Freezing pipes

Harv · Dec 22, 2000

<font color=blue>a vacuum which is stressing the pipe inwardly.</font color=blue>

Of course even at sea level a vacuum only runs you around 14.7 psi, which isn't much stress for a pipe.

This thread has made me wonder if I remember my physics as well as I thought I did. /w3tcompact/icons/crazy.gif

I'm at the age, however, where it's possible that the books have been re-written and I'm just not up to date. /w3tcompact/icons/smile.gif

Bird · Dec 22, 2000

Al, once again, I could be wrong, but I don't think you'd create enough vacuum to hurt even PVC pipe in your scenario; however, as I mentioned before, if you apply too much heat in your scenario and the ends are still frozen and plugged, I've been told you can create enough steam pressure to rupture the pipe. I haven't done it yet, so I can't say it's true, but the theory sounds right to me./w3tcompact/icons/wink.gif

Bird

TWINKLE_TOES · Dec 22, 2000

Bird,

I'm sure your right on the tremendous power of steam in a closed vessel. I think the volume ratio of water to vapor is something like 1200:1, maybe more. I also agree with Harv and you it's a pretty whimpy pipe that bursts at a 14.7psi differential. I was trying to envision any senerio which allowed a pipe to burst when thawed. Guess I didn't do to well, but still a fun subject. One time as a Boy Scout I put a can of chicken noodle soup in the fire, no holes, noodles everywhere. No cooking merit badge for me./w3tcompact/icons/smile.gif

Bird · Dec 22, 2000

Al, did you salvage enough noodles for supper?/w3tcompact/icons/laugh.gif/w3tcompact/icons/laugh.gif Heck, I'm one up on you in the Scouts; I won the pancake flippin' competition; practiced for days flipping one of Mother's potholders./w3tcompact/icons/laugh.gif

Bird

ddl · Dec 23, 2000

I just had to reply to this thread. First what Harv is talking about is pressure not a vaccumm, two different things. About the pipe freezing and thrawing the middle and the steam bursting the pipe, since the melting ice needs to go through two phase changes to reach steam and either end of the area of pipe has ice, as the center heated up to change phase the temperatutre increase would melt the ice, adding more water to the phase changes, thus increasing the amount of energy to make the phase change. In order to burst the pipe because of the pressure in the pipe because of steam, the phase change would have to happen very, very fast, like maybe a spilting a atom. Highly unlikely. What caused the pipe to burst is the fact that water expands as it changes phase from a liquid to a solid. The increase of size of the ice divides the pipe. Of couse you do not see the crack until the ice melts. Bet some of you think hot water freezes faster than cold water!!

Dan L p.s excuse the spelling, never claim to be a speller

Bird · Dec 23, 2000

Dan, do you mean that if you have a 5' to 10' length of 1" pipe, frozen solid, with water pressure beyond the ice in at least one end, and you apply heat with a torch to the middle of it, you can't get it hot enough to produce steam and enough pressure to rupture the pipe before the ice blockage is melted at the ends? Seems to me that you could, and that's what I've been told, but as I said, I haven't done it so I can't say for sure.

And you mean to tell us that hot water won't freeze faster than cold water?/w3tcompact/icons/wink.gif

Bird

gerard · Dec 23, 2000

ddl, While I don't know if hot water freezes faster than cold water (instinctivly I would have to say not) I have heard that hot water does in fact freeze faster due to having a lower dissolved oxygen content. Don't know if this is true or not but seems like it would be a pretty simple experiment to set up. As an aside I bought my house from an "inventor" who developed his company in the basement (smokeless liquid wax for restuarant wicked candles) so he was quite a tinkerer. I noticed my icemaker is hooked to the hotwater line. At first I just assumed it was a stupid mistake but when I mentioned to a co worker I was told that hot water actually will freeze quicker than cold for the afore stated reason. (Another interesting water fact is that only water with impurities freezes at 32deg F. I just read that ultra pure water can actually remain unfrozen down to 40deg below zero. (I assume this would have to be "laboratory pure water") Something to do with the ice having to have a place to start the crystalization process. Interesting trivia anyway!

Harv · Dec 23, 2000

Dan -

Like I said, they may have re-written the physics books since my college days, but ...

If you remove the pressure from the inside of a vessel (vacuum), the weight of the atmosphere (14.7 psi at sea level) is still acting on the outside, so the net pressure on the pipe is 14.7 psi, giving the pipe a "tendency" to implode.

Also, hot water does, as Gerard said, contain fewer gas molecules, which normally contribute a slight insulating property to the liquid. If you boil water for a time, for example, and then pop it immediately into the deep freeze, it will magically freeze much faster than the same volume of cold water. Didn't get this from a book -- we actually performed this experiment in one of my early physics labs.

I will not give up my ignorance status, however. If you're saying that when water goes from a solid state (ice) back to liquid, it passes through a stage of increased volume, I'm not prepared to deny it. I believe that there are actually different forms of ice itself. We're all familiar with ice cubes in our freezer (at 20 degrees or so), but I believe their molecular structure is different than ice at, say, minus 40, as you may find in some of your non-Californian pipes. /w3tcompact/icons/wink.gif I'm not at all sure what happens to the volume as you continue to decrease the temperature.

Wow!/w3tcompact/icons/shocked.gif This board gets, like, totally cerebral sometimes. /w3tcompact/icons/tongue.gif

TWINKLE_TOES · Dec 23, 2000

Who wouda thunk we could get this much mileage out of just a pipe and some water.
My lame hyposthisis on the vacuum senario was not one based on the absolute force created by the vacuum (and Harv has that right, the differential can be no larger than atmospheric pressure ~14.7 psia) but more based on the effect of the stress reversal. One section trying to explode another trying to implode. Kinda like placing a piece of steel in a vise and working it back and forth until it breaks. Even with this thought it still seems pretty lame.

Water can exist in two states at 0 deg C, solid and liquid. The difference is, to be ice the water must give up ~80 calories per gram for the state change from water to ice. The same energy transfer must occur when it changes back to water. Water has its highest density at 4 deg C.

One usefull thing that has come out of this thread, we have a world class pancake flipper among us. An addition to the many talents of Mr. Bird/w3tcompact/icons/smile.gif

Happy Holiday Season to all /w3tcompact/icons/smile.gif/w3tcompact/icons/smile.gif

ERNIEB · Dec 23, 2000

Normally, hot water does not freeze faster than cold water.http://www.sciam.com/askexpert/physics/physics21.html
Back in the days when I went through basic training, C rations came in an OD can. Beans & weenies, lima beans & ham, and so on. Sometimes when we were in the field, the cooks would warm these cans in a big pot of hot water. Now, I figure somewhere there was a 2nd Lt. who figured out how hot these cans could get before exploding. He must have wrote a TM simple enough that even the cooks we had could understand it. If only we could find that guy.

ErnieB
"We must defend our rights, ourselves, and our country by force of arms."
Stephen F. Austin