The principles of different methods of refrigeration are:
- Ice refrigeration
- Dry ice refrigeration
- Evaporative refrigeration
- Refrigeration by the expansion of air
- Refrigeration by throttling of the gas
- Steam -jet refrigeration
- Refrigeration by using liquid gases
- Thermo-electric refrigeration
- Vapour refrigeration
First Read this:
1. Ice refrigeration
2. Dry ice refrigeration
The carbon dioxide vapours are compressed to high pressure and high-temperature vapours and then condensed to high-pressure liquid CO2 in the condenser. It is made to pass through the expansion valve.
During expansion, the pressure drops below triple point and a mixture of solid and vapour CO2 is received in the snow chamber. The solid CO2 in the form of snow is removed and compressed by mechanical means to form CO2 cakes. The vapour CO2 is mixed with make-up CO2 and once again feed the compressor.
During the change of state from solid to vapour in the application areas, the dry ice absorbs heat equivalent to its latent heat of evaporation. It evaporates at -78*C at standard atmospheric pressure. So this method can produce lower temperatures than ice refrigeration. But the cost of production of solid CO2 is comparatively high due to very high power requirements.
3. Evaporative refrigeration
When a liquid evaporates, it absorbs heat from its surroundings, thereby the temperature of the surrounding is decreased. Thermodynamically, evaporative cooling is the adiabatic exchange of heat between air and water spray on a wetted surface. This method of cooling is commonly employed in room coolers.
4. Refrigeration by the expansion of air
In air expansion refrigeration, the cooling effect is produced by expanding air. If the air expansion is an adiabatic expansion, there is no heat transfer taking place.
According to the first law of thermodynamics
Q= W + △U;
[where Q=0(zero) for an adiabatic process]
W = – △U
As the internal energy is reduced, there is a reduction in temperature. Thus the cooling effect is produced by expanding air adiabatically without changing its phase.
5. Refrigeration by throttling of the gas
When air or some gas at high pressure is throttled through a small opening, escapes to the atmosphere after cooling the refrigerated space. This is due to the Joule – Thomson cooling effect.
Simple refrigeration system based on this principle where air or some other gas at high pressure is throttled through an orifice into a refrigerated space. The temperature of the gas falls while passing through the orifice and then escapes to the atmosphere after cooling the refrigeration space. The amount of temperature drop by this method depends upon:
- Joule Thomson co-efficient
- Pressure drop and
- The original state of the gas.
6. Steam -jet refrigeration
The principle of steam jet refrigeration is that the boiling temperature of the water can be reduced considerably by reducing the pressure on it. The above principle of boiling the water at low temperature by reducing its pressure is adopted in steam jet refrigeration.
The simple arrangement is based on this principle where the water is filled in a container known as a flash chamber. The pressure inside the flash chamber is reduced by means of a steam jet and ejector system. The steam passing through the nozzle and ejector acquires high velocity, which causes a low pressure above the surface of the water in the flash chamber. The condenser condenses the steam and water vapour coming through the ejector and maintains the vacuum. The partial vacuum existing in the flash chamber causes the water to evaporate at low temperatures.
During evaporation, the water absorbs the heat from the remaining water in the flash chamber causing it to cool. The water thus cooled is recirculated through the space to be refrigerated. The warm water coming from the refrigerated space is sprayed back to the flash chamber.
7. Refrigeration by using liquid gases
8. Thermo-electric refrigeration
9. Vapour refrigeration
- Vapour compression refrigeration system or Mechanical refrigeration system.
- Vapour absorption refrigeration system.