Quote:
Originally posted by crafty
I don't know hwere you learned chemistry, but it sure is an endothermic reaction. Physicial changes can have energy changes - some things when they dissolve are endothermic/exothermic.
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It's not an endothermic reaction. It's an endothermic phase change.
Pouring liquid N2 on something room temperature will cause the N2 to immediately evaporate. When things evaporate, they absorb heat. Thus, the object the N2 is being poured on gets very cold very fast.
These cans of compressed gas for blasting away dust usually contain some sort of flouroethane. When you spray it, the gas quickly escapes because it is under pressure. A little bit of liquid evaporates to make up for this loss of pressure, and it doesn't take much of that to get the can very, very cold.
Quote:
Originally posted by SonixOS
If you do end up LN2 cooling, make sure you wear gloves and such cuz if you dip ur dick (maybe your finger would be more likely) in it you lose it. Also, LN2 will evaporate rapidly and cause dissociation of O2 where the room you are in will lack O2 particles and be replaced with LN2. Therefore it is CRUCIAL that you have adiquate breeze going through the room you are in.
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I should point out that people would need cryogenic gloves. Latex gloves, or even Arctic expedition gloves, won't cut it.
And the dewar you mentioned is basically a thermos. LN2 won't evaporate as long as no heat gets to it, so you can keep a liter of it in a good dewar for a good day or two before you loose it all. Dewars are unsealed to allow a little bit of LN2 to evaporate, since heat will still get through the thermos, and if it was sealed it would pressurize until it eventually exploded.
I used nitrogen gas and LN2 in some of my research labs, and it's some fun stuff. It's very cheap - less than $50 for an 80 gallon tank, I belive. But that's only because we own the tanks and receive daily shipments of hundreds of dollars worth of compressed and liquefied gases. If I bought LN2 I wouldn't need to pay for delivery, plus, I get a massive discount simply due to the amount of business the supply company gets from us.
Of course, if you don't receive large daily shipments of compressed and liquified gases and a loading dock facility to accept them *and* you do not have a proper LN2 storage tank (*very* expensive, and dewars won't work if you expect to run your system for more than a few minutes) *and* you do not have the facilities to pump the LN2 (it's at a very low pressure and won't escape by itself) *and* you don't have an adequate ventilation system . . .
And that's just the stuff I could think up off the top of my head. Unless someone had access to all these facilities, building a LN2 cooling system would cost tens of thousands of dollars. If one intended to run a system continously, we'd be talking operating costs approaching a million dollars a year. This is *not* the sort of budget for a hobby.
BTW, the term is displacement, not dissociation. You got the idea right, though.
Alchemy