Measuring high velocity airflow

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SUMMARY

The forum discussion centers on measuring high-velocity airflow from a fan with a 12-inch blade diameter and a power consumption of 60 W, which operates at 60% efficiency, yielding an air velocity of approximately 9.5 m/s. Users suggest alternatives to commercial anemometers, which typically measure up to 40 m/s, including DIY Pitot tubes and hot-wire anemometers capable of measuring velocities up to 900 m/s. The conversation also highlights the importance of using correct calculations for airflow velocity and the potential for using digital manometers for accurate pressure measurements.

PREREQUISITES
  • Understanding of airflow dynamics and velocity calculations
  • Familiarity with Pitot tube and hot-wire anemometer technology
  • Knowledge of pressure measurement using digital manometers
  • Basic principles of fluid mechanics and compressibility effects
NEXT STEPS
  • Research the Rayleigh Pitot tube formula for high-velocity measurements
  • Explore the specifications and capabilities of hot-wire anemometers
  • Investigate digital manometers suitable for airflow measurement
  • Learn about online wind force calculators for airflow force calculations
USEFUL FOR

Engineers, HVAC professionals, and anyone involved in fluid dynamics or airflow measurement will benefit from this discussion, particularly those seeking to measure high-velocity airflows accurately.

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I have a fan that consumes 60 W and blade diameter is 12 inch. If it's just 60% efficient, then the velocity of air coming out of it is around 9.5 m/s. I also have a nozzle inlet of which fits the fan and the diameter at the throat cum exit is 3.5 inch. I want to know how to measure the velocity of the flow coming out of the nozzle as market available anemometers can't measure velocity more than 40 m/s.
 
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You can bend some tubing and make yourself a pito-static tube.

However, I did almost exactly this experiment as a kid. Have you actually tried a commercial anemometer yet? I think you will find you achieve a much lower velocity than you expect.

[edit]
Btw, I'm getting 32 m/s. How did you calculate 9.5 m/s?
 
Last edited:
Are you sure? 60 seconds of search found this on Amazon for $40. It says 0-40 m/s range.

1618489158012.png
 
anorlunda said:
Are you sure? 60 seconds of search found this on Amazon for $40. It says 0-40 m/s range.

View attachment 281565
He's asking for higher than 40m/s.
 
OK, here's one that claims 100 mph (44.7 m/s)
1618495090390.png


This one claims 50 m/s
1618495145026.png


Here's one using a hot wire, claims up to 68 m/s
1618496394967.png


Searches for airspeed sensors in aviation sources should easily find more products with ranges higher than 40 m/s.
 
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anorlunda said:
Searches for airspeed sensors in aviation sources should easily find more products with ranges higher than 40 m/s.
The alternative to an anemometer I suggested above is a DIY pito-static tube, but for a commercial version of it, you can buy a pito-static tube and digital manometer. I have these:
https://www.grainger.com/product/3T...B7B3hGjN16pzGI4HwXwaAvwuEALw_wcB&gclsrc=aw.ds
https://www.grainger.com/product/EX...YRgWJgI5r4n6ghsHozMaAsDYEALw_wcB&gclsrc=aw.ds

The one I have will give me a range of up to 75 m/s, but you can buy a manometer with a wider pressure range and measure up to perhaps a 100 before compressibility starts to be a factor.
 
russ_watters said:
Btw, I'm getting 32 m/s. How did you calculate 9.5 m/s?
How? 12 inch diameter means 6 inch radius and that means 15.24 cm i.e. 0.1524 m. Therefore area is 3.14 X (0.1524)^2. 65% of 60 W is 39 W. Now, it's (39/(0.5 X 1.2474 X 3.14 X (0.1524)^2)^(1/3). Calculate it yourself.
 
T C said:
How? 12 inch diameter means 6 inch radius and that means 15.24 cm i.e. 0.1524 m. Therefore area is 3.14 X (0.1524)^2. 65% of 60 W is 39 W. Now, it's (39/(0.5 X 1.2474 X 3.14 X (0.1524)^2)^(1/3). Calculate it yourself.
Don't be so aggressive, I'm trying to help. Of course I calculated it myself. But yep, you're right, I did a conversion wrong. 9.5 m/s is correct.
 
anorlunda said:
Here's one using a hot wire, claims up to 68 m/s
View attachment 281575

Searches for airspeed sensors in aviation sources should easily find more products with ranges higher than 40 m/s.

I've used hot-wire anemometers to measure air flows upwards of 900 m/s before. Mind you, it was technically a COTS system but not one that is particularly cheap.

russ_watters said:
The alternative to an anemometer I suggested above is a DIY pito-static tube, but for a commercial version of it, you can buy a pito-static tube and digital manometer. I have these:
https://www.grainger.com/product/3T...B7B3hGjN16pzGI4HwXwaAvwuEALw_wcB&gclsrc=aw.ds
https://www.grainger.com/product/EX...YRgWJgI5r4n6ghsHozMaAsDYEALw_wcB&gclsrc=aw.ds

The one I have will give me a range of up to 75 m/s, but you can buy a manometer with a wider pressure range and measure up to perhaps a 100 before compressibility starts to be a factor.

I have used Pitot tubes to measure velocity of upwards of 900 m/s before. It simply requires a different set of equations that account for compressibility. For example, see the Rayleigh Pitot tube formula.
 
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  • #10
Measure the force of the air hitting a flat surface and use an online wind force calculator.
https://www.engineeringtoolbox.com/wind-load-d_1775.html

That one is in metric so if you use a square of cardboard 3 inches on a side the area is 0.0058 Sq. meters. plugging that in, a 40m/s wind would yield a force of 5.57n, or 1.252lbs, or 20oz.

There are probably other websites that use English units and can convert the other direction, but I had to leave SOME of the work to you! :wink:

Cheers,
Tom

p.s. Please let us know the measurement/calculated results you get.
 
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  • #11
Tom.G said:
Measure the force of the air hitting a flat surface and use an online wind force calculator.
https://www.engineeringtoolbox.com/wind-load-d_1775.html

That one is in metric so if you use a square of cardboard 3 inches on a side the area is 0.0058 Sq. meters. plugging that in, a 40m/s wind would yield a force of 5.57n, or 1.252lbs, or 20oz.

There are probably other websites that use English units and can convert the other direction, but I had to leave SOME of the work to you! :wink:

Cheers,
Tom

p.s. Please let us know the measurement/calculated results you get.

That calculator isn't even correct. Who makes these things?
 
  • #12
boneh3ad said:
That calculator isn't even correct. Who makes these things?
:cry:

Ouch! Do you know of one that is accurate?

As for who makes them, a WhoIs lookup shows: "Registrant Name: Registration Private"
 
  • #13
Tom.G said:
:cry:

Ouch! Do you know of one that is accurate?

As for who makes them, a WhoIs lookup shows: "Registrant Name: Registration Private"

I mean, technically it works under a very specific set of circumstances I suppose.
 

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