Thermodynamics question



8 replies to this topic
  • MN_Kevin

Posted March 25, 2001 - 02:42 PM

#1

I have heard hot water freezes faster than cold water. I have yet to see this proven and other engineers I have asked have heard it also, again never seeing it proven. Common sense says this is BS, but in nuclear power, we throw common sense away.

Any takers?

If this is true, does cold water boil faster than hot water? Prove it.

  • Rick_Graham

Posted March 25, 2001 - 03:13 PM

#2

Kevin,
I can't prove with water but I do know when my wife get's mad (hot) she turns into an Ice queen (cold).

  • Guest_Guest_*

Posted March 25, 2001 - 03:42 PM

#3

I also worked at a Nuclear plant for 11 years. One night at a party we put 2 ice cube trays in the freezer, one with boiling water, the other with tap water. We saw nothing to make us think that the boiling water would freeze first. But it was suprisingly close.

The next day at work, we did it again (we were afraid that the alcohol might have clouded our judgement. Same results.

I worked at the Perry Nuclear power Plant,(reactor Operator) where do you work.

I was also a nuke in the navy. (USS Trepang, SSN 674)

Hope this snow goes away, I really want to ride.

  • MN_Kevin

Posted March 25, 2001 - 05:16 PM

#4

Seabrook Station in New Hampshire

USS Tennessee, "M" Division, class 8502.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • Mojo

Posted March 25, 2001 - 08:15 PM

#5

Stillerz,
nuke plant....alcohol.....clouded judgement. :)
hmmmmm, nice to know you don't work there anymore.

  • Rich_Rohrich

Posted March 25, 2001 - 10:03 PM

#6

From Joe Larsen, Researcher at the University of Southern California

The rate of heat transfer is proportional to the temperature difference between the two objects, so hot water will lose heat faster than cold water. In other words, if you have water at 90 degrees C and water at 10 degrees C and the freezer is at -10 degrees C, the hot water will lose heat five times faster than the cold water; however, the cold water will still win the race. As the hot water cools it's rate of heat transfer will decrease, so it will never catch up to the cold water.


[This message has been edited by Rich Rohrich (edited 03-26-2001).]

  • darbsitton

Posted March 25, 2001 - 10:53 PM

#7

All other things being equal, the cold water will freeze faster. However, it is possible to corrupt an experiment and come up with erroneous conclusions as outlined at the following link.
http://physics.about...y/aa071500b.htm

I actually performed this experiment back in college and came up with many of the same conclusions and observations. The first couple of times the hot water actually froze faster. :)

In disbelief I repeated the experiment taking great care to eliminate any sources of error I could think of. Take water from same tap. Heat all water first to reduce the amount of air dissolved in water. Repeat experiment with positions of hot/cold water swapped. In the end the cold water froze first and with renewed confidence I got back to the studies I should have been doing all along. :D

--Brad

  • MN_Kevin

Posted March 26, 2001 - 12:45 AM

#8

I concur wholeheartidly. The rate of heat xfer is greater with a greater delta T, however the water nearest it's target temp will win!

Thank you.

  • Ted_in_Massachusetts

Posted March 31, 2001 - 07:19 AM

#9

I realize that this topic has been dead for a few days but I'm just getting caught up on my reading. I've never done the experiment but have been told that the reason hot water is believed to freeze faster is that that when you put hot water in the freezer, more of it will evaporate than the cold, thus freezing faster. I guess this means you end up with smaller ice cubes...

For what its worth.




 
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