⇨ Fins or Extended Surfaces:
- It is possible to increase the heat transfer rate by increasing the surface used for increase heat transfer are called extended surface or fins.
- The fins are normally thin strips of highly conducting metals such as aluminum, copper, brass etc.
⇨Applications :
- Economizer's for steam power plants,
- Air cooled engine cylinder heads.
- For cooling electric power transformers and electric motors, ICs
- Attached fins on tubes to promote heat exchange between air and the working fluid of an air conditioner.
⇨Types of Fins:
Fins are of two types :
1. Fins of uniform cross-sectional area :
a. Fins of rectangular profile, and
b. Fins of circular profile.
2- Fins of non - uniform cross-sectional area :
a. Longitudinal fin of trapezoidal profile,
b. Longitudinal fin of parabolic profile, and
c. Truncated conical Spline.
⇨Advantages :
1. By using the fin, heat transfer rate can be increased without any preventive maintenance.
2. It is the cheapest way for increasing the heat transfer rate from the hot bodies.
⇨Disadvantages:
We know that the length of fins is directly proportional to the heat transferring rate. But the larger length is may be cause of bending in the fins and also increases the weight of engine. Therefore the overall efficiency will goes to decrease.
⇨Efficiency of Fin :
It is defined as the ratio of the actual heat transferred by the fin to the ideal maximum heat transferable by fin, if entire fin area were at base temperature.
⇨Effectiveness of fin:
Fin effectiveness is defined as the ratio of the fin heat transfer rate to that of which would occur from the surface on which the fin was attached, therefore,
⇨Derive an expression for temperature distribution heat transfer rate in a straight fin of rectangular profile, When.
i. Fin tip is insulated.
ii. Heat dissipation from an infinite long fin.
iii. The fin is of finite length and losses heat by convection.
