This is all known physics. It's almost exactly Newton's Law of cooling -- see https://en.wikipedia.org/wiki/Newton%27s_law_of_cooling#Standard_formulation https

This is all known physics. It's almost exactly Newton's Law of cooling -- see https://en.wikipedia.org/wiki/Newton%27s_law_of_cooling#Standard_formulation https://en.wikipedia.org/wiki/Newton%27s_law_of_cooling#Stan... -- which has been known for a long time and is a mono exp. The biexponential behaviour is because the _actual_ relevant differential equation, the Thermal Diffusion Equation, has a Fourier mode solution and you've picked out two coefficients. An infinite sum of them _is_ the answer. How you pick out the coefficients is the fun game of https://en.wikipedia.org/wiki/Spectral_methods https://en.wikipedia.org/wiki/Spectral_methods