Fins are the extended surfaces designed to increase the transfer rate for a fixed surface temperature or lower surface temperature for a fixed heat transfer rate.
These are generally used to increase the heat transfer rate to the environment. It can most commonly be seen in the internal combustion engine to transfer heat to the environment and prevent it from overheating.
There are mainly four types of fins :-
1) Constant Area Straight Fin
2) Variable Area Straight Fin
3) Pin Fin
4) Annular Fin
The fins are generally used in the following:-
1) Economizer for steam power plant.
2) Convectors for steam and hot water heating system.
3) Radiators of automobiles.
4) Air-cooled engine cylinder head.
5) Small Capacity Compressor.
6) Electric Motor Bodies.
7) Transformer and electric equipment etc.
Theory of Heat Transfer From Finned Surfaces:-
According to Newton’s Law Of Cooling, the rate of heat transfer from a surface at a temperature Ts to the surrounding medium at T∞ is given by Newton’s law of cooling as,
Qconv = h As ( Ts – T∞ )
As is the heat transfer surface area
h is the convectional heat transfer coefficient
Temperatures Ts and T∞ are fixed by design consideration.
Rate of heat transfer can be increased in two ways:-
1) Increase the convection heat transfer coefficient (h).
2) Increase the surface area (As).
If we want to increase the convection heat transfer coefficient, it will require installation of a fan or a pump but this approach may or may not be practical.
The alternative solution is the second way that is by increasing the surface area (As). Surface Area (As) can be increased by attaching extended surface to the surface called fins.
This fins are made of highly conductive materials such as aluminum. Dinner surfaces are manufactured by extruding, welding Or wrapping a thin metal sheet on a surface. Heat transfer rate is increased by finned surface by increasing the surface area which is exposed to radiation or convection. This finned surface increases the heat transfer multiple times the original transfer rate.
Following assumptions are made for the analysis of heat flow through the fins are:-
1) Steady State heat condition.
2) Negligible Contact thermal resistance,
3) No heat generation within the fins.
4) Homogenous and isotropic fins material.
5) Uniform heat transfer coefficient (h) over the entire shape of fins.
6) Heat conduction is one dimensional.