Air at atmospheric pressure and 100°C enters a 3 m long tube of 4 cm inner diameter with a velocity of 9 m/s and leaves at 192°C. An electric heater is wound on the outer surface of the tube such that...

Air at atmospheric pressure and 100°C enters a 3 m long tube of 4 cm inner diameter with a velocity of 9 m/s and leaves at 192°C. An electric heater is wound on the outer surface of the tube such that heat absorption rate by air per unit area is uniform throughout the length of the tube. If the mean velocity of air is also 9 m/s, find (a) the mass flow rate of air, (b) the rate of heat absorption by the tube from the heater in kW, and (c) the wall temperature of the tube at outlet. Assume average properties of air at 146°C as c_p
= 1.005 kJ/kg K, k = 0.035 W/m K, V = 28.8
 10^–6
m²
/s, Pr = 0.683.