Framework for Assessing Collection-Based Reactive Air Treatment Systems

The COVID-19 pandemic demonstrated the need for reactive air treatment systems, but a lack of understanding on the impact of different reactor geometries has stymied adoption of these technologies. This study uses a non-dimensional framework to examine the applicability of photocatalytic oxidation (PCO) to reduce bioaerosol concentration in indoor settings, particularly in heating, ventilation, and air conditioning (HVAC) systems. Three non-dimensional parameters: aspect ratio, collection efficiency, and dimensionless photon flux are used to evaluate the performance of two PCO reactor geometries: 1) honeycomb (HC) and 2) parallel plate (PP). Collection efficiencies of the HC for bioaerosols (0.01-10 µm) were modeled by varying aspect ratios from 25-100, air velocities from 0.5-2 m/s, and charge numbers from 10-10000. The collection efficiencies and the photon fluxes of HC and PP were compared using prior literature studies. The modeling results show that larger bioaerosols (5-10 µm) have a higher collection efficiency than other aerosols for low velocities and longer channels. Additionally, the air velocity impacted the collection efficiency of only larger bioaerosols. Longer aspect ratios are needed than those found in most commercial HC products, since the effects of gravitational settling and diffusion are inadequate for bioaerosol collection. Collection efficiency increased 2 to 5 times for 0.01-1 µm aerosols for charge numbers on the order of 1000; however, this increase is insufficient to enhance the performance of PCO systems. PP requires longer channel lengths than HC to achieve the same collection efficiencies. However, the PP configuration has superior radiation distribution characteristics than HC.