It is well known that wind makes cold air feel much colder as a result of the wind-chill effect, which is due to the increase in the convection heat transfer coefficient as a result of the increase in air velocity. The wind-chill effect is usually expressed in terms of the wind-chill factor, which is the difference between the actual air temperature and the equivalent calm-air temperature. For outdoor air temperature of 0 C, for example, the wind chill temperature -5 C at 20km/hr winds and -9 C at 60km/hr winds. That is, a person exposed to 0 C windy air at 20km/hr will feel as cold as a person exposed to -5 C calm air (air motion under 5 km/hr).
For heat transfer purposes, a standing man can be modeled as a 30-cm-diameter, 170-cm-long vertical cylinder with both the top and bottom surfaces insulated and with the side surface at an average temperature of 34 °C. For a convection heat transfer coefficient of 15 W/(m2.°C), determine the rate of heat loss from this man by convection in still air at 20 °C. What would your answer be if the convection heat transfer coefficient was increased to 30 W/(m2.°C) as a result of winds? What is the wind-chill factor in this case?