stevek@umcp-cs.UUCP (08/16/83)
know how true it is but ...) An engineer looked out his window in dead of winter and saw a bird on a telephone wire. All of a sudden he wondered how the bird kept from freezing his feet off. He looked up some constants and came to the conclusion that the bird had to be generating a tremendous amount of heat, more than the bird could possibly generate. He discussed this with some friends who collectively remembered some basic biology and chemistry concerning blood , counter-current multipliers , tissue , vaso-constriction ... They printed notes in one of the journals and the replies reverberated (sound familiar ?). This continued for some time until an Ornithologist (bird specialist) read it got a good laugh , showed it to his friends who also got a good laugh. They let the whole thing continue till one of them said enough. As an obserever and scientist he knew the answer - when a foot got cold the bird lifted it up under his feathers, thus he could keep both feet from freezing wihout carrying around a small power plant. As far as the chemistry for freezing water from cold vs hot water. Refer to any physical chemistry book. (BASIC PHYSICAL CHEMISTRY FOR THE LIFE SCIENCES . Williams and Williams Freeman press 1967 will do nicely.) Without going into thermodynamics, free energy, probability and the structure of water , once energy (heat) has been put into water the only way one can make ice out of it is to 1) lower its temperature 2) increase the pressure. Unless you have an unusual freezer #2 is out. Which would mean that hot water has to take longer to freeze. THERE IS AN OUT ! What you get out of your hot water tap is not the same as the cold! Several things have happened. 1) it is hotter 2) some of the dissolved gasses are gone 3) the ionic balance has been changed (salts etc from the walls of your old heater). 4) some of the other organic/inorganic "goodies" are changed Depending on what you heater did to the water I can construct reasons why some people observe the different rates. If your heater added salts the cooling curve is changed in favor of longer colder time to freeze , but if it has added what are called seeds for the ice crystals to form on , freezing time can be shortened. Water that has no seeds to form ice nuclei will freeze suddenly on shock ... . (It is quite an impressive basic chemistry demo usually done in the first year). My advice - run a controlled experiment to find out which will freeze faster with your water. In one tray hot tap water in a second cold tap water. Place both into your freezer at the same time then every few min's see if they are frozen. One warning - clean water with little gas (or air) freezes as very clear ice (sometimes you cannot tell it is frozen). The commercial ice plants know this and both clean up the water with filters and ion-collums and distillation plants to end up with "just water" and they sell that crystal clear "clean tasting" ice. As far as hot water freezing faster due to evaporation that's a new one. But for you skiers who have sometimes noticed that it gets warmer when it begins to snow something called heat of fusion when water changes from liquid to solid , warms the air. Stephen Kogge Dept. of Computer Science U. of Maryland
dee@cca.UUCP (Donald Eastlake) (08/20/83)
I thought that the reason that hot water froze more rapidly that cold
water a lot of the time in home refridgerators is that the temperature
in the freezer actually varies quite a bit depending on whether the
compressor is running or not. Putting in hot water will probably warm
things up enough to start a cooling cycle.
Maybe modern energy efficient refrigerators with better insulation
that tend to have their compressors running a higher fraction of the time
do not show this effect.
+ Donald E. Eastlake, III
ARPA: dee@CCA-UNIX usenet: {decvax,linus}!cca!dee