Tuesday, May 31, 2016

The Coriolis Effect Simply Explained. And Then Not So Simply Explained.

This video very simply (and very elegantly) demonstrates the Coriolis Force through the use of a ordinary garden hose.

An Now the Not So Simple Explanation

This force occurs, when the medium being measured is flowing at velocity ν through a tube that is rotating around an axis perpendicular to the direction of flow at angular ϖ.
coriolis force

When the medium moves away from the axis of rotation it must be accelerated to an increasingly high peripheral velocity. The force required for this is called Coriolis force, after its discoverer. The Coriolis force reduces the rotation. The opposite effect occurs, when the medium flows towards the axis of rotation. Then the Coriolis force amplifies the rotation.

The formula for the Coriolis force is as follows:
coriolis force

The entire measurement tube is deformed slightly by the Coriolis forces, in the way shown. This deformation is registered by movement sensors at points S1 and S2 .

For practical exploitation of this physical principle, it is sufficient for the tube to perform sympathetic oscillations on a small section of a circular path. This is achieved by exciting the measurement tube at point E by means of an electromagnetic exciter.

Coriolis flowmeters use the oscillating movement of two symmetric metal tubes that are made to vibrate from an internal driver coil.  When liquids or gases flow through the tubes, a phase shift occurs (like you see in the hose) and pickups measure the “twist” and then relate that value to the actual flow. In other words, the amount of twist is proportional to the mass flow rate of fluid passing through the tubes. The greater the twist, the larger the distance between, and the greater the flow.

The general construction of a Coriolis mass flowmeter looks like the following:
Coriolis flowmeter
Coriolis flowmeter diagram (Yokogawa)