Non-volatile Fraction Effects in Dispersed Vacuum Spray Flash Evaporation

摘要

Spray flash evaporation has been widely used in spray cooling and thermal distillation as a technology of heat/mass transfer enhancement. In a vacuum spray flash process, the vapor is instantly extracted by vacuuming, while the supersaturated droplets are further cooled by the continued spray flash until becoming saturated or discharged. Hence, in the evaporator, non-equilibrium exists not only in the flash evaporation driven by the pressure difference between droplet and ambient but also in the temperatures of yields, namely, generated vapor and discharged liquid with or without precipitates. To deeper understand such interesting thermal non-equilibrium between two phases in a spray flash evaporation of salty water, this paper establishes a multi-component spray flash evaporation model which coupled with diffusivity effect of non-volatile fraction, as well as the influence of spray polydispersion. An experimental system is also set up for evaporative coefficient determination, as well as model validation. The theoretical and experimental results meet a good agreement. It indicates the salinity and the superheat level of inlet feed have substantial impacts on such thermal non-equilibrium phenomenon of the temperature difference between the extracted vapor and the discharged liquid residue.