| Jet has extensive applications in many fields such as mixing and transmission process. Compare with the conventional impeller, the adjunction of jet nozzle could realize the internal circulation of crystal slurry in the axial propulsive direction for a DTB crystallizer, which could effectively reduce the secondary nucleation caused by collision between stirring paddle and crystal as well as improve granularity of the product. The optimal structure of draft tube and flow field in DTB crystallizer was studied by simulation and experiment. Then the results provide guidance for the design and optimization of jet cycle DTB crystallizer. Specific contents are as follows:Based on the systematical simulation of the single-phase flow field with the configuration of straight draft tube and jet nozzle for the DTB evaporator crystallizer using the RNG k-? turbulent model, the optimal draft tube diameter was determined. And then the simulation of the multiphase flow for the novel design DTB crystallizer was also conducted. The simulation results showed that the jet presented an excellent linear expansion in the draft tube and the axial velocity distribution basically meet the Gaussian distribution. For the jet flow at the entrance region of the draft tube, the reciprocal of axis velocity shows a good linearity with the flow distance, and the axial velocity accelerated attenuated. The area ratio (?) of the annulus between draft tube and the baffle to the cross-section of the draft tube significantly influences the circulation flow ratio (?). With the increase of ?, ? increases at first, and then decreases, there exists an optimal y. Although the particle concentration of crystal slurry decreases along the radial direction in the optimal draft tube, it still has a more even distribution within the optimized crystallizer and a lower circulation flow ratio comparing to the single-phase simulation results. So its hydraulics meet the requirements of DTB crystallizer.The draft tube was optimized based on the structure of jet pump, and the parameters of the DTB crystallizers considered in this work are fluid flow behavior, mixing characteristics, energy consumption, and particle concentration. Firstly, fluid flow behavior of the jet DTB crystallizer with different configuration of the draft tube was analyzed and optimized using RNG k-s turbulent model. Secondly, the mixing characteristics was determined through the investigation of tracing effective area of the crystallizer using species transport model. Thirdly, based on the simulation results of the fluid flow properties of conventional DTB crystallizer using sliding mesh method, the comparison of the flow field and energy consumption between the jet circulation crystallizer and the conventional stirring crystallizer was also carried out. Meanwhile, comparisons of the crystallized particle concentration in the jet circulation DTB crystallizer with different draft tubes using Eulerian multiphase flow model were also conducted in this work. The simulation results showed that the optimized draft tube improved the internal circulation with a maximum increase to 23% as well as enhanced mixing characteristics of DTB crystallizer. Meanwhile, comparing with the conventional stirring DTB crystallizer, the jet pump DTB crystallizers consumed less energy. More than that, optimized jet pump DTB crystallizer perform more uniform distribution of the particle concentration than other jet DTB crystallizers. Because of optimizing jet pump draft tube, the jet not only satisfies the hydraulics requirements such as mixture, particle suspension,, but also conduces to energy saving compared with conventional DTB crystallizer.The investigation of flow field based on particle image velocimetry (PIV) was respectively conducted under different stirring speed and position for conventional stirring DTB crystallizer and different flow rate of external circulation with different jet nozzle diameter for jet DTB crystallizer. The comparison results between the experiment and the simulation showed that, RNG k-? model display an accurate and effective simulation of the flow field either in the stirring crystallizer or in the jet DTB crystallizer. |
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