Abstract
When converting a baffled stirred reactor to work with a different fluid, usually the original impeller must be replaced with a customized one. If the original impeller was designed for mixing liquids, its performance for liquid–solid suspensions may not be satisfactory. A case study is presented, where a two-blade original impeller is replaced with a new three-blade design. The new impeller shows clear improvements in mixing a liquid–solid suspension, while keeping the shaft power practically at the same level. As a result, a practically homogenous liquid–solid mixture is obtained, thus ensuring the required quality of the final product. The present numerical investigations employ the Eulerian multiphase model with renormalization (RNG) k–ε turbulence model to simulate the three-dimensional unsteady free-surface liquid–solid flow in a stirred tank. A sliding mesh approach was used to account for the impeller rotation within the expert code, FLUENT 16. The comparative quantitative analysis of the solid phase distribution and the relevant velocity profiles show that the new design of three-blade-impeller is significantly increasing the sedimentation time of the solid phase beyond the chemical reaction specific time. The necessary power to drive the new impeller has a slightly higher value than for the original impeller but it can be sustained by the existing driving system.
Highlights
Stirred reactors have applications in many chemical processes where mixing is important for the overall performance of the system
Computational fluid dynamics (CFD) techniques have been used in the recent years to provide such information of the hydrodynamic and design parameters
In the literature [10,11,12,13,14], there are available results obtained from using these two models and these results show that the Eulerian multiphase model is more accurate than the Eulerian mixture model when working with a particle size higher than 100 μm and solid fraction ranging between 0.2 and 16%
Summary
Stirred reactors have applications in many chemical processes where mixing is important for the overall performance of the system. The above brief literature review on the numerical approaches for problems similar to the one addressed in the present paper led us to the conclusion that the Eulerian multiphase model is the suitable one for the liquid–solid mixture reactor further investigated. This model can accommodate the free-surface flow. The current study represents the second research paper from a series of three and focuses to analyze the hydrodynamic performance of a new impeller designed by our research team, which is fitted on a stirring mechanism of a chemical reactor.
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