Cold last night

[Moxi]

Does nucleation stop because the rest of the solution is warmer than room temperature or its a large volume ? and so the nucleation effectively stalls ? In all the examples I have seen in the past the nucleation goes through to completion.

Moxi

[dangermouse]

We have about 150kg of that stuff (super saturated sodium acetate trihydrate solution)

You really do have all the cool toys, don't you?

[Oldgreybeard]

Does nucleation stop because the rest of the solution is warmer than room temperature or its a large volume ? and so the nucleation effectively stalls ? In all the examples I have seen in the past the nucleation goes through to completion.

Moxi

As I understand it (and the manufacturer is very coy about nucleation control!) it's thermal equilibrium. I believe that what happens is that the partially solid, part discharged body of sodium acetate gets heated to 56°C (the phase transition temperature) and this then stalls further nucleation as very little heat can escape once the hot taps are closed. The temperature can then cool very slowly (the case is insulated with vacuum insulated panels, like a thermos) and this very slow cooling is too slow to allow nucleation to continue. As soon as another slug of cold water comes in (when a hot tap is opened) that thermal shock acts to create nucleation points at the heat exchanger and phase change starts up again. It's a pretty neat system, TBH, much smaller than an equivalent capacity hot water tank, but pretty heavy.

We have about 150kg of that stuff (super saturated sodium acetate trihydrate solution)

You really do have all the cool toys, don't you?

I try to collect as many as I can!