Hydrodynamics of Continuous Spiral Dryer with Rotatory Conical Sleeves: Experiments versus CFD Simulations

Abstract

In this study, a continuous and airtight twin-spiral dryer was developed in accordance with the characteristics and challenges in the process of disposing polysilicon slurry. Computational fluid dynamics (CFD) simulations were used to investigate the flow field in the rotating twin-spiral continuous dryer and an original discrete phase model was also elaborated to compare with the cold-modeling experimental results. The corresponding flow field was obtained using the available inlet velocity of 0.05–0.3 m/s and the rotational speed of the inner cone of 12–44 r/min, the residence time distribution, and tracked particles trajectory. Results showed that the residence time of the tracer particles in the cone cylinder was about 15.8–25.4% of the time spent out of it, and the particle’s residence time was much shorter in contrast to the rotational speed and inlet velocity. The external ribbon had a larger influence on the fluid, thereby leading to a larger velocity in the region outside the cone compared to that in the region inside the cone. In addition, the appearance of the vortex and boundary layer separation at the back of the ribbon and the spoke bar had secondary diversion effects on the fluid. Furthermore, the inlet velocity had little influence on the flow field while the rotational speed of the cone greatly affected the flow field. Hence, the CFD simulations showed good agreement with the experimental results.

Keywords

Polysilicon slurry / Continuous dryer / Cold-modeling experiment / CFD / DPM / RTD

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