Air flows through a 25 mm diameter tube with a mean velocity of 30 m/s. The tube wall temperature is 280°C and the air temperature increases from 20°C to 260°C. Using the simple Reynolds’s analogy calculate, the length of the tube required and the pumping power. For turbulent flow in a tube, take $f=\frac{0.046}{Re^{0.2}_{d}}$ The properties may be taken at the mean film temperature and from the Tables are:
k = 38.45 $\times$ 10–3 W/m °C ;cp= 1.0268 kJ/kg °C ; r = 0.7306 kg/m3 ;
m= 26.17 $\times$10–6 kg/ms