- Bejan, Adrian, Optimum hair strand diameter for minimum free-convection heat transfer from a surface covered with hair,
International Journal of Heat and Mass Transfer, vol. 33 no. 1
pp. 206 - 209 [0017-9310(90)90154-M] .
(last updated on 2007/04/08)
The objective of this note is to present an interesting trade-off that may determine the natural size (diameter) of the hair strand in the protective coat of an animal. The general view is that hairs provide an insulation effect by trapping a layer of air, which has a low thermal conductivity. This view, however, is incomplete. An additional function of the hair strand - an unwanted effect in the thermal insulation sense - is to act as a pin fin, and to augment the heat transfer from the otherwise bare area (the skin) Numerous thin hairs may be useful in slowing down the air flow that sweeps the skin, but they can also act as fins to the point that they can defeat the thermal insulation effect associated with the slower air flow.
Heat Transfer--Fins;Biological Materials--Skin;