Vapor Absorption Refrigeration System [PDF]

What is Vapor Absorption Refrigeration system?

A Vapor Absorption Refrigeration System consists of these following parts:

  • Generator
  • Condenser
  • Receiver
  • Expansion Valve
  • Evaporator
  • Absorber
  • Pump
  • Throttle Valve

In Vapor Absorption Refrigerant System, the low-pressure refrigerant vapor (NH3) from the evaporator is absorbed in the absorber by a weak solution of refrigerant which lowers the pressure in the absorber to draw more NH3 vapor from the evaporator. The cooling system is also used to remove the heat of solution to increase the absorption capacity.

The pumps draw strong solution (rich in refrigerant) from the absorber, builds pressure and forces in the generator. The strong solution of NH3 in the generator is heated by a gas or steam to drive out the NH3 and weak solution returns to the absorber.

After condensing in the condenser, the liquid NH3 with high pressure is passed through a throttle valve to the evaporator where it absorbs its latent heat for cooling.

Vapor Absorption Refrigeration System flow diagram
Vapor Absorption Refrigerant System

Actual Vapor Absorption Refrigeration System

In actual vapor absorption refrigeration system, when heat-exchanger and rectifier are used with a simple system to improve operating efficiency than it is called Practical Vapor Absorption System.

The low-pressure refrigerant vapor (NH3) from the evaporator is absorbed in the absorber by the weak solution of refrigerant. The pump draws the strong solution of NH3, build high pressure and forces to the generator through a heat exchanger where weak solution acts as cooling media. Therefore reduce the cost of heating in the generator and cost of cooling the absorber.


The analyzer is a direct contact heat exchanger consisting of a series of trays mounted above the generator which remove some unwanted water particles associated with NH3 vapor going to the condenser. The refrigerant from the analyzer enters the rectifier where the final reduction of water vapor occurs by cooling water circulation. The liquid refrigerant from the condenser expands in the expansion valve and enter the evaporator cooling.

Components in Vapour Absorption Refrigeration System


Evaporators play a crucial role in the cooling process. Their primary purpose is to cool the surrounding area by absorbing heat. When a liquid that has been cooled is introduced into the evaporator, it takes in the heat from the evaporator, causing it to turn into vapor. This vapor exists at a low pressure. Specifically for ammonia, the vapor at low pressure then exits the evaporator and proceeds towards the absorber.


Absorbers play a key role in absorbing refrigerants. Within the absorber, a mixture of water and ammonia known as a weak solution is present. The ammonia vapor from the evaporator then enters the absorber. It is absorbed by the water in the absorber. This absorption process leads to the formation of a strong solution containing ammonia and water.

As the water absorbs the ammonia, it releases heat. This causes the water’s ability to absorb more ammonia to decrease. To maintain a high absorptive capacity and ensure the absence of ammonia vapor, cold water is supplied to the absorber on a continuous basis. This helps to keep the water in the absorber at a low temperature, allowing it to effectively absorb any incoming ammonia vapor.


The pump is responsible for moving a concentrated solution of ammonia and water from the absorber to the generator.


In this system, ammonia and water solutions are utilized. Ammonia acts as the refrigerant, while water serves as the absorbent. Inside the absorber, a mixture of water and ammonia solutions is present due to the strong affinity water has for ammonia.

To convert the solution of ammonia and water into vapor, the generator receives additional heat from external sources. These auxiliary heat sources can include steam, hot water, or any type of heater. The purpose of providing heat is to facilitate the conversion of the ammonia and water solution into vapor.


On top of the generator, analyzers are positioned to monitor the system. During the process, ammonia vaporizes before water, but some water particles can also vaporize alongside ammonia. The purpose of the analyzer is to separate water particles from the ammonia vapor.

Allowing water particles to pass beyond the generator can negatively impact the system’s efficiency. In larger quantities, water particles can even cause damage to the system. To prevent this, the analyzer condenses the water particles, while allowing the ammonia vapor to pass through and continue further into the system. Although some ammonia may also condense in the vapor analyzer, the majority of the ammonia will successfully pass through the vapor analyzer.

Pressure-Reducing Valve

Once the ammonia vapor has passed through the analyzers, the weak solution present in the generator will flow through a pressure reducing valve and return to the absorber. This completes the cycle, as the solution is ready to absorb more ammonia vapor and continue the refrigeration process.

Expansion Valve

The main function of the expansion valve is to convert the liquid ammonia into cold liquid and direct it towards the evaporator. As the liquid ammonia flows through the expansion valve, its temperature and pressure decrease significantly. This transformation results in the liquid ammonia becoming extremely cold, setting the stage for efficient cooling in the evaporator.

Video on Vapor Absorption Refrigeration System

Credits: Academic Gain Tutorials

Do Check-out Vapour Compression Refrigeration System and Electrolux refrigeration System to learn more about thermal systems.

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