best starting point to build a homebrew centrifuge?

???

Aw yes! That is always a good starter for a LOOOOng thread. :-)] Watch you have done Larry. ...lew...

Come again Nick ? a ton is 2000 pounds. ...lew...

A ton is 2000 lb so your figures suggest 0.75 KT.

It is very unlikely that the motor was delivering 100 HP to acceleration for even an appreciable part of that time. If the cetrifuge were a 100 G 'fuge running at 300 RPM the energy would be about 49,000 joules. That's about the kinetic energy of a

2500 lb automobile travelling at 21 mph. The 100 kg mass in the 'fuge would have a tangential velocity of about 70 mph.

It can be misleadingly dramatic to cite energy in terms of tons (or pounds) of TNT (or dynamite). Propane has about 10X the energy per lb that TNT does. TNT just releases it more suddenly.

...

No - .75 ton or .00075 KT

Erm, it would doubtless be "killa" if you were standing nearby at the time of an uncontained failure but it isn't "kilo" (1.5 kT = 3 million pounds, said of the blast aspect of nuclear weapons in broad comparison to TNT).

I also think the amount of time needed to spin it up is irrelevant to a calculation of how much rotational kinetic energy it has when done (though perhaps highly relevant to how much energy will drain out of you when you get the electric bill!); and that's the key fact for safety.

BTW, I think the energy use is 268 MJ, not 3 GJ, if you run a 100 hp (input) motor for an hour. Check my logic... A horsepower is 745 W. A watt is a joule per second, so if you do that for 3600 seconds you get 268,200,000 joules.

See for instance

(one of the most eminently bookmarkworthy and explorable sites around)

--Joe "Whatever the numbers, centrifuges are built strong, and operated according to safety instructions, for a reason" Chew

Assuming you lose nothing to friction during that hour of the giant heavy drum spinning.

- Logan

Sure enough... that's why I took the liberty of specifying "100 hp (input"). That may not have answered quite exactly the question asked, but lends itself to doing a finite-envelope model without having to look around in the bottom drawer for another envelope.

Accounting for real-world efficiency, the actual power usage curve, and other things you'd want to tease out if you were designing or specifying equipment, rather than just getting a quick calculation onto the right order of magnitude, makes for big equations with a lot of moving parts.

Cheers,

--Joe

Agreed. I was just trying to imply that an hour's worth of friction might change the energy by an entire order of magnitude.

On the other hand, if it truly takes an hour to get up to speed, then maybe friction is only a small part of the battle...

- Logan

Tangential

On Thu, 27 Oct 2005 21:37:10 GMT, with neither quill nor qualm, Lew Hartswick quickly quoth:

GOTCHA!

-- SAVE THE PARROTS! Eschew the use of poly! ----------

Poly-free Website Development

Small kilotons :-) One site says 100 grams of dynamite is 0.43x10^6 joules.

Nick

.75 kt

Gunner

"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.

Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner

that's wrong too

i

There is no friction.An eddy current drive would be magneticly coupled.

The energy difference between what the motor supplies and what the load absorbs is dissipated as heat in the eddy current clutch. Just like a friction clutch would except that there are no wearing surfaces.

At the instant of startup, the drive is dissipating all the power and the load is absorbing none. At the instant of full speed, the load is absorbing all the power and drive is dissipating none. (This assumes no electronic ramp drive to the eddy current clutch) The actual solution to the stored energy problem is a nice little calculus problem but one can approximate by assuming that half is dissipated and half absorbed by the load. That's a spit-load of energy! I'd certainly not want to be in the building if the rotor disassembled itself.

John

I believe it is a couple hundred sticks of the stuff, maybe a whole ton of it. Although, it is the frissance of the dynamite, not the energy that makes it dangerous. Your typical chocolate chip cookie contains more chemical energy than a stick of dynamite. About the only way to fully realize this is to notice how flour, with an incendiary trigger, can make an adequite fuel air explosive.

Which is just the say the cookie not only tastes great, it has less filler