Deep eutectic solvents-based CNT nanofluid - A potential alternative to conventional heat transfer fluids

Abstract

We investigated Deep eutectic solvents (DES) in this study as a potential substitute for conventional heat transfer fluids. Methyl-triphenylphosphonium-bromide (MTPB) and choline chloride (ChCl) as the hydrogen bond acceptors (HBAs), and ethylene glycol (EG) and triethylene glycol (TEG) as the hydrogen bond donors (HBDs), were used to form DESs. The molar ratio of HBA to HBD was varied between 1:3 and 1:5 to produce a total of 11 DESs. In each of these DESs, carbon nanotube (CNT) was added and dispersed at a constant concentration of 0.04 wt% to form DES-CNT-nanofluids. There was no surfactant added for stabilisation. The nanofluids were homogenised using an ultrasonic bath at 37 kHz for 4 h at room temperature. The freezing points of DES-CNT-nanofluids were analysed using differential scanning calorimetry while their thermal degradations, vapour pressures and weight losses were analysed using a thermogravimetric analyser. DES-CNT-nanofluids were found to have lower freezing points (down to -117.90 °C) as compared to EG and TEG, valued at -13.40 and -4.0 °C, respectively. The addition of HBA, such as MTPB and ChCl to form DESs, was found to increase the thermal stability of EG and TEG from 105 to 128 °C to 130 and 220 °C, respectively. Furthermore, the vapour pressures of DESs derived from EG and TEG, independently, were lower than that of pure EG and TEG by about 73% and 45%, correspondingly. The dispersion of CNT in DESs enhanced their thermal stabilities, activation energies and their kinetic parameters. The degradation reaction order was also determined through Friedman and Avrami models, respectively. Thus, DES has been proven to be a potential substitute for conventional heat transfer fluids due to its improved properties.