Refrigeration technology has evolved over the years, and among the most energy-efficient and eco-friendly cooling technologies is the Vapour Absorption Refrigeration System (VARS). At the heart of VARS lies a critical component—the Absorber. Understanding how the absorber in vapour absorption refrigeration system works is key to grasping the fundamentals of thermal absorption cooling.

Understanding the Absorber in Vapour Absorption Refrigeration System (VARS)

This blog delves deep into the working principle, design, functions, and importance of the absorber in vapour absorption refrigeration system, catering to both mechanical engineering students and HVAC professionals.

What is Vapour Absorption Refrigeration System (VARS)?

The Vapour Absorption Refrigeration System (VARS) is a thermally-driven refrigeration cycle that uses a liquid absorbent and a refrigerant instead of a mechanical compressor to achieve cooling. Commonly used pairs include lithium bromide–water and ammonia–water systems.

Key Components of VARS:

• Generator
• Condenser
• Evaporator
• Absorber
• Pump
• Expansion Valve

Unlike traditional vapour compression systems, VARS uses heat energy (solar, waste heat, or gas flame) to operate, making it energy-efficient and sustainable.

What is an Absorber in Vapour Absorption Refrigeration System?

The absorber in VARS is a key component that plays a chemical role rather than a mechanical one. It absorbs the low-pressure refrigerant vapour (usually ammonia or water) coming from the evaporator into an absorbent solution.

Example:

In an ammonia-water system, the absorber absorbs ammonia vapour into water, forming a strong solution of ammonia-water which is then pumped to the generator.

Working Principle of Absorber in VARS

The absorber works based on the principle of chemical affinity and mass transfer.

Step-by-Step Process:

1. Low-pressure refrigerant vapour from the evaporator enters the absorber.
2. The absorbent solution (e.g., water) is sprayed or circulated to mix with the vapour.
3. Heat of absorption is released as the refrigerant dissolves in the absorbent.
4. A cooling medium (like water) removes the heat to maintain absorption efficiency.
5. The resulting strong solution is sent to the generator for separation.

Components and Materials Used in an Absorber

• Spray nozzles or distributor trays
• Cooling coils or water jackets
• Absorbent and refrigerant pair (e.g., lithium bromide-water or ammonia-water)
• Shell and tube or plate-type construction

These are designed to maximize surface area for contact between refrigerant and absorbent.

Functions of the Absorber in Absorption Refrigeration System

Here’s what the absorber does in a VARS:

• Absorbs refrigerant vapour efficiently from the evaporator
• Creates a pressure differential for continuous refrigerant flow
• Facilitates mass and heat transfer
• Provides the strong solution to the generator for regeneration
• Helps maintain the cycle continuity without mechanical compression

Types of Absorbers in VARS

There are several types of absorbers depending on system size and design:

1. Vertical Spray Absorber

• Suitable for small systems
• Uses spray nozzles for better contact

2. Horizontal Shell and Tube Absorber

• Used in large-scale VARS
• High surface area and efficient cooling

3. Plate Heat Exchanger Type Absorber

• Compact and high performance
• Ideal for modular refrigeration systems

Design Considerations for Absorbers

While designing an absorber, the following factors are crucial:

• Absorption rate of refrigerant vapour
• Heat removal capacity to avoid saturation
• Flow rate of absorbent
• Pressure and temperature conditions
• Material compatibility with refrigerant and absorbent

A poorly designed absorber can drastically reduce the overall Coefficient of Performance (COP) of the system.

Benefits and Limitations of Using Absorbers in VARS

✅ Advantages:

• No moving parts → Low maintenance
• Environmentally friendly (uses waste heat)
• High operational life
• Low noise operation

⚠️ Limitations:

• Requires continuous heat removal
• Slower response than mechanical systems
• Large system footprint

🏭 Real-world Applications of VARS with Absorbers

• Industrial cooling using waste heat
• Solar-powered air conditioning systems
• Food preservation and cold storage in remote areas
• Gas engine exhaust heat recovery systems

In each of these, the absorber in vapour absorption refrigeration system plays a key role in achieving cooling without electricity-driven compression.

❓ Frequently Asked Questions (FAQs)

🧾 Conclusion

The absorber in vapour absorption refrigeration system is more than just a passive container—it’s a critical chemical engine that powers eco-friendly and energy-efficient cooling systems. By understanding its working, functions, and design, engineers and HVAC technicians can optimize system performance and promote greener technologies.