Physical Properties of Fluids
Physical properties of fluids
Density or Mass Density:
Density or Mass Density of a fluid is defined as the ratio of the mass of a fluid to its volume.
The mass per unit volume of a fluid is called density. It is denoted by ῥ(rho)
Unit: kg/m3.
The density of liquids may be considered as constant while that of gases changed with the variation of pressure and temperature.
Mathematically,
ῥ = Mass of fluid/ Volume of fluid
Specific weight or weight density:
Specific weight or weight density of a fluid is the ratio between the weight of fluid to its volume. Weight per unit volume of a fluid is called weight density and it is denoted by the symbol w.
Mathematically,
w = weight of fluid/volume of fluid
= (mass of fluid) x Acceleration due to gravity/volume of fluid
= (mass of fluid)/ volume of fluid x g
- w = ῥ x g
The value of specific weight or weight density(w) is 9.81 x 1000 Newton(N)/m3
in S.I. Units
in S.I. Units
Specific Volume:
Specific volume of a fluid is defined as the volume of a fluid occupied by a unit mass or per unit mass of a fluid is called specific volume.
Mathematically
Specific volume = volume of fluid/mass of fluid
= volume of fluid/mass of fluid
= 1/ῥ
The specific volume is the reciprocal of mass density, it is expressed as m3/kg.
It is commonly applied to gases.
Specific Gravity:
Sp. Gr. is defined as the ratio of the weight density (or density) of a fluid
to the weight density (or density) of a standard fluid. For liquid standard fluid is taken as water and for gases, the standard fluid is taken as air. Sp. Gr. is also called relative density. It
is dimensionless quantity and is denoted by symbol S.
Mathematically
S (for liquids) = Weight density (or density) of liquid / Weight density (or density) of water
S (for gas) = Weight density (or density) of gas / Weight density (or density) of air
Weight density of liquid
= S x weight density of water
= S x 1000 x 9.81 N/m3
The density of liquid = S x density of water
= S x 1000 kg/m
The Sp. Gr. of a fluid is known, then the density of fluid will be equal to sp. gr. of fluid multiply by the density of water. For example, the sp. gr. of mercury is 13.6, therefore, density of mercury = 1000 x 13.6 = 1360 kg/m3.
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