What Properties Should the Gas Used As a Refrigerant Have?

In the refrigeration cycle, the refrigerant compresses the gas into high-temperature and high-pressure gas through the compressor, then cools and liquefies, expands and gasifies, and uses the low-temperature state at this time to lower the surrounding temperature. Various types of compressors are used for compression liquefaction. Among them, there is also a type in which the refrigerant is in direct contact with the motor. In such use, the refrigerant is required to have the following properties.

1. No toxicity and irritation
Refrigerant is generally used in a closed system and does not come into direct contact with the human body. However, when doing projects or encountering accidents, it is possible to inhale or come into contact with refrigerants. In this case, personal safety at work should also be guaranteed. Due to the irritating odor and toxicity of ammonia refrigerant, it will cause harm to the human body when it leaks, while Freon is almost non-toxic. However, when a large number of refrigerant leaks, due to the high specificity of Freon gas, it is easy to stay in a relatively low place. In addition, because it is colorless and odorless, it is not easy to find, so it is easy to cause hypoxia and even suffocation.

2. Non-flammable and explosive

Non-flammability and non-explosiveness are also reasons why leaks are not easy to detect. Freon used in the past is non-flammable.

3. The chemical and thermal properties are stable, and they will not decompose and deteriorate even if it is used for a long time.

4. It does not deteriorate the lubricating oil and has good solubility.

5. It is not easy to leak, and it is also easy to repair after leaking.

6. The price is cheap and easy to buy.

7. No pollution to the environment.

8. It can be liquefied under normal temperatures and low pressure.

9. At low temperatures, it can evaporate below atmospheric pressure.

10. Large latent heat of evaporation

When the liquid vaporizes, the more heat is taken from the surroundings, the greater the cooling capacity that can be produced with a smaller amount of refrigerant.

11. The volume of saturated steam per unit mass is small

When the saturated steam density is high, the displacement of the compressor is small, and the machine can be miniaturized.

12. Both the gas phase and liquid phase have low viscosity

As the refrigerant circulates through the unit, the higher the viscosity, the greater the resistance to flow and the less energy efficient the unit is.

13. High critical temperature and low freezing point

In general, when you pressurize a gas, it becomes a liquid. But above a certain temperature, no matter how much pressure is applied, it will not become a liquid. This temperature is called the critical temperature. Each gas has its own specific value.

14. Large thermal conductivity

In the refrigeration device, a heat exchanger is used, so the thermal conductivity is good, and the heat exchanger can be made small. Both gas and liquid need this property.

15. No damage to electrical insulation materials, good insulation.

In hermetic compressors, the refrigerant is in direct contact with electrical components such as motors during operation, so this property is important.

16. Does not corrode the metal parts of the machine

Ammonia reacts with copper and copper alloys to cause corrosion, so these metals cannot be used in the device. In the presence of moisture, Freon is almost non-corrosive to other metals except for aluminum alloys containing more magnesium.