Basic Definitions in Fluid Mechanics, Properties of Fluid explain with examples…..

Some Basic Definitions in Fluid Mechanics, Properties of Fluid explain with examples…..

Density: Density indicates the compactness of molecules of fluid means how compact they are arranged. If the space between any two adjacent molecules is in range of very small quantity, the fluid will be much denser. Density is a factor that affects the weight, Flow property, Volume, Mass, Molecular Compaction and many other relative quantities of Fluid. Density basically specifies How much harder our fluid is?  Simply Mass per unit volume is Density but to learn formula is not the way to understand Density, the fact what the funda is should also clear. Unit of density is Kg/m3. A Greek symbol Rho “ρ” is used to denote it.

Example: Let us assume we take a cube of edge 1m of any material [volume of this box is 1 cubic meter]. We filled it with water. Now the amount of mass in that cube as per unit volume is defined as Density of Fluid. Density of fluid is 1000Kg/m3, means in a cube of edge 1m can contain 1000Kg water.

Density is also called as “Mass Density”.

Density = Mass of Fluid/ Volume of Fluid

The word Denser even came from the term density. The mass of water in a closed box is greater than the mass of gas in the same box, that is why it is clear that the molecules of water has much cohesive property than the molecules of gas. Hence in the same volume water has a large quantity of molecules therefore weight and mass of that structure will be large. This all phenomenon indicates that water is much denser than gas. Similarly in case of Water and Mercury, Mercury (Hg) occurs little space to cover its molecules and in that same box Mercury covered a large quantity hence it is denser than water.

Specific Weight: Also named as “Weight Density”. We were talking about the mass in the above topic; here the mass term is replaced with Weight. Thus the term Weight occurred in unit volume is “Specific Weight” of the Fluid. Mathematically Specific Weight will be equals to weight of the fluid if the container has one cubic meter volume. Specific weight not includes the amount of matter present in the fluid but it includes the force (w) exerted by the molecules towards the earth under the gravitational acceleration (g).

Example: A same cubic container of side 1m is taken. As measurement occurs in the density case same things are done in this case except measurements are done taking Weight instead of Mass (m) of Fluid. Simply specific weight signifies the weight of fluid contained in a unit volume. It specifies the stiffness a well as the compactness of fluid particles.

Specific Weight = Weight of Fluid (W) / Volume of Fluid (V)

          Sp. Weight = m x g / V ………………….................................... [W = m x g]

          Sp. Weight = Density x g = ρg

Specific Volume: This property of fluid says that How much volume will be obtained in 1Kg mass?  It is basically the reciprocal of density. Hence its unit is m3/Kg. simply the definition for Sp. Volume is “Volume occupied in a unit mass is called as Sp. Volume.”

        Sp. Volume = Volume of Fluid / Mass of Fluid

        Sp. Volume = 1 / ρ

Specific Gravity: This property of fluid is defined in terms of Sp. Weight or weight density. How much percentage of weight density our liquid has with respect to the standard fluid (taken as water)? A fluid weight density to standard fluid weight density ratio is termed as Sp. Gravity.

         Sp. Gravity = wt. density of Fluid / wt. density of standard Fluid

In mostly liquid cases standard fluid is taken as Water (which has pH value of 7) because it is easily available in economy and the all type of measurements can easily operate upon it. Operations and reactions are conveniently resulted to the aim in case of water means each type of reaction shows its result upon it. Air is taken as standard fluid if we are taking measurements about Gas.

                             S = wt. density of Fluid / wt. density of Water

As the nominator and denominator both have same dimensions so Sp. Gravity is a dimensionless quantity.

Viscosity of Fluid: Viscosity is another property of fluid (say quality of fluid) which shows its “Quality to Flow in Layers”. The density and pressure of fluid is not same in all the layers of fluid flow while it changes from upward to downward incrementally. The liquid becomes denser as dip high. Hence the refractive index changes undergo due to change in denseness of fluid from one layer to another. Upper layer weighted upon the adjacent below layer and by the collision Shear Stresses produced. The below layer is denser than above so the velocity of above layer or water surface is higher. The adjacent below layer is respectively stationary and resists the flow of above layer. This stress produced is Shear stress in fluids flow.

Viscosity of fluid is denoted by Mu “μ” and its unit for measurement is N-s/m2.