The heat transfer efficiency of stainless steel coils is lower than that of copper coils, but in actual products, stainless steel coils tend to be larger and longer, and the heat transfer area is much larger than copper coils.
In addition, the diameter of the stainless steel coil is much larger than that of the copper coil, and the flow rate of the circulating working fluid is also large. The temperature difference between the circulating working medium and water, the working medium flow rate, the heat transfer area, and the heat transfer coefficient will ultimately affect the heat transfer efficiency. Many wall-hung boilers are equipped with stainless steel coils for heat transfer, and the heat transfer power can match tens of kilowatts of gas-fired wall-hung boilers.
The surface of the copper coil is treated with special anti-corrosion to ensure the service life of the copper coil. In fact, this is a big mistake. When the copper coil is installed in the liner, the coil itself is not corroded and no surface treatment is required. The real problem is that the presence of copper coils will accelerate the corrosion of the inner gallbladder and affect the life of the inner gallbladder.
Here we will discuss the chemistry of metal batteries. When copper and iron are placed in an acidic solution and there is no conductor connection, copper and iron will corrode. However, when copper and iron are connected through a wire, copper is not corroded, and iron corrosion is greatly accelerated. At this time, if the conductor is tested with an ammeter, it will be found that a current passes through the conductor. The battery was invented according to this principle.
Domestic water tanks are usually equipped with magnesium rods. Why install a magnesium rod? Because magnesium is more active than iron. Utilizing the principle of a metal primary battery, the magnesium rod is sacrificed to protect the fuel tank. When the copper coil is installed in the gallbladder, the metal activity of iron is stronger than that of copper, so iron must be used as a material in the gallbladder. If the inner water tank is corroded, the water tank with the highest performance will also leak.
The application of the stainless steel inner tube coil water tank in the vertical water tank centralized household system has no problem at all. But horizontal tanks have also been widely used in the market. Some manufacturers simply place the vertical water tank horizontally as a coiled water tank for centralized households. This ignores a very important issue, namely how to remove the gas accumulated in the heat exchanger coils when the system is running. This is what we often call the gas block problem.
The vertical coil is a circular interface. Gas can be exhausted through the interface, but the horizontal coil is not enough. The coil is the vertex of each circle, and each circle has a vertex. Gases cannot be eliminated, they accumulate more and more. Some people say that gas occupies the volume of the coil, making the heat transfer effect worse. In fact, this is also a misunderstanding. What really affects the effect is that the gas affects the flow of the working substance, resulting in greater flow resistance. The water tanks of centralized household systems are all connected in parallel. The resistance of one water tank increases, and the circulating working fluid of the other water tank increases, and the flow rate is easily reduced when there is resistance. So the gas-clogged fuel tank has almost no heat. So the built-in form of the coil needs to be changed.