In a pivot duct, the fluid flow rate is calculated based on the differential pressure and is usually used to measure the gas flow rate. The pitot tube is a small tube that is inserted directly into the fluid stream.
This equipment calculates the sum of static and dynamic pressure. Secondary calculation is required to obtain static pressure. The difference between the two measurements is equal to the amount of dynamic pressure.
The flow rate here, like other equipment, is calculated from the pressure root. To obtain the flow rate of the pressure, the combination depends on factors such as the design of the tube and the static sampling position in this system.
It is worth mentioning that the pitot element is also used to determine the shape of the velocity in the pipe. In this method, the velocity shape can be reconstructed by different measuring points at different distances from the pipe wall.
The pivot duct is a primary element. This equipment does not have a pressure drop in practice, therefore it is superior to perforated equipment.
What is its efficiency for fluids?
Its efficiency is limited to clean gases and liquids used by small holes. Foreign material blocks the holes in the tube. And since the classical pivot duct senses contact pressure at only one point, this factor reduces accuracy.
Because the differential pressure created by the pitot tube is very low, measurement with the secondary element is often difficult. It is worth noting that the accuracy of the equipment in this type of measurement depends on the shape of the fluid velocity. The shape of the fluid velocity is also affected by turbulence in the fluid flow.
Function theory:
The Pivot Duct was invented by Henry Pivot in 1732 to measure the velocity of fluids. Basically, a flowmeter measures differential pressures, such as a pipette duct. Static pressure and total contact pressure. Static pressure is the operating pressure inside the duct pipe or the environment. This pressure is measured at a right angle to the fluid flow path and in a position where the turbulence of the fluid is less.
The sum of the contact pressure is the sum of the static and dynamic pressures, and is revealed when the fluid collides with the flow to the pit pit. A small L-shaped duct with a straight opening in the direction of fluid flow is often used to calculate contact pressure in pitot tubes. The instantaneous velocity V P is calculated from the square root of the sum of the total pressure differences and the differential pressure coefficient in the C / D ratio.
Formula:
V p = C (pt-p) 1/2 ÷ D
C = a dimensional constant
D = density
Given that the flow rate is obtained by the instantaneous velocity coefficient at the cross-sectional area of the pipe or duct, it will be critical that the fluid velocity be measured at a point inside the pipe that corresponds to the average velocity. As the velocity of the fluid increases, the shape of the velocity inside the tube changes from a long, narrow state to a flat, flat state. This change causes a medium velocity point displacement and the need to adjust the equipment inlet depth. Pitot ducts are suitable for highly turbulent fluids or salads that tend to be flat. In this case, the inlet depth of the pitot is not important.
Advantages
- low price
- Irreversible pressure drop
- Ease of installation on running systems
Disadvantages
- Low accuracy
- Low limitability
- Since the pores are simply filled, the fluid should be a clean gaseous liquid or vapor
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