Fundamentals of energy efficient precipitation and inactivation of COVID-19 aerosols by means of an ozone-free electrostatic precipitator designed for indoor use.

• Applicant: Professor Dr.-Ing. Ulrich Riebel
• Subject Area: Mechanical Process Engineering
• Term: from 2021 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 468800814

Aerosols are seen as a decisive pathway for spreading COVID-19 and other viral or bacterial infections. The primary liquid aerosols are drying very fast in the air, forming residual aerosols in the size range from 0.1 to 100 µm. Due to the low deposition rate, aerosols below about 10 µm can accumulate in indoor air and reach critical concentrations. Meanwhile, the size range below 5 µm is suspected to be the most important for spreading infections. Electrostatic precipitators (ESPs) are ideally suited for the separation of fine aerosols in the size range from 0.1 to 100 µm. The extremely low pressure drop of ESPs (amounting to a few Pa only) allows the combination with low-noise ventilators. Low noise is an important factor for the acceptance of aerosol precipitators for indoor applications. More¬over, ESPs offer easy access for the inactivation of the precipitated aerosol by means of UV light or gas ions. A problem, however, is the formation of ozone in the corona discharges which are used, so far, as a source of gas ions for aerosol charging in all ESPs. Ozone is regarded as highly toxic in concentrations exceeding about 70 µg/m³. The present project intends to provide the basic knowledge for building a new type of ozone-free ESPs, which is well-suited for indoor use. As ozone is instable at higher temperatures, a moderate heating of the corona wire should be sufficient to suppress ozone formation. Further aspects which shall be addressed are the inactivation of virus model aerosols by UV light, interactions between ozone und UV, and the possible formation of secondary aerosols by reactions of VOCs in the active corona zone.

• DFG Programme: Research Grants