Water Cooling System in Engine | types of water cooling system
Water cooling system:
Cooling water jackets are provided around the cylinder, cylinder head, valve seats etc. The water when circulated through the jackets, it absorbs heat of combustion. This hot water will then be cooling in the radiator partially by a fan and partially by the flow developed by the forward motion of the vehicle. The cooled water is again recirculated through the water jackets.
In western countries if the water used in the radiator freezes because of cold climates, then ice formed has more volume and produces cracks in the cylinder blocks, pipes, and radiator. So, to prevent freezing antifreeze mixtures or solutions are added in the cooling water.
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Normally following are used as antifreeze solutions:
(i) Methyl, ethyl and isopropyl alcohols
(ii) A solution of alcohol and water
(iii) Ethylene Glycol raises the boiling temperature substantially and hence more heat dissipation
(iv) A solution of water and Ethylene Glycol
(v) Glycerin along with water, etc.
(vi) Chromates are used to prevents deposit
Water cooling system mainly consists of:
Various types of water cooling systems are given as;
(a) Thermo-syphon cooling
(b) Forced or pump cooling
(c) Cooling with thermostatic regulator
(d) Pressurised water cooling system
(e) Evaporative cooling
(a) Thermo-syphon cooling:
This system works on the principle that hot water being lighter rises up and the cold water being heavier goes down. In this system the radiator is placed at a higher level than the engine for the easy flow of water towards the engine. Heat is conducted to the water jackets from where it is taken away due to convection by the circulating water. As the water jacket becomes hot, it rises to the top of the radiator. Cold water from the radiator takes the place of the rising hot water and in this way a circulation of water is set up m the system. This helps in keeping the engine at working temperature.
Disadvantages of Thermo-syphon system,
-Rate of circulation is too slow.
-Circulation commences only when there is a marked difference in temperature.
-Circulation stops as the level of water falls below the top of the delivery pipe of the radiator. For these reasons this system has become obsolete and is no more in use.
(b) Forced or pump cooling:
-This system is used in large number of vehicles like car, buses, trucks and other heavy vehicles. Here circulation of water takes place with convection currents help by a pump.
-The water or coolant is circulated through jackets around the parts of the engine to be cooled, and is kept in motion by a centrifugal pump, driven from the engine through V-belt.
-Cooling is independent of temp.
-Engine is overcooled (when range of temp.=75-900C)
-Can be overcome by using thermostat
(c) Cooling with thermostatic regulator:
-Whenever the engine is started from cold, the coolant temperature has to be brought to the desired warm up time to avoid corrosion damage due to condensation of acids as well as help in easy starting of the engine. This can be done by the use of thermostatic device or thermostat.
-It is a kind of check valve which opens and closes with the effect of temperature. It is fitted in the water outlet of the engine. During the warm-up period, the thermostat is closed and the water pump circulates the water only throughout the cylinder block and cylinder head. When the normal operating temperature is reached, the thermostat valve opens and allows hot water to flow towards the radiator. Standard thermostats are designed to start opening at 70 to 75°C and they fully open at 82°C. High temperature thermostats, with permanent anti-freeze solutions (Prestine, Zerex, etc.), start opening at 80 to 90°C and fully open at 92°C.
– There are three types of thermostats:
(i) bellow type,
(ii) bimetallic type and
(iii) wax type.
Bellow type valve:
Flexible bellows are filled with alcohol or ether. When the bellows is heated, the liquid vaporises, creating enough pressure to expand the bellows. When the unit is cooled, the gas condenses. The pressure reduces and the bellows collapse to close the valve.
Bimetallic type valve:
This consists of a bimetallic strip. The unequal expansion of two metallic strips causes the valve to open and allows the water to flow in the radiator.
Wax type valve:
-Can operate reliably within the specified temperature range
– Heat is transmitted to wax, which has high coefficient of thermal expansion
-Upon being heated, wax expands and the rubber plug presses the plunger forcing it to move vertically upwards
(d) Pressurized water cooling system:
In the case of the ordinary water-cooling system where the cooling water is subjected to atmospheric pressure, the water boils at 212°F. But, when water is heated in a closed radiator under high pressure, the boiling temperature of water increases. The higher water temperature gives more efficient engine performance and affords additional protection under high altitude and tropical conditions for long hard driving periods. Therefore, a pressure-type radiator cap is used with the forced circulation cooling system. The cap is fitted on the radiator neck with an air tight seal. The pressure-release valve or safety valve is set to open at a pressure between 4 and 13 psi. With this increase in pressure, the boiling temperature of water increases to 243°F (at 4 psi boiling tap 225°F and 13 psi boiling temperature 243°F). Any increase in pressure is released by the pressure release valve or safety valve to the atmosphere. On cooling, the vapours will condense and a partial vacuum will be created which will result in the collapse of the hoses and tubes. To overcome this problem the pressure release valve is associated with a vacuum valve which opens the radiator to the atmosphere.
(e) Evaporation cooling system:
-In this system, the engine will be cooled because of the evaporation of the water in the cylinder jackets into steams.
-The advantage is being taken from the high latent heat of vaporization of water by allowing it to evaporate in the cylinder jackets. This system is used for cooling of many types of industrial engines.
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