Fluid dynamics studies on homemade facemasks and non-invasive eye procedures

Since the start of the COVID-19 pandemic, the use of homemade facemasks has been advised as a possible substitute for commercially available surgical or N95 masks. Researchers at IISc have carried out a detailed study on the fate of a large-sized surrogate cough droplet impinging at different velocities (corresponding to mild to severe coughs) on various locally procured cloth fabrics (stole, handkerchief, cotton towel, and surgical masks), specifically those which are convenient for people to use every day. A single quantity “ε” has been formed by combining the individual effects of pore size and porosity, giving a better insight into the correlation between liquid penetration and fabric properties. Based on their findings, the researchers recommend using a cotton towel (with at least three layers) as a face covering if the person cannot use an N95 or a surgical mask. Masks with three or more layers are ideally recommended since they can suppress aerosolisation significantly. The team also analysed the effect of washing on mask effectiveness, and results show a negligible influence of washing on mask efficacy up to 70 wash cycles. This study was carried out by Bal Krishan, Dipendra Gupta, Gautham Vadlamudi and Shubham Sharma under the guidance of Prof Saptarshi Basu (Department of Mechanical Engineering) and Prof Dipshikha Chakravortty (Department of Microbiology and Cell Biology).

In another study, Prof Saptarshi Basu’s group (Durbar Roy, Sophia M, Abdur Rasheed, Prasenjit Kabi) collaborated with Narayana Nethralaya Foundation (Dr Abhijit Sinha Roy and Dr Rohit Shetty). They provide a complete fluid dynamics interpretation of the unexplained droplet generation mechanism from corneal tear film during an eye procedure called non-contact tonometry (which involves an air puff) used routinely for glaucoma detection. Droplets generated from the rupture of the tear film in the human eye may carry viruses like SARS-CoV-2, which can subsequently spread unnoticed through aerosols and fomites. The researchers also describe the size scales (0.1 – 3 mm) and velocity ranges (0.1 – 5 m/s) of droplets ejected during such procedures, which may help ophthalmologists and medical practitioners conduct these procedures more safely following proper protocols.

(a) Cough droplet atomisation and various homemade facemasks (b) Droplet generation from corneal tear film during the non-contact tonometry process

References:

[1] B. Krishan, D. Gupta, G. Vadlamudi, S. Sharma, D. Chakravortty, S. Basu, Efficacy of homemade face masks against human coughs : Insights on penetration , atomization , and aerosolization of cough droplets Efficacy of homemade face masks against human coughs : Insights on penetration , atomization , and aerosolization of cough, Phys. Fluids. (2021) 093309. https://doi.org/10.1063/5.0061007.

[2] D. Roy, M. Sophia, A. Rasheed, P. Kabi, A.S. Roy, R. Shetty, S. Basu, Fluid dynamics of droplet generation from corneal tear film during non-contact tonometry in the context of pathogen transmission, (2020). Phys. Fluids. (2021) 092109 . https://doi.org/10.1063/5.0061007.

Lab website: https://www.saptarshibasulab.com/

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