1. Subject: Fluid Mechanics and Machinery (FMM)
FLUID, FLUID PROPERTIES AND TYPES OF FLUIDS
Prof. Pranit Mehata
ST. JOHN POLYTECHNIC, PALGHAR
A fluid is a substance which is capable of flowing.
A fluid is substance which deforms continuously when subjected
to external shearing force.
A fluid has following characteristics:
1. It has no definite shape of its own but conforms to the shape of
the containing vessels.
2. Even a small amount of shear force exerted on fluid will cause it
to undergo deformation which continuous as long as the force
continues to applied.
A fluid may be classified as: liquid, gas and vapor
3. FLUID MECHANICS???
It is branch of engineering science which deals with the behavior of fluid under the
conditions of rest and motion.
Three parts: Static, kinematics and dynamics
Fluid static: study of fluid under static conditions or fluid at rest
Fluid kinematics: study of fluids which are in motion, where pressure forces are nor
Fluid dynamics: study of fluids which are in motion and pressure forces are
4. PROPERTIES OF FLUIDS
Density or mass density
Specific weight or weight density
5. DENSITY OR MASS DENSITY
It is defined as the ratio of the mass of fluid to its volume.
It is denoted by letter 𝜌 (rho)
Mathematically it is given by ,𝝆 =
The SI unit of density is 𝑘𝑔/𝑚3
For water the density is 1000 𝑘𝑔/𝑚3
6. SPECIFIC WEIGHT OR WEIGHT DENSITY
It is defined as the ratio of the weight of fluid to its volume.
It is weight per unit volume at standard temperature and pressure.
It is denoted by 𝑤.
Mathematically,𝑤 = 𝜌𝑔
The SI unit of specific weight is 𝑁/𝑚3
The value for water is 9.81×1000 𝑁/𝑚3
7. SPECIFIC GRAVITY
It is the ratio of the specific weight of
the liquid to the specific weight of a
It is also called as relative density
It is dimensionless and has no units.
It is represented by S.
For liquid we take water as standard
fluid while for gases we take air.
8. SPECIFIC VOLUME
It is defined as volume per unit mass of fluid.
It is denoted by 𝑣𝑠
The SI unit of specific volume is 𝑚3/𝑘𝑔
Thus it is reciprocal of density.
It is commonly applied to the gases.
It is the property of fluid which offers resistance
to the movement of one layer over another
adjacent layer of the fluid.
The two layers causes shear stress on each other.
This shear stress is directly proportional to the
rate of change of velocity with respect to y.
It is denoted by 𝜏 (called Tau).
Mathematically, 𝜏 ∝
𝜏 = 𝜇
Where, 𝜇 is Constant of proportionality and is known as dynamic viscosity
Thus viscosity may also be defined as the shear stress required to produce unit rate of shear strain.
The SI unit of viscosity or dynamic viscosity is
The CGS unit is Poise 1 Poise=
11. KINEMATIC VISCOSITY
It is defined as the ratio of the dynamic viscosity to the density of fluid.
It is denoted by letter 𝜈 (Nu)
The SI unit of kinematic viscosity is 𝑚2/𝑠
The CGS unit is stokes (= 𝑐𝑚2/𝑠)
1 Stokes= 𝟏𝟎−𝟒𝒎𝟐/𝒔
12. NEWTON’S LAW OF VISCOSITY
This law states that the shear stress (τ) on a fluid element layer is directly proportional to the
rate of shear strain.
Mathematically, 𝝉 = 𝝁
The fluids which obeys this law are called as Newtonian Fluids
The fluids which do not obey this law are called as Non-Newtonian fluids.
13. SURFACE TENSION
It is defined as the tensile force acting on a surface
of liquid in a contact with gas or on the surface
between two immiscible liquids.
It is due to cohesion between particles at the
It is denoted by letter 𝜎 (Sigma)
The SI unit of surface tension is N/m.
The CGS unit is kgf/m.
14. SURFACE TENSION
Rain drops (A falling rain drop becomes spherical due to cohesion and surface tension).
Rise of sap in a tree.
Bird can drink water from ponds.
Capillary rise and capillary siphoning.
Collection of dust particles on water surface.
Break up of liquid jets.
For liquid droplet For soap bubble For liquid jet
It is a phenomenon by which a liquid (depending upon its specific gravity) rises into a thin
glass tube above or below its general level.
This phenomenon is due to the combined effect of cohesion and adhesion of liquid particles.
It is expressed in cm or mm of liquid
Its value is depend upon the specific weight of liquid, diameter of the tube and surface
tension of fluid.
Capillary Rise Capillary Fall
16. CAPILLARI RISE
The rise of liquid surface is called as Capillary
The rise of water is given by
𝟒𝝈 × 𝒄𝒐𝒔𝜽
𝝆 × 𝒈 × 𝒅
The value of 𝜃 for water is zero.
17. CAPILLARI FALL
The fall of liquid surface is called as Capillary
The fall of water is given by
𝟒𝝈 × 𝒄𝒐𝒔𝜽
𝝆 × 𝒈 × 𝒅
The value of 𝜃 for mercury is 128°.
The property by virtue of which fluids undergo a change in volume under
the action of external pressure is called as compressibility.
It decreases with increase in pressure.
It is also defined as reciprocal of bulk modulus (K).
19. TYPES OF FLUIDS
Newtonian fluids. The fluid which obey Newtons law
is called Newtonian Fluids For such fluids μ does not
change with rate of deformation. Examples. Water,
kerosene, air etc.
Non-Newtonian Fluids: The fluid which do not obey
Newton’s law is called Non-Newtonian Fluids. Examples:
blood, solutions, mud flows etc.
Ideal Fluids: A fluid which is incompressible and having
no viscosity is called as ideal fluid.
Real Fluid: A fluid possess viscosity is called as real