Flow sensors can be found across various industrial, medical and aerospace applications. Flow is defined as the mass or volume of a fluid that passes per unit of time. In practice, flow sensors (or flow meters) are essential in every operation that requires measuring the mass or volume of fluids or gases that are dispensed, distributed, or consumed per unit time.
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A flow meter (alternatively called flow sensor) is an instrument that has been manufactured to measure with precision the rate of flow in a pipe. The accurate gas or liquid flow measurement ensures a safe, efficient, and environmentally compliant operation in many applications. Measuring flow can vary from a very simple principle to a very complicated process. The way of measurement really depends on the technology used. In this article, we are going to look at the eight most commonly used technologies in gas or liquid flow measurement. These flow meter types are: For each application that demands gas flow measurement, different challenges might arise that require careful attention and consideration. Some of them include: Of course, there is no single, all-in-one technology that can be implemented for all operational requirements, performance, and conditions. There are at least 8 common gas flow measurement technologies being used today, all with their strengths and limitations. By understanding the advantages and disadvantages of each, costly mistakes can be prevented. Electromagnetic flow meters detect flow by using Faraday’s Law of induction. Inside an electromagnetic flow meter, there is an electromagnetic coil that generates a magnetic field, and electrodes that capture electromotive force (voltage). As the fluid flows through the pipe, the electromagnetic field changes due to the forces generated by induction. These changes are then translated to flow rate.
Pros: Cons: Best applied to: Electromagnetic flow meters are primarily used in food industries, chemical applications, natural gas supplies, and power utilities as they are largely unaffected by changes in pressure, density, and temperature. Vortex flowmeters make use of a principle called the von Kármán effect. According to this principle, flow will alternately generate vortices when passing by a bluff body. A bluff body has a broad, flat front. In a vortex meter, the bluff body is a piece of material with a broad, flat front that extends vertically into the flowstream. Flow velocity is proportional to the frequency of the vortices. Flowrate is calculated by multiplying the area of the pipe times the velocity of the flow. In some cases, vortex meters require the use of straightening vanes or straight upstream piping to eliminate distorted flow patterns and swirl. Low flowrates present a problem for vortex meters because they generate vortices irregularly under low flow conditions. The accuracy of vortex meters is from medium to high, depending on the model and manufacturer. In addition to liquid and gas flow measurement, vortex flowmeters are widely used to measure steam flow.
Pros: Cons: Best applied to: Vortex flow-meters are more commonly used in power generation and heat-supply systems such as compressed air, saturated steam, superheated steam etc. This is classified as a turbine flow meter. Paddle wheel flow meters are generally divided into two mechanical classes The flow and the revolutions of the paddle wheel are proportional to each other. Thus, by spinning the paddle wheel with the force from the flowing fluid, it becomes possible to measure the rate of this flow from the number of revolutions. By embedding a magnet in the rotation axis and on the edge of the paddle, pulses can be extracted as signals, converting the number of revolutions into the flow rate.
Pros: Cons: Best applied to: Paddle wheel flow meters can be used in fume scrubbers, reverse osmosis and in various other fields. Thermal dispersion flow meters use heat to measure the flow rate of a fluid. The usual structure is that there is a heating element in the middle and two temperature sensors on either side of the heating element. As gas flows, the heat is transferred towards the direction of the flow and the temperature sensor upstream is “getting colder” while the downstream temperature sensor is “getting hotter”. The flow rate can be calculated by measuring the difference between the temperature sensors.
Pros: Cons: Best applied to: Some of the typical applications can be found in the medical and industrial fields such as respiratory devices, anesthesia equipment, CPAP devices and central gas monitoring systems. ES Systems has developed two distinct product series of MEMS thermal sensors, ESRF-ESF and ESRF-HF. This is one of the simplest flow measurement technologies. The method usually involves float in a tapered pipe. When the fluid is forced in between the tapered pipe and the float, a differential pressure is generated which causes the float to be moved accordingly. You can measure the flow rate by reading the visual scale of the meter. Further reading: What is differential pressure?
Pros: Cons: Best applied to: They are widely used for numerous applications including chemicals, compressed air, and other gases. Ultrasonic flow sensors measure the volumetric flow rates of a wide variety of fluids relying on ultrasound and the Doppler Effect. This technology is very accurate and is independent of the pressure, temperature, and viscosity of the medium. In idle operation, the transmitter sends ultrasonic waves that are bounced in the pipe and perceived from the ultrasonic sensor. Since there is no fluid movement, the frequency of the received signal is the same as the transmitter. Once the flow starts, the frequency of the received waves is either higher or lower (depending on the direction of the flow) than the one transmitted. This frequency difference can be translated to flow rate.
Pros: Cons: Best applied to: Ultrasonic flow sensors have many applications, spanning from process flow to custody flow. Differential pressure sensors measure flow through capacitive pressure sensors using Bernoulli’s equation. Differential pressure flow meters use laminar plates, an orifice, nozzle, or Venturi tube to create an artificial constriction then measure the pressure loss of fluids as they pass that constriction. The higher the pressure drop, the higher the flow rate. These rugged, accurate meters are ideal for a wide range of clean liquids and gases. Further reading: Capacitive vs Piezoresistive Pressure Sensors – Differences & applications
Pros: With competitive price and timely delivery, tnma sincerely hope to be your supplier and partner. Cons: Best applied to: Due to their compatibility, there are used in many industries, such as power supply, food and beverage, medical, aerospace, and HVAC. ES Systems have designed the ESCP-BMS1 differential pressure sensor which has: The main working principle of coriolis flow meters is the use of a vibrating tube where the flow of gas can cause changes in frequency, or phase shift proportional to the mass flow rate. At an idle state, the tube vibrates at a predefined frequency. As the fluid flow begins, the vibration of the tube alters proportional to the flow rate of the medium. This change in vibration is measured by sensors across the tube and then translated to flow rate.
Pros: Cons: Best applied to: They are often applied in many different industrial sectors that need a measurement of sanitary and corrosive but relative clean gases. Before making your choice about a gas flow meter type, you should consider the location of the manufacturer’s installation requirements. It is possible that a stable gas-flow profile upstream and downstream from the point of meter installation might be required. Moreover, the degree of maintenance needed should be considered as some technologies differ from each other. Further Reading: Converting velocity to volumetric flow rate With long experience in designing innovative flow sensors, ES Systems provide high – end products with cutting edge technology, high-performance capabilities, and other unique features. Choose the one that covers the needs of your business and industry. View Flow SensorsWhat is a flow meter and how do we measure gas flow?
But how do we measure flow?
Challenges in Gas Flow Measurement
Gas Flow Meter Types – Technology Comparison
1. Electromagnetic Flow Meters
2. Vortex Time Flow Meter
3. Paddle Wheel Flow Meter
4. Thermal Dispersion Flow Sensor
5. Floating Element Flow Sensor
6. Ultrasonic Flow Meter Type
7. Differential Pressure Flow Meter
8. Coriolis Mass Flow Meter
Installation and Maintenance
Flow measurement is an important process with diverse applications like measuring the flow rate of blood in human beings to measuring and controlling the flow rate in an oil well useful for extraction of oil. It forms an important part of several industries like chemical, wastewater treatment, pulp and paper, oil and gas, and several others. The scope of flow measurement extends far beyond that covered in the following sections. This exhaustive system spans several processes, techniques, and technologies. We have attempted to touch the tip of the iceberg that is flow measurement.
The accuracy of flow measurement determines the functioning of the system. A well-functioning system will provide highly accurate results. Several new technologies are being developed in this realm to support flow measurement systems. These systems as well as direct and indirect processes can help organizations achieve brilliant results.
In this handbook, we will be discussing flow measurement concepts, processes, and systems that are useful to the amateur and professional. They encompass theoretical and practical topics peppered with interesting information and trivia about flow measurement. From the Mesopotamians to Doppler to the most recent group findings, this handbook promises to be an interesting as well as informative read.
As the name suggests, flow measurement is the process of measuring the flow rate and volume of a liquid or gas. This process can be employed to measure the liquid passing through an application (as seen in water purification systems), or stored in an application (as seen in fuel injectors). Flow measurement is a vital function used to monitor and control the rate of liquid flow in applications. This process is used to measure the flow of versatile substances like heavy oils, abrasive chemicals, and light gases. Hence, this process is utilized in applications across various industries.
Flow measurement is employed in critical applications where the flow rate or level of liquid stored needs to be administered regularly. The safe functioning of applications depends on flow meters. In terms of flow measurement, accuracy is of such importance that it can be the determining factor of a company making a profit or loss.
In some applications, the flow needs to be regulated within a specific range. This is achieved by using flow meters. A flow meter is a device used to facilitate flow measurement. Flow meters are broadly classified as:
Flow meters can be used to measure the flow rate of liquids or gases. The unit is decided depending on the function and parameters of flow measurement. The unit used varies according to the system of measurement being followed, as well as the material being measured. Dissimilar media need to be measured under diverse conditions and using different units.
Units Used to Measure Flow
The following units are used to measure liquid and gas flow:
The unit of measurement changes in accordance with the medium of material being measured. For example, the units of measurement of liquids, gases, and steam could vary. This is because the change in their density is dependent on different factors. The density of gases is dependent on pressure and temperature. On the other hand, the volume of liquid is independent of pressure. Hence, the units used to measure the different media change accordingly.
Mapping the history of fluid dynamics and the flow measurement process, this section takes a look at the milestones achieved.
When: 5000 B.C.
Who: Mesopotamians
What: The earliest record of flow measurement can be found in Sumerian cities that were located near the rivers Tigris and Euphrates. The Mesopotamians created channels from the rivers into the city to supply water to every household (an ancient plumbing system, so to say). They used simple methods of flow measurement to monitor the flow rate of water from the rivers into these channels.
When: 3500 B.C.
Who: Ancient Egyptians
What: The Nilometer
The Nilometer is a structure that was built to measure water flow throughout the year. This system helped the Ancient Egyptians predict floods, draughts, and well-balanced water flow throughout the season. It also helped them anticipate and prepare their food and supplies according to the volume of water expected in the upcoming season.
When: 1738
Who: Swiss Physicist Daniel Bernoulli
What: Bernoulli published Hydrodynamica, supporting his theory of conservation of energy in liquid flows. This thought process pioneered the processes used to determine pressure drop in various processes and equipment.
When: 1759
Who: Swiss Mathematician and Physicist Leonhard Euhler
What: Euhler applied Newton’s Second Law of Motion to fluid dynamics. He developed partial differential equations for motion of fluids.
When: 1832
Who: English Scientist Michael Faraday
What: Faraday invented the theory of the dynamo. He has also been attributed to developing the theory responsible for the invention of the magnetic flowmeter.
When: 1842
Who: Austrian Physicist Christian Doppler
What: Doppler discovered and established a relationship between distance and frequency of sound. Almost a century later, his discovery enabled the invention of the Doppler flow meter.
When: 1843
Who: French Civil Engineer Gaspard Coriolis
What: Coriolis is responsible for discovering the drifting of wind and ocean currents caused by the earth’s rotation. This drift varies depending on the location. For instance, the drift is dissimilar at the two poles. The direction of the drift is also dependent on the hemisphere. This has helped further the field of flow measurement greatly.
When: 1845
Who: Irish Mathematician, Physicist, Politician, and Theologian George Gabriel Stokes
What: Based on Claude Navier’s calculations and equations published for incompressible fluids, Stokes derived equations that helped describe the motion of liquids. These equations are known as Navier–Stokes equations. Stokes also developed theories that led him to invent the Stoke’s Law. This law helps calculate drag force in a viscous fluid.
When: 1883
Who: British Engineer Osborne Reynolds
What: He discovered the ‘Reynolds’s Number’, which is a dimensionless ratio. This number helps us calculate the viscosity of a liquid. This is extremely helpful in flow measurement calculation.
When: 1954
Who: Hungarian-American Aeronautical Engineer Theodore von Karman
What: Karman discovered that the vertices formed in water were always constant irrespective of the velocity of water. His discovery facilitated the discovery of the Vortex flow meter. Based on this principle, the first swirlmeter was made available to the public in 1968.
When: 1954
Who: Hungarian-American Applied Mathematician & Physician John Von Neumann
What: Neumann is regarded as the founding father of computational fluid dynamics. His efforts have helped shape major inventions in the field of fluid dynamics in recent times. His theories on artificial viscosity have also enhanced people’s understanding of shock waves.
TRIVIA: What Are Re-discoveries?
Sometimes, when discoveries are made, they are not utilized at that time. There could be several reasons why this happens. Sometimes, people are not able to comprehend the knowledge. At other times, the technology to support the theory has not been developed. Hence, the theory takes a backseat in the minds of people and it can be forgotten over time. When these theories are resurrected, they are known as re-discoveries. For example, when the sub-field of vortex dynamics within the field of fluid dynamics gained momentum, many discoveries and re-discoveries were made.
It is obvious that wherever needed, flow meters are critical to the functioning of the application. In fact, in some applications, precise measurement of liquid and gases is needed to maintain safety. However, one too many times, flow meters are installed when they are not needed. At other times, the requirements of the application are not assessed correctly. This causes several problems in terms of functionality, not to mention misdirection of company funds.
Flow meters can be used in conjunction with several types of liquids. Various configurations of these devices are available, which allow them to be used with liquids with varying chemical and physical properties. In terms of configurations, the flow meters can be designed with various functionalities, materials, and capacities. The specifications can be customized according to the needs of the application and industry.
For example, specialized flow meters are available for use in wastewater treatment plants. The material used for the construction of the flow meter will vary depending on the pH levels of the water. In addition, the flow meter will have to be designed to accommodate the inflow of the water. In order to ensure maximum accuracy, the capacity of the flow meter should match that of the wastewater flowing through the system.
A market survey has claimed that over 75% of industrial flow meters are not performing up to the expected mark. This is mainly caused due to improper product selection. In the initial stages of product selection, buyers can benefit from understanding the basic requirements of their applications. To do this, the right questions need to be asked.
Some tips to help you define your requirements:
Most Important Flow Meter Functions are:
QUESTIONS YOU SHOULD BE ASKING
Do I Need?
Is The Liquid Being Measured:
Also..
Flow Meter Features that Increase Efficiency
Look for the following features within your application to ensure maximum efficiency:
Every product has its own advantages and disadvantages. It is important to match your application’s requirements with those of the flow meter. When the features and needs of both are in harmony, the results are outstanding. Manufacturers and suppliers, alike are eager to assist buyers in their quest to finding the perfect flow meter that delivers on all counts of performance and efficiency.
Flow meter calibration along with other installation and maintenance procedures is needed to ensure safe operation of plants. Flow meters analyze a very important function. Hence, before purchasing a flow meter, the buyer should consider whether the device can be installed, used, and maintained in the best possible manner.
Why Calibrate?
Flow meters are used in critical applications and functions. Hence, they need to be calibrated to ensure accurate measurements. With constant use, components wear out and flow meters can fall out of calibration. This is true for the most ruggedly constructed devices. The accuracy of the measurement reduces over time. Regular calibration will ensure that all components function efficiently, providing brilliant results.
Common Problems that Demand Regular Calibration
Why should one calibrate? Here are some problems that could occur with a flow meter. These problems disrupt the functioning of machines. However, they can be solved by employing calibration methods. Some of the problems you should watch out for:
Best Practices of Flow Meter Calibration at a Micro Level
(Conducted at the Execution Level)
When calibrating flow meters, the following practices will allow you to get the most out of the process:
Industrial Dynamics Tip :
During the calibration process, the common error zone lies in the medium being measured. This zone comes in play when there is some difference between the liquid’s viscosity, density, or heat content at both the stages of testing.
For example, if the density of the liquid is slightly higher during the operation of the standard as compared to the density of the liquid during the operation of the test flow meter, your results will be inaccurate.
Best Practices of Flow Meter Calibration at a Macro Level
(Conducted at a Company Level)
The following practices should be employed by a company on a macro level. It is the responsibility of the managerial function of an organization to put these processes in place:
Although the calibration of most flow meters will fall out at some time due to wear and tear of components, the calibration could also be off due to improper installation or damaged components. Hence, regular calibration will ensure that the flow meter functions smoothly providing precise results.
Flow meters are used across several industries. Following are some examples of industries and applications, which use flow meters to accurately monitor and measure different liquids:
Several specifications of the application and flow meter have to be considered when finding the right fit. Several external factors including environmental conditions, budget, etc. also need to be taken into consideration during product selection. Factors such as the media to be measured, viscosity of media, operating conditions (like temperature and pressure), performance expectation, installation conditions, and material of the flow meter need to be paid attention to when selecting a flow meter. The right product will help improve efficiency of the entire process. You can even consult your manufacturer on the best kind of product that will integrate seamlessly with the rest of your system.
The maintenance of the product throughout its service life cycle should be taken into consideration when outlining the budget for the product. This will reduce the surprise factor and help you in planning your finances accordingly. Regular calibrations, among other maintenance procedures are needed to ensure proper functioning of your flow meter. Calibration, as most flow meter owners understand is an important process that helps mitigate any issues associated with performance. Maintaining the accuracy of a flow meter has to be the top most priority of any organization.
Discussion of several such important topics is the need of the hour, as every organization is looking for solutions to flow measurement issues. Understanding the basics will allow you to select, purchase, and handle the instrument better. Flow measurement knowledge is also useful in increasing the efficiency of your products.
Flow measurement is important for environmental sustainability, increased efficiency, safety, and process optimization.
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