Refrigerant gases and applications - Starget

Refrigerant Gas Application and Related

Refrigerant gas is the working fluid in the refrigerator. It circulates in the refrigerator system and continuously exchanges energy with the outside world through the cyclic changes of its thermal state to achieve the purpose of refrigeration. It is customary to call the refrigeration working fluid refrigerant gas or working fluid.

Traditional Refrigerant Gas

1. R717 (ammonia)

Ammonia has good thermal and thermophysical properties. The standard evaporation temperature of ammonia is -33.3 degrees, and the freezing temperature is -77.7 degrees. Its pressure is relatively moderate in the normal and low-temperature range, and its working range is 22% larger than R22.

It has a large cooling capacity per unit volume, low viscosity, small flow resistance, low density, and good heat transfer performance.In addition, ammonia is cheap and easy to obtain, so it began to be used as a refrigerant in the 1860s.

The main disadvantages of ammonia are that it is highly toxic, flammable, and explosive. Ammonia splashing onto human skin can cause swelling and even frostbite. Ammonia vapor is colorless and has a strong, pungent odor.

2. Freon

Freon is a colorless, odorless, basically toxic, chemically stable, non-flammable, and explosive refrigerant. The thermal properties of Freon, with different chemical compositions and structures, vary greatly. Freon can be used as a high-temperature, medium-temperature, and low-temperature refrigerant to adapt to different refrigeration temperatures.

Traditional Freon refrigerant gasesthat were widely used in refrigeration and air-conditioning equipment in the past were R11, R12, etc.

1) R12
R12 is the safest refrigerant gas except for water. Its standard evaporation temperature is -29.8 degrees, and its solidification temperature is -158 degrees. It is a medium-temperature refrigerant.

2) R22
R22 is also a relatively safe refrigerant gas. Its standard evaporation temperature is -40.8 degrees, and its solidification temperature is -160 degrees. Its saturation pressure characteristics are similar to those of ammonia. Its cooling capacity per unit volume is also similar to that of ammonia, which is about 60% higher than that of R12 but more reliable than ammonia in use.

3) R11
R11 has a standard boiling point of 23.7 degrees and a solidification temperature of -111 degrees. It is a high-temperature refrigerant gas commonly used in chillers for air conditioning and some production processes. It can also be used in heat pump devices. When R11 is used as a refrigerant, the working pressure is very low, and the evaporation pressure is often negative. At the same time, its relative molecular mass is large, and the cooling capacity per unit volume is small, so it is generally used in centrifugal compressors.

4) R114
The standard boiling point of R114 is 3.6 degrees, which is between R11 and R12. As a refrigerant gas, it has low condensation pressure and high condensation temperature. It is suitable for air-cooled air conditioning and refrigeration systems in high-temperature environments. It is mainly used in small refrigerators, such as cooling equipment in steelmaking workshops. R142b has similar properties to R114.

5) R13, R14 and R23
The standard boiling points of R13 and R14 are -81.4 degrees and -128 degrees, respectively. They are low-temperature refrigerant gases. They are generally used in the low-temperature chemical industry and low-temperature research as the low-temperature part of the cascade compressor (often used in conjunction with R22). The molecules of R13 and R14 contain more fluorine atoms and no hydrogen atoms, so their chemical properties are very stable, non-toxic, and non-flammable.

The ODP value of R13 is 1.0, which is very serious for ozone destruction. However, its effect is small, and R23 can be used as a transitional substitute. The standard boiling point of R23 is -82.1 degrees. Its refrigeration temperature is very close to that of R13, but it is less harmful to the ozone layer than R13.

3. Mixed refrigerant

Mixed refrigerants are mixtures of two or more pure refrigerant gases. The thermodynamic characteristics of mixtures during phase change under constant pressure include azeotropic mixtures, near-azeotropic mixtures, and non-azeotropic mixtures.

1) Azeotropic mixture
Like pure refrigerant gases, azeotropic mixtures evaporate under constant pressure, the evaporation temperature remains constant, and the compositions of the gas and liquid phases are always the same.

2) Near azeotropic mixture
Near-azeotropic mixtures do not have azeotropic characteristics, but their mixed components have similar boiling points. Hence, the temperature slip during phase change at constant pressure is not large and can be regarded as approximately isothermal. Near-azeotropic mixtures have great development potential but may change their composition in the event of leakage, making them ideal perfusion alternatives for CFCs.

3) Non-azeotropic mixture
When a non-azeotropic mixture boils under constant pressure, the dew point line and bubble point line form a fish-shaped curve, and the temperature and composition vary greatly during the evaporation and condensation processes.

Alternative refrigerants

1) Substitute for R12
R12 is the earliest refrigerant gas discovered, used in large quantities, and has excellent performance. However, it is now unacceptable to the environment. It damages the ozone layer very seriously and has a high GWP value. It is one of the main banned “CFC” refrigerant gases. Substitute substances for R22 include R22, R134a, R152a, etc.

2) Substitute for R22
As the restriction period for HCFC substances approaches, research on alternatives to R22 is also ongoing. Currently, there are three alternative directions for R22: R407c, R410a, and R134a.

3) Replacement of R11
R11 has an ODP value of 1.0 and a GWP100 annual value of 3500. Due to its unacceptable environmental impact, it is listed as a key banned substance. Substitutes include R123 (which can only be used as a transitional alternative refrigerant gas), R245fa, and R245fa.

4) Substitute for R114
The main substitutes for R114 are: R124, R142b, R600, R600a, R227ea, R236ea, R236fa, etc.

5) Substitute for R502
R502 has been banned in developed countries, and its alternatives include transitional substitutes R22 and R125. Long-term mixed refrigerant gas alternatives include R404a, R407a, R407b and R507.

Natural refrigerants

1) Water
Water is also a commonly used refrigerant; its code name is R718. Water has many advantages as a refrigerant, such as non-toxic, odorless, non-flammable, non-explosive, wide source, thermal and chemical stability at high temperatures, high COP, high thermal conductivity, easy to obtain, and safe and cheap refrigeration agent. However, it is not suitable for use in compression refrigeration machines and is only suitable as a refrigerant in absorption and evaporative jet chillers. In addition, the lubrication problem must be solved.

2) Air
It was used as a refrigerant on airplanes a long time ago. Although the COP is very low, it is still valuable due to special operating conditions and strict specifications. However, due to the low COP, the proportion of TEW1 in energy consumption will be very high, so whether it can tolerate its high TEW1 needs further research.

3) Carbon dioxide
Carbon dioxide as a refrigerant dates back to the early 20th century. CO2 is non-toxic and relatively safe, so it was used in marine refrigeration devices for 50 years until it was replaced by Freon refrigerant in 1955.
Now since CO2 is not harmful to the environment, its use as a refrigerant can reduce its emissions in the atmosphere and will have a positive impact on the environment. Currently, carbon dioxide-hydrocarbon mixtures are proposed as possible refrigerants. CO2 helps reduce the flammability of hydrocarbons.

4) Hydrocarbons
The common characteristics of hydrocarbon refrigerants are:

  • Low freezing point;
  • No reaction with water;
  • No corrosion of metal;
  • Good oil solubility;

Since they are products of petrochemical processes, they are easily available and cheap. The common disadvantage is that they are highly explosive.

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