基于微粒再悬浮的沉降微粒团的受力分析

Moment analysis of deposited aggregate based on particle rentrainment

以管流中柴油机排气沉降微粒为研究对象,通过建立的沉降微粒再悬浮的静态模型,从微粒再悬浮的角度对沉降微粒团所受到的黏附力矩、重力力矩、碰撞力矩以及曳力力矩进行了计算分析。得到了柴油机排气沉降微粒团所受力矩随微粒团直径的变化规律、各种力矩的取值范围以及在柴油机排气沉降微粒再悬浮中各种力矩的作用。沉降微粒的平衡主要受黏附力矩、碰撞力矩以及曳力力矩的影响。当微粒团直径为0.1～O.8μm时,黏附力矩作用显著并维持沉降微粒的稳定。随着微粒团直径的增加,曳力力矩和碰撞力矩快速增大,而黏附力矩的增大速率则相对比较缓慢,打破沉降微粒平衡的作用显著。

This paper is aimed at disclosing what kind of momentum plays the dominant role in particle reentraimnent, how the momentum changes with the diameter of particle aggregate as well as how the diameter of aggregate influences the particle reentrainment, because these are two important phenomena in controlling the particles of the diesel engine＇s exhaust. In proceeding with our research, we have first of all chosen the model of a momentum balance as particle reentrainment model. In this model, the momentum of the forces determines the mobile state of the particles. We have also worked out the momentum of forces, i.e., the particle adhesion, gravity, aerosol collision and aerodynamic drag, which are acting on the diesel engines deposited aggregate on the basis of the momentum balance. The analytical solutions we have gained indicate that the momentum regularly changes with the aggregate diameter, and the scale of each momentum, as well as the role each momentum plays in the particlereentrainment. The general tendency is that all the momentums of the forces tend to become bigger with the increase of the particle diameter. Of all the influential factors, the momentum of adhesion, the collision and the aerodynamic drags play the main roles in keeping the balance of the deposited particles. Assuming that when the particle diameter is 0.1μm, the aggregate of size 0.1 - 0.8 μm in diameter and the momentum of adhesion has effect on the depasited particle stabilization, for the increase of its movement tends to promote the increase of the aggregate diameter than the collision of an aerosol particle and the drag of aerosol flow. And, now, with the increase of the particle diameter, the collision of an aerosol particle and the drag of the aerosol flow tend to increase faster than the momentum of adhesion, which plays an important role in the reentrainment. However, if the aggregate is smaller, the drag of aerosol flow would have a larger proportion in the total momentum, which in turn actuates the particle reentrainment. On the contrary, the collision of aerosol particles now plays the main role. Therefore, when the momentum balance broke up, the motion state would like to change with the momentum of forces, the aggregate would now slip, roll or come into rentrainment.