
Homemade Liquid Nitrogen Generator - jeffreyrogers
http://homemadeliquidnitrogen.com/
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nabilhat
Needs more safety!

Commercial full pressure handling tubing starts at 0.049 to accomodate stress
at fittings and thermal cycling. Don't think I'd be comfortable next to 1/4" /
0.035 at full pressure after forming like that! Fittings deserve a mention,
they're specialized. LN storage needs more than a mention. An all-stainless
thermos can work, but if you've made it this far you can afford $150-200 for a
real LN dewar.

Source: Dad worked at an air liquefaction plant and is full of usually
hilarious stories about gas handling done wrong.

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wglb
Would love to hear them.

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ColinWright
There was a chap here in the UK who used to go around giving STEM
demonstrations, and in particular would do some wonderful lights, smells, and
bangs with simple chemistry.

Then the company supplying him with lox found out what he was doing and deemed
it too dangerous, so they stopped selling it to him.

So he bought liquid nitrogen and distilled his own lox instead. He said it was
a great demonstration, and cheaper to boot. He just made sure the supplier
never found out.

But with this rig he could have done the lot for himself ... I wonder why he
never did ...

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MaxBarraclough
I think I saw one of these demonstrations! I recall him mentioning the tiny
temperature difference being enough, as liquid nitrogen is a few degrees
colder than liquid oxygen. Wasn't sure at the time if he was kidding about his
supplier refusing to sell him oxygen; now I know he wasn't.

Assuming I have my memories straight, I must have been about 12 at the time. I
had the honour of being handed some candy from his stash [0]. Seemed like a
nice gesture. Of course, his next demonstration was some kind of sugar-fuelled
pyrotechnics. Evidently, he made a lasting impression.

It seems unfair that chemistry has fire and explosions as such a universal and
compelling demonstration. I suppose computer science has graphics.

[0] Of course, this being in England, I was in truth handed _sweets_ , but one
makes accommodations for our American cousins.

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michaelmcdonald
Fear not! I am a ~heathen~ American cousin and would have perfectly understood
the reference to sweets. Though I can't speak for all my brethren, I would
think most could at least infer what you were talking about.

~~~
MaxBarraclough
Almost the Queen's English, too. Purists discourage the ending of a sentence
with a preposition.

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idlewords
I don't see this mentioned elsewhere, so I'll mention it here.

Liquid N2 is benign and hard to harm yourself with, apart from frostbite. But
it is colder than the boiling point of oxygen, and if you leave open
containers of it around, or chill empty glassware, you can condense O2 out of
the air.

One dangerous scenario is where you chill an empty flask that has organic
residue in it, and liquid oxygen condenses onto that. It can go boom.

It's not easy to hurt yourself this way, but something to think about (while
running at top speed in the opposite direction) if you see pale blue liquid in
an N2-cooled apparatus.

On the bright side, you can make fantastic ice cream by pouring liquid N2 into
a bowl of heavy cream with walnuts and sugar added. The crystals are super
tiny so the ice cream has a fantastic texture.

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yomly
What kinds of safety risks are there in storing liquid nitrogen in a DIY
context? If your container is well sealed and sufficiently strong (define
sufficiently...) can you store it in a room temperature garage?

What happens if it's a freakishly hot summer one year? Do you have a ticking
time bomb in your garage?

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tptacek
There is no danger in storing LN in your garage. Your container won't be
tightly sealed (a tightly sealed container full of LN likely is a bomb);
gaseous LN will continually leak from your dewar. It's nitrogen, who cares?

The major risk with LN is storing it in enclosed spaces, as it can quickly
asphyxiate you. So, like, don't take it in an elevator.

I'm not sure I understand what the ambient temperature has to do with LN
safety.

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yomly
Actually can't leaking N2 cause asphyxiation via air displacement?

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tptacek
A large spill is what you're worried about. The container has to leak, so as
not to, you know, explode. It's worth keeping the asphyxiation risk in mind,
but you're probably overthinking this; people keep large dewars in tiny
restaurant kitchens.

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jojobas
A piston detander should work reasonably well for a small scale liquifier.

Last time I ran the numbers it was reasonably possible to liquify air with 2
relatively cheap compressors.

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tim333
Interesting to see how it works. I've sometimes pondered if you could do
cheaper cryosuspension awaiting the singularity.

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throwaw4y-plate
This wouldn't seem to be the sort of thing to cut corners on! Five nines and
all that.

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tim333
Though given the chances of it working at all are questionable you could argue
that's not such a big deal.

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itronitron
Neat article, the picture makes me think he refrigerated his entire
neighborhood.

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shmerl
It's better to use Celsius for such articles and in general too. Metrication
process in US is really way too slow.

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tzs
It would probably go faster if they just concentrated on length, area, volume,
and mass. With those you can make a good case for switching because we
routinely deal with quantities of those units over a range of several orders
of magnitude.

That means we regularly have use of smaller or larger units than the base unit
for each, and in the metric system all those smaller or larger units are
related to each other and the base units by powers of 10.

That fits well with our decimal number system, and makes conversions between
units nearly trivial. If you have, say, kilometers and you want millimeters it
is a lot easier than if you have miles and want inches.

You can make the case that we should switch to metric for length, area,
volume, and mass because it is better _and_ because it is used by almost all
of the rest of the world.

With temperature, on the other hand, we do not generally deal with a large
range, and generally don't use larger or smaller units. We just stick to the
base unit (C or F).

The only significant differences between C and F are the size of their degrees
and where the 0 point is. Historically, C set its 0 point at the freezing
point of water and the degree size indirectly by setting 100 as the boiling
point of water. F used the temperature of a specified eutectic mixture to set
0 and tried to set 96 as human body temperature.

(Actually, C _originally_ set 0 at the boiling point of water and 100 at the
freezing point, but that was fairly quickly reversed).

F came before C by about 20 years. People decided they liked using freezing
and boiling of water as their reference points.

What _should_ have happened is that F should have simply been redefined so
that its reference points were freezing of water at 32 and boiling at 212,
keeping the same size degree. That would be compatible with the old F. There
was no need to come up with a new degree size to switch to a freezing/boiling
of water basis.

So because C does not have any inherent superiority over F, unlike other
metric units compared to Imperial units, the case for switching comes down to
pretty much _only_ that it is what most of the rest of the world uses.

Furthermore, F actually has some advantages. F's smaller degree size means
many times an integer temperature is adequate where you might need to add a
decimal place with C. On F, 0 to 100 is a pretty good match for the weather in
most of the US. That would be about -17 to 38 in C.

So it is hard to make the case to most people in the US that they gain
anything tangible by switching to C, let alone gain enough to be worth the
switching cost.

Thus, I think US metrification efforts need to table temperature, and just
work on the others.

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shmerl
I'd simplify the above. It's hard to make any argument for switching, because
it's annoying to change habits. That's about it.

Even if it offers advantages, some will be reluctant, because of the above
habit issue. So they should just push metrication, period, instead of dragging
it for decades. Other countries did it successfully including for temperature,
so how is it a bigger problem in US than for them?

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lasermike026
Maybe he shouldn't have poured liquid nitrogen next to the cat.

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avmich
A really good description for how to do it. I've only found one instruction
for self-making liquid nitrogen before this site, the one by Ben Krasnow, but
that one cheats and uses helium cryocooler.

I don't really understand why separation of nitrogen from the air is so
essential. I'd also like to see a Kapitza liquifier, where in addition to
Joule-Thomson effect you use a turbine for cooling and you need less than 8
atm pressure from the compressor, that would be cool :) .

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altcognito
Something that struck me as pretty amazing was that if you can get liquid
nitrogen, you're already cold enough to get liquid oxygen (in fact separating
the two may be part of the process here, I don't know)

Anyway, liquid oxygen is pretty crazy blue and amazing in its own right.

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HPsquared
Definitely a hazard to be aware of - liquid oxygen can be a lot more dangerous
than liquid nitrogen, especially if you're not expecting it!

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m4rtink
Yeah - talk with a couple scientists after a liquid nitrogen experiments
demonstration. They mentioned even just liquid air is dangerous, as the liquid
oxygen in it makes many hydrocarbon materials flamable and even explosive in
some cases.

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raducu
Does the article/tutorial talk about how you remove water and oxygen from the
liquefied air?

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mlyle
Yes: he mentions (and links to) his home made pressure swing adsorber setup to
remove oxygen from the air before cooling.

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jmount
One of my favorite chemistry memories: "what is that dripping out the back of
the crystallography setup?" (ans: "okay would be a liquid nitrogen leak,
explosive risk oxygen condensing out of the atmosphere.")

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tgflynn
> okay would be a liquid nitrogen leak, explosive risk oxygen condensing out
> of the atmosphere

I don't think that's very likely. I used to work in cryogenic labs and a
simple LN2 leak would not have been considered a danger (except in a confined
space). The only concern we had related to LO2 condensation was to never let a
cryostat warm up or cool down while full of air.

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brandmeyer
(deleted - misinformation)

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kmm
Expansion into a vacuum, also called free expansion or Joule expansion, is not
the same as an adiabatic process, there is no piston and no work is done. For
an ideal gas the internal energy does not depend on the volume, so conversely
such an expansion does not change the temperature. And of course it's not
isentropic either, since the same amount of gas with same amount of kinetic
energy now can spread itself over a larger volume.

~~~
brandmeyer
I stand corrected.

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Gatsky
Homemade yes, DIY not really.

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jsjohnst
I’ve read over the plans, doesn’t look to be that hard assuming you already
know how to weld decently.

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dylan604
What plans? The sped up video of his hand made sketches? The video was so
poorly done, it's hard to even see what is occurring. He spent more time on
fucking with his cat with liquid nitrogen than he did on the actual
concept/plan/build.

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c22
There's a whole website there that includes images of the sketches, lots of
photos, and large blocks of explanatory text. If you only watched the video
you're missing out.

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dylan604
i saw the links at the bottom to his about the heater, but totally glossed
over the "next" link. i honestly thought it was just a simple write up and was
disappointed. thanks for letting me know there was more to be read

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visarga
> Celcius

ಠ_ಠ

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082349872349872
Despite the attempts at monetisation very nice content, containing both
theoretical and engineering exposition. Also has descriptions of dead ends on
the way to the final working design.

(how much revenue can a niche subject like this generate anyway? a dinner per
month?[1] at least now the ad-trackers have all incremented the geek bucket
for my profile. hope they use saturating addition; I'd hate to see what ads
I'll get if my geek score ever wraps around.)

[1] this is a serious question.

Edit: based on "web site value" sites (as if those are trustworthy), I was way
too optimistic with that estimate; it's more like the NPV of the whole domain
is a dinner.

