运动颗粒对传质过程影响的格子Boltzmann模拟

Lattice Boltzmann simulation of mass transfer process affected by a moving particle

颗粒的主动运动对传质过程有重要影响。以表面恒浓度的二维球形颗粒为研究对象,采用耦合传质的格子Boltzmann方法(LBM)模拟了颗粒在自旋和振动两种情况下的相间传质过程。选择浸入运动边界法和非平衡态外推法处理运动颗粒边界,研究了颗粒自旋速度、颗粒振幅及振动频率对传质过程的影响。结果表明,中等雷诺数的自旋颗粒绕流中,随着颗粒自旋转速增大,颗粒的传质舍尔伍德数反而降低,表明在强制对流的情况下,颗粒自旋减弱颗粒的传质效果。当颗粒振动时,颗粒振幅越大,传质舍尔伍德数增大;当颗粒振动频率造成锁定现象时,颗粒流体相间传质效果显著增强。本工作的数值结果不仅表明格子Boltzmann方法可以有效模拟强制对流传质的过程,也为强化传质提供了一种思路。

In the catalytic reaction system,the internal and external diffusion have a great impact on the total reaction rate through the influence on the mass transfer process.The internal diffusion in porous channels has been well investigated by statistical mechanics on the influence of wettability,roughness,and electric properties of channel walls.By contrast,the influence of external diffusion needs to be further studied such as,how the active motion of particles impacts the mass transfer.Herein,by using the lattice Boltzmann method coupled with mass transfer process,the influence of the forced rotation or vibration of the catalyst particle was studied.A circular particle with constant interfacial boundary concentration was considered,and the immersed moving boundary and non-equilibrium extrapolation methods were chosen to treat the liquid-particle interface.The effects of rotational speed,vibrational amplitude,and frequency on mass transfer were investigated.The simulations indicated that when only considering diffusion,particle rotation inhibited mass transfer.The higher the rotation speed,the worse the mass transfer,while the overall suppression effect was not significant.The particle streamwise vibration enhanced mass transfer significantly.The lock-on frequency was about 1.9,and the enhancement amplitude reached 10%.Increasing the amplitude and Reynolds number strengthened the mass transfer,and the lock-on frequency moved towards the low frequency direction,while the Schmidt number had little effect on the value of the lock-on frequency.The transverse vibration was also compared with the streamwise one and showed greater enhancement of Sherwood number at a lower frequency.This numerical results not only demonstrated the feasibility of the lattice Boltzmann method for simulating the forced convection mass transfer process but also provided a route for enhancing mass transfer.