What is the flow meter?
Flow meters are a device used to measure the rate at which a fluid, such as liquid or gas, flows through a system. It is an essential tool in various industries as it provides valuable information about the flow rate, volume, and velocity of the fluid. Flow meters are crucial for monitoring and controlling processes, ensuring efficiency, and maintaining safety standards. Without accurate flow measurements, it would be challenging to optimize operations and make informed decisions.
Types of flow meters
Flowmeter is one of the most important instruments in industrial measurement. From different perspectives, flow meters have different classification methods. There are two commonly used classification methods, one is to classify according to the measurement principle adopted by the flowmeter; the other is to classify according to the structural principle of the flowmeter. Also, you can divided the types of flow meters by the different measuring medium as well, such as water flow meters, gas flow meters and air flow meters etc.
Types of flow meters: classification by flow meters measurement principle
Electrical principle: The instruments used for this principle include electromagnetic type, differential capacitive type, inductive type, strain resistance type, etc.
Acoustic principle: There are ultrasonic methods for flow measurement using the acoustic principle. Acoustic type (shock wave type), etc.
Thermal principle: There are thermal, direct calorimetric and indirect calorimetric methods that use thermal principles to measure flow.
Optical principle: laser type, photoelectric type, etc. are instruments that belong to this type of principle.
Originally from the physical principle: nuclear magnetic resonance type, nuclear radiation type, etc. are instruments that belong to such principles.
Other principles: there are marking principles (tracer principle, nuclear magnetic resonance principle), related principles, etc.
Types of flow meters: classification according to the structure principle of flow meters
According to the actual situation of the current flowmeter products, according to the structure principle of the flowmeter, it can be roughly classified into the following types:
Positive displacement flowmeter
Mechanics principle: Instruments belonging to such principles include differential pressure type and rotor type using Bernoulli’s theorem; impulse type and movable tube type using the momentum theorem; direct mass type using Newton’s second law; Target type; turbine type using the angular momentum theorem; vortex type and vortex street type using the principle of fluid oscillation; Pitot tube type using total static pressure difference, volume type and weir, trough type, etc.
Impeller flowmeter
The working principle of the impeller flowmeter is that the impeller is placed in the fluid to be measured, and is rotated by the impact of the fluid flow, and the flow rate is reflected by the speed of the impeller rotation. Typical impeller flowmeters are water meters and turbine flowmeters, and their structures can be mechanical transmission output type or electrical pulse output type. Generally, the accuracy of the water meter output by mechanical transmission is low, and the error is about ±2%, but the structure is simple and the cost is low. It has been mass-produced in China, and is standardized, generalized and serialized. The accuracy of the turbine flowmeter output by the electrical pulse signal is high, and the general error is ±0.2% to 0.5%.
Differential pressure flowmeter (variable pressure drop flowmeter)
The differential pressure flowmeter consists of a primary device and a secondary device. The primary device is called a flow measuring element, which is installed in the pipeline of the measured fluid to generate a pressure difference proportional to the flow rate (velocity) for the secondary device to display the flow. The secondary device is called display instrument. It receives the differential pressure signal generated by the measuring element and converts it into the corresponding flow for display. The primary device of the differential pressure flowmeter is often a throttling device or a dynamic pressure measuring device (pitot tube, uniform velocity tube, etc.). The secondary device is a variety of mechanical, electronic and combined differential pressure gauges with flow display instruments. Differential pressure sensitive elements of differential pressure gauges are mostly elastic elements. Since the differential pressure and flow are in a square root relationship, the flow display instruments are equipped with a square root device to linearize the flow scale. Most instruments are also equipped with a flow accumulating device to display the accumulated flow for economical accounting.
Variable area flowmeter (equal pressure drop flowmeter)
The float placed in the upper and lower conical flow channels is moved by the force of the fluid flowing from the bottom up. When this force is balanced with the float’s “displayed weight” (the weight of the float minus the buoyancy of the fluid on which it is subjected), the captor is at rest. The height at which the float rests can be used as a measure of the flow rate. Since the flow cross-sectional area of the flowmeter varies with the height of the float, and the pressure difference between the upper and lower parts is equal when the float is stable, this type of flowmeter is called a variable area flowmeter or an equal pressure drop flowmeter. A typical instrument of this type of flowmeter is a rotor (float) flowmeter.
Momentum Flow Meter
A flowmeter that uses the momentum of the fluid to reflect the flow is called a momentum flowmeter. Since the momentum P of the flowing fluid is proportional to the density of the fluid and the square of the flow velocity v, that is, p v2, when the flow section is determined, v is proportional to the volume flow Q, so p Q2. Set the proportional coefficient as A, then Q=A. Therefore, when P is measured, the flow rate Q can be reflected. This type of flowmeter mostly uses the detection element to convert the momentum into pressure, displacement or force, etc., and then measure the flow. Typical instruments for such flowmeters are target and rotary vane flowmeters.
Impulse flow meter
The flowmeter that uses the impulse theorem to measure the flow is called an impulse flowmeter. It is mostly used to measure the flow of granular solid media, and it is also used to measure the flow of mud, crystalline liquids and abrasives. Flow measurement ranges from a few kilograms per hour to nearly 10,000 tons. A typical instrument is a horizontal component impulse flowmeter. The measurement principle is that when the measured medium falls freely from a certain height h to the detection plate with an inclined angle, an impulse is generated, and the horizontal component of the impulse is proportional to the mass flow rate, so Measuring this horizontal component can reflect the size of the mass flow. According to the detection method of signal (9), this type of flowmeter is divided into displacement detection type and direct force measurement type.
Electromagnetic Flowmeter
The electromagnetic flowmeter is made by using the electric conductor to move in the magnetic field to generate the induced electromotive force, and the induced electromotive force is proportional to the flow rate, and is made by measuring the electromotive force to reflect the principle of pipeline flow. Its measurement accuracy and sensitivity are high. In industry, it is mostly used to measure the flow of water, pulp and other media. The maximum pipe diameter that can be measured is 2m, and the pressure loss is extremely small. However, media with low conductivity, such as gas and steam, cannot be used.
The cost of electromagnetic flowmeter is high, and the signal is easily interfered by external magnetic field, which affects the wide application in industrial pipe flow measurement. To this end, the products are constantly improving and updating, and developing towards microcomputerization.
Ultrasonic flowmeter
The ultrasonic flowmeter is designed based on the principle that the speed of ultrasonic waves in the flowing medium is equal to the geometric sum of the average flow rate of the measured medium and the speed of the sound wave itself. It also reflects the flow rate by measuring the flow rate. Although the ultrasonic flowmeter only appeared in the 1970s, it is very popular because it can be made into a non-contact type and can be linked with an ultrasonic water level gauge for open flow measurement without disturbance and resistance to the fluid. A promising flowmeter.
Ultrasonic Doppler flowmeters manufactured using the Doppler effect have received extensive attention in recent years, and are considered to be ideal instruments for non-contact measurement of two-phase flow.
Fluid oscillating flowmeter
The fluid oscillating flowmeter is designed using the principle that the fluid will oscillate when it flows under specific flow channel conditions, and the frequency of the oscillation is proportional to the flow rate. When the flow cross section is constant, the flow velocity is proportional to the volume flow. Therefore, the flow can be measured by measuring the oscillation frequency. This flowmeter was developed and developed in the 1970s. Because it has the advantages of no rotating parts and pulse digital output, it is very promising. At present, the typical products are vortex flowmeter and precession vortex flowmeter.
Mass flowmeter
Since the volume of the fluid is affected by parameters such as temperature and pressure, the parameters of the medium need to be given when the volume flow is used to express the flow rate. When the medium parameters are constantly changing, it is often difficult to achieve this requirement, resulting in distortion of the displayed value of the instrument. Therefore, mass flow meters have been widely used and valued. There are two types of mass flow meters: direct and indirect. The direct mass flowmeter uses the principle directly related to the mass flow to measure. At present, the commonly used mass flowmeters are calorimetric, angular momentum, vibrating gyro, Magnus effect and Coriolis force. The indirect mass flowmeter is directly multiplied by the density meter and the volume flow to obtain the mass flow.
The flowmeters of the above-mentioned common structural principles are much more than the flowmeters of various structures, such as various weir flowmeters and trough flowmeters suitable for open channel flow measurement; insertion flowmeters suitable for large-diameter flow measurement; measurement layer Laminar flow flowmeter for flow rate; correlation method flowmeter suitable for two-phase flow measurement; as well as laser method, nuclear magnetic resonance method flowmeter and various tracer methods, dilution method flow measurement, etc. With the development of science and technology and the needs of practical applications, new flowmeters will continue to emerge and the types of flowmeters will be more complete.
Types of flow meters: classification according to the measuring medium
Water flow meters
Water flow meters are specifically designed to measure the flow rate of water in various applications. There are several types of water flow meters available, including positive displacement meters, turbine meters, electromagnetic meters, ultrasonic meters, and vortex meters. Each type has its own advantages and limitations, making it suitable for specific applications. For example, positive displacement meters are highly accurate but are not suitable for high flow rates, while ultrasonic meters are non-intrusive and can measure flow in both directions.
Gas flow meters
Gas flow meters are used to measure the flow of gases in systems. These meters are crucial in industries such as natural gas distribution, HVAC (heating, ventilation, and air conditioning), and chemical manufacturing. Common types of gas flow meters include thermal mass flow meters, differential pressure flow meters, ultrasonic flow meters, and vortex flow meters. Each type has its own advantages and is suitable for specific gas flow measurement requirements.
Air flow meters
Air flow meters are designed to measure the flow rate of air or gases in various applications. They are commonly used in HVAC systems, compressed air systems, and industrial processes. Some of the commonly used air flow meters include variable area flow meters, thermal dispersion flow meters, and laminar flow meters. Each type of air flow meter has its own advantages, such as simplicity, accuracy, or the ability to measure in a wide range of flow rates.
Types of flow meters used in the oil and gas industry
The oil and gas industry relies heavily on flow meters for accurate measurement of oil, gas, and other fluids. Some of the commonly used flow meters in this industry include positive displacement meters, turbine meters, Coriolis flow meters, and ultrasonic flow meters. These flow meters are designed to withstand the harsh conditions and high pressure commonly found in oil and gas applications. They provide accurate flow measurements, allowing operators to monitor production, control processes, and ensure compliance with regulations.
Choosing the right flow meter for your application
Selecting the right flow meter for a specific application is crucial to ensure accurate measurements and optimal performance. Several factors need to be considered when choosing a flow meter, including the type of fluid, flow rate, pressure, temperature, and the environment in which the meter will be installed. It is essential to understand the advantages, limitations, and operating principles of different flow meter types to make an informed decision. Consulting with flow meter experts or manufacturers can also help in selecting the most suitable flow meter for your application.
Flow meter installation and maintenance tips
Proper installation and regular maintenance are essential for ensuring the accurate and reliable performance of flow meters. During installation, it is crucial to follow the manufacturer’s guidelines and recommendations. This includes selecting the right location, ensuring proper alignment, and providing adequate support for the flow meter. Regular maintenance involves cleaning the meter, inspecting for any signs of damage or wear, and calibrating the meter if necessary. Following these installation and maintenance tips can help extend the lifespan of the flow meter and minimize measurement errors.
Conclusion
In conclusion, flow meters play a crucial role in various industries by providing accurate measurements of fluid flow. Understanding the different types of flow meters available is essential for selecting the right meter for a specific application. Proper installation, regular maintenance, and calibration are necessary to ensure the accurate and reliable performance of flow meters. By following these guidelines and considering the specific requirements of each application, operators can optimize processes, maintain safety standards, and make informed decisions based on accurate flow measurements.
CTA: To learn more about flow meters and their applications, visit SenTec‘s website or contact our flow meter experts for personalized assistance.
