An experimental and numerical study on the brine droplet evaporation considering salt precipitation

Spray evaporation is a promising and highly efficient desalination technology for treating high-salinity wastewater. However, the existing numerical studies on brine spray evaporation are mainly based on pure water assumption and ignore salt precipitation for simplicity. In the present study, the evaporation process of a single brine droplet considering salt precipitation was experimentally investigated using the pendent droplet method. The variation in brine droplet mass during the evaporation and crystallization process was measured for the first time. Based on the experimental data, a reaction engineering approach model for the brine droplets was developed and incorporated into ANSYS Fluent. The obtained reaction engineering approach model was proven compatible with the numerical simulation of brine spray evaporation. Thus, the numerical model was used to compare the spray evaporation behavior between pure water and NaCl solution. Results indicate that brine droplets have larger falling velocities and shorter residence time in the dryer than pure water droplets. The short residence time and large mass transfer resistance of brine droplets lead to a large axial dimension requirement of the dryer. The present study offers a new technological route for the numerical simulation of brine spray evaporation by considering salt precipitation.