Refrigeration is a process of cooling or maintain a body at lower temperature than surrounding. There are many type of refrigeration system one of them is vapour absoption refrigeration system. This refrigeration system is different from compression refrigeration system. In compression refrigeration system we used a compressor which is run by electricity  but absorption refrigeration system always runs by using a heat source. The heat firstly produced in the process will be used to provide the energy which runs the whole process of cooling. It is referred as a heat operated cycle because most of the energy required to operate the cycle is heat energy. Vapour Absorption refrigerators are often used for food storage in recreational vehicles.

The processes like compression, condensation, expansion and evaporation which are of the vapor compression refrigeration system will be the same in Vapor absorption refrigeration system. The refrigerants used in the vapor absorption system are ammonia, water and lithium bromide. At first the refrigerant are condensed in the condenser and it gets evaporated in the evaporator. Then the refrigerant starts cooling process in evaporator and releases the heat to the atmosphere via the condenser.

The method of the suction and compression of the refrigerant in the refrigeration cycle will be the major difference between the two systems. In the vapor compression system, the compressor sucks the refrigerant from evaporator and compresses it to the high pressure. The compressor also enables the flow of the refrigerant through the whole refrigeration cycle. In the vapor absorption cycle, the process of suction and compression are carried out by two different devices called as the absorber and the generator. Thus the absorber and the generator replace the compressor in the vapor absorption cycle.

 

Vapour Absorption Refrigeration Cycle:

Construction: 

The above cycle comprises of all the processes which are all involved in absorption refrigeration cycle.

 

12 to 1= E=Evaporator,   

1 to 2 = AB = Absorber, 

2 =          Exit of absorber,

3 =          Entry of pump, 

3 to 4 = Pump

4 to 5 = Strong aqua from pump to aqua heat exchanger (being heated in HE)

5 to 6 = Analyzer and generator bottom,

6 to 7 = Weak aqua from generator to aqua heat exchanger (being cooled in the HE)

8 =          Vapors coming out of analyzer,       

9 =          Water condensed from ammonia vapor and coming to generator called DRIP

10 =        Exit of rectifier and entry of condenser

11 =        Exit of condenser as well as exit of receiver

12 =        Exit of expansion valve

13 =        Entry of heating medium into the generator

14 =        Exit of heating medium from the generator

15–16 =  Cooling in the rectifier

17-18=    Cooling in the condenser

19–20 = Cooling in the absorber

E = Evaporator, AB = Absorber, HE = Aqua Heat Exchanger, A =Analyzer

G = Generator, R = Rectifier, C = Condenser, Re = Receiver.

 

Working:

• Starting from the evaporator the Vapor goes to absorber and is absorbed in water.
• This process of absorbing releases latent heat and the heat of mixing.
• Cooling will be done at the absorber so as to keep the temperature low.
• Low temperature in the absorber increases absorbing capacity. Strong aqua solution comprising of water and ammonia from absorber is sent to the top of the analyzer with a pump and through an aqua heat exchanger.
• Aqua Solution falls will be sent to the generator through the analyzer. And the heating in the generator separates low boiling ammonia from the solution.
• Heating may be done by steam/electric energy/solar energy etc…as the ammonia vapor raises through the analyzer. Analyzer is an open cooler and is an integral part of the generator. It is a vertical tower with baffle plates to provide a zigzag path and analyses the vapor and removes any water associated with ammonia vapor coming from the generator.
• Then dry vapors will be sent to condenser through the rectifier. Rectifier is a closed cooler, In this ammonia vapors are indirectly cooled by water .Any small traces of water associated are removed by the rectifier. 
• Water which is separated will goes back to the generator and is called DRIP. Only anhydrous ammonia vapors go to the condenser. Liquid ammonia from the condenser goes to evaporator through an expansion valve for repeating the cycle.
• Hot weak aqua from the generator comes to absorber through the aqua heat exchanger and an expansion valve. This weak aqua again absorbs ammonia vapors and the cycle is repeated.
• Aqua heat exchanger heats the strong aqua going to generator and thus reduces the heating requirements in the generator. This heat exchanger also cools the weak aqua going to the absorber and thus reduces the cooling requirement in the absorber. Thus it greatly improves the economy of the system.

 

Advantages:

• The whole system will operated at huge temperature range
• Circulation volume of refrigerant is low which reduces the running cost
• Evaporator size is also small when compared with others
• Coefficient of performance will be very high here
• Load variation does not affect performance
• More will be the capacity i.e.,> 1000 T, 30TR 91% electricity saves.

 

Disadvantages:

• Efficiency of absorption system will be very low when compared with others
• Time to quotient will be high so as to produce cooling effect
• As it uses kerosene/oil/gas flame it emits bad smell.
• Initial cost will be very high in the case of vapor absorption refrigeration system
• Leakage will also affects the vapor absorption refrigeration system
• Lithium bromide which will be used in VARS will is corrosive in nature which may affect the overall life of the system

 

Applications:

• Vapor absorption refrigeration system is usually applied in small applications like home refrigerators and Small capacity AC’s.
• Many chemical reactions are exothermic but these must take place at temperatures below atmospheric temperature therefore absorption refrigeration system is required to remove the heat of reaction.
• Heat is generated during fermentation and must be removed otherwise temperature will rise beyond control i.e. absorption refrigeration system maintains at 5 to 10⁰C.

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