Variations of thermophysical properties and heat transfer performance of nanoparticle-enhanced ionic liquids

The ionic liquid 1-ethyl-3-methylimidazolium acetate ([EMIm]Ac) was investigated as a promising absorbent for absorption refrigeration. To improve the thermal conductivity of pure [EMIm]Ac, ionic-liquid-based nanofluids (ionanofluids) were prepared by adding graphene nanoplatelets. The thermal stability of the ionic liquid and ionanofluids was analysed. The variations of the thermal conductivity, viscosity and specific heat capacity resulting from the addition of the graphene nanoplatelets were then measured over a wide range of temperatures and mass fractions. The measured data were fitted with appropriate equations and compared with the corresponding classical models. The results revealed that the ionic liquid and ionanofluids were thermally stable over the measurement range. The thermal conductivity greatly increased with increasing mass fraction, while only slightly changed with increasing temperature. A maximum enhancement in thermal conductivity of 43.2% was observed at a temperature of 373.15 K for the ionanofluid with a mass fraction of 5%. The numerical results revealed that the dispersion of the graphene nanoplatelets in the pure ionic liquid effectively improved the local heat transfer coefficient by up to 28.6%.