Microwaving liquid N2

Yepper yessiree Bob.

Methnks a more useufl test would be to get two plastic cups, one bigger than the other, and fill the big one halfway with water and the small one put a weight in it and place the small cup inside the big cup ( to avoid dangerous tipping in step #3). Step number 3 is to put a small amount of liquid N2 inside the small cup.

Transfer the whole thing with gloves to the microwave.

The real question is what happens if you suddenly HEAT liquid ntirogen, not just microwafge. Ithink., At least I’D ask that instead.

If you do that, I bet nothing spectacular happens, unless your microwave is airtigfht (microwaves for home are not). Then there will be a large amount of nitrogen in the microwave and maybe it’ll pop the door off.

Which brings to mind the related question: Will the fuse to a 4th of july type aerial shell burn while immersed in a gallon or two of N[sub]2[/sub] ?

Link to my (misposted) question.

One challenge to this experiment may be obtaining a sample of liquid nitrogen that does not contain small amounts of water. As we all know, water will condense on cold objects, and that is true ether the object is liquid or solid.

On the other hand, I can’t imagine that water is particularly soluble in N2, so it will quickly freeze and drop to the bottom. Then again, since that liquid nitrogen is probably boiling, the ice crystals will be well mixed.

Additionally, that “fog” you see dripping over the edges of a flask of liquid nitrogen is really just condensed water. (I put fog in quotes to distinguish it from early morning fog which is actually condensed meatballs.:smiley: )

erm… forgive me… that report mentions “the Leidenfrost effect” when the liquid nitrogen is poured onto the floor.

Whassat?

(forgive me if this question is too peurile…!)

If you keep it warm enough. The time fuse going from the lift charge to the break charge is essentially black powder in a tube, and the fuse to the lift charge is a cord impregnated with black powder inside a paper sleeve (Quickmatch) on 1.3 G shells, or a length of very fast green fuse (also basically black powder) on 1.4 G shells.

You’d want to remove the lift charge. I said “If you keep it warm enough.” because I suspect that the heat released by the fuse would be less than the heat necessary to get the next bit of fuse warm enough to ignite. Forgive me for totally forgetting the technical terms, I’m up a bit late.

The easiest way would be to suspend it above a bucket of N[sup]2[/sup] (l) so that it would drop when the time fuse was lit.

If you just want the nitrogen to explode, though, it’d be easiest to fill a 2 liter bottle with it, cap it, and toss it into a body of water. Enough nitrogen will vaporize that the bottle will burst, and then all of it will vaporize from hitting the water.

pierre, have you ever dropped water onto a very hot pan or griddle? The water on the bottom of the droplet will vaporize, and you get a little hover craft of water floating on a cushion of steam. If you have a big enough glob of water, and a hot enough pan (cast iron works well), you can get it to skim around for a few minutes. For liquid nitrogen, the floor is hot enough, so a cup full tossed across a floor will skitter around until it’s all vaporized.

It’s why you can lick your fingers and put out a candle, or lick a finger and test the temperature of an iron or pan. It’s also why you can dip your hand in water, then briefly submerge it in molten lead.

It’s not why people can walk on hot coals, despite what some people say or what Cecil originally thought.

I had the same question as pierre72 regarding what the heck was the Leidenfrost Effect.

Thanks for the explanation Wikkit. Can you say more about your offhand comment about it not being the reason for people being able to walk on hot coals? The web site I found that had anexplanation of the Leidenfrost Effect also mentions the hot coals phenomenon.

PS – Chronos, I liked your report. Nice job.

The column of Cecil’s I linked to mentions it, but the basic idea is that you can firewalk with dry feet, or with something on your feet that is both dry and temperature sensitive (like cotton socks) and have no problems. Thus, Leidenfrost (which I keep typing as Leidenfrotz) isn’t it.

What is it is the low conductivity of ash or burning wood and the low latent heat of ash, combined with the short time the feet are actually in contact with the coals.

Ahhh. Thanks Wikkit. Now that you explain it, I recall hearing or reading the same thing elsewhere.

I was considering putting the nitrogen in with a water “buffer”, so as to prevent the pyrotechnics display, but I was specifically trying to avoid the issue of secondary heating. We all know what happens when liquid nitrogen is heated by, say, contact with warm water: It boils. Presumably, heating it quickly would just boil it quickly. While this might conceivably cause a small explosion, it wouldn’t be particularly instructive.

Having liquid nitrogen lying around a pyrotechnics display would lead to one device I’ve been wanting to try, the high vapor pressure lampare.

We’re a bit diverging from microwaves, though. I guess the OP’s easy to answer, though; you’d get boiling nitrogen, then boiling water. Woo.

<b><i>And I digress…</b></i>

Why don’t we have pictures of these experimentations? The Leidenfrost effect sounds kinda cool, and pending my Google image search on said topic, I think it’d be fantastic to see what happened.

Has anybody tried microwaving everclear?

Also, if you want cool coasters, I recommend microwaving shitty CDs you don’t like anymore (or if you screw up burning one sometime). Not that you haven’t all heard that before. There’s this stuff called Zip-Change (in my trade we call it trim-cap… it goes on the side of plexiglass letters, used as faces for channel letters on big signs), you can use weld-on or other similar chemicals to bond it to the plastic of the CD (not unlike model glue), and it stands off the table a bit. Then you attach a little bit of that sticky window/door foam to the center hole to make it absorb at least a modest amount of condensate. Yep, it rules.

Sorry about the rant. The experiment wasn’t altogether interesting, so I hope somebody at least tries the coaster thing. <=

Ok lemme try this one more time… (the html that is)

*** And I suck… ***

I thought things like Nitrogen were only liquid under extreme pressure. Doesn’t it all evaporate/gasify at air temperature if just poured in a paper cup?

Or it is a slower process, like dry ice?

(Forgive the total non-physics person).

It will evaporate, but it is a slower process like dry ice. In a polystyrene cup, it takes a decent amount of time because the liquid nitrogen has to get the heat of vaporisation from the air, and the cup is a good insulator.

There is an easy way you can play with this sort of thing. Get a can of ‘air’, like they use for dusting computers and such. It’s actually 1,1,1,2 Tetrafluoroethane, and has a boiling point of -26 C (compared to -196C for nitrogen). If you turn the can over and spray it into a cup, a lot of it will evaporate because it had enough heat already in the can, but some will stay liquid. More will stay liquid if you freeze the can first.

I think you can do the leidenfrost effect with it, but if that’s all you want to do, you can just do the water on a frypan.

I just wanted to drop by and thank Chronos from the bottom of my heart for actually putting the liquid nitrogen in the microwave. I was reading the report, and he was droning away in his first paragraph, “…symmetric diatomic molecule…distinct rotational mode…one vibrational mode…resonance…” and I was getting ready to come over here and post impatiently, “Yes, but, has anyone ever actually PUT liquid nitrogen IN a microwave?”, when the second paragraph scrolled up, and glory be, he put the liquid nitrogen in the microwave.

Bless you. You made my day. :smiley:

i know, i should have had more faith

Hey Chronos

Could you put this part of you answer in english?

I’d be ever so grateful.

Me too. And is there a Seventh-Graders’ answer to the question, “If it’s liquid, why doesn’t it just heat up and boil?”

Nitrogen molecules look like this:


.....
.N-N.
.....

Water molecules look like this:


.......
...O...
../.\..
.H...H.
.......

Therefore, nitrogen molecules don’t have many ways to vibrate, and none of them are interesting, whereas molecules do all kinds of crazy things.

Microwaves are just radio waves in a part of the radio spectrum that made “micro” seem like a good name for them at the time that they were first being worked with.

OK, now, you know the classic schtick where an opera singer hits a note and makes a glass shatter? Well, that’s how a microwave oven works. It makes those water molecules (which are in all food) dance around like crazy – presto! instant heat!

But nitrogen molecules aren’t the same size, weight, or shape as water molecules, and only have a couple of ways to vibrate. To heat up nitrogen, the microwave would have to be especially tuned to the right frequency. Whereas water, with its off-center shape, will respond to lots of different waves.

Ergo, a microwave oven won’t affect nitrogen much.

So you don’t want me to use the term heat of vaporization?

Ok, here’s another try: Think of a bowl of room temperature water. Now stick it in an oven. As you heat the water up, the water will boil and then turn into steam. However, it won’t all instantly dissapear the moment you put it in the oven, right? The amount of time it takes to boil and then turn it all into steam depends on how cold the water was and how hot the oven is.

The idea is the same in liquid nitrogen. If you start with a cup of liquid nitrogen it’ll sit around until it gets heated up enough to boil. Instead of being heated by an oven, it’s getting heated by the air. If it’s in a thermos or styrofoam cup, it’ll take longer.

Eventually, though, it will start boiling, and then it will eventually all boil off. It takes heat to do that, though, just like it takes heat to boil a pot of water. If you throw a cup of liquid nitrogen on a warm floor, it’ll boil quickly and do the Leidenfrost thing. Same thing if you threw a cup of liquid water on a floor made of hot plates.

To sum it up, it will just heat up and boil. It just takes some time.

If you don’t understand all that, please say so. I want to know how to describe it as much as you want to understand it.

After I wrote that, I spent about two hours defining specific heat and heat of vaporization and the math thereof, and it sounds even worse. Someone else can do that.