Introduction
The domestic absorption type refrigerator was invented by two Swedish engineers Cars Munters and Baltzer Von Platan, in 1925 while they were studying for their undergraduate course of Royal Institute of Technology in Stockholm. The idea was first developed by the Electrolux Company' of Luton, England.
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| Electrolux refrigeration system/water,hyrogen,amonia refrigeration system |
This type of refrigerator is also called three-fluid absorption system: The main purpose of this system is to eliminate the pump so that in the absence of moving parts, the machine becomes noiseless. The three fluids used in this sytem are ammonia, hydrogen and water. The ammonia is used as a refrigerant because it possesses most of the desirable properties. It is toxic, but due to absence of moving parts, there is very little chance for the leakage and the total amount of refrigerant used is small. The hydrogen, being the lightest gas, is used to increase the rate of evaporation of the liquid ammonia passing through the evaporator . The hydrogen is also non-corrosive and insoluble in water. This is used in the low-pressure side of the system. The water is used as a solvent because it has the ability to absorb ammonia readily.
Principle
In the principle of the electrolux refrigeration system is "low boiling point tempreture refrigerant is used and this refrigerant passes through the evaporator, and then refrigerant absorb the heat from the evaporator, in this system pump replace by the rectifier, heat exchanger, and generator so there is no moving device in the system.
Working Process
The principle of operation of a domestic electrolux type refrigerator,The strong ammonia solution from the absorber through heat exchanger is heated in the generator by applying heat from an external source, usually a gas burner. During this heating process, ammonia vapours are removed from the solution and passed to the condenser. A rectifier or a water separator fitted before the condenser removes water vapour carried with the ammonia vapours, so that dry ammonia vapours are supplied to the condenser. These water vapours, if not removed, will enter into the evaporator causing freezing and choldng of the machine. The hot weak solution left behind in the generator flows to the absorber through the heat exchanger. This hot weak solution while passing through the exchanger is cooled. The heat removed by the weak solution is utilised in raising the temperature of strong solution passing through the heat exchanger. In this way, the absorption is accelerated and the improvement in the performance of a plant is achieved.
The ammonia vapours in the condenser are condensed by using external cooling source. The liquid refrigerant leaving the condenser flows under gravity to the evaporator where it meets the hydrogen gas. The hydrogen gas which is being fed to the evaporator permits the liquid ammonia to evaporate at a low pressure and temperature according to Dalton's principle. During the process of evaporation, the ammonia absorbs latent heat from the refrigerated space and thus produces cooling effect.
The mixture of ammonia vapour and hydrogen is passed to the absorber where ammonia is absorbed in water while the hydrogen rises to the top and flows back to the evaporator. This completes the cycle. The coefficient of performance of this refrigerator is given by :
C.O.P. = Heat absorbed in the evaporator / Heat Supplied to the generator
Notes
- The hydrogen gas only circulates from the absorber to the evaporator and back.
- The whole cycle is carried out entirely by gravity flow of the refrigerant.
- It cannot be used for industrial purposes as the C.O.P. of the system is very low.
- In this system there is no moving parts so, no noise problem.
- because of no moving parts, no leakage problem of refrigerant.
- because of no movings parts , so maintenence cost is very low of this system.
- No bear and tear or refrigeration system parts.
- Efficiency of this system is low compare to the vapour compression system.
- In this system water used as a absorber so, corrosion issue of the refrigeration parts.
- Low COP of the system.
Comparison between compression and absorption refrigeration systems
Compression systems
- Work operated
- High COP
- Performance (COP and capacity) very
- sensitive to evaporator temperatures
- System COP reduces considerably at part loads
- Liquid at the exit of evaporator may damage compressor
- Performance is sensitive to evaporator superheat
- Many moving parts
- Regular maintenance required
- Higher noise and vibration
- Small systems are compact and large
- systems are bulky
- Economical when electricity is available
Absorption refrigeration systems
- Heat operated
- Low COP (currently maximum ≈ 1.4)
- Performance not very sensitive to
- evaporator temperatures
- COP does not reduce significantly with load
- Presence of liquid at evaporator exit is not a serious problem
- Evaporator superheat is not very important
- Very few moving parts
- Very low maintenance required
- Less noise and vibration
- Small systems are bulky and large
- systems are compact
- Economical where low-cost fuels or
- waste heat is available