How do copper and aluminum tubes make air-conditioners both energy-efficient and long-lived?

Just entering the spring, some city air-conditioning battles set off. The reporter found in the mall that consumers pay more attention to their energy efficiency when choosing air conditioners. Fortunately, some energy-saving air conditioners adopt newly-invented copper-aluminum composite tubes instead of pure copper tubes, which has greatly improved the energy efficiency of air conditioners. So - how can copper and aluminum tubes make air-conditioning energy-efficient and long-lived?
People who have used air-conditioning almost have this feeling: The wind just blowing out from the installed air conditioner is very cool, but after six months, the wind is not so cool. Careful users will find that with the increase in the use of air conditioners, the monthly electricity bill is also quietly growing. Why is this? It turns out that this is because traditional air conditioners have become more and more useless as the energy efficiency ratio decays.
Air-conditioning is often more energy-efficient than the attenuation The ratio of the cooling capacity to the input power of an air conditioner is called the "energy efficiency ratio," and the higher the energy efficiency ratio, the more energy-efficient the air-conditioning is. Why does the air-conditioning system attenuate its energy efficiency ratio after a period of time? This is because the operating principle of air-conditioning is that it uses a pure copper tube to connect its condenser (outdoor unit for cooling) and evaporator (indoor unit for cooling). Although this copper pipe is a good heat exchange material, the fins of the air conditioner's condenser and evaporator are made of aluminum. After the aluminum pieces on the two devices are intertwined with the copper pipe, Inevitably, an electrochemical reaction (i.e., electrochemical corrosion) occurs. The compound, i.e., alumina, is firmly wrapped on the surface of the copper pipe as a layer of enamel, resulting in a greatly reduced heat exchange efficiency.
According to tests by authoritative organizations, after six months of air-conditioning use, its energy efficiency ratio is expected to drop by about 10%. When it is used for 4-5 years, its energy efficiency ratio will decrease by about 40%. In other words, after four to five years of air conditioning, the power consumption of the same cooling capacity is nearly twice that of the new air conditioner, which equals the power consumption of one air conditioner.
The attenuation of energy efficiency ratio stems from electrochemical corrosion. The material structure of traditional air conditioners has always been copper tubes with aluminum fin structures. From the point of view of material properties, there is a large potential between the copper tube and the aluminum fin. The potential of the copper to hydrogen is +0.34V, the potential of the aluminum to hydrogen is -1.66V, and the potential difference between the copper and aluminum is 2V. It is equivalent to 1.3 times the voltage of a dry cell. In the presence of electrolytes, a discharge reaction occurs between copper and aluminum, resulting in electrochemical corrosion: aluminum continuously loses electrons and becomes aluminum ions and reoxidizes to become aluminum oxide (Al2O3). The corrosion layer follows electrochemically. The corrosion time increases and gradually thickens.
Al2O3, also known as corundum ceramics, is an insulating, thermal insulating material with a very large thermal resistance. If such a material exists between the copper tubes and the aluminum fins of the air conditioner, the heat exchange efficiency will be directly reduced, resulting in a decrease in the air conditioning energy efficiency ratio. .
In particular, when air-conditioning is used for cooling, the indoor unit (evaporator) always has condensed water between the copper pipe and the aluminum fin, so electrochemical corrosion has always existed. The outdoor unit (condenser) under the action of acid rain, rain, moist air, etc., can not avoid the electrochemical corrosion. With the increase of the service life, the part of the aluminum foil without hydrophilic coating first corrodes, and gradually expands to the part with the hydrophilic coating, causing degeneration and fission of the hydrophilic coating.
It should be pointed out that the aluminum oxide generally produced in the air is dense, but the alumina produced by electrochemical corrosion is loose, and the corrosion layer is thickened year by year, resulting in a decline in the air-conditioning energy efficiency ratio year by year. When it cannot be tolerated, only the entire machine will be replaced.
Scientists and technicians have cut off the copper pipes and aluminum fins of the used “two devices”. On the cross section, they have seen that there is already a certain thickness of aluminum oxide at the flanges of the aluminum fins that are in direct contact with the copper pipes. exist. Although copper pipes and aluminum fins are brought together during the manufacture of air conditioners, the gap between copper and aluminum is unavoidable due to the thermal expansion and contraction of two different materials in the manufacturing process and use, and the gap absorbs water due to capillary action. The occurrence of electrochemical corrosion.
Copper-aluminum composite pipe solution to the problem In order to solve the problem of decline in air-conditioning energy efficiency, air-conditioning technology workers at home and abroad have been working hard. In 2005, an air-conditioning plant proposed the concept of titanium air-conditioning, coating titanium dioxide on air-conditioning aluminum fins to prevent the formation of bridges between the fins due to the failure of the air-conditioning hydrophilic coating, thus slowing down the energy efficiency ratio. attenuation. However, the cost is about 20% to 30% higher than traditional materials.
Jiangsu Xingrong’s scientific and technical workers invented the copper-aluminum composite pipe (abbreviated as ACC pipe) instead of the pure copper pipe for the connection of air conditioner “two devices” in 2005, and achieved unexpected results. Not only did the air-conditioning efficiency ratio increase by 3 %-5%! And it will not form electrochemical corrosion, making the air-conditioning service life greatly extended. What about production costs? Because the ACC pipe can save 85% copper, an air conditioner can save costs 120 yuan.
The ACC tube developed by Jiangsu Xingrong is a new type of tube with an outer layer of rust-proof aluminum alloy and an inner layer of oxygen-free copper. The two layers are copper-aluminum atomic bonding layers. Since there is no thermal resistance between the copper and aluminum of the composite pipe, there is no potential difference between the aluminum alloy of the outer layer and the aluminum fins of the “two devices”. Therefore, in the life cycle of the air conditioner, no electrochemical energy is theoretically generated. Corrosion, which fundamentally eliminates the cause of the substantial decline in energy efficiency. At the same time, air conditioning may also become a real "long-lasting air conditioner."
In addition, the ACC tube combines the advantages of copper and aluminum. On the one hand, the tube absorbs heat instantaneously with copper having a thermal conductivity 1.7 times higher than that of aluminum. On the other hand, it uses aluminum having a thermal capacity 2.33 times higher than that of copper for comprehensive heat dissipation, making the air-conditioning energy-efficiency ratio lower than that of conventional air conditioners in practical use. The internal thread brass air conditioner used is 5% higher, in other words, the new air conditioner energy-saving reaches 3%-5%.