Joule-Thomson Effect · Hydrate Risk · Heater Sizing
Understand temperature drop principles, calculations, and industry applications
When gas expands through a restriction (valve, orifice, regulator), temperature changes due to the Joule-Thomson effect—an isenthalpic process where enthalpy remains constant.
| Gas | μJT (°F/psi) | Notes |
|---|---|---|
| Natural Gas | 0.070 | SG ≈ 0.60–0.65 |
| Methane (C₁) | 0.072 | Primary NG component |
| Ethane (C₂) | 0.105 | Higher MW = larger effect |
| Propane (C₃) | 0.095 | — |
| Nitrogen | 0.015 | Low JT coefficient |
| CO₂ | 0.028 | Acid gas component |
| Air | 0.025 | Reference gas |
| Hydrogen | −0.005 | ⚠️ Heats on expansion |
Source: GPSA Engineering Data Book, Katz Handbook of Natural Gas Engineering
Gas hydrates are ice-like crystalline solids that form when water and light hydrocarbons combine at low temperature and high pressure.
Prevention methods: Line heating, methanol/glycol injection, dehydration, insulation
Assumptions: SG = 0.60, Heater efficiency = 80%, HHV = 1000 BTU/scf