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What Is Flow Measurement?

Written by Stéphane Roux

Published on 2022-04-04 & Updated on 2022-05-10

What Is Flow Measurement?

If you are working in any industry and the quantity of the processing fluid is not accurate, your company may suffer great loss.

To assure that the quantity of every fluid is accurate throughout the entire work process from beginning to end, measurements of those fluids are necessary and can't be ignored. 

Flow measurement of liquid or gas products is done periodically to assure that all the work processes like liquid transfer and fluid control are functioning accurately, smoothly, and safely. 

In this article, we will be discussing everything you need to know about flow measurement and its application in the industry, including its principal, the devices used for flow measurement, and the different methods of flow measurement. 

Let's start with what flow measurement is. 

What Is Flow Measurement? 

Flow measurement identifies the quantity of the fluid that passes through any pipe, channel, or space using flow measurement devices. Fluids that are measured include liquids, gas, or vapor.

What Is a Flow Measurement Device? 

Flow means the given quantity of a substance either in terms of mass or volume that passes through a pipe per unit time.  

To measure the flow of any fluid, there is a need for some device or instrument, and the device used to measure the flow is known as a flow measurement device. 

A flow measurement device commonly referred to as a flowmeter is an instrument that is used to measure the flow rate of a fluid per unit time (Volume or mass of the given fluid.) 

Working Principle of Flow Measurement

The working principle of a flow measurement device, also known as a flowmeter, is to measure the amount of fluid, i.e, liquid, gas, or stream. The flow meter calculates either volume or mass of the given liquid. 

Ways of Flow Measurement

As mentioned above, flow is measured in two ways:  in volume or mass per unit of time. 

1. Volume Flow 

The volumetric flow of a substance is defined as the measurement of the volume quantity that flows/passes through a given area or section per unit of time. 

2. Mass Flow  

The mass flow of a substance is defined as the measurement of the mass quantity that passes or flows through a given area or section per unit of time. 

Why Is Flow Measurement Important? 

In industries, flow measurement is important as it determines the functioning of your system. This means if the system in your industry where flow processes are occurring is functioning well, they will produce highly accurate results. Hence, the more accurate the results of your flow measurement, the more accurate is your system's functioning. 

Flow measurement is crucial to monitor, control, and keep a check on the rate of fluid that is flowing through a channel or section. The flow measurement process measures the flow of a wide range of liquids, including heavy oils, light gases, spirits, chemicals, water or food.  

Flow measurement is critical where the fluid needs to be used regularly. This assures that the flow rate of fluid passing is accurate. It also assures that the right fluid is being processed in the right place and at the right time. This helps to reveal the fluid quality as well. 

The accurate measurement of the liquid fluid flow is particularly important where critical applications are taking place in the industry because a little error can lead to a huge loss. 

Methods Of Flow Measurement

Flow can be measured using various methods and technologies. 

  • Mechanical Flowmeter 
  • Pressure drop based Flow Meter 
  • Vortex Flowmeter 
  • Optical Flowmeters 
  • Thermal Flowmeter 
  • Ultrasonic Flowmeters 
  • Electromagnetic Flowmeters 
  • Mass Flowmeter 

1. Mechanical Flowmeter 

Mechanical flow meters consist of a moving part or rotational devices like a propeller or paddle wheel. The liquid that passes through the mechanical flowmeter induces rotation of the moving part. The flow rate that is created in the flowmeter is proportional to the moving part of the device.  

There are various types of instruments that work on the principle of mechanical flowmeters. They include: 

  • Piston Meters 
  • Turbine Flow Meter 
  • Variable Area Meter 
  • Woltman Meter 
  • Single Jet Meter and Multiple Jet Meter 
  • Paddle Wheel Meter 
  • Nutating Disc Meter 
  • Oval Gear Meter 
  • Pelton Meter 

1. Piston Meters

Piston meters consist of a rotating piston inside its chamber. It has a known volume. As the liquid passes into the chamber, the piston displaces the volume of the liquid.  

While the chamber fills up and empties, the piston rotates. The rotating cycles are counted by which the total volume of liquid is determined.  

Piston meters work on the principle of positive displacement flowmeters. It is suitable for the measurement of the flow of low-volume fluids. 

2. Turbine Flow Meter

The turbine flow meter senses the volume of the liquid. It consists of freely suspended turbine blades, and when the fluid passes through the turbine, the turbine blades start to rotate. The velocity of the rotating turbine is directly proportional to the fluid velocity that is passing through the flowmeter. 

3. Variable Area Meter  

Variable area meter, a kind of rotameter consisting of a tube and float. A float is a solid object used as a flow indicator that is suspended in the tube. The liquid flows upward through the tube, and the created differential pressure across the float is measured. 

4. Woltman Meter 

Woltman meter is a turbine flowmeter that consists of a rotor with helical blades inserted axially into the Woltman meter. It measures the velocity of the liquid flowing with the help of a turbine. 

5. Single Jet Meter 

As the name indicates, a single jet meter uses a single port for creating a water jet. This causes the turbine to rotate. The turbine is mounted in a radial position and a single stream of water is directed towards the turbine. 

6. Paddle Wheel Meter 

The paddle wheel meter consists of a paddle that rotates when the fluid passes through the pipe. The paddle rotates at a speed which is proportional to the liquid flowing in the pipe. 

7. Nutating Disc Meter 

This flow meter includes a mounted nutating disc that determines the volume of liquid passing through the rotating chamber. The speed of rotation is proportional to the speed of the fluid. It is used for the measurement of the water supply. 

8. Oval Gear Meter 

Oval gear meters consist of two oval-shaped precision wheels. The wheels rotate proportionally as the fluid passes through the meter. The volume is measured by the number of rotations. The number of rotations is the volume measurement. 

9. Pelton Meter 

The Pelton meter consists of a rotating Pelton wheel which converts its mechanical action to a user-readable form. (A readable flow rate). 

2. Pressure drop-based Flow Meter  

Differential pressure flowmeters consist of some type of restrictions within their flowing body. The restrictions can be any of the following: 

  • Orifice Plate 
  • Pitot Tube 
  • Venturi meter  

These restrictions are responsible for creating differential pressure in the flowmeter between the upstream and the downstream of the restriction.  The pressure drop, measured by a differential pressure sensor, is proportional to the volume flow 

3. Vortex Flowmeter 

Vortex flowmeter holds the advantage of measuring all three phases of the fluid, i.e gas, liquid, and steam. Furthermore, it has no moving parts which make it cost-effective in terms of maintenance and in measuring fluids that can generate problems because of moving parts.

The working principle of the vortex flowmeter is known as the vortex shedding principle. When a fluid passes an obstacle, oscillating vortices occur downstream of it. A pulse sensor collects the frequency of these oscillations, which is proportional to the volume flow. 

4. Optical Flowmeters  

As the name indicates, optical flow meters use light to measure the liquid flow, i.e, the velocity of a fluid passing through the pipe. 

5. Thermal Mass Flowmeter 

In a thermal mass flow meter for gases, the fluid passes through a heating element. As the flow rate increases, the heating element cools. The flow meter measures the amount of energy required to maintain the temperature of the heating element which is proportional to the mass flow rate of the gas 

6. Ultrasonic Transit Time Flowmeters 

The ultrasonic transit time principle consists of two opposing probes, the first placed upstream and the second downstream. Each probe of a chord alternately transmits and receives an ultrasonic wave directed towards the other probe. 

The upstream-downstream and downstream-upstream travel times of the wave are different (when the fluid is moving, the downstream-upstream time is greater than the upstream-downstream time). The two travel times and the difference between the two times make it possible to determine the average flow velocity along the chord and from this to deduce the volume flow rate. 

7. Electromagnetic Flowmeters 

The measuring principle of electromagnetic flowmeters is based on Faraday's law: the voltage induced by a conductive liquid moving through a magnetic field is directly proportional to the speed of the conductive liquid. The induced voltage is measured across two diametrically opposed electrodes. 

8. Coriolis Mass Flowmeter 

A Coriolis flowmeter consists of a tube (or tubes) that is subjected to vibration. When a fluid (gas or liquid) passes through this tube, the inertia of the mass flow causes the vibrating tube to distort, resulting in a phase shift between the inlet and outlet of the flowmeter. The value of the phase shift can be measured and is proportional to the mass flow. 

Applications And Benefits Of Flow Measurement

Some applications of flow measurement in the liquid industry are as follows: 

  • Flow measurement involves using flow meters that measure the flow rate of steam, liquid, or gas flowing through a pipe. Measuring the flow rate of liquids is necessary to control plus check the quality of industrial processes. 
  • It assures the exactness in fluid quantity and quality. 
  • Flow measurement also helps to determine the functioning of your system. For example: if there is a leak in your system, i.e, flow meters, the quantity of the fluid will not be accurate. 
  • Flow measurement helps to compare the known quantity with the unknown quantity and helps to detect any type of fluid loss. 
  • The flow rate measurement is important for applications that require quality control, like batch control. 
  • Taking accurate flow measurements regularly assures a safe working environment which ultimately leads to a more productive work environment. This shows that the machinery is operating efficiently, and the quantity of fluids being processed is accurate. While operating with liquids and gasses, accurate flow is crucial for the health and safety of personnel. 
  • Flow measurement is useful in terms of cost-effectiveness. The early detection of leakage or wastage of fluids minimizes the risk of loss and increases industrial savings. 
  • Other applications of flow measurements include custody transfer to assure accuracy where transfer of liquids from one area to another takes place. 

Conclusion 

Flow measurements of the fluid are the basic yet most critical task done in the liquid industry. All the work processes depend on the accuracy of the fluid measurements.

It may sound basic, but only a minor error can hinder the final result of production. Instruments used in flow measurements are called flow measurement devices, i.e, flowmeters. There are various types of flowmeters used in the liquid industry depending on the necessity and requirements of production material. 

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