Pumping Liquid Nitrogen

[Guy Macon]

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.

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.

 

[Guy Macon]

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 .

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 (www.basicx.com)
could provide a pulsing heat source if needed.

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

 

[Paul Hovnanian P.E.]

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 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.

 

[Tim Williams]

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

 

[Robert Adsett]

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.

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

 

[Rich Grise]

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.

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

 

[Paul Hovnanian P.E.]

You mean smaller gap?

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

 

[Richard Henry]

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

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

 

[Guy Macon]

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 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 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.

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

 

[~misfit~]

Somewhere on teh intarweb "Richard Henry" typed:

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

Assuming similar materials for rotor and stator (housing).
--
TTFN,

Shaun.

"another academic failure.... trying to prove that your smart"
'blanking', nz.comp, 20 Dec 2007.

"your so predictable misfit"
'blanking', nz.comp, 21 Dec 2007.

 

[Guy Macon]

Hey, Guy, am I on plonk again, or what?

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.

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.

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.

 

[Glen Walpert]

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

The percolator pump can work well with LN2, for instance a percolator
pump is used for a 6 foot lift in one air separation plant I know of.

Air separation plants and bottle filling facilities generally fill
high pressure bottles from low pressure liquid storage tanks by
perssurizing the liquid to 3000+ PSI, evaporating the HP liquid in
those ice covered towers you see outside at these facilities, and
filling the tanks with warmed HP gas. It takes a lot less energy to
pressurize liquid than gas. The pumps are simple piston pumps with
extra long insulated parts, but hardly worth it for moving a few
liters a few feet.

 

[Paul Hovnanian P.E.]

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

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.

 

[~misfit~]

Somewhere on teh intarweb "Glen Walpert" typed:

It takes a lot less energy to
pressurize liquid than gas.

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.
--
TTFN,

Shaun.

"another academic failure.... trying to prove that your smart"
'blanking', nz.comp, 20 Dec 2007.

"your so predictable misfit"
'blanking', nz.comp, 21 Dec 2007.

 

[Richard Henry]

Somewhere on teh intarweb "Richard Henry" typed:



Assuming similar materials for rotor and stator (housing).
--
TTFN,

Shaun.

"another academic failure.... trying to prove that your smart"
'blanking', nz.comp,  20 Dec 2007.

"your so predictable misfit"
'blanking', nz.comp, 21 Dec 2007.

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.

 

[Tim Williams]

Lets see: The rotor gets smaller. The stator gets thinner and its
circumference decreases.

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

 

[Spehro Pefhany]

Somewhere on teh intarweb "Glen Walpert" typed:


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.

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


Best regards,
Spehro Pefhany

 

[Robert Adsett]

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 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.

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

Well, there is that

Robert

 

[~misfit~]

Somewhere on teh intarweb "Spehro Pefhany" typed:

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

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

Shaun.

"another academic failure.... trying to prove that your smart"
'blanking', nz.comp, 20 Dec 2007.

"your so predictable misfit"
'blanking', nz.comp, 21 Dec 2007.

 

[Robert Adsett]

The percolator pump can work well with LN2, for instance a percolator
pump is used for a 6 foot lift in one air separation plant I know of.

There we go.

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

Robert