| From: David Cecil | 1/07/99
11:33:39 |
| Subject: Hot Water Ice Cubes | post id:
21200 |
| Why is it that when you put two
trays of ice in the freezer, one with hot water and one with cold water,
the one with the hot water freezes at a faster
rate? David | |
| From: Mark | 1/07/99
11:53:53 |
| Subject: re: Hot Water Ice Cubes | post id:
21220 |
| It's got to do with the exchange
of energy - all of which I learnt at high school physics, but that was too
long ago. I remember though that because hot water is further away from
the frozen state, its energy is easier to dissipate and therefore it
freezes quicker. | |
| From: Martin B | 1/07/99
12:00:44 |
| Subject: re: Hot Water Ice Cubes | post id:
21237 |
| This information comes from
http://ugrad.phys.unsw.edu.au/physoc/physics_faq/ There are five factors that have been proposed to explain this much observed behaviour. 1. Evaporation. Hot water evaporates much more quickly than cold water. Water near 100 degrees may lose up to 16% of its volume before freezing. This not only reduces the volume needed to freeze, but also transfers heat from the liquid quite efficiently through latent theat etc. 2. Supercooling. Hot water will contain fewer dissolved gases that can act as nucleation sites for freezing. Thus hot water will be more likely to supercool below 0 degrees. When water freezes it forms a layer on top that forms quite a good insulator, that slows further freezing. Thus supercooled water will form a block of ice much more quickly than water at 0 degrees that freezes normally. This is believed to be the dominant effect in most cases. 3. Convection. Hot water will have stronger convection currents allowing heat transfer more efficiently. This is believed to be effective only down to 4 degrees, when convection reverses. 4. Dissolved gases. These may lower the freezing point of cold water, though no quantifiable data appears to be known. 5. Conduction. Hot water may defrost small containers which, upon refreezing form a better thermal contact. | |
| From: Daryn Voss | 1/07/99
12:35:07 |
| Subject: re: Hot Water Ice Cubes | post id:
21287 |
| Hey look guys! I have one data point to add to the plot. I have just done this experiment, and the cold water ice cubes have already formed a frozen shell, while the hot water ice cubes are still completely liquid. Anyone else actually tried it? | |
| From: Daryn Voss | 1/07/99
13:41:46 |
| Subject: re: Hot Water Ice Cubes | post id:
21319 |
| Later in the same experiment: the
cold water ice cubes are frozen solid, the hot water ice cubes still have
a bubbly liquid bit rolling around in the middle. I invite you all to try this out. Please post your results here. Hooray for the Empirical Method! 8^) | |
| From: Grant | 1/07/99
21:32:37 |
| Subject: re: Hot Water Ice Cubes | post id:
21383 |
Would the type of try make any difference (ie metal v plastic)? | |
| From: Alan | 1/07/99
22:31:37 |
| Subject: re: Hot Water Ice Cubes | post id:
21389 |
| Yes, metal trays would conduct
the heat away a bit faster than the plastic trays. So the water in either
case (boiling or cold) would freeze faster in a metal ice cube tray than
in a plastic one. | |