Coupled thermal transport and mass diffusion during vapor absorption at the droplet scale

This study focuses on the coupled heat and mass transfer during vapor absorption at the droplet scale. Driven by the vapor pressure difference between the ambient and the droplet surface, desiccant droplets expand due to water uptake. The droplet growth rate and expansion ratio depend on the ambient temperature and humidity. When looking into the infrared thermography, droplets experience the highest surface temperature right after being deposited. Then drops gradually cool down as heat transfers into the substrate and ambient atmosphere, coupled with the decrease in the vapor absorption rate. The initial temperature rise is due to the fast vapor absorption which proceeds during droplet deposition, and is verified by the order of absorption heat flux in the six conditions. The vapor pressure at the droplet surface is further evaluated taking account of the concentration variation and surface temperature variation, which demonstrates the evolution of driving force for vapor diffusion along with time. Contrast experiments with water droplets show different profile evolution, inverse contact line dynamics, and opposite evaporation cooling effect. Conclusions here help to understand the dehumidification process in more details.