Free-flow air filter

When we cough or sneeze we expel particles of mucus and phlegm from the lungs at fantastic speeds. Thankfully, these particles immediately slow down in the air as a result of friction in the same way as a car will be affected by the drag coefficient. Once the particle stops in the air it will be subjected to other forces such as the force of gravity. Depending on the size of the particle its weight will overcome other forces, and the particle falls to the ground. On the other hand, microscopic particles will tend to float in the air essentially indefinitely as a result of their much greater surface area and the effect of buoyancy provided by the air.

This fact is widely recognized, however governments are paralyzed by fear and the lack of budgets for retrofitting ventilation in buildings. Similarly, the bureaucrats and administrators simply don’t know what to do with filtering systems because they are cumbersome to install. A viable option is to install portable filtering systems to provide clean air, and in addition measure the quality of the air to ensure air hygiene in shared indoor spaces.

The thesis is that if we can provide portable ventilation systems that are very economical and convenient to install at the same time, governments will find some elasticity in their budgets to consider the benefits of ventilation, filtration and air quality. Only by doing this we will ultimately be able to go “back to normal”. Ideally we would like to bring the level of airborne transmissible diseases to zero, however bringing this to a manageable level will allow us to go on with our lives.

As a result of the pandemic I’ve developed a compact air filtration device that is based on 3D printed fluidic channels. Because this is a free-airflow device, it uses a small axial fan that is very economical. The materials (plastic) are also very cheap, lightweight and sturdy, so that it will be possible to install the device everywhere. I will be glad to present how the device works and how it can be used in public places such as stores, public transportation, open workspaces, schools, religious congregations, and more.

I’ve received some initial funding from the European Union AMable Covid-19 program. At this time I’m seeking more significant funding that will allow me to commercialize a proof of concept and run a pilot. I would appreciate the chance to further discuss this device with the relevant stakeholders and identify the most suitable channels for distribution.

Governments have been slow to act with regard to the implementation of effective measures against the spread of airborne pathogens. This is likely the result of slow to act bureaucracy coupled with the disproportionate effect of some missteps in the initial stages of the pandemic. Only on December 23, 2021, nominally two years after the start of the pandemic, the CDC recognized publically that the virus spreads through aerosols. For someone that worked in a cleanroom facility, this fact was intuitively obvious. In fact the discussion among the scientific community seems to recognize this fact all but universally after a cursory glance at the problem.

For nearly all this time the scientific community has been trying to communicate with the government the importance of effective prophylaxis measures to prevent the spread of the virus in indoor spaces. Now that the public health leadership has been confronted with the limitations of vaccines against mutating strains of the virus, they must embrace non pharmaceutical measures of prophylaxis such as ventilation and filtraion.

My proposition is that by providing a device with a superior design in terms of its usability, while at the same time making it more economical by an order of magnitude, people will be empowered to deploy it everywhere where there is a risk of transmission, i.e. crowded indoor spaces.

1. Design a device that is user friendly and not cumbersome to install or operate, to the point that it is completely ubiquitous and transparent.

2. Manufacture a very cost effective device with common materials (plastic) and sturdy components that inspire the confidence of the public.

3. Provide a a device that serves as a viable option for governments to enact meaningful indoor air quality standards.

4. Disseminate the importance of shared air hygiene in the long term and make it an integral part of our quality of life.

Out of the variables in the design, those related to the user experience are straight-forward: the device should be roughly 1 liter in volume (10cm x 10cm x 10cm), lightweight, quiet, and easy to operate. On the other hand, the technical variables are interlinked. Since the virus inactivation dose is known, fixing the volume of the device also determines the air flow that can be achieved. Therefore the overriding objective of the project is to improve the air flow to an equivalent 6 air changes per hour (ACH), which for a personal device is about 35cfm.

Another important parameter is the price. Recently a researcher compiled a
chart of portable fabric filters, showing their cost vs. the air flow.
Performing a regrression analysis the researcher revealed that the slope
of the curve is about 1.8 USD/cfm. Even taking into account some
outliers of cheap and effective filters such as the Corsi-Rosenthal box
and the filter sold by IKEA, the cost of the free-flow filter should be
brought down to about 0.2 USD/cfm, which is an order of magnitude lower.

Just like in the 19th century public works finally recognized the importance of water sanitation, the outcome of the present crisis should be cleaning the air in shared spaces. We practically take for granted the supply of clean water in most nations (making clean water available in the remaining places is the subject for another project); however it is really easy to get sick at the office, congregation, or school when someone comes in with a cold.

The scientists knew and recognized this, so in a way we are late by a century.
The thesis is that by providing a device that does not require retrofitting an entire building's HVAC system, it will be possible to achieve adequate air hygiene and not get sick. I feel that In order to do this, one of the important roadblocks that must be overcome is the cost of the solution: Once a solution that is eminently affordable and convenient is available, the general public will discover some price elasticity in their choices and recognize the importance of sanitazing the air.

So that leaves the work of the engineers. Here a multidisciplinary approach is key. Underneath an honest engineer there lies a scientist! So that even if we are trained in electrical engineering, embarking on a mechanical engineering project is not overstepping. Similarly in the present global crisis opening our notes from highschool biology on viruses is also reasonable. Moreover with all the material available online, there is simply no excuse for not coming up to speed on viruses and aerosols. Thus a single engineer working in his living- room can still make a difference by designing a very compact and economical 3D printed filter that works with UVC light and a PC fan.

The device is based on "structured packing" from the field of mathematical topology. According to this construct, it is possible to fit an infinite surface area inside a volume. In practice the surface area is still limited by the manufacturing method, but a 3D printer is able to approximate this and build a "maze" of fluidic channels to ensure the air is exposed to the inactivation dose of UVC light.

In fact one of intended advantages of 3d printing is for prototyping functional shapes of this sort. I have researched the possibility of using a plastic that is transparent to UVC light, and found COC (cyclic olefin co-polymer). This material is also resistant to UV radiation and has a similar manufacturing profile to regular extruded filaments. Moreover the filter can be wrapped in a reflective coating that causes UV light to be reflected several times inside the enclosure. For plastics this is nominally PTFE (0.95 reflectivity).

The UVC light is generated by a surface-mount "LED" diode. This device emits light in the optimal inactivation wavelength of about 265nm. The efficiency of the diodes is still low, but improving. The key is that with surface-mount technology the diodes are assembled right on top of the channels, so that there is very little attenuation. A feature of the device is that the diodes will be cooled by the air flow itself!

Finally since the filter is completely free-flow (i.e. no fabric media at all in the filter), it will be possible to use a very compact PC type fan to move the air.

UVC light is recognized for its germicidal properties. This is because organisms are not naturally adapted to this wavelength at all. The germicidal dose for viruses has been published in scientific papers, notably by the School of Medicine at Columbia University [www.nature.com (2018) 8:2752  | DOI:10.1038/s41598-018-21058-w]. Knowing the light intensity of the LED (e.g. 40mW), allows calculating the required dwell time inside the filter; and from here the total air flow is determined for a given volume.

CFD simulations we have carried out reveal that the average air speed in the channels is about 15 m/s, which is relatively high but achievable with a standard axial fan.

The significant breakthrough is achieving the required air flow while keeping the volume of the device constant. This is achieved thanks to the extremely large surface area of the walls in the channels. Please see a model of the device at: https://youtu.be/7n1_1zAAhU0

This is part of the activities in my technology development company. The ideal business model should ultimately be a spin-off as an independent firm, such as a B-Corporation.

I fully subscribe to MIT's committment on Race and Diversity.
I welcome people of all backgrounds.

The business model is that of providing a new technology for the benefit of humanity.

I plan to enter into license partnerships with manufacturers and distributors where I provide the technology and know-how for producing the devices.

Since the device is constructed with commonly available materials, the cost of manufacturing will also be very low. This means that the revenue stream should be more than enough to cover for the administrative expenses and working capital.

Manufacturing will be initially by means of 3D printers. Once the design is stable, it will be possible to transistion to traditional injection molding methods to bring down the cost further and scale.

I have received a grant from the European Commission, H2020, Innovation Action (IA), unde the AMable Covid-19 call.

I'm actively seeking to raise further capital from venture funds, accelerators, and collaboration with academia in the 2+2 program (Horizon Europe).

A friend of mine manages an important online commerce web site where he has agreed to initially list the device.