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Solids don't exert pressure on their surroundings. Gasses and liquids do. A pressure meter inside a solid won't register pressure. A pressure meter inside a liquid or gas will.
What happens if you place a pressure meter inside freezing ice? Water expands when it enters the solid phase. Will this be seen on the meter or will the ice form in such a way that the pressure on the meter will be zero? Imagine the water around the meter to be freely expandable upon entering the solid phase. If you envision the body of water to be free-floating in space, then it depends on where the freezing starts. When the freezing starts on the outside, the force on the pressure meter will rise, and when the freezing starts on the inside (around the meter) the water can expand so no pressure will be seen on the meter. But what if the ice freezes instantly everywhere? Will the shown pressure inside the water be frozen also (so no change occurs)?

I just found a nice music band's name. Here iiiiis "Flash freezing water in outer space"!

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    $\begingroup$ If in a rigid container, a lot of pressure. A mechE coworker once told me the pressure was some stupendously, ridiculous amount. I forget what he said exactly. If free to expand, I would think zero as the crystals could reorient outward. $\endgroup$
    – DKNguyen
    Commented Apr 27, 2021 at 4:20
  • $\begingroup$ @DKNguyen Clearer it can't be. Obviously, the water will not only expand in the free upon freezing. $\endgroup$
    – Deschele Schilder
    Commented Apr 27, 2021 at 4:24
  • $\begingroup$ I'm imagining a more gradual freezing where ice crystals are suspended in water and can therefore move around before solidifying. process rather than a flash freeze. $\endgroup$
    – DKNguyen
    Commented Apr 27, 2021 at 4:26
  • $\begingroup$ Imagine the water to be in free space. Does it matter in that case where the freezing starts? $\endgroup$
    – Deschele Schilder
    Commented Apr 27, 2021 at 4:28
  • $\begingroup$ Yes, along with how fast and how evenly it progresses. I think you may want to add that to your question. Like a flash frozen water blob in zero-G I assume is what you have in mind. $\endgroup$
    – DKNguyen
    Commented Apr 27, 2021 at 4:29

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The question is specifically about flash freezing but let me mention anyway the video by Derek Muller about water slowly freezing, in which case it makes no material difference whether gravity is at play or not.

The water cools down from the outside in, so the outside freezes first. The water trapped inside then finds a way out, and as that water makes it out to the surface an ice tube tends to form. The phenomenon is called 'ice spikes'

Flash freezing

So: a blob of supercooled water in zero-G, and you do something to trigger freezing.

We can scale that up, and make it a massive amount of supercooled water. The flash freeze must be triggered at some point, either inside or on the surface. From there a freeze front will propagate.

At that point I see a problem: as the water freezes there is a corresponding release of heat.

Some time ago there was a question here on physics.stackexchange whether a kilogram of ice can be cold enough to freeze a kilogram of just-above-zero-C water, if you bring the two in contact with each other. It turns out ice cannot be made cold enough to do that. The end result of the calculation was that even if the kilogram of ice was close to absolute zero at the start, the heat absorbing capacity would only be enough to freeze about 0.9 kilogram of just-above-zero-C water.

So in order for a body of supercooled water to flash freeze it must be sufficiently far below zero C to absorb all of the latent heat of freezing, which will be quite far. But a body of supercooled water is unstable. I assume flash freezing can be triggered by a random quantum event too.


For the sake of the thought experiment let's assume that the massive body of water can be supercooled to a sufficiently low temperature.

A freeze front will propagate. Let's say the flash freeze is triggered from the center of a spherical mass of supercooled water, so the freeze front will be an outward expanding shell. Let's assume the freezing comes with the known volume increase. So the freeze front has to do work. The freeze front has to displace the outer water. Because of the inertia of the outer water the need to exert a displacing force will give rise to a (transient) pressure in the ice.

Of course, once the seismic effects of the water displacement have dissipated the pressure will come down again.

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