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# How measure the air velocity of the duct through a pitot tube?

The simplest way to determine the velocity is to measure the velocity pressure in the pipe using a pitot tube assembly connected to a differential pressure sensor. The pitot tube device comprises a static pressure probe and a total pressure probe.

The velocity of the pitot tube is the invention of the French physicist pito. A simple pitot tube has a metal tube with a small hole at the end that ACTS as a pressure guide to measure the total pressure of the fluid in the opposite direction from the stream. Another pressure conduit is drawn from the main wall near the front of the metal tube to measure the static pressure.

The differential gauge is connected to two pressure pipes, and the measured pressure is dynamic pressure. According to Bernoulli's theorem, the dynamic pressure is proportional to the square of the velocity. Thus, the pitot tube can be used to measure the velocity of the fluid. After improving the structure, it became a combined pitot tube, that is, pitot static pressure tube. It is a double tube bent at right angles. The outer casing is sealed to the outer casing with several small holes around the outer casing. During the measurement, insert the casing into the middle of the pipe under test. The orifice of the inner shell is towards the direction of the stream stream, while the orifice of the holes around the shell is exactly perpendicular to the direction of the stream stream.

The total pressure probe can sense the velocity pressure and static pressure of the pipeline, and the static pressure is equal to the total pressure. Static pressure probes aligned at right angles to the flow can only sense static pressure. The difference between the total pressure reading and the static pressure reading is the velocity pressure. The fluid can be calculated by measuring the pressure difference between the inner shell and the outer shell.

If the total pressure probe is connected to the HIGH port on the differential pressure sensor and the static pressure probe is connected to the LOW port on the differential pressure sensor, the output of the sensor will be the velocity pressure

Then use the following formula to determine the flow rate:
V Δ P = 4005 x)
V is equal to the velocity in feet per minute.
The square root is equal to the square root of the number on the right.
Δ P = pressure sensors measured the speed of pressure

For example, measure.75 "W.C's velocity pressure. Is equal to the flow rate of 3,468 Ft/Min.

V = 0.75 4005 x)
√0.75= 0.866 times 4005 x 0.866 = 3,468• flow rate = 3,468 Ft/Min