pitot tube

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pitot tube

[pē′tō ‚tüb]
(engineering)
An instrument that measures the stagnation pressure of a flowing fluid, consisting of an open tube pointing into the fluid and connected to a pressure-indicating device. Also known as impact tube.

Pitot Tube

 

an L-shaped tube for measuring the total head of a flowing fluid. The tube is named after the French scientist H. Pitot, who invented it in 1732. The Pitot tube is used as a component of the Pitot-static (Pitot-Prandtl) tube.

Pitot tube

A device to measure the stagnation pressure due to isentropic deceleration of a flowing fluid. In its original form it was a glass tube bent at 90° and inserted in a stream flow, with its opening pointed upstream. Water rises in the tube a distance, h, above the surface, and if friction losses are negligible, the velocity of the stream, V, is approximately 2gh, where g is the acceleration of gravity. However, there is a significant measurement error if the probe is misaligned at an angle α with respect to the stream. For an open tube, the error is about 5% at α ≈ 10°.

The misalignment error of a pitot tube is greatly reduced if the probe is shielded, as in the Kiel-type probe. The Kiel probe is accurate up to α ≈ 45°.

The modern application is a pitot-static probe, which measures both the stagnation pressure, with a hole in the front, and the static pressure in the moving stream, with holes on the sides. A pressure transducer or manometer records the difference between these two pressures. Pitot-static tubes are generally unshielded and must be carefully aligned with the flow to carry out accurate measurements.

When used with gases, estimate of the stream velocity is only valid for a low-speed or nearly incompressible flow, where the stream velocity is less than about 30% of the speed of sound of the fluid. At higher velocities, estimate of the stream velocity must be replaced with a Bernoulli-type theory, which accounts for gas density and temperature changes. If the gas stream flow is supersonic, or the stream velocity is greater than the speed of sound of the gas, a shock wave forms in front of the probe and the theory must be further corrected by complicated supersonic-flow algebraic relations.

A disadvantage of pitot and pitot-static tubes is that they have substantial dynamic resistance to changing conditions and thus cannot accurately measure unsteady, accelerating, or fluctuating flows. See Flow measurement

pitot tube

A device, used in conjunction with a suitable manometer or other pressure-reading instrument, for measuring the velocity of air in a duct or water in a pipe.

pitot tube

An open-end tube that points directly into the air flowing over the aircraft structure, providing pressure for the pitot and, often, the static systems. See pitot pressure.
References in periodicals archive ?
When an internal support frame was present the absolute roughness of the ducts based on Pitot tube test data was 1.69 mm (0.0056 ft).
The averaging pitot tubes are described as being available in a wide variety of wetted materials to suit most liquid, gas and steam applications, whether flowing in circular or rectangular pipes or ductwork.
Airlines around the world have begun replacing Pitot tubes on their aircraft.
One theory about the cause of the crash is that the pitot tubes may have iced over, giving incorrect information which then led to the plane flying too fast or slow in rough weather.
The company inspection showed that the so-called pitot tubes installed in the nose section of the plane were clogged with bugs and apparently indicated incorrect speeds at the time of incident, leading the pilots to fail to carry out appropriate operations.
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Hot wire anemometry, pitot tubes, and smoke visualization techniques were used to characterize the flow field.
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Users can select from options including security level, set point or set point and alarm operation, auto or manual alarm reset, English or Metric engineering units, K-factor adjustment for use with various Pitot tubes and flow sensors, and circular or rectangular duct size for volumetric flow operation.
The lines are very similar, but the easiest identifying features are the three pitot tubes on the front end, which are unique to the D-21.
The stabilator received mixed inputs from the pitot tubes, so it remained programmed 20 to 25 degrees down, causing an excessive nose-down attitude.
Tenders are invited for 5-hole pitot tubes with pressure transducers and data acquisition system