Bioaerosol deposition, distribution, and detachment behavior on near surfaces from a cough is important for risk assessment and control of the contact route of respiratory disease transmission, such as SARS-2003, H1N1-2009, seasonal influenza, and Covid-19. A custom-built cough generator was used to simulate a real cough. E-coli and bacteriophage were used to represent the common respiratory bacteria and viruses, respectively. Firstly, bioaerosol deposition and distribution on front flat surfaces were studied. The cough jet impinges on the front surface and then forms a parallel spreading flow above the surface. The distributions of viable bacteria/viruses follow the skew normal equation. Survivability of bacterium/virus during the cough and deposition processes is almost uniform on near surfaces. Secondly, bioaerosol deposition and distribution on nearby seats in a cabin environment were studied, which is a common enclosed environment to cause respiratory disease transmission. The viable virus on front seat is one order of magnitude higher than that on the other near seats because of the large droplets on front seat. Increasing the height of the backrests or opening the air jet for the infector could reduce the virus deposited on front seat to less than 10%. Thirdly, the detachment behavior of deposited droplets from a solid surface was studied. The droplet detaches totally from a surface under a lateral force, while it detaches partially under a normal force, leaving a smaller droplet on surface. The adhesion of a droplet to a rough surface depends on the liquid film left on surface after droplet detachment. The surface energy analysis integrating the left liquid film has a good linear relationship with the experimental adhesion. The bioaerosol deposition, distribution, and detachment dynamics on near surfaces from a cough help understand the contact route and setup the engineering control of respiratory disease transmission.
(Supervisor: Prof. Huihe Qiu and Prof. Christopher Yu-Hang Chao)