Friday, February 6, 2009

Warm water freezes faster than cool water?

They say warm water freezes faster than cold water. Sounds plausible, doesn't it? Whenever someone says something totally opposite the way it should be, it sounds totally believable. So, I decided to test it.

Experiment #1

Using aluminum vessels to maximize heat transfer (speed up the cooling), and identical vessels at that, I added identical tap water. I let both acclimate to room temperature. However, one vessel must be cool, so I set it outside in the cold for a few hours to get it down to 39 degrees Fahrenheit.

The other vessel was 64 degrees, and so I placed it next to the cool vessel and recorded the time and temperatures by taking photos every 30 minutes.

Don't think that heat was transfered from the warm vessel to the cool vessel, or vice-versa. The updrafts created by the two vessels kept their heat well above them near the 10-foot tall ceiling, which was then removed by drafts from the warmer house. The outdoor temperature was consistently 5 degrees cooler than the temperature on the screened-in porch.

Radiated energy isn't a problem, either, thanks to the metal vessels.

You are probably predicting the outcome already, seeing as how I set the first vessel outside a few hours early. Shouldn't the second vessel be a few hours behind in cooling? No, that would be ridiculous.

As it turns out, it really was a few hours behind. Logic prevailed, thank God!

Interestingly enough, the warm water cooled faster than the cool water. It cooled faster, it didn't freeze faster. Big difference!

Maybe that's the source of the argument: a simple grammatical confusion. And this problem we have with the English language cost me about 16 hours of hassle. Do me a favor, the next time somebody says "warmer water freezes faster than cool water" exile him/her to a country where you're not allowed freedom of speech.

So, here are the results. Keep in mind the two thermometers used in each vessel were tested to be identical. However, the third thermometer for ambient temperature reads a little high. Plus, it was hard to read.

My results are the same as Isaac Newton's results over 300 years ago. Physics hasn't changed. Go figure!
http://demonstrations.wolfram.com/NewtonsLawOfCooling/

________ambient____warm water___________cool water
_time____temp_________temp_________________temp

_2:21____32_F_________64____________________39
_2:52____32___________53____________________38
_3:25____32___________46____________________36
_3:52____31___________42____________________34
_4:23____30___________37____________________32
_4:53____29___________35____________________31
-5:21____28.8_________33____________________30
-5:51____27___________31____________________28
_6:21____27___________30____________________27
_6:52____26.8_________28____________________26
_7:21____25___________27____________________25
_7:55____24.8_________26____________________24
_8:22____24.5_________25____________________23
_8:51____24.5_________24.5__________________31__(slushy surface)
_9:51____23.5_________24____________________31__(frozen surface)
10:51____23.2_________23.5__________________31.5
11:21____23.5_________33_(slushy surface)______31__(partly frozen
_______________________________________ throughout, frozen in
_______________________________________ vertical sheets)

And what's up with that water sitting at sub-freezing temperatures for four hours, but not freezing? Then when it does finally does freeze, the temperature jumps up to about 32. I'll have to ask a conspiracy theorist.

Start of experiment, warmer water on left, cooler water on right:

Warmer water cools faster:

Warmer water still cooling faster:

The cooler water turns to slush first, obscures C and F labels, difficult to impale slush with coin because it was frozen a while, so I laid the coin flat:

Warmer water turns to slush over 2.5 hours later. It wasn't as frozen, was easy to impale with coin. A fatter coin at that:

Experiment #2

My cousin tells me the myth is that HOT water feezes faster than cool water. So, I re-animated the experiment. This being the end of Winter, the tap water coming directly from underground city pipes to the basement can be as low as 42 degrees. It wasn't quite that low today, but I used it instaed of letting warm tap water (from upstairs) sit outside for 3 hours in order to cool it.

For the hot water sample I used water that had been sitting in the water heater for hours. This water has lost a lot of it's dissolved gassese, being 140 degrees or so. My Dad tells me this makes the water's heat transfer rate significantly higher. In other words, the dissolved gasses act as insulators, and the lack thereof acts as un-insulators.

After a few sceonds of running hot tap water, it was about 105 degrees (I guess we need our pipes insulated). I nuked it for 60 seconds (in a coffee cup) with an 1100 watt microwave oven, and that put it well over 120 degees. After pouring it into the aluminum vessel, it burned my hand in a few seconds, and my palms were sore for half an hour. Not sure how hot it was, but I'm estimating about 150 degees, seeing as how a 180 degree engine causes blisters or takes the skin off my fingers.

So, here we go. Highly gaseous cool water vs. low-gas hot water.

The results fried my brain. The cool water froze much faster than in the first experiment. The photo at 2 hours 20 minutes shows a nice layer of ice has formed. Equally brain-frying, the hot water dropped to near freezing in the same time.

Another hour hasn't changed things much. In fact, the warm vessel became warmer:

But, alas, for all you conspiracy nuts this is not your day. The hot water required 2 more hours to freeze.

The cold water's ice sheet could not be penetrated by the screw, even though I banged on it a dozen times. The warm water's ice sheet could easily be penetrated.

The warm water's ice sheet was easily chopped up by the screw. I tried to chop up the other but it held fast.

What I really liked was that the cool water froze as one would expect, outside-in and top-down. I was holding a nearly complete vessel made of ice.

The hot water froze like in the first experiment, in parallel sheets. And not much of them. I forgot to weigh both ice masses, but looks like the cool water had more ice than the hot water.

Conclusion: This was a realy cool experiment.