Temperature question

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Why is it that when you make ice cubes, they form faster when you pour lukewarm to cool water in the tray, and form slower when you pour colder water into the trays. What is this process called?

Also, related, why is it that if you have a steam hose filled with pressurized steam behind a nozzle, and you spray it onto a pipe encrusted with ice in -30 degree weather, the ice on the frozen pipe will melt faster when you hold the nozle 6-12 inches away from the pipe, and slower if you hold the nozzle 1-3 inches away from the pipe? What is this process called,when the steam is hotter slightly further away from the nozzle?

Brief descriptions of hows and whys of these questions woul;d be appreciated, thanx.
 

Answers and Replies

  • #2
berkeman
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Why is it that when you make ice cubes, they form faster when you pour lukewarm to cool water in the tray, and form slower when you pour colder water into the trays. What is this process called?

Also, related, why is it that if you have a steam hose filled with pressurized steam behind a nozzle, and you spray it onto a pipe encrusted with ice in -30 degree weather, the ice on the frozen pipe will melt faster when you hold the nozle 6-12 inches away from the pipe, and slower if you hold the nozzle 1-3 inches away from the pipe? What is this process called,when the steam is hotter slightly further away from the nozzle?

Brief descriptions of hows and whys of these questions woul;d be appreciated, thanx.
Welcome to the PF.

Can you please give us some mainstream scientific journal links to your assertions on the first question? Thanks.
 
  • #3
russ_watters
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I'm pretty sure this is an urban legend.
 
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Welcome to the PF.

Can you please give us some mainstream scientific journal links to your assertions on the first question? Thanks.
I'm not the OP, but there are a number of journal references listed on the Wikipedia page, mostly from the "American Journal of Physics" and "Physics Education", with a review in "Physics World":

http://en.wikipedia.org/wiki/Mpemba_effect

I believe these journals are peer reviewed, but feel free to correct me.

The main idea is that, naively, you would say that there is one number that characterizes the water in an ice-cube tray -- the temperature. In that case, warmer water necessarily has to become colder water before it freezes, and it's impossible for warmer water to ever freeze faster than cooler water. According to these observations, however, things can be more complicated, and there are certain circumstances where water that starts at a certain temperature can freeze solid faster than another system where the water starts at a lower temperature --- all with the same ambient temperature.

I haven't personally read the references, so maybe it's all BS, but superficially it appears to be a real, documented, phenomenon.
 
  • #5
russ_watters
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Well the quote from Physics world starts with "Even if the Mpemba effect is real...." implying they believe it is not. The issue is that though the question seems reasonably simply stated, there are actually a vast number of different parameters that allow you to create an inequality in the final states of the water (ice), such as evaporating some of the warmer water, forcing the dissolved air out, etc. IMO, such a successful demonstration - if it actually can be done and I don't remember having seen one - would imo be a trick or at least get an asterisk.

Btw, we've discussed it before, at great length: https://www.physicsforums.com/showthread.php?t=14591&highlight=Mpemba+effect
https://www.physicsforums.com/showthread.php?t=205920

Note, in the second link I did a reasonably scientific test with measured amounts of water at 4 different temperatures and a data logger and found nothing unusual. What I demonstrated is that under "normal" conditions like you'd likely find using your own water, your own containers and your own freezer, the effect does not present itself.
 
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No journal links, sorry, just observation, or so it seemed/seems...

Case 1: I get home from work, put telly on the NFL network, make myself a Jack Daniels and Pepsi and there's no ice. Pour t2 trays with cool water, 2 trays with cold water and the lukewarm trays freeze faster than the cold ones.
Backup evidence? I heard someone say that if you pour boiling water off a roof that it will freeze before it hits the ground, but pouring cold water will just keep pouring. Someone saw youtubes of this but I'm on a remote/narrow-band satellite connection now........ sloWWWWW

Case2: I work on a drilling rig where its below freezing for 5 months of the year. If we hold 1" steam-hoses right next to pipe with encrusted ice, we'll melt the ice much faster holding the nozzle 6-12 inches away, than if we hold it less than 3 inches away.

Are my observations questionable?
 
  • #7
russ_watters
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It's really tough to know without a more rigorous description/test.....though your case 2 sounds like an issue of maximizing contact-area of the steam and pipe.
 
  • #8
Pythagorean
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No journal links, sorry, just observation, or so it seemed/seems...

Case 1: I get home from work, put telly on the NFL network, make myself a Jack Daniels and Pepsi and there's no ice. Pour t2 trays with cool water, 2 trays with cold water and the lukewarm trays freeze faster than the cold ones.
Backup evidence? I heard someone say that if you pour boiling water off a roof that it will freeze before it hits the ground, but pouring cold water will just keep pouring. Someone saw youtubes of this but I'm on a remote/narrow-band satellite connection now........ sloWWWWW

Case2: I work on a drilling rig where its below freezing for 5 months of the year. If we hold 1" steam-hoses right next to pipe with encrusted ice, we'll melt the ice much faster holding the nozzle 6-12 inches away, than if we hold it less than 3 inches away.

Are my observations questionable?
Backup evidence for case1 has nothing to do with the discussion, methinks. Boiling water is transitioning already. It's in a high state of kinetic energy, molecules are further apart, so as russ said about c2, you're increasing your contact surface (each molecule of water is getting heat sucked out of it from air molecules on all sides now)

In the slow pour, you likely retain surface tension better, so the water moves more like a body of water (most water are sharing their boundaries with other water molecules, only the exposed surface is being drained by the air molecules now).

But besides that, I live in a -40 degree environment. I know already that when you throw hot boiling water into the cold it evaporates into a big cloud of steam (unless it's dirty water, so the ice crystal can nucleate). No visible ice (unless they're inconceivably small crystals).

Dirty water (say A hot cup of coffee) will send little shards out because the water has so many nucleation sites from the coffee that it's easy for it to ice up (along with the previous reasoning of increased contact area). The cold cup of coffee will just splash and freeze a lot more slower.
 

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