Construction of a Numerical Model for Flow Flash Evaporation with Non-Condensable Gas

Abstract

Flash evaporation processes are widely used in petroleum, food, chemical, power, and other industries to separate products or extract heat. The liquid is often entrained by non-condensing gas components. This study develops a multiphase, multicomponent, and pressure-driven phase-change-coupled model to numerically study water flash evaporation with non-condensing CO2. The model includes the mass, momentum, energy, volume of fluid (VOF), species transport, turbulence (RNG k-ε), modified phase-change Lee, and non-condensing CO2 release governing equations. The steam generation rate and mechanism for pure water and different concentrations of CO2 are considered. The results show that the numerical model can accurately predict the flash evaporation process and has high accuracy compared with the experimental data. Both the dissolved and entrained CO2 that are released can severely disturb the flow field, leading to an increase in the steam generation rate. Under a 1–10% volume concentration of dissolved CO2 and 0.0661–0.1688% mass concentration of entrained CO2, the maximum increase ratio of steam generation can reach 20%.

Keywords

• flash evaporation
• non-condensing gas
• numerical investigation
• heat and mass transfer
• steam generation rate