$\frac{d^{2}T}{d{x}^2}=0,0xD$ with $B.C.\{\begin{array}{ccc}-k\frac{dT}{dx}=h_1|T_{a1}-T(x=0)|& at& x=0\\ -k\frac{dT}{dx}=h_2|T(x=D)-T_{a2}|& at& x=D\end{array}$

where $h_1$ and $h_2$ are the uniform convective coefficients at $x=0$ and $x=D,$ respectively,

$T_{a1}$ and $T_{a2}(T_{a2}>T_{a1})$ are the respective uniform fluid temperatures.

Solution: $T(x)=T_{a1}+\frac{T_{a2}-T_{a1}}{\frac{1}{h_1}+\frac{D}{k}+\frac{1}{h_2}}(\frac{1}{h_1}+\frac{x}{k})$