4 ms·

I think the microwaving water issue is slightly different. It does indeed become superheated, but not of course from pressure; if the vessel lacks nucleation si

I think the microwaving water issue is slightly different. It does indeed become superheated, but not of course from pressure; if the vessel lacks nucleation sites (imperfections) for bubbles to form, the water can heat quite a bit higher than 100C as it’s not losing energy to the steam phase change. Eventually when a bubble does spontaneously form (or the vessel is jolted), a huge amount of water is instantly converted to steam. You don’t want to be nearby when this happens.

MengerSponge 3y ago
Pretty much everything inside the pressure cooker is a nucleation site, so if you could make the lid just disappear, the superheated contents would explode. Water is only converted to steam while there's energy for it, so only a fraction of the water actually boils*. The risk is that it's a rapid process that propels a lot 100C water outside of the vessel. *) I haven't done the full calculation, but I'm pretty sure the upper bound is something like 10%, with 2-4% being the best most normal people could accomplish in a microwave.
rootusrootus 3y ago
On a somewhat related note, I actually had this happen recently on the stove. I've done it a few times over the years in the microwave, and I didn't even think it was really possible to have happen on the stove. Plain stainless steel pot, small, good condition but still a couple years old. You'd think plenty of nucleation sites, right? Filled it with 195F water from the insta-hot tap, and put it on my induction stove and turned it on high to push it up to a roiling boil. But after 30 seconds -- nothing. Not a single bubble in the pan, which is weird all by itself. And at this point the range is pumping a fairly ridiculous amount of energy into what is already hot water. So I thought "it can't really be superheating, right? on the stove??" and then grabbed the pot and swished it really good while stepping back. Sure enough, it instantly erupted into a furious boil. I'd guess I'm unlikely to ever run into that situation again. The stars had to align pretty well, I think.

MengerSponge 3y ago

Pretty much everything inside the pressure cooker is a nucleation site, so if you could make the lid just disappear, the superheated contents would explode. Water is only converted to steam while there's energy for it, so only a fraction of the water actually boils*. The risk is that it's a rapid process that propels a lot 100C water outside of the vessel. *) I haven't done the full calculation, but I'm pretty sure the upper bound is something like 10%, with 2-4% being the best most normal people could accomplish in a microwave.

rootusrootus 3y ago

On a somewhat related note, I actually had this happen recently on the stove. I've done it a few times over the years in the microwave, and I didn't even think it was really possible to have happen on the stove. Plain stainless steel pot, small, good condition but still a couple years old. You'd think plenty of nucleation sites, right? Filled it with 195F water from the insta-hot tap, and put it on my induction stove and turned it on high to push it up to a roiling boil. But after 30 seconds -- nothing. Not a single bubble in the pan, which is weird all by itself. And at this point the range is pumping a fairly ridiculous amount of energy into what is already hot water. So I thought "it can't really be superheating, right? on the stove??" and then grabbed the pot and swished it really good while stepping back. Sure enough, it instantly erupted into a furious boil. I'd guess I'm unlikely to ever run into that situation again. The stars had to align pretty well, I think.