Copper capillary tubes possess exceptional low-temperature performance, primarily due to the unique physical properties of copper itself. Simply put, many metals become brittle like glass in extremely cold environments, breaking at the slightest touch, but copper remains resilient.
Here are four key advantages of copper capillary tubes in low-temperature environments:
Core Advantages: "Tougher, Not Brittle" at Low Temperatures
This is the most significant advantage of copper capillary tubes.
● Rejects Cold Brittleness: Most metals (such as ordinary carbon steel) experience "cold brittleness" when temperatures drop sharply. While hardness and strength increase, plasticity and toughness decrease drastically, making them highly susceptible to brittle fracture.
● Maintains Ductility: Copper is completely different. As the temperature decreases, its tensile strength and yield strength actually increase, while maintaining excellent ductility and toughness.
● Extreme Low Temperature Performance: Data shows that the mechanical properties of copper remain very stable at temperatures as low as -196°C (liquid nitrogen temperature). This means that in cryogenic, ultra-low temperature cold storage, or liquid oxygen/liquid nitrogen transport systems, copper capillary tubes will not become brittle and fail like other metals.
Strong Resistance to Thermal Expansion and Contraction Fatigue
During operation, refrigeration systems (such as refrigerators and air conditioners) subject capillary tubes to repeated cycles of "high temperature (condensation) - low temperature (evaporation)".
● Low coefficient of linear expansion: Copper has a very small coefficient of linear expansion (approximately 1/10 that of plastic tubes). This means that the length of copper tubes changes very little during drastic temperature changes.
● Resistance to stress fatigue: Due to its small range of thermal expansion and contraction and the inherent toughness of the material, copper capillary tubes are less prone to stress fatigue cracking during repeated freeze-thaw cycles. In contrast, some plastic or composite material tubes are prone to aging and cracking under long-term alternating hot and cold temperatures.
Extremely Low Permeability and Sealing
In cryogenic systems, preventing refrigerant leakage and the ingress of external impurities (such as moisture and air) is crucial.
● Dense Structure: The copper tube has an extremely dense structure, preventing grease, bacteria, oxygen, and ultraviolet light from penetrating its walls.
● Cryogenic Sealing: Under low-temperature, high-pressure differential conditions, the copper capillary tube maintains extremely high airtightness, unlike some rubber or plastic hoses that experience loosening at low temperatures or increased permeability due to shrinkage.
Excellent Cryogenic Thermal Conductivity
Although the thermal conductivity of copper changes with decreasing temperature, copper generally maintains extremely high thermal conductivity at low temperatures.
● Highly Efficient Heat Exchange: During refrigeration throttling, the copper capillary tube can rapidly exchange heat with the surrounding environment (especially when welded to the return pipe), contributing to the subcooling of the liquid refrigerant and thus improving the overall energy efficiency ratio of the refrigeration system.
