Design Challenge: Low Cost Air Filtration Systems

It is becoming clearer and clearer that a primary mode of transmission for covid is airborne transmission. To protect against this, there are several things that would need to work in conjunction.

  1. Mask – to control the virus at source
  2. Ventilation - to clear out the air, and reduce the build up of virus laden aerosol particles
  3. Air Filteration - to clean the air in a room where huge changes in ventilation are not feasible and otherwise also.

Here’s a wired article on air purifiers:

Air purifiers are expensive. The challenge is to design a low cost air purifier system that is mobile and can be easily put in a room, classroom, restaurant/eatery, and other spaces. Production and maintenance cost, ease of assembly, easy availability of materials on the market, low noise, portability would all be important criterion that will jostle for attention. Getting appropriate parameters for flow rates, filtration efficiency, relative to room size and occupancy would be important.

Basically, throwing this out as a design challenge if someone wants to take that up. Ventilation and filtration are now being recognised as important risk mitigation tools in the fight against COVID. Cheap, portable, accessible air filtration systems would also help with a host of other respiratory illnesses that plague folks in India. The need for this will not subside any time soon.


One method is to use UVC dis infection lamps in the inlet of AC.

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Details on the Corsi Rosenthal box fan filtration. I wonder if the box fan can be replaced with a cheap exhaust fan. …

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One could use a cheap exhaust fan, the limitation being noise produced by unbalanced exhaust fans And the danger of accidents due to lack of a grill.

great points. the design would need to incorporate some way to take these into account.

Kerala is in the grip of in-home transmission of covid-19 virus. 35 % of the infected are at houses. MIT chemical engineer Bazant and mathematician Bush in A guideline to limit indoor airborne transmission of COVID-19 insist: the pathogen is distributed uniformly throughout. In such well-mixed spaces, one is no safer from airborne pathogens at 60 ft than 6 ft. They find the Cumulative Exposure Time (CET) after which it is better to escape from the room. CET is 3 minutes without masks, 5 hours with masks and 58 hours with ventilation too. We can wear masks, but ventilation is difficult. Most of the buildings in India have ceiling fans. The air flow under the ceiling fan can be used to trap the virus onto soap water on a wetted towel that then deactivates the virus.

Here is more information about the Corsi-Rosenthal Box Air Cleaner found by Ayush from Wired. Corsi/Rosenthal Box

The horizontal airflow is created by shrouded fan in the improved Corsi/Rosenthal Box. After passing through the MERV 13 filters, the cleaned air flows out at 30 cubic metre per minute (CMM).

Our Ceiling Fan Air Cleaner (CFAC) reuses the ceiling fan with 220 CMM airflow, has no MERV or HEPA Filters but a Centrifugal Separator, and a virus deactivator in the detergent wetted towel. We have to occasionally wet the towel. Wash the towel once a week.

Jim Rosenthal measured the efficiency of Corsi-Rosenthal Box Air Cleaner in his TexAirFilters company. We should measure the efficiency of CFAC and if it is low, think of ways to improve. I will not say what I thought. Invite young students to find a better CFAC!

MIT chemical engineer Bazant and mathematician Bush wrote and still work on A guideline to limit indoor airborne transmission of COVID-19. Please visit COVID-19 Indoor Safety Guideline to see that Bazant offers a free, self-paced massive, open, online course (MOOC) on The Physics of COVID-19 Transmission. The course is archived at EDX and MIT but we can watch on youtube! MIT RES.10-S95 Physics of COVID-19 Transmission, Fall 2020

We could stack A4 size filter paper on each other and spray sanitizer regularly on it.
It will work with air circulation in the room and catch the small organisms and the sanitizer will kill them.
This method is not that reliable and not efficient at all but it is what I can come with in 5 minutes.
Sorry if I have wasted your time

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The shape of the surface onto which the air flows is important. Flat surface will trap less of virions than a curved surface. Paper cannot be wetted continuously.

We can use A4 papers as HariSharanKalia suggests, form a suitable trap shape with Origami, make it waterproof by dipping in molten wax, and place wetted cloth on the trap surfaces.

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