Homemade Liquid Nitrogen Generator

Would love to hear them.

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.

I would be more worried about asphyxiation due to accidental release.

>can you store it in a room temperature garage?

I'm from texas, and that's just a strange use of words in a sentence to read. The air temp outside is 95+ (in the shade) this time of year, and lately >50% humidity. It's stifling hot. Step into the garage, and it is even hotter. Most garages have zero air flow, and rarely are they insulated. It's the least friendly "room" of my house.

>What happens if it's a freakishly hot summer one year?

We call that a Tuesday.

I’ve never seen a fully sealed LN2 tank. Granted I’ve only worked with the ones for university labs, but all of them have a pressure release valve that’s goes off periodically, with a secondary back up valve.

Is this what you consider sealed? If not, you’ll most likely be creating a bomb.

Okay I’ve read a story about a fully sealed tank: https://corante.com/how-not-to-do-it/how-not-to-do-it-liquid...

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.

You don't want it to be completely sealed, because it will eventually warm up and boil. If it does so in a sealed container, PV=nRT implies that your container will either need to expand dramatically or handle a lot of pressure. This can be....unexpectedly invigorating, especially if the container is strong.

Instead, it's common to have a pressure-relief valve, often coupled with a gas sensor to make sure everything remains safe.

>If your container is well sealed and sufficiently strong

Trying to contain it in a strong sealed container is a very very bad idea. That's a bomb, even if it's freezing out.

You store it in dewers that allow it to slowly boil off, and replenish it as needed.

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

Or even better - SI Kelvin scale

> Metrication process in US is really way too slow.

I've thought that too, but wonder about what metrification would mean for things like screw thread pitch (which is measured in TPI, and I assume would change if the units changed).

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.

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!

A magnet would help with the oxygen. And water would be frozen.

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

> 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.

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.

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