engines and power stations
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.
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.
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.
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.