In the refrigeration system, the refrigerant may be contaminated by a variety of impurities, including moisture, non-condensable gases, refrigeration oil, metal debris, grease, fibers, dust, etc. The presence of these impurities can have a significant negative impact on refrigeration equipment. For those working in the refrigeration industry, it is very important to understand the problems these impurities can cause and their corresponding removal methods.
Undesirable phenomena:
Moisture: can cause ice blockage and corrosion, reducing the heat exchange efficiency of the system.
Non-condensable gas: Reduce the effective heat exchange area of the condenser and increase the workload of the compressor.
Refrigeration oil: Excessive accumulation reduces heat transfer efficiency and may clog filters or expansion valves.
Metal shavings and fibers: Can wear down mechanical parts and cause pipe blockage.
Grease and dust: accumulate on the heat exchange surface, affecting heat transfer performance
1. The impact of moisture on the system
The effects of moisture on the system are as follows:
Ice jam: Moisture can freeze at the expansion valve, causing the liquid supply to be blocked.
Lubricating oil emulsification: Moisture can cause some lubricating oils to emulsify, thereby reducing their lubrication performance.
Corrosion: In the refrigerant system, moisture can generate corrosive substances such as hydrochloric acid and hydrogen fluoride. These substances will especially corrode key components such as valve plates, bearings and shaft seals.
Reduced electrical insulation performance: Moisture will also reduce the electrical insulation performance of the refrigerant, which may cause the fully enclosed compressor to burn out in severe cases.
Methods for dealing with moisture: If the degree of moisture contamination in the refrigeration system is minor, it can be solved by replacing the dry filter once or twice. If there is a large amount of moisture in the system, more comprehensive treatment measures will be required:
Use nitrogen to flush the system in stages to remove moisture and impurities from the system.
Replace the filter drier to ensure system dryness.
Replace the refrigeration oil as the original refrigeration oil may have deteriorated due to moisture.
Replace the refrigerant to ensure purity inside the system.
Monitor the system status until the color in the sight glass changes to green, indicating that the system is back to normal.
Through these maintenance measures, the impact of moisture on the refrigeration system can be effectively reduced and ensure its normal operation.
2. The impact of non-condensable gases on the system
The so-called non-condensable gas refers to a gas that cannot be condensed into a liquid under specific temperature and pressure conditions in the condenser when the refrigeration system is working and is always in a gas state. These gases mainly include nitrogen, oxygen, hydrogen, carbon dioxide, hydrocarbon gases, inert gases and their mixtures.
The impact of non-condensable gases on the system:
Increase condensing pressure: The presence of non-condensable gases will increase the pressure in the condenser, which in turn will cause the discharge temperature of the compressor to increase.
Reduce refrigeration efficiency: Non-condensable gas will occupy the space of the condenser and reduce the effective condensation area of the refrigerant, thereby reducing the refrigeration capacity of the refrigeration system.
Increased energy consumption: Since the compressor requires additional work to compress these gases, it increases the power consumption of the system.
Methods for handling non-condensable gases:
Close the condenser liquid outlet valve: First, you need to close the condenser liquid outlet valve.
Transfer refrigerant: Start the compressor and pump the refrigerant in the low-pressure system to the condenser or high-pressure reservoir.
Discharge non-condensable gas: stop the compressor, close the suction valve, and open the exhaust valve at the highest point of the condenser.
Monitor gas temperature: Feel the temperature of the exhaust gas with your hand. When the discharged gas does not feel cool or feels relatively hot, it means that the discharged gas is mainly non-condensable gas rather than refrigerant gas.
Check the temperature difference: Check the temperature difference between the saturation temperature corresponding to the pressure in the high-pressure system and the condenser outlet temperature. If the temperature difference is large, it means that there is more non-condensable gas in the system.
Repeated discharge: After the mixed gas is fully cooled, discharge the non-condensable gas intermittently until the temperature difference returns to the normal range.
3. The impact of lubricating oil (oil film) on the system
In the refrigeration system, lubricating oil is another important factor. It is not only used to lubricate the moving parts of the compressor, but also enters the system as the refrigerant circulates, affecting the performance of the system.
Impact of lubricating oil (oil film) on the system: Although the refrigeration system is usually equipped with an oil separator to recover lubricating oil, there is still a possibility that some lubricating oil is not completely separated and enters the system, flowing with the refrigerant in the tube, forming The so-called "oil cycle". If an oil film adheres to the surface of the heat exchanger, it will have the following effects on the performance of the system:
Rise in condensation temperature: When a 0.1mm oil film is attached to the surface of the condenser, the condensation temperature will rise, thereby reducing the cooling capacity of the refrigeration compressor by approximately 16% and increasing electricity consumption by approximately 12.4%.
Evaporation temperature drops: When the oil film in the evaporator reaches 0.1mm, the evaporation temperature will drop by 2.5°C, resulting in an increase in system energy consumption of approximately 11%.
How to deal with lubricating oil (oil film):
Improved design: For oil return problems caused by improper design of the evaporator and return pipeline, the occurrence of such problems can be reduced through optimized design.
Use an efficient oil separator: Using an efficient oil separator can greatly reduce the amount of oil entering the system pipeline.
Nitrogen flushing: If an oil film has formed in the system, nitrogen can be used for multiple flushes until no more foggy refrigeration oil is brought out.
