Introduction to Hydraulics
Hydraulics
• The word hydraulics has been derived from the Greek word
Hudour, which means "water."
• Hydraulics may be defined as the science that deals with the
mechanical behavior of water at rest or in motion. The
science of fluids at rest is called hydrostatics, and the
science of moving fluids is called hydrodynamics; they
both are embedded in hydraulics.
Hydraulics
• Hydraulics is an applied science of fluid mechanics and
studies, for the most part, the flow of incompressible fluids,
which do not exhibit any changes in density as the pressure
exerted on them is varied.
Deals with the application of fluid mechanics to
engineering devices involving liquids, usually water or oil
Hydraulics
Hydraulics
Hydraulics
Units
Metric System
- The metric system is an internationally agreed
decimal system of measurement created in France in
1799. The International System of Units (SI)abbreviated SI after the French “Système International
d’Unités,”, the official system of measurement in almost
every country in the world, is based upon the metric
system.
Units
US Customary Units
- The US English System
of measurement grew out of
the manner in which people
secured measurements using
body parts and familiar
objects.
Units
Fluid Mechanics
A physical science dealing with the action of fluids
at rest or in motion and with applications and devices in
engineering using fluids.
Divided into two portions:
1. Fluid Statics- Deals with fluid at rest
2. Fluid Dynamics – deals with fluid in motion
What is a Fluid?
A substance that deforms continuously
when acted upon by a shearing stress of any
magnitude
What is a Fluid?
A substance that deforms continuously
when acted upon by a shearing stress of any
magnitude
Types of Fluids
Ideal Fluids
-Assumed to have viscosity
-Incompressible
- Have uniform velocity when
flowing
- No friction between moving
layers of fluid
-No eddy currents or turbulence
Types of Fluids
Real Fluids
-Exhibit infinite viscosity
- Non uniform velocity
distribution when flowing
- Compressible
- Experience friction and
turbulence in flow
Properties of Fluids
Mass density or Specific Mass,
-ratio of its mass per unit volume
For water:
Ideal gas density,
-found from the specific gas constant and ideal gas
law
For air:
Ideal gas density,
For air:
Specific Volume,
-Volume occupied by a unit mass of a fluid
Unit Weight or Specific Weight,
- ratio of its weight per unit volume
For water:
Specific Gravity, s
- dimensionless ratio of a fluid’s density to
some standard reference density. For liquids
and solids, the reference density is water at
For gases,
; air density=
Viscosity,
- Determines the amount of resistance to
shearing forces
Viscosity,
- Determines the amount of resistance to
shearing forces
Note: 1 poise = 0.1 Pa-s
Kinematic Viscosity,
- ratio of dynamic viscosity of the fluid to its
mass density
Note: 1 stoke = 0.0001
Example :
If the viscosity of water at 80 degrees Celsius is 0.00302
poise and its specific gravity is 0.95.
a. Determine its absolute viscosity in Pa – s
b.
c.
Determine its kinematic viscosity in
Determine its kinematic viscosity in stokes.
Answer:
a)
b)
Surface tension,
Pressure inside a Droplet of Liquid
P
4
d
Surface Tension of water at room temperature:
𝜎 = 0.073 𝑁/𝑚
Capillary rise/fall,
F=W
Example:
Find the capillary rise in the tube of a
mercury-air-glass interface with
if the
surface tension on the walls of the tube (diameter=
2mm) is 0.514 N/m. (Hg)=13,570 kg/
.
Answer:
-
Bulk Modulus of Elasticity,
- ratio of change in unit pressure to the
corresponding volume change per unit of volume
i
Bulk Modulus of Elasticity,
- ratio of change in unit pressure to the
corresponding volume change per unit of volume
i
Example :
Water having a volume of 1000
pressure of 2 x
Use
Answer:
a)
is subjected to a
. Find the volume after the pressure is applied.
Pa.
Compressibility,
- fractional change in the volume of a
liquid per unit change in pressure in a constant
temperature process
Celerity,
- the velocity of pressure waves
Absolute Pressure,
- the datum reference of zero pressure
Gage Pressure,
- referred from the local atmospheric
pressure (can be positive or negative -vacuum)
Standard Pressure Values: Sea level
Absolute Pressure,
- the datum reference of zero pressure
Gage Pressure,
- referred from the local atmospheric
pressure (can be positive or negative -vacuum)
Standard Pressure Values: Sea level
Example:
What are the values of absolute pressures
of Point A and B? Point A reads a 180 kPa while
Point B reads a 60 kPa vacuum.
Answer:
Example 1:
A reservoir of glycerin has a mass of 1200
kg and a volume of 0.952
. Find its (a) Weight ,
(b) Unit Weight, (c) Mass Density, (d) Specific
gravity.
Answer:
a)
b)
c)
d) s.g.= 1.261
Example 2:
If 200
of oil weighs 10520 lb, calculate
its specific weight, density, and specific gravity.
Hint: 1 slug = 32.2 lb
1 lb = 1 slug-ft/
Answer:
c) s.g.=
Example 3:
One kilogram of hydrogen is confined in a volume
of 200 L at -45
. What is the absolute pressure if
R is 4115
Answer:
°
Example 4:
A gas at 40 under a pressure of 21.868
bar (abs) has a density of 36.9 kg/
What is the
value of gas constant, R for this gas?
Hint: 1 bar = 100 000 Pa
Answer:
Example 5:
An oil (density= 888 kg/ ) of 7 mm
thick has a viscosity of 0.44 Pa-s at 20
What shear stress (Pa) is required to move the
plate at 3.5 m/s?
Answer: