What is venturi tube and how does it work

A venturi tube contains a throat that is smaller in diameter than the pipeline it is placed in. The limited diameter should not be less than 0.224 and not more than 0.742 of the diameter of the pipe.

When the fluid passes through the venturi tube, the pressure at the throat is less than the pressure upstream (due to the increase in kinetic energy due to the increase in velocity, ½ mv2) and thus the decrease in flow energy (Ef = P •. v).

The flow rate or discharge is proportional to the pressure difference, P1 – P2.

where k depends on the pipeline and throat diameter, density and discharge coefficient

A venturi flow meter should always be used for turbulent flow. Its accuracy for a wide range of instruments is about 0.5%, ideal for use in heating, ventilation and air conditioning. Applications (HVAC) or air to furnaces and boilers and liquids containing particles and slurry.

What is venturi effect?

The venturi effect is the reduction in fluid pressure that occurs when a fluid passes through a constricted (or choked) section of pipe. The Venturi effect is named after Giovanni Battista Venturi (1822-1746), an Italian physicist.

In fluid dynamics, the velocity of a fluid must increase as it passes through a contraction according to the principle of conservation of mass, while its static pressure must decrease according to the principle of conservation of mechanical energy. Therefore, any increase in the fluid’s kinetic energy due to its increased velocity through contraction is balanced by a decrease in pressure.

By measuring the pressure change, the amount of flow can be determined in different flow measuring devices such as venturi meter, venturi nozzle and orifice plate.

Main features of venturi tube meter

• Pressure recovery is much better for venturi tubes compared to orifice plates.
• Venturi tubes are suitable for clean, dirty and viscous liquid as well as slurry service.
• The ability of the venturi tube range is variable from 4 to 1.
• In venturi tubes, the pressure drop is low and the effect of viscosity is high.
• Usually, the accuracy of a venturi tube is 1% of its full range.
• The necessary upstream tube length of a venturi tube is 5 to 20 times the diameter.
• Venturi tubes are available in sizes up to 72 inches.
• A venturi tube can pass 25-50% more flow than the orifice plate while maintaining the same pressure drop.
• Since the initial cost of a venturi tube is very high, it is mainly used in larger flows and in more complex or challenging flow.
• Unlike orifice plates, venturi tubes are almost insensitive to the effects of the velocity profile and thus require less direct tube run from the orifice.
• Due to their contoured nature, venturi tubes are resistant to corrosion, erosion and internal scale formation, which is combined with the self-washing action of the flow through the tube.
• The use of venturi tubes saves a lot of installation and maintenance costs.
• Venturi tube flowmeters are often used in applications involving higher drawdown rates or lower pressure drops, particularly in areas where orifice plates are not employed.
• Using accurate instrumentation and flow calibration, the flow rate of a venturi can be accurately reduced to about 10% of its full range, which in turn results in a 10:1 reduction rate.

Advantages of venturi meter

• They can handle large flow volumes at low pressure drops.
• Venturi tube flowmeters do not contain any moving parts.
• They can be installed in large diameter pipes through flanged, welded or threaded connections.
• They can be used with almost all liquids as well as liquids containing strong solids.
• Venturi tubes do not contain any protrusions into the fluid or sharp corners. There are also no quick changes in contour.

Disadvantages of venturi meter

• it is very expensive.
• It takes up a lot of space.
• Cannot be changed to measure pressure over maximum speed.

Venturi tube design and construction:

Venturi tubes are designed, manufactured and delivered based on the needs of the project.