Effect of PEG functionalized carbon nanotubes on the enhancement of thermal and physical properties of nanofluids

In this study, pristine carbon nanotubes and polyethylene glycol functionalized carbon nanotubes (CNTPEG) have been used to enhance the heat capacity, viscosity, thermal conductivity, heat transfer rate and pressure drop of nanofluids. Multi-walled carbon nanotubes (MWCNT) were functionalized with polyethylene glycol (PEG) using a Fischer esterification method to improve their dispersion in aqueous media. Three concentrations of 0.01 wt%, 0.05 wt% and 0.1 wt% of pristine and functionalized CNTs in the nanofluids have been used. The heat-transfer rate and pressure drop of these nanofluids have been measured in a shell and tube heat exchanger. Differential Scanning Calorimetry (DSC) was used to study the specific heat capacity of the nanofluids. The specific heat capacity of pristine and functionalized CNTs mixed with water was found to be significantly higher than of the pure water by 10% and 45% respectively. The results of the heat transfer of the nanofluids increased suddenly with the increasing the concentrations of both pristine and functionalized CNTs. It can be concluded that the functionalizing CNT with Polyethylene glycol enhanced the dispersion of the CNTs and increased their heat capacities. The viscosity of the nanofluids was found to be dependent on the concentration of CNTs in solution. The pressure drop of the nanofluid compared with that of pure water was almost unchanged resulting in no extra pumping energy penalty. (C) 2017 Elsevier Inc. All rights reserved.