The Pitot Tube
INTRODUCTION
Nowadays, a Pitot tube would be of use as a speedometer on aeroplanes. It is also found useful in industries where velocity measurements are required, where an anemometer may not be the most efficient instrument to use. There are three types of pitot tubes: Pitot tubes, Static tubes, and Pitot-Static tubes.
The simple pitot tube essentially consists of a tube bent at - usually - 90°, with an open end pointing directly towards the fluid flow. As the fluid flows in the tube, it becomes stagnant since there is no direct opening at the other end for it to exit from. As the inert fluid rises, it creates a pressure of its own. This pressure is equivalent to the dynamic pressure, which can be seen as the kinetic energy of the fluid per unit weight.
F.X. Pitot originally used this device to analyze the pressure created by the stagnating fluid at the other end of the tube. He did this by calculating the sum of the dynamic pressure and static pressure. The pressure created by the stagnant fluid (stagnation pressure) is found where the velocity component is zero. Using these principles, it is possible to determine a fluids velocity.
This has manifested itself in the form of the Bernoulli equation. It describes this phenomenon as it states that an inviscid fluid’s increase in velocity is accompanied with a concurrent decrease in pressure or in the fluid 's potential energy. However, this equation works on two assumptions – the first, that the fluid is incompressible; the second, that friction caused by viscous forces are to be considered negligible. The Bernoulli equation can nevertheless be used for compressible flows, but only at low Mach numbers.
In the experiment, we measured the radial velocity profile at a cross-section of a pipe using the Pitot tube. As the Pitot probe is shifted along the pipe, we can record the stagnation pressure and static pressure at that cross-section of the pipe. The velocity of the inviscid fluid can
Nowadays, a Pitot tube would be of use as a speedometer on aeroplanes. It is also found useful in industries where velocity measurements are required, where an anemometer may not be the most efficient instrument to use. There are three types of pitot tubes: Pitot tubes, Static tubes, and Pitot-Static tubes.
The simple pitot tube essentially consists of a tube bent at - usually - 90°, with an open end pointing directly towards the fluid flow. As the fluid flows in the tube, it becomes stagnant since there is no direct opening at the other end for it to exit from. As the inert fluid rises, it creates a pressure of its own. This pressure is equivalent to the dynamic pressure, which can be seen as the kinetic energy of the fluid per unit weight.
F.X. Pitot originally used this device to analyze the pressure created by the stagnating fluid at the other end of the tube. He did this by calculating the sum of the dynamic pressure and static pressure. The pressure created by the stagnant fluid (stagnation pressure) is found where the velocity component is zero. Using these principles, it is possible to determine a fluids velocity.
This has manifested itself in the form of the Bernoulli equation. It describes this phenomenon as it states that an inviscid fluid’s increase in velocity is accompanied with a concurrent decrease in pressure or in the fluid 's potential energy. However, this equation works on two assumptions – the first, that the fluid is incompressible; the second, that friction caused by viscous forces are to be considered negligible. The Bernoulli equation can nevertheless be used for compressible flows, but only at low Mach numbers.
In the experiment, we measured the radial velocity profile at a cross-section of a pipe using the Pitot tube. As the Pitot probe is shifted along the pipe, we can record the stagnation pressure and static pressure at that cross-section of the pipe. The velocity of the inviscid fluid can
References: http://gallica.bnf.fr/ark:/12148/bpt6k408489d.image.f354 accessed on 28/12/10 at 13:31 Munson et al, 2009, Fundamentals of Fluid Mechanics, 6th edition, Wiley: Hoboken