The Experimental Study of Evaporation of Water and Nanofluid Droplets on the Surfaces of Materials with Different Thermal Conductivities

The article presents the results of experimental studying evaporation of water and nanofluid droplets on the surfaces of various materials. Plates made of materials with significantly different thermal conductivity coefficients have been used as substrates: copper (lambda = 401 W/m degrees C), Teflon (lambda = 0.25 W/m degrees C), and extruded foamed polystyrene (lambda = 0.03 W/m degrees C). In the experiments, the evaporation of water and nanofluid droplets with a volume of 5 mu L has been considered at a constant temperature and humidity of the ambient air. A nanofluid (a mixture of water with gold nanoparticles) has been prepared by laser ablation. The concentration of nanoparticles in the nanofluid is about 0.1 wt %. Infrared thermography has been employed to determine the average temperatures of evaporating droplet surfaces. The results obtained have shown that, for all studied materials, the surface temperature of evaporating water droplets is higher than the temperature of adiabatic evaporation. Therewith, the lower the thermal conductivity coefficient of a substrate material, the lower the surface temperature of the droplet and the longer the time of its evaporation. The performed experiments have shown that the minimum temperature of nanofluid droplets is lower than that of water droplets, and the evaporation time of nanofluid droplets is longer than that of water droplets on the corresponding surfaces.