Advantages and Disadvantages of Carbon Dioxide Refrigerant

r744 40l

Carbon dioxide can be used as an ultra-low temperature refrigerant, code-named R744 refrigerant. Today, I will introduce the advantages and disadvantages of carbon dioxide refrigerants.

Carbon dioxide is a substance in nature, and it is also a very good refrigeration substance. In fact, carbon dioxide has been used as a refrigerant for hundreds of years, and it was widely used from the end of the 19th century to the 1930s. With the application of ammonia and freon refrigerants, carbon dioxide refrigerants were quickly replaced.

Can carbon dioxide be used as a refrigerant?

A refrigerant is a chemical substance that acts as an intermediary in a refrigeration unit. There are many substances that can be used as refrigerants, and the common ones are halogenated hydrocarbons and non-halogenated hydrocarbons.

Carbon dioxide can be used as a refrigerant. Refrigerants mainly realize the cooling effect through the mutual conversion between liquid and gas, and carbon dioxide can also convert gas and solid. Solid carbon dioxide is dry ice, which absorbs a lot of heat when it sublimes, so it can be used as a refrigerant.

Advantages of CO2 refrigerant

  1. Safety: CO2 refrigerant is non-toxic, non-flammable, has 0 ozone depletion potential and 1 global warming potential, and is environmentally friendly.
  2. Stable physical and chemical properties: CO2 refrigerant has a very low viscosity, has good compatibility with lubricating oil, and the pressure drop will not be too large, which can further reduce the size of components and the weight of the system.
  3. It has thermophysical properties compatible with the refrigeration cycle and equipment: the molecular weight of CO2 is small, the refrigeration capacity is large, and the unit refrigeration capacity at 0°C is 5-8 times higher than that of conventional refrigerants.
  4. Low critical temperature: It can be in a transcritical state in the cycle of the heat pump system, and the large temperature glide during the heat release process can be better matched with the variable temperature heat source.

Disadvantages of CO2 refrigerant

  1. High critical pressure: The critical pressure of CO2 refrigerant reaches 7.38MPa. The working pressure of the transcritical refrigeration cycle is much higher than that of the traditional subcritical two-phase refrigeration cycle, so the piping system through which the working medium flows in the refrigeration system must be analyzed for safety.
  2. The coefficient of performance of CO2 single-stage compression transcritical cycle is lower than that of conventional refrigerants at the same temperature. It may be possible to improve through research, such as perfecting the system circulation mode, optimizing system equipment, and using expanders, etc.

What fields are carbon dioxide refrigerants mainly used in?

Because of the disadvantages of carbon dioxide refrigerant, the efficiency of the carbon dioxide refrigeration system is still relatively low, and it is not widely used. It is mainly used in three aspects:

1. Automobile air conditioner

Automobile air-conditioning refrigerants emit a large amount of and are harmful to the environment. Therefore, harmless and environmentally friendly refrigerants should be used.

2. Heat pump water heater

There is a considerable temperature glide in the heat release of carbon dioxide under supercritical conditions, which is favorable for heating hot water to a higher temperature.

3. Act as a low-temperature grade refrigerant in a cascade refrigeration cycle, which is mainly due to the good low-temperature flow performance and heat transfer characteristics of carbon dioxide.


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