Shandong Zhilin Environmental Protection Technology Co., Ltd.

Advantages and disadvantages of various finned tubes in finned tube heat exchangers

Release time:

2021-04-26 15:41

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Finned tube heat exchangers are mainly composed of three rows of parallel helical finned tube bundles with air flowing between them. Using them saves space, provides better heat dissipation, and conserves energy.

Finned tube heat exchangers primarily consist of three rows of parallel helical finned tube bundles with air flowing between them. Using this type of exchanger saves space, offers better heat dissipation, and conserves energy. Its attractive appearance and energy efficiency have made it a popular choice since its market launch, proving to be an excellent heating product. There are several types of finned tubes; let's briefly introduce the advantages and disadvantages of each.

1. High-Frequency Welded Finned Tubes

High-frequency welded finned tubes are made by winding a steel strip around a steel pipe and welding it using high-frequency current. Its advantage is its low cost. Among commonly used materials in steam heat exchangers, steel strip is arguably the cheapest.

Its disadvantages are: high energy consumption during high-frequency welding; generally incomplete welding, resulting in high contact thermal resistance; process limitations restrict fin height to generally no more than 15 mm, with larger fin spacing, leading to insufficient heat transfer area and lower thermal efficiency; susceptibility to rust on both the steel pipe and strip. When the heating system uses plastic pipes, the steel pipes in the steam heat exchanger appear inferior. Some manufacturers recognize this as a transitional product.

2. Roll-Bonded Finned Tube Heat Exchangers

The advancement of roll-bonded finned tubes was highlighted as early as the 1940s. Books on finned tube steam heat exchangers often compare various types, and roll-bonded finned tubes consistently rank among the top performers. They are a replacement for L-type finned tubes. Advantages of roll-bonded finned tube heat exchangers include: very tight bonding, with contact pressure reaching 75 kg/cm², ensuring no loosening under repeated thermal cycling; fins are formed by cold extrusion of aluminum tubes, undergoing cold work hardening to achieve excellent rigidity, durability, and high thermal efficiency.

3. L-Type Wrap-Finned Tube Heat Exchangers

Advantages and Disadvantages: L-type wrap-finned tubes are made by wrapping an aluminum strip around a steel or copper pipe to form L-shaped fins. In industrial air coolers, compared to roll-bonded finned tubes, L-type wrap-finned tubes are considered obsolete. This is because: the bond is loose, with contact pressure only one-fifth that of roll-bonded finned tubes. When the pipe wall temperature exceeds 70°C, the L-shaped fins begin to loosen, increasing contact thermal resistance; the fins are made of aluminum strip (0.6 mm thick) and although they undergo tensile deformation during winding, the cold work hardening is insufficient, resulting in softer, easily damaged fins and poor reliability.

The type of fin is closely related to the process environment. For example, high-temperature flue gas (coal-fired) currently uses high-frequency helical finned tubes with stainless steel or DN steel base pipes and larger fin spacing. This design ensures that the finned tubes do not melt at high temperatures, maintaining low thermal resistance while considering corrosion and ash cleaning requirements. However, for flue gas from gas-fired systems, where outlet temperatures are lower and there are no corrosion or ash cleaning requirements, steel-aluminum composite finned tubes can be used for waste heat recovery.

Currently, the main heat transfer element in finned tube steam heat exchangers is the steel-aluminum composite finned tube. High-frequency welded finned tubes have the highest manufacturing costs compared to other heat exchangers. Traditional wrap-finned tubes have a small unit heat transfer area and are prone to iron oxide dust entering the circulating air path system. Steel-aluminum composite finned tubes, however, have virtually zero contact thermal resistance, can be cleaned with a high-pressure water jet, have high heat transfer efficiency, and are resistant to mechanical vibrations.

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