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Properties of Fluids in Fluid Mechanics

 

Properties of Fluids in Fluid Mechanics



 mass density, weight density, specific volume, specific gravity, viscosity. Lets understand these properties of fluids one by one in detail. The knowledge of these properties is very essential to make the study of fluid mechanics comprehensive.

The properties of fluids are as follows

1. Density or mass density
2. Specific weight or Weight density
3. Specific volume
4. Specific Gravity
5. Viscosity

1. Density or Mass Density:

It is defined as the ratio of the mass of the fluid to its volume.

  • It is represented by the symbol  ρ (rho).
  • The unit of density is Kg per cubic metre (Kg/m3)
  • The density of liquid is taken as constant while the density of the gases changes with the change in the pressure and temperature

.In mathematical form the density is given as

Properties of Fluids in Fluid Mechanics

 

  • The value of the mass density for the water is 1000 Kg/m3.

 

2. Specific Weight or Weight Density

When the ratio of weight of the fluid to the volume of the fluid is taken out and the quantity that obtained after that is called specific weight or weight density.

  • In other words the weight per unit volume is called weight density.
  • It is denoted by the symbol w

Mathematically it is written as

Properties of Fluids in Fluid Mechanics

 

  • The value for the specific weight or weight density of water is 9.81 x 1000 N/m3

 

3. Specific gravity:

It is the ratio of weight density of a fluid to the weight density of a standard fluid .

  • Water is taken as the standard fluid for liquids and for gases it is air.
  • Specific gravity is also known as relative density.
  • The specific gravity is represented by the symbol ‘S’.

Mathematically

Properties of Fluids in Fluid Mechanics

From this
Weight density of a liquid = S X Weight density of water

  • The specific gravity of mercury is 13.6

4. Specific Volume:

The volume occupied by a unit mass is called specific volume. In other words it is the volume per unit mass.

Mathematically

Properties of Fluids in Fluid Mechanics

 

5. Viscosity

It is the property of the fluid which offers resistance to the movement of a fluid over another adjacent layer of fluid.

  • It is denoted by the symbol μ.

Mathematically

Properties of Fluids in Fluid Mechanics

Where
τ = shear stress
du/dy = shear strain or rate of shear deformation or velocity gradient

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