Short Answer:
An absorption refrigeration system works on the principle of removing heat from a space using a heat source instead of mechanical energy. Unlike the vapor compression system that uses a compressor, this system uses a generator, absorber, pump, and heat exchanger to circulate the refrigerant.
In this system, a refrigerant (like ammonia) is absorbed in an absorbent (like water), then separated using heat. The refrigerant is then condensed, expanded, and evaporated to produce cooling. It is mainly used in places where waste heat or solar energy is available and electricity is limited.
Detailed Explanation:
Working principle of an absorption refrigeration system
The absorption refrigeration system is a type of cooling system that uses thermal energy (like gas flame, steam, solar energy, or hot water) to produce refrigeration. This system is a great alternative where electricity supply is not available or expensive, as it does not use a motor-driven compressor like the vapor compression system.
Instead of a compressor, it uses a combination of absorber, generator, pump, and heat exchanger to circulate the refrigerant. The most common working pair is ammonia as refrigerant and water as absorbent in large systems, and water-lithium bromide in air conditioning systems.
Main Components and Their Functions
- Evaporator
- The refrigerant (low-pressure liquid) evaporates by absorbing heat from the space to be cooled.
- This is where the cooling effect is produced.
- Absorber
- The vapor refrigerant is absorbed by the absorbent solution (e.g., ammonia in water).
- This creates a strong solution which is sent to the generator.
- Pump
- It pumps the strong solution (refrigerant + absorbent) to the generator.
- This requires very little electrical energy compared to a compressor.
- Generator (or Desorber)
- Heat is applied here (from gas, solar, steam, etc.).
- The refrigerant separates from the absorbent due to heating and becomes vapor.
- The weak solution (without refrigerant) returns to the absorber.
- Condenser
- The refrigerant vapor is cooled and condensed into a high-pressure liquid.
- Heat is rejected to the surroundings.
- Expansion Valve
- The high-pressure liquid refrigerant passes through the valve, reducing pressure and temperature.
After this, the refrigerant enters the evaporator, and the cycle repeats.
Step-by-Step Working Process
- Cooling occurs in the evaporator as refrigerant absorbs heat and evaporates.
- The absorber collects the vapor and dissolves it in an absorbent.
- The solution is pumped to the generator, where heat separates the refrigerant.
- The vapor refrigerant goes to the condenser, releases heat, and turns to liquid.
- The liquid passes through the expansion valve and re-enters the evaporator.
This continuous cycle provides refrigeration without using a compressor.
Common Working Fluids
- Ammonia-Water System: Used for refrigeration at low temperatures.
- Water-Lithium Bromide System: Common in large air-conditioning systems, operates under vacuum.
Advantages of Absorption Refrigeration
- Low electricity use (only for the pump)
- Can use waste heat, solar, or exhaust heat
- No moving parts in major components, so low maintenance
- Quiet operation
Disadvantages
- Larger in size than vapor compression systems
- Slower cooling response
- Requires constant heat input
Applications
- Domestic gas refrigerators in remote areas
- Solar-powered cooling systems
- Industrial waste heat recovery cooling
- HVAC systems in large buildings using steam or hot water
Conclusion
The absorption refrigeration system is a useful cooling method that works by using heat energy instead of mechanical power. It uses an absorber and generator to replace the compressor. This system is especially suitable for locations where electricity is limited or where waste heat is readily available. Though not as compact as vapor compression systems, it is energy-efficient, eco-friendly, and useful for specialized applications.