Timeline for Why doesn't water boil in the oven?
Current License: CC BY-SA 4.0
15 events
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| Jun 9, 2020 at 2:18 | comment | added | cesaruliana | @rob As far as I know it should be the same for the boiling transition. Microwaved water is taken to be dangerous because when superheated it tends to vigorously boil (that is, explode) when slightly perturbed. Your experience seems indeed different, and, from what you describe, I don't think it was just a matter of superheat. I apologise for presuming too much. It seems something else is at play. Again let me thank you for doing the experiment and sharing, this is most interesting, that is how real life experiments are not as easy as textbook descriptions may imply, | |
| Jun 9, 2020 at 0:05 | comment | added | rob♦ | @cesaruliana Interesting suggestion. With super-cooled liquids, triggering the phase change in one part of the liquid trigger the phase change to travel through the entire liquid very rapidly. Is that the same for the boiling transition? Because what I recall is that, when I removed the hot pan from the oven, the sloshing water made plenty of bubble nucleation on the hotter part of the glass just above the horizontal surface, but that didn't transmit the phase change into the bulk of the hot liquid. | |
| Jun 8, 2020 at 21:01 | comment | added | Peter - Reinstate Monica | @rob Interesting. At least when thermal (dynamic) equilibrium is reached there must be cooling of the water next to the glass walls and bottom. Granted, it could be radiating, but the oven walls are probably much hotter, so if anything there is radiative heating... | |
| Jun 8, 2020 at 21:01 | comment | added | cesaruliana | @rob, I commend you for your experiment, that's some great info. Unfortunately thereis a complication. Boiling is usually identified by observing bubbling in the heat liquid. But bubbling is a nucleation effect, and as such it is affected by the container, in this case iron pots contain more imperfections than glass vessels, and water boils easier in iron pots than in glass. What you observed was that in the glass vessel the water was superheated. During the 18th century there was a controversy of boiling temperatures precisely because it was observed to be dependent on the container. | |
| Jun 8, 2020 at 20:01 | comment | added | rob♦ | @Peter, I remember concluding that convection driven by evaporative cooling was not a factor in my setup. (At least, not in the glass dish, and not in the cryoliquid system that I actually cared about.) But I don't remember the logic behind that argument --- other than, when I wrote it down, it was way too complex for an SE comment. | |
| Jun 8, 2020 at 17:19 | history | edited | rob♦ | CC BY-SA 4.0 |
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| Jun 8, 2020 at 17:15 | comment | added | rob♦ | @CaiusJard Yes, just so. I measured the initial and final volumes using an ordinary measuring cup. I probably started with about a liter in each pan. I don't remember the final volumes, but half-ish of the water boiled away sounds like a stopping point that I could have chosen while peeking through the oven glass. | |
| Jun 8, 2020 at 17:04 | comment | added | Caius Jard | When you say "the glass pan was missing about half as much water as the iron skillet" do you mean that you had started with equal volumes of water, but at the end of the experiment glass was e.g. ~75% full compared to the skillet's ~50% full? | |
| Jun 8, 2020 at 16:13 | comment | added | Peter - Reinstate Monica | @fishinear "Evaporating water does not cool it down" -- excuse me? For example in a Sauna the evaporating sweat cools the skin down to manageable levels even though the air is up to 110 centigrade. | |
| Jun 8, 2020 at 15:26 | comment | added | fishinear | @Peter-ReinstateMonica Evaporating water does not cool it down. The evaporation only makes sure the water stays at 100 degrees, it does not lower its temperature. That is, when the water only evaporates from the top, as in the glass container, then only the water at the top is at 100 degrees, the rest has a lower temperature. Therefore, there is no incentive for the water to circulate. | |
| Jun 8, 2020 at 14:16 | history | edited | rob♦ | CC BY-SA 4.0 |
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| Jun 8, 2020 at 9:37 | comment | added | Peter - Reinstate Monica | I would interpret your experiment thus: The water at greater depths of a glass vessel never reaches boiling temperature, even though the outside is >100 deg. C. This implies cooling from the inside which can only be effected by convection (which is also why the non-convecting Lasagne does bubble). The only area which can shed excess heat though is the upper surface. This means that the evaporation keeps the water surface well below 100 deg. C! It never "boils", not even on top. The "cold" water from the surface sinks to the bottom, where it is heated and rises again... | |
| Jun 8, 2020 at 9:30 | comment | added | Peter - Reinstate Monica | If you have an oven which allows you to adjust heat from above and below separately one could try with heat from below on max, and none from above. That should also create a "roiling boil", if the heat is sufficient. | |
| Jun 8, 2020 at 6:26 | vote | accept | Hovercouch | ||
| Jun 7, 2020 at 22:53 | history | answered | rob♦ | CC BY-SA 4.0 |