| MadSci Network: Chemistry |
Very interesting...I'm not sure I understand your argument. Normally, solids are more dense than liquids, but the opposite is true for water. So, ice floats on top of water. Knowing this, the ice patches must be floating at the surface, correct? OK, getting this straight means you must be asking if the ice patches would work better if we place water over the patch. Well, this would certainly smooth the ice, but as for practical application to ice-building... well, it would take an experiment to prove this to me.
On one hand, you are correct: Rivers and lakes are cooled by the air cooling the top layer of water. The cooler water is more dense than warm water, so we get overturn (supplying much needed oxygen to lower depths). Once the upper layer reaches a temperature below 4 C, the water becomes LESS dense than the water below it (Ice is less dense than water.) Thus, the overturn ceases and the top layer becomes ice. So, if we could keep the body of water transporting the cooler water to the bottom, we could freeze it more quickly.
On the other hand: As we add water on top of ice, we are increasing the pressure on the sides of our ice pocket. As pressure increases, we can get melting of the ice, because it tends to revert back to the phase which takes up less volume in order to relieve some of the pressure. This is why a heavy snowfall can do more harm than good to a frozen lake in terms of ice-skating use. Another points against your argument is that you can freeze ice then go well below that freezing point before placing it in the river. Placing ice at -70 C would certainly be faster than waiting for ai r near freezing to absorb the heat from the water or adding water above 40 C. If you are worried about the heat transport taking too long with huge chunks of ice, then break it into smaller bits before adding it.
Ask the question again if I did not answer what you were asking! jt