Pumping Liquid Nitrogen

Lets see: The rotor gets smaller. The stator gets thinner and its circumference decreases. Unlike a solid ring, the interior of a rotor is (usually) slotted, so its circumferential shrinkage doesn't reduce the ID in the same manner as with a solid ring. The pole pieces do shrink in length, increasing the stator ID.

I've seen the results of the reverse problem, heating a motor with a very small air gap to the point that the rotor hit the poles.

Wow! Things have sure changed since I studied physics. You can pressurize liquids now? Easier than gas no less! I guess that means my car brakes aren't going to work anymore. Thanks for the heads-up, I could have been killed.

True, but the difference in shrinkage betwen the rotor and stator would have to be greater that the shrinkage of the stator in order for the gap to become larger.

The circumference, inside and out, decreases. It gets thinner, but the inside diameter does not increase; that would be absurd.

If the rotor and stator are made of the same material (they are in an induction motor, made of laminated steel) and are the same temperature, then the gap will get smaller as the temperature decreases.

If the materials are not equal (e.g., aluminum housing or rotor, permanent magnets, etc.), behavior may differ.

Most likely, in a DC motor, the rotor heats up more than the stator/housing, so the gap will tend to shrink, regardless of the outside air temperature. Different types of induction motors (wound, fixed and permanent rotors, etc.) may behave differently.

Tim

-- Deep Fryer: A very philosophical monk. Website @

Do you know the difference between "pressurize" and "compress"?

Best regards, Spehro Pefhany

I was thinking the off portion would be a second or two. Not enough to fill the Dewar, just let in whatever has been generated. I was assuming there would be enough of a head on the nitrogen to handle a short off period. A nice wide input valve and a short off cycle.

Well, there is that :)

Robert

Sometimes. Obviously this wasn't one of them. ;-)

There we go.

How large is the diameter of the pipes in the percolator?

Robert

Absurd? That's how one gets a press fit bearing race on a shaft (by heating it).

That may be the case. I've seen generators fail at high temps by rubbing the rotor/stator due to decreased clearance. At first, it seemed to be counter intuitive.

That's possible as well. Behavior of a stator and rotor in contact with LN2 may have different effects than a machine cooled mainly from the outside.

Well, I've never had any intent to hurt you, and if some of my offhand comments, intended as humour, were a little sharp or hurtful, then I apologize.

Sorry to hear about your medical condition - I wish I knew the right thing to say.

Get Well, OK?

Thanks, Rich

Not simultaneously. The bearing (or other socket) is kept at room temperature or heated, while the shaft (or peg, or...) is cooled or kept at room temperature, respectively. Heat makes the inner diameter expand, not cold.

Tim

-- Deep Fryer: A very philosophical monk. Website @

And you have exactly one chance to get them into the correct position before the temperature equalizes...

Best regards, Spehro Pefhany

...which is why we design and use jigs rather than trying to eyball it.

I don't recall the pipe size anymore but it was way too big for just a few liters per day. You could calculate the optimal diameter using the rather complicated methods described in "Two Phase Flows and Heat Transfer" by Ginoux, or you could wing it and try 1/4" OD 3/16" ID tubing or therabouts. Effective insulation will be the hard part.

Having once spent 3 days on a single cryo transfer choking calculation, I suggest the "wing it" approach :-).

"Guy Macon" skrev i en meddelelse news:A_6dncuGjuhtK snipped-for-privacy@giganews.com...

Lucky bastard! That what I want for chrismas.

How about a "bubble pump" or "vapour lift pump"?

Basically the principle used by aquariums. That way you "only" need to pump very cold nitrogen gas - which could be the gas boiled off from the CPU cooler

That makes me wonder. You are in fact creating some sort of heat-pump which doesn't sound very efficient (you will be heating the room!). Isn't it easier to use a modified air-conditioner? All you need is to evaporate gas in the CPU's heatsink and chipset's heatsink.

Pretty much, but it still depends on the materials TCE.

That's how you get a press fit bearing race _off_ a shaft as well. Not much chance of maintaining a temp difference between them in this case.

Except for certain circumstances: I've heard of CNC heads which have ferrite transformers in the cutting head to inductively heat the spindle, expanding it away from the cutter's shank quickly. Sweet!

Tim

-- Deep Fryer: A very philosophical monk. Website @