声场导向管喷流床流动特性的数值模拟

Numerical Simulation of the Fluidization Characteristics in an Acoustic Spout-Fluid Bed with a Draft Tube

在内径120 mm、高1 000 mm的导向管喷流床中,以空气为气相,原生粒径290 nm的TiO_2超细颗粒为固相,借助CFD软件ANSYS Fluent 15.0,将声场模型与欧拉双流体模型相结合,将声场对导向管喷流床中超细粉聚团的流动特性进行数值模拟,研究了声场对气泡和固含率云图、固相时均浓度分布、固(气)相时均速度分布以及流化气旁路分率的影响。结果表明:声场的震荡作用促进环隙区颗粒在气流中均匀分散,减小气泡尺寸,从而使固含率分布变得更均匀;而导向管内由于射流速度较高,声场对固相浓度分布影响很小,但在壁面附近,由于射流速度下降,声场的震荡作用使固相浓度下降;声场增大了环隙和喷泉区的湍动强度,轴向时均速度在径向上分布得更加均匀;声场能够有效抑制流化气的旁路,显著减小流化气旁路分率。

The sound field model and Eulerian-Eulerian two-fluid model were combined to simulate the effects of sound field on fluidization behaviors of ultrafine powder agglomerates in an acoustic spout-fluid bed with a draft tube. The simulation was performed in the tube with an internal diameter of 120 mm and height of 1 000 mm using the ANSYS Fluent 15.0 of CFD software and the Ti O2 ultrafine particles with an average diameter of 290 nm were employed as the solid phase and the air was utilized as the gas phase. The effects of sound field on bubbles and the contours of solid volume fraction, the time-averaged distribution of solid phase concentration, the time-averaged distribution of solid（gas） phase velocity, and the bypass fraction of fluidized gas were studied. The results showed that the acoustic vibration and acoustic turbulence promoted the uniform dispersion of the particles in the annulus and reduced the bubble size, and thus the distribution of solid volume fraction became more uniform. However, due to the higher jet velocity in the tube, the acoustic field had little effect on the solid phase concentration distribution, while due to the decrease of jet velocity near the wall, the solid state concentration decreased. The sound field increased the turbulence intensity in the annular and spouting region, and the axial time-averaged velocity was more evenly distributed in the radial direction. The sound field can effectively inhibit the bypass of the fluidized gas and significantly reduced the bypass fraction of the fluidized gas.