09-03-5 Topic - About bimetal heat exchange tubes (prizes for participation)

my understanding: The heat exchange tube is a composite tube, that is, the inner and outer walls are compounded together by mechanical methods (not much is known about other methods such as explosive compounding) of two types of pipes (such as carbon steel pipes and stainless steel pipes, generally carbon steel pipes are used as the base layer) to achieve the required strength and heat transfer performance. Advantages of this pipe: When the corrosive medium flows through the tube side and ordinary cooling water flows through the shell side, only the stainless steel layer is in contact with the corrosive medium, which avoids the occurrence of corrosion and saves the consumption cost of stainless steel materials to the maximum extent.

The heat exchange tube is a composite tube, that is, the inner and outer walls are compounded together by mechanical methods (not much is known about other methods such as explosive compounding) of two types of pipes (such as carbon steel pipes and stainless steel pipes, generally carbon steel pipes are used as the base layer) to achieve the required strength and heat transfer performance. Advantages of this pipe: When the corrosive medium flows through the tube side and ordinary cooling water flows through the shell side, only the stainless steel layer is in contact with the corrosive medium, which avoids the occurrence of corrosion and saves the consumption cost of stainless steel materials to the maximum extent.

Bimetallic heat exchange tubes are composed of two kinds of pipes, and the inner and outer walls are combined together through some special methods such as machinery to achieve the required strength and heat transfer performance. It is generally used for heat exchange with certain corrosive media. When the corrosive medium flows through the tube side and ordinary cooling water flows through the shell side, only the stainless steel layer is in contact with the corrosive medium, which avoids the occurrence of corrosion and saves the consumption cost of stainless steel materials to the maximum extent.

Bimetallic pipes are actually two pipes made of different metals, one pipe is placed outside the other, and there is no gap between the joint surfaces. Generally, the outer tube is expanded or put on the inner tube, and the liquid can be made by other mechanical methods. Bimetallic tubes are used when the fluids on both the tube side and the shell side are corrosive and there is a metal shell that is compatible with both fluids at the same time, so that the fluid on the shell side contacts one metal and the fluid on the tube side contacts the other metal. Materials must be selected so that the two metals are corroded by different fluids at similar rates. There are currently approximately one hundred types of metals that can be combined into bimetallic tubes. A typical example is: In an ammonia condenser, when the coolant on the tube side is water, the inner wall of the tube used is copper-nickel alloy, and the outer wall is steel.

1. Bimetal fin tube, which is made of composite rolling of metal tubes of two different materials. Its base tube types include: Copper, copper alloy, stainless steel, carbon steel, etc. ； Fin material is pure aluminum ； Thus forming two types of bimetallic finned tubes: Copper-aluminum composite pipe, steel-aluminum composite pipe. 2. The bimetal rolled tube is produced by tightly fitting the aluminum tube on the base tube, and using computer-aided technology (CAD), it is integrated into a row on the rolling machine to roll out high-quality fins. Then carry out efficient cleaning and decontamination treatment to make the fins smooth and bright. On this basis, individual pipes were sampled for thermal testing to ensure good composite performance. Rolled finned tubes are currently used internationally for their high heat exchange efficiency, strong corrosion resistance, long service life and good earthquake resistance.

Bimetallic heat exchange tubes generally refer to metal composite tubes. There are various composite processes. It is usually hoped to achieve seamless composite； The selection of metal materials mainly considers functionality. On the one hand, it is based on the corrosive requirements of the medium inside and outside the tube during the heat exchange process. In order to reduce costs, two materials are used to achieve special functional requirements, such as copper-aluminum composite tubes. ； The other is considered from the perspective of heat transfer enhancement, such as steel-aluminum composite finned tubes, which have a simple processing technology, which can not only reduce the weight of the product but also improve the heat transfer efficiency. The difference in thermal expansion coefficient should be considered when using it. If the difference is large, it cannot be used under large temperature difference conditions.

Also pay attention to bimetallic pipes with two materials inside and outside. (Similar to the air cooler tube, but the outside of the air cooler tube has bottom, middle and high fin threaded fin types, which mainly enhance the heat transfer on the air side. ) The inner layer mainly bears pressure, and the outer layer is processed into T-shaped fins or other fin shapes. This arrangement is mainly used in some low-temperature design situations, in shell and tube heat exchangers. Due to the sensitivity of the material to "small defects" at low temperatures, it is not allowed to directly process the "fin-shaped" finned tube on the outer surface of the tube, so this tube type appeared.

The discussion by the people above is quite detailed. No matter what kind of bimetallic pipe, it must be ensured that the two metals can be well welded to the tube plate.