The main duct of an air conditioning system is rectangular in cross-section (400 mm 800 mm) and has air at atmospheric pressure and at 20°C flowing with a velocity of 7 m/s. Estimate the heat leakage...

The main duct of an air conditioning system is rectangular in cross-section (400 mm

800 mm) and has air at atmospheric pressure and at 20°C flowing with a velocity of 7 m/s. Estimate the heat leakage per metre length per unit temperature difference.

Hints: Find properties of air at 20°C from the Appendix:
, c_p, k,
, n and Pr. The hydraulic diameter

and Re_d
=

. From Dittus–Boelter equation Nu_d
= 0.023

Pr^0.4, find h and Q/L = h.P(T_w
– T_b).