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Heat Transfer through Fins

By BYJU'S Exam Prep

Updated on: September 25th, 2023

Heat transfer through fins is a fundamental process that plays a vital role in various engineering applications. The process involves transferring heat from a surface to the surrounding fluid through a finned surface, which significantly enhances the rate of heat transfer. Fins are widely used in various thermal systems such as air-cooled heat exchangers, refrigeration systems, electronic cooling devices, and many more. The primary purpose of using fins is to increase the surface area of a heat transfer device and thereby improve its heat transfer efficiency.

Fins are slender extensions or protrusions that are attached to the surface of a heat transfer device. The shape and size of fins can vary significantly depending on the application and the nature of the heat transfer problem. The most commonly used fin geometries are rectangular, triangular, and circular. Fins can be made of various materials such as metals, plastics, ceramics, and composites, depending on the operating conditions and the desired properties. Let’s take deep dive into the concepts related to heat transfer through fins.

Heat Transfer Through Fins

The mechanism of heat transfer through fins is primarily based on the principles of conduction, convection, and radiation. The heat from the base surface is conducted through the fin and then convected to the surrounding fluid, which is typically air. The heat transfer rate through a finned surface depends on various factors such as the fin geometry, fin material, fluid properties, and the temperature difference between the surface and the surrounding fluid. Therefore, designing an optimal finned surface requires a thorough understanding of these factors and their interplay.

The most commonly used fin geometries are rectangular and triangular fins, although other shapes such as circular, elliptical, and annular fins are also used in specific applications. The choice of fin material is important as it affects thermal conductivity, which is a measure of the ability of a material to conduct heat. Commonly used materials for fins include aluminium, copper, and steel. The fluid properties, including the flow rate and temperature, also play a crucial role in determining the effectiveness of the fins in heat transfer.

Process of Heat Transfer Through Fins

Heat transfer through fins is a process that involves the transfer of heat from a hotter surface to a cooler one through a finned surface. Fins are thin, elongated structures that are attached to a base surface, which can be a wall, a pipe, or a plate, and are designed to increase the surface area for heat transfer. The transfer of heat occurs through three modes: conduction, convection, and radiation.

Conduction Heat Transfer

Conduction is one of the three modes of heat transfer, which is the transfer of heat energy between two objects in contact due to a temperature gradient. In other words, it is the transfer of heat from a hotter object to a cooler object through a medium or a material without any bulk motion of the medium.

Conduction occurs due to the movement of the free electrons in a material or a medium when they collide with other particles, transferring energy in the process. Materials with higher thermal conductivity, such as metals, conduct heat more efficiently than materials with lower thermal conductivity, such as insulators.

Convection Heat Transfer

Convection is one of the three modes of heat transfer, which involves the transfer of heat energy by the motion of fluids, such as liquids and gases. In convection, heat is transferred from a hotter object to a cooler one through the movement of the fluid.

Convection occurs in two forms: natural convection and forced convection. Natural convection happens when the fluid motion is caused by the temperature difference alone, without any external force, while forced convection occurs when the fluid motion is caused by external means, such as a fan or a pump.

Radiation Heat Transfer

Radiation is one of the three modes of heat transfer, which involves the transfer of energy through electromagnetic waves, such as infrared radiation, visible light, and ultraviolet radiation. Unlike conduction and convection, radiation does not require any medium for energy transfer and can occur even in a vacuum.

All objects emit and absorb radiation, with the rate of emission and absorption being proportional to the temperature of the object and its emissivity. Emissivity is a property of an object that describes how well it can emit and absorb radiation. Objects with a high emissivity are good absorbers and emitters of radiation, while those with low emissivity are poor absorbers and emitters of radiation.

Heat Transfer from Extended Surface (Fin)

Heat transfer from extended surfaces, or fins, is a common heat transfer process used in many engineering applications, such as heat exchangers, electronic cooling, and air conditioning. Fins are thin, elongated structures that are attached to a base surface, which can be a wall, a pipe, or a plate, and are designed to increase the surface area for heat transfer.

  • A fin is a surface that extends from an object to increase the rate of heat transfer to or from the environment by increasing convection.
  • Adding a fin to an object increases the surface area and can sometimes be an economical solution to heat transfer problems.
  • Finned surfaces are commonly used in practice to enhance heat transfer. In the analysis of the fins, we consider steady operation with no heat generation in the fin.
  • We also assume that the convection heat transfer coefficient h is constant and uniform over the entire surface of the fin.

Heat

  • The rate of heat transfer from a solid surface to the atmosphere is given by Q = hA ∆ T where h and ∆T are not controllable.
  • So, to increase the value of Q surface area should be increased. The extended surface which increases the rate of heat transfer is known as the fin.

Generalized Equation for Fin Rectangular fin:
Heat Transfer through Fins

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