These days there is a lot of talk about the effectiveness of ultraviolet rays (UVC) for the sterilization of air and surfaces against covid-19 contamination. Almost all the discussions lack solid scientific bases and no comparison with scientific data because covid-19 still has little understood aspects.
The big news is that scientific studies are now published on the effectiveness of sterilization of covid-19 with UVC rays.
Scientists studied the effectiveness of UVC irradiation of covid-19 virus cultures in the laboratory and published the results including the UVC energies required to ensure complete destruction of the virus at various concentrations.
In the scientific paper "UV-C irradiation is highly effective in inactivating and inhibiting SARS-CoV-2 replication", which can be found on Researchgate at the following link it has been shown that an energy equal to 3.7 mJ/cm2 at a wavelength of 254 nm is sufficient for 3-log inactivation (99.9% see link) of covid-19 and that an energy of 16.9 mJ/cm2 completely inhibits any concentration of the virus.
The problem is that the majority of consumer products for the air sterilization of the rooms do not reach these energy levels because the consumer products are not able to guarantee an air crossing time in the UVC lamp long enough to obtain the energy values reported in the scientific results.
This project solves the problem because it provides a spiral-shaped air path around the UVC lamp and a subsequent path along the axis of the lamp, obtaining a long travel time and also the necessary cooling of the lamp.
You can find the 3D STL model of the complete cylinder in the file section. The diameter of the complete cylinder is 10 cm and the height 20 cm. The internal cylinder that houses the lamp has a diameter of 5 cm. The air path consists of 10 turns of rectangular section 2.5x2 cm and therefore the median path of the air is 235 cm long. To this length must also be added the return path of the air along the lamp which is equal to 20 cm, therefore the total path of the air is equal to 255 cm.
With an air flow speed of 1 m/s, the air remains in the device for 2.55 sec.
A Philips TUV PL-L UVC lamp with a length of 20 cm and 18 W of power generates 5.5 W of light power at a wavelength of 254 nm, the radiation produced is equal to 25 mW/cm2, therefore the air that moves at 1 m/s receives a UVC dose of 63.75 mJ/cm2 which is almost 4 times greater than that reported in the scientific paper. This definitively ensures the effectiveness of sterilization.
The complete project can be found on Github