The Fluid Does the Work
A heat pipe transfers heat through evaporation and condensation of a sealed working fluid. The fluid must stay liquid at the cold end and vapour at the hot end across your operating range.
Common Fluids
| Fluid | Typical range | Use |
|---|---|---|
| Water | Moderate to high temp | Building HVAC, above freezing |
| Ammonia | Low temp | Cold storage, freezers |
| Refrigerants (R134a etc.) | Low to moderate | General HVAC |
| Acetone / methanol | Very low temp | Specialty, cryogenic |
Selection Criteria
- Operating temperature - pick a fluid whose range brackets your duty
- Freeze risk - for sub-zero, use ammonia or a low-temp refrigerant
- Compatibility - fluid must not corrode the tube wall
- Pressure - vapour pressure at hot end must stay safe
Watch-out
Mismatched fluid is the most common heat-pipe failure. Specify the fluid from the coldest and hottest expected temperatures, not the average.