Heat transfer through the cladding

There is usually a fairly significant temperature difference across the cladding. The heat transfer area, A, at an arbitrary distance, r, along a radius will be given by 

Since the heat passing, 4 will be constant in the steady state, it is a simple matter to integrate equation (A8.22) from one side of the cladding to the other, i.e. from r = bto r = d and thus produce  

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