Evaporation characteristics of ethanol droplets containing graphite nanoparticles under infrared radiation

The evaporation characteristics of liquid ethanol droplets containing graphite nanoparticles under infrared radiation were studied both experimentally and numerically. The experimental results show that the droplet evaporation rate is higher in the presence of a 2 mW infrared radiation field with a fixed wavelength of 2.3 μm than without radiation. The evaporation rate, however, decreases over time. Additionally, with particle addition, the evaporation rate no longer follows the classical D²-law. The deviation is greater at higher particle concentrations. A model was developed to simulate the instantaneous evaporation rate, considering both effects of particle accumulation on the droplet surface and radiation energy absorption by the nanoparticles. In particular, a stochastic Monte Carlo method coupled with Mie theory and Beer–Lambert law of volumetric absorption was used to calculate the distribution of the absorbed radiation energy within the droplet, which was then used to compute the temperature profiles of the droplet. The modeling results show under infrared radiation, the evaporation rate of the nanofluid droplet increases as a function of particle concentration. This is due to rising droplet surface temperature through radiation absorption by the nanoparticles near the droplet surface. However, at the later stage of evaporation, as the particles start to accumulate on the droplet surface, the effective surface area for evaporation decreases and hence reduces the evaporation rate. These two competing mechanisms combine to control the instantaneous evaporation rate.