A probe, used to measure the velocity of air in a low- speed wind tunnel, is fabricated of an L = 100 mm long, D = 8-mm outside diameter horizontal alu- minum tube. Power resistors are inserted into the sta- tionary tube and dissipate P = 1.5 W. The surface temperature of the tube is determined experimentally by measuring the emitted radiation from the exterior of the tube. To maximize surface emission, the exte- rior of the tube is painted with flat black paint having an emissivity of s = 0.95.

(a)  For air at a temperature and cross flow velocity of Too = 25°C, V = 0.1 m/s, respectively, determine the surface temperature of the tube. The surround- ings temperature is Tsur = 25°C.

(b) For the conditions of part (a), plot the tube surface temperature versus the cross flow velocity over the range 0.05 m/s V 1 m/s.