Aerogel Catalyst Pellet: Transient Pore Diffusion (2D)

The 3D version of this simulator colours a static cloud of pellet nodes from the closed-form steady-state formula for a first-order reaction in a sphere. This 2D counterpart instead solves the real time-dependent spherical diffusion-reaction PDE with an implicit finite-volume scheme on a graded radial grid (clustered toward the pellet surface, where the concentration gradient is steepest for a high Thiele modulus), and animates the concentration field as it actually diffuses in from the surface and settles — watch a fresh reactant front invade the pellet every time you move a slider, converging onto the same Thiele-modulus effectiveness factor η the analytical theory predicts, plotted live against the exact steady-state curve for comparison.