What Are the Different Types of Commercial Refrigeration?
Refrigerants , also known as refrigerants , refrigerants , and refrigerants , are the media materials through which various types of heat engines complete energy conversion. These substances usually increase power with reversible phase transitions (such as gas-liquid phase transitions). Such as steam in steam engines, snow in refrigerators, and so on. When a normal steam engine is in operation, the thermal energy of the steam is released and converted into mechanical energy to generate the motive power; while the snow of the refrigerator is used to transmit the heat at low temperature to the high temperature.
1805
The code name of the refrigerant was first stipulated for Freon. At the time of publication, the world generally used the provisions of the American Heating and Refrigerating Engineering Association (ASHRAE Standard 34-67) in 1967. This standard numbering method is to associate the code of a refrigerant with its species and chemical composition. As long as you know its chemical formula, you can write its code. The code name is composed of the letter "R" and the digits after it. R stands for Refrigerant (Refrigerant), and F stands for Freon. In the text, R was named as a refrigerant. [2]
(1) It has excellent thermodynamic characteristics in order to have higher cycle efficiency when operating in a given temperature range. The specific requirements are: the critical temperature is higher than
At the time of publication, the number of refrigerants used has reached 70 to 80, and is constantly increasing. But only a dozen or more are used in the food industry and air-conditioning refrigeration. Among them, only the following are widely used: [2]
1. There are several types of ingredients.
(1) Inorganic compounds. Water, ammonia, carbon dioxide, etc.
(2) Derivatives of saturated hydrocarbons, commonly known as Freon. Mainly derivatives of methane and ethane. Such as R12, R22, R134a and so on.
(3) Saturated hydrocarbons. Such as propane, isobutane, etc.
(4) Unsaturated hydrocarbons. Such as ethylene, propylene and so on.
(5) Azeotropic refrigerant mixture. Such as R502 and so on.
(6) Non-azeotropic mixed refrigerant. Such as R407c, R410 and so on.
Generally according to the standard evaporation temperature of the refrigerant, it is divided into three types: high, medium and low temperature. Standard evaporation temperature refers to the evaporation temperature at standard atmospheric pressure, which is the boiling point.
(1) High temperature (low pressure): standard evaporation temperature (tS)> 0 , condensing pressure (PC) 0.2 0.3Mpa, commonly used R123, etc.
(2) Medium temperature (medium pressure): 0 > tS> -60 , 0.3Mpa <PC <2.0 Mpa, commonly used are ammonia, R12, R22, R134a, propane and so on.
(3) Low temperature (high pressure): tS -60 ° C. Commonly used are R13, ethylene, R744 (CO2), etc.
2. Numbering and labeling methods;
In accordance with international uniform regulations, the letter R is used to represent the refrigerant, plus the following numbers and letters are clearly specified in GB7778-1987. Briefly described as follows:
(1) Inorganic compounds.
Integer composition specified as R700 plus the relative molecular mass of the inorganic compound
NH3 (ammonia) H2O (water) CO2 (carbon dioxide)
Molecular weight 17 18 44
ReferenceR717 R718 R744
(2) Freons and alkanes:
Molecular formula of alkane compounds: CmH2m + 2
Freon is a general term for halogenated hydrocarbon derivatives (alkanes). The molecular formula is R (m-1) (n + 1) (X). If there is a Br (bromine) atom, add the letter. B and the number of atoms. If (m-1) = 0, "0" is omitted and not written.
Here are some of the numbers
Name molecular formula m, n, x, z value number
Monochlorodifluoromethane CHF2Cl m = 1, n = 1, x = 2, z = 0 R22
Dichlorotrifluoroethane C 2 HF 3 Cl 2 m = 2, n = 1, x = 3, z = 0 R123
CF3Br m = 1, n = 0, x = 3, z = 1 R13B1
Propane C3H8 m = 3, n = 8, x = 0, z = 0 R290
(3) Mixed refrigerant.
Mix refrigerants to get named sequence numbers
The azeotropic mixed refrigerant is numbered R5, starting with R500, R501, R502, etc.
Non-azeotropic mixed refrigerants are numbered R4, from R401, R404, R410, etc.
Allotropes with lower case letters, such as CHF2-CHF2 R134, CF3-CH2F R134a
3. Properties of common refrigerants
(1) Ammonia: The standard evaporation temperature is -33.4 , the freezing temperature is -77.7 , the pressure is moderate, the refrigeration capacity per unit volume is large, the flow resistance is small, and the thermal conductivity is large. The low price has no destructive effect on the atmospheric ozone layer, so it is widely used in large and medium-sized refrigerators with an evaporation temperature above -65 ° C.
The disadvantage is that it is more toxic, flammable, explosive, has a strong pungent odor, has a large isentropic index, and has a corrosive effect on zinc and copper.
(2) Freon: focus on analysis of commonly used water heaters
1) R22: It has a slight destructive effect on the atmospheric ozone layer and produces a greenhouse effect. It is listed as the second batch of restricted and banned refrigerants. China will ban production and use from January 1, 2040.
R22 is the most widely used medium temperature refrigerant. It has a boiling point of -40.8 ° C and a freezing point of -160 ° C. It is colorless, has a weak odor, does not burn, and does not explode. It is a safe refrigerant. It is partially miscible with the lubricating oil, and oil return measures need to be taken.
2) R142b. Boiling point is higher-9.25 ° C. Freezing point is -130.8 ° C. The biggest feature is that the condensation pressure is not high at high condensation temperature. For example, it is only 1.35 Mpa at 80 ° C, so it is suitable for use in heat pump devices and high ambient temperatures.
It has a weak effect on the atmospheric ozone layer and will also be banned in 2040.
3) R134a. Boiling point -26.5 , freezing point -101 , colorless, odorless, non-combustible, non-explosive,
However, it is incompatible with mineral lubricating oils. Polyester synthetic oils (such as polyolefin glycol) must be used. It is incompatible with nitrile rubber. Therefore, the seal must be changed to polybutyronitrile rubber. Easily react with water to generate acid, corrode piping and compressors, and require higher system dryness. The desiccant in the system should be replaced with XH-7 or XH-9 molecular sieve. The compressor motor coil insulation material must be reinforced and is a less mature refrigerant.
4) R407c and R410A are the more promising R22 substitutes that are considered more promising at the time of publication.
R407c is a ternary non-azeotropic refrigerant consisting of R32R125 R134a with a mass percentage of 23:25:52. The evaporation pressure and refrigeration pressure are very close to R22. However, the cooling capacity per unit volume and COP are less than R22 under heating conditions. In the heat pump hot water system of the same design operation capacity, the power consumption of the R407c hot water heating system is significantly higher than that of the R22 system. This makes the COP lower than the R22 system at high water temperatures.
R410A is a near-azeotropic mixed refrigerant composed of R32 and R125 in a mass ratio of 50:50. Its temperature slip does not exceed 0.2 ° C, which facilitates refrigerant filling and equipment replacement. However, the COP under R410A heating conditions is about 9% smaller than R22. Its evaporation pressure, condensation pressure, and volume cooling capacity are much larger than R22. At the same temperature, its pressure value is about 60% higher than R22. Heat transfer performance And better fluidity. It cannot be used directly on the R22 system. Compressors, heat exchangers, piping and systems must be redesigned.
5) C02 refrigerant
The green environmental protection natural working fluid C02 is again valued by people because of its non-toxicity, no impact on the ozone layer, no greenhouse effect and good thermodynamic properties. In addition, CO2 gives the higher exhaust temperature of the critical environment system and the larger temperature slip of the gas cooler. It has other unparalleled advantages in the field of heat pump water heaters.
Key advantages:
Non-toxic and non-combustible. Has good security. Ozone depletion potential (ODP) = 0, global warming potential (GWP) = 1, which has good economics, does not have recycling problems, and is environmentally friendly.
Stable physical and chemical properties. Good compatibility with lubricating oil. The viscosity is very low, which can increase the flow rate, the pressure drop will not be too large, improve heat transfer, and further reduce component size and system weight.
The value of insulation index (K) is high. Although it has the problem that the discharge temperature of the compressor is high, it meets the requirements for making hot water with higher temperature. At the same time, because C02 is lower than the working pressure P0, the compressor compression ratio is much lower than other systems, and the compressor efficiency is high.
The molecular weight of C02 is much smaller than that of polymer compounds, so its latent heat of evaporation (vaporization) is relatively large compared to a certain evaporation temperature. In addition, the high working pressure makes the compressor's suction specific volume smaller and the unit volume refrigeration A larger amount can reduce the size and make the system compact.
The low critical temperature of C02 makes it in a transcritical state in the heat pump system cycle. The large temperature slip during the exothermic process can better match the variable temperature heat source.
An important area of C02 applied research is heat pump water heaters (HPWH). The higher exhaust temperature, larger temperature slip of the gas cooler in the C02 transcritical cycle, and the temperature rise process of the cooling medium are matched, which makes it a unique advantage in the heat pump cycle.
By adjusting the exhaust pressure of the cycle, the heat removal process of the gas cooler can be better adapted to the temperature and temperature rise requirements of the external heat source. The research results show that when the ambient air is used as the heat source, the ambient water temperature is 0 ° C and the hot water outlet temperature is 60 ° C, the COP value of the system is as high as 4.3. A greater advantage is that it can produce 90 ° C without difficulty The hot water COP value is still high. The ordinary heat pump water heater limits the temperature of the produced water below 55 ° C.
Therefore, the C02 heat pump system can better meet the heating, air conditioning and domestic hot water heating requirements. The application of C02 as a refrigerant in heat pumps will effectively solve the resource and environmental pressures faced by air conditioning cold and heat sources, and has a good application prospect.
Comparison table of general properties and theoretical cycles of R407C, R410A, R22 |
parameter | R407C | R410A | R22 |
ingredient | HFC32 / 125 / 134a | HFC32 / 125 | HcFC22 |
Mass mixing ratio | 23/25/52 | 50/50 | 100 |
Relative molecular weight | 86.2 | 72.59 | 86.48 |
Normal boiling point | -43.77 | -51.56 | -40.76 |
Freezing point | -115 | | -160 |
Critical temperature | 86.08 | 70.22 | 96 |
Critical pressure Mpa | 4.653 | 4.852 | 4.974 |
Critical density Kg / m ^ 3 | 506 | 547.5 | 525 |
Saturated liquid density Kg / m ^ 3 | 1137.6 | 1060.2 | 1191 |
Saturated steam density Kg / m ^ 3 | 51.374 | 65.97 | 44.44 |
Viscosity (saturated liquid) mPa.s | 0.164 | 0.178 | 0.178 |
Viscosity (saturated vapor) mPa.s | 0.0128 | 0.0132 | 0.0128 |
Specific heat capacity (saturated liquid) KJ / (Kg.K) | 1.53 | 1.692 | 1.256 |
Specific heat capacity (saturated gas) KJ / (Kg.K) | 1.143 | 1.306 | 0.662 |
Latent heat of evaporation KJ / Kg | 185.11 | 186.85 | 233.5 |
Thermal conductivity (saturated liquid) W / (mK) | 0.0863 | 0.081 | 0.0869 |
Thermal conductivity (saturated vapor) W / (mK) | 0.0131 | 0.0128 | 0.0113 |
ODP | 0 | 0 | 0.0113 |
GWP | 1500 | 1700 | 1700 |
Theoretical cycle data | | | |
Evaporation pressure Kpa | 499 | 804 | 498 |
Condensing pressure Kpa | 2112 | 3061 | 1943 |
Temperature slip | 4.3 | 0.07 | 0 |
Exhaust gas temperature | 67.4 | 72.5 | 70.3 |
Refrigeration COP | 3.94 | 3.69 | 4.14 |
Volume cooling capacity KJ / m ^ 3 | 2947 | 4190 | 3010 |
Heating COP | 5.03 | 4.69 | 5.14 |
Volume heating capacity KJ / m ^ 3 | 3762 | 5326 | 3737 |
Comparison of design and production process |
| R22 | R407C | R410A |
compressor | | Special compressor Lubricant changed to POE, PVE | Same as 407C |
Condenser | | System design pressure increased to 3.3Mpa, Recheck the pressure of copper pipes Increase the heat exchange area, increase the fan, and reduce the condensation temperature Increased temperature slip, using media and air to flow in the opposite direction | When the condensing pressure is increased by 60%, the system pressure is increased to 4.15Mpa. Correspondingly 8mm and 7mm copper pipes are used. |
Evaporator | | · Recheck of copper tube pressure resistance · Improve heat transfer coefficient by changing the structure of heat exchanger | Recheck of the pressure resistance of copper pipes |
Throttling device | | · Use expansion valve, · Improve the processing precision of throttle capillary and increase the diameter | · Recheck the pressure resistance of the throttling device · The use of expansion valve improves the precision of throttle capillary processing and increases the diameter |
Four-way valve | | dedicated | dedicated |
Copper tube | | 10% increase in system withstand voltage Increase wall thickness | Recheck of copper tube pressure resistance Increased thickness to more than 0.7mm |
Dry filter | | HFC32 has a small molecular diameter and uses molecular sieve XH-10C, 11C | Same as 407C |
Polymer Materials | CR Hop Into rubber | HNBR synthetic rubber | |
Two-piece processing | | Residual moisture and reduced impurities Processing equipment changed to POE volatile oil | Residual moisture and reduced impurities Processing equipment changed to POE volatile oil |
Welding process | | Use chloride ion flux | Use chloride ion flux |
In the vapor compression refrigerator, in addition to having good thermal and physical and chemical properties, the refrigerant should have excellent environmental characteristics. Specific requirements are as follows:
(1) No damage to human ecological environment. Does not damage the atmospheric ozone layer and does not produce a greenhouse effect.
(2) The critical temperature is high. It can be liquefied at normal temperature or ordinary low temperature. It is hoped that the critical temperature is much higher than the ambient temperature in order to reduce the throttling loss of the refrigerant and improve the cycle economy.
(3) Within the operating temperature range, it has an appropriate saturated steam pressure. At least the evaporation pressure must not be lower than atmospheric pressure to prevent outside air from penetrating into the system. The condensing pressure should not be too high, otherwise it will increase the compressor power consumption and Require the system to have a higher pressure capacity, increase equipment costs.
(4) Large cooling capacity per unit volume. Can reduce the amount of air delivered by the compressor.
(5) The viscosity and density are small. Reduce flow resistance losses in the system.
(6) High thermal conductivity. It can increase the heat transfer coefficient of the heat exchanger, reduce the heat transfer area of the heat exchange equipment, and reduce material consumption.
(7) Non-combustible, non-explosive, non-toxic. Does not corrode metal materials, has no chemical effect on lubricants, and does not decompose at high temperatures.
(8) The isentropic index is small. It can reduce the exhaust temperature, reduce the power consumption during the compression process, facilitate safe operation and increase the service life.
(9) Low solidification temperature. Avoid solidification at evaporation temperatures.
(10) Has good insulation performance.
(11) Low price and easy access.
(12) The compression work per unit volume is small.
At the time of writing, no refrigerant that fully met the above 12 requirements was found. However, when selecting, you can take full consideration according to the conditions of use.
For small enclosed compressor household devices, fluorine refrigerants are mostly used. Large-scale industrial refrigeration mostly uses ammonia, and petrochemicals mostly uses hydrocarbons.
The selection of refrigerant is a relatively complicated technical and economic issue, and many factors need to be considered. When selecting, a comprehensive technical analysis should be performed according to the specific situation.
1. Consider environmental requirements.
Refrigerants must be selected in accordance with national environmental regulations.
2. Consider the requirements of refrigeration temperature.
Depending on the refrigerant temperature and cooling conditions, high temperature (low pressure), medium temperature (medium pressure), and low temperature (high pressure) refrigerants are selected. Generally, the standard evaporation temperature of the selected refrigerant is 10 ° C lower than the refrigeration temperature. The choice of refrigerant should also take into account the cooling conditions of the refrigeration device, the use environment, and so on. The condensing pressure during operation should not exceed the value specified for the compressor's safe use conditions. Automotive air conditioners can only use the outside air as a cooling medium. The factors such as temperature, wind speed, solar radiation, and heat radiation that frequently affect them frequently change. Their operating conditions determine that they can only use high temperature (low pressure) refrigerants. Choose R12, mostly use R134a when posting.
3. Consider the nature of the refrigerant.
According to the thermal, physical, and chemical properties of the refrigerant, select those that are non-toxic, non-explosive, and non-combustible; choose a refrigerant that has good heat transfer, low resistance, and good compatibility with the materials used in the refrigeration system.
4. Consider the type of compressor.
Different refrigeration compressors work differently. Volumetric compressors increase the pressure by reducing the volume of the refrigerant vapor. Generally, refrigerants with a large refrigeration capacity per unit volume are used, such as R134a, R22 and so on. There are many types of refrigerants, with the advancement of science and technology. New working fluids are constantly emerging to suit different refrigeration installations.
Air working media has been used in homes, vehicles, and
Refrigerants are also called refrigerants. It is a working substance that continuously circulates in a refrigeration system and achieves refrigeration through its own state change. The refrigerant is vaporized by the heat absorbed by the cooling medium (water or air, etc.) in the evaporator, and the heat is transferred to the surrounding air or water in the condenser to condense. Such as ammonia and water, lithium bromide and water; steam jet refrigerators use water as a refrigerant.
There are three main factors for the rise in refrigerant prices: first, the state has upgraded fluorite to a strategic resource and implemented protective development; second, the increase in consumption of air conditioners (including automotive air conditioners) has driven demand for refrigerants; and finally There is also the factor of capital hype. There is also an international factor for the rise in refrigerant prices. According to the Montreal Protocol, in 2010, the production capacity of low-end refrigerants (such as R22) in developed countries has been basically shut down. R22 is no longer used as a refrigerant in developed countries, but R22 is used as a downstream Fluoropolymer's main raw material, its demand for R22 still exists. Because developing countries will completely phase out R22 and wait until 2030, this is also a good news for refrigerant manufacturers in developing countries. At the time of writing, the supply and demand gap of R22 remained at least until 2013, which also meant that the refrigerant industry boom could continue for at least two years.
At present, the most widely used refrigerant in China's air-conditioning industry is HCFC substance R22. The basic physical properties of R290 and R22, such as the standard boiling point, freezing point, and critical point, are very close, and they have the basic conditions to replace R22. In a saturated liquid state, the density of R290 is smaller than that of R22. Therefore, the perfusion volume of R290 is smaller under the same volume. Experiments show that the perfusion volume of R290 is about 43% of R22 under the same system volume. In addition, since the latent heat of vaporization of R290 is about twice that of R22, the refrigerant circulation of the refrigeration system using R290 is smaller. R290 has good material compatibility, and is compatible with copper, steel, cast iron, and lubricants. In the future, China will further increase the pilot demonstration of the reconstruction of air-conditioning production lines using R290 refrigerant. With the continuous deepening of R290 application technology research and continuous accumulation of experience, environmentally friendly refrigerant R290 will have a broad market application prospect in the future.
