CFD simulation of isolated spray flash evaporation with active vapor extraction

Spray flash evaporation is an ultrafast evaporation phenomenon that happens when the superheated liquid is sprayed into a low-pressure environment, which has gained more attention due to the great potential in the enhancement of evaporation capacity. In the isolated evaporation of spray flash, the latent heat is self-supplied by droplets, leading to a temperature reduction in droplet residue. In an evaporator with active vapor extraction (vacuuming), there can be a significant temperature difference between the extracted vapor and discharged liquid of droplet residue. The overall evaporation capacity and the non-equilibrium in temperature between the extracted vapor and liquid residue, however, depend strongly upon the geometric design of evaporation chamber, the spray characteristics, and associated operation conditions including feeding flow rate and temperature and vacuuming pressure. Quantification of such a complicated system requires the establishment of a physical modeling and corresponding numerical simulation. This paper presents a three-dimensional CFD modeling and simulation, using ANSYS software, to investigate an isolated evaporation of spray flash in a cylindrical chamber with active vapor extraction. Due to the polydispersed atomization in spray, a two-way-coupled Lagrangian-Eulerian modeling is adopted. Discrete phase model with user-defined functions (UDF) is applied to simulate the coupled heat, mass and momentum transfer between droplets and vapor. The simulated results are compared with the experimental measurements, which shows a good agreement.