Half a croissant, on a plate, with a sign in front of it saying '50c'
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Hot cubes

Keep your hot drink hot
  (+35, -3)(+35, -3)(+35, -3)
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Ice cubes rely on a solid-to-liquid phase change (er, they melt) to cool a drink. I propose similar-sized cubes of stainless steel, filled with a suitable substance with a melting point of perhaps 80C. A quick Google search suggested sodium ammonium phosphate; not very nice but fine as long as it stays within the cube. Alternatives might be safer or have more appropriate melting points; a plastic outer might permit microwave use if this could be done safely.

Once heated up above the melting point, they would cool to 80C relatively quickly, then stay at that temperature until all the salt had solidified.

Put a couple in your coffee; it'll stay warmer for longer. Best of all, they're reusable!

david_scothern, Jul 11 2006

http://antoine.fros...ice-and-water.shtml the contribution that phase change makes in energy absorbed by melting ice [xaviergisz, Jul 11 2006]

Ooooh http://www.pbase.co...uber/image/24272958
Ahhhh [2 fries shy of a happy meal, Jul 11 2006]

2 cups of coffee? We don't need no 2 cups of coffee: we want to order one of these; that's what we want to be doing. http://www.physorg.com/news170425949.html
Phase Change Material Cup [Ling, Apr 10 2010]

mcdeltaT calculator http://hyperphysics...SE/thermo/spht.html
[ShawnBob, Apr 10 2010]

Enthalpy of Fusion http://en.wikipedia...ecific_melting_heat
[ShawnBob, Apr 10 2010]

Specific Heats http://hyperphysics...e/tables/sphtt.html
[ShawnBob, Apr 10 2010]

Phase-change mug http://www.gizmag.c...4c968e36a4-90474673
[xaviergisz, Dec 13 2013]

[link]






       I think you just invented the coffee cup grenade +
xenzag, Jul 11 2006
  

       Googling for Hot Cubes turns up something similar, but without the phase change. As proposed here, they would be more effective.
david_scothern, Jul 11 2006
  

       Surprisingly logical and useful for a halfbakery idea.
wagster, Jul 11 2006
  

       is there something that would keep baby milk at the right temperature. the little mites hate cold milk   

       :)
po, Jul 11 2006
  

       In my current experience, her mother is ideal for this purpose :) although to make a baby bottle with this feature and a colour-changing temperature indicator built in would be good. Perhaps immerse it, filled with milk, in boiling water until it changes colour, at which point it is fractionally above the correct temperature and can be relied upon to maintain optimum conditions for a long period.
david_scothern, Jul 11 2006
  

       I wouldn't use a baby bottle with anything less than an lcd display and onboard computer.
wagster, Jul 11 2006
  

       with built-in MP3, GPS, and bluetooth. Let's not get cheap, [wagster].
NotTheSharpestSpoon, Jul 11 2006
  

       Stirling or cold fusion for power?
Galbinus_Caeli, Jul 11 2006
  

       stirling of course
tatmkr, Jul 11 2006
  

       [+]
MikeD, Mar 18 2010
  

       Possibly, a better name for this product might be "Hot Rocks". I'll have a Hot Toddy, on the Rocks.
jurist, Mar 18 2010
  

       What a good idea!   

       I think it could be built into the cup itself, and could also be used to prevent scalding if the cup was cold before pouring hot water.
Ling, Mar 18 2010
  

       You could do this with sodium acetate (the same type of stuff that you find in some hand warmers) that, upon crystallization, releases heat.   

       It's not very toxic, but not exactly edible either. But if it's encased,it might work.   

       On the other hand, ice cubes generally do not damage your lips if you touch them (except if they are very cold -- different topic entirely). I think anything hot enough to heat coffee might also be dangerous.
cowtamer, Mar 19 2010
  

       //[Sodium Acetate]
It's not very toxic, but not exactly edible either.//
  

       It's the salt and vinegar flavouring in salt and vinegar crisps. Should be fine.
The ability to supercool is not necessarily an asset in this situation though, and the melting temperature is a bit low at 58 degrees C.
Loris, Mar 19 2010
  

       Wouldn't you risk burning your lips if the cubes came in contact with them? Obviously, they would sink to the bottom of the cup, but what if you forget about them when you are drinking the last few sips of coffee and you have already tipped the cup all the way up?
Alx_xlA, Mar 20 2010
  

       See link. I think these should sell like, um, hot cakes.
Ling, Apr 10 2010
  

       I hate to be a party pooper, but I fear this may not work. I'll try to explain (perhaps poorly)...   

       With ice, what happens is that heat flows from the hot liquid into the ice, eventually melting it. There is also a continuous flow of extra heat coming IN from the surroundings into the liquid because it is at a lower temperature than ambient.   

       With a hot beverage, what would happen is that heat would flow from the very hot beverage into the cubes at 80 degrees. But there is also heat loss going OUT because the beverage is hotter than ambient.   

       So at some point, the mixture (beverage + cubes) would cool eventually to the surrounding temperature. My point is that if the enthalpy of fusion (the energy it takes to melt) plus the specific heat of whatever is in the cubes is less than the specific heat of water (which is insanely high), there would be a net loss.   

       I.E. it would indeed drop to 80 degrees and stay there for a while but then drop faster than it otherwise would after it passes 80 degrees, with the result of a net shorter time going from 100 to room temperature.   

       So for example *not real numbers here* but just guesses to illustrate.   

       A) 20 minutes cooling from 100 to 27 degrees   

       B) 2 minutes cooling from 100 to 80. 5 minutes stable temperature at 80. 6 minutes cooling from 80 to 27.   

       So yes, even though B) flatlines at 80 for a while, net cooling rate is faster taken as a whole.   

       Not sure if that makes sense or not. If I wasn't so lazy I'd whip out my calculator and do real numbers, but that would all depend on what you choose to fill the cubes with.   

       P.S. I LOVE your thought process though on this one.
ShawnBob, Apr 10 2010
  

       wots needed for a single-cup hotcube is an enclosed substance that:   

       a) has a melting point of 60C;
b) has pretty massive fusion enthalpy;
c) isn't poisonous.
  

       If you were going to use them only for the tea/coffeepot where the user wouldn't accidentally touch it, >100C would be fine except you still have to transfer the cube from the heating device to the pot (which of course begs the question "why not just use the heating device?")   

       [edit] ie: paraffin wax.
FlyingToaster, Apr 10 2010
  

       Granite has a pretty high specific heat capacity. A couple of 1 inch cubes heated to above the desired temperature should store and transfer a lot of heat to your beverage. Handle with care.
BunsenHoneydew, Apr 10 2010
  

       Bunsen:   

       The specific heat of granite is .19 Cal/gC vs. water at 1.00 Cal/gC...which means that a cube of granite would be about 19% as efficient as well...a cube of water.   

       If you assume that a beverage is pretty close to water...like coffee, you can make some assumptions. I'm not sure what the specific heat of hot chocolate would be.
ShawnBob, Apr 10 2010
  

       You might be onto something there ShawnBob. All we need to do is encase the drink in several times its volume of water at the desired temperature, and it'll take longer to cool down.   

       Seriously, you are a bit quick to dismiss the concept using 'not real numbers' calculation. You are correct that ice works to keep a drink cool because of the high latent heat of melting of icewater (334 kJ/kg). But sodium acetate, discussed earlier in the thread isn't that far behind (approx 270 kJ/kg). Paraffin wax is behind that (approx 210kJ/kg). So either of these would work to some extent in theory - not quite as well as ice-cubes, but significantly. There may be practical issues with both of these (I think approx 60 degrees - the melting point of both these substances) is a bit low, sodium acetate will supercool and there may be other issues with paraffin. But the potential is certainly there.
Loris, Apr 11 2010
  

       Clever
doctorremulac3, Apr 11 2010
  

       [ShawnBob]: Yes, but the density of granite is 2.75 g/cm3, so a one inch cube weighs 45g with a specific capacity of 8.56 Cal/C. A similar cube of water weighs only 16.4g - heat capacity 16.4g.   

       Oh. You still win. Never mind.
BunsenHoneydew, Apr 11 2010
  

       well... granite would certainly look the best, but I still think we're down to paraffin or sodium acetate for personal-sized drinks. I'm starting to lean towards s.a. (even though I was championing paraffin earlier): as well as the higher fusion-enthalpy, it's over 1.5x as dense. A couple cubes dropped into a too-hot coffee will cool them down a bit then regulate the temperature @ 58C.
FlyingToaster, Apr 11 2010
  

       With Sodium acetate, there could be an added trick of letting the coffee cool down to, say, 45C, and then triggering the super-cooled liquid to suddenly crystalise and heat the coffee back up to, say, 60C.   

       Jojoba wax would have the advantage of looking good as well...
Ling, Apr 12 2010
  
      
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