Heat conduction in an annulus (Fig. 10B.4), (a) Heat is

Heat conduction in an annulus (Fig. 10B.4), 

(a) Heat is flowing through an annular wall of inside radius r0 and outside radius r1. The thermal conductivity varies linearly with temperature from k0 at T0 to k1 at T1. Develop an expression for the heat flow through the wall. 

(b) Show how the expression in (a) can be simplified when (r1 - r0)/r0 is very small. Interpret the result physically.

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