Operating Principle of A Coriolis Flow Meter
There are two basic configurations of coriolis flow meter: the curved tube flow meter and the straight tube flow meter. This article discusses the curved tube design.
The animations on the right do not represent an actually existing coriolis flow meter design. The purpose of the animations is to illustrate the operating principle, and to show the connection with rotation.
Fluid is being pumped through the mass flow meter. When there is mass flow, the tube twists slightly. The arm through which fluid flows away from the axis of rotation must exert a force on the fluid, to increase its angular momentum, so it bends backwards. The arm through which fluid is pushed back to the axis of rotation must exert a force on the fluid to decrease the fluid's angular momentum again, hence that arm will bend forward.
In other words, the inlet arm is lagging behind the overall rotation, and the outlet arm leads the overall rotation.
The animation on the right represents how curved tube mass flow meters are designed. When the fluid is flowing, it is led through two parallel tubes. An actuator (not shown) induces a vibration of the tubes. The two parallel tubes are counter-vibrating, to make the measuring device less sensitive to outside vibrations. The actual frequency of the vibration depends on the size of the mass flow meter, and ranges from 80 to 1000 vibrations per second. The amplitude of the vibration is too small to be seen, but it can be felt by touch.
When no fluid is flowing, the vibration of the two tubes is symmetrical, as shown in the animations.
The animation on the right represents what happens during mass flow. When there is mass flow, there is some twisting of the tubes. The arm through which fluid flows away from the axis of rotation must exert a force on the fluid to increase its angular momentum, so it is lagging behind the overall vibration. The arm through which fluid is pushed back towards the axis of rotation must exert a force on the fluid to decrease the fluid's angular momentum again, hence that arm leads the overall vibration.
The inlet arm and the outlet arm vibrate with the same frequency as the overall vibration, but when there is mass flow the two vibrations are out of sync: the inlet arm is behind, the outlet arm is ahead. The two vibrations are shifted in phase with respect to each other, and the degree of phase-shift is a measure for the amount of mass that is flowing through the tubes.
Read more about this topic: Mass Flow Meter
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