Water / Liquid cooling systems

The cooling system is needed to keep the engine from not getting so hot as to cause problems and yet to permit it to run hot enough to ensure the maximum efficiency of the engine. During the process of converting the thermal energy to mechanical energy, high temperatures are produced in the cylinders because of the combustion process. A large portion of this heat is transferred to the cylinder head and walls, piston and valves. Unless this excess heat is carried away and these parts are adequately cooled, the engine will be damaged. So the adequate cooling system must be provided to prevent the damage of mechanical parts as well as to obtain maximum performance of the engine

Parts of water cooling systems

Radiator: The purpose of the radiator is to cool down the water received from the engine.

Function: To ensure the close contact of the hot coolant coming out of the engine with the outside air, so as to ensure a high rate of heat transfer from the coolant to air.

The radiator consists of three main parts:

(i) upper tank,
(ii) lower tank and
(iii) tubes.

Hot water from the upper tank, which comes from the engine, flows downwards through the tubes. The heat contained in the hot water is conducted to the copper fins provided around the tubes. An overflow pipe, connected to the upper1 tank, permits excess water or steam to escape.

Read more: Water Cooling System in Engine | types of water cooling system

There are three types of radiators:

(i) gilled tube radiator,
(ii) tubular radiator and
(iii) honeycomb or cellular radiator

Gilled tube radiator:
This is perhaps the oldest type of radiator, although it is still in use. In this, water flows inside the tubes. Each tube has a large number of annular rings or fins pressed firmly over its outside surface.

Tubular radiator:

The only difference between a gilled tubes radiator and a tubular one is that in this case there are no separate fins for individual tubes. The radiator vertical tubes pass through thin fine copper sheets that run horizontally.

Honeycomb or cellular radiator:

The cellular radiator consists of a large number of individual air cells that are surrounded by water. In this, the clogging of any passage affects only a small part of the cooling surface. However, in the tubular radiator, if one tube becomes clogged, the cooling effect of the entire tube is lost.

Water Pump:

Function: To increase the velocity of the circulating water.

This is a centrifugal type pump. It is centrally mounted at the front of the cylinder block and is usually driven by means of a belt.

This type of pump consists of the following parts:

(i) body or casing,
(ii) impeller (rotor),
(iii) shaft,
(iv) bearings, or bush,
(v) water pump seal and
(vi) pulley.

The bottom of the radiator is connected to the suction side of the pump. The power is transmitted to the pump spindle from a pulley mounted at the end of the crankshaft. Seals of various designs are incorporated in the pump to prevent loss of coolant from the system.

Cooling Fan:

Function: To maintain an adequate airflow across the radiator matrix especially at low car speeds and under-engine idling conditions.

The fan is generally mounted on the water pump pulley, although on some engines it is attached directly to the crankshaft. It serves two purposes in the cooling system of an engine.

(i) It draws atmospheric air through the radiator and thus increases the efficiency of the radiator in cooling hot water.
(ii) It throws fresh air over the outer surface of the engine, which takes away the heat conducted by the engine parts and thus increases the efficiency of the entire cooling system.

Thermostat:

To regulate the circulation of water in system to maintain the normal working temperature of the engine parts during the different operating conditions.

Pressure cap:

To form an airtight joint due to which the coolant is maintained at some pressure higher than the atmosphere.

Expansion tank:

To recover the excess coolant as the engine temperature increases and when the cooling water cools down, to return the coolant to the reservoir.

Diagram of Water Cooling / Liquid cooling System :

Working of Water Cooling System : 

• A water-cooled engine block and cylinder head have interconnected coolant channels running through them. At the top of the cylinder head all the channels converge to a single outlet.
• A pump, driven by a pulley and belt from the crankshaft, drives hot coolant out of the engine to the radiator, which is a form of heat exchanger.
• Unwanted heat is passed from the radiator into the air stream, and the cooled liquid then returns to an inlet at the bottom of the block and flows back into the channels again. Usually the pump sends coolant up through the engine and down through the radiator, taking advantage of the fact that hot water expands, becomes lighter and rises above cool water when heated. Its natural tendency is to flow upwards, and the pump assists circulation.
• The radiator is linked to the engine by rubber hoses and has a top and bottom tank connected by a core bank of many fine tubes.
• The tubes pass through holes in a stack of thin sheet-metal fins so that the core has a very large surface area and can lose heat rapidly to the cooler air passing through it.
• On older cars the tubes run vertically, but modern, low-fronted cars have crossflow radiators with tubes that run from side to side.
• In an engine at its ordinary working temperature, the coolant is only just below normal boiling point.
• The risk of boiling is avoided by increasing the pressure in the system, which raises the boiling point.
• The extra pressure is limited by the radiator cap, which has a pressure valve in it.
• Excessive pressure opens the valve, and the coolant flows out through an overflow pipe.
• In a cooling system of this type there is a continual slight loss of coolant if the engine runs very hot. The system needs topping up from time to time. Later cars have a sealed system in which any overflow goes into an expansion tank, from which it is sucked back into the engine when the remaining liquid cools.

Advantages of a water cooling system

• Because of even cooling of cylinder barrel and head (due to jacketing) makes it possible to reduce the cylinder head and valve seat temperatures.
• The volumetric efficiency of water-cooled engines is higher than that of air-cooled engines.
• The compact design of engines with an appreciably smaller frontal area is possible.
• In the case of water-cooled engines, installation is not necessarily at the front of the mobile vehicles, aircraft, etc. as the cooling system can be conveniently located.

Advantages of water cooling system over Air Cooling System : 

1. Engine can be installed anywhere on the vehicle
2. Volumetric Efficiency of the water-cooled engine is more than the air-cooled engine
3. Uniform cooling of the cylinder, cylinder head, and valves.
4. The specific fuel consumption of the engine improves by using a water cooling system.
5. Engine is less noisy as compared with air-cooled engines, as it has water for damping noise.

Disadvantages of water cooling system

• The system requires more maintenance.
• The engine performance becomes sensitive to climatic conditions.
• The power absorbed by the pump is considerable and affects the power output of the engine.
• In the event of failure of the cooling system serious damage may be caused to the engine.

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