The new correlation for viscosity of synthesized viscoelastic-based nanoliquid using functionalized MWCNT: Stability, thermal conductivity, and rheology

In different industries, non-Newtonian fluids, especially viscoelastic fluids, are processed with variable transport properties, such as viscosity. Thus, it is of great importance for design and engineering purposes to determine the relationship between transfer properties such as viscosity and thermal conductivity coefficients. Even though there have been more studies on nanofluids, they are all based on three components of viscoelastic fluids that are inadequate. Thus, in this research, to begin with, multiwalled carbon nanotubes (MWCNT) have been chemically functionalized with COOH groups in order to obtain f-MWCNT nanoparticles. A series of tests were conducted to characterize the synthesized f-MWCNT nanoparticles, including X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FT-IR), dynamic light scattering (DLS), and transmission electron microscopy (TEM). Further, three components, viscoelastic-based nanoliquids (VNLs) have been prepared using (i) polyacrylamide, glycerol, and water as the base liquid, and (ii) carboxylic-functionalized multiwalled carbon nanotubes (f-MWCNTs) as the nanoparticles. In addition, a study of the stability of the VNL (i + ii) solution has been conducted by examining the variations in thermal conductivity (TC) as well as viscosity of the VNL at various time intervals. Results showed that 0.2 wt% of f-MWCNT in VNL was stable for at least 40 days. f-MWCNT in VNL (0.2 wt%) had a size distribution less than 50 nm. Furthermore, the investigation of the effect of f-MWCNT concentrations in VNL on TC at different temperatures showed that the thermal conductivity variation of VNL as a function of f-MWCNT mass fraction was nearly constant (1.25 W/m.K). A novel correlation was also proposed for the shear viscosity of the VNL, which was well supported by the experimental data. Lastly, we investigated the viscoelastic properties of the VNL and determined that the storage and loss modulus, as well as the first normal stress difference, increased with an increasing mass concentration of f-MWCNT.