A Venturi meter is used to measure the rate of flow of liquid (speed, and velocity) in a pipe.
Principle of Venturi:
Venturi meter is based on the principle of Bernoulli’s theorem.
It consists of two tapered sections in the pipeline with a gradual conspiction (throat) at its center.
When fluid is passed through the venturi meter, there are changes in the pressure head (ΔH) and an increase in the velocity due to the conspiction of the venturi meter. (as per Bernoulli). The velocity of the fluid is easily measured by the formula given below:
Uv=v √2g. ΔH
Construction of Venturi meter:
- It consists of two tapered sections and is inserted in a pipeline with constriction at the meter’s center.
- The upstream cone is normally shorter than the downstream.
- The tapers are smooth and gradual
- A manometer is connected at points A and B to measure the pressure difference.
Working of Venturi Meter:
First venturi meter is inserted between the pipeline
When fluid is passed through the venturi meter, the velocity of the fluid is increased at the throat, due to the constriction.
this result in decreased pressure in the upstream core (or change in the pressure head) which is further calculated through a manometer. the calculating formula is:
Uv=Cv √2g. ΔH
Uv= is the velocity of the fluid through venturimeter
Cv= Co-efficient of the venturi meter
ΔH= Pressure Head Difference
Now, find out the velocity of the fluid by putting the value of ΔH (which is measured in a manometer) in this equation.
Advantages:
- Lower probability of being clogged with sediment
- High discharge coefficient.
Its actions are entirely predictable. - Installable in a vertical, horizontal, or inclined position.
- Low-pressure drop (10% of p or less)
- Less susceptible to damage
- Much better suited to gas flows with entrained liquid
- Comprehensive guidelines (ISO 5167)
Disadvantages
- Because of their size, they cannot be employed in places with the limited size of space.
- The initial investment, installation, and maintenance costs are high.
long laying length is necessary. That is, for the venturi meter to function properly, a straight pipe free of fittings and misalignments must come before it in order to prevent flow turbulence. Vanes must be straightened as a result. - Higher manufacturing costs
- Due to the high-velocity fluid passing the pressure tapping at the throat, high Reynolds number gas flows are more susceptible to “tapping errors.”
Related: Hammer Mill
Usage/ Applications of venturi meter
- It is commonly used for liquid (water) and also for gases.
- Wherever high-pressure recovery is necessary, it is used.
- Can be used to measure the flow rates of liquids that are filthy, gaseous, suspended, and water.
- Enables the measurement of high flow rates in pipelines with a few-meter diameter.
References:
- Pharmaceutical engineering books by CVS Subrahmanyam
- Instrumentation tools venturi
