I realized that my vacuum cleaner does not have a HEPA air filter, and I was wondering if I could just put a few layers of tissue paper to filter the air. I looked at the surface of the existing filter and tissue paper with a 120x magnifying microscope, and the tissue paper seems to have a denser surface/less gaps than the original vacuum cleaner filter. Is that a good idea? Will it actually filter air? Will it ruin my vacuum cleaner?
tissue paper can be used as a filter for particulates in air, but because the material itself is so weak, a strong flow of air through it will cause it to tear to pieces.
In addition, even if it were mechanically strong, the particles it filters out would sit right on its surface, pile up there, and quickly plug up the pores in it and stop the flow of air through it.
For these reasons, air filters are often made with some metal mesh structure embedded in them to furnish mechanical strength and with a filter material that traps particulates within its thickness and not on its surface. This "thick" filter lets the filter last longer and trap a larger quantity of particles before it gets plugged up.
First: When you say "the particles it filters out would sit right on its surface, pile up there, and quickly plug up the pores in it and stop the flow of air through it" don't forget that in reality, this is what also happens with commercial air filters.
Second: You say the tissue paper is weak, so is the paper in commercial filter before it was treated and protected. In that sense, we can do the same thing, by providing a support before installing the paper tissue.
I personally first pre-install a mosquito screen, then add the paper towel. When the paper tissue filter is no more efficient, I simply install a new one.
Simple, efficient and cost effective.