Cooling System
COOLING SYSTEM
Cooling system is the one of the basic need system to engine, the cooling system is very important to remove the excess heat from the engine.
All the heat produced by the combustion of fuel in the engine cylinders is not converted
into useful power at the crankshaft.
A typical distribution for the fuel energy is given below:
Useful work at the crank shaft = 20 percentLoss to the cylinders walls = 35 percentLoss in exhaust gases = 35 percentLoss in friction = 10 percent
It is seen that the quantity of heat given to the cylinder walls is considerable and if this
heat is not removed from the cylinders it would result in the pre-ignition of the charge. In
addition, the lubricant would also burn away, thereby, causing the seizing of piston.
Excess heating will also damage the cylinder material.
Keeping the above factors in view, it is observed that suitable means must be
provided to dissipate the excess heat from the cylinder walls, so as to maintain the
temperature below certain limits. The engine gives best performance at temperature from
70 to 85 degree Celsius, which is called the optimum temperature limit.
Methods of Cooling
Various methods used for cooling of automobiles engine are:
1. Air Cooling
2. Water Cooling
• Air Cooling:
Source : The engineers post
The basic principle involved in this method is to have the current of air
flowing continuously over the heated metal surface from where the heat is to be
removed. The heat dissipation depends upon following factors:
1. Surface area of metal in contact with air.
2. Mass flow rate of air.
3. Temperature difference between the heated surface and air.
4. Conductivity of metal used for engine.
Use of copper, aluminum and steel alloys has been made to improve heat
transfer because of their better thermal conductivity.
• Water Cooling:
Source: ResearchGate
In water cooling, the engine cylinders are surrounded by water
jackets through which the cooling water flows. Heat flows from the cylinder walls
into water which goes to the radiator where it loses its heat to the air. Water cooling systems are of two types:
(a) Thermo-siphon System
(b) Pump Circulation System
In the modern automobiles,
pump circulation system is employed because in this system
the required size of the radiator is much smaller than the thermo-siphon system and the
cooling is also faster.
Other Methods of Cylinder Cooling
Apart from the two widely used methods, i.e. air cooling and water cooling as
discussed above, various other methods have been used to increase the cooling efficiency
according to the need of the circumstances.
The methods are:
• Liquid cooling:
Sometimes instead of water, other liquids having higher boiling
points are used for engine cooling. The examples are glycerin (boiling point 290.0C)
and ethylene glycol (boiling point 195.0C). Higher boiling point increases the capacity of the
liquid to carry heat and consequently weight of the coolant and hence that of the
radiator is decreased.
• Pressure sealed cooling:
The boiling point of water is raised at higher pressures,
with consequent reduction in coolant and the radiator weights and greater thermal
efficiency of the engine due to higher operating temperatures. For approximately 10
kN/m2
increase in pressure, the boiling point is raised by 2.50C. To achieve this
special pressure, a sealed radiator cap is used. The pressure blow off valve opens
when the pressure in the system exceeds a certain predetermined value, say 50
kN/m2
. A vacuum valve is provided to safeguard against the radiator collapse due
to vacuum if the steam inside suddenly condenses to form a vacuum.
In some engines, instead of an overflow pipe, an expansion reservoir is provided.
This is so connected with the radiator that it receives the excess cooling water as
the engine temperature and hence the cooling water temperature increases. When
the cooling water cools down, its volume decreases and the cooling water in the
reservoir returns to the radiator. The reservoir is usually made of translucent plastic
so that it can indicate the level of the coolant anytime.
Advantages of Pressure sealed cooling system
• There is no loss of coolant.
• Cooling efficiency of the system is not decreased at high altitudes, where due to
low temperature pressure; the boiling point is otherwise low.
The cooling system is made up of the passages inside the engine block and heads, a
water pump to circulate the coolant, a thermostat to control the temperature of the coolant,
a radiator to cool the coolant, a radiator cap to control the pressure in the system, and
some plumbing, consisting of interconnecting hoses to transfer the coolant from the
engine to radiator.
The main components of water cooling system
• The Radiator
• Radiator Cooling Fans
• Pressure Cap & Reserve Tank
• Water Pump
• Thermostat
• Bypass System
• Freeze Plugs
• Head Gaskets & Intake Manifold Gaskets
• Hoses
How Does a Cooling System Work?
Source : How a car works
A cooling system works by sending a liquid coolant through passages in the engine block
and heads. As the coolant flows through these passages, it picks up heat from the engine.
The heated fluid then makes its way through a rubber hose to the radiator in front of the
car. As it flows through the thin tubes in the radiator, the hot liquid is cooled by the air
stream entering the engine compartment from the grill in front of the car. Once the fluid is
cooled, it returns to the engine to absorb more heat. The water pump has the job of
keeping the fluid moving through this system of plumbing and hidden passages.
A thermostat is placed between the engine and the radiator to make sure that the coolant
stays above a certain preset temperature. If the coolant temperature falls below this
temperature, the thermostat blocks the coolant flow to the radiator, forcing the fluid instead
through a bypass directly back to the engine. The coolant will continue to circulate like this
until it reaches the design temperature, at which point, the thermostat will open a valve
and allow the coolant back through the radiator.
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