Joule-Thomson Cryogenic Throttle

Working Gas

Throttle Conditions

Inlet temperature 300 K

High-side pressure 200 bar

Valve opening 40%

Live Readout

Cooling by expansion

Outlet temperature

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ΔT across valve

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Joule-Thomson coeff. μ_JT

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How it works

Throttling a real gas through a valve or porous plug at constant enthalpy (no work extracted, no heat exchanged) changes its temperature. For a van der Waals gas, the Joule-Thomson coefficient is:

μ_JT = (1/Cp) · (2a/RT − b)
ΔT ≈ μ_JT · ΔP        (ΔP = P_low − P_high < 0)
T_inversion = 2a / (R·b)

Below the inversion temperature, μ_JT > 0 and a pressure drop cools the gas — this is exactly how the Linde-Hampson liquefaction cycle turns compressed gas into cryogenic liquid, with each pass regeneratively pre-cooling the next. Above the inversion temperature, μ_JT < 0 and the same pressure drop heats the gas instead.

N₂ has an inversion temperature near 620 K, so it cools throttling straight from room temperature — this is how industrial nitrogen liquefiers work.
H₂ inverts near 205–360 K depending on pressure — it must first be pre-cooled (historically with liquid nitrogen) before a throttle valve can cool it further, or it heats up and can ignite near the valve.
He inverts near 40–50 K — it needs pre-cooling with liquid hydrogen or a cryocooler before Joule-Thomson liquefaction works at all.

When the computed outlet temperature drops below the gas's normal boiling point (N₂ 77 K, H₂ 20 K, He 4.2 K) at 1 bar, the stream condenses — particles downstream collect at the bottom of the pipe as liquid droplets and the reservoir gauge fills.

Warm / high-pressure gas Cooled gas after valve Liquefied droplets

Liquid collected
0.0 mL

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