THE BASIS OF WIND CHILL

The practical success of the wind chill index has often been vaguely a ttributed to the effect of wind on heat transfer from bare skin, usual ly the face. To test this theory, facial heat loss and the wind chill index were compared. The effect of wind speed on heat transfer from a thermal model of a head was investigated in a wind tunnel. When the th ermal model was facing the wind, wind speed affected the heat transfer from its face in much the same manner as it would affect the heal tra nsfer from a small cylinder, such as that used in the original wind ch ill experiments carried out in Antarctica fifty years ago. A mathemati cal model of heat transfer from the face was developed and compared to other models of wind chill. Skin temperatures calculated from the mod el 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 roug hly proportional to it. Wind chill equivalent temperature were recalcu lated on the basis of facial cooling. An equivalent temperature increm ent was derived to account for the effect of bright sunshine.