Numerical Model of the Influence of Ultrasonic Crossed Fields onthe Formation of Smoke Particle Agglomerates

A method for calculating the behavior and formation of smoke particle agglomerates in crossed ultrasonic fields is proposed. The proposed method takes into account: the convergence of agglomerates with allowance for the moments of flow forces from the gas flow, the rotation of agglomerates due to the moments of forces from the flow around the gas flow, and a phase shift between ultrasonic cross fields, leading to the rotation of the resulting vibrational velocity vector and, consequently, to an increase in the effective collision cross-sectional area due to the rotation of the agglomerates. A description of the morphology and position of agglomerates is constructed when representing the agglomerate as a solid body, typical for solid-phase aerosols in the form of smoke. An equation for the dynamics of translational and rotational motion of an agglomerate is obtained taking into account the interaction of particles. The statement about the presence of rotational motion with a limited angular velocity proportional to the sound pressure level is proven, with a phase shift of cross fields equal to 90 deg. By means of numerical experiments a critical value of the phase shift angle is established at which the pseudo-rotational motion (change in the rotation angle in a limited range the width of which is less than 180 deg) transforms into rotational motion (the agglomerate makes a full revolution through 360 deg). The critical phase shift depends (weakly) on the sound pressure level and ranges from 82 to 85 deg. The transition to rotational motion increases the efficiency of forming larger agglomerates due to an increase in the average cross section during particle collisions, caused by the difference in the sizes of agglomerates along different axes. It was established that for the practical implementation of increasing the efficiency of smoke deposition, the most appropriate and feasible is ultrasonic action in cross fields with a frequency difference much lower than the fundamental frequency (from approximaterly 100 to 200 Hz). Such action is much easier to implement compared to maintaining a constant phase shift between the cross fields and increases the collision cross-sectional area up to several times.