In other news, recent event have pushed me to crack the whip again on the respirator.
Sorry, I don't have the latest photos yet, as I have been busy adapting to a new rush schedule. Basically I need to finish the respirator in one week. There is a lot of progress that I've done in the last two days, but what I have here is what happened before this week. I'll post the latest as soon as I can.
I started last month with tests designed to convince myself that a regular PC fan would not be a good substitute for the centrifugal blowers/compressors. Basically confirming something I knew, but had never analyzed personally.
The issue at hand was whether I could build an axial compressor (more like a modern post WWII jet engine) from a larger electric fan(s), instead of a centrifugal compressor like these tiny blowers that take a month to arrive from China. But I knew the answer to that: it would require high speed, and it depends on the angle of attack of the fan blades.
After this project, I know that most PC fans are designed to move air, not build pressure. Whether you can compress air or not with a fan is a very delicate function of how the blades are slanted to "bite into the air." If the angle is too high or too low, the pressure built up drops off dramatically. You can get prodigious amounts of air from a fan, but the minute the exhaust encounters an obstacle like pressure or drag, the stream may not be able to overcome it.
I'll skip over the maths and just give you the link, if you're interested in looking at theory. Under less rushed circumstances, I'd find a quick way to explain it.
I tried to use a computer CPU fan to blow air into a half of a plastic 1L soda bottle bottle - used as a nozzle - which is about the same diameter as the fan. To my surprise, absolutely no air came out of the neck of the bottle! Nothing at all. The flow was reversed and the air was blown backward along the perimeter of the fan.
I tried other combinations, including streamlining the electric motor housing. .. Nothing. Zero. I wasn't expecting such a dramatic result. That fan is much bigger than the blowers and consumes the same electric power - ½ A, as the two blowers combined, but it can't build up pressure. It made the little centrifugal blowers look very good in contrast. I realized I have to stick to the tiny blowers or design my own rotors.
Here's the fan (without the plastic bottle. Basically useless to build pressure.
The good news (I'll post later) is that I found a way to increase flow by about 20-40% using the existing setup. Basically I increased the size of the stagnation chamber by hacking the screw top of the canister (next photos will show that)
The other good news is that I finally achieved positive pressure inside the mask. The caveat is that I had to increase the diameter of the tube to 0.9-1cm, and basically reduce the length of the flexible tube to zero
In other words, basically I have like 4-5 inches of maximum tube length before the drag eats up all of the pressure energy that the blowers produce. With more time, I'd design a helmet with the fans attached to the helmet.
The final configuration will rely on a tube slightly wider than a standard copper pipe (½ inch in the US) and in fact the joints used to connect the mask to the filter canister will be standard water fitting joints. I may be able to find a flexible copper tube to join both! The canister will be worn around the neck like some oversized rapper's necklace...
Flavor Flav in concert, 2009
