Abstract

SARS-CoV-2 (COVID-19) led to the development of air purifiers systems for classrooms, offices and workshops. The quality and efficiency of these systems is strongly dependent on the position of the air purifier in the room, the direction of the outflow, the dimensions of the room, additional air conditioning systems, etc. Previous studies reported about the influence of volume flows of the air purifier, position of infected persons, etc, a detailed study on the influence of the position was not considered in literature so far. In this study, the impact of the position of the air purifier and the direction of the flow at the outlet on the flow distribution has been analysed. An empty and closed classroom with a volume of approx. 200 m³ was used in the simulation model. The aerosol transport was modelled with a combination of a steady-state flow simulation which is followed by the simulation of a transient solution of the aerosol transport based on a frozen flow approach. To evaluate the efficiency, two characteristic numbers are determined. First, the volume ratio of the volume in the room with velocities smaller than 0.1 m/s related to the total volume of the room was determined for various positions of the air purifier (coordinates x and y) as well as the angle of the outflow angle (), i.e. in total 25 simulations. A minimum volume ratio was found for x/l=0.7610, y/b=0.294,  =-15° with the dimensions of the room b and l. Second, the ratio of mean concentrations in the room at the beginning (t=0 s) and for 1,200 s were determined by solving the transport equation for the aerosol. The two characteristic numbers show a similar behaviour within a range between 0 and -20%, but show no direct correlation. Within this accuracy, the reduced model can be used for extended parameter studies. For the simulations the Open Source Computational Fluid Dynamics (CFD) code OpenFOAM® (version 6) was used. In next steps, different configurations of classrooms with persons including different positions of infected persons will be considered.