This article contains all the information you need to know about Coriolis Flow Meters.
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A Coriolis flow meter determines mass flow by utilizing the inertia of a fluid or gas passing through a vibrating tube. Sensors placed at the meter’s inlets and outlets detect the oscillations caused by the flow. These oscillations are proportional to the mass of the substance flowing through the meter. The advanced design and operation of Coriolis flow meters make them highly reliable for measuring fluids and gases.
Coriolis flow meters are commonly used across various industries that handle fluid, liquid, or gas flow. Their precise technology provides accurate and dependable measurements of mass flow rate, fluid density, viscosity, and temperature.
To grasp the operation of a Coriolis flow meter, it’s essential to understand the Coriolis principle, first described by Gaspard-Gustave de Coriolis in his 1835 paper, "On the Equations of Relative Motion of a System of Bodies." This principle led to what is now known as "The Coriolis Effect."
In simple terms, the Coriolis effect explains that any moving object on or above the Earth's surface, such as ocean currents or air masses, will experience a lateral drift due to the Earth's rotation. Similarly, in a Coriolis flow meter, the flow of fluid through the meter’s tubes causes them to twist. This twisting is measured and interpreted to provide accurate readings, analogous to the sideways drift observed in the Coriolis effect.
Substances such as fluids and gases are frequently transported through pipelines, each with unique properties that require specific measurement techniques. Coriolis flow meters are one method used to gather data and measurements, providing direct readings of mass flow and density.
Unlike volumetric flow meters, which measure the volume of flow (e.g., gallons per minute), Coriolis flow meters are true mass meters. They measure the mass flow rate directly, which remains consistent regardless of the substance’s characteristics. As a result, there is no need to recalibrate the meter for different materials, as mass is a constant factor.
The U-shaped tube in a Coriolis flow meter is crucial for its operation, as the movements of this tube generate the meter's readings. As a material flows through the tube, it causes the tube to oscillate in a harmonic motion, leading to deformation. This deformation is represented by the fluid force arrows in the diagram below.
The exciter maintains continuous oscillation and movement of the tube. In the absence of flow, this oscillation remains uniform. As illustrated in the image below, the exciter is positioned at the lowest point of the tube, situated between the measurement sensors.
Sensors are positioned at both the inlet and outlet of the tube to monitor its oscillation. When no fluid or gas is flowing, the oscillation is uniform. However, once a fluid or gas enters the tube, it disrupts this uniformity. The inertia of the liquid causes the oscillation patterns at the inlet and outlet sections of the tube to differ. The sensors detect these changes in oscillation, known as phase shift, in both time and space.
The phase shift directly measures the quantity of fluid or gas flowing through the pipe, resulting from the oscillation of the tube. This measurement provides a linear output that is proportional to the flow rate. Since this method measures mass flow directly, it is versatile and applicable to any type of material passing through the tube.
In addition to phase shift, the sensors also monitor the natural frequency of the fluid or gas. This frequency, which indicates how often the tube oscillates per second, correlates with the material's density. By measuring both mass flow rate and density, the volume flow rate can be calculated. Temperature measurements are also taken to adjust for dynamic changes, such as the expansion and contraction of the tube.
The data acquired from the tube fluctuations and phase shift is fed into a flow meter that provides information on the mass, volume, and density of the fluid or gas. The mass flow readings are provided on the display in pounds or kilograms, which can be set on the face of the meter depending on the type of meter.
Coriolis flow meters offer significant flexibility and adaptability. They can range from very small sizes, such as 0.04 inches (1 mm), to large models suited for oil and petroleum industries. Several factors need to be considered when selecting a flow meter, which should be determined before purchasing and installation.
Beyond size, the type of data a meter provides can vary based on its complexity. While most meters deliver similar data, they may differ in their configuration methods. Some of the settings and features of a Coriolis flow meter include:
Measurement instruments for fluid and gas flow are crucial for producers, as their accuracy directly impacts profitability and operational efficiency. Even minor errors or defects can be expensive, necessitating rigorous and ongoing monitoring of the entire measurement system.
Coriolis flow meters vary based on their tube design, which can include single or dual tubes, and various unique configurations. The earliest Coriolis flow meter featured a single-tube design, which has since undergone significant refinement and improvement over the years.
The single-tube design is used to measure high fluid velocities by constricting the cross-sectional area relative to the pipe. Distortion in the tube is assessed against a fixed reference point or plane. The tube is subjected to high-amplitude bending forces applied at a fixed anchoring point to induce this distortion.
In the dual-tube design of a Coriolis flow meter, a manifold divides the flow between two tubes. These vibrating tubes oscillate around two fixed endpoints, generating the Coriolis effect. As fluid moves through the U-shaped tubes, the twist in the tubes accelerates on the inlet side and decelerates on the outlet side. This differential force causes a slight twist in the tubes, which is proportional to the mass flow rate. To amplify the Coriolis effect, a magnet and pickoff coil are positioned at the inlet and outlet ends of the tubes. The coil, moving within the magnetic field, generates a sine wave that corresponds to the tube's oscillation.
The continuous loop design is a variant of the single-tube configuration where the fluid flows through a series of interconnected tubes without being divided. It operates on the same Coriolis principle and provides similar data to other types of Coriolis flow meters. This design often includes additional components such as drivers and magnets. The continuous loop Coriolis flow meter is especially suited for materials that might coat or clog the meter, as it features larger tubes to minimize the risk of obstruction.
The straight-tube design of a Coriolis flow meter can feature either a single or dual tube configuration. As fluid flows through the tubes, Coriolis forces induce a flexural distortion, which is then detected by the meter’s sensors. Due to the inherent rigidity of the straight tubes, strain gauges are specifically required in this design to monitor and measure any dimensional changes in the tubes.
U shaped flow meters are the dual tube variety with two tubes shaped like a U with a magnetic and coil assembly. Sensors are placed at the inlet and outlets of the tubes. The Coriolis forces caused by the flow of the material determine the mass flow rate and density.
The micro-bend Coriolis flow meter features a U-shaped configuration with an exceptionally small radius. This design allows for a more compact meter and results in a reduced pressure differential.
The triangle-shaped flow meter is highly compact and optimized for low-pressure applications. Its single tube design is smaller than the U-shaped models, allowing for more efficient use of installation space. Typically, triangle-shaped flow meters are capable of providing multivariable measurements.
Coriolis flow meters are versatile and can be installed in various types of pipes, regardless of orientation or vibrations. To ensure optimal performance, it is recommended to place piping supports on both sides of the meter. If the installation guidelines specify the need for special supports, it indicates that the meter may be sensitive to vibrations. Manufacturers often supply pulsation dampeners, flexible connectors, or clamping brackets to mitigate the effects of vibrations.
There are several types of supports available for Coriolis flow meters, which include U rest, Y rest, U bolt clamp, pipe hangers, and block clamps. These support mechanisms are not normally necessary, especially for newer versions.
Before starting the installation process, several factors need to be carefully considered to ensure the meter operates correctly. While modern Coriolis flow meters are generally resilient to vibrations, they should still be supported with standard piping supports on both sides of the meter.
It’s essential to assess the installation environment for temperature extremes and hazardous conditions before purchasing the meter. If the environment has special requirements, there are Coriolis flow meters designed to withstand high temperatures and hazardous conditions.
Coriolis flow meters are classified into various categories such as Class I, Class II, and so on, with further subdivisions into groups like A, B, C, D, etc. These classifications specify the appropriate use of the meter, including the types of fluids or gases it can measure. Ensuring that the meter matches the correct classification for its intended application is crucial, as using an incorrect meter could lead to inaccurate readings or safety issues.
The installation orientation of a Coriolis flow meter should align with the type of material being monitored. Meters must be positioned correctly to accommodate the specific fluids, gases, liquids, water, or slurries they will measure. The chart below provides a brief overview of various orientations.
Be sure to compare the preferred orientations with alternate options and consider the inclusion of the three different types of Coriolis flow meters depicted.
Sensors should be positioned away from potential sources of interference, such as pumps, as their vibrations can affect readings. When installing sensors in a series, ensure they are spaced at least two meters apart. Regardless of the flow meter's temperature range, consider the effects of pipe expansion and contraction.
In addition to following orientation guidelines, the meter should be mounted along a straight section of piping, avoiding high or low points and drop lines. During installation, ensure that the measuring tube or tubes are filled with the medium to be measured.
Each model, type, design, and size of Coriolis flow meter requires its own specific zeroing procedure. Zeroing is an automated calibration process accessible through the meter's zero setting menu. Simply selecting 'yes' initiates the zero calibration.
Before performing the zeroing process, allow the meter to warm up according to the manufacturer's instructions, which could range from five to twenty minutes depending on the model.
For accurate zeroing, ensure that the meter's tubes are filled with the measuring fluid or gas, avoiding any trapped air. This can be achieved by circulating the fluid through the meter at speeds between two to six feet per second for several minutes.
Successful calibration requires that the meter is fully charged with the material being measured while ensuring zero flow conditions. The standard error factor is 0.05 kilograms per minute, which represents the maximum deviation during measurement.
After setting the zero stability, the meter should deliver optimal performance, often surpassing other measurement methods. It is recommended to perform the zeroing process three or four times to check for any potential interference.
Among various types of flow meters, Coriolis flow meters stand out as the most versatile, precise, and adaptable. They utilize the Coriolis effect to measure mass flow, density, and temperature. As fluid moves through a pipe, it encounters a deflecting force due to the Coriolis inertial effect, which correlates with the mass flow rate. The force exerted by the fluid on the oscillating tube determines the mass flow rate.
The distinctive design of Coriolis flow meters enables them to accurately measure both viscous and non-conductive fluids, which other meters may not be able to handle. A single Coriolis flow meter is capable of measuring mass flow, volumetric flow, density, and temperature. The oscillatory movement of the meter's tubes generates Coriolis force, which is directly related to the mass of the flowing substance.
The measurement of mass flow is preferred over volumetric flow, which measures in terms of gallons per minute. Mass flow meters measure fluid flow in terms of weight such as pounds or kilometers per second, which is considered to be a more accurate measure especially in custody transfer.
Inside the flow tube of the meter, a drive coil induces vibrations at the tube's natural frequency. Even in the absence of flow, the tube vibrates, and the pickoffs generate signals based on these vibrations. This movement is observed between the two tubes.
When fluid enters the tube or tubes, they start to twist or oscillate rapidly. This acceleration creates a measurable force on the tubes that correlates with the mass of the flowing material. The material inside the tube interacts with this force, known as the Coriolis force. The distinction between no flow and flow is illustrated in the diagram below.
The time difference recorded between the inlet and outlet sensors is used to calculate the mass flow rate. Additionally, this signal can be utilized to determine the material's density. The Coriolis flow meter measures by observing the tube or tubes' movement at its operational frequency. As the material's density changes, so does the frequency; increased density leads to a decrease in frequency, while decreased density results in an increased frequency. For measuring the density of gases, a different type of measurement device is required, as Coriolis flow meters are not suitable for this purpose.
The viscosity of a fluid is assessed through the torsional action occurring at the center of the tube, where a counter-oscillating mass is positioned. As the fluid flows, the shear force exerted by the moving tube affects the fluid's viscosity. This change in viscosity alters the tube's oscillation pattern, which the meter detects and translates into a numerical value.
Higher viscosity results in reduced torsional oscillation of the tube, requiring additional power to maintain the oscillation. This power requirement reflects the dynamic viscosity of the fluid. In a dual-tube Coriolis flow meter, the oscillation can be observed through the blue arrows in the diagram, representing the upward and downward movements of tubes A and B.
The process temperature effect refers to the variation in sensor accuracy resulting from changes in the process temperature compared to the temperature at which the sensor was calibrated. This variation is managed during the zeroing procedure under actual process conditions.
Additionally, the accuracy of density measurements can be influenced by the process temperature if it deviates from the calibration temperature.
Coriolis flow meters are widely used for measuring mass, density, temperature, and viscosity across various substances due to their adaptability and precision. They maintain accurate measurements regardless of material disturbances and can be installed at any point along a pipe.
Their inherent ability to measure mass flow, combined with their linearity and accuracy, makes Coriolis flow meters particularly suitable for custody transfer operations, where precise measurement of fluids or gases is crucial during transactions.
Coriolis flow meters are preferred for their exceptional accuracy, which can be as precise as 0.1%. This high level of precision is a major factor behind their widespread adoption in recent years.
These flow meters are highly versatile, capable of measuring a broad range of substances. They are unaffected by ambient conditions and can handle a variety of gases, liquids, and fluids, including high-viscosity liquids, two-phase liquid-solid or liquid-gas mixtures, and dense high-pressure gases.
Coriolis flow meters are resilient to variations in flow velocity caused by upstream or downstream disturbances. For optimal performance, especially in cases of non-uniform flow, installing the meter on a straight section of pipe can enhance accuracy, as illustrated in the diagram below.
Measuring viscosity—essentially the thickness or texture of a fluid, or its resistance to deformation—can be challenging for many standard meters. However, Coriolis flow meters are designed to accurately measure viscosity without being affected by it. These meters provide detailed information on a fluid's thickness and its flow properties. For instance, as shown in the image below, fluids vary in how easily they flow, with the fluid on the left demonstrating smoother flow compared to the more resistant fluid on the right.
A Coriolis flow meter is a versatile instrument that offers a comprehensive set of readings on the movement and properties of materials within a pipeline. While its primary function is to measure mass flow, it also provides data on volume, density, temperature, and other parameters. Although specific readings may vary among different Coriolis flow meter models, they generally include measurements for mass, density, temperature, and viscosity.
Bidirectional flow, while less common in production settings, requires accurate measurement in both flow directions. Unlike many meters that need extensive calibration for bidirectional flow, Coriolis flow meters are designed to handle such measurements with ease due to their inherent adaptability and straightforward adjustment capabilities.
Some fluids are complex mixtures of liquids and gases, presenting challenges for measurement due to their unique properties. Coriolis flow meters excel in these situations, adapting to various fluid characteristics without issue. They are capable of measuring diverse substances such as asphalt, molasses, syrup, glucose, and slurries, contributing to their widespread adoption.
In food production, equipment must adhere to strict standards set by the Food and Drug Administration (FDA), which includes regular cleaning and sanitization. Coriolis flow meters are well-suited for this environment as they can be easily cleaned and sanitized to comply with FDA regulations. They are commonly used to monitor the transfer of oils, cooking solutions, and water in the food industry.
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