Optimizing Aerosol Distribution in Allergen Exposure Chambers: A Comprehensive CFD Study

FATEMEH RAZAVI, Laura Haya, Suzanne Kelly, Rachel Friedrich, Alissa Belanger, Jimmy Yang, William Yang, Edgar Matida, Carleton University

     Abstract Number: 781
     Working Group: Aerosol Exposure

Abstract
Allergen Exposure Chambers (AECs, sometimes also referred to in the literature as Environmental Exposure Units, EEUs) are specially designed rooms in which patients can be exposed to airborne allergens for clinical studies. Advantages of AECs include: 1) A controlled environment that avoids pollution and weather conditions, 2) Elimination of other competing allergens (e.g., mold spores) as experiments can be conducted outside the allergy season, and 3) Controlled concentration levels of airborne allergens. Aiming for uniformity in both spatial and temporal distribution of allergens (particularly pollen) in newly designed AECs, numerical studies have been performed to analyze factors such as tower-type oscillating fan configuration, room ventilation rate, exhaust locations, and the allergen dispersion system. The airflow was solved using Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations with a shear-stress-transport turbulence model. The particulate matter was simulated using Lagrangian particle-tracking techniques.

Clean air entered the chamber from the ceiling, while particles representing pollen were introduced at ceiling points and tracked over time. Four oscillating mixing fans placed at each wall of the room were modeled to simulate airflow. The particle volume fraction at the level of participants' heads was analyzed to assess uniformity. The ongoing investigation has revealed the impact of several factors, especially the number and location of ventilation intake diffusers, exhausts, and aerosolizers, on the uniformity of the allergen field, guiding the overall AEC design. Synchronization of fans has also proven crucial for achieving the desired particle dispersion. An efficiency coefficient was introduced to evaluate the particle distribution uniformity, and a tentative AEC configuration has been proposed. Validation of the tentative design in an actual AEC will be performed in a separate investigation.

Keywords: Allergen Exposure Chamber, Computational Fluid Dynamics (CFD), Particle Dispersion, Fan Configuration, Exhaust Locations, Ventilation Rate, Unsteady Reynolds-Averaged Navier-Stokes (URANS), Particle Tracking, Efficiency Coefficient, Allergen Exposure Control.