Using a 5V blower with a USB battery bank would be very simple and so I looked for a suitable blower but I couldn't find one making the 3.5CFM or 200Pa static pressure you mentioned so I have gone back to looking at 12V blowers, of which many meet the criteria. Indeed, getting the fan output right is important. It will be operating somewhere along its curve given in the datasheet and not at one end (static pressure with zero flow) or the other (CFM flow rate with zero pressure). To further investigate the operational point on the curve I have ordered a pressure sensor, part 223-1437-ND - should work with an Arduino hack. Digikey delivery times to where I am in New Zealand is very long at 13 days at present, so I wait for now. Regarding the 5->12V boost I am proposing to drive the fan, we could make the output voltage adjustable thereby making a wider range of blowers suitable and for a wider range of conditions. By the way, great work. I think what you have done so far is amazing!
Another idea. To make it possible to use different blowers (whatever is available and at hand), you could put multiple mounting options on your 3D part.
Have you considered using the ubiquitous USB power bank for the power supply? A step-up DC-DC converter would be required for the 5V->12V for the fan. (I just looked and the available 5V blowers are a bit low when it comes to static pressure)
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