Simulation study of particle–fluid two-phase coupling flow field and its influencing factors of crystallization process

Obtaining the morphology of two-phase flow field accurately through experiments is very challenging, due to the complexity and the drainage area diversity of particle–fluid two-phase flow. Depending on the particle concentration, size, flow velocity, and so on, the two-phase flow tends to be in a more complex form, known as coupled flow status. Crystallisation process within a crystalliser is a typical engineering application of particle–fluid two-phase flow, and hence, the flow field within a potassium salt crystallizer is implemented to simulate the crystal suspension and to mix flow state during a continuous crystallisation process. Because the two-fluid model treats the particle phase and fluid phase as two distinct continuous media, this simulation model takes the effect of virtual mass force into considerations. The enhanced two-fluid model is then applied to investigate the influencing factors of the coupled flow field between the potassium salt particles and the fluid in the crystalliser under various operating conditions. The results indicated that the stirring speed, the concentration of the feed particles, and the particle size affected the distribution of coupled flow field at different levels and, thus, affected the crystallisation phenomena of a potassium salt. Among those factors, the stirring speed appears to have the most obvious effect on the flow field, as it affects the velocity of the two-phase flow. In the conditions listed in this paper, the minimum stirring speed is roughly 50 rpm to form a stable and circular flow field in the crystallizer, and the maximum particle size is controlled at around 12 mm and the feed particle concentration of roughly 32% to ensure cyclic crystallization. The research method used in this article provides a baseline for the study of the coupled flow field of particle–fluid two-phase flow and its influencing factors. This research also states theoretical guidance for the optimisation of operating conditions in the production and application of potassium salt crystallizer.