A question of water?

Panserborn

Does water freeze faster if there is already a chunk of ice in it?

As in, if I fill a container with tap water, drop in an ice cube (about a tenth of the total volume) and put it at -20C, will it freeze faster then the same container with no ice cube?

Capt'n Midnight

The ice would help seed new crystals. Also have a look for nucleation sites.

Shabadu

What's also interesting is that boiling hot water will freeze faster than cold water, under the right conditions. it's called the Mpemba effect.



http://math.ucr.edu/home/baez/physics/General/hot_water.html

nesf

Capt'n Midnight wrote:

The ice would help seed new crystals. Also have a look for nucleation sites.

Not necessarily.

In some cases, ice can form but the majority of the water can reach a super-cooled liquid state.

In the lab I've gotten a balance of a thin ice ring around the centre of water which has gotten to just below -18 Deg Cel. Small container here, about 2 cm wide and 4 cm deep, cooled in specific ways though. A temp gradient of 18 degrees across 1 cm of water using relatively simple equipment. With complicated (read: expensive) compression gear and special cooling chambers you can get far more impressive results.


How water freezes and the mechanism behind it is a very complicated topic. The whole seeding theory is by no means definitive.

Fascinating topic btw

(I'm using very pure water here, not tap water. Tap water can't achieve the same results. Too many impurities effecting the freezing process.)

Capt'n Midnight

since there are no convection currents in what manner does water freeze in zero g ?

THE FAN

Deleted this post because I made so many supid errors because i was rushed, I just wasnt arse fixing it. So anyone who read it sorry

nesf

Capt'n Midnight wrote:

since there are no convection currents in what manner does water freeze in zero g ?

You can freeze water without convection. Usually by conduction. But conduction in water sucks.

What kind of container and how are you freezing this water?

Capt'n Midnight

In zero g you can get beautiful spherical fires - just wondering how water behaves.

it's more a question of how the freezing would progress, using a container is cheating
If you had a sphere of water in a cold atmosphere wouldn't the outside freeze first and then gradually freeze inwards by conduction - but how would the expansion work, would the inside be under pressure if the crust has already frozen over ?

Panserborn

nesf wrote:

What kind of container and how are you freezing this water?

I'm in a cell biology lab and we use a contraption to transfer proteins from a gel to a membrane. The rig has to be kept cool due to the voltage and we use ice-packs for this. Plastic, about 13cm x 11cm x 2cm filled usually with tap water but we have d.H2O as well is it freezes faster.

Its really annoying when someone uses it and "forgets" to put the ice pack in the freezer so was just wondering if there was a way to help the freezing along. We have a -70C freezer as well but I don't think the plastic would like that!

nesf

Capt'n Midnight wrote:

In zero g you can get beautiful spherical fires - just wondering how water behaves.

it's more a question of how the freezing would progress, using a container is cheating
If you had a sphere of water in a cold atmosphere wouldn't the outside freeze first and then gradually freeze inwards by conduction - but how would the expansion work, would the inside be under pressure if the crust has already frozen over ?

Way more complicated than that. The whole "sphere" thing is down to surface tension and such. Which if memory serves me correct, changes with temperature.

I could be wrong, but from the depths of my memory is something telling me that it isn't that simple.

nesf

Panserborn wrote:

I'm in a cell biology lab and we use a contraption to transfer proteins from a gel to a membrane. The rig has to be kept cool due to the voltage and we use ice-packs for this. Plastic, about 13cm x 11cm x 2cm filled usually with tap water but we have d.H2O as well is it freezes faster.

Its really annoying when someone uses it and "forgets" to put the ice pack in the freezer so was just wondering if there was a way to help the freezing along. We have a -70C freezer as well but I don't think the plastic would like that!

Ahh, ok, a practical question! Excellent

Hmmm, one of my pet hates is people not putting lab equipment back as they found it. Can be a trigger for a rant if I'm not in good form


Hmm. No need for the -70C freezer and it possibly could be bad for the plastic. I don't know tbh, but at that temperature quite a lot of things aren't very happy and tend to "show it".

I can't think of any real short cut outside of using something other than water. Hot water does freeze faster, that is true, but the plastic mighn't like very hot water so you'd have to be careful. I'm thinking here that these aren't just generic ice packs that you could get normally and thus replace easily.

Even warm water would increase the speed. Heat it up a bit, put it in and put the ice pack in the normal freezer. Should do the trick.

If I think of anything else I'll post it up. Am just tired now etc.

Panserborn

nesf wrote:

Hmmm, one of my pet hates is people not putting lab equipment back as they found it. Can be a trigger for a rant if I'm not in good form

Hmm. No need for the -70C freezer and it possibly could be bad for the plastic. I don't know tbh, but at that temperature quite a lot of things aren't very happy and tend to "show it".

Too right, forgotten lab equipment has sparked quite a few "discussions" in the lab. A painter once put his sandwich roll in our -70C thinking it was a regular fridge, we used it to play lab-baseball for an hour before it melted!

Even warm water would increase the speed. Heat it up a bit, put it in and put the ice pack in the normal freezer. Should do the trick.

Sound, should speed things up a bit! Any suggestions are always welcome!