In this article, we will learn the basics of refrigerant, various types, properties, working principles, basic details of R134a, R22, R410a, R290, R32, R407c, etc.
What is a Refrigerant? Basics & Definition
The refrigerant absorbs heat and leaves the cool air behind when moved forward in the refrigerating machine. Its state changes between liquid and gas due to the thermodynamic process. In air conditioners and refrigerators, refrigerants play a crucial role.
The number of refrigerants that can be used is limited. The most commonly used refrigerants were CFCs (chlorofluorocarbon) called freons, now replaced by HCFCs (hydrochlorofluorocarbon). We will explain in detail the various types of refrigerants in the latter part of this article.
Definition of Refrigerant
A heat-carrying medium that absorbs heat from a low-temperature system and discards this heat to a high-temperature system is called a refrigerant. It acts as a working fluid through which heat transfer takes place in the refrigeration cycle.
How Does Refrigerant Work?
Let’s see how does refrigerant work,
- In a refrigerating cycle, the refrigerant is in a liquid state when it reaches the expansion valve. Up to this point, its temperature gets reduced but its pressure is still high.
- When it passes through the expansion valve, expansion occurs and there is a sharp decrease in its pressure.
- This results in the reduction of its temperature. In this way, the refrigerants get chilled and converted to gas. Then the gaseous refrigerants enter the evaporator and absorbs heat from the surrounding area of the evaporator.
- Due to the absorption of heat, the refrigerating effect produces and the temperature of the refrigerant increases.
- Now gaseous refrigerant with temperature moves towards the compressor where its pressure increases.
- The hot refrigerant enters the condenser under high pressure. Its heat is released by the refrigerant to the fluid inside the condenser coil. The condenser can be water-cooled or air-cooled.
- After releasing heat, the refrigerant again converts to liquid and reaches the expansion valve to get chilled.
- This process is repeated continuously to produce a refrigerating effect in air conditioners and refrigerators.
Desirable Properties of Refrigerant
A single refrigerant is not suitable in all conditions. The choice of refrigerant is based on its chemical, physical and thermodynamic properties. There are some desirable properties that we need to look for during the refrigerant selection process.
We will mention some of the desirable properties of refrigerants. A selected refrigerant should have as many properties out of the following.
- The condensing pressure should be lower so that less power is required for compression. If the boiling point is high, condensing pressure will be low and vice versa. To work safely, the condenser tubes should be designed for high pressure.
- The critical pressure should be higher than condenser pressure. Similarly, the critical temperature needs to be higher.
- Low values of boiling and freezing point.
- The evaporator pressure should be higher. It will result in a reduction of moisture leakage and choking. It also reduces the power cost as compressor suction pressure increases.
- High latent heat of vaporization. According to the mass transfer equation, this will result in a lower value of the mass flow rate of refrigerant. Very small flow rates are also not desirable.
- The refrigerant in use should be non-toxic to humans and food materials.
- To keep a smaller compressor the refrigerant should have high vapor density and low specific volume.
- Another useful property is the high heat transfer coefficient.
- It should have low solubility of water, this will enhance resistance against corrosion. We can also avoid bursting of the tubes due to choking caused by the freezing of water particles.
- Low reactivity is another desirable property. The refrigerant should not react with the materials used in the thermodynamic cycle.
- It needs to be non-flammable, non-explosive, and mix well in oil.
- It should be of low cost and easily available in the market.
- Refrigerants are higher in price compared to other chemicals. Therefore, it is important to detect leaks on time. To do so we can use the odour method (ammonia, SO2) or using a leak indicator like a halide torch (freon leak).
- It needs to be environment friendly. It should have less ozone depletion potential (ODP) and less global warming potential (GWP).
Types of Refrigerants
Refrigerants used in the refrigerating machine are of two types.
- Primary refrigerants
- Secondary refrigerants
Those refrigerants which are used directly as working fluids are called primary refrigerants. It is used in vapor compression and vapor absorption refrigeration systems.
Here the refrigerants take part in the refrigeration cycle.
- R-32 and
- freon group.
Classification of Primary refrigerants
- Hydrocarbons (Methane, Ethane, Propane)
- Inorganic compounds (ammonia, CO2, SO2, air)
- Halocarbon compounds (R-11, R-12, R-13, R-21)
- Azeotropes (mixture of different refrigerants)
- Unsaturated organic compounds (refrigerants with ethylene and propylene base)
- Oxygen compounds (contains elements of oxygen, ethyl ether)
- Nitrogen compounds (contains elements of nitrogen, methylamine)
The refrigerants that are cooled by primary refrigerants and then used for cooling purposes are called secondary refrigerants. With the use of secondary refrigerants, the harmful environmental impacts of primary refrigerants can be minimized.
As it works safely, they are preferred to be used in refrigerating cycles.
- glycol, etc.
We use water in air conditioning systems for the purpose of cooling and dehumidification. Similarly, brine is used in refrigerating systems to maintain low temperatures.
Secondary refrigerants can be easily handled and their flow can be easily controlled. By controlling the flow, we can set the temperature at the desired value. By using secondary refrigerants, we can get rid of toxic refrigerants like ammonia.
Uses of Refrigerant
Let’s see the uses of refrigerants,
- Refrigerants have various applications. They are utilized both at a small scale like in-room air conditions and large scales like industrial spaces and commercial buildings. We will discuss some of the common refrigerants with their use.
- Refrigerants used in industrial spaces are water, R-134a, CO2, and ammonia. Refrigerants used in buildings are R-22, R-410a and R600.
- Being refrigerant water has perfect chemical and thermodynamic properties. Due to its ease of use, water is practiced as a refrigerant for decades.
- R-134a is also in refrigerant piping. The features of this refrigerant include minimum toxicity, thermal stability, and resistance to corrosion and combustion.
- Ammonia is the most commonly used refrigerant in refrigeration plants. It has a high COP (Coefficient of performance) value, and lower molecular weight.
- The refrigerant CO2 R744 has heavyweight, non-flammable and non-toxic nature. It is an environment-friendly refrigerant.
- R-410a is a commonly used refrigerant as it has no potential to cause ozone depletion. It can be used as an alternative to R-22.
- R-600 series refrigerant is environment-friendly as it doesn’t deplete the ozone layer and cannot cause global warming. It should be used with care.
- Hydrocarbon-based refrigerants along with chemicals can be utilized in air conditions, domestic and commercial refrigerating systems. These refrigerants need extra care during installations. Welding should be avoided in areas where this refrigerant is present.
- The refrigerants used in air conditions are R-22 and R-144.
- R-22 is also used in heat pumps, however, it can cause ozone depletion.
- For domestic refrigerators and water coolers, we make use of R-12, R-143a.
- In an ice plant, the first circuit uses ammonia and the second circuit uses brine.
- Inside car air conditioning, refrigerants like R-12, R-134a, R-22, and R-32 are applied.
Some of the common environment-friendly refrigerants are named:
- R-290 (second name- Care 40)
- R-450a (Recommended for refrigerators)
- R-513a (second name- Opteon X10)
- R-600a (second name- Care 10)
Properties of Common Refrigerants
As we had discussed various types of refrigerants, now the important properties of commonly used refrigerants are discussed below.
It is a stable, non-toxic, and non-flammable refrigerant. It is a low-pressure refrigerant. Leaks of this refrigerant can be detected by soap solution, halide torch method, or using an electronic detector.
The cylinder color code of R-11 is orange. Taking advantage of its low pressure it can be used in large centrifugal compressors of 200 TR and above.
It is a popular refrigerant, non-toxic and non-flammable. It is a colorless, odorless, and non-corrosive liquid.
Leaks of this refrigerant can be detected by soap solution, halide torch method, or using an electronic detector.
- The cylinder colour code of R-12 is white.
- It is used in refrigerators, freezers, air conditions, and water coolers.
- Taking advantage of its low latent heat value, it can be used in small refrigerating machines.
It is stable, non-toxic, and non-flammable. It is non-corrosive and has good solubility in oil.
- Leaks of this refrigerant can be detected that way as R-11 and R-12.
- The cylinder colour code of R-22 is green.
- It is used in reciprocating and centrifugal compressors.
R-32 is a flammable hydrofluorocarbon (HFC) refrigerant used as a replacement for R-22 and R-502. The chemical name is difluoromethane.
- It has the advantage of low GWP (Global Warming Potential) value.
- The performance of this refrigerant can be improved when combined with Hydrofluoroolefins (HFOs).
- It has a critical pressure of 5.78 MPa and a critical temperature of 78.11° C.
- It has zero ODP (Ozone Depletion Potential) value.
An HFC refrigerant is used as a replacement for R-12. This refrigerant is non-toxic, non-flammable, and non-corrosive.
- It has the chemical name tetrafluoroethylene.
- Being a high-pressure refrigerant, it has a critical pressure of 4.059 MPa and a critical temperature of 101.06° C.
- Currently, it is used in air-conditions of automobiles, and manufacturing processes.
- The cylinder color code is light blue. It has zero ODP value.
Propane is the chemical name of R-290 used as an alternative to R-22 and R-502.
- This refrigerant is highly flammable with a low GWP (Global Warming Potential) value.
- It has a critical pressure of 4.24 MPa and a critical temperature of 96.7° C.
- It is used in heat pumps and commercial refrigeration systems.
R-407c is a zeotropic HFC blend of R-32, R-125, R-134a.
- It is the first alternative to R-22 commercially.
- This refrigerant has very similar properties to R-22.
- It has a critical pressure of 4.63 MPa and a critical temperature of 86.03° C.
- The cylinder color code is burnt orange. It has zero ODP value.
R-410a is a zeotropic HFC blend of R-12 and R-125.
- This refrigerant is non-flammable and safe to use.
- Being a high-pressure refrigerant, it has a critical pressure of 4.902 MPa and a critical temperature of 71.8° C.
- It is used in domestic and commercial air-conditioning.
- The cylinder colour code is rose.
- It has zero ODP value.
Ammonia is the oldest and widely used refrigerant. It is a colorless gas. It is non-corrosive and has good solubility in oil.
Leaks of this refrigerant can be detected by burning sulphur candles which lead to the formation of white fumes.
- It is used in reciprocating compression systems and absorption systems.
- Other applications include cold storage, ice manufacturing plants, and food freezing plants.
Carbon dioxide (CO2)
Acting as dry ice, this refrigerant is non-toxic, non-irritating, and non-flammable. It is a non-corrosive, colorless, and odorless liquid.
Due to low efficiency, it is not used at a small scale in household units. However, the refrigerant can be utilized for large-scale industrial applications.
Sulphur dioxide, (SO2)
Produced by the combustion of sulphur in the air, this refrigerant is stable, non-flammable, and non-explosive. It has a very unpleasant and irritating odor.
- Leaks of this refrigerant can be detected by soap solution and ammonia swab.
- It is used in households and small commercial units.
- This refrigerant is used commercially as a preservative of food.
Disadvantage of Refrigerant
The ozone layer is a protective layer all around the earth’s atmosphere (stratosphere) that protects us from harmful sun rays. CFCs (chlorofluorocarbon) based refrigerants after release were causing continuous depletion of the ozone layer in the past. Other refrigerants sharing the same drawbacks are the halons group.
- Once depletion of the ozone layer is caused, holes appear in the ozone layer.
- In this case, harmful rays can easily pass through these holes and reach the earth’s surface.
- These harmful rays contain UV light which can cause damage to the human immune system, skin cancer, and eye disorder, etc.
Therefore, it is recommended to use only those refrigerants which don’t cause any damage to the ozone layer. As alternative HCFCs (hydrochlorofluorocarbon) are used in many refrigerating systems.
Another problem is global warming. Some refrigerants lead to an increase in earth temperature. The most common are CFCs and HCFCs. Therefore, it’s important to consider these factors while selecting a suitable refrigerant.
This article lists different types of refrigerants used in the refrigeration cycle and their properties. Hope you got familiar with famous refrigerants in detail. This will also help you in selecting a refrigerant that fits your needs. If you think anything is missed, please mention it by writing to us.
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