Refrigerant
A Refrigerant is a substance used in refrigeration systems that undergoes phase transitions (from liquid to gas and back) to transfer heat and provide cooling. Its main functions include absorbing heat from a space or substance, carrying that heat away through the refrigeration cycle, and releasing the absorbed heat outside the system.
Classification of Refrigerant
The refrigerants may be classified into two main groups according to their manner of absorption or extraction of heat from the substance to be refrigerated.
1. Primary Refrigerant
2. Secondary Refrigerant
1. Primary Refrigerant: The refrigerant which directly take part in the refrigeration system and cool substances by absorption of latent heat are called primacy refrigerant.
NOTE: Latent heat refers to the heat energy absorbed or released by a substance during a phase change, such as melting, freezing, evaporation, or condensation, without causing a change in temperature.
Such refrigerant are ammonia, carbon dioxide, Sulphur dioxide, and fluorinated hydrocarbons etc.
The primary refrigerant are further classified as:
- Halo-carbon Refrigerants
- Azeotrope Refrigerants
- Hydro-carbon Refrigerants
- Inorganic Refrigerants
- Unsaturated organic Refrigerants
2. Secondary Refrigerant: The refrigerant which are first cooled by primary refrigerant and then used for cooling substances by absorption of sensible heat are called secondary refrigerants.
NOTE: Sensible heat refers to the heat that causes a change in temperature of a substance without a change in phase. In other words, it is the heat transfer that results in a change in the temperature of a substance without causing it to change from a solid to a liquid, or from a liquid to a gas,
Such refrigerant are air, water, Calcium chloride brine, Sodium chloride brine, and similar non-freezing solutions. Secondary refrigerants are adopted for cooling in big commercial and industrial refrigeration plants like air conditioning installations and Ice factories.
Important properties of Refrigerant
Following are some of the important properties that a refrigerant should possess:
- It should have low Boiling point.
- It should be safe to Handle.
- It should be non-poisonous.
- It should be no explosive.
- It should be non-corrosive to metals.
- It should be non-flammable.
- It should be non-toxic.
- Its cost should be low.
- It should be easy to detect the leakage.
- It should be easily available.
- It should be able to withstand operating temperature and pressure.
- It should have low viscosity for a high heat transfer co-efficient.
- It should have low critical pressure to have low condensing pressure.
- Its freezing point should be lower than any temperature to be maintained in the refrigerating system.
Commonly used Refrigerants
1. R-11 (Trichlorofluoromethane):
Chemical Formula: CCl3F
Boiling Point: 23.8°C
The cylinder code for R-11 is orange.
Application: Used as a refrigerant in industrial applications, including centrifugal chillers and some HVAC systems. It also used where low freezing point and non-corrosive properties are important. Its leak may be detected by using a soap solution, a halide torch. However, its use has declined due to environmental concerns, as it is an ozone-depleting substance (ODP: 1).
2. R-12 (Dichloro-difluoro-methane):
Chemical Formula: CCl2F2
Boiling Point: -29.8°C
The cylinder code for R-12 is white.
Application: This refrigerant used in different types of industries and commercial applications equipped with reciprocating or rotary type compressors. Previously used in automotive air conditioning systems, refrigerators, and industrial chillers. Its leak may be detected by using a soap solution, a halide torch. However, it has been phased out due to its high ozone depletion potential (ODP: 1).
3. R-717 (Ammonia):
Chemical Formula: NH3
Boiling Point: -33.3°C
The cylinder code for R-717 (ammonia) is black.
Application: Widely used in industrial refrigeration systems, cold storage facilities, food processing, and ice rinks. Ammonia is known for its high efficiency, low cost, and minimal environmental impact, making it a preferred choice in large-scale refrigeration. To detect its leakage, a Sulphur candle is used which gives off a dense white smoke when ammonia vapour is present.
4. R-134a (1,1,1,2-Tetrafluoroethane):
Chemical Formula: C2H2F4
Boiling Point: -26.3°C
The cylinder code for R-134 (a) is sky blue.
Application: Commonly used in automotive air conditioning systems, residential and commercial refrigeration, and heat pumps. It is non-corrosive, non-flammable and having low toxicity. R-134a has replaced R-12 in many applications due to its lower environmental impact (ODP: 0) and relatively low global warming potential (GWP: 1430).
Selection of Refrigerant
The selection of a refrigerant depends on several factors, including environmental impact, performance, safety, regulatory compliance, cost, and application requirements. Here are important considerations for selecting a refrigerant:
1. Environmental Impact:
Global Warming Potential (GWP): Choose refrigerants with lower GWP to reduce their contribution to climate change.
Ozone Depletion Potential (ODP): Prefer refrigerants with zero or low ODP to protect the ozone layer.
2. Performance:
Efficiency: Select refrigerants with high energy efficiency to minimize operating costs.
Capacity: Consider the refrigeration capacity required for the application.
Temperature Range: Ensure the refrigerant can operate effectively within the required temperature range.
3. Safety:
Flammability: Choose non-flammable or low-flammability refrigerants for safety, especially in enclosed spaces.
Toxicity: Opt for non-toxic refrigerants to ensure safety for occupants and workers.
4. Regulatory Compliance:
Consider local and international regulations regarding refrigerant use, phase-outs, and environmental standards.
Ensure the selected refrigerant complies with industry standards and codes.
5. Application Requirements:
System Compatibility: Ensure the refrigerant is compatible with system materials, lubricants, and components.
Operating Conditions: Consider the operating pressure, temperature, and environmental conditions of the refrigeration system.
Application Type: Choose a refrigerant suitable for the specific application, such as residential, commercial, industrial, or automotive.
6. Cost:
Evaluate the cost of the refrigerant, including initial purchase, maintenance, and disposal/recycling costs.
Consider long-term cost savings through energy efficiency and environmental benefits.
7. Availability:
Ensure the refrigerant is readily available from suppliers and manufacturers.
Consider future availability and potential phase-outs or replacements.
8. Environmental Sustainability:
Consider the overall environmental impact of the refrigerant throughout its lifecycle, including production, use, and disposal/recycling.
Explore options for natural refrigerants or alternatives with minimal environmental impact.
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