Lignin as dispersant for water-based carbon nanotubes nanofluids: Impact on viscosity and thermal conductivity

The viscosity and thermal conductivity of water-based nanofluids containing carbon nanotubes, stabilized by lignin as surfactant, are measured. These experiments were performed at 20 °C and we study the effect of nanotube volume fraction which ranges from 0.0055% to 0.55%. In comparison with SDBS, we show that lignin reduces viscosity and shear-thinning behavior of nanofluids at high volume fraction, without penalizing thermal conductivity enhancement. Viscosity enhancement at high shear rate with respect to nanoparticle content is well modeled by the Maron–Pierce equation, suggesting that lignin is better than SDBS at dispersing carbon nanotubes within water at high volume fraction. The impact of surfactant on base fluid thermal conductivity is also reported and thermal conductivity enhancement of nanofluids with nanoparticle volume fraction is finally compared with previous published models.