I. Refrigerant Selection
Freon is an odorless, transparent, and low-toxicity refrigerant. It is not easily flammable or explosive and is chemically very stable. However, different Freon refrigerants with different chemical structures have significantly different refrigeration properties, so the appropriate refrigerant can be selected based on the required cooling temperature. Currently, the most commonly used refrigerants in low-temperature coolant circulating pumps are R404A and R22. R404A is a better refrigerant; it does not deplete the ozone layer and is an environmentally friendly refrigerant. Its characteristics include low toxicity, non-flammability, cleanliness, and good cooling effect, making it suitable for most medium and low-temperature refrigeration systems. R22 is a widely used refrigerant; its standard vaporization temperature is -40°C. Due to its non-flammable and non-explosive properties, it has a high safety factor and is frequently used in household air conditioners and low-temperature refrigerators. A new refrigerant, "R410A," has emerged, which is recognized as an environmentally friendly refrigerant that can replace R22. Because its working pressure is 1.6 times that of ordinary R22, its cooling effect is better, and it does not deplete the ozone layer. When selecting a refrigerant for a low-temperature coolant circulating pump, various factors should be considered, such as the working pressure, safety factor, stability, and whether the refrigerant depletes the ozone layer or contributes to the greenhouse effect. Choosing a suitable refrigerant will ensure better performance of the low-temperature coolant circulating pump.
II. Coolant Selection
The coolants used in low-temperature coolant circulating pumps mainly include heat transfer oil, water, ethanol, and antifreeze. Heat transfer oil has a wide temperature range, reaching as low as -120°C and as high as 300°C and above. The temperature range varies depending on the composition of the heat transfer oil. Antifreeze is a coolant with specific additives, mostly used in the cooling systems of automobile engines. Antifreeze has the advantages of corrosion resistance and scale prevention, but its freezing point is -38°C, which may not meet the temperature requirements of some equipment. Water has an even more limited temperature range, but it is the most environmentally friendly and convenient option and can be used according to experimental needs.
The most commonly used coolant in low-temperature circulating pumps is ethanol mixed with water. During mixing, the ratio is crucial; it must be 95% ethanol and 5% water. A higher ethanol concentration makes it highly flammable. If the water ratio is too high and the ethanol ratio is low, ice will form on the cooling copper coil. In this case, the ethanol content needs to be increased. Because ethanol is highly volatile, the level in the cooling tank must be constantly monitored. The coolant level should be at least 2 cm above the cooling copper coil. If the coolant level decreases, it must be replenished promptly. Dust and other debris on the ventilation cover should also be cleaned regularly to prevent affecting heat dissipation.
III. Daily Maintenance and Troubleshooting
During prolonged use, low-temperature circulating pumps may experience poor cooling performance. In this case, check for impurities blocking the water circuit, which can cause poor water return through the filter. This can also lead to unusual noises from the machine. Also, check if the coolant level has decreased due to evaporation. The liquid in the cooling tank should cover the cooling copper coil; if not, add more coolant. Regularly clean dust and debris from the ventilation cover to prevent affecting heat dissipation.
During long-term operation, low-temperature circulating pumps are prone to making unusual noises. This can be due to poor water return or mechanical wear. Regular inspections are necessary, and bearings and wear parts should be replaced periodically. The pump body should also be inspected regularly. Every instrument requires regular inspection and maintenance of its components to ensure its longevity. There are many other aspects of daily maintenance for low-temperature circulating pumps, requiring a diligent attitude and rigorous procedures during operation.