Selection of fins
In any application, selection of a particular fin
configuration may depend on space, weight, manufacturing,
and cost consideration, as well as on the
extent to which the fins reduce the surface convection
coefficient and increase the pressure drop associated
with flow over the fins [8]. Theoretically, fins are used
to increase the heat transfer from a surface by
increasing the effective surface area. However, the fin
itself represents a conduction resistance to heat
transfer from the original surface. In addition, the
significant potential improvements in convective heat
transfer can be offset by the increased amount of
energy that is stored, and subsequently removed from the mold. For these reasons, there is no
assurance that the heat transfer rate will be increased
through the use of fins. Fin effectiveness can be
enhanced by the choice of a material of high thermal
conductivity. Aluminum alloys and copper come to
mind. However, although copper is superior from
the standpoint of thermal conductivity, aluminum
alloys are the more common choice because of
additional benefits related to lower cost and weight.
Fin effectiveness is also enhanced by increasing the
ratio of the perimeter to the cross-sectional area. For
this reason the use of thin, but closed spaced fins is
preferred, with the proviso that the fin gap not be
reduced to a value for which flow between the fins is
severely impeded, thereby reducing the convection
coefficient.