Question

Which area is used in case of heat flow by conduction through a cylinder

Answer 1

I guess the Logarithmic mean are is used in case of heat flow by conduction through a cylinder.

as heat transfer area in case of cylinder is contineously varying from inner radius to outer radius, so the utility of log mean area is to deduce a constant area for the same amount of heat transfer. So if we want to find out the area of slab for the same amount of heat transfer then log mean area is used.