Vacuum Chamber Outreach Demo: Boyle's Law & the Armstrong Limit

Vacuum Chamber Control

Target pressure 101.3 kPa

Pump speed 6 kPa/s

Live Readouts

Water: not boiling

Chamber pressure

101.3 kPa

Equiv. altitude

0.0 km

Marshmallow V/V₀

1.00×

Water boil temp

100 °C

How it works

Two real physiological limits that every crewed life-support system is engineered around, shown together in one chamber:

Boyle's Law (isothermal): P₁V₁ = P₂V₂
  → V(P) = V₀ · P₀ / P

Barometric formula (troposphere):
  P(h) = P₀ · (1 − 2.25577×10⁻⁵ · h)^5.25588

Clausius–Clapeyron (water saturation pressure):
  boils when local pressure < P_sat(T_body)
  Armstrong limit ≈ 6.3 kPa (≈19 km) at 37 °C

Pressure slider / pump speed — sets the chamber's target pressure and how fast the pump reaches it; the trapped gas in the marshmallow's cell walls obeys Boyle's Law and swells as P drops.
Everest summit — jumps to ≈33.7 kPa, the pressure at 8,849 m where unprotected humans need supplemental oxygen.
Armstrong limit — jumps to ≈6.3 kPa (≈19 km / 63,000 ft), the pressure at which exposed body fluids boil at normal body temperature (37 °C) even though the air itself is cold — this is why every spacesuit and every spacecraft cabin is designed to never let pressure fall anywhere near this line.
Water droplet — its boiling point is recomputed live from the chamber pressure; once it drops below body-temperature saturation pressure, bubbles nucleate and the status box turns red.

Real-world relevance: this exact bell-jar demonstration (marshmallow + reduced pressure) is a staple of NASA/ESA public-outreach events and university aerospace courses — it is the single most direct way to make a room understand, in thirty seconds, why cabin and suit pressurization is a life-support requirement and not a comfort feature.

Marshmallow (Boyle's Law) Water droplet (Armstrong limit)

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