The Basis of Wind Chill

Abstract

The practical success of the wind chill index has often been vaguely attributed to the effect of wind on heat transfer from bare skin, usually the face. To test this theory, facial heat loss and the wind chill index were compared. The effects of wind speed on heat transfer from a thermal model of a head was investigated in a wind tunnel. When the thermal model was facing the wind, wind speed affected the heat transfer from its face in much the same manner as it would affect the heat transfer from a small cylinder, such as that used in the original wind chill experiments carried out in Antarctica fifty years ago. A mathematical model of heat transfer from the face was developed and compared to other models of wind chill. Skin temperatures calculated from the model were consistent with observations of frostbite and discomfort at a range of wind speeds and temperatures. The wind chill index was shown to be several times larger than the calculated heat transfer, but roughly proportional to it. Wind chill equivalent temperatures were recalculated on the basis of facial cooling. An equivalent temperature increment was derived to account for the effect of bright sunshine.

Key words: bioclimatology, cold injuries, cold weather, convective heat transfer, face cooling, frostbite, heat loss, survival, wind chill