Air-borne transmission can pose a major risk of infection spread in enclosed spaces. Venting the air out using exhaust fans and ducts is a common approach to mitigate the risk. In this work, we study the air flow set up by an exhaust fan in a typical shared washroom that can be a potential hot spot for COVID-19 transmission. The primary focus is on the regions of recirculating flow that can harbor infectious aerosol for much longer than the well-ventilated parts of the room. Computational fluid dynamics is used to obtain the steady state air flow field, and Lagrangian tracking of particles gives the spatial and temporal distribution of infectious aerosol in the domain. It is found that the washbasin located next to the door is in a prominent recirculation zone, and particles injected in this region take much longer to be evacuated. The ventilation rate is found to be governed by the air residence time in the recirculation zone, and it is much higher than the timescale based on fully mixed reactor model of the room. Increasing the fan flow rate can reduce the ventilation time, but cannot eliminate the recirculation zones in the washroom. The talk will complement the CFD study with simple flow visualization experiments done in a real washroom, and show how the combined CFD-experimental approach can be applied to other scenarios, like classrooms, research labs and hostel common rooms.
Krishnendu Sinha received his Bachelor of Technology in Aerospace Engineering from Indian Institute of Technology Kanpur, followed by M.S. and Ph.D. at the University of Minnesota. He has served on the faculty of Aerospace Engineering at IIT Madras and is currently a professor at IIT Bombay. His research interests are in the area of computational fluid dynamics, turbulent flows and hypersonic aero-thermodynamics.