Question

Heat is lost from a 100 mm diameter steam pipe placed horizontally in ambient air at 30°C. If the Nusselt number of air is 25 and the thermal conductivity of air is 0.03 W/mK, then the heat transfer co-efficient of air will be_______ W/m^2K.

Answer 1

answer : 7.5 W/m²K

explanation : we know the relation,

$N=\frac{hd}{k}$

where , N is Nusselt number , h is heat transfer co - efficient, d is diameter and k is thermal conductivity.

here, N = 25 , d = 100mm = 0.1m, k = 0.03 W/mk

so, 25 = h × 0.1/0.03

or, h = 25 × 0.03/0.1 = 7.5 W/m²k

hence, heat transfer co-efficient of air will be 7.5 W/m²k