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- Newsgroups: sci.engr.mech
- Path: sparky!uunet!usc!zaphod.mps.ohio-state.edu!swrinde!cs.utexas.edu!bcm!aio!drseus.jsc.nasa.gov!mike
- From: mike@drseus.jsc.nasa.gov (Mike Ross)
- Subject: Re: Warm water freezes first. why?
- Message-ID: <1992Dec18.143813.16785@aio.jsc.nasa.gov>
- Sender: news@aio.jsc.nasa.gov (USENET News System)
- Organization: Lockheed Engineering & Sciences Company
- References: <1fliu2INNeou@usenet.INS.CWRU.Edu> <1flklaINNg2l@usenet.INS.CWRU.Edu> <1992Dec17.162456.214@janus.arc.ab.ca>
- Date: Fri, 18 Dec 1992 14:38:13 GMT
- Lines: 49
-
- In article <1992Dec17.162456.214@janus.arc.ab.ca> morgan@arc.ab.ca (Sean Morgan) writes:
- >In article <1flklaINNg2l@usenet.INS.CWRU.Edu> sxs@r2d2.eeap.cwru.edu (Soheil
- >Sayeh) writes:
- >>This question is actually asked in one of the Heat Transfer classic text
- >books.
- >>I belive it was Holman. This is what I think:
- >>
- >>The combined effect of higher temperature gradient and evaporation is the
- >cause.
- >>because of low temperature in the freezer the air is extremely dry, so the hot
- >>water starts to evaporate, and at the same time it cools down. what happens is
- >
- >>,we are freezing less amount of water in the warm tray. and the amount of
- >>heat requred to do it is less than the cold tray.
- >>
- >
- >Yes, would INITIALLY have a higher temperature gradient, but after a few hours
- >the warm water would be where the cold water was to start with!
- >
- >I thought it was because there are fewer dissolved gases in the warm water.
- >Now how that affects the cooling rate, I don't know. Can't see how it would
- >reduce the specific heat very much.
- >
-
- I'm the original poster who asked this question. This is the biggest
- thread I've ever generated. A thoroughly interesting engineering
- discussion by a lot of learned individuals regarding my question!
-
- It appears the answer is as many people have pointed out, that the
- evaporation rate causes there to be less water when the hot tray
- reaches the temperature that the cold tray started out from, and so
- less energy actually needed to be removed to freeze. I had been told
- that the phenomenon could be explained via differential equations,
- so the evaporation rate fits that.
-
- Of course, I'm still drawing my conclusions from the net.discussion,
- I've not checked that explanation, it just seems the most plausible.
- The rationale that the warm water makes better contact with the metal
- tray doesn't wash, because the cold water would also melt the ice on the
- grill and get good contact.
-
- My thanks to all the learned participants from this auguste group.
-
-
- --
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