Vapours and gasses:-
Vapour and gasses aate highly compressible.
Any changing pressure and temperature the density of vapour and gasses will change.
Types of fluid:-
- Ideal fluid
- Real fluid
- Thixitropic liquid
- Ideal plastic fluid
1. Ideal fluid:-
- A ideal fluid is one that is incompatible and has no viscosity and surface tension.
- Ideal fluid doesn't actually exist.
- It is also called perfectfluid or inviscid fluid.
2. Real fluid:-
A fluid which posses viscosity, surface tension and compatibility is known as real fluid. In actual practice all the fluids aate real fluids.
Real fluid further classified as-
- Newtonian fluid
- Non- newtonian fluid.
Fluid which obey the neon laws of viscosity is known as newtonian fluid.
Or
The fluid in which shear stress, developed during fluid flow is directly proportional to the velocity gradient is called newtonian fluid.
Eg:- Water, Kerosene, diesel, Petrol, etc;
- Gasses and thin liquid behave like newtonian fluid.
ii. Non- newtonian fluid:-
Fluid which doesn't obey the neon law of viscosity is known as non- newtonian fluid.
Eg:- Mud, Gels, Polymer solution, Blood, Colloidal liquid of clay.
3. Thixotropic fluid:-
The fluid which have non- linear relation between shear stress and rate of angular deformation beyondan initial yield stresses is known as thixotropic fluid.
Eg:- printer ink or crude oil.
4. Ideal Plastic Fluid:-
A fluid in which shear stress is more than yield stress and shear stress is proportional to the velocity gradient is called ideal plastic fluid.
Eg:- Fly ash and water suspension of clay.
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| Velocity gradient and Shear stress graph of fluids. |
Branches of fluid mechanics:-
1. Hydrostatic:-
Hydrostatic is the study of liquid at rest.
2. Hydro- Kinematics:-
Hydrokinametics is the study of liquid motion without the consideration of any forces or energy which cause the motion.
3. Hydrodynamic:-
Hydrodynamics is the study of liquid motion with the consideration of forces or energies which cause the motion.
Properties of fluid:-
The main properties of fluid are
1. Density or Mass- Density:-
Density or mass- density of a liquid is the ratio of mass of fluid to its volume.
It is denoted by ρ (Rho).
ρ= mass of fluid/ volume of fluid
ρ=Kg/m^3
- Density of water is 1000Kg/m^3 or 1g/cm^3.
- The variation in density of water with the variation of pressure and temperature is so small that is generally considered as neglected for all purpose.
2. Specific weight:-
Specific weight of fluid is ratio between the weight of fluid to its volume.
It is denoted by ω.
ω= weight of fluid/ volume of weight
ω= (m×g)/ volume of fluid
ω= ρ×g
Unit= N/m^3.
- Specific weight of water is 9.81 KN/m^3.
- Specific weight of fluid changes from one place to another place because of change in gravitational acceleration.
3. Specific Volume:-
Specific weight of fluid is the volume per unit mass of the fluid.
Specific volume=volume of fluid/ mass of fluid.
=1/(mass of fluid/volume of fluid)
=1/ρ
Unit= m^3/Kg
4. Specific gravity:-
- It is also called relative density.
- It is defined as the ratio of specific weight of fluid to that of standard fluid.
- The standard fluid is assumed as water and gasses.
- It is denoted by S.
S=ω of fluid /ω of water or air.
- It is dimension less.
ω of fluid= S of fluid × ω of water.
= S × ρ × g
= S × 1000× 9.81
= S × 9.81 KN/m^3.
Specific gravity of mercury is 13.6 means that it's weight(or mass) is 13.6 times that of same volume of water.
In other words mercury is 13.6 times heavier that water.
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