2.3 Vapor Absorption Refrigeration System Explained
Key Concepts
The Vapor Absorption Refrigeration System (VARS) is an alternative to the traditional vapor compression system. It operates on the principles of absorption and desorption of refrigerant vapor, using heat as the primary energy source rather than mechanical energy.
Key Components:
- Generator: Heats the refrigerant-absorbent mixture, causing the refrigerant to vaporize.
- Condenser: Cools and condenses the high-pressure refrigerant vapor into liquid form.
- Absorber: Absorbs the refrigerant vapor into a liquid absorbent solution.
- Evaporator: Evaporates the refrigerant, absorbing heat from the surrounding environment.
- Heat Exchanger: Recovers heat from the absorbent solution to improve efficiency.
- Pump: Circulates the absorbent solution between the absorber and the generator.
Operation:
In the VARS, a refrigerant (often ammonia) is absorbed into a liquid absorbent (such as water). The mixture is heated in the generator, causing the refrigerant to vaporize and separate from the absorbent. The refrigerant vapor then flows to the condenser, where it is cooled and condensed into a liquid. The liquid refrigerant then passes through the evaporator, where it absorbs heat from the surrounding environment and evaporates. The vaporized refrigerant is then absorbed back into the absorbent solution in the absorber, completing the cycle.
Example:
Consider the absorption system as a sponge that absorbs water (refrigerant) and then is heated to release the water. The released water is cooled and then allowed to evaporate, absorbing heat from the environment. The evaporated water is then reabsorbed by the sponge, and the cycle continues. This process allows for efficient cooling without the need for a mechanical compressor.
Advantages:
- Energy Efficiency: Uses heat as the primary energy source, making it suitable for waste heat recovery applications.
- Environmental Friendliness: Often uses natural refrigerants like ammonia, which have low global warming potential.
- Quiet Operation: Does not require a mechanical compressor, resulting in quieter operation.
Applications:
VARS is commonly used in large-scale refrigeration applications, such as industrial cooling, district heating and cooling systems, and solar-powered refrigeration systems. It is particularly advantageous in scenarios where waste heat is available or where mechanical compression systems are impractical.
Analogies:
Think of the VARS as a thermal battery. Just as a battery stores and releases electrical energy, the VARS stores and releases thermal energy. The generator acts like a charger, the condenser like a cooler, the evaporator like a heater, and the absorber like a storage unit. This continuous cycle of absorption and desorption allows for efficient cooling and heating.