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What Is a Centrifugal Separator?

Centrifugal separators use different types of force to divide two or more substances.
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  • Written By: Heather Phillips
  • Edited By: Michelle Arevalo
  • Last Modified Date: 27 September 2014
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A centrifugal separator is a machine that uses centrifugal, gravitational, and inertial forces to divide two or more substances. This device can be used to separate solutions, gas mixtures, or other matter that can be physically parted. Centrifugal separation occurs when a mixture in the machine's chamber is spun very quickly, and heavy materials typically settle differently than lighter ones. Centrifugal separators have a wide variety of applications, in many industries.

When a mixture enters the spinning chamber of a centrifugal separator, distinct substances within it are affected differently by the force created by the spinning. For example, gravitational force generally pulls heavier particles down more quickly than lighter ones, and the force of inertia affects the mixture as it spins. As the substances separate, they can be collected in various ways. Sometimes, they are collected mechanically, but, other times, they are physically separated. One method of this can be by screening.

Heavier solid particles are often allowed to settle as they slide down the walls of the separator. They are then typically collected from the bottom. Generally, a gas can be purified by spinning any particulate matter and moisture out of it. The gas can then be collected, as it rises to the top and through an exit opening in the centrifugal separator. Liquids of different weights and viscosities may be divided into differing chambers of a separator as it moves.

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Some of the applications in which a centrifugal separator can be used include dividing cream from milk, sand from gravel, and oil from water. The food and beverage industries often use these machines in the making of syrups, sugars, and malt liquors. Manufacturers of paints and varnish also use these machines, as do pharmaceutical manufacturers, animal feed makers, and the ceramics and abrasives industries.

A particular kind of machine, known as a centrifugal water separator, is often used to remove water from compressed air. This is important because water in the air can cause rust to occur in the metal components of a compressor, and in any attached machines or tools that utilize the compressed air. Typically, any condensate is spun out of the air by the separator, and collected in bowls where it is then pumped out of the compressor.

As the technology of the centrifugal separator has progressed, new applications have been found for its use. There are devices known as ultracentrifuges that are being used to separate larger molecules into their components. This advancing technology is particularly useful in the pharmaceutical industry.

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anon275664
Post 5

If you are confused about why heavier particles go to the outside, try spinning around with your arms out, and note the force which you can feel pulling your arms outwards. Then do the same again, but holding something heavy in each hand, like two heavy bags or something, and note the outwards force now pulling the bags (and your arms) out. It should be much more.

This is the force on the heavier particles that is causing them to end up on the outside, and the lighter particles (when you weren't holding anything) end up on the inside. Hope this helps you to understand the process better.

matthewc23
Post 4

@stl156 - That is an interesting point. I don't remember all my physics, but wouldn't it be sort of like throwing a baseball versus throwing a wadded up piece of paper? The force applied to the heavier materials in a centrifuge would cause them to do more work and they would push the paper out of the way. Something like that, at least.

I did like the mention of liquid separation in the air compressor. I had never really thought about all the water in the air, and how you probably wouldn't want that in your tires or something. If there were a lot of water, you would eventually have water settling in your tires, and that would be bad.

stl156
Post 3

@kentuckycat - The size really just depends on what you are separating. I used to work in a plant biology lab, and what we would do is crush up plant leaves and stems and then separate out the different proteins. In that case, the centrifuge was just about a foot and a half in diameter, and we put everything in test tubes. I have never seen a dairy separator, but I would have to imagine it is quite large, so that they can process a lot of milk all at once.

At some point, though, I would think the centrifuge would start to get unstable. If you have a lot of liquid spinning around very quickly, there would be a lot of force pushing out on the device.

Even though I have used a centrifuge before, I never really understood how the centrifuge separation worked. The heavier stuff gets sent to the outside, but it seems like the lighter material would travel easier, so it should be on the outside.

kentuckycat
Post 2

The thing I am really wondering about is, after everything has been separated, how do they get the different parts permanently separated? Using the cream separator example from the article, you might have the heavier stuff at the one end and the lighter at another, but if you just let them sit, they will rejoin eventually. What do they have to do to skim the lighter stuff away from the heavier material? They must have some sort of centrifugal separator or something, right?

Also, how big are these centrifuges? I am imagining a large, spinning wheel. Is that what they look like, or are there different kinds depending on what kind of work you need them for?

Emilski
Post 1

Wow, I didn't realize there were so many different uses for centrifuges. I think the example I am most familiar with is separating blood.

For a while, I used to donate blood plasma, and part of the process is having the blood circulated through a machine where the plasma is removed from the rest of the blood. One of the days I was there, I asked a technician how they got the plasma separated, and they said that the blood goes into a little reservoir, and then it spins really fast.

Since the plasma is heavier than the rest of the blood, it goes to the outside of the reservoir, and then they can separate it that way. After the plasma is removed, then they can return the rest of the blood cells back into your body.

I am curious who was able to realize how to do something like that.

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