Introduction to venturimeter

Fluid flow measurement is crucial in various industries and applications. The Venturi meter stands out as a reliable and versatile device for precise flow rate measurements. In this detailed guide, we will explore the Venturi meter, its parts, materials, working principle, equations, coefficient of discharge, types, applications, advantages, disadvantages, codes, and standards. Additionally, we will compare the Venturi meter to the orifice meter to understand their differences and best use cases.

what is venturimeter

A venturimeter, also known as a Venturi meter, is a widely used flow measurement device that operates on the principle of the Venturi effect. It is named after its inventor, Giovanni Battista Venturi, an Italian physicist who first described the concept in the 18th century. The venturimeter is a simple yet ingenious device designed to measure the flow rate of a fluid passing through a pipe.

The basic construction of a venturimeter consists of four main parts: a cylindrical inlet section, a conical convergent section, a cylindrical throat, and a conical divergent outlet. The fluid enters the venturimeter through the cylindrical inlet section and then flows through the conical convergent section, where the pipe diameter gradually decreases. As the fluid passes through this section, its velocity increases, resulting in a decrease in pressure according to Bernoulli’s principle.

At the throat, which is the narrowest part of the venturimeter, the fluid reaches its maximum velocity and experiences the lowest pressure. After passing through the throat, the fluid enters the conical divergent section, where the pipe diameter gradually increases. In this section, the fluid’s velocity decreases, causing the pressure to rise again, allowing for pressure recovery.

The pressure difference between the upstream and throat sections of the venturimeter is proportional to the square of the flow rate, and this pressure difference can be measured using pressure taps connected to a manometer. By applying the principles of fluid dynamics and utilizing the pressure difference, the volumetric flow rate of the fluid passing through the venturimeter can be calculated.

Venturimeters are widely used in various industries, including water treatment, oil and gas, chemical processing, HVAC systems, and more. They offer several advantages, such as high accuracy, low pressure loss, and versatility in measuring a wide range of flow rates. However, their installation may require sufficient straight pipe lengths upstream and downstream to achieve accurate readings.

venturimeter is used to measure

Venturimeters are widely used in various industries, including water supply systems, oil and gas, chemical processing, and HVAC systems. They offer several advantages, such as high accuracy, minimal pressure loss, and versatility in measuring a wide range of flow rates. Due to their reliability and simplicity, venturimeters remain a popular choice for fluid flow measurement in many applications.

venturimeter diagram

A typical Venturi meter consists of four main parts:

1. Cylindrical Inlet Section: This straight cylindrical section serves as the starting point of the Venturi meter. Its length is usually 5 to 8 times the pipe diameter (D), ensuring a smooth entry of fluid into the meter.
2. Conical Convergent Section: The pipe diameter gradually decreases in this section, forming a conical shape. The conical angle typically measures 210 ± 20 degrees. As the fluid flows through the conical section, its velocity increases while the pressure decreases, adhering to the Venturi effect.
3. Cylindrical Throat: Located at the minimum diameter point, the throat represents the narrowest part of the Venturi meter. Here, the fluid reaches its maximum velocity and experiences the lowest pressure.
4. Conical Divergent Section: After passing through the throat, the pipe diameter gradually increases in this section. As a result, the fluid’s velocity decreases, leading to an increase in pressure, allowing for pressure recovery.

Pressure Tapping Points: The Venturi meter has two pressure tapping points. The upstream pressure tapping is located at a distance of one-half of the pipe diameter (D/2) upstream of the convergent entry. The downstream pressure tapping is located in the throat (d/2).

Venturi Meter Materials

Venturimeters are manufactured using various materials, depending on the fluid being measured and the operating conditions. Common materials include brass, glass, bronze, cast iron, steel, and stainless steel. For aggressive fluids or high-temperature applications, specialized materials such as Hastelloy or titanium may be used to ensure accuracy and longevity.

Selecting the appropriate materials for a Venturi meter

Selecting the appropriate materials for a Venturi meter involves several crucial steps to ensure accurate and reliable flow measurement. Here’s a step-by-step guide:

1. Identify the Fluid Properties:
   Start by understanding the properties of the fluid that will flow through the Venturi meter. Consider factors such as the type of fluid (liquid or gas), temperature, pressure, corrosiveness, and potential presence of solids or abrasive particles.
2. Determine the Operating Conditions:
   Next, analyze the operating conditions of the Venturi meter. Take into account the flow rate range, maximum and minimum operating pressures, temperature variations, and the overall environmental conditions.
3. Material Compatibility:
   Based on the fluid properties and operating conditions, consider the compatibility of different materials with the fluid. Choose materials that are resistant to chemical corrosion, erosion, and damage caused by the fluid’s properties.
4. Common Material Options:
   The most common materials used for Venturi meters are stainless steel, carbon steel, brass, bronze, and various corrosion-resistant alloys. Stainless steel is often preferred for its excellent corrosion resistance and durability.
5. Fluid Velocity Considerations:
   Take into account the fluid’s velocity, as high-velocity flows can result in erosion or cavitation. Select materials that can withstand the impact of high-velocity flows without significant wear or damage.
6. Budget Constraints:
   Consider budget constraints while selecting materials. While stainless steel and corrosion-resistant alloys offer superior performance, they may be more expensive than carbon steel or other materials.
7. Consult Manufacturer Guidelines:
   Consult the Venturi meter manufacturer’s guidelines and recommendations for material selection. They may provide specific material options based on the intended application and operating conditions.
8. Environmental Regulations:
   Ensure that the chosen materials comply with any environmental regulations or industry standards relevant to the application.
9. Testing and Validation:
   Before finalizing the material selection, consider conducting material testing and validation to ensure its suitability for the specific application. This may include tests for chemical compatibility, pressure resistance, and erosion resistance.
10. Consider Long-Term Maintenance:
    Finally, think about the long-term maintenance and lifecycle costs associated with the selected materials. Opting for materials with low maintenance requirements and long-lasting performance can lead to cost savings over time.

Working Principle of Venturi Meter

The Venturi meter operates based on the Venturi effect, which states that when fluid flows through a constricted passage, its velocity increases, and its pressure decreases. As the fluid enters the Venturi meter through the cylindrical inlet section, it accelerates in the conical convergent section, creating a low-pressure zone at the throat. After passing through the throat, the fluid decelerates in the conical divergent section, leading to an increase in pressure, this principle of venturimeter.

venturimeter principle

Venturi Meter Equations

The equations used in Venturi meters are derived from the principles of fluid mechanics and the application of Bernoulli’s equation and the principle of continuity. These equations are essential for calculating the flow rate of fluid passing through the Venturi meter. Let’s go through the equations in detail:

venturimeter formula

Bernoulli’s Equation

Bernoulli’s equation is a fundamental principle in fluid dynamics that describes the relationship between pressure, velocity, and elevation in a flowing fluid. The equation is given as follows:

P + 1/2 * ρ * v^2 + ρ * g * h = constant

Where:
P = Pressure of the fluid
ρ = Density of the fluid
v = Velocity of the fluid
g = Acceleration due to gravity
h = Elevation or height above a reference point

Continuity Equation

The principle of continuity states that the mass flow rate of an incompressible fluid remains constant throughout a system. The continuity equation for fluid flow in a pipe is expressed as:

A1 * v1 = A2 * v2

Where:
A1 = Cross-sectional area of the pipe at the inlet
A2 = Cross-sectional area of the pipe at the throat
v1 = Velocity of the fluid at the inlet
v2 = Velocity of the fluid at the throat

Venturi Meter Equation

The Venturi meter equation is derived by applying Bernoulli’s equation and the continuity equation to the Venturi meter’s design. For an incompressible fluid flowing through a Venturi meter, the equation is as follows:

Q = Cd * A2 * √(2 * ΔP / ρ)

Where:
Q = Flow rate of the fluid
Cd = Coefficient of discharge (dimensionless parameter accounting for losses and imperfections)
A2 = Cross-sectional area of the throat
ΔP = Pressure difference between the inlet and throat of the Venturi meter
ρ = Density of the fluid

In this equation, Cd is a key parameter that accounts for frictional losses and inefficiencies in the Venturi meter design. It is experimentally determined and typically ranges from 0.95 to 0.99 for well-designed Venturi meters.

By measuring the pressure difference (ΔP) between the upstream and throat sections of the Venturi meter and knowing the fluid properties (ρ), the cross-sectional area of the throat (A2), and the coefficient of discharge (Cd), the Venturi meter equation allows for the accurate calculation of the flow rate (Q) of the fluid passing through the Venturi meter.

Coefficient of Discharge (Cd) of Venturi Meter

The Coefficient of Discharge (Cd) of a Venturi meter is a dimensionless parameter that represents the ratio of the actual flow rate to the theoretical flow rate predicted by the Venturi meter equation. It accounts for losses and inefficiencies in the Venturi meter design, ensuring accurate flow rate measurements. Let’s explore the coefficient of discharge (Cd) of a Venturi meter in detail:

Read Rotameter vs Flow Meter

1. Importance of Cd: The Venturi meter equation, Q = Cd * A2 * √(2 * ΔP / ρ), provides the theoretical flow rate (Q) based on the pressure difference (ΔP) between the inlet and throat of the Venturi meter, the cross-sectional area of the throat (A2), and the fluid density (ρ). However, in real-world applications, there are frictional losses, imperfections, and other factors that affect the actual flow rate. The coefficient of discharge (Cd) corrects for these deviations, allowing for more accurate flow rate measurements.
2. Experimental Determination of Cd: The coefficient of discharge (Cd) is experimentally determined for each specific Venturi meter design. Manufacturers conduct calibration tests using a standard fluid flow to establish the Cd value for a particular Venturi meter model. The calibration tests involve comparing the actual flow rate measured by the Venturi meter with a reference flow rate obtained from a flow standard. This process allows engineers to calculate the Cd value based on the known flow rates.
3. Typical Range of Cd: The typical range of the coefficient of discharge (Cd) for well-designed Venturi meters is between 0.95 and 0.99. A Cd value of 1.0 would imply a perfectly efficient Venturi meter with no losses. However, due to friction, turbulence, and other factors, Cd values are always less than 1.0. The actual value of Cd can vary depending on the specific Venturi meter geometry, Reynolds number, and installation conditions.
4. Factors Affecting Cd: Several factors can influence the value of Cd in a Venturi meter. These include the surface roughness of the Venturi meter, the shape and design of the convergent and divergent sections, the Reynolds number of the fluid flow, and the presence of any obstructions or disturbances in the flow path. As such, the accuracy and consistency of Cd values depend on the quality of the Venturi meter construction and calibration.

Types of Venturi Meters

Venturi meters come in various types, each designed for specific applications:

1. Horizontal Venturi Meter
2. Vertical Venturi Meter
3. Inclined Venturi Meter

Horizontal Venturi Meter

A horizontal Venturimeter is a type of flow measurement device used to measure the flow rate of fluids in a horizontal pipe. It consists of a gradually tapering constriction in the pipe, known as the Venturi tube. As the fluid flows through the Venturi tube, its velocity increases while the pressure decreases. The pressure difference between the inlet and throat sections of the Venturi meter is used to calculate the flow rate using the Venturi meter equation. Horizontal Venturi meters are widely used in various industries for accurate and reliable flow measurements in horizontal pipe installations, offering advantages such as high accuracy, low pressure loss, and ease of installation.

Vertical Venturi Meter

A vertical Venturi meter is a flow measurement device used to measure the flow rate of fluids in a vertical pipe. It operates based on the principle of the Venturi effect, where the fluid’s velocity increases and pressure decreases as it passes through a constricted section in the pipe. The pressure difference between the inlet and throat sections is used to calculate the flow rate using the Venturi meter equation. Vertical Venturi meters are suitable for applications where the pipe orientation is vertical, offering accurate and reliable flow measurements in such installations.

Inclined Venturi Meter

An inclined Venturimeter is a flow measurement device used to measure the flow rate of fluids in a pipe with an inclined orientation. It operates on the same principles as a standard Venturi meter, utilizing the Venturi effect to measure the flow rate. The inclined Venturi meter is designed to accommodate situations where the pipe is not horizontal or vertical. By accurately measuring the pressure difference between the inlet and throat sections, it provides reliable flow rate measurements in inclined pipe installations. This type of Venturi meter offers versatility and efficiency in various industrial applications.

Applications of Venturi Meters

Venturi meters find widespread application in fluid industries, including:

1. Engine Carburetors (Automobile Sector) to measure airflow.
2. Process and Power Piping Industries to measure and control process flow.
3. Medical industry for measuring blood flow in arteries.
4. Oil & Gas Industries for measuring fluid flow inside pipelines.
5. Water treatment plants, chemical processing, HVAC systems, power generation systems, etc.

Advantages and Disadvantages of Venturi Meters

Advantages:

1. Accurate results with minimal pressure drop.
2. Versatile, suitable for a wide range of fluids.
3. High discharge coefficient and pressure recovery.
4. No moving parts, leading to low maintenance requirements.
5. Suitable for horizontal, inclined, and vertical installations.
6. Resistant to clogging.

Disadvantages:

1. Relatively larger in size, challenging to install in limited space.
2. Higher cost compared to some other flow meters.
3. Limited range of flow measurement.
4. Not suitable for very small diameter pipes.

Advantages and disadvantages of Venturi meters:

Above is nothing but difference between orifice meter and venturimeter

Advantages of Venturi Meter	Disadvantages of Venturi Meter
High Accuracy	Large Size
Low Pressure Loss	Requires Sufficient Straight Pipe Length
Versatility in Flow Measurement	Relatively Expensive
Minimal Energy Loss	Not Suitable for Very Small Diameter Pipes
No Moving Parts	Limited Flow Range
Wide Range of Applications
High Pressure Recovery
Low Chance of Clogging
Suitable for Various Fluids
Can be Installed in Various Orientations

Codes and Standards of Venturi Meters

Several codes and standards provide guidelines related to Venturi meters, ensuring accuracy and consistency in design, installation, and use:

1. ISO 5167
2. ISO 9300
3. AWWA M33
4. ISO TR 15377
5. BS 1042
6. ASME MFC-8M
7. ASTM D2458

Selecting a specific code or standard for Venturimeters

1. ISO 5167: This international standard provides guidance on the measurement of fluid flow by various differential pressure devices, including Venturi meters. It covers the principles of operation, installation requirements, calibration, and uncertainty considerations for flow measurements.
2. ASME MFC-3M: The American Society of Mechanical Engineers (ASME) Measurement of Fluid Flow in Pipes Using Orifice, Nozzle, and Venturi is a code that outlines the procedures for the design, installation, and calibration of Venturi meters in fluid flow applications, venturimeter diagram.
3. AWWA MCD Manual: The American Water Works Association (AWWA) Manual of Water Supply Practices – Measurement of Flow in Closed Conduits – Parshall, Palmer-Bowlus, and Venturi Flumes is a comprehensive guide that includes specifications and procedures for installing and using Venturi meters in water supply systems.
4. AGA Report No. 3: The American Gas Association (AGA) Report No. 3 – Orifice Metering of Natural Gas and Other Related Hydrocarbon Fluids is a widely referenced document that provides guidelines for the use of Venturi meters and other orifice meters in natural gas flow measurement applications.
5. ISO TR 15377: This technical report provides additional guidance on the use of Venturi tubes for fluid flow measurement. It covers topics such as uncertainty considerations and recommendations for the use of Venturi meters in specific applications.
6. BS 1042: British Standard BS 1042 – Specification for Venturi tubes is a standard that provides detailed specifications for the design and construction of Venturi meters.

When selecting a specific code or standard for Venturi meters, it is essential to consider the intended application and the regulations or industry practices that apply in that particular region or industry. Compliance with the relevant code ensures that the Venturi meter is correctly designed, installed, and calibrated, leading to accurate and reliable flow measurements.

Installation of a Venturi Meter

Proper installation of a Venturi meter is critical for optimal operation. Following manufacturer guidelines, the installation process involves:

1. Aligning the flow direction arrow with the fluid flow direction.
2. Proper alignment of flanges with the piping flanges.
3. Avoiding placing pipe support on the Venturi meter.
4. Ensuring proper torque for bolts.
5. Maintaining installation tolerances within industry standards.
6. Orienting pressure taps horizontally for liquid service applications.

Venturi Meter Upstream and Downstream Pipe Straight Leg Requirement (venturimeter diagram).

For accurate measurements, the flow through Venturi meters should stabilize, necessitating minimum straight pipe lengths upstream and downstream of the meter. The requirements vary based on the type of fitting, Venturi meter type, and beta ratio (throat diameter divided by inlet diameter). Adhering to proper straight leg requirements ensures precise flow rate readings.

difference between orifice meter and venturimeter

Here’s a table summarizing the key differences between Venturi meters and orifice meters:

Aspect	Venturi Meter	Orifice Meter
Design	Gradual taper in the throat section	Flat plate with a precisely machined hole (orifice plate)
Pressure Recovery	Better pressure recovery	Lesser pressure recovery
Accuracy	Generally higher accuracy, especially at low flow rates	Relatively lower accuracy, especially at low flow rates
Applications	Suitable for high and low flow rates, critical flow rate measurements	Suitable for a wide range of flow rates
Pressure Drop	Lower pressure drop	Higher pressure drop
Cost	Relatively higher cost	Cost-effective solution
Installation Requirements	Requires longer straight pipe sections both upstream and downstream	Requires less straight pipe sections for installation
Size and Space	Larger size, may be challenging to install in limited space	Smaller size, more space-efficient installation
Flow Range	Suitable for a wide flow rate range	Limited flow rate range
Coefficient of Discharge (Cd)	Typically higher Cd values (0.95 to 0.99)	Typically lower Cd values (0.6 to 0.8)
Flow Profile	Well-defined flow profile	Turbulent flow profile
Material Selection	Variety of materials, including stainless steel, carbon steel, etc.	Materials like stainless steel, carbon steel, or other corrosion-resistant alloys
Energy Loss	Lower energy loss	Higher energy loss
Maintenance	Low maintenance requirements	Low maintenance requirements

Note: The differences mentioned in the table are general characteristics and may vary based on specific Venturimeter and orifice meter designs, applications, and installations. Both meters have their unique advantages and limitations, and the choice between them depends on the specific flow measurement requirements and conditions of the application.

Conclusion

The Venturimeter, with its innovative design and precision, remains a critical instrument for accurate and reliable fluid flow measurement across various industries. Understanding its parts, working principle, equations, coefficient of discharge, types, applications, advantages, and disadvantages helps engineers and professionals make informed decisions when selecting flow measurement devices for specific needs. Moreover, adherence to codes and standards ensures consistent and accurate performance of Venturi meters, contributing to the efficiency and productivity of industrial processes and systems.

Some Keywords,

difference between orifice meter and venturimeter

venturimeter diagram

Types of pump

heat exchanger