Refrigerants & Basic principles for selection of refrigerants

A refrigerant is a substance or mixture, usually a fluid, used in a heat pump and refrigeration cycle. In most cycles it undergoes phase transitions from a liquid to a gas and back again. Many working fluids have been used for such purposes. Fluorocarbons, especially chlorofluorocarbons, became commonplace in the 20th century, but they are being phased out because of their ozone depletion effects. Other common refrigerants used in various applications are ammonia, sulfur dioxide, and non halogenated hydrocarbons such as propane.

How Refrigerant Works

Without refrigerant, there would be no air conditioning, refrigeration or freezing technology. Air conditioners contain refrigerant inside copper coils. As refrigerant absorbs heat from indoor air, it transitions from a low-pressure gas to a high-pressure liquid. Air conditioning components send the refrigerant outside where a fan blows hot air over the coils and exhausts it to the exterior.

The refrigerant then cools down and turns back into a low-pressure gas. Another fan located inside the home blows air over the cool coils to distribute the resulting cold air throughout the building. Then the cycle repeats.

Types of Refrigerants

The most common refrigerants used for air conditioning over the years include:

  • Chlorofluorocarbons (CFCs), including R12. This is known to contribute to the greenhouse gas effect. Production of new stocks ceased in 1994.
  • Hydrochlorofluorocarbons (HCFCs), including R22. Slightly less damaging to the ozone than R12, but the EPA has still mandated a phase out as a result of the Clean Air Act of 2010. R22 will phase out completely by 2020.
  • Hydrofluorocarbons (HFCs), including R410A and R134. With no chlorine in the mix, this is safer for the environment and is now being used in place of R22. Air conditioners that run on R410A are more efficient, offer better air quality, increase comfort and improve reliability.

Basic principles for selection of refrigerants:

1. The critical temperature should be higher, and the phase transition can occur at room temperature or under normal temperature.

2. Low freezing temperature, so as to avoid the solidification of the refrigerant at the evaporation temperature.

3. Small viscosity and density, so as to reduce the loss of flow resistance of the refrigeration system.

4. High thermal conductivity, so as to improve the heat transfer coefficient of the heat exchanger and reduce the heat transfer area and metal material consumption.

5. Small adiabatic exponent.

6. Small liquid heat capacity.

7. Low price and easy to get.

8. No burning, no explosion, no poison, no corrosive effect on metals, no decomposition under high temperature and no harmless to human body.

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