Freezing……

[Ady1Participant @ady1]

We get this big freeze up about once every 10 years, not much fun when it happens

On the plus side the Beeb stops clacking about global warming for a while

[not done it yetParticipant @notdoneityet]

Posted by DMB on 13/12/2022 09:27:17:

May I remind all previous posters about freezing temperatures that water actually expands a few degrees above freezing point. So when water is actually frozen it has already expanded and busted the weakest point like say a pipe. There is, therefore, a need to keep the temperature about 5° F above the freezing temperature.

Not true. Liquid water certainly has its maximum density at close to 4 degrees Celsius, but it also expands above 4 Celsius and does not break pipes (yes, it is still a liquid (until it actually freezes) and as such conforms in shape to the containing vessel. The large expansion which can rupture pipes, on freezing, far exceeds the change in volume between 4 degrees Celsius and freezing point.

[not done it yetParticipant @notdoneityet]

Posted by Hopper on 13/12/2022 10:22:13:

Posted by not done it yet on 13/12/2022 07:49:32:

Explanations include Evaporation, dissolved gasses, convection, effect on the surrounding air, and supercooling. It is quite complex and totally counterintuitive.

Re this phenomenon – I put part of it down to viscosity – and possibly thixotropy in water (London bonding and all that).

The way it has been demonstrated by some is to throw a container of each hot and cold water on frozen ground – where the hot freezes first. I argue, in this particular case, that viscosity is a major factor as the hot water would spread much further than the cold.

Is there much difference in viscosity of water at say 80C and 20C? I can't say I have noticed the boiled water poured out of the kettle into the teapot as noticeably less viscous than the cold water out of the tap going into the kettle. Hardly scientific though!

I have no idea, but heating a liquid generally reduces the viscosity? Try spilling containers of hot and cold water and see which spreads out the most? Try running hot and cold water through a fixed size orifice at a fixed head or volume? Several ways to find out, if you are that interested.

Water is a unique liquid in that it exhibits non-normal characteristics such as a maximum density above the freezing point. If it was not like that, water courses would freeze at the bottom, not on the surface – and not thaw out so easily afterwards. The Earth would likely not support life, as it does, as we know it. Possibly think, here, of fauna that hibernate in the mud at the bottom of waterways?

These ‘peculiar’ characteristics is attributable to London bonding, which is found between water molecules.

[File HandleParticipant @filehandle]

These ‘peculiar’ characteristics is attributable to London bonding, which is found between water molecules.

I have always called the polar bonds in water Hydrogen bons. However, I have always been fascinated by the untypical behaviour of water, including that a charged rod will attract / repel a column of water.

[Nigel Graham 2Participant @nigelgraham2]

Water certainly is a strange compound, considering how simple it is:

– Maximum density only 4 degrees above a sharp triple-point – hence ensuring lakes and oceans are not frozen solid; and still able to evaporate at only just above freezing, into dry air. The hibernating animals in the pond-fl0or gunge might also be helped by slight heat generated by the organic ooze slowly decomposing around them. Cosy, eh?

– Able to dissolve or hydrolyse more compounds physically than any other liquid.

– Able perhaps to react chemically with more compounds than any other. Even more so when slightly acidic or in the presence of oxygen.

– Is the flux in subduction areas to help the partial melting of the sinking rock – and is subsequently partly why the resulting volcanoes above these plate-tectonic mechanisms are so explosive.

'

I know of an example of how destructive ice can be, and that at a small scale. It is a square U-tube about 8 X 8 inches, of ordinary copper 15mm plumbing-pipe joined by soldered elbows. Left hanging outdoors with its open ends upwards it had filled with rain-water. As the water cooled, it contracted, dropping the level in the 'U' harmlessly, to 4ºC. Then it started to expand again, and froze, most likely at the water surfaces first. The result is an impressive, split bulge about an inch long in the horizontal section. Yet the tube is open at its ends.

Who's good at sums so can calculate the rupture-pressure responsible?

For keeping a steam-engine safe in freezing conditions it is best either to keep it always above 0ºC anyway, or to drain it fully. That includes the feed-water tank and fittings and pressure-gauge syphon; and the blow-down, gauge-glass cocks and cylinder drain-cocks left open.

[SamsarandaParticipant @samsaranda]

I think an important characteristic of watercourses and the life that they support is the fact that the bottom of the watercourse will always be warmed by heat from the ground. I have a Koi pond that is six foot deep and it never freezes in winter because of ground heat coming from below, in fact during the coldest periods in winter the fish will lie on the bottom as it’s the warmest layer of the pond. I also have a pond that is only three feet deep, this pond does freeze during cold spells, probably because there is less ground heat transferred because the bottom of the pond is shallower more ground heat has dissipated. In the real world rivers and streams usually have a layer of water at the bottom that remains unfrozen, this helps fish and invertebrates to survive the winter freezes. Dave W

[SillyOldDufferModerator @sillyoldduffer]

Posted by Nigel Graham 2 on 01/01/2023 19:19:25:

…

Who's good at sums so can calculate the rupture-pressure responsible?

…

Not me but this website has the numbers. 15mm copper pipe bursts at about 3865psi, and, depending on how far and how quickly the temperature drops, and how much pressure the tube can take, freezing exerts pressure between 32,000 and 114,000psi.

Dave

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