Among them, only the following are widely used:
1, ammonia
(code: R7 17)
Ammonia is the most widely used medium and medium temperature refrigerant. The solidification temperature of ammonia is -77.7℃, the standard evaporation temperature is -33.3℃, and the normal temperature condensation pressure is generally1.1~1.3 MPa. Even when the temperature of cooling water is as high as 30℃ in summer, it will never exceed 1.5MPa, and the refrigeration capacity per unit standard volume of ammonia is about 520kcal/m3.
Ammonia water has good water absorption, so it will not precipitate from ammonia solution and freeze even if it is launched at low temperature, so there will be no "ice jam" in the system. Ammonia has no corrosive effect on steel, but it has corrosive effect on copper and copper alloys after containing water in ammonia solution, and the evaporation temperature rises slightly. Therefore, copper and copper alloy materials cannot be used in ammonia refrigeration equipment, and the moisture content in ammonia should not exceed 0.2%.
2. Freon-12
(code: R 12)
R 12 is haloalkane, the scientific name is difluoromethane, and the molecular formula is CF2Cl2. It is a medium-pressure and medium-temperature refrigerant widely used in small and medium-sized refrigeration devices in China. The standard evaporation temperature of R 12 is -29.8℃, the condensation pressure is generally 0.78 ~ 0.98 MPa, the solidification temperature is-155℃, and the standard refrigerating capacity per unit volume is about 288kcal/m3.
R 12 is a colorless, transparent, tasteless, almost non-toxic, non-flammable, non-explosive and very safe refrigerant. Only when the volume concentration in the air exceeds 80% can people suffocate. However, when exposed to naked flame or the temperature reaches above 400℃, gases harmful to human body will be decomposed.
R 12 can be mixed with lubricating oil in any proportion, and can dissolve various organic substances, but its water absorption is extremely weak. Therefore, in a small Freon refrigeration unit, there is no oil separator but a dryer. At the same time, it is stipulated that the water content in R 12 should not be greater than 0.0025%, and ordinary natural rubber should not be used as sealing gasket in the system, but artificial rubber such as nitrile rubber or chloroethanol should be used. Otherwise, the gasket will expand and the refrigerant will leak.
3. Freon -22
(code name: R22)
R22 is also a haloalkane, the scientific name is dichloromethane, the molecular formula is CHClF2, the standard evaporation temperature is about -4 1℃, the solidification temperature is about-160℃, the condensation pressure is similar to that of ammonia, and the standard refrigeration capacity per unit volume is about 454kcal/m3.
Many properties of R22 are similar to R 12, but its chemical stability is not as good as R 12, and its toxicity is slightly higher than R 12. The refrigerating capacity per unit volume of R22 is much larger than that of R 12 and close to that of ammonia. When the low temperature of -40 ~-70℃ is needed, R22 is more suitable than R 12, so R22 is widely used in the two-stage compression or air conditioning refrigeration system of -40 ~-60℃.
4、R- 134a
(code: R 134a)
Molecular formula: CH 2 FCF 3 (tetrafluoroethane), molecular weight: 102.03.
Boiling point: -26.26℃, freezing point: -96.6℃, critical temperature: 10 1. 1℃, critical pressure: 4067kpa.
Saturated liquid density: 25℃, 1.207g/cm 3, liquid specific heat: 25℃, 1.5 1kJ/(kg℃).
Solubility (in water at 25℃): 0. 15%, critical density: 0.5 12g/cm3.
Ozone destruction potential (ODP): 0, global warming coefficient (GWP) :0.29.
Evaporation potential at boiling point: 2 15 kJ/kg.
Quality indicators: purity ≥ 99.9%, moisture PPm≤ 0.00 10, acidity PPm≤ 0.0000 1, evaporation residue PPm≤ 0.0 1.
As an alternative refrigerant of R 134a, many characteristics of R 12 are very similar.
R 134a is extremely low in toxicity and nonflammable in air. The safety category is A 1, which is a very safe refrigerant.
5.R-404A refrigerant
Physical and chemical characteristics: R404A is a chlorine-free non-boiling mixed refrigerant, which is colorless gas at normal temperature and pressure, compressed liquefied gas and stored in steel cylinders. Its ODP is 0, so R404A is an environmentally friendly refrigerant that does not destroy the atmospheric ozone layer. Main uses: R404A is mainly used to replace R22 and R502. It is clean, low toxic, non-flammable and has good refrigeration effect, and is widely used in medium and low temperature refrigeration systems.
6.R-4 10A refrigerant
Physical and chemical characteristics: At normal temperature and pressure, R4 10A is a non-boiling mixed refrigerant without chlorofluoroalkyl, a colorless gas, and a compressed liquefied gas stored in a steel cylinder. Its ODP is 0, so R4 10A is an environmentally friendly refrigerant that does not destroy the atmospheric ozone layer.
Main uses: widely used in household air conditioners, small commercial air conditioners, household central air conditioners, etc.
7, * * * boiling refrigerant
This formula was not published. When used in cascade refrigerator, the evaporation temperature can reach about-150 degrees under the premise of air condensation.
8. hydrocarbon refrigerants
Mainly energy saving and environmental protection; Energy saving: R433b air conditioner can save energy 134, R22 air conditioner can save energy by about 35% to 15%. Environmental protection: Hydrocarbon refrigerant is a natural working medium, so it has no pollution to the atmosphere and no damage to the ozone layer, and the greenhouse effect is almost zero.
Extended data
harm
1, ozone layer depletion.
1February, 985, J.Farman, the captain of the British Antarctic expedition, reported for the first time that from 1977, it was found that the total ozone over the Antarctic began to decrease by about half in late September every year, forming an "ozone hole", which continued to recover gradually from165438+1October, causing
Ozone-depleting compounds are not only used in snow seeds, but also used as aerosol propellants, foaming agents and cleaning agents in the production of electronic equipment. Long-lived bromine-containing compounds, such as Haion fire extinguishing agent, also play a great role in ozone depletion.
Chlorine atoms and nitric oxide (NO) can react with ozone. CFCs are produced and used in large quantities in the world. Because of its good chemical stability (for example, CFC 12 in atmospheric lifetime is 102), it is not easy to decompose in the troposphere and enters the stratosphere where the ozone layer is located through atmospheric circulation. Under the irradiation of short-wave ultraviolet (UV-C), they decompose CI free radicals and participate in ozone consumption.
To sum up, in order to consume ozone, this substance must have two characteristics: chlorine, bromine or another similar atom participates in the chemical reaction of ozone to produce oxygen; It must be very stable in the lower atmosphere (that is, it has a long enough atmospheric lifetime) so that it can reach the ozone layer.
For example, HCF22 and HCFC 123 have a chlorine atom, which can consume ozone. Their atmospheric lifetime values are 12. 1 and 14 years respectively. The chlorine atom is relatively active and can be decomposed in the lower atmosphere, so the amount reaching the ozone layer is very small. Therefore, the ability of HCFC22 and HCFC 123 to destroy ozone is much less than that of CFCs.
2. Timetable
The timetable for eliminating snow species in China's national plan;
1) Since1July 1999, the annual production and consumption of CFCs have been frozen at the average level of 1995- 1997;
2) Reduce the freezing level by 50% from June 65438+1 October12005;
3) Reduce the freezing level from 1 in 2007 by 85%;
4) CFC was completely stopped from 20 1 0 65438+10/month1.
3. Objectives
The national plan stipulates the specific elimination targets of the air-conditioning industry.
1) industrial and commercial refrigeration
The new filling of CFC11/2 stopped in 2003, and the refilling of CFC112 maintenance supplement stopped in 20 10.
2) Household appliances
1999 40% of newly produced refrigerators and freezers were replaced, 70% of newly produced refrigerators and freezers were replaced in 2003 and 0/00% of newly produced refrigerators and freezers were replaced in 2005.
3) Automobile air conditioning
In 2002, the new production of CFC 12 air conditioners was stopped, and after 2009, only recycled CFC was allowed to be used in automobile air conditioners.
China has only signed the London Amendment to the Protocol, so there is no commitment to phase out HCFCs.
Baidu encyclopedia -HCFCs
Baidu encyclopedia-refrigerant