关键词: 计算流体力学, 临界离底悬浮转速, 搅拌槽, 湍流动能

Abstract: Based on the function provided by CFX5.5.1, the critical suspension impeller speed, Njs, was simulated. The investigation was carried out in a fully baffled, flat bottom, cylindrical vessel, with 476 mm diameter, equipped with CBY (long thin blade) impeller. The clearance between the impeller and the bottom of the tank was D/3. The glass beads of 15~150 mm were chosen as the dispersed phase. The particle volume fraction was from 15% to 50%. Two different criteria were used to determine Njs from the numerical results. The original criterion is to identify the critical suspension by a sudden velocity increase with the impeller speed at the bottom center. The modified criterion is by observation of the velocity increase at the point with the most difficulty in suspension, i.e., at the radial position about 50 mm off the bottom center. The CFD predictions by the modified criterion are in good agreement with experimental data. At the bottom of the tank, turbulence kinetic energy at the critical impeller speed was also discussed.

Key words: computational fluid dynamic, critical suspension speed of impeller, stirred tank, turbulence kinetic energy