Finned Tubes, Forced Draft - air heaters, air coolers, air cooled oil coolers, wire wound fin tubes (pin fin tubes), turbulators, fin tube heat exchangers

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Finned Tube Heat Exchangers

Air Heaters

Air Coolers

Oil Coolers

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Spiral Crimped Fin Tubes

Wire Inserts (Turbulators)

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Finned Tubes

Generally, addition of any metal piece to a heat transfer tube is an extended surface. The addition or attachment of these metal pieces serves a purpose greater than just increase in external area. These pieces are commonly referred to as fins. The fins increase the total heat transfer area, but the process of heat transfer in these is quite different than simple conduction and convection.

Finned Tube Heat Exchangers

Heat exchangers of forced draft type for  heating or cooling of gases, more commonly air and viscous fluids like lube oil, hydraulic oil, gear oil almost always necessitate use of fin tubes or extended surfaces to enhance the heat transfer film coefficient on gas and oil side.

In most applications, the arrangement of pass partitions makes it possible to optimize mass flow rate of the heating or cooling medium to provide optimum tube side heat transfer coefficient. However, the controlling film resistance is on the air or gas side. Use un finned tubes results in very low film heat transfer coefficients thereby 'wasting' high tube side coefficient, resulting in a design requiring large number of tubes and several rows of bare tubes. This results in high pressure losses.

Fins create turbulence around the  tube as well as between the fins. This reduces the air side film resistance and increases air side heat transfer coefficient many fold. The resulting design is compact heat exchanger, economical, with low pressure drops.

Air Heaters

Hot air is required in dryers. Forced draft air heaters are used for this purpose. Process Air is heated using steam, hot water, Hot Oil, Thermic Fluid or Hot Gas. Electrical Heating is expensive though electrical heaters have low initial cost. Fluid heated Air Heaters have a low operating cost compared to Electric Heaters though the initial investment is higher.

Steam Air Heaters or Steam Radiators

Steam air heaters or steam coils or Steam Radiators are forced draft heat exchangers in  which steam is condensed in the tubes while the other medium is air or gas being heated when forced through the finned exchanger. Condensing coefficient of steam is very high and makes the air side heat transfer coefficient controlling. Hence it is very important that the air side heat transfer coefficient be improved as much as possible as dictated by pressure drop constraints. When the temperature of heated air desired is not high Steam Air Heaters is a good choice. Generally Steam Air Heater uses low-pressure steam, which is readily available. Steam Air Heaters using high pressure steam are not uncommon.

Thermic Fluid Air Heaters, Hot Oil Heated Air Heaters

Thermic Fluid heated air heaters are used when higher temperatures say over 160 deg C of heated air are required. Though hot oil heated and thermic fluid or thermic oil heated Air Heater can and is used to heat air to lower temperatures in the range 60 C - 120 C too. Commonly used thermic fluids are Dowtherm, Therminol, Marlotherm.

Hot Water heated Air Heaters

Hot water (with or without additives) under pressure is also used as heating medium for heating gases to temperatures up to about 120 degree C.

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Air Coolers

Several applications require cooled, dehumidified air and others require hot air or hot gas generated in the plant to be cooled down before sending to exhaust. To cool air, a cooling medium such as cooling water, brine, glycol, cooling air is passed through the fin tubes.

Oil Coolers - Air Cooled, Air Blast

Oil Coolers cooled by ambient air may be called air cooled oil cooler or air blast oil cooler. Oils like hydraulic oil, lube oil, gear oil are viscous, thereby flow in streamline flow in most cases. Even otherwise, these have very low heat transfer coefficient. As explained above air too offers low heat transfer coefficient making it necessary to provide external as well as internal fins to improve the overall heat transfer coefficient.

To increase the tube side heat transfer coefficient, turbulators ( also called tube inserts, internal fins) are inserted inside the tubes. The tube insert causes turbulence and reduces the resistance to heat transfer by the oil side film. Turbulators of various types can be used: wire wound tube inserts soldered to the inner surface of the fin tube,  spring stretched in  tube, twisted tape inserts.

Transverse Fins

Transverse or radial fins are attached perpendicular to the axis of the base tube. The fins may be applied or attached to the tube or rolled up from the parent metal of the tube. The common types of transverse or radial fin tubes are:

Helically Wound Spiral or Crimped Fin Tubes

These fin tubes consist of a strip of metal  tension wound on tube . Unless root  soldered along the base, the percentage void space between the fin and base tube  cannot be ascertained. This leaves some doubt  about the actual performance. The maximum operating wall temperature for this type of root soldered finned tubes (manufactured by us) is 290 deg C.

Wire Wound Fin Tubes

Root soldered wire wound tubes consist of loops of wire helically wound over tube. The foot of each loop is root soldered to the base tube. The key factor here is use of proper tension wire and good soft soldered bond of the fins to base tube to eliminate all voids between loop and the base tube. The maximum operating wall temperature for this type (manufactured by us) is 290 deg C.