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Four Flammable and Explosive Refrigerants
- October 8, 2022
- Fonsum
The refrigerant is the working medium of the refrigeration cycle. It uses the phase change of the refrigerant to transfer heat, that is, the refrigerant absorbs heat when it vaporizes in the evaporator and releases heat when it condenses in the condenser. At present, there are more than 80 kinds of substances that can be used as refrigerants, and the more commonly used ones are ammonia, freons, water and a few hydrocarbons. The following four flammable and explosive refrigerants must be used and purchased carefully.
1. R32 refrigerant
R32, also known as difluoromethane and carbon difluoride, is colorless and odorless, and its safety level is A2. R32 is a freon substitute with excellent thermodynamic properties, with a low boiling point, low vapor pressure and pressure ratio, large refrigeration coefficient, zero ozone depletion value, small greenhouse effect coefficient, flammable and explosive, etc. The combustion limit in the air is 15%~31%, and it will burn and explode in case of an open fire. R32 has a lower viscosity coefficient and higher thermal conductivity. Although R32 has many advantages, R32 is a flammable and explosive refrigerant, and the installation and maintenance of air conditioners is a dangerous job. Now coupled with the uncertain factors of R32, safety issues have to be considered. Vacuuming is required for the installation and welding of R32 refrigeration equipment.
2. R290 refrigerant
R290 (propane) is a new type of environmentally friendly refrigerant, mainly used in central air conditioners, heat pump air conditioners, household air conditioners, and other small refrigeration equipment. As a hydrocarbon refrigerant, R290 has an ODP value of 0 and a GWP value of less than 20. Compared with common refrigerants, R290 has obvious environmental protection advantages.
In addition, R290 refrigerant has the characteristics of larger latent heat of evaporation, good fluidity, and energy saving. However, due to its flammable and explosive characteristics, the filling amount is limited, and the safety level is A3. When using R290 refrigerant, a vacuum is required, and open flames are prohibited because the mixture of air (oxygen) can form an explosive mixture, and there is a danger of combustion and explosion in case of heat sources and open flames.
3. R600a refrigerant
R600a (isobutane) is a new type of hydrocarbon refrigerant with excellent performance, which is derived from natural ingredients, does not damage the ozone layer, has no greenhouse effect, and is environmentally friendly. It is characterized by the large latent heat of evaporation, strong cooling capacity, good flow performance, low delivery pressure, low power consumption, slow load temperature recovery, and compatibility with various compressor lubricating oils. It is a colorless gas at room temperature and a colorless and transparent liquid under its own pressure. R600a is mainly used to replace R12 refrigerant, and now it is mostly used in household refrigerator equipment. The explosion limit volume of R600a refrigerant is 1.9% to 8.4%, and the safety level is A3. It can form an explosive mixture when mixed with air. It may burn and explode when it encounters heat sources and open flames, and it reacts violently when it contacts with oxidants. Its vapor is heavier than air and can spread to a considerable distance at a lower place.
4. R717 (ammonia) refrigerant
Finally, let’s talk about R717 (ammonia) refrigerant. Ammonia is more dangerous than the above three refrigerants, it belongs to the toxic medium, and the toxicity is grade 2. When the volume concentration of ammonia vapor in the air reaches 0.5 to 0.6%, people can be poisoned if they stay in it for half an hour. The nature of ammonia determines that the ammonia system must be operated and maintained properly.
Ammonia is a medium-temperature refrigerant. Pure ammonia has no adverse effect on lubricating oil, but when there is moisture, it will reduce the lubricating effect of refrigeration oil. Copper and copper alloys are not used for pipes and valves in ammonia refrigeration systems. The advantages of ammonia as a refrigerant are easy availability, low price, moderate pressure, large unit cooling capacity, high heat release coefficient, almost insoluble in oil, low flow resistance, easy to find when leaking, no damage to the ozone layer, and no greenhouse effect. The disadvantage is that it has a pungent odor, is toxic, can burn and explode, and has a corrosive effect on copper and copper alloys.
When the volume of ammonia vapor in the air reaches 0.5-0.6%, it can cause an explosion. Therefore, the concentration of ammonia in the air in the equipment room shall not exceed 0.02 mg/L. Ammonia is a combustible gas at room temperature, the explosion limit is 16% to 25%, the most easily ignited concentration is 17%, and the concentration when the maximum explosion pressure is generated is 22.5%.
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