Page 213 - WCS - Electrical

WORKSHOP CALCULATION & SCIENCE - CITS

EXERCISE 19 : Introduction to Fluid Mechanics

Heat & Temperature
Introduction
The Fluid Mechanics is the branch of engineering science which deals with the behavior of fluids systems also the
action of forces on the fluids and corresponding flow patterns.
Fluid
Any substance which is capable to flow is called as fluid.

Fluid is a substance that deform continuously under the action of shear stress, no matter if it is small
It has no definite shape of its own, but confirms to the shape of the container.
Fluid consists of liquid and gases.
Example: breathing, drinking, blood circulation in the human body, Fluid is everywhere, in the ocean, in the
atmosphere and around the aircraft or a missile etc.
Liquids and Gases
Liquid
Fluids, which are not able to compress, but possess a definite volume, which are not affected appreciably by the
change in pressure and temperature is called as liquid. e.g. Water, Kerosene, Petrol etc
A liquid being composed of relatively closed-packed molecules with strong cohesive forces tends to retain its
volume and will form a free surface in gravitational field or in container
Gases
A fluid which are compressible and posses no definite volume, it is compressed or expands at any change in
temperature is called as gases, e.g. Air, Ammonia, CO, etc. Gas molecules are widely spaced with negligible
cohesive forces, so that it is free to expand until it encounters confining walls
Fluid Properties
Density or Mass Density

The density of a liquid is defined as the mass per unit volume.
Weight m m.g
p.g
vγ = = = = It is denoted by “p” (rho). S.1. unit is kg/m².
Volume v v
Mass density of water is 1000kg/m².
Mass m
Volume v P = =
v = = Volume v
Weight m
Weight Density or Specific Weight or Unit Density
The specific weight of a fluid is defined as weight per unit volume at a valet temperature and pressure.
Volume v
v = = It is denoted by ‘w’ or ‘Y’ (gamma). It has S.1. unit is N/m². Specific weight of water is 9810 N/m² (9.81kN/m²).
2 Mass m
Weight m m.g
Weight W Y= Volume vγ = = = = p.g
Density of any substance Volume v v
Density of water at 4 c °

Mass
m
The specific weight is depends on gravitational acceleration and the mass density, S gravitational attraction varies

=
Volume
P =
v
from place to place, the specific weight will also vary Volume v
=
v =
du Weight m
τα Specific weight of pure water under standard atmospheric pressure of 76 cm of mercury at mean sea level and
dy a temperature of 4°C, is 9810 N/m
Volume v
du v = =
dy 2 Mass m
τ
μ = Density of any substance
 du 
    Density of water at 4 c ° 200
 dy 
2 τα du
μ = Shear stress = N/m = Newton sec dy
 Change of Velocity  m/s 2
    m
 Change of distance  m du
dy

Dyne.sec μ = τ
cm 2  du 
   
 dy 
Newton sec
m 2
2
1 μ = Shear stress = N/m = Newton sec
100   Change of Velocity   m/s m 2

  Change of distance   m
Force
Area Dyne.sec

cm 2

Newton sec
m 2
1
100

Force
Area