Vortex Shedding Flow Meter – Material Selection Criteria & Design

This article is about Vortex Shedding Flow Meter, It’s Material Selection Criteria and Design notes of plants and refineries. This article is for Flow Measurement of Instrumentation and Control Systems as per International Codes and standards for Commercial Buildings, Plants and Refinery Projects.

Vortex Shedding Flow Meter - Material Selection Criteria

What is Vortex Shedding Flow Meter?

A Vortex Shedding Flow Meter is a type of flow meter used to measure the flow rate of liquids or gases in pipelines. It operates based on the principle of vortex shedding, where vortices or swirling patterns are generated behind an obstruction (often called a bluff body or shedder bar) placed in the flow path. These vortices alternate from side to side as the fluid flows past the obstruction.

Key components and working principle:

  1. Bluff Body: The bluff body is a sturdy obstruction mounted perpendicular to the flow direction. It creates disturbances in the fluid flow, generating vortices downstream.
  2. Sensor: The flow meter has a sensor that detects the vortices shed by the bluff body. Common sensors include piezoelectric crystals or strain gauges.

Vortex Shedding Flow Meter Working principle:

As the fluid passes the bluff body, it separates into two streams, creating alternating vortices on either side. These vortices are proportional to the fluid’s velocity, and their frequency is directly related to the flow rate. The sensor detects these vortices, and the flow meter converts the frequency into a flow rate measurement.

Advantages of Vortex Shedding Flow Meters:

  1. Low pressure drop: Vortex shedding flow meters offer minimal pressure loss due to the bluff body’s simple design, making them suitable for a wide range of applications.
  2. Wide flow range: They can accurately measure a wide range of flow rates, making them versatile for various flow conditions.
  3. Low maintenance: Vortex shedding flow meters have no moving parts, reducing the need for frequent maintenance and ensuring long-term reliability.
  4. Suitable for dirty fluids: They can handle fluids with particles or debris, making them suitable for challenging environments.

Applications:

Vortex shedding flow meters are commonly used in various industries, including oil and gas, chemical, water treatment, and HVAC (Heating, Ventilation, and Air Conditioning) systems. They are suitable for measuring liquid and gas flows in both process and utility applications.

Overall, vortex shedding flow meters provide a reliable and cost-effective solution for flow rate measurement, especially when accurate readings are essential for process control and optimization.

Material Receiving General Checklist for Instrumentation & Control

General Requirements in Plants and Refineries

Following are main points to meet international codes and standards of Vortex Shedding Flow Meters for installation in plants and refineries.

  1. Purchase Order and Instrument specification sheet criteria shall be confirmed and compared with instrument stainless steel tags / labels and nameplates, all possible visual checks and shipment checked for damage, prior to acceptance of the shipment.
  2. Verify that all the instruments are from technically acceptable vendors (Attachment 1)
  3. Vortex shedding flow meters and transmitters shall be smart. (PIP PCCFL 001 Sec 3.16.4).
  4. Materials of construction shall be compatible with the process fluid. (PIP PCCFL001 Sec. 3.13.4)
  5. Proper gasket sizing shall be followed to avoid protrusion into the process piping. (PIP PCCFL001, Sec 3.13.7 ).
  6. The meter factor data shall be provided by the manufacturer and be based on the actual piping schedule. (PIP PCCFL001, Sec 3.13.5)
  7. The minimum value of the pipe Reynolds number at the lowest expected flow should exceed 10,000 for liquids and 50,000 for gases. Below these values the vortex meter may not generate a reliable flow signal. These Reynolds number limitations may vary between manufacturers. (PIP PCEFL001, Sec 4.17.6)
  8. The meter should be centered in the piping. The meter factors should be based on the piping schedule used. (PIP PCEFL001, Sec 4.17.8 & 4.17.9)
  9. Welds on mounting flanges should be ground smooth. Gaskets should be selected to ensure that no part of the gasket protrudes into the flowing stream. (PIP PCEFL 001 Sec. 4.17.10)

International Codes and Standards

  1. Flow Nozzle Material Selection Criteria Design & Flow Measurement
  2. Venturi Tube Material Selection Criteria Design & Flow Measurement
  3. SAES-J-002 – Technically acceptable instruments
  4. SAES-J-003 – Instrumentation Basic Design
  5. SAES-J-100 – Process Flow Metering
  6. PIP PCCFL 001 – Flow Measurement Criteria , August 2006, Process Industry Practices Process Control.
  7. PIP PCEFL 001 – Flow Measurement Guidelines , August 2006, Process Industry Practices Process Control.

1. Attachment 1: Technically Acceptable Instruments, SAES-J-002

1. Attachment 1: Technically Acceptable Instruments, SAES-J-002

FAQs:

  1. What is Vortex Shedding?

    Vortex shedding is a fluid dynamics phenomenon that occurs when a fluid flows past an obstruction, resulting in the formation of vortices or swirling patterns in the wake of the obstruction. This phenomenon is commonly observed in various natural and engineered systems, including fluid flow in pipes, around buildings, bridges, or other structures, and in the wake of vehicles traveling at high speeds.

    The vortex shedding process begins when a fluid, such as air or a liquid, encounters an object (often referred to as a bluff body) placed in its path. The bluff body creates disturbances in the fluid flow, causing the fluid to separate into two streams as it flows around the object. This separation creates regions of low-pressure vortices on either side of the object.

  2. What types of fluids (liquids or gases) can be accurately measured using Vortex Shedding Flow Meters?

    Answer: Vortex Shedding Flow Meters can accurately measure both liquids and gases. They are suitable for a wide range of applications and can handle various fluid types, making them versatile for different industries.

  3. How does the bluff body design influence the accuracy and performance of the Vortex Shedding Flow Meter?

    Answer: The bluff body design significantly influences the accuracy and performance of the Vortex Shedding Flow Meter. Factors such as bluff body shape, size, and material can affect the shedding frequency and the meter’s sensitivity to changes in flow rates. Proper bluff body design is essential to ensure accurate and reliable flow measurements.

  4. What are the advantages and limitations of Vortex Shedding Flow Meters compared to other flow measurement technologies, such as electromagnetic or ultrasonic flow meters?

    Answer: Advantages of Vortex Shedding Flow Meters include low pressure drop, wide flow range, low maintenance, and suitability for dirty fluids. However, they may have limitations in low flow applications, and their accuracy can be affected by certain fluid properties, such as viscosity. Other flow measurement technologies may be more suitable for specific applications, and the choice depends on factors like flow rate, fluid properties, and budget constraints.

  5. What factors influence the shedding frequency and shedding pattern in a vortex shedding phenomenon?

    Answer: The shedding frequency in a vortex shedding phenomenon is influenced by various factors, including the fluid velocity, flow profile, Reynolds number, and the geometry of the bluff body (such as its shape and size). Additionally, changes in fluid properties, such as density and viscosity, can also affect the shedding frequency. The shedding pattern depends on the interaction between the flow velocity and the bluff body’s geometry, resulting in the formation of vortices and their periodic shedding.

  6. How do flow disturbances, boundary layer separation, and unsteady flow conditions contribute to vortex shedding in fluid flow?

    Answer: Vortex shedding occurs due to flow disturbances caused by obstacles or irregularities in the flow path, leading to boundary layer separation around the bluff body. When the flow velocity reaches a critical value, the boundary layer separates, and vortices are formed and shed alternately on both sides of the bluff body. Unsteady flow conditions, such as turbulence or changes in flow direction, can further enhance vortex shedding and affect its frequency and pattern. Understanding these complex flow phenomena is crucial for predicting and managing vortex shedding effects in various engineering applications.

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