Centrifuges

[runwestierun]

Does anyone with a copy of the book remember what it said about centrifuges--what the recommended capacity and RPM capabilities are?

[Chris Hennes]

They only speak to restaurant use, and suggest a machine with a three liter capacity that can spin at 30,000 RPM. One gets the sense that they are well aware that centrifuges will likely remain unobtainable resources for nearly everyone, but that they had fun with theirs and wanted to talk about it.

[ermintrude]

As a kid, way way back, when chemestry sets were real cheistry sets that you could blow things up with, make poison gases and have a whole load of fun, unlike know when just having those chemicals would get you arested as a terorist or drug laboritory I rememer improvising a centrifuge using a circle of wood with radiall spaces for the test tube and my grandmothers spin dryer Something like this not sure it would compare at all to a 30,000 rpm centrifuge but it was fun for me to mess around with and did manage to seperate some things (and make a mess when test tubes flew off inside.

Finally remember it's not just RPM it's also the diameter of the rotors. The forces at the edge or a rotor 10cm in diameter at 30,000 rpm is a lot less than a 1m rotor at the same RPM.

[andiesenji]

They only speak to restaurant use, and suggest a machine with a three liter capacity that can spin at 30,000 RPM. One gets the sense that they are well aware that centrifuges will likely remain unobtainable resources for nearly everyone, but that they had fun with theirs and wanted to talk about it.

Any large city should have at least one place that sells used medical and laboratory equipment.

Call and ask if they have one or more in stock.

These folks do have prices but they are open to negotiation. Bargain, it usually works.

We bought a used centrifuge - I think it held ten 20 milliliter vials - from such a place in L.A. for $125.00 which was considerably less than their original asking price.

When they buy these things from doctors offices and from labs, they pay ten cents on the dollar or less.

You do not want a "Micro" centrifuge.

Here's a sample of listings from one place.

Edited February 22, 2011 by andiesenji (log)

[gfweb]

So what are you spinning in 20 ml volumes?

[runwestierun]

They only speak to restaurant use, and suggest a machine with a three liter capacity that can spin at 30,000 RPM. One gets the sense that they are well aware that centrifuges will likely remain unobtainable resources for nearly everyone, but that they had fun with theirs and wanted to talk about it.

Any large city should have at least one place that sells used medical and laboratory equipment.

Call and ask if they have one or more in stock.

These folks do have prices but they are open to negotiation. Bargain, it usually works.

We bought a used centrifuge - I think it held ten 20 milliliter vials - from such a place in L.A. for $125.00 which was considerably less than their original asking price.

When they buy these things from doctors offices and from labs, they pay ten cents on the dollar or less.

You do not want a "Micro" centrifuge.

Here's a sample of listings from one place.

Thank you, Andie. I am a retired biochemist and I just can't buy a used one for the kitchen. I know what we put in them. I've seen lots and lots of new ones in the $125 range with a 90-150 ml capacity and about 3000rpm's. I guess I'll just have to wait for the book to see if that might be enough. I am also quite curious to know what kind of g's my washer's spin cycle pulls. This whole thing is just so fascinating.

[dcarch]

RPM is an important factor.

The other equally important factor is the diameter of the rotating device.

dcarch

[runwestierun]

RPM is an important factor.

The other equally important factor is the diameter of the rotating device.

dcarch

Yes. And certainly the one Chris mentions that spins 30Krpm with a 3L capacity would have a large rotor. I am going to try to build a "rotor" for my washer's spin cycle and see what happens. I understand that it would be nothing like Nathan's machine. My intuition tells me that I wouldn't need anything that fast or powerful to pull fat out of a pea emulsion, though. I am probably wrong but I am going to try.

[dcarch]

Washing machine has a low HP induction motor. They are less than one horse power and very slow speed (less than 3,600 rpm). Also, you can't change the direction of rotation.

To get any usefulness, I think you will need may be a two HP router universal motor (more than 20,000 rpm)

At that speed, you will need high stength material, and a very well balancing system. You can get killed if it breaks.

dcarch

[technophile50]

I think what Dr. Myrhvold's lab has is one of these. There are various heads available; the one here, the 4th pic down looks like a GSA rotor, 3 L capacity, 13000 rpm, 27500 g's. There aren't any rotors which will hold 3 liters and run at 30,000 RPM. The higher speeds (and g forces) are only for smaller volume rotors made from titanium or carbon fiber ($$$$).

These machines, if improperly used, are MUCH more dangerous than your average kitchen equipment. If you are thinking about buying one of these, or building your own, PLEASE read this.

"Rotor Failure is much less common than the kind of incidents listed above, but can present extraordinary safety risks."

"During rotor failure the entire centrifuge can move with enough force to crack concrete walls."

They weigh about 700 pounds. Consider the energy required to accelerate something of that weight, to a speed that would crack a wall, in only a few feet.

I used to work in research at Duke University, and was involved in analyzing the cause of failure and rebuilding a centrifuge after a rotor failure at 30,000 rpm. Because of the number of hours on the rotor, it was supposed to be de-rated to lower RPM; the user chose to run it at higher speed to save time, and thought that since it worked for a while, it would continue to do so. The stainless steel refrigeration liner (which you can see surrounding the rotor in the pic from Dr. Myrhvold's lab) was shredded into confetti. The titanium rotor was disintegrated into thousands of pieces, the largest of which about half the size of my fist. The lid, sides, and bottom of the tub are armored with 1/2-3/4" thick steel which contained the explosion, but it took two of us leaning on a serious crowbar to pry the lid open because of severe deformation.

If you mount a couple of jars on the shaft of a 2 HP industrial router, without a full understanding of the forces it will create, you're gonna make shrapnel.

"You can get killed if it breaks."

Absolutely. (This rotor was likely running at 65k rpm, but with much smaller volume. YMMV)

Be safe.

[dcarch]

I repeat, "You can get killed if it breaks." Not seriously injured, but mortally killed.

You will ask how two horsepower can be so powerful.

It’s all physics. Assuming you can ignore air friction, it takes no energy to move mass horizontally once you overcome initial inertia. You can actually move a ten ton object to very high speed. The potential energy just keeps on building up more and more to an immense degree.

A device such as this will need to have very special consideration in design, construction, and use. For instance, ball bearings for rotating parts will fail quickly; you will need special specification roller bearings to take the kind of force.

dcarch

[gfweb]

I'll second that. The bigger and faster the 'fuge the more potential for problems. A home built rig would require a skilled machinist to do it right. Balance is everything. A little off and the thing would walk across the floor or off the counter...if it didn't shake itself apart.

Small blood centrifuges can be had at reasonable price (used on ebay) and could handle about 80 cc divided among several tubes. Probably a better bet. They are fast enough to spin down bacteria, so they ought to handle most kitchen tasks.

Edited February 23, 2011 by gfweb (log)

[dcarch]

I don't remember exactly. I think jet engines use metallurgical single crystal metals for each of the turbine blades. This is to avoid hidden material flaws. Even that, a bird gets sucked in the engine can upset the balance and explode the engine.

dcarch

[natasha1270]

I wonder if a centrifugal omega juicer wouldn't suffice?

[Chris Hennes]

All we are doing with a centrifuge is accelerating the action of gravity (OK, sometimes we are accelerating it A LOT). So pretty much any centrifuge is going to be better than no centrifuge ... but it's not like this is a critical piece of equipment. One thing is for sure: you should NOT be trying to build your own that can equal or even come close to the power of a lab centrifuge. Playing around with your washing machine is safe, and it may even be modestly effective. But please don't go mounting things to your router!

[ermintrude]

When your talking "Washing Machine" I assume you mean those in where the drum is horizontally mounted with the hole at the top. In Europe the drum is comenly mounted vertically with the hole in the the side, these won't work as when slowing down the test tube will get remixed when the force on the tube cannot over come gravity. Hence using a dedicated spin drier as in Europe these are mounted vertically. For seperating larger particulates it does work, fining a way to keep your tubes in place is the trick, luckilly as the macines are in a steel drum it's safer, but if glass or stuff goes through the holes in the drum it could ruin the machine.

[runwestierun]

I am not trying to build Nathan's centrifuge. I won't use glass in my washing machine. I seriously doubt if my washing machine pulls more than 100 g's. I don't want 10,000 g's in my home, and I don't want a $20,000 centrifuge in my home. I just want to see if I can secure some plastic vials with styrofoam and duct tape in my washer and spin water from fat from solid. Right now I am working out how to stop the machine without sloshing everything around. This is fun.

[technophile50]

Here's a discussion of some alternate/adjunct clarification methods.

http://www.cookingissues.com/2010/07/20/simple-agar-clarification-1-year-anniversary-plus-a-rundown-of-current-clarification-techniques/

You're right - tinkering is fun. And a little forethought, like you clearly have done, to rule out hazards like broken glass, will make it safe.

If you are washerfuging liquids that can gel or be frozen, you might try putting them in hot, and adding crushed CO2 to the bottom. With the correct ratio of dry ice to the liquid you're separating, the hot liquid could separate, then cool, gel/freeze so it wouldn't remix. Since water won't hurt the washing machine, ice could be used.

There are old tinkerers;

There are bold tinkerers-

"Let me just say this: BAD IDEA. We call it the dangerfuge. It has no protective casing at all – just a 50 year old aluminum rotor spinning like a bat-out-of-hell in the middle of the room. It doesn’t even have a switch, just a plug. It is the scariest piece of equipment I have ever fired up (and that’s saying A LOT) and I never intend on firing it up again."

Unfortunately, there are a few old bold tinkerers, which can give a false sense of security to the rest of us.

I once had to replace the power cord on a centrifuge like the one pictured, with a hospital grade plug and 3 wire ground, to comply with new safety regs . The 80 year old emeritus professor whose lab used it found that amusing. He plugged it into a timer, retreated to his office until it shut down, and didn't allow others into the lab while it ran.

[dcarch]

A 12 inch diameter circle rotating at 20,000 RPM will have a peripheral (Tangential )

speed of 1,047.2 feet per second.

That is much faster than bullets from many BB rifles.

dcarch

Edited February 23, 2011 by dcarch (log)

[Paul Kierstead]

OK, we get it, they can kill you. So can bicycles (quite easily I'll add). Don't try it, but if you do ....

I think the fundamental question is: Does a higher .. force ... centrifuge do a better job of separation, or just a faster one, for this kind of application? If I ran a centrifuge that applied, say, 1/10 the force for the same volume of liquid, but ran it longer, would the same level of separation occur? How about if I ran one with 1/10 the force but a lot less volume?

[lancastermike]

It is a well know fact that i am not very enlightened in the modernist ways. I hesitate to ask. Of what purpose would a centrifuge of the kind being discussed here serve the average home cook? I mean, what am I supposed to be separating?

My apologies to all for being such a dunce.

[Chris Hennes]

I'd say that a centrifuge is of no use whatsoever to the "average home cook." There are many products you can make in it that cannot be achieved in any other way, but they are hardly the sort of thing you expect from a home kitchen. Then again, a smoker doesn't find a place in many average home kitchens either, but I think we can agree that you can make some mighty fine food with it.

[dcarch]

I'd say that a centrifuge is of no use whatsoever to the "average home cook." ----

Really?

I actually think you can make crystal clear ice cubes with it. It will definitely separate the air bubbles and any impurity.

:-)

dcarch

[Paul Kierstead]

Well, its a tautology of sorts; you aren't an average home cook if you have a use for a centrifuge.

[runwestierun]

It is a well know fact that i am not very enlightened in the modernist ways. I hesitate to ask. Of what purpose would a centrifuge of the kind being discussed here serve the average home cook? I mean, what am I supposed to be separating?

My apologies to all for being such a dunce.

Mike,

I became interested in rigging a centrifuge when I read about Nathan Myrvold's pea butter. He centrifuged pureed peas into water, fibrous starchy solid and pea "butter". He used this lipid layer on crustini and said it was delicious. I believe him. If I can rig a strong enough spinner to get this kind of separation out of stuff I already have, well then buy me a new dress and call me Rube Goldberg, it'll be a good day.

Edited February 23, 2011 by runwestierun (log)