# Heat-transfer fluids and heat pipes: Technology advances Salt in solar fields, wafer-thin heat pipes and liquid-cooled AI Source page: https://www.materialinsights.org/energy/e_heat_carriers/advances/ 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 · 2021 Salt pumped directly through parabolic troughs, removing the oil-to-salt heat exchanger^[2](https://solarthermalworld.org/news/molten-salt-suitable-heat-transfer-fluid-for-concentrating-collector-fields/) *Improves:* Higher temperature and lower investment; DLR test plant at Évora, Portugal **Low-GWP HFO refrigerants** in service · 2025 Hydrofluoroolefins such as Chemours' Opteon range^[13](https://www.sec.gov/Archives/edgar/data/1627223/000119312526065201/cc-20251231.htm) *Improves:* Much lower global warming potential than older HFCs **Ultra-thin heat pipes and vapour chambers** in service · 2025 0.6 to 1.5 mm heat pipes for phones; vapour chambers for high-power server chips^[8](https://www.fujikura.com/solutions/thermal/) *Improves:* Spread chip heat with small temperature drop **Liquid cooling for AI servers** being deployed · 2026 Cold plates and liquid loops replacing air-cooled heat sinks^[15](https://www.taiwannews.com.tw/news/6336454) *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 · 2026 Containers of sodium acetate trihydrate charged with waste heat^[10](https://www.bayern-innovativ.de/en/emagazine/detail/waste-heat-is-transported-to-the-customer-by-truck) *Improves:* Supplies heat where a network is uneconomic **Permafrost thermosiphons** in service · long in service Passive ammonia heat pipes in pipeline supports^[9](https://www.pbs.org/wgbh/americanexperience/features/pipeline-designs-protect-permafrost/) *Improves:* Keep ground frozen along 420 miles of elevated pipeline #### Comparing the options | Option | Efficiency | Cost | Capacity or distance | Maturity | |---|---|---|---|---| | **Thermal oil**^[2](https://solarthermalworld.org/news/molten-salt-suitable-heat-transfer-fluid-for-concentrating-collector-fields/)^[5](https://www.therminol.com/product/71093459) | good below 400 C | described as an immense cost in solar fields | 12 to 400 C | mature | | **Molten nitrate salt**^[2](https://solarthermalworld.org/news/molten-salt-suitable-heat-transfer-fluid-for-concentrating-collector-fields/)^[3](https://digital.library.unt.edu/ark:/67531/metadc741985/m2/1/high_res_d/793226.pdf)^[4](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2020/Nov/IRENA_Innovation_Outlook_TES_2020.pdf) | 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 loop**^[12](https://eia-international.org/wp-content/uploads/2026-EIA-A-Concise-Guide-to-the-EU-F-Gas-Regulation-5.pdf)^[13](https://www.sec.gov/Archives/edgar/data/1627223/000119312526065201/cc-20251231.htm) | large heat per kg via boiling | not stated | not stated | mature | | **Heat pipe**^[7](https://www.electronics-cooling.com/?p=20921) | 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 container**^[10](https://www.bayern-innovativ.de/en/emagazine/detail/waste-heat-is-transported-to-the-customer-by-truck) | almost loss-free over short trips | EUR 1.5 million demonstration | about 2.5 MWh per unit | demonstration | | **Natural ice (historic)**^[11](https://www.americanheritage.com/cold-mine) | 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 1. [Molten salt suitable heat transfer fluid for concentrating collector fields](https://solarthermalworld.org/news/molten-salt-suitable-heat-transfer-fluid-for-concentrating-collector-fields/) solarthermalworld.org, 2021 2. [Final Test and Evaluation Results from the Solar Two Project (SAND2002-0120)](https://digital.library.unt.edu/ark:/67531/metadc741985/m2/1/high_res_d/793226.pdf) Sandia National Laboratories (via UNT Digital Library), 2002 3. [Innovation Outlook: Thermal Energy Storage](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2020/Nov/IRENA_Innovation_Outlook_TES_2020.pdf) IRENA, 2020 4. [Therminol VP-1 heat transfer fluid (company data)](https://www.therminol.com/product/71093459) Eastman, 2026 5. [Design Considerations When Using Heat Pipes (George Meyer)](https://www.electronics-cooling.com/?p=20921) Electronics Cooling, 2016 6. [Thermal solutions (company data)](https://www.fujikura.com/solutions/thermal/) Fujikura, 2026 7. [Pipeline designs protect permafrost](https://www.pbs.org/wgbh/americanexperience/features/pipeline-designs-protect-permafrost/) PBS American Experience, 2006 8. [Waste heat is transported to the customer by truck](https://www.bayern-innovativ.de/en/emagazine/detail/waste-heat-is-transported-to-the-customer-by-truck) Bayern Innovativ, 2026 9. [Cold Mine (Susan S. Bean, on the Boston to Calcutta ice trade)](https://www.americanheritage.com/cold-mine) American Heritage, 1991 10. [A Concise Guide to the EU F-Gas Regulation](https://eia-international.org/wp-content/uploads/2026-EIA-A-Concise-Guide-to-the-EU-F-Gas-Regulation-5.pdf) Environmental Investigation Agency, 2026 11. [The Chemours Company Form 10-K for fiscal year 2025](https://www.sec.gov/Archives/edgar/data/1627223/000119312526065201/cc-20251231.htm) US SEC, 2026 12. [AI demand lifts Taiwan cooling suppliers to record monthly sales](https://www.taiwannews.com.tw/news/6336454) Taiwan News, 2026 ## Other sections - [Summary](https://www.materialinsights.org/energy/e_heat_carriers/index.md) - [Overview](https://www.materialinsights.org/energy/e_heat_carriers/overview/index.md) - [Correlation](https://www.materialinsights.org/energy/e_heat_carriers/correlation/index.md) - [How it works](https://www.materialinsights.org/energy/e_heat_carriers/explain/index.md) - [Efficiency and losses](https://www.materialinsights.org/energy/e_heat_carriers/efficiency/index.md) - [Value chain](https://www.materialinsights.org/energy/e_heat_carriers/valuechain/index.md) - [Geopolitics and regulation](https://www.materialinsights.org/energy/e_heat_carriers/geopolitics/index.md) - [Unit economics](https://www.materialinsights.org/energy/e_heat_carriers/economics/index.md) - [Impact on the biosphere](https://www.materialinsights.org/energy/e_heat_carriers/biosphere/index.md) - [Relationships](https://www.materialinsights.org/energy/e_heat_carriers/links/index.md)