Short Answer:

The vapor absorption system works on the principle of using a liquid absorbent to absorb refrigerant vapor, instead of mechanically compressing it as in a vapor compression system. In this system, the refrigerant evaporates at low pressure to absorb heat from the space, and the vapor is absorbed by a liquid absorbent, forming a solution. This solution is then heated in a generator to release the refrigerant vapor, which is condensed and sent back to the evaporator, completing the cycle.

This system uses heat energy instead of electrical energy for compression, making it suitable for places where heat is available, such as solar energy, steam, or hot water. It is commonly used in industrial and large-scale refrigeration applications.

Detailed Explanation :

Working Principle of Vapor Absorption System

The vapor absorption refrigeration system is an alternative to the vapor compression system and is widely used where heat energy is more readily available than electricity. Its working is based on the absorption of refrigerant vapor by a suitable absorbent, rather than mechanical compression. The main components of the system include the evaporator, absorber, generator, and condenser, along with necessary solution and refrigerant pumps.

1. Evaporation:
   In the evaporator, the refrigerant (such as ammonia or water) evaporates at low pressure and temperature. During this process, it absorbs heat from the space or substance to be cooled. This is the cooling effect of the system.
2. Absorption:
   The refrigerant vapor then enters the absorber where it comes into contact with a liquid absorbent (like water for ammonia systems or lithium bromide for water systems). The vapor is absorbed, forming a strong solution. This absorption process releases heat, which is removed by cooling water.
3. Generation:
   The strong solution is pumped to the generator where it is heated, usually by steam, hot water, or other sources of heat. Heating causes the refrigerant to desorb or separate from the absorbent as vapor. The remaining absorbent becomes a weak solution, which is returned to the absorber for reuse.
4. Condensation:
   The refrigerant vapor released from the generator passes to the condenser, where it is cooled by water or air. The refrigerant condenses into a high-pressure liquid, releasing heat to the surroundings.
5. Expansion and Evaporation:
   The condensed refrigerant then passes through an expansion valve or throttling device to reduce its pressure. It returns to the evaporator, completing the cycle.
6. Energy Source:
   Unlike vapor compression systems, the vapor absorption system does not require a mechanical compressor. Instead, it uses thermal energy to drive the separation of refrigerant from the absorbent. This makes the system useful in places where electricity is expensive or unavailable.
7. Applications:
   • Large industrial refrigeration plants.
   • Air conditioning systems for buildings, ships, and trains.
   • Where waste heat or solar heat is available.
   • Cold storage and ice-making plants.
8. Advantages:
   • Can use low-grade heat sources.
   • Less electrical energy is required.
   • Suitable for large-scale and continuous operation.
9. Disadvantages:
   • Lower coefficient of performance (COP) compared to vapor compression systems.
   • Larger size and higher initial cost.
   • Requires careful maintenance and handling of absorbents.

Conclusion

The vapor absorption system operates on the principle of using a liquid absorbent to absorb refrigerant vapor, with heat providing the driving force instead of a mechanical compressor. By evaporating refrigerant at low pressure and absorbing it into a solution, then separating it using heat, the system completes the refrigeration cycle efficiently. It is particularly advantageous in industrial applications or locations where waste heat or alternative heat sources are available, offering a low-electricity method of refrigeration.