A heat transfer fluid which absorbs heat from a source and transfers
the heat in an indirect heating system
Two Basic Types:
| Mineral Oil Based | Synthetic |
| Paraffins, Naphthenes | Aromatics, Toluene, Diphenyl + Diphenyl Oxide |
Mineral oil based Thermic fluids:
- Produced in a crude oil refinery
- Reasonably stable thermally at 260 C
- Mostly straight chain Hydrocarbons
- Most fluids blended with additives, like anti- oxidants and stabilizers
- Light coloured, transparent, feel like lubricants
- When heated, low boiling chemicals, volatile, moisture come out.
- These vaporize and get vented – normal for all fluids.
- Annual top-up: 5-10% of system holdup, depends on % of volatile & leakage in system.
- When overheated, carbonize
- When oxidized, acidic and viscous like grease
Synthetic Thermic fluids:
- ‘Synthesized’ from petrochemicals as thermic fluid
- Full temperature range covered by different fluids
- Mostly Benzene ring / cyclic compounds
- More stable thermally - long life, hence used in India for temperatures above 300 C
- Easily combine with oxygen and moisture, require Nitrogen blanket in expansion tank
- Some require pressurized expansion tank to remain in liquid phase
- Require negligible top-ups
- Very expensive in high temperature ranges
- Long life and almost zero top-ups can support high initial investment