Page 174 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

iii Radiation
Heat (energy) from a hot source is transmitted in the form of electromagnetic waves, this is called ‘radiation’.
There is no need of medium for this. Earth receives heat from the Sun only through radiation.
3 Pressure
The magnitude of the perpendicular force acting on the unit area of a plane is called the pressure acting on that
plane.
that is
Pressure = vertical force / area
p= F /A
Where, F = force, p = pressure and A = area.
4 Centrifugal force

When an object moves in uniform circular motion, a force acts on it. The force which tries to push an object
outward from the center is called centrifugal force.
Centrifugal force = mv²/r
= mrw2. (V=rw)
where,
m = mass of the object,
V = velocity of the object,
@ = angular velocity
r = radius of the circle
Properties of coolant used in vehicles
The ideal coolant to be used in an engine should have the following properties

i High thermal capacity: The thermal capacity of the coolant should be high, that is, heat should be absorbed
by the coolant with great efficiency.
ii Low viscosity: A good coolant is one in which viscosity is almost negligible. Coolants with low viscosity flow
faster.
iii Low cost: coolants should be available in the market at low prices, so that they can be purchased easily.
iv Non-toxic: Coolants should be non-toxic, otherwise when they come in contact with heat, they react chemically
and release toxic gases, which can prove fatal for human health.
v Chemical inertness: Coolant should not be a chemical reagent, otherwise the coolant reacts chemically with
the engine parts, resulting in problems like rusting etc.
vi Electrical insulator: The coolant should be a bad conductor of electricity. If the coolant is a good conductor
of electricity, there is a possibility of spark in the engine.
Recommended change of interval of coolant
Coolant is one of the most overlooked fluids in vehicle maintenance. When coolant gets old, its pH value changes
which can damage various engine parts, gaskets and seals. Therefore, for smooth operation of the internal
parts of the engine, the coolant should be changed every 3 years, but some vehicle manufacturers recommend
changing the coolant after 10 years or 10,000 miles.
Types of cooling system
The following cooling systems are used to cool the internal combustion engine or keep it at normal temperature.

1 Air cooling system (direct cooling system)
2 Water cooling system (indirect cooling system)
A Thermo syphon system
B Pump circulation system

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CITS : Automotive - Mechanic Diesel - Lesson 47 - 56