Fan Testing Round 5 (Working Thread)Are "NANO" Bearings the new sliced bread?

[meanmoe]

pitot tube + electronic pressure transducer (£50) + usb datalogger (£140) = nice automated system.

we use sensors by these people:
http://www.sensortechnics.com/index....a65aa2f14103b5

EDIT: best one in link gives ~0.05 inH2O

bit expensive but very reliable and easy to use,

also the construction of your fan test chamber is very much like an orrifice plate http://en.wikipedia.org/wiki/Orifice_plate
so you could probably get away without using the pitot probe

Hey another person with wind tunnel exp... I've never used the term before, but I've used the principle behind the orifice plate before for velocity measurements. There's no need for a pitot probe. I believe that the total pressure is constant in this regime (isentropic) so you can use continuity (vdot == vdot) and bernoulli to get velocity by varying area and taking multiple static measurements.

Thanks! I'm looking into it, I'm just not sure with these lower CFM levels if I can measure pressures that small. Even with a 3.5" diameter reduction, I'm still only measuring velocities from about 100-600 feet/min, and my particular meter seems to struggle below around 100 and make noise at 500.

If I understand this right, using a pitot tube would require measuring pressures down under .01" H2O. That's getting really small. I know dwyer has some meters that measure down to .001", but that seems like a challenge.
...

You may be able to get solid state transducers that are fairly accurate with that type of precision and accuracy. That is pretty small though... If you want to use a manometer you would have to incline it. This offers a large increase in precision. I've inclined down to 18.5 degrees before for precision. Technically you could go further if you wanted to stretch it across a wall. At this level you might have to correct for temperature though depending on materials used - ah, maybe not for differentials. I'd look for a couple of good cheap solid state pressure transducers... After I put the kids to bed, I'll think about it some more.


To answer your question about the hot film response... my experience matches SuperSilents. The response is excellent, but I do not remember ever using it for free stream velocity measurements. We backed that out using tunnel pressure taps - using the method referred to above.


EDIT: you need a good atmospheric pressure measurement too

EDIT: I just watched the videos... awesome setup - but now you have to watch the vids for the review. seems it'd be nice to use the serial bus for the anemometer and an a/d card for the rest, throw together a quick data acquisition program in labview and instant results - I miss my lab