Effect of nanoparticle sizes and number densities on the evaporation and dryout characteristics for strongly pinned nanofluid droplets.

A microfabricated linear heater array operating in a constant voltage mode has been used to study the effect of nanoparticle size on the evaporation and dryout characteristics of strongly pinned nanofluid droplets. Four different nanofluids have been tested, containing 2-nm Au, 30-nm CuO, 11-nm Al2O3, and 47-nm Al2O3 nanoparticles, each of 5-muL droplets with 0.5 vol % in water. Nanofluid droplets show strong pinning along the droplet perimeter and, upon evaporation, leave a ring-shaped nanoparticle stain. Particle size is seen to have a clear and strong effect on the dryout stain pattern, while heater temperature seems to have little effect. With the assumption of axi-symmetry, tomographic deconvolution of measured data from the linear heater array allows for examination of the spatially and temporally resolved temperature and heat flux characteristics of the evaporating nanofluid droplets.