Answer:
U = 11.67 W/m² °C
Explanation:
Inner diameter, d = 2.5 cm = 0.025 m
Thickness of the wall, t = 2 mm = 0.002 m
thus, the outer diameter, D = d + 2t = 0.025 + 2 x 0.002 = 0.029 m
[tex]h_i =500 W/m^2.^oC[/tex]
[tex]h_0 =12 W/m^2.^oC[/tex]
Now, based on outside convection heat transfer
we have
[tex]\frac{1}{UA_o}=\frac{1}{h_iA_i}+\frac{1}{h_oA_o}[/tex]
on rearranging, we get
[tex]\frac{1}{U}=\frac{1}{h_i}\frac{A_o}{A_i}+\frac{1}{h_o}[/tex]
where, [tex]A_i\ \textup{and}\ A_o[/tex] are the perimeter respective to inner and and outer diameter
on substituting the values, we get
[tex]\frac{1}{U}=\frac{1}{500}\frac{0.029^2}{0.025}+\frac{1}{12}[/tex]
or
U = 11.67 W/m² °C
