What are the properties of fluids

Today in this article we will learn some interesting things which are the properties of fluids. Before reading the properties of fluids, we have to know what a fluid is. As we know there are 3-types of substance that is solid, liquid and gas.

Example of solid (Wood, ice, gold) liquid (Water, oil, tea) and gas ( Air, water vapor, oxygen).

Here we can say liquid and gas as fluid because if we apply a little amount of force on liquid or gas then they get deform easily. But in solid state we cannot deform easily, solid is deformed only by applying too much force.

And in simple words, the substance which has the ability to flow is know as fluid. The various fluids properties are explain below.

What are the properties of fluids

(1) Density

The density of a liquid can be defined as the mass per unit volume (m/v) at a standard temperature and pressure. and it is usually denoted by ‘ρ’. Its unit are kg/m³ .

ρ = m/v

(2) Specific gravity

It is the ratio of the mass density of a particular substance to the mass density of water.

or,

Specific gravity is the ratio of the specific weight of the liquid to the specific weight of a standard fluid. So it is dimensionless and has no units. It is represent by S.

For liquids, the standard fluid is pure water at 4°C.

$Specific gravity = \frac{specific weight of liquid}{specific weight of pure water} = \frac{W_{Liquid}}{W_{Water}} What are the properties of fluids$

(3) Viscosity

Viscosity can be define as the property of a fluid which determines its resistance to shearing stresses :

Newton’s low of viscosity states that the shear stress (Z) on a fluid element layer is directly proportional to the rate of shear strain. The constant of proportionality is called the co-efficient of viscosity.

$Mathematically, Z = \mu \times \frac{du}{dy}$

Where, μ = Co-efficient of dynamic viscosity, and

(du) / (dy) = rate of shear deformation or velocity gradient.

Kinematic viscosity is the ratio between the dynamic viscosity and the density of the fluid. It is represent by v (nu).

v = μ / ρ

So the units of viscosity : In S.I units – N.S/m² and in M.K.S units – Kgf sec/km²

(4) Vapor pressure

All liquids have a tendency to evaporate or vaporize that is to change from liquid to the gaseous state. and molecules are continuously launched from the free surface to the atmosphere.

These ejected molecules are in the gaseous state and exert their partial vapor pressure on the liquid surface. Hence this pressure is know as the vapor pressure of the liquid ( P_v ).

If the surface above the liquid is confined, the partial vapor pressure exerted by the molecules increases until the molecules re-enter the liquid, at which rate they exit the surface, when the equilibrium position vapor pressure is reached saturation is called vapor pressure ( P_vs ).

Read also this Types of friction in engineering mechanics

(5) Cohesion

Cohesion means intermolecular attraction between the molecules of the same liquid. So this enables a liquid to resist small amounts of tensile stresses. and cohesion is the tendency of a liquid to remain as a group of particles.

(6) Adhesion

Adhesion means the attraction between the molecules of a liquid and the molecules of a solid boundary surface in contact with the liquid. and this property enables a liquid to stick to another body. Capillary action is due to both cohesion and adhesion.

(7) Surface tension

Surface tension (ρ) is caused by the force of cohesion at the free surface. So it is usually expressed in N/m.

Inside pressure :

Water droplet : P = 4σ/d
Soap bubble : P = 8σ/d
Liquid jet : P = 2σ/d

Where, d stands for diameter.

(8) Capillarity

Capillarity is the phenomenon by which a liquid (depending on its specific gravity) rises into a thin glass tube or below its normal level. and this phenomenon is due to the combined effect of cohesion and adhesion of liquid particles.

h = 4σ cosθ / wd

Where, h = Height of capillary rise

d = Diameter of the capillary tube

θ = Angle of contact of the water surface

σ = Surface tension per unit length

w = Weight density (ρg)

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(9) Compressibility

Compressibility is the property due to which the volume of a fluid changes under the action of external pressure. So it is the reciprocal of the bulk modulus of elasticity (k).

$K = dp (increase of pressure)/ - \frac{dv}{d} (volumetric strain) What are the properties of fluids$

So , (compressibility = 1/k)

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