This workbook implements a simple 1D extended surface heat transfer model in a completely open and transparent form.   The geometry implemented here is a straight, annular fin.  The control volume energy balance is stated:

In by Conduction – Out by Conduction – Out by Convection = 0

The resulting tridiagonal system of linear equations for the temperature distribution involve what Excel calls a “circular reference,” but Excel’s iteration capability takes care of that.     The coefficients linking successive cells and implemented in cell formulae may easily be changed to accommodate other 1D extended surface geometries (triangular, straight rectangle, pin, etc.).   It may be easily revised to include spatially variable convection coefficient or thermal conductivity.

This workbook computes the temperature distribution and plots it in the bottom left corner.   The computed temperature distribution can, if desired, be used to find the fin efficiency or fin effectiveness.   Another HTT workbook computes the former from the analytical solution for this same annular fin geometry.