Measurements of ionic liquids thermal conductivity and thermal diffusivity

Abstract

Thermal conductivity and thermal diffusivity of ionic liquids (ILs) are investigated in this work. A hot disk method for ILs thermal conductivity and thermal diffusivity measurement is utilized. Firstly, the thermal conductivity of water is measured to check the reliability of the hot disk method. In addition, the thermal conductivity of pure ILs, including BmimBF₄, BmimPF₆, OmimCl, BmimFeCl₄, and OmimFeCl₄, is measured. By comparison with thermal conductivity values of water, BmimBF₄, and BmimPF₆ in the literatures, it is found that the thermal conductivity values of ILs using hot disk method have high reliability. Therefore, the hot disk method is utilized for thermal conductivity measurement of ILs in this work. The experimental results also show that all the average thermal conductivity values of the five pure ILs are no more than 0.1898 W m⁻¹ K⁻¹, which is much lower than the average measured thermal conductivity of water, namely 0.6033 W m⁻¹ K⁻¹. Effect of nanoparticles (NPs) on thermal conductivity of ILs is also investigated. It is shown that the thermal conductivity of BmimBF₄ does not change significantly in the presence of Fe₂O₃ NPs. However, the thermal conductivity of BmimPF₆ decreases somewhat in the presence of R711 NPs. In addition, the thermal diffusivity of pure ILs, including BmimBF₄, BmimPF₆, BmimFeCl₄, OmimCl, and OmimFeCl₄, is measured. All the average thermal diffusivity values of the ILs of BmimBF₄, BmimPF₆, BmimFeCl₄, OmimCl, and OmimFeCl₄ are no more than 0.1185 mm² s⁻¹. The thermal diffusivity of water is 0.143 mm² s⁻¹ in the literature. It illustrates that the ILs also have a better thermal property than water for energy storage. ILs may be utilized as novel materials for energy storage. Effect of NPs on thermal diffusivity of ILs is also investigated. The results are similar to how NPs influence thermal conductivity of BmimBF₄ and BmimPF₆. In the presence of Fe₂O₃ NPs, thermal diffusivity of BmimBF₄ does not change significantly. However, in the presence of R711 NPs, thermal diffusivity of BmimPF₆ decreases somewhat.