Pumping Liquid Nitrogen

Wouldn't your time be better spent correcting the it's/its errors on your site, beard-boy?

"Before examining Structured Engineering, it is instructive to examine it's predecessor,"

Argh.

Anyways, go spend some time with a woman this Christmas instead of an inert box of crap that only excites teenagers and 45 year old teenagers. With horror-beards. At least it's not a neck beard, I suppose.

I just got involved with cooling a microscope chamber. The first design, not by me, was a failure in every respect. Trying to cool a copper chamber by a copper pipe about a foot long, from a thermos filled around the end coil of the copper tubing. Gas was allowed to go through the tube. Temp drop after several minutes was a couple degrees below room temp. Next design gets the fluid right around the chamber.

I also recently was working with a pumped unit, rather expensive, out of date, and didn't work right. Sometimes these things are not repairable or is too costly. I would be interested in knowing what type of pumps are suitable for moving the fluid around.

greg

'Guy Macon' wrote, in part: | A: Because it messes up the order in which people normally read text. | | Q: Why is top-posting such a bad thing? | | A: Top-posting. | | Q: What is the most annoying thing on Usenet? ______

Being that you are more interested in heat than light, why the post on liquid Nitrogen in the first place?

Phil Weldon

How about a magnetically coupled centrifugal pump. A magnet in a rotor can be spun by a magnet on a motor or by coils that emulate a rotating mag field. This is not too different than my interest in magnetic stirrers. (See DIY Magnetic Stirrer post and my posts on etchant pumps.) Some liquid nitrogen can probably be fed to the field inductors to enhance the drive performance. Likewise I think the rotor magnet gets a boost too from the cold temperature. (I can't recall what magnets do when super cooled.)

I"ve been tempted to design a pump like this, but it would be to pump etchant. If you make one, let me know.. :)

D from BC

True. Some time ago, I had to stop someone from setting up a refrigeration system with the LN2 generator located in a different area. It made too much noise.

Resistor maybe. Evaporate a little nitrogen, use the pressure to move the rest. Use the exhausted nitrogen from the other end to keep the rest of the box cool and dry.

Robert

How about a percolator arrangement; can't get much simpler and no moving parts? I think that if you submerge one end of a piece of tubing in the LN2 you will get spurts of LN2 forced up the tube. I don't know what geometry would be best but I think a few small entrance holes with area a good bit less than the inside cross sectional area of the tubing. Maybe look online at pulse jets for ideas, or your oldfashioned coffee pot :-).

-- Regards, Carl Ijames carl dott ijames aat verizon dott net (remove nospm or make the obvious changes before replying)

Indeed, what one would expect from someone with little grasp of the English language.

I'm a great believer in the passage that you quoted above. That's why I don't engage in *arguments* "on the internet". (Hint: Look up the word, re-read my post...)

Oh, and from your website:

"HARDWARE DESIGN; I am an *expert* in *all areas* of electronics, including analog, digital, microcontroller, high-power, low-power, high volume, aerospace and consumer electronics."

(My ** emphasis)

Seems that you should be helping us instead of only coming here for help. Mr. Expert.

Buh-bye.

That was my original thought as well, and is the method I have used in larger cryogenic systems. There is even an outfit that will sell you a microcontroller-operated sensor/valve that you put on the gas vent to regulate flow through the liquid output

-- sort of like an aerosol can that never loses pressure.

The problem is that those systems all depebded on deliveries of liquid nitrogen, so getting a full dewar to self-pressurize was no problem. The system I am looking at here generates liquid nitrogen from the air (it was originally used in a medical office) and gravity-fills a half liter dewar. I am pretty sure that if I let it self-pressurize the gas will escape through the intake tube rather than by forcing liquid out through the output tube. thus the question about a pump.

That's a really good idea! If the percolator doesn'y do it, I could also use check valves; I haven't found a suitible pump, but small teflon check valves are easy to get. A resistor controoled by a BasicX controller

Thanks! I will let you know if I can make that work.

I don't think motors mind low temperatures too much as long as the materials tolerate them (I'm thinking about bearing lubricants, brittle insulation, etc.)

Some superconductors don't do too well in high magnetic fields, but I think that is a problem with the older generation type. Superconducting rotating machines are a very interesting field of R&D. As long as the motor doesn't depend on superconduction properties at LN2 temps, it should run fine.

There are quite a few pump designs (both centrifugal and others) in which the impeller, bearings, rotors, etc. are immersed in the pumped fluid. The stator windings are potted to keep the fluid out. Small water pumps and immersed gasoline pumps in your car's tank are built this way.

With an LN2 environment, the rotor and stator might shrink a bit, so the design should account for a slightly larger air gap than at room temperature.

^^^

You mean smaller gap?

Tim

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

Ah, any reason you need continuous flow?

Pressurize to pump, let off pressure to let accumulated liquid nitrogen into the dewar. You'd need check valves on the inlet an outlet lines.

I rather like the percolator idea as well but isn;t the surface tension of liquid nitrogen rather low compared to water? You might just end up with a stream of cool nitrogen vapour coming up the tube.

Robert

Hey, Guy, am I on plonk again, or what? I suggested that if you have your own place, and two stories to work with, just make a 15 foot tall dewar, and gravity feed the stuff from the second floor.

I mean, it makes as much sense as tracking down and buying a rocket fuel pump.

And the fact that you want to chill your CPU to LN2 temperatures is prima facie evidence that you're already quite insane, so what the hell, go for it! ;-D

Cheers! Rich

I think if the rotor and stator shrink, the gap gets larger.

he

=A0^^^

Everything shrinks proportionally in all dimension. "Everything" includes the gap.

I would have to either shut down the PC or drop the clock rate on the CPU and GPU. It wouldn't take long to burn up a 3GHz proessor overclocked to 5GHz. Then again, I probably need a shutdown on loss of coolant anyway.

I was envisioning a constant flow with a simple servo to hold a certain CPU temperature. A put-put variation as in a percolator or pistom pump wouldn't be too bad, but an interuprtion long enough to refill a dewar seems like it would be a problem.

I am beginning to think that designing a LN2 perolator might be the part that I find to be the most fun. :)

Assuming similar materials for rotor and stator (housing).

Not at all. I have been reluctant to reply to you, but the reason has a lot more to do with me than with you.

Emotionally (and not a particularly rational emotion) my gut feels like I have tried and tried to be friendly and have been rewarded with a series of distinctly unfriendly comments.

Intellectually I am 99% sure that the above emotion has no basis in reality and that you are just being you, not meaning to actually hurt anyone. I also suspect that I am letting my personal problems (a health issue that the docs can't figure out is scaring the sh*t out of me -- I cant help thinking that the cancer is back after a 14 year break) influence my emotional attitude.

Then another emotional reaction kicks in and I tell myself to stop being such a wimp and suck it up like a man. :(

Alas, This is a one-story house. Also, doing that would tend to fill the downstairs room with nitrogen and the upstairs room with oxygen. :(