B3. A 3-cm-diameter thin-walled horizontal steam pipe passes through a large room whose air and wall
temperatures are 20°C. Due to high flow rate of steam, the pipe assumes the temperature of the steam at 120°
C. The steam pipe is covered by a 2-cm-layer of insulation ($k_{ins}$ = 0.036 W/m-K), as shown below. The
outer insulation surface is painted acrylic white.
(a) Determine the temperature at the outer insulation surface (in °C).
(b) Determine the rate of natural convection heat transfer (in W) per meter of the pipe.
(c) Determine the emissivity of the outer insulation surface and rate of net radiation heat transfer (in W)
per meter of the pipe.
I
2 cm
$T_{\infty}=T_{surr}=20^{\circ}C$
D=3 cm
Insulation
