Endothermic reactions and processes

[RoadWarrior]

Is there a Chemistry major in the house?

So I was lying in bed last night, trying to come up with more harebrained cooling schemes, and I hit on the idea of endothermic chemical reactions. So I've been searching up on google trying to find some likely reactants, and so far nothing particularly promising is coming to light.

Now I see it mentioned that Ammonium nitrate dissolving in water is endothermic, but I can't come up with a sensible way to use this piece of information. I kinda had visions of a fluidised powder flow of ammonium nitrate meeting a stream of water in a waterblock reaction chamber, but I think we all might see what the problems with that might be. However, I was wondering whether a saturated solution of ammonium nitrate with extra crystals in suspension would do anything useful in the way of absorbing heat. Of course then you'd have to figure a good way to half undissolve it, maybe if you dropped it down a bong or something, hmmmmm......

Anyway, apart from that I didn't really see anything that might help us at all, CO2 plus H20 is an endo thermic reaction, but somehow I think you'd have to be over 100C or so to get that, or we'd all be good running soda water in our systems.

Photosysthesis is an endothermic process, energy wise, but I don't suppose thermal energy really has a lot to do with that, otherwise people would be shouting about how they got algae in their water and the temps went down

Anyway, can anybody come up with something that might be worthy of investigation, seems like most endothermic reactions are complicated processes with exotic chemicals, or take place between dry compounds, or at high temperatures. What would be really nice is to find something that takes place at "our" temps with a solid non-soluble catalyst present, and can be undone with another simple process. Guess refrigeration engineers might have though have something like that by now, but heck, you never know. They've kinda been concentration on taking a lot of heat out of a largish area and dumping it into another largish area, we're more interested in getting heat out of a very small area and dumping it in a comparitively massive area.

Anyhoo, anybody want to brainstorm and shoot the crap on this?

Road Warrior

 

[Karsta]

Problem with endothermic reactions is that you have to keep the reaction going the time you want cooling. This means of course consumption of chemicals and to make it worthwhile they have to be recyclable. Dissolving salts is an easy example of endothermic reaction. You can regenerate salts by drying them but to do it same time as cooling is happening is difficult.

Here are some cooling baths I know. They can't be used for continuous work as such but may be useful for testing purposes:

1 part sodium chloride (NaCl), 3 parts ice: theoretically -20°C,
1,5 parts calcium chloride hexahydrate (CaCl2x6(H2O)), 1 part ice: theor. -50°C,
1 part ammonium chloride (NH4Cl), 1 part sodium nitrate (NaNO3), 1-2 parts water: theoretically -20°C
Dry ice+ethanol (or acetone or 2-propanol): theoretically -72°C

 

[ocean]

FYI, 2-propanol is the same as isopropyl alcohol. That is what I used once. Lasts a long time, doesn't smell too bad. Forms kind of a thick bubbling gel.

 

[Gurudas]

Endothermic cooling

Hi RW,
Yep, there are lots of endothermic reactions. In fact many exothermic reactions that are reversible are endothermic in the reverse direction (kida like a refrigeration cycle ehh?), but a practical miniature one? How about the Li ion cell or nickel-metal hydride ...check out :
http://www.google.com/search?hl=en&q=lithium+ion+endothermic

How about a cell an inch thick by 3" square (the more mass, the more moles of reactants to liberate/take-on heat. The charging cycle is endothermic so the thingie could charge (cool) from the power supply DC while it is used to drive fans/ht sink and a Peltier to discharge it (exothermic) in some sort of array with hi thermal conductivity shell which is not electrically conductive see (http://www.huanyubattery.com/know/12.htm)for standard shell etc. but methinks that the useful life due to the physico-chemical nature of the cells would preclude their use. The refrigeration compression expansion cycle is so much more efficient whereas a gas/liquid equilibrium is set up with an electrically driven compressor..like Asetek's.
(don't let the practicality of the last statement stop you though...."keep on thinking free" (Moody Blues 1969) Best regards, gd

 

[Spartacus51]

It is indeed a difficult thing to do. The way it would quite possibly work is not as a replacement for a block but as a replacement for a rad. Pass you water over the container in which your reaction is taking place. Note a couple of the endothermic reactions mentioned above are indeed endothermic, but require the use of substances already cool enough to use for cooling. (Ice, dry ice, etc.)

 

[Karsta]

It is indeed a difficult thing to do. The way it would quite possibly work is not as a replacement for a block but as a replacement for a rad. Pass you water over the container in which your reaction is taking place. Note a couple of the endothermic reactions mentioned above are indeed endothermic, but require the use of substances already cool enough to use for cooling. (Ice, dry ice, etc.)

Yep. Just what I was thinking. Solvation assisted water cooling. Of course the innards of cold bath would not have direct contact with coolant. The first baths are meant for getting lower temperatures if there is no dry ice available. Ammonium chloride-sodium nitrate can be used if there is no ice available. I think that none of the baths I suggested are useful for normal continuous use.

Endothermic solvation of two liquids combined with distillation could be a way for continuous system. Supposedly that would not be very efficient and definitely not an easy solution.

Evaporative cooling is possibly the best way to take advantage of endothermicity - that's why it is widely used...

 

[Crash893]

i saw a pretty neat new cooling thing coming down the pipe some time in the future


its gets its cooling power from permanent magnet

it takes the heat out useing powdered form of gadolinium ( used in mri's)

the gadolinium is attached to a wheel that spins in and out of the magnetic feild


when the gadolinium is magnitized it lines up and give off heat when it goes out it becomes un magitized and do your endothermic thing

then that is used to chil some water pipes and bingo cold water

 

[RoadWarrior]

Thanks Karsta those cooling baths are interesting, I knew Ice and common salt got cold, but I thought it wasn't as much as -20C, anyway, hmmm calcium chloride hexahydrate, is the hexhydrate just water absorbed into the regular crystal form of calcium chloride?

Dang, I know I saw something with a high proportion of calcium chloride in the other day but I can't think what the hell it was now. Hmm, calcium carbonate + Hydrochloric acid = calcium chloride??? Dang, sometime I wish I'd done Chem instead of physics.

Anyway, I know those are only temporary cooling baths, but I've been wondering for a while how to get some temporary cryogenic temperatures, to attempt "cryogenic burn in" that's meant to allow better overclocking potential at normal temps. Liquid N2 was kind of out, and dry ice was next best but difficult, CaCl and ice seems doable.


Hmmm guess I would have realised if I thought about it that dissolving salts was endothermic, however, when I saw Ammonium Nitrate given as an example I wondered if that was particularly so. Are there other common salts that might be more endothermic when dissolved? What am I looking for for this data, latent heat of crystallisation energy comparison tables or something?


Hmmm interesting information about the battery cells that are endothermic , however I notive of LiOn that they say "almost endothermic" which I guess means not very. While NiMh is endothermic in discharge, now, I beleive that one, because my Cellphone battery goes real dead if I get it cold, have to wear it under my coat instead of clipped outside in the Canadian winters. Thing I find hard to beleive is that NiCad batteries are endothermic in the charge cycle, the damn things always seem to get hot to me, both charging and discharging.

Anyhoo, though interesting those effects in those cells doesn't seem like it will be great enough to be able to use very practicably, though I guess laptop and notebook designers should be taking these into account.


Hey crash that sounds really neat, though I am kinda of mystified how one might efficiently thermally couple anything to a spinning wheel, I guess you have to run the fluid over it directly or something.


Anyway, apart from for temporary cryo experiments, I am still kinda fascinated with the idea of combining a water tower or "bong" with a supersaturated salt solution, with free crystals in suspension. Yes salts are bad electrolytically, and in a system where they are merely in a normal solution there's probably no benefit over straight water. But if extra salts would dissolve at the waterblock, and then would come out of solution in the cooling process, whether it would be a bong or whatever, then more heat might be transferred from the CPU.

I guess the thing is, finding the salt that needs the most energy to dissolve.
I don't know that we need to worry too much about the efficiency of the system, I mean there's guys running 2KW of refrigeration to get maybe 200W out of their CPU. . . . .

Anyway, thanks all very much for the comments so far, keep them coming,

Road Warrior

 

[RoadWarrior]

Yeah, that's it! I have seen calcium chloride in deicing salts. They are probably on sale right now. Hafta go get some. From what I gather then calcium chloride hexhydrate is just a dihydrate that has sucked up more water from the atmosphere.

It is meant to attack aluminum and brass pretty bad though, so I guess I'll have to get an all copper system to try it out on.
I see that this stuff is also what I am looking for to use in solution, it's usage in this kinda of phase change system is well known for solar heating storage it seems.

Got a couple of data sheets on it that are useful....
http://www.luminet.net/~wenonah/hydro/cacl.htm
http://www.chess.cornell.edu/Safety/MSDS/calcium_chloride.htm

I see that it's only really "cover your ***" toxic, so shouldn't be a problem in an open bong.

-50c with Ice, and you can probably get it on sale at the moment, . . . . . . now I need that info on cryo burn in before my new XP arrives.
Road Warrior

 

[Crash893]

Inhalation:
Remove to fresh air. If not breathing, give artificial respiration. If breathing is difficult, give oxygen. Get medical attention.

 

[Crash893]

have you seen that technique where they use a fairly large pipe and a sub wolfer to cool one end of pipe

something with compressing teh attoms at the opposet end of the pipe im not sure on the spesifics ill look into it more after ive had my dr recomened 3 hours of sleep

 

[RoadWarrior]

Heh, I think that should read:
"Inhalation (If mistaken for cocaine)..... "
's'about the only way you'd get enough in to be a problem.

That sub woofer things sounds interesting, probably some way of reducing the thermal inertia or something, they've done it with tuned lasers too.

 

[ol' man]

Thanks Karsta those cooling baths are interesting, I knew Ice and common salt got cold, but I thought it wasn't as much as -20C, anyway, hmmm calcium chloride hexahydrate, is the hexhydrate just water absorbed into the regular crystal form of calcium chloride?

Dang, I know I saw something with a high proportion of calcium chloride in the other day but I can't think what the hell it was now. Hmm, calcium carbonate + Hydrochloric acid = calcium chloride??? Dang, sometime I wish I'd done Chem instead of physics.

Anyway, I know those are only temporary cooling baths, but I've been wondering for a while how to get some temporary cryogenic temperatures, to attempt "cryogenic burn in" that's meant to allow better overclocking potential at normal temps. Liquid N2 was kind of out, and dry ice was next best but difficult, CaCl and ice seems doable.


Hmmm guess I would have realised if I thought about it that dissolving salts was endothermic, however, when I saw Ammonium Nitrate given as an example I wondered if that was particularly so. Are there other common salts that might be more endothermic when dissolved? What am I looking for for this data, latent heat of crystallisation energy comparison tables or something?


Hmmm interesting information about the battery cells that are endothermic , however I notive of LiOn that they say "almost endothermic" which I guess means not very. While NiMh is endothermic in discharge, now, I beleive that one, because my Cellphone battery goes real dead if I get it cold, have to wear it under my coat instead of clipped outside in the Canadian winters. Thing I find hard to beleive is that NiCad batteries are endothermic in the charge cycle, the damn things always seem to get hot to me, both charging and discharging.

Anyhoo, though interesting those effects in those cells doesn't seem like it will be great enough to be able to use very practicably, though I guess laptop and notebook designers should be taking these into account.


Hey crash that sounds really neat, though I am kinda of mystified how one might efficiently thermally couple anything to a spinning wheel, I guess you have to run the fluid over it directly or something.


Anyway, apart from for temporary cryo experiments, I am still kinda fascinated with the idea of combining a water tower or "bong" with a supersaturated salt solution, with free crystals in suspension. Yes salts are bad electrolytically, and in a system where they are merely in a normal solution there's probably no benefit over straight water. But if extra salts would dissolve at the waterblock, and then would come out of solution in the cooling process, whether it would be a bong or whatever, then more heat might be transferred from the CPU.

I guess the thing is, finding the salt that needs the most energy to dissolve.
I don't know that we need to worry too much about the efficiency of the system, I mean there's guys running 2KW of refrigeration to get maybe 200W out of their CPU. . . . .

Anyway, thanks all very much for the comments so far, keep them coming,

Road Warrior

Dry ice is not difficult.

 

[RoadWarrior]

Not to use, to get hold of, if I send you a SASE can you mail me some?

Wasn't it yu that was talking about cryo burn in a while back, ol' man? Did you ever find any good english sites about it?


Road Warrior