Vapour Absorption Refrigeration System

Introduction

Refrigeration systems play a crucial role in various industries and applications, providing cooling and preservation of perishable goods, comfort in buildings, and many other benefits. There are different types of refrigeration systems, each with its own working principle and components. One such type is the Vapour Absorption Refrigeration System (VARS).

Fundamentals of Vapour Absorption Refrigeration System

The Vapour Absorption Refrigeration System (VARS) operates on a different principle than the more commonly used Vapour Compression Refrigeration System (VCRS). While VCRS uses a compressor to increase the pressure of the refrigerant vapor, VARS uses an absorber, generator, condenser, evaporator, and solution pump to achieve the cooling effect.

Components of Vapour Absorption Refrigeration System

1. Absorber: The absorber is responsible for absorbing the refrigerant vapor into a liquid solution.
2. Generator: The generator heats the liquid solution, causing the refrigerant to vaporize.
3. Condenser: The condenser cools down the refrigerant vapor, converting it back into a liquid state.
4. Evaporator: The evaporator absorbs heat from the surroundings, causing the refrigerant to evaporate and cool the desired space.
5. Solution Pump: The solution pump circulates the liquid solution between the absorber and generator.

Working Cycle of Vapour Absorption Refrigeration System

The working cycle of VARS consists of four main processes:

1. Absorption Process: In this process, the refrigerant vapor is absorbed by the liquid solution in the absorber.
2. Generation Process: The liquid solution is heated in the generator, causing the refrigerant to vaporize.
3. Condensation Process: The refrigerant vapor is cooled down in the condenser, converting it back into a liquid state.
4. Expansion Process: The liquid refrigerant passes through an expansion valve, where it undergoes a pressure drop, resulting in evaporation and cooling in the evaporator.

Key Differences between Vapour Absorption Refrigeration System and Vapour Compression Refrigeration System

While both VARS and VCRS serve the purpose of refrigeration, there are several key differences between the two:

• VARS uses a liquid solution to absorb and release the refrigerant, while VCRS uses a compressor to increase the pressure of the refrigerant vapor.
• VARS can utilize low-grade or waste heat as an energy source, making it more energy-efficient in certain applications.
• VARS does not require CFCs or HFCs, making it more environmentally friendly.

Step-by-Step Walkthrough of a Typical Vapour Absorption Refrigeration System Problem

To better understand the application of VARS, let's go through a step-by-step walkthrough of a typical problem:

Problem Statement and Given Data

Suppose we have a Vapour Absorption Refrigeration System with the following specifications:

• Refrigerant: Ammonia (NH3)
• Absorber Temperature: 40°C
• Generator Temperature: 100°C
• Condenser Temperature: 30°C
• Evaporator Temperature: -10°C

Calculation of Refrigeration Capacity

The refrigeration capacity of a VARS is the amount of heat that can be removed from the desired space. It can be calculated using the following formula:

$$Refrigeration Capacity = \dot{m} \times (h_{evap} - h_{cond})$$

Where:

• $$\dot{m}$$ is the mass flow rate of the refrigerant
• $$h_{evap}$$ is the enthalpy of the refrigerant at the evaporator
• $$h_{cond}$$ is the enthalpy of the refrigerant at the condenser

Calculation of COP (Coefficient of Performance)

The Coefficient of Performance (COP) of a VARS is a measure of its efficiency and can be calculated using the following formula:

$$COP = \frac{Refrigeration Capacity}{Heat Input}$$

Where:

• Heat Input is the amount of heat supplied to the generator

Calculation of Heat Input and Heat Output

The heat input to the generator can be calculated using the following formula:

$$Heat Input = \dot{m} \times (h_{gen} - h_{abs})$$

Where:

• $$h_{gen}$$ is the enthalpy of the refrigerant at the generator
• $$h_{abs}$$ is the enthalpy of the refrigerant at the absorber

The heat output from the condenser can be calculated using the following formula:

$$Heat Output = \dot{m} \times (h_{cond} - h_{evap})$$

Solution to the Problem

Using the given data and the calculated values, we can determine the refrigeration capacity, COP, heat input, and heat output of the Vapour Absorption Refrigeration System.

Real-World Applications and Examples of Vapour Absorption Refrigeration System

Vapour Absorption Refrigeration Systems have various real-world applications, including:

Industrial Refrigeration Systems

VARS are commonly used in industries that require large-scale refrigeration, such as food processing, chemical manufacturing, and pharmaceutical production. These systems can efficiently cool and preserve perishable goods.

Air Conditioning Systems in Large Buildings

VARS can be used in air conditioning systems for large buildings, such as shopping malls, hotels, and office complexes. They can provide cooling while utilizing waste heat from other processes, making them energy-efficient.

Refrigeration Systems in Remote Areas or Places with Limited Electricity Supply

In remote areas or places with limited electricity supply, VARS can be a viable option for refrigeration. They can utilize low-grade or waste heat sources, such as solar energy or waste heat from industrial processes, to provide cooling.

Advantages and Disadvantages of Vapour Absorption Refrigeration System

Advantages

1. Use of low-grade or waste heat as an energy source: VARS can utilize low-grade or waste heat sources, making them more energy-efficient and cost-effective in certain applications.
2. Environmentally friendly due to the absence of CFCs or HFCs: VARS do not require CFCs or HFCs, which are harmful to the environment and contribute to ozone depletion and global warming.
3. Lower operating costs in certain applications: VARS can have lower operating costs compared to Vapour Compression Refrigeration Systems in applications where waste heat is readily available.

Disadvantages

1. Lower COP compared to Vapour Compression Refrigeration System: VARS typically have a lower Coefficient of Performance (COP) compared to Vapour Compression Refrigeration Systems, resulting in lower efficiency.
2. Larger physical size and higher initial cost: VARS systems are generally larger in size and have a higher initial cost compared to Vapour Compression Refrigeration Systems.
3. Limited range of refrigerants available: VARS systems have a limited range of refrigerants available compared to Vapour Compression Refrigeration Systems, which can limit their application in certain industries.

Conclusion

In conclusion, the Vapour Absorption Refrigeration System (VARS) is an alternative refrigeration system that operates on a different principle than the more commonly used Vapour Compression Refrigeration System (VCRS). VARS utilizes an absorber, generator, condenser, evaporator, and solution pump to achieve the cooling effect. It can utilize low-grade or waste heat as an energy source, making it more energy-efficient in certain applications. However, VARS has a lower COP compared to VCRS, larger physical size, and higher initial cost. Despite these disadvantages, VARS has various real-world applications in industries, large buildings, and remote areas with limited electricity supply.

Summary

The Vapour Absorption Refrigeration System (VARS) is an alternative refrigeration system that operates on a different principle than the more commonly used Vapour Compression Refrigeration System (VCRS). VARS utilizes an absorber, generator, condenser, evaporator, and solution pump to achieve the cooling effect. It can utilize low-grade or waste heat as an energy source, making it more energy-efficient in certain applications. However, VARS has a lower COP compared to VCRS, larger physical size, and higher initial cost. Despite these disadvantages, VARS has various real-world applications in industries, large buildings, and remote areas with limited electricity supply.

Analogy

Imagine a Vapour Absorption Refrigeration System (VARS) as a sponge that absorbs water and releases it when squeezed. In this analogy, the sponge represents the absorber, which absorbs the refrigerant vapor, and the squeezing action represents the generator, which heats the liquid solution to release the refrigerant vapor. The condensed water represents the refrigerant in the condenser, and the evaporation of water from the sponge represents the cooling effect in the evaporator. The solution pump can be compared to the movement of the sponge between the absorber and generator. This analogy helps visualize the working principle and components of VARS.