How to Choose Refrigerant of the Cold Storage Refrigerator?

No matter what kind of cold storage it is, whether it is fresh-keeping cold storage, pharmaceutical cold storage, or quick-freezing cold storage, refrigerant is a very important part and is indispensable.

Thermodynamic Requirements

1. The boiling point should be low, and a lower evaporation temperature can be obtained. At the same time, a refrigerant with a low boiling point has a higher vapor pressure.

2. The critical temperature should be high and the solidification temperature should be low. The critical temperature should be high and the freezing temperature should be low to ensure that the refrigerant works safely in a wide temperature range.

3. The refrigerant should have suitable working pressure. The evaporating pressure of the refrigerant is required to be close to or slightly higher than the atmospheric pressure, so as to avoid the occurrence of vacuum in the low-pressure part of the refrigeration system and increase the chance of air mixing into the system. It is required that the condensing pressure should not be too high. Low condensing pressure can reduce the strength and construction requirements of refrigeration equipment and pipelines, reduce the construction investment of refrigeration systems, and the possibility of refrigerant leakage. The pressure ratio and the pressure difference between the condensing pressure and the evaporating pressure are required to be small.

4. The latent heat of vaporization of the refrigerant should be large. When the refrigeration system obtains the same cooling capacity, the larger latent heat of vaporization can reduce the circulation amount of the refrigerant. At the same time, it can also reduce investment in refrigerators and equipment, reduce operating energy consumption, and improve refrigeration efficiency.

5. For large refrigeration systems, the refrigeration capacity per unit volume of the refrigerant is required to be as large as possible. In this way, when the cooling capacity is constant, the circulation amount of the refrigerant can be reduced, and the size of the refrigerator and the diameter of the pipeline can be reduced. However, for small refrigeration systems, the cooling capacity per unit volume is required to be small, so that the passage section of the refrigerant can be appropriately increased and the flow resistance can be reduced.

6. The adiabatic index of the refrigerant should be small. This results in reduced compression power consumption, lower discharge temperature, improved operating performance, and simplified system design.

7. For centrifugal refrigeration compressors, refrigerants with moderate molecular weight should be used. Because the relative molecular mass is large, the boost ratio of each stage can be increased, and the number of compression stages can be reduced when the pressure ratio of the system is constant. In addition, most substances have similar molar increases when they vaporize at the boiling point. Therefore, when the relative molecular mass of refrigerants with similar difficult boiling points is large, the latent heat of vaporization is small.

8. The thermal conductivity should be high. This can improve the heat transfer coefficient of the heat exchange equipment and reduce the heat exchange area of ​​the heat exchange equipment.

Physical and Chemical Requirements

1. The viscosity of the refrigerant should be small, the viscosity of refrigerant should be small, the flow resistance of the refrigerant in the system should be reduced, and the diameter of the refrigeration system pipeline should be reduced. Small viscosity can also increase the heat transfer performance of the refrigerant.

2. The purity of the refrigerant should be high, and the selected refrigerant should be free of insoluble impurities. The refrigerant must have a certain water absorption. When a very small amount of water penetrates into the refrigerant, it will cause ice plugs at low temperatures and affect the refrigeration system. normal work.

3. The thermochemical stability of the refrigerant is better. It is not easy to decompose at high temperatures. When the refrigerant is mixed with oil and water, it should not have an obvious corrosive effect on metal materials, and the swelling effect on the sealing material of the refrigerator should be as small as possible.

4. The oil solubility of refrigerants is shown as complete dissolution, slight dissolution, and complete insolubility. When the refrigerant and the refrigerating machine oil are completely decomposed, it can create good conditions for the lubrication of the machine parts, and it is not easy to form an oil film on the heat exchange surface of the heat exchanger such as the condenser, and the heat transfer effect is excellent. However, it will increase the evaporation temperature of the refrigerant, reduce the temperature of the refrigerator oil at low temperatures, and also increase the foam when the refrigerant boils, the liquid level in the evaporator is unstable, and the oil consumption of the refrigerator increases during operation. System oil return is not easy. When the refrigerant and the refrigerating machine oil are completely unclear, the effect on the evaporation temperature of the refrigeration system is small, but an oil film is easily formed on the heat exchange surface of the heat exchanger, which affects the heat exchange. The advantages and disadvantages of refrigerants that are slightly soluble in oil lie somewhere in between.

5. The effect of the refrigerant on the coil insulating material is as small as possible. In semi-closed and fully-closed refrigerators, the direct contact between the motor coil of the compressor and the refrigerant and refrigerating machine oil not only requires good electrical insulation of the refrigerator but also requires the refrigerant to have as little effect on the coil insulating material as possible.

Safety Requirements

1. The refrigerant should not burn or explode within the working temperature range. When certain flammable and explosive refrigerants must be used, fire and explosion safety measures must be taken.

2. The refrigerant should be non-toxic or low-toxic and relatively safe. The toxicity, flammability, and explosiveness of the refrigerant are all indicators to evaluate its safety of the refrigerant. Every country has a minimum level of safety.

3. Choose a refrigerant that is easy to detect leaks. Since some refrigerants have certain toxicity and danger, it is required that the selected refrigerant should have the characteristics of easy detection to ensure safe operation.

4. Choose a refrigerant that is not harmful to human health and has no irritating odor. In case the leaked refrigerant comes into contact with food, it is required that the food will not change color, or taste, and will not be contaminated and damage the tissue. Refrigerants for air-conditioning should not harm human health and have no irritating odor.

Requirements for Environmental Impact

The latest research finds that certain chemical substances may have an impact on the global environment, which has attracted the attention of the international community. The selected refrigerant should meet the following requirements:

1. The lifetime in the atmosphere is low.
2. The potential damage to the ozone layer is small.
3. The potential effect of the global greenhouse is lower.
4. There is no light fog reaction, and the impact on the atmosphere, water source, and soil is small.

Economic Requirements

1. The production process of the refrigerant should be simple and the production cost should be low.
2. The refrigerant is cheap and easy to obtain.
3. Due to the wide variety of refrigerants and their very different properties, there is no ideal refrigerant that fully meets the requirements. In the selection, it should be comprehensively considered according to the actual situation.