Why did this happen?

[YoshiSato]

I was heating up my lunch in a microwave bowl with a lid. The lid was covering the bowl however it was sealed in order to vent steam. I turn the radiation box on for 2:30 minutes after it was done heating I open the microwave and found my bowl and lunch sort of vacuum sealed. The lid was closed and the bowl sort of imploded. When I took the was a suction force trying to keep the lid on.
a

I may have slept through physicis but I though heat expands air and should then have blown the lid off not create a vacuum

 

[Parkre]

what were you cooking?

 

[Gibsons]

You heat the liquid to near boiling, filling the gas volume with steam/water vapor (removing atmospheric air). Excess vents to the outside. Then when heating stops, some of the water condenses around the lid, forming an airtight seal. A little more cooling, more water condenses, causing a vacuum (region of much lower pressure) inside the bowl. Atmospheric pressure crushes your bowl/lid.

 

[Witling]

Mr. Wizard, a science guy on '50's TV used to have an impressive demonstration. He'd take a metal screw-top syrup can (they were common then), put some water in it and start the water boiling. Take the can off the hot plate and screw the lid on. Spray water on the can. It would collapse immediately. Incidentally, steam engines soon evolved to take advantage of this phenomenon by spraying water into a steam cylinder as it started on the evacuation cycle.

But, I think this particular subject just barely qualifies as "highly technical." At least it ain't "How do I fix . . . .?"

 

[YoshiSato]

Originally posted by: Parkre
what were you cooking?

Ravoli with tomato sause.

 

[Bassyhead]

Gibsons got it right.

 

[Mday]

Originally posted by: YoshiSato
I was heating up my lunch in a microwave bowl with a lid. The lid was covering the bowl however it was sealed in order to vent steam. I turn the radiation box on for 2:30 minutes after it was done heating I open the microwave and found my bowl and lunch sort of vacuum sealed. The lid was closed and the bowl sort of imploded. When I took the was a suction force trying to keep the lid on.
a

I may have slept through physicis but I though heat expands air and should then have blown the lid off not create a vacuum

you SEALED it to VENT steam? makes no sense...

 

[Soccerman06]

***Disclaimer-Do Not Attempt***

Put a toothpick or cd/dvd in the microwave and see what happens. Its cool.

***Disclaimer-Do Not Attempt***

 

[OCedHrt]

Put aluminum foil in. That's cool too. Not sure if you need water, I had water but I don't really know why it does what it does

 

[Soccerman06]

Originally posted by: OCedHrt
Put aluminum foil in. That's cool too. Not sure if you need water, I had water but I don't really know why it does what it does

***Disclaimer-Do Not Attempt***

Water and aluminum foil dont do anything together as far as I know. But get pure water through electrolicis or by boiling water, and then microwave it for a few minutes. Take it out and put anything in it (even tap water) and it exlodes .

***Disclaimer-Do Not Attempt***

 

Originally posted by: Soccerman06

Originally posted by: OCedHrt
Put aluminum foil in. That's cool too. Not sure if you need water, I had water but I don't really know why it does what it does

Water and aluminum foil dont do anything together as far as I know. But get pure water through electrolicis or by boiling water, and then microwave it for a few minutes. Take it out and put anything in it (even tap water) and it exlodes .

thats a good way to get steam burned.

 

[AnthraX101]

Originally posted by: Soccerman06

Originally posted by: OCedHrt
Put aluminum foil in. That's cool too. Not sure if you need water, I had water but I don't really know why it does what it does

Water and aluminum foil dont do anything together as far as I know. But get pure water through electrolicis or by boiling water, and then microwave it for a few minutes. Take it out and put anything in it (even tap water) and it exlodes .

First note: These things can kill you, start a fire, release toxic chemicals, or burn you. Don't do them in real life.

Technical descriptions:

When you put a piece of foil (or other conductive materials) in the microwave, the conductor begins acting as an antenna. If the object has sharp edges or points a electric field will build up in that area and then discharge where ever it can, resulting in sparks if the air has to be broken down to do it. Interestingly, smooth metal objects usually don't have the points needed to form uneven charges. This means you may be able to place a metal spoon in the microwave and not have sparks while a metal fork will spark.

Remember that this both produces toxic chemicals and can cause a fire. It may also damage your magnetron, depending on the size of the object.

As for the trick with water, it's called "superheating". Water can be heated above its boiling point if the conditions are just right. This is because the molecules are not likely to form steam bubbles spontaneously, they tend to form around nucleation sites. If there are no existing pockets of steam or hard edges in the container, the water may remain liquid far above its boiling point.

Almost anything can introduce a nucleation site. Even bumping the cup a little bit can cause the site to form. Certainly any amount of other material will cause it to form.

Once the first nucleus is formed, all the heat in the liquid gets drained into energy to perform the liquid->gas conversion step, causing an extremely large amount of steam to form quickly. This can be so quick that a large steam bubble forms under water, and rises quickly, splashing water at boiling temperature.

Remember, this can burn or even kill you. I don't recommend doing it.

AnthraX101

 

[Soccerman06]

LOL guys I will put a disclaimer up on my post, but seriously who would try to do these things, besides me of course . I know what Im doing though, I have the microwave set outside, away from anything considered hazardous and I hide behind something, generally behind something big.

 

[mjia]

MythBusters (from the Discovery Channel) actually tested both the effects of putting metal objects in the microwave and heating pure water. They were able to confirm the phenomena suggested by AnthraX101 (after taking sufficient safety measures of course).

 

[DrPizza]

By far, the most interesting thing I've ever seen done with a microwave is slicing a grape nearly in half, folding it over, and putting it in the microwave. It forms (allegedly) a dipole antenna. The results are spectacular. A video link has been posted here before. I'd search for it, but on dial-up, it's not worth the bother.

 

[JasonSix78]

Grape in Microwave thread

-Jason

 

[xSauronx]

Originally posted by: AnthraX101

Originally posted by: Soccerman06

Originally posted by: OCedHrt
Put aluminum foil in. That's cool too. Not sure if you need water, I had water but I don't really know why it does what it does

Water and aluminum foil dont do anything together as far as I know. But get pure water through electrolicis or by boiling water, and then microwave it for a few minutes. Take it out and put anything in it (even tap water) and it exlodes .

First note: These things can kill you, start a fire, release toxic chemicals, or burn you. Don't do them in real life.

Technical descriptions:

When you put a piece of foil (or other conductive materials) in the microwave, the conductor begins acting as an antenna. If the object has sharp edges or points a electric field will build up in that area and then discharge where ever it can, resulting in sparks if the air has to be broken down to do it. Interestingly, smooth metal objects usually don't have the points needed to form uneven charges. This means you may be able to place a metal spoon in the microwave and not have sparks while a metal fork will spark.

Remember that this both produces toxic chemicals and can cause a fire. It may also damage your magnetron, depending on the size of the object.

As for the trick with water, it's called "superheating". Water can be heated above its boiling point if the conditions are just right. This is because the molecules are not likely to form steam bubbles spontaneously, they tend to form around nucleation sites. If there are no existing pockets of steam or hard edges in the container, the water may remain liquid far above its boiling point.

Almost anything can introduce a nucleation site. Even bumping the cup a little bit can cause the site to form. Certainly any amount of other material will cause it to form.

Once the first nucleus is formed, all the heat in the liquid gets drained into energy to perform the liquid->gas conversion step, causing an extremely large amount of steam to form quickly. This can be so quick that a large steam bubble forms under water, and rises quickly, splashing water at boiling temperature.

Remember, this can burn or even kill you. I don't recommend doing it.

AnthraX101

i knew about this but have never experienced it
i watch alot of foodtv, alton browns show being a favorite of mine, and a few times he boils water in the microwave he always tells viewers to put a wooden spoon in the bowl because of this, so that you dont have it flash-boil in your face.

burnination by steam is not fun, ive been burned by it many times, owie.

 

[xSauronx]

Originally posted by: JasonSix78
Grape in Microwave thread

-Jason

that was pretty damn cool

 

[xtknight]

Originally posted by: Soccerman06
LOL guys I will put a disclaimer up on my post, but seriously who would try to do these things, besides me of course . I know what Im doing though, I have the microwave set outside, away from anything considered hazardous and I hide behind something, generally behind something big.

lol, i did that with an AOL CD and the microwave in my kitchen, it was cool. the microwave still works fine, and the CD, well, no it doesn't work anymore, not that I care.