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Nanoparticle-Enhanced Ionic Liquids (NEILs)

Heat Transfer Fluids with high volumetric heat capacity as well as favorable physical properties to improve the efficiency of CSP systems

Savannah River National Laboratory

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Technology Marketing Summary

A good HTF must be able to absorb a substantial amount of energy in a given volume, a property known as volumetric heat capacity. Physical properties such as viscosity, thermal stability, and thermal conductivity must also be considered. Ionic liquids (IL) were discovered more than 30 years ago and are organic compounds with negligible vapor pressure. ILs are molten salts with low melting points below 100°C, high liquid range above 400°C, in some cases, freezing points below 0°C. For example, experiments conducted at SRNL examined the ionic liquid known as [C4mmim][NTf2] due to commercial availability, good thermal stability, and tolerable viscosity. The studies indicate that the addition of Al2O3 nanoparticles to the ionic liquid can increase density of the liquid by 10%, and increase volumetric heat capacity by 40% compared to neat ILs and 70% compared to traditional volatile organic fluids, such as commercially used Therminol (VP-1). The incorporation of nanoparticles into ILs, which can potentially increase thermal conductivity by 7%, forms suspensions known as a nanoparticle-enhanced ionic liquids (NEILS).


CSP systems function by first using mirrors to direct sunlight into a collector filled with HTF. Once in the collector, the HTF converts the concentrated energy into steam, which is used to generate power. Because the electrical energy production efficiency hinges on the properties of the HTF, finding a liquid than can store more energy per volumetric unit will improve the CSP system. SRNL has investigated an alternative to conventional organic liquids used as HTF in the CSP process. In experiments conducted at SRNL, NEILs were used in the solar concentrating section of the system chiefly due to their higher heat capacity, higher volumetric density, and higher volumetric heat capacity. The process is complemented by the lack of appreciable vapor pressure and volatilization of NEILs, which allows for simplification of the system design that typically requires engineering to prevent phase change of traditional liquids. Careful material selection of both the IL but particularly the incorporated nanoparticle is vital to optimization of the nanofluid properties.

  • higher heat capacity and volumetric heat capacity
  • more energy stored per volumetric unit
  • greater efficiency in increased steam pressure
  • lack of vapor pressure; no volatilization
  • more simplistic design of heat transfer fluid system
Applications and Industries

These fluids will be useful for engines, microsystems, solar power heat transfer fluids.

Technology Status
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To: Dale Haas, Commercialization Manager<>