Effect of Stirring Paddle Geometry on Nucleation and Growth Crystal Size of Ammonium Sulfate Crystals

Stirring paddle selection is a critical part of the design and optimization of the crystallization processes, directly influencing crystal nucleation and crystal quality. This work investigates the effect of two different stirring paddles, the propeller and anchor paddle, on the properties of the metastable zone and the nucleation kinetics of ammonium sulfate. The experiments were conducted by determining the metastable zone widths with two different types of stirring paddles and deriving the nucleation kinetics parameters from a dual analytical point of view by using the self-consistent Nývlt equation with the classical 3D nucleation theory. It is found that the nucleation mechanism under the action of both stirring devices is progressive nucleation, and the interfacial energy increases with decreasing saturation temperature. The anchor paddle system exhibits higher nucleation rates at the same chemical potential difference. In addition, crystal products prepared with the propeller were significantly larger in size than the anchor paddle, and crystal growth was more regular. This study provides a theoretical basis for the selection of stirring paddles in the industrial crystallization process.