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How Do Finned Tube Heat Exchangers Work?

The surface area which is available for the transfer of heat is extremely important in determining the general heat transfer. The finned tube heat exchangers are essential as they will maximize the transfer of heat across surface areas, and below is an overview of how they work.

Device Functionality

These heat exchangers utilize tubes that feature fins or an external surface area that is extended. Their purpose is to boost the transfer of heat by boosting the transfer area that exists among tubes and the fluid that surrounds them. Finned tubes come in two types, which are transverse and longitudinal.

Transverse Fins

Transverse fins will be typically applied to turbulent and gas flows as well as cross-flow style exchanges.  Tubes that use transverse fins are well suited to air coolers. This is because these fins appear in the form of hollow metallic discs which are spaced and then fitted along a finned tube’s length. The fin discs themselves may be tapered or flat, and the heated transfer coefficients along the fin’s surface will depend heavily on finned disc geometry.

Longitudinal Fins

Longitudinal style fins are well suited to applications where external tube flow is streamlined along the length of the cylinder. An example of this would be dual-pipe heated exchangers that have fluid that is highly viscous outside their finned tube. The majority of longitudinal fins within a tube will run along its length. They have a cross-sectional form which may either be tapered or flat.

Design

To design a finned tube heated exchanger in a manner that will boost the heated transfer area, the designer will need specific heat calculations as well as optimal spacing for the tubes to create the right environment. Generally speaking, a greater heat transfer region usually culminates in higher heated exchange efficiency.

This is because heated transfer coefficients near surfaces outside and inside these tubes will be calculated through the usage of correlations that have been experimentally determined.  The heated transfer efficiency for the fins will also be calculated by utilizing corrections. Distinct correlation sets have been made available to calculate the transfer efficiency of heat for both transverse and longitudinal fins. When the fin region is multiplied by the finned heated transfer efficiency and then subsequently added to the bare tube region, the result will be an external heated transfer area that is effective.

The general heated transfer coefficient may be determined through the addition of heated transfer resistances which have been evaluated in the interior and exterior tube surface areas. For the external area, the value for an effective area will be utilized. Lastly, if the velocity of the external fluid is altered significantly, this means the heated transfer coefficients, as well as the needed tube area, should be reevaluated.

Applications

These heat exchangers are ideal in scenarios where you have a lower heated transfer coefficient outside the tubes. In this case, the additional heated transfer area which is generated by the fins will assist in ensuring the needed heat transfer rate has been made possible. This means they can be used for applications that entail external air and liquid within the tubes.

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