Comparing Vapour Compression and Vapour Absorption Refrigeration Systems

Refrigeration systems are used to maintain a temperature below the surroundings. There are two main types of refrigeration systems: Vapour Compression Refrigeration (VCR) systems and Vapour Absorption Refrigeration (VAR) systems. While both achieve the same goal, they use different methods and components to cycle the refrigerant.

Understanding Vapour Compression Refrigeration (VCR)

A standard VCR system involves four primary components:

• Evaporator: Where the liquid refrigerant absorbs heat from the space to be cooled and turns into vapour.
• Compressor: This device compresses the low-pressure refrigerant vapour into a high-pressure, high-temperature vapour. This is the main power-consuming component.
• Condenser: The high-pressure vapour releases heat to the surroundings and condenses back into a liquid.
• Throttling Valve (or Expansion Valve): This device reduces the pressure and temperature of the liquid refrigerant before it enters the evaporator.

Understanding Vapour Absorption Refrigeration (VAR)

A VAR system uses heat energy (instead of mechanical work like a compressor) to create the pressure difference needed for the refrigeration cycle. A common VAR system uses a refrigerant (like water) and an absorbent (like lithium bromide). The main components in a basic VAR system are:

• Evaporator: Similar to the VCR system, the refrigerant absorbs heat here and evaporates.
• Absorber: The refrigerant vapour from the evaporator is absorbed by a liquid absorbent, creating a solution. This reduces the pressure, drawing more vapour from the evaporator.
• Pump: A small pump moves the low-pressure solution from the absorber to the generator.
• Generator: Heat is added to the solution in the generator, which boils the refrigerant out of the absorbent, creating high-pressure refrigerant vapour. The remaining weak absorbent solution returns to the absorber.
• Condenser: The high-pressure refrigerant vapour from the generator is condensed back into liquid, similar to the VCR system.
• Throttling Valve (or Expansion Valve): Similar to the VCR system, the liquid refrigerant's pressure is reduced before entering the evaporator.

Comparing Components: VCR vs VAR

Let's compare the key components in both systems:

Identifying the Unique Component

Based on the comparison, the components present in the VCR system are the Evaporator, Compressor, Condenser, and Throttling valve. The components present in the VAR system are the Evaporator, Absorber, Pump, Generator, Condenser, and Throttling valve.

We are looking for a device present in the vapour absorption refrigeration system and absent in the vapour compression refrigeration system.

• Evaporator: Present in both.
• Throttling valve: Present in both.
• Generator: Present in VAR, absent in VCR.
• Compressor: Present in VCR, absent in VAR.

The component that fits the description is the Generator. The Generator's function in the VAR system is crucial; it uses heat to separate the refrigerant from the absorbent, thus raising the refrigerant's pressure, taking over the role of the compressor in a VCR system.

Conclusion

The device present in the vapour absorption refrigeration system and absent in the vapour compression refrigeration system is the Generator.