Hot water flows inside a PVC pipe $($conductivity $0\mathrm{.}15$ W m $1$ K$1)$ of inner diameter $25$ mm

and wall thickness $2\mathrm{.}5$ mm$.$ The inside surface temperature is $60$C and the outside surface

temperature is $55$C$.$ What is the heat transfer rate through the pipe wall, per unit length of

pipe? What error would result from treating the pipe as a plane wall $($neglecting its

curvature$)$