Same well-mixed single-compartment model as the 3D version: crew shed bioaerosols at rate G while the ECLSS pulls cabin air through a HEPA filter at flow Q with single-pass efficiency η. This 2D companion adds a live strip chart of N(t) below the duct view so the exponential relaxation curve itself — not just the animated particle density — is directly visible and measurable against N∞.
dN/dt = G − λ·N
λ = (Q/V)·η = (ACH/60)·η (V cancels — verified numerically)
N∞ = G/λ, τ = 1/λ
N(t) = N∞ + (N₀ − N∞)·e^(−λt) (exact analytic solution, used here
instead of a forward-Euler step)
Here G is the total crew bioaerosol generation rate (particles/min, scales with crew size), Q is the volumetric airflow through the filter (m³/min, set by ACH and cabin volume V), and η is the single-pass HEPA capture efficiency. Because clearance is proportional to N itself, the system always relaxes exponentially toward N∞ = G/λ — the same first-order model used to size real spacecraft and cleanroom ventilation (ISS uses ~99.97%-efficient HEPA stages sized to the target ACH).
- Crew size — more people means a proportionally higher generation rate G.
- Air exchange rate (ACH) — how many cabin volumes are pushed through the filter per hour; raising it increases Q and lowers both N∞ and τ.
- HEPA efficiency η — the fraction of particles captured per pass; a clogged or bypassed filter drops this and lets N∞ climb sharply since it appears in the denominator.
- Cabin volume — a bigger volume dilutes the same generation rate but also needs more airflow to hit the same ACH, so λ (and therefore N∞ and τ) depends only on ACH and η, not on V itself.
The duct view is time-accelerated (~4 simulated minutes per real second, same as the 3D sim) so the approach to N∞ is visible in seconds; particle density in the loop scales with the live concentration N(t), and particles crossing the filter line are captured with probability η per pass — the rest recirculate. Drag the duct view to pan and scroll/pinch to zoom.