Breakup and droplet formation of thin liquid jets in prilling applications

Abstract

Prilling is a spray solidification process of producing spherical beads, or prills, typically for fertilizers like urea and ammonium nitrate. The process involves molten material passing through perforated rotating containers, forming spiraling jets and breaking up into droplets due to a Rayleigh-Plateau instability by surface tension. These droplets undergo heat exchange with a cooling air stream and turn into solid prills. However, controlling prill size and shape remains challenging due to complex fluid dynamics, thermal effects, and non-Newtonian material properties. This research focuses on understanding jet breakup under the influence of thermal effects and body forces related to gravity and rotation (centrifugal and Coriolis forces). The overarching goal is to optimize the prilling process for a desired narrow prill size distribution by predicting and controlling the jet breakup process. A fundamental and holistic approach was taken based on a combination of experiments, stability analysis and various types of numerical simulations.
The study begins by exploring the dynamics of a spiraling liquid jet emitted from a rotating orifice. Using experiments, linear stability analysis and a nonlinear slender-jet model, the influence of the body forces from rotation and gravity on jet thinning and breakup is quantified. Imposed mechanical vibrations within the nozzle modulate the jet conditions at nozzle exit, enabling control over the jet breakup length and droplet size. The findings reveal that spiraling jets behave similarly to straight jets under gravity, where the body forces influence the thinning rate of the base jet and local base jet conditions control the growth rate of unstable jet perturbations. This insight opens pathways for more precise control mechanisms in various jet-based industrial applications....