Joule-Thomson
Calculate Joule-Thomson coefficient, temperature change during throttling, and inversion temperature for gases using thermodynamic principles.
Compact Examples
Inputs
Input Parameters
⚠️For educational and informational purposes only. Verify with a qualified professional.
📋 Key Takeaways
- • μJT = (∂T/∂P)H | Temperature change per pressure at constant H
- • ΔT = μJT × ΔP | Throttling temperature change
- • Ti = 2a/(Rb) | Inversion temperature (van der Waals)
- • μJT > 0 | Cooling; μJT < 0 | Heating
Did You Know?
N₂ cools on expansion at room T; used for liquid nitrogen.
Source: Cryogenics
H₂ and He heat on expansion at room T (above Ti).
Source: Thermodynamics
CO₂ has high Ti ≈ 1500 K; strong cooling effect.
Source: Refrigeration
Ideal gas: μJT = 0 (no temp change).
Source: Kinetic theory
μJT ≈ (2a/(RT) - b) / Cp for van der Waals gas.
Source: VdW equation
Throttling is isenthalpic (constant H).
Source: First law
How the Joule-Thomson Calculator Works
Select gas, enter T and P. Calculator uses van der Waals to find μJT, ΔT, or Ti.
μJT
(2a/(RT) - b) / Cp
ΔT
μJT × (P₂ - P₁)
Expert Tips
Gas Database
N₂, O₂, H₂, He, Ar, CO₂, CH₄ with VdW params.
Inversion
Below Ti: cool; above Ti: heat.
Custom
Enter a, b, Cp for custom gas.
Units
Use atm, bar, kPa, or psi.
Gas Inversion Temperatures (K)
| Gas | Ti (K) |
|---|---|
| Nitrogen | 621 |
| Oxygen | 764 |
| Hydrogen | 202 |
| Helium | 40 |
| Argon | 723 |
| Carbon Dioxide | 1500 |
FAQ
What is Joule-Thomson effect?
Temp change when gas throttles at constant H. Real gases cool or heat.
Why does N₂ cool?
Below inversion temp; μJT > 0. Intermolecular attraction dominates.
Why does H₂ heat?
Above Ti at room T. Repulsion dominates.
What is Ti?
Temp where μJT = 0. Ti = 2a/(Rb) for VdW.
Ideal gas μJT?
Zero. No temp change on throttling.
Applications?
LNG, liquid N₂, refrigeration, cryogenics.
Key Numbers
📚 Official Sources
⚠️ Disclaimer: Uses van der Waals. Consult NIST for precise J-T data.