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Finned Tube also called extended surface tubes

Finned Tube also called extended surface tubes
Fin tubes generally and regularly used efficient cooling or heating is required. These kind of extended surface tubes are used for the production of air-cooled heat exchangers, shell and tube heat exchangers, Evaporator, condensers and even convection coils used in furnaces.
Fins are basically external and extended surfaces located or inserted on outside of tubes and or pipes in order to increase the total surface area and thermal efficiency, resulting in compact heat transfer equipment. The method of attaching the fins over the tube is very important, since any slightness, air gap between the tube and fins may create an additional resistance to heat flow. When the heat transfer coefficient on the outside of the tube is significantly lower than the heat transfer coefficient on the inside of the tube, there is a major advantage to incorporate fins on the outside tube surface to take full advantage of the high heat transfer rate on the inside of the tube.
If the fin and tube have different thermal coefficients of expansion, the bond may loosen due to a differential movement between them. The loosening effect will increase as the bond temperature increases and consideration must be given to the bond temperature which be attained should the fan fail. The bond may loosen due to the weakening effect of thermal and pressure cycling and also because of corrosion at the fin-base tube junction. Operating temperature limits for the various fin-tubes attachments that our company can offer are given in each section.

Finned Tube
— Extruded, Integral, Bi-metallic Fin
Extruded fin tubes are formed in a cold rotary extrusion process, where continuous helical fins are radically extruded from a thick aluminum muff over a liner tube. The extruded fin is formed from an outer aluminum tube with a large wall thickness (muff), which is aligned over an inner base tube. The two tubes are pushed through three arbors with rotating discs that literally squeeze or extrude the aluminum fins up and out of the muff material in a spiral shape in one operation. The process of extrusion hardens the fins and prevents dissimilar metal contacts at the fin root. Compared to other products, fins do not break, unwind or become loose which affects greatly thermal efficiency. During the finning process a tight mechanical bond is made between the finned aluminum outer tube and inner base tube of the required metal, which is usually steel. The exposed external surface is aluminum and there are no minute gaps between adjacent fins where moisture can penetrate. As the outer tube and fins are integral with one on the temperature, lack of contact between outer and inner tubes can occur to create an additional resistance to heat transfer. The applicable temperature is up to 540 F degree (280 C degree)
Finned Tube

Advantages:
High-efficiency fins for higher temperature applications giving complete and permanent atmospheric corrosion protection of the base tube.
The extended fin is strong enough and resistant to mechanical damage and stand the handling shocks better, compared to other types
Finned tubes can be cleaned without damage using either steam or high-pressure water
The bonding of the outer and inner tubes removes the risk of loss of contact with the aluminium due to thermal stress.
The transfer coefficient remains steady.
As the outer sleeve is continuous no electrolytic couple is created and no galvanic corrosion at the base of the fins can be accrued
Higher heat transfer performance for the life of the unit
No need to fix the fins at ends

Weakness:
This is a costly manufacturing method because of needing a considerable amount of finning material
Total weight of equipment which use this kind of finned tube will be bigger, resulting stronger supporting structure
Maximum operating temperature limits to 280°C.

Application:
Oil and gas refineries
Petroleum, chemical and petrochemical industries
Natural gas treatment
Steel making industry
Power plants
Air conditioning
Compressor coolers
— G-type, Embedded
Geometry:
A helical groove 0.2-0.3 mm (0.008-0.012 in) is ploughed into the outside of the base-tube wall such that metal is only displaced, not removed. The aluminium fin is wound mechanically into the groove under tension, after which the displace metal is rolled back on each side of the fin to hold it in place. That is why this type is also called embedded finned tube. The affective thickness of the base-tube wall is the thickness beneath the groove . This type provides excellent contact, both thermal and mechanical, between fin and groove. Although the base-tube metal is exposed to the atmosphere, tests under server conditions showed that corrosion over a long period is required before any bond weakness occurs.
The G-type fin tube is applicable to high temperature up to 150 F degree (400 C degree)

Finned Tube

Application:
Oil and gas refineries
Petroleum, chemical and petrochemical industries
Natural gas treatment
Steel making industry
Power plants
Air conditioning
Compressor coolers

Advantages:
The fin/tube wall contact is constant because of the setting and makes it possible to use a wall temperature of up to 400°C.
The fin is set throughout its length and consequently does not unwind even when partially uprooted.
This kind of finned tube is one of optimum choices for having good effectiveness/cost ratio.

Weakness:
The fin is not so strong to resist mechanical damage when external forces applied on fin area
Handling shall be done with care to avoid any damage.
Finned tubes may be damaged while using either steam or high-pressure water for cleaning
As the fins are helically wrapped in grouves, un-finned area is not covered which can be exposed to corrosive media and galvanic corrosion at the base of the fins can be accrued
Tube shall be straight with smooth out side area to make a good finned tube
It is hard to use core tube again when finning is failed.
Fins should be fixed at both ends avoiding un-wrapping
— Footed L shape
Geometry:
The L-shaped aluminum fin tube is standard fin for low-temperature application where some degree of tube wall protection is required. The fin is wound mechanically under tension on to the base tube. The short horizontal limb of each L is in contact with the base-tube surface to cover it completely. This construction provides greatly improved fin-tube contact over the knurled base tube. It has been demonstrated by tests that a greatly superior fin-tube contact is achieved by knurling the outside of the base tube and foot of the L-shaped fin. In both designs the whole of the exposed external surface is aluminum. L Foot or shoulder tension construction assures uniform fin spacing, rigidly interlocked by the fin radius overlap over the exposed shoulder edge. The applicable temperature is up to 270 F degree (130 C degree)

Advantages:
Suitable for low-temperature application
The finning type is the most cost effective method compared to the others.
The failed fins can be easily removed during production and bare tube can be used again for finning.
There is no need for make a helical grove over the core tube.
It is possible to place the fins on a very thin-walled tube with is particularly desirable when using expensive alloys as core tube.
The tube can withstand a temperature of up to 130°C without the risk of atmospheric corrosion or thermal stress.

Weakness:
The fin is not so strong to resist mechanical damage when external forces applied on fin area
Handling shall be done with care to avoid any damage.
Finned tubes may be damaged while using either steam or high-pressure water for cleaning
As the fins are helically wrapped in grooves, un-finned area is not covered which can be exposed to corrosive media and galvanic corrosion at the base of the fins can be accrued
Tube shall be straight with smooth out side area to make a good finned tube
Fins should be fixed at both ends avoiding un-wrapping

Application:
Oil and gas refineries
Petroleum, chemical and petrochemical industries
Natural gas treatment
Steel making industry
Power plants
Air conditioning
Compressor coolers

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