In literal terms, a  Coriolis effect is used to explain wind current deflection in geography classes. But when it comes to the world of Process Automation, Automation Engineers will immediately start thinking about a Coriolis flow meter. The article explains this concept in details.

What is the Coriolis effect?

Even though we might have forgotten about the Coriolis effect, we do remember Newton’s laws of motion. The first law of motion, also known as the law of inertia, states that an object will stay in the same state, either resting or moving uniformly in a straight line, if no external forces affect it. The important bit to remember here – in a straight line.

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Got the law fresh in your mind again? But this law just applies to an inertial frame of reference. What if we have a rotating frame? Hers is where the Coriolis effect comes in. We shall illustrate this with an example.

Let’s say we’re playing with a friend in a merry-go-round, with the friend in the middle and we are on the outer edge. For the purpose of this example, we’ll say that there is no wind at the moment, which means no external forces interfere with the ball’s path.

The merry-go-round is still and our friend throws the ball at us. With no wind interference, the ball goes from the center of the merry-go-round out to us in a straight line. Now, when our friend throws the ball at us, it’ll still go in a straight line in an inertial reference frame.

However, in a rotating perspective, the ball makes a curve. this curve is what we call as the Coriolis effect.

Analyzing the example, we can see that the Coriolis force describes a matter of perception. The ball still goes straight, but we see it making a curve because we are moving. Since there’s no actual force affecting the ball, many people now call it Coriolis effect instead of force. But for mathematical purposes, we still say Coriolis force for the inertial or fictitious force.

 

To know more about the types of flow meters in the market, you can read the Visaya Article on Flow Meter Types

The math

Although no force affects the ball trajectory in the merry-go-round, we and our friend in the rotating frame see it making a curve. We can calculate the acceleration here because the ball’s inertia is proportional to (a) the velocity of the ball in the straight line and (b) the velocity of the merry-go-round’s rotation.

We call this the Coriolis acceleration and use the following formula to reveal it:

ac = 2*ω*v

  • ac = Coriolis acceleration
  • ω = rotational speed (merry-go-round)
  • v = velocity perpendicular to the axis of rotation (ball in a straight line)

If we go back to Newton’s laws of motion, to the second one specifically, we can find a relation between force and acceleration:

F = m*a

  • F = force
  • m = mass
  • a = acceleration

So when we multiply both sides by the mass of the object, in our example the ball, and replace the acceleration with the Coriolis formula, we can find the Coriolis force with the resulting formula:

Fc = m*2*ω*v

So to wrap up, the Coriolis force is proportional to the angular velocity, rotational velocity, and mass. And that’s why we can use a Coriolis flow meter as a mass flow meter.

Other applications of the Coriolis effect

We used the merry-go-round example to explain the effect. However, we have another – very big – object that also creates a rotating reference frame by spinning around an axis.

Meteorologists use the Coriolis effect. Winds blow across the Earth from the poles (high-pressure systems) to the equator (low-pressure systems). However, at the equator, they move faster than at the poles, because a point in the equator has to travel farther in 24 hours than a point near one of the poles.

Coriolis effect on earth
Courtesy of Encyclopedia Britannica

So, let’s recall the merry-go-round example again, but with the Earth as the rotating frame. If we’re at the North Pole and throw a ball to our friend at the equator, then the trajectory will look like it curves right, because he’s traveling faster than we are.

If our friend throws the ball back, then it will seem to him that the ball also curves right, because we’re slower than him. So the winds in the southern hemisphere deflect to the left and in the northern hemisphere to the right because of the Coriolis effect.

In the past, navigators used this effect to forecast the so-called trade winds that influenced travel between Europe and South America. Airplanes and rockets also experience it, so pilots must take the Earth’s rotation into account when flying long distances. If they try to travel in a straight line between two places, they’ll probably miss the target!

 

If you would like to know more about Coriolis flow meters and how they are used, check out the Definitive Guide on Coriolis.

 

To know more about Coriolis flow meters, you can get in touch with our engineers and we will be happy to help.

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