Mass transfer from nanofluid drops in a pulsed liquid-liquid extraction column

Mass transfer in gas-liquid systems has been significantly enhanced by recent developments in nanotechnology. However, the influence of nanoparticles in liquid-liquid systems has received much less attention. In the present study, both experimental and theoretical works were performed to investigate the influence of nanoparticles on the mass transfer behaviour of drops inside a pulsed liquid-liquid extraction column (PLLEC). The chemical system of kerosene-acetic acid-water was used, and the drops were organic nanofluids containing hydrophobic SiO2 nanoparticles at concentrations of 0.01, 0.05, and 0.1 vol%. The experimental results indicate that the addition of 0.1 vol% nanoparticles to the base fluid improves the mass transfer performance by up to 60%. The increase in mass transfer with increased nanoparticle content was more apparent for lower pulsation intensities (0.3-1.3 cm/s). At high pulsation intensities, the Sauter mean diameter (d32) decreased to smaller sizes (1.1-2.2 mm), leading to decreased Brownian motion in the nanoparticles. Using an analogy for heat and mass transfer, an approach for determining the mass diffusion coefficient was suggested. A new predictive correlation was proposed to calculate the effective diffusivity and mass transfer coefficient in terms of the nanoparticle volume fraction, Reynolds number, and Schmidt number. Finally, model predictions were directly compared with the experimental results for different nanofluids. The absolute average relative error (%AARE) of the proposed correlation for the mass transfer coefficient and effective diffusivity were 5.3% and 5.4%, respectively.