Venturimeter Diagram, Parts, Principle,3 Types, Derivation, Apps, Pros & Cons [PDF]

In this article, we shall learn about the parts, working principles, applications, advantages, and disadvantages of the Venturimeter. We have provided a PDF for the same.

What is a Venturimeter

Venturi Meter is a device in which pressure energy is converted into kinetic energy and it is used for measuring the rate of flow of liquid through pipes. It is invented by American Engineer Clemens Herschel and named by the Italian physicist Giovanni Venturi. It works on the basic principle of Bernoulli’s Equation.

Parts of Venturimeter

A Venturimeter consists of the following

• Converging cone or Diameter (the area is decreasing).
• Throat Diameter (the area is constant).
• Diverging cone (the area is increasing).

let’s consider a pipe in which there is a venturi meter is fixed. In the pipe, different types of fluid flow so first it enters into a converging cone then the Throat, and then Diverging Cone.

Converging Cone

When water flows through this cone the area is decreasing, therefore, the speed of flowing water increases and pressure decreases.

Throat Diameter

When water flows through this cone the area remains constant therefore the speed of flowing water and pressure remain constant.

Diverging Cone

When water flows through this cone the area is increasing, therefore, the speed of flowing water decreases and pressure decreases.

Types of venturimeter

There are three different types of venturimeter which are as follows

• Horizontal Venturimeter
• Vertical Venturimeter
• Inclined Venturimeter

Horizontal Venturimeter

• This type of venturimeter is designed with a horizontal orientation and has the highest kinetic energy among the three types. Kinetic energy refers to the energy of motion that the fluid possesses, and it is the lowest potential energy. The venturimeter is mainly used for measuring the flow rate of liquids.

Vertical Venturimeter

• The vertical Venturimeter is designed with a vertical orientation and has the maximum potential energy among the three types. Potential energy refers to the energy that the fluid possesses due to its position or elevation, and it has the minimum kinetic energy. The Venturimeter is mainly used for measuring the flow rate of liquids.

Inclined Venturimeter

• The inclined venturimeter is designed with an inclined orientation, and both potential and kinetic energy is in between the above two types mentioned. The venturimeter is mainly used for measuring the flow rate of liquids.

Working Principle of Venturimeter

As mentioned previously that Venturimeter works on Bernoulli’s Principle, so let’s find out how it depends on Bernoulli’s Principle.

Suppose the quantity of liquid v1 enters the pipe, as per the continuity equation volume flow rate at the inlet (Q₁), is equal to the discharge at the outlet (Q₂), so if v₁ amount of water enters the inlet of the venturi meter the same amount of water should be discharged at the outlet, that means at unit second v₁/t₁= v₂/t₂. As the area of section 1 (according to the above diagram) is more than the area of section 2, that means due to the decreased area the pressure at the throttling section is decreased and velocity will be increased to maintain the flow (Q₁=Q₂).

In the throat position, the velocity of flow is maximum and pressure is minimum. After throttling there again is a diverging cone (diffuser) which restores the pressure as nearly possible to the actual value. By this, we can easily determine the volume flow rate with the help of the U-Tube Manometer which is shown in the above diagram, by finding the pressure difference between section 1 (converging section) and section 2 which is throat.

Difference between Venturimeter and Orifice meter

Venturimeter Formula/Derivation of Discharge

The following notations are used in this derivation

• A₁= Inlet area in m².
• D₁= Diameter of Inlet.
• D₂= Diameter of the throat.
• A₂= Throat area in m².
• P₁= Pressure at the inlet in N/m².
• P₂= Pressure at the throat in N/m².
• v₁= Velocity at inlet in m/sec
• v₂= Velocity at throat in m/sec.
• h= Pressure heads.
• C_d= Coefficient of Discharge. This is unitless.
• Q_act= Actual discharge in m³/sec.
• Q_the= Theoretical discharge in m₃/sec.

• Applying Bernoulli’s equations at sections 1 and 2, we get:

• As pipe is horizontal Z₁= Z₂,

• Where [h= (p₁-p₂)/ρg], difference of pressure heads at sections 1 and 2.

• From the continuity equation at sections 1 and 2, we get,

• This expression is the Theoretical Discharge of the Venturi Meter. In general actual discharge is always less than Theoretical Discharge. So if we multiply C_d (Coefficient of discharge by the above equation, then we get an actual discharge, and here is the expression of actual discharge,

The other way to find h (Pressure heads) by using differential U–Tube Manometer

The liquid in the manometer is heavier than the flowing fluid in the pipe.

• S_h= Specific gravity of the heavier liquid.
• x = Difference of the heavier liquid column in U-tube
• S₀= The Specific gravity of flowing fluid.
• S_l= Specific gravity of the lighter liquid.

• h = x [ (S_h / S₀) – 1]

The liquid in the manometer is lighter than the flowing fluid in the pipe.

• h = x [1- (S_l / S₀)]

Applications of Venturimeter

• Calculating the flow rate of fluid that is discharged through the pipe.
• In the industrial sector, it is used to determine the pressure as well as the quantity of gas and liquid inside a pipe.
• The flow of chemicals in pipelines.
• This is widely used in the waste treatment process where large-diameter pipes are used.
• Also used in the medical sector the measure the flow rate of blood in arteries.
• This is also used where high-pressure recovery is required.

Advantages of Venturimeter

• Power loss is very less.
• This can be used where a small head is available.
• High reproducibility (the extent to which consistent results are obtained when an experiment is repeated).
• Accuracy is high over wide flow ranges.
• This can also be used for compressible and incompressible fluid.
• This device is easy to operate.
• The coefficient of discharge (C_d) for the venturi meter is high.
• This is widely used for a high flow rate (Discharge).

Disadvantages of Venturimeter

• The installation cost of a venturi meter is high.
• There are difficulties while maintaining.
• This device can not be used where the pipe has a small diameter of 76.2 mm.
• Non-linear.
• This system occupies more space as compared to the orifice meter.
• It has a limitation of the lower Reynolds number of 150,000.
• It is expensive and a little bulky.

Codes and Standards of Venturimeter

The Codes and Standards of venturi meter as are as follows

• ISO 5167: This series of standards specifies the general requirements and methods for flow measurement in closed conduits, including the use of venturi meters.
• ISO 9300: This code provides guidelines for the proper installation and operation of venturi meters used for measuring fluid flow in closed conduits.
• AWWA M33: This manual outlines the design, installation, and operation guidelines for venturi meters used in water supply systems.
• ISO TR 15377: This code provides guidelines for the selection, installation, and operation of venturi meters used for measuring gas flow in closed conduits.
• BS 1042: This code specifies the requirements and test methods for the calibration of venturi meters used in fluid flow measurement.
• ASME MFC-8M: This code provides guidelines for the design, installation, and operation of venturi meters used in the measurement of fluid flow in closed conduits.
• ASTM D2458: This code provides guidelines for the selection, installation, and operation of venturi meters used in the measurement of gas flow in closed conduits.
• AGA 9: This code provides guidelines for the measurement of gas flow using differential pressure devices, including venturi meters.

FAQ

What is venturimeter flow rate

Venturimeter flow rate refers to the volume or mass of fluid that passes through a Venturimeter per unit time. It is measured in standard units such as liters per minute (LPM) or cubic meters per hour (m³/h) for volumetric flow rate, and kilograms per second (kg/s) or pounds per hour (lb/h) for mass flow rate. The flow rate through a venturimeter is determined by measuring the pressure difference between the inlet and throat sections of the venturimeter, which is then used to calculate the flow rate using specific equations or charts.

What is venturi flow meter upstream and downstream length

The upstream and downstream lengths required for a venturi flow meter depend on the flow conditions and the size of the venturi meter. In general, the straight pipe lengths required are determined by industry standards and guidelines, such as those established by ISO, ASME, and API.

For most venturi flow meters, a straight pipe length of at least 10 diameters upstream of the meter and 5 diameters downstream of the meter is recommended to ensure an accurate flow measurement. However, the actual length required may vary depending on factors such as the flow rate, fluid viscosity, Reynolds number, and pipe roughness.

It is important to follow the recommended upstream and downstream lengths to ensure that the fluid flow is fully developed and free from turbulence, which can affect the accuracy of the flow measurement.

Whats is the price of venturimeter

The price of a venturi meter can vary widely depending on the type, size, material, and manufacturer. Simple, small-sized venturi meters for low flow rates can cost as low as a few hundred dollars, while large, complex venturi meters designed for high flow rates and demanding applications can cost tens of thousands of dollars.

Other factors that may affect the price of a venturi meter include the type of end connections (flanged or threaded), the level of customization required, and additional features such as flow conditioning elements, temperature and pressure sensors, and digital displays.

It is important to note that the cost of a venturi meter is not the only factor to consider when selecting a flow meter. Factors such as accuracy, reliability, and maintenance requirements should also be taken into account to ensure that the chosen flow meter meets the specific requirements of the application.

Conclusion

In conclusion, a Venturimeter is a tool used to measure the flow of fluid in a pipe. It works by using a principle called Bernoulli’s equation and is known for being accurate and reliable. However, it can be expensive and cause pressure drops. Knowing the parts, how it works, and its pros and cons can help choose the right flow meter for different fluid flow measurements.

References

• Venturi effect