INVESTIGATION OF THE EFFECT OF MULTIWALLED CARBON NANOTUBES ON THE VISCOSITY INDEX OF LUBE OIL CUTS

In the present work, the influence of temperature and concentration on the viscosity index of oil-multiwalled carbon nanotube (MWCNT) nanofluids has been investigated theoretically and experimentally. Data were collected for temperatures ranging from ambient to 100°C and for concentrations ranging from 0.01 to 0.2 wt.% of MWCNT. The results show that viscosity is enhanced with increasing the MWCNT concentration and decreasing temperature. Experimental results emphasize that the maximum enhancement of the viscosity index is 14.11% for MWCNT-oil nanofluid. Stability examinations of the nanofluids have been performed by a UV-vis spectrophotometer. It has been found that the Einstein formula and those derived from the linear fluid theory are valid for relatively low particle volume fractions of MWCNT, and for higher MWCNT concentrations the discrepancy between these formulas and experimental data is significant, indicating that the linear fluid theory is no longer appropriate to represent the real behavior of these nanofluids.     

Effects of SiC,SiO2 and CNTs nanoadditives on the properties of porous alumina-zirconia ceramics produced by a hybrid freeze casting-space holder method

Highly porous alumina-zirconia ceramics were produced by adding space-holder materials during freeze casting. To increase the strength of porous ceramics, different amounts of nanoadditives (silicon carbide-SiC, silica-SiO₂, and multi-wall carbon nanotubes-CNTs) were added. Space-holder materials were removed by preheating, and solid samples were produced by sintering. Up to 68% porosity was achieved when 40% space-holder was added to the solid load of slurry. Wall thicknesses between pores were more uniform and thinner when nanoadditives were added. Compressive tests revealed that SiC nanoparticles increased the strength more than other nanoadditives, and this was attributed to formation of an alumina-SiC phase and a uniform distribution of SiC nanoparticles. Results indicated that by including 20% space-holder materials and 15% SiC nanoparticles, the density decreases by 33.8% while maintaining a compressive strength of 132.5 MPa and porosity of 43.4%. Relatively low thermal conductivities, less than 3.5 W/K-m, were measured for samples with SiC nanoparticles.