Randall D. Knight — Work, Heat, and the First Law of Thermodynamics: Problem 37

Radiation from the head is a major source of heat loss from the human body. Model a head as a 20-cm-diameter, 20-cm tall cylinder with a flat top. If the body’s surface temperature is \(35^{\circ}\text{C}\), what is the net rate of heat loss on a chilly \(5^{\circ}\text{C}\) day? All skin, regardless of color, is effectively black in the infrared where the radiation occurs, so use an emissivity of 0.95.