# Influence of Acoustic Streams on the Efficiency of Ultrasonic Particle Agglomeration
## 1 Introduction
Due to this, a swirling flow is created in the agglomeration chamber and the particles (under the influence of centrifugal forces) are pushed to the outer part of the vortex. As the authors state, an area of increased concentration is created there and this area is affected with maximum efficiency. This approach makes it possible to increase the efficiency of agglomeration; however, due to the small size of the particles and the high degree of their entrainment by the swirling flow, the action of centrifugal forces is not effective enough. Therefore, this approach does not allow efficient implementation of acoustic agglomeration. Therefore, it is proposed additional impact on small particles in the ultrasonic field through the use utilization of secondary effects arising under certain conditions of generation of high-intensity ultrasound impact. One of such secondary intensifying effects is the so-called \"ultrasonic wind\". This is a second-order effect due to momentum transfer, represented by the Reynolds voltage. Theoretical studies of acoustic flows are well developed [24; 25] and carefully modeled [26; 27]. However, when ultrasonic (US) impact is implemented in an open space or a long gas duct, the radiation pressure generated enables the particles to be moved only in one direction without significant increase in efficiency of interaction between particles [28]. For this reason, in order to increase the efficiency of small-particle interaction in the maximum ultrasonic field in terms of sound pressure level, it is essential to generate the motion of particles in different directions, so that their mutual movement and interaction is realized. In addition, it is required to increase the concentration of particles in certain areas by moving them to significantly increase the efficiency of particle agglomeration, especially at their low concentration [8; 11; 20; 23; 29]. This can be provided by generation of vortex flows, because only vortex flows will increase the efficiency of interaction (aggregation) of particles due to the following factors:  
1. Increasing the speed of mutual movement of particles of different sizes. 2. Increasing duration of interaction of particles due to their confinement in vortex areas;
3. Generating zones with increased concentration of particles. There are known attempts to achieve this by initiating vortex acoustic flows near obstacles or reflectors. Such approaches can improve the efficiency of coagulation. But due to the fact that acoustic flows are not created in the entire volume of the agglomeration chamber, but in a small near-wall region, the maximum increase in efficiency is not ensured [30]. For this reason, this work proposes a new approach, which consists of creating in the entire volume of the agglomeration chamber a sequence of adjacently located elementary acoustic flows of the vortex type, corresponding in scale to the zones of pressure drop in the oscillatory process. This allows the volume of the agglomeration chamber to be filled as much as possible with vortex flows and increases the efficiency of agglomeration. Therefore, the research results presented below are focused on identification of conditions for generation of vortex flows in ultrasonic fields with the maximum sound pressure level of ultrasonic impact. Comparative studies of the process of agglomeration of particles with a size of 2.5 \(\upmu\)m in the presence of vortex flows and without them allows to establish the actual values of increasing the efficiency of ultrasonic agglomeration due to vortex formation of gas-dispersion flow by acoustic streaming.