Principles of Unidirectional Heat Transfer

In spite of the fact that the film is circular in shape, the process of heat transfer can be taken as unidirectional through its thickness, because the thickness of the film is much smaller than the radius of the cross-section (circular in shape), either for the sheath or for the bottle. 

The following modes of heat transmission are considered conduction and convection, since radiation does not seem to play an important role. 

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