Influence of Airflow Velocity and Applied Voltage on the Agglomeration of Ultrafine Particles of Different Origin in a Cold-Plasma Device with an Oval-to-Square Flow Transition

Ultrafine particulate matter is difficult to control because its low inertia, high mobility, and material-dependent electrical properties limit collision and enlargement processes in conventional gas-cleaning systems. This study investigates the combined influence of airflow velocity and applied voltage on the agglomeration of ultrafine particles of different origin in a cold-plasma device operating with an alternating bipolar electric field. The experimental system includes an oval inlet duct connected to a square treatment chamber containing parallel electrode channels. This transition in cross-sectional shape affects flow development, residence time, and particle exposure to the electric field.
Experiments are conducted at several controlled airflow velocities and voltage levels using hematite particles and ISO 12103-1 A2 Arizona Test Dust. These materials differ in origin, composition, morphology, and electrical behaviour, enabling comparison of their response to bipolar charging and interparticle interactions. Particle size distributions are measured upstream and downstream of the treatment chamber to assess changes in the ultrafine fraction and the formation of larger agglomerates. Airflow measurements are used to verify repeatable operating conditions. In addition, computational fluid dynamics is applied to characterize flow development through the oval-to-square transition and within the electrode channels; however, the primary focus is the agglomeration process.
The study evaluates how airflow velocity modifies particle residence time and how applied voltage influences charging intensity and agglomeration behaviour. Comparison of the two particulate materials provides insight into the role of particle origin and physicochemical properties. The findings support the selection of suitable operating conditions for cold-plasma pretreatment systems intended to improve subsequent particulate-matter separation.