Nanofluid pendant droplet evaporation: Experiments and modeling

Abstract

Nanofluids, stable colloidal suspensions of nanoparticles in a base fluid, have potential applications in the heat transfer, combustion and propulsion, manufacturing, and medical fields. Experiments were conducted to determine the evaporation rate of room temperature, millimeter-sized pendant droplets of ethanol laden with varying amounts (0–3% by weight) of 40–60nm aluminum nanoparticles (nAl). Time-resolved high-resolution droplet images were collected for the determination of early-time evaporation rate (D2/D02>0.75), shown to exhibit D-square law behavior, and surface tension. Results show an asymptotic decrease in droplet evaporation rate with increasing nAl loading. The evaporation rate decreases by approximately 15% at around 1–3% nAl loading relative to the evaporation rate of pure ethanol. Surface tension was observed to be unaffected by nAl loading up to 3% by weight. A model was developed to describe the evaporation of the nanofluid pendant droplets based on D-square law analysis for the gas domain and a description of the reduction in liquid fraction available for evaporation due to nanoparticle agglomerate packing near the evaporating droplet surface. Model predictions are in relatively good agreement with experiment, within a few percent of measured nanofluid evaporation rate.