On isobaric heat capacity of ionanofluids with carbon nanotubes - An experimental study

Ionanofluids (INFs) are defined as ionic liquids (ILs) with therein dispersed nanoparticles. The addition of nanoparticles results in an increase in the thermal conductivity of INFs. In terms of specific isobaric heat capacity (cp) this influence is not yet clear due to contradictory results published up to date. In this work, we assessed the influence of carbon nanotubes (CNTs) on the cp of INFs by means of DSC. We selected 13 different types of ILs and two mixtures of them as the base for INFs. 9 different types of CNTs were chosen: (singlewalled carbon nano-tubes) SWCNTs, helical CNTs, Nanocyl multiwalled carbon nanotubes (MWCNTs) and in-house 16h MWCNTs, MWCNTs functionalized with carboxylic groups (-COOH), hydroxylic groups (-OH), C18 n-alkyl chain or polyethylene glycol (PEG). Functionalized MWCNTs have never been investigated in terms of the cp of INFs. A total of 43 INFs were obtained and studied. The influence of CNTs on the cp of INFs was critically analyzed with consideration to the cp of base liquid and its agreement with data available in the literature, and with consideration to measurement uncertainty. Also, the cp of some pristine CNTs (as a bulk material), namely Nanocyl MWCNTs and in-house 16h MWCNTs, was examined. In the most of systems, the addition of CNTs did not affect the cp of INFs. In the others, the effects were minor and not greater than 3.1 %. In the end, the model proposed to estimate the cp of nanofluid, including the existence of nanolayer of IL on the CNT, was critically examined.