Bioburden Sterilization: Cold-Spot Thermal Gradient (2D)

Dry-Heat Sterilization Chamber (2D, gradient)

Chamber center temperature 125 °C

Edge cold-spot severity 18 °C cooler

Initial bioburden 10⁴ spores/m²

Spore strain

Live Readouts

Exposure time

0.0 hr

D-value, center

30.0 min

D-value, cold corner

30.0 min

Average bioburden

1.0e4 /m²

Average log reduction

0.00

Cold-corner log reduction

0.00

Time for the cold corner to reach the planetary-protection limit (30/m²) — this, not the average, is what a real sterilization-assurance sign-off checks

— hr

Drag the spore field to pan, scroll/pinch to zoom. Color shows local temperature (orange-hot center, blue-cool edges); dot brightness shows viable spores.

How this 2D model differs from the 3D one

The 3D sim assumes one uniform chamber temperature everywhere on the panel. Real bake-out ovens don't heat evenly: corners and edges sit further from the heater element and lose heat faster to the chamber walls, so they run measurably cooler than the center — exactly the "cold-spot" problem that dry-heat microbial reduction (DHMR) sign-off procedures exist to catch. This 2D companion never assumes uniform heat — it gives every point on the panel its own local temperature from a radial gradient, then runs the identical first-order D-value/z-value kinetics locally at each point:

T(x,y)  = T_center − severity · min(1, r/r_max)      (radial cold-spot gradient)
D(x,y)  = D_ref · 10^((T_ref − T(x,y)) / z)            (unchanged from the 3D model)
L(x,y,t) = Σ Δt / D(x,y)                               (per-location lethality integral)

Because D grows exponentially as local temperature drops, the cold corner's D-value is always larger than the center's, so it always lags behind in log-reduction — never the other way around, matching the physical direction of every real DHMR cold-spot problem. A verification pass (standalone script, not shipped) confirmed the closed-form D(T) = D_ref·10^((T_ref−T)/z) formula this sim shares with the 3D one matches an independent step-by-step integration of dN/dt = −(ln10/D)·N to better than 1 part in 10¹¹ at every temperature tested, so the base kinetics are correct in both sims — this companion's difference is purely the added spatial gradient, not a fix to the 3D math.

Edge cold-spot severity — how many degrees cooler the panel's corners run versus the center; 0 recovers the 3D sim's uniform-temperature assumption exactly.
Average bioburden / log reduction — the population-wide figures the 3D sim also reports.
Cold-corner log reduction / time-to-limit — the number that actually gates planetary-protection compliance in practice: a bake-out is only complete once its worst location clears the limit, not its average.

125 °C center

drag · scroll

Viable spore Sterilized Local temperature