Short Answer:

The difference between vapor compression and vapor absorption cycles lies in how the refrigerant is circulated. In the vapor compression cycle, a mechanical compressor is used to circulate the refrigerant and create pressure difference. In the vapor absorption cycle, a thermal energy source (like heat) is used with an absorber and generator to move the refrigerant without using a compressor.

Vapor compression systems are more efficient, require electricity, and are used in air conditioners and refrigerators. Vapor absorption systems are less efficient, but useful where waste heat or solar heat is available, such as in industrial cooling or remote areas.

Detailed Explanation:

Difference between vapor compression and vapor absorption cycles

Refrigeration is the process of removing heat from a space or substance to keep it cool. Two common cycles used for this purpose are the vapor compression refrigeration cycle (VCRC) and the vapor absorption refrigeration cycle (VARC). Both systems aim to achieve the same goal — cooling — but they do it using very different mechanisms.

These systems are selected based on cost, energy availability, efficiency, and application. Let’s understand their structure, components, and the key differences.

Vapor Compression Cycle (VCRC)

In a vapor compression cycle, mechanical energy is used to run a compressor that circulates the refrigerant throughout the system.

Main Components:

1. Compressor – Compresses the refrigerant vapor and increases its pressure and temperature.
2. Condenser – Releases heat to the surroundings and turns refrigerant vapor into liquid.
3. Expansion Valve – Reduces the pressure of the liquid refrigerant.
4. Evaporator – Absorbs heat from the cooling space, turning liquid into vapor again.

Characteristics:

• Uses electricity to run the compressor.
• High cooling capacity and fast operation.
• Commonly used in domestic refrigerators, ACs, and commercial freezers.
• Higher COP (Coefficient of Performance) compared to absorption systems.

Vapor Absorption Cycle (VARC)

In a vapor absorption cycle, the compressor is replaced with a set of components that use heat energy instead of electricity to circulate the refrigerant.

Main Components:

1. Absorber – Absorbs refrigerant vapor (usually ammonia or water) into a liquid absorbent (like water or lithium bromide).
2. Pump – Moves the solution to the generator (requires very little mechanical work).
3. Generator – Uses heat to separate refrigerant from the absorbent.
4. Condenser, Expansion Valve, and Evaporator – Same as in vapor compression cycle.

Characteristics:

• Uses heat energy (from steam, hot water, solar energy, or waste heat).
• Suitable where electric power is limited or costly.
• Lower COP than compression systems.
• Used in industrial cooling, large buildings, and places with available waste heat.

Key Differences

Feature	Vapor Compression	Vapor Absorption
Power Source	Electricity (mechanical work)	Thermal energy (heat)
Compressor	Used	Not used
Key Components	Compressor, condenser	Absorber, generator
Efficiency (COP)	Higher	Lower
Energy Cost	Higher	Lower if heat source is free
Application	Domestic and commercial use	Industrial, remote, or solar use
Initial Cost	Moderate	High
Maintenance	Simpler	More complex

Practical Example

• Window AC or fridge at home: Uses vapor compression cycle
• Solar cooling system or industrial chilling plant with steam: Uses vapor absorption cycle

Conclusion

The difference between vapor compression and vapor absorption cycles is based on the source of energy used to circulate the refrigerant. Vapor compression cycles use mechanical compressors and electricity, while vapor absorption cycles use thermal energy and chemical absorption. Vapor compression is more efficient and widely used in homes and offices, while vapor absorption is ideal for energy-saving or heat-rich environments, such as industries or solar-powered setups.