Short Answer:
A Venturi meter measures the flow rate of a fluid by using the change in pressure that occurs when the fluid flows through a narrowed section of pipe. It has three parts: a wide inlet, a narrow throat, and a gradually expanding outlet. As fluid enters the narrow throat, its speed increases and pressure decreases.
This pressure drop between the wide section and the throat is measured using pressure sensors. The flow rate is calculated using Bernoulli’s principle, which relates the pressure difference to the fluid velocity. It is a simple, accurate, and commonly used method in pipelines and water systems.
Detailed Explanation:
Venturi meter flow measurement
A Venturi meter is a specially designed device used to measure the flow rate of fluids (liquids or gases) in a closed pipe. It operates on the principle of Bernoulli’s equation, which states that when the velocity of a fluid increases, its pressure decreases. This pressure change can be used to determine how fast the fluid is flowing.
The Venturi meter has three main sections:
Converging section (Inlet): The fluid enters this wide section and starts to speed up as it moves toward the narrow part.
Throat (Narrow section): This is the smallest cross-sectional area of the pipe. Here, the fluid reaches its highest speed and lowest pressure.
Diverging section (Outlet): After the throat, the pipe widens again, and the fluid slows down, and pressure starts to recover.
As fluid flows through the Venturi meter, it experiences a change in pressure between the inlet and the throat. According to Bernoulli’s principle, this pressure drop occurs because the fluid speeds up in the throat. The more fluid that flows, the greater the pressure difference. This pressure difference is measured using two pressure taps—one placed at the inlet and the other at the throat.
Using the known values of the pressure difference and the pipe’s cross-sectional areas, the flow rate can be calculated using a formula derived from Bernoulli’s and continuity equations:
Q = A × √(2 × ΔP / ρ)
Where:
Q = Flow rate
A = Area of throat
ΔP = Pressure difference between inlet and throat
ρ = Density of the fluid
Key Working Steps of a Venturi Meter:
The fluid enters the wider section of the meter with normal speed and pressure.
As it moves into the throat, the fluid accelerates, and its pressure decreases.
The pressure sensors measure the difference between the wide section and the throat.
This pressure drop is used to calculate the fluid’s velocity.
Once the velocity is known, the flow rate is found by multiplying it with the cross-sectional area.
Why Venturi Meters Are Used:
They provide accurate and reliable flow measurements.
They have low energy loss due to smooth transitions between sections.
They can handle large volumes of flow and are used in water pipelines, irrigation systems, fuel lines, and chemical plants.
Limitations:
Not suitable for very dirty or particle-filled fluids because blockage may occur.
Installation needs more space due to the long pipe shape.
Higher cost compared to simple orifice meters.
Despite these limitations, the Venturi meter remains popular due to its accuracy and durability in various industries.
Conclusion:
A Venturi meter measures flow by creating a pressure difference between the wide inlet and the narrow throat of a pipe. The faster the fluid flows, the greater the pressure drop. By applying Bernoulli’s principle, the flow rate can be accurately calculated. It is widely used in pipelines, water treatment, and chemical systems for its accuracy and simplicity. Understanding how a Venturi meter works helps in selecting the right flow measurement tool for efficient fluid control.