Tilted Forum Project Discussion Community

Quote:

Originally Posted by C4 Diesel

I don't think "moving fast" is a condition that allows supercooling. Agitation is normally a condition that causes nucleation and propagation of phase change. I would be interested to know why this phenomena occurs, though.

Also, supercooling normally does not occur, even in a "clean" water supply. I'm not questioning the added energy requirement necessary to overcome the surface tension which occurs when a particle of a different phase is created, it's just that ordinary water (yes, even distilled water) is normally not that clean. There is already particluate in it which acts as a nucleation center and greatly reduces the surface tension of the new phase. Water that is actually clean is called nanopure water, and we buy it to make buffers which will be used in chemical detection instruments.

The jug thing baffles me. The entire contents turned to ice? The enthalpy of fusion of ice is 334 joules per mL (or gram). This is 80 calories. Even assuming that 1/4 of the jug froze and this was enough to break it, that would still mean that the water was at -20*C.

...Oh, and don't think it's not cold here. I'll wake up and it'll be -25*C (-13*F) here, so it's not like I don't know cold.

The fast moving water I mentioned is moving 180,000 CFS in a very LARGE river in -40C degree conditions. The average civil engineer plans for this when building in a northern climate. Bridges, dams etc are greatly weakened by these effects.

The firm we work for is situated 1000 kilometers (620 miles) north of the American Border near the coast of the Hudson's Bay. In the months of December and January we had 26 days where at 1:00 pm the temperature was below - 25C. Even with a 30 kilometer per hour wind there was still open water in the forbay and the tailrace water of the Generating Stations especially near our medium head plants.

1. Supercooling is a normal winter condition. It's occurance was planned for in the 1960's during the construction of the plants mentioned in my last post. (did I mention them... whatever...) Currently our Hydraulic Engineering and Operations (HEO) staff plan our generation strategy around these conditions.

Supercooling of water occurs (in this case) when fast moving open water is cooled below the normal freezing point of water... It loves to form ice quickly when it flows around a static object such as a bridge beam or intake screen.

2. Frazzle ice clogs the intake screens on at least 3 of our units over a period of 1- 2 months every other year because of these conditions.

3. The frazzle ice that sticks to the Rip-rap on the tailrace (outlet) end of our plants inpinges on the channel enough to cause a 2 - 3 meter (6 - 10) foot rise in tailwater elevation and the subsequent Head loss at the plant is enough to cost about 1 million dollars in lost generation every year at each of the plants when it does occur. Unfortunately this condition affects all of the generators when it occurs, because of the change in tailwater elevation.

Oh yeah... in case you are doing the math here all three of these plants is 1300 megawatts in size or larger. Hence the 180,000 cubic feet per second flow rate... The output is worth many thousands of dollars per hour.

4. I was surprised that the jug of water was actually -20 as you say it had to have been... cool! .... super coool? ha ha

p.s. It was -47C this morning... it warmed up to -26C today... brrrr.