2.5 Fins

Heat transfer from a solid surface to the ambient (or any fluid) takes place by convection. The rate of heat transfer by convection is given by \[Q = hA(T_s - T_\infty)\] This convective heat transfer from a surface at \(T_s\) can be increased by two methods:

  • increasing the convective heat transfer coefficient, \(h\)

  • increasing the surface area, \(A\)

Increasing the convective heat transfer coefficient may not be practical and/or adequate in certain cases. An increase in surface area by attaching extended surfaces, as thin strips of metal, called as fins to the surface is more convenient.

  • When heat transfer takes place by convection from both interior and exterior surfaces of a tube or a plate, generally fins are used on the surface where the heat transfer coefficient is low.

  • Examples of fin:

    • Thin rods on condenser in back of refrigerator

    • Honeycomb surface of a car radiator

    • Corrugated surface of a motorcycle engine

Typical shapes of fins are given in Fig.(5).