Droplet evaporation is a complex phase change process with a wide range of cooling applications, such as spray cooling and dropwise hotspot cooling in microelectronics, to name a few. The hybrid nanofluid droplet evaporation and its residue effects on evaporation of the subsequent hybrid nanofluid droplet is investigated in this research. Silver-graphene (Ag-GNP) hybrid nanofluid exhibiting synergistic thermal properties is investigated and prepared by dispersing silver nanoparticles along with graphene nanoplatelets in water at 0.1% volume fraction and with different mixing ratios, followed by ultrasonication. The evaporation rate and wetting characteristics of a 3 μl volume of Ag-GNP hybrid nanofluid droplet on a copper surface were studied using an optical tensiometer. Once dried, the nanoporous structure of the residue surface was examined using a scanning electron microscope, while the surface roughness was measured using an optical profiler. Experiments were continued to further investigate the evaporation rate and wetting effects of the subsequent Ag-GNP hybrid nanofluid droplet over the residue surface. The results showed improved wetting characteristics, with 88% reduction in initial static contact angle and 163–196% enhancement in evaporation rate of the subsequent Ag-GNP hybrid nanofluid droplets over the residue surfaces as compared to the copper surface.

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