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ated with a dual Rushton impel-ler. The MRF method was irstly used to obtain a converged solution of the liquid flow field, the result of which was then used as an input for the solution of the scalar transport equation using the fully transient SM method in order to predict the time-dependent mixing process. In agreement with the findings of Osman and Varley [9], their predictions were again found to be generally 2–3 times higher than the experimental value. Bujalski et al. [11] performed simulations on the same stirred system as that employed by Jaworski et al. [10] . They used a finer grid in the regions of high velocity gradients and solved the transient sca-lar transport equation in a stationary reference frame. Although improved results were obtained, discrepancies in the order of 100% still have been found between the predicted and experimen-tally determined mixing time values. In a further investigation, Bujalski et al.[12] studied the influence of modeling strategy and the addition position of a tracer on the mixing time in a baffled stirred tank agitated with a Rushton turbine using the SM method. The former was found to have little effect of the numerical result but, the effect of the position of the feed point was very important. When the addition point was close to the stirred tank wall, a large discrepancy can be observed. By comparison, for the flow with low Reynolds number, the situation is much better. Shekhar and Jayanti [13] successfully simulated the flow and mixing characteristics in an unbaffled stirred tank agitated with a eight-blade paddle impel-ler using the SM method and the low Reynolds k– e model for rather low Reynolds numbers (up to 480). Good agreements with the experimental data and the correlations from the literature were obtained.

In order to predict the turbulent quantities at small scales pre-cisely, large eddy simulation (LES) or direct numerical simulation (DNS) is needed. In the last few years, LES studies on the mixing process have been successfully carried out. Yeoh et al.[14] per-formed LES study to characterize the mixing of an inert scalar in a baffled stirred tank agitated with a Rushton turbine. It was found that LES can provide a very detailed picture of the spatial and tem-poral evolution of the scalar concentration that cannot be obtained with the standard RANS approach. The predicted mixing time com-pared well, on average within 18%, with values determined from correlations reported in the literature. Hartmann et al.[15] per-formed a lattice-Boltzmann based LES study of the flow in a baffled Rushton turbine stirred tank at Reynolds number Re= 24,000. The mixing time was found to be significantly influenced by the impel-ler size but, has little effect with the position of the tracer injection point. The simulated mixing times overestimate the experimen-tally determined values but the discrepancies are no more than 30%. Min and Gao [16] and Zadghaffari et al. [17] employed the combination of SM and LES technique to study the mixing process in a baffled stirred tank agitated with a 3-narrow blade hydrofoil CBY impeller and a Rushton turbine, respectively. They all con-cluded that LES is a reliable tool to investigate the unsteady behav-ior of the turbulent flow in stirred tanks.

References
[1] Nere NK, Patwardhan AW, Joshi JB. Liquid-phase mixing in stirred vessels: turbulent flow regime. Ind Eng Chem Res 2003;42(12):2661–98.本论文由英语论文网提供整理，提供论文代写，英语论文代写，代写论文，代写英语论文，代写留学生论文，代写英文论文，留学生论文代写相关核心关键词搜索。