Heat-transfer fluids and heat pipes: Technology advances
Salt in solar fields, wafer-thin heat pipes and liquid-cooled AI
What this tab covers The newest technologies in service or close to adoption, what each improves, and how the main options compare.Developments push carriers to higher temperatures (salt replacing oil in solar fields), lower climate impact (low-GWP and natural refrigerants) and denser cooling for computer chips, while trucked heat stores are being trialled where pipes do not pay.
Latest advances
Molten salt as the solar-field fluid demonstration · 2021Salt pumped directly through parabolic troughs, removing the oil-to-salt heat exchanger2
Improves: Higher temperature and lower investment; DLR test plant at Évora, Portugal
Low-GWP HFO refrigerants in service · 2025Hydrofluoroolefins such as Chemours' Opteon range13
Improves: Much lower global warming potential than older HFCs
Ultra-thin heat pipes and vapour chambers in service · 20250.6 to 1.5 mm heat pipes for phones; vapour chambers for high-power server chips8
Improves: Spread chip heat with small temperature drop
Liquid cooling for AI servers being deployed · 2026Cold plates and liquid loops replacing air-cooled heat sinks15
Improves: Handles higher chip power; rising liquid-cooling shipments lifted Taiwanese thermal firms AVC and Auras to record monthly sales in March 2026
Trucked phase-change heat stores demonstration · 2026Containers of sodium acetate trihydrate charged with waste heat10
Improves: Supplies heat where a network is uneconomic
Permafrost thermosiphons in service · long in servicePassive ammonia heat pipes in pipeline supports9
Improves: Keep ground frozen along 420 miles of elevated pipeline
Comparing the options
| Option | Efficiency | Cost | Capacity or distance | Maturity |
|---|---|---|---|---|
| Thermal oil25 | good below 400 C | described as an immense cost in solar fields | 12 to 400 C | mature |
| Molten nitrate salt234 | over 98% daily storage efficiency | USD 26 to 40 per kWh of heat stored (2020) | about 290 to 565 C | mature in storage, demonstration as field fluid |
| Refrigerant two-phase loop1213 | large heat per kg via boiling | not stated | not stated | mature |
| Heat pipe7 | no pump; effective conductivity up to 100,000 W/m C | not stated | tens of watts per pipe in electronics (38 to 52 W examples) | mature |
| Mobile PCM container10 | almost loss-free over short trips | EUR 1.5 million demonstration | about 2.5 MWh per unit | demonstration |
| Natural ice (historic)11 | about 33 to 44% melted on a four-month voyage | not stated | 180 tonnes per ship (1833) | obsolete |
The choice follows temperature: oil up to 400 C, salt from about 290 to 565 C, water and steam in between for buildings and industry, refrigerants and heat pipes where compactness matters. Phase change beats sensible heat on density but fixes the delivery temperature. Mobile stores and the old ice trade show that heat (or cold) can be shipped as a stock, but the energy per lorry or ship is small, so they only suit short trips or high-value uses.
Sources
- Molten salt suitable heat transfer fluid for concentrating collector fields solarthermalworld.org, 2021
- Final Test and Evaluation Results from the Solar Two Project (SAND2002-0120) Sandia National Laboratories (via UNT Digital Library), 2002
- Innovation Outlook: Thermal Energy Storage IRENA, 2020
- Therminol VP-1 heat transfer fluid (company data) Eastman, 2026
- Design Considerations When Using Heat Pipes (George Meyer) Electronics Cooling, 2016
- Thermal solutions (company data) Fujikura, 2026
- Pipeline designs protect permafrost PBS American Experience, 2006
- Waste heat is transported to the customer by truck Bayern Innovativ, 2026
- Cold Mine (Susan S. Bean, on the Boston to Calcutta ice trade) American Heritage, 1991
- A Concise Guide to the EU F-Gas Regulation Environmental Investigation Agency, 2026
- The Chemours Company Form 10-K for fiscal year 2025 US SEC, 2026
- AI demand lifts Taiwan cooling suppliers to record monthly sales Taiwan News, 2026