Wrong in the surface area of each section

[JRY-Zheng]

The amount of heat lost from each section is qh=-h*Asi*(Ti-Tamb), where Asi is the surface area of the i-th section, which, hence, should be 2*pi*R*L/n.
But in the implementation, As is 2*pi*R*L and qh is calculated by -h*As*(Ti*Tamb).
I've checked all issues containing "Rod" to make sure this issue is not duplicated. Some relative issues are:
#243 suggests to add an area term in the convective term and to consider the convective term for every section besides the first and the last elements.
#454 suggests the unit of h is wrong due to the added area term in #243 .