Basics of Coriolis Mass Flowmeters

At its most basic description, a Coriolis mass flowmeter is a U-shaped tube that vibrates or deflects as fluid flows through it. This type of mass flow meter is based on angular momentum conservation as it applies to the Coriolis acceleration of a fluid. The tangential force felt when walking radially outward on a rotating platform is known as Coriolis acceleration. The force occurs when one's position with the center of rotation changes. 

Principle of Operation  of Coriolis Mass Flowmeters

Fluid enters the U-shaped tube is forced to move vertically in response to the vibrating tube. The fluid flowing into the meter resists the force by pushing down on the tube when the tube moves upward. The fluid flowing out of the meter, having been forced upward, resists, reducing its vertical motion by pushing up on the tube — the tube twists due to the two opposing forces acting on it. The twist is proportional to the mass rate of fluid flowing through the tube. 

Operation and Major Components Coriolis Mass Flowmeters

A mass flow meter includes a vibrating U-shaped tube that generates and measures Coriolis acceleration. In place of the previously described rotational motion, the inlet and outlet of the tube remain fixed. In contrast, the tube is vibrated sinusoidally about an axis formed between the inlet and outlet, typically by a magnetic device located in the bend. Most devices use magnetic sensors on each side of the flow tube to measure the velocities, which change as the tube twists. 

Coriolis mass flowmeters apply to liquid applications such as harsh chemicals, low to medium viscosity, foods, slurries, and blending systems. Gas applications are somewhat limited because the density of low-pressure gases is usually too low to operate the flow meter accurately. 

For more information about Coriolis mass flow meters, contact Power Specialties by visiting https://powerspecialties.com or by calling (816) 353-6550.

Understanding the Operation of Coriolis Flow Meters

Coriolis flow meter (Yokogawa ROTAMASS)

The Coriolis patents for industrial application were filed back in the 1950s, and the first Coriolis flow meter was introduced in the 1970s. The device can accurately measure the density, mass flow, volumetric flow, and temperature of almost all types of fluids.

Coriolis flow meters are used in a variety of industries ranging from oil and gas, petrochemicals, and food to chemical, life sciences, and — particularly — in transfer applications.


How Does a Coriolis Flow Meter Work?

Coriolis flow meters work on the principle of Coriolis Force that was first explained by a French engineer and mathematician Gaspard-Gustave de Coriolis in the 19th century.  The Coriolis force represents an inertial force that acts on bodies in a rotating frame of reference.

Also known as inertial mass flow meters, Coriolis flow meters measure fluid flow through inertia. The device has one or more measuring tubes that vibrate due to the force produced by an actuator. The twisting force inside the measuring tube is directly proportional to the mass flow of the liquid.

Measurement Principle of the Coriolis Flow Meter (1)
(courtesy of Yokogawa)

Coriolis meters have sensors inside the measuring flow tube made of magnet and coil assemblies. The sensors are located both at the inlet and outlet of the tube. A voltage in the form a sine wave is created as the coils move through the magnetic field.

The sine waves are in phase with each other when there is no liquid flow. Once the liquid flows through the tube, the measuring tubes twist depending on the mass flow. The sensors detect the extent of the twist by assessing the phase shift in the sine waves. The difference in phase shift helps in determining the mass flow rate.

Volumetric flow is determined by dividing the mass flow rate by the density of the liquid.

Density change is determined by assessing the change in oscillation frequency in response to the excitation inside the tube. The higher the mass flow rate, the lower will be the frequency change and density of the liquid flow.

Measurement Principle of the Coriolis Flow Meter (2)
(courtesy of Yokogawa)

Lastly, Coriolis flow meters can also be used to measure the temperature inside the tube. The device has sensors inside the tube that can detect temperatures of up to 752 F or 400 C.

The Pros and Cons of Coriolis Flow Meters  

Coriolis flow meters can assess liquid flow in both forward and reverse directions. Advanced Coriolis meters have dual curved tubes that can measure with more accuracy. Moreover, the device with curved tubes is characterized by lower pressure drop, making them ideal in specific situations such as wastewater handling, chemical processing, pulp and paper processing, and oil and gas industries.

Another application of Coriolis flow meters is in the pharmaceuticals and food and beverage industries. They can be used with a straight tube design so they are easy to clean. The flow meters are also used in scientific studies for measuring corrosion and assessing liquids and gases. In addition, the flow meters are used in mining operations to monitor liquid flow rate.

While Coriolis meters allow accurate assessment of fluid flow, they are not free from errors. The device can show inaccurate reading when air bubbles are present. The bubbles create splashing that results in generate inaccurate readings. They change the energy required for tube oscillation, resulting in a false assessment of fluid flow.

A lot of energy is spent in the vibration of the tube, especially in case of large spaces. This can also result in failure of accurate assessment of liquid flow inside the tube.

Installation and Calibration of Coriolis Flow Meter

Coriolis flow meter must be installed with full liquid so that no air gets trapped inside the tube. The meter should also be drained completely before use. The ideal location for the flow meter is a vertical pipe mount with an upward flow of fluid.

The Reynolds number is not a limitation with the Coriolis meter. In addition, there is no need for accounting for swirl and velocity profile distortion. As a result, the device can be used without adjusting for straight runs of relaxation piping to condition the liquid flow.

An air release upstream of the meter should be installed if there is a likelihood of air bubbles. In addition, filters, strainers, or air/vapor eliminators can help prevent air bubbles inside the tube. Control valves can also be installed to increase the back-pressure and reduce the likelihood of flashing.

For more information on Coriolis flow meters contact Power Specialties by calling (816) 353-6550 or by visiting https://powerspecialties.com.

Coriolis Mass Flow Meters

Coriolis Mass Flow Meter (Yokogawa)

A Coriolis mass flow meter consists of a U-shaped tube that deflects or vibrates as the fluid flows through it. The operation of this type of mass flow meter is based on the conservation of angular momentum as it applies to the Coriolis acceleration of a fluid. Coriolis acceleration is that tangential force experienced when one walks radially outward on a rotating platform. The force is only experienced when one changes position in relation to the center of rotation.

Operating Principle

As fluid enters the U-shaped tube, it is forced to take on the vertical movement of the vibrating tube. When the tube is moving upward, the fluid flowing into the meter resists being forced up by pushing down on the tube. Having been forced upward, the fluid flowing out of the meter resists having its vertical motion decreased by pushing up on the tube. The two opposing forces on the tube cause it to twist. The amount of twist is directly proportional to the mass rate of fluid flowing through the tube.

Major Components and Operation

A mass flow meter consists of a vibrating U-shaped tube in which the Coriolis acceleration is created and measured. In place of the rotational motion described above, the inlet and outlet of the tube are held fixed while the tube is vibrated sinusoidally about an axis formed between the inlet and outlet, typically by a magnetic device located in the bend. In most devices, magnetic sensors located on each side of the flow tube measure the respective velocities, which change as the tube twists. Newer models have two U-shaped tubes to measure fluid flow.

Coriolis mass flow meters are generally used in the following liquid applications: harsh chemicals, low to medium viscosity, foods, slurries, and blending systems. Gas applications are somewhat limited since the density of low-pressure gases is usually too low to accurately operate the flow meter. Typically, thin walled tubes are used for gas applications. However, when applicable, the mass flow meter eliminates the need for pressure and temperature compensation and the hardware necessary to implement these functions.

For more information about Coriolis mass flow meters, contact Power Specialties by visiting https://powerspecialties.com or by calling (816) 353-6550.

Operating Principles, Applications, and Advantages of Coriolis Mass Flowmeters

Image courtesy of
Wikipedia

Oscillation without flow
(courtesy of Wikipedia)

The Coriolis effect acts on a medium that is accelerated through a rotating system, like a ball on a rotating disk its movement is straight, however, if the observer turns with the disk the ball is apparently deflected.

The same effect occurs with a water hose that rotates around its own axis, like a skipping rope. As soon as water flows through the host also twists. The twisting is stronger or weaker, depending on the amount of water flowing through the hose.

Oscillation with flow
(courtesy of Wikipedia)

The Coriolis effect also appears with an oscillating movement, and in a Coriolis flowmeter, two symmetric metal tubes are set vibrating by an internal driver coil. The tubes oscillate with a resonance frequency similarly to that of a tuning fork.

The oscillation is measured precisely by two pick-ups at the inlet and outlet sections. If liquids or gases flow through the tubes, a phase shift occurs the pickups measure the spatial and temporal displacement (twist). The amount of twist is proportional to the mass flow rate of fluid passing through the tubes. The greater the amount, the stronger the tubes oscillate outwards.

Finally, sensors and transmitters are used to measure the twist and create a linear flow signal as an output for monitoring and control.

Coriolis mass flowmeters are widely used throughout the process measurement and control field. Their basic operating principle, combined with modern sensor and signal processing technology,

Yokogawa ROTAMASS
Coriolis Flowmeter

provide a list of positive aspects.

• Directly measure mass flow rate based on the principle of measurement.
• Measure the mass flow rate with high accuracy of ±0.1%.
• Provide a wide usable measurement range.
• Deliver density measurement based on oscillating frequency.
• Not materially impacted by fluid viscosity or density.

Coriolis flowmeters also do not need straight pipe sections upstream or downstream of the flowmeter. They also have the ability to measure non-conductive fluids.

The video below is produced by Yokogawa, a world class manufacturer of industrial process measurement and control instrumentation. It provides a clear and insightful illustration of the Coriolis principle and how it is used to provide accurate mass flow measurement.