Quote:
Originally Posted by 3-Wheeler
Hi Wink,
Well, reading what it says from Wikipedia versus actually working with pitot tubes and calibrating them for air flow are two different things.
Yes, you are correct about the stagnation pressure, but if you take a close look *inside* the pitot tube you will be presented with a series of small drilled holes that measure the *dynamic* pressure, which is the velocity component of the air flow.
And like I've mentioned already, proper usage and calibration of pitot tubes requires a differential sensor designed to measure both pressure taps.
If I must tell you, we have such devices at work, and yes, I have calibrated them with precision sub-sonic nozzles, so everything is very straight-forward on the theory of the device and actual usage.
By the way, the pitot tube is only good at measuring air velocity, and is not a good *mass flow* device. It does not measure air molecules and their relative mass, only the velocity of the particles.
Pitot tubes are of a family of devices that output a signal velocity-squared to the actual air velocity. For example, if you flow the air at 100 feet per second, you will measure a differential pressure of let's say 10 inches water across the two pressure taps. If you increase the air stream to 200 feet per second, the differential pressure does not double, but instead goes up by the square of the air velocity, or to 40 inches water difference. Because of this, pitot tubes have only a 10:1 usable range for differential pressure transducers measuring a range of 100:1.
Jim.
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Is this statement true or false?
The pressure inside the pitot tube is higher than atmospheric pressure because of the force of airflow pushing on the "bubble".
How about this statement?
The high pressure bubble inside the pitot tube exerts a rearward force on the device.