Naked Science Forum
General Science => General Science => Topic started by: julie redwood on 26/09/2011 10:01:05
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julie redwood asked the Naked Scientists:
Salutations Naked Scientists,
Love your show (http://www.thenakedscientists.com/HTML/podcasts/). Â I listen to your podcast (http://www.thenakedscientists.com/HTML/podcasts/) via iTunes. Â It is great to find that many of my hypothesis, actually have a scientific basis to them. Â Then after all, science is my secret love. Â
I am stumped by something that happened while boiling water for my morning coffee. Â I had a clean pan, clean burner, and fresh water ( well, as fresh as San Diego, CA can be! ) added to the pan from the faucet. Â I was working away on my computer waiting for the water to boil, Â then all of a sudden the water, acting in geyser fashion, sent the water out of the pan in a tall column. Â It did not boil over, the water exploded out of the pan up two feet in the air, then onto the floor.
That was weird! Â Any explanations you can offer.
Thanks, Â Julie Redwood
What do you think?
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Hi Julie,
If it launched two feet into the air, it sounds like it's probably due to an effect called superheating. Water usually boils at 100 C (212 F), but to boil it needs to form bubbles. Usually the sides and bottom of a pan are rough enough for little bubbles to easily form. Once the bubbles start to form, it's easy for them to get bigger and float to the surface, making the water boil.
However, if the sides of the pan are smooth enough an the water is pure enough, there are no places for bubbles to easily form. In this case, the water can get above the boiling temperature without actually boiling. Eventually a bubble will form, and because the water is so hot it will grow incredibly fast and send water splashing out of the pan all over the floor.
I've never actually seen this happen on a stovetop, but I've had it happen a lot when microwaving water in a clean coffee mug.
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I've never actually seen this happen on a stovetop, but I've had it happen a lot when microwaving water in a clean coffee mug.
Good explanation.
Your hypothesis is that bubbles first form at the sides of the pan, then float.
Due to focusing, I believe that a microwave will cook from the inside out. So, the hottest spot in the coffee mug would be farthest from the edge. Thus fewer nucleation spots, and a greater chance of superheating.
I think I'll have to consider it safer to never get my pans spotless [::)] Imagine if Julie had been closer to the stove.
Julie, what type of stove & pans were you using? Perhaps you have excellent uniform heat distribution qualities.
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Hi, Thanks for your response. The pan I used was an All Clad sauce pan. I cleaned it in the normal fashion before adding water. Appreciate your answer. It sounds logical! [:)] Julie
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Julie,
Welcome to the website.
I see with the "All Clad", there are both copper bottom and all steel kettles. The copper bottom would give more uniform heat distribution, and perhaps inhibit the formation of bubbles.
Another thought. Did you mention a lid? Perhaps you got some kind of a seal which would have caused a slight pressure buildup. Moisture might actually improve the sealing ability of the lid. Anyway, were you using a lid? Was it blown off? Is the lid vented?
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I think it was a rogue waterspout. Is there a history of the these occurring in San Diego kitchens ? It happens you know !
[;)]
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I enjoy reading the responses... Thank you! No, I did not apply a lid or a cover of any find. To respond to other comment, I can't wait to explore these rouge waterspouts! [;D] [;D] Sounds like great fun and entertaining!
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It almost certainly is superheating, you were very lucky that you weren't leaning over the pan when it did this, as in "why isn't this boiling yet?" and then virtually ANYTHING that falls into the pan, a hair, can cause a nucleation site and kick off the geyser; it could have blinded or scalded you quite badly.
If you manage to get it superheating again, you can kick it off with a LONG wooden spoon with sugar or salt in it.
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acting in geyser fashion,
I resent the implication here.
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I recognize that I am replying to an old post, but it is exactly what I needed to find on the Internet when I went looking this morning. I have had water explode out of a pan THREE times, using a small Revere-ware saucepan (steel pan, copper bottom, no lid) on a stove. Now that I've read your explanation, I think I know why: I used SoftScrub on the pan, which undoubtedly made the surface very smooth. I had burned something in the pan that caused it to discolor, and I was hoping that the SoftScrub would remove the discoloration. I think I'll use a different saucepan until this one gets scratched up again, or scour it with something abrasive.
Thanks for your help!
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I just posted the answer at "new theories"
I found a new law for metastable states, also for overheated water.
You may it read also there:
http://science-technology-inventions.weebly.com/
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Another instance of this can occur when heating new oil in a clean deep fryer. These devices get well above the normal boiling temperature of water (100C).
If it is not entirely dried before pouring in the oil, or if you let some water splash into the oil, you can have a droplet of pure water floating around in pure oil, with no nucleation sites. When it gets well above 100C it can burst into steam, spraying hot oil around, and perhaps causing a fire.
In the chemistry lab, we were always told when boiling oil (for fractionation, for example) to drop some "bumping stones" in the bottom of the oil. This was some sort of rock with a rough surface and lots of nucleation sites. That way any water would turn into steam at around 100C, rather than blowing up the apparatus at a much higher temperature.
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I think I'll use a different saucepan until this one gets scratched up again, or scour it with something abrasive.
Back in the day, cooks used to put a bit of broken crockery into pans when boiling water and milk. It provides lots of nucleation sites, so the boil develops more smoothly and controllably.
ETA - oops, I didn't notice that evan_au got there first. Sorry 'bout that.
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Again, like the last post, I know this is old, but I just had a similar situation, but somewhat different happen to us last night. Here is the situation as it played out:
My wife started boiling water with some olive oil in a stainless steal pot with a stainless steal strainer that slides down into it on our gas stove top. It had started to boil when she had to leave the house, so she turned off the burner. There wasn't any lid involved in this event either. When she returned to the house to cook the spagetti more than an hour later, she simply just turned the burner back on. At some later point, she said she heard the water starting to boil and got up to go put in the spagetti, but before she got to the kitchen, the sudden burst of boiling water pushed up out of the pot about 3-4 feet in the air and out over a 7 foot radius in the kitchen! The pot was never disturbed to initiate the burst. Out of the approximately 9 inches or so of water and oil that was originally in the pan, only about 1-2 inches remained still in the pot. The burner was turned off and the mess cleaned up and thank goodness nobody was in the kitchen at the time it happened.
From some of the reading I was doing, I couldn't find this type of situation, but I am guessing from my reading that we had some type of steam bubble that collapsed during the cooling process and possibly trapped between the strainer insert and the side of the pot that then rapidly expanded at some point after the water was being reheated. Am I on the right track? If so, we need to let folks know of the danger of reheating a previously boiled pot of water with an insert strainer, otherwise, I need to help understand what else could have been the cause.
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From some of the reading I was doing, I couldn't find this type of situation, but I am guessing from my reading that we had some type of steam bubble that collapsed during the cooling process and possibly trapped between the strainer insert and the side of the pot that then rapidly expanded at some point after the water was being reheated. Am I on the right track? If so, we need to let folks know of the danger of reheating a previously boiled pot of water with an insert strainer, otherwise, I need to help understand what else could have been the cause.
I don't know, but I'll guess would be that boiling the water the first time cleared out all the dissolved gases that might otherwise come out of solution and provide additional nucleation sites to start the boil as the water approached boiling point again, and maybe the olive oil had coated the surface of the pan and strainer, smoothing out any nucleation sites there. So the second time, there were no nucleation sites and the water superheated sufficiently for an explosive boil to eventually occur.
Don't know if it would stand up in court though...
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Thanks for the reply. It would be neat to see if someone could replicate it in a controlled setting (not in my house), then maybe post the observations that point to a cause. Any takers?
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Hi All,
I am new to forum and don't know know where to start a new question? can somebody send me a link where to start a new post?
Please anybody of you suggest a way to how to keep the continuously boiling water at a particular surface within any pot so it don't explodes and just continuously evaporates to collect distilled water. I have connected solar evacuated tube to heater hose to boil the water but water explodes from the heater hose.
Thanks for any help.
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You could try adding something to the thing you're trying to distill; like cooking oil, or a silicone.
It helps the bubbles collapse or something.
edit: adding a whole bunch of broken glass might help. It acts as an insulator and keeps the vapour at about 100C whereas the outside may be a little hotter. Also adds nucleation sites which can help prevent superheating.
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Dear wolfekeeper,
Thanks for your support.
Please watch the video below to give some idea....!
.160766617439530&type=2&theater
As far as I understand is to get a metal mesh and pour come crushed glass ant to hang it with in the heater hose as shown in the video. Will that work for me? Will this glass within the heater hose cavity will work as insulator?
Please recommend.
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The video doesn't load for me; but yes, sounds like it.
It's called 'anti-bumping', a bump is when the water/steam suddenly jets out the hose. You can buy special granules for chemistry just for that purpose or just use smashed glass.
There is a gotcha here- if you use very high power it is possible to make the metal so hot the water can't touch the sides due to the Leidenfrost effect- a layer of steam forms that acts as an insulator. So you may (or may not) find that there's an optimum light intensity.
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I see this is a very old post, but thought I would post anyhow. I had the same thing happen to me several times now. We moved near Denver, Colo, and at first we thought it was the 6500 ft elevation we were not use to. Most of the time water boils normally, but there have been about 10 instances in the 6 years we have been here that water exploded on the stove top when we tried to bring it to boil. We even switched to medium heat instead of high heat and it still exploded. It didn't quite form a funnel, but just a very sudden explosive overflowing all over stove top, countertop and floor, and the height was enough to go over to countertops. The episodes instantly nearly empties the pan of the 3-6 cups or so of water (filled about 3/4 the way of pan). We use stainless steel pans, but I don't think they have a copper bottom, with straight sides and no lid on. After this happened a couple times, we did notice that the barometric pressure was higher than normal. Since this also occured in places like San Diego, which is near where we moved from, it doesn't seem to be an elevation issue. Anyone know if barometric pressure can cause this? I did get my arm burned the first time, but now I stay my distance until I see the water boiling normally. Any info would be helpful, as well as interesting.
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Hi.
Just to be safer, don't boil a pan of just water. Leave a wooden spoon in the pan (straight away, i.e. from cold as you start to heat it). Otherwise just add some peas. Shooting blobs of water due to a rapid growth of gas bubbles is often called "bumping". Peas make good anti-bumping granules but rough edges on a wooden spoon will also often be enough to reduce the risk of bumping.
Best Wishes.
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GOOD