The temperature of air flowing through a 25-cm-diameter duct whose inner walls are at 320°C is to be measured with a thermocouple soldered in a cylindrical steel wall of 1.2 cm OD, whose exterior is oxidized as shown in the accompanying sketch. The air flows normal to the cylinder at a mass velocity of 17,600 kg/(h m2). If the temperature indicated by the thermocouple is 200°C, estimate the actual temperature of the air.
GIVEN
Cylindrical thermocouple wall in an air duct
Duct diameter (Dd) = 25 cm = 0.25 m
Duct wall temperature (Tds) = 320°C =m 593 K
Wall outside diameter (Dw) = 1.2 cm = 0.012 m
Exterior of wall is oxidized
Air mass velocity (m