Download PRINCIPLES OF COLD PRODUCTION

REFRIGERATION PRINCIPLES OF COLD PRODUCTION
BASIC KNOWLEDGE
PRINCIPLES OF COLD PRODUCTION
Different types of cold production
ABSORPTION REFRIGERATION SYSTEM
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Compression refrigeration system
Cold gas refrigeration system (Stirling principle)
Absorption refrigeration system
Thermoelectric cold production (Peltier element)
In an absorption system ammonia (NH3) is used as refrigerant. As in
a compression refrigeration system, liquid ammonia evaporates in an
evaporator and thereby absorbs heat. The vaporous ammonia is then
dissolved in water in an absorber. The ammonia solution is heated releasing vaporous ammonia. The ammonia vapour is condensed into liquid
ammonia again in a condenser.
Vortex cold generator
To ensure a temperature difference between evaporation and condensation, a pressure difference must be present. This difference is created by
a pump for the solution or a so-called auxiliary gas (hydrogen H2). When
using the auxiliary gas, a pump can be omitted and the refrigerating
machine does not have any moving parts. The supply of the drive energy
is purely thermal via a boiler. The boiler can be heated electrically or by
gas. The use of waste heat or solar energy is also possible.
COMPRESSION REFRIGERATION SYSTEM
The compression refrigeration system is used most
frequently for cooling. It uses the effect that during
evaporation of a liquid a lot of heat is absorbed. When
condensing the vapour this heat is discharged again.
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With different pressures during evaporation and
condensing the temperature levels can be adjusted
in such a way that heat is transported from the cold to
the hot side.
Because the refrigerant circulates in a closed circuit,
this is called the refrigeration cycle. Instead of the
piston compressor shown, screw, scroll, turbo or
steam jet compressors can also be used.
As refrigerant, liquids with a low boiling point, such as
fluorinated hydrocarbons (FC), propane, CO2 or NH3,
are used.
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In the most simple case a compression refrigeration system consists of an evaporator 2 in the room to be
cooled 1, a compressor 3, a condenser 4 and an expansion element 5.
low concentration ammonia solution
hydrogen and ammonia vapour
THERMOELECTRIC REFRIGERATION SYSTEM
and heat, are easy to control and do not have any
moving parts or liquid fillings.
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Very low temperatures can be achieved, but the efficiency reduces greatly with increasing temperature
difference.
COLD GAS REFRIGERATION SYSTEM
The cold gas refrigeration system corresponds to the familiar Stirling
motor, but the direction of rotation is reversed. This reverses the cycle
flow and the power generator becomes a work machine operating as
a heat pump.
liquid ammonia
hydrogen
Thermoelectric refrigeration systems operate using the
Peltier effect. The principle of function corresponds to
the reversal of the function of the thermocouple known
from temperature measurements. A special semiconductor material is used in the Peltier element.
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The cold gas refrigeration system based on the Stirling principle is
used to generate very low temperatures. Areas of application are the
liquefaction of air or the cooling of infrared cameras.
ammonia vapour
high concentration ammonia solution
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Peltier elements are operated with direct current; the
direction of the current determines the direction of the
heat transport. Therefore, Peltier elements can cool
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The cold gas refrigeration system consists of an operating cylinder 6 and a displacement cylinder 7.
In the operating cylinder the operating gas (usually helium) is alternately compressed and expanded.
The compressed hot gas discharges its heat in the heat exchanger 4 . During the expansion the gas cools
down and absorbs on the cold side 2 of the displacement cylinder heat from the room to be cooled 1.
Displacement pistons 8 and operating pistons 6 are moved via a crank drive 5 with offset phases.
The recuperator 3 increases the efficiency.
VORTEX COLD GENERATOR
The vortex cold generator is an extraordinary refrigerating machine. Here a cold and a hot air flow is generated from a compressed air flow at room temperature.
The compressed air enters a vortex chamber tangentially and is moved into fast rotation. At the centre of
the vortex a cold air flow forms, while the outer layer
of the vortex heats up. The cold air is extracted at the
centre and can be used for cooling.
The benefit of this refrigerating machine is that it is
of a very simple design, does not have any moving
parts, no toxic working materials and does not require
a power supply. The low efficiency is a disadvantage.
Cold air
Hot air
Compressed air
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