nx_ice_recrystal.nx

nx_ice_recrystal.nx -- HOW FROZEN DESSERT ACTUALLY DIES. ===== WHY THIS EXISTS ============================================ The stability stack in this lane models first-order CHEMICAL degradation: a molecule decays, potency falls, an expiry date follows. For most products that is the failure mode. For ice cream it is not. Ice cream almost never fails chemically. It fails because its ice crystals GROW -- small crystals melt and re-deposit onto large ones until the texture turns coarse and sandy. That process is not first order, it has no activation energy in the Arrhenius sense, and it is driven mainly by temperature FLUCTUATION rather than by mean temperature. So the lane had a complete frozen-dessert stack and a complete stability stack, and nothing that could say when an ice cream goes bad. ===== THE MECHANISM ============================================== Ostwald ripening. A small crystal has high surface curvature, which by the Gibbs-Thomson effect depresses its local melting point -- so on any warming it is the small crystals that melt first. On the following cooling that water refreezes, but onto the crystals that survived, which are the large ones. Every cycle therefore removes small crystals and feeds large ones. Nothing is lost or gained in mass; the DISTRIBUTION coarsens, and coarseness is what the tongue detects. Isothermal growth follows the cube law of Lifshitz-Slyozov-Wagner: D(t)^3 = D(0)^3 + k*t The cube is the signature of diffusion-limited ripening and is why recrystallisation cannot be written as a rate constant on concentration. ===== WHAT IS COMPUTED VS ASSERTED =============================== ★THE CYCLING TERM IS DERIVED, NOT ASSERTED, AND THAT IS THE POINT. The mass of ice that melts and refreezes on a warm excursion is exactly the change in frozen fraction between the two temperatures -- and this lane already computes frozen fraction from colligative physics (ic_frozen_water_permil). So cycling damage falls straight out of the