Steam power generation plant: Though the main process in a
steam power station is the conversion of heat energy into electrical energy, it
comprises of many steps for its proper working and good efficiency. The whole
arrangement of a steam power station could be divided into following steps: The
steam generating plant consist of the boiler and its auxiliary equipment for
the utilisation of flue gases.
Boiler: The heat produced by the burning of coal in the
boiler is used to produce steam at high temperature and pressure. The flue
gases produced at the time of combustion is passed through the superheater,
economiser, air- preheater and finally exhausted into the atmosphere through
Super Heater: The steam produced in the boiler has got
moisture content so it is dried and superheated (i.e. steam temperature is
increased above the boiling point of water)by the flue gases on the way to
chimney. Superheating ensures two benefits at first the overall efficiency of
the system is increased and secondly, the corrosion of the turbine blades due
to condensation in later stages is prevented. The superheated steam from
superheater is fed to the steam turbine by means of the main valve.
Air preheater: Air preheater increases the temperature of
the air supplied to coal for combustion using flue gases. Air is drawn in using
a forced draught fan and is passed through preheater before supplying it to the
boiler. This process increases the thermal efficiency and steam capacity per
square meter of the boiler surface.
Steam Turbine: The dry and superheated steam from
superheater is fed to the turbine by means of the main valve. Due to the
striking or reaction impact of the steam on the blades of the turbine, it
starts rotating i.e. heat energy is converted to mechanical energy. After
giving heat energy to the turbine the steam is exhausted to a condenser which
condenses the exhausted steam by means of a cold water circulation.
Alternator: The steam turbine is coupled to an alternator;
the alternator converts the mechanical energy into electrical energy. The
electrical output is transferred to the bus bars through a transformer, circuit
breaker and isolators.
Feed Water: The condensed water produced in the condenser is
used as feed water, some amount of water may be lost in the cycle but it is
compensated using an external source and the cycle repeats and gives a better
efficiency to the system.
Cooling Arrangement: In order to increase the efficiency of
the plant the steam coming from the turbine is condensed using a condenser. The
water circulation for cooling steam in the condenser is taken from a natural
source like river, stream etc and the outcoming hot water from the condenser is
discharged in some lower portion of the water source. In the scarcity of water,
the water from the condenser is cooled and reused with the help of a cooling
There are several heat transfer loops in a refrigeration
system as shown above. Thermal energy moves from left to right as it is
extracted from the space and expelled into the outdoors through five loops of
Indoor air loop. In the left loop, indoor air is driven by
the supply air fan through cooling coil, where it transfers its heat to chilled
water. The cool air then cools the building space.
Chilled water loop. Driven by the chilled water pump, water
returns from the cooling coil to the chiller’s evaporator to be re-cooled.
Refrigerant loop. Using a phase-change refrigerant, the
chiller’s compressor pumps heat from the chilled water to the condenser water.
Condenser water loop. Water absorbs heat from the chiller’s
condenser, and the condenser water pump sends it to the cooling tower.
Cooling tower loop. The cooling tower’s fan drives air
across an open flow of the hot condenser water, transferring the heat to the
There are two fundamental types of the refrigeration system.
They are the;
The vapour-absorption system.
The two types are used for commercial purposes and domestic
refrigerators and the two of them work on the standard that when a liquid
vanishes, it takes in concealed heat from its surroundings. The liquids used in
refrigerators and freezers are called refrigerants. They are made to evaporate
at a temperature below 0 degrees Celsius and in doing so; they take in latent
heat and maintain the cold space at a sub-zero temperature.
A refrigerant must have a low freezing point so that it does
not solidify or form slush in the low-temperature part of the refrigeration
cycle. Also, it should have a high value for its latent heat of vaporisation to
maximise the transfer of heat energy during the cycle.
Compression refrigeration cycles take advantage of the fact
that highly compressed fluids at a certain temperature tend to get colder when
they are allowed to expand. If the pressure change is high enough, then the
compressed gas will be hotter than our source of cooling (outside air, for
instance) and the expanded gas will be cooler than our desired cold
temperature. In this case, fluid is used to cool a low-temperature environment
and reject them
Heat to a high-temperature environment. Vapour compression
refrigeration cycles have two advantages. First, a large amount of thermal
energy is required to change a liquid to a vapour, and therefore a lot of heat
Removed from the air-conditioned space. Second, the
isothermal nature of the vaporization allows extraction of heat without raising
the temperature of the working fluid to the temperature of whatever is being
cooled. This means that the heat transfer rate remains high because the closer
the working fluid temperature approaches that of the surroundings, the lower
the rate of heat transfer.
An air condition
system: An Air-condition system is the fully automatic control of the indoor
atmosphere to maintain comfortable and healthy conditions. Its objective is to
provide clean, fresh air at a temperature and humidity level that is
comfortable to the occupants. The essential ingredients in an air conditioning
system are a fan to blow air around, a cold surface to cool and dehumidify the
air, a warm surface and a source of water vapour. In a large system, there will
also be a tangle of tubes to distribute the air and collect it again. Notice
that the cold surface has two independent jobs to do: it is used to cool the
air and it is also used to dehumidify, by condensing water from the air.