The letter “R” and a group of numbers or letters behind it represent refrigerants, which are written according to certain rules based on the composition of refrigerant molecules
1. Inorganic compounds
The abbreviation is specified as R7( )()
The numbers in parentheses are the integer part of the molecular weight of the inorganic substance.
2. Freon and alkanes CmH(2m+2)
The abbreviation is specified as R(m-1)(n+1)(x)B(z)
When the value is zero, it is omitted to write, and isomers are distinguished by adding lowercase English letters at the end.
Exceptions are n-butane and isobutane, represented by R600 and R600a (or R601)
3. Non-azeotropic mixing working fluid
The shorthand notation is R4( )()
The numbers in parentheses are the sequence numbers of the working fluid. Starting from 00, if the pure substances constituting the non-azeotropic mixture are the same, but the component content is different, capital English letters should be added at the end to show the distinction.
4. Azeotropic mixing working fluid
The shorthand notation is R5( )()
The number in brackets is the sequence number of the working fluid, starting from 00
5. Cycloalkanes, alkenes, and their halogenated substances
Abbreviated symbol requirements:
The halogenated substances of cycloalkanes and cycloalkanes start with the letter “RC”, and the halogenated substances of alkene and alkene start with the letter “R1”, and the subsequent number exclusion rules are indicated by the symbols of Freon and alkane. The digits in the layout rules are the same.
Examples of refrigerant symbols
|Compound name||Molecular formula||m、n、x、z||Sign|
|Compound name Molecular formula m, n, x, z value Abbreviation symbol
CFCl3 m=1, n=0, x=1 R11
GESON CHILLER GESON CHILLER commonly used refrigerants are R12, R22, R502, R134a, R404a, R407C, R417A, R-507, R-23, R-508A, R-508B, R-152a, but the most commonly used are R22, R404.
Principles of refrigerant selection
1.3.1, thermodynamic properties
There is a suitable pressure and pressure ratio within the working temperature range.
The unit cooling capacity q0 and the unit volume cooling capacity are relatively large.
The specific work w and the compression work per unit volume are small, and the cycle efficiency is high.
The final temperature of isentropic compression should not be too high to avoid deterioration of lubrication conditions or decomposition of the refrigerant itself at high temperatures.
1.3.2. The nature of migration
The viscosity and density should be as small as possible.
The thermal conductivity is large, which can increase the heat transfer coefficient and reduce the heat transfer area.
Evaporation pressure≧atmospheric pressure
The condensing pressure should not be too high
The ratio of condensing pressure to evaporating pressure should not be too large
The effect of refrigerants on metals and non-metals: Ammonia has no corrosive effect on steel,
and has a slight corrosive effect on copper, aluminum or copper alloys.
However, if there is water in NH3, it has strong effects on copper and copper alloys (except phosphor bronze).
The corrosive effect of halogenated hydrocarbons;
when containing water, halogenated hydrocarbons will corrode metals, so the mixture of water-containing refrigerant and lubricating oil can dissolve copper,
and then deposit on the higher temperature steel parts to form a copper film, which is the so-called copper plating Phenomenon.
It will affect the fitting clearance of the moving parts of the compressor and the sealing of the suction and exhaust valves, and make the compressor unable to work in severe cases.
- The electrical insulation of the refrigerant: In a hermetic compressor, the coil of the motor is in direct contact with the refrigerant, and the refrigerant is required to have good electrical insulation properties.
Currently, commonly used refrigerants are R22, R134a, R407C, etc.
• Solubility with water:
NH3 is easily soluble in water, and the freezing point of its aqueous solution is below 0℃, so there will be no ice blockage in the NH3 system, but it is corrosive to metals; water in the fluorine system will cause ice blockage. In addition, Hydrolysis will also occur, generating acidic substances, corroding metals, and reducing the electrical insulation performance of the windings, so no water is allowed in the system.
• Solubility with lubricating oil:
different refrigerants and lubricating oil have different solubilities. NH3 is almost insoluble with lubricating oil; R22 is partially miscible with mineral oil and is completely miscible at high temperatures. At low temperatures, it is layered. Mineral oil is insoluble.
• When the refrigerant and lubricating oil are mutually soluble.
they can penetrate into various parts together with the refrigerant to form good lubrication, but the viscosity of the oil after the refrigerant is dissolved decreases.
Boiling point -33.3℃, freezing point -77.9℃
Large cooling capacity per unit volume, low viscosity, good heat transfer, low flow resistance
Toxic, with certain flammability, safety classification is B2
Ammonia vapor is colorless and has a strong pungent odor
Ammonia splash on the skin can cause swelling and even frostbite
Moisture in the ammonia system will increase metal corrosion and reduce cooling capacity
It is miscible with water in any ratio but has little solubility in mineral lubricating oil
The free hydrogen separated by ammonia in the system accumulates to a certain extent and explodes in air
The specific gravity of ammonia liquid is smaller than that of mineral lubricating oil, and the lower part of the oil deposit needs to be discharged regularly
Copper and copper alloy materials are not used in ammonia refrigerators (except phosphor bronze)
(1) R134a (Tetrafluoroethane CH2FCF3)
Non-toxic, non-flammable and safe.
Incompatible with mineral lubricants, but can be completely dissolved in polyol esters.
The chemical stability is very good, the water solubility is much stronger than that of R12, and the system has higher requirements for dryness and cleanliness. Use a different desiccant from R12.
(2) R22 (Difluorochloromethane CHF2Cl)
The boiling point is -40.8°C, and the freezing point is -160°C.
Non-toxic, colorless, tasteless, non-flammable, and non-explosive, safe.
The water solubility is slightly greater than R12, and a dryer should be installed in the system.
Partly miscible with mineral lubricants.
The chemical properties are not as stable as R12, and the swelling effect on the organic matter is stronger.
The effect on metals and non-metals and the leakage characteristics are similar to those of R12.
Refrigerants belonging to the HCFC category must also be restricted and prohibited from being used.
When evaporating under a certain evaporating pressure, the evaporating temperature is almost constant, and the evaporating temperature is generally lower than the evaporating temperature of the single component that composes it.
At a certain evaporating temperature, the refrigerating capacity per unit volume of an azeotropic refrigerant is greater than the volumetric refrigerating capacity of the single refrigerant that composes it.
The chemical stability of azeotropic refrigerant is better than that of the single refrigerant that composes it. In hermetic and semi-hermetic compressors, the use of azeotropic refrigerants can provide better cooling of the motor and reduce the temperature rise of the motor windings.
1) Non-azeotropic refrigerants R401A and R401B
Can be used as a transitional substitute
Performance is closer to R12.
2) Non-azeotropic refrigerant R407C ternary non-azeotropic mixed refrigerant
It is soluble in polyol and polyester lubricants. The bubble and dew point temperature difference is large, so it is best to use the heat exchanger as a counter-current type; under low-temperature conditions, the volumetric refrigeration capacity is much lower than R22. Not miscible with mineral lubricants, but soluble in polyester synthetic lubricants
3) Non-azeotropic refrigerant R410A binary mixed refrigerant
The bubble dew point temperature difference is only 0.2℃, which can be called a near-azeotropic mixed refrigerant.
Not miscible with mineral lubricating oil, but soluble in polyester synthetic lubricating oil.
It has similar advantages as an azeotropic refrigerant.
It cannot be used directly to replace the R22 refrigeration system.
The heat in the object or space to be cooled is transferred to the coolant through an intermediate medium, which is called the coolant
(1) When choosing coolant, the following factors should be considered:
It should be in a liquid state at working temperature;
the freezing temperature should be lower than the working temperature, and the boiling point should be higher than the working temperature;
The specific heat capacity is large, and when a certain amount of cold is transferred, the flow can be reduced, thus improving the economy of the cycle;
Small density and viscosity to reduce flow resistance, improve heat transfer effect, and reduce energy consumption;
Good chemical stability. It does not decompose at working temperature, does not chemically react with oxygen in the air, and does not change physical and chemical properties;
Non-toxic, tasteless, non-flammable and explosive, good chemical stability, non-corrosive to metals, and does not pollute the environment;
Low price and easy to obtain.
Commonly used refrigerants for GESON CHILLER are water, brine, ethylene glycol or propylene glycol solution, dichloromethane and trichloroethylene.
Commonly used coolants include air, water, brine, organic compounds, and their aqueous solutions.
The price is low and easy to obtain, but the specific heat capacity is small (about 1kj/kg.K), and the thermal conductivity is small, which affects the scope of use.
Suitable refrigerants for air-conditioning systems have the advantages of large specific heat capacity, large thermal conductivity, low price, and easy availability, but they have a low freezing point and will freeze at 0°C. Therefore, it cannot be used in refrigeration systems below 0 ℃
- Brine water:
Salts, such as aqueous solutions of sodium chloride and calcium chloride, are called brine.
The freezing point of brine is lower than that of pure water,
so it can be used as a refrigerant in devices where the evaporation temperature is lower than 0 ℃. His main disadvantage is that it is corrosive to some metal materials.
- Organic refrigerant:
The aqueous solutions of ethylene glycol, glycerol, and glycerol are all low-temperature refrigerants with better performance.
The freezing point of these aqueous solutions is lower than that of water and has no corrosive effect on metal materials such as pipes and containers. Among them, ethylene glycol aqueous solution is the most widely used organic refrigerant.
25% ethylene glycol aqueous solution is commonly used in ice storage systems.
- The principle of using brine solution is:
to ensure that the brine in the evaporator does not freeze, and the freezing point of the brine solution should not be selected too low, because this will increase the density, increase the flow resistance, and reduce the specific heat capacity to deliver the same cold. The amount of circulation required to increase the amount of energy will increase the power consumption. Generally, the freezing point temperature of the brine solution is about 5°C lower than the refrigerant evaporation temperature.
- The salt solution has a strong corrosive effect on metals and will corrode pipelines and equipment.
In order to reduce its corrosiveness, the following measures can be taken: a. Improve the purity of the salt; b. Reduce the contact with the air and adopt a closed cycle; c. Add corrosion inhibitor
- Sodium chloride and calcium chloride have a corrosive effect on metals, so corrosion inhibitors should be added during use, and the pH of the solution should be adjusted to 7-8.5.
The role of lubricating oil
Lubricate all moving parts to reduce friction and wear;
Lubrication: part of the injected oil is attached to the working cavity and between the spiral surfaces of the rotor to lubricate the rotor and provide lubrication for the bearing to keep the moving parts at a low temperature to improve efficiency;
For cooling, the injected oil is in the form of droplets and mixes with the gas to form a strong heat exchange surface, which quickly absorbs the compression heat of the gas, cools the medium and rotor, and lowers the exhaust temperature.
An oil film is formed between the rotors of the screw compressor and between the rotor and the body to play a sealing role;
In the screw compressor, the pressure difference of the lubricating oil is used to push the slide valve to adjust the energy.
Performance Index of Lubricant
(1) Under operating conditions, the lubricating oil should have an appropriate viscosity
(2) The viscosity of lubricating oil should be as small as possible with temperature changes
The proper lubricating oil viscosity is the guarantee to ensure the normal operation of the refrigeration compressor. If the viscosity is too low, a suitable oil film cannot be formed, and it also affects the sealing performance; if the viscosity is too high, the compressor will consume too much work. In addition, because the viscosity of the lubricating oil on the high-temperature side of the compressor should not be reduced too much, and the viscosity of the lubricating oil on the low-temperature side should not be too large, the lubricating oil must not only have a certain viscosity but also ensure that the lubricating oil changes with temperature. Try to be as small as possible.
(3) The freezing point should be low, and it has better fluidity at low temperatures
(4) No moisture, non-condensable gas and paraffin wax
(5) It has good compatibility with refrigerants, and has good thermal and chemical stability.
Because the lubricating oil is in direct contact with the refrigerant, and part of it circulates with the refrigerant, it contacts the motor coils, gaskets, etc., that is, it has to experience the highest temperature of the compressor discharge, but also the lowest temperature of the expansion valve and evaporator. Therefore, lubricating oil is required to have stable chemical properties and compatibility, excellent low-temperature fluidity, lubricity, and no pollution to the environment.
(6) The insulation withstand voltage should be high
(7) Low price and easy to obtain
According to the manufacturing process, it can be divided into two categories:
(1) Natural mineral oil: referred to as mineral oil. That is, lubricating oil extracted from petroleum. It usually has a smaller polarity, and they can only be dissolved in weakly polar or non-polar refrigerants, such as R600a, R12, R22, etc.
(2) Synthetic oil: referred to as synthetic oil. That is, according to the requirements of specific refrigerants, synthetic lubricants are synthesized by artificial chemical methods. Synthetic oils usually have strong polarity, and they can be dissolved in strong polar refrigerants, such as R134a, R717, etc. Synthetic lubricants mainly include: polyols, polyesters and polar synthetic hydrocarbons.
The solubility of refrigerant and lubricating oil is an important characteristic of the refrigerant. According to the degree of mutual solubility of refrigerant and lubricating oil, it can be divided into three categories:
(1) Insoluble or slightly soluble in lubricating oil
This type of refrigerant hardly dissolves in lubricating oil. When they are mixed with lubricating oil, there is obvious stratification, and the oil is easily separated from the refrigerant. In this type of refrigeration punishment, there are R717, NR13, R115 and R12 substitutes R134a and so on.
(2) Completely dissolve in lubricating oil
Such refrigerants and oils dissolve into uniform solution refrigerants such as R11, R12, R113, R500, etc.
(3) Limited dissolution in lubricating oil
This kind of refrigeration punishment dissolves infinitely with oil at high temperature, but the dissolution of refrigerant and oil at low temperature is divided into two layers, namely the oil supply layer and the oil lean layer. These refrigerants include R 22, R114, R502 and so on.
- Refrigerant dissolved in lubricating oil has the following benefits:
No oil film will be formed on the surface of the heat exchanger, thus avoiding the adverse effect of grease on heat transfer. The lubricating oil is decomposed into the refrigerant to lower its freezing point, which is beneficial for low-temperature systems; the lubricating oil can penetrate with the refrigerant To all parts of the compressor, a good lubrication condition is formed; good oil return from the condenser and evaporator to the compressor, etc.
- The disadvantage is that after the compressor has been shut down for a long time, a large amount of refrigerant will accumulate in the crankcase. When the compressor restarts, the pressure in the crankcase suddenly drops, and a large amount of working fluid escapes from the lubricating oil, causing the lubricating oil to boil and foam, forming a phenomenon of “oil running”, making it difficult to build up oil pressure; the refrigerant dissolves in the lubricating oil, Reduce the concentration of lubricating oil, causing the lubricating surface oil film to be too thin or not to form an oil film, which affects its lubrication; the characteristics of the solution of the refrigerant and the lubricating oil deviate from the characteristics of the pure refrigerant, and it dissolves in the refrigeration torture under the same pressure The more lubricating oil, the higher the evaporation temperature.
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