Cooling engines and power stations

Water is used as a coolant in car engines. Cool water is pumped around the cylinders of the engine where the fuel is burned, removing excess heat. From there it is passed through the radiator where it loses its heat energy to the air. A car radiator is said to be a form of heat exchanger. The hot water in the tubes of the radiator comes into contact with cooler air from outside and the heat energy is transferred to the air. The water in the radiator is therefore cooler than when it entered the radiator. When the car is moving, air is forced over the radiator. However, engines could overheat while the car is stationary or moving very slowly. Therefore a fan is often provided to force air over the radiator if the car is stationary. The cool water from the radiator then passes back around the cylinders. Some of the hot water passes through a smaller heat exchanger from which hot air can be used to heat the passenger compartment of the car in winter. In cold weather, an antifreeze is added to the water in the coolant system to stop it from freezing and cracking the pipes of the radiator.

Water is frequently used as a coolant in power stations. Most power stations are built beside a river or by the sea from which an adequate supply of water can be pumped easily and cheaply. A coal-fired power station burns coal inside a furnace. The heat is used to turn water into high pressure steam. This steam turns huge fans, called steam turbines, that are coupled to electromagnets called rotors. The rotors revolve inside a stationary coil of copper wire and generate electricity. The whole process involves two transformations of energy: the heat energy in the steam is transformed into kinetic (movement) energy in the rotating turbines and rotors. This kinetic energy is then converted into electrical energy.

Although the steam is cooler than it leaves the turbine, it is not cool enough to condense back into water. To reduce its temperature and make it return to its liquid state, the steam passes through enormous cooling towers where it comes into contract with tubes containing cold water from the river or sea. The steam thus cools further and condenses. It is then returned to the furnace. The sea or river water in the tubes, now several degrees warmer, will be pumped back to where it came. In some places, the warm water leaving the power station is sufficient to keep the nearby water ice-free all winter. For example, in northern Canada many birds are attracted to the ice-free lakes beside power station because it allows them to feed all through the winter.

In some power stations, where there are factories and building nearly, the warm waste water from the power station is not released into the river but is used as a cheap source of heat to warm the buildings during the winter. This makes the power station more efficient.

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