2015 Ricardo Application of Euler−Lagrange Approach to Predict the Droplet Solidification in a Prilling Tower
ABSTRACT: This paper deals with the phenomenological characteristics of the multiphase flow in a 3D urea prilling tower under conditions close to those of the industrial-scale process, considering the simultaneous heat and momentum transfer and the droplet solidification, using the computational fluid dynamics technique. The Euler−Lagrange approach is used to represent the multiphase flow. Solidification of the droplets was considered by means of an unsolidified core model, which predicts the thickness of the solid phase formed from the surface to the center of the droplets during the evolution of their trajectories in the continuous phase. The global operational performance of the process was evaluated on the basis of the solidification and breaking indexes defined from local variables obtained from numerical simulations. Solidification index values in the range of 0.83−1.00 were obtained from simulations, and the internal resistance to heat transfer was found to strongly affect the solidification phenomenon. A nonsymmetrical flow was used to evaluate the breaking index of droplets broken because of impact with the walls. The global thermal properties associated with the droplets, i.e., the surface and core temperatures and the overall heattransfer coefficient, had values of 34.37 °C, 115.79 °C, and 19.29 W/m2K, respectively, for droplets with a diameter of 1.2 mm. The air temperature at the top of the tower was 74.26 °C for droplets of this diameter.