Properties of Fluids

     

there are the following properties of fluid :-

1.Density/ mass density

2.specific wt/ wt density

3.Specific Volume

4.Specific gravity

5.viscosity

    a) Dynamic viscosity

    b) Kinematic viscosity

(1) Density or mass density -:

• Density or mass density is the property of fluid defined as the ratio of mass of fluid to its volume. Thus mass per unit volume of a fluid is called density.
• It is denoted by the symbol ρ( rho).

• The density of liquid may be consider as constant while the of gases changes with the variation of pressure and temperature. Mathematically , mass density is written as 

                     ρ = Mass of fluid / volume of fluid

• The unit of mass density in SI unit is kg per cubic metre, i.e.,kg/m^3 .

The value of denisty of water is 1 gm/cm^3 or 1000 kg/m^3 .

• Dimensional formula : M1 L-3 T0

(2) Specific weight or weight density -:

• Specific weight or weight density is property of  fluid defined as  the ratio between the weight of fluid to its volume. Thus weight per unit volume iof a fluid is called weight density.
• It is denoted by the symbol w .
• Thus methametically ,

             w = weight of fluid / volume of fluid

       = Mass of fluid X Acceleration due to gravity / volume of fluid

           = Mass of fluid X g / volume of fluid

                ( Mass of fluid / Volume of fluid = ρ)

    

                       w = ρ.g

The value of specific weight or weight density (w) for water is 9.81 * 1000 Newton /m^3

• Dimensional formula : 

(3) Specific volume -:

• Specific volume of a fluid is defined as the volume of the fluid occupied by a unit mass or volume per unit mass of a fluid is called specific volume .
• Methametically , it is expressed as

         Specific volume = volume of fluid / mass of fluid

                                        = 1/ volume of fluid / mass of fluid

                        Specific volume = 1/ρ

• The specific volume is recipocal of mass density .

• It is commonly applied to gasses .
• It is expressed as m³/kg .
• Dimensional formula : M^-1L³T⁰ 

(4) Specific gravity -:

• Specific gravity is defined as the ratio of the weight density (or density) of fluid to the weight density (or density) of a standard fluid . 
• For liquids the standard fluid is taken water and for gases the standard fluid is taken air .
• Specific gravity is also called relative density .
• It is dimension less quantitiy.
• it is denoted by the symbol S.
• Mathematically

   S(liquid)= wt density of liquid/wt density of water

   S(gas)= wt densityof gas /wt density of air

Thus wt density of liquid = S* wt density of water

                                               = S * 1000 * 9.81 N/m^3

     Thusdensity of a liquid = S * Density of water

                                                = S * 1000 kg/m^3

• If the specific gravity of fluid is known then the density of fliud will be equal to specific gravity of fluid multiplied by the density of water . 

• For example : specific gravity of mercury is 13.6 ,hence density of mercury = 13.6 *1000                                                                             = 13600 kg/m^3 .

(5) Viscosity : it is defined as Resistance to flow.

 i) dynamic Viscosity : 

•  Viscosity is defined as the property of fluid that offers resistance to the fluid.
• From Newton's law of viscosity

                       

• Unit of dynamic Viscosity = N.s/m²

• Dimensional formula :

ii) Kinematic viscosity 

• Kinematic viscosity is property of fluid defined as the ratio of  dynamic Viscosity to the  density of fluid.

                

• SI Unit of kinematic viscosity : m²/s
• CGS unit of Kinematic viscosity : stoke

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Read also :

FLUID AND TYPES OF FLUIDS CLASSIFICATION OF FLUIDS

Surface tension and Capillarity effects

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