WATER / LIQUID COOLING SYSTEM
In water cooling system, water is continuously circulated through passage (water jackets) around the cylinder. The heat removal from the cylinder is effected by transfer of heat to circulating water. This system is more effective than air cooling and is used for the engines having large capacity. It is used in light and heavy vehicles such as bus, lorry, trucks etc...the inlet water should be about 85-90°C and outlet water is about 95°C -105°C.
Types of water cooling system
According to the method of circulation of water, this system is classified as
a. Thermosyphon system (or) Gravity circulation system.
b. Pump circulation system (or) Forced circulation system.
♦️ THERMOSYPHON SYSTEM
Figure shows the arrangement of thermosyphon cooling system. Generally it consists of radiator, radiator tubes, cylinder water jacket, filler cap, drain tap, fan etc...
In this method water circulation is achieved due to difference between the density of hot water and cold water. Cold water flows into the jackets at the bottom. While it is circulating in the jacket, it absorbs heat from the engine and hot water comes out at the top. Hot water flows down the radiator where it is cooled by the atmospheric air. Atmospheric air is drawn through radiator by a fan which is driven by engine. In this system the radiator is placed above the engine so that water flows down due to gravity.This system is simple and needs no pump to maintain circulation of water however, rate of circulation is slow and insufficient. It needs a bigger radiator to cool the circulating water. It is used for small engines.
♦️ PUMP CIRCULATION SYSTEM
Figure shows the arrangement of pump circulation system. It consists of radiator, radiator tube, cylinder water jacket, water pump, thermostat valve, fan etc...
In this system water circulation is maintained by a pump operated by the engine itself. Cooling water enters at lower position of the engine and absorbs heat while it is passing through the jacket. The hot water comes out from the top and passes into the radiator where it is cooled and then return to the jacket. Cooling of water in radiator is effective by atmospheric air drawn through the radiator by fan.
In modern cooling system, a thermostat valve is used. It controls the jacket water temperature. When the water temperature is low, thermostat closes the valve and water circulation is cut off. When the temperature of water in jacket reaches a suitable value (above 75°c) for efficient operation, thermostat opens the valve and circulation of water is maintained by the pump.
In this system the cooling is effective under all conditions of operation. But cooling is stopped as soon as the engine is stopped This is undesirable because the cooling must continue till the temperature is reduced to normal value. This system is used for cooling large and medium size engines. When the engine becomes, hot the radiator shutters are opened to allow more air to flow through radiator tubes. It increases the rate of cooling.
