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__Introduction of Fins:__

__Introduction of Fins:__

Fins
are the extended surfaces designed to Increase heat transfer rate for a fixed
surface temperature, or lower surface temperature for a fixed heat transfer
rate.

__Types of Fins:__Types Of Fins |

__HEAT TRANSFER FROM FINNED SURFACES__

The
rate of heat transfer from a surface at a temperature

*Ts*to the surrounding medium at*T*_{infinity}is given by Newton’s law of cooling as,Equation of fins |

where.

*As*is the heat transfer surface area and

*h*is the convection heat transfer coefficient

temperatures

*Ts*and*T*_{infinity}are fixed by design considerations,
There
are

**to increase the***two ways*to increase the rate of heat transfer:*or to increase the*__convection heat transfer coefficient h__*surface area As.*Increasing*h*may require the installation of a pump or fan, or replacing the existing one with a larger one, but this approach may or may not be practical. Besides, it may not be adequate.
The
alternative is to increase the

**by attaching to the surface**__surface area__*extended surfaces*called*fins*made of highly conductive materials such as aluminum. Finned surfaces are manufactured by extruding, welding, or wrapping a thin metal sheet on a surface. Fins enhance heat transfer from a surface by exposing a larger surface area to convection and radiation.
Finned
surfaces are commonly used in practice to enhance heat transfer, and they often
increase the rate of heat transfer from a surface several fold. The car
radiator shown in Fig. below is an example of a finned surface. The closely
packed thin metal sheets attached to the hot water tubes increase the surface
area for convection and thus the rate of convection heat transfer from the
tubes to the air many times. There are a variety of innovative fin designs
available in the market, and they seem to be limited only by imagination.

Innovation In Fins |

In
the analysis of fins, we consider

*steady*operation with*in the fin, and we assume the thermal conductivity***no heat generation***k*of the material to remain*constant.*
We
also assume the convection heat transfer coefficient

*h*to be*constant*and*uniform*over the entire surface of the fin for convenience in the*analysis.*
We
recognize that the convection heat transfer coefficient

*h*, in general,*varies along the fin as well as its circumference, and its value at a point**is a strong function of the**fluid motion*at that point.
The value of

*h*is usually*much lower at the**fin base*than it is at the*fin tip*because the fluid is surrounded*by solid surfaces near the base, which seriously disrupt its motion to the point of***“suffocating”**it, while the fluid near the fin tip has little contact*with a solid surface and thus encounters little resistance to flow.*

**Therefore,**

*adding too many fins on a surface may actually decrease the overall heat**transfer when the decrease in**h*offsets any gain resulting from the increase in*the surface area.*
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