Question: Two thermometers are placed in an air stream flowing through a circular duct. One of these thermometers, which has been silvered on the outside, reads 100°F. The other is a plain mercury-in-glass thermometer and reads 150°F. The heat transfer coefficient for both thermometers is 2 Btu/(h ft2 OF). The emissivity for the silvered surface is 0.02 and that of the glass surface 0.94. Assuming that the readings are correct, calculate the temperature of the duct walls and that of the gas.