A Colorful Demonstration of Thermal Refraction
  The wave nature of heat flow mechanisms, such as lattice waves is discussed. Tan and Holland's Tangent Law of heat flow refraction is reviewed. A classroom demonstration of heat flow refraction through conductors in series is presented, and sample results are examined for consistency with the Tangent Law. To predict results, the Tangent Law is derived from the Principle of Least Resistance for this demonstration. User-modifiable simulations in Ruby and Ruby on Rails are presented, along with simulation results for various combinations of conductors. Results are interpreted in terms of the Principle of Least Time, illustrating a powerful unification in physics between disparate areas such as optics and thermodynamics. 
Mark Ciotola and Olivia Mah
physics.ed-ph