Numerical investigation on vacuum spray flash evaporation of ethanol-water solution

Abstract

To investigate the flash evaporation of aqueous ethanol in vacuum environment, a correction factor is introduced to modify the flash evaporation rate equation. The modified method is based on the Lagrangian-Eulerian model that couples the momentum and mass transfer of continuous and discrete phases. The results for droplets temperature exhibit average errors of less than 3.28 K compared to experimental data, thereby verifying accuracy of the method. Through the analysis of the flash evaporation behavior of two-component droplets, two distinct stages can be identified. “The first stage of flashing” is characterized by high flash evaporation rate, rapid temperature decline, and short duration, while “the second stage of flashing” is opposite to the Stage I. As the droplet size increases and the initial ethanol concentration decreases, it is observed that the duration of Stage I increases. This phenomenon extends the duration of high flash evaporation rate, thereby enhancing the mass transfer to the vapor, leads to larger decline of ethanol mass fraction. Increasing the spray temperature or decreasing the vacuum pressure can also enhance the mass transfer and flash evaporation rate. However, spray temperature shows a more significant effect on the flash evaporation rate and evaporated mass than that of vacuum pressure.