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llanitedave
Humble Megalomaniac

Reged: 09/26/05

Loc: Amargosa Valley, NV, USA
Re: Mpemba effect? Home experiments... [Re: gavinm]
#6268380 - 12/23/13 11:19 AM

Quote:

We have an experiment, which no-one seems to be able to reproduce reliably, there is no theory to explain it and we can't even agree on the starting conditions...

If this was called the E-Cat effect, would this thread be different? Would the members posting be as consistent? or supportive? or..

I wonder...

Have a great Christmas everyone (yes.. I'm on the other side of the date-line so this may be premature...)

If somebody was trying to package and sell it, I'd definitely be a bit more critical.

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Mxplx2
sage

Reged: 09/12/12

Loc: NE PA USA
Re: Mpemba effect? Home experiments... [Re: groz]
#6268421 - 12/23/13 11:57 AM

http://amrita.vlab.co.in/?sub=1&brch=194&sim=354&cnt=1

The curve shows a starting temperature and an ending temperature depending on the ambient. Imagine a second curve depicting another temperature on the same graph. It would curve down to the ambient in it's own path and never equal the other curve until it reached ambient. So if they are never equal any where but ambient, they could never be 32 degrees at the same time.

To look at it by way of the formula, the temperature at time "t" is proportional to the difference between the original temperature T(H) and ambient T(A). In the formula it's shown as (T(H)-T(A)).

At least that's the way I see it.

I should add in summary, that the cooler cup of water will reach 32 degrees before the warmer cup, but both cups will reach 0 degrees at the same time.

Edited by Mxplx2 (12/23/13 01:15 PM)

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Footbag
Post Laureate

Reged: 04/13/09

Loc: Scranton, PA
Re: Mpemba effect? Home experiments... [Re: groz]
#6268524 - 12/23/13 01:00 PM

Quote:

I've done this experiment, but it was worded completely different. Does a tray of ice cubes freeze faster if you use hot water, than if you use cold. LOTS of folks will tell you it does.

We did a semi-controlled experiment. Water just boiled in one tray, and tap water in the tray beside it. Sure enough, the hot tray froze faster. BUT, then we continued, we let both trays thaw, and measured how much water came out of each after the freeze / thaw cycle. About 2/3 of the amount of water came from the hot tray.

Final conclusion, hot tray lost a lot of water to evaporation during the process, ended up with more surface area per unit volume because of it, and heat transfer out of the water is a function of surface area per unit volume. We got ice cubes faster, but, they were smaller. Shape of the ice cube tray plays a big role in this experiment, hunt around and you can find trays that work both ways.

FYI, back when we did this, experiment was accelerated slightly by using a freezer set to -42 degrees C, conditions that were available 'on the front porch' at the time. We had an argument during the experiment about 'is it cold outside', and came up with a simple way to answer that question, formally. Take a normal drinking glass, fill it half full of tap water. Put the glass out on the porch, wait 15 minutes. Tip over the glass. If no water runs out of the glass, it's cold. If water runs out of the glass, it's not cold out. Simple definition, with a proof that can be re-created using no fancy equipment.

Some friends came over last night. We discussed the effect. My friend pointed out that he fills his ice cube trays with cold water and his wife hot. He says her cubes are too small and very brittle. His cubes are much harder and last longer. They didn't notice which froze first.

Evaporation would play a factor in any experiment it's not controlled for. That said, if evaporation, convection, dissolved gassed or any combination of the suggested mechanisms are responsible and the hot sample freezes first, that means it doesn't violate Newton's laws, but does exist.

Edited by Footbag (12/23/13 01:04 PM)

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FirstSight
Duke of Deneb

Reged: 12/26/05

Loc: Raleigh, NC
Re: Mpemba effect? Home experiments... [Re: Footbag]
#6270583 - 12/24/13 12:27 PM

Quote:

Quote:

I've heard of it from the standpoint of someone claiming that their hot water pipes had frozen in severe cold while the cold water pipes remained clear. There are a lot of hidden variables that could be in play, but some of the stories are are nevertheless interesting.

That's actually common. My friend does plumbing and it's frequently the hot pipes that burst as opposed to the cold. When I brought up the effect, he brought up the pipe issue.

Couldn't this phoenomena be due to the fact that hot water pipes in general experience vastly greater, faster, and more frequent fluctuations in temperature than cold water piples, thus being subjected to greater stress from repeated thermal expansion and contraction, eventually causing stress fractures that finally break open enough to cause a leak under the additional stress of a severe cold spell? In short, hot water pipes are subjected to far greater and more frequent mechanical stress than are cold water pipes, and hence are more likely to reach an earlier failure point.

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mich_al
Carpal Tunnel

Reged: 05/10/09

Loc: Rural central lower Michigan ...
Re: Mpemba effect? Home experiments... [Re: FirstSight]
#6271800 - 12/25/13 07:56 AM

Quote:

Some friends came over last night. We discussed the effect. My friend pointed out that he fills his ice cube trays with cold water and his wife hot. He says her cubes are too small and very brittle. His cubes are much harder and last longer. They didn't notice which froze first.

Sounds like time to flush out that hot water tank!

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Footbag
Post Laureate

Reged: 04/13/09

Loc: Scranton, PA
Re: Mpemba effect? Home experiments... [Re: mich_al]
#6327965 - 01/22/14 10:06 AM

Well... I woke up this morning and went to get in the shower. Sure enough, my pipe was frozen.

Guess which one... Yup, the hot.

I got it thawed out with a hairdryer and there doesn't seem to be any leaking. Good thing!

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ColoHank
Carpal Tunnel

Reged: 06/07/07

Re: Mpemba effect? Home experiments... [Re: Footbag]
#6328201 - 01/22/14 12:05 PM

Minerals such as lime which are dissolved in water have a greater tendency to precipitate and accumulate in water heaters than in cold water pipes. Perhaps bits of those precipitates which are subsequently carried through the hot water pipes act as seeds for the crystallization of water ice. No?

I once had an old electric water heater whose tank was so full of precipitated "rocks" that it had little residual capacity for water. One had to shower quickly before the hot water gave way to cold.

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Footbag
Post Laureate

Reged: 04/13/09

Loc: Scranton, PA
Re: Mpemba effect? Home experiments... [Re: ColoHank]
#6328262 - 01/22/14 12:26 PM

Quote:

Minerals such as lime which are dissolved in water have a greater tendency to precipitate and accumulate in water heaters than in cold water pipes. Perhaps bits of those precipitates which are subsequently carried through the hot water pipes act as seeds for the crystallization of water ice. No?

I once had an old electric water heater whose tank was so full of precipitated "rocks" that it had little residual capacity for water. One had to shower quickly before the hot water gave way to cold.

Yes. That was most likely the cause. Just irony that it actually happened to me weeks after thinking about it.

I was just thinking about something. Every time I did the test, I used reverse osmosis water. Had I used tap water, I may have gotten different results.

Edited by Footbag (01/22/14 12:47 PM)

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