Properties of Fluids

Density or Mass Density

Density or mass density of fluid define as the ratio of the mass of a fluid to it's volume.Thus mass per unit volume is called density.

It is denoted by the symbol of ρ\rho(rho).

SI unit of density is kg/m3kg/m^3

ρ=Mass of fluidVolume of fluidkgm3 \rho = \frac{\text{Mass of fluid}}{\text{Volume of fluid}} \frac{kg}{m^3}

The value of density of water is 1000 kg/m3kg/m^3

Specific Weight or Weight Density

Specific weight or weight density of a fluid is the ratio between the weight of a fluid to it's volume.

It is denoted by the symbol of W

w=Weight of fluidVolume of fluidNm3 w = \frac{\text{Weight of fluid}}{\text{Volume of fluid}} \frac{N}{m^3}

The value of specific weight for water is 9.81×103N/m39.81\times10^3 N/m^3.

Specific Volume

Specific volume of a fluid is defined as the volume of a fluid occupied by a unit mass or volume per unit mass of a fluid.

SI unit of a specific volume is m3/kgm^3/kg.

Specific Volume=Volume of fluidMass of fluid=1ρ\text{Specific Volume}=\frac{\text{Volume of fluid}}{\text{Mass of fluid}}=\frac{1}{\rho}

Specific volume is reciprocal of mass density.

Specific Gravity

Specific gravity is defined as the ratio of the weight density of a fluid to the weight density of a standard fluid.

For liquids, standard fluid is taken water and for the gases, the standard fluid is taken air.

It is also called relative density. It is a dimensionless quantity and is denoted by SS.

S=Weight density of fluidWeight density of standard fluidS=\frac{\text{Weight density of fluid}}{\text{Weight density of standard fluid}}