Hydraulic fluids and their properties, pascal law

1. FLUIDS AND
THEIR PROPERTIES

2. WHAT IS FLUID?
 Fluid is a substance that is capable of flowing. It
has no definite shape of its own. It assumes the
shape of its container.
 Both liquids and gases are fluids.
 Examples of fluids are :
i. water
ii. milk
iii. kerosene
iv. petrol
v. emulsions etc.

3. TYPES OF FLUIDS
 Fluids can be classified into five basic types. They
are:
 Ideal Fluid
 Real Fluid
 Pseudo-plastic Fluid
 Newtonian Fluid
 Non-Newtonian Fluid

4. IDEAL FLUID
 An Ideal Fluid is a fluid that has no viscosity.
 It is incompressible in nature.
 Practically, no ideal fluid exists.

5. REAL FLUID
 Real fluids are compressible in nature. They have
some viscosity.
 Real fluids implies friction effects.
 Examples: Kerosene, Petrol, Castor oil

6. PSEUDO-PLASTIC FLUID
 A fluid whose apparent viscosity or consistency de
shea
creases instantaneously with an increase in
r rate.
 Examples are:
i. quick sand
ii. ketch-up etc.

7. NEWTONIAN FLUID
 Fluids that obey Newton’s law of viscosity are
known as Newtonian Fluids. For a Newtonian fluid,
viscosity is entirely dependent upon
the temperature and pressure of the fluid.
 Examples: water, air, emulsions

8. NON-NEWTONIAN FLUIDS
 Fluids that do not obey Newton’s law of viscosity
are non-Newtonian fluids.
 Examples: Flubber, Oobleck (suspension of starch
in water), Pastes, Gels & Polymer solutions.

10. PROPERTIES OF FLUIDS
 Properties of fluids determine how fluids can be
used in engineering and technology. They also
determine the behaviour of fluids in fluid
mechanics. They are:
 Density
 Viscosity
 Surface Tension
 Capillary Action
 Specific Weight
 Specific Gravity

11. DENSITY
 Density is the mass per unit volume of a fluid. In
other words, it is the ratio between mass (m) and
volume (V) of a fluid.
 Density is denoted by the symbol ‘ρ’. Its unit is
kg/m3.

12. VISCOSITY
 Viscosity is the fluid property that determines the
amount of resistance of the fluid to shear stress.
 It is the property of the fluid due to which the fluid
offers resistance to flow of one layer of the fluid
over another adjacent layer.

13. DYNAMIC VISCOSITY
 The Dynamic (shear) viscosity of a fluid expresses
its resistance to shearing flows, where adjacent
layers move parallel to each other with different
speeds.

14. KINEMATIC VISCOSITY
 The kinematic viscosity (also called "momentum
diffusivity") is the ratio of the dynamic viscosity μ to
the density of the fluid ρ.

15. SURFACE TENSION
 The property of fluids to resist tensile stresses on
their surface is called as Surface Tension.

16. CAPILLARY ACTION
 Capillary action is the property of fluid to flow in a
narrow spaces without assistance of and in
opposition to external forces like gravity.
 The effect can be seen in the drawing up of liquids
between the hairs of a paint-brush, in a thin tube, in
porous materials such as paper and plaster, in
some non-porous materials such as sand or in a
cell.
 It occurs because of intermolecular forces between
the liquid and surrounding solid surfaces.

18. SPECIFIC WEIGHT
 Specific weight is the weight possessed by unit
volume of a fluid. It is denoted by ‘w’. Its unit is
N/m3.
 Specific weight varies from place to place due to
the change of acceleration due to gravity (g).

19. SPECIFIC GRAVITY
 Specific gravity is the ratio of specific weight of the
given fluid to the specific weight of standard fluid.
 It is denoted by the letter ‘S’. It has no unit.

20. PASCAL’S LAW
Pascal Law – which is the basis for all hydraulic
systems, is named after the French Scientist –
Blaise Pascal, who established the law.

21. PASCAL’S LAW ILLUSTRATION

22. Pascal’s Law
It states that “Pressure exerted anywhere in a confined fluid is transmitted
equally in all directions throughout the fluid.
The basic idea behind all hydraulic system is based upon that principle &
can be simply stated as:
Force applied at one point is transmitted to another point using an
incompressible fluid.

23. Working Principle of a Hydraulic Press

24. Functions of Hydraulic Oil
•It transmits power.
It dissipates heat
It lubricates moving parts
It sealsclearances

25. Variable speed : Possible to control speed through valve.
Reversible : Instant reverse motion is possible. No to stop the system
to change
Over load protection : Protected through relief valve from loading.
Small package : Components are smaller than other transmitting
system.
Can be stalled : Not possible on direct drive system from Electric motor /
Diesel engine.
Simple design : Pre- engineered components available.
Self lubricated : Hydraulic oil lubricates the parts.
Flexible : Flexible hoses virtually eliminate the problem of the hydraulic
Smooth: Incompressible, no vibration.
Acts as seal : It dissipates heat / cools the component, It seals clearances
between two, No noise.
Advantages of oil in Hydraulics

26. Force that is applied at one point is transmitted
to another point using an Incompressible.
In this drawing, two pistons (green) fit into two glass cylinders filled with oil
(blue) and connected to one another with an oil-filled pipe. If you apply a
downward force to one piston (the left one in this drawing), then the force is
transmitted to the second piston through the oil in the pipe;

27. Force Multiplication
Assume that the piston on the left is 2 inches in diameter (1-inch radius),
while the piston on the right is 6 inches in diameter (3-inch radius). The area of
the two pistons is Pi * r2 . The area of the left piston is therefore 3.14, while the
area of the piston on the right is 28.26. The piston on the right is 9 times larger
than the piston on the left.
What that means is that any force applied to the left-hand piston will
appear 9 times greater on the right-hand piston. So if you apply a 100-pound
downward force to the left piston, a 900- pound upward force will appear on the
right