Flow Measurement: Types and Applications

In the field of instrumentation and control engineering, accurate measurement of the flow of liquids, gases and steam is essential to ensure efficiency, safety and quality in industrial processes. Flow instrumentation enables monitoring, control and optimization of critical systems, from water supply to chemical production and power generation. There are multiple technologies designed to suit different conditions and requirements, each with specific measurement principles, advantages and limitations.

In this note, we will explore the main types of flow instrumentation, highlighting their operating principle, characteristics, applications and criteria for their selection.

1. Variable Area Flow Meters

a. Rotameters

• Measuring Principle: A float moves inside a conical tube, rising or falling according to the flow rate. The position of the float indicates the flow rate.

• Advantages:

  • Simple and economical design.

  • It does not require electrical energy.

• Disadvantages:

  • Limited to clean liquids and low flow rates.

  • They are not suitable for viscous fluids or suspended solids.

• Uses:

  • Laboratory systems.

  • Non-corrosive fluids in industrial processes.

2. Differential Pressure Flow Meters

a. Orifice Plates

• Measurement Principle: The orifice plate creates a restriction in the flow, generating a pressure drop proportional to the flow rate.

• Advantages:

  • Robust and economical design.

  • Easy installation on existing pipes.

• Disadvantages:

  • High pressure loss.

  • Sensitive to obstructions and dirt.

• Uses:

  • Natural gas measurement.

  • Industrial steam and water lines.

b. Venturi tube

• Measuring Principle: Similar to orifice plate, but with a conical design that minimizes energy loss.

• Advantages:

  • Low pressure loss.

  • Precision at high flow rates.

• Disadvantages:

  • Higher initial cost compared to orifice plate.

  • Bulky size.

• Uses:

  • Drinking water systems.

  • Petrochemical plants.

c. Flow Nozzles

• Measuring Principle: Similar to the Venturi tube, but with a more compact design.

• Advantages:

  • High resistance to abrasive fluids.

  • Less maintenance.

• Disadvantages:

  • Less efficient in terms of pressure drop.

• Uses:

  • Mining processes.

  • High pressure steam lines.

3. Positive Displacement Flow Meters

a. Oval Gear Meters

• Measuring Principle: Two gears rotate with the flow of fluid, displacing a fixed volume per revolution.

• Advantages:

  • High precision in viscous liquids.

  • They do not require external energy.

• Disadvantages:

  • Sensitive to suspended solids.

  • Limited to clean liquids.

• Uses:

  • Measurement of oils and fuels.

  • Viscous liquids in the chemical industry.

b. Oscillating Piston Gauges

• Measuring Principle: A piston moves within a chamber, displacing a fixed volume per cycle.

• Advantages:

  • Accuracy at low flow rates.

  • Works with corrosive liquids.

• Disadvantages:

  • Low capacity for high flow rates.

  • Requires frequent maintenance.

• Uses:

  • Dosage in the pharmaceutical industry.

  • Food and beverage processes.

4. Electromagnetic Flow Meters

• Measuring Principle: Based on Faraday's law, they generate a magnetic field; the conductive liquid when passing through generates a voltage proportional to the flow.

• Advantages:

  • No moving parts, low maintenance required.

  • High precision in conductive liquids.

• Disadvantages:

  • They do not work with non-conductive liquids (such as oils).

  • Expensive compared to mechanical technologies.

• Uses:

  • Wastewater treatment.

  • Corrosive liquids in the chemical industry.

5. Mass Flow Meters

a. Coriolis meters

• Measuring Principle: They detect the Coriolis force generated by the mass of the fluid moving through a vibrating tube.

• Advantages:

  • They directly measure mass flow.

  • High precision and versatility.

• Disadvantages:

  • High cost.

  • Sensitive to external vibrations.

• Uses:

  • Food and pharmaceutical industry.

  • Critical chemical processes.

b. Thermal meters

• Measurement Principle: They measure the heat transfer between the fluid and a heated sensor to determine the mass flow.

• Advantages:

  • Ideal for low density gases.

  • Low maintenance.

• Disadvantages:

  • They don't work well with liquids.

  • Sensitive to changes in fluid temperature.

• Uses:

  • Compressed air monitoring.

  • Gases in environmental applications.

6. Ultrasonic Flow Meters

a. Transit Time

• Measurement Principle: They measure the difference in travel time of ultrasonic signals between two sensors.

• Advantages:

  • No direct contact with the fluid.

  • They work in clean liquids and gases.

• Disadvantages:

  • Less accuracy in turbid liquids or with solids.

• Uses:

  • Drinking water systems.

  • Oil pipelines.

b. Doppler

• Measurement Principle: Based on the frequency change of an ultrasonic wave reflected by moving particles in the fluid.

• Advantages:

  • Works with dirty liquids or suspended solids.

  • Non-intrusive installation.

• Disadvantages:

  • Less accuracy in clear liquids.

• Uses:

  • Wastewater systems.

  • Mining processes.

7. Vortex Flow Meters

• Measurement Principle: Detects vortices generated by an obstacle placed in the flow. The frequency of the vortices is proportional to the flow rate.

• Advantages:

  • No moving parts, low maintenance.

  • Suitable for liquids, gases and steam.

• Disadvantages:

  • Not suitable for viscous fluids.

  • Sensitive to external vibrations.

• Uses:

  • Power plants.

  • Petrochemical processes.

Criteria for the Selection of Flow Meters

When choosing the appropriate instrumentation, it is crucial to consider the following factors:

1. Fluid type: Liquid, gas or vapor.

2. Flow Range: Determines the capacity of the meter.

3. Process conditions: Temperature, pressure and corrosion.

4. Required accuracy: According to system tolerances.

5. Budget: Initial, operation and maintenance costs.

Conclusion

Flow instrumentation is an indispensable tool for optimizing industrial processes and ensuring efficient and safe control. Each type of meter, from simple rotameters to advanced Coriolis meters, offers unique features that adapt to different conditions and applications.

At Acciomate Engineering & Projects , we have experience in the selection, design and implementation of customized flow measurement systems to meet the specific needs of each industry.