1. Subject: Fluid Mechanics and Machinery (FMM)
FLUID, FLUID PROPERTIES AND TYPES OF FLUIDS
BY
Prof. Pranit Mehata
ST. JOHN POLYTECHNIC, PALGHAR

2. FLUID??????
 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
considered.
 Fluid dynamics: study of fluids which are in motion and pressure forces are
considered.

4. PROPERTIES OF FLUIDS
 Density or mass density
 Specific weight or weight density
 Specific gravity
 Specific volume
 Viscosity
 Surface tension
 Capillarity
 Adhesion
 Cohesion
 Compressibility
 Vapour pressure

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 =
𝒎
𝑽
 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
standard fluid.
 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
 Mathematically, 𝑣𝑠=
𝑉
𝑚
 The SI unit of specific volume is 𝑚3/𝑘𝑔
 𝑣𝑠=
𝑉
𝑚
=
1
𝑚
𝑉
=
1
𝜌
 Thus it is reciprocal of density.
 It is commonly applied to the gases.

9. VISCOSITY
 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 ∝
𝑑𝑢
𝑑𝑦

10. VISCOSITY
𝜏 ∝
𝑑𝑢
𝑑𝑦
𝜏 = 𝜇
𝑑𝑢
𝑑𝑦
 Where, 𝜇 is Constant of proportionality and is known as dynamic viscosity
𝝁 =
𝝉
𝒅𝒖
𝒅𝒚
 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
𝑁.𝑠
𝑚2
 The CGS unit is Poise 1 Poise=
𝟏
𝟏𝟎
𝑵.𝒔
𝒎𝟐

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)
 Mathematically, 𝜈=
𝜇
𝜌
 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
𝒅𝒖
𝒅𝒚
 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
surface.
 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
𝒑=
𝟒𝝈
𝒅
𝒑=
𝟖𝝈
𝒅
𝒑=
𝟐𝝈
𝒅

15. CAPILLARITY
 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 Action
Capillary Rise Capillary Fall

16. CAPILLARI RISE
 The rise of liquid surface is called as Capillary
rise.
 The rise of water is given by
𝒉 =
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
rise.
 The fall of water is given by
𝒉 =
𝟒𝝈 × 𝒄𝒐𝒔𝜽
𝝆 × 𝒈 × 𝒅
 The value of 𝜃 for mercury is 128°.

18. COMPRESSIBILITY
 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).
 Compressibility=
1
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
fluid.