A probe is a device used for point pressure measurement in a flowing fluid. This point measurement of pressure is done to determine fluid flow rate. The most popular probe is the “PITOT TUBE” which is one of the total pressure probes. The Pitot tube measures the combined pressure (static pressure + impact pressure). The pitot tube has one impact opening and eight static openings as shown in the diagram. The impact opening is provided to sense impact pressure and the static opening are provide to sense static pressure.
Operation of Pitot Tube:
The pitot tube is introduced in the fluid flow area where point pressure details is required (which is an indirect measure of flow rate).
The pressure in the outer tube is the static pressure in the line. The total pressure in the inner tube is greater than static pressure. That is, total pressure is the static pressure plus the impact pressure. The differential pressure (P1-P2) is measured using a differential pressure sensor. This differential pressure becomes a measure of flow rate at that point where the pitot tube is present in the flowing fluid.
Applications of pitot tube
Pitot tubes are extensively used in laboratories to measure velocity, pressure and flow rates of fluids.
Advantages of pitot tube:
- It causes no pressure loss in the flowing fluid.
- Pitot tube is cheap and very easy to install.
Limitations of Pitot tube
- It is difficult to obtain proper alignment of the pitot tube with flowing direction.
- It cannot be used in fluids with suspended solids and impurities.
- The fluid velocity should be high in order to get a measurable pressure difference.